1 \input texinfo @c -*-texinfo-*-
2 @c Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996,
3 @c 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009,
4 @c 2010, 2011 Free Software Foundation, Inc.
7 @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use
8 @c of @set vars. However, you can override filename with makeinfo -o.
13 @settitle Debugging with @value{GDBN}
14 @setchapternewpage odd
26 @c readline appendices use @vindex, @findex and @ftable,
27 @c annotate.texi and gdbmi use @findex.
31 @c !!set GDB manual's edition---not the same as GDB version!
32 @c This is updated by GNU Press.
35 @c !!set GDB edit command default editor
38 @c THIS MANUAL REQUIRES TEXINFO 4.0 OR LATER.
40 @c This is a dir.info fragment to support semi-automated addition of
41 @c manuals to an info tree.
42 @dircategory Software development
44 * Gdb: (gdb). The GNU debugger.
48 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996,
49 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
50 Free Software Foundation, Inc.
52 Permission is granted to copy, distribute and/or modify this document
53 under the terms of the GNU Free Documentation License, Version 1.3 or
54 any later version published by the Free Software Foundation; with the
55 Invariant Sections being ``Free Software'' and ``Free Software Needs
56 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
57 and with the Back-Cover Texts as in (a) below.
59 (a) The FSF's Back-Cover Text is: ``You are free to copy and modify
60 this GNU Manual. Buying copies from GNU Press supports the FSF in
61 developing GNU and promoting software freedom.''
65 This file documents the @sc{gnu} debugger @value{GDBN}.
67 This is the @value{EDITION} Edition, of @cite{Debugging with
68 @value{GDBN}: the @sc{gnu} Source-Level Debugger} for @value{GDBN}
69 @ifset VERSION_PACKAGE
70 @value{VERSION_PACKAGE}
72 Version @value{GDBVN}.
78 @title Debugging with @value{GDBN}
79 @subtitle The @sc{gnu} Source-Level Debugger
81 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
82 @ifset VERSION_PACKAGE
84 @subtitle @value{VERSION_PACKAGE}
86 @author Richard Stallman, Roland Pesch, Stan Shebs, et al.
90 \hfill (Send bugs and comments on @value{GDBN} to @value{BUGURL}.)\par
91 \hfill {\it Debugging with @value{GDBN}}\par
92 \hfill \TeX{}info \texinfoversion\par
96 @vskip 0pt plus 1filll
97 Published by the Free Software Foundation @*
98 51 Franklin Street, Fifth Floor,
99 Boston, MA 02110-1301, USA@*
100 ISBN 978-0-9831592-3-0 @*
107 @node Top, Summary, (dir), (dir)
109 @top Debugging with @value{GDBN}
111 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
113 This is the @value{EDITION} Edition, for @value{GDBN}
114 @ifset VERSION_PACKAGE
115 @value{VERSION_PACKAGE}
117 Version @value{GDBVN}.
119 Copyright (C) 1988-2010 Free Software Foundation, Inc.
121 This edition of the GDB manual is dedicated to the memory of Fred
122 Fish. Fred was a long-standing contributor to GDB and to Free
123 software in general. We will miss him.
126 * Summary:: Summary of @value{GDBN}
127 * Sample Session:: A sample @value{GDBN} session
129 * Invocation:: Getting in and out of @value{GDBN}
130 * Commands:: @value{GDBN} commands
131 * Running:: Running programs under @value{GDBN}
132 * Stopping:: Stopping and continuing
133 * Reverse Execution:: Running programs backward
134 * Process Record and Replay:: Recording inferior's execution and replaying it
135 * Stack:: Examining the stack
136 * Source:: Examining source files
137 * Data:: Examining data
138 * Optimized Code:: Debugging optimized code
139 * Macros:: Preprocessor Macros
140 * Tracepoints:: Debugging remote targets non-intrusively
141 * Overlays:: Debugging programs that use overlays
143 * Languages:: Using @value{GDBN} with different languages
145 * Symbols:: Examining the symbol table
146 * Altering:: Altering execution
147 * GDB Files:: @value{GDBN} files
148 * Targets:: Specifying a debugging target
149 * Remote Debugging:: Debugging remote programs
150 * Configurations:: Configuration-specific information
151 * Controlling GDB:: Controlling @value{GDBN}
152 * Extending GDB:: Extending @value{GDBN}
153 * Interpreters:: Command Interpreters
154 * TUI:: @value{GDBN} Text User Interface
155 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
156 * GDB/MI:: @value{GDBN}'s Machine Interface.
157 * Annotations:: @value{GDBN}'s annotation interface.
158 * JIT Interface:: Using the JIT debugging interface.
160 * GDB Bugs:: Reporting bugs in @value{GDBN}
162 @ifset SYSTEM_READLINE
163 * Command Line Editing: (rluserman). Command Line Editing
164 * Using History Interactively: (history). Using History Interactively
166 @ifclear SYSTEM_READLINE
167 * Command Line Editing:: Command Line Editing
168 * Using History Interactively:: Using History Interactively
170 * In Memoriam:: In Memoriam
171 * Formatting Documentation:: How to format and print @value{GDBN} documentation
172 * Installing GDB:: Installing GDB
173 * Maintenance Commands:: Maintenance Commands
174 * Remote Protocol:: GDB Remote Serial Protocol
175 * Agent Expressions:: The GDB Agent Expression Mechanism
176 * Target Descriptions:: How targets can describe themselves to
178 * Operating System Information:: Getting additional information from
180 * Trace File Format:: GDB trace file format
181 * Index Section Format:: .gdb_index section format
182 * Copying:: GNU General Public License says
183 how you can copy and share GDB
184 * GNU Free Documentation License:: The license for this documentation
193 @unnumbered Summary of @value{GDBN}
195 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
196 going on ``inside'' another program while it executes---or what another
197 program was doing at the moment it crashed.
199 @value{GDBN} can do four main kinds of things (plus other things in support of
200 these) to help you catch bugs in the act:
204 Start your program, specifying anything that might affect its behavior.
207 Make your program stop on specified conditions.
210 Examine what has happened, when your program has stopped.
213 Change things in your program, so you can experiment with correcting the
214 effects of one bug and go on to learn about another.
217 You can use @value{GDBN} to debug programs written in C and C@t{++}.
218 For more information, see @ref{Supported Languages,,Supported Languages}.
219 For more information, see @ref{C,,C and C++}.
221 Support for D is partial. For information on D, see
225 Support for Modula-2 is partial. For information on Modula-2, see
226 @ref{Modula-2,,Modula-2}.
228 Support for OpenCL C is partial. For information on OpenCL C, see
229 @ref{OpenCL C,,OpenCL C}.
232 Debugging Pascal programs which use sets, subranges, file variables, or
233 nested functions does not currently work. @value{GDBN} does not support
234 entering expressions, printing values, or similar features using Pascal
238 @value{GDBN} can be used to debug programs written in Fortran, although
239 it may be necessary to refer to some variables with a trailing
242 @value{GDBN} can be used to debug programs written in Objective-C,
243 using either the Apple/NeXT or the GNU Objective-C runtime.
246 * Free Software:: Freely redistributable software
247 * Contributors:: Contributors to GDB
251 @unnumberedsec Free Software
253 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
254 General Public License
255 (GPL). The GPL gives you the freedom to copy or adapt a licensed
256 program---but every person getting a copy also gets with it the
257 freedom to modify that copy (which means that they must get access to
258 the source code), and the freedom to distribute further copies.
259 Typical software companies use copyrights to limit your freedoms; the
260 Free Software Foundation uses the GPL to preserve these freedoms.
262 Fundamentally, the General Public License is a license which says that
263 you have these freedoms and that you cannot take these freedoms away
266 @unnumberedsec Free Software Needs Free Documentation
268 The biggest deficiency in the free software community today is not in
269 the software---it is the lack of good free documentation that we can
270 include with the free software. Many of our most important
271 programs do not come with free reference manuals and free introductory
272 texts. Documentation is an essential part of any software package;
273 when an important free software package does not come with a free
274 manual and a free tutorial, that is a major gap. We have many such
277 Consider Perl, for instance. The tutorial manuals that people
278 normally use are non-free. How did this come about? Because the
279 authors of those manuals published them with restrictive terms---no
280 copying, no modification, source files not available---which exclude
281 them from the free software world.
283 That wasn't the first time this sort of thing happened, and it was far
284 from the last. Many times we have heard a GNU user eagerly describe a
285 manual that he is writing, his intended contribution to the community,
286 only to learn that he had ruined everything by signing a publication
287 contract to make it non-free.
289 Free documentation, like free software, is a matter of freedom, not
290 price. The problem with the non-free manual is not that publishers
291 charge a price for printed copies---that in itself is fine. (The Free
292 Software Foundation sells printed copies of manuals, too.) The
293 problem is the restrictions on the use of the manual. Free manuals
294 are available in source code form, and give you permission to copy and
295 modify. Non-free manuals do not allow this.
297 The criteria of freedom for a free manual are roughly the same as for
298 free software. Redistribution (including the normal kinds of
299 commercial redistribution) must be permitted, so that the manual can
300 accompany every copy of the program, both on-line and on paper.
302 Permission for modification of the technical content is crucial too.
303 When people modify the software, adding or changing features, if they
304 are conscientious they will change the manual too---so they can
305 provide accurate and clear documentation for the modified program. A
306 manual that leaves you no choice but to write a new manual to document
307 a changed version of the program is not really available to our
310 Some kinds of limits on the way modification is handled are
311 acceptable. For example, requirements to preserve the original
312 author's copyright notice, the distribution terms, or the list of
313 authors, are ok. It is also no problem to require modified versions
314 to include notice that they were modified. Even entire sections that
315 may not be deleted or changed are acceptable, as long as they deal
316 with nontechnical topics (like this one). These kinds of restrictions
317 are acceptable because they don't obstruct the community's normal use
320 However, it must be possible to modify all the @emph{technical}
321 content of the manual, and then distribute the result in all the usual
322 media, through all the usual channels. Otherwise, the restrictions
323 obstruct the use of the manual, it is not free, and we need another
324 manual to replace it.
326 Please spread the word about this issue. Our community continues to
327 lose manuals to proprietary publishing. If we spread the word that
328 free software needs free reference manuals and free tutorials, perhaps
329 the next person who wants to contribute by writing documentation will
330 realize, before it is too late, that only free manuals contribute to
331 the free software community.
333 If you are writing documentation, please insist on publishing it under
334 the GNU Free Documentation License or another free documentation
335 license. Remember that this decision requires your approval---you
336 don't have to let the publisher decide. Some commercial publishers
337 will use a free license if you insist, but they will not propose the
338 option; it is up to you to raise the issue and say firmly that this is
339 what you want. If the publisher you are dealing with refuses, please
340 try other publishers. If you're not sure whether a proposed license
341 is free, write to @email{licensing@@gnu.org}.
343 You can encourage commercial publishers to sell more free, copylefted
344 manuals and tutorials by buying them, and particularly by buying
345 copies from the publishers that paid for their writing or for major
346 improvements. Meanwhile, try to avoid buying non-free documentation
347 at all. Check the distribution terms of a manual before you buy it,
348 and insist that whoever seeks your business must respect your freedom.
349 Check the history of the book, and try to reward the publishers that
350 have paid or pay the authors to work on it.
352 The Free Software Foundation maintains a list of free documentation
353 published by other publishers, at
354 @url{http://www.fsf.org/doc/other-free-books.html}.
357 @unnumberedsec Contributors to @value{GDBN}
359 Richard Stallman was the original author of @value{GDBN}, and of many
360 other @sc{gnu} programs. Many others have contributed to its
361 development. This section attempts to credit major contributors. One
362 of the virtues of free software is that everyone is free to contribute
363 to it; with regret, we cannot actually acknowledge everyone here. The
364 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
365 blow-by-blow account.
367 Changes much prior to version 2.0 are lost in the mists of time.
370 @emph{Plea:} Additions to this section are particularly welcome. If you
371 or your friends (or enemies, to be evenhanded) have been unfairly
372 omitted from this list, we would like to add your names!
375 So that they may not regard their many labors as thankless, we
376 particularly thank those who shepherded @value{GDBN} through major
378 Andrew Cagney (releases 6.3, 6.2, 6.1, 6.0, 5.3, 5.2, 5.1 and 5.0);
379 Jim Blandy (release 4.18);
380 Jason Molenda (release 4.17);
381 Stan Shebs (release 4.14);
382 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
383 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
384 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
385 Jim Kingdon (releases 3.5, 3.4, and 3.3);
386 and Randy Smith (releases 3.2, 3.1, and 3.0).
388 Richard Stallman, assisted at various times by Peter TerMaat, Chris
389 Hanson, and Richard Mlynarik, handled releases through 2.8.
391 Michael Tiemann is the author of most of the @sc{gnu} C@t{++} support
392 in @value{GDBN}, with significant additional contributions from Per
393 Bothner and Daniel Berlin. James Clark wrote the @sc{gnu} C@t{++}
394 demangler. Early work on C@t{++} was by Peter TerMaat (who also did
395 much general update work leading to release 3.0).
397 @value{GDBN} uses the BFD subroutine library to examine multiple
398 object-file formats; BFD was a joint project of David V.
399 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
401 David Johnson wrote the original COFF support; Pace Willison did
402 the original support for encapsulated COFF.
404 Brent Benson of Harris Computer Systems contributed DWARF 2 support.
406 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
407 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
409 Jean-Daniel Fekete contributed Sun 386i support.
410 Chris Hanson improved the HP9000 support.
411 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
412 David Johnson contributed Encore Umax support.
413 Jyrki Kuoppala contributed Altos 3068 support.
414 Jeff Law contributed HP PA and SOM support.
415 Keith Packard contributed NS32K support.
416 Doug Rabson contributed Acorn Risc Machine support.
417 Bob Rusk contributed Harris Nighthawk CX-UX support.
418 Chris Smith contributed Convex support (and Fortran debugging).
419 Jonathan Stone contributed Pyramid support.
420 Michael Tiemann contributed SPARC support.
421 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
422 Pace Willison contributed Intel 386 support.
423 Jay Vosburgh contributed Symmetry support.
424 Marko Mlinar contributed OpenRISC 1000 support.
426 Andreas Schwab contributed M68K @sc{gnu}/Linux support.
428 Rich Schaefer and Peter Schauer helped with support of SunOS shared
431 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
432 about several machine instruction sets.
434 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
435 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
436 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
437 and RDI targets, respectively.
439 Brian Fox is the author of the readline libraries providing
440 command-line editing and command history.
442 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
443 Modula-2 support, and contributed the Languages chapter of this manual.
445 Fred Fish wrote most of the support for Unix System Vr4.
446 He also enhanced the command-completion support to cover C@t{++} overloaded
449 Hitachi America (now Renesas America), Ltd. sponsored the support for
450 H8/300, H8/500, and Super-H processors.
452 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
454 Mitsubishi (now Renesas) sponsored the support for D10V, D30V, and M32R/D
457 Toshiba sponsored the support for the TX39 Mips processor.
459 Matsushita sponsored the support for the MN10200 and MN10300 processors.
461 Fujitsu sponsored the support for SPARClite and FR30 processors.
463 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
466 Michael Snyder added support for tracepoints.
468 Stu Grossman wrote gdbserver.
470 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
471 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
473 The following people at the Hewlett-Packard Company contributed
474 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
475 (narrow mode), HP's implementation of kernel threads, HP's aC@t{++}
476 compiler, and the Text User Interface (nee Terminal User Interface):
477 Ben Krepp, Richard Title, John Bishop, Susan Macchia, Kathy Mann,
478 Satish Pai, India Paul, Steve Rehrauer, and Elena Zannoni. Kim Haase
479 provided HP-specific information in this manual.
481 DJ Delorie ported @value{GDBN} to MS-DOS, for the DJGPP project.
482 Robert Hoehne made significant contributions to the DJGPP port.
484 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
485 development since 1991. Cygnus engineers who have worked on @value{GDBN}
486 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
487 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
488 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
489 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
490 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
491 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
492 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
493 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
494 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
495 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
496 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
497 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
498 Zuhn have made contributions both large and small.
500 Andrew Cagney, Fernando Nasser, and Elena Zannoni, while working for
501 Cygnus Solutions, implemented the original @sc{gdb/mi} interface.
503 Jim Blandy added support for preprocessor macros, while working for Red
506 Andrew Cagney designed @value{GDBN}'s architecture vector. Many
507 people including Andrew Cagney, Stephane Carrez, Randolph Chung, Nick
508 Duffek, Richard Henderson, Mark Kettenis, Grace Sainsbury, Kei
509 Sakamoto, Yoshinori Sato, Michael Snyder, Andreas Schwab, Jason
510 Thorpe, Corinna Vinschen, Ulrich Weigand, and Elena Zannoni, helped
511 with the migration of old architectures to this new framework.
513 Andrew Cagney completely re-designed and re-implemented @value{GDBN}'s
514 unwinder framework, this consisting of a fresh new design featuring
515 frame IDs, independent frame sniffers, and the sentinel frame. Mark
516 Kettenis implemented the @sc{dwarf 2} unwinder, Jeff Johnston the
517 libunwind unwinder, and Andrew Cagney the dummy, sentinel, tramp, and
518 trad unwinders. The architecture-specific changes, each involving a
519 complete rewrite of the architecture's frame code, were carried out by
520 Jim Blandy, Joel Brobecker, Kevin Buettner, Andrew Cagney, Stephane
521 Carrez, Randolph Chung, Orjan Friberg, Richard Henderson, Daniel
522 Jacobowitz, Jeff Johnston, Mark Kettenis, Theodore A. Roth, Kei
523 Sakamoto, Yoshinori Sato, Michael Snyder, Corinna Vinschen, and Ulrich
526 Christian Zankel, Ross Morley, Bob Wilson, and Maxim Grigoriev from
527 Tensilica, Inc.@: contributed support for Xtensa processors. Others
528 who have worked on the Xtensa port of @value{GDBN} in the past include
529 Steve Tjiang, John Newlin, and Scott Foehner.
531 Michael Eager and staff of Xilinx, Inc., contributed support for the
532 Xilinx MicroBlaze architecture.
535 @chapter A Sample @value{GDBN} Session
537 You can use this manual at your leisure to read all about @value{GDBN}.
538 However, a handful of commands are enough to get started using the
539 debugger. This chapter illustrates those commands.
542 In this sample session, we emphasize user input like this: @b{input},
543 to make it easier to pick out from the surrounding output.
546 @c FIXME: this example may not be appropriate for some configs, where
547 @c FIXME...primary interest is in remote use.
549 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
550 processor) exhibits the following bug: sometimes, when we change its
551 quote strings from the default, the commands used to capture one macro
552 definition within another stop working. In the following short @code{m4}
553 session, we define a macro @code{foo} which expands to @code{0000}; we
554 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
555 same thing. However, when we change the open quote string to
556 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
557 procedure fails to define a new synonym @code{baz}:
566 @b{define(bar,defn(`foo'))}
570 @b{changequote(<QUOTE>,<UNQUOTE>)}
572 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
575 m4: End of input: 0: fatal error: EOF in string
579 Let us use @value{GDBN} to try to see what is going on.
582 $ @b{@value{GDBP} m4}
583 @c FIXME: this falsifies the exact text played out, to permit smallbook
584 @c FIXME... format to come out better.
585 @value{GDBN} is free software and you are welcome to distribute copies
586 of it under certain conditions; type "show copying" to see
588 There is absolutely no warranty for @value{GDBN}; type "show warranty"
591 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
596 @value{GDBN} reads only enough symbol data to know where to find the
597 rest when needed; as a result, the first prompt comes up very quickly.
598 We now tell @value{GDBN} to use a narrower display width than usual, so
599 that examples fit in this manual.
602 (@value{GDBP}) @b{set width 70}
606 We need to see how the @code{m4} built-in @code{changequote} works.
607 Having looked at the source, we know the relevant subroutine is
608 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
609 @code{break} command.
612 (@value{GDBP}) @b{break m4_changequote}
613 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
617 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
618 control; as long as control does not reach the @code{m4_changequote}
619 subroutine, the program runs as usual:
622 (@value{GDBP}) @b{run}
623 Starting program: /work/Editorial/gdb/gnu/m4/m4
631 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
632 suspends execution of @code{m4}, displaying information about the
633 context where it stops.
636 @b{changequote(<QUOTE>,<UNQUOTE>)}
638 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
640 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
644 Now we use the command @code{n} (@code{next}) to advance execution to
645 the next line of the current function.
649 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
654 @code{set_quotes} looks like a promising subroutine. We can go into it
655 by using the command @code{s} (@code{step}) instead of @code{next}.
656 @code{step} goes to the next line to be executed in @emph{any}
657 subroutine, so it steps into @code{set_quotes}.
661 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
663 530 if (lquote != def_lquote)
667 The display that shows the subroutine where @code{m4} is now
668 suspended (and its arguments) is called a stack frame display. It
669 shows a summary of the stack. We can use the @code{backtrace}
670 command (which can also be spelled @code{bt}), to see where we are
671 in the stack as a whole: the @code{backtrace} command displays a
672 stack frame for each active subroutine.
675 (@value{GDBP}) @b{bt}
676 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
678 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
680 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
681 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
683 #4 0x79dc in expand_input () at macro.c:40
684 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
688 We step through a few more lines to see what happens. The first two
689 times, we can use @samp{s}; the next two times we use @code{n} to avoid
690 falling into the @code{xstrdup} subroutine.
694 0x3b5c 532 if (rquote != def_rquote)
696 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
697 def_lquote : xstrdup(lq);
699 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
702 538 len_lquote = strlen(rquote);
706 The last line displayed looks a little odd; we can examine the variables
707 @code{lquote} and @code{rquote} to see if they are in fact the new left
708 and right quotes we specified. We use the command @code{p}
709 (@code{print}) to see their values.
712 (@value{GDBP}) @b{p lquote}
713 $1 = 0x35d40 "<QUOTE>"
714 (@value{GDBP}) @b{p rquote}
715 $2 = 0x35d50 "<UNQUOTE>"
719 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
720 To look at some context, we can display ten lines of source
721 surrounding the current line with the @code{l} (@code{list}) command.
727 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
729 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
732 538 len_lquote = strlen(rquote);
733 539 len_rquote = strlen(lquote);
740 Let us step past the two lines that set @code{len_lquote} and
741 @code{len_rquote}, and then examine the values of those variables.
745 539 len_rquote = strlen(lquote);
748 (@value{GDBP}) @b{p len_lquote}
750 (@value{GDBP}) @b{p len_rquote}
755 That certainly looks wrong, assuming @code{len_lquote} and
756 @code{len_rquote} are meant to be the lengths of @code{lquote} and
757 @code{rquote} respectively. We can set them to better values using
758 the @code{p} command, since it can print the value of
759 any expression---and that expression can include subroutine calls and
763 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
765 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
770 Is that enough to fix the problem of using the new quotes with the
771 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
772 executing with the @code{c} (@code{continue}) command, and then try the
773 example that caused trouble initially:
779 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
786 Success! The new quotes now work just as well as the default ones. The
787 problem seems to have been just the two typos defining the wrong
788 lengths. We allow @code{m4} exit by giving it an EOF as input:
792 Program exited normally.
796 The message @samp{Program exited normally.} is from @value{GDBN}; it
797 indicates @code{m4} has finished executing. We can end our @value{GDBN}
798 session with the @value{GDBN} @code{quit} command.
801 (@value{GDBP}) @b{quit}
805 @chapter Getting In and Out of @value{GDBN}
807 This chapter discusses how to start @value{GDBN}, and how to get out of it.
811 type @samp{@value{GDBP}} to start @value{GDBN}.
813 type @kbd{quit} or @kbd{Ctrl-d} to exit.
817 * Invoking GDB:: How to start @value{GDBN}
818 * Quitting GDB:: How to quit @value{GDBN}
819 * Shell Commands:: How to use shell commands inside @value{GDBN}
820 * Logging Output:: How to log @value{GDBN}'s output to a file
824 @section Invoking @value{GDBN}
826 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
827 @value{GDBN} reads commands from the terminal until you tell it to exit.
829 You can also run @code{@value{GDBP}} with a variety of arguments and options,
830 to specify more of your debugging environment at the outset.
832 The command-line options described here are designed
833 to cover a variety of situations; in some environments, some of these
834 options may effectively be unavailable.
836 The most usual way to start @value{GDBN} is with one argument,
837 specifying an executable program:
840 @value{GDBP} @var{program}
844 You can also start with both an executable program and a core file
848 @value{GDBP} @var{program} @var{core}
851 You can, instead, specify a process ID as a second argument, if you want
852 to debug a running process:
855 @value{GDBP} @var{program} 1234
859 would attach @value{GDBN} to process @code{1234} (unless you also have a file
860 named @file{1234}; @value{GDBN} does check for a core file first).
862 Taking advantage of the second command-line argument requires a fairly
863 complete operating system; when you use @value{GDBN} as a remote
864 debugger attached to a bare board, there may not be any notion of
865 ``process'', and there is often no way to get a core dump. @value{GDBN}
866 will warn you if it is unable to attach or to read core dumps.
868 You can optionally have @code{@value{GDBP}} pass any arguments after the
869 executable file to the inferior using @code{--args}. This option stops
872 @value{GDBP} --args gcc -O2 -c foo.c
874 This will cause @code{@value{GDBP}} to debug @code{gcc}, and to set
875 @code{gcc}'s command-line arguments (@pxref{Arguments}) to @samp{-O2 -c foo.c}.
877 You can run @code{@value{GDBP}} without printing the front material, which describes
878 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
885 You can further control how @value{GDBN} starts up by using command-line
886 options. @value{GDBN} itself can remind you of the options available.
896 to display all available options and briefly describe their use
897 (@samp{@value{GDBP} -h} is a shorter equivalent).
899 All options and command line arguments you give are processed
900 in sequential order. The order makes a difference when the
901 @samp{-x} option is used.
905 * File Options:: Choosing files
906 * Mode Options:: Choosing modes
907 * Startup:: What @value{GDBN} does during startup
911 @subsection Choosing Files
913 When @value{GDBN} starts, it reads any arguments other than options as
914 specifying an executable file and core file (or process ID). This is
915 the same as if the arguments were specified by the @samp{-se} and
916 @samp{-c} (or @samp{-p}) options respectively. (@value{GDBN} reads the
917 first argument that does not have an associated option flag as
918 equivalent to the @samp{-se} option followed by that argument; and the
919 second argument that does not have an associated option flag, if any, as
920 equivalent to the @samp{-c}/@samp{-p} option followed by that argument.)
921 If the second argument begins with a decimal digit, @value{GDBN} will
922 first attempt to attach to it as a process, and if that fails, attempt
923 to open it as a corefile. If you have a corefile whose name begins with
924 a digit, you can prevent @value{GDBN} from treating it as a pid by
925 prefixing it with @file{./}, e.g.@: @file{./12345}.
927 If @value{GDBN} has not been configured to included core file support,
928 such as for most embedded targets, then it will complain about a second
929 argument and ignore it.
931 Many options have both long and short forms; both are shown in the
932 following list. @value{GDBN} also recognizes the long forms if you truncate
933 them, so long as enough of the option is present to be unambiguous.
934 (If you prefer, you can flag option arguments with @samp{--} rather
935 than @samp{-}, though we illustrate the more usual convention.)
937 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
938 @c way, both those who look for -foo and --foo in the index, will find
942 @item -symbols @var{file}
944 @cindex @code{--symbols}
946 Read symbol table from file @var{file}.
948 @item -exec @var{file}
950 @cindex @code{--exec}
952 Use file @var{file} as the executable file to execute when appropriate,
953 and for examining pure data in conjunction with a core dump.
957 Read symbol table from file @var{file} and use it as the executable
960 @item -core @var{file}
962 @cindex @code{--core}
964 Use file @var{file} as a core dump to examine.
966 @item -pid @var{number}
967 @itemx -p @var{number}
970 Connect to process ID @var{number}, as with the @code{attach} command.
972 @item -command @var{file}
974 @cindex @code{--command}
976 Execute commands from file @var{file}. The contents of this file is
977 evaluated exactly as the @code{source} command would.
978 @xref{Command Files,, Command files}.
980 @item -eval-command @var{command}
981 @itemx -ex @var{command}
982 @cindex @code{--eval-command}
984 Execute a single @value{GDBN} command.
986 This option may be used multiple times to call multiple commands. It may
987 also be interleaved with @samp{-command} as required.
990 @value{GDBP} -ex 'target sim' -ex 'load' \
991 -x setbreakpoints -ex 'run' a.out
994 @item -directory @var{directory}
995 @itemx -d @var{directory}
996 @cindex @code{--directory}
998 Add @var{directory} to the path to search for source and script files.
1002 @cindex @code{--readnow}
1004 Read each symbol file's entire symbol table immediately, rather than
1005 the default, which is to read it incrementally as it is needed.
1006 This makes startup slower, but makes future operations faster.
1011 @subsection Choosing Modes
1013 You can run @value{GDBN} in various alternative modes---for example, in
1014 batch mode or quiet mode.
1021 Do not execute commands found in any initialization files. Normally,
1022 @value{GDBN} executes the commands in these files after all the command
1023 options and arguments have been processed. @xref{Command Files,,Command
1029 @cindex @code{--quiet}
1030 @cindex @code{--silent}
1032 ``Quiet''. Do not print the introductory and copyright messages. These
1033 messages are also suppressed in batch mode.
1036 @cindex @code{--batch}
1037 Run in batch mode. Exit with status @code{0} after processing all the
1038 command files specified with @samp{-x} (and all commands from
1039 initialization files, if not inhibited with @samp{-n}). Exit with
1040 nonzero status if an error occurs in executing the @value{GDBN} commands
1041 in the command files. Batch mode also disables pagination, sets unlimited
1042 terminal width and height @pxref{Screen Size}, and acts as if @kbd{set confirm
1043 off} were in effect (@pxref{Messages/Warnings}).
1045 Batch mode may be useful for running @value{GDBN} as a filter, for
1046 example to download and run a program on another computer; in order to
1047 make this more useful, the message
1050 Program exited normally.
1054 (which is ordinarily issued whenever a program running under
1055 @value{GDBN} control terminates) is not issued when running in batch
1059 @cindex @code{--batch-silent}
1060 Run in batch mode exactly like @samp{-batch}, but totally silently. All
1061 @value{GDBN} output to @code{stdout} is prevented (@code{stderr} is
1062 unaffected). This is much quieter than @samp{-silent} and would be useless
1063 for an interactive session.
1065 This is particularly useful when using targets that give @samp{Loading section}
1066 messages, for example.
1068 Note that targets that give their output via @value{GDBN}, as opposed to
1069 writing directly to @code{stdout}, will also be made silent.
1071 @item -return-child-result
1072 @cindex @code{--return-child-result}
1073 The return code from @value{GDBN} will be the return code from the child
1074 process (the process being debugged), with the following exceptions:
1078 @value{GDBN} exits abnormally. E.g., due to an incorrect argument or an
1079 internal error. In this case the exit code is the same as it would have been
1080 without @samp{-return-child-result}.
1082 The user quits with an explicit value. E.g., @samp{quit 1}.
1084 The child process never runs, or is not allowed to terminate, in which case
1085 the exit code will be -1.
1088 This option is useful in conjunction with @samp{-batch} or @samp{-batch-silent},
1089 when @value{GDBN} is being used as a remote program loader or simulator
1094 @cindex @code{--nowindows}
1096 ``No windows''. If @value{GDBN} comes with a graphical user interface
1097 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
1098 interface. If no GUI is available, this option has no effect.
1102 @cindex @code{--windows}
1104 If @value{GDBN} includes a GUI, then this option requires it to be
1107 @item -cd @var{directory}
1109 Run @value{GDBN} using @var{directory} as its working directory,
1110 instead of the current directory.
1112 @item -data-directory @var{directory}
1113 @cindex @code{--data-directory}
1114 Run @value{GDBN} using @var{directory} as its data directory.
1115 The data directory is where @value{GDBN} searches for its
1116 auxiliary files. @xref{Data Files}.
1120 @cindex @code{--fullname}
1122 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
1123 subprocess. It tells @value{GDBN} to output the full file name and line
1124 number in a standard, recognizable fashion each time a stack frame is
1125 displayed (which includes each time your program stops). This
1126 recognizable format looks like two @samp{\032} characters, followed by
1127 the file name, line number and character position separated by colons,
1128 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
1129 @samp{\032} characters as a signal to display the source code for the
1133 @cindex @code{--epoch}
1134 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
1135 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
1136 routines so as to allow Epoch to display values of expressions in a
1139 @item -annotate @var{level}
1140 @cindex @code{--annotate}
1141 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
1142 effect is identical to using @samp{set annotate @var{level}}
1143 (@pxref{Annotations}). The annotation @var{level} controls how much
1144 information @value{GDBN} prints together with its prompt, values of
1145 expressions, source lines, and other types of output. Level 0 is the
1146 normal, level 1 is for use when @value{GDBN} is run as a subprocess of
1147 @sc{gnu} Emacs, level 3 is the maximum annotation suitable for programs
1148 that control @value{GDBN}, and level 2 has been deprecated.
1150 The annotation mechanism has largely been superseded by @sc{gdb/mi}
1154 @cindex @code{--args}
1155 Change interpretation of command line so that arguments following the
1156 executable file are passed as command line arguments to the inferior.
1157 This option stops option processing.
1159 @item -baud @var{bps}
1161 @cindex @code{--baud}
1163 Set the line speed (baud rate or bits per second) of any serial
1164 interface used by @value{GDBN} for remote debugging.
1166 @item -l @var{timeout}
1168 Set the timeout (in seconds) of any communication used by @value{GDBN}
1169 for remote debugging.
1171 @item -tty @var{device}
1172 @itemx -t @var{device}
1173 @cindex @code{--tty}
1175 Run using @var{device} for your program's standard input and output.
1176 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1178 @c resolve the situation of these eventually
1180 @cindex @code{--tui}
1181 Activate the @dfn{Text User Interface} when starting. The Text User
1182 Interface manages several text windows on the terminal, showing
1183 source, assembly, registers and @value{GDBN} command outputs
1184 (@pxref{TUI, ,@value{GDBN} Text User Interface}). Alternatively, the
1185 Text User Interface can be enabled by invoking the program
1186 @samp{@value{GDBTUI}}. Do not use this option if you run @value{GDBN} from
1187 Emacs (@pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}).
1190 @c @cindex @code{--xdb}
1191 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1192 @c For information, see the file @file{xdb_trans.html}, which is usually
1193 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1196 @item -interpreter @var{interp}
1197 @cindex @code{--interpreter}
1198 Use the interpreter @var{interp} for interface with the controlling
1199 program or device. This option is meant to be set by programs which
1200 communicate with @value{GDBN} using it as a back end.
1201 @xref{Interpreters, , Command Interpreters}.
1203 @samp{--interpreter=mi} (or @samp{--interpreter=mi2}) causes
1204 @value{GDBN} to use the @dfn{@sc{gdb/mi} interface} (@pxref{GDB/MI, ,
1205 The @sc{gdb/mi} Interface}) included since @value{GDBN} version 6.0. The
1206 previous @sc{gdb/mi} interface, included in @value{GDBN} version 5.3 and
1207 selected with @samp{--interpreter=mi1}, is deprecated. Earlier
1208 @sc{gdb/mi} interfaces are no longer supported.
1211 @cindex @code{--write}
1212 Open the executable and core files for both reading and writing. This
1213 is equivalent to the @samp{set write on} command inside @value{GDBN}
1217 @cindex @code{--statistics}
1218 This option causes @value{GDBN} to print statistics about time and
1219 memory usage after it completes each command and returns to the prompt.
1222 @cindex @code{--version}
1223 This option causes @value{GDBN} to print its version number and
1224 no-warranty blurb, and exit.
1229 @subsection What @value{GDBN} Does During Startup
1230 @cindex @value{GDBN} startup
1232 Here's the description of what @value{GDBN} does during session startup:
1236 Sets up the command interpreter as specified by the command line
1237 (@pxref{Mode Options, interpreter}).
1241 Reads the system-wide @dfn{init file} (if @option{--with-system-gdbinit} was
1242 used when building @value{GDBN}; @pxref{System-wide configuration,
1243 ,System-wide configuration and settings}) and executes all the commands in
1247 Reads the init file (if any) in your home directory@footnote{On
1248 DOS/Windows systems, the home directory is the one pointed to by the
1249 @code{HOME} environment variable.} and executes all the commands in
1253 Processes command line options and operands.
1256 Reads and executes the commands from init file (if any) in the current
1257 working directory. This is only done if the current directory is
1258 different from your home directory. Thus, you can have more than one
1259 init file, one generic in your home directory, and another, specific
1260 to the program you are debugging, in the directory where you invoke
1264 If the command line specified a program to debug, or a process to
1265 attach to, or a core file, @value{GDBN} loads any auto-loaded
1266 scripts provided for the program or for its loaded shared libraries.
1267 @xref{Auto-loading}.
1269 If you wish to disable the auto-loading during startup,
1270 you must do something like the following:
1273 $ gdb -ex "set auto-load-scripts off" -ex "file myprogram"
1276 The following does not work because the auto-loading is turned off too late:
1279 $ gdb -ex "set auto-load-scripts off" myprogram
1283 Reads command files specified by the @samp{-x} option. @xref{Command
1284 Files}, for more details about @value{GDBN} command files.
1287 Reads the command history recorded in the @dfn{history file}.
1288 @xref{Command History}, for more details about the command history and the
1289 files where @value{GDBN} records it.
1292 Init files use the same syntax as @dfn{command files} (@pxref{Command
1293 Files}) and are processed by @value{GDBN} in the same way. The init
1294 file in your home directory can set options (such as @samp{set
1295 complaints}) that affect subsequent processing of command line options
1296 and operands. Init files are not executed if you use the @samp{-nx}
1297 option (@pxref{Mode Options, ,Choosing Modes}).
1299 To display the list of init files loaded by gdb at startup, you
1300 can use @kbd{gdb --help}.
1302 @cindex init file name
1303 @cindex @file{.gdbinit}
1304 @cindex @file{gdb.ini}
1305 The @value{GDBN} init files are normally called @file{.gdbinit}.
1306 The DJGPP port of @value{GDBN} uses the name @file{gdb.ini}, due to
1307 the limitations of file names imposed by DOS filesystems. The Windows
1308 ports of @value{GDBN} use the standard name, but if they find a
1309 @file{gdb.ini} file, they warn you about that and suggest to rename
1310 the file to the standard name.
1314 @section Quitting @value{GDBN}
1315 @cindex exiting @value{GDBN}
1316 @cindex leaving @value{GDBN}
1319 @kindex quit @r{[}@var{expression}@r{]}
1320 @kindex q @r{(@code{quit})}
1321 @item quit @r{[}@var{expression}@r{]}
1323 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1324 @code{q}), or type an end-of-file character (usually @kbd{Ctrl-d}). If you
1325 do not supply @var{expression}, @value{GDBN} will terminate normally;
1326 otherwise it will terminate using the result of @var{expression} as the
1331 An interrupt (often @kbd{Ctrl-c}) does not exit from @value{GDBN}, but rather
1332 terminates the action of any @value{GDBN} command that is in progress and
1333 returns to @value{GDBN} command level. It is safe to type the interrupt
1334 character at any time because @value{GDBN} does not allow it to take effect
1335 until a time when it is safe.
1337 If you have been using @value{GDBN} to control an attached process or
1338 device, you can release it with the @code{detach} command
1339 (@pxref{Attach, ,Debugging an Already-running Process}).
1341 @node Shell Commands
1342 @section Shell Commands
1344 If you need to execute occasional shell commands during your
1345 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1346 just use the @code{shell} command.
1350 @cindex shell escape
1351 @item shell @var{command string}
1352 Invoke a standard shell to execute @var{command string}.
1353 If it exists, the environment variable @code{SHELL} determines which
1354 shell to run. Otherwise @value{GDBN} uses the default shell
1355 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1358 The utility @code{make} is often needed in development environments.
1359 You do not have to use the @code{shell} command for this purpose in
1364 @cindex calling make
1365 @item make @var{make-args}
1366 Execute the @code{make} program with the specified
1367 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1370 @node Logging Output
1371 @section Logging Output
1372 @cindex logging @value{GDBN} output
1373 @cindex save @value{GDBN} output to a file
1375 You may want to save the output of @value{GDBN} commands to a file.
1376 There are several commands to control @value{GDBN}'s logging.
1380 @item set logging on
1382 @item set logging off
1384 @cindex logging file name
1385 @item set logging file @var{file}
1386 Change the name of the current logfile. The default logfile is @file{gdb.txt}.
1387 @item set logging overwrite [on|off]
1388 By default, @value{GDBN} will append to the logfile. Set @code{overwrite} if
1389 you want @code{set logging on} to overwrite the logfile instead.
1390 @item set logging redirect [on|off]
1391 By default, @value{GDBN} output will go to both the terminal and the logfile.
1392 Set @code{redirect} if you want output to go only to the log file.
1393 @kindex show logging
1395 Show the current values of the logging settings.
1399 @chapter @value{GDBN} Commands
1401 You can abbreviate a @value{GDBN} command to the first few letters of the command
1402 name, if that abbreviation is unambiguous; and you can repeat certain
1403 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1404 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1405 show you the alternatives available, if there is more than one possibility).
1408 * Command Syntax:: How to give commands to @value{GDBN}
1409 * Completion:: Command completion
1410 * Help:: How to ask @value{GDBN} for help
1413 @node Command Syntax
1414 @section Command Syntax
1416 A @value{GDBN} command is a single line of input. There is no limit on
1417 how long it can be. It starts with a command name, which is followed by
1418 arguments whose meaning depends on the command name. For example, the
1419 command @code{step} accepts an argument which is the number of times to
1420 step, as in @samp{step 5}. You can also use the @code{step} command
1421 with no arguments. Some commands do not allow any arguments.
1423 @cindex abbreviation
1424 @value{GDBN} command names may always be truncated if that abbreviation is
1425 unambiguous. Other possible command abbreviations are listed in the
1426 documentation for individual commands. In some cases, even ambiguous
1427 abbreviations are allowed; for example, @code{s} is specially defined as
1428 equivalent to @code{step} even though there are other commands whose
1429 names start with @code{s}. You can test abbreviations by using them as
1430 arguments to the @code{help} command.
1432 @cindex repeating commands
1433 @kindex RET @r{(repeat last command)}
1434 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1435 repeat the previous command. Certain commands (for example, @code{run})
1436 will not repeat this way; these are commands whose unintentional
1437 repetition might cause trouble and which you are unlikely to want to
1438 repeat. User-defined commands can disable this feature; see
1439 @ref{Define, dont-repeat}.
1441 The @code{list} and @code{x} commands, when you repeat them with
1442 @key{RET}, construct new arguments rather than repeating
1443 exactly as typed. This permits easy scanning of source or memory.
1445 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1446 output, in a way similar to the common utility @code{more}
1447 (@pxref{Screen Size,,Screen Size}). Since it is easy to press one
1448 @key{RET} too many in this situation, @value{GDBN} disables command
1449 repetition after any command that generates this sort of display.
1451 @kindex # @r{(a comment)}
1453 Any text from a @kbd{#} to the end of the line is a comment; it does
1454 nothing. This is useful mainly in command files (@pxref{Command
1455 Files,,Command Files}).
1457 @cindex repeating command sequences
1458 @kindex Ctrl-o @r{(operate-and-get-next)}
1459 The @kbd{Ctrl-o} binding is useful for repeating a complex sequence of
1460 commands. This command accepts the current line, like @key{RET}, and
1461 then fetches the next line relative to the current line from the history
1465 @section Command Completion
1468 @cindex word completion
1469 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1470 only one possibility; it can also show you what the valid possibilities
1471 are for the next word in a command, at any time. This works for @value{GDBN}
1472 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1474 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1475 of a word. If there is only one possibility, @value{GDBN} fills in the
1476 word, and waits for you to finish the command (or press @key{RET} to
1477 enter it). For example, if you type
1479 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1480 @c complete accuracy in these examples; space introduced for clarity.
1481 @c If texinfo enhancements make it unnecessary, it would be nice to
1482 @c replace " @key" by "@key" in the following...
1484 (@value{GDBP}) info bre @key{TAB}
1488 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1489 the only @code{info} subcommand beginning with @samp{bre}:
1492 (@value{GDBP}) info breakpoints
1496 You can either press @key{RET} at this point, to run the @code{info
1497 breakpoints} command, or backspace and enter something else, if
1498 @samp{breakpoints} does not look like the command you expected. (If you
1499 were sure you wanted @code{info breakpoints} in the first place, you
1500 might as well just type @key{RET} immediately after @samp{info bre},
1501 to exploit command abbreviations rather than command completion).
1503 If there is more than one possibility for the next word when you press
1504 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1505 characters and try again, or just press @key{TAB} a second time;
1506 @value{GDBN} displays all the possible completions for that word. For
1507 example, you might want to set a breakpoint on a subroutine whose name
1508 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1509 just sounds the bell. Typing @key{TAB} again displays all the
1510 function names in your program that begin with those characters, for
1514 (@value{GDBP}) b make_ @key{TAB}
1515 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1516 make_a_section_from_file make_environ
1517 make_abs_section make_function_type
1518 make_blockvector make_pointer_type
1519 make_cleanup make_reference_type
1520 make_command make_symbol_completion_list
1521 (@value{GDBP}) b make_
1525 After displaying the available possibilities, @value{GDBN} copies your
1526 partial input (@samp{b make_} in the example) so you can finish the
1529 If you just want to see the list of alternatives in the first place, you
1530 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1531 means @kbd{@key{META} ?}. You can type this either by holding down a
1532 key designated as the @key{META} shift on your keyboard (if there is
1533 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1535 @cindex quotes in commands
1536 @cindex completion of quoted strings
1537 Sometimes the string you need, while logically a ``word'', may contain
1538 parentheses or other characters that @value{GDBN} normally excludes from
1539 its notion of a word. To permit word completion to work in this
1540 situation, you may enclose words in @code{'} (single quote marks) in
1541 @value{GDBN} commands.
1543 The most likely situation where you might need this is in typing the
1544 name of a C@t{++} function. This is because C@t{++} allows function
1545 overloading (multiple definitions of the same function, distinguished
1546 by argument type). For example, when you want to set a breakpoint you
1547 may need to distinguish whether you mean the version of @code{name}
1548 that takes an @code{int} parameter, @code{name(int)}, or the version
1549 that takes a @code{float} parameter, @code{name(float)}. To use the
1550 word-completion facilities in this situation, type a single quote
1551 @code{'} at the beginning of the function name. This alerts
1552 @value{GDBN} that it may need to consider more information than usual
1553 when you press @key{TAB} or @kbd{M-?} to request word completion:
1556 (@value{GDBP}) b 'bubble( @kbd{M-?}
1557 bubble(double,double) bubble(int,int)
1558 (@value{GDBP}) b 'bubble(
1561 In some cases, @value{GDBN} can tell that completing a name requires using
1562 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1563 completing as much as it can) if you do not type the quote in the first
1567 (@value{GDBP}) b bub @key{TAB}
1568 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1569 (@value{GDBP}) b 'bubble(
1573 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1574 you have not yet started typing the argument list when you ask for
1575 completion on an overloaded symbol.
1577 For more information about overloaded functions, see @ref{C Plus Plus
1578 Expressions, ,C@t{++} Expressions}. You can use the command @code{set
1579 overload-resolution off} to disable overload resolution;
1580 see @ref{Debugging C Plus Plus, ,@value{GDBN} Features for C@t{++}}.
1582 @cindex completion of structure field names
1583 @cindex structure field name completion
1584 @cindex completion of union field names
1585 @cindex union field name completion
1586 When completing in an expression which looks up a field in a
1587 structure, @value{GDBN} also tries@footnote{The completer can be
1588 confused by certain kinds of invalid expressions. Also, it only
1589 examines the static type of the expression, not the dynamic type.} to
1590 limit completions to the field names available in the type of the
1594 (@value{GDBP}) p gdb_stdout.@kbd{M-?}
1595 magic to_fputs to_rewind
1596 to_data to_isatty to_write
1597 to_delete to_put to_write_async_safe
1602 This is because the @code{gdb_stdout} is a variable of the type
1603 @code{struct ui_file} that is defined in @value{GDBN} sources as
1610 ui_file_flush_ftype *to_flush;
1611 ui_file_write_ftype *to_write;
1612 ui_file_write_async_safe_ftype *to_write_async_safe;
1613 ui_file_fputs_ftype *to_fputs;
1614 ui_file_read_ftype *to_read;
1615 ui_file_delete_ftype *to_delete;
1616 ui_file_isatty_ftype *to_isatty;
1617 ui_file_rewind_ftype *to_rewind;
1618 ui_file_put_ftype *to_put;
1625 @section Getting Help
1626 @cindex online documentation
1629 You can always ask @value{GDBN} itself for information on its commands,
1630 using the command @code{help}.
1633 @kindex h @r{(@code{help})}
1636 You can use @code{help} (abbreviated @code{h}) with no arguments to
1637 display a short list of named classes of commands:
1641 List of classes of commands:
1643 aliases -- Aliases of other commands
1644 breakpoints -- Making program stop at certain points
1645 data -- Examining data
1646 files -- Specifying and examining files
1647 internals -- Maintenance commands
1648 obscure -- Obscure features
1649 running -- Running the program
1650 stack -- Examining the stack
1651 status -- Status inquiries
1652 support -- Support facilities
1653 tracepoints -- Tracing of program execution without
1654 stopping the program
1655 user-defined -- User-defined commands
1657 Type "help" followed by a class name for a list of
1658 commands in that class.
1659 Type "help" followed by command name for full
1661 Command name abbreviations are allowed if unambiguous.
1664 @c the above line break eliminates huge line overfull...
1666 @item help @var{class}
1667 Using one of the general help classes as an argument, you can get a
1668 list of the individual commands in that class. For example, here is the
1669 help display for the class @code{status}:
1672 (@value{GDBP}) help status
1677 @c Line break in "show" line falsifies real output, but needed
1678 @c to fit in smallbook page size.
1679 info -- Generic command for showing things
1680 about the program being debugged
1681 show -- Generic command for showing things
1684 Type "help" followed by command name for full
1686 Command name abbreviations are allowed if unambiguous.
1690 @item help @var{command}
1691 With a command name as @code{help} argument, @value{GDBN} displays a
1692 short paragraph on how to use that command.
1695 @item apropos @var{args}
1696 The @code{apropos} command searches through all of the @value{GDBN}
1697 commands, and their documentation, for the regular expression specified in
1698 @var{args}. It prints out all matches found. For example:
1709 set symbol-reloading -- Set dynamic symbol table reloading
1710 multiple times in one run
1711 show symbol-reloading -- Show dynamic symbol table reloading
1712 multiple times in one run
1717 @item complete @var{args}
1718 The @code{complete @var{args}} command lists all the possible completions
1719 for the beginning of a command. Use @var{args} to specify the beginning of the
1720 command you want completed. For example:
1726 @noindent results in:
1737 @noindent This is intended for use by @sc{gnu} Emacs.
1740 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1741 and @code{show} to inquire about the state of your program, or the state
1742 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1743 manual introduces each of them in the appropriate context. The listings
1744 under @code{info} and under @code{show} in the Index point to
1745 all the sub-commands. @xref{Index}.
1750 @kindex i @r{(@code{info})}
1752 This command (abbreviated @code{i}) is for describing the state of your
1753 program. For example, you can show the arguments passed to a function
1754 with @code{info args}, list the registers currently in use with @code{info
1755 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1756 You can get a complete list of the @code{info} sub-commands with
1757 @w{@code{help info}}.
1761 You can assign the result of an expression to an environment variable with
1762 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1763 @code{set prompt $}.
1767 In contrast to @code{info}, @code{show} is for describing the state of
1768 @value{GDBN} itself.
1769 You can change most of the things you can @code{show}, by using the
1770 related command @code{set}; for example, you can control what number
1771 system is used for displays with @code{set radix}, or simply inquire
1772 which is currently in use with @code{show radix}.
1775 To display all the settable parameters and their current
1776 values, you can use @code{show} with no arguments; you may also use
1777 @code{info set}. Both commands produce the same display.
1778 @c FIXME: "info set" violates the rule that "info" is for state of
1779 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1780 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1784 Here are three miscellaneous @code{show} subcommands, all of which are
1785 exceptional in lacking corresponding @code{set} commands:
1788 @kindex show version
1789 @cindex @value{GDBN} version number
1791 Show what version of @value{GDBN} is running. You should include this
1792 information in @value{GDBN} bug-reports. If multiple versions of
1793 @value{GDBN} are in use at your site, you may need to determine which
1794 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1795 commands are introduced, and old ones may wither away. Also, many
1796 system vendors ship variant versions of @value{GDBN}, and there are
1797 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1798 The version number is the same as the one announced when you start
1801 @kindex show copying
1802 @kindex info copying
1803 @cindex display @value{GDBN} copyright
1806 Display information about permission for copying @value{GDBN}.
1808 @kindex show warranty
1809 @kindex info warranty
1811 @itemx info warranty
1812 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1813 if your version of @value{GDBN} comes with one.
1818 @chapter Running Programs Under @value{GDBN}
1820 When you run a program under @value{GDBN}, you must first generate
1821 debugging information when you compile it.
1823 You may start @value{GDBN} with its arguments, if any, in an environment
1824 of your choice. If you are doing native debugging, you may redirect
1825 your program's input and output, debug an already running process, or
1826 kill a child process.
1829 * Compilation:: Compiling for debugging
1830 * Starting:: Starting your program
1831 * Arguments:: Your program's arguments
1832 * Environment:: Your program's environment
1834 * Working Directory:: Your program's working directory
1835 * Input/Output:: Your program's input and output
1836 * Attach:: Debugging an already-running process
1837 * Kill Process:: Killing the child process
1839 * Inferiors and Programs:: Debugging multiple inferiors and programs
1840 * Threads:: Debugging programs with multiple threads
1841 * Forks:: Debugging forks
1842 * Checkpoint/Restart:: Setting a @emph{bookmark} to return to later
1846 @section Compiling for Debugging
1848 In order to debug a program effectively, you need to generate
1849 debugging information when you compile it. This debugging information
1850 is stored in the object file; it describes the data type of each
1851 variable or function and the correspondence between source line numbers
1852 and addresses in the executable code.
1854 To request debugging information, specify the @samp{-g} option when you run
1857 Programs that are to be shipped to your customers are compiled with
1858 optimizations, using the @samp{-O} compiler option. However, some
1859 compilers are unable to handle the @samp{-g} and @samp{-O} options
1860 together. Using those compilers, you cannot generate optimized
1861 executables containing debugging information.
1863 @value{NGCC}, the @sc{gnu} C/C@t{++} compiler, supports @samp{-g} with or
1864 without @samp{-O}, making it possible to debug optimized code. We
1865 recommend that you @emph{always} use @samp{-g} whenever you compile a
1866 program. You may think your program is correct, but there is no sense
1867 in pushing your luck. For more information, see @ref{Optimized Code}.
1869 Older versions of the @sc{gnu} C compiler permitted a variant option
1870 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1871 format; if your @sc{gnu} C compiler has this option, do not use it.
1873 @value{GDBN} knows about preprocessor macros and can show you their
1874 expansion (@pxref{Macros}). Most compilers do not include information
1875 about preprocessor macros in the debugging information if you specify
1876 the @option{-g} flag alone, because this information is rather large.
1877 Version 3.1 and later of @value{NGCC}, the @sc{gnu} C compiler,
1878 provides macro information if you specify the options
1879 @option{-gdwarf-2} and @option{-g3}; the former option requests
1880 debugging information in the Dwarf 2 format, and the latter requests
1881 ``extra information''. In the future, we hope to find more compact
1882 ways to represent macro information, so that it can be included with
1887 @section Starting your Program
1893 @kindex r @r{(@code{run})}
1896 Use the @code{run} command to start your program under @value{GDBN}.
1897 You must first specify the program name (except on VxWorks) with an
1898 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1899 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1900 (@pxref{Files, ,Commands to Specify Files}).
1904 If you are running your program in an execution environment that
1905 supports processes, @code{run} creates an inferior process and makes
1906 that process run your program. In some environments without processes,
1907 @code{run} jumps to the start of your program. Other targets,
1908 like @samp{remote}, are always running. If you get an error
1909 message like this one:
1912 The "remote" target does not support "run".
1913 Try "help target" or "continue".
1917 then use @code{continue} to run your program. You may need @code{load}
1918 first (@pxref{load}).
1920 The execution of a program is affected by certain information it
1921 receives from its superior. @value{GDBN} provides ways to specify this
1922 information, which you must do @emph{before} starting your program. (You
1923 can change it after starting your program, but such changes only affect
1924 your program the next time you start it.) This information may be
1925 divided into four categories:
1928 @item The @emph{arguments.}
1929 Specify the arguments to give your program as the arguments of the
1930 @code{run} command. If a shell is available on your target, the shell
1931 is used to pass the arguments, so that you may use normal conventions
1932 (such as wildcard expansion or variable substitution) in describing
1934 In Unix systems, you can control which shell is used with the
1935 @code{SHELL} environment variable.
1936 @xref{Arguments, ,Your Program's Arguments}.
1938 @item The @emph{environment.}
1939 Your program normally inherits its environment from @value{GDBN}, but you can
1940 use the @value{GDBN} commands @code{set environment} and @code{unset
1941 environment} to change parts of the environment that affect
1942 your program. @xref{Environment, ,Your Program's Environment}.
1944 @item The @emph{working directory.}
1945 Your program inherits its working directory from @value{GDBN}. You can set
1946 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1947 @xref{Working Directory, ,Your Program's Working Directory}.
1949 @item The @emph{standard input and output.}
1950 Your program normally uses the same device for standard input and
1951 standard output as @value{GDBN} is using. You can redirect input and output
1952 in the @code{run} command line, or you can use the @code{tty} command to
1953 set a different device for your program.
1954 @xref{Input/Output, ,Your Program's Input and Output}.
1957 @emph{Warning:} While input and output redirection work, you cannot use
1958 pipes to pass the output of the program you are debugging to another
1959 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1963 When you issue the @code{run} command, your program begins to execute
1964 immediately. @xref{Stopping, ,Stopping and Continuing}, for discussion
1965 of how to arrange for your program to stop. Once your program has
1966 stopped, you may call functions in your program, using the @code{print}
1967 or @code{call} commands. @xref{Data, ,Examining Data}.
1969 If the modification time of your symbol file has changed since the last
1970 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1971 table, and reads it again. When it does this, @value{GDBN} tries to retain
1972 your current breakpoints.
1977 @cindex run to main procedure
1978 The name of the main procedure can vary from language to language.
1979 With C or C@t{++}, the main procedure name is always @code{main}, but
1980 other languages such as Ada do not require a specific name for their
1981 main procedure. The debugger provides a convenient way to start the
1982 execution of the program and to stop at the beginning of the main
1983 procedure, depending on the language used.
1985 The @samp{start} command does the equivalent of setting a temporary
1986 breakpoint at the beginning of the main procedure and then invoking
1987 the @samp{run} command.
1989 @cindex elaboration phase
1990 Some programs contain an @dfn{elaboration} phase where some startup code is
1991 executed before the main procedure is called. This depends on the
1992 languages used to write your program. In C@t{++}, for instance,
1993 constructors for static and global objects are executed before
1994 @code{main} is called. It is therefore possible that the debugger stops
1995 before reaching the main procedure. However, the temporary breakpoint
1996 will remain to halt execution.
1998 Specify the arguments to give to your program as arguments to the
1999 @samp{start} command. These arguments will be given verbatim to the
2000 underlying @samp{run} command. Note that the same arguments will be
2001 reused if no argument is provided during subsequent calls to
2002 @samp{start} or @samp{run}.
2004 It is sometimes necessary to debug the program during elaboration. In
2005 these cases, using the @code{start} command would stop the execution of
2006 your program too late, as the program would have already completed the
2007 elaboration phase. Under these circumstances, insert breakpoints in your
2008 elaboration code before running your program.
2010 @kindex set exec-wrapper
2011 @item set exec-wrapper @var{wrapper}
2012 @itemx show exec-wrapper
2013 @itemx unset exec-wrapper
2014 When @samp{exec-wrapper} is set, the specified wrapper is used to
2015 launch programs for debugging. @value{GDBN} starts your program
2016 with a shell command of the form @kbd{exec @var{wrapper}
2017 @var{program}}. Quoting is added to @var{program} and its
2018 arguments, but not to @var{wrapper}, so you should add quotes if
2019 appropriate for your shell. The wrapper runs until it executes
2020 your program, and then @value{GDBN} takes control.
2022 You can use any program that eventually calls @code{execve} with
2023 its arguments as a wrapper. Several standard Unix utilities do
2024 this, e.g.@: @code{env} and @code{nohup}. Any Unix shell script ending
2025 with @code{exec "$@@"} will also work.
2027 For example, you can use @code{env} to pass an environment variable to
2028 the debugged program, without setting the variable in your shell's
2032 (@value{GDBP}) set exec-wrapper env 'LD_PRELOAD=libtest.so'
2036 This command is available when debugging locally on most targets, excluding
2037 @sc{djgpp}, Cygwin, MS Windows, and QNX Neutrino.
2039 @kindex set disable-randomization
2040 @item set disable-randomization
2041 @itemx set disable-randomization on
2042 This option (enabled by default in @value{GDBN}) will turn off the native
2043 randomization of the virtual address space of the started program. This option
2044 is useful for multiple debugging sessions to make the execution better
2045 reproducible and memory addresses reusable across debugging sessions.
2047 This feature is implemented only on certain targets, including @sc{gnu}/Linux.
2048 On @sc{gnu}/Linux you can get the same behavior using
2051 (@value{GDBP}) set exec-wrapper setarch `uname -m` -R
2054 @item set disable-randomization off
2055 Leave the behavior of the started executable unchanged. Some bugs rear their
2056 ugly heads only when the program is loaded at certain addresses. If your bug
2057 disappears when you run the program under @value{GDBN}, that might be because
2058 @value{GDBN} by default disables the address randomization on platforms, such
2059 as @sc{gnu}/Linux, which do that for stand-alone programs. Use @kbd{set
2060 disable-randomization off} to try to reproduce such elusive bugs.
2062 On targets where it is available, virtual address space randomization
2063 protects the programs against certain kinds of security attacks. In these
2064 cases the attacker needs to know the exact location of a concrete executable
2065 code. Randomizing its location makes it impossible to inject jumps misusing
2066 a code at its expected addresses.
2068 Prelinking shared libraries provides a startup performance advantage but it
2069 makes addresses in these libraries predictable for privileged processes by
2070 having just unprivileged access at the target system. Reading the shared
2071 library binary gives enough information for assembling the malicious code
2072 misusing it. Still even a prelinked shared library can get loaded at a new
2073 random address just requiring the regular relocation process during the
2074 startup. Shared libraries not already prelinked are always loaded at
2075 a randomly chosen address.
2077 Position independent executables (PIE) contain position independent code
2078 similar to the shared libraries and therefore such executables get loaded at
2079 a randomly chosen address upon startup. PIE executables always load even
2080 already prelinked shared libraries at a random address. You can build such
2081 executable using @command{gcc -fPIE -pie}.
2083 Heap (malloc storage), stack and custom mmap areas are always placed randomly
2084 (as long as the randomization is enabled).
2086 @item show disable-randomization
2087 Show the current setting of the explicit disable of the native randomization of
2088 the virtual address space of the started program.
2093 @section Your Program's Arguments
2095 @cindex arguments (to your program)
2096 The arguments to your program can be specified by the arguments of the
2098 They are passed to a shell, which expands wildcard characters and
2099 performs redirection of I/O, and thence to your program. Your
2100 @code{SHELL} environment variable (if it exists) specifies what shell
2101 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
2102 the default shell (@file{/bin/sh} on Unix).
2104 On non-Unix systems, the program is usually invoked directly by
2105 @value{GDBN}, which emulates I/O redirection via the appropriate system
2106 calls, and the wildcard characters are expanded by the startup code of
2107 the program, not by the shell.
2109 @code{run} with no arguments uses the same arguments used by the previous
2110 @code{run}, or those set by the @code{set args} command.
2115 Specify the arguments to be used the next time your program is run. If
2116 @code{set args} has no arguments, @code{run} executes your program
2117 with no arguments. Once you have run your program with arguments,
2118 using @code{set args} before the next @code{run} is the only way to run
2119 it again without arguments.
2123 Show the arguments to give your program when it is started.
2127 @section Your Program's Environment
2129 @cindex environment (of your program)
2130 The @dfn{environment} consists of a set of environment variables and
2131 their values. Environment variables conventionally record such things as
2132 your user name, your home directory, your terminal type, and your search
2133 path for programs to run. Usually you set up environment variables with
2134 the shell and they are inherited by all the other programs you run. When
2135 debugging, it can be useful to try running your program with a modified
2136 environment without having to start @value{GDBN} over again.
2140 @item path @var{directory}
2141 Add @var{directory} to the front of the @code{PATH} environment variable
2142 (the search path for executables) that will be passed to your program.
2143 The value of @code{PATH} used by @value{GDBN} does not change.
2144 You may specify several directory names, separated by whitespace or by a
2145 system-dependent separator character (@samp{:} on Unix, @samp{;} on
2146 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
2147 is moved to the front, so it is searched sooner.
2149 You can use the string @samp{$cwd} to refer to whatever is the current
2150 working directory at the time @value{GDBN} searches the path. If you
2151 use @samp{.} instead, it refers to the directory where you executed the
2152 @code{path} command. @value{GDBN} replaces @samp{.} in the
2153 @var{directory} argument (with the current path) before adding
2154 @var{directory} to the search path.
2155 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
2156 @c document that, since repeating it would be a no-op.
2160 Display the list of search paths for executables (the @code{PATH}
2161 environment variable).
2163 @kindex show environment
2164 @item show environment @r{[}@var{varname}@r{]}
2165 Print the value of environment variable @var{varname} to be given to
2166 your program when it starts. If you do not supply @var{varname},
2167 print the names and values of all environment variables to be given to
2168 your program. You can abbreviate @code{environment} as @code{env}.
2170 @kindex set environment
2171 @item set environment @var{varname} @r{[}=@var{value}@r{]}
2172 Set environment variable @var{varname} to @var{value}. The value
2173 changes for your program only, not for @value{GDBN} itself. @var{value} may
2174 be any string; the values of environment variables are just strings, and
2175 any interpretation is supplied by your program itself. The @var{value}
2176 parameter is optional; if it is eliminated, the variable is set to a
2178 @c "any string" here does not include leading, trailing
2179 @c blanks. Gnu asks: does anyone care?
2181 For example, this command:
2188 tells the debugged program, when subsequently run, that its user is named
2189 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
2190 are not actually required.)
2192 @kindex unset environment
2193 @item unset environment @var{varname}
2194 Remove variable @var{varname} from the environment to be passed to your
2195 program. This is different from @samp{set env @var{varname} =};
2196 @code{unset environment} removes the variable from the environment,
2197 rather than assigning it an empty value.
2200 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
2202 by your @code{SHELL} environment variable if it exists (or
2203 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
2204 that runs an initialization file---such as @file{.cshrc} for C-shell, or
2205 @file{.bashrc} for BASH---any variables you set in that file affect
2206 your program. You may wish to move setting of environment variables to
2207 files that are only run when you sign on, such as @file{.login} or
2210 @node Working Directory
2211 @section Your Program's Working Directory
2213 @cindex working directory (of your program)
2214 Each time you start your program with @code{run}, it inherits its
2215 working directory from the current working directory of @value{GDBN}.
2216 The @value{GDBN} working directory is initially whatever it inherited
2217 from its parent process (typically the shell), but you can specify a new
2218 working directory in @value{GDBN} with the @code{cd} command.
2220 The @value{GDBN} working directory also serves as a default for the commands
2221 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
2226 @cindex change working directory
2227 @item cd @var{directory}
2228 Set the @value{GDBN} working directory to @var{directory}.
2232 Print the @value{GDBN} working directory.
2235 It is generally impossible to find the current working directory of
2236 the process being debugged (since a program can change its directory
2237 during its run). If you work on a system where @value{GDBN} is
2238 configured with the @file{/proc} support, you can use the @code{info
2239 proc} command (@pxref{SVR4 Process Information}) to find out the
2240 current working directory of the debuggee.
2243 @section Your Program's Input and Output
2248 By default, the program you run under @value{GDBN} does input and output to
2249 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
2250 to its own terminal modes to interact with you, but it records the terminal
2251 modes your program was using and switches back to them when you continue
2252 running your program.
2255 @kindex info terminal
2257 Displays information recorded by @value{GDBN} about the terminal modes your
2261 You can redirect your program's input and/or output using shell
2262 redirection with the @code{run} command. For example,
2269 starts your program, diverting its output to the file @file{outfile}.
2272 @cindex controlling terminal
2273 Another way to specify where your program should do input and output is
2274 with the @code{tty} command. This command accepts a file name as
2275 argument, and causes this file to be the default for future @code{run}
2276 commands. It also resets the controlling terminal for the child
2277 process, for future @code{run} commands. For example,
2284 directs that processes started with subsequent @code{run} commands
2285 default to do input and output on the terminal @file{/dev/ttyb} and have
2286 that as their controlling terminal.
2288 An explicit redirection in @code{run} overrides the @code{tty} command's
2289 effect on the input/output device, but not its effect on the controlling
2292 When you use the @code{tty} command or redirect input in the @code{run}
2293 command, only the input @emph{for your program} is affected. The input
2294 for @value{GDBN} still comes from your terminal. @code{tty} is an alias
2295 for @code{set inferior-tty}.
2297 @cindex inferior tty
2298 @cindex set inferior controlling terminal
2299 You can use the @code{show inferior-tty} command to tell @value{GDBN} to
2300 display the name of the terminal that will be used for future runs of your
2304 @item set inferior-tty /dev/ttyb
2305 @kindex set inferior-tty
2306 Set the tty for the program being debugged to /dev/ttyb.
2308 @item show inferior-tty
2309 @kindex show inferior-tty
2310 Show the current tty for the program being debugged.
2314 @section Debugging an Already-running Process
2319 @item attach @var{process-id}
2320 This command attaches to a running process---one that was started
2321 outside @value{GDBN}. (@code{info files} shows your active
2322 targets.) The command takes as argument a process ID. The usual way to
2323 find out the @var{process-id} of a Unix process is with the @code{ps} utility,
2324 or with the @samp{jobs -l} shell command.
2326 @code{attach} does not repeat if you press @key{RET} a second time after
2327 executing the command.
2330 To use @code{attach}, your program must be running in an environment
2331 which supports processes; for example, @code{attach} does not work for
2332 programs on bare-board targets that lack an operating system. You must
2333 also have permission to send the process a signal.
2335 When you use @code{attach}, the debugger finds the program running in
2336 the process first by looking in the current working directory, then (if
2337 the program is not found) by using the source file search path
2338 (@pxref{Source Path, ,Specifying Source Directories}). You can also use
2339 the @code{file} command to load the program. @xref{Files, ,Commands to
2342 The first thing @value{GDBN} does after arranging to debug the specified
2343 process is to stop it. You can examine and modify an attached process
2344 with all the @value{GDBN} commands that are ordinarily available when
2345 you start processes with @code{run}. You can insert breakpoints; you
2346 can step and continue; you can modify storage. If you would rather the
2347 process continue running, you may use the @code{continue} command after
2348 attaching @value{GDBN} to the process.
2353 When you have finished debugging the attached process, you can use the
2354 @code{detach} command to release it from @value{GDBN} control. Detaching
2355 the process continues its execution. After the @code{detach} command,
2356 that process and @value{GDBN} become completely independent once more, and you
2357 are ready to @code{attach} another process or start one with @code{run}.
2358 @code{detach} does not repeat if you press @key{RET} again after
2359 executing the command.
2362 If you exit @value{GDBN} while you have an attached process, you detach
2363 that process. If you use the @code{run} command, you kill that process.
2364 By default, @value{GDBN} asks for confirmation if you try to do either of these
2365 things; you can control whether or not you need to confirm by using the
2366 @code{set confirm} command (@pxref{Messages/Warnings, ,Optional Warnings and
2370 @section Killing the Child Process
2375 Kill the child process in which your program is running under @value{GDBN}.
2378 This command is useful if you wish to debug a core dump instead of a
2379 running process. @value{GDBN} ignores any core dump file while your program
2382 On some operating systems, a program cannot be executed outside @value{GDBN}
2383 while you have breakpoints set on it inside @value{GDBN}. You can use the
2384 @code{kill} command in this situation to permit running your program
2385 outside the debugger.
2387 The @code{kill} command is also useful if you wish to recompile and
2388 relink your program, since on many systems it is impossible to modify an
2389 executable file while it is running in a process. In this case, when you
2390 next type @code{run}, @value{GDBN} notices that the file has changed, and
2391 reads the symbol table again (while trying to preserve your current
2392 breakpoint settings).
2394 @node Inferiors and Programs
2395 @section Debugging Multiple Inferiors and Programs
2397 @value{GDBN} lets you run and debug multiple programs in a single
2398 session. In addition, @value{GDBN} on some systems may let you run
2399 several programs simultaneously (otherwise you have to exit from one
2400 before starting another). In the most general case, you can have
2401 multiple threads of execution in each of multiple processes, launched
2402 from multiple executables.
2405 @value{GDBN} represents the state of each program execution with an
2406 object called an @dfn{inferior}. An inferior typically corresponds to
2407 a process, but is more general and applies also to targets that do not
2408 have processes. Inferiors may be created before a process runs, and
2409 may be retained after a process exits. Inferiors have unique
2410 identifiers that are different from process ids. Usually each
2411 inferior will also have its own distinct address space, although some
2412 embedded targets may have several inferiors running in different parts
2413 of a single address space. Each inferior may in turn have multiple
2414 threads running in it.
2416 To find out what inferiors exist at any moment, use @w{@code{info
2420 @kindex info inferiors
2421 @item info inferiors
2422 Print a list of all inferiors currently being managed by @value{GDBN}.
2424 @value{GDBN} displays for each inferior (in this order):
2428 the inferior number assigned by @value{GDBN}
2431 the target system's inferior identifier
2434 the name of the executable the inferior is running.
2439 An asterisk @samp{*} preceding the @value{GDBN} inferior number
2440 indicates the current inferior.
2444 @c end table here to get a little more width for example
2447 (@value{GDBP}) info inferiors
2448 Num Description Executable
2449 2 process 2307 hello
2450 * 1 process 3401 goodbye
2453 To switch focus between inferiors, use the @code{inferior} command:
2456 @kindex inferior @var{infno}
2457 @item inferior @var{infno}
2458 Make inferior number @var{infno} the current inferior. The argument
2459 @var{infno} is the inferior number assigned by @value{GDBN}, as shown
2460 in the first field of the @samp{info inferiors} display.
2464 You can get multiple executables into a debugging session via the
2465 @code{add-inferior} and @w{@code{clone-inferior}} commands. On some
2466 systems @value{GDBN} can add inferiors to the debug session
2467 automatically by following calls to @code{fork} and @code{exec}. To
2468 remove inferiors from the debugging session use the
2469 @w{@code{remove-inferiors}} command.
2472 @kindex add-inferior
2473 @item add-inferior [ -copies @var{n} ] [ -exec @var{executable} ]
2474 Adds @var{n} inferiors to be run using @var{executable} as the
2475 executable. @var{n} defaults to 1. If no executable is specified,
2476 the inferiors begins empty, with no program. You can still assign or
2477 change the program assigned to the inferior at any time by using the
2478 @code{file} command with the executable name as its argument.
2480 @kindex clone-inferior
2481 @item clone-inferior [ -copies @var{n} ] [ @var{infno} ]
2482 Adds @var{n} inferiors ready to execute the same program as inferior
2483 @var{infno}. @var{n} defaults to 1. @var{infno} defaults to the
2484 number of the current inferior. This is a convenient command when you
2485 want to run another instance of the inferior you are debugging.
2488 (@value{GDBP}) info inferiors
2489 Num Description Executable
2490 * 1 process 29964 helloworld
2491 (@value{GDBP}) clone-inferior
2494 (@value{GDBP}) info inferiors
2495 Num Description Executable
2497 * 1 process 29964 helloworld
2500 You can now simply switch focus to inferior 2 and run it.
2502 @kindex remove-inferiors
2503 @item remove-inferiors @var{infno}@dots{}
2504 Removes the inferior or inferiors @var{infno}@dots{}. It is not
2505 possible to remove an inferior that is running with this command. For
2506 those, use the @code{kill} or @code{detach} command first.
2510 To quit debugging one of the running inferiors that is not the current
2511 inferior, you can either detach from it by using the @w{@code{detach
2512 inferior}} command (allowing it to run independently), or kill it
2513 using the @w{@code{kill inferiors}} command:
2516 @kindex detach inferiors @var{infno}@dots{}
2517 @item detach inferior @var{infno}@dots{}
2518 Detach from the inferior or inferiors identified by @value{GDBN}
2519 inferior number(s) @var{infno}@dots{}. Note that the inferior's entry
2520 still stays on the list of inferiors shown by @code{info inferiors},
2521 but its Description will show @samp{<null>}.
2523 @kindex kill inferiors @var{infno}@dots{}
2524 @item kill inferiors @var{infno}@dots{}
2525 Kill the inferior or inferiors identified by @value{GDBN} inferior
2526 number(s) @var{infno}@dots{}. Note that the inferior's entry still
2527 stays on the list of inferiors shown by @code{info inferiors}, but its
2528 Description will show @samp{<null>}.
2531 After the successful completion of a command such as @code{detach},
2532 @code{detach inferiors}, @code{kill} or @code{kill inferiors}, or after
2533 a normal process exit, the inferior is still valid and listed with
2534 @code{info inferiors}, ready to be restarted.
2537 To be notified when inferiors are started or exit under @value{GDBN}'s
2538 control use @w{@code{set print inferior-events}}:
2541 @kindex set print inferior-events
2542 @cindex print messages on inferior start and exit
2543 @item set print inferior-events
2544 @itemx set print inferior-events on
2545 @itemx set print inferior-events off
2546 The @code{set print inferior-events} command allows you to enable or
2547 disable printing of messages when @value{GDBN} notices that new
2548 inferiors have started or that inferiors have exited or have been
2549 detached. By default, these messages will not be printed.
2551 @kindex show print inferior-events
2552 @item show print inferior-events
2553 Show whether messages will be printed when @value{GDBN} detects that
2554 inferiors have started, exited or have been detached.
2557 Many commands will work the same with multiple programs as with a
2558 single program: e.g., @code{print myglobal} will simply display the
2559 value of @code{myglobal} in the current inferior.
2562 Occasionaly, when debugging @value{GDBN} itself, it may be useful to
2563 get more info about the relationship of inferiors, programs, address
2564 spaces in a debug session. You can do that with the @w{@code{maint
2565 info program-spaces}} command.
2568 @kindex maint info program-spaces
2569 @item maint info program-spaces
2570 Print a list of all program spaces currently being managed by
2573 @value{GDBN} displays for each program space (in this order):
2577 the program space number assigned by @value{GDBN}
2580 the name of the executable loaded into the program space, with e.g.,
2581 the @code{file} command.
2586 An asterisk @samp{*} preceding the @value{GDBN} program space number
2587 indicates the current program space.
2589 In addition, below each program space line, @value{GDBN} prints extra
2590 information that isn't suitable to display in tabular form. For
2591 example, the list of inferiors bound to the program space.
2594 (@value{GDBP}) maint info program-spaces
2597 Bound inferiors: ID 1 (process 21561)
2601 Here we can see that no inferior is running the program @code{hello},
2602 while @code{process 21561} is running the program @code{goodbye}. On
2603 some targets, it is possible that multiple inferiors are bound to the
2604 same program space. The most common example is that of debugging both
2605 the parent and child processes of a @code{vfork} call. For example,
2608 (@value{GDBP}) maint info program-spaces
2611 Bound inferiors: ID 2 (process 18050), ID 1 (process 18045)
2614 Here, both inferior 2 and inferior 1 are running in the same program
2615 space as a result of inferior 1 having executed a @code{vfork} call.
2619 @section Debugging Programs with Multiple Threads
2621 @cindex threads of execution
2622 @cindex multiple threads
2623 @cindex switching threads
2624 In some operating systems, such as HP-UX and Solaris, a single program
2625 may have more than one @dfn{thread} of execution. The precise semantics
2626 of threads differ from one operating system to another, but in general
2627 the threads of a single program are akin to multiple processes---except
2628 that they share one address space (that is, they can all examine and
2629 modify the same variables). On the other hand, each thread has its own
2630 registers and execution stack, and perhaps private memory.
2632 @value{GDBN} provides these facilities for debugging multi-thread
2636 @item automatic notification of new threads
2637 @item @samp{thread @var{threadno}}, a command to switch among threads
2638 @item @samp{info threads}, a command to inquire about existing threads
2639 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
2640 a command to apply a command to a list of threads
2641 @item thread-specific breakpoints
2642 @item @samp{set print thread-events}, which controls printing of
2643 messages on thread start and exit.
2644 @item @samp{set libthread-db-search-path @var{path}}, which lets
2645 the user specify which @code{libthread_db} to use if the default choice
2646 isn't compatible with the program.
2650 @emph{Warning:} These facilities are not yet available on every
2651 @value{GDBN} configuration where the operating system supports threads.
2652 If your @value{GDBN} does not support threads, these commands have no
2653 effect. For example, a system without thread support shows no output
2654 from @samp{info threads}, and always rejects the @code{thread} command,
2658 (@value{GDBP}) info threads
2659 (@value{GDBP}) thread 1
2660 Thread ID 1 not known. Use the "info threads" command to
2661 see the IDs of currently known threads.
2663 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
2664 @c doesn't support threads"?
2667 @cindex focus of debugging
2668 @cindex current thread
2669 The @value{GDBN} thread debugging facility allows you to observe all
2670 threads while your program runs---but whenever @value{GDBN} takes
2671 control, one thread in particular is always the focus of debugging.
2672 This thread is called the @dfn{current thread}. Debugging commands show
2673 program information from the perspective of the current thread.
2675 @cindex @code{New} @var{systag} message
2676 @cindex thread identifier (system)
2677 @c FIXME-implementors!! It would be more helpful if the [New...] message
2678 @c included GDB's numeric thread handle, so you could just go to that
2679 @c thread without first checking `info threads'.
2680 Whenever @value{GDBN} detects a new thread in your program, it displays
2681 the target system's identification for the thread with a message in the
2682 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2683 whose form varies depending on the particular system. For example, on
2684 @sc{gnu}/Linux, you might see
2687 [New Thread 0x41e02940 (LWP 25582)]
2691 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
2692 the @var{systag} is simply something like @samp{process 368}, with no
2695 @c FIXME!! (1) Does the [New...] message appear even for the very first
2696 @c thread of a program, or does it only appear for the
2697 @c second---i.e.@: when it becomes obvious we have a multithread
2699 @c (2) *Is* there necessarily a first thread always? Or do some
2700 @c multithread systems permit starting a program with multiple
2701 @c threads ab initio?
2703 @cindex thread number
2704 @cindex thread identifier (GDB)
2705 For debugging purposes, @value{GDBN} associates its own thread
2706 number---always a single integer---with each thread in your program.
2709 @kindex info threads
2710 @item info threads @r{[}@var{id}@dots{}@r{]}
2711 Display a summary of all threads currently in your program. Optional
2712 argument @var{id}@dots{} is one or more thread ids separated by spaces, and
2713 means to print information only about the specified thread or threads.
2714 @value{GDBN} displays for each thread (in this order):
2718 the thread number assigned by @value{GDBN}
2721 the target system's thread identifier (@var{systag})
2724 the thread's name, if one is known. A thread can either be named by
2725 the user (see @code{thread name}, below), or, in some cases, by the
2729 the current stack frame summary for that thread
2733 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2734 indicates the current thread.
2738 @c end table here to get a little more width for example
2741 (@value{GDBP}) info threads
2743 3 process 35 thread 27 0x34e5 in sigpause ()
2744 2 process 35 thread 23 0x34e5 in sigpause ()
2745 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2749 On Solaris, you can display more information about user threads with a
2750 Solaris-specific command:
2753 @item maint info sol-threads
2754 @kindex maint info sol-threads
2755 @cindex thread info (Solaris)
2756 Display info on Solaris user threads.
2760 @kindex thread @var{threadno}
2761 @item thread @var{threadno}
2762 Make thread number @var{threadno} the current thread. The command
2763 argument @var{threadno} is the internal @value{GDBN} thread number, as
2764 shown in the first field of the @samp{info threads} display.
2765 @value{GDBN} responds by displaying the system identifier of the thread
2766 you selected, and its current stack frame summary:
2769 (@value{GDBP}) thread 2
2770 [Switching to thread 2 (Thread 0xb7fdab70 (LWP 12747))]
2771 #0 some_function (ignore=0x0) at example.c:8
2772 8 printf ("hello\n");
2776 As with the @samp{[New @dots{}]} message, the form of the text after
2777 @samp{Switching to} depends on your system's conventions for identifying
2780 @vindex $_thread@r{, convenience variable}
2781 The debugger convenience variable @samp{$_thread} contains the number
2782 of the current thread. You may find this useful in writing breakpoint
2783 conditional expressions, command scripts, and so forth. See
2784 @xref{Convenience Vars,, Convenience Variables}, for general
2785 information on convenience variables.
2787 @kindex thread apply
2788 @cindex apply command to several threads
2789 @item thread apply [@var{threadno} | all] @var{command}
2790 The @code{thread apply} command allows you to apply the named
2791 @var{command} to one or more threads. Specify the numbers of the
2792 threads that you want affected with the command argument
2793 @var{threadno}. It can be a single thread number, one of the numbers
2794 shown in the first field of the @samp{info threads} display; or it
2795 could be a range of thread numbers, as in @code{2-4}. To apply a
2796 command to all threads, type @kbd{thread apply all @var{command}}.
2799 @cindex name a thread
2800 @item thread name [@var{name}]
2801 This command assigns a name to the current thread. If no argument is
2802 given, any existing user-specified name is removed. The thread name
2803 appears in the @samp{info threads} display.
2805 On some systems, such as @sc{gnu}/Linux, @value{GDBN} is able to
2806 determine the name of the thread as given by the OS. On these
2807 systems, a name specified with @samp{thread name} will override the
2808 system-give name, and removing the user-specified name will cause
2809 @value{GDBN} to once again display the system-specified name.
2812 @cindex search for a thread
2813 @item thread find [@var{regexp}]
2814 Search for and display thread ids whose name or @var{systag}
2815 matches the supplied regular expression.
2817 As well as being the complement to the @samp{thread name} command,
2818 this command also allows you to identify a thread by its target
2819 @var{systag}. For instance, on @sc{gnu}/Linux, the target @var{systag}
2823 (@value{GDBN}) thread find 26688
2824 Thread 4 has target id 'Thread 0x41e02940 (LWP 26688)'
2825 (@value{GDBN}) info thread 4
2827 4 Thread 0x41e02940 (LWP 26688) 0x00000031ca6cd372 in select ()
2830 @kindex set print thread-events
2831 @cindex print messages on thread start and exit
2832 @item set print thread-events
2833 @itemx set print thread-events on
2834 @itemx set print thread-events off
2835 The @code{set print thread-events} command allows you to enable or
2836 disable printing of messages when @value{GDBN} notices that new threads have
2837 started or that threads have exited. By default, these messages will
2838 be printed if detection of these events is supported by the target.
2839 Note that these messages cannot be disabled on all targets.
2841 @kindex show print thread-events
2842 @item show print thread-events
2843 Show whether messages will be printed when @value{GDBN} detects that threads
2844 have started and exited.
2847 @xref{Thread Stops,,Stopping and Starting Multi-thread Programs}, for
2848 more information about how @value{GDBN} behaves when you stop and start
2849 programs with multiple threads.
2851 @xref{Set Watchpoints,,Setting Watchpoints}, for information about
2852 watchpoints in programs with multiple threads.
2855 @kindex set libthread-db-search-path
2856 @cindex search path for @code{libthread_db}
2857 @item set libthread-db-search-path @r{[}@var{path}@r{]}
2858 If this variable is set, @var{path} is a colon-separated list of
2859 directories @value{GDBN} will use to search for @code{libthread_db}.
2860 If you omit @var{path}, @samp{libthread-db-search-path} will be reset to
2861 its default value (@code{$sdir:$pdir} on @sc{gnu}/Linux and Solaris systems).
2862 Internally, the default value comes from the @code{LIBTHREAD_DB_SEARCH_PATH}
2865 On @sc{gnu}/Linux and Solaris systems, @value{GDBN} uses a ``helper''
2866 @code{libthread_db} library to obtain information about threads in the
2867 inferior process. @value{GDBN} will use @samp{libthread-db-search-path}
2868 to find @code{libthread_db}.
2870 A special entry @samp{$sdir} for @samp{libthread-db-search-path}
2871 refers to the default system directories that are
2872 normally searched for loading shared libraries.
2874 A special entry @samp{$pdir} for @samp{libthread-db-search-path}
2875 refers to the directory from which @code{libpthread}
2876 was loaded in the inferior process.
2878 For any @code{libthread_db} library @value{GDBN} finds in above directories,
2879 @value{GDBN} attempts to initialize it with the current inferior process.
2880 If this initialization fails (which could happen because of a version
2881 mismatch between @code{libthread_db} and @code{libpthread}), @value{GDBN}
2882 will unload @code{libthread_db}, and continue with the next directory.
2883 If none of @code{libthread_db} libraries initialize successfully,
2884 @value{GDBN} will issue a warning and thread debugging will be disabled.
2886 Setting @code{libthread-db-search-path} is currently implemented
2887 only on some platforms.
2889 @kindex show libthread-db-search-path
2890 @item show libthread-db-search-path
2891 Display current libthread_db search path.
2893 @kindex set debug libthread-db
2894 @kindex show debug libthread-db
2895 @cindex debugging @code{libthread_db}
2896 @item set debug libthread-db
2897 @itemx show debug libthread-db
2898 Turns on or off display of @code{libthread_db}-related events.
2899 Use @code{1} to enable, @code{0} to disable.
2903 @section Debugging Forks
2905 @cindex fork, debugging programs which call
2906 @cindex multiple processes
2907 @cindex processes, multiple
2908 On most systems, @value{GDBN} has no special support for debugging
2909 programs which create additional processes using the @code{fork}
2910 function. When a program forks, @value{GDBN} will continue to debug the
2911 parent process and the child process will run unimpeded. If you have
2912 set a breakpoint in any code which the child then executes, the child
2913 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2914 will cause it to terminate.
2916 However, if you want to debug the child process there is a workaround
2917 which isn't too painful. Put a call to @code{sleep} in the code which
2918 the child process executes after the fork. It may be useful to sleep
2919 only if a certain environment variable is set, or a certain file exists,
2920 so that the delay need not occur when you don't want to run @value{GDBN}
2921 on the child. While the child is sleeping, use the @code{ps} program to
2922 get its process ID. Then tell @value{GDBN} (a new invocation of
2923 @value{GDBN} if you are also debugging the parent process) to attach to
2924 the child process (@pxref{Attach}). From that point on you can debug
2925 the child process just like any other process which you attached to.
2927 On some systems, @value{GDBN} provides support for debugging programs that
2928 create additional processes using the @code{fork} or @code{vfork} functions.
2929 Currently, the only platforms with this feature are HP-UX (11.x and later
2930 only?) and @sc{gnu}/Linux (kernel version 2.5.60 and later).
2932 By default, when a program forks, @value{GDBN} will continue to debug
2933 the parent process and the child process will run unimpeded.
2935 If you want to follow the child process instead of the parent process,
2936 use the command @w{@code{set follow-fork-mode}}.
2939 @kindex set follow-fork-mode
2940 @item set follow-fork-mode @var{mode}
2941 Set the debugger response to a program call of @code{fork} or
2942 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2943 process. The @var{mode} argument can be:
2947 The original process is debugged after a fork. The child process runs
2948 unimpeded. This is the default.
2951 The new process is debugged after a fork. The parent process runs
2956 @kindex show follow-fork-mode
2957 @item show follow-fork-mode
2958 Display the current debugger response to a @code{fork} or @code{vfork} call.
2961 @cindex debugging multiple processes
2962 On Linux, if you want to debug both the parent and child processes, use the
2963 command @w{@code{set detach-on-fork}}.
2966 @kindex set detach-on-fork
2967 @item set detach-on-fork @var{mode}
2968 Tells gdb whether to detach one of the processes after a fork, or
2969 retain debugger control over them both.
2973 The child process (or parent process, depending on the value of
2974 @code{follow-fork-mode}) will be detached and allowed to run
2975 independently. This is the default.
2978 Both processes will be held under the control of @value{GDBN}.
2979 One process (child or parent, depending on the value of
2980 @code{follow-fork-mode}) is debugged as usual, while the other
2985 @kindex show detach-on-fork
2986 @item show detach-on-fork
2987 Show whether detach-on-fork mode is on/off.
2990 If you choose to set @samp{detach-on-fork} mode off, then @value{GDBN}
2991 will retain control of all forked processes (including nested forks).
2992 You can list the forked processes under the control of @value{GDBN} by
2993 using the @w{@code{info inferiors}} command, and switch from one fork
2994 to another by using the @code{inferior} command (@pxref{Inferiors and
2995 Programs, ,Debugging Multiple Inferiors and Programs}).
2997 To quit debugging one of the forked processes, you can either detach
2998 from it by using the @w{@code{detach inferiors}} command (allowing it
2999 to run independently), or kill it using the @w{@code{kill inferiors}}
3000 command. @xref{Inferiors and Programs, ,Debugging Multiple Inferiors
3003 If you ask to debug a child process and a @code{vfork} is followed by an
3004 @code{exec}, @value{GDBN} executes the new target up to the first
3005 breakpoint in the new target. If you have a breakpoint set on
3006 @code{main} in your original program, the breakpoint will also be set on
3007 the child process's @code{main}.
3009 On some systems, when a child process is spawned by @code{vfork}, you
3010 cannot debug the child or parent until an @code{exec} call completes.
3012 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
3013 call executes, the new target restarts. To restart the parent
3014 process, use the @code{file} command with the parent executable name
3015 as its argument. By default, after an @code{exec} call executes,
3016 @value{GDBN} discards the symbols of the previous executable image.
3017 You can change this behaviour with the @w{@code{set follow-exec-mode}}
3021 @kindex set follow-exec-mode
3022 @item set follow-exec-mode @var{mode}
3024 Set debugger response to a program call of @code{exec}. An
3025 @code{exec} call replaces the program image of a process.
3027 @code{follow-exec-mode} can be:
3031 @value{GDBN} creates a new inferior and rebinds the process to this
3032 new inferior. The program the process was running before the
3033 @code{exec} call can be restarted afterwards by restarting the
3039 (@value{GDBP}) info inferiors
3041 Id Description Executable
3044 process 12020 is executing new program: prog2
3045 Program exited normally.
3046 (@value{GDBP}) info inferiors
3047 Id Description Executable
3053 @value{GDBN} keeps the process bound to the same inferior. The new
3054 executable image replaces the previous executable loaded in the
3055 inferior. Restarting the inferior after the @code{exec} call, with
3056 e.g., the @code{run} command, restarts the executable the process was
3057 running after the @code{exec} call. This is the default mode.
3062 (@value{GDBP}) info inferiors
3063 Id Description Executable
3066 process 12020 is executing new program: prog2
3067 Program exited normally.
3068 (@value{GDBP}) info inferiors
3069 Id Description Executable
3076 You can use the @code{catch} command to make @value{GDBN} stop whenever
3077 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
3078 Catchpoints, ,Setting Catchpoints}.
3080 @node Checkpoint/Restart
3081 @section Setting a @emph{Bookmark} to Return to Later
3086 @cindex snapshot of a process
3087 @cindex rewind program state
3089 On certain operating systems@footnote{Currently, only
3090 @sc{gnu}/Linux.}, @value{GDBN} is able to save a @dfn{snapshot} of a
3091 program's state, called a @dfn{checkpoint}, and come back to it
3094 Returning to a checkpoint effectively undoes everything that has
3095 happened in the program since the @code{checkpoint} was saved. This
3096 includes changes in memory, registers, and even (within some limits)
3097 system state. Effectively, it is like going back in time to the
3098 moment when the checkpoint was saved.
3100 Thus, if you're stepping thru a program and you think you're
3101 getting close to the point where things go wrong, you can save
3102 a checkpoint. Then, if you accidentally go too far and miss
3103 the critical statement, instead of having to restart your program
3104 from the beginning, you can just go back to the checkpoint and
3105 start again from there.
3107 This can be especially useful if it takes a lot of time or
3108 steps to reach the point where you think the bug occurs.
3110 To use the @code{checkpoint}/@code{restart} method of debugging:
3115 Save a snapshot of the debugged program's current execution state.
3116 The @code{checkpoint} command takes no arguments, but each checkpoint
3117 is assigned a small integer id, similar to a breakpoint id.
3119 @kindex info checkpoints
3120 @item info checkpoints
3121 List the checkpoints that have been saved in the current debugging
3122 session. For each checkpoint, the following information will be
3129 @item Source line, or label
3132 @kindex restart @var{checkpoint-id}
3133 @item restart @var{checkpoint-id}
3134 Restore the program state that was saved as checkpoint number
3135 @var{checkpoint-id}. All program variables, registers, stack frames
3136 etc.@: will be returned to the values that they had when the checkpoint
3137 was saved. In essence, gdb will ``wind back the clock'' to the point
3138 in time when the checkpoint was saved.
3140 Note that breakpoints, @value{GDBN} variables, command history etc.
3141 are not affected by restoring a checkpoint. In general, a checkpoint
3142 only restores things that reside in the program being debugged, not in
3145 @kindex delete checkpoint @var{checkpoint-id}
3146 @item delete checkpoint @var{checkpoint-id}
3147 Delete the previously-saved checkpoint identified by @var{checkpoint-id}.
3151 Returning to a previously saved checkpoint will restore the user state
3152 of the program being debugged, plus a significant subset of the system
3153 (OS) state, including file pointers. It won't ``un-write'' data from
3154 a file, but it will rewind the file pointer to the previous location,
3155 so that the previously written data can be overwritten. For files
3156 opened in read mode, the pointer will also be restored so that the
3157 previously read data can be read again.
3159 Of course, characters that have been sent to a printer (or other
3160 external device) cannot be ``snatched back'', and characters received
3161 from eg.@: a serial device can be removed from internal program buffers,
3162 but they cannot be ``pushed back'' into the serial pipeline, ready to
3163 be received again. Similarly, the actual contents of files that have
3164 been changed cannot be restored (at this time).
3166 However, within those constraints, you actually can ``rewind'' your
3167 program to a previously saved point in time, and begin debugging it
3168 again --- and you can change the course of events so as to debug a
3169 different execution path this time.
3171 @cindex checkpoints and process id
3172 Finally, there is one bit of internal program state that will be
3173 different when you return to a checkpoint --- the program's process
3174 id. Each checkpoint will have a unique process id (or @var{pid}),
3175 and each will be different from the program's original @var{pid}.
3176 If your program has saved a local copy of its process id, this could
3177 potentially pose a problem.
3179 @subsection A Non-obvious Benefit of Using Checkpoints
3181 On some systems such as @sc{gnu}/Linux, address space randomization
3182 is performed on new processes for security reasons. This makes it
3183 difficult or impossible to set a breakpoint, or watchpoint, on an
3184 absolute address if you have to restart the program, since the
3185 absolute location of a symbol will change from one execution to the
3188 A checkpoint, however, is an @emph{identical} copy of a process.
3189 Therefore if you create a checkpoint at (eg.@:) the start of main,
3190 and simply return to that checkpoint instead of restarting the
3191 process, you can avoid the effects of address randomization and
3192 your symbols will all stay in the same place.
3195 @chapter Stopping and Continuing
3197 The principal purposes of using a debugger are so that you can stop your
3198 program before it terminates; or so that, if your program runs into
3199 trouble, you can investigate and find out why.
3201 Inside @value{GDBN}, your program may stop for any of several reasons,
3202 such as a signal, a breakpoint, or reaching a new line after a
3203 @value{GDBN} command such as @code{step}. You may then examine and
3204 change variables, set new breakpoints or remove old ones, and then
3205 continue execution. Usually, the messages shown by @value{GDBN} provide
3206 ample explanation of the status of your program---but you can also
3207 explicitly request this information at any time.
3210 @kindex info program
3212 Display information about the status of your program: whether it is
3213 running or not, what process it is, and why it stopped.
3217 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
3218 * Continuing and Stepping:: Resuming execution
3220 * Thread Stops:: Stopping and starting multi-thread programs
3224 @section Breakpoints, Watchpoints, and Catchpoints
3227 A @dfn{breakpoint} makes your program stop whenever a certain point in
3228 the program is reached. For each breakpoint, you can add conditions to
3229 control in finer detail whether your program stops. You can set
3230 breakpoints with the @code{break} command and its variants (@pxref{Set
3231 Breaks, ,Setting Breakpoints}), to specify the place where your program
3232 should stop by line number, function name or exact address in the
3235 On some systems, you can set breakpoints in shared libraries before
3236 the executable is run. There is a minor limitation on HP-UX systems:
3237 you must wait until the executable is run in order to set breakpoints
3238 in shared library routines that are not called directly by the program
3239 (for example, routines that are arguments in a @code{pthread_create}
3243 @cindex data breakpoints
3244 @cindex memory tracing
3245 @cindex breakpoint on memory address
3246 @cindex breakpoint on variable modification
3247 A @dfn{watchpoint} is a special breakpoint that stops your program
3248 when the value of an expression changes. The expression may be a value
3249 of a variable, or it could involve values of one or more variables
3250 combined by operators, such as @samp{a + b}. This is sometimes called
3251 @dfn{data breakpoints}. You must use a different command to set
3252 watchpoints (@pxref{Set Watchpoints, ,Setting Watchpoints}), but aside
3253 from that, you can manage a watchpoint like any other breakpoint: you
3254 enable, disable, and delete both breakpoints and watchpoints using the
3257 You can arrange to have values from your program displayed automatically
3258 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
3262 @cindex breakpoint on events
3263 A @dfn{catchpoint} is another special breakpoint that stops your program
3264 when a certain kind of event occurs, such as the throwing of a C@t{++}
3265 exception or the loading of a library. As with watchpoints, you use a
3266 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
3267 Catchpoints}), but aside from that, you can manage a catchpoint like any
3268 other breakpoint. (To stop when your program receives a signal, use the
3269 @code{handle} command; see @ref{Signals, ,Signals}.)
3271 @cindex breakpoint numbers
3272 @cindex numbers for breakpoints
3273 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
3274 catchpoint when you create it; these numbers are successive integers
3275 starting with one. In many of the commands for controlling various
3276 features of breakpoints you use the breakpoint number to say which
3277 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
3278 @dfn{disabled}; if disabled, it has no effect on your program until you
3281 @cindex breakpoint ranges
3282 @cindex ranges of breakpoints
3283 Some @value{GDBN} commands accept a range of breakpoints on which to
3284 operate. A breakpoint range is either a single breakpoint number, like
3285 @samp{5}, or two such numbers, in increasing order, separated by a
3286 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
3287 all breakpoints in that range are operated on.
3290 * Set Breaks:: Setting breakpoints
3291 * Set Watchpoints:: Setting watchpoints
3292 * Set Catchpoints:: Setting catchpoints
3293 * Delete Breaks:: Deleting breakpoints
3294 * Disabling:: Disabling breakpoints
3295 * Conditions:: Break conditions
3296 * Break Commands:: Breakpoint command lists
3297 * Save Breakpoints:: How to save breakpoints in a file
3298 * Error in Breakpoints:: ``Cannot insert breakpoints''
3299 * Breakpoint-related Warnings:: ``Breakpoint address adjusted...''
3303 @subsection Setting Breakpoints
3305 @c FIXME LMB what does GDB do if no code on line of breakpt?
3306 @c consider in particular declaration with/without initialization.
3308 @c FIXME 2 is there stuff on this already? break at fun start, already init?
3311 @kindex b @r{(@code{break})}
3312 @vindex $bpnum@r{, convenience variable}
3313 @cindex latest breakpoint
3314 Breakpoints are set with the @code{break} command (abbreviated
3315 @code{b}). The debugger convenience variable @samp{$bpnum} records the
3316 number of the breakpoint you've set most recently; see @ref{Convenience
3317 Vars,, Convenience Variables}, for a discussion of what you can do with
3318 convenience variables.
3321 @item break @var{location}
3322 Set a breakpoint at the given @var{location}, which can specify a
3323 function name, a line number, or an address of an instruction.
3324 (@xref{Specify Location}, for a list of all the possible ways to
3325 specify a @var{location}.) The breakpoint will stop your program just
3326 before it executes any of the code in the specified @var{location}.
3328 When using source languages that permit overloading of symbols, such as
3329 C@t{++}, a function name may refer to more than one possible place to break.
3330 @xref{Ambiguous Expressions,,Ambiguous Expressions}, for a discussion of
3333 It is also possible to insert a breakpoint that will stop the program
3334 only if a specific thread (@pxref{Thread-Specific Breakpoints})
3335 or a specific task (@pxref{Ada Tasks}) hits that breakpoint.
3338 When called without any arguments, @code{break} sets a breakpoint at
3339 the next instruction to be executed in the selected stack frame
3340 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
3341 innermost, this makes your program stop as soon as control
3342 returns to that frame. This is similar to the effect of a
3343 @code{finish} command in the frame inside the selected frame---except
3344 that @code{finish} does not leave an active breakpoint. If you use
3345 @code{break} without an argument in the innermost frame, @value{GDBN} stops
3346 the next time it reaches the current location; this may be useful
3349 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
3350 least one instruction has been executed. If it did not do this, you
3351 would be unable to proceed past a breakpoint without first disabling the
3352 breakpoint. This rule applies whether or not the breakpoint already
3353 existed when your program stopped.
3355 @item break @dots{} if @var{cond}
3356 Set a breakpoint with condition @var{cond}; evaluate the expression
3357 @var{cond} each time the breakpoint is reached, and stop only if the
3358 value is nonzero---that is, if @var{cond} evaluates as true.
3359 @samp{@dots{}} stands for one of the possible arguments described
3360 above (or no argument) specifying where to break. @xref{Conditions,
3361 ,Break Conditions}, for more information on breakpoint conditions.
3364 @item tbreak @var{args}
3365 Set a breakpoint enabled only for one stop. @var{args} are the
3366 same as for the @code{break} command, and the breakpoint is set in the same
3367 way, but the breakpoint is automatically deleted after the first time your
3368 program stops there. @xref{Disabling, ,Disabling Breakpoints}.
3371 @cindex hardware breakpoints
3372 @item hbreak @var{args}
3373 Set a hardware-assisted breakpoint. @var{args} are the same as for the
3374 @code{break} command and the breakpoint is set in the same way, but the
3375 breakpoint requires hardware support and some target hardware may not
3376 have this support. The main purpose of this is EPROM/ROM code
3377 debugging, so you can set a breakpoint at an instruction without
3378 changing the instruction. This can be used with the new trap-generation
3379 provided by SPARClite DSU and most x86-based targets. These targets
3380 will generate traps when a program accesses some data or instruction
3381 address that is assigned to the debug registers. However the hardware
3382 breakpoint registers can take a limited number of breakpoints. For
3383 example, on the DSU, only two data breakpoints can be set at a time, and
3384 @value{GDBN} will reject this command if more than two are used. Delete
3385 or disable unused hardware breakpoints before setting new ones
3386 (@pxref{Disabling, ,Disabling Breakpoints}).
3387 @xref{Conditions, ,Break Conditions}.
3388 For remote targets, you can restrict the number of hardware
3389 breakpoints @value{GDBN} will use, see @ref{set remote
3390 hardware-breakpoint-limit}.
3393 @item thbreak @var{args}
3394 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
3395 are the same as for the @code{hbreak} command and the breakpoint is set in
3396 the same way. However, like the @code{tbreak} command,
3397 the breakpoint is automatically deleted after the
3398 first time your program stops there. Also, like the @code{hbreak}
3399 command, the breakpoint requires hardware support and some target hardware
3400 may not have this support. @xref{Disabling, ,Disabling Breakpoints}.
3401 See also @ref{Conditions, ,Break Conditions}.
3404 @cindex regular expression
3405 @cindex breakpoints at functions matching a regexp
3406 @cindex set breakpoints in many functions
3407 @item rbreak @var{regex}
3408 Set breakpoints on all functions matching the regular expression
3409 @var{regex}. This command sets an unconditional breakpoint on all
3410 matches, printing a list of all breakpoints it set. Once these
3411 breakpoints are set, they are treated just like the breakpoints set with
3412 the @code{break} command. You can delete them, disable them, or make
3413 them conditional the same way as any other breakpoint.
3415 The syntax of the regular expression is the standard one used with tools
3416 like @file{grep}. Note that this is different from the syntax used by
3417 shells, so for instance @code{foo*} matches all functions that include
3418 an @code{fo} followed by zero or more @code{o}s. There is an implicit
3419 @code{.*} leading and trailing the regular expression you supply, so to
3420 match only functions that begin with @code{foo}, use @code{^foo}.
3422 @cindex non-member C@t{++} functions, set breakpoint in
3423 When debugging C@t{++} programs, @code{rbreak} is useful for setting
3424 breakpoints on overloaded functions that are not members of any special
3427 @cindex set breakpoints on all functions
3428 The @code{rbreak} command can be used to set breakpoints in
3429 @strong{all} the functions in a program, like this:
3432 (@value{GDBP}) rbreak .
3435 @item rbreak @var{file}:@var{regex}
3436 If @code{rbreak} is called with a filename qualification, it limits
3437 the search for functions matching the given regular expression to the
3438 specified @var{file}. This can be used, for example, to set breakpoints on
3439 every function in a given file:
3442 (@value{GDBP}) rbreak file.c:.
3445 The colon separating the filename qualifier from the regex may
3446 optionally be surrounded by spaces.
3448 @kindex info breakpoints
3449 @cindex @code{$_} and @code{info breakpoints}
3450 @item info breakpoints @r{[}@var{n}@dots{}@r{]}
3451 @itemx info break @r{[}@var{n}@dots{}@r{]}
3452 Print a table of all breakpoints, watchpoints, and catchpoints set and
3453 not deleted. Optional argument @var{n} means print information only
3454 about the specified breakpoint(s) (or watchpoint(s) or catchpoint(s)).
3455 For each breakpoint, following columns are printed:
3458 @item Breakpoint Numbers
3460 Breakpoint, watchpoint, or catchpoint.
3462 Whether the breakpoint is marked to be disabled or deleted when hit.
3463 @item Enabled or Disabled
3464 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
3465 that are not enabled.
3467 Where the breakpoint is in your program, as a memory address. For a
3468 pending breakpoint whose address is not yet known, this field will
3469 contain @samp{<PENDING>}. Such breakpoint won't fire until a shared
3470 library that has the symbol or line referred by breakpoint is loaded.
3471 See below for details. A breakpoint with several locations will
3472 have @samp{<MULTIPLE>} in this field---see below for details.
3474 Where the breakpoint is in the source for your program, as a file and
3475 line number. For a pending breakpoint, the original string passed to
3476 the breakpoint command will be listed as it cannot be resolved until
3477 the appropriate shared library is loaded in the future.
3481 If a breakpoint is conditional, @code{info break} shows the condition on
3482 the line following the affected breakpoint; breakpoint commands, if any,
3483 are listed after that. A pending breakpoint is allowed to have a condition
3484 specified for it. The condition is not parsed for validity until a shared
3485 library is loaded that allows the pending breakpoint to resolve to a
3489 @code{info break} with a breakpoint
3490 number @var{n} as argument lists only that breakpoint. The
3491 convenience variable @code{$_} and the default examining-address for
3492 the @code{x} command are set to the address of the last breakpoint
3493 listed (@pxref{Memory, ,Examining Memory}).
3496 @code{info break} displays a count of the number of times the breakpoint
3497 has been hit. This is especially useful in conjunction with the
3498 @code{ignore} command. You can ignore a large number of breakpoint
3499 hits, look at the breakpoint info to see how many times the breakpoint
3500 was hit, and then run again, ignoring one less than that number. This
3501 will get you quickly to the last hit of that breakpoint.
3504 @value{GDBN} allows you to set any number of breakpoints at the same place in
3505 your program. There is nothing silly or meaningless about this. When
3506 the breakpoints are conditional, this is even useful
3507 (@pxref{Conditions, ,Break Conditions}).
3509 @cindex multiple locations, breakpoints
3510 @cindex breakpoints, multiple locations
3511 It is possible that a breakpoint corresponds to several locations
3512 in your program. Examples of this situation are:
3516 For a C@t{++} constructor, the @value{NGCC} compiler generates several
3517 instances of the function body, used in different cases.
3520 For a C@t{++} template function, a given line in the function can
3521 correspond to any number of instantiations.
3524 For an inlined function, a given source line can correspond to
3525 several places where that function is inlined.
3528 In all those cases, @value{GDBN} will insert a breakpoint at all
3529 the relevant locations@footnote{
3530 As of this writing, multiple-location breakpoints work only if there's
3531 line number information for all the locations. This means that they
3532 will generally not work in system libraries, unless you have debug
3533 info with line numbers for them.}.
3535 A breakpoint with multiple locations is displayed in the breakpoint
3536 table using several rows---one header row, followed by one row for
3537 each breakpoint location. The header row has @samp{<MULTIPLE>} in the
3538 address column. The rows for individual locations contain the actual
3539 addresses for locations, and show the functions to which those
3540 locations belong. The number column for a location is of the form
3541 @var{breakpoint-number}.@var{location-number}.
3546 Num Type Disp Enb Address What
3547 1 breakpoint keep y <MULTIPLE>
3549 breakpoint already hit 1 time
3550 1.1 y 0x080486a2 in void foo<int>() at t.cc:8
3551 1.2 y 0x080486ca in void foo<double>() at t.cc:8
3554 Each location can be individually enabled or disabled by passing
3555 @var{breakpoint-number}.@var{location-number} as argument to the
3556 @code{enable} and @code{disable} commands. Note that you cannot
3557 delete the individual locations from the list, you can only delete the
3558 entire list of locations that belong to their parent breakpoint (with
3559 the @kbd{delete @var{num}} command, where @var{num} is the number of
3560 the parent breakpoint, 1 in the above example). Disabling or enabling
3561 the parent breakpoint (@pxref{Disabling}) affects all of the locations
3562 that belong to that breakpoint.
3564 @cindex pending breakpoints
3565 It's quite common to have a breakpoint inside a shared library.
3566 Shared libraries can be loaded and unloaded explicitly,
3567 and possibly repeatedly, as the program is executed. To support
3568 this use case, @value{GDBN} updates breakpoint locations whenever
3569 any shared library is loaded or unloaded. Typically, you would
3570 set a breakpoint in a shared library at the beginning of your
3571 debugging session, when the library is not loaded, and when the
3572 symbols from the library are not available. When you try to set
3573 breakpoint, @value{GDBN} will ask you if you want to set
3574 a so called @dfn{pending breakpoint}---breakpoint whose address
3575 is not yet resolved.
3577 After the program is run, whenever a new shared library is loaded,
3578 @value{GDBN} reevaluates all the breakpoints. When a newly loaded
3579 shared library contains the symbol or line referred to by some
3580 pending breakpoint, that breakpoint is resolved and becomes an
3581 ordinary breakpoint. When a library is unloaded, all breakpoints
3582 that refer to its symbols or source lines become pending again.
3584 This logic works for breakpoints with multiple locations, too. For
3585 example, if you have a breakpoint in a C@t{++} template function, and
3586 a newly loaded shared library has an instantiation of that template,
3587 a new location is added to the list of locations for the breakpoint.
3589 Except for having unresolved address, pending breakpoints do not
3590 differ from regular breakpoints. You can set conditions or commands,
3591 enable and disable them and perform other breakpoint operations.
3593 @value{GDBN} provides some additional commands for controlling what
3594 happens when the @samp{break} command cannot resolve breakpoint
3595 address specification to an address:
3597 @kindex set breakpoint pending
3598 @kindex show breakpoint pending
3600 @item set breakpoint pending auto
3601 This is the default behavior. When @value{GDBN} cannot find the breakpoint
3602 location, it queries you whether a pending breakpoint should be created.
3604 @item set breakpoint pending on
3605 This indicates that an unrecognized breakpoint location should automatically
3606 result in a pending breakpoint being created.
3608 @item set breakpoint pending off
3609 This indicates that pending breakpoints are not to be created. Any
3610 unrecognized breakpoint location results in an error. This setting does
3611 not affect any pending breakpoints previously created.
3613 @item show breakpoint pending
3614 Show the current behavior setting for creating pending breakpoints.
3617 The settings above only affect the @code{break} command and its
3618 variants. Once breakpoint is set, it will be automatically updated
3619 as shared libraries are loaded and unloaded.
3621 @cindex automatic hardware breakpoints
3622 For some targets, @value{GDBN} can automatically decide if hardware or
3623 software breakpoints should be used, depending on whether the
3624 breakpoint address is read-only or read-write. This applies to
3625 breakpoints set with the @code{break} command as well as to internal
3626 breakpoints set by commands like @code{next} and @code{finish}. For
3627 breakpoints set with @code{hbreak}, @value{GDBN} will always use hardware
3630 You can control this automatic behaviour with the following commands::
3632 @kindex set breakpoint auto-hw
3633 @kindex show breakpoint auto-hw
3635 @item set breakpoint auto-hw on
3636 This is the default behavior. When @value{GDBN} sets a breakpoint, it
3637 will try to use the target memory map to decide if software or hardware
3638 breakpoint must be used.
3640 @item set breakpoint auto-hw off
3641 This indicates @value{GDBN} should not automatically select breakpoint
3642 type. If the target provides a memory map, @value{GDBN} will warn when
3643 trying to set software breakpoint at a read-only address.
3646 @value{GDBN} normally implements breakpoints by replacing the program code
3647 at the breakpoint address with a special instruction, which, when
3648 executed, given control to the debugger. By default, the program
3649 code is so modified only when the program is resumed. As soon as
3650 the program stops, @value{GDBN} restores the original instructions. This
3651 behaviour guards against leaving breakpoints inserted in the
3652 target should gdb abrubptly disconnect. However, with slow remote
3653 targets, inserting and removing breakpoint can reduce the performance.
3654 This behavior can be controlled with the following commands::
3656 @kindex set breakpoint always-inserted
3657 @kindex show breakpoint always-inserted
3659 @item set breakpoint always-inserted off
3660 All breakpoints, including newly added by the user, are inserted in
3661 the target only when the target is resumed. All breakpoints are
3662 removed from the target when it stops.
3664 @item set breakpoint always-inserted on
3665 Causes all breakpoints to be inserted in the target at all times. If
3666 the user adds a new breakpoint, or changes an existing breakpoint, the
3667 breakpoints in the target are updated immediately. A breakpoint is
3668 removed from the target only when breakpoint itself is removed.
3670 @cindex non-stop mode, and @code{breakpoint always-inserted}
3671 @item set breakpoint always-inserted auto
3672 This is the default mode. If @value{GDBN} is controlling the inferior
3673 in non-stop mode (@pxref{Non-Stop Mode}), gdb behaves as if
3674 @code{breakpoint always-inserted} mode is on. If @value{GDBN} is
3675 controlling the inferior in all-stop mode, @value{GDBN} behaves as if
3676 @code{breakpoint always-inserted} mode is off.
3679 @cindex negative breakpoint numbers
3680 @cindex internal @value{GDBN} breakpoints
3681 @value{GDBN} itself sometimes sets breakpoints in your program for
3682 special purposes, such as proper handling of @code{longjmp} (in C
3683 programs). These internal breakpoints are assigned negative numbers,
3684 starting with @code{-1}; @samp{info breakpoints} does not display them.
3685 You can see these breakpoints with the @value{GDBN} maintenance command
3686 @samp{maint info breakpoints} (@pxref{maint info breakpoints}).
3689 @node Set Watchpoints
3690 @subsection Setting Watchpoints
3692 @cindex setting watchpoints
3693 You can use a watchpoint to stop execution whenever the value of an
3694 expression changes, without having to predict a particular place where
3695 this may happen. (This is sometimes called a @dfn{data breakpoint}.)
3696 The expression may be as simple as the value of a single variable, or
3697 as complex as many variables combined by operators. Examples include:
3701 A reference to the value of a single variable.
3704 An address cast to an appropriate data type. For example,
3705 @samp{*(int *)0x12345678} will watch a 4-byte region at the specified
3706 address (assuming an @code{int} occupies 4 bytes).
3709 An arbitrarily complex expression, such as @samp{a*b + c/d}. The
3710 expression can use any operators valid in the program's native
3711 language (@pxref{Languages}).
3714 You can set a watchpoint on an expression even if the expression can
3715 not be evaluated yet. For instance, you can set a watchpoint on
3716 @samp{*global_ptr} before @samp{global_ptr} is initialized.
3717 @value{GDBN} will stop when your program sets @samp{global_ptr} and
3718 the expression produces a valid value. If the expression becomes
3719 valid in some other way than changing a variable (e.g.@: if the memory
3720 pointed to by @samp{*global_ptr} becomes readable as the result of a
3721 @code{malloc} call), @value{GDBN} may not stop until the next time
3722 the expression changes.
3724 @cindex software watchpoints
3725 @cindex hardware watchpoints
3726 Depending on your system, watchpoints may be implemented in software or
3727 hardware. @value{GDBN} does software watchpointing by single-stepping your
3728 program and testing the variable's value each time, which is hundreds of
3729 times slower than normal execution. (But this may still be worth it, to
3730 catch errors where you have no clue what part of your program is the
3733 On some systems, such as HP-UX, PowerPC, @sc{gnu}/Linux and most other
3734 x86-based targets, @value{GDBN} includes support for hardware
3735 watchpoints, which do not slow down the running of your program.
3739 @item watch @r{[}-l@r{|}-location@r{]} @var{expr} @r{[}thread @var{threadnum}@r{]} @r{[}mask @var{maskvalue}@r{]}
3740 Set a watchpoint for an expression. @value{GDBN} will break when the
3741 expression @var{expr} is written into by the program and its value
3742 changes. The simplest (and the most popular) use of this command is
3743 to watch the value of a single variable:
3746 (@value{GDBP}) watch foo
3749 If the command includes a @code{@r{[}thread @var{threadnum}@r{]}}
3750 argument, @value{GDBN} breaks only when the thread identified by
3751 @var{threadnum} changes the value of @var{expr}. If any other threads
3752 change the value of @var{expr}, @value{GDBN} will not break. Note
3753 that watchpoints restricted to a single thread in this way only work
3754 with Hardware Watchpoints.
3756 Ordinarily a watchpoint respects the scope of variables in @var{expr}
3757 (see below). The @code{-location} argument tells @value{GDBN} to
3758 instead watch the memory referred to by @var{expr}. In this case,
3759 @value{GDBN} will evaluate @var{expr}, take the address of the result,
3760 and watch the memory at that address. The type of the result is used
3761 to determine the size of the watched memory. If the expression's
3762 result does not have an address, then @value{GDBN} will print an
3765 The @code{@r{[}mask @var{maskvalue}@r{]}} argument allows creation
3766 of masked watchpoints, if the current architecture supports this
3767 feature (e.g., PowerPC Embedded architecture, see @ref{PowerPC
3768 Embedded}.) A @dfn{masked watchpoint} specifies a mask in addition
3769 to an address to watch. The mask specifies that some bits of an address
3770 (the bits which are reset in the mask) should be ignored when matching
3771 the address accessed by the inferior against the watchpoint address.
3772 Thus, a masked watchpoint watches many addresses simultaneously---those
3773 addresses whose unmasked bits are identical to the unmasked bits in the
3774 watchpoint address. The @code{mask} argument implies @code{-location}.
3778 (@value{GDBP}) watch foo mask 0xffff00ff
3779 (@value{GDBP}) watch *0xdeadbeef mask 0xffffff00
3783 @item rwatch @r{[}-l@r{|}-location@r{]} @var{expr} @r{[}thread @var{threadnum}@r{]} @r{[}mask @var{maskvalue}@r{]}
3784 Set a watchpoint that will break when the value of @var{expr} is read
3788 @item awatch @r{[}-l@r{|}-location@r{]} @var{expr} @r{[}thread @var{threadnum}@r{]} @r{[}mask @var{maskvalue}@r{]}
3789 Set a watchpoint that will break when @var{expr} is either read from
3790 or written into by the program.
3792 @kindex info watchpoints @r{[}@var{n}@dots{}@r{]}
3793 @item info watchpoints @r{[}@var{n}@dots{}@r{]}
3794 This command prints a list of watchpoints, using the same format as
3795 @code{info break} (@pxref{Set Breaks}).
3798 If you watch for a change in a numerically entered address you need to
3799 dereference it, as the address itself is just a constant number which will
3800 never change. @value{GDBN} refuses to create a watchpoint that watches
3801 a never-changing value:
3804 (@value{GDBP}) watch 0x600850
3805 Cannot watch constant value 0x600850.
3806 (@value{GDBP}) watch *(int *) 0x600850
3807 Watchpoint 1: *(int *) 6293584
3810 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
3811 watchpoints execute very quickly, and the debugger reports a change in
3812 value at the exact instruction where the change occurs. If @value{GDBN}
3813 cannot set a hardware watchpoint, it sets a software watchpoint, which
3814 executes more slowly and reports the change in value at the next
3815 @emph{statement}, not the instruction, after the change occurs.
3817 @cindex use only software watchpoints
3818 You can force @value{GDBN} to use only software watchpoints with the
3819 @kbd{set can-use-hw-watchpoints 0} command. With this variable set to
3820 zero, @value{GDBN} will never try to use hardware watchpoints, even if
3821 the underlying system supports them. (Note that hardware-assisted
3822 watchpoints that were set @emph{before} setting
3823 @code{can-use-hw-watchpoints} to zero will still use the hardware
3824 mechanism of watching expression values.)
3827 @item set can-use-hw-watchpoints
3828 @kindex set can-use-hw-watchpoints
3829 Set whether or not to use hardware watchpoints.
3831 @item show can-use-hw-watchpoints
3832 @kindex show can-use-hw-watchpoints
3833 Show the current mode of using hardware watchpoints.
3836 For remote targets, you can restrict the number of hardware
3837 watchpoints @value{GDBN} will use, see @ref{set remote
3838 hardware-breakpoint-limit}.
3840 When you issue the @code{watch} command, @value{GDBN} reports
3843 Hardware watchpoint @var{num}: @var{expr}
3847 if it was able to set a hardware watchpoint.
3849 Currently, the @code{awatch} and @code{rwatch} commands can only set
3850 hardware watchpoints, because accesses to data that don't change the
3851 value of the watched expression cannot be detected without examining
3852 every instruction as it is being executed, and @value{GDBN} does not do
3853 that currently. If @value{GDBN} finds that it is unable to set a
3854 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
3855 will print a message like this:
3858 Expression cannot be implemented with read/access watchpoint.
3861 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
3862 data type of the watched expression is wider than what a hardware
3863 watchpoint on the target machine can handle. For example, some systems
3864 can only watch regions that are up to 4 bytes wide; on such systems you
3865 cannot set hardware watchpoints for an expression that yields a
3866 double-precision floating-point number (which is typically 8 bytes
3867 wide). As a work-around, it might be possible to break the large region
3868 into a series of smaller ones and watch them with separate watchpoints.
3870 If you set too many hardware watchpoints, @value{GDBN} might be unable
3871 to insert all of them when you resume the execution of your program.
3872 Since the precise number of active watchpoints is unknown until such
3873 time as the program is about to be resumed, @value{GDBN} might not be
3874 able to warn you about this when you set the watchpoints, and the
3875 warning will be printed only when the program is resumed:
3878 Hardware watchpoint @var{num}: Could not insert watchpoint
3882 If this happens, delete or disable some of the watchpoints.
3884 Watching complex expressions that reference many variables can also
3885 exhaust the resources available for hardware-assisted watchpoints.
3886 That's because @value{GDBN} needs to watch every variable in the
3887 expression with separately allocated resources.
3889 If you call a function interactively using @code{print} or @code{call},
3890 any watchpoints you have set will be inactive until @value{GDBN} reaches another
3891 kind of breakpoint or the call completes.
3893 @value{GDBN} automatically deletes watchpoints that watch local
3894 (automatic) variables, or expressions that involve such variables, when
3895 they go out of scope, that is, when the execution leaves the block in
3896 which these variables were defined. In particular, when the program
3897 being debugged terminates, @emph{all} local variables go out of scope,
3898 and so only watchpoints that watch global variables remain set. If you
3899 rerun the program, you will need to set all such watchpoints again. One
3900 way of doing that would be to set a code breakpoint at the entry to the
3901 @code{main} function and when it breaks, set all the watchpoints.
3903 @cindex watchpoints and threads
3904 @cindex threads and watchpoints
3905 In multi-threaded programs, watchpoints will detect changes to the
3906 watched expression from every thread.
3909 @emph{Warning:} In multi-threaded programs, software watchpoints
3910 have only limited usefulness. If @value{GDBN} creates a software
3911 watchpoint, it can only watch the value of an expression @emph{in a
3912 single thread}. If you are confident that the expression can only
3913 change due to the current thread's activity (and if you are also
3914 confident that no other thread can become current), then you can use
3915 software watchpoints as usual. However, @value{GDBN} may not notice
3916 when a non-current thread's activity changes the expression. (Hardware
3917 watchpoints, in contrast, watch an expression in all threads.)
3920 @xref{set remote hardware-watchpoint-limit}.
3922 @node Set Catchpoints
3923 @subsection Setting Catchpoints
3924 @cindex catchpoints, setting
3925 @cindex exception handlers
3926 @cindex event handling
3928 You can use @dfn{catchpoints} to cause the debugger to stop for certain
3929 kinds of program events, such as C@t{++} exceptions or the loading of a
3930 shared library. Use the @code{catch} command to set a catchpoint.
3934 @item catch @var{event}
3935 Stop when @var{event} occurs. @var{event} can be any of the following:
3938 @cindex stop on C@t{++} exceptions
3939 The throwing of a C@t{++} exception.
3942 The catching of a C@t{++} exception.
3945 @cindex Ada exception catching
3946 @cindex catch Ada exceptions
3947 An Ada exception being raised. If an exception name is specified
3948 at the end of the command (eg @code{catch exception Program_Error}),
3949 the debugger will stop only when this specific exception is raised.
3950 Otherwise, the debugger stops execution when any Ada exception is raised.
3952 When inserting an exception catchpoint on a user-defined exception whose
3953 name is identical to one of the exceptions defined by the language, the
3954 fully qualified name must be used as the exception name. Otherwise,
3955 @value{GDBN} will assume that it should stop on the pre-defined exception
3956 rather than the user-defined one. For instance, assuming an exception
3957 called @code{Constraint_Error} is defined in package @code{Pck}, then
3958 the command to use to catch such exceptions is @kbd{catch exception
3959 Pck.Constraint_Error}.
3961 @item exception unhandled
3962 An exception that was raised but is not handled by the program.
3965 A failed Ada assertion.
3968 @cindex break on fork/exec
3969 A call to @code{exec}. This is currently only available for HP-UX
3973 @itemx syscall @r{[}@var{name} @r{|} @var{number}@r{]} @dots{}
3974 @cindex break on a system call.
3975 A call to or return from a system call, a.k.a.@: @dfn{syscall}. A
3976 syscall is a mechanism for application programs to request a service
3977 from the operating system (OS) or one of the OS system services.
3978 @value{GDBN} can catch some or all of the syscalls issued by the
3979 debuggee, and show the related information for each syscall. If no
3980 argument is specified, calls to and returns from all system calls
3983 @var{name} can be any system call name that is valid for the
3984 underlying OS. Just what syscalls are valid depends on the OS. On
3985 GNU and Unix systems, you can find the full list of valid syscall
3986 names on @file{/usr/include/asm/unistd.h}.
3988 @c For MS-Windows, the syscall names and the corresponding numbers
3989 @c can be found, e.g., on this URL:
3990 @c http://www.metasploit.com/users/opcode/syscalls.html
3991 @c but we don't support Windows syscalls yet.
3993 Normally, @value{GDBN} knows in advance which syscalls are valid for
3994 each OS, so you can use the @value{GDBN} command-line completion
3995 facilities (@pxref{Completion,, command completion}) to list the
3998 You may also specify the system call numerically. A syscall's
3999 number is the value passed to the OS's syscall dispatcher to
4000 identify the requested service. When you specify the syscall by its
4001 name, @value{GDBN} uses its database of syscalls to convert the name
4002 into the corresponding numeric code, but using the number directly
4003 may be useful if @value{GDBN}'s database does not have the complete
4004 list of syscalls on your system (e.g., because @value{GDBN} lags
4005 behind the OS upgrades).
4007 The example below illustrates how this command works if you don't provide
4011 (@value{GDBP}) catch syscall
4012 Catchpoint 1 (syscall)
4014 Starting program: /tmp/catch-syscall
4016 Catchpoint 1 (call to syscall 'close'), \
4017 0xffffe424 in __kernel_vsyscall ()
4021 Catchpoint 1 (returned from syscall 'close'), \
4022 0xffffe424 in __kernel_vsyscall ()
4026 Here is an example of catching a system call by name:
4029 (@value{GDBP}) catch syscall chroot
4030 Catchpoint 1 (syscall 'chroot' [61])
4032 Starting program: /tmp/catch-syscall
4034 Catchpoint 1 (call to syscall 'chroot'), \
4035 0xffffe424 in __kernel_vsyscall ()
4039 Catchpoint 1 (returned from syscall 'chroot'), \
4040 0xffffe424 in __kernel_vsyscall ()
4044 An example of specifying a system call numerically. In the case
4045 below, the syscall number has a corresponding entry in the XML
4046 file, so @value{GDBN} finds its name and prints it:
4049 (@value{GDBP}) catch syscall 252
4050 Catchpoint 1 (syscall(s) 'exit_group')
4052 Starting program: /tmp/catch-syscall
4054 Catchpoint 1 (call to syscall 'exit_group'), \
4055 0xffffe424 in __kernel_vsyscall ()
4059 Program exited normally.
4063 However, there can be situations when there is no corresponding name
4064 in XML file for that syscall number. In this case, @value{GDBN} prints
4065 a warning message saying that it was not able to find the syscall name,
4066 but the catchpoint will be set anyway. See the example below:
4069 (@value{GDBP}) catch syscall 764
4070 warning: The number '764' does not represent a known syscall.
4071 Catchpoint 2 (syscall 764)
4075 If you configure @value{GDBN} using the @samp{--without-expat} option,
4076 it will not be able to display syscall names. Also, if your
4077 architecture does not have an XML file describing its system calls,
4078 you will not be able to see the syscall names. It is important to
4079 notice that these two features are used for accessing the syscall
4080 name database. In either case, you will see a warning like this:
4083 (@value{GDBP}) catch syscall
4084 warning: Could not open "syscalls/i386-linux.xml"
4085 warning: Could not load the syscall XML file 'syscalls/i386-linux.xml'.
4086 GDB will not be able to display syscall names.
4087 Catchpoint 1 (syscall)
4091 Of course, the file name will change depending on your architecture and system.
4093 Still using the example above, you can also try to catch a syscall by its
4094 number. In this case, you would see something like:
4097 (@value{GDBP}) catch syscall 252
4098 Catchpoint 1 (syscall(s) 252)
4101 Again, in this case @value{GDBN} would not be able to display syscall's names.
4104 A call to @code{fork}. This is currently only available for HP-UX
4108 A call to @code{vfork}. This is currently only available for HP-UX
4113 @item tcatch @var{event}
4114 Set a catchpoint that is enabled only for one stop. The catchpoint is
4115 automatically deleted after the first time the event is caught.
4119 Use the @code{info break} command to list the current catchpoints.
4121 There are currently some limitations to C@t{++} exception handling
4122 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
4126 If you call a function interactively, @value{GDBN} normally returns
4127 control to you when the function has finished executing. If the call
4128 raises an exception, however, the call may bypass the mechanism that
4129 returns control to you and cause your program either to abort or to
4130 simply continue running until it hits a breakpoint, catches a signal
4131 that @value{GDBN} is listening for, or exits. This is the case even if
4132 you set a catchpoint for the exception; catchpoints on exceptions are
4133 disabled within interactive calls.
4136 You cannot raise an exception interactively.
4139 You cannot install an exception handler interactively.
4142 @cindex raise exceptions
4143 Sometimes @code{catch} is not the best way to debug exception handling:
4144 if you need to know exactly where an exception is raised, it is better to
4145 stop @emph{before} the exception handler is called, since that way you
4146 can see the stack before any unwinding takes place. If you set a
4147 breakpoint in an exception handler instead, it may not be easy to find
4148 out where the exception was raised.
4150 To stop just before an exception handler is called, you need some
4151 knowledge of the implementation. In the case of @sc{gnu} C@t{++}, exceptions are
4152 raised by calling a library function named @code{__raise_exception}
4153 which has the following ANSI C interface:
4156 /* @var{addr} is where the exception identifier is stored.
4157 @var{id} is the exception identifier. */
4158 void __raise_exception (void **addr, void *id);
4162 To make the debugger catch all exceptions before any stack
4163 unwinding takes place, set a breakpoint on @code{__raise_exception}
4164 (@pxref{Breakpoints, ,Breakpoints; Watchpoints; and Exceptions}).
4166 With a conditional breakpoint (@pxref{Conditions, ,Break Conditions})
4167 that depends on the value of @var{id}, you can stop your program when
4168 a specific exception is raised. You can use multiple conditional
4169 breakpoints to stop your program when any of a number of exceptions are
4174 @subsection Deleting Breakpoints
4176 @cindex clearing breakpoints, watchpoints, catchpoints
4177 @cindex deleting breakpoints, watchpoints, catchpoints
4178 It is often necessary to eliminate a breakpoint, watchpoint, or
4179 catchpoint once it has done its job and you no longer want your program
4180 to stop there. This is called @dfn{deleting} the breakpoint. A
4181 breakpoint that has been deleted no longer exists; it is forgotten.
4183 With the @code{clear} command you can delete breakpoints according to
4184 where they are in your program. With the @code{delete} command you can
4185 delete individual breakpoints, watchpoints, or catchpoints by specifying
4186 their breakpoint numbers.
4188 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
4189 automatically ignores breakpoints on the first instruction to be executed
4190 when you continue execution without changing the execution address.
4195 Delete any breakpoints at the next instruction to be executed in the
4196 selected stack frame (@pxref{Selection, ,Selecting a Frame}). When
4197 the innermost frame is selected, this is a good way to delete a
4198 breakpoint where your program just stopped.
4200 @item clear @var{location}
4201 Delete any breakpoints set at the specified @var{location}.
4202 @xref{Specify Location}, for the various forms of @var{location}; the
4203 most useful ones are listed below:
4206 @item clear @var{function}
4207 @itemx clear @var{filename}:@var{function}
4208 Delete any breakpoints set at entry to the named @var{function}.
4210 @item clear @var{linenum}
4211 @itemx clear @var{filename}:@var{linenum}
4212 Delete any breakpoints set at or within the code of the specified
4213 @var{linenum} of the specified @var{filename}.
4216 @cindex delete breakpoints
4218 @kindex d @r{(@code{delete})}
4219 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
4220 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
4221 ranges specified as arguments. If no argument is specified, delete all
4222 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
4223 confirm off}). You can abbreviate this command as @code{d}.
4227 @subsection Disabling Breakpoints
4229 @cindex enable/disable a breakpoint
4230 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
4231 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
4232 it had been deleted, but remembers the information on the breakpoint so
4233 that you can @dfn{enable} it again later.
4235 You disable and enable breakpoints, watchpoints, and catchpoints with
4236 the @code{enable} and @code{disable} commands, optionally specifying
4237 one or more breakpoint numbers as arguments. Use @code{info break} to
4238 print a list of all breakpoints, watchpoints, and catchpoints if you
4239 do not know which numbers to use.
4241 Disabling and enabling a breakpoint that has multiple locations
4242 affects all of its locations.
4244 A breakpoint, watchpoint, or catchpoint can have any of four different
4245 states of enablement:
4249 Enabled. The breakpoint stops your program. A breakpoint set
4250 with the @code{break} command starts out in this state.
4252 Disabled. The breakpoint has no effect on your program.
4254 Enabled once. The breakpoint stops your program, but then becomes
4257 Enabled for deletion. The breakpoint stops your program, but
4258 immediately after it does so it is deleted permanently. A breakpoint
4259 set with the @code{tbreak} command starts out in this state.
4262 You can use the following commands to enable or disable breakpoints,
4263 watchpoints, and catchpoints:
4267 @kindex dis @r{(@code{disable})}
4268 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
4269 Disable the specified breakpoints---or all breakpoints, if none are
4270 listed. A disabled breakpoint has no effect but is not forgotten. All
4271 options such as ignore-counts, conditions and commands are remembered in
4272 case the breakpoint is enabled again later. You may abbreviate
4273 @code{disable} as @code{dis}.
4276 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
4277 Enable the specified breakpoints (or all defined breakpoints). They
4278 become effective once again in stopping your program.
4280 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
4281 Enable the specified breakpoints temporarily. @value{GDBN} disables any
4282 of these breakpoints immediately after stopping your program.
4284 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
4285 Enable the specified breakpoints to work once, then die. @value{GDBN}
4286 deletes any of these breakpoints as soon as your program stops there.
4287 Breakpoints set by the @code{tbreak} command start out in this state.
4290 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
4291 @c confusing: tbreak is also initially enabled.
4292 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
4293 ,Setting Breakpoints}), breakpoints that you set are initially enabled;
4294 subsequently, they become disabled or enabled only when you use one of
4295 the commands above. (The command @code{until} can set and delete a
4296 breakpoint of its own, but it does not change the state of your other
4297 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
4301 @subsection Break Conditions
4302 @cindex conditional breakpoints
4303 @cindex breakpoint conditions
4305 @c FIXME what is scope of break condition expr? Context where wanted?
4306 @c in particular for a watchpoint?
4307 The simplest sort of breakpoint breaks every time your program reaches a
4308 specified place. You can also specify a @dfn{condition} for a
4309 breakpoint. A condition is just a Boolean expression in your
4310 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
4311 a condition evaluates the expression each time your program reaches it,
4312 and your program stops only if the condition is @emph{true}.
4314 This is the converse of using assertions for program validation; in that
4315 situation, you want to stop when the assertion is violated---that is,
4316 when the condition is false. In C, if you want to test an assertion expressed
4317 by the condition @var{assert}, you should set the condition
4318 @samp{! @var{assert}} on the appropriate breakpoint.
4320 Conditions are also accepted for watchpoints; you may not need them,
4321 since a watchpoint is inspecting the value of an expression anyhow---but
4322 it might be simpler, say, to just set a watchpoint on a variable name,
4323 and specify a condition that tests whether the new value is an interesting
4326 Break conditions can have side effects, and may even call functions in
4327 your program. This can be useful, for example, to activate functions
4328 that log program progress, or to use your own print functions to
4329 format special data structures. The effects are completely predictable
4330 unless there is another enabled breakpoint at the same address. (In
4331 that case, @value{GDBN} might see the other breakpoint first and stop your
4332 program without checking the condition of this one.) Note that
4333 breakpoint commands are usually more convenient and flexible than break
4335 purpose of performing side effects when a breakpoint is reached
4336 (@pxref{Break Commands, ,Breakpoint Command Lists}).
4338 Break conditions can be specified when a breakpoint is set, by using
4339 @samp{if} in the arguments to the @code{break} command. @xref{Set
4340 Breaks, ,Setting Breakpoints}. They can also be changed at any time
4341 with the @code{condition} command.
4343 You can also use the @code{if} keyword with the @code{watch} command.
4344 The @code{catch} command does not recognize the @code{if} keyword;
4345 @code{condition} is the only way to impose a further condition on a
4350 @item condition @var{bnum} @var{expression}
4351 Specify @var{expression} as the break condition for breakpoint,
4352 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
4353 breakpoint @var{bnum} stops your program only if the value of
4354 @var{expression} is true (nonzero, in C). When you use
4355 @code{condition}, @value{GDBN} checks @var{expression} immediately for
4356 syntactic correctness, and to determine whether symbols in it have
4357 referents in the context of your breakpoint. If @var{expression} uses
4358 symbols not referenced in the context of the breakpoint, @value{GDBN}
4359 prints an error message:
4362 No symbol "foo" in current context.
4367 not actually evaluate @var{expression} at the time the @code{condition}
4368 command (or a command that sets a breakpoint with a condition, like
4369 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
4371 @item condition @var{bnum}
4372 Remove the condition from breakpoint number @var{bnum}. It becomes
4373 an ordinary unconditional breakpoint.
4376 @cindex ignore count (of breakpoint)
4377 A special case of a breakpoint condition is to stop only when the
4378 breakpoint has been reached a certain number of times. This is so
4379 useful that there is a special way to do it, using the @dfn{ignore
4380 count} of the breakpoint. Every breakpoint has an ignore count, which
4381 is an integer. Most of the time, the ignore count is zero, and
4382 therefore has no effect. But if your program reaches a breakpoint whose
4383 ignore count is positive, then instead of stopping, it just decrements
4384 the ignore count by one and continues. As a result, if the ignore count
4385 value is @var{n}, the breakpoint does not stop the next @var{n} times
4386 your program reaches it.
4390 @item ignore @var{bnum} @var{count}
4391 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
4392 The next @var{count} times the breakpoint is reached, your program's
4393 execution does not stop; other than to decrement the ignore count, @value{GDBN}
4396 To make the breakpoint stop the next time it is reached, specify
4399 When you use @code{continue} to resume execution of your program from a
4400 breakpoint, you can specify an ignore count directly as an argument to
4401 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
4402 Stepping,,Continuing and Stepping}.
4404 If a breakpoint has a positive ignore count and a condition, the
4405 condition is not checked. Once the ignore count reaches zero,
4406 @value{GDBN} resumes checking the condition.
4408 You could achieve the effect of the ignore count with a condition such
4409 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
4410 is decremented each time. @xref{Convenience Vars, ,Convenience
4414 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
4417 @node Break Commands
4418 @subsection Breakpoint Command Lists
4420 @cindex breakpoint commands
4421 You can give any breakpoint (or watchpoint or catchpoint) a series of
4422 commands to execute when your program stops due to that breakpoint. For
4423 example, you might want to print the values of certain expressions, or
4424 enable other breakpoints.
4428 @kindex end@r{ (breakpoint commands)}
4429 @item commands @r{[}@var{range}@dots{}@r{]}
4430 @itemx @dots{} @var{command-list} @dots{}
4432 Specify a list of commands for the given breakpoints. The commands
4433 themselves appear on the following lines. Type a line containing just
4434 @code{end} to terminate the commands.
4436 To remove all commands from a breakpoint, type @code{commands} and
4437 follow it immediately with @code{end}; that is, give no commands.
4439 With no argument, @code{commands} refers to the last breakpoint,
4440 watchpoint, or catchpoint set (not to the breakpoint most recently
4441 encountered). If the most recent breakpoints were set with a single
4442 command, then the @code{commands} will apply to all the breakpoints
4443 set by that command. This applies to breakpoints set by
4444 @code{rbreak}, and also applies when a single @code{break} command
4445 creates multiple breakpoints (@pxref{Ambiguous Expressions,,Ambiguous
4449 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
4450 disabled within a @var{command-list}.
4452 You can use breakpoint commands to start your program up again. Simply
4453 use the @code{continue} command, or @code{step}, or any other command
4454 that resumes execution.
4456 Any other commands in the command list, after a command that resumes
4457 execution, are ignored. This is because any time you resume execution
4458 (even with a simple @code{next} or @code{step}), you may encounter
4459 another breakpoint---which could have its own command list, leading to
4460 ambiguities about which list to execute.
4463 If the first command you specify in a command list is @code{silent}, the
4464 usual message about stopping at a breakpoint is not printed. This may
4465 be desirable for breakpoints that are to print a specific message and
4466 then continue. If none of the remaining commands print anything, you
4467 see no sign that the breakpoint was reached. @code{silent} is
4468 meaningful only at the beginning of a breakpoint command list.
4470 The commands @code{echo}, @code{output}, and @code{printf} allow you to
4471 print precisely controlled output, and are often useful in silent
4472 breakpoints. @xref{Output, ,Commands for Controlled Output}.
4474 For example, here is how you could use breakpoint commands to print the
4475 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
4481 printf "x is %d\n",x
4486 One application for breakpoint commands is to compensate for one bug so
4487 you can test for another. Put a breakpoint just after the erroneous line
4488 of code, give it a condition to detect the case in which something
4489 erroneous has been done, and give it commands to assign correct values
4490 to any variables that need them. End with the @code{continue} command
4491 so that your program does not stop, and start with the @code{silent}
4492 command so that no output is produced. Here is an example:
4503 @node Save Breakpoints
4504 @subsection How to save breakpoints to a file
4506 To save breakpoint definitions to a file use the @w{@code{save
4507 breakpoints}} command.
4510 @kindex save breakpoints
4511 @cindex save breakpoints to a file for future sessions
4512 @item save breakpoints [@var{filename}]
4513 This command saves all current breakpoint definitions together with
4514 their commands and ignore counts, into a file @file{@var{filename}}
4515 suitable for use in a later debugging session. This includes all
4516 types of breakpoints (breakpoints, watchpoints, catchpoints,
4517 tracepoints). To read the saved breakpoint definitions, use the
4518 @code{source} command (@pxref{Command Files}). Note that watchpoints
4519 with expressions involving local variables may fail to be recreated
4520 because it may not be possible to access the context where the
4521 watchpoint is valid anymore. Because the saved breakpoint definitions
4522 are simply a sequence of @value{GDBN} commands that recreate the
4523 breakpoints, you can edit the file in your favorite editing program,
4524 and remove the breakpoint definitions you're not interested in, or
4525 that can no longer be recreated.
4528 @c @ifclear BARETARGET
4529 @node Error in Breakpoints
4530 @subsection ``Cannot insert breakpoints''
4532 If you request too many active hardware-assisted breakpoints and
4533 watchpoints, you will see this error message:
4535 @c FIXME: the precise wording of this message may change; the relevant
4536 @c source change is not committed yet (Sep 3, 1999).
4538 Stopped; cannot insert breakpoints.
4539 You may have requested too many hardware breakpoints and watchpoints.
4543 This message is printed when you attempt to resume the program, since
4544 only then @value{GDBN} knows exactly how many hardware breakpoints and
4545 watchpoints it needs to insert.
4547 When this message is printed, you need to disable or remove some of the
4548 hardware-assisted breakpoints and watchpoints, and then continue.
4550 @node Breakpoint-related Warnings
4551 @subsection ``Breakpoint address adjusted...''
4552 @cindex breakpoint address adjusted
4554 Some processor architectures place constraints on the addresses at
4555 which breakpoints may be placed. For architectures thus constrained,
4556 @value{GDBN} will attempt to adjust the breakpoint's address to comply
4557 with the constraints dictated by the architecture.
4559 One example of such an architecture is the Fujitsu FR-V. The FR-V is
4560 a VLIW architecture in which a number of RISC-like instructions may be
4561 bundled together for parallel execution. The FR-V architecture
4562 constrains the location of a breakpoint instruction within such a
4563 bundle to the instruction with the lowest address. @value{GDBN}
4564 honors this constraint by adjusting a breakpoint's address to the
4565 first in the bundle.
4567 It is not uncommon for optimized code to have bundles which contain
4568 instructions from different source statements, thus it may happen that
4569 a breakpoint's address will be adjusted from one source statement to
4570 another. Since this adjustment may significantly alter @value{GDBN}'s
4571 breakpoint related behavior from what the user expects, a warning is
4572 printed when the breakpoint is first set and also when the breakpoint
4575 A warning like the one below is printed when setting a breakpoint
4576 that's been subject to address adjustment:
4579 warning: Breakpoint address adjusted from 0x00010414 to 0x00010410.
4582 Such warnings are printed both for user settable and @value{GDBN}'s
4583 internal breakpoints. If you see one of these warnings, you should
4584 verify that a breakpoint set at the adjusted address will have the
4585 desired affect. If not, the breakpoint in question may be removed and
4586 other breakpoints may be set which will have the desired behavior.
4587 E.g., it may be sufficient to place the breakpoint at a later
4588 instruction. A conditional breakpoint may also be useful in some
4589 cases to prevent the breakpoint from triggering too often.
4591 @value{GDBN} will also issue a warning when stopping at one of these
4592 adjusted breakpoints:
4595 warning: Breakpoint 1 address previously adjusted from 0x00010414
4599 When this warning is encountered, it may be too late to take remedial
4600 action except in cases where the breakpoint is hit earlier or more
4601 frequently than expected.
4603 @node Continuing and Stepping
4604 @section Continuing and Stepping
4608 @cindex resuming execution
4609 @dfn{Continuing} means resuming program execution until your program
4610 completes normally. In contrast, @dfn{stepping} means executing just
4611 one more ``step'' of your program, where ``step'' may mean either one
4612 line of source code, or one machine instruction (depending on what
4613 particular command you use). Either when continuing or when stepping,
4614 your program may stop even sooner, due to a breakpoint or a signal. (If
4615 it stops due to a signal, you may want to use @code{handle}, or use
4616 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
4620 @kindex c @r{(@code{continue})}
4621 @kindex fg @r{(resume foreground execution)}
4622 @item continue @r{[}@var{ignore-count}@r{]}
4623 @itemx c @r{[}@var{ignore-count}@r{]}
4624 @itemx fg @r{[}@var{ignore-count}@r{]}
4625 Resume program execution, at the address where your program last stopped;
4626 any breakpoints set at that address are bypassed. The optional argument
4627 @var{ignore-count} allows you to specify a further number of times to
4628 ignore a breakpoint at this location; its effect is like that of
4629 @code{ignore} (@pxref{Conditions, ,Break Conditions}).
4631 The argument @var{ignore-count} is meaningful only when your program
4632 stopped due to a breakpoint. At other times, the argument to
4633 @code{continue} is ignored.
4635 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
4636 debugged program is deemed to be the foreground program) are provided
4637 purely for convenience, and have exactly the same behavior as
4641 To resume execution at a different place, you can use @code{return}
4642 (@pxref{Returning, ,Returning from a Function}) to go back to the
4643 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
4644 Different Address}) to go to an arbitrary location in your program.
4646 A typical technique for using stepping is to set a breakpoint
4647 (@pxref{Breakpoints, ,Breakpoints; Watchpoints; and Catchpoints}) at the
4648 beginning of the function or the section of your program where a problem
4649 is believed to lie, run your program until it stops at that breakpoint,
4650 and then step through the suspect area, examining the variables that are
4651 interesting, until you see the problem happen.
4655 @kindex s @r{(@code{step})}
4657 Continue running your program until control reaches a different source
4658 line, then stop it and return control to @value{GDBN}. This command is
4659 abbreviated @code{s}.
4662 @c "without debugging information" is imprecise; actually "without line
4663 @c numbers in the debugging information". (gcc -g1 has debugging info but
4664 @c not line numbers). But it seems complex to try to make that
4665 @c distinction here.
4666 @emph{Warning:} If you use the @code{step} command while control is
4667 within a function that was compiled without debugging information,
4668 execution proceeds until control reaches a function that does have
4669 debugging information. Likewise, it will not step into a function which
4670 is compiled without debugging information. To step through functions
4671 without debugging information, use the @code{stepi} command, described
4675 The @code{step} command only stops at the first instruction of a source
4676 line. This prevents the multiple stops that could otherwise occur in
4677 @code{switch} statements, @code{for} loops, etc. @code{step} continues
4678 to stop if a function that has debugging information is called within
4679 the line. In other words, @code{step} @emph{steps inside} any functions
4680 called within the line.
4682 Also, the @code{step} command only enters a function if there is line
4683 number information for the function. Otherwise it acts like the
4684 @code{next} command. This avoids problems when using @code{cc -gl}
4685 on MIPS machines. Previously, @code{step} entered subroutines if there
4686 was any debugging information about the routine.
4688 @item step @var{count}
4689 Continue running as in @code{step}, but do so @var{count} times. If a
4690 breakpoint is reached, or a signal not related to stepping occurs before
4691 @var{count} steps, stepping stops right away.
4694 @kindex n @r{(@code{next})}
4695 @item next @r{[}@var{count}@r{]}
4696 Continue to the next source line in the current (innermost) stack frame.
4697 This is similar to @code{step}, but function calls that appear within
4698 the line of code are executed without stopping. Execution stops when
4699 control reaches a different line of code at the original stack level
4700 that was executing when you gave the @code{next} command. This command
4701 is abbreviated @code{n}.
4703 An argument @var{count} is a repeat count, as for @code{step}.
4706 @c FIX ME!! Do we delete this, or is there a way it fits in with
4707 @c the following paragraph? --- Vctoria
4709 @c @code{next} within a function that lacks debugging information acts like
4710 @c @code{step}, but any function calls appearing within the code of the
4711 @c function are executed without stopping.
4713 The @code{next} command only stops at the first instruction of a
4714 source line. This prevents multiple stops that could otherwise occur in
4715 @code{switch} statements, @code{for} loops, etc.
4717 @kindex set step-mode
4719 @cindex functions without line info, and stepping
4720 @cindex stepping into functions with no line info
4721 @itemx set step-mode on
4722 The @code{set step-mode on} command causes the @code{step} command to
4723 stop at the first instruction of a function which contains no debug line
4724 information rather than stepping over it.
4726 This is useful in cases where you may be interested in inspecting the
4727 machine instructions of a function which has no symbolic info and do not
4728 want @value{GDBN} to automatically skip over this function.
4730 @item set step-mode off
4731 Causes the @code{step} command to step over any functions which contains no
4732 debug information. This is the default.
4734 @item show step-mode
4735 Show whether @value{GDBN} will stop in or step over functions without
4736 source line debug information.
4739 @kindex fin @r{(@code{finish})}
4741 Continue running until just after function in the selected stack frame
4742 returns. Print the returned value (if any). This command can be
4743 abbreviated as @code{fin}.
4745 Contrast this with the @code{return} command (@pxref{Returning,
4746 ,Returning from a Function}).
4749 @kindex u @r{(@code{until})}
4750 @cindex run until specified location
4753 Continue running until a source line past the current line, in the
4754 current stack frame, is reached. This command is used to avoid single
4755 stepping through a loop more than once. It is like the @code{next}
4756 command, except that when @code{until} encounters a jump, it
4757 automatically continues execution until the program counter is greater
4758 than the address of the jump.
4760 This means that when you reach the end of a loop after single stepping
4761 though it, @code{until} makes your program continue execution until it
4762 exits the loop. In contrast, a @code{next} command at the end of a loop
4763 simply steps back to the beginning of the loop, which forces you to step
4764 through the next iteration.
4766 @code{until} always stops your program if it attempts to exit the current
4769 @code{until} may produce somewhat counterintuitive results if the order
4770 of machine code does not match the order of the source lines. For
4771 example, in the following excerpt from a debugging session, the @code{f}
4772 (@code{frame}) command shows that execution is stopped at line
4773 @code{206}; yet when we use @code{until}, we get to line @code{195}:
4777 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
4779 (@value{GDBP}) until
4780 195 for ( ; argc > 0; NEXTARG) @{
4783 This happened because, for execution efficiency, the compiler had
4784 generated code for the loop closure test at the end, rather than the
4785 start, of the loop---even though the test in a C @code{for}-loop is
4786 written before the body of the loop. The @code{until} command appeared
4787 to step back to the beginning of the loop when it advanced to this
4788 expression; however, it has not really gone to an earlier
4789 statement---not in terms of the actual machine code.
4791 @code{until} with no argument works by means of single
4792 instruction stepping, and hence is slower than @code{until} with an
4795 @item until @var{location}
4796 @itemx u @var{location}
4797 Continue running your program until either the specified location is
4798 reached, or the current stack frame returns. @var{location} is any of
4799 the forms described in @ref{Specify Location}.
4800 This form of the command uses temporary breakpoints, and
4801 hence is quicker than @code{until} without an argument. The specified
4802 location is actually reached only if it is in the current frame. This
4803 implies that @code{until} can be used to skip over recursive function
4804 invocations. For instance in the code below, if the current location is
4805 line @code{96}, issuing @code{until 99} will execute the program up to
4806 line @code{99} in the same invocation of factorial, i.e., after the inner
4807 invocations have returned.
4810 94 int factorial (int value)
4812 96 if (value > 1) @{
4813 97 value *= factorial (value - 1);
4820 @kindex advance @var{location}
4821 @itemx advance @var{location}
4822 Continue running the program up to the given @var{location}. An argument is
4823 required, which should be of one of the forms described in
4824 @ref{Specify Location}.
4825 Execution will also stop upon exit from the current stack
4826 frame. This command is similar to @code{until}, but @code{advance} will
4827 not skip over recursive function calls, and the target location doesn't
4828 have to be in the same frame as the current one.
4832 @kindex si @r{(@code{stepi})}
4834 @itemx stepi @var{arg}
4836 Execute one machine instruction, then stop and return to the debugger.
4838 It is often useful to do @samp{display/i $pc} when stepping by machine
4839 instructions. This makes @value{GDBN} automatically display the next
4840 instruction to be executed, each time your program stops. @xref{Auto
4841 Display,, Automatic Display}.
4843 An argument is a repeat count, as in @code{step}.
4847 @kindex ni @r{(@code{nexti})}
4849 @itemx nexti @var{arg}
4851 Execute one machine instruction, but if it is a function call,
4852 proceed until the function returns.
4854 An argument is a repeat count, as in @code{next}.
4861 A signal is an asynchronous event that can happen in a program. The
4862 operating system defines the possible kinds of signals, and gives each
4863 kind a name and a number. For example, in Unix @code{SIGINT} is the
4864 signal a program gets when you type an interrupt character (often @kbd{Ctrl-c});
4865 @code{SIGSEGV} is the signal a program gets from referencing a place in
4866 memory far away from all the areas in use; @code{SIGALRM} occurs when
4867 the alarm clock timer goes off (which happens only if your program has
4868 requested an alarm).
4870 @cindex fatal signals
4871 Some signals, including @code{SIGALRM}, are a normal part of the
4872 functioning of your program. Others, such as @code{SIGSEGV}, indicate
4873 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
4874 program has not specified in advance some other way to handle the signal.
4875 @code{SIGINT} does not indicate an error in your program, but it is normally
4876 fatal so it can carry out the purpose of the interrupt: to kill the program.
4878 @value{GDBN} has the ability to detect any occurrence of a signal in your
4879 program. You can tell @value{GDBN} in advance what to do for each kind of
4882 @cindex handling signals
4883 Normally, @value{GDBN} is set up to let the non-erroneous signals like
4884 @code{SIGALRM} be silently passed to your program
4885 (so as not to interfere with their role in the program's functioning)
4886 but to stop your program immediately whenever an error signal happens.
4887 You can change these settings with the @code{handle} command.
4890 @kindex info signals
4894 Print a table of all the kinds of signals and how @value{GDBN} has been told to
4895 handle each one. You can use this to see the signal numbers of all
4896 the defined types of signals.
4898 @item info signals @var{sig}
4899 Similar, but print information only about the specified signal number.
4901 @code{info handle} is an alias for @code{info signals}.
4904 @item handle @var{signal} @r{[}@var{keywords}@dots{}@r{]}
4905 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
4906 can be the number of a signal or its name (with or without the
4907 @samp{SIG} at the beginning); a list of signal numbers of the form
4908 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
4909 known signals. Optional arguments @var{keywords}, described below,
4910 say what change to make.
4914 The keywords allowed by the @code{handle} command can be abbreviated.
4915 Their full names are:
4919 @value{GDBN} should not stop your program when this signal happens. It may
4920 still print a message telling you that the signal has come in.
4923 @value{GDBN} should stop your program when this signal happens. This implies
4924 the @code{print} keyword as well.
4927 @value{GDBN} should print a message when this signal happens.
4930 @value{GDBN} should not mention the occurrence of the signal at all. This
4931 implies the @code{nostop} keyword as well.
4935 @value{GDBN} should allow your program to see this signal; your program
4936 can handle the signal, or else it may terminate if the signal is fatal
4937 and not handled. @code{pass} and @code{noignore} are synonyms.
4941 @value{GDBN} should not allow your program to see this signal.
4942 @code{nopass} and @code{ignore} are synonyms.
4946 When a signal stops your program, the signal is not visible to the
4948 continue. Your program sees the signal then, if @code{pass} is in
4949 effect for the signal in question @emph{at that time}. In other words,
4950 after @value{GDBN} reports a signal, you can use the @code{handle}
4951 command with @code{pass} or @code{nopass} to control whether your
4952 program sees that signal when you continue.
4954 The default is set to @code{nostop}, @code{noprint}, @code{pass} for
4955 non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and
4956 @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the
4959 You can also use the @code{signal} command to prevent your program from
4960 seeing a signal, or cause it to see a signal it normally would not see,
4961 or to give it any signal at any time. For example, if your program stopped
4962 due to some sort of memory reference error, you might store correct
4963 values into the erroneous variables and continue, hoping to see more
4964 execution; but your program would probably terminate immediately as
4965 a result of the fatal signal once it saw the signal. To prevent this,
4966 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
4969 @cindex extra signal information
4970 @anchor{extra signal information}
4972 On some targets, @value{GDBN} can inspect extra signal information
4973 associated with the intercepted signal, before it is actually
4974 delivered to the program being debugged. This information is exported
4975 by the convenience variable @code{$_siginfo}, and consists of data
4976 that is passed by the kernel to the signal handler at the time of the
4977 receipt of a signal. The data type of the information itself is
4978 target dependent. You can see the data type using the @code{ptype
4979 $_siginfo} command. On Unix systems, it typically corresponds to the
4980 standard @code{siginfo_t} type, as defined in the @file{signal.h}
4983 Here's an example, on a @sc{gnu}/Linux system, printing the stray
4984 referenced address that raised a segmentation fault.
4988 (@value{GDBP}) continue
4989 Program received signal SIGSEGV, Segmentation fault.
4990 0x0000000000400766 in main ()
4992 (@value{GDBP}) ptype $_siginfo
4999 struct @{...@} _kill;
5000 struct @{...@} _timer;
5002 struct @{...@} _sigchld;
5003 struct @{...@} _sigfault;
5004 struct @{...@} _sigpoll;
5007 (@value{GDBP}) ptype $_siginfo._sifields._sigfault
5011 (@value{GDBP}) p $_siginfo._sifields._sigfault.si_addr
5012 $1 = (void *) 0x7ffff7ff7000
5016 Depending on target support, @code{$_siginfo} may also be writable.
5019 @section Stopping and Starting Multi-thread Programs
5021 @cindex stopped threads
5022 @cindex threads, stopped
5024 @cindex continuing threads
5025 @cindex threads, continuing
5027 @value{GDBN} supports debugging programs with multiple threads
5028 (@pxref{Threads,, Debugging Programs with Multiple Threads}). There
5029 are two modes of controlling execution of your program within the
5030 debugger. In the default mode, referred to as @dfn{all-stop mode},
5031 when any thread in your program stops (for example, at a breakpoint
5032 or while being stepped), all other threads in the program are also stopped by
5033 @value{GDBN}. On some targets, @value{GDBN} also supports
5034 @dfn{non-stop mode}, in which other threads can continue to run freely while
5035 you examine the stopped thread in the debugger.
5038 * All-Stop Mode:: All threads stop when GDB takes control
5039 * Non-Stop Mode:: Other threads continue to execute
5040 * Background Execution:: Running your program asynchronously
5041 * Thread-Specific Breakpoints:: Controlling breakpoints
5042 * Interrupted System Calls:: GDB may interfere with system calls
5043 * Observer Mode:: GDB does not alter program behavior
5047 @subsection All-Stop Mode
5049 @cindex all-stop mode
5051 In all-stop mode, whenever your program stops under @value{GDBN} for any reason,
5052 @emph{all} threads of execution stop, not just the current thread. This
5053 allows you to examine the overall state of the program, including
5054 switching between threads, without worrying that things may change
5057 Conversely, whenever you restart the program, @emph{all} threads start
5058 executing. @emph{This is true even when single-stepping} with commands
5059 like @code{step} or @code{next}.
5061 In particular, @value{GDBN} cannot single-step all threads in lockstep.
5062 Since thread scheduling is up to your debugging target's operating
5063 system (not controlled by @value{GDBN}), other threads may
5064 execute more than one statement while the current thread completes a
5065 single step. Moreover, in general other threads stop in the middle of a
5066 statement, rather than at a clean statement boundary, when the program
5069 You might even find your program stopped in another thread after
5070 continuing or even single-stepping. This happens whenever some other
5071 thread runs into a breakpoint, a signal, or an exception before the
5072 first thread completes whatever you requested.
5074 @cindex automatic thread selection
5075 @cindex switching threads automatically
5076 @cindex threads, automatic switching
5077 Whenever @value{GDBN} stops your program, due to a breakpoint or a
5078 signal, it automatically selects the thread where that breakpoint or
5079 signal happened. @value{GDBN} alerts you to the context switch with a
5080 message such as @samp{[Switching to Thread @var{n}]} to identify the
5083 On some OSes, you can modify @value{GDBN}'s default behavior by
5084 locking the OS scheduler to allow only a single thread to run.
5087 @item set scheduler-locking @var{mode}
5088 @cindex scheduler locking mode
5089 @cindex lock scheduler
5090 Set the scheduler locking mode. If it is @code{off}, then there is no
5091 locking and any thread may run at any time. If @code{on}, then only the
5092 current thread may run when the inferior is resumed. The @code{step}
5093 mode optimizes for single-stepping; it prevents other threads
5094 from preempting the current thread while you are stepping, so that
5095 the focus of debugging does not change unexpectedly.
5096 Other threads only rarely (or never) get a chance to run
5097 when you step. They are more likely to run when you @samp{next} over a
5098 function call, and they are completely free to run when you use commands
5099 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
5100 thread hits a breakpoint during its timeslice, @value{GDBN} does not change
5101 the current thread away from the thread that you are debugging.
5103 @item show scheduler-locking
5104 Display the current scheduler locking mode.
5107 @cindex resume threads of multiple processes simultaneously
5108 By default, when you issue one of the execution commands such as
5109 @code{continue}, @code{next} or @code{step}, @value{GDBN} allows only
5110 threads of the current inferior to run. For example, if @value{GDBN}
5111 is attached to two inferiors, each with two threads, the
5112 @code{continue} command resumes only the two threads of the current
5113 inferior. This is useful, for example, when you debug a program that
5114 forks and you want to hold the parent stopped (so that, for instance,
5115 it doesn't run to exit), while you debug the child. In other
5116 situations, you may not be interested in inspecting the current state
5117 of any of the processes @value{GDBN} is attached to, and you may want
5118 to resume them all until some breakpoint is hit. In the latter case,
5119 you can instruct @value{GDBN} to allow all threads of all the
5120 inferiors to run with the @w{@code{set schedule-multiple}} command.
5123 @kindex set schedule-multiple
5124 @item set schedule-multiple
5125 Set the mode for allowing threads of multiple processes to be resumed
5126 when an execution command is issued. When @code{on}, all threads of
5127 all processes are allowed to run. When @code{off}, only the threads
5128 of the current process are resumed. The default is @code{off}. The
5129 @code{scheduler-locking} mode takes precedence when set to @code{on},
5130 or while you are stepping and set to @code{step}.
5132 @item show schedule-multiple
5133 Display the current mode for resuming the execution of threads of
5138 @subsection Non-Stop Mode
5140 @cindex non-stop mode
5142 @c This section is really only a place-holder, and needs to be expanded
5143 @c with more details.
5145 For some multi-threaded targets, @value{GDBN} supports an optional
5146 mode of operation in which you can examine stopped program threads in
5147 the debugger while other threads continue to execute freely. This
5148 minimizes intrusion when debugging live systems, such as programs
5149 where some threads have real-time constraints or must continue to
5150 respond to external events. This is referred to as @dfn{non-stop} mode.
5152 In non-stop mode, when a thread stops to report a debugging event,
5153 @emph{only} that thread is stopped; @value{GDBN} does not stop other
5154 threads as well, in contrast to the all-stop mode behavior. Additionally,
5155 execution commands such as @code{continue} and @code{step} apply by default
5156 only to the current thread in non-stop mode, rather than all threads as
5157 in all-stop mode. This allows you to control threads explicitly in
5158 ways that are not possible in all-stop mode --- for example, stepping
5159 one thread while allowing others to run freely, stepping
5160 one thread while holding all others stopped, or stepping several threads
5161 independently and simultaneously.
5163 To enter non-stop mode, use this sequence of commands before you run
5164 or attach to your program:
5167 # Enable the async interface.
5170 # If using the CLI, pagination breaks non-stop.
5173 # Finally, turn it on!
5177 You can use these commands to manipulate the non-stop mode setting:
5180 @kindex set non-stop
5181 @item set non-stop on
5182 Enable selection of non-stop mode.
5183 @item set non-stop off
5184 Disable selection of non-stop mode.
5185 @kindex show non-stop
5187 Show the current non-stop enablement setting.
5190 Note these commands only reflect whether non-stop mode is enabled,
5191 not whether the currently-executing program is being run in non-stop mode.
5192 In particular, the @code{set non-stop} preference is only consulted when
5193 @value{GDBN} starts or connects to the target program, and it is generally
5194 not possible to switch modes once debugging has started. Furthermore,
5195 since not all targets support non-stop mode, even when you have enabled
5196 non-stop mode, @value{GDBN} may still fall back to all-stop operation by
5199 In non-stop mode, all execution commands apply only to the current thread
5200 by default. That is, @code{continue} only continues one thread.
5201 To continue all threads, issue @code{continue -a} or @code{c -a}.
5203 You can use @value{GDBN}'s background execution commands
5204 (@pxref{Background Execution}) to run some threads in the background
5205 while you continue to examine or step others from @value{GDBN}.
5206 The MI execution commands (@pxref{GDB/MI Program Execution}) are
5207 always executed asynchronously in non-stop mode.
5209 Suspending execution is done with the @code{interrupt} command when
5210 running in the background, or @kbd{Ctrl-c} during foreground execution.
5211 In all-stop mode, this stops the whole process;
5212 but in non-stop mode the interrupt applies only to the current thread.
5213 To stop the whole program, use @code{interrupt -a}.
5215 Other execution commands do not currently support the @code{-a} option.
5217 In non-stop mode, when a thread stops, @value{GDBN} doesn't automatically make
5218 that thread current, as it does in all-stop mode. This is because the
5219 thread stop notifications are asynchronous with respect to @value{GDBN}'s
5220 command interpreter, and it would be confusing if @value{GDBN} unexpectedly
5221 changed to a different thread just as you entered a command to operate on the
5222 previously current thread.
5224 @node Background Execution
5225 @subsection Background Execution
5227 @cindex foreground execution
5228 @cindex background execution
5229 @cindex asynchronous execution
5230 @cindex execution, foreground, background and asynchronous
5232 @value{GDBN}'s execution commands have two variants: the normal
5233 foreground (synchronous) behavior, and a background
5234 (asynchronous) behavior. In foreground execution, @value{GDBN} waits for
5235 the program to report that some thread has stopped before prompting for
5236 another command. In background execution, @value{GDBN} immediately gives
5237 a command prompt so that you can issue other commands while your program runs.
5239 You need to explicitly enable asynchronous mode before you can use
5240 background execution commands. You can use these commands to
5241 manipulate the asynchronous mode setting:
5244 @kindex set target-async
5245 @item set target-async on
5246 Enable asynchronous mode.
5247 @item set target-async off
5248 Disable asynchronous mode.
5249 @kindex show target-async
5250 @item show target-async
5251 Show the current target-async setting.
5254 If the target doesn't support async mode, @value{GDBN} issues an error
5255 message if you attempt to use the background execution commands.
5257 To specify background execution, add a @code{&} to the command. For example,
5258 the background form of the @code{continue} command is @code{continue&}, or
5259 just @code{c&}. The execution commands that accept background execution
5265 @xref{Starting, , Starting your Program}.
5269 @xref{Attach, , Debugging an Already-running Process}.
5273 @xref{Continuing and Stepping, step}.
5277 @xref{Continuing and Stepping, stepi}.
5281 @xref{Continuing and Stepping, next}.
5285 @xref{Continuing and Stepping, nexti}.
5289 @xref{Continuing and Stepping, continue}.
5293 @xref{Continuing and Stepping, finish}.
5297 @xref{Continuing and Stepping, until}.
5301 Background execution is especially useful in conjunction with non-stop
5302 mode for debugging programs with multiple threads; see @ref{Non-Stop Mode}.
5303 However, you can also use these commands in the normal all-stop mode with
5304 the restriction that you cannot issue another execution command until the
5305 previous one finishes. Examples of commands that are valid in all-stop
5306 mode while the program is running include @code{help} and @code{info break}.
5308 You can interrupt your program while it is running in the background by
5309 using the @code{interrupt} command.
5316 Suspend execution of the running program. In all-stop mode,
5317 @code{interrupt} stops the whole process, but in non-stop mode, it stops
5318 only the current thread. To stop the whole program in non-stop mode,
5319 use @code{interrupt -a}.
5322 @node Thread-Specific Breakpoints
5323 @subsection Thread-Specific Breakpoints
5325 When your program has multiple threads (@pxref{Threads,, Debugging
5326 Programs with Multiple Threads}), you can choose whether to set
5327 breakpoints on all threads, or on a particular thread.
5330 @cindex breakpoints and threads
5331 @cindex thread breakpoints
5332 @kindex break @dots{} thread @var{threadno}
5333 @item break @var{linespec} thread @var{threadno}
5334 @itemx break @var{linespec} thread @var{threadno} if @dots{}
5335 @var{linespec} specifies source lines; there are several ways of
5336 writing them (@pxref{Specify Location}), but the effect is always to
5337 specify some source line.
5339 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
5340 to specify that you only want @value{GDBN} to stop the program when a
5341 particular thread reaches this breakpoint. @var{threadno} is one of the
5342 numeric thread identifiers assigned by @value{GDBN}, shown in the first
5343 column of the @samp{info threads} display.
5345 If you do not specify @samp{thread @var{threadno}} when you set a
5346 breakpoint, the breakpoint applies to @emph{all} threads of your
5349 You can use the @code{thread} qualifier on conditional breakpoints as
5350 well; in this case, place @samp{thread @var{threadno}} before or
5351 after the breakpoint condition, like this:
5354 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
5359 @node Interrupted System Calls
5360 @subsection Interrupted System Calls
5362 @cindex thread breakpoints and system calls
5363 @cindex system calls and thread breakpoints
5364 @cindex premature return from system calls
5365 There is an unfortunate side effect when using @value{GDBN} to debug
5366 multi-threaded programs. If one thread stops for a
5367 breakpoint, or for some other reason, and another thread is blocked in a
5368 system call, then the system call may return prematurely. This is a
5369 consequence of the interaction between multiple threads and the signals
5370 that @value{GDBN} uses to implement breakpoints and other events that
5373 To handle this problem, your program should check the return value of
5374 each system call and react appropriately. This is good programming
5377 For example, do not write code like this:
5383 The call to @code{sleep} will return early if a different thread stops
5384 at a breakpoint or for some other reason.
5386 Instead, write this:
5391 unslept = sleep (unslept);
5394 A system call is allowed to return early, so the system is still
5395 conforming to its specification. But @value{GDBN} does cause your
5396 multi-threaded program to behave differently than it would without
5399 Also, @value{GDBN} uses internal breakpoints in the thread library to
5400 monitor certain events such as thread creation and thread destruction.
5401 When such an event happens, a system call in another thread may return
5402 prematurely, even though your program does not appear to stop.
5405 @subsection Observer Mode
5407 If you want to build on non-stop mode and observe program behavior
5408 without any chance of disruption by @value{GDBN}, you can set
5409 variables to disable all of the debugger's attempts to modify state,
5410 whether by writing memory, inserting breakpoints, etc. These operate
5411 at a low level, intercepting operations from all commands.
5413 When all of these are set to @code{off}, then @value{GDBN} is said to
5414 be @dfn{observer mode}. As a convenience, the variable
5415 @code{observer} can be set to disable these, plus enable non-stop
5418 Note that @value{GDBN} will not prevent you from making nonsensical
5419 combinations of these settings. For instance, if you have enabled
5420 @code{may-insert-breakpoints} but disabled @code{may-write-memory},
5421 then breakpoints that work by writing trap instructions into the code
5422 stream will still not be able to be placed.
5427 @item set observer on
5428 @itemx set observer off
5429 When set to @code{on}, this disables all the permission variables
5430 below (except for @code{insert-fast-tracepoints}), plus enables
5431 non-stop debugging. Setting this to @code{off} switches back to
5432 normal debugging, though remaining in non-stop mode.
5435 Show whether observer mode is on or off.
5437 @kindex may-write-registers
5438 @item set may-write-registers on
5439 @itemx set may-write-registers off
5440 This controls whether @value{GDBN} will attempt to alter the values of
5441 registers, such as with assignment expressions in @code{print}, or the
5442 @code{jump} command. It defaults to @code{on}.
5444 @item show may-write-registers
5445 Show the current permission to write registers.
5447 @kindex may-write-memory
5448 @item set may-write-memory on
5449 @itemx set may-write-memory off
5450 This controls whether @value{GDBN} will attempt to alter the contents
5451 of memory, such as with assignment expressions in @code{print}. It
5452 defaults to @code{on}.
5454 @item show may-write-memory
5455 Show the current permission to write memory.
5457 @kindex may-insert-breakpoints
5458 @item set may-insert-breakpoints on
5459 @itemx set may-insert-breakpoints off
5460 This controls whether @value{GDBN} will attempt to insert breakpoints.
5461 This affects all breakpoints, including internal breakpoints defined
5462 by @value{GDBN}. It defaults to @code{on}.
5464 @item show may-insert-breakpoints
5465 Show the current permission to insert breakpoints.
5467 @kindex may-insert-tracepoints
5468 @item set may-insert-tracepoints on
5469 @itemx set may-insert-tracepoints off
5470 This controls whether @value{GDBN} will attempt to insert (regular)
5471 tracepoints at the beginning of a tracing experiment. It affects only
5472 non-fast tracepoints, fast tracepoints being under the control of
5473 @code{may-insert-fast-tracepoints}. It defaults to @code{on}.
5475 @item show may-insert-tracepoints
5476 Show the current permission to insert tracepoints.
5478 @kindex may-insert-fast-tracepoints
5479 @item set may-insert-fast-tracepoints on
5480 @itemx set may-insert-fast-tracepoints off
5481 This controls whether @value{GDBN} will attempt to insert fast
5482 tracepoints at the beginning of a tracing experiment. It affects only
5483 fast tracepoints, regular (non-fast) tracepoints being under the
5484 control of @code{may-insert-tracepoints}. It defaults to @code{on}.
5486 @item show may-insert-fast-tracepoints
5487 Show the current permission to insert fast tracepoints.
5489 @kindex may-interrupt
5490 @item set may-interrupt on
5491 @itemx set may-interrupt off
5492 This controls whether @value{GDBN} will attempt to interrupt or stop
5493 program execution. When this variable is @code{off}, the
5494 @code{interrupt} command will have no effect, nor will
5495 @kbd{Ctrl-c}. It defaults to @code{on}.
5497 @item show may-interrupt
5498 Show the current permission to interrupt or stop the program.
5502 @node Reverse Execution
5503 @chapter Running programs backward
5504 @cindex reverse execution
5505 @cindex running programs backward
5507 When you are debugging a program, it is not unusual to realize that
5508 you have gone too far, and some event of interest has already happened.
5509 If the target environment supports it, @value{GDBN} can allow you to
5510 ``rewind'' the program by running it backward.
5512 A target environment that supports reverse execution should be able
5513 to ``undo'' the changes in machine state that have taken place as the
5514 program was executing normally. Variables, registers etc.@: should
5515 revert to their previous values. Obviously this requires a great
5516 deal of sophistication on the part of the target environment; not
5517 all target environments can support reverse execution.
5519 When a program is executed in reverse, the instructions that
5520 have most recently been executed are ``un-executed'', in reverse
5521 order. The program counter runs backward, following the previous
5522 thread of execution in reverse. As each instruction is ``un-executed'',
5523 the values of memory and/or registers that were changed by that
5524 instruction are reverted to their previous states. After executing
5525 a piece of source code in reverse, all side effects of that code
5526 should be ``undone'', and all variables should be returned to their
5527 prior values@footnote{
5528 Note that some side effects are easier to undo than others. For instance,
5529 memory and registers are relatively easy, but device I/O is hard. Some
5530 targets may be able undo things like device I/O, and some may not.
5532 The contract between @value{GDBN} and the reverse executing target
5533 requires only that the target do something reasonable when
5534 @value{GDBN} tells it to execute backwards, and then report the
5535 results back to @value{GDBN}. Whatever the target reports back to
5536 @value{GDBN}, @value{GDBN} will report back to the user. @value{GDBN}
5537 assumes that the memory and registers that the target reports are in a
5538 consistant state, but @value{GDBN} accepts whatever it is given.
5541 If you are debugging in a target environment that supports
5542 reverse execution, @value{GDBN} provides the following commands.
5545 @kindex reverse-continue
5546 @kindex rc @r{(@code{reverse-continue})}
5547 @item reverse-continue @r{[}@var{ignore-count}@r{]}
5548 @itemx rc @r{[}@var{ignore-count}@r{]}
5549 Beginning at the point where your program last stopped, start executing
5550 in reverse. Reverse execution will stop for breakpoints and synchronous
5551 exceptions (signals), just like normal execution. Behavior of
5552 asynchronous signals depends on the target environment.
5554 @kindex reverse-step
5555 @kindex rs @r{(@code{step})}
5556 @item reverse-step @r{[}@var{count}@r{]}
5557 Run the program backward until control reaches the start of a
5558 different source line; then stop it, and return control to @value{GDBN}.
5560 Like the @code{step} command, @code{reverse-step} will only stop
5561 at the beginning of a source line. It ``un-executes'' the previously
5562 executed source line. If the previous source line included calls to
5563 debuggable functions, @code{reverse-step} will step (backward) into
5564 the called function, stopping at the beginning of the @emph{last}
5565 statement in the called function (typically a return statement).
5567 Also, as with the @code{step} command, if non-debuggable functions are
5568 called, @code{reverse-step} will run thru them backward without stopping.
5570 @kindex reverse-stepi
5571 @kindex rsi @r{(@code{reverse-stepi})}
5572 @item reverse-stepi @r{[}@var{count}@r{]}
5573 Reverse-execute one machine instruction. Note that the instruction
5574 to be reverse-executed is @emph{not} the one pointed to by the program
5575 counter, but the instruction executed prior to that one. For instance,
5576 if the last instruction was a jump, @code{reverse-stepi} will take you
5577 back from the destination of the jump to the jump instruction itself.
5579 @kindex reverse-next
5580 @kindex rn @r{(@code{reverse-next})}
5581 @item reverse-next @r{[}@var{count}@r{]}
5582 Run backward to the beginning of the previous line executed in
5583 the current (innermost) stack frame. If the line contains function
5584 calls, they will be ``un-executed'' without stopping. Starting from
5585 the first line of a function, @code{reverse-next} will take you back
5586 to the caller of that function, @emph{before} the function was called,
5587 just as the normal @code{next} command would take you from the last
5588 line of a function back to its return to its caller
5589 @footnote{Unless the code is too heavily optimized.}.
5591 @kindex reverse-nexti
5592 @kindex rni @r{(@code{reverse-nexti})}
5593 @item reverse-nexti @r{[}@var{count}@r{]}
5594 Like @code{nexti}, @code{reverse-nexti} executes a single instruction
5595 in reverse, except that called functions are ``un-executed'' atomically.
5596 That is, if the previously executed instruction was a return from
5597 another function, @code{reverse-nexti} will continue to execute
5598 in reverse until the call to that function (from the current stack
5601 @kindex reverse-finish
5602 @item reverse-finish
5603 Just as the @code{finish} command takes you to the point where the
5604 current function returns, @code{reverse-finish} takes you to the point
5605 where it was called. Instead of ending up at the end of the current
5606 function invocation, you end up at the beginning.
5608 @kindex set exec-direction
5609 @item set exec-direction
5610 Set the direction of target execution.
5611 @itemx set exec-direction reverse
5612 @cindex execute forward or backward in time
5613 @value{GDBN} will perform all execution commands in reverse, until the
5614 exec-direction mode is changed to ``forward''. Affected commands include
5615 @code{step, stepi, next, nexti, continue, and finish}. The @code{return}
5616 command cannot be used in reverse mode.
5617 @item set exec-direction forward
5618 @value{GDBN} will perform all execution commands in the normal fashion.
5619 This is the default.
5623 @node Process Record and Replay
5624 @chapter Recording Inferior's Execution and Replaying It
5625 @cindex process record and replay
5626 @cindex recording inferior's execution and replaying it
5628 On some platforms, @value{GDBN} provides a special @dfn{process record
5629 and replay} target that can record a log of the process execution, and
5630 replay it later with both forward and reverse execution commands.
5633 When this target is in use, if the execution log includes the record
5634 for the next instruction, @value{GDBN} will debug in @dfn{replay
5635 mode}. In the replay mode, the inferior does not really execute code
5636 instructions. Instead, all the events that normally happen during
5637 code execution are taken from the execution log. While code is not
5638 really executed in replay mode, the values of registers (including the
5639 program counter register) and the memory of the inferior are still
5640 changed as they normally would. Their contents are taken from the
5644 If the record for the next instruction is not in the execution log,
5645 @value{GDBN} will debug in @dfn{record mode}. In this mode, the
5646 inferior executes normally, and @value{GDBN} records the execution log
5649 The process record and replay target supports reverse execution
5650 (@pxref{Reverse Execution}), even if the platform on which the
5651 inferior runs does not. However, the reverse execution is limited in
5652 this case by the range of the instructions recorded in the execution
5653 log. In other words, reverse execution on platforms that don't
5654 support it directly can only be done in the replay mode.
5656 When debugging in the reverse direction, @value{GDBN} will work in
5657 replay mode as long as the execution log includes the record for the
5658 previous instruction; otherwise, it will work in record mode, if the
5659 platform supports reverse execution, or stop if not.
5661 For architecture environments that support process record and replay,
5662 @value{GDBN} provides the following commands:
5665 @kindex target record
5669 This command starts the process record and replay target. The process
5670 record and replay target can only debug a process that is already
5671 running. Therefore, you need first to start the process with the
5672 @kbd{run} or @kbd{start} commands, and then start the recording with
5673 the @kbd{target record} command.
5675 Both @code{record} and @code{rec} are aliases of @code{target record}.
5677 @cindex displaced stepping, and process record and replay
5678 Displaced stepping (@pxref{Maintenance Commands,, displaced stepping})
5679 will be automatically disabled when process record and replay target
5680 is started. That's because the process record and replay target
5681 doesn't support displaced stepping.
5683 @cindex non-stop mode, and process record and replay
5684 @cindex asynchronous execution, and process record and replay
5685 If the inferior is in the non-stop mode (@pxref{Non-Stop Mode}) or in
5686 the asynchronous execution mode (@pxref{Background Execution}), the
5687 process record and replay target cannot be started because it doesn't
5688 support these two modes.
5693 Stop the process record and replay target. When process record and
5694 replay target stops, the entire execution log will be deleted and the
5695 inferior will either be terminated, or will remain in its final state.
5697 When you stop the process record and replay target in record mode (at
5698 the end of the execution log), the inferior will be stopped at the
5699 next instruction that would have been recorded. In other words, if
5700 you record for a while and then stop recording, the inferior process
5701 will be left in the same state as if the recording never happened.
5703 On the other hand, if the process record and replay target is stopped
5704 while in replay mode (that is, not at the end of the execution log,
5705 but at some earlier point), the inferior process will become ``live''
5706 at that earlier state, and it will then be possible to continue the
5707 usual ``live'' debugging of the process from that state.
5709 When the inferior process exits, or @value{GDBN} detaches from it,
5710 process record and replay target will automatically stop itself.
5713 @item record save @var{filename}
5714 Save the execution log to a file @file{@var{filename}}.
5715 Default filename is @file{gdb_record.@var{process_id}}, where
5716 @var{process_id} is the process ID of the inferior.
5718 @kindex record restore
5719 @item record restore @var{filename}
5720 Restore the execution log from a file @file{@var{filename}}.
5721 File must have been created with @code{record save}.
5723 @kindex set record insn-number-max
5724 @item set record insn-number-max @var{limit}
5725 Set the limit of instructions to be recorded. Default value is 200000.
5727 If @var{limit} is a positive number, then @value{GDBN} will start
5728 deleting instructions from the log once the number of the record
5729 instructions becomes greater than @var{limit}. For every new recorded
5730 instruction, @value{GDBN} will delete the earliest recorded
5731 instruction to keep the number of recorded instructions at the limit.
5732 (Since deleting recorded instructions loses information, @value{GDBN}
5733 lets you control what happens when the limit is reached, by means of
5734 the @code{stop-at-limit} option, described below.)
5736 If @var{limit} is zero, @value{GDBN} will never delete recorded
5737 instructions from the execution log. The number of recorded
5738 instructions is unlimited in this case.
5740 @kindex show record insn-number-max
5741 @item show record insn-number-max
5742 Show the limit of instructions to be recorded.
5744 @kindex set record stop-at-limit
5745 @item set record stop-at-limit
5746 Control the behavior when the number of recorded instructions reaches
5747 the limit. If ON (the default), @value{GDBN} will stop when the limit
5748 is reached for the first time and ask you whether you want to stop the
5749 inferior or continue running it and recording the execution log. If
5750 you decide to continue recording, each new recorded instruction will
5751 cause the oldest one to be deleted.
5753 If this option is OFF, @value{GDBN} will automatically delete the
5754 oldest record to make room for each new one, without asking.
5756 @kindex show record stop-at-limit
5757 @item show record stop-at-limit
5758 Show the current setting of @code{stop-at-limit}.
5760 @kindex set record memory-query
5761 @item set record memory-query
5762 Control the behavior when @value{GDBN} is unable to record memory
5763 changes caused by an instruction. If ON, @value{GDBN} will query
5764 whether to stop the inferior in that case.
5766 If this option is OFF (the default), @value{GDBN} will automatically
5767 ignore the effect of such instructions on memory. Later, when
5768 @value{GDBN} replays this execution log, it will mark the log of this
5769 instruction as not accessible, and it will not affect the replay
5772 @kindex show record memory-query
5773 @item show record memory-query
5774 Show the current setting of @code{memory-query}.
5778 Show various statistics about the state of process record and its
5779 in-memory execution log buffer, including:
5783 Whether in record mode or replay mode.
5785 Lowest recorded instruction number (counting from when the current execution log started recording instructions).
5787 Highest recorded instruction number.
5789 Current instruction about to be replayed (if in replay mode).
5791 Number of instructions contained in the execution log.
5793 Maximum number of instructions that may be contained in the execution log.
5796 @kindex record delete
5799 When record target runs in replay mode (``in the past''), delete the
5800 subsequent execution log and begin to record a new execution log starting
5801 from the current address. This means you will abandon the previously
5802 recorded ``future'' and begin recording a new ``future''.
5807 @chapter Examining the Stack
5809 When your program has stopped, the first thing you need to know is where it
5810 stopped and how it got there.
5813 Each time your program performs a function call, information about the call
5815 That information includes the location of the call in your program,
5816 the arguments of the call,
5817 and the local variables of the function being called.
5818 The information is saved in a block of data called a @dfn{stack frame}.
5819 The stack frames are allocated in a region of memory called the @dfn{call
5822 When your program stops, the @value{GDBN} commands for examining the
5823 stack allow you to see all of this information.
5825 @cindex selected frame
5826 One of the stack frames is @dfn{selected} by @value{GDBN} and many
5827 @value{GDBN} commands refer implicitly to the selected frame. In
5828 particular, whenever you ask @value{GDBN} for the value of a variable in
5829 your program, the value is found in the selected frame. There are
5830 special @value{GDBN} commands to select whichever frame you are
5831 interested in. @xref{Selection, ,Selecting a Frame}.
5833 When your program stops, @value{GDBN} automatically selects the
5834 currently executing frame and describes it briefly, similar to the
5835 @code{frame} command (@pxref{Frame Info, ,Information about a Frame}).
5838 * Frames:: Stack frames
5839 * Backtrace:: Backtraces
5840 * Selection:: Selecting a frame
5841 * Frame Info:: Information on a frame
5846 @section Stack Frames
5848 @cindex frame, definition
5850 The call stack is divided up into contiguous pieces called @dfn{stack
5851 frames}, or @dfn{frames} for short; each frame is the data associated
5852 with one call to one function. The frame contains the arguments given
5853 to the function, the function's local variables, and the address at
5854 which the function is executing.
5856 @cindex initial frame
5857 @cindex outermost frame
5858 @cindex innermost frame
5859 When your program is started, the stack has only one frame, that of the
5860 function @code{main}. This is called the @dfn{initial} frame or the
5861 @dfn{outermost} frame. Each time a function is called, a new frame is
5862 made. Each time a function returns, the frame for that function invocation
5863 is eliminated. If a function is recursive, there can be many frames for
5864 the same function. The frame for the function in which execution is
5865 actually occurring is called the @dfn{innermost} frame. This is the most
5866 recently created of all the stack frames that still exist.
5868 @cindex frame pointer
5869 Inside your program, stack frames are identified by their addresses. A
5870 stack frame consists of many bytes, each of which has its own address; each
5871 kind of computer has a convention for choosing one byte whose
5872 address serves as the address of the frame. Usually this address is kept
5873 in a register called the @dfn{frame pointer register}
5874 (@pxref{Registers, $fp}) while execution is going on in that frame.
5876 @cindex frame number
5877 @value{GDBN} assigns numbers to all existing stack frames, starting with
5878 zero for the innermost frame, one for the frame that called it,
5879 and so on upward. These numbers do not really exist in your program;
5880 they are assigned by @value{GDBN} to give you a way of designating stack
5881 frames in @value{GDBN} commands.
5883 @c The -fomit-frame-pointer below perennially causes hbox overflow
5884 @c underflow problems.
5885 @cindex frameless execution
5886 Some compilers provide a way to compile functions so that they operate
5887 without stack frames. (For example, the @value{NGCC} option
5889 @samp{-fomit-frame-pointer}
5891 generates functions without a frame.)
5892 This is occasionally done with heavily used library functions to save
5893 the frame setup time. @value{GDBN} has limited facilities for dealing
5894 with these function invocations. If the innermost function invocation
5895 has no stack frame, @value{GDBN} nevertheless regards it as though
5896 it had a separate frame, which is numbered zero as usual, allowing
5897 correct tracing of the function call chain. However, @value{GDBN} has
5898 no provision for frameless functions elsewhere in the stack.
5901 @kindex frame@r{, command}
5902 @cindex current stack frame
5903 @item frame @var{args}
5904 The @code{frame} command allows you to move from one stack frame to another,
5905 and to print the stack frame you select. @var{args} may be either the
5906 address of the frame or the stack frame number. Without an argument,
5907 @code{frame} prints the current stack frame.
5909 @kindex select-frame
5910 @cindex selecting frame silently
5912 The @code{select-frame} command allows you to move from one stack frame
5913 to another without printing the frame. This is the silent version of
5921 @cindex call stack traces
5922 A backtrace is a summary of how your program got where it is. It shows one
5923 line per frame, for many frames, starting with the currently executing
5924 frame (frame zero), followed by its caller (frame one), and on up the
5929 @kindex bt @r{(@code{backtrace})}
5932 Print a backtrace of the entire stack: one line per frame for all
5933 frames in the stack.
5935 You can stop the backtrace at any time by typing the system interrupt
5936 character, normally @kbd{Ctrl-c}.
5938 @item backtrace @var{n}
5940 Similar, but print only the innermost @var{n} frames.
5942 @item backtrace -@var{n}
5944 Similar, but print only the outermost @var{n} frames.
5946 @item backtrace full
5948 @itemx bt full @var{n}
5949 @itemx bt full -@var{n}
5950 Print the values of the local variables also. @var{n} specifies the
5951 number of frames to print, as described above.
5956 The names @code{where} and @code{info stack} (abbreviated @code{info s})
5957 are additional aliases for @code{backtrace}.
5959 @cindex multiple threads, backtrace
5960 In a multi-threaded program, @value{GDBN} by default shows the
5961 backtrace only for the current thread. To display the backtrace for
5962 several or all of the threads, use the command @code{thread apply}
5963 (@pxref{Threads, thread apply}). For example, if you type @kbd{thread
5964 apply all backtrace}, @value{GDBN} will display the backtrace for all
5965 the threads; this is handy when you debug a core dump of a
5966 multi-threaded program.
5968 Each line in the backtrace shows the frame number and the function name.
5969 The program counter value is also shown---unless you use @code{set
5970 print address off}. The backtrace also shows the source file name and
5971 line number, as well as the arguments to the function. The program
5972 counter value is omitted if it is at the beginning of the code for that
5975 Here is an example of a backtrace. It was made with the command
5976 @samp{bt 3}, so it shows the innermost three frames.
5980 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
5982 #1 0x6e38 in expand_macro (sym=0x2b600, data=...) at macro.c:242
5983 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
5985 (More stack frames follow...)
5990 The display for frame zero does not begin with a program counter
5991 value, indicating that your program has stopped at the beginning of the
5992 code for line @code{993} of @code{builtin.c}.
5995 The value of parameter @code{data} in frame 1 has been replaced by
5996 @code{@dots{}}. By default, @value{GDBN} prints the value of a parameter
5997 only if it is a scalar (integer, pointer, enumeration, etc). See command
5998 @kbd{set print frame-arguments} in @ref{Print Settings} for more details
5999 on how to configure the way function parameter values are printed.
6001 @cindex optimized out, in backtrace
6002 @cindex function call arguments, optimized out
6003 If your program was compiled with optimizations, some compilers will
6004 optimize away arguments passed to functions if those arguments are
6005 never used after the call. Such optimizations generate code that
6006 passes arguments through registers, but doesn't store those arguments
6007 in the stack frame. @value{GDBN} has no way of displaying such
6008 arguments in stack frames other than the innermost one. Here's what
6009 such a backtrace might look like:
6013 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
6015 #1 0x6e38 in expand_macro (sym=<optimized out>) at macro.c:242
6016 #2 0x6840 in expand_token (obs=0x0, t=<optimized out>, td=0xf7fffb08)
6018 (More stack frames follow...)
6023 The values of arguments that were not saved in their stack frames are
6024 shown as @samp{<optimized out>}.
6026 If you need to display the values of such optimized-out arguments,
6027 either deduce that from other variables whose values depend on the one
6028 you are interested in, or recompile without optimizations.
6030 @cindex backtrace beyond @code{main} function
6031 @cindex program entry point
6032 @cindex startup code, and backtrace
6033 Most programs have a standard user entry point---a place where system
6034 libraries and startup code transition into user code. For C this is
6035 @code{main}@footnote{
6036 Note that embedded programs (the so-called ``free-standing''
6037 environment) are not required to have a @code{main} function as the
6038 entry point. They could even have multiple entry points.}.
6039 When @value{GDBN} finds the entry function in a backtrace
6040 it will terminate the backtrace, to avoid tracing into highly
6041 system-specific (and generally uninteresting) code.
6043 If you need to examine the startup code, or limit the number of levels
6044 in a backtrace, you can change this behavior:
6047 @item set backtrace past-main
6048 @itemx set backtrace past-main on
6049 @kindex set backtrace
6050 Backtraces will continue past the user entry point.
6052 @item set backtrace past-main off
6053 Backtraces will stop when they encounter the user entry point. This is the
6056 @item show backtrace past-main
6057 @kindex show backtrace
6058 Display the current user entry point backtrace policy.
6060 @item set backtrace past-entry
6061 @itemx set backtrace past-entry on
6062 Backtraces will continue past the internal entry point of an application.
6063 This entry point is encoded by the linker when the application is built,
6064 and is likely before the user entry point @code{main} (or equivalent) is called.
6066 @item set backtrace past-entry off
6067 Backtraces will stop when they encounter the internal entry point of an
6068 application. This is the default.
6070 @item show backtrace past-entry
6071 Display the current internal entry point backtrace policy.
6073 @item set backtrace limit @var{n}
6074 @itemx set backtrace limit 0
6075 @cindex backtrace limit
6076 Limit the backtrace to @var{n} levels. A value of zero means
6079 @item show backtrace limit
6080 Display the current limit on backtrace levels.
6084 @section Selecting a Frame
6086 Most commands for examining the stack and other data in your program work on
6087 whichever stack frame is selected at the moment. Here are the commands for
6088 selecting a stack frame; all of them finish by printing a brief description
6089 of the stack frame just selected.
6092 @kindex frame@r{, selecting}
6093 @kindex f @r{(@code{frame})}
6096 Select frame number @var{n}. Recall that frame zero is the innermost
6097 (currently executing) frame, frame one is the frame that called the
6098 innermost one, and so on. The highest-numbered frame is the one for
6101 @item frame @var{addr}
6103 Select the frame at address @var{addr}. This is useful mainly if the
6104 chaining of stack frames has been damaged by a bug, making it
6105 impossible for @value{GDBN} to assign numbers properly to all frames. In
6106 addition, this can be useful when your program has multiple stacks and
6107 switches between them.
6109 On the SPARC architecture, @code{frame} needs two addresses to
6110 select an arbitrary frame: a frame pointer and a stack pointer.
6112 On the MIPS and Alpha architecture, it needs two addresses: a stack
6113 pointer and a program counter.
6115 On the 29k architecture, it needs three addresses: a register stack
6116 pointer, a program counter, and a memory stack pointer.
6120 Move @var{n} frames up the stack. For positive numbers @var{n}, this
6121 advances toward the outermost frame, to higher frame numbers, to frames
6122 that have existed longer. @var{n} defaults to one.
6125 @kindex do @r{(@code{down})}
6127 Move @var{n} frames down the stack. For positive numbers @var{n}, this
6128 advances toward the innermost frame, to lower frame numbers, to frames
6129 that were created more recently. @var{n} defaults to one. You may
6130 abbreviate @code{down} as @code{do}.
6133 All of these commands end by printing two lines of output describing the
6134 frame. The first line shows the frame number, the function name, the
6135 arguments, and the source file and line number of execution in that
6136 frame. The second line shows the text of that source line.
6144 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
6146 10 read_input_file (argv[i]);
6150 After such a printout, the @code{list} command with no arguments
6151 prints ten lines centered on the point of execution in the frame.
6152 You can also edit the program at the point of execution with your favorite
6153 editing program by typing @code{edit}.
6154 @xref{List, ,Printing Source Lines},
6158 @kindex down-silently
6160 @item up-silently @var{n}
6161 @itemx down-silently @var{n}
6162 These two commands are variants of @code{up} and @code{down},
6163 respectively; they differ in that they do their work silently, without
6164 causing display of the new frame. They are intended primarily for use
6165 in @value{GDBN} command scripts, where the output might be unnecessary and
6170 @section Information About a Frame
6172 There are several other commands to print information about the selected
6178 When used without any argument, this command does not change which
6179 frame is selected, but prints a brief description of the currently
6180 selected stack frame. It can be abbreviated @code{f}. With an
6181 argument, this command is used to select a stack frame.
6182 @xref{Selection, ,Selecting a Frame}.
6185 @kindex info f @r{(@code{info frame})}
6188 This command prints a verbose description of the selected stack frame,
6193 the address of the frame
6195 the address of the next frame down (called by this frame)
6197 the address of the next frame up (caller of this frame)
6199 the language in which the source code corresponding to this frame is written
6201 the address of the frame's arguments
6203 the address of the frame's local variables
6205 the program counter saved in it (the address of execution in the caller frame)
6207 which registers were saved in the frame
6210 @noindent The verbose description is useful when
6211 something has gone wrong that has made the stack format fail to fit
6212 the usual conventions.
6214 @item info frame @var{addr}
6215 @itemx info f @var{addr}
6216 Print a verbose description of the frame at address @var{addr}, without
6217 selecting that frame. The selected frame remains unchanged by this
6218 command. This requires the same kind of address (more than one for some
6219 architectures) that you specify in the @code{frame} command.
6220 @xref{Selection, ,Selecting a Frame}.
6224 Print the arguments of the selected frame, each on a separate line.
6228 Print the local variables of the selected frame, each on a separate
6229 line. These are all variables (declared either static or automatic)
6230 accessible at the point of execution of the selected frame.
6233 @cindex catch exceptions, list active handlers
6234 @cindex exception handlers, how to list
6236 Print a list of all the exception handlers that are active in the
6237 current stack frame at the current point of execution. To see other
6238 exception handlers, visit the associated frame (using the @code{up},
6239 @code{down}, or @code{frame} commands); then type @code{info catch}.
6240 @xref{Set Catchpoints, , Setting Catchpoints}.
6246 @chapter Examining Source Files
6248 @value{GDBN} can print parts of your program's source, since the debugging
6249 information recorded in the program tells @value{GDBN} what source files were
6250 used to build it. When your program stops, @value{GDBN} spontaneously prints
6251 the line where it stopped. Likewise, when you select a stack frame
6252 (@pxref{Selection, ,Selecting a Frame}), @value{GDBN} prints the line where
6253 execution in that frame has stopped. You can print other portions of
6254 source files by explicit command.
6256 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
6257 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
6258 @value{GDBN} under @sc{gnu} Emacs}.
6261 * List:: Printing source lines
6262 * Specify Location:: How to specify code locations
6263 * Edit:: Editing source files
6264 * Search:: Searching source files
6265 * Source Path:: Specifying source directories
6266 * Machine Code:: Source and machine code
6270 @section Printing Source Lines
6273 @kindex l @r{(@code{list})}
6274 To print lines from a source file, use the @code{list} command
6275 (abbreviated @code{l}). By default, ten lines are printed.
6276 There are several ways to specify what part of the file you want to
6277 print; see @ref{Specify Location}, for the full list.
6279 Here are the forms of the @code{list} command most commonly used:
6282 @item list @var{linenum}
6283 Print lines centered around line number @var{linenum} in the
6284 current source file.
6286 @item list @var{function}
6287 Print lines centered around the beginning of function
6291 Print more lines. If the last lines printed were printed with a
6292 @code{list} command, this prints lines following the last lines
6293 printed; however, if the last line printed was a solitary line printed
6294 as part of displaying a stack frame (@pxref{Stack, ,Examining the
6295 Stack}), this prints lines centered around that line.
6298 Print lines just before the lines last printed.
6301 @cindex @code{list}, how many lines to display
6302 By default, @value{GDBN} prints ten source lines with any of these forms of
6303 the @code{list} command. You can change this using @code{set listsize}:
6306 @kindex set listsize
6307 @item set listsize @var{count}
6308 Make the @code{list} command display @var{count} source lines (unless
6309 the @code{list} argument explicitly specifies some other number).
6311 @kindex show listsize
6313 Display the number of lines that @code{list} prints.
6316 Repeating a @code{list} command with @key{RET} discards the argument,
6317 so it is equivalent to typing just @code{list}. This is more useful
6318 than listing the same lines again. An exception is made for an
6319 argument of @samp{-}; that argument is preserved in repetition so that
6320 each repetition moves up in the source file.
6322 In general, the @code{list} command expects you to supply zero, one or two
6323 @dfn{linespecs}. Linespecs specify source lines; there are several ways
6324 of writing them (@pxref{Specify Location}), but the effect is always
6325 to specify some source line.
6327 Here is a complete description of the possible arguments for @code{list}:
6330 @item list @var{linespec}
6331 Print lines centered around the line specified by @var{linespec}.
6333 @item list @var{first},@var{last}
6334 Print lines from @var{first} to @var{last}. Both arguments are
6335 linespecs. When a @code{list} command has two linespecs, and the
6336 source file of the second linespec is omitted, this refers to
6337 the same source file as the first linespec.
6339 @item list ,@var{last}
6340 Print lines ending with @var{last}.
6342 @item list @var{first},
6343 Print lines starting with @var{first}.
6346 Print lines just after the lines last printed.
6349 Print lines just before the lines last printed.
6352 As described in the preceding table.
6355 @node Specify Location
6356 @section Specifying a Location
6357 @cindex specifying location
6360 Several @value{GDBN} commands accept arguments that specify a location
6361 of your program's code. Since @value{GDBN} is a source-level
6362 debugger, a location usually specifies some line in the source code;
6363 for that reason, locations are also known as @dfn{linespecs}.
6365 Here are all the different ways of specifying a code location that
6366 @value{GDBN} understands:
6370 Specifies the line number @var{linenum} of the current source file.
6373 @itemx +@var{offset}
6374 Specifies the line @var{offset} lines before or after the @dfn{current
6375 line}. For the @code{list} command, the current line is the last one
6376 printed; for the breakpoint commands, this is the line at which
6377 execution stopped in the currently selected @dfn{stack frame}
6378 (@pxref{Frames, ,Frames}, for a description of stack frames.) When
6379 used as the second of the two linespecs in a @code{list} command,
6380 this specifies the line @var{offset} lines up or down from the first
6383 @item @var{filename}:@var{linenum}
6384 Specifies the line @var{linenum} in the source file @var{filename}.
6386 @item @var{function}
6387 Specifies the line that begins the body of the function @var{function}.
6388 For example, in C, this is the line with the open brace.
6390 @item @var{function}:@var{label}
6391 Specifies the line where @var{label} appears in @var{function}.
6393 @item @var{filename}:@var{function}
6394 Specifies the line that begins the body of the function @var{function}
6395 in the file @var{filename}. You only need the file name with a
6396 function name to avoid ambiguity when there are identically named
6397 functions in different source files.
6400 Specifies the line at which the label named @var{label} appears.
6401 @value{GDBN} searches for the label in the function corresponding to
6402 the currently selected stack frame. If there is no current selected
6403 stack frame (for instance, if the inferior is not running), then
6404 @value{GDBN} will not search for a label.
6406 @item *@var{address}
6407 Specifies the program address @var{address}. For line-oriented
6408 commands, such as @code{list} and @code{edit}, this specifies a source
6409 line that contains @var{address}. For @code{break} and other
6410 breakpoint oriented commands, this can be used to set breakpoints in
6411 parts of your program which do not have debugging information or
6414 Here @var{address} may be any expression valid in the current working
6415 language (@pxref{Languages, working language}) that specifies a code
6416 address. In addition, as a convenience, @value{GDBN} extends the
6417 semantics of expressions used in locations to cover the situations
6418 that frequently happen during debugging. Here are the various forms
6422 @item @var{expression}
6423 Any expression valid in the current working language.
6425 @item @var{funcaddr}
6426 An address of a function or procedure derived from its name. In C,
6427 C@t{++}, Java, Objective-C, Fortran, minimal, and assembly, this is
6428 simply the function's name @var{function} (and actually a special case
6429 of a valid expression). In Pascal and Modula-2, this is
6430 @code{&@var{function}}. In Ada, this is @code{@var{function}'Address}
6431 (although the Pascal form also works).
6433 This form specifies the address of the function's first instruction,
6434 before the stack frame and arguments have been set up.
6436 @item '@var{filename}'::@var{funcaddr}
6437 Like @var{funcaddr} above, but also specifies the name of the source
6438 file explicitly. This is useful if the name of the function does not
6439 specify the function unambiguously, e.g., if there are several
6440 functions with identical names in different source files.
6447 @section Editing Source Files
6448 @cindex editing source files
6451 @kindex e @r{(@code{edit})}
6452 To edit the lines in a source file, use the @code{edit} command.
6453 The editing program of your choice
6454 is invoked with the current line set to
6455 the active line in the program.
6456 Alternatively, there are several ways to specify what part of the file you
6457 want to print if you want to see other parts of the program:
6460 @item edit @var{location}
6461 Edit the source file specified by @code{location}. Editing starts at
6462 that @var{location}, e.g., at the specified source line of the
6463 specified file. @xref{Specify Location}, for all the possible forms
6464 of the @var{location} argument; here are the forms of the @code{edit}
6465 command most commonly used:
6468 @item edit @var{number}
6469 Edit the current source file with @var{number} as the active line number.
6471 @item edit @var{function}
6472 Edit the file containing @var{function} at the beginning of its definition.
6477 @subsection Choosing your Editor
6478 You can customize @value{GDBN} to use any editor you want
6480 The only restriction is that your editor (say @code{ex}), recognizes the
6481 following command-line syntax:
6483 ex +@var{number} file
6485 The optional numeric value +@var{number} specifies the number of the line in
6486 the file where to start editing.}.
6487 By default, it is @file{@value{EDITOR}}, but you can change this
6488 by setting the environment variable @code{EDITOR} before using
6489 @value{GDBN}. For example, to configure @value{GDBN} to use the
6490 @code{vi} editor, you could use these commands with the @code{sh} shell:
6496 or in the @code{csh} shell,
6498 setenv EDITOR /usr/bin/vi
6503 @section Searching Source Files
6504 @cindex searching source files
6506 There are two commands for searching through the current source file for a
6511 @kindex forward-search
6512 @item forward-search @var{regexp}
6513 @itemx search @var{regexp}
6514 The command @samp{forward-search @var{regexp}} checks each line,
6515 starting with the one following the last line listed, for a match for
6516 @var{regexp}. It lists the line that is found. You can use the
6517 synonym @samp{search @var{regexp}} or abbreviate the command name as
6520 @kindex reverse-search
6521 @item reverse-search @var{regexp}
6522 The command @samp{reverse-search @var{regexp}} checks each line, starting
6523 with the one before the last line listed and going backward, for a match
6524 for @var{regexp}. It lists the line that is found. You can abbreviate
6525 this command as @code{rev}.
6529 @section Specifying Source Directories
6532 @cindex directories for source files
6533 Executable programs sometimes do not record the directories of the source
6534 files from which they were compiled, just the names. Even when they do,
6535 the directories could be moved between the compilation and your debugging
6536 session. @value{GDBN} has a list of directories to search for source files;
6537 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
6538 it tries all the directories in the list, in the order they are present
6539 in the list, until it finds a file with the desired name.
6541 For example, suppose an executable references the file
6542 @file{/usr/src/foo-1.0/lib/foo.c}, and our source path is
6543 @file{/mnt/cross}. The file is first looked up literally; if this
6544 fails, @file{/mnt/cross/usr/src/foo-1.0/lib/foo.c} is tried; if this
6545 fails, @file{/mnt/cross/foo.c} is opened; if this fails, an error
6546 message is printed. @value{GDBN} does not look up the parts of the
6547 source file name, such as @file{/mnt/cross/src/foo-1.0/lib/foo.c}.
6548 Likewise, the subdirectories of the source path are not searched: if
6549 the source path is @file{/mnt/cross}, and the binary refers to
6550 @file{foo.c}, @value{GDBN} would not find it under
6551 @file{/mnt/cross/usr/src/foo-1.0/lib}.
6553 Plain file names, relative file names with leading directories, file
6554 names containing dots, etc.@: are all treated as described above; for
6555 instance, if the source path is @file{/mnt/cross}, and the source file
6556 is recorded as @file{../lib/foo.c}, @value{GDBN} would first try
6557 @file{../lib/foo.c}, then @file{/mnt/cross/../lib/foo.c}, and after
6558 that---@file{/mnt/cross/foo.c}.
6560 Note that the executable search path is @emph{not} used to locate the
6563 Whenever you reset or rearrange the source path, @value{GDBN} clears out
6564 any information it has cached about where source files are found and where
6565 each line is in the file.
6569 When you start @value{GDBN}, its source path includes only @samp{cdir}
6570 and @samp{cwd}, in that order.
6571 To add other directories, use the @code{directory} command.
6573 The search path is used to find both program source files and @value{GDBN}
6574 script files (read using the @samp{-command} option and @samp{source} command).
6576 In addition to the source path, @value{GDBN} provides a set of commands
6577 that manage a list of source path substitution rules. A @dfn{substitution
6578 rule} specifies how to rewrite source directories stored in the program's
6579 debug information in case the sources were moved to a different
6580 directory between compilation and debugging. A rule is made of
6581 two strings, the first specifying what needs to be rewritten in
6582 the path, and the second specifying how it should be rewritten.
6583 In @ref{set substitute-path}, we name these two parts @var{from} and
6584 @var{to} respectively. @value{GDBN} does a simple string replacement
6585 of @var{from} with @var{to} at the start of the directory part of the
6586 source file name, and uses that result instead of the original file
6587 name to look up the sources.
6589 Using the previous example, suppose the @file{foo-1.0} tree has been
6590 moved from @file{/usr/src} to @file{/mnt/cross}, then you can tell
6591 @value{GDBN} to replace @file{/usr/src} in all source path names with
6592 @file{/mnt/cross}. The first lookup will then be
6593 @file{/mnt/cross/foo-1.0/lib/foo.c} in place of the original location
6594 of @file{/usr/src/foo-1.0/lib/foo.c}. To define a source path
6595 substitution rule, use the @code{set substitute-path} command
6596 (@pxref{set substitute-path}).
6598 To avoid unexpected substitution results, a rule is applied only if the
6599 @var{from} part of the directory name ends at a directory separator.
6600 For instance, a rule substituting @file{/usr/source} into
6601 @file{/mnt/cross} will be applied to @file{/usr/source/foo-1.0} but
6602 not to @file{/usr/sourceware/foo-2.0}. And because the substitution
6603 is applied only at the beginning of the directory name, this rule will
6604 not be applied to @file{/root/usr/source/baz.c} either.
6606 In many cases, you can achieve the same result using the @code{directory}
6607 command. However, @code{set substitute-path} can be more efficient in
6608 the case where the sources are organized in a complex tree with multiple
6609 subdirectories. With the @code{directory} command, you need to add each
6610 subdirectory of your project. If you moved the entire tree while
6611 preserving its internal organization, then @code{set substitute-path}
6612 allows you to direct the debugger to all the sources with one single
6615 @code{set substitute-path} is also more than just a shortcut command.
6616 The source path is only used if the file at the original location no
6617 longer exists. On the other hand, @code{set substitute-path} modifies
6618 the debugger behavior to look at the rewritten location instead. So, if
6619 for any reason a source file that is not relevant to your executable is
6620 located at the original location, a substitution rule is the only
6621 method available to point @value{GDBN} at the new location.
6623 @cindex @samp{--with-relocated-sources}
6624 @cindex default source path substitution
6625 You can configure a default source path substitution rule by
6626 configuring @value{GDBN} with the
6627 @samp{--with-relocated-sources=@var{dir}} option. The @var{dir}
6628 should be the name of a directory under @value{GDBN}'s configured
6629 prefix (set with @samp{--prefix} or @samp{--exec-prefix}), and
6630 directory names in debug information under @var{dir} will be adjusted
6631 automatically if the installed @value{GDBN} is moved to a new
6632 location. This is useful if @value{GDBN}, libraries or executables
6633 with debug information and corresponding source code are being moved
6637 @item directory @var{dirname} @dots{}
6638 @item dir @var{dirname} @dots{}
6639 Add directory @var{dirname} to the front of the source path. Several
6640 directory names may be given to this command, separated by @samp{:}
6641 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
6642 part of absolute file names) or
6643 whitespace. You may specify a directory that is already in the source
6644 path; this moves it forward, so @value{GDBN} searches it sooner.
6648 @vindex $cdir@r{, convenience variable}
6649 @vindex $cwd@r{, convenience variable}
6650 @cindex compilation directory
6651 @cindex current directory
6652 @cindex working directory
6653 @cindex directory, current
6654 @cindex directory, compilation
6655 You can use the string @samp{$cdir} to refer to the compilation
6656 directory (if one is recorded), and @samp{$cwd} to refer to the current
6657 working directory. @samp{$cwd} is not the same as @samp{.}---the former
6658 tracks the current working directory as it changes during your @value{GDBN}
6659 session, while the latter is immediately expanded to the current
6660 directory at the time you add an entry to the source path.
6663 Reset the source path to its default value (@samp{$cdir:$cwd} on Unix systems). This requires confirmation.
6665 @c RET-repeat for @code{directory} is explicitly disabled, but since
6666 @c repeating it would be a no-op we do not say that. (thanks to RMS)
6668 @item set directories @var{path-list}
6669 @kindex set directories
6670 Set the source path to @var{path-list}.
6671 @samp{$cdir:$cwd} are added if missing.
6673 @item show directories
6674 @kindex show directories
6675 Print the source path: show which directories it contains.
6677 @anchor{set substitute-path}
6678 @item set substitute-path @var{from} @var{to}
6679 @kindex set substitute-path
6680 Define a source path substitution rule, and add it at the end of the
6681 current list of existing substitution rules. If a rule with the same
6682 @var{from} was already defined, then the old rule is also deleted.
6684 For example, if the file @file{/foo/bar/baz.c} was moved to
6685 @file{/mnt/cross/baz.c}, then the command
6688 (@value{GDBP}) set substitute-path /usr/src /mnt/cross
6692 will tell @value{GDBN} to replace @samp{/usr/src} with
6693 @samp{/mnt/cross}, which will allow @value{GDBN} to find the file
6694 @file{baz.c} even though it was moved.
6696 In the case when more than one substitution rule have been defined,
6697 the rules are evaluated one by one in the order where they have been
6698 defined. The first one matching, if any, is selected to perform
6701 For instance, if we had entered the following commands:
6704 (@value{GDBP}) set substitute-path /usr/src/include /mnt/include
6705 (@value{GDBP}) set substitute-path /usr/src /mnt/src
6709 @value{GDBN} would then rewrite @file{/usr/src/include/defs.h} into
6710 @file{/mnt/include/defs.h} by using the first rule. However, it would
6711 use the second rule to rewrite @file{/usr/src/lib/foo.c} into
6712 @file{/mnt/src/lib/foo.c}.
6715 @item unset substitute-path [path]
6716 @kindex unset substitute-path
6717 If a path is specified, search the current list of substitution rules
6718 for a rule that would rewrite that path. Delete that rule if found.
6719 A warning is emitted by the debugger if no rule could be found.
6721 If no path is specified, then all substitution rules are deleted.
6723 @item show substitute-path [path]
6724 @kindex show substitute-path
6725 If a path is specified, then print the source path substitution rule
6726 which would rewrite that path, if any.
6728 If no path is specified, then print all existing source path substitution
6733 If your source path is cluttered with directories that are no longer of
6734 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
6735 versions of source. You can correct the situation as follows:
6739 Use @code{directory} with no argument to reset the source path to its default value.
6742 Use @code{directory} with suitable arguments to reinstall the
6743 directories you want in the source path. You can add all the
6744 directories in one command.
6748 @section Source and Machine Code
6749 @cindex source line and its code address
6751 You can use the command @code{info line} to map source lines to program
6752 addresses (and vice versa), and the command @code{disassemble} to display
6753 a range of addresses as machine instructions. You can use the command
6754 @code{set disassemble-next-line} to set whether to disassemble next
6755 source line when execution stops. When run under @sc{gnu} Emacs
6756 mode, the @code{info line} command causes the arrow to point to the
6757 line specified. Also, @code{info line} prints addresses in symbolic form as
6762 @item info line @var{linespec}
6763 Print the starting and ending addresses of the compiled code for
6764 source line @var{linespec}. You can specify source lines in any of
6765 the ways documented in @ref{Specify Location}.
6768 For example, we can use @code{info line} to discover the location of
6769 the object code for the first line of function
6770 @code{m4_changequote}:
6772 @c FIXME: I think this example should also show the addresses in
6773 @c symbolic form, as they usually would be displayed.
6775 (@value{GDBP}) info line m4_changequote
6776 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
6780 @cindex code address and its source line
6781 We can also inquire (using @code{*@var{addr}} as the form for
6782 @var{linespec}) what source line covers a particular address:
6784 (@value{GDBP}) info line *0x63ff
6785 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
6788 @cindex @code{$_} and @code{info line}
6789 @cindex @code{x} command, default address
6790 @kindex x@r{(examine), and} info line
6791 After @code{info line}, the default address for the @code{x} command
6792 is changed to the starting address of the line, so that @samp{x/i} is
6793 sufficient to begin examining the machine code (@pxref{Memory,
6794 ,Examining Memory}). Also, this address is saved as the value of the
6795 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
6800 @cindex assembly instructions
6801 @cindex instructions, assembly
6802 @cindex machine instructions
6803 @cindex listing machine instructions
6805 @itemx disassemble /m
6806 @itemx disassemble /r
6807 This specialized command dumps a range of memory as machine
6808 instructions. It can also print mixed source+disassembly by specifying
6809 the @code{/m} modifier and print the raw instructions in hex as well as
6810 in symbolic form by specifying the @code{/r}.
6811 The default memory range is the function surrounding the
6812 program counter of the selected frame. A single argument to this
6813 command is a program counter value; @value{GDBN} dumps the function
6814 surrounding this value. When two arguments are given, they should
6815 be separated by a comma, possibly surrounded by whitespace. The
6816 arguments specify a range of addresses to dump, in one of two forms:
6819 @item @var{start},@var{end}
6820 the addresses from @var{start} (inclusive) to @var{end} (exclusive)
6821 @item @var{start},+@var{length}
6822 the addresses from @var{start} (inclusive) to
6823 @code{@var{start}+@var{length}} (exclusive).
6827 When 2 arguments are specified, the name of the function is also
6828 printed (since there could be several functions in the given range).
6830 The argument(s) can be any expression yielding a numeric value, such as
6831 @samp{0x32c4}, @samp{&main+10} or @samp{$pc - 8}.
6833 If the range of memory being disassembled contains current program counter,
6834 the instruction at that location is shown with a @code{=>} marker.
6837 The following example shows the disassembly of a range of addresses of
6838 HP PA-RISC 2.0 code:
6841 (@value{GDBP}) disas 0x32c4, 0x32e4
6842 Dump of assembler code from 0x32c4 to 0x32e4:
6843 0x32c4 <main+204>: addil 0,dp
6844 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
6845 0x32cc <main+212>: ldil 0x3000,r31
6846 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
6847 0x32d4 <main+220>: ldo 0(r31),rp
6848 0x32d8 <main+224>: addil -0x800,dp
6849 0x32dc <main+228>: ldo 0x588(r1),r26
6850 0x32e0 <main+232>: ldil 0x3000,r31
6851 End of assembler dump.
6854 Here is an example showing mixed source+assembly for Intel x86, when the
6855 program is stopped just after function prologue:
6858 (@value{GDBP}) disas /m main
6859 Dump of assembler code for function main:
6861 0x08048330 <+0>: push %ebp
6862 0x08048331 <+1>: mov %esp,%ebp
6863 0x08048333 <+3>: sub $0x8,%esp
6864 0x08048336 <+6>: and $0xfffffff0,%esp
6865 0x08048339 <+9>: sub $0x10,%esp
6867 6 printf ("Hello.\n");
6868 => 0x0804833c <+12>: movl $0x8048440,(%esp)
6869 0x08048343 <+19>: call 0x8048284 <puts@@plt>
6873 0x08048348 <+24>: mov $0x0,%eax
6874 0x0804834d <+29>: leave
6875 0x0804834e <+30>: ret
6877 End of assembler dump.
6880 Here is another example showing raw instructions in hex for AMD x86-64,
6883 (gdb) disas /r 0x400281,+10
6884 Dump of assembler code from 0x400281 to 0x40028b:
6885 0x0000000000400281: 38 36 cmp %dh,(%rsi)
6886 0x0000000000400283: 2d 36 34 2e 73 sub $0x732e3436,%eax
6887 0x0000000000400288: 6f outsl %ds:(%rsi),(%dx)
6888 0x0000000000400289: 2e 32 00 xor %cs:(%rax),%al
6889 End of assembler dump.
6892 Some architectures have more than one commonly-used set of instruction
6893 mnemonics or other syntax.
6895 For programs that were dynamically linked and use shared libraries,
6896 instructions that call functions or branch to locations in the shared
6897 libraries might show a seemingly bogus location---it's actually a
6898 location of the relocation table. On some architectures, @value{GDBN}
6899 might be able to resolve these to actual function names.
6902 @kindex set disassembly-flavor
6903 @cindex Intel disassembly flavor
6904 @cindex AT&T disassembly flavor
6905 @item set disassembly-flavor @var{instruction-set}
6906 Select the instruction set to use when disassembling the
6907 program via the @code{disassemble} or @code{x/i} commands.
6909 Currently this command is only defined for the Intel x86 family. You
6910 can set @var{instruction-set} to either @code{intel} or @code{att}.
6911 The default is @code{att}, the AT&T flavor used by default by Unix
6912 assemblers for x86-based targets.
6914 @kindex show disassembly-flavor
6915 @item show disassembly-flavor
6916 Show the current setting of the disassembly flavor.
6920 @kindex set disassemble-next-line
6921 @kindex show disassemble-next-line
6922 @item set disassemble-next-line
6923 @itemx show disassemble-next-line
6924 Control whether or not @value{GDBN} will disassemble the next source
6925 line or instruction when execution stops. If ON, @value{GDBN} will
6926 display disassembly of the next source line when execution of the
6927 program being debugged stops. This is @emph{in addition} to
6928 displaying the source line itself, which @value{GDBN} always does if
6929 possible. If the next source line cannot be displayed for some reason
6930 (e.g., if @value{GDBN} cannot find the source file, or there's no line
6931 info in the debug info), @value{GDBN} will display disassembly of the
6932 next @emph{instruction} instead of showing the next source line. If
6933 AUTO, @value{GDBN} will display disassembly of next instruction only
6934 if the source line cannot be displayed. This setting causes
6935 @value{GDBN} to display some feedback when you step through a function
6936 with no line info or whose source file is unavailable. The default is
6937 OFF, which means never display the disassembly of the next line or
6943 @chapter Examining Data
6945 @cindex printing data
6946 @cindex examining data
6949 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
6950 @c document because it is nonstandard... Under Epoch it displays in a
6951 @c different window or something like that.
6952 The usual way to examine data in your program is with the @code{print}
6953 command (abbreviated @code{p}), or its synonym @code{inspect}. It
6954 evaluates and prints the value of an expression of the language your
6955 program is written in (@pxref{Languages, ,Using @value{GDBN} with
6956 Different Languages}). It may also print the expression using a
6957 Python-based pretty-printer (@pxref{Pretty Printing}).
6960 @item print @var{expr}
6961 @itemx print /@var{f} @var{expr}
6962 @var{expr} is an expression (in the source language). By default the
6963 value of @var{expr} is printed in a format appropriate to its data type;
6964 you can choose a different format by specifying @samp{/@var{f}}, where
6965 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
6969 @itemx print /@var{f}
6970 @cindex reprint the last value
6971 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
6972 @dfn{value history}; @pxref{Value History, ,Value History}). This allows you to
6973 conveniently inspect the same value in an alternative format.
6976 A more low-level way of examining data is with the @code{x} command.
6977 It examines data in memory at a specified address and prints it in a
6978 specified format. @xref{Memory, ,Examining Memory}.
6980 If you are interested in information about types, or about how the
6981 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
6982 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
6986 * Expressions:: Expressions
6987 * Ambiguous Expressions:: Ambiguous Expressions
6988 * Variables:: Program variables
6989 * Arrays:: Artificial arrays
6990 * Output Formats:: Output formats
6991 * Memory:: Examining memory
6992 * Auto Display:: Automatic display
6993 * Print Settings:: Print settings
6994 * Pretty Printing:: Python pretty printing
6995 * Value History:: Value history
6996 * Convenience Vars:: Convenience variables
6997 * Registers:: Registers
6998 * Floating Point Hardware:: Floating point hardware
6999 * Vector Unit:: Vector Unit
7000 * OS Information:: Auxiliary data provided by operating system
7001 * Memory Region Attributes:: Memory region attributes
7002 * Dump/Restore Files:: Copy between memory and a file
7003 * Core File Generation:: Cause a program dump its core
7004 * Character Sets:: Debugging programs that use a different
7005 character set than GDB does
7006 * Caching Remote Data:: Data caching for remote targets
7007 * Searching Memory:: Searching memory for a sequence of bytes
7011 @section Expressions
7014 @code{print} and many other @value{GDBN} commands accept an expression and
7015 compute its value. Any kind of constant, variable or operator defined
7016 by the programming language you are using is valid in an expression in
7017 @value{GDBN}. This includes conditional expressions, function calls,
7018 casts, and string constants. It also includes preprocessor macros, if
7019 you compiled your program to include this information; see
7022 @cindex arrays in expressions
7023 @value{GDBN} supports array constants in expressions input by
7024 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
7025 you can use the command @code{print @{1, 2, 3@}} to create an array
7026 of three integers. If you pass an array to a function or assign it
7027 to a program variable, @value{GDBN} copies the array to memory that
7028 is @code{malloc}ed in the target program.
7030 Because C is so widespread, most of the expressions shown in examples in
7031 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
7032 Languages}, for information on how to use expressions in other
7035 In this section, we discuss operators that you can use in @value{GDBN}
7036 expressions regardless of your programming language.
7038 @cindex casts, in expressions
7039 Casts are supported in all languages, not just in C, because it is so
7040 useful to cast a number into a pointer in order to examine a structure
7041 at that address in memory.
7042 @c FIXME: casts supported---Mod2 true?
7044 @value{GDBN} supports these operators, in addition to those common
7045 to programming languages:
7049 @samp{@@} is a binary operator for treating parts of memory as arrays.
7050 @xref{Arrays, ,Artificial Arrays}, for more information.
7053 @samp{::} allows you to specify a variable in terms of the file or
7054 function where it is defined. @xref{Variables, ,Program Variables}.
7056 @cindex @{@var{type}@}
7057 @cindex type casting memory
7058 @cindex memory, viewing as typed object
7059 @cindex casts, to view memory
7060 @item @{@var{type}@} @var{addr}
7061 Refers to an object of type @var{type} stored at address @var{addr} in
7062 memory. @var{addr} may be any expression whose value is an integer or
7063 pointer (but parentheses are required around binary operators, just as in
7064 a cast). This construct is allowed regardless of what kind of data is
7065 normally supposed to reside at @var{addr}.
7068 @node Ambiguous Expressions
7069 @section Ambiguous Expressions
7070 @cindex ambiguous expressions
7072 Expressions can sometimes contain some ambiguous elements. For instance,
7073 some programming languages (notably Ada, C@t{++} and Objective-C) permit
7074 a single function name to be defined several times, for application in
7075 different contexts. This is called @dfn{overloading}. Another example
7076 involving Ada is generics. A @dfn{generic package} is similar to C@t{++}
7077 templates and is typically instantiated several times, resulting in
7078 the same function name being defined in different contexts.
7080 In some cases and depending on the language, it is possible to adjust
7081 the expression to remove the ambiguity. For instance in C@t{++}, you
7082 can specify the signature of the function you want to break on, as in
7083 @kbd{break @var{function}(@var{types})}. In Ada, using the fully
7084 qualified name of your function often makes the expression unambiguous
7087 When an ambiguity that needs to be resolved is detected, the debugger
7088 has the capability to display a menu of numbered choices for each
7089 possibility, and then waits for the selection with the prompt @samp{>}.
7090 The first option is always @samp{[0] cancel}, and typing @kbd{0 @key{RET}}
7091 aborts the current command. If the command in which the expression was
7092 used allows more than one choice to be selected, the next option in the
7093 menu is @samp{[1] all}, and typing @kbd{1 @key{RET}} selects all possible
7096 For example, the following session excerpt shows an attempt to set a
7097 breakpoint at the overloaded symbol @code{String::after}.
7098 We choose three particular definitions of that function name:
7100 @c FIXME! This is likely to change to show arg type lists, at least
7103 (@value{GDBP}) b String::after
7106 [2] file:String.cc; line number:867
7107 [3] file:String.cc; line number:860
7108 [4] file:String.cc; line number:875
7109 [5] file:String.cc; line number:853
7110 [6] file:String.cc; line number:846
7111 [7] file:String.cc; line number:735
7113 Breakpoint 1 at 0xb26c: file String.cc, line 867.
7114 Breakpoint 2 at 0xb344: file String.cc, line 875.
7115 Breakpoint 3 at 0xafcc: file String.cc, line 846.
7116 Multiple breakpoints were set.
7117 Use the "delete" command to delete unwanted
7124 @kindex set multiple-symbols
7125 @item set multiple-symbols @var{mode}
7126 @cindex multiple-symbols menu
7128 This option allows you to adjust the debugger behavior when an expression
7131 By default, @var{mode} is set to @code{all}. If the command with which
7132 the expression is used allows more than one choice, then @value{GDBN}
7133 automatically selects all possible choices. For instance, inserting
7134 a breakpoint on a function using an ambiguous name results in a breakpoint
7135 inserted on each possible match. However, if a unique choice must be made,
7136 then @value{GDBN} uses the menu to help you disambiguate the expression.
7137 For instance, printing the address of an overloaded function will result
7138 in the use of the menu.
7140 When @var{mode} is set to @code{ask}, the debugger always uses the menu
7141 when an ambiguity is detected.
7143 Finally, when @var{mode} is set to @code{cancel}, the debugger reports
7144 an error due to the ambiguity and the command is aborted.
7146 @kindex show multiple-symbols
7147 @item show multiple-symbols
7148 Show the current value of the @code{multiple-symbols} setting.
7152 @section Program Variables
7154 The most common kind of expression to use is the name of a variable
7157 Variables in expressions are understood in the selected stack frame
7158 (@pxref{Selection, ,Selecting a Frame}); they must be either:
7162 global (or file-static)
7169 visible according to the scope rules of the
7170 programming language from the point of execution in that frame
7173 @noindent This means that in the function
7188 you can examine and use the variable @code{a} whenever your program is
7189 executing within the function @code{foo}, but you can only use or
7190 examine the variable @code{b} while your program is executing inside
7191 the block where @code{b} is declared.
7193 @cindex variable name conflict
7194 There is an exception: you can refer to a variable or function whose
7195 scope is a single source file even if the current execution point is not
7196 in this file. But it is possible to have more than one such variable or
7197 function with the same name (in different source files). If that
7198 happens, referring to that name has unpredictable effects. If you wish,
7199 you can specify a static variable in a particular function or file,
7200 using the colon-colon (@code{::}) notation:
7202 @cindex colon-colon, context for variables/functions
7204 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
7205 @cindex @code{::}, context for variables/functions
7208 @var{file}::@var{variable}
7209 @var{function}::@var{variable}
7213 Here @var{file} or @var{function} is the name of the context for the
7214 static @var{variable}. In the case of file names, you can use quotes to
7215 make sure @value{GDBN} parses the file name as a single word---for example,
7216 to print a global value of @code{x} defined in @file{f2.c}:
7219 (@value{GDBP}) p 'f2.c'::x
7222 @cindex C@t{++} scope resolution
7223 This use of @samp{::} is very rarely in conflict with the very similar
7224 use of the same notation in C@t{++}. @value{GDBN} also supports use of the C@t{++}
7225 scope resolution operator in @value{GDBN} expressions.
7226 @c FIXME: Um, so what happens in one of those rare cases where it's in
7229 @cindex wrong values
7230 @cindex variable values, wrong
7231 @cindex function entry/exit, wrong values of variables
7232 @cindex optimized code, wrong values of variables
7234 @emph{Warning:} Occasionally, a local variable may appear to have the
7235 wrong value at certain points in a function---just after entry to a new
7236 scope, and just before exit.
7238 You may see this problem when you are stepping by machine instructions.
7239 This is because, on most machines, it takes more than one instruction to
7240 set up a stack frame (including local variable definitions); if you are
7241 stepping by machine instructions, variables may appear to have the wrong
7242 values until the stack frame is completely built. On exit, it usually
7243 also takes more than one machine instruction to destroy a stack frame;
7244 after you begin stepping through that group of instructions, local
7245 variable definitions may be gone.
7247 This may also happen when the compiler does significant optimizations.
7248 To be sure of always seeing accurate values, turn off all optimization
7251 @cindex ``No symbol "foo" in current context''
7252 Another possible effect of compiler optimizations is to optimize
7253 unused variables out of existence, or assign variables to registers (as
7254 opposed to memory addresses). Depending on the support for such cases
7255 offered by the debug info format used by the compiler, @value{GDBN}
7256 might not be able to display values for such local variables. If that
7257 happens, @value{GDBN} will print a message like this:
7260 No symbol "foo" in current context.
7263 To solve such problems, either recompile without optimizations, or use a
7264 different debug info format, if the compiler supports several such
7265 formats. For example, @value{NGCC}, the @sc{gnu} C/C@t{++} compiler,
7266 usually supports the @option{-gstabs+} option. @option{-gstabs+}
7267 produces debug info in a format that is superior to formats such as
7268 COFF. You may be able to use DWARF 2 (@option{-gdwarf-2}), which is also
7269 an effective form for debug info. @xref{Debugging Options,,Options
7270 for Debugging Your Program or GCC, gcc.info, Using the @sc{gnu}
7271 Compiler Collection (GCC)}.
7272 @xref{C, ,C and C@t{++}}, for more information about debug info formats
7273 that are best suited to C@t{++} programs.
7275 If you ask to print an object whose contents are unknown to
7276 @value{GDBN}, e.g., because its data type is not completely specified
7277 by the debug information, @value{GDBN} will say @samp{<incomplete
7278 type>}. @xref{Symbols, incomplete type}, for more about this.
7280 Strings are identified as arrays of @code{char} values without specified
7281 signedness. Arrays of either @code{signed char} or @code{unsigned char} get
7282 printed as arrays of 1 byte sized integers. @code{-fsigned-char} or
7283 @code{-funsigned-char} @value{NGCC} options have no effect as @value{GDBN}
7284 defines literal string type @code{"char"} as @code{char} without a sign.
7289 signed char var1[] = "A";
7292 You get during debugging
7297 $2 = @{65 'A', 0 '\0'@}
7301 @section Artificial Arrays
7303 @cindex artificial array
7305 @kindex @@@r{, referencing memory as an array}
7306 It is often useful to print out several successive objects of the
7307 same type in memory; a section of an array, or an array of
7308 dynamically determined size for which only a pointer exists in the
7311 You can do this by referring to a contiguous span of memory as an
7312 @dfn{artificial array}, using the binary operator @samp{@@}. The left
7313 operand of @samp{@@} should be the first element of the desired array
7314 and be an individual object. The right operand should be the desired length
7315 of the array. The result is an array value whose elements are all of
7316 the type of the left argument. The first element is actually the left
7317 argument; the second element comes from bytes of memory immediately
7318 following those that hold the first element, and so on. Here is an
7319 example. If a program says
7322 int *array = (int *) malloc (len * sizeof (int));
7326 you can print the contents of @code{array} with
7332 The left operand of @samp{@@} must reside in memory. Array values made
7333 with @samp{@@} in this way behave just like other arrays in terms of
7334 subscripting, and are coerced to pointers when used in expressions.
7335 Artificial arrays most often appear in expressions via the value history
7336 (@pxref{Value History, ,Value History}), after printing one out.
7338 Another way to create an artificial array is to use a cast.
7339 This re-interprets a value as if it were an array.
7340 The value need not be in memory:
7342 (@value{GDBP}) p/x (short[2])0x12345678
7343 $1 = @{0x1234, 0x5678@}
7346 As a convenience, if you leave the array length out (as in
7347 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
7348 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
7350 (@value{GDBP}) p/x (short[])0x12345678
7351 $2 = @{0x1234, 0x5678@}
7354 Sometimes the artificial array mechanism is not quite enough; in
7355 moderately complex data structures, the elements of interest may not
7356 actually be adjacent---for example, if you are interested in the values
7357 of pointers in an array. One useful work-around in this situation is
7358 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
7359 Variables}) as a counter in an expression that prints the first
7360 interesting value, and then repeat that expression via @key{RET}. For
7361 instance, suppose you have an array @code{dtab} of pointers to
7362 structures, and you are interested in the values of a field @code{fv}
7363 in each structure. Here is an example of what you might type:
7373 @node Output Formats
7374 @section Output Formats
7376 @cindex formatted output
7377 @cindex output formats
7378 By default, @value{GDBN} prints a value according to its data type. Sometimes
7379 this is not what you want. For example, you might want to print a number
7380 in hex, or a pointer in decimal. Or you might want to view data in memory
7381 at a certain address as a character string or as an instruction. To do
7382 these things, specify an @dfn{output format} when you print a value.
7384 The simplest use of output formats is to say how to print a value
7385 already computed. This is done by starting the arguments of the
7386 @code{print} command with a slash and a format letter. The format
7387 letters supported are:
7391 Regard the bits of the value as an integer, and print the integer in
7395 Print as integer in signed decimal.
7398 Print as integer in unsigned decimal.
7401 Print as integer in octal.
7404 Print as integer in binary. The letter @samp{t} stands for ``two''.
7405 @footnote{@samp{b} cannot be used because these format letters are also
7406 used with the @code{x} command, where @samp{b} stands for ``byte'';
7407 see @ref{Memory,,Examining Memory}.}
7410 @cindex unknown address, locating
7411 @cindex locate address
7412 Print as an address, both absolute in hexadecimal and as an offset from
7413 the nearest preceding symbol. You can use this format used to discover
7414 where (in what function) an unknown address is located:
7417 (@value{GDBP}) p/a 0x54320
7418 $3 = 0x54320 <_initialize_vx+396>
7422 The command @code{info symbol 0x54320} yields similar results.
7423 @xref{Symbols, info symbol}.
7426 Regard as an integer and print it as a character constant. This
7427 prints both the numerical value and its character representation. The
7428 character representation is replaced with the octal escape @samp{\nnn}
7429 for characters outside the 7-bit @sc{ascii} range.
7431 Without this format, @value{GDBN} displays @code{char},
7432 @w{@code{unsigned char}}, and @w{@code{signed char}} data as character
7433 constants. Single-byte members of vectors are displayed as integer
7437 Regard the bits of the value as a floating point number and print
7438 using typical floating point syntax.
7441 @cindex printing strings
7442 @cindex printing byte arrays
7443 Regard as a string, if possible. With this format, pointers to single-byte
7444 data are displayed as null-terminated strings and arrays of single-byte data
7445 are displayed as fixed-length strings. Other values are displayed in their
7448 Without this format, @value{GDBN} displays pointers to and arrays of
7449 @code{char}, @w{@code{unsigned char}}, and @w{@code{signed char}} as
7450 strings. Single-byte members of a vector are displayed as an integer
7454 @cindex raw printing
7455 Print using the @samp{raw} formatting. By default, @value{GDBN} will
7456 use a Python-based pretty-printer, if one is available (@pxref{Pretty
7457 Printing}). This typically results in a higher-level display of the
7458 value's contents. The @samp{r} format bypasses any Python
7459 pretty-printer which might exist.
7462 For example, to print the program counter in hex (@pxref{Registers}), type
7469 Note that no space is required before the slash; this is because command
7470 names in @value{GDBN} cannot contain a slash.
7472 To reprint the last value in the value history with a different format,
7473 you can use the @code{print} command with just a format and no
7474 expression. For example, @samp{p/x} reprints the last value in hex.
7477 @section Examining Memory
7479 You can use the command @code{x} (for ``examine'') to examine memory in
7480 any of several formats, independently of your program's data types.
7482 @cindex examining memory
7484 @kindex x @r{(examine memory)}
7485 @item x/@var{nfu} @var{addr}
7488 Use the @code{x} command to examine memory.
7491 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
7492 much memory to display and how to format it; @var{addr} is an
7493 expression giving the address where you want to start displaying memory.
7494 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
7495 Several commands set convenient defaults for @var{addr}.
7498 @item @var{n}, the repeat count
7499 The repeat count is a decimal integer; the default is 1. It specifies
7500 how much memory (counting by units @var{u}) to display.
7501 @c This really is **decimal**; unaffected by 'set radix' as of GDB
7504 @item @var{f}, the display format
7505 The display format is one of the formats used by @code{print}
7506 (@samp{x}, @samp{d}, @samp{u}, @samp{o}, @samp{t}, @samp{a}, @samp{c},
7507 @samp{f}, @samp{s}), and in addition @samp{i} (for machine instructions).
7508 The default is @samp{x} (hexadecimal) initially. The default changes
7509 each time you use either @code{x} or @code{print}.
7511 @item @var{u}, the unit size
7512 The unit size is any of
7518 Halfwords (two bytes).
7520 Words (four bytes). This is the initial default.
7522 Giant words (eight bytes).
7525 Each time you specify a unit size with @code{x}, that size becomes the
7526 default unit the next time you use @code{x}. For the @samp{i} format,
7527 the unit size is ignored and is normally not written. For the @samp{s} format,
7528 the unit size defaults to @samp{b}, unless it is explicitly given.
7529 Use @kbd{x /hs} to display 16-bit char strings and @kbd{x /ws} to display
7530 32-bit strings. The next use of @kbd{x /s} will again display 8-bit strings.
7531 Note that the results depend on the programming language of the
7532 current compilation unit. If the language is C, the @samp{s}
7533 modifier will use the UTF-16 encoding while @samp{w} will use
7534 UTF-32. The encoding is set by the programming language and cannot
7537 @item @var{addr}, starting display address
7538 @var{addr} is the address where you want @value{GDBN} to begin displaying
7539 memory. The expression need not have a pointer value (though it may);
7540 it is always interpreted as an integer address of a byte of memory.
7541 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
7542 @var{addr} is usually just after the last address examined---but several
7543 other commands also set the default address: @code{info breakpoints} (to
7544 the address of the last breakpoint listed), @code{info line} (to the
7545 starting address of a line), and @code{print} (if you use it to display
7546 a value from memory).
7549 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
7550 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
7551 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
7552 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
7553 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
7555 Since the letters indicating unit sizes are all distinct from the
7556 letters specifying output formats, you do not have to remember whether
7557 unit size or format comes first; either order works. The output
7558 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
7559 (However, the count @var{n} must come first; @samp{wx4} does not work.)
7561 Even though the unit size @var{u} is ignored for the formats @samp{s}
7562 and @samp{i}, you might still want to use a count @var{n}; for example,
7563 @samp{3i} specifies that you want to see three machine instructions,
7564 including any operands. For convenience, especially when used with
7565 the @code{display} command, the @samp{i} format also prints branch delay
7566 slot instructions, if any, beyond the count specified, which immediately
7567 follow the last instruction that is within the count. The command
7568 @code{disassemble} gives an alternative way of inspecting machine
7569 instructions; see @ref{Machine Code,,Source and Machine Code}.
7571 All the defaults for the arguments to @code{x} are designed to make it
7572 easy to continue scanning memory with minimal specifications each time
7573 you use @code{x}. For example, after you have inspected three machine
7574 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
7575 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
7576 the repeat count @var{n} is used again; the other arguments default as
7577 for successive uses of @code{x}.
7579 When examining machine instructions, the instruction at current program
7580 counter is shown with a @code{=>} marker. For example:
7583 (@value{GDBP}) x/5i $pc-6
7584 0x804837f <main+11>: mov %esp,%ebp
7585 0x8048381 <main+13>: push %ecx
7586 0x8048382 <main+14>: sub $0x4,%esp
7587 => 0x8048385 <main+17>: movl $0x8048460,(%esp)
7588 0x804838c <main+24>: call 0x80482d4 <puts@@plt>
7591 @cindex @code{$_}, @code{$__}, and value history
7592 The addresses and contents printed by the @code{x} command are not saved
7593 in the value history because there is often too much of them and they
7594 would get in the way. Instead, @value{GDBN} makes these values available for
7595 subsequent use in expressions as values of the convenience variables
7596 @code{$_} and @code{$__}. After an @code{x} command, the last address
7597 examined is available for use in expressions in the convenience variable
7598 @code{$_}. The contents of that address, as examined, are available in
7599 the convenience variable @code{$__}.
7601 If the @code{x} command has a repeat count, the address and contents saved
7602 are from the last memory unit printed; this is not the same as the last
7603 address printed if several units were printed on the last line of output.
7605 @cindex remote memory comparison
7606 @cindex verify remote memory image
7607 When you are debugging a program running on a remote target machine
7608 (@pxref{Remote Debugging}), you may wish to verify the program's image in the
7609 remote machine's memory against the executable file you downloaded to
7610 the target. The @code{compare-sections} command is provided for such
7614 @kindex compare-sections
7615 @item compare-sections @r{[}@var{section-name}@r{]}
7616 Compare the data of a loadable section @var{section-name} in the
7617 executable file of the program being debugged with the same section in
7618 the remote machine's memory, and report any mismatches. With no
7619 arguments, compares all loadable sections. This command's
7620 availability depends on the target's support for the @code{"qCRC"}
7625 @section Automatic Display
7626 @cindex automatic display
7627 @cindex display of expressions
7629 If you find that you want to print the value of an expression frequently
7630 (to see how it changes), you might want to add it to the @dfn{automatic
7631 display list} so that @value{GDBN} prints its value each time your program stops.
7632 Each expression added to the list is given a number to identify it;
7633 to remove an expression from the list, you specify that number.
7634 The automatic display looks like this:
7638 3: bar[5] = (struct hack *) 0x3804
7642 This display shows item numbers, expressions and their current values. As with
7643 displays you request manually using @code{x} or @code{print}, you can
7644 specify the output format you prefer; in fact, @code{display} decides
7645 whether to use @code{print} or @code{x} depending your format
7646 specification---it uses @code{x} if you specify either the @samp{i}
7647 or @samp{s} format, or a unit size; otherwise it uses @code{print}.
7651 @item display @var{expr}
7652 Add the expression @var{expr} to the list of expressions to display
7653 each time your program stops. @xref{Expressions, ,Expressions}.
7655 @code{display} does not repeat if you press @key{RET} again after using it.
7657 @item display/@var{fmt} @var{expr}
7658 For @var{fmt} specifying only a display format and not a size or
7659 count, add the expression @var{expr} to the auto-display list but
7660 arrange to display it each time in the specified format @var{fmt}.
7661 @xref{Output Formats,,Output Formats}.
7663 @item display/@var{fmt} @var{addr}
7664 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
7665 number of units, add the expression @var{addr} as a memory address to
7666 be examined each time your program stops. Examining means in effect
7667 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining Memory}.
7670 For example, @samp{display/i $pc} can be helpful, to see the machine
7671 instruction about to be executed each time execution stops (@samp{$pc}
7672 is a common name for the program counter; @pxref{Registers, ,Registers}).
7675 @kindex delete display
7677 @item undisplay @var{dnums}@dots{}
7678 @itemx delete display @var{dnums}@dots{}
7679 Remove items from the list of expressions to display. Specify the
7680 numbers of the displays that you want affected with the command
7681 argument @var{dnums}. It can be a single display number, one of the
7682 numbers shown in the first field of the @samp{info display} display;
7683 or it could be a range of display numbers, as in @code{2-4}.
7685 @code{undisplay} does not repeat if you press @key{RET} after using it.
7686 (Otherwise you would just get the error @samp{No display number @dots{}}.)
7688 @kindex disable display
7689 @item disable display @var{dnums}@dots{}
7690 Disable the display of item numbers @var{dnums}. A disabled display
7691 item is not printed automatically, but is not forgotten. It may be
7692 enabled again later. Specify the numbers of the displays that you
7693 want affected with the command argument @var{dnums}. It can be a
7694 single display number, one of the numbers shown in the first field of
7695 the @samp{info display} display; or it could be a range of display
7696 numbers, as in @code{2-4}.
7698 @kindex enable display
7699 @item enable display @var{dnums}@dots{}
7700 Enable display of item numbers @var{dnums}. It becomes effective once
7701 again in auto display of its expression, until you specify otherwise.
7702 Specify the numbers of the displays that you want affected with the
7703 command argument @var{dnums}. It can be a single display number, one
7704 of the numbers shown in the first field of the @samp{info display}
7705 display; or it could be a range of display numbers, as in @code{2-4}.
7708 Display the current values of the expressions on the list, just as is
7709 done when your program stops.
7711 @kindex info display
7713 Print the list of expressions previously set up to display
7714 automatically, each one with its item number, but without showing the
7715 values. This includes disabled expressions, which are marked as such.
7716 It also includes expressions which would not be displayed right now
7717 because they refer to automatic variables not currently available.
7720 @cindex display disabled out of scope
7721 If a display expression refers to local variables, then it does not make
7722 sense outside the lexical context for which it was set up. Such an
7723 expression is disabled when execution enters a context where one of its
7724 variables is not defined. For example, if you give the command
7725 @code{display last_char} while inside a function with an argument
7726 @code{last_char}, @value{GDBN} displays this argument while your program
7727 continues to stop inside that function. When it stops elsewhere---where
7728 there is no variable @code{last_char}---the display is disabled
7729 automatically. The next time your program stops where @code{last_char}
7730 is meaningful, you can enable the display expression once again.
7732 @node Print Settings
7733 @section Print Settings
7735 @cindex format options
7736 @cindex print settings
7737 @value{GDBN} provides the following ways to control how arrays, structures,
7738 and symbols are printed.
7741 These settings are useful for debugging programs in any language:
7745 @item set print address
7746 @itemx set print address on
7747 @cindex print/don't print memory addresses
7748 @value{GDBN} prints memory addresses showing the location of stack
7749 traces, structure values, pointer values, breakpoints, and so forth,
7750 even when it also displays the contents of those addresses. The default
7751 is @code{on}. For example, this is what a stack frame display looks like with
7752 @code{set print address on}:
7757 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
7759 530 if (lquote != def_lquote)
7763 @item set print address off
7764 Do not print addresses when displaying their contents. For example,
7765 this is the same stack frame displayed with @code{set print address off}:
7769 (@value{GDBP}) set print addr off
7771 #0 set_quotes (lq="<<", rq=">>") at input.c:530
7772 530 if (lquote != def_lquote)
7776 You can use @samp{set print address off} to eliminate all machine
7777 dependent displays from the @value{GDBN} interface. For example, with
7778 @code{print address off}, you should get the same text for backtraces on
7779 all machines---whether or not they involve pointer arguments.
7782 @item show print address
7783 Show whether or not addresses are to be printed.
7786 When @value{GDBN} prints a symbolic address, it normally prints the
7787 closest earlier symbol plus an offset. If that symbol does not uniquely
7788 identify the address (for example, it is a name whose scope is a single
7789 source file), you may need to clarify. One way to do this is with
7790 @code{info line}, for example @samp{info line *0x4537}. Alternately,
7791 you can set @value{GDBN} to print the source file and line number when
7792 it prints a symbolic address:
7795 @item set print symbol-filename on
7796 @cindex source file and line of a symbol
7797 @cindex symbol, source file and line
7798 Tell @value{GDBN} to print the source file name and line number of a
7799 symbol in the symbolic form of an address.
7801 @item set print symbol-filename off
7802 Do not print source file name and line number of a symbol. This is the
7805 @item show print symbol-filename
7806 Show whether or not @value{GDBN} will print the source file name and
7807 line number of a symbol in the symbolic form of an address.
7810 Another situation where it is helpful to show symbol filenames and line
7811 numbers is when disassembling code; @value{GDBN} shows you the line
7812 number and source file that corresponds to each instruction.
7814 Also, you may wish to see the symbolic form only if the address being
7815 printed is reasonably close to the closest earlier symbol:
7818 @item set print max-symbolic-offset @var{max-offset}
7819 @cindex maximum value for offset of closest symbol
7820 Tell @value{GDBN} to only display the symbolic form of an address if the
7821 offset between the closest earlier symbol and the address is less than
7822 @var{max-offset}. The default is 0, which tells @value{GDBN}
7823 to always print the symbolic form of an address if any symbol precedes it.
7825 @item show print max-symbolic-offset
7826 Ask how large the maximum offset is that @value{GDBN} prints in a
7830 @cindex wild pointer, interpreting
7831 @cindex pointer, finding referent
7832 If you have a pointer and you are not sure where it points, try
7833 @samp{set print symbol-filename on}. Then you can determine the name
7834 and source file location of the variable where it points, using
7835 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
7836 For example, here @value{GDBN} shows that a variable @code{ptt} points
7837 at another variable @code{t}, defined in @file{hi2.c}:
7840 (@value{GDBP}) set print symbol-filename on
7841 (@value{GDBP}) p/a ptt
7842 $4 = 0xe008 <t in hi2.c>
7846 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
7847 does not show the symbol name and filename of the referent, even with
7848 the appropriate @code{set print} options turned on.
7851 Other settings control how different kinds of objects are printed:
7854 @item set print array
7855 @itemx set print array on
7856 @cindex pretty print arrays
7857 Pretty print arrays. This format is more convenient to read,
7858 but uses more space. The default is off.
7860 @item set print array off
7861 Return to compressed format for arrays.
7863 @item show print array
7864 Show whether compressed or pretty format is selected for displaying
7867 @cindex print array indexes
7868 @item set print array-indexes
7869 @itemx set print array-indexes on
7870 Print the index of each element when displaying arrays. May be more
7871 convenient to locate a given element in the array or quickly find the
7872 index of a given element in that printed array. The default is off.
7874 @item set print array-indexes off
7875 Stop printing element indexes when displaying arrays.
7877 @item show print array-indexes
7878 Show whether the index of each element is printed when displaying
7881 @item set print elements @var{number-of-elements}
7882 @cindex number of array elements to print
7883 @cindex limit on number of printed array elements
7884 Set a limit on how many elements of an array @value{GDBN} will print.
7885 If @value{GDBN} is printing a large array, it stops printing after it has
7886 printed the number of elements set by the @code{set print elements} command.
7887 This limit also applies to the display of strings.
7888 When @value{GDBN} starts, this limit is set to 200.
7889 Setting @var{number-of-elements} to zero means that the printing is unlimited.
7891 @item show print elements
7892 Display the number of elements of a large array that @value{GDBN} will print.
7893 If the number is 0, then the printing is unlimited.
7895 @item set print frame-arguments @var{value}
7896 @kindex set print frame-arguments
7897 @cindex printing frame argument values
7898 @cindex print all frame argument values
7899 @cindex print frame argument values for scalars only
7900 @cindex do not print frame argument values
7901 This command allows to control how the values of arguments are printed
7902 when the debugger prints a frame (@pxref{Frames}). The possible
7907 The values of all arguments are printed.
7910 Print the value of an argument only if it is a scalar. The value of more
7911 complex arguments such as arrays, structures, unions, etc, is replaced
7912 by @code{@dots{}}. This is the default. Here is an example where
7913 only scalar arguments are shown:
7916 #1 0x08048361 in call_me (i=3, s=@dots{}, ss=0xbf8d508c, u=@dots{}, e=green)
7921 None of the argument values are printed. Instead, the value of each argument
7922 is replaced by @code{@dots{}}. In this case, the example above now becomes:
7925 #1 0x08048361 in call_me (i=@dots{}, s=@dots{}, ss=@dots{}, u=@dots{}, e=@dots{})
7930 By default, only scalar arguments are printed. This command can be used
7931 to configure the debugger to print the value of all arguments, regardless
7932 of their type. However, it is often advantageous to not print the value
7933 of more complex parameters. For instance, it reduces the amount of
7934 information printed in each frame, making the backtrace more readable.
7935 Also, it improves performance when displaying Ada frames, because
7936 the computation of large arguments can sometimes be CPU-intensive,
7937 especially in large applications. Setting @code{print frame-arguments}
7938 to @code{scalars} (the default) or @code{none} avoids this computation,
7939 thus speeding up the display of each Ada frame.
7941 @item show print frame-arguments
7942 Show how the value of arguments should be displayed when printing a frame.
7944 @item set print repeats
7945 @cindex repeated array elements
7946 Set the threshold for suppressing display of repeated array
7947 elements. When the number of consecutive identical elements of an
7948 array exceeds the threshold, @value{GDBN} prints the string
7949 @code{"<repeats @var{n} times>"}, where @var{n} is the number of
7950 identical repetitions, instead of displaying the identical elements
7951 themselves. Setting the threshold to zero will cause all elements to
7952 be individually printed. The default threshold is 10.
7954 @item show print repeats
7955 Display the current threshold for printing repeated identical
7958 @item set print null-stop
7959 @cindex @sc{null} elements in arrays
7960 Cause @value{GDBN} to stop printing the characters of an array when the first
7961 @sc{null} is encountered. This is useful when large arrays actually
7962 contain only short strings.
7965 @item show print null-stop
7966 Show whether @value{GDBN} stops printing an array on the first
7967 @sc{null} character.
7969 @item set print pretty on
7970 @cindex print structures in indented form
7971 @cindex indentation in structure display
7972 Cause @value{GDBN} to print structures in an indented format with one member
7973 per line, like this:
7988 @item set print pretty off
7989 Cause @value{GDBN} to print structures in a compact format, like this:
7993 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
7994 meat = 0x54 "Pork"@}
7999 This is the default format.
8001 @item show print pretty
8002 Show which format @value{GDBN} is using to print structures.
8004 @item set print sevenbit-strings on
8005 @cindex eight-bit characters in strings
8006 @cindex octal escapes in strings
8007 Print using only seven-bit characters; if this option is set,
8008 @value{GDBN} displays any eight-bit characters (in strings or
8009 character values) using the notation @code{\}@var{nnn}. This setting is
8010 best if you are working in English (@sc{ascii}) and you use the
8011 high-order bit of characters as a marker or ``meta'' bit.
8013 @item set print sevenbit-strings off
8014 Print full eight-bit characters. This allows the use of more
8015 international character sets, and is the default.
8017 @item show print sevenbit-strings
8018 Show whether or not @value{GDBN} is printing only seven-bit characters.
8020 @item set print union on
8021 @cindex unions in structures, printing
8022 Tell @value{GDBN} to print unions which are contained in structures
8023 and other unions. This is the default setting.
8025 @item set print union off
8026 Tell @value{GDBN} not to print unions which are contained in
8027 structures and other unions. @value{GDBN} will print @code{"@{...@}"}
8030 @item show print union
8031 Ask @value{GDBN} whether or not it will print unions which are contained in
8032 structures and other unions.
8034 For example, given the declarations
8037 typedef enum @{Tree, Bug@} Species;
8038 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
8039 typedef enum @{Caterpillar, Cocoon, Butterfly@}
8050 struct thing foo = @{Tree, @{Acorn@}@};
8054 with @code{set print union on} in effect @samp{p foo} would print
8057 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
8061 and with @code{set print union off} in effect it would print
8064 $1 = @{it = Tree, form = @{...@}@}
8068 @code{set print union} affects programs written in C-like languages
8074 These settings are of interest when debugging C@t{++} programs:
8077 @cindex demangling C@t{++} names
8078 @item set print demangle
8079 @itemx set print demangle on
8080 Print C@t{++} names in their source form rather than in the encoded
8081 (``mangled'') form passed to the assembler and linker for type-safe
8082 linkage. The default is on.
8084 @item show print demangle
8085 Show whether C@t{++} names are printed in mangled or demangled form.
8087 @item set print asm-demangle
8088 @itemx set print asm-demangle on
8089 Print C@t{++} names in their source form rather than their mangled form, even
8090 in assembler code printouts such as instruction disassemblies.
8093 @item show print asm-demangle
8094 Show whether C@t{++} names in assembly listings are printed in mangled
8097 @cindex C@t{++} symbol decoding style
8098 @cindex symbol decoding style, C@t{++}
8099 @kindex set demangle-style
8100 @item set demangle-style @var{style}
8101 Choose among several encoding schemes used by different compilers to
8102 represent C@t{++} names. The choices for @var{style} are currently:
8106 Allow @value{GDBN} to choose a decoding style by inspecting your program.
8109 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
8110 This is the default.
8113 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
8116 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
8119 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
8120 @strong{Warning:} this setting alone is not sufficient to allow
8121 debugging @code{cfront}-generated executables. @value{GDBN} would
8122 require further enhancement to permit that.
8125 If you omit @var{style}, you will see a list of possible formats.
8127 @item show demangle-style
8128 Display the encoding style currently in use for decoding C@t{++} symbols.
8130 @item set print object
8131 @itemx set print object on
8132 @cindex derived type of an object, printing
8133 @cindex display derived types
8134 When displaying a pointer to an object, identify the @emph{actual}
8135 (derived) type of the object rather than the @emph{declared} type, using
8136 the virtual function table.
8138 @item set print object off
8139 Display only the declared type of objects, without reference to the
8140 virtual function table. This is the default setting.
8142 @item show print object
8143 Show whether actual, or declared, object types are displayed.
8145 @item set print static-members
8146 @itemx set print static-members on
8147 @cindex static members of C@t{++} objects
8148 Print static members when displaying a C@t{++} object. The default is on.
8150 @item set print static-members off
8151 Do not print static members when displaying a C@t{++} object.
8153 @item show print static-members
8154 Show whether C@t{++} static members are printed or not.
8156 @item set print pascal_static-members
8157 @itemx set print pascal_static-members on
8158 @cindex static members of Pascal objects
8159 @cindex Pascal objects, static members display
8160 Print static members when displaying a Pascal object. The default is on.
8162 @item set print pascal_static-members off
8163 Do not print static members when displaying a Pascal object.
8165 @item show print pascal_static-members
8166 Show whether Pascal static members are printed or not.
8168 @c These don't work with HP ANSI C++ yet.
8169 @item set print vtbl
8170 @itemx set print vtbl on
8171 @cindex pretty print C@t{++} virtual function tables
8172 @cindex virtual functions (C@t{++}) display
8173 @cindex VTBL display
8174 Pretty print C@t{++} virtual function tables. The default is off.
8175 (The @code{vtbl} commands do not work on programs compiled with the HP
8176 ANSI C@t{++} compiler (@code{aCC}).)
8178 @item set print vtbl off
8179 Do not pretty print C@t{++} virtual function tables.
8181 @item show print vtbl
8182 Show whether C@t{++} virtual function tables are pretty printed, or not.
8185 @node Pretty Printing
8186 @section Pretty Printing
8188 @value{GDBN} provides a mechanism to allow pretty-printing of values using
8189 Python code. It greatly simplifies the display of complex objects. This
8190 mechanism works for both MI and the CLI.
8193 * Pretty-Printer Introduction:: Introduction to pretty-printers
8194 * Pretty-Printer Example:: An example pretty-printer
8195 * Pretty-Printer Commands:: Pretty-printer commands
8198 @node Pretty-Printer Introduction
8199 @subsection Pretty-Printer Introduction
8201 When @value{GDBN} prints a value, it first sees if there is a pretty-printer
8202 registered for the value. If there is then @value{GDBN} invokes the
8203 pretty-printer to print the value. Otherwise the value is printed normally.
8205 Pretty-printers are normally named. This makes them easy to manage.
8206 The @samp{info pretty-printer} command will list all the installed
8207 pretty-printers with their names.
8208 If a pretty-printer can handle multiple data types, then its
8209 @dfn{subprinters} are the printers for the individual data types.
8210 Each such subprinter has its own name.
8211 The format of the name is @var{printer-name};@var{subprinter-name}.
8213 Pretty-printers are installed by @dfn{registering} them with @value{GDBN}.
8214 Typically they are automatically loaded and registered when the corresponding
8215 debug information is loaded, thus making them available without having to
8216 do anything special.
8218 There are three places where a pretty-printer can be registered.
8222 Pretty-printers registered globally are available when debugging
8226 Pretty-printers registered with a program space are available only
8227 when debugging that program.
8228 @xref{Progspaces In Python}, for more details on program spaces in Python.
8231 Pretty-printers registered with an objfile are loaded and unloaded
8232 with the corresponding objfile (e.g., shared library).
8233 @xref{Objfiles In Python}, for more details on objfiles in Python.
8236 @xref{Selecting Pretty-Printers}, for further information on how
8237 pretty-printers are selected,
8239 @xref{Writing a Pretty-Printer}, for implementing pretty printers
8242 @node Pretty-Printer Example
8243 @subsection Pretty-Printer Example
8245 Here is how a C@t{++} @code{std::string} looks without a pretty-printer:
8248 (@value{GDBP}) print s
8250 static npos = 4294967295,
8252 <std::allocator<char>> = @{
8253 <__gnu_cxx::new_allocator<char>> = @{
8254 <No data fields>@}, <No data fields>
8256 members of std::basic_string<char, std::char_traits<char>,
8257 std::allocator<char> >::_Alloc_hider:
8258 _M_p = 0x804a014 "abcd"
8263 With a pretty-printer for @code{std::string} only the contents are printed:
8266 (@value{GDBP}) print s
8270 @node Pretty-Printer Commands
8271 @subsection Pretty-Printer Commands
8272 @cindex pretty-printer commands
8275 @kindex info pretty-printer
8276 @item info pretty-printer [@var{object-regexp} [@var{name-regexp}]]
8277 Print the list of installed pretty-printers.
8278 This includes disabled pretty-printers, which are marked as such.
8280 @var{object-regexp} is a regular expression matching the objects
8281 whose pretty-printers to list.
8282 Objects can be @code{global}, the program space's file
8283 (@pxref{Progspaces In Python}),
8284 and the object files within that program space (@pxref{Objfiles In Python}).
8285 @xref{Selecting Pretty-Printers}, for details on how @value{GDBN}
8286 looks up a printer from these three objects.
8288 @var{name-regexp} is a regular expression matching the name of the printers
8291 @kindex disable pretty-printer
8292 @item disable pretty-printer [@var{object-regexp} [@var{name-regexp}]]
8293 Disable pretty-printers matching @var{object-regexp} and @var{name-regexp}.
8294 A disabled pretty-printer is not forgotten, it may be enabled again later.
8296 @kindex enable pretty-printer
8297 @item enable pretty-printer [@var{object-regexp} [@var{name-regexp}]]
8298 Enable pretty-printers matching @var{object-regexp} and @var{name-regexp}.
8303 Suppose we have three pretty-printers installed: one from library1.so
8304 named @code{foo} that prints objects of type @code{foo}, and
8305 another from library2.so named @code{bar} that prints two types of objects,
8306 @code{bar1} and @code{bar2}.
8309 (gdb) info pretty-printer
8316 (gdb) info pretty-printer library2
8321 (gdb) disable pretty-printer library1
8323 2 of 3 printers enabled
8324 (gdb) info pretty-printer
8331 (gdb) disable pretty-printer library2 bar:bar1
8333 1 of 3 printers enabled
8334 (gdb) info pretty-printer library2
8341 (gdb) disable pretty-printer library2 bar
8343 0 of 3 printers enabled
8344 (gdb) info pretty-printer library2
8353 Note that for @code{bar} the entire printer can be disabled,
8354 as can each individual subprinter.
8357 @section Value History
8359 @cindex value history
8360 @cindex history of values printed by @value{GDBN}
8361 Values printed by the @code{print} command are saved in the @value{GDBN}
8362 @dfn{value history}. This allows you to refer to them in other expressions.
8363 Values are kept until the symbol table is re-read or discarded
8364 (for example with the @code{file} or @code{symbol-file} commands).
8365 When the symbol table changes, the value history is discarded,
8366 since the values may contain pointers back to the types defined in the
8371 @cindex history number
8372 The values printed are given @dfn{history numbers} by which you can
8373 refer to them. These are successive integers starting with one.
8374 @code{print} shows you the history number assigned to a value by
8375 printing @samp{$@var{num} = } before the value; here @var{num} is the
8378 To refer to any previous value, use @samp{$} followed by the value's
8379 history number. The way @code{print} labels its output is designed to
8380 remind you of this. Just @code{$} refers to the most recent value in
8381 the history, and @code{$$} refers to the value before that.
8382 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
8383 is the value just prior to @code{$$}, @code{$$1} is equivalent to
8384 @code{$$}, and @code{$$0} is equivalent to @code{$}.
8386 For example, suppose you have just printed a pointer to a structure and
8387 want to see the contents of the structure. It suffices to type
8393 If you have a chain of structures where the component @code{next} points
8394 to the next one, you can print the contents of the next one with this:
8401 You can print successive links in the chain by repeating this
8402 command---which you can do by just typing @key{RET}.
8404 Note that the history records values, not expressions. If the value of
8405 @code{x} is 4 and you type these commands:
8413 then the value recorded in the value history by the @code{print} command
8414 remains 4 even though the value of @code{x} has changed.
8419 Print the last ten values in the value history, with their item numbers.
8420 This is like @samp{p@ $$9} repeated ten times, except that @code{show
8421 values} does not change the history.
8423 @item show values @var{n}
8424 Print ten history values centered on history item number @var{n}.
8427 Print ten history values just after the values last printed. If no more
8428 values are available, @code{show values +} produces no display.
8431 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
8432 same effect as @samp{show values +}.
8434 @node Convenience Vars
8435 @section Convenience Variables
8437 @cindex convenience variables
8438 @cindex user-defined variables
8439 @value{GDBN} provides @dfn{convenience variables} that you can use within
8440 @value{GDBN} to hold on to a value and refer to it later. These variables
8441 exist entirely within @value{GDBN}; they are not part of your program, and
8442 setting a convenience variable has no direct effect on further execution
8443 of your program. That is why you can use them freely.
8445 Convenience variables are prefixed with @samp{$}. Any name preceded by
8446 @samp{$} can be used for a convenience variable, unless it is one of
8447 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
8448 (Value history references, in contrast, are @emph{numbers} preceded
8449 by @samp{$}. @xref{Value History, ,Value History}.)
8451 You can save a value in a convenience variable with an assignment
8452 expression, just as you would set a variable in your program.
8456 set $foo = *object_ptr
8460 would save in @code{$foo} the value contained in the object pointed to by
8463 Using a convenience variable for the first time creates it, but its
8464 value is @code{void} until you assign a new value. You can alter the
8465 value with another assignment at any time.
8467 Convenience variables have no fixed types. You can assign a convenience
8468 variable any type of value, including structures and arrays, even if
8469 that variable already has a value of a different type. The convenience
8470 variable, when used as an expression, has the type of its current value.
8473 @kindex show convenience
8474 @cindex show all user variables
8475 @item show convenience
8476 Print a list of convenience variables used so far, and their values.
8477 Abbreviated @code{show conv}.
8479 @kindex init-if-undefined
8480 @cindex convenience variables, initializing
8481 @item init-if-undefined $@var{variable} = @var{expression}
8482 Set a convenience variable if it has not already been set. This is useful
8483 for user-defined commands that keep some state. It is similar, in concept,
8484 to using local static variables with initializers in C (except that
8485 convenience variables are global). It can also be used to allow users to
8486 override default values used in a command script.
8488 If the variable is already defined then the expression is not evaluated so
8489 any side-effects do not occur.
8492 One of the ways to use a convenience variable is as a counter to be
8493 incremented or a pointer to be advanced. For example, to print
8494 a field from successive elements of an array of structures:
8498 print bar[$i++]->contents
8502 Repeat that command by typing @key{RET}.
8504 Some convenience variables are created automatically by @value{GDBN} and given
8505 values likely to be useful.
8508 @vindex $_@r{, convenience variable}
8510 The variable @code{$_} is automatically set by the @code{x} command to
8511 the last address examined (@pxref{Memory, ,Examining Memory}). Other
8512 commands which provide a default address for @code{x} to examine also
8513 set @code{$_} to that address; these commands include @code{info line}
8514 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
8515 except when set by the @code{x} command, in which case it is a pointer
8516 to the type of @code{$__}.
8518 @vindex $__@r{, convenience variable}
8520 The variable @code{$__} is automatically set by the @code{x} command
8521 to the value found in the last address examined. Its type is chosen
8522 to match the format in which the data was printed.
8525 @vindex $_exitcode@r{, convenience variable}
8526 The variable @code{$_exitcode} is automatically set to the exit code when
8527 the program being debugged terminates.
8530 @vindex $_sdata@r{, inspect, convenience variable}
8531 The variable @code{$_sdata} contains extra collected static tracepoint
8532 data. @xref{Tracepoint Actions,,Tracepoint Action Lists}. Note that
8533 @code{$_sdata} could be empty, if not inspecting a trace buffer, or
8534 if extra static tracepoint data has not been collected.
8537 @vindex $_siginfo@r{, convenience variable}
8538 The variable @code{$_siginfo} contains extra signal information
8539 (@pxref{extra signal information}). Note that @code{$_siginfo}
8540 could be empty, if the application has not yet received any signals.
8541 For example, it will be empty before you execute the @code{run} command.
8544 @vindex $_tlb@r{, convenience variable}
8545 The variable @code{$_tlb} is automatically set when debugging
8546 applications running on MS-Windows in native mode or connected to
8547 gdbserver that supports the @code{qGetTIBAddr} request.
8548 @xref{General Query Packets}.
8549 This variable contains the address of the thread information block.
8553 On HP-UX systems, if you refer to a function or variable name that
8554 begins with a dollar sign, @value{GDBN} searches for a user or system
8555 name first, before it searches for a convenience variable.
8557 @cindex convenience functions
8558 @value{GDBN} also supplies some @dfn{convenience functions}. These
8559 have a syntax similar to convenience variables. A convenience
8560 function can be used in an expression just like an ordinary function;
8561 however, a convenience function is implemented internally to
8566 @kindex help function
8567 @cindex show all convenience functions
8568 Print a list of all convenience functions.
8575 You can refer to machine register contents, in expressions, as variables
8576 with names starting with @samp{$}. The names of registers are different
8577 for each machine; use @code{info registers} to see the names used on
8581 @kindex info registers
8582 @item info registers
8583 Print the names and values of all registers except floating-point
8584 and vector registers (in the selected stack frame).
8586 @kindex info all-registers
8587 @cindex floating point registers
8588 @item info all-registers
8589 Print the names and values of all registers, including floating-point
8590 and vector registers (in the selected stack frame).
8592 @item info registers @var{regname} @dots{}
8593 Print the @dfn{relativized} value of each specified register @var{regname}.
8594 As discussed in detail below, register values are normally relative to
8595 the selected stack frame. @var{regname} may be any register name valid on
8596 the machine you are using, with or without the initial @samp{$}.
8599 @cindex stack pointer register
8600 @cindex program counter register
8601 @cindex process status register
8602 @cindex frame pointer register
8603 @cindex standard registers
8604 @value{GDBN} has four ``standard'' register names that are available (in
8605 expressions) on most machines---whenever they do not conflict with an
8606 architecture's canonical mnemonics for registers. The register names
8607 @code{$pc} and @code{$sp} are used for the program counter register and
8608 the stack pointer. @code{$fp} is used for a register that contains a
8609 pointer to the current stack frame, and @code{$ps} is used for a
8610 register that contains the processor status. For example,
8611 you could print the program counter in hex with
8618 or print the instruction to be executed next with
8625 or add four to the stack pointer@footnote{This is a way of removing
8626 one word from the stack, on machines where stacks grow downward in
8627 memory (most machines, nowadays). This assumes that the innermost
8628 stack frame is selected; setting @code{$sp} is not allowed when other
8629 stack frames are selected. To pop entire frames off the stack,
8630 regardless of machine architecture, use @code{return};
8631 see @ref{Returning, ,Returning from a Function}.} with
8637 Whenever possible, these four standard register names are available on
8638 your machine even though the machine has different canonical mnemonics,
8639 so long as there is no conflict. The @code{info registers} command
8640 shows the canonical names. For example, on the SPARC, @code{info
8641 registers} displays the processor status register as @code{$psr} but you
8642 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
8643 is an alias for the @sc{eflags} register.
8645 @value{GDBN} always considers the contents of an ordinary register as an
8646 integer when the register is examined in this way. Some machines have
8647 special registers which can hold nothing but floating point; these
8648 registers are considered to have floating point values. There is no way
8649 to refer to the contents of an ordinary register as floating point value
8650 (although you can @emph{print} it as a floating point value with
8651 @samp{print/f $@var{regname}}).
8653 Some registers have distinct ``raw'' and ``virtual'' data formats. This
8654 means that the data format in which the register contents are saved by
8655 the operating system is not the same one that your program normally
8656 sees. For example, the registers of the 68881 floating point
8657 coprocessor are always saved in ``extended'' (raw) format, but all C
8658 programs expect to work with ``double'' (virtual) format. In such
8659 cases, @value{GDBN} normally works with the virtual format only (the format
8660 that makes sense for your program), but the @code{info registers} command
8661 prints the data in both formats.
8663 @cindex SSE registers (x86)
8664 @cindex MMX registers (x86)
8665 Some machines have special registers whose contents can be interpreted
8666 in several different ways. For example, modern x86-based machines
8667 have SSE and MMX registers that can hold several values packed
8668 together in several different formats. @value{GDBN} refers to such
8669 registers in @code{struct} notation:
8672 (@value{GDBP}) print $xmm1
8674 v4_float = @{0, 3.43859137e-038, 1.54142831e-044, 1.821688e-044@},
8675 v2_double = @{9.92129282474342e-303, 2.7585945287983262e-313@},
8676 v16_int8 = "\000\000\000\000\3706;\001\v\000\000\000\r\000\000",
8677 v8_int16 = @{0, 0, 14072, 315, 11, 0, 13, 0@},
8678 v4_int32 = @{0, 20657912, 11, 13@},
8679 v2_int64 = @{88725056443645952, 55834574859@},
8680 uint128 = 0x0000000d0000000b013b36f800000000
8685 To set values of such registers, you need to tell @value{GDBN} which
8686 view of the register you wish to change, as if you were assigning
8687 value to a @code{struct} member:
8690 (@value{GDBP}) set $xmm1.uint128 = 0x000000000000000000000000FFFFFFFF
8693 Normally, register values are relative to the selected stack frame
8694 (@pxref{Selection, ,Selecting a Frame}). This means that you get the
8695 value that the register would contain if all stack frames farther in
8696 were exited and their saved registers restored. In order to see the
8697 true contents of hardware registers, you must select the innermost
8698 frame (with @samp{frame 0}).
8700 However, @value{GDBN} must deduce where registers are saved, from the machine
8701 code generated by your compiler. If some registers are not saved, or if
8702 @value{GDBN} is unable to locate the saved registers, the selected stack
8703 frame makes no difference.
8705 @node Floating Point Hardware
8706 @section Floating Point Hardware
8707 @cindex floating point
8709 Depending on the configuration, @value{GDBN} may be able to give
8710 you more information about the status of the floating point hardware.
8715 Display hardware-dependent information about the floating
8716 point unit. The exact contents and layout vary depending on the
8717 floating point chip. Currently, @samp{info float} is supported on
8718 the ARM and x86 machines.
8722 @section Vector Unit
8725 Depending on the configuration, @value{GDBN} may be able to give you
8726 more information about the status of the vector unit.
8731 Display information about the vector unit. The exact contents and
8732 layout vary depending on the hardware.
8735 @node OS Information
8736 @section Operating System Auxiliary Information
8737 @cindex OS information
8739 @value{GDBN} provides interfaces to useful OS facilities that can help
8740 you debug your program.
8742 @cindex @code{ptrace} system call
8743 @cindex @code{struct user} contents
8744 When @value{GDBN} runs on a @dfn{Posix system} (such as GNU or Unix
8745 machines), it interfaces with the inferior via the @code{ptrace}
8746 system call. The operating system creates a special sata structure,
8747 called @code{struct user}, for this interface. You can use the
8748 command @code{info udot} to display the contents of this data
8754 Display the contents of the @code{struct user} maintained by the OS
8755 kernel for the program being debugged. @value{GDBN} displays the
8756 contents of @code{struct user} as a list of hex numbers, similar to
8757 the @code{examine} command.
8760 @cindex auxiliary vector
8761 @cindex vector, auxiliary
8762 Some operating systems supply an @dfn{auxiliary vector} to programs at
8763 startup. This is akin to the arguments and environment that you
8764 specify for a program, but contains a system-dependent variety of
8765 binary values that tell system libraries important details about the
8766 hardware, operating system, and process. Each value's purpose is
8767 identified by an integer tag; the meanings are well-known but system-specific.
8768 Depending on the configuration and operating system facilities,
8769 @value{GDBN} may be able to show you this information. For remote
8770 targets, this functionality may further depend on the remote stub's
8771 support of the @samp{qXfer:auxv:read} packet, see
8772 @ref{qXfer auxiliary vector read}.
8777 Display the auxiliary vector of the inferior, which can be either a
8778 live process or a core dump file. @value{GDBN} prints each tag value
8779 numerically, and also shows names and text descriptions for recognized
8780 tags. Some values in the vector are numbers, some bit masks, and some
8781 pointers to strings or other data. @value{GDBN} displays each value in the
8782 most appropriate form for a recognized tag, and in hexadecimal for
8783 an unrecognized tag.
8786 On some targets, @value{GDBN} can access operating-system-specific information
8787 and display it to user, without interpretation. For remote targets,
8788 this functionality depends on the remote stub's support of the
8789 @samp{qXfer:osdata:read} packet, see @ref{qXfer osdata read}.
8794 List the types of OS information available for the target. If the
8795 target does not return a list of possible types, this command will
8798 @kindex info os processes
8799 @item info os processes
8800 Display the list of processes on the target. For each process,
8801 @value{GDBN} prints the process identifier, the name of the user, and
8802 the command corresponding to the process.
8805 @node Memory Region Attributes
8806 @section Memory Region Attributes
8807 @cindex memory region attributes
8809 @dfn{Memory region attributes} allow you to describe special handling
8810 required by regions of your target's memory. @value{GDBN} uses
8811 attributes to determine whether to allow certain types of memory
8812 accesses; whether to use specific width accesses; and whether to cache
8813 target memory. By default the description of memory regions is
8814 fetched from the target (if the current target supports this), but the
8815 user can override the fetched regions.
8817 Defined memory regions can be individually enabled and disabled. When a
8818 memory region is disabled, @value{GDBN} uses the default attributes when
8819 accessing memory in that region. Similarly, if no memory regions have
8820 been defined, @value{GDBN} uses the default attributes when accessing
8823 When a memory region is defined, it is given a number to identify it;
8824 to enable, disable, or remove a memory region, you specify that number.
8828 @item mem @var{lower} @var{upper} @var{attributes}@dots{}
8829 Define a memory region bounded by @var{lower} and @var{upper} with
8830 attributes @var{attributes}@dots{}, and add it to the list of regions
8831 monitored by @value{GDBN}. Note that @var{upper} == 0 is a special
8832 case: it is treated as the target's maximum memory address.
8833 (0xffff on 16 bit targets, 0xffffffff on 32 bit targets, etc.)
8836 Discard any user changes to the memory regions and use target-supplied
8837 regions, if available, or no regions if the target does not support.
8840 @item delete mem @var{nums}@dots{}
8841 Remove memory regions @var{nums}@dots{} from the list of regions
8842 monitored by @value{GDBN}.
8845 @item disable mem @var{nums}@dots{}
8846 Disable monitoring of memory regions @var{nums}@dots{}.
8847 A disabled memory region is not forgotten.
8848 It may be enabled again later.
8851 @item enable mem @var{nums}@dots{}
8852 Enable monitoring of memory regions @var{nums}@dots{}.
8856 Print a table of all defined memory regions, with the following columns
8860 @item Memory Region Number
8861 @item Enabled or Disabled.
8862 Enabled memory regions are marked with @samp{y}.
8863 Disabled memory regions are marked with @samp{n}.
8866 The address defining the inclusive lower bound of the memory region.
8869 The address defining the exclusive upper bound of the memory region.
8872 The list of attributes set for this memory region.
8877 @subsection Attributes
8879 @subsubsection Memory Access Mode
8880 The access mode attributes set whether @value{GDBN} may make read or
8881 write accesses to a memory region.
8883 While these attributes prevent @value{GDBN} from performing invalid
8884 memory accesses, they do nothing to prevent the target system, I/O DMA,
8885 etc.@: from accessing memory.
8889 Memory is read only.
8891 Memory is write only.
8893 Memory is read/write. This is the default.
8896 @subsubsection Memory Access Size
8897 The access size attribute tells @value{GDBN} to use specific sized
8898 accesses in the memory region. Often memory mapped device registers
8899 require specific sized accesses. If no access size attribute is
8900 specified, @value{GDBN} may use accesses of any size.
8904 Use 8 bit memory accesses.
8906 Use 16 bit memory accesses.
8908 Use 32 bit memory accesses.
8910 Use 64 bit memory accesses.
8913 @c @subsubsection Hardware/Software Breakpoints
8914 @c The hardware/software breakpoint attributes set whether @value{GDBN}
8915 @c will use hardware or software breakpoints for the internal breakpoints
8916 @c used by the step, next, finish, until, etc. commands.
8920 @c Always use hardware breakpoints
8921 @c @item swbreak (default)
8924 @subsubsection Data Cache
8925 The data cache attributes set whether @value{GDBN} will cache target
8926 memory. While this generally improves performance by reducing debug
8927 protocol overhead, it can lead to incorrect results because @value{GDBN}
8928 does not know about volatile variables or memory mapped device
8933 Enable @value{GDBN} to cache target memory.
8935 Disable @value{GDBN} from caching target memory. This is the default.
8938 @subsection Memory Access Checking
8939 @value{GDBN} can be instructed to refuse accesses to memory that is
8940 not explicitly described. This can be useful if accessing such
8941 regions has undesired effects for a specific target, or to provide
8942 better error checking. The following commands control this behaviour.
8945 @kindex set mem inaccessible-by-default
8946 @item set mem inaccessible-by-default [on|off]
8947 If @code{on} is specified, make @value{GDBN} treat memory not
8948 explicitly described by the memory ranges as non-existent and refuse accesses
8949 to such memory. The checks are only performed if there's at least one
8950 memory range defined. If @code{off} is specified, make @value{GDBN}
8951 treat the memory not explicitly described by the memory ranges as RAM.
8952 The default value is @code{on}.
8953 @kindex show mem inaccessible-by-default
8954 @item show mem inaccessible-by-default
8955 Show the current handling of accesses to unknown memory.
8959 @c @subsubsection Memory Write Verification
8960 @c The memory write verification attributes set whether @value{GDBN}
8961 @c will re-reads data after each write to verify the write was successful.
8965 @c @item noverify (default)
8968 @node Dump/Restore Files
8969 @section Copy Between Memory and a File
8970 @cindex dump/restore files
8971 @cindex append data to a file
8972 @cindex dump data to a file
8973 @cindex restore data from a file
8975 You can use the commands @code{dump}, @code{append}, and
8976 @code{restore} to copy data between target memory and a file. The
8977 @code{dump} and @code{append} commands write data to a file, and the
8978 @code{restore} command reads data from a file back into the inferior's
8979 memory. Files may be in binary, Motorola S-record, Intel hex, or
8980 Tektronix Hex format; however, @value{GDBN} can only append to binary
8986 @item dump @r{[}@var{format}@r{]} memory @var{filename} @var{start_addr} @var{end_addr}
8987 @itemx dump @r{[}@var{format}@r{]} value @var{filename} @var{expr}
8988 Dump the contents of memory from @var{start_addr} to @var{end_addr},
8989 or the value of @var{expr}, to @var{filename} in the given format.
8991 The @var{format} parameter may be any one of:
8998 Motorola S-record format.
9000 Tektronix Hex format.
9003 @value{GDBN} uses the same definitions of these formats as the
9004 @sc{gnu} binary utilities, like @samp{objdump} and @samp{objcopy}. If
9005 @var{format} is omitted, @value{GDBN} dumps the data in raw binary
9009 @item append @r{[}binary@r{]} memory @var{filename} @var{start_addr} @var{end_addr}
9010 @itemx append @r{[}binary@r{]} value @var{filename} @var{expr}
9011 Append the contents of memory from @var{start_addr} to @var{end_addr},
9012 or the value of @var{expr}, to the file @var{filename}, in raw binary form.
9013 (@value{GDBN} can only append data to files in raw binary form.)
9016 @item restore @var{filename} @r{[}binary@r{]} @var{bias} @var{start} @var{end}
9017 Restore the contents of file @var{filename} into memory. The
9018 @code{restore} command can automatically recognize any known @sc{bfd}
9019 file format, except for raw binary. To restore a raw binary file you
9020 must specify the optional keyword @code{binary} after the filename.
9022 If @var{bias} is non-zero, its value will be added to the addresses
9023 contained in the file. Binary files always start at address zero, so
9024 they will be restored at address @var{bias}. Other bfd files have
9025 a built-in location; they will be restored at offset @var{bias}
9028 If @var{start} and/or @var{end} are non-zero, then only data between
9029 file offset @var{start} and file offset @var{end} will be restored.
9030 These offsets are relative to the addresses in the file, before
9031 the @var{bias} argument is applied.
9035 @node Core File Generation
9036 @section How to Produce a Core File from Your Program
9037 @cindex dump core from inferior
9039 A @dfn{core file} or @dfn{core dump} is a file that records the memory
9040 image of a running process and its process status (register values
9041 etc.). Its primary use is post-mortem debugging of a program that
9042 crashed while it ran outside a debugger. A program that crashes
9043 automatically produces a core file, unless this feature is disabled by
9044 the user. @xref{Files}, for information on invoking @value{GDBN} in
9045 the post-mortem debugging mode.
9047 Occasionally, you may wish to produce a core file of the program you
9048 are debugging in order to preserve a snapshot of its state.
9049 @value{GDBN} has a special command for that.
9053 @kindex generate-core-file
9054 @item generate-core-file [@var{file}]
9055 @itemx gcore [@var{file}]
9056 Produce a core dump of the inferior process. The optional argument
9057 @var{file} specifies the file name where to put the core dump. If not
9058 specified, the file name defaults to @file{core.@var{pid}}, where
9059 @var{pid} is the inferior process ID.
9061 Note that this command is implemented only for some systems (as of
9062 this writing, @sc{gnu}/Linux, FreeBSD, Solaris, Unixware, and S390).
9065 @node Character Sets
9066 @section Character Sets
9067 @cindex character sets
9069 @cindex translating between character sets
9070 @cindex host character set
9071 @cindex target character set
9073 If the program you are debugging uses a different character set to
9074 represent characters and strings than the one @value{GDBN} uses itself,
9075 @value{GDBN} can automatically translate between the character sets for
9076 you. The character set @value{GDBN} uses we call the @dfn{host
9077 character set}; the one the inferior program uses we call the
9078 @dfn{target character set}.
9080 For example, if you are running @value{GDBN} on a @sc{gnu}/Linux system, which
9081 uses the ISO Latin 1 character set, but you are using @value{GDBN}'s
9082 remote protocol (@pxref{Remote Debugging}) to debug a program
9083 running on an IBM mainframe, which uses the @sc{ebcdic} character set,
9084 then the host character set is Latin-1, and the target character set is
9085 @sc{ebcdic}. If you give @value{GDBN} the command @code{set
9086 target-charset EBCDIC-US}, then @value{GDBN} translates between
9087 @sc{ebcdic} and Latin 1 as you print character or string values, or use
9088 character and string literals in expressions.
9090 @value{GDBN} has no way to automatically recognize which character set
9091 the inferior program uses; you must tell it, using the @code{set
9092 target-charset} command, described below.
9094 Here are the commands for controlling @value{GDBN}'s character set
9098 @item set target-charset @var{charset}
9099 @kindex set target-charset
9100 Set the current target character set to @var{charset}. To display the
9101 list of supported target character sets, type
9102 @kbd{@w{set target-charset @key{TAB}@key{TAB}}}.
9104 @item set host-charset @var{charset}
9105 @kindex set host-charset
9106 Set the current host character set to @var{charset}.
9108 By default, @value{GDBN} uses a host character set appropriate to the
9109 system it is running on; you can override that default using the
9110 @code{set host-charset} command. On some systems, @value{GDBN} cannot
9111 automatically determine the appropriate host character set. In this
9112 case, @value{GDBN} uses @samp{UTF-8}.
9114 @value{GDBN} can only use certain character sets as its host character
9115 set. If you type @kbd{@w{set host-charset @key{TAB}@key{TAB}}},
9116 @value{GDBN} will list the host character sets it supports.
9118 @item set charset @var{charset}
9120 Set the current host and target character sets to @var{charset}. As
9121 above, if you type @kbd{@w{set charset @key{TAB}@key{TAB}}},
9122 @value{GDBN} will list the names of the character sets that can be used
9123 for both host and target.
9126 @kindex show charset
9127 Show the names of the current host and target character sets.
9129 @item show host-charset
9130 @kindex show host-charset
9131 Show the name of the current host character set.
9133 @item show target-charset
9134 @kindex show target-charset
9135 Show the name of the current target character set.
9137 @item set target-wide-charset @var{charset}
9138 @kindex set target-wide-charset
9139 Set the current target's wide character set to @var{charset}. This is
9140 the character set used by the target's @code{wchar_t} type. To
9141 display the list of supported wide character sets, type
9142 @kbd{@w{set target-wide-charset @key{TAB}@key{TAB}}}.
9144 @item show target-wide-charset
9145 @kindex show target-wide-charset
9146 Show the name of the current target's wide character set.
9149 Here is an example of @value{GDBN}'s character set support in action.
9150 Assume that the following source code has been placed in the file
9151 @file{charset-test.c}:
9157 = @{72, 101, 108, 108, 111, 44, 32, 119,
9158 111, 114, 108, 100, 33, 10, 0@};
9159 char ibm1047_hello[]
9160 = @{200, 133, 147, 147, 150, 107, 64, 166,
9161 150, 153, 147, 132, 90, 37, 0@};
9165 printf ("Hello, world!\n");
9169 In this program, @code{ascii_hello} and @code{ibm1047_hello} are arrays
9170 containing the string @samp{Hello, world!} followed by a newline,
9171 encoded in the @sc{ascii} and @sc{ibm1047} character sets.
9173 We compile the program, and invoke the debugger on it:
9176 $ gcc -g charset-test.c -o charset-test
9177 $ gdb -nw charset-test
9178 GNU gdb 2001-12-19-cvs
9179 Copyright 2001 Free Software Foundation, Inc.
9184 We can use the @code{show charset} command to see what character sets
9185 @value{GDBN} is currently using to interpret and display characters and
9189 (@value{GDBP}) show charset
9190 The current host and target character set is `ISO-8859-1'.
9194 For the sake of printing this manual, let's use @sc{ascii} as our
9195 initial character set:
9197 (@value{GDBP}) set charset ASCII
9198 (@value{GDBP}) show charset
9199 The current host and target character set is `ASCII'.
9203 Let's assume that @sc{ascii} is indeed the correct character set for our
9204 host system --- in other words, let's assume that if @value{GDBN} prints
9205 characters using the @sc{ascii} character set, our terminal will display
9206 them properly. Since our current target character set is also
9207 @sc{ascii}, the contents of @code{ascii_hello} print legibly:
9210 (@value{GDBP}) print ascii_hello
9211 $1 = 0x401698 "Hello, world!\n"
9212 (@value{GDBP}) print ascii_hello[0]
9217 @value{GDBN} uses the target character set for character and string
9218 literals you use in expressions:
9221 (@value{GDBP}) print '+'
9226 The @sc{ascii} character set uses the number 43 to encode the @samp{+}
9229 @value{GDBN} relies on the user to tell it which character set the
9230 target program uses. If we print @code{ibm1047_hello} while our target
9231 character set is still @sc{ascii}, we get jibberish:
9234 (@value{GDBP}) print ibm1047_hello
9235 $4 = 0x4016a8 "\310\205\223\223\226k@@\246\226\231\223\204Z%"
9236 (@value{GDBP}) print ibm1047_hello[0]
9241 If we invoke the @code{set target-charset} followed by @key{TAB}@key{TAB},
9242 @value{GDBN} tells us the character sets it supports:
9245 (@value{GDBP}) set target-charset
9246 ASCII EBCDIC-US IBM1047 ISO-8859-1
9247 (@value{GDBP}) set target-charset
9250 We can select @sc{ibm1047} as our target character set, and examine the
9251 program's strings again. Now the @sc{ascii} string is wrong, but
9252 @value{GDBN} translates the contents of @code{ibm1047_hello} from the
9253 target character set, @sc{ibm1047}, to the host character set,
9254 @sc{ascii}, and they display correctly:
9257 (@value{GDBP}) set target-charset IBM1047
9258 (@value{GDBP}) show charset
9259 The current host character set is `ASCII'.
9260 The current target character set is `IBM1047'.
9261 (@value{GDBP}) print ascii_hello
9262 $6 = 0x401698 "\110\145%%?\054\040\167?\162%\144\041\012"
9263 (@value{GDBP}) print ascii_hello[0]
9265 (@value{GDBP}) print ibm1047_hello
9266 $8 = 0x4016a8 "Hello, world!\n"
9267 (@value{GDBP}) print ibm1047_hello[0]
9272 As above, @value{GDBN} uses the target character set for character and
9273 string literals you use in expressions:
9276 (@value{GDBP}) print '+'
9281 The @sc{ibm1047} character set uses the number 78 to encode the @samp{+}
9284 @node Caching Remote Data
9285 @section Caching Data of Remote Targets
9286 @cindex caching data of remote targets
9288 @value{GDBN} caches data exchanged between the debugger and a
9289 remote target (@pxref{Remote Debugging}). Such caching generally improves
9290 performance, because it reduces the overhead of the remote protocol by
9291 bundling memory reads and writes into large chunks. Unfortunately, simply
9292 caching everything would lead to incorrect results, since @value{GDBN}
9293 does not necessarily know anything about volatile values, memory-mapped I/O
9294 addresses, etc. Furthermore, in non-stop mode (@pxref{Non-Stop Mode})
9295 memory can be changed @emph{while} a gdb command is executing.
9296 Therefore, by default, @value{GDBN} only caches data
9297 known to be on the stack@footnote{In non-stop mode, it is moderately
9298 rare for a running thread to modify the stack of a stopped thread
9299 in a way that would interfere with a backtrace, and caching of
9300 stack reads provides a significant speed up of remote backtraces.}.
9301 Other regions of memory can be explicitly marked as
9302 cacheable; see @pxref{Memory Region Attributes}.
9305 @kindex set remotecache
9306 @item set remotecache on
9307 @itemx set remotecache off
9308 This option no longer does anything; it exists for compatibility
9311 @kindex show remotecache
9312 @item show remotecache
9313 Show the current state of the obsolete remotecache flag.
9315 @kindex set stack-cache
9316 @item set stack-cache on
9317 @itemx set stack-cache off
9318 Enable or disable caching of stack accesses. When @code{ON}, use
9319 caching. By default, this option is @code{ON}.
9321 @kindex show stack-cache
9322 @item show stack-cache
9323 Show the current state of data caching for memory accesses.
9326 @item info dcache @r{[}line@r{]}
9327 Print the information about the data cache performance. The
9328 information displayed includes the dcache width and depth, and for
9329 each cache line, its number, address, and how many times it was
9330 referenced. This command is useful for debugging the data cache
9333 If a line number is specified, the contents of that line will be
9336 @item set dcache size @var{size}
9338 @kindex set dcache size
9339 Set maximum number of entries in dcache (dcache depth above).
9341 @item set dcache line-size @var{line-size}
9342 @cindex dcache line-size
9343 @kindex set dcache line-size
9344 Set number of bytes each dcache entry caches (dcache width above).
9345 Must be a power of 2.
9347 @item show dcache size
9348 @kindex show dcache size
9349 Show maximum number of dcache entries. See also @ref{Caching Remote Data, info dcache}.
9351 @item show dcache line-size
9352 @kindex show dcache line-size
9353 Show default size of dcache lines. See also @ref{Caching Remote Data, info dcache}.
9357 @node Searching Memory
9358 @section Search Memory
9359 @cindex searching memory
9361 Memory can be searched for a particular sequence of bytes with the
9362 @code{find} command.
9366 @item find @r{[}/@var{sn}@r{]} @var{start_addr}, +@var{len}, @var{val1} @r{[}, @var{val2}, @dots{}@r{]}
9367 @itemx find @r{[}/@var{sn}@r{]} @var{start_addr}, @var{end_addr}, @var{val1} @r{[}, @var{val2}, @dots{}@r{]}
9368 Search memory for the sequence of bytes specified by @var{val1}, @var{val2},
9369 etc. The search begins at address @var{start_addr} and continues for either
9370 @var{len} bytes or through to @var{end_addr} inclusive.
9373 @var{s} and @var{n} are optional parameters.
9374 They may be specified in either order, apart or together.
9377 @item @var{s}, search query size
9378 The size of each search query value.
9384 halfwords (two bytes)
9388 giant words (eight bytes)
9391 All values are interpreted in the current language.
9392 This means, for example, that if the current source language is C/C@t{++}
9393 then searching for the string ``hello'' includes the trailing '\0'.
9395 If the value size is not specified, it is taken from the
9396 value's type in the current language.
9397 This is useful when one wants to specify the search
9398 pattern as a mixture of types.
9399 Note that this means, for example, that in the case of C-like languages
9400 a search for an untyped 0x42 will search for @samp{(int) 0x42}
9401 which is typically four bytes.
9403 @item @var{n}, maximum number of finds
9404 The maximum number of matches to print. The default is to print all finds.
9407 You can use strings as search values. Quote them with double-quotes
9409 The string value is copied into the search pattern byte by byte,
9410 regardless of the endianness of the target and the size specification.
9412 The address of each match found is printed as well as a count of the
9413 number of matches found.
9415 The address of the last value found is stored in convenience variable
9417 A count of the number of matches is stored in @samp{$numfound}.
9419 For example, if stopped at the @code{printf} in this function:
9425 static char hello[] = "hello-hello";
9426 static struct @{ char c; short s; int i; @}
9427 __attribute__ ((packed)) mixed
9428 = @{ 'c', 0x1234, 0x87654321 @};
9429 printf ("%s\n", hello);
9434 you get during debugging:
9437 (gdb) find &hello[0], +sizeof(hello), "hello"
9438 0x804956d <hello.1620+6>
9440 (gdb) find &hello[0], +sizeof(hello), 'h', 'e', 'l', 'l', 'o'
9441 0x8049567 <hello.1620>
9442 0x804956d <hello.1620+6>
9444 (gdb) find /b1 &hello[0], +sizeof(hello), 'h', 0x65, 'l'
9445 0x8049567 <hello.1620>
9447 (gdb) find &mixed, +sizeof(mixed), (char) 'c', (short) 0x1234, (int) 0x87654321
9448 0x8049560 <mixed.1625>
9450 (gdb) print $numfound
9453 $2 = (void *) 0x8049560
9456 @node Optimized Code
9457 @chapter Debugging Optimized Code
9458 @cindex optimized code, debugging
9459 @cindex debugging optimized code
9461 Almost all compilers support optimization. With optimization
9462 disabled, the compiler generates assembly code that corresponds
9463 directly to your source code, in a simplistic way. As the compiler
9464 applies more powerful optimizations, the generated assembly code
9465 diverges from your original source code. With help from debugging
9466 information generated by the compiler, @value{GDBN} can map from
9467 the running program back to constructs from your original source.
9469 @value{GDBN} is more accurate with optimization disabled. If you
9470 can recompile without optimization, it is easier to follow the
9471 progress of your program during debugging. But, there are many cases
9472 where you may need to debug an optimized version.
9474 When you debug a program compiled with @samp{-g -O}, remember that the
9475 optimizer has rearranged your code; the debugger shows you what is
9476 really there. Do not be too surprised when the execution path does not
9477 exactly match your source file! An extreme example: if you define a
9478 variable, but never use it, @value{GDBN} never sees that
9479 variable---because the compiler optimizes it out of existence.
9481 Some things do not work as well with @samp{-g -O} as with just
9482 @samp{-g}, particularly on machines with instruction scheduling. If in
9483 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
9484 please report it to us as a bug (including a test case!).
9485 @xref{Variables}, for more information about debugging optimized code.
9488 * Inline Functions:: How @value{GDBN} presents inlining
9491 @node Inline Functions
9492 @section Inline Functions
9493 @cindex inline functions, debugging
9495 @dfn{Inlining} is an optimization that inserts a copy of the function
9496 body directly at each call site, instead of jumping to a shared
9497 routine. @value{GDBN} displays inlined functions just like
9498 non-inlined functions. They appear in backtraces. You can view their
9499 arguments and local variables, step into them with @code{step}, skip
9500 them with @code{next}, and escape from them with @code{finish}.
9501 You can check whether a function was inlined by using the
9502 @code{info frame} command.
9504 For @value{GDBN} to support inlined functions, the compiler must
9505 record information about inlining in the debug information ---
9506 @value{NGCC} using the @sc{dwarf 2} format does this, and several
9507 other compilers do also. @value{GDBN} only supports inlined functions
9508 when using @sc{dwarf 2}. Versions of @value{NGCC} before 4.1
9509 do not emit two required attributes (@samp{DW_AT_call_file} and
9510 @samp{DW_AT_call_line}); @value{GDBN} does not display inlined
9511 function calls with earlier versions of @value{NGCC}. It instead
9512 displays the arguments and local variables of inlined functions as
9513 local variables in the caller.
9515 The body of an inlined function is directly included at its call site;
9516 unlike a non-inlined function, there are no instructions devoted to
9517 the call. @value{GDBN} still pretends that the call site and the
9518 start of the inlined function are different instructions. Stepping to
9519 the call site shows the call site, and then stepping again shows
9520 the first line of the inlined function, even though no additional
9521 instructions are executed.
9523 This makes source-level debugging much clearer; you can see both the
9524 context of the call and then the effect of the call. Only stepping by
9525 a single instruction using @code{stepi} or @code{nexti} does not do
9526 this; single instruction steps always show the inlined body.
9528 There are some ways that @value{GDBN} does not pretend that inlined
9529 function calls are the same as normal calls:
9533 You cannot set breakpoints on inlined functions. @value{GDBN}
9534 either reports that there is no symbol with that name, or else sets the
9535 breakpoint only on non-inlined copies of the function. This limitation
9536 will be removed in a future version of @value{GDBN}; until then,
9537 set a breakpoint by line number on the first line of the inlined
9541 Setting breakpoints at the call site of an inlined function may not
9542 work, because the call site does not contain any code. @value{GDBN}
9543 may incorrectly move the breakpoint to the next line of the enclosing
9544 function, after the call. This limitation will be removed in a future
9545 version of @value{GDBN}; until then, set a breakpoint on an earlier line
9546 or inside the inlined function instead.
9549 @value{GDBN} cannot locate the return value of inlined calls after
9550 using the @code{finish} command. This is a limitation of compiler-generated
9551 debugging information; after @code{finish}, you can step to the next line
9552 and print a variable where your program stored the return value.
9558 @chapter C Preprocessor Macros
9560 Some languages, such as C and C@t{++}, provide a way to define and invoke
9561 ``preprocessor macros'' which expand into strings of tokens.
9562 @value{GDBN} can evaluate expressions containing macro invocations, show
9563 the result of macro expansion, and show a macro's definition, including
9564 where it was defined.
9566 You may need to compile your program specially to provide @value{GDBN}
9567 with information about preprocessor macros. Most compilers do not
9568 include macros in their debugging information, even when you compile
9569 with the @option{-g} flag. @xref{Compilation}.
9571 A program may define a macro at one point, remove that definition later,
9572 and then provide a different definition after that. Thus, at different
9573 points in the program, a macro may have different definitions, or have
9574 no definition at all. If there is a current stack frame, @value{GDBN}
9575 uses the macros in scope at that frame's source code line. Otherwise,
9576 @value{GDBN} uses the macros in scope at the current listing location;
9579 Whenever @value{GDBN} evaluates an expression, it always expands any
9580 macro invocations present in the expression. @value{GDBN} also provides
9581 the following commands for working with macros explicitly.
9585 @kindex macro expand
9586 @cindex macro expansion, showing the results of preprocessor
9587 @cindex preprocessor macro expansion, showing the results of
9588 @cindex expanding preprocessor macros
9589 @item macro expand @var{expression}
9590 @itemx macro exp @var{expression}
9591 Show the results of expanding all preprocessor macro invocations in
9592 @var{expression}. Since @value{GDBN} simply expands macros, but does
9593 not parse the result, @var{expression} need not be a valid expression;
9594 it can be any string of tokens.
9597 @item macro expand-once @var{expression}
9598 @itemx macro exp1 @var{expression}
9599 @cindex expand macro once
9600 @i{(This command is not yet implemented.)} Show the results of
9601 expanding those preprocessor macro invocations that appear explicitly in
9602 @var{expression}. Macro invocations appearing in that expansion are
9603 left unchanged. This command allows you to see the effect of a
9604 particular macro more clearly, without being confused by further
9605 expansions. Since @value{GDBN} simply expands macros, but does not
9606 parse the result, @var{expression} need not be a valid expression; it
9607 can be any string of tokens.
9610 @cindex macro definition, showing
9611 @cindex definition of a macro, showing
9612 @cindex macros, from debug info
9613 @item info macro @var{macro}
9614 Show the current definition of the named @var{macro}, and describe the
9615 source location or compiler command-line where that definition was established.
9618 @item info macros @var{linespec}
9619 Show all macro definitions that are in effect at the location specified
9620 by @var{linespec}, and describe the source location or compiler
9621 command-line where those definitions were established.
9623 @kindex info definitions
9624 @item info definitions @var{macro}
9625 Show all definitions of the named @var{macro} that are defined in the current
9626 compilation unit, and describe the source location or compiler command-line
9627 where those definitions were established.
9629 @kindex macro define
9630 @cindex user-defined macros
9631 @cindex defining macros interactively
9632 @cindex macros, user-defined
9633 @item macro define @var{macro} @var{replacement-list}
9634 @itemx macro define @var{macro}(@var{arglist}) @var{replacement-list}
9635 Introduce a definition for a preprocessor macro named @var{macro},
9636 invocations of which are replaced by the tokens given in
9637 @var{replacement-list}. The first form of this command defines an
9638 ``object-like'' macro, which takes no arguments; the second form
9639 defines a ``function-like'' macro, which takes the arguments given in
9642 A definition introduced by this command is in scope in every
9643 expression evaluated in @value{GDBN}, until it is removed with the
9644 @code{macro undef} command, described below. The definition overrides
9645 all definitions for @var{macro} present in the program being debugged,
9646 as well as any previous user-supplied definition.
9649 @item macro undef @var{macro}
9650 Remove any user-supplied definition for the macro named @var{macro}.
9651 This command only affects definitions provided with the @code{macro
9652 define} command, described above; it cannot remove definitions present
9653 in the program being debugged.
9657 List all the macros defined using the @code{macro define} command.
9660 @cindex macros, example of debugging with
9661 Here is a transcript showing the above commands in action. First, we
9662 show our source files:
9670 #define ADD(x) (M + x)
9675 printf ("Hello, world!\n");
9677 printf ("We're so creative.\n");
9679 printf ("Goodbye, world!\n");
9686 Now, we compile the program using the @sc{gnu} C compiler, @value{NGCC}.
9687 We pass the @option{-gdwarf-2} and @option{-g3} flags to ensure the
9688 compiler includes information about preprocessor macros in the debugging
9692 $ gcc -gdwarf-2 -g3 sample.c -o sample
9696 Now, we start @value{GDBN} on our sample program:
9700 GNU gdb 2002-05-06-cvs
9701 Copyright 2002 Free Software Foundation, Inc.
9702 GDB is free software, @dots{}
9706 We can expand macros and examine their definitions, even when the
9707 program is not running. @value{GDBN} uses the current listing position
9708 to decide which macro definitions are in scope:
9711 (@value{GDBP}) list main
9714 5 #define ADD(x) (M + x)
9719 10 printf ("Hello, world!\n");
9721 12 printf ("We're so creative.\n");
9722 (@value{GDBP}) info macro ADD
9723 Defined at /home/jimb/gdb/macros/play/sample.c:5
9724 #define ADD(x) (M + x)
9725 (@value{GDBP}) info macro Q
9726 Defined at /home/jimb/gdb/macros/play/sample.h:1
9727 included at /home/jimb/gdb/macros/play/sample.c:2
9729 (@value{GDBP}) macro expand ADD(1)
9730 expands to: (42 + 1)
9731 (@value{GDBP}) macro expand-once ADD(1)
9732 expands to: once (M + 1)
9736 In the example above, note that @code{macro expand-once} expands only
9737 the macro invocation explicit in the original text --- the invocation of
9738 @code{ADD} --- but does not expand the invocation of the macro @code{M},
9739 which was introduced by @code{ADD}.
9741 Once the program is running, @value{GDBN} uses the macro definitions in
9742 force at the source line of the current stack frame:
9745 (@value{GDBP}) break main
9746 Breakpoint 1 at 0x8048370: file sample.c, line 10.
9748 Starting program: /home/jimb/gdb/macros/play/sample
9750 Breakpoint 1, main () at sample.c:10
9751 10 printf ("Hello, world!\n");
9755 At line 10, the definition of the macro @code{N} at line 9 is in force:
9758 (@value{GDBP}) info macro N
9759 Defined at /home/jimb/gdb/macros/play/sample.c:9
9761 (@value{GDBP}) macro expand N Q M
9763 (@value{GDBP}) print N Q M
9768 As we step over directives that remove @code{N}'s definition, and then
9769 give it a new definition, @value{GDBN} finds the definition (or lack
9770 thereof) in force at each point:
9775 12 printf ("We're so creative.\n");
9776 (@value{GDBP}) info macro N
9777 The symbol `N' has no definition as a C/C++ preprocessor macro
9778 at /home/jimb/gdb/macros/play/sample.c:12
9781 14 printf ("Goodbye, world!\n");
9782 (@value{GDBP}) info macro N
9783 Defined at /home/jimb/gdb/macros/play/sample.c:13
9785 (@value{GDBP}) macro expand N Q M
9786 expands to: 1729 < 42
9787 (@value{GDBP}) print N Q M
9792 In addition to source files, macros can be defined on the compilation command
9793 line using the @option{-D@var{name}=@var{value}} syntax. For macros defined in
9794 such a way, @value{GDBN} displays the location of their definition as line zero
9795 of the source file submitted to the compiler.
9798 (@value{GDBP}) info macro __STDC__
9799 Defined at /home/jimb/gdb/macros/play/sample.c:0
9806 @chapter Tracepoints
9807 @c This chapter is based on the documentation written by Michael
9808 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
9811 In some applications, it is not feasible for the debugger to interrupt
9812 the program's execution long enough for the developer to learn
9813 anything helpful about its behavior. If the program's correctness
9814 depends on its real-time behavior, delays introduced by a debugger
9815 might cause the program to change its behavior drastically, or perhaps
9816 fail, even when the code itself is correct. It is useful to be able
9817 to observe the program's behavior without interrupting it.
9819 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
9820 specify locations in the program, called @dfn{tracepoints}, and
9821 arbitrary expressions to evaluate when those tracepoints are reached.
9822 Later, using the @code{tfind} command, you can examine the values
9823 those expressions had when the program hit the tracepoints. The
9824 expressions may also denote objects in memory---structures or arrays,
9825 for example---whose values @value{GDBN} should record; while visiting
9826 a particular tracepoint, you may inspect those objects as if they were
9827 in memory at that moment. However, because @value{GDBN} records these
9828 values without interacting with you, it can do so quickly and
9829 unobtrusively, hopefully not disturbing the program's behavior.
9831 The tracepoint facility is currently available only for remote
9832 targets. @xref{Targets}. In addition, your remote target must know
9833 how to collect trace data. This functionality is implemented in the
9834 remote stub; however, none of the stubs distributed with @value{GDBN}
9835 support tracepoints as of this writing. The format of the remote
9836 packets used to implement tracepoints are described in @ref{Tracepoint
9839 It is also possible to get trace data from a file, in a manner reminiscent
9840 of corefiles; you specify the filename, and use @code{tfind} to search
9841 through the file. @xref{Trace Files}, for more details.
9843 This chapter describes the tracepoint commands and features.
9847 * Analyze Collected Data::
9848 * Tracepoint Variables::
9852 @node Set Tracepoints
9853 @section Commands to Set Tracepoints
9855 Before running such a @dfn{trace experiment}, an arbitrary number of
9856 tracepoints can be set. A tracepoint is actually a special type of
9857 breakpoint (@pxref{Set Breaks}), so you can manipulate it using
9858 standard breakpoint commands. For instance, as with breakpoints,
9859 tracepoint numbers are successive integers starting from one, and many
9860 of the commands associated with tracepoints take the tracepoint number
9861 as their argument, to identify which tracepoint to work on.
9863 For each tracepoint, you can specify, in advance, some arbitrary set
9864 of data that you want the target to collect in the trace buffer when
9865 it hits that tracepoint. The collected data can include registers,
9866 local variables, or global data. Later, you can use @value{GDBN}
9867 commands to examine the values these data had at the time the
9870 Tracepoints do not support every breakpoint feature. Ignore counts on
9871 tracepoints have no effect, and tracepoints cannot run @value{GDBN}
9872 commands when they are hit. Tracepoints may not be thread-specific
9875 @cindex fast tracepoints
9876 Some targets may support @dfn{fast tracepoints}, which are inserted in
9877 a different way (such as with a jump instead of a trap), that is
9878 faster but possibly restricted in where they may be installed.
9880 @cindex static tracepoints
9881 @cindex markers, static tracepoints
9882 @cindex probing markers, static tracepoints
9883 Regular and fast tracepoints are dynamic tracing facilities, meaning
9884 that they can be used to insert tracepoints at (almost) any location
9885 in the target. Some targets may also support controlling @dfn{static
9886 tracepoints} from @value{GDBN}. With static tracing, a set of
9887 instrumentation points, also known as @dfn{markers}, are embedded in
9888 the target program, and can be activated or deactivated by name or
9889 address. These are usually placed at locations which facilitate
9890 investigating what the target is actually doing. @value{GDBN}'s
9891 support for static tracing includes being able to list instrumentation
9892 points, and attach them with @value{GDBN} defined high level
9893 tracepoints that expose the whole range of convenience of
9894 @value{GDBN}'s tracepoints support. Namely, support for collecting
9895 registers values and values of global or local (to the instrumentation
9896 point) variables; tracepoint conditions and trace state variables.
9897 The act of installing a @value{GDBN} static tracepoint on an
9898 instrumentation point, or marker, is referred to as @dfn{probing} a
9899 static tracepoint marker.
9901 @code{gdbserver} supports tracepoints on some target systems.
9902 @xref{Server,,Tracepoints support in @code{gdbserver}}.
9904 This section describes commands to set tracepoints and associated
9905 conditions and actions.
9908 * Create and Delete Tracepoints::
9909 * Enable and Disable Tracepoints::
9910 * Tracepoint Passcounts::
9911 * Tracepoint Conditions::
9912 * Trace State Variables::
9913 * Tracepoint Actions::
9914 * Listing Tracepoints::
9915 * Listing Static Tracepoint Markers::
9916 * Starting and Stopping Trace Experiments::
9917 * Tracepoint Restrictions::
9920 @node Create and Delete Tracepoints
9921 @subsection Create and Delete Tracepoints
9924 @cindex set tracepoint
9926 @item trace @var{location}
9927 The @code{trace} command is very similar to the @code{break} command.
9928 Its argument @var{location} can be a source line, a function name, or
9929 an address in the target program. @xref{Specify Location}. The
9930 @code{trace} command defines a tracepoint, which is a point in the
9931 target program where the debugger will briefly stop, collect some
9932 data, and then allow the program to continue. Setting a tracepoint or
9933 changing its actions doesn't take effect until the next @code{tstart}
9934 command, and once a trace experiment is running, further changes will
9935 not have any effect until the next trace experiment starts.
9937 Here are some examples of using the @code{trace} command:
9940 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
9942 (@value{GDBP}) @b{trace +2} // 2 lines forward
9944 (@value{GDBP}) @b{trace my_function} // first source line of function
9946 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
9948 (@value{GDBP}) @b{trace *0x2117c4} // an address
9952 You can abbreviate @code{trace} as @code{tr}.
9954 @item trace @var{location} if @var{cond}
9955 Set a tracepoint with condition @var{cond}; evaluate the expression
9956 @var{cond} each time the tracepoint is reached, and collect data only
9957 if the value is nonzero---that is, if @var{cond} evaluates as true.
9958 @xref{Tracepoint Conditions, ,Tracepoint Conditions}, for more
9959 information on tracepoint conditions.
9961 @item ftrace @var{location} [ if @var{cond} ]
9962 @cindex set fast tracepoint
9963 @cindex fast tracepoints, setting
9965 The @code{ftrace} command sets a fast tracepoint. For targets that
9966 support them, fast tracepoints will use a more efficient but possibly
9967 less general technique to trigger data collection, such as a jump
9968 instruction instead of a trap, or some sort of hardware support. It
9969 may not be possible to create a fast tracepoint at the desired
9970 location, in which case the command will exit with an explanatory
9973 @value{GDBN} handles arguments to @code{ftrace} exactly as for
9976 @item strace @var{location} [ if @var{cond} ]
9977 @cindex set static tracepoint
9978 @cindex static tracepoints, setting
9979 @cindex probe static tracepoint marker
9981 The @code{strace} command sets a static tracepoint. For targets that
9982 support it, setting a static tracepoint probes a static
9983 instrumentation point, or marker, found at @var{location}. It may not
9984 be possible to set a static tracepoint at the desired location, in
9985 which case the command will exit with an explanatory message.
9987 @value{GDBN} handles arguments to @code{strace} exactly as for
9988 @code{trace}, with the addition that the user can also specify
9989 @code{-m @var{marker}} as @var{location}. This probes the marker
9990 identified by the @var{marker} string identifier. This identifier
9991 depends on the static tracepoint backend library your program is
9992 using. You can find all the marker identifiers in the @samp{ID} field
9993 of the @code{info static-tracepoint-markers} command output.
9994 @xref{Listing Static Tracepoint Markers,,Listing Static Tracepoint
9995 Markers}. For example, in the following small program using the UST
10001 trace_mark(ust, bar33, "str %s", "FOOBAZ");
10006 the marker id is composed of joining the first two arguments to the
10007 @code{trace_mark} call with a slash, which translates to:
10010 (@value{GDBP}) info static-tracepoint-markers
10011 Cnt Enb ID Address What
10012 1 n ust/bar33 0x0000000000400ddc in main at stexample.c:22
10018 so you may probe the marker above with:
10021 (@value{GDBP}) strace -m ust/bar33
10024 Static tracepoints accept an extra collect action --- @code{collect
10025 $_sdata}. This collects arbitrary user data passed in the probe point
10026 call to the tracing library. In the UST example above, you'll see
10027 that the third argument to @code{trace_mark} is a printf-like format
10028 string. The user data is then the result of running that formating
10029 string against the following arguments. Note that @code{info
10030 static-tracepoint-markers} command output lists that format string in
10031 the @samp{Data:} field.
10033 You can inspect this data when analyzing the trace buffer, by printing
10034 the $_sdata variable like any other variable available to
10035 @value{GDBN}. @xref{Tracepoint Actions,,Tracepoint Action Lists}.
10038 @cindex last tracepoint number
10039 @cindex recent tracepoint number
10040 @cindex tracepoint number
10041 The convenience variable @code{$tpnum} records the tracepoint number
10042 of the most recently set tracepoint.
10044 @kindex delete tracepoint
10045 @cindex tracepoint deletion
10046 @item delete tracepoint @r{[}@var{num}@r{]}
10047 Permanently delete one or more tracepoints. With no argument, the
10048 default is to delete all tracepoints. Note that the regular
10049 @code{delete} command can remove tracepoints also.
10054 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
10056 (@value{GDBP}) @b{delete trace} // remove all tracepoints
10060 You can abbreviate this command as @code{del tr}.
10063 @node Enable and Disable Tracepoints
10064 @subsection Enable and Disable Tracepoints
10066 These commands are deprecated; they are equivalent to plain @code{disable} and @code{enable}.
10069 @kindex disable tracepoint
10070 @item disable tracepoint @r{[}@var{num}@r{]}
10071 Disable tracepoint @var{num}, or all tracepoints if no argument
10072 @var{num} is given. A disabled tracepoint will have no effect during
10073 a trace experiment, but it is not forgotten. You can re-enable
10074 a disabled tracepoint using the @code{enable tracepoint} command.
10075 If the command is issued during a trace experiment and the debug target
10076 has support for disabling tracepoints during a trace experiment, then the
10077 change will be effective immediately. Otherwise, it will be applied to the
10078 next trace experiment.
10080 @kindex enable tracepoint
10081 @item enable tracepoint @r{[}@var{num}@r{]}
10082 Enable tracepoint @var{num}, or all tracepoints. If this command is
10083 issued during a trace experiment and the debug target supports enabling
10084 tracepoints during a trace experiment, then the enabled tracepoints will
10085 become effective immediately. Otherwise, they will become effective the
10086 next time a trace experiment is run.
10089 @node Tracepoint Passcounts
10090 @subsection Tracepoint Passcounts
10094 @cindex tracepoint pass count
10095 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
10096 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
10097 automatically stop a trace experiment. If a tracepoint's passcount is
10098 @var{n}, then the trace experiment will be automatically stopped on
10099 the @var{n}'th time that tracepoint is hit. If the tracepoint number
10100 @var{num} is not specified, the @code{passcount} command sets the
10101 passcount of the most recently defined tracepoint. If no passcount is
10102 given, the trace experiment will run until stopped explicitly by the
10108 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of
10109 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// tracepoint 2}
10111 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
10112 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// most recently defined tracepoint.}
10113 (@value{GDBP}) @b{trace foo}
10114 (@value{GDBP}) @b{pass 3}
10115 (@value{GDBP}) @b{trace bar}
10116 (@value{GDBP}) @b{pass 2}
10117 (@value{GDBP}) @b{trace baz}
10118 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
10119 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// executed 3 times OR when bar has}
10120 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// been executed 2 times}
10121 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// OR when baz has been executed 1 time.}
10125 @node Tracepoint Conditions
10126 @subsection Tracepoint Conditions
10127 @cindex conditional tracepoints
10128 @cindex tracepoint conditions
10130 The simplest sort of tracepoint collects data every time your program
10131 reaches a specified place. You can also specify a @dfn{condition} for
10132 a tracepoint. A condition is just a Boolean expression in your
10133 programming language (@pxref{Expressions, ,Expressions}). A
10134 tracepoint with a condition evaluates the expression each time your
10135 program reaches it, and data collection happens only if the condition
10138 Tracepoint conditions can be specified when a tracepoint is set, by
10139 using @samp{if} in the arguments to the @code{trace} command.
10140 @xref{Create and Delete Tracepoints, ,Setting Tracepoints}. They can
10141 also be set or changed at any time with the @code{condition} command,
10142 just as with breakpoints.
10144 Unlike breakpoint conditions, @value{GDBN} does not actually evaluate
10145 the conditional expression itself. Instead, @value{GDBN} encodes the
10146 expression into an agent expression (@pxref{Agent Expressions})
10147 suitable for execution on the target, independently of @value{GDBN}.
10148 Global variables become raw memory locations, locals become stack
10149 accesses, and so forth.
10151 For instance, suppose you have a function that is usually called
10152 frequently, but should not be called after an error has occurred. You
10153 could use the following tracepoint command to collect data about calls
10154 of that function that happen while the error code is propagating
10155 through the program; an unconditional tracepoint could end up
10156 collecting thousands of useless trace frames that you would have to
10160 (@value{GDBP}) @kbd{trace normal_operation if errcode > 0}
10163 @node Trace State Variables
10164 @subsection Trace State Variables
10165 @cindex trace state variables
10167 A @dfn{trace state variable} is a special type of variable that is
10168 created and managed by target-side code. The syntax is the same as
10169 that for GDB's convenience variables (a string prefixed with ``$''),
10170 but they are stored on the target. They must be created explicitly,
10171 using a @code{tvariable} command. They are always 64-bit signed
10174 Trace state variables are remembered by @value{GDBN}, and downloaded
10175 to the target along with tracepoint information when the trace
10176 experiment starts. There are no intrinsic limits on the number of
10177 trace state variables, beyond memory limitations of the target.
10179 @cindex convenience variables, and trace state variables
10180 Although trace state variables are managed by the target, you can use
10181 them in print commands and expressions as if they were convenience
10182 variables; @value{GDBN} will get the current value from the target
10183 while the trace experiment is running. Trace state variables share
10184 the same namespace as other ``$'' variables, which means that you
10185 cannot have trace state variables with names like @code{$23} or
10186 @code{$pc}, nor can you have a trace state variable and a convenience
10187 variable with the same name.
10191 @item tvariable $@var{name} [ = @var{expression} ]
10193 The @code{tvariable} command creates a new trace state variable named
10194 @code{$@var{name}}, and optionally gives it an initial value of
10195 @var{expression}. @var{expression} is evaluated when this command is
10196 entered; the result will be converted to an integer if possible,
10197 otherwise @value{GDBN} will report an error. A subsequent
10198 @code{tvariable} command specifying the same name does not create a
10199 variable, but instead assigns the supplied initial value to the
10200 existing variable of that name, overwriting any previous initial
10201 value. The default initial value is 0.
10203 @item info tvariables
10204 @kindex info tvariables
10205 List all the trace state variables along with their initial values.
10206 Their current values may also be displayed, if the trace experiment is
10209 @item delete tvariable @r{[} $@var{name} @dots{} @r{]}
10210 @kindex delete tvariable
10211 Delete the given trace state variables, or all of them if no arguments
10216 @node Tracepoint Actions
10217 @subsection Tracepoint Action Lists
10221 @cindex tracepoint actions
10222 @item actions @r{[}@var{num}@r{]}
10223 This command will prompt for a list of actions to be taken when the
10224 tracepoint is hit. If the tracepoint number @var{num} is not
10225 specified, this command sets the actions for the one that was most
10226 recently defined (so that you can define a tracepoint and then say
10227 @code{actions} without bothering about its number). You specify the
10228 actions themselves on the following lines, one action at a time, and
10229 terminate the actions list with a line containing just @code{end}. So
10230 far, the only defined actions are @code{collect}, @code{teval}, and
10231 @code{while-stepping}.
10233 @code{actions} is actually equivalent to @code{commands} (@pxref{Break
10234 Commands, ,Breakpoint Command Lists}), except that only the defined
10235 actions are allowed; any other @value{GDBN} command is rejected.
10237 @cindex remove actions from a tracepoint
10238 To remove all actions from a tracepoint, type @samp{actions @var{num}}
10239 and follow it immediately with @samp{end}.
10242 (@value{GDBP}) @b{collect @var{data}} // collect some data
10244 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times, collect data
10246 (@value{GDBP}) @b{end} // signals the end of actions.
10249 In the following example, the action list begins with @code{collect}
10250 commands indicating the things to be collected when the tracepoint is
10251 hit. Then, in order to single-step and collect additional data
10252 following the tracepoint, a @code{while-stepping} command is used,
10253 followed by the list of things to be collected after each step in a
10254 sequence of single steps. The @code{while-stepping} command is
10255 terminated by its own separate @code{end} command. Lastly, the action
10256 list is terminated by an @code{end} command.
10259 (@value{GDBP}) @b{trace foo}
10260 (@value{GDBP}) @b{actions}
10261 Enter actions for tracepoint 1, one per line:
10264 > while-stepping 12
10265 > collect $pc, arr[i]
10270 @kindex collect @r{(tracepoints)}
10271 @item collect @var{expr1}, @var{expr2}, @dots{}
10272 Collect values of the given expressions when the tracepoint is hit.
10273 This command accepts a comma-separated list of any valid expressions.
10274 In addition to global, static, or local variables, the following
10275 special arguments are supported:
10279 Collect all registers.
10282 Collect all function arguments.
10285 Collect all local variables.
10288 Collect the return address. This is helpful if you want to see more
10292 @vindex $_sdata@r{, collect}
10293 Collect static tracepoint marker specific data. Only available for
10294 static tracepoints. @xref{Tracepoint Actions,,Tracepoint Action
10295 Lists}. On the UST static tracepoints library backend, an
10296 instrumentation point resembles a @code{printf} function call. The
10297 tracing library is able to collect user specified data formatted to a
10298 character string using the format provided by the programmer that
10299 instrumented the program. Other backends have similar mechanisms.
10300 Here's an example of a UST marker call:
10303 const char master_name[] = "$your_name";
10304 trace_mark(channel1, marker1, "hello %s", master_name)
10307 In this case, collecting @code{$_sdata} collects the string
10308 @samp{hello $yourname}. When analyzing the trace buffer, you can
10309 inspect @samp{$_sdata} like any other variable available to
10313 You can give several consecutive @code{collect} commands, each one
10314 with a single argument, or one @code{collect} command with several
10315 arguments separated by commas; the effect is the same.
10317 The command @code{info scope} (@pxref{Symbols, info scope}) is
10318 particularly useful for figuring out what data to collect.
10320 @kindex teval @r{(tracepoints)}
10321 @item teval @var{expr1}, @var{expr2}, @dots{}
10322 Evaluate the given expressions when the tracepoint is hit. This
10323 command accepts a comma-separated list of expressions. The results
10324 are discarded, so this is mainly useful for assigning values to trace
10325 state variables (@pxref{Trace State Variables}) without adding those
10326 values to the trace buffer, as would be the case if the @code{collect}
10329 @kindex while-stepping @r{(tracepoints)}
10330 @item while-stepping @var{n}
10331 Perform @var{n} single-step instruction traces after the tracepoint,
10332 collecting new data after each step. The @code{while-stepping}
10333 command is followed by the list of what to collect while stepping
10334 (followed by its own @code{end} command):
10337 > while-stepping 12
10338 > collect $regs, myglobal
10344 Note that @code{$pc} is not automatically collected by
10345 @code{while-stepping}; you need to explicitly collect that register if
10346 you need it. You may abbreviate @code{while-stepping} as @code{ws} or
10349 @item set default-collect @var{expr1}, @var{expr2}, @dots{}
10350 @kindex set default-collect
10351 @cindex default collection action
10352 This variable is a list of expressions to collect at each tracepoint
10353 hit. It is effectively an additional @code{collect} action prepended
10354 to every tracepoint action list. The expressions are parsed
10355 individually for each tracepoint, so for instance a variable named
10356 @code{xyz} may be interpreted as a global for one tracepoint, and a
10357 local for another, as appropriate to the tracepoint's location.
10359 @item show default-collect
10360 @kindex show default-collect
10361 Show the list of expressions that are collected by default at each
10366 @node Listing Tracepoints
10367 @subsection Listing Tracepoints
10370 @kindex info tracepoints @r{[}@var{n}@dots{}@r{]}
10371 @kindex info tp @r{[}@var{n}@dots{}@r{]}
10372 @cindex information about tracepoints
10373 @item info tracepoints @r{[}@var{num}@dots{}@r{]}
10374 Display information about the tracepoint @var{num}. If you don't
10375 specify a tracepoint number, displays information about all the
10376 tracepoints defined so far. The format is similar to that used for
10377 @code{info breakpoints}; in fact, @code{info tracepoints} is the same
10378 command, simply restricting itself to tracepoints.
10380 A tracepoint's listing may include additional information specific to
10385 its passcount as given by the @code{passcount @var{n}} command
10389 (@value{GDBP}) @b{info trace}
10390 Num Type Disp Enb Address What
10391 1 tracepoint keep y 0x0804ab57 in foo() at main.cxx:7
10393 collect globfoo, $regs
10402 This command can be abbreviated @code{info tp}.
10405 @node Listing Static Tracepoint Markers
10406 @subsection Listing Static Tracepoint Markers
10409 @kindex info static-tracepoint-markers
10410 @cindex information about static tracepoint markers
10411 @item info static-tracepoint-markers
10412 Display information about all static tracepoint markers defined in the
10415 For each marker, the following columns are printed:
10419 An incrementing counter, output to help readability. This is not a
10422 The marker ID, as reported by the target.
10423 @item Enabled or Disabled
10424 Probed markers are tagged with @samp{y}. @samp{n} identifies marks
10425 that are not enabled.
10427 Where the marker is in your program, as a memory address.
10429 Where the marker is in the source for your program, as a file and line
10430 number. If the debug information included in the program does not
10431 allow @value{GDBN} to locate the source of the marker, this column
10432 will be left blank.
10436 In addition, the following information may be printed for each marker:
10440 User data passed to the tracing library by the marker call. In the
10441 UST backend, this is the format string passed as argument to the
10443 @item Static tracepoints probing the marker
10444 The list of static tracepoints attached to the marker.
10448 (@value{GDBP}) info static-tracepoint-markers
10449 Cnt ID Enb Address What
10450 1 ust/bar2 y 0x0000000000400e1a in main at stexample.c:25
10451 Data: number1 %d number2 %d
10452 Probed by static tracepoints: #2
10453 2 ust/bar33 n 0x0000000000400c87 in main at stexample.c:24
10459 @node Starting and Stopping Trace Experiments
10460 @subsection Starting and Stopping Trace Experiments
10464 @cindex start a new trace experiment
10465 @cindex collected data discarded
10467 This command takes no arguments. It starts the trace experiment, and
10468 begins collecting data. This has the side effect of discarding all
10469 the data collected in the trace buffer during the previous trace
10473 @cindex stop a running trace experiment
10475 This command takes no arguments. It ends the trace experiment, and
10476 stops collecting data.
10478 @strong{Note}: a trace experiment and data collection may stop
10479 automatically if any tracepoint's passcount is reached
10480 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
10483 @cindex status of trace data collection
10484 @cindex trace experiment, status of
10486 This command displays the status of the current trace data
10490 Here is an example of the commands we described so far:
10493 (@value{GDBP}) @b{trace gdb_c_test}
10494 (@value{GDBP}) @b{actions}
10495 Enter actions for tracepoint #1, one per line.
10496 > collect $regs,$locals,$args
10497 > while-stepping 11
10501 (@value{GDBP}) @b{tstart}
10502 [time passes @dots{}]
10503 (@value{GDBP}) @b{tstop}
10506 @anchor{disconnected tracing}
10507 @cindex disconnected tracing
10508 You can choose to continue running the trace experiment even if
10509 @value{GDBN} disconnects from the target, voluntarily or
10510 involuntarily. For commands such as @code{detach}, the debugger will
10511 ask what you want to do with the trace. But for unexpected
10512 terminations (@value{GDBN} crash, network outage), it would be
10513 unfortunate to lose hard-won trace data, so the variable
10514 @code{disconnected-tracing} lets you decide whether the trace should
10515 continue running without @value{GDBN}.
10518 @item set disconnected-tracing on
10519 @itemx set disconnected-tracing off
10520 @kindex set disconnected-tracing
10521 Choose whether a tracing run should continue to run if @value{GDBN}
10522 has disconnected from the target. Note that @code{detach} or
10523 @code{quit} will ask you directly what to do about a running trace no
10524 matter what this variable's setting, so the variable is mainly useful
10525 for handling unexpected situations, such as loss of the network.
10527 @item show disconnected-tracing
10528 @kindex show disconnected-tracing
10529 Show the current choice for disconnected tracing.
10533 When you reconnect to the target, the trace experiment may or may not
10534 still be running; it might have filled the trace buffer in the
10535 meantime, or stopped for one of the other reasons. If it is running,
10536 it will continue after reconnection.
10538 Upon reconnection, the target will upload information about the
10539 tracepoints in effect. @value{GDBN} will then compare that
10540 information to the set of tracepoints currently defined, and attempt
10541 to match them up, allowing for the possibility that the numbers may
10542 have changed due to creation and deletion in the meantime. If one of
10543 the target's tracepoints does not match any in @value{GDBN}, the
10544 debugger will create a new tracepoint, so that you have a number with
10545 which to specify that tracepoint. This matching-up process is
10546 necessarily heuristic, and it may result in useless tracepoints being
10547 created; you may simply delete them if they are of no use.
10549 @cindex circular trace buffer
10550 If your target agent supports a @dfn{circular trace buffer}, then you
10551 can run a trace experiment indefinitely without filling the trace
10552 buffer; when space runs out, the agent deletes already-collected trace
10553 frames, oldest first, until there is enough room to continue
10554 collecting. This is especially useful if your tracepoints are being
10555 hit too often, and your trace gets terminated prematurely because the
10556 buffer is full. To ask for a circular trace buffer, simply set
10557 @samp{circular-trace-buffer} to on. You can set this at any time,
10558 including during tracing; if the agent can do it, it will change
10559 buffer handling on the fly, otherwise it will not take effect until
10563 @item set circular-trace-buffer on
10564 @itemx set circular-trace-buffer off
10565 @kindex set circular-trace-buffer
10566 Choose whether a tracing run should use a linear or circular buffer
10567 for trace data. A linear buffer will not lose any trace data, but may
10568 fill up prematurely, while a circular buffer will discard old trace
10569 data, but it will have always room for the latest tracepoint hits.
10571 @item show circular-trace-buffer
10572 @kindex show circular-trace-buffer
10573 Show the current choice for the trace buffer. Note that this may not
10574 match the agent's current buffer handling, nor is it guaranteed to
10575 match the setting that might have been in effect during a past run,
10576 for instance if you are looking at frames from a trace file.
10580 @node Tracepoint Restrictions
10581 @subsection Tracepoint Restrictions
10583 @cindex tracepoint restrictions
10584 There are a number of restrictions on the use of tracepoints. As
10585 described above, tracepoint data gathering occurs on the target
10586 without interaction from @value{GDBN}. Thus the full capabilities of
10587 the debugger are not available during data gathering, and then at data
10588 examination time, you will be limited by only having what was
10589 collected. The following items describe some common problems, but it
10590 is not exhaustive, and you may run into additional difficulties not
10596 Tracepoint expressions are intended to gather objects (lvalues). Thus
10597 the full flexibility of GDB's expression evaluator is not available.
10598 You cannot call functions, cast objects to aggregate types, access
10599 convenience variables or modify values (except by assignment to trace
10600 state variables). Some language features may implicitly call
10601 functions (for instance Objective-C fields with accessors), and therefore
10602 cannot be collected either.
10605 Collection of local variables, either individually or in bulk with
10606 @code{$locals} or @code{$args}, during @code{while-stepping} may
10607 behave erratically. The stepping action may enter a new scope (for
10608 instance by stepping into a function), or the location of the variable
10609 may change (for instance it is loaded into a register). The
10610 tracepoint data recorded uses the location information for the
10611 variables that is correct for the tracepoint location. When the
10612 tracepoint is created, it is not possible, in general, to determine
10613 where the steps of a @code{while-stepping} sequence will advance the
10614 program---particularly if a conditional branch is stepped.
10617 Collection of an incompletely-initialized or partially-destroyed object
10618 may result in something that @value{GDBN} cannot display, or displays
10619 in a misleading way.
10622 When @value{GDBN} displays a pointer to character it automatically
10623 dereferences the pointer to also display characters of the string
10624 being pointed to. However, collecting the pointer during tracing does
10625 not automatically collect the string. You need to explicitly
10626 dereference the pointer and provide size information if you want to
10627 collect not only the pointer, but the memory pointed to. For example,
10628 @code{*ptr@@50} can be used to collect the 50 element array pointed to
10632 It is not possible to collect a complete stack backtrace at a
10633 tracepoint. Instead, you may collect the registers and a few hundred
10634 bytes from the stack pointer with something like @code{*(unsigned char *)$esp@@300}
10635 (adjust to use the name of the actual stack pointer register on your
10636 target architecture, and the amount of stack you wish to capture).
10637 Then the @code{backtrace} command will show a partial backtrace when
10638 using a trace frame. The number of stack frames that can be examined
10639 depends on the sizes of the frames in the collected stack. Note that
10640 if you ask for a block so large that it goes past the bottom of the
10641 stack, the target agent may report an error trying to read from an
10645 If you do not collect registers at a tracepoint, @value{GDBN} can
10646 infer that the value of @code{$pc} must be the same as the address of
10647 the tracepoint and use that when you are looking at a trace frame
10648 for that tracepoint. However, this cannot work if the tracepoint has
10649 multiple locations (for instance if it was set in a function that was
10650 inlined), or if it has a @code{while-stepping} loop. In those cases
10651 @value{GDBN} will warn you that it can't infer @code{$pc}, and default
10656 @node Analyze Collected Data
10657 @section Using the Collected Data
10659 After the tracepoint experiment ends, you use @value{GDBN} commands
10660 for examining the trace data. The basic idea is that each tracepoint
10661 collects a trace @dfn{snapshot} every time it is hit and another
10662 snapshot every time it single-steps. All these snapshots are
10663 consecutively numbered from zero and go into a buffer, and you can
10664 examine them later. The way you examine them is to @dfn{focus} on a
10665 specific trace snapshot. When the remote stub is focused on a trace
10666 snapshot, it will respond to all @value{GDBN} requests for memory and
10667 registers by reading from the buffer which belongs to that snapshot,
10668 rather than from @emph{real} memory or registers of the program being
10669 debugged. This means that @strong{all} @value{GDBN} commands
10670 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
10671 behave as if we were currently debugging the program state as it was
10672 when the tracepoint occurred. Any requests for data that are not in
10673 the buffer will fail.
10676 * tfind:: How to select a trace snapshot
10677 * tdump:: How to display all data for a snapshot
10678 * save tracepoints:: How to save tracepoints for a future run
10682 @subsection @code{tfind @var{n}}
10685 @cindex select trace snapshot
10686 @cindex find trace snapshot
10687 The basic command for selecting a trace snapshot from the buffer is
10688 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
10689 counting from zero. If no argument @var{n} is given, the next
10690 snapshot is selected.
10692 Here are the various forms of using the @code{tfind} command.
10696 Find the first snapshot in the buffer. This is a synonym for
10697 @code{tfind 0} (since 0 is the number of the first snapshot).
10700 Stop debugging trace snapshots, resume @emph{live} debugging.
10703 Same as @samp{tfind none}.
10706 No argument means find the next trace snapshot.
10709 Find the previous trace snapshot before the current one. This permits
10710 retracing earlier steps.
10712 @item tfind tracepoint @var{num}
10713 Find the next snapshot associated with tracepoint @var{num}. Search
10714 proceeds forward from the last examined trace snapshot. If no
10715 argument @var{num} is given, it means find the next snapshot collected
10716 for the same tracepoint as the current snapshot.
10718 @item tfind pc @var{addr}
10719 Find the next snapshot associated with the value @var{addr} of the
10720 program counter. Search proceeds forward from the last examined trace
10721 snapshot. If no argument @var{addr} is given, it means find the next
10722 snapshot with the same value of PC as the current snapshot.
10724 @item tfind outside @var{addr1}, @var{addr2}
10725 Find the next snapshot whose PC is outside the given range of
10726 addresses (exclusive).
10728 @item tfind range @var{addr1}, @var{addr2}
10729 Find the next snapshot whose PC is between @var{addr1} and
10730 @var{addr2} (inclusive).
10732 @item tfind line @r{[}@var{file}:@r{]}@var{n}
10733 Find the next snapshot associated with the source line @var{n}. If
10734 the optional argument @var{file} is given, refer to line @var{n} in
10735 that source file. Search proceeds forward from the last examined
10736 trace snapshot. If no argument @var{n} is given, it means find the
10737 next line other than the one currently being examined; thus saying
10738 @code{tfind line} repeatedly can appear to have the same effect as
10739 stepping from line to line in a @emph{live} debugging session.
10742 The default arguments for the @code{tfind} commands are specifically
10743 designed to make it easy to scan through the trace buffer. For
10744 instance, @code{tfind} with no argument selects the next trace
10745 snapshot, and @code{tfind -} with no argument selects the previous
10746 trace snapshot. So, by giving one @code{tfind} command, and then
10747 simply hitting @key{RET} repeatedly you can examine all the trace
10748 snapshots in order. Or, by saying @code{tfind -} and then hitting
10749 @key{RET} repeatedly you can examine the snapshots in reverse order.
10750 The @code{tfind line} command with no argument selects the snapshot
10751 for the next source line executed. The @code{tfind pc} command with
10752 no argument selects the next snapshot with the same program counter
10753 (PC) as the current frame. The @code{tfind tracepoint} command with
10754 no argument selects the next trace snapshot collected by the same
10755 tracepoint as the current one.
10757 In addition to letting you scan through the trace buffer manually,
10758 these commands make it easy to construct @value{GDBN} scripts that
10759 scan through the trace buffer and print out whatever collected data
10760 you are interested in. Thus, if we want to examine the PC, FP, and SP
10761 registers from each trace frame in the buffer, we can say this:
10764 (@value{GDBP}) @b{tfind start}
10765 (@value{GDBP}) @b{while ($trace_frame != -1)}
10766 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
10767 $trace_frame, $pc, $sp, $fp
10771 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
10772 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
10773 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
10774 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
10775 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
10776 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
10777 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
10778 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
10779 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
10780 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
10781 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
10784 Or, if we want to examine the variable @code{X} at each source line in
10788 (@value{GDBP}) @b{tfind start}
10789 (@value{GDBP}) @b{while ($trace_frame != -1)}
10790 > printf "Frame %d, X == %d\n", $trace_frame, X
10800 @subsection @code{tdump}
10802 @cindex dump all data collected at tracepoint
10803 @cindex tracepoint data, display
10805 This command takes no arguments. It prints all the data collected at
10806 the current trace snapshot.
10809 (@value{GDBP}) @b{trace 444}
10810 (@value{GDBP}) @b{actions}
10811 Enter actions for tracepoint #2, one per line:
10812 > collect $regs, $locals, $args, gdb_long_test
10815 (@value{GDBP}) @b{tstart}
10817 (@value{GDBP}) @b{tfind line 444}
10818 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
10820 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
10822 (@value{GDBP}) @b{tdump}
10823 Data collected at tracepoint 2, trace frame 1:
10824 d0 0xc4aa0085 -995491707
10828 d4 0x71aea3d 119204413
10831 d7 0x380035 3670069
10832 a0 0x19e24a 1696330
10833 a1 0x3000668 50333288
10835 a3 0x322000 3284992
10836 a4 0x3000698 50333336
10837 a5 0x1ad3cc 1758156
10838 fp 0x30bf3c 0x30bf3c
10839 sp 0x30bf34 0x30bf34
10841 pc 0x20b2c8 0x20b2c8
10845 p = 0x20e5b4 "gdb-test"
10852 gdb_long_test = 17 '\021'
10857 @code{tdump} works by scanning the tracepoint's current collection
10858 actions and printing the value of each expression listed. So
10859 @code{tdump} can fail, if after a run, you change the tracepoint's
10860 actions to mention variables that were not collected during the run.
10862 Also, for tracepoints with @code{while-stepping} loops, @code{tdump}
10863 uses the collected value of @code{$pc} to distinguish between trace
10864 frames that were collected at the tracepoint hit, and frames that were
10865 collected while stepping. This allows it to correctly choose whether
10866 to display the basic list of collections, or the collections from the
10867 body of the while-stepping loop. However, if @code{$pc} was not collected,
10868 then @code{tdump} will always attempt to dump using the basic collection
10869 list, and may fail if a while-stepping frame does not include all the
10870 same data that is collected at the tracepoint hit.
10871 @c This is getting pretty arcane, example would be good.
10873 @node save tracepoints
10874 @subsection @code{save tracepoints @var{filename}}
10875 @kindex save tracepoints
10876 @kindex save-tracepoints
10877 @cindex save tracepoints for future sessions
10879 This command saves all current tracepoint definitions together with
10880 their actions and passcounts, into a file @file{@var{filename}}
10881 suitable for use in a later debugging session. To read the saved
10882 tracepoint definitions, use the @code{source} command (@pxref{Command
10883 Files}). The @w{@code{save-tracepoints}} command is a deprecated
10884 alias for @w{@code{save tracepoints}}
10886 @node Tracepoint Variables
10887 @section Convenience Variables for Tracepoints
10888 @cindex tracepoint variables
10889 @cindex convenience variables for tracepoints
10892 @vindex $trace_frame
10893 @item (int) $trace_frame
10894 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
10895 snapshot is selected.
10897 @vindex $tracepoint
10898 @item (int) $tracepoint
10899 The tracepoint for the current trace snapshot.
10901 @vindex $trace_line
10902 @item (int) $trace_line
10903 The line number for the current trace snapshot.
10905 @vindex $trace_file
10906 @item (char []) $trace_file
10907 The source file for the current trace snapshot.
10909 @vindex $trace_func
10910 @item (char []) $trace_func
10911 The name of the function containing @code{$tracepoint}.
10914 Note: @code{$trace_file} is not suitable for use in @code{printf},
10915 use @code{output} instead.
10917 Here's a simple example of using these convenience variables for
10918 stepping through all the trace snapshots and printing some of their
10919 data. Note that these are not the same as trace state variables,
10920 which are managed by the target.
10923 (@value{GDBP}) @b{tfind start}
10925 (@value{GDBP}) @b{while $trace_frame != -1}
10926 > output $trace_file
10927 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
10933 @section Using Trace Files
10934 @cindex trace files
10936 In some situations, the target running a trace experiment may no
10937 longer be available; perhaps it crashed, or the hardware was needed
10938 for a different activity. To handle these cases, you can arrange to
10939 dump the trace data into a file, and later use that file as a source
10940 of trace data, via the @code{target tfile} command.
10945 @item tsave [ -r ] @var{filename}
10946 Save the trace data to @var{filename}. By default, this command
10947 assumes that @var{filename} refers to the host filesystem, so if
10948 necessary @value{GDBN} will copy raw trace data up from the target and
10949 then save it. If the target supports it, you can also supply the
10950 optional argument @code{-r} (``remote'') to direct the target to save
10951 the data directly into @var{filename} in its own filesystem, which may be
10952 more efficient if the trace buffer is very large. (Note, however, that
10953 @code{target tfile} can only read from files accessible to the host.)
10955 @kindex target tfile
10957 @item target tfile @var{filename}
10958 Use the file named @var{filename} as a source of trace data. Commands
10959 that examine data work as they do with a live target, but it is not
10960 possible to run any new trace experiments. @code{tstatus} will report
10961 the state of the trace run at the moment the data was saved, as well
10962 as the current trace frame you are examining. @var{filename} must be
10963 on a filesystem accessible to the host.
10968 @chapter Debugging Programs That Use Overlays
10971 If your program is too large to fit completely in your target system's
10972 memory, you can sometimes use @dfn{overlays} to work around this
10973 problem. @value{GDBN} provides some support for debugging programs that
10977 * How Overlays Work:: A general explanation of overlays.
10978 * Overlay Commands:: Managing overlays in @value{GDBN}.
10979 * Automatic Overlay Debugging:: @value{GDBN} can find out which overlays are
10980 mapped by asking the inferior.
10981 * Overlay Sample Program:: A sample program using overlays.
10984 @node How Overlays Work
10985 @section How Overlays Work
10986 @cindex mapped overlays
10987 @cindex unmapped overlays
10988 @cindex load address, overlay's
10989 @cindex mapped address
10990 @cindex overlay area
10992 Suppose you have a computer whose instruction address space is only 64
10993 kilobytes long, but which has much more memory which can be accessed by
10994 other means: special instructions, segment registers, or memory
10995 management hardware, for example. Suppose further that you want to
10996 adapt a program which is larger than 64 kilobytes to run on this system.
10998 One solution is to identify modules of your program which are relatively
10999 independent, and need not call each other directly; call these modules
11000 @dfn{overlays}. Separate the overlays from the main program, and place
11001 their machine code in the larger memory. Place your main program in
11002 instruction memory, but leave at least enough space there to hold the
11003 largest overlay as well.
11005 Now, to call a function located in an overlay, you must first copy that
11006 overlay's machine code from the large memory into the space set aside
11007 for it in the instruction memory, and then jump to its entry point
11010 @c NB: In the below the mapped area's size is greater or equal to the
11011 @c size of all overlays. This is intentional to remind the developer
11012 @c that overlays don't necessarily need to be the same size.
11016 Data Instruction Larger
11017 Address Space Address Space Address Space
11018 +-----------+ +-----------+ +-----------+
11020 +-----------+ +-----------+ +-----------+<-- overlay 1
11021 | program | | main | .----| overlay 1 | load address
11022 | variables | | program | | +-----------+
11023 | and heap | | | | | |
11024 +-----------+ | | | +-----------+<-- overlay 2
11025 | | +-----------+ | | | load address
11026 +-----------+ | | | .-| overlay 2 |
11028 mapped --->+-----------+ | | +-----------+
11029 address | | | | | |
11030 | overlay | <-' | | |
11031 | area | <---' +-----------+<-- overlay 3
11032 | | <---. | | load address
11033 +-----------+ `--| overlay 3 |
11040 @anchor{A code overlay}A code overlay
11044 The diagram (@pxref{A code overlay}) shows a system with separate data
11045 and instruction address spaces. To map an overlay, the program copies
11046 its code from the larger address space to the instruction address space.
11047 Since the overlays shown here all use the same mapped address, only one
11048 may be mapped at a time. For a system with a single address space for
11049 data and instructions, the diagram would be similar, except that the
11050 program variables and heap would share an address space with the main
11051 program and the overlay area.
11053 An overlay loaded into instruction memory and ready for use is called a
11054 @dfn{mapped} overlay; its @dfn{mapped address} is its address in the
11055 instruction memory. An overlay not present (or only partially present)
11056 in instruction memory is called @dfn{unmapped}; its @dfn{load address}
11057 is its address in the larger memory. The mapped address is also called
11058 the @dfn{virtual memory address}, or @dfn{VMA}; the load address is also
11059 called the @dfn{load memory address}, or @dfn{LMA}.
11061 Unfortunately, overlays are not a completely transparent way to adapt a
11062 program to limited instruction memory. They introduce a new set of
11063 global constraints you must keep in mind as you design your program:
11068 Before calling or returning to a function in an overlay, your program
11069 must make sure that overlay is actually mapped. Otherwise, the call or
11070 return will transfer control to the right address, but in the wrong
11071 overlay, and your program will probably crash.
11074 If the process of mapping an overlay is expensive on your system, you
11075 will need to choose your overlays carefully to minimize their effect on
11076 your program's performance.
11079 The executable file you load onto your system must contain each
11080 overlay's instructions, appearing at the overlay's load address, not its
11081 mapped address. However, each overlay's instructions must be relocated
11082 and its symbols defined as if the overlay were at its mapped address.
11083 You can use GNU linker scripts to specify different load and relocation
11084 addresses for pieces of your program; see @ref{Overlay Description,,,
11085 ld.info, Using ld: the GNU linker}.
11088 The procedure for loading executable files onto your system must be able
11089 to load their contents into the larger address space as well as the
11090 instruction and data spaces.
11094 The overlay system described above is rather simple, and could be
11095 improved in many ways:
11100 If your system has suitable bank switch registers or memory management
11101 hardware, you could use those facilities to make an overlay's load area
11102 contents simply appear at their mapped address in instruction space.
11103 This would probably be faster than copying the overlay to its mapped
11104 area in the usual way.
11107 If your overlays are small enough, you could set aside more than one
11108 overlay area, and have more than one overlay mapped at a time.
11111 You can use overlays to manage data, as well as instructions. In
11112 general, data overlays are even less transparent to your design than
11113 code overlays: whereas code overlays only require care when you call or
11114 return to functions, data overlays require care every time you access
11115 the data. Also, if you change the contents of a data overlay, you
11116 must copy its contents back out to its load address before you can copy a
11117 different data overlay into the same mapped area.
11122 @node Overlay Commands
11123 @section Overlay Commands
11125 To use @value{GDBN}'s overlay support, each overlay in your program must
11126 correspond to a separate section of the executable file. The section's
11127 virtual memory address and load memory address must be the overlay's
11128 mapped and load addresses. Identifying overlays with sections allows
11129 @value{GDBN} to determine the appropriate address of a function or
11130 variable, depending on whether the overlay is mapped or not.
11132 @value{GDBN}'s overlay commands all start with the word @code{overlay};
11133 you can abbreviate this as @code{ov} or @code{ovly}. The commands are:
11138 Disable @value{GDBN}'s overlay support. When overlay support is
11139 disabled, @value{GDBN} assumes that all functions and variables are
11140 always present at their mapped addresses. By default, @value{GDBN}'s
11141 overlay support is disabled.
11143 @item overlay manual
11144 @cindex manual overlay debugging
11145 Enable @dfn{manual} overlay debugging. In this mode, @value{GDBN}
11146 relies on you to tell it which overlays are mapped, and which are not,
11147 using the @code{overlay map-overlay} and @code{overlay unmap-overlay}
11148 commands described below.
11150 @item overlay map-overlay @var{overlay}
11151 @itemx overlay map @var{overlay}
11152 @cindex map an overlay
11153 Tell @value{GDBN} that @var{overlay} is now mapped; @var{overlay} must
11154 be the name of the object file section containing the overlay. When an
11155 overlay is mapped, @value{GDBN} assumes it can find the overlay's
11156 functions and variables at their mapped addresses. @value{GDBN} assumes
11157 that any other overlays whose mapped ranges overlap that of
11158 @var{overlay} are now unmapped.
11160 @item overlay unmap-overlay @var{overlay}
11161 @itemx overlay unmap @var{overlay}
11162 @cindex unmap an overlay
11163 Tell @value{GDBN} that @var{overlay} is no longer mapped; @var{overlay}
11164 must be the name of the object file section containing the overlay.
11165 When an overlay is unmapped, @value{GDBN} assumes it can find the
11166 overlay's functions and variables at their load addresses.
11169 Enable @dfn{automatic} overlay debugging. In this mode, @value{GDBN}
11170 consults a data structure the overlay manager maintains in the inferior
11171 to see which overlays are mapped. For details, see @ref{Automatic
11172 Overlay Debugging}.
11174 @item overlay load-target
11175 @itemx overlay load
11176 @cindex reloading the overlay table
11177 Re-read the overlay table from the inferior. Normally, @value{GDBN}
11178 re-reads the table @value{GDBN} automatically each time the inferior
11179 stops, so this command should only be necessary if you have changed the
11180 overlay mapping yourself using @value{GDBN}. This command is only
11181 useful when using automatic overlay debugging.
11183 @item overlay list-overlays
11184 @itemx overlay list
11185 @cindex listing mapped overlays
11186 Display a list of the overlays currently mapped, along with their mapped
11187 addresses, load addresses, and sizes.
11191 Normally, when @value{GDBN} prints a code address, it includes the name
11192 of the function the address falls in:
11195 (@value{GDBP}) print main
11196 $3 = @{int ()@} 0x11a0 <main>
11199 When overlay debugging is enabled, @value{GDBN} recognizes code in
11200 unmapped overlays, and prints the names of unmapped functions with
11201 asterisks around them. For example, if @code{foo} is a function in an
11202 unmapped overlay, @value{GDBN} prints it this way:
11205 (@value{GDBP}) overlay list
11206 No sections are mapped.
11207 (@value{GDBP}) print foo
11208 $5 = @{int (int)@} 0x100000 <*foo*>
11211 When @code{foo}'s overlay is mapped, @value{GDBN} prints the function's
11215 (@value{GDBP}) overlay list
11216 Section .ov.foo.text, loaded at 0x100000 - 0x100034,
11217 mapped at 0x1016 - 0x104a
11218 (@value{GDBP}) print foo
11219 $6 = @{int (int)@} 0x1016 <foo>
11222 When overlay debugging is enabled, @value{GDBN} can find the correct
11223 address for functions and variables in an overlay, whether or not the
11224 overlay is mapped. This allows most @value{GDBN} commands, like
11225 @code{break} and @code{disassemble}, to work normally, even on unmapped
11226 code. However, @value{GDBN}'s breakpoint support has some limitations:
11230 @cindex breakpoints in overlays
11231 @cindex overlays, setting breakpoints in
11232 You can set breakpoints in functions in unmapped overlays, as long as
11233 @value{GDBN} can write to the overlay at its load address.
11235 @value{GDBN} can not set hardware or simulator-based breakpoints in
11236 unmapped overlays. However, if you set a breakpoint at the end of your
11237 overlay manager (and tell @value{GDBN} which overlays are now mapped, if
11238 you are using manual overlay management), @value{GDBN} will re-set its
11239 breakpoints properly.
11243 @node Automatic Overlay Debugging
11244 @section Automatic Overlay Debugging
11245 @cindex automatic overlay debugging
11247 @value{GDBN} can automatically track which overlays are mapped and which
11248 are not, given some simple co-operation from the overlay manager in the
11249 inferior. If you enable automatic overlay debugging with the
11250 @code{overlay auto} command (@pxref{Overlay Commands}), @value{GDBN}
11251 looks in the inferior's memory for certain variables describing the
11252 current state of the overlays.
11254 Here are the variables your overlay manager must define to support
11255 @value{GDBN}'s automatic overlay debugging:
11259 @item @code{_ovly_table}:
11260 This variable must be an array of the following structures:
11265 /* The overlay's mapped address. */
11268 /* The size of the overlay, in bytes. */
11269 unsigned long size;
11271 /* The overlay's load address. */
11274 /* Non-zero if the overlay is currently mapped;
11276 unsigned long mapped;
11280 @item @code{_novlys}:
11281 This variable must be a four-byte signed integer, holding the total
11282 number of elements in @code{_ovly_table}.
11286 To decide whether a particular overlay is mapped or not, @value{GDBN}
11287 looks for an entry in @w{@code{_ovly_table}} whose @code{vma} and
11288 @code{lma} members equal the VMA and LMA of the overlay's section in the
11289 executable file. When @value{GDBN} finds a matching entry, it consults
11290 the entry's @code{mapped} member to determine whether the overlay is
11293 In addition, your overlay manager may define a function called
11294 @code{_ovly_debug_event}. If this function is defined, @value{GDBN}
11295 will silently set a breakpoint there. If the overlay manager then
11296 calls this function whenever it has changed the overlay table, this
11297 will enable @value{GDBN} to accurately keep track of which overlays
11298 are in program memory, and update any breakpoints that may be set
11299 in overlays. This will allow breakpoints to work even if the
11300 overlays are kept in ROM or other non-writable memory while they
11301 are not being executed.
11303 @node Overlay Sample Program
11304 @section Overlay Sample Program
11305 @cindex overlay example program
11307 When linking a program which uses overlays, you must place the overlays
11308 at their load addresses, while relocating them to run at their mapped
11309 addresses. To do this, you must write a linker script (@pxref{Overlay
11310 Description,,, ld.info, Using ld: the GNU linker}). Unfortunately,
11311 since linker scripts are specific to a particular host system, target
11312 architecture, and target memory layout, this manual cannot provide
11313 portable sample code demonstrating @value{GDBN}'s overlay support.
11315 However, the @value{GDBN} source distribution does contain an overlaid
11316 program, with linker scripts for a few systems, as part of its test
11317 suite. The program consists of the following files from
11318 @file{gdb/testsuite/gdb.base}:
11322 The main program file.
11324 A simple overlay manager, used by @file{overlays.c}.
11329 Overlay modules, loaded and used by @file{overlays.c}.
11332 Linker scripts for linking the test program on the @code{d10v-elf}
11333 and @code{m32r-elf} targets.
11336 You can build the test program using the @code{d10v-elf} GCC
11337 cross-compiler like this:
11340 $ d10v-elf-gcc -g -c overlays.c
11341 $ d10v-elf-gcc -g -c ovlymgr.c
11342 $ d10v-elf-gcc -g -c foo.c
11343 $ d10v-elf-gcc -g -c bar.c
11344 $ d10v-elf-gcc -g -c baz.c
11345 $ d10v-elf-gcc -g -c grbx.c
11346 $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
11347 baz.o grbx.o -Wl,-Td10v.ld -o overlays
11350 The build process is identical for any other architecture, except that
11351 you must substitute the appropriate compiler and linker script for the
11352 target system for @code{d10v-elf-gcc} and @code{d10v.ld}.
11356 @chapter Using @value{GDBN} with Different Languages
11359 Although programming languages generally have common aspects, they are
11360 rarely expressed in the same manner. For instance, in ANSI C,
11361 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
11362 Modula-2, it is accomplished by @code{p^}. Values can also be
11363 represented (and displayed) differently. Hex numbers in C appear as
11364 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
11366 @cindex working language
11367 Language-specific information is built into @value{GDBN} for some languages,
11368 allowing you to express operations like the above in your program's
11369 native language, and allowing @value{GDBN} to output values in a manner
11370 consistent with the syntax of your program's native language. The
11371 language you use to build expressions is called the @dfn{working
11375 * Setting:: Switching between source languages
11376 * Show:: Displaying the language
11377 * Checks:: Type and range checks
11378 * Supported Languages:: Supported languages
11379 * Unsupported Languages:: Unsupported languages
11383 @section Switching Between Source Languages
11385 There are two ways to control the working language---either have @value{GDBN}
11386 set it automatically, or select it manually yourself. You can use the
11387 @code{set language} command for either purpose. On startup, @value{GDBN}
11388 defaults to setting the language automatically. The working language is
11389 used to determine how expressions you type are interpreted, how values
11392 In addition to the working language, every source file that
11393 @value{GDBN} knows about has its own working language. For some object
11394 file formats, the compiler might indicate which language a particular
11395 source file is in. However, most of the time @value{GDBN} infers the
11396 language from the name of the file. The language of a source file
11397 controls whether C@t{++} names are demangled---this way @code{backtrace} can
11398 show each frame appropriately for its own language. There is no way to
11399 set the language of a source file from within @value{GDBN}, but you can
11400 set the language associated with a filename extension. @xref{Show, ,
11401 Displaying the Language}.
11403 This is most commonly a problem when you use a program, such
11404 as @code{cfront} or @code{f2c}, that generates C but is written in
11405 another language. In that case, make the
11406 program use @code{#line} directives in its C output; that way
11407 @value{GDBN} will know the correct language of the source code of the original
11408 program, and will display that source code, not the generated C code.
11411 * Filenames:: Filename extensions and languages.
11412 * Manually:: Setting the working language manually
11413 * Automatically:: Having @value{GDBN} infer the source language
11417 @subsection List of Filename Extensions and Languages
11419 If a source file name ends in one of the following extensions, then
11420 @value{GDBN} infers that its language is the one indicated.
11438 C@t{++} source file
11444 Objective-C source file
11448 Fortran source file
11451 Modula-2 source file
11455 Assembler source file. This actually behaves almost like C, but
11456 @value{GDBN} does not skip over function prologues when stepping.
11459 In addition, you may set the language associated with a filename
11460 extension. @xref{Show, , Displaying the Language}.
11463 @subsection Setting the Working Language
11465 If you allow @value{GDBN} to set the language automatically,
11466 expressions are interpreted the same way in your debugging session and
11469 @kindex set language
11470 If you wish, you may set the language manually. To do this, issue the
11471 command @samp{set language @var{lang}}, where @var{lang} is the name of
11472 a language, such as
11473 @code{c} or @code{modula-2}.
11474 For a list of the supported languages, type @samp{set language}.
11476 Setting the language manually prevents @value{GDBN} from updating the working
11477 language automatically. This can lead to confusion if you try
11478 to debug a program when the working language is not the same as the
11479 source language, when an expression is acceptable to both
11480 languages---but means different things. For instance, if the current
11481 source file were written in C, and @value{GDBN} was parsing Modula-2, a
11489 might not have the effect you intended. In C, this means to add
11490 @code{b} and @code{c} and place the result in @code{a}. The result
11491 printed would be the value of @code{a}. In Modula-2, this means to compare
11492 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
11494 @node Automatically
11495 @subsection Having @value{GDBN} Infer the Source Language
11497 To have @value{GDBN} set the working language automatically, use
11498 @samp{set language local} or @samp{set language auto}. @value{GDBN}
11499 then infers the working language. That is, when your program stops in a
11500 frame (usually by encountering a breakpoint), @value{GDBN} sets the
11501 working language to the language recorded for the function in that
11502 frame. If the language for a frame is unknown (that is, if the function
11503 or block corresponding to the frame was defined in a source file that
11504 does not have a recognized extension), the current working language is
11505 not changed, and @value{GDBN} issues a warning.
11507 This may not seem necessary for most programs, which are written
11508 entirely in one source language. However, program modules and libraries
11509 written in one source language can be used by a main program written in
11510 a different source language. Using @samp{set language auto} in this
11511 case frees you from having to set the working language manually.
11514 @section Displaying the Language
11516 The following commands help you find out which language is the
11517 working language, and also what language source files were written in.
11520 @item show language
11521 @kindex show language
11522 Display the current working language. This is the
11523 language you can use with commands such as @code{print} to
11524 build and compute expressions that may involve variables in your program.
11527 @kindex info frame@r{, show the source language}
11528 Display the source language for this frame. This language becomes the
11529 working language if you use an identifier from this frame.
11530 @xref{Frame Info, ,Information about a Frame}, to identify the other
11531 information listed here.
11534 @kindex info source@r{, show the source language}
11535 Display the source language of this source file.
11536 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
11537 information listed here.
11540 In unusual circumstances, you may have source files with extensions
11541 not in the standard list. You can then set the extension associated
11542 with a language explicitly:
11545 @item set extension-language @var{ext} @var{language}
11546 @kindex set extension-language
11547 Tell @value{GDBN} that source files with extension @var{ext} are to be
11548 assumed as written in the source language @var{language}.
11550 @item info extensions
11551 @kindex info extensions
11552 List all the filename extensions and the associated languages.
11556 @section Type and Range Checking
11559 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
11560 checking are included, but they do not yet have any effect. This
11561 section documents the intended facilities.
11563 @c FIXME remove warning when type/range code added
11565 Some languages are designed to guard you against making seemingly common
11566 errors through a series of compile- and run-time checks. These include
11567 checking the type of arguments to functions and operators, and making
11568 sure mathematical overflows are caught at run time. Checks such as
11569 these help to ensure a program's correctness once it has been compiled
11570 by eliminating type mismatches, and providing active checks for range
11571 errors when your program is running.
11573 @value{GDBN} can check for conditions like the above if you wish.
11574 Although @value{GDBN} does not check the statements in your program,
11575 it can check expressions entered directly into @value{GDBN} for
11576 evaluation via the @code{print} command, for example. As with the
11577 working language, @value{GDBN} can also decide whether or not to check
11578 automatically based on your program's source language.
11579 @xref{Supported Languages, ,Supported Languages}, for the default
11580 settings of supported languages.
11583 * Type Checking:: An overview of type checking
11584 * Range Checking:: An overview of range checking
11587 @cindex type checking
11588 @cindex checks, type
11589 @node Type Checking
11590 @subsection An Overview of Type Checking
11592 Some languages, such as Modula-2, are strongly typed, meaning that the
11593 arguments to operators and functions have to be of the correct type,
11594 otherwise an error occurs. These checks prevent type mismatch
11595 errors from ever causing any run-time problems. For example,
11603 The second example fails because the @code{CARDINAL} 1 is not
11604 type-compatible with the @code{REAL} 2.3.
11606 For the expressions you use in @value{GDBN} commands, you can tell the
11607 @value{GDBN} type checker to skip checking;
11608 to treat any mismatches as errors and abandon the expression;
11609 or to only issue warnings when type mismatches occur,
11610 but evaluate the expression anyway. When you choose the last of
11611 these, @value{GDBN} evaluates expressions like the second example above, but
11612 also issues a warning.
11614 Even if you turn type checking off, there may be other reasons
11615 related to type that prevent @value{GDBN} from evaluating an expression.
11616 For instance, @value{GDBN} does not know how to add an @code{int} and
11617 a @code{struct foo}. These particular type errors have nothing to do
11618 with the language in use, and usually arise from expressions, such as
11619 the one described above, which make little sense to evaluate anyway.
11621 Each language defines to what degree it is strict about type. For
11622 instance, both Modula-2 and C require the arguments to arithmetical
11623 operators to be numbers. In C, enumerated types and pointers can be
11624 represented as numbers, so that they are valid arguments to mathematical
11625 operators. @xref{Supported Languages, ,Supported Languages}, for further
11626 details on specific languages.
11628 @value{GDBN} provides some additional commands for controlling the type checker:
11630 @kindex set check type
11631 @kindex show check type
11633 @item set check type auto
11634 Set type checking on or off based on the current working language.
11635 @xref{Supported Languages, ,Supported Languages}, for the default settings for
11638 @item set check type on
11639 @itemx set check type off
11640 Set type checking on or off, overriding the default setting for the
11641 current working language. Issue a warning if the setting does not
11642 match the language default. If any type mismatches occur in
11643 evaluating an expression while type checking is on, @value{GDBN} prints a
11644 message and aborts evaluation of the expression.
11646 @item set check type warn
11647 Cause the type checker to issue warnings, but to always attempt to
11648 evaluate the expression. Evaluating the expression may still
11649 be impossible for other reasons. For example, @value{GDBN} cannot add
11650 numbers and structures.
11653 Show the current setting of the type checker, and whether or not @value{GDBN}
11654 is setting it automatically.
11657 @cindex range checking
11658 @cindex checks, range
11659 @node Range Checking
11660 @subsection An Overview of Range Checking
11662 In some languages (such as Modula-2), it is an error to exceed the
11663 bounds of a type; this is enforced with run-time checks. Such range
11664 checking is meant to ensure program correctness by making sure
11665 computations do not overflow, or indices on an array element access do
11666 not exceed the bounds of the array.
11668 For expressions you use in @value{GDBN} commands, you can tell
11669 @value{GDBN} to treat range errors in one of three ways: ignore them,
11670 always treat them as errors and abandon the expression, or issue
11671 warnings but evaluate the expression anyway.
11673 A range error can result from numerical overflow, from exceeding an
11674 array index bound, or when you type a constant that is not a member
11675 of any type. Some languages, however, do not treat overflows as an
11676 error. In many implementations of C, mathematical overflow causes the
11677 result to ``wrap around'' to lower values---for example, if @var{m} is
11678 the largest integer value, and @var{s} is the smallest, then
11681 @var{m} + 1 @result{} @var{s}
11684 This, too, is specific to individual languages, and in some cases
11685 specific to individual compilers or machines. @xref{Supported Languages, ,
11686 Supported Languages}, for further details on specific languages.
11688 @value{GDBN} provides some additional commands for controlling the range checker:
11690 @kindex set check range
11691 @kindex show check range
11693 @item set check range auto
11694 Set range checking on or off based on the current working language.
11695 @xref{Supported Languages, ,Supported Languages}, for the default settings for
11698 @item set check range on
11699 @itemx set check range off
11700 Set range checking on or off, overriding the default setting for the
11701 current working language. A warning is issued if the setting does not
11702 match the language default. If a range error occurs and range checking is on,
11703 then a message is printed and evaluation of the expression is aborted.
11705 @item set check range warn
11706 Output messages when the @value{GDBN} range checker detects a range error,
11707 but attempt to evaluate the expression anyway. Evaluating the
11708 expression may still be impossible for other reasons, such as accessing
11709 memory that the process does not own (a typical example from many Unix
11713 Show the current setting of the range checker, and whether or not it is
11714 being set automatically by @value{GDBN}.
11717 @node Supported Languages
11718 @section Supported Languages
11720 @value{GDBN} supports C, C@t{++}, D, Objective-C, Fortran, Java, OpenCL C, Pascal,
11721 assembly, Modula-2, and Ada.
11722 @c This is false ...
11723 Some @value{GDBN} features may be used in expressions regardless of the
11724 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
11725 and the @samp{@{type@}addr} construct (@pxref{Expressions,
11726 ,Expressions}) can be used with the constructs of any supported
11729 The following sections detail to what degree each source language is
11730 supported by @value{GDBN}. These sections are not meant to be language
11731 tutorials or references, but serve only as a reference guide to what the
11732 @value{GDBN} expression parser accepts, and what input and output
11733 formats should look like for different languages. There are many good
11734 books written on each of these languages; please look to these for a
11735 language reference or tutorial.
11738 * C:: C and C@t{++}
11740 * Objective-C:: Objective-C
11741 * OpenCL C:: OpenCL C
11742 * Fortran:: Fortran
11744 * Modula-2:: Modula-2
11749 @subsection C and C@t{++}
11751 @cindex C and C@t{++}
11752 @cindex expressions in C or C@t{++}
11754 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
11755 to both languages. Whenever this is the case, we discuss those languages
11759 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
11760 @cindex @sc{gnu} C@t{++}
11761 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
11762 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
11763 effectively, you must compile your C@t{++} programs with a supported
11764 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
11765 compiler (@code{aCC}).
11767 For best results when using @sc{gnu} C@t{++}, use the DWARF 2 debugging
11768 format; if it doesn't work on your system, try the stabs+ debugging
11769 format. You can select those formats explicitly with the @code{g++}
11770 command-line options @option{-gdwarf-2} and @option{-gstabs+}.
11771 @xref{Debugging Options,,Options for Debugging Your Program or GCC,
11772 gcc.info, Using the @sc{gnu} Compiler Collection (GCC)}.
11775 * C Operators:: C and C@t{++} operators
11776 * C Constants:: C and C@t{++} constants
11777 * C Plus Plus Expressions:: C@t{++} expressions
11778 * C Defaults:: Default settings for C and C@t{++}
11779 * C Checks:: C and C@t{++} type and range checks
11780 * Debugging C:: @value{GDBN} and C
11781 * Debugging C Plus Plus:: @value{GDBN} features for C@t{++}
11782 * Decimal Floating Point:: Numbers in Decimal Floating Point format
11786 @subsubsection C and C@t{++} Operators
11788 @cindex C and C@t{++} operators
11790 Operators must be defined on values of specific types. For instance,
11791 @code{+} is defined on numbers, but not on structures. Operators are
11792 often defined on groups of types.
11794 For the purposes of C and C@t{++}, the following definitions hold:
11799 @emph{Integral types} include @code{int} with any of its storage-class
11800 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
11803 @emph{Floating-point types} include @code{float}, @code{double}, and
11804 @code{long double} (if supported by the target platform).
11807 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
11810 @emph{Scalar types} include all of the above.
11815 The following operators are supported. They are listed here
11816 in order of increasing precedence:
11820 The comma or sequencing operator. Expressions in a comma-separated list
11821 are evaluated from left to right, with the result of the entire
11822 expression being the last expression evaluated.
11825 Assignment. The value of an assignment expression is the value
11826 assigned. Defined on scalar types.
11829 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
11830 and translated to @w{@code{@var{a} = @var{a op b}}}.
11831 @w{@code{@var{op}=}} and @code{=} have the same precedence.
11832 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
11833 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
11836 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
11837 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
11841 Logical @sc{or}. Defined on integral types.
11844 Logical @sc{and}. Defined on integral types.
11847 Bitwise @sc{or}. Defined on integral types.
11850 Bitwise exclusive-@sc{or}. Defined on integral types.
11853 Bitwise @sc{and}. Defined on integral types.
11856 Equality and inequality. Defined on scalar types. The value of these
11857 expressions is 0 for false and non-zero for true.
11859 @item <@r{, }>@r{, }<=@r{, }>=
11860 Less than, greater than, less than or equal, greater than or equal.
11861 Defined on scalar types. The value of these expressions is 0 for false
11862 and non-zero for true.
11865 left shift, and right shift. Defined on integral types.
11868 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
11871 Addition and subtraction. Defined on integral types, floating-point types and
11874 @item *@r{, }/@r{, }%
11875 Multiplication, division, and modulus. Multiplication and division are
11876 defined on integral and floating-point types. Modulus is defined on
11880 Increment and decrement. When appearing before a variable, the
11881 operation is performed before the variable is used in an expression;
11882 when appearing after it, the variable's value is used before the
11883 operation takes place.
11886 Pointer dereferencing. Defined on pointer types. Same precedence as
11890 Address operator. Defined on variables. Same precedence as @code{++}.
11892 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
11893 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
11894 to examine the address
11895 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
11899 Negative. Defined on integral and floating-point types. Same
11900 precedence as @code{++}.
11903 Logical negation. Defined on integral types. Same precedence as
11907 Bitwise complement operator. Defined on integral types. Same precedence as
11912 Structure member, and pointer-to-structure member. For convenience,
11913 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
11914 pointer based on the stored type information.
11915 Defined on @code{struct} and @code{union} data.
11918 Dereferences of pointers to members.
11921 Array indexing. @code{@var{a}[@var{i}]} is defined as
11922 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
11925 Function parameter list. Same precedence as @code{->}.
11928 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
11929 and @code{class} types.
11932 Doubled colons also represent the @value{GDBN} scope operator
11933 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
11937 If an operator is redefined in the user code, @value{GDBN} usually
11938 attempts to invoke the redefined version instead of using the operator's
11939 predefined meaning.
11942 @subsubsection C and C@t{++} Constants
11944 @cindex C and C@t{++} constants
11946 @value{GDBN} allows you to express the constants of C and C@t{++} in the
11951 Integer constants are a sequence of digits. Octal constants are
11952 specified by a leading @samp{0} (i.e.@: zero), and hexadecimal constants
11953 by a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
11954 @samp{l}, specifying that the constant should be treated as a
11958 Floating point constants are a sequence of digits, followed by a decimal
11959 point, followed by a sequence of digits, and optionally followed by an
11960 exponent. An exponent is of the form:
11961 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
11962 sequence of digits. The @samp{+} is optional for positive exponents.
11963 A floating-point constant may also end with a letter @samp{f} or
11964 @samp{F}, specifying that the constant should be treated as being of
11965 the @code{float} (as opposed to the default @code{double}) type; or with
11966 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
11970 Enumerated constants consist of enumerated identifiers, or their
11971 integral equivalents.
11974 Character constants are a single character surrounded by single quotes
11975 (@code{'}), or a number---the ordinal value of the corresponding character
11976 (usually its @sc{ascii} value). Within quotes, the single character may
11977 be represented by a letter or by @dfn{escape sequences}, which are of
11978 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
11979 of the character's ordinal value; or of the form @samp{\@var{x}}, where
11980 @samp{@var{x}} is a predefined special character---for example,
11981 @samp{\n} for newline.
11984 String constants are a sequence of character constants surrounded by
11985 double quotes (@code{"}). Any valid character constant (as described
11986 above) may appear. Double quotes within the string must be preceded by
11987 a backslash, so for instance @samp{"a\"b'c"} is a string of five
11991 Pointer constants are an integral value. You can also write pointers
11992 to constants using the C operator @samp{&}.
11995 Array constants are comma-separated lists surrounded by braces @samp{@{}
11996 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
11997 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
11998 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
12001 @node C Plus Plus Expressions
12002 @subsubsection C@t{++} Expressions
12004 @cindex expressions in C@t{++}
12005 @value{GDBN} expression handling can interpret most C@t{++} expressions.
12007 @cindex debugging C@t{++} programs
12008 @cindex C@t{++} compilers
12009 @cindex debug formats and C@t{++}
12010 @cindex @value{NGCC} and C@t{++}
12012 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the
12013 proper compiler and the proper debug format. Currently, @value{GDBN}
12014 works best when debugging C@t{++} code that is compiled with
12015 @value{NGCC} 2.95.3 or with @value{NGCC} 3.1 or newer, using the options
12016 @option{-gdwarf-2} or @option{-gstabs+}. DWARF 2 is preferred over
12017 stabs+. Most configurations of @value{NGCC} emit either DWARF 2 or
12018 stabs+ as their default debug format, so you usually don't need to
12019 specify a debug format explicitly. Other compilers and/or debug formats
12020 are likely to work badly or not at all when using @value{GDBN} to debug
12026 @cindex member functions
12028 Member function calls are allowed; you can use expressions like
12031 count = aml->GetOriginal(x, y)
12034 @vindex this@r{, inside C@t{++} member functions}
12035 @cindex namespace in C@t{++}
12037 While a member function is active (in the selected stack frame), your
12038 expressions have the same namespace available as the member function;
12039 that is, @value{GDBN} allows implicit references to the class instance
12040 pointer @code{this} following the same rules as C@t{++}.
12042 @cindex call overloaded functions
12043 @cindex overloaded functions, calling
12044 @cindex type conversions in C@t{++}
12046 You can call overloaded functions; @value{GDBN} resolves the function
12047 call to the right definition, with some restrictions. @value{GDBN} does not
12048 perform overload resolution involving user-defined type conversions,
12049 calls to constructors, or instantiations of templates that do not exist
12050 in the program. It also cannot handle ellipsis argument lists or
12053 It does perform integral conversions and promotions, floating-point
12054 promotions, arithmetic conversions, pointer conversions, conversions of
12055 class objects to base classes, and standard conversions such as those of
12056 functions or arrays to pointers; it requires an exact match on the
12057 number of function arguments.
12059 Overload resolution is always performed, unless you have specified
12060 @code{set overload-resolution off}. @xref{Debugging C Plus Plus,
12061 ,@value{GDBN} Features for C@t{++}}.
12063 You must specify @code{set overload-resolution off} in order to use an
12064 explicit function signature to call an overloaded function, as in
12066 p 'foo(char,int)'('x', 13)
12069 The @value{GDBN} command-completion facility can simplify this;
12070 see @ref{Completion, ,Command Completion}.
12072 @cindex reference declarations
12074 @value{GDBN} understands variables declared as C@t{++} references; you can use
12075 them in expressions just as you do in C@t{++} source---they are automatically
12078 In the parameter list shown when @value{GDBN} displays a frame, the values of
12079 reference variables are not displayed (unlike other variables); this
12080 avoids clutter, since references are often used for large structures.
12081 The @emph{address} of a reference variable is always shown, unless
12082 you have specified @samp{set print address off}.
12085 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
12086 expressions can use it just as expressions in your program do. Since
12087 one scope may be defined in another, you can use @code{::} repeatedly if
12088 necessary, for example in an expression like
12089 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
12090 resolving name scope by reference to source files, in both C and C@t{++}
12091 debugging (@pxref{Variables, ,Program Variables}).
12094 In addition, when used with HP's C@t{++} compiler, @value{GDBN} supports
12095 calling virtual functions correctly, printing out virtual bases of
12096 objects, calling functions in a base subobject, casting objects, and
12097 invoking user-defined operators.
12100 @subsubsection C and C@t{++} Defaults
12102 @cindex C and C@t{++} defaults
12104 If you allow @value{GDBN} to set type and range checking automatically, they
12105 both default to @code{off} whenever the working language changes to
12106 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
12107 selects the working language.
12109 If you allow @value{GDBN} to set the language automatically, it
12110 recognizes source files whose names end with @file{.c}, @file{.C}, or
12111 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
12112 these files, it sets the working language to C or C@t{++}.
12113 @xref{Automatically, ,Having @value{GDBN} Infer the Source Language},
12114 for further details.
12116 @c Type checking is (a) primarily motivated by Modula-2, and (b)
12117 @c unimplemented. If (b) changes, it might make sense to let this node
12118 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
12121 @subsubsection C and C@t{++} Type and Range Checks
12123 @cindex C and C@t{++} checks
12125 By default, when @value{GDBN} parses C or C@t{++} expressions, type checking
12126 is not used. However, if you turn type checking on, @value{GDBN}
12127 considers two variables type equivalent if:
12131 The two variables are structured and have the same structure, union, or
12135 The two variables have the same type name, or types that have been
12136 declared equivalent through @code{typedef}.
12139 @c leaving this out because neither J Gilmore nor R Pesch understand it.
12142 The two @code{struct}, @code{union}, or @code{enum} variables are
12143 declared in the same declaration. (Note: this may not be true for all C
12148 Range checking, if turned on, is done on mathematical operations. Array
12149 indices are not checked, since they are often used to index a pointer
12150 that is not itself an array.
12153 @subsubsection @value{GDBN} and C
12155 The @code{set print union} and @code{show print union} commands apply to
12156 the @code{union} type. When set to @samp{on}, any @code{union} that is
12157 inside a @code{struct} or @code{class} is also printed. Otherwise, it
12158 appears as @samp{@{...@}}.
12160 The @code{@@} operator aids in the debugging of dynamic arrays, formed
12161 with pointers and a memory allocation function. @xref{Expressions,
12164 @node Debugging C Plus Plus
12165 @subsubsection @value{GDBN} Features for C@t{++}
12167 @cindex commands for C@t{++}
12169 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
12170 designed specifically for use with C@t{++}. Here is a summary:
12173 @cindex break in overloaded functions
12174 @item @r{breakpoint menus}
12175 When you want a breakpoint in a function whose name is overloaded,
12176 @value{GDBN} has the capability to display a menu of possible breakpoint
12177 locations to help you specify which function definition you want.
12178 @xref{Ambiguous Expressions,,Ambiguous Expressions}.
12180 @cindex overloading in C@t{++}
12181 @item rbreak @var{regex}
12182 Setting breakpoints using regular expressions is helpful for setting
12183 breakpoints on overloaded functions that are not members of any special
12185 @xref{Set Breaks, ,Setting Breakpoints}.
12187 @cindex C@t{++} exception handling
12190 Debug C@t{++} exception handling using these commands. @xref{Set
12191 Catchpoints, , Setting Catchpoints}.
12193 @cindex inheritance
12194 @item ptype @var{typename}
12195 Print inheritance relationships as well as other information for type
12197 @xref{Symbols, ,Examining the Symbol Table}.
12199 @cindex C@t{++} symbol display
12200 @item set print demangle
12201 @itemx show print demangle
12202 @itemx set print asm-demangle
12203 @itemx show print asm-demangle
12204 Control whether C@t{++} symbols display in their source form, both when
12205 displaying code as C@t{++} source and when displaying disassemblies.
12206 @xref{Print Settings, ,Print Settings}.
12208 @item set print object
12209 @itemx show print object
12210 Choose whether to print derived (actual) or declared types of objects.
12211 @xref{Print Settings, ,Print Settings}.
12213 @item set print vtbl
12214 @itemx show print vtbl
12215 Control the format for printing virtual function tables.
12216 @xref{Print Settings, ,Print Settings}.
12217 (The @code{vtbl} commands do not work on programs compiled with the HP
12218 ANSI C@t{++} compiler (@code{aCC}).)
12220 @kindex set overload-resolution
12221 @cindex overloaded functions, overload resolution
12222 @item set overload-resolution on
12223 Enable overload resolution for C@t{++} expression evaluation. The default
12224 is on. For overloaded functions, @value{GDBN} evaluates the arguments
12225 and searches for a function whose signature matches the argument types,
12226 using the standard C@t{++} conversion rules (see @ref{C Plus Plus
12227 Expressions, ,C@t{++} Expressions}, for details).
12228 If it cannot find a match, it emits a message.
12230 @item set overload-resolution off
12231 Disable overload resolution for C@t{++} expression evaluation. For
12232 overloaded functions that are not class member functions, @value{GDBN}
12233 chooses the first function of the specified name that it finds in the
12234 symbol table, whether or not its arguments are of the correct type. For
12235 overloaded functions that are class member functions, @value{GDBN}
12236 searches for a function whose signature @emph{exactly} matches the
12239 @kindex show overload-resolution
12240 @item show overload-resolution
12241 Show the current setting of overload resolution.
12243 @item @r{Overloaded symbol names}
12244 You can specify a particular definition of an overloaded symbol, using
12245 the same notation that is used to declare such symbols in C@t{++}: type
12246 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
12247 also use the @value{GDBN} command-line word completion facilities to list the
12248 available choices, or to finish the type list for you.
12249 @xref{Completion,, Command Completion}, for details on how to do this.
12252 @node Decimal Floating Point
12253 @subsubsection Decimal Floating Point format
12254 @cindex decimal floating point format
12256 @value{GDBN} can examine, set and perform computations with numbers in
12257 decimal floating point format, which in the C language correspond to the
12258 @code{_Decimal32}, @code{_Decimal64} and @code{_Decimal128} types as
12259 specified by the extension to support decimal floating-point arithmetic.
12261 There are two encodings in use, depending on the architecture: BID (Binary
12262 Integer Decimal) for x86 and x86-64, and DPD (Densely Packed Decimal) for
12263 PowerPC. @value{GDBN} will use the appropriate encoding for the configured
12266 Because of a limitation in @file{libdecnumber}, the library used by @value{GDBN}
12267 to manipulate decimal floating point numbers, it is not possible to convert
12268 (using a cast, for example) integers wider than 32-bit to decimal float.
12270 In addition, in order to imitate @value{GDBN}'s behaviour with binary floating
12271 point computations, error checking in decimal float operations ignores
12272 underflow, overflow and divide by zero exceptions.
12274 In the PowerPC architecture, @value{GDBN} provides a set of pseudo-registers
12275 to inspect @code{_Decimal128} values stored in floating point registers.
12276 See @ref{PowerPC,,PowerPC} for more details.
12282 @value{GDBN} can be used to debug programs written in D and compiled with
12283 GDC, LDC or DMD compilers. Currently @value{GDBN} supports only one D
12284 specific feature --- dynamic arrays.
12287 @subsection Objective-C
12289 @cindex Objective-C
12290 This section provides information about some commands and command
12291 options that are useful for debugging Objective-C code. See also
12292 @ref{Symbols, info classes}, and @ref{Symbols, info selectors}, for a
12293 few more commands specific to Objective-C support.
12296 * Method Names in Commands::
12297 * The Print Command with Objective-C::
12300 @node Method Names in Commands
12301 @subsubsection Method Names in Commands
12303 The following commands have been extended to accept Objective-C method
12304 names as line specifications:
12306 @kindex clear@r{, and Objective-C}
12307 @kindex break@r{, and Objective-C}
12308 @kindex info line@r{, and Objective-C}
12309 @kindex jump@r{, and Objective-C}
12310 @kindex list@r{, and Objective-C}
12314 @item @code{info line}
12319 A fully qualified Objective-C method name is specified as
12322 -[@var{Class} @var{methodName}]
12325 where the minus sign is used to indicate an instance method and a
12326 plus sign (not shown) is used to indicate a class method. The class
12327 name @var{Class} and method name @var{methodName} are enclosed in
12328 brackets, similar to the way messages are specified in Objective-C
12329 source code. For example, to set a breakpoint at the @code{create}
12330 instance method of class @code{Fruit} in the program currently being
12334 break -[Fruit create]
12337 To list ten program lines around the @code{initialize} class method,
12341 list +[NSText initialize]
12344 In the current version of @value{GDBN}, the plus or minus sign is
12345 required. In future versions of @value{GDBN}, the plus or minus
12346 sign will be optional, but you can use it to narrow the search. It
12347 is also possible to specify just a method name:
12353 You must specify the complete method name, including any colons. If
12354 your program's source files contain more than one @code{create} method,
12355 you'll be presented with a numbered list of classes that implement that
12356 method. Indicate your choice by number, or type @samp{0} to exit if
12359 As another example, to clear a breakpoint established at the
12360 @code{makeKeyAndOrderFront:} method of the @code{NSWindow} class, enter:
12363 clear -[NSWindow makeKeyAndOrderFront:]
12366 @node The Print Command with Objective-C
12367 @subsubsection The Print Command With Objective-C
12368 @cindex Objective-C, print objects
12369 @kindex print-object
12370 @kindex po @r{(@code{print-object})}
12372 The print command has also been extended to accept methods. For example:
12375 print -[@var{object} hash]
12378 @cindex print an Objective-C object description
12379 @cindex @code{_NSPrintForDebugger}, and printing Objective-C objects
12381 will tell @value{GDBN} to send the @code{hash} message to @var{object}
12382 and print the result. Also, an additional command has been added,
12383 @code{print-object} or @code{po} for short, which is meant to print
12384 the description of an object. However, this command may only work
12385 with certain Objective-C libraries that have a particular hook
12386 function, @code{_NSPrintForDebugger}, defined.
12389 @subsection OpenCL C
12392 This section provides information about @value{GDBN}s OpenCL C support.
12395 * OpenCL C Datatypes::
12396 * OpenCL C Expressions::
12397 * OpenCL C Operators::
12400 @node OpenCL C Datatypes
12401 @subsubsection OpenCL C Datatypes
12403 @cindex OpenCL C Datatypes
12404 @value{GDBN} supports the builtin scalar and vector datatypes specified
12405 by OpenCL 1.1. In addition the half- and double-precision floating point
12406 data types of the @code{cl_khr_fp16} and @code{cl_khr_fp64} OpenCL
12407 extensions are also known to @value{GDBN}.
12409 @node OpenCL C Expressions
12410 @subsubsection OpenCL C Expressions
12412 @cindex OpenCL C Expressions
12413 @value{GDBN} supports accesses to vector components including the access as
12414 lvalue where possible. Since OpenCL C is based on C99 most C expressions
12415 supported by @value{GDBN} can be used as well.
12417 @node OpenCL C Operators
12418 @subsubsection OpenCL C Operators
12420 @cindex OpenCL C Operators
12421 @value{GDBN} supports the operators specified by OpenCL 1.1 for scalar and
12425 @subsection Fortran
12426 @cindex Fortran-specific support in @value{GDBN}
12428 @value{GDBN} can be used to debug programs written in Fortran, but it
12429 currently supports only the features of Fortran 77 language.
12431 @cindex trailing underscore, in Fortran symbols
12432 Some Fortran compilers (@sc{gnu} Fortran 77 and Fortran 95 compilers
12433 among them) append an underscore to the names of variables and
12434 functions. When you debug programs compiled by those compilers, you
12435 will need to refer to variables and functions with a trailing
12439 * Fortran Operators:: Fortran operators and expressions
12440 * Fortran Defaults:: Default settings for Fortran
12441 * Special Fortran Commands:: Special @value{GDBN} commands for Fortran
12444 @node Fortran Operators
12445 @subsubsection Fortran Operators and Expressions
12447 @cindex Fortran operators and expressions
12449 Operators must be defined on values of specific types. For instance,
12450 @code{+} is defined on numbers, but not on characters or other non-
12451 arithmetic types. Operators are often defined on groups of types.
12455 The exponentiation operator. It raises the first operand to the power
12459 The range operator. Normally used in the form of array(low:high) to
12460 represent a section of array.
12463 The access component operator. Normally used to access elements in derived
12464 types. Also suitable for unions. As unions aren't part of regular Fortran,
12465 this can only happen when accessing a register that uses a gdbarch-defined
12469 @node Fortran Defaults
12470 @subsubsection Fortran Defaults
12472 @cindex Fortran Defaults
12474 Fortran symbols are usually case-insensitive, so @value{GDBN} by
12475 default uses case-insensitive matches for Fortran symbols. You can
12476 change that with the @samp{set case-insensitive} command, see
12477 @ref{Symbols}, for the details.
12479 @node Special Fortran Commands
12480 @subsubsection Special Fortran Commands
12482 @cindex Special Fortran commands
12484 @value{GDBN} has some commands to support Fortran-specific features,
12485 such as displaying common blocks.
12488 @cindex @code{COMMON} blocks, Fortran
12489 @kindex info common
12490 @item info common @r{[}@var{common-name}@r{]}
12491 This command prints the values contained in the Fortran @code{COMMON}
12492 block whose name is @var{common-name}. With no argument, the names of
12493 all @code{COMMON} blocks visible at the current program location are
12500 @cindex Pascal support in @value{GDBN}, limitations
12501 Debugging Pascal programs which use sets, subranges, file variables, or
12502 nested functions does not currently work. @value{GDBN} does not support
12503 entering expressions, printing values, or similar features using Pascal
12506 The Pascal-specific command @code{set print pascal_static-members}
12507 controls whether static members of Pascal objects are displayed.
12508 @xref{Print Settings, pascal_static-members}.
12511 @subsection Modula-2
12513 @cindex Modula-2, @value{GDBN} support
12515 The extensions made to @value{GDBN} to support Modula-2 only support
12516 output from the @sc{gnu} Modula-2 compiler (which is currently being
12517 developed). Other Modula-2 compilers are not currently supported, and
12518 attempting to debug executables produced by them is most likely
12519 to give an error as @value{GDBN} reads in the executable's symbol
12522 @cindex expressions in Modula-2
12524 * M2 Operators:: Built-in operators
12525 * Built-In Func/Proc:: Built-in functions and procedures
12526 * M2 Constants:: Modula-2 constants
12527 * M2 Types:: Modula-2 types
12528 * M2 Defaults:: Default settings for Modula-2
12529 * Deviations:: Deviations from standard Modula-2
12530 * M2 Checks:: Modula-2 type and range checks
12531 * M2 Scope:: The scope operators @code{::} and @code{.}
12532 * GDB/M2:: @value{GDBN} and Modula-2
12536 @subsubsection Operators
12537 @cindex Modula-2 operators
12539 Operators must be defined on values of specific types. For instance,
12540 @code{+} is defined on numbers, but not on structures. Operators are
12541 often defined on groups of types. For the purposes of Modula-2, the
12542 following definitions hold:
12547 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
12551 @emph{Character types} consist of @code{CHAR} and its subranges.
12554 @emph{Floating-point types} consist of @code{REAL}.
12557 @emph{Pointer types} consist of anything declared as @code{POINTER TO
12561 @emph{Scalar types} consist of all of the above.
12564 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
12567 @emph{Boolean types} consist of @code{BOOLEAN}.
12571 The following operators are supported, and appear in order of
12572 increasing precedence:
12576 Function argument or array index separator.
12579 Assignment. The value of @var{var} @code{:=} @var{value} is
12583 Less than, greater than on integral, floating-point, or enumerated
12587 Less than or equal to, greater than or equal to
12588 on integral, floating-point and enumerated types, or set inclusion on
12589 set types. Same precedence as @code{<}.
12591 @item =@r{, }<>@r{, }#
12592 Equality and two ways of expressing inequality, valid on scalar types.
12593 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
12594 available for inequality, since @code{#} conflicts with the script
12598 Set membership. Defined on set types and the types of their members.
12599 Same precedence as @code{<}.
12602 Boolean disjunction. Defined on boolean types.
12605 Boolean conjunction. Defined on boolean types.
12608 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
12611 Addition and subtraction on integral and floating-point types, or union
12612 and difference on set types.
12615 Multiplication on integral and floating-point types, or set intersection
12619 Division on floating-point types, or symmetric set difference on set
12620 types. Same precedence as @code{*}.
12623 Integer division and remainder. Defined on integral types. Same
12624 precedence as @code{*}.
12627 Negative. Defined on @code{INTEGER} and @code{REAL} data.
12630 Pointer dereferencing. Defined on pointer types.
12633 Boolean negation. Defined on boolean types. Same precedence as
12637 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
12638 precedence as @code{^}.
12641 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
12644 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
12648 @value{GDBN} and Modula-2 scope operators.
12652 @emph{Warning:} Set expressions and their operations are not yet supported, so @value{GDBN}
12653 treats the use of the operator @code{IN}, or the use of operators
12654 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
12655 @code{<=}, and @code{>=} on sets as an error.
12659 @node Built-In Func/Proc
12660 @subsubsection Built-in Functions and Procedures
12661 @cindex Modula-2 built-ins
12663 Modula-2 also makes available several built-in procedures and functions.
12664 In describing these, the following metavariables are used:
12669 represents an @code{ARRAY} variable.
12672 represents a @code{CHAR} constant or variable.
12675 represents a variable or constant of integral type.
12678 represents an identifier that belongs to a set. Generally used in the
12679 same function with the metavariable @var{s}. The type of @var{s} should
12680 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
12683 represents a variable or constant of integral or floating-point type.
12686 represents a variable or constant of floating-point type.
12692 represents a variable.
12695 represents a variable or constant of one of many types. See the
12696 explanation of the function for details.
12699 All Modula-2 built-in procedures also return a result, described below.
12703 Returns the absolute value of @var{n}.
12706 If @var{c} is a lower case letter, it returns its upper case
12707 equivalent, otherwise it returns its argument.
12710 Returns the character whose ordinal value is @var{i}.
12713 Decrements the value in the variable @var{v} by one. Returns the new value.
12715 @item DEC(@var{v},@var{i})
12716 Decrements the value in the variable @var{v} by @var{i}. Returns the
12719 @item EXCL(@var{m},@var{s})
12720 Removes the element @var{m} from the set @var{s}. Returns the new
12723 @item FLOAT(@var{i})
12724 Returns the floating point equivalent of the integer @var{i}.
12726 @item HIGH(@var{a})
12727 Returns the index of the last member of @var{a}.
12730 Increments the value in the variable @var{v} by one. Returns the new value.
12732 @item INC(@var{v},@var{i})
12733 Increments the value in the variable @var{v} by @var{i}. Returns the
12736 @item INCL(@var{m},@var{s})
12737 Adds the element @var{m} to the set @var{s} if it is not already
12738 there. Returns the new set.
12741 Returns the maximum value of the type @var{t}.
12744 Returns the minimum value of the type @var{t}.
12747 Returns boolean TRUE if @var{i} is an odd number.
12750 Returns the ordinal value of its argument. For example, the ordinal
12751 value of a character is its @sc{ascii} value (on machines supporting the
12752 @sc{ascii} character set). @var{x} must be of an ordered type, which include
12753 integral, character and enumerated types.
12755 @item SIZE(@var{x})
12756 Returns the size of its argument. @var{x} can be a variable or a type.
12758 @item TRUNC(@var{r})
12759 Returns the integral part of @var{r}.
12761 @item TSIZE(@var{x})
12762 Returns the size of its argument. @var{x} can be a variable or a type.
12764 @item VAL(@var{t},@var{i})
12765 Returns the member of the type @var{t} whose ordinal value is @var{i}.
12769 @emph{Warning:} Sets and their operations are not yet supported, so
12770 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
12774 @cindex Modula-2 constants
12776 @subsubsection Constants
12778 @value{GDBN} allows you to express the constants of Modula-2 in the following
12784 Integer constants are simply a sequence of digits. When used in an
12785 expression, a constant is interpreted to be type-compatible with the
12786 rest of the expression. Hexadecimal integers are specified by a
12787 trailing @samp{H}, and octal integers by a trailing @samp{B}.
12790 Floating point constants appear as a sequence of digits, followed by a
12791 decimal point and another sequence of digits. An optional exponent can
12792 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
12793 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
12794 digits of the floating point constant must be valid decimal (base 10)
12798 Character constants consist of a single character enclosed by a pair of
12799 like quotes, either single (@code{'}) or double (@code{"}). They may
12800 also be expressed by their ordinal value (their @sc{ascii} value, usually)
12801 followed by a @samp{C}.
12804 String constants consist of a sequence of characters enclosed by a
12805 pair of like quotes, either single (@code{'}) or double (@code{"}).
12806 Escape sequences in the style of C are also allowed. @xref{C
12807 Constants, ,C and C@t{++} Constants}, for a brief explanation of escape
12811 Enumerated constants consist of an enumerated identifier.
12814 Boolean constants consist of the identifiers @code{TRUE} and
12818 Pointer constants consist of integral values only.
12821 Set constants are not yet supported.
12825 @subsubsection Modula-2 Types
12826 @cindex Modula-2 types
12828 Currently @value{GDBN} can print the following data types in Modula-2
12829 syntax: array types, record types, set types, pointer types, procedure
12830 types, enumerated types, subrange types and base types. You can also
12831 print the contents of variables declared using these type.
12832 This section gives a number of simple source code examples together with
12833 sample @value{GDBN} sessions.
12835 The first example contains the following section of code:
12844 and you can request @value{GDBN} to interrogate the type and value of
12845 @code{r} and @code{s}.
12848 (@value{GDBP}) print s
12850 (@value{GDBP}) ptype s
12852 (@value{GDBP}) print r
12854 (@value{GDBP}) ptype r
12859 Likewise if your source code declares @code{s} as:
12863 s: SET ['A'..'Z'] ;
12867 then you may query the type of @code{s} by:
12870 (@value{GDBP}) ptype s
12871 type = SET ['A'..'Z']
12875 Note that at present you cannot interactively manipulate set
12876 expressions using the debugger.
12878 The following example shows how you might declare an array in Modula-2
12879 and how you can interact with @value{GDBN} to print its type and contents:
12883 s: ARRAY [-10..10] OF CHAR ;
12887 (@value{GDBP}) ptype s
12888 ARRAY [-10..10] OF CHAR
12891 Note that the array handling is not yet complete and although the type
12892 is printed correctly, expression handling still assumes that all
12893 arrays have a lower bound of zero and not @code{-10} as in the example
12896 Here are some more type related Modula-2 examples:
12900 colour = (blue, red, yellow, green) ;
12901 t = [blue..yellow] ;
12909 The @value{GDBN} interaction shows how you can query the data type
12910 and value of a variable.
12913 (@value{GDBP}) print s
12915 (@value{GDBP}) ptype t
12916 type = [blue..yellow]
12920 In this example a Modula-2 array is declared and its contents
12921 displayed. Observe that the contents are written in the same way as
12922 their @code{C} counterparts.
12926 s: ARRAY [1..5] OF CARDINAL ;
12932 (@value{GDBP}) print s
12933 $1 = @{1, 0, 0, 0, 0@}
12934 (@value{GDBP}) ptype s
12935 type = ARRAY [1..5] OF CARDINAL
12938 The Modula-2 language interface to @value{GDBN} also understands
12939 pointer types as shown in this example:
12943 s: POINTER TO ARRAY [1..5] OF CARDINAL ;
12950 and you can request that @value{GDBN} describes the type of @code{s}.
12953 (@value{GDBP}) ptype s
12954 type = POINTER TO ARRAY [1..5] OF CARDINAL
12957 @value{GDBN} handles compound types as we can see in this example.
12958 Here we combine array types, record types, pointer types and subrange
12969 myarray = ARRAY myrange OF CARDINAL ;
12970 myrange = [-2..2] ;
12972 s: POINTER TO ARRAY myrange OF foo ;
12976 and you can ask @value{GDBN} to describe the type of @code{s} as shown
12980 (@value{GDBP}) ptype s
12981 type = POINTER TO ARRAY [-2..2] OF foo = RECORD
12984 f3 : ARRAY [-2..2] OF CARDINAL;
12989 @subsubsection Modula-2 Defaults
12990 @cindex Modula-2 defaults
12992 If type and range checking are set automatically by @value{GDBN}, they
12993 both default to @code{on} whenever the working language changes to
12994 Modula-2. This happens regardless of whether you or @value{GDBN}
12995 selected the working language.
12997 If you allow @value{GDBN} to set the language automatically, then entering
12998 code compiled from a file whose name ends with @file{.mod} sets the
12999 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN}
13000 Infer the Source Language}, for further details.
13003 @subsubsection Deviations from Standard Modula-2
13004 @cindex Modula-2, deviations from
13006 A few changes have been made to make Modula-2 programs easier to debug.
13007 This is done primarily via loosening its type strictness:
13011 Unlike in standard Modula-2, pointer constants can be formed by
13012 integers. This allows you to modify pointer variables during
13013 debugging. (In standard Modula-2, the actual address contained in a
13014 pointer variable is hidden from you; it can only be modified
13015 through direct assignment to another pointer variable or expression that
13016 returned a pointer.)
13019 C escape sequences can be used in strings and characters to represent
13020 non-printable characters. @value{GDBN} prints out strings with these
13021 escape sequences embedded. Single non-printable characters are
13022 printed using the @samp{CHR(@var{nnn})} format.
13025 The assignment operator (@code{:=}) returns the value of its right-hand
13029 All built-in procedures both modify @emph{and} return their argument.
13033 @subsubsection Modula-2 Type and Range Checks
13034 @cindex Modula-2 checks
13037 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
13040 @c FIXME remove warning when type/range checks added
13042 @value{GDBN} considers two Modula-2 variables type equivalent if:
13046 They are of types that have been declared equivalent via a @code{TYPE
13047 @var{t1} = @var{t2}} statement
13050 They have been declared on the same line. (Note: This is true of the
13051 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
13054 As long as type checking is enabled, any attempt to combine variables
13055 whose types are not equivalent is an error.
13057 Range checking is done on all mathematical operations, assignment, array
13058 index bounds, and all built-in functions and procedures.
13061 @subsubsection The Scope Operators @code{::} and @code{.}
13063 @cindex @code{.}, Modula-2 scope operator
13064 @cindex colon, doubled as scope operator
13066 @vindex colon-colon@r{, in Modula-2}
13067 @c Info cannot handle :: but TeX can.
13070 @vindex ::@r{, in Modula-2}
13073 There are a few subtle differences between the Modula-2 scope operator
13074 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
13079 @var{module} . @var{id}
13080 @var{scope} :: @var{id}
13084 where @var{scope} is the name of a module or a procedure,
13085 @var{module} the name of a module, and @var{id} is any declared
13086 identifier within your program, except another module.
13088 Using the @code{::} operator makes @value{GDBN} search the scope
13089 specified by @var{scope} for the identifier @var{id}. If it is not
13090 found in the specified scope, then @value{GDBN} searches all scopes
13091 enclosing the one specified by @var{scope}.
13093 Using the @code{.} operator makes @value{GDBN} search the current scope for
13094 the identifier specified by @var{id} that was imported from the
13095 definition module specified by @var{module}. With this operator, it is
13096 an error if the identifier @var{id} was not imported from definition
13097 module @var{module}, or if @var{id} is not an identifier in
13101 @subsubsection @value{GDBN} and Modula-2
13103 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
13104 Five subcommands of @code{set print} and @code{show print} apply
13105 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
13106 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
13107 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
13108 analogue in Modula-2.
13110 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
13111 with any language, is not useful with Modula-2. Its
13112 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
13113 created in Modula-2 as they can in C or C@t{++}. However, because an
13114 address can be specified by an integral constant, the construct
13115 @samp{@{@var{type}@}@var{adrexp}} is still useful.
13117 @cindex @code{#} in Modula-2
13118 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
13119 interpreted as the beginning of a comment. Use @code{<>} instead.
13125 The extensions made to @value{GDBN} for Ada only support
13126 output from the @sc{gnu} Ada (GNAT) compiler.
13127 Other Ada compilers are not currently supported, and
13128 attempting to debug executables produced by them is most likely
13132 @cindex expressions in Ada
13134 * Ada Mode Intro:: General remarks on the Ada syntax
13135 and semantics supported by Ada mode
13137 * Omissions from Ada:: Restrictions on the Ada expression syntax.
13138 * Additions to Ada:: Extensions of the Ada expression syntax.
13139 * Stopping Before Main Program:: Debugging the program during elaboration.
13140 * Ada Tasks:: Listing and setting breakpoints in tasks.
13141 * Ada Tasks and Core Files:: Tasking Support when Debugging Core Files
13142 * Ravenscar Profile:: Tasking Support when using the Ravenscar
13144 * Ada Glitches:: Known peculiarities of Ada mode.
13147 @node Ada Mode Intro
13148 @subsubsection Introduction
13149 @cindex Ada mode, general
13151 The Ada mode of @value{GDBN} supports a fairly large subset of Ada expression
13152 syntax, with some extensions.
13153 The philosophy behind the design of this subset is
13157 That @value{GDBN} should provide basic literals and access to operations for
13158 arithmetic, dereferencing, field selection, indexing, and subprogram calls,
13159 leaving more sophisticated computations to subprograms written into the
13160 program (which therefore may be called from @value{GDBN}).
13163 That type safety and strict adherence to Ada language restrictions
13164 are not particularly important to the @value{GDBN} user.
13167 That brevity is important to the @value{GDBN} user.
13170 Thus, for brevity, the debugger acts as if all names declared in
13171 user-written packages are directly visible, even if they are not visible
13172 according to Ada rules, thus making it unnecessary to fully qualify most
13173 names with their packages, regardless of context. Where this causes
13174 ambiguity, @value{GDBN} asks the user's intent.
13176 The debugger will start in Ada mode if it detects an Ada main program.
13177 As for other languages, it will enter Ada mode when stopped in a program that
13178 was translated from an Ada source file.
13180 While in Ada mode, you may use `@t{--}' for comments. This is useful
13181 mostly for documenting command files. The standard @value{GDBN} comment
13182 (@samp{#}) still works at the beginning of a line in Ada mode, but not in the
13183 middle (to allow based literals).
13185 The debugger supports limited overloading. Given a subprogram call in which
13186 the function symbol has multiple definitions, it will use the number of
13187 actual parameters and some information about their types to attempt to narrow
13188 the set of definitions. It also makes very limited use of context, preferring
13189 procedures to functions in the context of the @code{call} command, and
13190 functions to procedures elsewhere.
13192 @node Omissions from Ada
13193 @subsubsection Omissions from Ada
13194 @cindex Ada, omissions from
13196 Here are the notable omissions from the subset:
13200 Only a subset of the attributes are supported:
13204 @t{'First}, @t{'Last}, and @t{'Length}
13205 on array objects (not on types and subtypes).
13208 @t{'Min} and @t{'Max}.
13211 @t{'Pos} and @t{'Val}.
13217 @t{'Range} on array objects (not subtypes), but only as the right
13218 operand of the membership (@code{in}) operator.
13221 @t{'Access}, @t{'Unchecked_Access}, and
13222 @t{'Unrestricted_Access} (a GNAT extension).
13230 @code{Characters.Latin_1} are not available and
13231 concatenation is not implemented. Thus, escape characters in strings are
13232 not currently available.
13235 Equality tests (@samp{=} and @samp{/=}) on arrays test for bitwise
13236 equality of representations. They will generally work correctly
13237 for strings and arrays whose elements have integer or enumeration types.
13238 They may not work correctly for arrays whose element
13239 types have user-defined equality, for arrays of real values
13240 (in particular, IEEE-conformant floating point, because of negative
13241 zeroes and NaNs), and for arrays whose elements contain unused bits with
13242 indeterminate values.
13245 The other component-by-component array operations (@code{and}, @code{or},
13246 @code{xor}, @code{not}, and relational tests other than equality)
13247 are not implemented.
13250 @cindex array aggregates (Ada)
13251 @cindex record aggregates (Ada)
13252 @cindex aggregates (Ada)
13253 There is limited support for array and record aggregates. They are
13254 permitted only on the right sides of assignments, as in these examples:
13257 (@value{GDBP}) set An_Array := (1, 2, 3, 4, 5, 6)
13258 (@value{GDBP}) set An_Array := (1, others => 0)
13259 (@value{GDBP}) set An_Array := (0|4 => 1, 1..3 => 2, 5 => 6)
13260 (@value{GDBP}) set A_2D_Array := ((1, 2, 3), (4, 5, 6), (7, 8, 9))
13261 (@value{GDBP}) set A_Record := (1, "Peter", True);
13262 (@value{GDBP}) set A_Record := (Name => "Peter", Id => 1, Alive => True)
13266 discriminant's value by assigning an aggregate has an
13267 undefined effect if that discriminant is used within the record.
13268 However, you can first modify discriminants by directly assigning to
13269 them (which normally would not be allowed in Ada), and then performing an
13270 aggregate assignment. For example, given a variable @code{A_Rec}
13271 declared to have a type such as:
13274 type Rec (Len : Small_Integer := 0) is record
13276 Vals : IntArray (1 .. Len);
13280 you can assign a value with a different size of @code{Vals} with two
13284 (@value{GDBP}) set A_Rec.Len := 4
13285 (@value{GDBP}) set A_Rec := (Id => 42, Vals => (1, 2, 3, 4))
13288 As this example also illustrates, @value{GDBN} is very loose about the usual
13289 rules concerning aggregates. You may leave out some of the
13290 components of an array or record aggregate (such as the @code{Len}
13291 component in the assignment to @code{A_Rec} above); they will retain their
13292 original values upon assignment. You may freely use dynamic values as
13293 indices in component associations. You may even use overlapping or
13294 redundant component associations, although which component values are
13295 assigned in such cases is not defined.
13298 Calls to dispatching subprograms are not implemented.
13301 The overloading algorithm is much more limited (i.e., less selective)
13302 than that of real Ada. It makes only limited use of the context in
13303 which a subexpression appears to resolve its meaning, and it is much
13304 looser in its rules for allowing type matches. As a result, some
13305 function calls will be ambiguous, and the user will be asked to choose
13306 the proper resolution.
13309 The @code{new} operator is not implemented.
13312 Entry calls are not implemented.
13315 Aside from printing, arithmetic operations on the native VAX floating-point
13316 formats are not supported.
13319 It is not possible to slice a packed array.
13322 The names @code{True} and @code{False}, when not part of a qualified name,
13323 are interpreted as if implicitly prefixed by @code{Standard}, regardless of
13325 Should your program
13326 redefine these names in a package or procedure (at best a dubious practice),
13327 you will have to use fully qualified names to access their new definitions.
13330 @node Additions to Ada
13331 @subsubsection Additions to Ada
13332 @cindex Ada, deviations from
13334 As it does for other languages, @value{GDBN} makes certain generic
13335 extensions to Ada (@pxref{Expressions}):
13339 If the expression @var{E} is a variable residing in memory (typically
13340 a local variable or array element) and @var{N} is a positive integer,
13341 then @code{@var{E}@@@var{N}} displays the values of @var{E} and the
13342 @var{N}-1 adjacent variables following it in memory as an array. In
13343 Ada, this operator is generally not necessary, since its prime use is
13344 in displaying parts of an array, and slicing will usually do this in
13345 Ada. However, there are occasional uses when debugging programs in
13346 which certain debugging information has been optimized away.
13349 @code{@var{B}::@var{var}} means ``the variable named @var{var} that
13350 appears in function or file @var{B}.'' When @var{B} is a file name,
13351 you must typically surround it in single quotes.
13354 The expression @code{@{@var{type}@} @var{addr}} means ``the variable of type
13355 @var{type} that appears at address @var{addr}.''
13358 A name starting with @samp{$} is a convenience variable
13359 (@pxref{Convenience Vars}) or a machine register (@pxref{Registers}).
13362 In addition, @value{GDBN} provides a few other shortcuts and outright
13363 additions specific to Ada:
13367 The assignment statement is allowed as an expression, returning
13368 its right-hand operand as its value. Thus, you may enter
13371 (@value{GDBP}) set x := y + 3
13372 (@value{GDBP}) print A(tmp := y + 1)
13376 The semicolon is allowed as an ``operator,'' returning as its value
13377 the value of its right-hand operand.
13378 This allows, for example,
13379 complex conditional breaks:
13382 (@value{GDBP}) break f
13383 (@value{GDBP}) condition 1 (report(i); k += 1; A(k) > 100)
13387 Rather than use catenation and symbolic character names to introduce special
13388 characters into strings, one may instead use a special bracket notation,
13389 which is also used to print strings. A sequence of characters of the form
13390 @samp{["@var{XX}"]} within a string or character literal denotes the
13391 (single) character whose numeric encoding is @var{XX} in hexadecimal. The
13392 sequence of characters @samp{["""]} also denotes a single quotation mark
13393 in strings. For example,
13395 "One line.["0a"]Next line.["0a"]"
13398 contains an ASCII newline character (@code{Ada.Characters.Latin_1.LF})
13402 The subtype used as a prefix for the attributes @t{'Pos}, @t{'Min}, and
13403 @t{'Max} is optional (and is ignored in any case). For example, it is valid
13407 (@value{GDBP}) print 'max(x, y)
13411 When printing arrays, @value{GDBN} uses positional notation when the
13412 array has a lower bound of 1, and uses a modified named notation otherwise.
13413 For example, a one-dimensional array of three integers with a lower bound
13414 of 3 might print as
13421 That is, in contrast to valid Ada, only the first component has a @code{=>}
13425 You may abbreviate attributes in expressions with any unique,
13426 multi-character subsequence of
13427 their names (an exact match gets preference).
13428 For example, you may use @t{a'len}, @t{a'gth}, or @t{a'lh}
13429 in place of @t{a'length}.
13432 @cindex quoting Ada internal identifiers
13433 Since Ada is case-insensitive, the debugger normally maps identifiers you type
13434 to lower case. The GNAT compiler uses upper-case characters for
13435 some of its internal identifiers, which are normally of no interest to users.
13436 For the rare occasions when you actually have to look at them,
13437 enclose them in angle brackets to avoid the lower-case mapping.
13440 (@value{GDBP}) print <JMPBUF_SAVE>[0]
13444 Printing an object of class-wide type or dereferencing an
13445 access-to-class-wide value will display all the components of the object's
13446 specific type (as indicated by its run-time tag). Likewise, component
13447 selection on such a value will operate on the specific type of the
13452 @node Stopping Before Main Program
13453 @subsubsection Stopping at the Very Beginning
13455 @cindex breakpointing Ada elaboration code
13456 It is sometimes necessary to debug the program during elaboration, and
13457 before reaching the main procedure.
13458 As defined in the Ada Reference
13459 Manual, the elaboration code is invoked from a procedure called
13460 @code{adainit}. To run your program up to the beginning of
13461 elaboration, simply use the following two commands:
13462 @code{tbreak adainit} and @code{run}.
13465 @subsubsection Extensions for Ada Tasks
13466 @cindex Ada, tasking
13468 Support for Ada tasks is analogous to that for threads (@pxref{Threads}).
13469 @value{GDBN} provides the following task-related commands:
13474 This command shows a list of current Ada tasks, as in the following example:
13481 (@value{GDBP}) info tasks
13482 ID TID P-ID Pri State Name
13483 1 8088000 0 15 Child Activation Wait main_task
13484 2 80a4000 1 15 Accept Statement b
13485 3 809a800 1 15 Child Activation Wait a
13486 * 4 80ae800 3 15 Runnable c
13491 In this listing, the asterisk before the last task indicates it to be the
13492 task currently being inspected.
13496 Represents @value{GDBN}'s internal task number.
13502 The parent's task ID (@value{GDBN}'s internal task number).
13505 The base priority of the task.
13508 Current state of the task.
13512 The task has been created but has not been activated. It cannot be
13516 The task is not blocked for any reason known to Ada. (It may be waiting
13517 for a mutex, though.) It is conceptually "executing" in normal mode.
13520 The task is terminated, in the sense of ARM 9.3 (5). Any dependents
13521 that were waiting on terminate alternatives have been awakened and have
13522 terminated themselves.
13524 @item Child Activation Wait
13525 The task is waiting for created tasks to complete activation.
13527 @item Accept Statement
13528 The task is waiting on an accept or selective wait statement.
13530 @item Waiting on entry call
13531 The task is waiting on an entry call.
13533 @item Async Select Wait
13534 The task is waiting to start the abortable part of an asynchronous
13538 The task is waiting on a select statement with only a delay
13541 @item Child Termination Wait
13542 The task is sleeping having completed a master within itself, and is
13543 waiting for the tasks dependent on that master to become terminated or
13544 waiting on a terminate Phase.
13546 @item Wait Child in Term Alt
13547 The task is sleeping waiting for tasks on terminate alternatives to
13548 finish terminating.
13550 @item Accepting RV with @var{taskno}
13551 The task is accepting a rendez-vous with the task @var{taskno}.
13555 Name of the task in the program.
13559 @kindex info task @var{taskno}
13560 @item info task @var{taskno}
13561 This command shows detailled informations on the specified task, as in
13562 the following example:
13567 (@value{GDBP}) info tasks
13568 ID TID P-ID Pri State Name
13569 1 8077880 0 15 Child Activation Wait main_task
13570 * 2 807c468 1 15 Runnable task_1
13571 (@value{GDBP}) info task 2
13572 Ada Task: 0x807c468
13575 Parent: 1 (main_task)
13581 @kindex task@r{ (Ada)}
13582 @cindex current Ada task ID
13583 This command prints the ID of the current task.
13589 (@value{GDBP}) info tasks
13590 ID TID P-ID Pri State Name
13591 1 8077870 0 15 Child Activation Wait main_task
13592 * 2 807c458 1 15 Runnable t
13593 (@value{GDBP}) task
13594 [Current task is 2]
13597 @item task @var{taskno}
13598 @cindex Ada task switching
13599 This command is like the @code{thread @var{threadno}}
13600 command (@pxref{Threads}). It switches the context of debugging
13601 from the current task to the given task.
13607 (@value{GDBP}) info tasks
13608 ID TID P-ID Pri State Name
13609 1 8077870 0 15 Child Activation Wait main_task
13610 * 2 807c458 1 15 Runnable t
13611 (@value{GDBP}) task 1
13612 [Switching to task 1]
13613 #0 0x8067726 in pthread_cond_wait ()
13615 #0 0x8067726 in pthread_cond_wait ()
13616 #1 0x8056714 in system.os_interface.pthread_cond_wait ()
13617 #2 0x805cb63 in system.task_primitives.operations.sleep ()
13618 #3 0x806153e in system.tasking.stages.activate_tasks ()
13619 #4 0x804aacc in un () at un.adb:5
13622 @item break @var{linespec} task @var{taskno}
13623 @itemx break @var{linespec} task @var{taskno} if @dots{}
13624 @cindex breakpoints and tasks, in Ada
13625 @cindex task breakpoints, in Ada
13626 @kindex break @dots{} task @var{taskno}@r{ (Ada)}
13627 These commands are like the @code{break @dots{} thread @dots{}}
13628 command (@pxref{Thread Stops}).
13629 @var{linespec} specifies source lines, as described
13630 in @ref{Specify Location}.
13632 Use the qualifier @samp{task @var{taskno}} with a breakpoint command
13633 to specify that you only want @value{GDBN} to stop the program when a
13634 particular Ada task reaches this breakpoint. @var{taskno} is one of the
13635 numeric task identifiers assigned by @value{GDBN}, shown in the first
13636 column of the @samp{info tasks} display.
13638 If you do not specify @samp{task @var{taskno}} when you set a
13639 breakpoint, the breakpoint applies to @emph{all} tasks of your
13642 You can use the @code{task} qualifier on conditional breakpoints as
13643 well; in this case, place @samp{task @var{taskno}} before the
13644 breakpoint condition (before the @code{if}).
13652 (@value{GDBP}) info tasks
13653 ID TID P-ID Pri State Name
13654 1 140022020 0 15 Child Activation Wait main_task
13655 2 140045060 1 15 Accept/Select Wait t2
13656 3 140044840 1 15 Runnable t1
13657 * 4 140056040 1 15 Runnable t3
13658 (@value{GDBP}) b 15 task 2
13659 Breakpoint 5 at 0x120044cb0: file test_task_debug.adb, line 15.
13660 (@value{GDBP}) cont
13665 Breakpoint 5, test_task_debug () at test_task_debug.adb:15
13667 (@value{GDBP}) info tasks
13668 ID TID P-ID Pri State Name
13669 1 140022020 0 15 Child Activation Wait main_task
13670 * 2 140045060 1 15 Runnable t2
13671 3 140044840 1 15 Runnable t1
13672 4 140056040 1 15 Delay Sleep t3
13676 @node Ada Tasks and Core Files
13677 @subsubsection Tasking Support when Debugging Core Files
13678 @cindex Ada tasking and core file debugging
13680 When inspecting a core file, as opposed to debugging a live program,
13681 tasking support may be limited or even unavailable, depending on
13682 the platform being used.
13683 For instance, on x86-linux, the list of tasks is available, but task
13684 switching is not supported. On Tru64, however, task switching will work
13687 On certain platforms, including Tru64, the debugger needs to perform some
13688 memory writes in order to provide Ada tasking support. When inspecting
13689 a core file, this means that the core file must be opened with read-write
13690 privileges, using the command @samp{"set write on"} (@pxref{Patching}).
13691 Under these circumstances, you should make a backup copy of the core
13692 file before inspecting it with @value{GDBN}.
13694 @node Ravenscar Profile
13695 @subsubsection Tasking Support when using the Ravenscar Profile
13696 @cindex Ravenscar Profile
13698 The @dfn{Ravenscar Profile} is a subset of the Ada tasking features,
13699 specifically designed for systems with safety-critical real-time
13703 @kindex set ravenscar task-switching on
13704 @cindex task switching with program using Ravenscar Profile
13705 @item set ravenscar task-switching on
13706 Allows task switching when debugging a program that uses the Ravenscar
13707 Profile. This is the default.
13709 @kindex set ravenscar task-switching off
13710 @item set ravenscar task-switching off
13711 Turn off task switching when debugging a program that uses the Ravenscar
13712 Profile. This is mostly intended to disable the code that adds support
13713 for the Ravenscar Profile, in case a bug in either @value{GDBN} or in
13714 the Ravenscar runtime is preventing @value{GDBN} from working properly.
13715 To be effective, this command should be run before the program is started.
13717 @kindex show ravenscar task-switching
13718 @item show ravenscar task-switching
13719 Show whether it is possible to switch from task to task in a program
13720 using the Ravenscar Profile.
13725 @subsubsection Known Peculiarities of Ada Mode
13726 @cindex Ada, problems
13728 Besides the omissions listed previously (@pxref{Omissions from Ada}),
13729 we know of several problems with and limitations of Ada mode in
13731 some of which will be fixed with planned future releases of the debugger
13732 and the GNU Ada compiler.
13736 Static constants that the compiler chooses not to materialize as objects in
13737 storage are invisible to the debugger.
13740 Named parameter associations in function argument lists are ignored (the
13741 argument lists are treated as positional).
13744 Many useful library packages are currently invisible to the debugger.
13747 Fixed-point arithmetic, conversions, input, and output is carried out using
13748 floating-point arithmetic, and may give results that only approximate those on
13752 The GNAT compiler never generates the prefix @code{Standard} for any of
13753 the standard symbols defined by the Ada language. @value{GDBN} knows about
13754 this: it will strip the prefix from names when you use it, and will never
13755 look for a name you have so qualified among local symbols, nor match against
13756 symbols in other packages or subprograms. If you have
13757 defined entities anywhere in your program other than parameters and
13758 local variables whose simple names match names in @code{Standard},
13759 GNAT's lack of qualification here can cause confusion. When this happens,
13760 you can usually resolve the confusion
13761 by qualifying the problematic names with package
13762 @code{Standard} explicitly.
13765 Older versions of the compiler sometimes generate erroneous debugging
13766 information, resulting in the debugger incorrectly printing the value
13767 of affected entities. In some cases, the debugger is able to work
13768 around an issue automatically. In other cases, the debugger is able
13769 to work around the issue, but the work-around has to be specifically
13772 @kindex set ada trust-PAD-over-XVS
13773 @kindex show ada trust-PAD-over-XVS
13776 @item set ada trust-PAD-over-XVS on
13777 Configure GDB to strictly follow the GNAT encoding when computing the
13778 value of Ada entities, particularly when @code{PAD} and @code{PAD___XVS}
13779 types are involved (see @code{ada/exp_dbug.ads} in the GCC sources for
13780 a complete description of the encoding used by the GNAT compiler).
13781 This is the default.
13783 @item set ada trust-PAD-over-XVS off
13784 This is related to the encoding using by the GNAT compiler. If @value{GDBN}
13785 sometimes prints the wrong value for certain entities, changing @code{ada
13786 trust-PAD-over-XVS} to @code{off} activates a work-around which may fix
13787 the issue. It is always safe to set @code{ada trust-PAD-over-XVS} to
13788 @code{off}, but this incurs a slight performance penalty, so it is
13789 recommended to leave this setting to @code{on} unless necessary.
13793 @node Unsupported Languages
13794 @section Unsupported Languages
13796 @cindex unsupported languages
13797 @cindex minimal language
13798 In addition to the other fully-supported programming languages,
13799 @value{GDBN} also provides a pseudo-language, called @code{minimal}.
13800 It does not represent a real programming language, but provides a set
13801 of capabilities close to what the C or assembly languages provide.
13802 This should allow most simple operations to be performed while debugging
13803 an application that uses a language currently not supported by @value{GDBN}.
13805 If the language is set to @code{auto}, @value{GDBN} will automatically
13806 select this language if the current frame corresponds to an unsupported
13810 @chapter Examining the Symbol Table
13812 The commands described in this chapter allow you to inquire about the
13813 symbols (names of variables, functions and types) defined in your
13814 program. This information is inherent in the text of your program and
13815 does not change as your program executes. @value{GDBN} finds it in your
13816 program's symbol table, in the file indicated when you started @value{GDBN}
13817 (@pxref{File Options, ,Choosing Files}), or by one of the
13818 file-management commands (@pxref{Files, ,Commands to Specify Files}).
13820 @cindex symbol names
13821 @cindex names of symbols
13822 @cindex quoting names
13823 Occasionally, you may need to refer to symbols that contain unusual
13824 characters, which @value{GDBN} ordinarily treats as word delimiters. The
13825 most frequent case is in referring to static variables in other
13826 source files (@pxref{Variables,,Program Variables}). File names
13827 are recorded in object files as debugging symbols, but @value{GDBN} would
13828 ordinarily parse a typical file name, like @file{foo.c}, as the three words
13829 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
13830 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
13837 looks up the value of @code{x} in the scope of the file @file{foo.c}.
13840 @cindex case-insensitive symbol names
13841 @cindex case sensitivity in symbol names
13842 @kindex set case-sensitive
13843 @item set case-sensitive on
13844 @itemx set case-sensitive off
13845 @itemx set case-sensitive auto
13846 Normally, when @value{GDBN} looks up symbols, it matches their names
13847 with case sensitivity determined by the current source language.
13848 Occasionally, you may wish to control that. The command @code{set
13849 case-sensitive} lets you do that by specifying @code{on} for
13850 case-sensitive matches or @code{off} for case-insensitive ones. If
13851 you specify @code{auto}, case sensitivity is reset to the default
13852 suitable for the source language. The default is case-sensitive
13853 matches for all languages except for Fortran, for which the default is
13854 case-insensitive matches.
13856 @kindex show case-sensitive
13857 @item show case-sensitive
13858 This command shows the current setting of case sensitivity for symbols
13861 @kindex info address
13862 @cindex address of a symbol
13863 @item info address @var{symbol}
13864 Describe where the data for @var{symbol} is stored. For a register
13865 variable, this says which register it is kept in. For a non-register
13866 local variable, this prints the stack-frame offset at which the variable
13869 Note the contrast with @samp{print &@var{symbol}}, which does not work
13870 at all for a register variable, and for a stack local variable prints
13871 the exact address of the current instantiation of the variable.
13873 @kindex info symbol
13874 @cindex symbol from address
13875 @cindex closest symbol and offset for an address
13876 @item info symbol @var{addr}
13877 Print the name of a symbol which is stored at the address @var{addr}.
13878 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
13879 nearest symbol and an offset from it:
13882 (@value{GDBP}) info symbol 0x54320
13883 _initialize_vx + 396 in section .text
13887 This is the opposite of the @code{info address} command. You can use
13888 it to find out the name of a variable or a function given its address.
13890 For dynamically linked executables, the name of executable or shared
13891 library containing the symbol is also printed:
13894 (@value{GDBP}) info symbol 0x400225
13895 _start + 5 in section .text of /tmp/a.out
13896 (@value{GDBP}) info symbol 0x2aaaac2811cf
13897 __read_nocancel + 6 in section .text of /usr/lib64/libc.so.6
13901 @item whatis [@var{arg}]
13902 Print the data type of @var{arg}, which can be either an expression
13903 or a name of a data type. With no argument, print the data type of
13904 @code{$}, the last value in the value history.
13906 If @var{arg} is an expression (@pxref{Expressions, ,Expressions}), it
13907 is not actually evaluated, and any side-effecting operations (such as
13908 assignments or function calls) inside it do not take place.
13910 If @var{arg} is a variable or an expression, @code{whatis} prints its
13911 literal type as it is used in the source code. If the type was
13912 defined using a @code{typedef}, @code{whatis} will @emph{not} print
13913 the data type underlying the @code{typedef}. If the type of the
13914 variable or the expression is a compound data type, such as
13915 @code{struct} or @code{class}, @code{whatis} never prints their
13916 fields or methods. It just prints the @code{struct}/@code{class}
13917 name (a.k.a.@: its @dfn{tag}). If you want to see the members of
13918 such a compound data type, use @code{ptype}.
13920 If @var{arg} is a type name that was defined using @code{typedef},
13921 @code{whatis} @dfn{unrolls} only one level of that @code{typedef}.
13922 Unrolling means that @code{whatis} will show the underlying type used
13923 in the @code{typedef} declaration of @var{arg}. However, if that
13924 underlying type is also a @code{typedef}, @code{whatis} will not
13927 For C code, the type names may also have the form @samp{class
13928 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
13929 @var{union-tag}} or @samp{enum @var{enum-tag}}.
13932 @item ptype [@var{arg}]
13933 @code{ptype} accepts the same arguments as @code{whatis}, but prints a
13934 detailed description of the type, instead of just the name of the type.
13935 @xref{Expressions, ,Expressions}.
13937 Contrary to @code{whatis}, @code{ptype} always unrolls any
13938 @code{typedef}s in its argument declaration, whether the argument is
13939 a variable, expression, or a data type. This means that @code{ptype}
13940 of a variable or an expression will not print literally its type as
13941 present in the source code---use @code{whatis} for that. @code{typedef}s at
13942 the pointer or reference targets are also unrolled. Only @code{typedef}s of
13943 fields, methods and inner @code{class typedef}s of @code{struct}s,
13944 @code{class}es and @code{union}s are not unrolled even with @code{ptype}.
13946 For example, for this variable declaration:
13949 typedef double real_t;
13950 struct complex @{ real_t real; double imag; @};
13951 typedef struct complex complex_t;
13953 real_t *real_pointer_var;
13957 the two commands give this output:
13961 (@value{GDBP}) whatis var
13963 (@value{GDBP}) ptype var
13964 type = struct complex @{
13968 (@value{GDBP}) whatis complex_t
13969 type = struct complex
13970 (@value{GDBP}) whatis struct complex
13971 type = struct complex
13972 (@value{GDBP}) ptype struct complex
13973 type = struct complex @{
13977 (@value{GDBP}) whatis real_pointer_var
13979 (@value{GDBP}) ptype real_pointer_var
13985 As with @code{whatis}, using @code{ptype} without an argument refers to
13986 the type of @code{$}, the last value in the value history.
13988 @cindex incomplete type
13989 Sometimes, programs use opaque data types or incomplete specifications
13990 of complex data structure. If the debug information included in the
13991 program does not allow @value{GDBN} to display a full declaration of
13992 the data type, it will say @samp{<incomplete type>}. For example,
13993 given these declarations:
13997 struct foo *fooptr;
14001 but no definition for @code{struct foo} itself, @value{GDBN} will say:
14004 (@value{GDBP}) ptype foo
14005 $1 = <incomplete type>
14009 ``Incomplete type'' is C terminology for data types that are not
14010 completely specified.
14013 @item info types @var{regexp}
14015 Print a brief description of all types whose names match the regular
14016 expression @var{regexp} (or all types in your program, if you supply
14017 no argument). Each complete typename is matched as though it were a
14018 complete line; thus, @samp{i type value} gives information on all
14019 types in your program whose names include the string @code{value}, but
14020 @samp{i type ^value$} gives information only on types whose complete
14021 name is @code{value}.
14023 This command differs from @code{ptype} in two ways: first, like
14024 @code{whatis}, it does not print a detailed description; second, it
14025 lists all source files where a type is defined.
14028 @cindex local variables
14029 @item info scope @var{location}
14030 List all the variables local to a particular scope. This command
14031 accepts a @var{location} argument---a function name, a source line, or
14032 an address preceded by a @samp{*}, and prints all the variables local
14033 to the scope defined by that location. (@xref{Specify Location}, for
14034 details about supported forms of @var{location}.) For example:
14037 (@value{GDBP}) @b{info scope command_line_handler}
14038 Scope for command_line_handler:
14039 Symbol rl is an argument at stack/frame offset 8, length 4.
14040 Symbol linebuffer is in static storage at address 0x150a18, length 4.
14041 Symbol linelength is in static storage at address 0x150a1c, length 4.
14042 Symbol p is a local variable in register $esi, length 4.
14043 Symbol p1 is a local variable in register $ebx, length 4.
14044 Symbol nline is a local variable in register $edx, length 4.
14045 Symbol repeat is a local variable at frame offset -8, length 4.
14049 This command is especially useful for determining what data to collect
14050 during a @dfn{trace experiment}, see @ref{Tracepoint Actions,
14053 @kindex info source
14055 Show information about the current source file---that is, the source file for
14056 the function containing the current point of execution:
14059 the name of the source file, and the directory containing it,
14061 the directory it was compiled in,
14063 its length, in lines,
14065 which programming language it is written in,
14067 whether the executable includes debugging information for that file, and
14068 if so, what format the information is in (e.g., STABS, Dwarf 2, etc.), and
14070 whether the debugging information includes information about
14071 preprocessor macros.
14075 @kindex info sources
14077 Print the names of all source files in your program for which there is
14078 debugging information, organized into two lists: files whose symbols
14079 have already been read, and files whose symbols will be read when needed.
14081 @kindex info functions
14082 @item info functions
14083 Print the names and data types of all defined functions.
14085 @item info functions @var{regexp}
14086 Print the names and data types of all defined functions
14087 whose names contain a match for regular expression @var{regexp}.
14088 Thus, @samp{info fun step} finds all functions whose names
14089 include @code{step}; @samp{info fun ^step} finds those whose names
14090 start with @code{step}. If a function name contains characters
14091 that conflict with the regular expression language (e.g.@:
14092 @samp{operator*()}), they may be quoted with a backslash.
14094 @kindex info variables
14095 @item info variables
14096 Print the names and data types of all variables that are defined
14097 outside of functions (i.e.@: excluding local variables).
14099 @item info variables @var{regexp}
14100 Print the names and data types of all variables (except for local
14101 variables) whose names contain a match for regular expression
14104 @kindex info classes
14105 @cindex Objective-C, classes and selectors
14107 @itemx info classes @var{regexp}
14108 Display all Objective-C classes in your program, or
14109 (with the @var{regexp} argument) all those matching a particular regular
14112 @kindex info selectors
14113 @item info selectors
14114 @itemx info selectors @var{regexp}
14115 Display all Objective-C selectors in your program, or
14116 (with the @var{regexp} argument) all those matching a particular regular
14120 This was never implemented.
14121 @kindex info methods
14123 @itemx info methods @var{regexp}
14124 The @code{info methods} command permits the user to examine all defined
14125 methods within C@t{++} program, or (with the @var{regexp} argument) a
14126 specific set of methods found in the various C@t{++} classes. Many
14127 C@t{++} classes provide a large number of methods. Thus, the output
14128 from the @code{ptype} command can be overwhelming and hard to use. The
14129 @code{info-methods} command filters the methods, printing only those
14130 which match the regular-expression @var{regexp}.
14133 @cindex reloading symbols
14134 Some systems allow individual object files that make up your program to
14135 be replaced without stopping and restarting your program. For example,
14136 in VxWorks you can simply recompile a defective object file and keep on
14137 running. If you are running on one of these systems, you can allow
14138 @value{GDBN} to reload the symbols for automatically relinked modules:
14141 @kindex set symbol-reloading
14142 @item set symbol-reloading on
14143 Replace symbol definitions for the corresponding source file when an
14144 object file with a particular name is seen again.
14146 @item set symbol-reloading off
14147 Do not replace symbol definitions when encountering object files of the
14148 same name more than once. This is the default state; if you are not
14149 running on a system that permits automatic relinking of modules, you
14150 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
14151 may discard symbols when linking large programs, that may contain
14152 several modules (from different directories or libraries) with the same
14155 @kindex show symbol-reloading
14156 @item show symbol-reloading
14157 Show the current @code{on} or @code{off} setting.
14160 @cindex opaque data types
14161 @kindex set opaque-type-resolution
14162 @item set opaque-type-resolution on
14163 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
14164 declared as a pointer to a @code{struct}, @code{class}, or
14165 @code{union}---for example, @code{struct MyType *}---that is used in one
14166 source file although the full declaration of @code{struct MyType} is in
14167 another source file. The default is on.
14169 A change in the setting of this subcommand will not take effect until
14170 the next time symbols for a file are loaded.
14172 @item set opaque-type-resolution off
14173 Tell @value{GDBN} not to resolve opaque types. In this case, the type
14174 is printed as follows:
14176 @{<no data fields>@}
14179 @kindex show opaque-type-resolution
14180 @item show opaque-type-resolution
14181 Show whether opaque types are resolved or not.
14183 @kindex maint print symbols
14184 @cindex symbol dump
14185 @kindex maint print psymbols
14186 @cindex partial symbol dump
14187 @item maint print symbols @var{filename}
14188 @itemx maint print psymbols @var{filename}
14189 @itemx maint print msymbols @var{filename}
14190 Write a dump of debugging symbol data into the file @var{filename}.
14191 These commands are used to debug the @value{GDBN} symbol-reading code. Only
14192 symbols with debugging data are included. If you use @samp{maint print
14193 symbols}, @value{GDBN} includes all the symbols for which it has already
14194 collected full details: that is, @var{filename} reflects symbols for
14195 only those files whose symbols @value{GDBN} has read. You can use the
14196 command @code{info sources} to find out which files these are. If you
14197 use @samp{maint print psymbols} instead, the dump shows information about
14198 symbols that @value{GDBN} only knows partially---that is, symbols defined in
14199 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
14200 @samp{maint print msymbols} dumps just the minimal symbol information
14201 required for each object file from which @value{GDBN} has read some symbols.
14202 @xref{Files, ,Commands to Specify Files}, for a discussion of how
14203 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
14205 @kindex maint info symtabs
14206 @kindex maint info psymtabs
14207 @cindex listing @value{GDBN}'s internal symbol tables
14208 @cindex symbol tables, listing @value{GDBN}'s internal
14209 @cindex full symbol tables, listing @value{GDBN}'s internal
14210 @cindex partial symbol tables, listing @value{GDBN}'s internal
14211 @item maint info symtabs @r{[} @var{regexp} @r{]}
14212 @itemx maint info psymtabs @r{[} @var{regexp} @r{]}
14214 List the @code{struct symtab} or @code{struct partial_symtab}
14215 structures whose names match @var{regexp}. If @var{regexp} is not
14216 given, list them all. The output includes expressions which you can
14217 copy into a @value{GDBN} debugging this one to examine a particular
14218 structure in more detail. For example:
14221 (@value{GDBP}) maint info psymtabs dwarf2read
14222 @{ objfile /home/gnu/build/gdb/gdb
14223 ((struct objfile *) 0x82e69d0)
14224 @{ psymtab /home/gnu/src/gdb/dwarf2read.c
14225 ((struct partial_symtab *) 0x8474b10)
14228 text addresses 0x814d3c8 -- 0x8158074
14229 globals (* (struct partial_symbol **) 0x8507a08 @@ 9)
14230 statics (* (struct partial_symbol **) 0x40e95b78 @@ 2882)
14231 dependencies (none)
14234 (@value{GDBP}) maint info symtabs
14238 We see that there is one partial symbol table whose filename contains
14239 the string @samp{dwarf2read}, belonging to the @samp{gdb} executable;
14240 and we see that @value{GDBN} has not read in any symtabs yet at all.
14241 If we set a breakpoint on a function, that will cause @value{GDBN} to
14242 read the symtab for the compilation unit containing that function:
14245 (@value{GDBP}) break dwarf2_psymtab_to_symtab
14246 Breakpoint 1 at 0x814e5da: file /home/gnu/src/gdb/dwarf2read.c,
14248 (@value{GDBP}) maint info symtabs
14249 @{ objfile /home/gnu/build/gdb/gdb
14250 ((struct objfile *) 0x82e69d0)
14251 @{ symtab /home/gnu/src/gdb/dwarf2read.c
14252 ((struct symtab *) 0x86c1f38)
14255 blockvector ((struct blockvector *) 0x86c1bd0) (primary)
14256 linetable ((struct linetable *) 0x8370fa0)
14257 debugformat DWARF 2
14266 @chapter Altering Execution
14268 Once you think you have found an error in your program, you might want to
14269 find out for certain whether correcting the apparent error would lead to
14270 correct results in the rest of the run. You can find the answer by
14271 experiment, using the @value{GDBN} features for altering execution of the
14274 For example, you can store new values into variables or memory
14275 locations, give your program a signal, restart it at a different
14276 address, or even return prematurely from a function.
14279 * Assignment:: Assignment to variables
14280 * Jumping:: Continuing at a different address
14281 * Signaling:: Giving your program a signal
14282 * Returning:: Returning from a function
14283 * Calling:: Calling your program's functions
14284 * Patching:: Patching your program
14288 @section Assignment to Variables
14291 @cindex setting variables
14292 To alter the value of a variable, evaluate an assignment expression.
14293 @xref{Expressions, ,Expressions}. For example,
14300 stores the value 4 into the variable @code{x}, and then prints the
14301 value of the assignment expression (which is 4).
14302 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
14303 information on operators in supported languages.
14305 @kindex set variable
14306 @cindex variables, setting
14307 If you are not interested in seeing the value of the assignment, use the
14308 @code{set} command instead of the @code{print} command. @code{set} is
14309 really the same as @code{print} except that the expression's value is
14310 not printed and is not put in the value history (@pxref{Value History,
14311 ,Value History}). The expression is evaluated only for its effects.
14313 If the beginning of the argument string of the @code{set} command
14314 appears identical to a @code{set} subcommand, use the @code{set
14315 variable} command instead of just @code{set}. This command is identical
14316 to @code{set} except for its lack of subcommands. For example, if your
14317 program has a variable @code{width}, you get an error if you try to set
14318 a new value with just @samp{set width=13}, because @value{GDBN} has the
14319 command @code{set width}:
14322 (@value{GDBP}) whatis width
14324 (@value{GDBP}) p width
14326 (@value{GDBP}) set width=47
14327 Invalid syntax in expression.
14331 The invalid expression, of course, is @samp{=47}. In
14332 order to actually set the program's variable @code{width}, use
14335 (@value{GDBP}) set var width=47
14338 Because the @code{set} command has many subcommands that can conflict
14339 with the names of program variables, it is a good idea to use the
14340 @code{set variable} command instead of just @code{set}. For example, if
14341 your program has a variable @code{g}, you run into problems if you try
14342 to set a new value with just @samp{set g=4}, because @value{GDBN} has
14343 the command @code{set gnutarget}, abbreviated @code{set g}:
14347 (@value{GDBP}) whatis g
14351 (@value{GDBP}) set g=4
14355 The program being debugged has been started already.
14356 Start it from the beginning? (y or n) y
14357 Starting program: /home/smith/cc_progs/a.out
14358 "/home/smith/cc_progs/a.out": can't open to read symbols:
14359 Invalid bfd target.
14360 (@value{GDBP}) show g
14361 The current BFD target is "=4".
14366 The program variable @code{g} did not change, and you silently set the
14367 @code{gnutarget} to an invalid value. In order to set the variable
14371 (@value{GDBP}) set var g=4
14374 @value{GDBN} allows more implicit conversions in assignments than C; you can
14375 freely store an integer value into a pointer variable or vice versa,
14376 and you can convert any structure to any other structure that is the
14377 same length or shorter.
14378 @comment FIXME: how do structs align/pad in these conversions?
14379 @comment /doc@cygnus.com 18dec1990
14381 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
14382 construct to generate a value of specified type at a specified address
14383 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
14384 to memory location @code{0x83040} as an integer (which implies a certain size
14385 and representation in memory), and
14388 set @{int@}0x83040 = 4
14392 stores the value 4 into that memory location.
14395 @section Continuing at a Different Address
14397 Ordinarily, when you continue your program, you do so at the place where
14398 it stopped, with the @code{continue} command. You can instead continue at
14399 an address of your own choosing, with the following commands:
14403 @item jump @var{linespec}
14404 @itemx jump @var{location}
14405 Resume execution at line @var{linespec} or at address given by
14406 @var{location}. Execution stops again immediately if there is a
14407 breakpoint there. @xref{Specify Location}, for a description of the
14408 different forms of @var{linespec} and @var{location}. It is common
14409 practice to use the @code{tbreak} command in conjunction with
14410 @code{jump}. @xref{Set Breaks, ,Setting Breakpoints}.
14412 The @code{jump} command does not change the current stack frame, or
14413 the stack pointer, or the contents of any memory location or any
14414 register other than the program counter. If line @var{linespec} is in
14415 a different function from the one currently executing, the results may
14416 be bizarre if the two functions expect different patterns of arguments or
14417 of local variables. For this reason, the @code{jump} command requests
14418 confirmation if the specified line is not in the function currently
14419 executing. However, even bizarre results are predictable if you are
14420 well acquainted with the machine-language code of your program.
14423 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
14424 On many systems, you can get much the same effect as the @code{jump}
14425 command by storing a new value into the register @code{$pc}. The
14426 difference is that this does not start your program running; it only
14427 changes the address of where it @emph{will} run when you continue. For
14435 makes the next @code{continue} command or stepping command execute at
14436 address @code{0x485}, rather than at the address where your program stopped.
14437 @xref{Continuing and Stepping, ,Continuing and Stepping}.
14439 The most common occasion to use the @code{jump} command is to back
14440 up---perhaps with more breakpoints set---over a portion of a program
14441 that has already executed, in order to examine its execution in more
14446 @section Giving your Program a Signal
14447 @cindex deliver a signal to a program
14451 @item signal @var{signal}
14452 Resume execution where your program stopped, but immediately give it the
14453 signal @var{signal}. @var{signal} can be the name or the number of a
14454 signal. For example, on many systems @code{signal 2} and @code{signal
14455 SIGINT} are both ways of sending an interrupt signal.
14457 Alternatively, if @var{signal} is zero, continue execution without
14458 giving a signal. This is useful when your program stopped on account of
14459 a signal and would ordinary see the signal when resumed with the
14460 @code{continue} command; @samp{signal 0} causes it to resume without a
14463 @code{signal} does not repeat when you press @key{RET} a second time
14464 after executing the command.
14468 Invoking the @code{signal} command is not the same as invoking the
14469 @code{kill} utility from the shell. Sending a signal with @code{kill}
14470 causes @value{GDBN} to decide what to do with the signal depending on
14471 the signal handling tables (@pxref{Signals}). The @code{signal} command
14472 passes the signal directly to your program.
14476 @section Returning from a Function
14479 @cindex returning from a function
14482 @itemx return @var{expression}
14483 You can cancel execution of a function call with the @code{return}
14484 command. If you give an
14485 @var{expression} argument, its value is used as the function's return
14489 When you use @code{return}, @value{GDBN} discards the selected stack frame
14490 (and all frames within it). You can think of this as making the
14491 discarded frame return prematurely. If you wish to specify a value to
14492 be returned, give that value as the argument to @code{return}.
14494 This pops the selected stack frame (@pxref{Selection, ,Selecting a
14495 Frame}), and any other frames inside of it, leaving its caller as the
14496 innermost remaining frame. That frame becomes selected. The
14497 specified value is stored in the registers used for returning values
14500 The @code{return} command does not resume execution; it leaves the
14501 program stopped in the state that would exist if the function had just
14502 returned. In contrast, the @code{finish} command (@pxref{Continuing
14503 and Stepping, ,Continuing and Stepping}) resumes execution until the
14504 selected stack frame returns naturally.
14506 @value{GDBN} needs to know how the @var{expression} argument should be set for
14507 the inferior. The concrete registers assignment depends on the OS ABI and the
14508 type being returned by the selected stack frame. For example it is common for
14509 OS ABI to return floating point values in FPU registers while integer values in
14510 CPU registers. Still some ABIs return even floating point values in CPU
14511 registers. Larger integer widths (such as @code{long long int}) also have
14512 specific placement rules. @value{GDBN} already knows the OS ABI from its
14513 current target so it needs to find out also the type being returned to make the
14514 assignment into the right register(s).
14516 Normally, the selected stack frame has debug info. @value{GDBN} will always
14517 use the debug info instead of the implicit type of @var{expression} when the
14518 debug info is available. For example, if you type @kbd{return -1}, and the
14519 function in the current stack frame is declared to return a @code{long long
14520 int}, @value{GDBN} transparently converts the implicit @code{int} value of -1
14521 into a @code{long long int}:
14524 Breakpoint 1, func () at gdb.base/return-nodebug.c:29
14526 (@value{GDBP}) return -1
14527 Make func return now? (y or n) y
14528 #0 0x004004f6 in main () at gdb.base/return-nodebug.c:43
14529 43 printf ("result=%lld\n", func ());
14533 However, if the selected stack frame does not have a debug info, e.g., if the
14534 function was compiled without debug info, @value{GDBN} has to find out the type
14535 to return from user. Specifying a different type by mistake may set the value
14536 in different inferior registers than the caller code expects. For example,
14537 typing @kbd{return -1} with its implicit type @code{int} would set only a part
14538 of a @code{long long int} result for a debug info less function (on 32-bit
14539 architectures). Therefore the user is required to specify the return type by
14540 an appropriate cast explicitly:
14543 Breakpoint 2, 0x0040050b in func ()
14544 (@value{GDBP}) return -1
14545 Return value type not available for selected stack frame.
14546 Please use an explicit cast of the value to return.
14547 (@value{GDBP}) return (long long int) -1
14548 Make selected stack frame return now? (y or n) y
14549 #0 0x00400526 in main ()
14554 @section Calling Program Functions
14557 @cindex calling functions
14558 @cindex inferior functions, calling
14559 @item print @var{expr}
14560 Evaluate the expression @var{expr} and display the resulting value.
14561 @var{expr} may include calls to functions in the program being
14565 @item call @var{expr}
14566 Evaluate the expression @var{expr} without displaying @code{void}
14569 You can use this variant of the @code{print} command if you want to
14570 execute a function from your program that does not return anything
14571 (a.k.a.@: @dfn{a void function}), but without cluttering the output
14572 with @code{void} returned values that @value{GDBN} will otherwise
14573 print. If the result is not void, it is printed and saved in the
14577 It is possible for the function you call via the @code{print} or
14578 @code{call} command to generate a signal (e.g., if there's a bug in
14579 the function, or if you passed it incorrect arguments). What happens
14580 in that case is controlled by the @code{set unwindonsignal} command.
14582 Similarly, with a C@t{++} program it is possible for the function you
14583 call via the @code{print} or @code{call} command to generate an
14584 exception that is not handled due to the constraints of the dummy
14585 frame. In this case, any exception that is raised in the frame, but has
14586 an out-of-frame exception handler will not be found. GDB builds a
14587 dummy-frame for the inferior function call, and the unwinder cannot
14588 seek for exception handlers outside of this dummy-frame. What happens
14589 in that case is controlled by the
14590 @code{set unwind-on-terminating-exception} command.
14593 @item set unwindonsignal
14594 @kindex set unwindonsignal
14595 @cindex unwind stack in called functions
14596 @cindex call dummy stack unwinding
14597 Set unwinding of the stack if a signal is received while in a function
14598 that @value{GDBN} called in the program being debugged. If set to on,
14599 @value{GDBN} unwinds the stack it created for the call and restores
14600 the context to what it was before the call. If set to off (the
14601 default), @value{GDBN} stops in the frame where the signal was
14604 @item show unwindonsignal
14605 @kindex show unwindonsignal
14606 Show the current setting of stack unwinding in the functions called by
14609 @item set unwind-on-terminating-exception
14610 @kindex set unwind-on-terminating-exception
14611 @cindex unwind stack in called functions with unhandled exceptions
14612 @cindex call dummy stack unwinding on unhandled exception.
14613 Set unwinding of the stack if a C@t{++} exception is raised, but left
14614 unhandled while in a function that @value{GDBN} called in the program being
14615 debugged. If set to on (the default), @value{GDBN} unwinds the stack
14616 it created for the call and restores the context to what it was before
14617 the call. If set to off, @value{GDBN} the exception is delivered to
14618 the default C@t{++} exception handler and the inferior terminated.
14620 @item show unwind-on-terminating-exception
14621 @kindex show unwind-on-terminating-exception
14622 Show the current setting of stack unwinding in the functions called by
14627 @cindex weak alias functions
14628 Sometimes, a function you wish to call is actually a @dfn{weak alias}
14629 for another function. In such case, @value{GDBN} might not pick up
14630 the type information, including the types of the function arguments,
14631 which causes @value{GDBN} to call the inferior function incorrectly.
14632 As a result, the called function will function erroneously and may
14633 even crash. A solution to that is to use the name of the aliased
14637 @section Patching Programs
14639 @cindex patching binaries
14640 @cindex writing into executables
14641 @cindex writing into corefiles
14643 By default, @value{GDBN} opens the file containing your program's
14644 executable code (or the corefile) read-only. This prevents accidental
14645 alterations to machine code; but it also prevents you from intentionally
14646 patching your program's binary.
14648 If you'd like to be able to patch the binary, you can specify that
14649 explicitly with the @code{set write} command. For example, you might
14650 want to turn on internal debugging flags, or even to make emergency
14656 @itemx set write off
14657 If you specify @samp{set write on}, @value{GDBN} opens executable and
14658 core files for both reading and writing; if you specify @kbd{set write
14659 off} (the default), @value{GDBN} opens them read-only.
14661 If you have already loaded a file, you must load it again (using the
14662 @code{exec-file} or @code{core-file} command) after changing @code{set
14663 write}, for your new setting to take effect.
14667 Display whether executable files and core files are opened for writing
14668 as well as reading.
14672 @chapter @value{GDBN} Files
14674 @value{GDBN} needs to know the file name of the program to be debugged,
14675 both in order to read its symbol table and in order to start your
14676 program. To debug a core dump of a previous run, you must also tell
14677 @value{GDBN} the name of the core dump file.
14680 * Files:: Commands to specify files
14681 * Separate Debug Files:: Debugging information in separate files
14682 * Index Files:: Index files speed up GDB
14683 * Symbol Errors:: Errors reading symbol files
14684 * Data Files:: GDB data files
14688 @section Commands to Specify Files
14690 @cindex symbol table
14691 @cindex core dump file
14693 You may want to specify executable and core dump file names. The usual
14694 way to do this is at start-up time, using the arguments to
14695 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
14696 Out of @value{GDBN}}).
14698 Occasionally it is necessary to change to a different file during a
14699 @value{GDBN} session. Or you may run @value{GDBN} and forget to
14700 specify a file you want to use. Or you are debugging a remote target
14701 via @code{gdbserver} (@pxref{Server, file, Using the @code{gdbserver}
14702 Program}). In these situations the @value{GDBN} commands to specify
14703 new files are useful.
14706 @cindex executable file
14708 @item file @var{filename}
14709 Use @var{filename} as the program to be debugged. It is read for its
14710 symbols and for the contents of pure memory. It is also the program
14711 executed when you use the @code{run} command. If you do not specify a
14712 directory and the file is not found in the @value{GDBN} working directory,
14713 @value{GDBN} uses the environment variable @code{PATH} as a list of
14714 directories to search, just as the shell does when looking for a program
14715 to run. You can change the value of this variable, for both @value{GDBN}
14716 and your program, using the @code{path} command.
14718 @cindex unlinked object files
14719 @cindex patching object files
14720 You can load unlinked object @file{.o} files into @value{GDBN} using
14721 the @code{file} command. You will not be able to ``run'' an object
14722 file, but you can disassemble functions and inspect variables. Also,
14723 if the underlying BFD functionality supports it, you could use
14724 @kbd{gdb -write} to patch object files using this technique. Note
14725 that @value{GDBN} can neither interpret nor modify relocations in this
14726 case, so branches and some initialized variables will appear to go to
14727 the wrong place. But this feature is still handy from time to time.
14730 @code{file} with no argument makes @value{GDBN} discard any information it
14731 has on both executable file and the symbol table.
14734 @item exec-file @r{[} @var{filename} @r{]}
14735 Specify that the program to be run (but not the symbol table) is found
14736 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
14737 if necessary to locate your program. Omitting @var{filename} means to
14738 discard information on the executable file.
14740 @kindex symbol-file
14741 @item symbol-file @r{[} @var{filename} @r{]}
14742 Read symbol table information from file @var{filename}. @code{PATH} is
14743 searched when necessary. Use the @code{file} command to get both symbol
14744 table and program to run from the same file.
14746 @code{symbol-file} with no argument clears out @value{GDBN} information on your
14747 program's symbol table.
14749 The @code{symbol-file} command causes @value{GDBN} to forget the contents of
14750 some breakpoints and auto-display expressions. This is because they may
14751 contain pointers to the internal data recording symbols and data types,
14752 which are part of the old symbol table data being discarded inside
14755 @code{symbol-file} does not repeat if you press @key{RET} again after
14758 When @value{GDBN} is configured for a particular environment, it
14759 understands debugging information in whatever format is the standard
14760 generated for that environment; you may use either a @sc{gnu} compiler, or
14761 other compilers that adhere to the local conventions.
14762 Best results are usually obtained from @sc{gnu} compilers; for example,
14763 using @code{@value{NGCC}} you can generate debugging information for
14766 For most kinds of object files, with the exception of old SVR3 systems
14767 using COFF, the @code{symbol-file} command does not normally read the
14768 symbol table in full right away. Instead, it scans the symbol table
14769 quickly to find which source files and which symbols are present. The
14770 details are read later, one source file at a time, as they are needed.
14772 The purpose of this two-stage reading strategy is to make @value{GDBN}
14773 start up faster. For the most part, it is invisible except for
14774 occasional pauses while the symbol table details for a particular source
14775 file are being read. (The @code{set verbose} command can turn these
14776 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
14777 Warnings and Messages}.)
14779 We have not implemented the two-stage strategy for COFF yet. When the
14780 symbol table is stored in COFF format, @code{symbol-file} reads the
14781 symbol table data in full right away. Note that ``stabs-in-COFF''
14782 still does the two-stage strategy, since the debug info is actually
14786 @cindex reading symbols immediately
14787 @cindex symbols, reading immediately
14788 @item symbol-file @r{[} -readnow @r{]} @var{filename}
14789 @itemx file @r{[} -readnow @r{]} @var{filename}
14790 You can override the @value{GDBN} two-stage strategy for reading symbol
14791 tables by using the @samp{-readnow} option with any of the commands that
14792 load symbol table information, if you want to be sure @value{GDBN} has the
14793 entire symbol table available.
14795 @c FIXME: for now no mention of directories, since this seems to be in
14796 @c flux. 13mar1992 status is that in theory GDB would look either in
14797 @c current dir or in same dir as myprog; but issues like competing
14798 @c GDB's, or clutter in system dirs, mean that in practice right now
14799 @c only current dir is used. FFish says maybe a special GDB hierarchy
14800 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
14804 @item core-file @r{[}@var{filename}@r{]}
14806 Specify the whereabouts of a core dump file to be used as the ``contents
14807 of memory''. Traditionally, core files contain only some parts of the
14808 address space of the process that generated them; @value{GDBN} can access the
14809 executable file itself for other parts.
14811 @code{core-file} with no argument specifies that no core file is
14814 Note that the core file is ignored when your program is actually running
14815 under @value{GDBN}. So, if you have been running your program and you
14816 wish to debug a core file instead, you must kill the subprocess in which
14817 the program is running. To do this, use the @code{kill} command
14818 (@pxref{Kill Process, ,Killing the Child Process}).
14820 @kindex add-symbol-file
14821 @cindex dynamic linking
14822 @item add-symbol-file @var{filename} @var{address}
14823 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]}
14824 @itemx add-symbol-file @var{filename} @var{address} -s @var{section} @var{address} @dots{}
14825 The @code{add-symbol-file} command reads additional symbol table
14826 information from the file @var{filename}. You would use this command
14827 when @var{filename} has been dynamically loaded (by some other means)
14828 into the program that is running. @var{address} should be the memory
14829 address at which the file has been loaded; @value{GDBN} cannot figure
14830 this out for itself. You can additionally specify an arbitrary number
14831 of @samp{-s @var{section} @var{address}} pairs, to give an explicit
14832 section name and base address for that section. You can specify any
14833 @var{address} as an expression.
14835 The symbol table of the file @var{filename} is added to the symbol table
14836 originally read with the @code{symbol-file} command. You can use the
14837 @code{add-symbol-file} command any number of times; the new symbol data
14838 thus read keeps adding to the old. To discard all old symbol data
14839 instead, use the @code{symbol-file} command without any arguments.
14841 @cindex relocatable object files, reading symbols from
14842 @cindex object files, relocatable, reading symbols from
14843 @cindex reading symbols from relocatable object files
14844 @cindex symbols, reading from relocatable object files
14845 @cindex @file{.o} files, reading symbols from
14846 Although @var{filename} is typically a shared library file, an
14847 executable file, or some other object file which has been fully
14848 relocated for loading into a process, you can also load symbolic
14849 information from relocatable @file{.o} files, as long as:
14853 the file's symbolic information refers only to linker symbols defined in
14854 that file, not to symbols defined by other object files,
14856 every section the file's symbolic information refers to has actually
14857 been loaded into the inferior, as it appears in the file, and
14859 you can determine the address at which every section was loaded, and
14860 provide these to the @code{add-symbol-file} command.
14864 Some embedded operating systems, like Sun Chorus and VxWorks, can load
14865 relocatable files into an already running program; such systems
14866 typically make the requirements above easy to meet. However, it's
14867 important to recognize that many native systems use complex link
14868 procedures (@code{.linkonce} section factoring and C@t{++} constructor table
14869 assembly, for example) that make the requirements difficult to meet. In
14870 general, one cannot assume that using @code{add-symbol-file} to read a
14871 relocatable object file's symbolic information will have the same effect
14872 as linking the relocatable object file into the program in the normal
14875 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
14877 @kindex add-symbol-file-from-memory
14878 @cindex @code{syscall DSO}
14879 @cindex load symbols from memory
14880 @item add-symbol-file-from-memory @var{address}
14881 Load symbols from the given @var{address} in a dynamically loaded
14882 object file whose image is mapped directly into the inferior's memory.
14883 For example, the Linux kernel maps a @code{syscall DSO} into each
14884 process's address space; this DSO provides kernel-specific code for
14885 some system calls. The argument can be any expression whose
14886 evaluation yields the address of the file's shared object file header.
14887 For this command to work, you must have used @code{symbol-file} or
14888 @code{exec-file} commands in advance.
14890 @kindex add-shared-symbol-files
14892 @item add-shared-symbol-files @var{library-file}
14893 @itemx assf @var{library-file}
14894 The @code{add-shared-symbol-files} command can currently be used only
14895 in the Cygwin build of @value{GDBN} on MS-Windows OS, where it is an
14896 alias for the @code{dll-symbols} command (@pxref{Cygwin Native}).
14897 @value{GDBN} automatically looks for shared libraries, however if
14898 @value{GDBN} does not find yours, you can invoke
14899 @code{add-shared-symbol-files}. It takes one argument: the shared
14900 library's file name. @code{assf} is a shorthand alias for
14901 @code{add-shared-symbol-files}.
14904 @item section @var{section} @var{addr}
14905 The @code{section} command changes the base address of the named
14906 @var{section} of the exec file to @var{addr}. This can be used if the
14907 exec file does not contain section addresses, (such as in the
14908 @code{a.out} format), or when the addresses specified in the file
14909 itself are wrong. Each section must be changed separately. The
14910 @code{info files} command, described below, lists all the sections and
14914 @kindex info target
14917 @code{info files} and @code{info target} are synonymous; both print the
14918 current target (@pxref{Targets, ,Specifying a Debugging Target}),
14919 including the names of the executable and core dump files currently in
14920 use by @value{GDBN}, and the files from which symbols were loaded. The
14921 command @code{help target} lists all possible targets rather than
14924 @kindex maint info sections
14925 @item maint info sections
14926 Another command that can give you extra information about program sections
14927 is @code{maint info sections}. In addition to the section information
14928 displayed by @code{info files}, this command displays the flags and file
14929 offset of each section in the executable and core dump files. In addition,
14930 @code{maint info sections} provides the following command options (which
14931 may be arbitrarily combined):
14935 Display sections for all loaded object files, including shared libraries.
14936 @item @var{sections}
14937 Display info only for named @var{sections}.
14938 @item @var{section-flags}
14939 Display info only for sections for which @var{section-flags} are true.
14940 The section flags that @value{GDBN} currently knows about are:
14943 Section will have space allocated in the process when loaded.
14944 Set for all sections except those containing debug information.
14946 Section will be loaded from the file into the child process memory.
14947 Set for pre-initialized code and data, clear for @code{.bss} sections.
14949 Section needs to be relocated before loading.
14951 Section cannot be modified by the child process.
14953 Section contains executable code only.
14955 Section contains data only (no executable code).
14957 Section will reside in ROM.
14959 Section contains data for constructor/destructor lists.
14961 Section is not empty.
14963 An instruction to the linker to not output the section.
14964 @item COFF_SHARED_LIBRARY
14965 A notification to the linker that the section contains
14966 COFF shared library information.
14968 Section contains common symbols.
14971 @kindex set trust-readonly-sections
14972 @cindex read-only sections
14973 @item set trust-readonly-sections on
14974 Tell @value{GDBN} that readonly sections in your object file
14975 really are read-only (i.e.@: that their contents will not change).
14976 In that case, @value{GDBN} can fetch values from these sections
14977 out of the object file, rather than from the target program.
14978 For some targets (notably embedded ones), this can be a significant
14979 enhancement to debugging performance.
14981 The default is off.
14983 @item set trust-readonly-sections off
14984 Tell @value{GDBN} not to trust readonly sections. This means that
14985 the contents of the section might change while the program is running,
14986 and must therefore be fetched from the target when needed.
14988 @item show trust-readonly-sections
14989 Show the current setting of trusting readonly sections.
14992 All file-specifying commands allow both absolute and relative file names
14993 as arguments. @value{GDBN} always converts the file name to an absolute file
14994 name and remembers it that way.
14996 @cindex shared libraries
14997 @anchor{Shared Libraries}
14998 @value{GDBN} supports @sc{gnu}/Linux, MS-Windows, HP-UX, SunOS, SVr4, Irix,
14999 and IBM RS/6000 AIX shared libraries.
15001 On MS-Windows @value{GDBN} must be linked with the Expat library to support
15002 shared libraries. @xref{Expat}.
15004 @value{GDBN} automatically loads symbol definitions from shared libraries
15005 when you use the @code{run} command, or when you examine a core file.
15006 (Before you issue the @code{run} command, @value{GDBN} does not understand
15007 references to a function in a shared library, however---unless you are
15008 debugging a core file).
15010 On HP-UX, if the program loads a library explicitly, @value{GDBN}
15011 automatically loads the symbols at the time of the @code{shl_load} call.
15013 @c FIXME: some @value{GDBN} release may permit some refs to undef
15014 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
15015 @c FIXME...lib; check this from time to time when updating manual
15017 There are times, however, when you may wish to not automatically load
15018 symbol definitions from shared libraries, such as when they are
15019 particularly large or there are many of them.
15021 To control the automatic loading of shared library symbols, use the
15025 @kindex set auto-solib-add
15026 @item set auto-solib-add @var{mode}
15027 If @var{mode} is @code{on}, symbols from all shared object libraries
15028 will be loaded automatically when the inferior begins execution, you
15029 attach to an independently started inferior, or when the dynamic linker
15030 informs @value{GDBN} that a new library has been loaded. If @var{mode}
15031 is @code{off}, symbols must be loaded manually, using the
15032 @code{sharedlibrary} command. The default value is @code{on}.
15034 @cindex memory used for symbol tables
15035 If your program uses lots of shared libraries with debug info that
15036 takes large amounts of memory, you can decrease the @value{GDBN}
15037 memory footprint by preventing it from automatically loading the
15038 symbols from shared libraries. To that end, type @kbd{set
15039 auto-solib-add off} before running the inferior, then load each
15040 library whose debug symbols you do need with @kbd{sharedlibrary
15041 @var{regexp}}, where @var{regexp} is a regular expression that matches
15042 the libraries whose symbols you want to be loaded.
15044 @kindex show auto-solib-add
15045 @item show auto-solib-add
15046 Display the current autoloading mode.
15049 @cindex load shared library
15050 To explicitly load shared library symbols, use the @code{sharedlibrary}
15054 @kindex info sharedlibrary
15056 @item info share @var{regex}
15057 @itemx info sharedlibrary @var{regex}
15058 Print the names of the shared libraries which are currently loaded
15059 that match @var{regex}. If @var{regex} is omitted then print
15060 all shared libraries that are loaded.
15062 @kindex sharedlibrary
15064 @item sharedlibrary @var{regex}
15065 @itemx share @var{regex}
15066 Load shared object library symbols for files matching a
15067 Unix regular expression.
15068 As with files loaded automatically, it only loads shared libraries
15069 required by your program for a core file or after typing @code{run}. If
15070 @var{regex} is omitted all shared libraries required by your program are
15073 @item nosharedlibrary
15074 @kindex nosharedlibrary
15075 @cindex unload symbols from shared libraries
15076 Unload all shared object library symbols. This discards all symbols
15077 that have been loaded from all shared libraries. Symbols from shared
15078 libraries that were loaded by explicit user requests are not
15082 Sometimes you may wish that @value{GDBN} stops and gives you control
15083 when any of shared library events happen. Use the @code{set
15084 stop-on-solib-events} command for this:
15087 @item set stop-on-solib-events
15088 @kindex set stop-on-solib-events
15089 This command controls whether @value{GDBN} should give you control
15090 when the dynamic linker notifies it about some shared library event.
15091 The most common event of interest is loading or unloading of a new
15094 @item show stop-on-solib-events
15095 @kindex show stop-on-solib-events
15096 Show whether @value{GDBN} stops and gives you control when shared
15097 library events happen.
15100 Shared libraries are also supported in many cross or remote debugging
15101 configurations. @value{GDBN} needs to have access to the target's libraries;
15102 this can be accomplished either by providing copies of the libraries
15103 on the host system, or by asking @value{GDBN} to automatically retrieve the
15104 libraries from the target. If copies of the target libraries are
15105 provided, they need to be the same as the target libraries, although the
15106 copies on the target can be stripped as long as the copies on the host are
15109 @cindex where to look for shared libraries
15110 For remote debugging, you need to tell @value{GDBN} where the target
15111 libraries are, so that it can load the correct copies---otherwise, it
15112 may try to load the host's libraries. @value{GDBN} has two variables
15113 to specify the search directories for target libraries.
15116 @cindex prefix for shared library file names
15117 @cindex system root, alternate
15118 @kindex set solib-absolute-prefix
15119 @kindex set sysroot
15120 @item set sysroot @var{path}
15121 Use @var{path} as the system root for the program being debugged. Any
15122 absolute shared library paths will be prefixed with @var{path}; many
15123 runtime loaders store the absolute paths to the shared library in the
15124 target program's memory. If you use @code{set sysroot} to find shared
15125 libraries, they need to be laid out in the same way that they are on
15126 the target, with e.g.@: a @file{/lib} and @file{/usr/lib} hierarchy
15129 If @var{path} starts with the sequence @file{remote:}, @value{GDBN} will
15130 retrieve the target libraries from the remote system. This is only
15131 supported when using a remote target that supports the @code{remote get}
15132 command (@pxref{File Transfer,,Sending files to a remote system}).
15133 The part of @var{path} following the initial @file{remote:}
15134 (if present) is used as system root prefix on the remote file system.
15135 @footnote{If you want to specify a local system root using a directory
15136 that happens to be named @file{remote:}, you need to use some equivalent
15137 variant of the name like @file{./remote:}.}
15139 For targets with an MS-DOS based filesystem, such as MS-Windows and
15140 SymbianOS, @value{GDBN} tries prefixing a few variants of the target
15141 absolute file name with @var{path}. But first, on Unix hosts,
15142 @value{GDBN} converts all backslash directory separators into forward
15143 slashes, because the backslash is not a directory separator on Unix:
15146 c:\foo\bar.dll @result{} c:/foo/bar.dll
15149 Then, @value{GDBN} attempts prefixing the target file name with
15150 @var{path}, and looks for the resulting file name in the host file
15154 c:/foo/bar.dll @result{} /path/to/sysroot/c:/foo/bar.dll
15157 If that does not find the shared library, @value{GDBN} tries removing
15158 the @samp{:} character from the drive spec, both for convenience, and,
15159 for the case of the host file system not supporting file names with
15163 c:/foo/bar.dll @result{} /path/to/sysroot/c/foo/bar.dll
15166 This makes it possible to have a system root that mirrors a target
15167 with more than one drive. E.g., you may want to setup your local
15168 copies of the target system shared libraries like so (note @samp{c} vs
15172 @file{/path/to/sysroot/c/sys/bin/foo.dll}
15173 @file{/path/to/sysroot/c/sys/bin/bar.dll}
15174 @file{/path/to/sysroot/z/sys/bin/bar.dll}
15178 and point the system root at @file{/path/to/sysroot}, so that
15179 @value{GDBN} can find the correct copies of both
15180 @file{c:\sys\bin\foo.dll}, and @file{z:\sys\bin\bar.dll}.
15182 If that still does not find the shared library, @value{GDBN} tries
15183 removing the whole drive spec from the target file name:
15186 c:/foo/bar.dll @result{} /path/to/sysroot/foo/bar.dll
15189 This last lookup makes it possible to not care about the drive name,
15190 if you don't want or need to.
15192 The @code{set solib-absolute-prefix} command is an alias for @code{set
15195 @cindex default system root
15196 @cindex @samp{--with-sysroot}
15197 You can set the default system root by using the configure-time
15198 @samp{--with-sysroot} option. If the system root is inside
15199 @value{GDBN}'s configured binary prefix (set with @samp{--prefix} or
15200 @samp{--exec-prefix}), then the default system root will be updated
15201 automatically if the installed @value{GDBN} is moved to a new
15204 @kindex show sysroot
15206 Display the current shared library prefix.
15208 @kindex set solib-search-path
15209 @item set solib-search-path @var{path}
15210 If this variable is set, @var{path} is a colon-separated list of
15211 directories to search for shared libraries. @samp{solib-search-path}
15212 is used after @samp{sysroot} fails to locate the library, or if the
15213 path to the library is relative instead of absolute. If you want to
15214 use @samp{solib-search-path} instead of @samp{sysroot}, be sure to set
15215 @samp{sysroot} to a nonexistent directory to prevent @value{GDBN} from
15216 finding your host's libraries. @samp{sysroot} is preferred; setting
15217 it to a nonexistent directory may interfere with automatic loading
15218 of shared library symbols.
15220 @kindex show solib-search-path
15221 @item show solib-search-path
15222 Display the current shared library search path.
15224 @cindex DOS file-name semantics of file names.
15225 @kindex set target-file-system-kind (unix|dos-based|auto)
15226 @kindex show target-file-system-kind
15227 @item set target-file-system-kind @var{kind}
15228 Set assumed file system kind for target reported file names.
15230 Shared library file names as reported by the target system may not
15231 make sense as is on the system @value{GDBN} is running on. For
15232 example, when remote debugging a target that has MS-DOS based file
15233 system semantics, from a Unix host, the target may be reporting to
15234 @value{GDBN} a list of loaded shared libraries with file names such as
15235 @file{c:\Windows\kernel32.dll}. On Unix hosts, there's no concept of
15236 drive letters, so the @samp{c:\} prefix is not normally understood as
15237 indicating an absolute file name, and neither is the backslash
15238 normally considered a directory separator character. In that case,
15239 the native file system would interpret this whole absolute file name
15240 as a relative file name with no directory components. This would make
15241 it impossible to point @value{GDBN} at a copy of the remote target's
15242 shared libraries on the host using @code{set sysroot}, and impractical
15243 with @code{set solib-search-path}. Setting
15244 @code{target-file-system-kind} to @code{dos-based} tells @value{GDBN}
15245 to interpret such file names similarly to how the target would, and to
15246 map them to file names valid on @value{GDBN}'s native file system
15247 semantics. The value of @var{kind} can be @code{"auto"}, in addition
15248 to one of the supported file system kinds. In that case, @value{GDBN}
15249 tries to determine the appropriate file system variant based on the
15250 current target's operating system (@pxref{ABI, ,Configuring the
15251 Current ABI}). The supported file system settings are:
15255 Instruct @value{GDBN} to assume the target file system is of Unix
15256 kind. Only file names starting the forward slash (@samp{/}) character
15257 are considered absolute, and the directory separator character is also
15261 Instruct @value{GDBN} to assume the target file system is DOS based.
15262 File names starting with either a forward slash, or a drive letter
15263 followed by a colon (e.g., @samp{c:}), are considered absolute, and
15264 both the slash (@samp{/}) and the backslash (@samp{\\}) characters are
15265 considered directory separators.
15268 Instruct @value{GDBN} to use the file system kind associated with the
15269 target operating system (@pxref{ABI, ,Configuring the Current ABI}).
15270 This is the default.
15275 @node Separate Debug Files
15276 @section Debugging Information in Separate Files
15277 @cindex separate debugging information files
15278 @cindex debugging information in separate files
15279 @cindex @file{.debug} subdirectories
15280 @cindex debugging information directory, global
15281 @cindex global debugging information directory
15282 @cindex build ID, and separate debugging files
15283 @cindex @file{.build-id} directory
15285 @value{GDBN} allows you to put a program's debugging information in a
15286 file separate from the executable itself, in a way that allows
15287 @value{GDBN} to find and load the debugging information automatically.
15288 Since debugging information can be very large---sometimes larger
15289 than the executable code itself---some systems distribute debugging
15290 information for their executables in separate files, which users can
15291 install only when they need to debug a problem.
15293 @value{GDBN} supports two ways of specifying the separate debug info
15298 The executable contains a @dfn{debug link} that specifies the name of
15299 the separate debug info file. The separate debug file's name is
15300 usually @file{@var{executable}.debug}, where @var{executable} is the
15301 name of the corresponding executable file without leading directories
15302 (e.g., @file{ls.debug} for @file{/usr/bin/ls}). In addition, the
15303 debug link specifies a 32-bit @dfn{Cyclic Redundancy Check} (CRC)
15304 checksum for the debug file, which @value{GDBN} uses to validate that
15305 the executable and the debug file came from the same build.
15308 The executable contains a @dfn{build ID}, a unique bit string that is
15309 also present in the corresponding debug info file. (This is supported
15310 only on some operating systems, notably those which use the ELF format
15311 for binary files and the @sc{gnu} Binutils.) For more details about
15312 this feature, see the description of the @option{--build-id}
15313 command-line option in @ref{Options, , Command Line Options, ld.info,
15314 The GNU Linker}. The debug info file's name is not specified
15315 explicitly by the build ID, but can be computed from the build ID, see
15319 Depending on the way the debug info file is specified, @value{GDBN}
15320 uses two different methods of looking for the debug file:
15324 For the ``debug link'' method, @value{GDBN} looks up the named file in
15325 the directory of the executable file, then in a subdirectory of that
15326 directory named @file{.debug}, and finally under the global debug
15327 directory, in a subdirectory whose name is identical to the leading
15328 directories of the executable's absolute file name.
15331 For the ``build ID'' method, @value{GDBN} looks in the
15332 @file{.build-id} subdirectory of the global debug directory for a file
15333 named @file{@var{nn}/@var{nnnnnnnn}.debug}, where @var{nn} are the
15334 first 2 hex characters of the build ID bit string, and @var{nnnnnnnn}
15335 are the rest of the bit string. (Real build ID strings are 32 or more
15336 hex characters, not 10.)
15339 So, for example, suppose you ask @value{GDBN} to debug
15340 @file{/usr/bin/ls}, which has a debug link that specifies the
15341 file @file{ls.debug}, and a build ID whose value in hex is
15342 @code{abcdef1234}. If the global debug directory is
15343 @file{/usr/lib/debug}, then @value{GDBN} will look for the following
15344 debug information files, in the indicated order:
15348 @file{/usr/lib/debug/.build-id/ab/cdef1234.debug}
15350 @file{/usr/bin/ls.debug}
15352 @file{/usr/bin/.debug/ls.debug}
15354 @file{/usr/lib/debug/usr/bin/ls.debug}.
15357 You can set the global debugging info directory's name, and view the
15358 name @value{GDBN} is currently using.
15362 @kindex set debug-file-directory
15363 @item set debug-file-directory @var{directories}
15364 Set the directories which @value{GDBN} searches for separate debugging
15365 information files to @var{directory}. Multiple directory components can be set
15366 concatenating them by a directory separator.
15368 @kindex show debug-file-directory
15369 @item show debug-file-directory
15370 Show the directories @value{GDBN} searches for separate debugging
15375 @cindex @code{.gnu_debuglink} sections
15376 @cindex debug link sections
15377 A debug link is a special section of the executable file named
15378 @code{.gnu_debuglink}. The section must contain:
15382 A filename, with any leading directory components removed, followed by
15385 zero to three bytes of padding, as needed to reach the next four-byte
15386 boundary within the section, and
15388 a four-byte CRC checksum, stored in the same endianness used for the
15389 executable file itself. The checksum is computed on the debugging
15390 information file's full contents by the function given below, passing
15391 zero as the @var{crc} argument.
15394 Any executable file format can carry a debug link, as long as it can
15395 contain a section named @code{.gnu_debuglink} with the contents
15398 @cindex @code{.note.gnu.build-id} sections
15399 @cindex build ID sections
15400 The build ID is a special section in the executable file (and in other
15401 ELF binary files that @value{GDBN} may consider). This section is
15402 often named @code{.note.gnu.build-id}, but that name is not mandatory.
15403 It contains unique identification for the built files---the ID remains
15404 the same across multiple builds of the same build tree. The default
15405 algorithm SHA1 produces 160 bits (40 hexadecimal characters) of the
15406 content for the build ID string. The same section with an identical
15407 value is present in the original built binary with symbols, in its
15408 stripped variant, and in the separate debugging information file.
15410 The debugging information file itself should be an ordinary
15411 executable, containing a full set of linker symbols, sections, and
15412 debugging information. The sections of the debugging information file
15413 should have the same names, addresses, and sizes as the original file,
15414 but they need not contain any data---much like a @code{.bss} section
15415 in an ordinary executable.
15417 The @sc{gnu} binary utilities (Binutils) package includes the
15418 @samp{objcopy} utility that can produce
15419 the separated executable / debugging information file pairs using the
15420 following commands:
15423 @kbd{objcopy --only-keep-debug foo foo.debug}
15428 These commands remove the debugging
15429 information from the executable file @file{foo} and place it in the file
15430 @file{foo.debug}. You can use the first, second or both methods to link the
15435 The debug link method needs the following additional command to also leave
15436 behind a debug link in @file{foo}:
15439 @kbd{objcopy --add-gnu-debuglink=foo.debug foo}
15442 Ulrich Drepper's @file{elfutils} package, starting with version 0.53, contains
15443 a version of the @code{strip} command such that the command @kbd{strip foo -f
15444 foo.debug} has the same functionality as the two @code{objcopy} commands and
15445 the @code{ln -s} command above, together.
15448 Build ID gets embedded into the main executable using @code{ld --build-id} or
15449 the @value{NGCC} counterpart @code{gcc -Wl,--build-id}. Build ID support plus
15450 compatibility fixes for debug files separation are present in @sc{gnu} binary
15451 utilities (Binutils) package since version 2.18.
15456 @cindex CRC algorithm definition
15457 The CRC used in @code{.gnu_debuglink} is the CRC-32 defined in
15458 IEEE 802.3 using the polynomial:
15460 @c TexInfo requires naked braces for multi-digit exponents for Tex
15461 @c output, but this causes HTML output to barf. HTML has to be set using
15462 @c raw commands. So we end up having to specify this equation in 2
15467 <em>x</em><sup>32</sup> + <em>x</em><sup>26</sup> + <em>x</em><sup>23</sup> + <em>x</em><sup>22</sup> + <em>x</em><sup>16</sup> + <em>x</em><sup>12</sup> + <em>x</em><sup>11</sup>
15468 + <em>x</em><sup>10</sup> + <em>x</em><sup>8</sup> + <em>x</em><sup>7</sup> + <em>x</em><sup>5</sup> + <em>x</em><sup>4</sup> + <em>x</em><sup>2</sup> + <em>x</em> + 1
15474 @math{x^{32} + x^{26} + x^{23} + x^{22} + x^{16} + x^{12} + x^{11}}
15475 @math{+ x^{10} + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1}
15479 The function is computed byte at a time, taking the least
15480 significant bit of each byte first. The initial pattern
15481 @code{0xffffffff} is used, to ensure leading zeros affect the CRC and
15482 the final result is inverted to ensure trailing zeros also affect the
15485 @emph{Note:} This is the same CRC polynomial as used in handling the
15486 @dfn{Remote Serial Protocol} @code{qCRC} packet (@pxref{Remote Protocol,
15487 , @value{GDBN} Remote Serial Protocol}). However in the
15488 case of the Remote Serial Protocol, the CRC is computed @emph{most}
15489 significant bit first, and the result is not inverted, so trailing
15490 zeros have no effect on the CRC value.
15492 To complete the description, we show below the code of the function
15493 which produces the CRC used in @code{.gnu_debuglink}. Inverting the
15494 initially supplied @code{crc} argument means that an initial call to
15495 this function passing in zero will start computing the CRC using
15498 @kindex gnu_debuglink_crc32
15501 gnu_debuglink_crc32 (unsigned long crc,
15502 unsigned char *buf, size_t len)
15504 static const unsigned long crc32_table[256] =
15506 0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419,
15507 0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4,
15508 0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07,
15509 0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
15510 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856,
15511 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
15512 0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4,
15513 0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
15514 0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3,
15515 0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a,
15516 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599,
15517 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
15518 0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190,
15519 0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f,
15520 0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e,
15521 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
15522 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed,
15523 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
15524 0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3,
15525 0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
15526 0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a,
15527 0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5,
15528 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010,
15529 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
15530 0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17,
15531 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6,
15532 0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615,
15533 0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
15534 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344,
15535 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
15536 0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a,
15537 0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
15538 0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1,
15539 0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c,
15540 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef,
15541 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
15542 0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe,
15543 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31,
15544 0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c,
15545 0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
15546 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b,
15547 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
15548 0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1,
15549 0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
15550 0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278,
15551 0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7,
15552 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66,
15553 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
15554 0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605,
15555 0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8,
15556 0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b,
15559 unsigned char *end;
15561 crc = ~crc & 0xffffffff;
15562 for (end = buf + len; buf < end; ++buf)
15563 crc = crc32_table[(crc ^ *buf) & 0xff] ^ (crc >> 8);
15564 return ~crc & 0xffffffff;
15569 This computation does not apply to the ``build ID'' method.
15573 @section Index Files Speed Up @value{GDBN}
15574 @cindex index files
15575 @cindex @samp{.gdb_index} section
15577 When @value{GDBN} finds a symbol file, it scans the symbols in the
15578 file in order to construct an internal symbol table. This lets most
15579 @value{GDBN} operations work quickly---at the cost of a delay early
15580 on. For large programs, this delay can be quite lengthy, so
15581 @value{GDBN} provides a way to build an index, which speeds up
15584 The index is stored as a section in the symbol file. @value{GDBN} can
15585 write the index to a file, then you can put it into the symbol file
15586 using @command{objcopy}.
15588 To create an index file, use the @code{save gdb-index} command:
15591 @item save gdb-index @var{directory}
15592 @kindex save gdb-index
15593 Create an index file for each symbol file currently known by
15594 @value{GDBN}. Each file is named after its corresponding symbol file,
15595 with @samp{.gdb-index} appended, and is written into the given
15599 Once you have created an index file you can merge it into your symbol
15600 file, here named @file{symfile}, using @command{objcopy}:
15603 $ objcopy --add-section .gdb_index=symfile.gdb-index \
15604 --set-section-flags .gdb_index=readonly symfile symfile
15607 There are currently some limitation on indices. They only work when
15608 for DWARF debugging information, not stabs. And, they do not
15609 currently work for programs using Ada.
15611 @node Symbol Errors
15612 @section Errors Reading Symbol Files
15614 While reading a symbol file, @value{GDBN} occasionally encounters problems,
15615 such as symbol types it does not recognize, or known bugs in compiler
15616 output. By default, @value{GDBN} does not notify you of such problems, since
15617 they are relatively common and primarily of interest to people
15618 debugging compilers. If you are interested in seeing information
15619 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
15620 only one message about each such type of problem, no matter how many
15621 times the problem occurs; or you can ask @value{GDBN} to print more messages,
15622 to see how many times the problems occur, with the @code{set
15623 complaints} command (@pxref{Messages/Warnings, ,Optional Warnings and
15626 The messages currently printed, and their meanings, include:
15629 @item inner block not inside outer block in @var{symbol}
15631 The symbol information shows where symbol scopes begin and end
15632 (such as at the start of a function or a block of statements). This
15633 error indicates that an inner scope block is not fully contained
15634 in its outer scope blocks.
15636 @value{GDBN} circumvents the problem by treating the inner block as if it had
15637 the same scope as the outer block. In the error message, @var{symbol}
15638 may be shown as ``@code{(don't know)}'' if the outer block is not a
15641 @item block at @var{address} out of order
15643 The symbol information for symbol scope blocks should occur in
15644 order of increasing addresses. This error indicates that it does not
15647 @value{GDBN} does not circumvent this problem, and has trouble
15648 locating symbols in the source file whose symbols it is reading. (You
15649 can often determine what source file is affected by specifying
15650 @code{set verbose on}. @xref{Messages/Warnings, ,Optional Warnings and
15653 @item bad block start address patched
15655 The symbol information for a symbol scope block has a start address
15656 smaller than the address of the preceding source line. This is known
15657 to occur in the SunOS 4.1.1 (and earlier) C compiler.
15659 @value{GDBN} circumvents the problem by treating the symbol scope block as
15660 starting on the previous source line.
15662 @item bad string table offset in symbol @var{n}
15665 Symbol number @var{n} contains a pointer into the string table which is
15666 larger than the size of the string table.
15668 @value{GDBN} circumvents the problem by considering the symbol to have the
15669 name @code{foo}, which may cause other problems if many symbols end up
15672 @item unknown symbol type @code{0x@var{nn}}
15674 The symbol information contains new data types that @value{GDBN} does
15675 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
15676 uncomprehended information, in hexadecimal.
15678 @value{GDBN} circumvents the error by ignoring this symbol information.
15679 This usually allows you to debug your program, though certain symbols
15680 are not accessible. If you encounter such a problem and feel like
15681 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
15682 on @code{complain}, then go up to the function @code{read_dbx_symtab}
15683 and examine @code{*bufp} to see the symbol.
15685 @item stub type has NULL name
15687 @value{GDBN} could not find the full definition for a struct or class.
15689 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
15690 The symbol information for a C@t{++} member function is missing some
15691 information that recent versions of the compiler should have output for
15694 @item info mismatch between compiler and debugger
15696 @value{GDBN} could not parse a type specification output by the compiler.
15701 @section GDB Data Files
15703 @cindex prefix for data files
15704 @value{GDBN} will sometimes read an auxiliary data file. These files
15705 are kept in a directory known as the @dfn{data directory}.
15707 You can set the data directory's name, and view the name @value{GDBN}
15708 is currently using.
15711 @kindex set data-directory
15712 @item set data-directory @var{directory}
15713 Set the directory which @value{GDBN} searches for auxiliary data files
15714 to @var{directory}.
15716 @kindex show data-directory
15717 @item show data-directory
15718 Show the directory @value{GDBN} searches for auxiliary data files.
15721 @cindex default data directory
15722 @cindex @samp{--with-gdb-datadir}
15723 You can set the default data directory by using the configure-time
15724 @samp{--with-gdb-datadir} option. If the data directory is inside
15725 @value{GDBN}'s configured binary prefix (set with @samp{--prefix} or
15726 @samp{--exec-prefix}), then the default data directory will be updated
15727 automatically if the installed @value{GDBN} is moved to a new
15730 The data directory may also be specified with the
15731 @code{--data-directory} command line option.
15732 @xref{Mode Options}.
15735 @chapter Specifying a Debugging Target
15737 @cindex debugging target
15738 A @dfn{target} is the execution environment occupied by your program.
15740 Often, @value{GDBN} runs in the same host environment as your program;
15741 in that case, the debugging target is specified as a side effect when
15742 you use the @code{file} or @code{core} commands. When you need more
15743 flexibility---for example, running @value{GDBN} on a physically separate
15744 host, or controlling a standalone system over a serial port or a
15745 realtime system over a TCP/IP connection---you can use the @code{target}
15746 command to specify one of the target types configured for @value{GDBN}
15747 (@pxref{Target Commands, ,Commands for Managing Targets}).
15749 @cindex target architecture
15750 It is possible to build @value{GDBN} for several different @dfn{target
15751 architectures}. When @value{GDBN} is built like that, you can choose
15752 one of the available architectures with the @kbd{set architecture}
15756 @kindex set architecture
15757 @kindex show architecture
15758 @item set architecture @var{arch}
15759 This command sets the current target architecture to @var{arch}. The
15760 value of @var{arch} can be @code{"auto"}, in addition to one of the
15761 supported architectures.
15763 @item show architecture
15764 Show the current target architecture.
15766 @item set processor
15768 @kindex set processor
15769 @kindex show processor
15770 These are alias commands for, respectively, @code{set architecture}
15771 and @code{show architecture}.
15775 * Active Targets:: Active targets
15776 * Target Commands:: Commands for managing targets
15777 * Byte Order:: Choosing target byte order
15780 @node Active Targets
15781 @section Active Targets
15783 @cindex stacking targets
15784 @cindex active targets
15785 @cindex multiple targets
15787 There are multiple classes of targets such as: processes, executable files or
15788 recording sessions. Core files belong to the process class, making core file
15789 and process mutually exclusive. Otherwise, @value{GDBN} can work concurrently
15790 on multiple active targets, one in each class. This allows you to (for
15791 example) start a process and inspect its activity, while still having access to
15792 the executable file after the process finishes. Or if you start process
15793 recording (@pxref{Reverse Execution}) and @code{reverse-step} there, you are
15794 presented a virtual layer of the recording target, while the process target
15795 remains stopped at the chronologically last point of the process execution.
15797 Use the @code{core-file} and @code{exec-file} commands to select a new core
15798 file or executable target (@pxref{Files, ,Commands to Specify Files}). To
15799 specify as a target a process that is already running, use the @code{attach}
15800 command (@pxref{Attach, ,Debugging an Already-running Process}).
15802 @node Target Commands
15803 @section Commands for Managing Targets
15806 @item target @var{type} @var{parameters}
15807 Connects the @value{GDBN} host environment to a target machine or
15808 process. A target is typically a protocol for talking to debugging
15809 facilities. You use the argument @var{type} to specify the type or
15810 protocol of the target machine.
15812 Further @var{parameters} are interpreted by the target protocol, but
15813 typically include things like device names or host names to connect
15814 with, process numbers, and baud rates.
15816 The @code{target} command does not repeat if you press @key{RET} again
15817 after executing the command.
15819 @kindex help target
15821 Displays the names of all targets available. To display targets
15822 currently selected, use either @code{info target} or @code{info files}
15823 (@pxref{Files, ,Commands to Specify Files}).
15825 @item help target @var{name}
15826 Describe a particular target, including any parameters necessary to
15829 @kindex set gnutarget
15830 @item set gnutarget @var{args}
15831 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
15832 knows whether it is reading an @dfn{executable},
15833 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
15834 with the @code{set gnutarget} command. Unlike most @code{target} commands,
15835 with @code{gnutarget} the @code{target} refers to a program, not a machine.
15838 @emph{Warning:} To specify a file format with @code{set gnutarget},
15839 you must know the actual BFD name.
15843 @xref{Files, , Commands to Specify Files}.
15845 @kindex show gnutarget
15846 @item show gnutarget
15847 Use the @code{show gnutarget} command to display what file format
15848 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
15849 @value{GDBN} will determine the file format for each file automatically,
15850 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
15853 @cindex common targets
15854 Here are some common targets (available, or not, depending on the GDB
15859 @item target exec @var{program}
15860 @cindex executable file target
15861 An executable file. @samp{target exec @var{program}} is the same as
15862 @samp{exec-file @var{program}}.
15864 @item target core @var{filename}
15865 @cindex core dump file target
15866 A core dump file. @samp{target core @var{filename}} is the same as
15867 @samp{core-file @var{filename}}.
15869 @item target remote @var{medium}
15870 @cindex remote target
15871 A remote system connected to @value{GDBN} via a serial line or network
15872 connection. This command tells @value{GDBN} to use its own remote
15873 protocol over @var{medium} for debugging. @xref{Remote Debugging}.
15875 For example, if you have a board connected to @file{/dev/ttya} on the
15876 machine running @value{GDBN}, you could say:
15879 target remote /dev/ttya
15882 @code{target remote} supports the @code{load} command. This is only
15883 useful if you have some other way of getting the stub to the target
15884 system, and you can put it somewhere in memory where it won't get
15885 clobbered by the download.
15887 @item target sim @r{[}@var{simargs}@r{]} @dots{}
15888 @cindex built-in simulator target
15889 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
15897 works; however, you cannot assume that a specific memory map, device
15898 drivers, or even basic I/O is available, although some simulators do
15899 provide these. For info about any processor-specific simulator details,
15900 see the appropriate section in @ref{Embedded Processors, ,Embedded
15905 Some configurations may include these targets as well:
15909 @item target nrom @var{dev}
15910 @cindex NetROM ROM emulator target
15911 NetROM ROM emulator. This target only supports downloading.
15915 Different targets are available on different configurations of @value{GDBN};
15916 your configuration may have more or fewer targets.
15918 Many remote targets require you to download the executable's code once
15919 you've successfully established a connection. You may wish to control
15920 various aspects of this process.
15925 @kindex set hash@r{, for remote monitors}
15926 @cindex hash mark while downloading
15927 This command controls whether a hash mark @samp{#} is displayed while
15928 downloading a file to the remote monitor. If on, a hash mark is
15929 displayed after each S-record is successfully downloaded to the
15933 @kindex show hash@r{, for remote monitors}
15934 Show the current status of displaying the hash mark.
15936 @item set debug monitor
15937 @kindex set debug monitor
15938 @cindex display remote monitor communications
15939 Enable or disable display of communications messages between
15940 @value{GDBN} and the remote monitor.
15942 @item show debug monitor
15943 @kindex show debug monitor
15944 Show the current status of displaying communications between
15945 @value{GDBN} and the remote monitor.
15950 @kindex load @var{filename}
15951 @item load @var{filename}
15953 Depending on what remote debugging facilities are configured into
15954 @value{GDBN}, the @code{load} command may be available. Where it exists, it
15955 is meant to make @var{filename} (an executable) available for debugging
15956 on the remote system---by downloading, or dynamic linking, for example.
15957 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
15958 the @code{add-symbol-file} command.
15960 If your @value{GDBN} does not have a @code{load} command, attempting to
15961 execute it gets the error message ``@code{You can't do that when your
15962 target is @dots{}}''
15964 The file is loaded at whatever address is specified in the executable.
15965 For some object file formats, you can specify the load address when you
15966 link the program; for other formats, like a.out, the object file format
15967 specifies a fixed address.
15968 @c FIXME! This would be a good place for an xref to the GNU linker doc.
15970 Depending on the remote side capabilities, @value{GDBN} may be able to
15971 load programs into flash memory.
15973 @code{load} does not repeat if you press @key{RET} again after using it.
15977 @section Choosing Target Byte Order
15979 @cindex choosing target byte order
15980 @cindex target byte order
15982 Some types of processors, such as the MIPS, PowerPC, and Renesas SH,
15983 offer the ability to run either big-endian or little-endian byte
15984 orders. Usually the executable or symbol will include a bit to
15985 designate the endian-ness, and you will not need to worry about
15986 which to use. However, you may still find it useful to adjust
15987 @value{GDBN}'s idea of processor endian-ness manually.
15991 @item set endian big
15992 Instruct @value{GDBN} to assume the target is big-endian.
15994 @item set endian little
15995 Instruct @value{GDBN} to assume the target is little-endian.
15997 @item set endian auto
15998 Instruct @value{GDBN} to use the byte order associated with the
16002 Display @value{GDBN}'s current idea of the target byte order.
16006 Note that these commands merely adjust interpretation of symbolic
16007 data on the host, and that they have absolutely no effect on the
16011 @node Remote Debugging
16012 @chapter Debugging Remote Programs
16013 @cindex remote debugging
16015 If you are trying to debug a program running on a machine that cannot run
16016 @value{GDBN} in the usual way, it is often useful to use remote debugging.
16017 For example, you might use remote debugging on an operating system kernel,
16018 or on a small system which does not have a general purpose operating system
16019 powerful enough to run a full-featured debugger.
16021 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
16022 to make this work with particular debugging targets. In addition,
16023 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
16024 but not specific to any particular target system) which you can use if you
16025 write the remote stubs---the code that runs on the remote system to
16026 communicate with @value{GDBN}.
16028 Other remote targets may be available in your
16029 configuration of @value{GDBN}; use @code{help target} to list them.
16032 * Connecting:: Connecting to a remote target
16033 * File Transfer:: Sending files to a remote system
16034 * Server:: Using the gdbserver program
16035 * Remote Configuration:: Remote configuration
16036 * Remote Stub:: Implementing a remote stub
16040 @section Connecting to a Remote Target
16042 On the @value{GDBN} host machine, you will need an unstripped copy of
16043 your program, since @value{GDBN} needs symbol and debugging information.
16044 Start up @value{GDBN} as usual, using the name of the local copy of your
16045 program as the first argument.
16047 @cindex @code{target remote}
16048 @value{GDBN} can communicate with the target over a serial line, or
16049 over an @acronym{IP} network using @acronym{TCP} or @acronym{UDP}. In
16050 each case, @value{GDBN} uses the same protocol for debugging your
16051 program; only the medium carrying the debugging packets varies. The
16052 @code{target remote} command establishes a connection to the target.
16053 Its arguments indicate which medium to use:
16057 @item target remote @var{serial-device}
16058 @cindex serial line, @code{target remote}
16059 Use @var{serial-device} to communicate with the target. For example,
16060 to use a serial line connected to the device named @file{/dev/ttyb}:
16063 target remote /dev/ttyb
16066 If you're using a serial line, you may want to give @value{GDBN} the
16067 @w{@samp{--baud}} option, or use the @code{set remotebaud} command
16068 (@pxref{Remote Configuration, set remotebaud}) before the
16069 @code{target} command.
16071 @item target remote @code{@var{host}:@var{port}}
16072 @itemx target remote @code{tcp:@var{host}:@var{port}}
16073 @cindex @acronym{TCP} port, @code{target remote}
16074 Debug using a @acronym{TCP} connection to @var{port} on @var{host}.
16075 The @var{host} may be either a host name or a numeric @acronym{IP}
16076 address; @var{port} must be a decimal number. The @var{host} could be
16077 the target machine itself, if it is directly connected to the net, or
16078 it might be a terminal server which in turn has a serial line to the
16081 For example, to connect to port 2828 on a terminal server named
16085 target remote manyfarms:2828
16088 If your remote target is actually running on the same machine as your
16089 debugger session (e.g.@: a simulator for your target running on the
16090 same host), you can omit the hostname. For example, to connect to
16091 port 1234 on your local machine:
16094 target remote :1234
16098 Note that the colon is still required here.
16100 @item target remote @code{udp:@var{host}:@var{port}}
16101 @cindex @acronym{UDP} port, @code{target remote}
16102 Debug using @acronym{UDP} packets to @var{port} on @var{host}. For example, to
16103 connect to @acronym{UDP} port 2828 on a terminal server named @code{manyfarms}:
16106 target remote udp:manyfarms:2828
16109 When using a @acronym{UDP} connection for remote debugging, you should
16110 keep in mind that the `U' stands for ``Unreliable''. @acronym{UDP}
16111 can silently drop packets on busy or unreliable networks, which will
16112 cause havoc with your debugging session.
16114 @item target remote | @var{command}
16115 @cindex pipe, @code{target remote} to
16116 Run @var{command} in the background and communicate with it using a
16117 pipe. The @var{command} is a shell command, to be parsed and expanded
16118 by the system's command shell, @code{/bin/sh}; it should expect remote
16119 protocol packets on its standard input, and send replies on its
16120 standard output. You could use this to run a stand-alone simulator
16121 that speaks the remote debugging protocol, to make net connections
16122 using programs like @code{ssh}, or for other similar tricks.
16124 If @var{command} closes its standard output (perhaps by exiting),
16125 @value{GDBN} will try to send it a @code{SIGTERM} signal. (If the
16126 program has already exited, this will have no effect.)
16130 Once the connection has been established, you can use all the usual
16131 commands to examine and change data. The remote program is already
16132 running; you can use @kbd{step} and @kbd{continue}, and you do not
16133 need to use @kbd{run}.
16135 @cindex interrupting remote programs
16136 @cindex remote programs, interrupting
16137 Whenever @value{GDBN} is waiting for the remote program, if you type the
16138 interrupt character (often @kbd{Ctrl-c}), @value{GDBN} attempts to stop the
16139 program. This may or may not succeed, depending in part on the hardware
16140 and the serial drivers the remote system uses. If you type the
16141 interrupt character once again, @value{GDBN} displays this prompt:
16144 Interrupted while waiting for the program.
16145 Give up (and stop debugging it)? (y or n)
16148 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
16149 (If you decide you want to try again later, you can use @samp{target
16150 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
16151 goes back to waiting.
16154 @kindex detach (remote)
16156 When you have finished debugging the remote program, you can use the
16157 @code{detach} command to release it from @value{GDBN} control.
16158 Detaching from the target normally resumes its execution, but the results
16159 will depend on your particular remote stub. After the @code{detach}
16160 command, @value{GDBN} is free to connect to another target.
16164 The @code{disconnect} command behaves like @code{detach}, except that
16165 the target is generally not resumed. It will wait for @value{GDBN}
16166 (this instance or another one) to connect and continue debugging. After
16167 the @code{disconnect} command, @value{GDBN} is again free to connect to
16170 @cindex send command to remote monitor
16171 @cindex extend @value{GDBN} for remote targets
16172 @cindex add new commands for external monitor
16174 @item monitor @var{cmd}
16175 This command allows you to send arbitrary commands directly to the
16176 remote monitor. Since @value{GDBN} doesn't care about the commands it
16177 sends like this, this command is the way to extend @value{GDBN}---you
16178 can add new commands that only the external monitor will understand
16182 @node File Transfer
16183 @section Sending files to a remote system
16184 @cindex remote target, file transfer
16185 @cindex file transfer
16186 @cindex sending files to remote systems
16188 Some remote targets offer the ability to transfer files over the same
16189 connection used to communicate with @value{GDBN}. This is convenient
16190 for targets accessible through other means, e.g.@: @sc{gnu}/Linux systems
16191 running @code{gdbserver} over a network interface. For other targets,
16192 e.g.@: embedded devices with only a single serial port, this may be
16193 the only way to upload or download files.
16195 Not all remote targets support these commands.
16199 @item remote put @var{hostfile} @var{targetfile}
16200 Copy file @var{hostfile} from the host system (the machine running
16201 @value{GDBN}) to @var{targetfile} on the target system.
16204 @item remote get @var{targetfile} @var{hostfile}
16205 Copy file @var{targetfile} from the target system to @var{hostfile}
16206 on the host system.
16208 @kindex remote delete
16209 @item remote delete @var{targetfile}
16210 Delete @var{targetfile} from the target system.
16215 @section Using the @code{gdbserver} Program
16218 @cindex remote connection without stubs
16219 @code{gdbserver} is a control program for Unix-like systems, which
16220 allows you to connect your program with a remote @value{GDBN} via
16221 @code{target remote}---but without linking in the usual debugging stub.
16223 @code{gdbserver} is not a complete replacement for the debugging stubs,
16224 because it requires essentially the same operating-system facilities
16225 that @value{GDBN} itself does. In fact, a system that can run
16226 @code{gdbserver} to connect to a remote @value{GDBN} could also run
16227 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
16228 because it is a much smaller program than @value{GDBN} itself. It is
16229 also easier to port than all of @value{GDBN}, so you may be able to get
16230 started more quickly on a new system by using @code{gdbserver}.
16231 Finally, if you develop code for real-time systems, you may find that
16232 the tradeoffs involved in real-time operation make it more convenient to
16233 do as much development work as possible on another system, for example
16234 by cross-compiling. You can use @code{gdbserver} to make a similar
16235 choice for debugging.
16237 @value{GDBN} and @code{gdbserver} communicate via either a serial line
16238 or a TCP connection, using the standard @value{GDBN} remote serial
16242 @emph{Warning:} @code{gdbserver} does not have any built-in security.
16243 Do not run @code{gdbserver} connected to any public network; a
16244 @value{GDBN} connection to @code{gdbserver} provides access to the
16245 target system with the same privileges as the user running
16249 @subsection Running @code{gdbserver}
16250 @cindex arguments, to @code{gdbserver}
16251 @cindex @code{gdbserver}, command-line arguments
16253 Run @code{gdbserver} on the target system. You need a copy of the
16254 program you want to debug, including any libraries it requires.
16255 @code{gdbserver} does not need your program's symbol table, so you can
16256 strip the program if necessary to save space. @value{GDBN} on the host
16257 system does all the symbol handling.
16259 To use the server, you must tell it how to communicate with @value{GDBN};
16260 the name of your program; and the arguments for your program. The usual
16264 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
16267 @var{comm} is either a device name (to use a serial line) or a TCP
16268 hostname and portnumber. For example, to debug Emacs with the argument
16269 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
16273 target> gdbserver /dev/com1 emacs foo.txt
16276 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
16279 To use a TCP connection instead of a serial line:
16282 target> gdbserver host:2345 emacs foo.txt
16285 The only difference from the previous example is the first argument,
16286 specifying that you are communicating with the host @value{GDBN} via
16287 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
16288 expect a TCP connection from machine @samp{host} to local TCP port 2345.
16289 (Currently, the @samp{host} part is ignored.) You can choose any number
16290 you want for the port number as long as it does not conflict with any
16291 TCP ports already in use on the target system (for example, @code{23} is
16292 reserved for @code{telnet}).@footnote{If you choose a port number that
16293 conflicts with another service, @code{gdbserver} prints an error message
16294 and exits.} You must use the same port number with the host @value{GDBN}
16295 @code{target remote} command.
16297 @subsubsection Attaching to a Running Program
16298 @cindex attach to a program, @code{gdbserver}
16299 @cindex @option{--attach}, @code{gdbserver} option
16301 On some targets, @code{gdbserver} can also attach to running programs.
16302 This is accomplished via the @code{--attach} argument. The syntax is:
16305 target> gdbserver --attach @var{comm} @var{pid}
16308 @var{pid} is the process ID of a currently running process. It isn't necessary
16309 to point @code{gdbserver} at a binary for the running process.
16312 You can debug processes by name instead of process ID if your target has the
16313 @code{pidof} utility:
16316 target> gdbserver --attach @var{comm} `pidof @var{program}`
16319 In case more than one copy of @var{program} is running, or @var{program}
16320 has multiple threads, most versions of @code{pidof} support the
16321 @code{-s} option to only return the first process ID.
16323 @subsubsection Multi-Process Mode for @code{gdbserver}
16324 @cindex @code{gdbserver}, multiple processes
16325 @cindex multiple processes with @code{gdbserver}
16327 When you connect to @code{gdbserver} using @code{target remote},
16328 @code{gdbserver} debugs the specified program only once. When the
16329 program exits, or you detach from it, @value{GDBN} closes the connection
16330 and @code{gdbserver} exits.
16332 If you connect using @kbd{target extended-remote}, @code{gdbserver}
16333 enters multi-process mode. When the debugged program exits, or you
16334 detach from it, @value{GDBN} stays connected to @code{gdbserver} even
16335 though no program is running. The @code{run} and @code{attach}
16336 commands instruct @code{gdbserver} to run or attach to a new program.
16337 The @code{run} command uses @code{set remote exec-file} (@pxref{set
16338 remote exec-file}) to select the program to run. Command line
16339 arguments are supported, except for wildcard expansion and I/O
16340 redirection (@pxref{Arguments}).
16342 @cindex @option{--multi}, @code{gdbserver} option
16343 To start @code{gdbserver} without supplying an initial command to run
16344 or process ID to attach, use the @option{--multi} command line option.
16345 Then you can connect using @kbd{target extended-remote} and start
16346 the program you want to debug.
16348 In multi-process mode @code{gdbserver} does not automatically exit unless you
16349 use the option @option{--once}. You can terminate it by using
16350 @code{monitor exit} (@pxref{Monitor Commands for gdbserver}). Note that the
16351 conditions under which @code{gdbserver} terminates depend on how @value{GDBN}
16352 connects to it (@kbd{target remote} or @kbd{target extended-remote}). The
16353 @option{--multi} option to @code{gdbserver} has no influence on that.
16355 @subsubsection TCP port allocation lifecycle of @code{gdbserver}
16357 This section applies only when @code{gdbserver} is run to listen on a TCP port.
16359 @code{gdbserver} normally terminates after all of its debugged processes have
16360 terminated in @kbd{target remote} mode. On the other hand, for @kbd{target
16361 extended-remote}, @code{gdbserver} stays running even with no processes left.
16362 @value{GDBN} normally terminates the spawned debugged process on its exit,
16363 which normally also terminates @code{gdbserver} in the @kbd{target remote}
16364 mode. Therefore, when the connection drops unexpectedly, and @value{GDBN}
16365 cannot ask @code{gdbserver} to kill its debugged processes, @code{gdbserver}
16366 stays running even in the @kbd{target remote} mode.
16368 When @code{gdbserver} stays running, @value{GDBN} can connect to it again later.
16369 Such reconnecting is useful for features like @ref{disconnected tracing}. For
16370 completeness, at most one @value{GDBN} can be connected at a time.
16372 @cindex @option{--once}, @code{gdbserver} option
16373 By default, @code{gdbserver} keeps the listening TCP port open, so that
16374 additional connections are possible. However, if you start @code{gdbserver}
16375 with the @option{--once} option, it will stop listening for any further
16376 connection attempts after connecting to the first @value{GDBN} session. This
16377 means no further connections to @code{gdbserver} will be possible after the
16378 first one. It also means @code{gdbserver} will terminate after the first
16379 connection with remote @value{GDBN} has closed, even for unexpectedly closed
16380 connections and even in the @kbd{target extended-remote} mode. The
16381 @option{--once} option allows reusing the same port number for connecting to
16382 multiple instances of @code{gdbserver} running on the same host, since each
16383 instance closes its port after the first connection.
16385 @subsubsection Other Command-Line Arguments for @code{gdbserver}
16387 @cindex @option{--debug}, @code{gdbserver} option
16388 The @option{--debug} option tells @code{gdbserver} to display extra
16389 status information about the debugging process.
16390 @cindex @option{--remote-debug}, @code{gdbserver} option
16391 The @option{--remote-debug} option tells @code{gdbserver} to display
16392 remote protocol debug output. These options are intended for
16393 @code{gdbserver} development and for bug reports to the developers.
16395 @cindex @option{--wrapper}, @code{gdbserver} option
16396 The @option{--wrapper} option specifies a wrapper to launch programs
16397 for debugging. The option should be followed by the name of the
16398 wrapper, then any command-line arguments to pass to the wrapper, then
16399 @kbd{--} indicating the end of the wrapper arguments.
16401 @code{gdbserver} runs the specified wrapper program with a combined
16402 command line including the wrapper arguments, then the name of the
16403 program to debug, then any arguments to the program. The wrapper
16404 runs until it executes your program, and then @value{GDBN} gains control.
16406 You can use any program that eventually calls @code{execve} with
16407 its arguments as a wrapper. Several standard Unix utilities do
16408 this, e.g.@: @code{env} and @code{nohup}. Any Unix shell script ending
16409 with @code{exec "$@@"} will also work.
16411 For example, you can use @code{env} to pass an environment variable to
16412 the debugged program, without setting the variable in @code{gdbserver}'s
16416 $ gdbserver --wrapper env LD_PRELOAD=libtest.so -- :2222 ./testprog
16419 @subsection Connecting to @code{gdbserver}
16421 Run @value{GDBN} on the host system.
16423 First make sure you have the necessary symbol files. Load symbols for
16424 your application using the @code{file} command before you connect. Use
16425 @code{set sysroot} to locate target libraries (unless your @value{GDBN}
16426 was compiled with the correct sysroot using @code{--with-sysroot}).
16428 The symbol file and target libraries must exactly match the executable
16429 and libraries on the target, with one exception: the files on the host
16430 system should not be stripped, even if the files on the target system
16431 are. Mismatched or missing files will lead to confusing results
16432 during debugging. On @sc{gnu}/Linux targets, mismatched or missing
16433 files may also prevent @code{gdbserver} from debugging multi-threaded
16436 Connect to your target (@pxref{Connecting,,Connecting to a Remote Target}).
16437 For TCP connections, you must start up @code{gdbserver} prior to using
16438 the @code{target remote} command. Otherwise you may get an error whose
16439 text depends on the host system, but which usually looks something like
16440 @samp{Connection refused}. Don't use the @code{load}
16441 command in @value{GDBN} when using @code{gdbserver}, since the program is
16442 already on the target.
16444 @subsection Monitor Commands for @code{gdbserver}
16445 @cindex monitor commands, for @code{gdbserver}
16446 @anchor{Monitor Commands for gdbserver}
16448 During a @value{GDBN} session using @code{gdbserver}, you can use the
16449 @code{monitor} command to send special requests to @code{gdbserver}.
16450 Here are the available commands.
16454 List the available monitor commands.
16456 @item monitor set debug 0
16457 @itemx monitor set debug 1
16458 Disable or enable general debugging messages.
16460 @item monitor set remote-debug 0
16461 @itemx monitor set remote-debug 1
16462 Disable or enable specific debugging messages associated with the remote
16463 protocol (@pxref{Remote Protocol}).
16465 @item monitor set libthread-db-search-path [PATH]
16466 @cindex gdbserver, search path for @code{libthread_db}
16467 When this command is issued, @var{path} is a colon-separated list of
16468 directories to search for @code{libthread_db} (@pxref{Threads,,set
16469 libthread-db-search-path}). If you omit @var{path},
16470 @samp{libthread-db-search-path} will be reset to its default value.
16472 The special entry @samp{$pdir} for @samp{libthread-db-search-path} is
16473 not supported in @code{gdbserver}.
16476 Tell gdbserver to exit immediately. This command should be followed by
16477 @code{disconnect} to close the debugging session. @code{gdbserver} will
16478 detach from any attached processes and kill any processes it created.
16479 Use @code{monitor exit} to terminate @code{gdbserver} at the end
16480 of a multi-process mode debug session.
16484 @subsection Tracepoints support in @code{gdbserver}
16485 @cindex tracepoints support in @code{gdbserver}
16487 On some targets, @code{gdbserver} supports tracepoints, fast
16488 tracepoints and static tracepoints.
16490 For fast or static tracepoints to work, a special library called the
16491 @dfn{in-process agent} (IPA), must be loaded in the inferior process.
16492 This library is built and distributed as an integral part of
16493 @code{gdbserver}. In addition, support for static tracepoints
16494 requires building the in-process agent library with static tracepoints
16495 support. At present, the UST (LTTng Userspace Tracer,
16496 @url{http://lttng.org/ust}) tracing engine is supported. This support
16497 is automatically available if UST development headers are found in the
16498 standard include path when @code{gdbserver} is built, or if
16499 @code{gdbserver} was explicitly configured using @option{--with-ust}
16500 to point at such headers. You can explicitly disable the support
16501 using @option{--with-ust=no}.
16503 There are several ways to load the in-process agent in your program:
16506 @item Specifying it as dependency at link time
16508 You can link your program dynamically with the in-process agent
16509 library. On most systems, this is accomplished by adding
16510 @code{-linproctrace} to the link command.
16512 @item Using the system's preloading mechanisms
16514 You can force loading the in-process agent at startup time by using
16515 your system's support for preloading shared libraries. Many Unixes
16516 support the concept of preloading user defined libraries. In most
16517 cases, you do that by specifying @code{LD_PRELOAD=libinproctrace.so}
16518 in the environment. See also the description of @code{gdbserver}'s
16519 @option{--wrapper} command line option.
16521 @item Using @value{GDBN} to force loading the agent at run time
16523 On some systems, you can force the inferior to load a shared library,
16524 by calling a dynamic loader function in the inferior that takes care
16525 of dynamically looking up and loading a shared library. On most Unix
16526 systems, the function is @code{dlopen}. You'll use the @code{call}
16527 command for that. For example:
16530 (@value{GDBP}) call dlopen ("libinproctrace.so", ...)
16533 Note that on most Unix systems, for the @code{dlopen} function to be
16534 available, the program needs to be linked with @code{-ldl}.
16537 On systems that have a userspace dynamic loader, like most Unix
16538 systems, when you connect to @code{gdbserver} using @code{target
16539 remote}, you'll find that the program is stopped at the dynamic
16540 loader's entry point, and no shared library has been loaded in the
16541 program's address space yet, including the in-process agent. In that
16542 case, before being able to use any of the fast or static tracepoints
16543 features, you need to let the loader run and load the shared
16544 libraries. The simplest way to do that is to run the program to the
16545 main procedure. E.g., if debugging a C or C@t{++} program, start
16546 @code{gdbserver} like so:
16549 $ gdbserver :9999 myprogram
16552 Start GDB and connect to @code{gdbserver} like so, and run to main:
16556 (@value{GDBP}) target remote myhost:9999
16557 0x00007f215893ba60 in ?? () from /lib64/ld-linux-x86-64.so.2
16558 (@value{GDBP}) b main
16559 (@value{GDBP}) continue
16562 The in-process tracing agent library should now be loaded into the
16563 process; you can confirm it with the @code{info sharedlibrary}
16564 command, which will list @file{libinproctrace.so} as loaded in the
16565 process. You are now ready to install fast tracepoints, list static
16566 tracepoint markers, probe static tracepoints markers, and start
16569 @node Remote Configuration
16570 @section Remote Configuration
16573 @kindex show remote
16574 This section documents the configuration options available when
16575 debugging remote programs. For the options related to the File I/O
16576 extensions of the remote protocol, see @ref{system,
16577 system-call-allowed}.
16580 @item set remoteaddresssize @var{bits}
16581 @cindex address size for remote targets
16582 @cindex bits in remote address
16583 Set the maximum size of address in a memory packet to the specified
16584 number of bits. @value{GDBN} will mask off the address bits above
16585 that number, when it passes addresses to the remote target. The
16586 default value is the number of bits in the target's address.
16588 @item show remoteaddresssize
16589 Show the current value of remote address size in bits.
16591 @item set remotebaud @var{n}
16592 @cindex baud rate for remote targets
16593 Set the baud rate for the remote serial I/O to @var{n} baud. The
16594 value is used to set the speed of the serial port used for debugging
16597 @item show remotebaud
16598 Show the current speed of the remote connection.
16600 @item set remotebreak
16601 @cindex interrupt remote programs
16602 @cindex BREAK signal instead of Ctrl-C
16603 @anchor{set remotebreak}
16604 If set to on, @value{GDBN} sends a @code{BREAK} signal to the remote
16605 when you type @kbd{Ctrl-c} to interrupt the program running
16606 on the remote. If set to off, @value{GDBN} sends the @samp{Ctrl-C}
16607 character instead. The default is off, since most remote systems
16608 expect to see @samp{Ctrl-C} as the interrupt signal.
16610 @item show remotebreak
16611 Show whether @value{GDBN} sends @code{BREAK} or @samp{Ctrl-C} to
16612 interrupt the remote program.
16614 @item set remoteflow on
16615 @itemx set remoteflow off
16616 @kindex set remoteflow
16617 Enable or disable hardware flow control (@code{RTS}/@code{CTS})
16618 on the serial port used to communicate to the remote target.
16620 @item show remoteflow
16621 @kindex show remoteflow
16622 Show the current setting of hardware flow control.
16624 @item set remotelogbase @var{base}
16625 Set the base (a.k.a.@: radix) of logging serial protocol
16626 communications to @var{base}. Supported values of @var{base} are:
16627 @code{ascii}, @code{octal}, and @code{hex}. The default is
16630 @item show remotelogbase
16631 Show the current setting of the radix for logging remote serial
16634 @item set remotelogfile @var{file}
16635 @cindex record serial communications on file
16636 Record remote serial communications on the named @var{file}. The
16637 default is not to record at all.
16639 @item show remotelogfile.
16640 Show the current setting of the file name on which to record the
16641 serial communications.
16643 @item set remotetimeout @var{num}
16644 @cindex timeout for serial communications
16645 @cindex remote timeout
16646 Set the timeout limit to wait for the remote target to respond to
16647 @var{num} seconds. The default is 2 seconds.
16649 @item show remotetimeout
16650 Show the current number of seconds to wait for the remote target
16653 @cindex limit hardware breakpoints and watchpoints
16654 @cindex remote target, limit break- and watchpoints
16655 @anchor{set remote hardware-watchpoint-limit}
16656 @anchor{set remote hardware-breakpoint-limit}
16657 @item set remote hardware-watchpoint-limit @var{limit}
16658 @itemx set remote hardware-breakpoint-limit @var{limit}
16659 Restrict @value{GDBN} to using @var{limit} remote hardware breakpoint or
16660 watchpoints. A limit of -1, the default, is treated as unlimited.
16662 @cindex limit hardware watchpoints length
16663 @cindex remote target, limit watchpoints length
16664 @anchor{set remote hardware-watchpoint-length-limit}
16665 @item set remote hardware-watchpoint-length-limit @var{limit}
16666 Restrict @value{GDBN} to using @var{limit} bytes for the maximum length of
16667 a remote hardware watchpoint. A limit of -1, the default, is treated
16670 @item show remote hardware-watchpoint-length-limit
16671 Show the current limit (in bytes) of the maximum length of
16672 a remote hardware watchpoint.
16674 @item set remote exec-file @var{filename}
16675 @itemx show remote exec-file
16676 @anchor{set remote exec-file}
16677 @cindex executable file, for remote target
16678 Select the file used for @code{run} with @code{target
16679 extended-remote}. This should be set to a filename valid on the
16680 target system. If it is not set, the target will use a default
16681 filename (e.g.@: the last program run).
16683 @item set remote interrupt-sequence
16684 @cindex interrupt remote programs
16685 @cindex select Ctrl-C, BREAK or BREAK-g
16686 Allow the user to select one of @samp{Ctrl-C}, a @code{BREAK} or
16687 @samp{BREAK-g} as the
16688 sequence to the remote target in order to interrupt the execution.
16689 @samp{Ctrl-C} is a default. Some system prefers @code{BREAK} which
16690 is high level of serial line for some certain time.
16691 Linux kernel prefers @samp{BREAK-g}, a.k.a Magic SysRq g.
16692 It is @code{BREAK} signal followed by character @code{g}.
16694 @item show interrupt-sequence
16695 Show which of @samp{Ctrl-C}, @code{BREAK} or @code{BREAK-g}
16696 is sent by @value{GDBN} to interrupt the remote program.
16697 @code{BREAK-g} is BREAK signal followed by @code{g} and
16698 also known as Magic SysRq g.
16700 @item set remote interrupt-on-connect
16701 @cindex send interrupt-sequence on start
16702 Specify whether interrupt-sequence is sent to remote target when
16703 @value{GDBN} connects to it. This is mostly needed when you debug
16704 Linux kernel. Linux kernel expects @code{BREAK} followed by @code{g}
16705 which is known as Magic SysRq g in order to connect @value{GDBN}.
16707 @item show interrupt-on-connect
16708 Show whether interrupt-sequence is sent
16709 to remote target when @value{GDBN} connects to it.
16713 @item set tcp auto-retry on
16714 @cindex auto-retry, for remote TCP target
16715 Enable auto-retry for remote TCP connections. This is useful if the remote
16716 debugging agent is launched in parallel with @value{GDBN}; there is a race
16717 condition because the agent may not become ready to accept the connection
16718 before @value{GDBN} attempts to connect. When auto-retry is
16719 enabled, if the initial attempt to connect fails, @value{GDBN} reattempts
16720 to establish the connection using the timeout specified by
16721 @code{set tcp connect-timeout}.
16723 @item set tcp auto-retry off
16724 Do not auto-retry failed TCP connections.
16726 @item show tcp auto-retry
16727 Show the current auto-retry setting.
16729 @item set tcp connect-timeout @var{seconds}
16730 @cindex connection timeout, for remote TCP target
16731 @cindex timeout, for remote target connection
16732 Set the timeout for establishing a TCP connection to the remote target to
16733 @var{seconds}. The timeout affects both polling to retry failed connections
16734 (enabled by @code{set tcp auto-retry on}) and waiting for connections
16735 that are merely slow to complete, and represents an approximate cumulative
16738 @item show tcp connect-timeout
16739 Show the current connection timeout setting.
16742 @cindex remote packets, enabling and disabling
16743 The @value{GDBN} remote protocol autodetects the packets supported by
16744 your debugging stub. If you need to override the autodetection, you
16745 can use these commands to enable or disable individual packets. Each
16746 packet can be set to @samp{on} (the remote target supports this
16747 packet), @samp{off} (the remote target does not support this packet),
16748 or @samp{auto} (detect remote target support for this packet). They
16749 all default to @samp{auto}. For more information about each packet,
16750 see @ref{Remote Protocol}.
16752 During normal use, you should not have to use any of these commands.
16753 If you do, that may be a bug in your remote debugging stub, or a bug
16754 in @value{GDBN}. You may want to report the problem to the
16755 @value{GDBN} developers.
16757 For each packet @var{name}, the command to enable or disable the
16758 packet is @code{set remote @var{name}-packet}. The available settings
16761 @multitable @columnfractions 0.28 0.32 0.25
16764 @tab Related Features
16766 @item @code{fetch-register}
16768 @tab @code{info registers}
16770 @item @code{set-register}
16774 @item @code{binary-download}
16776 @tab @code{load}, @code{set}
16778 @item @code{read-aux-vector}
16779 @tab @code{qXfer:auxv:read}
16780 @tab @code{info auxv}
16782 @item @code{symbol-lookup}
16783 @tab @code{qSymbol}
16784 @tab Detecting multiple threads
16786 @item @code{attach}
16787 @tab @code{vAttach}
16790 @item @code{verbose-resume}
16792 @tab Stepping or resuming multiple threads
16798 @item @code{software-breakpoint}
16802 @item @code{hardware-breakpoint}
16806 @item @code{write-watchpoint}
16810 @item @code{read-watchpoint}
16814 @item @code{access-watchpoint}
16818 @item @code{target-features}
16819 @tab @code{qXfer:features:read}
16820 @tab @code{set architecture}
16822 @item @code{library-info}
16823 @tab @code{qXfer:libraries:read}
16824 @tab @code{info sharedlibrary}
16826 @item @code{memory-map}
16827 @tab @code{qXfer:memory-map:read}
16828 @tab @code{info mem}
16830 @item @code{read-sdata-object}
16831 @tab @code{qXfer:sdata:read}
16832 @tab @code{print $_sdata}
16834 @item @code{read-spu-object}
16835 @tab @code{qXfer:spu:read}
16836 @tab @code{info spu}
16838 @item @code{write-spu-object}
16839 @tab @code{qXfer:spu:write}
16840 @tab @code{info spu}
16842 @item @code{read-siginfo-object}
16843 @tab @code{qXfer:siginfo:read}
16844 @tab @code{print $_siginfo}
16846 @item @code{write-siginfo-object}
16847 @tab @code{qXfer:siginfo:write}
16848 @tab @code{set $_siginfo}
16850 @item @code{threads}
16851 @tab @code{qXfer:threads:read}
16852 @tab @code{info threads}
16854 @item @code{get-thread-local-@*storage-address}
16855 @tab @code{qGetTLSAddr}
16856 @tab Displaying @code{__thread} variables
16858 @item @code{get-thread-information-block-address}
16859 @tab @code{qGetTIBAddr}
16860 @tab Display MS-Windows Thread Information Block.
16862 @item @code{search-memory}
16863 @tab @code{qSearch:memory}
16866 @item @code{supported-packets}
16867 @tab @code{qSupported}
16868 @tab Remote communications parameters
16870 @item @code{pass-signals}
16871 @tab @code{QPassSignals}
16872 @tab @code{handle @var{signal}}
16874 @item @code{hostio-close-packet}
16875 @tab @code{vFile:close}
16876 @tab @code{remote get}, @code{remote put}
16878 @item @code{hostio-open-packet}
16879 @tab @code{vFile:open}
16880 @tab @code{remote get}, @code{remote put}
16882 @item @code{hostio-pread-packet}
16883 @tab @code{vFile:pread}
16884 @tab @code{remote get}, @code{remote put}
16886 @item @code{hostio-pwrite-packet}
16887 @tab @code{vFile:pwrite}
16888 @tab @code{remote get}, @code{remote put}
16890 @item @code{hostio-unlink-packet}
16891 @tab @code{vFile:unlink}
16892 @tab @code{remote delete}
16894 @item @code{noack-packet}
16895 @tab @code{QStartNoAckMode}
16896 @tab Packet acknowledgment
16898 @item @code{osdata}
16899 @tab @code{qXfer:osdata:read}
16900 @tab @code{info os}
16902 @item @code{query-attached}
16903 @tab @code{qAttached}
16904 @tab Querying remote process attach state.
16906 @item @code{traceframe-info}
16907 @tab @code{qXfer:traceframe-info:read}
16908 @tab Traceframe info
16910 @item @code{disable-randomization}
16911 @tab @code{QDisableRandomization}
16912 @tab @code{set disable-randomization}
16916 @section Implementing a Remote Stub
16918 @cindex debugging stub, example
16919 @cindex remote stub, example
16920 @cindex stub example, remote debugging
16921 The stub files provided with @value{GDBN} implement the target side of the
16922 communication protocol, and the @value{GDBN} side is implemented in the
16923 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
16924 these subroutines to communicate, and ignore the details. (If you're
16925 implementing your own stub file, you can still ignore the details: start
16926 with one of the existing stub files. @file{sparc-stub.c} is the best
16927 organized, and therefore the easiest to read.)
16929 @cindex remote serial debugging, overview
16930 To debug a program running on another machine (the debugging
16931 @dfn{target} machine), you must first arrange for all the usual
16932 prerequisites for the program to run by itself. For example, for a C
16937 A startup routine to set up the C runtime environment; these usually
16938 have a name like @file{crt0}. The startup routine may be supplied by
16939 your hardware supplier, or you may have to write your own.
16942 A C subroutine library to support your program's
16943 subroutine calls, notably managing input and output.
16946 A way of getting your program to the other machine---for example, a
16947 download program. These are often supplied by the hardware
16948 manufacturer, but you may have to write your own from hardware
16952 The next step is to arrange for your program to use a serial port to
16953 communicate with the machine where @value{GDBN} is running (the @dfn{host}
16954 machine). In general terms, the scheme looks like this:
16958 @value{GDBN} already understands how to use this protocol; when everything
16959 else is set up, you can simply use the @samp{target remote} command
16960 (@pxref{Targets,,Specifying a Debugging Target}).
16962 @item On the target,
16963 you must link with your program a few special-purpose subroutines that
16964 implement the @value{GDBN} remote serial protocol. The file containing these
16965 subroutines is called a @dfn{debugging stub}.
16967 On certain remote targets, you can use an auxiliary program
16968 @code{gdbserver} instead of linking a stub into your program.
16969 @xref{Server,,Using the @code{gdbserver} Program}, for details.
16972 The debugging stub is specific to the architecture of the remote
16973 machine; for example, use @file{sparc-stub.c} to debug programs on
16976 @cindex remote serial stub list
16977 These working remote stubs are distributed with @value{GDBN}:
16982 @cindex @file{i386-stub.c}
16985 For Intel 386 and compatible architectures.
16988 @cindex @file{m68k-stub.c}
16989 @cindex Motorola 680x0
16991 For Motorola 680x0 architectures.
16994 @cindex @file{sh-stub.c}
16997 For Renesas SH architectures.
17000 @cindex @file{sparc-stub.c}
17002 For @sc{sparc} architectures.
17004 @item sparcl-stub.c
17005 @cindex @file{sparcl-stub.c}
17008 For Fujitsu @sc{sparclite} architectures.
17012 The @file{README} file in the @value{GDBN} distribution may list other
17013 recently added stubs.
17016 * Stub Contents:: What the stub can do for you
17017 * Bootstrapping:: What you must do for the stub
17018 * Debug Session:: Putting it all together
17021 @node Stub Contents
17022 @subsection What the Stub Can Do for You
17024 @cindex remote serial stub
17025 The debugging stub for your architecture supplies these three
17029 @item set_debug_traps
17030 @findex set_debug_traps
17031 @cindex remote serial stub, initialization
17032 This routine arranges for @code{handle_exception} to run when your
17033 program stops. You must call this subroutine explicitly near the
17034 beginning of your program.
17036 @item handle_exception
17037 @findex handle_exception
17038 @cindex remote serial stub, main routine
17039 This is the central workhorse, but your program never calls it
17040 explicitly---the setup code arranges for @code{handle_exception} to
17041 run when a trap is triggered.
17043 @code{handle_exception} takes control when your program stops during
17044 execution (for example, on a breakpoint), and mediates communications
17045 with @value{GDBN} on the host machine. This is where the communications
17046 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
17047 representative on the target machine. It begins by sending summary
17048 information on the state of your program, then continues to execute,
17049 retrieving and transmitting any information @value{GDBN} needs, until you
17050 execute a @value{GDBN} command that makes your program resume; at that point,
17051 @code{handle_exception} returns control to your own code on the target
17055 @cindex @code{breakpoint} subroutine, remote
17056 Use this auxiliary subroutine to make your program contain a
17057 breakpoint. Depending on the particular situation, this may be the only
17058 way for @value{GDBN} to get control. For instance, if your target
17059 machine has some sort of interrupt button, you won't need to call this;
17060 pressing the interrupt button transfers control to
17061 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
17062 simply receiving characters on the serial port may also trigger a trap;
17063 again, in that situation, you don't need to call @code{breakpoint} from
17064 your own program---simply running @samp{target remote} from the host
17065 @value{GDBN} session gets control.
17067 Call @code{breakpoint} if none of these is true, or if you simply want
17068 to make certain your program stops at a predetermined point for the
17069 start of your debugging session.
17072 @node Bootstrapping
17073 @subsection What You Must Do for the Stub
17075 @cindex remote stub, support routines
17076 The debugging stubs that come with @value{GDBN} are set up for a particular
17077 chip architecture, but they have no information about the rest of your
17078 debugging target machine.
17080 First of all you need to tell the stub how to communicate with the
17084 @item int getDebugChar()
17085 @findex getDebugChar
17086 Write this subroutine to read a single character from the serial port.
17087 It may be identical to @code{getchar} for your target system; a
17088 different name is used to allow you to distinguish the two if you wish.
17090 @item void putDebugChar(int)
17091 @findex putDebugChar
17092 Write this subroutine to write a single character to the serial port.
17093 It may be identical to @code{putchar} for your target system; a
17094 different name is used to allow you to distinguish the two if you wish.
17097 @cindex control C, and remote debugging
17098 @cindex interrupting remote targets
17099 If you want @value{GDBN} to be able to stop your program while it is
17100 running, you need to use an interrupt-driven serial driver, and arrange
17101 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
17102 character). That is the character which @value{GDBN} uses to tell the
17103 remote system to stop.
17105 Getting the debugging target to return the proper status to @value{GDBN}
17106 probably requires changes to the standard stub; one quick and dirty way
17107 is to just execute a breakpoint instruction (the ``dirty'' part is that
17108 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
17110 Other routines you need to supply are:
17113 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
17114 @findex exceptionHandler
17115 Write this function to install @var{exception_address} in the exception
17116 handling tables. You need to do this because the stub does not have any
17117 way of knowing what the exception handling tables on your target system
17118 are like (for example, the processor's table might be in @sc{rom},
17119 containing entries which point to a table in @sc{ram}).
17120 @var{exception_number} is the exception number which should be changed;
17121 its meaning is architecture-dependent (for example, different numbers
17122 might represent divide by zero, misaligned access, etc). When this
17123 exception occurs, control should be transferred directly to
17124 @var{exception_address}, and the processor state (stack, registers,
17125 and so on) should be just as it is when a processor exception occurs. So if
17126 you want to use a jump instruction to reach @var{exception_address}, it
17127 should be a simple jump, not a jump to subroutine.
17129 For the 386, @var{exception_address} should be installed as an interrupt
17130 gate so that interrupts are masked while the handler runs. The gate
17131 should be at privilege level 0 (the most privileged level). The
17132 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
17133 help from @code{exceptionHandler}.
17135 @item void flush_i_cache()
17136 @findex flush_i_cache
17137 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
17138 instruction cache, if any, on your target machine. If there is no
17139 instruction cache, this subroutine may be a no-op.
17141 On target machines that have instruction caches, @value{GDBN} requires this
17142 function to make certain that the state of your program is stable.
17146 You must also make sure this library routine is available:
17149 @item void *memset(void *, int, int)
17151 This is the standard library function @code{memset} that sets an area of
17152 memory to a known value. If you have one of the free versions of
17153 @code{libc.a}, @code{memset} can be found there; otherwise, you must
17154 either obtain it from your hardware manufacturer, or write your own.
17157 If you do not use the GNU C compiler, you may need other standard
17158 library subroutines as well; this varies from one stub to another,
17159 but in general the stubs are likely to use any of the common library
17160 subroutines which @code{@value{NGCC}} generates as inline code.
17163 @node Debug Session
17164 @subsection Putting it All Together
17166 @cindex remote serial debugging summary
17167 In summary, when your program is ready to debug, you must follow these
17172 Make sure you have defined the supporting low-level routines
17173 (@pxref{Bootstrapping,,What You Must Do for the Stub}):
17175 @code{getDebugChar}, @code{putDebugChar},
17176 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
17180 Insert these lines near the top of your program:
17188 For the 680x0 stub only, you need to provide a variable called
17189 @code{exceptionHook}. Normally you just use:
17192 void (*exceptionHook)() = 0;
17196 but if before calling @code{set_debug_traps}, you set it to point to a
17197 function in your program, that function is called when
17198 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
17199 error). The function indicated by @code{exceptionHook} is called with
17200 one parameter: an @code{int} which is the exception number.
17203 Compile and link together: your program, the @value{GDBN} debugging stub for
17204 your target architecture, and the supporting subroutines.
17207 Make sure you have a serial connection between your target machine and
17208 the @value{GDBN} host, and identify the serial port on the host.
17211 @c The "remote" target now provides a `load' command, so we should
17212 @c document that. FIXME.
17213 Download your program to your target machine (or get it there by
17214 whatever means the manufacturer provides), and start it.
17217 Start @value{GDBN} on the host, and connect to the target
17218 (@pxref{Connecting,,Connecting to a Remote Target}).
17222 @node Configurations
17223 @chapter Configuration-Specific Information
17225 While nearly all @value{GDBN} commands are available for all native and
17226 cross versions of the debugger, there are some exceptions. This chapter
17227 describes things that are only available in certain configurations.
17229 There are three major categories of configurations: native
17230 configurations, where the host and target are the same, embedded
17231 operating system configurations, which are usually the same for several
17232 different processor architectures, and bare embedded processors, which
17233 are quite different from each other.
17238 * Embedded Processors::
17245 This section describes details specific to particular native
17250 * BSD libkvm Interface:: Debugging BSD kernel memory images
17251 * SVR4 Process Information:: SVR4 process information
17252 * DJGPP Native:: Features specific to the DJGPP port
17253 * Cygwin Native:: Features specific to the Cygwin port
17254 * Hurd Native:: Features specific to @sc{gnu} Hurd
17255 * Neutrino:: Features specific to QNX Neutrino
17256 * Darwin:: Features specific to Darwin
17262 On HP-UX systems, if you refer to a function or variable name that
17263 begins with a dollar sign, @value{GDBN} searches for a user or system
17264 name first, before it searches for a convenience variable.
17267 @node BSD libkvm Interface
17268 @subsection BSD libkvm Interface
17271 @cindex kernel memory image
17272 @cindex kernel crash dump
17274 BSD-derived systems (FreeBSD/NetBSD/OpenBSD) have a kernel memory
17275 interface that provides a uniform interface for accessing kernel virtual
17276 memory images, including live systems and crash dumps. @value{GDBN}
17277 uses this interface to allow you to debug live kernels and kernel crash
17278 dumps on many native BSD configurations. This is implemented as a
17279 special @code{kvm} debugging target. For debugging a live system, load
17280 the currently running kernel into @value{GDBN} and connect to the
17284 (@value{GDBP}) @b{target kvm}
17287 For debugging crash dumps, provide the file name of the crash dump as an
17291 (@value{GDBP}) @b{target kvm /var/crash/bsd.0}
17294 Once connected to the @code{kvm} target, the following commands are
17300 Set current context from the @dfn{Process Control Block} (PCB) address.
17303 Set current context from proc address. This command isn't available on
17304 modern FreeBSD systems.
17307 @node SVR4 Process Information
17308 @subsection SVR4 Process Information
17310 @cindex examine process image
17311 @cindex process info via @file{/proc}
17313 Many versions of SVR4 and compatible systems provide a facility called
17314 @samp{/proc} that can be used to examine the image of a running
17315 process using file-system subroutines. If @value{GDBN} is configured
17316 for an operating system with this facility, the command @code{info
17317 proc} is available to report information about the process running
17318 your program, or about any process running on your system. @code{info
17319 proc} works only on SVR4 systems that include the @code{procfs} code.
17320 This includes, as of this writing, @sc{gnu}/Linux, OSF/1 (Digital
17321 Unix), Solaris, Irix, and Unixware, but not HP-UX, for example.
17327 @itemx info proc @var{process-id}
17328 Summarize available information about any running process. If a
17329 process ID is specified by @var{process-id}, display information about
17330 that process; otherwise display information about the program being
17331 debugged. The summary includes the debugged process ID, the command
17332 line used to invoke it, its current working directory, and its
17333 executable file's absolute file name.
17335 On some systems, @var{process-id} can be of the form
17336 @samp{[@var{pid}]/@var{tid}} which specifies a certain thread ID
17337 within a process. If the optional @var{pid} part is missing, it means
17338 a thread from the process being debugged (the leading @samp{/} still
17339 needs to be present, or else @value{GDBN} will interpret the number as
17340 a process ID rather than a thread ID).
17342 @item info proc mappings
17343 @cindex memory address space mappings
17344 Report the memory address space ranges accessible in the program, with
17345 information on whether the process has read, write, or execute access
17346 rights to each range. On @sc{gnu}/Linux systems, each memory range
17347 includes the object file which is mapped to that range, instead of the
17348 memory access rights to that range.
17350 @item info proc stat
17351 @itemx info proc status
17352 @cindex process detailed status information
17353 These subcommands are specific to @sc{gnu}/Linux systems. They show
17354 the process-related information, including the user ID and group ID;
17355 how many threads are there in the process; its virtual memory usage;
17356 the signals that are pending, blocked, and ignored; its TTY; its
17357 consumption of system and user time; its stack size; its @samp{nice}
17358 value; etc. For more information, see the @samp{proc} man page
17359 (type @kbd{man 5 proc} from your shell prompt).
17361 @item info proc all
17362 Show all the information about the process described under all of the
17363 above @code{info proc} subcommands.
17366 @comment These sub-options of 'info proc' were not included when
17367 @comment procfs.c was re-written. Keep their descriptions around
17368 @comment against the day when someone finds the time to put them back in.
17369 @kindex info proc times
17370 @item info proc times
17371 Starting time, user CPU time, and system CPU time for your program and
17374 @kindex info proc id
17376 Report on the process IDs related to your program: its own process ID,
17377 the ID of its parent, the process group ID, and the session ID.
17380 @item set procfs-trace
17381 @kindex set procfs-trace
17382 @cindex @code{procfs} API calls
17383 This command enables and disables tracing of @code{procfs} API calls.
17385 @item show procfs-trace
17386 @kindex show procfs-trace
17387 Show the current state of @code{procfs} API call tracing.
17389 @item set procfs-file @var{file}
17390 @kindex set procfs-file
17391 Tell @value{GDBN} to write @code{procfs} API trace to the named
17392 @var{file}. @value{GDBN} appends the trace info to the previous
17393 contents of the file. The default is to display the trace on the
17396 @item show procfs-file
17397 @kindex show procfs-file
17398 Show the file to which @code{procfs} API trace is written.
17400 @item proc-trace-entry
17401 @itemx proc-trace-exit
17402 @itemx proc-untrace-entry
17403 @itemx proc-untrace-exit
17404 @kindex proc-trace-entry
17405 @kindex proc-trace-exit
17406 @kindex proc-untrace-entry
17407 @kindex proc-untrace-exit
17408 These commands enable and disable tracing of entries into and exits
17409 from the @code{syscall} interface.
17412 @kindex info pidlist
17413 @cindex process list, QNX Neutrino
17414 For QNX Neutrino only, this command displays the list of all the
17415 processes and all the threads within each process.
17418 @kindex info meminfo
17419 @cindex mapinfo list, QNX Neutrino
17420 For QNX Neutrino only, this command displays the list of all mapinfos.
17424 @subsection Features for Debugging @sc{djgpp} Programs
17425 @cindex @sc{djgpp} debugging
17426 @cindex native @sc{djgpp} debugging
17427 @cindex MS-DOS-specific commands
17430 @sc{djgpp} is a port of the @sc{gnu} development tools to MS-DOS and
17431 MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs
17432 that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on
17433 top of real-mode DOS systems and their emulations.
17435 @value{GDBN} supports native debugging of @sc{djgpp} programs, and
17436 defines a few commands specific to the @sc{djgpp} port. This
17437 subsection describes those commands.
17442 This is a prefix of @sc{djgpp}-specific commands which print
17443 information about the target system and important OS structures.
17446 @cindex MS-DOS system info
17447 @cindex free memory information (MS-DOS)
17448 @item info dos sysinfo
17449 This command displays assorted information about the underlying
17450 platform: the CPU type and features, the OS version and flavor, the
17451 DPMI version, and the available conventional and DPMI memory.
17456 @cindex segment descriptor tables
17457 @cindex descriptor tables display
17459 @itemx info dos ldt
17460 @itemx info dos idt
17461 These 3 commands display entries from, respectively, Global, Local,
17462 and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor
17463 tables are data structures which store a descriptor for each segment
17464 that is currently in use. The segment's selector is an index into a
17465 descriptor table; the table entry for that index holds the
17466 descriptor's base address and limit, and its attributes and access
17469 A typical @sc{djgpp} program uses 3 segments: a code segment, a data
17470 segment (used for both data and the stack), and a DOS segment (which
17471 allows access to DOS/BIOS data structures and absolute addresses in
17472 conventional memory). However, the DPMI host will usually define
17473 additional segments in order to support the DPMI environment.
17475 @cindex garbled pointers
17476 These commands allow to display entries from the descriptor tables.
17477 Without an argument, all entries from the specified table are
17478 displayed. An argument, which should be an integer expression, means
17479 display a single entry whose index is given by the argument. For
17480 example, here's a convenient way to display information about the
17481 debugged program's data segment:
17484 @exdent @code{(@value{GDBP}) info dos ldt $ds}
17485 @exdent @code{0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)}
17489 This comes in handy when you want to see whether a pointer is outside
17490 the data segment's limit (i.e.@: @dfn{garbled}).
17492 @cindex page tables display (MS-DOS)
17494 @itemx info dos pte
17495 These two commands display entries from, respectively, the Page
17496 Directory and the Page Tables. Page Directories and Page Tables are
17497 data structures which control how virtual memory addresses are mapped
17498 into physical addresses. A Page Table includes an entry for every
17499 page of memory that is mapped into the program's address space; there
17500 may be several Page Tables, each one holding up to 4096 entries. A
17501 Page Directory has up to 4096 entries, one each for every Page Table
17502 that is currently in use.
17504 Without an argument, @kbd{info dos pde} displays the entire Page
17505 Directory, and @kbd{info dos pte} displays all the entries in all of
17506 the Page Tables. An argument, an integer expression, given to the
17507 @kbd{info dos pde} command means display only that entry from the Page
17508 Directory table. An argument given to the @kbd{info dos pte} command
17509 means display entries from a single Page Table, the one pointed to by
17510 the specified entry in the Page Directory.
17512 @cindex direct memory access (DMA) on MS-DOS
17513 These commands are useful when your program uses @dfn{DMA} (Direct
17514 Memory Access), which needs physical addresses to program the DMA
17517 These commands are supported only with some DPMI servers.
17519 @cindex physical address from linear address
17520 @item info dos address-pte @var{addr}
17521 This command displays the Page Table entry for a specified linear
17522 address. The argument @var{addr} is a linear address which should
17523 already have the appropriate segment's base address added to it,
17524 because this command accepts addresses which may belong to @emph{any}
17525 segment. For example, here's how to display the Page Table entry for
17526 the page where a variable @code{i} is stored:
17529 @exdent @code{(@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i}
17530 @exdent @code{Page Table entry for address 0x11a00d30:}
17531 @exdent @code{Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30}
17535 This says that @code{i} is stored at offset @code{0xd30} from the page
17536 whose physical base address is @code{0x02698000}, and shows all the
17537 attributes of that page.
17539 Note that you must cast the addresses of variables to a @code{char *},
17540 since otherwise the value of @code{__djgpp_base_address}, the base
17541 address of all variables and functions in a @sc{djgpp} program, will
17542 be added using the rules of C pointer arithmetics: if @code{i} is
17543 declared an @code{int}, @value{GDBN} will add 4 times the value of
17544 @code{__djgpp_base_address} to the address of @code{i}.
17546 Here's another example, it displays the Page Table entry for the
17550 @exdent @code{(@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)}
17551 @exdent @code{Page Table entry for address 0x29110:}
17552 @exdent @code{Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110}
17556 (The @code{+ 3} offset is because the transfer buffer's address is the
17557 3rd member of the @code{_go32_info_block} structure.) The output
17558 clearly shows that this DPMI server maps the addresses in conventional
17559 memory 1:1, i.e.@: the physical (@code{0x00029000} + @code{0x110}) and
17560 linear (@code{0x29110}) addresses are identical.
17562 This command is supported only with some DPMI servers.
17565 @cindex DOS serial data link, remote debugging
17566 In addition to native debugging, the DJGPP port supports remote
17567 debugging via a serial data link. The following commands are specific
17568 to remote serial debugging in the DJGPP port of @value{GDBN}.
17571 @kindex set com1base
17572 @kindex set com1irq
17573 @kindex set com2base
17574 @kindex set com2irq
17575 @kindex set com3base
17576 @kindex set com3irq
17577 @kindex set com4base
17578 @kindex set com4irq
17579 @item set com1base @var{addr}
17580 This command sets the base I/O port address of the @file{COM1} serial
17583 @item set com1irq @var{irq}
17584 This command sets the @dfn{Interrupt Request} (@code{IRQ}) line to use
17585 for the @file{COM1} serial port.
17587 There are similar commands @samp{set com2base}, @samp{set com3irq},
17588 etc.@: for setting the port address and the @code{IRQ} lines for the
17591 @kindex show com1base
17592 @kindex show com1irq
17593 @kindex show com2base
17594 @kindex show com2irq
17595 @kindex show com3base
17596 @kindex show com3irq
17597 @kindex show com4base
17598 @kindex show com4irq
17599 The related commands @samp{show com1base}, @samp{show com1irq} etc.@:
17600 display the current settings of the base address and the @code{IRQ}
17601 lines used by the COM ports.
17604 @kindex info serial
17605 @cindex DOS serial port status
17606 This command prints the status of the 4 DOS serial ports. For each
17607 port, it prints whether it's active or not, its I/O base address and
17608 IRQ number, whether it uses a 16550-style FIFO, its baudrate, and the
17609 counts of various errors encountered so far.
17613 @node Cygwin Native
17614 @subsection Features for Debugging MS Windows PE Executables
17615 @cindex MS Windows debugging
17616 @cindex native Cygwin debugging
17617 @cindex Cygwin-specific commands
17619 @value{GDBN} supports native debugging of MS Windows programs, including
17620 DLLs with and without symbolic debugging information.
17622 @cindex Ctrl-BREAK, MS-Windows
17623 @cindex interrupt debuggee on MS-Windows
17624 MS-Windows programs that call @code{SetConsoleMode} to switch off the
17625 special meaning of the @samp{Ctrl-C} keystroke cannot be interrupted
17626 by typing @kbd{C-c}. For this reason, @value{GDBN} on MS-Windows
17627 supports @kbd{C-@key{BREAK}} as an alternative interrupt key
17628 sequence, which can be used to interrupt the debuggee even if it
17631 There are various additional Cygwin-specific commands, described in
17632 this section. Working with DLLs that have no debugging symbols is
17633 described in @ref{Non-debug DLL Symbols}.
17638 This is a prefix of MS Windows-specific commands which print
17639 information about the target system and important OS structures.
17641 @item info w32 selector
17642 This command displays information returned by
17643 the Win32 API @code{GetThreadSelectorEntry} function.
17644 It takes an optional argument that is evaluated to
17645 a long value to give the information about this given selector.
17646 Without argument, this command displays information
17647 about the six segment registers.
17649 @item info w32 thread-information-block
17650 This command displays thread specific information stored in the
17651 Thread Information Block (readable on the X86 CPU family using @code{$fs}
17652 selector for 32-bit programs and @code{$gs} for 64-bit programs).
17656 This is a Cygwin-specific alias of @code{info shared}.
17658 @kindex dll-symbols
17660 This command loads symbols from a dll similarly to
17661 add-sym command but without the need to specify a base address.
17663 @kindex set cygwin-exceptions
17664 @cindex debugging the Cygwin DLL
17665 @cindex Cygwin DLL, debugging
17666 @item set cygwin-exceptions @var{mode}
17667 If @var{mode} is @code{on}, @value{GDBN} will break on exceptions that
17668 happen inside the Cygwin DLL. If @var{mode} is @code{off},
17669 @value{GDBN} will delay recognition of exceptions, and may ignore some
17670 exceptions which seem to be caused by internal Cygwin DLL
17671 ``bookkeeping''. This option is meant primarily for debugging the
17672 Cygwin DLL itself; the default value is @code{off} to avoid annoying
17673 @value{GDBN} users with false @code{SIGSEGV} signals.
17675 @kindex show cygwin-exceptions
17676 @item show cygwin-exceptions
17677 Displays whether @value{GDBN} will break on exceptions that happen
17678 inside the Cygwin DLL itself.
17680 @kindex set new-console
17681 @item set new-console @var{mode}
17682 If @var{mode} is @code{on} the debuggee will
17683 be started in a new console on next start.
17684 If @var{mode} is @code{off}, the debuggee will
17685 be started in the same console as the debugger.
17687 @kindex show new-console
17688 @item show new-console
17689 Displays whether a new console is used
17690 when the debuggee is started.
17692 @kindex set new-group
17693 @item set new-group @var{mode}
17694 This boolean value controls whether the debuggee should
17695 start a new group or stay in the same group as the debugger.
17696 This affects the way the Windows OS handles
17699 @kindex show new-group
17700 @item show new-group
17701 Displays current value of new-group boolean.
17703 @kindex set debugevents
17704 @item set debugevents
17705 This boolean value adds debug output concerning kernel events related
17706 to the debuggee seen by the debugger. This includes events that
17707 signal thread and process creation and exit, DLL loading and
17708 unloading, console interrupts, and debugging messages produced by the
17709 Windows @code{OutputDebugString} API call.
17711 @kindex set debugexec
17712 @item set debugexec
17713 This boolean value adds debug output concerning execute events
17714 (such as resume thread) seen by the debugger.
17716 @kindex set debugexceptions
17717 @item set debugexceptions
17718 This boolean value adds debug output concerning exceptions in the
17719 debuggee seen by the debugger.
17721 @kindex set debugmemory
17722 @item set debugmemory
17723 This boolean value adds debug output concerning debuggee memory reads
17724 and writes by the debugger.
17728 This boolean values specifies whether the debuggee is called
17729 via a shell or directly (default value is on).
17733 Displays if the debuggee will be started with a shell.
17738 * Non-debug DLL Symbols:: Support for DLLs without debugging symbols
17741 @node Non-debug DLL Symbols
17742 @subsubsection Support for DLLs without Debugging Symbols
17743 @cindex DLLs with no debugging symbols
17744 @cindex Minimal symbols and DLLs
17746 Very often on windows, some of the DLLs that your program relies on do
17747 not include symbolic debugging information (for example,
17748 @file{kernel32.dll}). When @value{GDBN} doesn't recognize any debugging
17749 symbols in a DLL, it relies on the minimal amount of symbolic
17750 information contained in the DLL's export table. This section
17751 describes working with such symbols, known internally to @value{GDBN} as
17752 ``minimal symbols''.
17754 Note that before the debugged program has started execution, no DLLs
17755 will have been loaded. The easiest way around this problem is simply to
17756 start the program --- either by setting a breakpoint or letting the
17757 program run once to completion. It is also possible to force
17758 @value{GDBN} to load a particular DLL before starting the executable ---
17759 see the shared library information in @ref{Files}, or the
17760 @code{dll-symbols} command in @ref{Cygwin Native}. Currently,
17761 explicitly loading symbols from a DLL with no debugging information will
17762 cause the symbol names to be duplicated in @value{GDBN}'s lookup table,
17763 which may adversely affect symbol lookup performance.
17765 @subsubsection DLL Name Prefixes
17767 In keeping with the naming conventions used by the Microsoft debugging
17768 tools, DLL export symbols are made available with a prefix based on the
17769 DLL name, for instance @code{KERNEL32!CreateFileA}. The plain name is
17770 also entered into the symbol table, so @code{CreateFileA} is often
17771 sufficient. In some cases there will be name clashes within a program
17772 (particularly if the executable itself includes full debugging symbols)
17773 necessitating the use of the fully qualified name when referring to the
17774 contents of the DLL. Use single-quotes around the name to avoid the
17775 exclamation mark (``!'') being interpreted as a language operator.
17777 Note that the internal name of the DLL may be all upper-case, even
17778 though the file name of the DLL is lower-case, or vice-versa. Since
17779 symbols within @value{GDBN} are @emph{case-sensitive} this may cause
17780 some confusion. If in doubt, try the @code{info functions} and
17781 @code{info variables} commands or even @code{maint print msymbols}
17782 (@pxref{Symbols}). Here's an example:
17785 (@value{GDBP}) info function CreateFileA
17786 All functions matching regular expression "CreateFileA":
17788 Non-debugging symbols:
17789 0x77e885f4 CreateFileA
17790 0x77e885f4 KERNEL32!CreateFileA
17794 (@value{GDBP}) info function !
17795 All functions matching regular expression "!":
17797 Non-debugging symbols:
17798 0x6100114c cygwin1!__assert
17799 0x61004034 cygwin1!_dll_crt0@@0
17800 0x61004240 cygwin1!dll_crt0(per_process *)
17804 @subsubsection Working with Minimal Symbols
17806 Symbols extracted from a DLL's export table do not contain very much
17807 type information. All that @value{GDBN} can do is guess whether a symbol
17808 refers to a function or variable depending on the linker section that
17809 contains the symbol. Also note that the actual contents of the memory
17810 contained in a DLL are not available unless the program is running. This
17811 means that you cannot examine the contents of a variable or disassemble
17812 a function within a DLL without a running program.
17814 Variables are generally treated as pointers and dereferenced
17815 automatically. For this reason, it is often necessary to prefix a
17816 variable name with the address-of operator (``&'') and provide explicit
17817 type information in the command. Here's an example of the type of
17821 (@value{GDBP}) print 'cygwin1!__argv'
17826 (@value{GDBP}) x 'cygwin1!__argv'
17827 0x10021610: "\230y\""
17830 And two possible solutions:
17833 (@value{GDBP}) print ((char **)'cygwin1!__argv')[0]
17834 $2 = 0x22fd98 "/cygdrive/c/mydirectory/myprogram"
17838 (@value{GDBP}) x/2x &'cygwin1!__argv'
17839 0x610c0aa8 <cygwin1!__argv>: 0x10021608 0x00000000
17840 (@value{GDBP}) x/x 0x10021608
17841 0x10021608: 0x0022fd98
17842 (@value{GDBP}) x/s 0x0022fd98
17843 0x22fd98: "/cygdrive/c/mydirectory/myprogram"
17846 Setting a break point within a DLL is possible even before the program
17847 starts execution. However, under these circumstances, @value{GDBN} can't
17848 examine the initial instructions of the function in order to skip the
17849 function's frame set-up code. You can work around this by using ``*&''
17850 to set the breakpoint at a raw memory address:
17853 (@value{GDBP}) break *&'python22!PyOS_Readline'
17854 Breakpoint 1 at 0x1e04eff0
17857 The author of these extensions is not entirely convinced that setting a
17858 break point within a shared DLL like @file{kernel32.dll} is completely
17862 @subsection Commands Specific to @sc{gnu} Hurd Systems
17863 @cindex @sc{gnu} Hurd debugging
17865 This subsection describes @value{GDBN} commands specific to the
17866 @sc{gnu} Hurd native debugging.
17871 @kindex set signals@r{, Hurd command}
17872 @kindex set sigs@r{, Hurd command}
17873 This command toggles the state of inferior signal interception by
17874 @value{GDBN}. Mach exceptions, such as breakpoint traps, are not
17875 affected by this command. @code{sigs} is a shorthand alias for
17880 @kindex show signals@r{, Hurd command}
17881 @kindex show sigs@r{, Hurd command}
17882 Show the current state of intercepting inferior's signals.
17884 @item set signal-thread
17885 @itemx set sigthread
17886 @kindex set signal-thread
17887 @kindex set sigthread
17888 This command tells @value{GDBN} which thread is the @code{libc} signal
17889 thread. That thread is run when a signal is delivered to a running
17890 process. @code{set sigthread} is the shorthand alias of @code{set
17893 @item show signal-thread
17894 @itemx show sigthread
17895 @kindex show signal-thread
17896 @kindex show sigthread
17897 These two commands show which thread will run when the inferior is
17898 delivered a signal.
17901 @kindex set stopped@r{, Hurd command}
17902 This commands tells @value{GDBN} that the inferior process is stopped,
17903 as with the @code{SIGSTOP} signal. The stopped process can be
17904 continued by delivering a signal to it.
17907 @kindex show stopped@r{, Hurd command}
17908 This command shows whether @value{GDBN} thinks the debuggee is
17911 @item set exceptions
17912 @kindex set exceptions@r{, Hurd command}
17913 Use this command to turn off trapping of exceptions in the inferior.
17914 When exception trapping is off, neither breakpoints nor
17915 single-stepping will work. To restore the default, set exception
17918 @item show exceptions
17919 @kindex show exceptions@r{, Hurd command}
17920 Show the current state of trapping exceptions in the inferior.
17922 @item set task pause
17923 @kindex set task@r{, Hurd commands}
17924 @cindex task attributes (@sc{gnu} Hurd)
17925 @cindex pause current task (@sc{gnu} Hurd)
17926 This command toggles task suspension when @value{GDBN} has control.
17927 Setting it to on takes effect immediately, and the task is suspended
17928 whenever @value{GDBN} gets control. Setting it to off will take
17929 effect the next time the inferior is continued. If this option is set
17930 to off, you can use @code{set thread default pause on} or @code{set
17931 thread pause on} (see below) to pause individual threads.
17933 @item show task pause
17934 @kindex show task@r{, Hurd commands}
17935 Show the current state of task suspension.
17937 @item set task detach-suspend-count
17938 @cindex task suspend count
17939 @cindex detach from task, @sc{gnu} Hurd
17940 This command sets the suspend count the task will be left with when
17941 @value{GDBN} detaches from it.
17943 @item show task detach-suspend-count
17944 Show the suspend count the task will be left with when detaching.
17946 @item set task exception-port
17947 @itemx set task excp
17948 @cindex task exception port, @sc{gnu} Hurd
17949 This command sets the task exception port to which @value{GDBN} will
17950 forward exceptions. The argument should be the value of the @dfn{send
17951 rights} of the task. @code{set task excp} is a shorthand alias.
17953 @item set noninvasive
17954 @cindex noninvasive task options
17955 This command switches @value{GDBN} to a mode that is the least
17956 invasive as far as interfering with the inferior is concerned. This
17957 is the same as using @code{set task pause}, @code{set exceptions}, and
17958 @code{set signals} to values opposite to the defaults.
17960 @item info send-rights
17961 @itemx info receive-rights
17962 @itemx info port-rights
17963 @itemx info port-sets
17964 @itemx info dead-names
17967 @cindex send rights, @sc{gnu} Hurd
17968 @cindex receive rights, @sc{gnu} Hurd
17969 @cindex port rights, @sc{gnu} Hurd
17970 @cindex port sets, @sc{gnu} Hurd
17971 @cindex dead names, @sc{gnu} Hurd
17972 These commands display information about, respectively, send rights,
17973 receive rights, port rights, port sets, and dead names of a task.
17974 There are also shorthand aliases: @code{info ports} for @code{info
17975 port-rights} and @code{info psets} for @code{info port-sets}.
17977 @item set thread pause
17978 @kindex set thread@r{, Hurd command}
17979 @cindex thread properties, @sc{gnu} Hurd
17980 @cindex pause current thread (@sc{gnu} Hurd)
17981 This command toggles current thread suspension when @value{GDBN} has
17982 control. Setting it to on takes effect immediately, and the current
17983 thread is suspended whenever @value{GDBN} gets control. Setting it to
17984 off will take effect the next time the inferior is continued.
17985 Normally, this command has no effect, since when @value{GDBN} has
17986 control, the whole task is suspended. However, if you used @code{set
17987 task pause off} (see above), this command comes in handy to suspend
17988 only the current thread.
17990 @item show thread pause
17991 @kindex show thread@r{, Hurd command}
17992 This command shows the state of current thread suspension.
17994 @item set thread run
17995 This command sets whether the current thread is allowed to run.
17997 @item show thread run
17998 Show whether the current thread is allowed to run.
18000 @item set thread detach-suspend-count
18001 @cindex thread suspend count, @sc{gnu} Hurd
18002 @cindex detach from thread, @sc{gnu} Hurd
18003 This command sets the suspend count @value{GDBN} will leave on a
18004 thread when detaching. This number is relative to the suspend count
18005 found by @value{GDBN} when it notices the thread; use @code{set thread
18006 takeover-suspend-count} to force it to an absolute value.
18008 @item show thread detach-suspend-count
18009 Show the suspend count @value{GDBN} will leave on the thread when
18012 @item set thread exception-port
18013 @itemx set thread excp
18014 Set the thread exception port to which to forward exceptions. This
18015 overrides the port set by @code{set task exception-port} (see above).
18016 @code{set thread excp} is the shorthand alias.
18018 @item set thread takeover-suspend-count
18019 Normally, @value{GDBN}'s thread suspend counts are relative to the
18020 value @value{GDBN} finds when it notices each thread. This command
18021 changes the suspend counts to be absolute instead.
18023 @item set thread default
18024 @itemx show thread default
18025 @cindex thread default settings, @sc{gnu} Hurd
18026 Each of the above @code{set thread} commands has a @code{set thread
18027 default} counterpart (e.g., @code{set thread default pause}, @code{set
18028 thread default exception-port}, etc.). The @code{thread default}
18029 variety of commands sets the default thread properties for all
18030 threads; you can then change the properties of individual threads with
18031 the non-default commands.
18036 @subsection QNX Neutrino
18037 @cindex QNX Neutrino
18039 @value{GDBN} provides the following commands specific to the QNX
18043 @item set debug nto-debug
18044 @kindex set debug nto-debug
18045 When set to on, enables debugging messages specific to the QNX
18048 @item show debug nto-debug
18049 @kindex show debug nto-debug
18050 Show the current state of QNX Neutrino messages.
18057 @value{GDBN} provides the following commands specific to the Darwin target:
18060 @item set debug darwin @var{num}
18061 @kindex set debug darwin
18062 When set to a non zero value, enables debugging messages specific to
18063 the Darwin support. Higher values produce more verbose output.
18065 @item show debug darwin
18066 @kindex show debug darwin
18067 Show the current state of Darwin messages.
18069 @item set debug mach-o @var{num}
18070 @kindex set debug mach-o
18071 When set to a non zero value, enables debugging messages while
18072 @value{GDBN} is reading Darwin object files. (@dfn{Mach-O} is the
18073 file format used on Darwin for object and executable files.) Higher
18074 values produce more verbose output. This is a command to diagnose
18075 problems internal to @value{GDBN} and should not be needed in normal
18078 @item show debug mach-o
18079 @kindex show debug mach-o
18080 Show the current state of Mach-O file messages.
18082 @item set mach-exceptions on
18083 @itemx set mach-exceptions off
18084 @kindex set mach-exceptions
18085 On Darwin, faults are first reported as a Mach exception and are then
18086 mapped to a Posix signal. Use this command to turn on trapping of
18087 Mach exceptions in the inferior. This might be sometimes useful to
18088 better understand the cause of a fault. The default is off.
18090 @item show mach-exceptions
18091 @kindex show mach-exceptions
18092 Show the current state of exceptions trapping.
18097 @section Embedded Operating Systems
18099 This section describes configurations involving the debugging of
18100 embedded operating systems that are available for several different
18104 * VxWorks:: Using @value{GDBN} with VxWorks
18107 @value{GDBN} includes the ability to debug programs running on
18108 various real-time operating systems.
18111 @subsection Using @value{GDBN} with VxWorks
18117 @kindex target vxworks
18118 @item target vxworks @var{machinename}
18119 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
18120 is the target system's machine name or IP address.
18124 On VxWorks, @code{load} links @var{filename} dynamically on the
18125 current target system as well as adding its symbols in @value{GDBN}.
18127 @value{GDBN} enables developers to spawn and debug tasks running on networked
18128 VxWorks targets from a Unix host. Already-running tasks spawned from
18129 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
18130 both the Unix host and on the VxWorks target. The program
18131 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
18132 installed with the name @code{vxgdb}, to distinguish it from a
18133 @value{GDBN} for debugging programs on the host itself.)
18136 @item VxWorks-timeout @var{args}
18137 @kindex vxworks-timeout
18138 All VxWorks-based targets now support the option @code{vxworks-timeout}.
18139 This option is set by the user, and @var{args} represents the number of
18140 seconds @value{GDBN} waits for responses to rpc's. You might use this if
18141 your VxWorks target is a slow software simulator or is on the far side
18142 of a thin network line.
18145 The following information on connecting to VxWorks was current when
18146 this manual was produced; newer releases of VxWorks may use revised
18149 @findex INCLUDE_RDB
18150 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
18151 to include the remote debugging interface routines in the VxWorks
18152 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
18153 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
18154 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
18155 source debugging task @code{tRdbTask} when VxWorks is booted. For more
18156 information on configuring and remaking VxWorks, see the manufacturer's
18158 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
18160 Once you have included @file{rdb.a} in your VxWorks system image and set
18161 your Unix execution search path to find @value{GDBN}, you are ready to
18162 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
18163 @code{vxgdb}, depending on your installation).
18165 @value{GDBN} comes up showing the prompt:
18172 * VxWorks Connection:: Connecting to VxWorks
18173 * VxWorks Download:: VxWorks download
18174 * VxWorks Attach:: Running tasks
18177 @node VxWorks Connection
18178 @subsubsection Connecting to VxWorks
18180 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
18181 network. To connect to a target whose host name is ``@code{tt}'', type:
18184 (vxgdb) target vxworks tt
18188 @value{GDBN} displays messages like these:
18191 Attaching remote machine across net...
18196 @value{GDBN} then attempts to read the symbol tables of any object modules
18197 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
18198 these files by searching the directories listed in the command search
18199 path (@pxref{Environment, ,Your Program's Environment}); if it fails
18200 to find an object file, it displays a message such as:
18203 prog.o: No such file or directory.
18206 When this happens, add the appropriate directory to the search path with
18207 the @value{GDBN} command @code{path}, and execute the @code{target}
18210 @node VxWorks Download
18211 @subsubsection VxWorks Download
18213 @cindex download to VxWorks
18214 If you have connected to the VxWorks target and you want to debug an
18215 object that has not yet been loaded, you can use the @value{GDBN}
18216 @code{load} command to download a file from Unix to VxWorks
18217 incrementally. The object file given as an argument to the @code{load}
18218 command is actually opened twice: first by the VxWorks target in order
18219 to download the code, then by @value{GDBN} in order to read the symbol
18220 table. This can lead to problems if the current working directories on
18221 the two systems differ. If both systems have NFS mounted the same
18222 filesystems, you can avoid these problems by using absolute paths.
18223 Otherwise, it is simplest to set the working directory on both systems
18224 to the directory in which the object file resides, and then to reference
18225 the file by its name, without any path. For instance, a program
18226 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
18227 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
18228 program, type this on VxWorks:
18231 -> cd "@var{vxpath}/vw/demo/rdb"
18235 Then, in @value{GDBN}, type:
18238 (vxgdb) cd @var{hostpath}/vw/demo/rdb
18239 (vxgdb) load prog.o
18242 @value{GDBN} displays a response similar to this:
18245 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
18248 You can also use the @code{load} command to reload an object module
18249 after editing and recompiling the corresponding source file. Note that
18250 this makes @value{GDBN} delete all currently-defined breakpoints,
18251 auto-displays, and convenience variables, and to clear the value
18252 history. (This is necessary in order to preserve the integrity of
18253 debugger's data structures that reference the target system's symbol
18256 @node VxWorks Attach
18257 @subsubsection Running Tasks
18259 @cindex running VxWorks tasks
18260 You can also attach to an existing task using the @code{attach} command as
18264 (vxgdb) attach @var{task}
18268 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
18269 or suspended when you attach to it. Running tasks are suspended at
18270 the time of attachment.
18272 @node Embedded Processors
18273 @section Embedded Processors
18275 This section goes into details specific to particular embedded
18278 @cindex send command to simulator
18279 Whenever a specific embedded processor has a simulator, @value{GDBN}
18280 allows to send an arbitrary command to the simulator.
18283 @item sim @var{command}
18284 @kindex sim@r{, a command}
18285 Send an arbitrary @var{command} string to the simulator. Consult the
18286 documentation for the specific simulator in use for information about
18287 acceptable commands.
18293 * M32R/D:: Renesas M32R/D
18294 * M68K:: Motorola M68K
18295 * MicroBlaze:: Xilinx MicroBlaze
18296 * MIPS Embedded:: MIPS Embedded
18297 * OpenRISC 1000:: OpenRisc 1000
18298 * PA:: HP PA Embedded
18299 * PowerPC Embedded:: PowerPC Embedded
18300 * Sparclet:: Tsqware Sparclet
18301 * Sparclite:: Fujitsu Sparclite
18302 * Z8000:: Zilog Z8000
18305 * Super-H:: Renesas Super-H
18314 @item target rdi @var{dev}
18315 ARM Angel monitor, via RDI library interface to ADP protocol. You may
18316 use this target to communicate with both boards running the Angel
18317 monitor, or with the EmbeddedICE JTAG debug device.
18320 @item target rdp @var{dev}
18325 @value{GDBN} provides the following ARM-specific commands:
18328 @item set arm disassembler
18330 This commands selects from a list of disassembly styles. The
18331 @code{"std"} style is the standard style.
18333 @item show arm disassembler
18335 Show the current disassembly style.
18337 @item set arm apcs32
18338 @cindex ARM 32-bit mode
18339 This command toggles ARM operation mode between 32-bit and 26-bit.
18341 @item show arm apcs32
18342 Display the current usage of the ARM 32-bit mode.
18344 @item set arm fpu @var{fputype}
18345 This command sets the ARM floating-point unit (FPU) type. The
18346 argument @var{fputype} can be one of these:
18350 Determine the FPU type by querying the OS ABI.
18352 Software FPU, with mixed-endian doubles on little-endian ARM
18355 GCC-compiled FPA co-processor.
18357 Software FPU with pure-endian doubles.
18363 Show the current type of the FPU.
18366 This command forces @value{GDBN} to use the specified ABI.
18369 Show the currently used ABI.
18371 @item set arm fallback-mode (arm|thumb|auto)
18372 @value{GDBN} uses the symbol table, when available, to determine
18373 whether instructions are ARM or Thumb. This command controls
18374 @value{GDBN}'s default behavior when the symbol table is not
18375 available. The default is @samp{auto}, which causes @value{GDBN} to
18376 use the current execution mode (from the @code{T} bit in the @code{CPSR}
18379 @item show arm fallback-mode
18380 Show the current fallback instruction mode.
18382 @item set arm force-mode (arm|thumb|auto)
18383 This command overrides use of the symbol table to determine whether
18384 instructions are ARM or Thumb. The default is @samp{auto}, which
18385 causes @value{GDBN} to use the symbol table and then the setting
18386 of @samp{set arm fallback-mode}.
18388 @item show arm force-mode
18389 Show the current forced instruction mode.
18391 @item set debug arm
18392 Toggle whether to display ARM-specific debugging messages from the ARM
18393 target support subsystem.
18395 @item show debug arm
18396 Show whether ARM-specific debugging messages are enabled.
18399 The following commands are available when an ARM target is debugged
18400 using the RDI interface:
18403 @item rdilogfile @r{[}@var{file}@r{]}
18405 @cindex ADP (Angel Debugger Protocol) logging
18406 Set the filename for the ADP (Angel Debugger Protocol) packet log.
18407 With an argument, sets the log file to the specified @var{file}. With
18408 no argument, show the current log file name. The default log file is
18411 @item rdilogenable @r{[}@var{arg}@r{]}
18412 @kindex rdilogenable
18413 Control logging of ADP packets. With an argument of 1 or @code{"yes"}
18414 enables logging, with an argument 0 or @code{"no"} disables it. With
18415 no arguments displays the current setting. When logging is enabled,
18416 ADP packets exchanged between @value{GDBN} and the RDI target device
18417 are logged to a file.
18419 @item set rdiromatzero
18420 @kindex set rdiromatzero
18421 @cindex ROM at zero address, RDI
18422 Tell @value{GDBN} whether the target has ROM at address 0. If on,
18423 vector catching is disabled, so that zero address can be used. If off
18424 (the default), vector catching is enabled. For this command to take
18425 effect, it needs to be invoked prior to the @code{target rdi} command.
18427 @item show rdiromatzero
18428 @kindex show rdiromatzero
18429 Show the current setting of ROM at zero address.
18431 @item set rdiheartbeat
18432 @kindex set rdiheartbeat
18433 @cindex RDI heartbeat
18434 Enable or disable RDI heartbeat packets. It is not recommended to
18435 turn on this option, since it confuses ARM and EPI JTAG interface, as
18436 well as the Angel monitor.
18438 @item show rdiheartbeat
18439 @kindex show rdiheartbeat
18440 Show the setting of RDI heartbeat packets.
18444 @item target sim @r{[}@var{simargs}@r{]} @dots{}
18445 The @value{GDBN} ARM simulator accepts the following optional arguments.
18448 @item --swi-support=@var{type}
18449 Tell the simulator which SWI interfaces to support.
18450 @var{type} may be a comma separated list of the following values.
18451 The default value is @code{all}.
18464 @subsection Renesas M32R/D and M32R/SDI
18467 @kindex target m32r
18468 @item target m32r @var{dev}
18469 Renesas M32R/D ROM monitor.
18471 @kindex target m32rsdi
18472 @item target m32rsdi @var{dev}
18473 Renesas M32R SDI server, connected via parallel port to the board.
18476 The following @value{GDBN} commands are specific to the M32R monitor:
18479 @item set download-path @var{path}
18480 @kindex set download-path
18481 @cindex find downloadable @sc{srec} files (M32R)
18482 Set the default path for finding downloadable @sc{srec} files.
18484 @item show download-path
18485 @kindex show download-path
18486 Show the default path for downloadable @sc{srec} files.
18488 @item set board-address @var{addr}
18489 @kindex set board-address
18490 @cindex M32-EVA target board address
18491 Set the IP address for the M32R-EVA target board.
18493 @item show board-address
18494 @kindex show board-address
18495 Show the current IP address of the target board.
18497 @item set server-address @var{addr}
18498 @kindex set server-address
18499 @cindex download server address (M32R)
18500 Set the IP address for the download server, which is the @value{GDBN}'s
18503 @item show server-address
18504 @kindex show server-address
18505 Display the IP address of the download server.
18507 @item upload @r{[}@var{file}@r{]}
18508 @kindex upload@r{, M32R}
18509 Upload the specified @sc{srec} @var{file} via the monitor's Ethernet
18510 upload capability. If no @var{file} argument is given, the current
18511 executable file is uploaded.
18513 @item tload @r{[}@var{file}@r{]}
18514 @kindex tload@r{, M32R}
18515 Test the @code{upload} command.
18518 The following commands are available for M32R/SDI:
18523 @cindex reset SDI connection, M32R
18524 This command resets the SDI connection.
18528 This command shows the SDI connection status.
18531 @kindex debug_chaos
18532 @cindex M32R/Chaos debugging
18533 Instructs the remote that M32R/Chaos debugging is to be used.
18535 @item use_debug_dma
18536 @kindex use_debug_dma
18537 Instructs the remote to use the DEBUG_DMA method of accessing memory.
18540 @kindex use_mon_code
18541 Instructs the remote to use the MON_CODE method of accessing memory.
18544 @kindex use_ib_break
18545 Instructs the remote to set breakpoints by IB break.
18547 @item use_dbt_break
18548 @kindex use_dbt_break
18549 Instructs the remote to set breakpoints by DBT.
18555 The Motorola m68k configuration includes ColdFire support, and a
18556 target command for the following ROM monitor.
18560 @kindex target dbug
18561 @item target dbug @var{dev}
18562 dBUG ROM monitor for Motorola ColdFire.
18567 @subsection MicroBlaze
18568 @cindex Xilinx MicroBlaze
18569 @cindex XMD, Xilinx Microprocessor Debugger
18571 The MicroBlaze is a soft-core processor supported on various Xilinx
18572 FPGAs, such as Spartan or Virtex series. Boards with these processors
18573 usually have JTAG ports which connect to a host system running the Xilinx
18574 Embedded Development Kit (EDK) or Software Development Kit (SDK).
18575 This host system is used to download the configuration bitstream to
18576 the target FPGA. The Xilinx Microprocessor Debugger (XMD) program
18577 communicates with the target board using the JTAG interface and
18578 presents a @code{gdbserver} interface to the board. By default
18579 @code{xmd} uses port @code{1234}. (While it is possible to change
18580 this default port, it requires the use of undocumented @code{xmd}
18581 commands. Contact Xilinx support if you need to do this.)
18583 Use these GDB commands to connect to the MicroBlaze target processor.
18586 @item target remote :1234
18587 Use this command to connect to the target if you are running @value{GDBN}
18588 on the same system as @code{xmd}.
18590 @item target remote @var{xmd-host}:1234
18591 Use this command to connect to the target if it is connected to @code{xmd}
18592 running on a different system named @var{xmd-host}.
18595 Use this command to download a program to the MicroBlaze target.
18597 @item set debug microblaze @var{n}
18598 Enable MicroBlaze-specific debugging messages if non-zero.
18600 @item show debug microblaze @var{n}
18601 Show MicroBlaze-specific debugging level.
18604 @node MIPS Embedded
18605 @subsection MIPS Embedded
18607 @cindex MIPS boards
18608 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
18609 MIPS board attached to a serial line. This is available when
18610 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
18613 Use these @value{GDBN} commands to specify the connection to your target board:
18616 @item target mips @var{port}
18617 @kindex target mips @var{port}
18618 To run a program on the board, start up @code{@value{GDBP}} with the
18619 name of your program as the argument. To connect to the board, use the
18620 command @samp{target mips @var{port}}, where @var{port} is the name of
18621 the serial port connected to the board. If the program has not already
18622 been downloaded to the board, you may use the @code{load} command to
18623 download it. You can then use all the usual @value{GDBN} commands.
18625 For example, this sequence connects to the target board through a serial
18626 port, and loads and runs a program called @var{prog} through the
18630 host$ @value{GDBP} @var{prog}
18631 @value{GDBN} is free software and @dots{}
18632 (@value{GDBP}) target mips /dev/ttyb
18633 (@value{GDBP}) load @var{prog}
18637 @item target mips @var{hostname}:@var{portnumber}
18638 On some @value{GDBN} host configurations, you can specify a TCP
18639 connection (for instance, to a serial line managed by a terminal
18640 concentrator) instead of a serial port, using the syntax
18641 @samp{@var{hostname}:@var{portnumber}}.
18643 @item target pmon @var{port}
18644 @kindex target pmon @var{port}
18647 @item target ddb @var{port}
18648 @kindex target ddb @var{port}
18649 NEC's DDB variant of PMON for Vr4300.
18651 @item target lsi @var{port}
18652 @kindex target lsi @var{port}
18653 LSI variant of PMON.
18655 @kindex target r3900
18656 @item target r3900 @var{dev}
18657 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
18659 @kindex target array
18660 @item target array @var{dev}
18661 Array Tech LSI33K RAID controller board.
18667 @value{GDBN} also supports these special commands for MIPS targets:
18670 @item set mipsfpu double
18671 @itemx set mipsfpu single
18672 @itemx set mipsfpu none
18673 @itemx set mipsfpu auto
18674 @itemx show mipsfpu
18675 @kindex set mipsfpu
18676 @kindex show mipsfpu
18677 @cindex MIPS remote floating point
18678 @cindex floating point, MIPS remote
18679 If your target board does not support the MIPS floating point
18680 coprocessor, you should use the command @samp{set mipsfpu none} (if you
18681 need this, you may wish to put the command in your @value{GDBN} init
18682 file). This tells @value{GDBN} how to find the return value of
18683 functions which return floating point values. It also allows
18684 @value{GDBN} to avoid saving the floating point registers when calling
18685 functions on the board. If you are using a floating point coprocessor
18686 with only single precision floating point support, as on the @sc{r4650}
18687 processor, use the command @samp{set mipsfpu single}. The default
18688 double precision floating point coprocessor may be selected using
18689 @samp{set mipsfpu double}.
18691 In previous versions the only choices were double precision or no
18692 floating point, so @samp{set mipsfpu on} will select double precision
18693 and @samp{set mipsfpu off} will select no floating point.
18695 As usual, you can inquire about the @code{mipsfpu} variable with
18696 @samp{show mipsfpu}.
18698 @item set timeout @var{seconds}
18699 @itemx set retransmit-timeout @var{seconds}
18700 @itemx show timeout
18701 @itemx show retransmit-timeout
18702 @cindex @code{timeout}, MIPS protocol
18703 @cindex @code{retransmit-timeout}, MIPS protocol
18704 @kindex set timeout
18705 @kindex show timeout
18706 @kindex set retransmit-timeout
18707 @kindex show retransmit-timeout
18708 You can control the timeout used while waiting for a packet, in the MIPS
18709 remote protocol, with the @code{set timeout @var{seconds}} command. The
18710 default is 5 seconds. Similarly, you can control the timeout used while
18711 waiting for an acknowledgment of a packet with the @code{set
18712 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
18713 You can inspect both values with @code{show timeout} and @code{show
18714 retransmit-timeout}. (These commands are @emph{only} available when
18715 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
18717 The timeout set by @code{set timeout} does not apply when @value{GDBN}
18718 is waiting for your program to stop. In that case, @value{GDBN} waits
18719 forever because it has no way of knowing how long the program is going
18720 to run before stopping.
18722 @item set syn-garbage-limit @var{num}
18723 @kindex set syn-garbage-limit@r{, MIPS remote}
18724 @cindex synchronize with remote MIPS target
18725 Limit the maximum number of characters @value{GDBN} should ignore when
18726 it tries to synchronize with the remote target. The default is 10
18727 characters. Setting the limit to -1 means there's no limit.
18729 @item show syn-garbage-limit
18730 @kindex show syn-garbage-limit@r{, MIPS remote}
18731 Show the current limit on the number of characters to ignore when
18732 trying to synchronize with the remote system.
18734 @item set monitor-prompt @var{prompt}
18735 @kindex set monitor-prompt@r{, MIPS remote}
18736 @cindex remote monitor prompt
18737 Tell @value{GDBN} to expect the specified @var{prompt} string from the
18738 remote monitor. The default depends on the target:
18748 @item show monitor-prompt
18749 @kindex show monitor-prompt@r{, MIPS remote}
18750 Show the current strings @value{GDBN} expects as the prompt from the
18753 @item set monitor-warnings
18754 @kindex set monitor-warnings@r{, MIPS remote}
18755 Enable or disable monitor warnings about hardware breakpoints. This
18756 has effect only for the @code{lsi} target. When on, @value{GDBN} will
18757 display warning messages whose codes are returned by the @code{lsi}
18758 PMON monitor for breakpoint commands.
18760 @item show monitor-warnings
18761 @kindex show monitor-warnings@r{, MIPS remote}
18762 Show the current setting of printing monitor warnings.
18764 @item pmon @var{command}
18765 @kindex pmon@r{, MIPS remote}
18766 @cindex send PMON command
18767 This command allows sending an arbitrary @var{command} string to the
18768 monitor. The monitor must be in debug mode for this to work.
18771 @node OpenRISC 1000
18772 @subsection OpenRISC 1000
18773 @cindex OpenRISC 1000
18775 @cindex or1k boards
18776 See OR1k Architecture document (@uref{www.opencores.org}) for more information
18777 about platform and commands.
18781 @kindex target jtag
18782 @item target jtag jtag://@var{host}:@var{port}
18784 Connects to remote JTAG server.
18785 JTAG remote server can be either an or1ksim or JTAG server,
18786 connected via parallel port to the board.
18788 Example: @code{target jtag jtag://localhost:9999}
18791 @item or1ksim @var{command}
18792 If connected to @code{or1ksim} OpenRISC 1000 Architectural
18793 Simulator, proprietary commands can be executed.
18795 @kindex info or1k spr
18796 @item info or1k spr
18797 Displays spr groups.
18799 @item info or1k spr @var{group}
18800 @itemx info or1k spr @var{groupno}
18801 Displays register names in selected group.
18803 @item info or1k spr @var{group} @var{register}
18804 @itemx info or1k spr @var{register}
18805 @itemx info or1k spr @var{groupno} @var{registerno}
18806 @itemx info or1k spr @var{registerno}
18807 Shows information about specified spr register.
18810 @item spr @var{group} @var{register} @var{value}
18811 @itemx spr @var{register @var{value}}
18812 @itemx spr @var{groupno} @var{registerno @var{value}}
18813 @itemx spr @var{registerno @var{value}}
18814 Writes @var{value} to specified spr register.
18817 Some implementations of OpenRISC 1000 Architecture also have hardware trace.
18818 It is very similar to @value{GDBN} trace, except it does not interfere with normal
18819 program execution and is thus much faster. Hardware breakpoints/watchpoint
18820 triggers can be set using:
18823 Load effective address/data
18825 Store effective address/data
18827 Access effective address ($SEA or $LEA) or data ($SDATA/$LDATA)
18832 When triggered, it can capture low level data, like: @code{PC}, @code{LSEA},
18833 @code{LDATA}, @code{SDATA}, @code{READSPR}, @code{WRITESPR}, @code{INSTR}.
18835 @code{htrace} commands:
18836 @cindex OpenRISC 1000 htrace
18839 @item hwatch @var{conditional}
18840 Set hardware watchpoint on combination of Load/Store Effective Address(es)
18841 or Data. For example:
18843 @code{hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)}
18845 @code{hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)}
18849 Display information about current HW trace configuration.
18851 @item htrace trigger @var{conditional}
18852 Set starting criteria for HW trace.
18854 @item htrace qualifier @var{conditional}
18855 Set acquisition qualifier for HW trace.
18857 @item htrace stop @var{conditional}
18858 Set HW trace stopping criteria.
18860 @item htrace record [@var{data}]*
18861 Selects the data to be recorded, when qualifier is met and HW trace was
18864 @item htrace enable
18865 @itemx htrace disable
18866 Enables/disables the HW trace.
18868 @item htrace rewind [@var{filename}]
18869 Clears currently recorded trace data.
18871 If filename is specified, new trace file is made and any newly collected data
18872 will be written there.
18874 @item htrace print [@var{start} [@var{len}]]
18875 Prints trace buffer, using current record configuration.
18877 @item htrace mode continuous
18878 Set continuous trace mode.
18880 @item htrace mode suspend
18881 Set suspend trace mode.
18885 @node PowerPC Embedded
18886 @subsection PowerPC Embedded
18888 @cindex DVC register
18889 @value{GDBN} supports using the DVC (Data Value Compare) register to
18890 implement in hardware simple hardware watchpoint conditions of the form:
18893 (@value{GDBP}) watch @var{ADDRESS|VARIABLE} \
18894 if @var{ADDRESS|VARIABLE} == @var{CONSTANT EXPRESSION}
18897 The DVC register will be automatically used when @value{GDBN} detects
18898 such pattern in a condition expression, and the created watchpoint uses one
18899 debug register (either the @code{exact-watchpoints} option is on and the
18900 variable is scalar, or the variable has a length of one byte). This feature
18901 is available in native @value{GDBN} running on a Linux kernel version 2.6.34
18904 When running on PowerPC embedded processors, @value{GDBN} automatically uses
18905 ranged hardware watchpoints, unless the @code{exact-watchpoints} option is on,
18906 in which case watchpoints using only one debug register are created when
18907 watching variables of scalar types.
18909 You can create an artificial array to watch an arbitrary memory
18910 region using one of the following commands (@pxref{Expressions}):
18913 (@value{GDBP}) watch *((char *) @var{address})@@@var{length}
18914 (@value{GDBP}) watch @{char[@var{length}]@} @var{address}
18917 PowerPC embedded processors support masked watchpoints. See the discussion
18918 about the @code{mask} argument in @ref{Set Watchpoints}.
18920 @cindex ranged breakpoint
18921 PowerPC embedded processors support hardware accelerated
18922 @dfn{ranged breakpoints}. A ranged breakpoint stops execution of
18923 the inferior whenever it executes an instruction at any address within
18924 the range it specifies. To set a ranged breakpoint in @value{GDBN},
18925 use the @code{break-range} command.
18927 @value{GDBN} provides the following PowerPC-specific commands:
18930 @kindex break-range
18931 @item break-range @var{start-location}, @var{end-location}
18932 Set a breakpoint for an address range.
18933 @var{start-location} and @var{end-location} can specify a function name,
18934 a line number, an offset of lines from the current line or from the start
18935 location, or an address of an instruction (see @ref{Specify Location},
18936 for a list of all the possible ways to specify a @var{location}.)
18937 The breakpoint will stop execution of the inferior whenever it
18938 executes an instruction at any address within the specified range,
18939 (including @var{start-location} and @var{end-location}.)
18941 @kindex set powerpc
18942 @item set powerpc soft-float
18943 @itemx show powerpc soft-float
18944 Force @value{GDBN} to use (or not use) a software floating point calling
18945 convention. By default, @value{GDBN} selects the calling convention based
18946 on the selected architecture and the provided executable file.
18948 @item set powerpc vector-abi
18949 @itemx show powerpc vector-abi
18950 Force @value{GDBN} to use the specified calling convention for vector
18951 arguments and return values. The valid options are @samp{auto};
18952 @samp{generic}, to avoid vector registers even if they are present;
18953 @samp{altivec}, to use AltiVec registers; and @samp{spe} to use SPE
18954 registers. By default, @value{GDBN} selects the calling convention
18955 based on the selected architecture and the provided executable file.
18957 @item set powerpc exact-watchpoints
18958 @itemx show powerpc exact-watchpoints
18959 Allow @value{GDBN} to use only one debug register when watching a variable
18960 of scalar type, thus assuming that the variable is accessed through the
18961 address of its first byte.
18963 @kindex target dink32
18964 @item target dink32 @var{dev}
18965 DINK32 ROM monitor.
18967 @kindex target ppcbug
18968 @item target ppcbug @var{dev}
18969 @kindex target ppcbug1
18970 @item target ppcbug1 @var{dev}
18971 PPCBUG ROM monitor for PowerPC.
18974 @item target sds @var{dev}
18975 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
18978 @cindex SDS protocol
18979 The following commands specific to the SDS protocol are supported
18983 @item set sdstimeout @var{nsec}
18984 @kindex set sdstimeout
18985 Set the timeout for SDS protocol reads to be @var{nsec} seconds. The
18986 default is 2 seconds.
18988 @item show sdstimeout
18989 @kindex show sdstimeout
18990 Show the current value of the SDS timeout.
18992 @item sds @var{command}
18993 @kindex sds@r{, a command}
18994 Send the specified @var{command} string to the SDS monitor.
18999 @subsection HP PA Embedded
19003 @kindex target op50n
19004 @item target op50n @var{dev}
19005 OP50N monitor, running on an OKI HPPA board.
19007 @kindex target w89k
19008 @item target w89k @var{dev}
19009 W89K monitor, running on a Winbond HPPA board.
19014 @subsection Tsqware Sparclet
19018 @value{GDBN} enables developers to debug tasks running on
19019 Sparclet targets from a Unix host.
19020 @value{GDBN} uses code that runs on
19021 both the Unix host and on the Sparclet target. The program
19022 @code{@value{GDBP}} is installed and executed on the Unix host.
19025 @item remotetimeout @var{args}
19026 @kindex remotetimeout
19027 @value{GDBN} supports the option @code{remotetimeout}.
19028 This option is set by the user, and @var{args} represents the number of
19029 seconds @value{GDBN} waits for responses.
19032 @cindex compiling, on Sparclet
19033 When compiling for debugging, include the options @samp{-g} to get debug
19034 information and @samp{-Ttext} to relocate the program to where you wish to
19035 load it on the target. You may also want to add the options @samp{-n} or
19036 @samp{-N} in order to reduce the size of the sections. Example:
19039 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
19042 You can use @code{objdump} to verify that the addresses are what you intended:
19045 sparclet-aout-objdump --headers --syms prog
19048 @cindex running, on Sparclet
19050 your Unix execution search path to find @value{GDBN}, you are ready to
19051 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
19052 (or @code{sparclet-aout-gdb}, depending on your installation).
19054 @value{GDBN} comes up showing the prompt:
19061 * Sparclet File:: Setting the file to debug
19062 * Sparclet Connection:: Connecting to Sparclet
19063 * Sparclet Download:: Sparclet download
19064 * Sparclet Execution:: Running and debugging
19067 @node Sparclet File
19068 @subsubsection Setting File to Debug
19070 The @value{GDBN} command @code{file} lets you choose with program to debug.
19073 (gdbslet) file prog
19077 @value{GDBN} then attempts to read the symbol table of @file{prog}.
19078 @value{GDBN} locates
19079 the file by searching the directories listed in the command search
19081 If the file was compiled with debug information (option @samp{-g}), source
19082 files will be searched as well.
19083 @value{GDBN} locates
19084 the source files by searching the directories listed in the directory search
19085 path (@pxref{Environment, ,Your Program's Environment}).
19087 to find a file, it displays a message such as:
19090 prog: No such file or directory.
19093 When this happens, add the appropriate directories to the search paths with
19094 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
19095 @code{target} command again.
19097 @node Sparclet Connection
19098 @subsubsection Connecting to Sparclet
19100 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
19101 To connect to a target on serial port ``@code{ttya}'', type:
19104 (gdbslet) target sparclet /dev/ttya
19105 Remote target sparclet connected to /dev/ttya
19106 main () at ../prog.c:3
19110 @value{GDBN} displays messages like these:
19116 @node Sparclet Download
19117 @subsubsection Sparclet Download
19119 @cindex download to Sparclet
19120 Once connected to the Sparclet target,
19121 you can use the @value{GDBN}
19122 @code{load} command to download the file from the host to the target.
19123 The file name and load offset should be given as arguments to the @code{load}
19125 Since the file format is aout, the program must be loaded to the starting
19126 address. You can use @code{objdump} to find out what this value is. The load
19127 offset is an offset which is added to the VMA (virtual memory address)
19128 of each of the file's sections.
19129 For instance, if the program
19130 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
19131 and bss at 0x12010170, in @value{GDBN}, type:
19134 (gdbslet) load prog 0x12010000
19135 Loading section .text, size 0xdb0 vma 0x12010000
19138 If the code is loaded at a different address then what the program was linked
19139 to, you may need to use the @code{section} and @code{add-symbol-file} commands
19140 to tell @value{GDBN} where to map the symbol table.
19142 @node Sparclet Execution
19143 @subsubsection Running and Debugging
19145 @cindex running and debugging Sparclet programs
19146 You can now begin debugging the task using @value{GDBN}'s execution control
19147 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
19148 manual for the list of commands.
19152 Breakpoint 1 at 0x12010000: file prog.c, line 3.
19154 Starting program: prog
19155 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
19156 3 char *symarg = 0;
19158 4 char *execarg = "hello!";
19163 @subsection Fujitsu Sparclite
19167 @kindex target sparclite
19168 @item target sparclite @var{dev}
19169 Fujitsu sparclite boards, used only for the purpose of loading.
19170 You must use an additional command to debug the program.
19171 For example: target remote @var{dev} using @value{GDBN} standard
19177 @subsection Zilog Z8000
19180 @cindex simulator, Z8000
19181 @cindex Zilog Z8000 simulator
19183 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
19186 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
19187 unsegmented variant of the Z8000 architecture) or the Z8001 (the
19188 segmented variant). The simulator recognizes which architecture is
19189 appropriate by inspecting the object code.
19192 @item target sim @var{args}
19194 @kindex target sim@r{, with Z8000}
19195 Debug programs on a simulated CPU. If the simulator supports setup
19196 options, specify them via @var{args}.
19200 After specifying this target, you can debug programs for the simulated
19201 CPU in the same style as programs for your host computer; use the
19202 @code{file} command to load a new program image, the @code{run} command
19203 to run your program, and so on.
19205 As well as making available all the usual machine registers
19206 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
19207 additional items of information as specially named registers:
19212 Counts clock-ticks in the simulator.
19215 Counts instructions run in the simulator.
19218 Execution time in 60ths of a second.
19222 You can refer to these values in @value{GDBN} expressions with the usual
19223 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
19224 conditional breakpoint that suspends only after at least 5000
19225 simulated clock ticks.
19228 @subsection Atmel AVR
19231 When configured for debugging the Atmel AVR, @value{GDBN} supports the
19232 following AVR-specific commands:
19235 @item info io_registers
19236 @kindex info io_registers@r{, AVR}
19237 @cindex I/O registers (Atmel AVR)
19238 This command displays information about the AVR I/O registers. For
19239 each register, @value{GDBN} prints its number and value.
19246 When configured for debugging CRIS, @value{GDBN} provides the
19247 following CRIS-specific commands:
19250 @item set cris-version @var{ver}
19251 @cindex CRIS version
19252 Set the current CRIS version to @var{ver}, either @samp{10} or @samp{32}.
19253 The CRIS version affects register names and sizes. This command is useful in
19254 case autodetection of the CRIS version fails.
19256 @item show cris-version
19257 Show the current CRIS version.
19259 @item set cris-dwarf2-cfi
19260 @cindex DWARF-2 CFI and CRIS
19261 Set the usage of DWARF-2 CFI for CRIS debugging. The default is @samp{on}.
19262 Change to @samp{off} when using @code{gcc-cris} whose version is below
19265 @item show cris-dwarf2-cfi
19266 Show the current state of using DWARF-2 CFI.
19268 @item set cris-mode @var{mode}
19270 Set the current CRIS mode to @var{mode}. It should only be changed when
19271 debugging in guru mode, in which case it should be set to
19272 @samp{guru} (the default is @samp{normal}).
19274 @item show cris-mode
19275 Show the current CRIS mode.
19279 @subsection Renesas Super-H
19282 For the Renesas Super-H processor, @value{GDBN} provides these
19287 @kindex regs@r{, Super-H}
19288 Show the values of all Super-H registers.
19290 @item set sh calling-convention @var{convention}
19291 @kindex set sh calling-convention
19292 Set the calling-convention used when calling functions from @value{GDBN}.
19293 Allowed values are @samp{gcc}, which is the default setting, and @samp{renesas}.
19294 With the @samp{gcc} setting, functions are called using the @value{NGCC} calling
19295 convention. If the DWARF-2 information of the called function specifies
19296 that the function follows the Renesas calling convention, the function
19297 is called using the Renesas calling convention. If the calling convention
19298 is set to @samp{renesas}, the Renesas calling convention is always used,
19299 regardless of the DWARF-2 information. This can be used to override the
19300 default of @samp{gcc} if debug information is missing, or the compiler
19301 does not emit the DWARF-2 calling convention entry for a function.
19303 @item show sh calling-convention
19304 @kindex show sh calling-convention
19305 Show the current calling convention setting.
19310 @node Architectures
19311 @section Architectures
19313 This section describes characteristics of architectures that affect
19314 all uses of @value{GDBN} with the architecture, both native and cross.
19321 * HPPA:: HP PA architecture
19322 * SPU:: Cell Broadband Engine SPU architecture
19327 @subsection x86 Architecture-specific Issues
19330 @item set struct-convention @var{mode}
19331 @kindex set struct-convention
19332 @cindex struct return convention
19333 @cindex struct/union returned in registers
19334 Set the convention used by the inferior to return @code{struct}s and
19335 @code{union}s from functions to @var{mode}. Possible values of
19336 @var{mode} are @code{"pcc"}, @code{"reg"}, and @code{"default"} (the
19337 default). @code{"default"} or @code{"pcc"} means that @code{struct}s
19338 are returned on the stack, while @code{"reg"} means that a
19339 @code{struct} or a @code{union} whose size is 1, 2, 4, or 8 bytes will
19340 be returned in a register.
19342 @item show struct-convention
19343 @kindex show struct-convention
19344 Show the current setting of the convention to return @code{struct}s
19353 @kindex set rstack_high_address
19354 @cindex AMD 29K register stack
19355 @cindex register stack, AMD29K
19356 @item set rstack_high_address @var{address}
19357 On AMD 29000 family processors, registers are saved in a separate
19358 @dfn{register stack}. There is no way for @value{GDBN} to determine the
19359 extent of this stack. Normally, @value{GDBN} just assumes that the
19360 stack is ``large enough''. This may result in @value{GDBN} referencing
19361 memory locations that do not exist. If necessary, you can get around
19362 this problem by specifying the ending address of the register stack with
19363 the @code{set rstack_high_address} command. The argument should be an
19364 address, which you probably want to precede with @samp{0x} to specify in
19367 @kindex show rstack_high_address
19368 @item show rstack_high_address
19369 Display the current limit of the register stack, on AMD 29000 family
19377 See the following section.
19382 @cindex stack on Alpha
19383 @cindex stack on MIPS
19384 @cindex Alpha stack
19386 Alpha- and MIPS-based computers use an unusual stack frame, which
19387 sometimes requires @value{GDBN} to search backward in the object code to
19388 find the beginning of a function.
19390 @cindex response time, MIPS debugging
19391 To improve response time (especially for embedded applications, where
19392 @value{GDBN} may be restricted to a slow serial line for this search)
19393 you may want to limit the size of this search, using one of these
19397 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
19398 @item set heuristic-fence-post @var{limit}
19399 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
19400 search for the beginning of a function. A value of @var{0} (the
19401 default) means there is no limit. However, except for @var{0}, the
19402 larger the limit the more bytes @code{heuristic-fence-post} must search
19403 and therefore the longer it takes to run. You should only need to use
19404 this command when debugging a stripped executable.
19406 @item show heuristic-fence-post
19407 Display the current limit.
19411 These commands are available @emph{only} when @value{GDBN} is configured
19412 for debugging programs on Alpha or MIPS processors.
19414 Several MIPS-specific commands are available when debugging MIPS
19418 @item set mips abi @var{arg}
19419 @kindex set mips abi
19420 @cindex set ABI for MIPS
19421 Tell @value{GDBN} which MIPS ABI is used by the inferior. Possible
19422 values of @var{arg} are:
19426 The default ABI associated with the current binary (this is the
19437 @item show mips abi
19438 @kindex show mips abi
19439 Show the MIPS ABI used by @value{GDBN} to debug the inferior.
19442 @itemx show mipsfpu
19443 @xref{MIPS Embedded, set mipsfpu}.
19445 @item set mips mask-address @var{arg}
19446 @kindex set mips mask-address
19447 @cindex MIPS addresses, masking
19448 This command determines whether the most-significant 32 bits of 64-bit
19449 MIPS addresses are masked off. The argument @var{arg} can be
19450 @samp{on}, @samp{off}, or @samp{auto}. The latter is the default
19451 setting, which lets @value{GDBN} determine the correct value.
19453 @item show mips mask-address
19454 @kindex show mips mask-address
19455 Show whether the upper 32 bits of MIPS addresses are masked off or
19458 @item set remote-mips64-transfers-32bit-regs
19459 @kindex set remote-mips64-transfers-32bit-regs
19460 This command controls compatibility with 64-bit MIPS targets that
19461 transfer data in 32-bit quantities. If you have an old MIPS 64 target
19462 that transfers 32 bits for some registers, like @sc{sr} and @sc{fsr},
19463 and 64 bits for other registers, set this option to @samp{on}.
19465 @item show remote-mips64-transfers-32bit-regs
19466 @kindex show remote-mips64-transfers-32bit-regs
19467 Show the current setting of compatibility with older MIPS 64 targets.
19469 @item set debug mips
19470 @kindex set debug mips
19471 This command turns on and off debugging messages for the MIPS-specific
19472 target code in @value{GDBN}.
19474 @item show debug mips
19475 @kindex show debug mips
19476 Show the current setting of MIPS debugging messages.
19482 @cindex HPPA support
19484 When @value{GDBN} is debugging the HP PA architecture, it provides the
19485 following special commands:
19488 @item set debug hppa
19489 @kindex set debug hppa
19490 This command determines whether HPPA architecture-specific debugging
19491 messages are to be displayed.
19493 @item show debug hppa
19494 Show whether HPPA debugging messages are displayed.
19496 @item maint print unwind @var{address}
19497 @kindex maint print unwind@r{, HPPA}
19498 This command displays the contents of the unwind table entry at the
19499 given @var{address}.
19505 @subsection Cell Broadband Engine SPU architecture
19506 @cindex Cell Broadband Engine
19509 When @value{GDBN} is debugging the Cell Broadband Engine SPU architecture,
19510 it provides the following special commands:
19513 @item info spu event
19515 Display SPU event facility status. Shows current event mask
19516 and pending event status.
19518 @item info spu signal
19519 Display SPU signal notification facility status. Shows pending
19520 signal-control word and signal notification mode of both signal
19521 notification channels.
19523 @item info spu mailbox
19524 Display SPU mailbox facility status. Shows all pending entries,
19525 in order of processing, in each of the SPU Write Outbound,
19526 SPU Write Outbound Interrupt, and SPU Read Inbound mailboxes.
19529 Display MFC DMA status. Shows all pending commands in the MFC
19530 DMA queue. For each entry, opcode, tag, class IDs, effective
19531 and local store addresses and transfer size are shown.
19533 @item info spu proxydma
19534 Display MFC Proxy-DMA status. Shows all pending commands in the MFC
19535 Proxy-DMA queue. For each entry, opcode, tag, class IDs, effective
19536 and local store addresses and transfer size are shown.
19540 When @value{GDBN} is debugging a combined PowerPC/SPU application
19541 on the Cell Broadband Engine, it provides in addition the following
19545 @item set spu stop-on-load @var{arg}
19547 Set whether to stop for new SPE threads. When set to @code{on}, @value{GDBN}
19548 will give control to the user when a new SPE thread enters its @code{main}
19549 function. The default is @code{off}.
19551 @item show spu stop-on-load
19553 Show whether to stop for new SPE threads.
19555 @item set spu auto-flush-cache @var{arg}
19556 Set whether to automatically flush the software-managed cache. When set to
19557 @code{on}, @value{GDBN} will automatically cause the SPE software-managed
19558 cache to be flushed whenever SPE execution stops. This provides a consistent
19559 view of PowerPC memory that is accessed via the cache. If an application
19560 does not use the software-managed cache, this option has no effect.
19562 @item show spu auto-flush-cache
19563 Show whether to automatically flush the software-managed cache.
19568 @subsection PowerPC
19569 @cindex PowerPC architecture
19571 When @value{GDBN} is debugging the PowerPC architecture, it provides a set of
19572 pseudo-registers to enable inspection of 128-bit wide Decimal Floating Point
19573 numbers stored in the floating point registers. These values must be stored
19574 in two consecutive registers, always starting at an even register like
19575 @code{f0} or @code{f2}.
19577 The pseudo-registers go from @code{$dl0} through @code{$dl15}, and are formed
19578 by joining the even/odd register pairs @code{f0} and @code{f1} for @code{$dl0},
19579 @code{f2} and @code{f3} for @code{$dl1} and so on.
19581 For POWER7 processors, @value{GDBN} provides a set of pseudo-registers, the 64-bit
19582 wide Extended Floating Point Registers (@samp{f32} through @samp{f63}).
19585 @node Controlling GDB
19586 @chapter Controlling @value{GDBN}
19588 You can alter the way @value{GDBN} interacts with you by using the
19589 @code{set} command. For commands controlling how @value{GDBN} displays
19590 data, see @ref{Print Settings, ,Print Settings}. Other settings are
19595 * Editing:: Command editing
19596 * Command History:: Command history
19597 * Screen Size:: Screen size
19598 * Numbers:: Numbers
19599 * ABI:: Configuring the current ABI
19600 * Messages/Warnings:: Optional warnings and messages
19601 * Debugging Output:: Optional messages about internal happenings
19602 * Other Misc Settings:: Other Miscellaneous Settings
19610 @value{GDBN} indicates its readiness to read a command by printing a string
19611 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
19612 can change the prompt string with the @code{set prompt} command. For
19613 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
19614 the prompt in one of the @value{GDBN} sessions so that you can always tell
19615 which one you are talking to.
19617 @emph{Note:} @code{set prompt} does not add a space for you after the
19618 prompt you set. This allows you to set a prompt which ends in a space
19619 or a prompt that does not.
19623 @item set prompt @var{newprompt}
19624 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
19626 @kindex show prompt
19628 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
19631 Versions of @value{GDBN} that ship with Python scripting enabled have
19632 prompt extensions. The commands for interacting with these extensions
19636 @kindex set extended-prompt
19637 @item set extended-prompt @var{prompt}
19638 Set an extended prompt that allows for substitutions.
19639 @xref{gdb.prompt}, for a list of escape sequences that can be used for
19640 substitution. Any escape sequences specified as part of the prompt
19641 string are replaced with the corresponding strings each time the prompt
19647 set extended-prompt Current working directory: \w (gdb)
19650 Note that when an extended-prompt is set, it takes control of the
19651 @var{prompt_hook} hook. @xref{prompt_hook}, for further information.
19653 @kindex show extended-prompt
19654 @item show extended-prompt
19655 Prints the extended prompt. Any escape sequences specified as part of
19656 the prompt string with @code{set extended-prompt}, are replaced with the
19657 corresponding strings each time the prompt is displayed.
19661 @section Command Editing
19663 @cindex command line editing
19665 @value{GDBN} reads its input commands via the @dfn{Readline} interface. This
19666 @sc{gnu} library provides consistent behavior for programs which provide a
19667 command line interface to the user. Advantages are @sc{gnu} Emacs-style
19668 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
19669 substitution, and a storage and recall of command history across
19670 debugging sessions.
19672 You may control the behavior of command line editing in @value{GDBN} with the
19673 command @code{set}.
19676 @kindex set editing
19679 @itemx set editing on
19680 Enable command line editing (enabled by default).
19682 @item set editing off
19683 Disable command line editing.
19685 @kindex show editing
19687 Show whether command line editing is enabled.
19690 @ifset SYSTEM_READLINE
19691 @xref{Command Line Editing, , , rluserman, GNU Readline Library},
19693 @ifclear SYSTEM_READLINE
19694 @xref{Command Line Editing},
19696 for more details about the Readline
19697 interface. Users unfamiliar with @sc{gnu} Emacs or @code{vi} are
19698 encouraged to read that chapter.
19700 @node Command History
19701 @section Command History
19702 @cindex command history
19704 @value{GDBN} can keep track of the commands you type during your
19705 debugging sessions, so that you can be certain of precisely what
19706 happened. Use these commands to manage the @value{GDBN} command
19709 @value{GDBN} uses the @sc{gnu} History library, a part of the Readline
19710 package, to provide the history facility.
19711 @ifset SYSTEM_READLINE
19712 @xref{Using History Interactively, , , history, GNU History Library},
19714 @ifclear SYSTEM_READLINE
19715 @xref{Using History Interactively},
19717 for the detailed description of the History library.
19719 To issue a command to @value{GDBN} without affecting certain aspects of
19720 the state which is seen by users, prefix it with @samp{server }
19721 (@pxref{Server Prefix}). This
19722 means that this command will not affect the command history, nor will it
19723 affect @value{GDBN}'s notion of which command to repeat if @key{RET} is
19724 pressed on a line by itself.
19726 @cindex @code{server}, command prefix
19727 The server prefix does not affect the recording of values into the value
19728 history; to print a value without recording it into the value history,
19729 use the @code{output} command instead of the @code{print} command.
19731 Here is the description of @value{GDBN} commands related to command
19735 @cindex history substitution
19736 @cindex history file
19737 @kindex set history filename
19738 @cindex @env{GDBHISTFILE}, environment variable
19739 @item set history filename @var{fname}
19740 Set the name of the @value{GDBN} command history file to @var{fname}.
19741 This is the file where @value{GDBN} reads an initial command history
19742 list, and where it writes the command history from this session when it
19743 exits. You can access this list through history expansion or through
19744 the history command editing characters listed below. This file defaults
19745 to the value of the environment variable @code{GDBHISTFILE}, or to
19746 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
19749 @cindex save command history
19750 @kindex set history save
19751 @item set history save
19752 @itemx set history save on
19753 Record command history in a file, whose name may be specified with the
19754 @code{set history filename} command. By default, this option is disabled.
19756 @item set history save off
19757 Stop recording command history in a file.
19759 @cindex history size
19760 @kindex set history size
19761 @cindex @env{HISTSIZE}, environment variable
19762 @item set history size @var{size}
19763 Set the number of commands which @value{GDBN} keeps in its history list.
19764 This defaults to the value of the environment variable
19765 @code{HISTSIZE}, or to 256 if this variable is not set.
19768 History expansion assigns special meaning to the character @kbd{!}.
19769 @ifset SYSTEM_READLINE
19770 @xref{Event Designators, , , history, GNU History Library},
19772 @ifclear SYSTEM_READLINE
19773 @xref{Event Designators},
19777 @cindex history expansion, turn on/off
19778 Since @kbd{!} is also the logical not operator in C, history expansion
19779 is off by default. If you decide to enable history expansion with the
19780 @code{set history expansion on} command, you may sometimes need to
19781 follow @kbd{!} (when it is used as logical not, in an expression) with
19782 a space or a tab to prevent it from being expanded. The readline
19783 history facilities do not attempt substitution on the strings
19784 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
19786 The commands to control history expansion are:
19789 @item set history expansion on
19790 @itemx set history expansion
19791 @kindex set history expansion
19792 Enable history expansion. History expansion is off by default.
19794 @item set history expansion off
19795 Disable history expansion.
19798 @kindex show history
19800 @itemx show history filename
19801 @itemx show history save
19802 @itemx show history size
19803 @itemx show history expansion
19804 These commands display the state of the @value{GDBN} history parameters.
19805 @code{show history} by itself displays all four states.
19810 @kindex show commands
19811 @cindex show last commands
19812 @cindex display command history
19813 @item show commands
19814 Display the last ten commands in the command history.
19816 @item show commands @var{n}
19817 Print ten commands centered on command number @var{n}.
19819 @item show commands +
19820 Print ten commands just after the commands last printed.
19824 @section Screen Size
19825 @cindex size of screen
19826 @cindex pauses in output
19828 Certain commands to @value{GDBN} may produce large amounts of
19829 information output to the screen. To help you read all of it,
19830 @value{GDBN} pauses and asks you for input at the end of each page of
19831 output. Type @key{RET} when you want to continue the output, or @kbd{q}
19832 to discard the remaining output. Also, the screen width setting
19833 determines when to wrap lines of output. Depending on what is being
19834 printed, @value{GDBN} tries to break the line at a readable place,
19835 rather than simply letting it overflow onto the following line.
19837 Normally @value{GDBN} knows the size of the screen from the terminal
19838 driver software. For example, on Unix @value{GDBN} uses the termcap data base
19839 together with the value of the @code{TERM} environment variable and the
19840 @code{stty rows} and @code{stty cols} settings. If this is not correct,
19841 you can override it with the @code{set height} and @code{set
19848 @kindex show height
19849 @item set height @var{lpp}
19851 @itemx set width @var{cpl}
19853 These @code{set} commands specify a screen height of @var{lpp} lines and
19854 a screen width of @var{cpl} characters. The associated @code{show}
19855 commands display the current settings.
19857 If you specify a height of zero lines, @value{GDBN} does not pause during
19858 output no matter how long the output is. This is useful if output is to a
19859 file or to an editor buffer.
19861 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
19862 from wrapping its output.
19864 @item set pagination on
19865 @itemx set pagination off
19866 @kindex set pagination
19867 Turn the output pagination on or off; the default is on. Turning
19868 pagination off is the alternative to @code{set height 0}. Note that
19869 running @value{GDBN} with the @option{--batch} option (@pxref{Mode
19870 Options, -batch}) also automatically disables pagination.
19872 @item show pagination
19873 @kindex show pagination
19874 Show the current pagination mode.
19879 @cindex number representation
19880 @cindex entering numbers
19882 You can always enter numbers in octal, decimal, or hexadecimal in
19883 @value{GDBN} by the usual conventions: octal numbers begin with
19884 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
19885 begin with @samp{0x}. Numbers that neither begin with @samp{0} or
19886 @samp{0x}, nor end with a @samp{.} are, by default, entered in base
19887 10; likewise, the default display for numbers---when no particular
19888 format is specified---is base 10. You can change the default base for
19889 both input and output with the commands described below.
19892 @kindex set input-radix
19893 @item set input-radix @var{base}
19894 Set the default base for numeric input. Supported choices
19895 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
19896 specified either unambiguously or using the current input radix; for
19900 set input-radix 012
19901 set input-radix 10.
19902 set input-radix 0xa
19906 sets the input base to decimal. On the other hand, @samp{set input-radix 10}
19907 leaves the input radix unchanged, no matter what it was, since
19908 @samp{10}, being without any leading or trailing signs of its base, is
19909 interpreted in the current radix. Thus, if the current radix is 16,
19910 @samp{10} is interpreted in hex, i.e.@: as 16 decimal, which doesn't
19913 @kindex set output-radix
19914 @item set output-radix @var{base}
19915 Set the default base for numeric display. Supported choices
19916 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
19917 specified either unambiguously or using the current input radix.
19919 @kindex show input-radix
19920 @item show input-radix
19921 Display the current default base for numeric input.
19923 @kindex show output-radix
19924 @item show output-radix
19925 Display the current default base for numeric display.
19927 @item set radix @r{[}@var{base}@r{]}
19931 These commands set and show the default base for both input and output
19932 of numbers. @code{set radix} sets the radix of input and output to
19933 the same base; without an argument, it resets the radix back to its
19934 default value of 10.
19939 @section Configuring the Current ABI
19941 @value{GDBN} can determine the @dfn{ABI} (Application Binary Interface) of your
19942 application automatically. However, sometimes you need to override its
19943 conclusions. Use these commands to manage @value{GDBN}'s view of the
19950 One @value{GDBN} configuration can debug binaries for multiple operating
19951 system targets, either via remote debugging or native emulation.
19952 @value{GDBN} will autodetect the @dfn{OS ABI} (Operating System ABI) in use,
19953 but you can override its conclusion using the @code{set osabi} command.
19954 One example where this is useful is in debugging of binaries which use
19955 an alternate C library (e.g.@: @sc{uClibc} for @sc{gnu}/Linux) which does
19956 not have the same identifying marks that the standard C library for your
19961 Show the OS ABI currently in use.
19964 With no argument, show the list of registered available OS ABI's.
19966 @item set osabi @var{abi}
19967 Set the current OS ABI to @var{abi}.
19970 @cindex float promotion
19972 Generally, the way that an argument of type @code{float} is passed to a
19973 function depends on whether the function is prototyped. For a prototyped
19974 (i.e.@: ANSI/ISO style) function, @code{float} arguments are passed unchanged,
19975 according to the architecture's convention for @code{float}. For unprototyped
19976 (i.e.@: K&R style) functions, @code{float} arguments are first promoted to type
19977 @code{double} and then passed.
19979 Unfortunately, some forms of debug information do not reliably indicate whether
19980 a function is prototyped. If @value{GDBN} calls a function that is not marked
19981 as prototyped, it consults @kbd{set coerce-float-to-double}.
19984 @kindex set coerce-float-to-double
19985 @item set coerce-float-to-double
19986 @itemx set coerce-float-to-double on
19987 Arguments of type @code{float} will be promoted to @code{double} when passed
19988 to an unprototyped function. This is the default setting.
19990 @item set coerce-float-to-double off
19991 Arguments of type @code{float} will be passed directly to unprototyped
19994 @kindex show coerce-float-to-double
19995 @item show coerce-float-to-double
19996 Show the current setting of promoting @code{float} to @code{double}.
20000 @kindex show cp-abi
20001 @value{GDBN} needs to know the ABI used for your program's C@t{++}
20002 objects. The correct C@t{++} ABI depends on which C@t{++} compiler was
20003 used to build your application. @value{GDBN} only fully supports
20004 programs with a single C@t{++} ABI; if your program contains code using
20005 multiple C@t{++} ABI's or if @value{GDBN} can not identify your
20006 program's ABI correctly, you can tell @value{GDBN} which ABI to use.
20007 Currently supported ABI's include ``gnu-v2'', for @code{g++} versions
20008 before 3.0, ``gnu-v3'', for @code{g++} versions 3.0 and later, and
20009 ``hpaCC'' for the HP ANSI C@t{++} compiler. Other C@t{++} compilers may
20010 use the ``gnu-v2'' or ``gnu-v3'' ABI's as well. The default setting is
20015 Show the C@t{++} ABI currently in use.
20018 With no argument, show the list of supported C@t{++} ABI's.
20020 @item set cp-abi @var{abi}
20021 @itemx set cp-abi auto
20022 Set the current C@t{++} ABI to @var{abi}, or return to automatic detection.
20025 @node Messages/Warnings
20026 @section Optional Warnings and Messages
20028 @cindex verbose operation
20029 @cindex optional warnings
20030 By default, @value{GDBN} is silent about its inner workings. If you are
20031 running on a slow machine, you may want to use the @code{set verbose}
20032 command. This makes @value{GDBN} tell you when it does a lengthy
20033 internal operation, so you will not think it has crashed.
20035 Currently, the messages controlled by @code{set verbose} are those
20036 which announce that the symbol table for a source file is being read;
20037 see @code{symbol-file} in @ref{Files, ,Commands to Specify Files}.
20040 @kindex set verbose
20041 @item set verbose on
20042 Enables @value{GDBN} output of certain informational messages.
20044 @item set verbose off
20045 Disables @value{GDBN} output of certain informational messages.
20047 @kindex show verbose
20049 Displays whether @code{set verbose} is on or off.
20052 By default, if @value{GDBN} encounters bugs in the symbol table of an
20053 object file, it is silent; but if you are debugging a compiler, you may
20054 find this information useful (@pxref{Symbol Errors, ,Errors Reading
20059 @kindex set complaints
20060 @item set complaints @var{limit}
20061 Permits @value{GDBN} to output @var{limit} complaints about each type of
20062 unusual symbols before becoming silent about the problem. Set
20063 @var{limit} to zero to suppress all complaints; set it to a large number
20064 to prevent complaints from being suppressed.
20066 @kindex show complaints
20067 @item show complaints
20068 Displays how many symbol complaints @value{GDBN} is permitted to produce.
20072 @anchor{confirmation requests}
20073 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
20074 lot of stupid questions to confirm certain commands. For example, if
20075 you try to run a program which is already running:
20079 The program being debugged has been started already.
20080 Start it from the beginning? (y or n)
20083 If you are willing to unflinchingly face the consequences of your own
20084 commands, you can disable this ``feature'':
20088 @kindex set confirm
20090 @cindex confirmation
20091 @cindex stupid questions
20092 @item set confirm off
20093 Disables confirmation requests. Note that running @value{GDBN} with
20094 the @option{--batch} option (@pxref{Mode Options, -batch}) also
20095 automatically disables confirmation requests.
20097 @item set confirm on
20098 Enables confirmation requests (the default).
20100 @kindex show confirm
20102 Displays state of confirmation requests.
20106 @cindex command tracing
20107 If you need to debug user-defined commands or sourced files you may find it
20108 useful to enable @dfn{command tracing}. In this mode each command will be
20109 printed as it is executed, prefixed with one or more @samp{+} symbols, the
20110 quantity denoting the call depth of each command.
20113 @kindex set trace-commands
20114 @cindex command scripts, debugging
20115 @item set trace-commands on
20116 Enable command tracing.
20117 @item set trace-commands off
20118 Disable command tracing.
20119 @item show trace-commands
20120 Display the current state of command tracing.
20123 @node Debugging Output
20124 @section Optional Messages about Internal Happenings
20125 @cindex optional debugging messages
20127 @value{GDBN} has commands that enable optional debugging messages from
20128 various @value{GDBN} subsystems; normally these commands are of
20129 interest to @value{GDBN} maintainers, or when reporting a bug. This
20130 section documents those commands.
20133 @kindex set exec-done-display
20134 @item set exec-done-display
20135 Turns on or off the notification of asynchronous commands'
20136 completion. When on, @value{GDBN} will print a message when an
20137 asynchronous command finishes its execution. The default is off.
20138 @kindex show exec-done-display
20139 @item show exec-done-display
20140 Displays the current setting of asynchronous command completion
20143 @cindex gdbarch debugging info
20144 @cindex architecture debugging info
20145 @item set debug arch
20146 Turns on or off display of gdbarch debugging info. The default is off
20148 @item show debug arch
20149 Displays the current state of displaying gdbarch debugging info.
20150 @item set debug aix-thread
20151 @cindex AIX threads
20152 Display debugging messages about inner workings of the AIX thread
20154 @item show debug aix-thread
20155 Show the current state of AIX thread debugging info display.
20156 @item set debug check-physname
20158 Check the results of the ``physname'' computation. When reading DWARF
20159 debugging information for C@t{++}, @value{GDBN} attempts to compute
20160 each entity's name. @value{GDBN} can do this computation in two
20161 different ways, depending on exactly what information is present.
20162 When enabled, this setting causes @value{GDBN} to compute the names
20163 both ways and display any discrepancies.
20164 @item show debug check-physname
20165 Show the current state of ``physname'' checking.
20166 @item set debug dwarf2-die
20167 @cindex DWARF2 DIEs
20168 Dump DWARF2 DIEs after they are read in.
20169 The value is the number of nesting levels to print.
20170 A value of zero turns off the display.
20171 @item show debug dwarf2-die
20172 Show the current state of DWARF2 DIE debugging.
20173 @item set debug displaced
20174 @cindex displaced stepping debugging info
20175 Turns on or off display of @value{GDBN} debugging info for the
20176 displaced stepping support. The default is off.
20177 @item show debug displaced
20178 Displays the current state of displaying @value{GDBN} debugging info
20179 related to displaced stepping.
20180 @item set debug event
20181 @cindex event debugging info
20182 Turns on or off display of @value{GDBN} event debugging info. The
20184 @item show debug event
20185 Displays the current state of displaying @value{GDBN} event debugging
20187 @item set debug expression
20188 @cindex expression debugging info
20189 Turns on or off display of debugging info about @value{GDBN}
20190 expression parsing. The default is off.
20191 @item show debug expression
20192 Displays the current state of displaying debugging info about
20193 @value{GDBN} expression parsing.
20194 @item set debug frame
20195 @cindex frame debugging info
20196 Turns on or off display of @value{GDBN} frame debugging info. The
20198 @item show debug frame
20199 Displays the current state of displaying @value{GDBN} frame debugging
20201 @item set debug gnu-nat
20202 @cindex @sc{gnu}/Hurd debug messages
20203 Turns on or off debugging messages from the @sc{gnu}/Hurd debug support.
20204 @item show debug gnu-nat
20205 Show the current state of @sc{gnu}/Hurd debugging messages.
20206 @item set debug infrun
20207 @cindex inferior debugging info
20208 Turns on or off display of @value{GDBN} debugging info for running the inferior.
20209 The default is off. @file{infrun.c} contains GDB's runtime state machine used
20210 for implementing operations such as single-stepping the inferior.
20211 @item show debug infrun
20212 Displays the current state of @value{GDBN} inferior debugging.
20213 @item set debug jit
20214 @cindex just-in-time compilation, debugging messages
20215 Turns on or off debugging messages from JIT debug support.
20216 @item show debug jit
20217 Displays the current state of @value{GDBN} JIT debugging.
20218 @item set debug lin-lwp
20219 @cindex @sc{gnu}/Linux LWP debug messages
20220 @cindex Linux lightweight processes
20221 Turns on or off debugging messages from the Linux LWP debug support.
20222 @item show debug lin-lwp
20223 Show the current state of Linux LWP debugging messages.
20224 @item set debug observer
20225 @cindex observer debugging info
20226 Turns on or off display of @value{GDBN} observer debugging. This
20227 includes info such as the notification of observable events.
20228 @item show debug observer
20229 Displays the current state of observer debugging.
20230 @item set debug overload
20231 @cindex C@t{++} overload debugging info
20232 Turns on or off display of @value{GDBN} C@t{++} overload debugging
20233 info. This includes info such as ranking of functions, etc. The default
20235 @item show debug overload
20236 Displays the current state of displaying @value{GDBN} C@t{++} overload
20238 @cindex expression parser, debugging info
20239 @cindex debug expression parser
20240 @item set debug parser
20241 Turns on or off the display of expression parser debugging output.
20242 Internally, this sets the @code{yydebug} variable in the expression
20243 parser. @xref{Tracing, , Tracing Your Parser, bison, Bison}, for
20244 details. The default is off.
20245 @item show debug parser
20246 Show the current state of expression parser debugging.
20247 @cindex packets, reporting on stdout
20248 @cindex serial connections, debugging
20249 @cindex debug remote protocol
20250 @cindex remote protocol debugging
20251 @cindex display remote packets
20252 @item set debug remote
20253 Turns on or off display of reports on all packets sent back and forth across
20254 the serial line to the remote machine. The info is printed on the
20255 @value{GDBN} standard output stream. The default is off.
20256 @item show debug remote
20257 Displays the state of display of remote packets.
20258 @item set debug serial
20259 Turns on or off display of @value{GDBN} serial debugging info. The
20261 @item show debug serial
20262 Displays the current state of displaying @value{GDBN} serial debugging
20264 @item set debug solib-frv
20265 @cindex FR-V shared-library debugging
20266 Turns on or off debugging messages for FR-V shared-library code.
20267 @item show debug solib-frv
20268 Display the current state of FR-V shared-library code debugging
20270 @item set debug target
20271 @cindex target debugging info
20272 Turns on or off display of @value{GDBN} target debugging info. This info
20273 includes what is going on at the target level of GDB, as it happens. The
20274 default is 0. Set it to 1 to track events, and to 2 to also track the
20275 value of large memory transfers. Changes to this flag do not take effect
20276 until the next time you connect to a target or use the @code{run} command.
20277 @item show debug target
20278 Displays the current state of displaying @value{GDBN} target debugging
20280 @item set debug timestamp
20281 @cindex timestampping debugging info
20282 Turns on or off display of timestamps with @value{GDBN} debugging info.
20283 When enabled, seconds and microseconds are displayed before each debugging
20285 @item show debug timestamp
20286 Displays the current state of displaying timestamps with @value{GDBN}
20288 @item set debugvarobj
20289 @cindex variable object debugging info
20290 Turns on or off display of @value{GDBN} variable object debugging
20291 info. The default is off.
20292 @item show debugvarobj
20293 Displays the current state of displaying @value{GDBN} variable object
20295 @item set debug xml
20296 @cindex XML parser debugging
20297 Turns on or off debugging messages for built-in XML parsers.
20298 @item show debug xml
20299 Displays the current state of XML debugging messages.
20302 @node Other Misc Settings
20303 @section Other Miscellaneous Settings
20304 @cindex miscellaneous settings
20307 @kindex set interactive-mode
20308 @item set interactive-mode
20309 If @code{on}, forces @value{GDBN} to assume that GDB was started
20310 in a terminal. In practice, this means that @value{GDBN} should wait
20311 for the user to answer queries generated by commands entered at
20312 the command prompt. If @code{off}, forces @value{GDBN} to operate
20313 in the opposite mode, and it uses the default answers to all queries.
20314 If @code{auto} (the default), @value{GDBN} tries to determine whether
20315 its standard input is a terminal, and works in interactive-mode if it
20316 is, non-interactively otherwise.
20318 In the vast majority of cases, the debugger should be able to guess
20319 correctly which mode should be used. But this setting can be useful
20320 in certain specific cases, such as running a MinGW @value{GDBN}
20321 inside a cygwin window.
20323 @kindex show interactive-mode
20324 @item show interactive-mode
20325 Displays whether the debugger is operating in interactive mode or not.
20328 @node Extending GDB
20329 @chapter Extending @value{GDBN}
20330 @cindex extending GDB
20332 @value{GDBN} provides two mechanisms for extension. The first is based
20333 on composition of @value{GDBN} commands, and the second is based on the
20334 Python scripting language.
20336 To facilitate the use of these extensions, @value{GDBN} is capable
20337 of evaluating the contents of a file. When doing so, @value{GDBN}
20338 can recognize which scripting language is being used by looking at
20339 the filename extension. Files with an unrecognized filename extension
20340 are always treated as a @value{GDBN} Command Files.
20341 @xref{Command Files,, Command files}.
20343 You can control how @value{GDBN} evaluates these files with the following
20347 @kindex set script-extension
20348 @kindex show script-extension
20349 @item set script-extension off
20350 All scripts are always evaluated as @value{GDBN} Command Files.
20352 @item set script-extension soft
20353 The debugger determines the scripting language based on filename
20354 extension. If this scripting language is supported, @value{GDBN}
20355 evaluates the script using that language. Otherwise, it evaluates
20356 the file as a @value{GDBN} Command File.
20358 @item set script-extension strict
20359 The debugger determines the scripting language based on filename
20360 extension, and evaluates the script using that language. If the
20361 language is not supported, then the evaluation fails.
20363 @item show script-extension
20364 Display the current value of the @code{script-extension} option.
20369 * Sequences:: Canned Sequences of Commands
20370 * Python:: Scripting @value{GDBN} using Python
20374 @section Canned Sequences of Commands
20376 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
20377 Command Lists}), @value{GDBN} provides two ways to store sequences of
20378 commands for execution as a unit: user-defined commands and command
20382 * Define:: How to define your own commands
20383 * Hooks:: Hooks for user-defined commands
20384 * Command Files:: How to write scripts of commands to be stored in a file
20385 * Output:: Commands for controlled output
20389 @subsection User-defined Commands
20391 @cindex user-defined command
20392 @cindex arguments, to user-defined commands
20393 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
20394 which you assign a new name as a command. This is done with the
20395 @code{define} command. User commands may accept up to 10 arguments
20396 separated by whitespace. Arguments are accessed within the user command
20397 via @code{$arg0@dots{}$arg9}. A trivial example:
20401 print $arg0 + $arg1 + $arg2
20406 To execute the command use:
20413 This defines the command @code{adder}, which prints the sum of
20414 its three arguments. Note the arguments are text substitutions, so they may
20415 reference variables, use complex expressions, or even perform inferior
20418 @cindex argument count in user-defined commands
20419 @cindex how many arguments (user-defined commands)
20420 In addition, @code{$argc} may be used to find out how many arguments have
20421 been passed. This expands to a number in the range 0@dots{}10.
20426 print $arg0 + $arg1
20429 print $arg0 + $arg1 + $arg2
20437 @item define @var{commandname}
20438 Define a command named @var{commandname}. If there is already a command
20439 by that name, you are asked to confirm that you want to redefine it.
20440 @var{commandname} may be a bare command name consisting of letters,
20441 numbers, dashes, and underscores. It may also start with any predefined
20442 prefix command. For example, @samp{define target my-target} creates
20443 a user-defined @samp{target my-target} command.
20445 The definition of the command is made up of other @value{GDBN} command lines,
20446 which are given following the @code{define} command. The end of these
20447 commands is marked by a line containing @code{end}.
20450 @kindex end@r{ (user-defined commands)}
20451 @item document @var{commandname}
20452 Document the user-defined command @var{commandname}, so that it can be
20453 accessed by @code{help}. The command @var{commandname} must already be
20454 defined. This command reads lines of documentation just as @code{define}
20455 reads the lines of the command definition, ending with @code{end}.
20456 After the @code{document} command is finished, @code{help} on command
20457 @var{commandname} displays the documentation you have written.
20459 You may use the @code{document} command again to change the
20460 documentation of a command. Redefining the command with @code{define}
20461 does not change the documentation.
20463 @kindex dont-repeat
20464 @cindex don't repeat command
20466 Used inside a user-defined command, this tells @value{GDBN} that this
20467 command should not be repeated when the user hits @key{RET}
20468 (@pxref{Command Syntax, repeat last command}).
20470 @kindex help user-defined
20471 @item help user-defined
20472 List all user-defined commands, with the first line of the documentation
20477 @itemx show user @var{commandname}
20478 Display the @value{GDBN} commands used to define @var{commandname} (but
20479 not its documentation). If no @var{commandname} is given, display the
20480 definitions for all user-defined commands.
20482 @cindex infinite recursion in user-defined commands
20483 @kindex show max-user-call-depth
20484 @kindex set max-user-call-depth
20485 @item show max-user-call-depth
20486 @itemx set max-user-call-depth
20487 The value of @code{max-user-call-depth} controls how many recursion
20488 levels are allowed in user-defined commands before @value{GDBN} suspects an
20489 infinite recursion and aborts the command.
20492 In addition to the above commands, user-defined commands frequently
20493 use control flow commands, described in @ref{Command Files}.
20495 When user-defined commands are executed, the
20496 commands of the definition are not printed. An error in any command
20497 stops execution of the user-defined command.
20499 If used interactively, commands that would ask for confirmation proceed
20500 without asking when used inside a user-defined command. Many @value{GDBN}
20501 commands that normally print messages to say what they are doing omit the
20502 messages when used in a user-defined command.
20505 @subsection User-defined Command Hooks
20506 @cindex command hooks
20507 @cindex hooks, for commands
20508 @cindex hooks, pre-command
20511 You may define @dfn{hooks}, which are a special kind of user-defined
20512 command. Whenever you run the command @samp{foo}, if the user-defined
20513 command @samp{hook-foo} exists, it is executed (with no arguments)
20514 before that command.
20516 @cindex hooks, post-command
20518 A hook may also be defined which is run after the command you executed.
20519 Whenever you run the command @samp{foo}, if the user-defined command
20520 @samp{hookpost-foo} exists, it is executed (with no arguments) after
20521 that command. Post-execution hooks may exist simultaneously with
20522 pre-execution hooks, for the same command.
20524 It is valid for a hook to call the command which it hooks. If this
20525 occurs, the hook is not re-executed, thereby avoiding infinite recursion.
20527 @c It would be nice if hookpost could be passed a parameter indicating
20528 @c if the command it hooks executed properly or not. FIXME!
20530 @kindex stop@r{, a pseudo-command}
20531 In addition, a pseudo-command, @samp{stop} exists. Defining
20532 (@samp{hook-stop}) makes the associated commands execute every time
20533 execution stops in your program: before breakpoint commands are run,
20534 displays are printed, or the stack frame is printed.
20536 For example, to ignore @code{SIGALRM} signals while
20537 single-stepping, but treat them normally during normal execution,
20542 handle SIGALRM nopass
20546 handle SIGALRM pass
20549 define hook-continue
20550 handle SIGALRM pass
20554 As a further example, to hook at the beginning and end of the @code{echo}
20555 command, and to add extra text to the beginning and end of the message,
20563 define hookpost-echo
20567 (@value{GDBP}) echo Hello World
20568 <<<---Hello World--->>>
20573 You can define a hook for any single-word command in @value{GDBN}, but
20574 not for command aliases; you should define a hook for the basic command
20575 name, e.g.@: @code{backtrace} rather than @code{bt}.
20576 @c FIXME! So how does Joe User discover whether a command is an alias
20578 You can hook a multi-word command by adding @code{hook-} or
20579 @code{hookpost-} to the last word of the command, e.g.@:
20580 @samp{define target hook-remote} to add a hook to @samp{target remote}.
20582 If an error occurs during the execution of your hook, execution of
20583 @value{GDBN} commands stops and @value{GDBN} issues a prompt
20584 (before the command that you actually typed had a chance to run).
20586 If you try to define a hook which does not match any known command, you
20587 get a warning from the @code{define} command.
20589 @node Command Files
20590 @subsection Command Files
20592 @cindex command files
20593 @cindex scripting commands
20594 A command file for @value{GDBN} is a text file made of lines that are
20595 @value{GDBN} commands. Comments (lines starting with @kbd{#}) may
20596 also be included. An empty line in a command file does nothing; it
20597 does not mean to repeat the last command, as it would from the
20600 You can request the execution of a command file with the @code{source}
20601 command. Note that the @code{source} command is also used to evaluate
20602 scripts that are not Command Files. The exact behavior can be configured
20603 using the @code{script-extension} setting.
20604 @xref{Extending GDB,, Extending GDB}.
20608 @cindex execute commands from a file
20609 @item source [-s] [-v] @var{filename}
20610 Execute the command file @var{filename}.
20613 The lines in a command file are generally executed sequentially,
20614 unless the order of execution is changed by one of the
20615 @emph{flow-control commands} described below. The commands are not
20616 printed as they are executed. An error in any command terminates
20617 execution of the command file and control is returned to the console.
20619 @value{GDBN} first searches for @var{filename} in the current directory.
20620 If the file is not found there, and @var{filename} does not specify a
20621 directory, then @value{GDBN} also looks for the file on the source search path
20622 (specified with the @samp{directory} command);
20623 except that @file{$cdir} is not searched because the compilation directory
20624 is not relevant to scripts.
20626 If @code{-s} is specified, then @value{GDBN} searches for @var{filename}
20627 on the search path even if @var{filename} specifies a directory.
20628 The search is done by appending @var{filename} to each element of the
20629 search path. So, for example, if @var{filename} is @file{mylib/myscript}
20630 and the search path contains @file{/home/user} then @value{GDBN} will
20631 look for the script @file{/home/user/mylib/myscript}.
20632 The search is also done if @var{filename} is an absolute path.
20633 For example, if @var{filename} is @file{/tmp/myscript} and
20634 the search path contains @file{/home/user} then @value{GDBN} will
20635 look for the script @file{/home/user/tmp/myscript}.
20636 For DOS-like systems, if @var{filename} contains a drive specification,
20637 it is stripped before concatenation. For example, if @var{filename} is
20638 @file{d:myscript} and the search path contains @file{c:/tmp} then @value{GDBN}
20639 will look for the script @file{c:/tmp/myscript}.
20641 If @code{-v}, for verbose mode, is given then @value{GDBN} displays
20642 each command as it is executed. The option must be given before
20643 @var{filename}, and is interpreted as part of the filename anywhere else.
20645 Commands that would ask for confirmation if used interactively proceed
20646 without asking when used in a command file. Many @value{GDBN} commands that
20647 normally print messages to say what they are doing omit the messages
20648 when called from command files.
20650 @value{GDBN} also accepts command input from standard input. In this
20651 mode, normal output goes to standard output and error output goes to
20652 standard error. Errors in a command file supplied on standard input do
20653 not terminate execution of the command file---execution continues with
20657 gdb < cmds > log 2>&1
20660 (The syntax above will vary depending on the shell used.) This example
20661 will execute commands from the file @file{cmds}. All output and errors
20662 would be directed to @file{log}.
20664 Since commands stored on command files tend to be more general than
20665 commands typed interactively, they frequently need to deal with
20666 complicated situations, such as different or unexpected values of
20667 variables and symbols, changes in how the program being debugged is
20668 built, etc. @value{GDBN} provides a set of flow-control commands to
20669 deal with these complexities. Using these commands, you can write
20670 complex scripts that loop over data structures, execute commands
20671 conditionally, etc.
20678 This command allows to include in your script conditionally executed
20679 commands. The @code{if} command takes a single argument, which is an
20680 expression to evaluate. It is followed by a series of commands that
20681 are executed only if the expression is true (its value is nonzero).
20682 There can then optionally be an @code{else} line, followed by a series
20683 of commands that are only executed if the expression was false. The
20684 end of the list is marked by a line containing @code{end}.
20688 This command allows to write loops. Its syntax is similar to
20689 @code{if}: the command takes a single argument, which is an expression
20690 to evaluate, and must be followed by the commands to execute, one per
20691 line, terminated by an @code{end}. These commands are called the
20692 @dfn{body} of the loop. The commands in the body of @code{while} are
20693 executed repeatedly as long as the expression evaluates to true.
20697 This command exits the @code{while} loop in whose body it is included.
20698 Execution of the script continues after that @code{while}s @code{end}
20701 @kindex loop_continue
20702 @item loop_continue
20703 This command skips the execution of the rest of the body of commands
20704 in the @code{while} loop in whose body it is included. Execution
20705 branches to the beginning of the @code{while} loop, where it evaluates
20706 the controlling expression.
20708 @kindex end@r{ (if/else/while commands)}
20710 Terminate the block of commands that are the body of @code{if},
20711 @code{else}, or @code{while} flow-control commands.
20716 @subsection Commands for Controlled Output
20718 During the execution of a command file or a user-defined command, normal
20719 @value{GDBN} output is suppressed; the only output that appears is what is
20720 explicitly printed by the commands in the definition. This section
20721 describes three commands useful for generating exactly the output you
20726 @item echo @var{text}
20727 @c I do not consider backslash-space a standard C escape sequence
20728 @c because it is not in ANSI.
20729 Print @var{text}. Nonprinting characters can be included in
20730 @var{text} using C escape sequences, such as @samp{\n} to print a
20731 newline. @strong{No newline is printed unless you specify one.}
20732 In addition to the standard C escape sequences, a backslash followed
20733 by a space stands for a space. This is useful for displaying a
20734 string with spaces at the beginning or the end, since leading and
20735 trailing spaces are otherwise trimmed from all arguments.
20736 To print @samp{@w{ }and foo =@w{ }}, use the command
20737 @samp{echo \@w{ }and foo = \@w{ }}.
20739 A backslash at the end of @var{text} can be used, as in C, to continue
20740 the command onto subsequent lines. For example,
20743 echo This is some text\n\
20744 which is continued\n\
20745 onto several lines.\n
20748 produces the same output as
20751 echo This is some text\n
20752 echo which is continued\n
20753 echo onto several lines.\n
20757 @item output @var{expression}
20758 Print the value of @var{expression} and nothing but that value: no
20759 newlines, no @samp{$@var{nn} = }. The value is not entered in the
20760 value history either. @xref{Expressions, ,Expressions}, for more information
20763 @item output/@var{fmt} @var{expression}
20764 Print the value of @var{expression} in format @var{fmt}. You can use
20765 the same formats as for @code{print}. @xref{Output Formats,,Output
20766 Formats}, for more information.
20769 @item printf @var{template}, @var{expressions}@dots{}
20770 Print the values of one or more @var{expressions} under the control of
20771 the string @var{template}. To print several values, make
20772 @var{expressions} be a comma-separated list of individual expressions,
20773 which may be either numbers or pointers. Their values are printed as
20774 specified by @var{template}, exactly as a C program would do by
20775 executing the code below:
20778 printf (@var{template}, @var{expressions}@dots{});
20781 As in @code{C} @code{printf}, ordinary characters in @var{template}
20782 are printed verbatim, while @dfn{conversion specification} introduced
20783 by the @samp{%} character cause subsequent @var{expressions} to be
20784 evaluated, their values converted and formatted according to type and
20785 style information encoded in the conversion specifications, and then
20788 For example, you can print two values in hex like this:
20791 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
20794 @code{printf} supports all the standard @code{C} conversion
20795 specifications, including the flags and modifiers between the @samp{%}
20796 character and the conversion letter, with the following exceptions:
20800 The argument-ordering modifiers, such as @samp{2$}, are not supported.
20803 The modifier @samp{*} is not supported for specifying precision or
20807 The @samp{'} flag (for separation of digits into groups according to
20808 @code{LC_NUMERIC'}) is not supported.
20811 The type modifiers @samp{hh}, @samp{j}, @samp{t}, and @samp{z} are not
20815 The conversion letter @samp{n} (as in @samp{%n}) is not supported.
20818 The conversion letters @samp{a} and @samp{A} are not supported.
20822 Note that the @samp{ll} type modifier is supported only if the
20823 underlying @code{C} implementation used to build @value{GDBN} supports
20824 the @code{long long int} type, and the @samp{L} type modifier is
20825 supported only if @code{long double} type is available.
20827 As in @code{C}, @code{printf} supports simple backslash-escape
20828 sequences, such as @code{\n}, @samp{\t}, @samp{\\}, @samp{\"},
20829 @samp{\a}, and @samp{\f}, that consist of backslash followed by a
20830 single character. Octal and hexadecimal escape sequences are not
20833 Additionally, @code{printf} supports conversion specifications for DFP
20834 (@dfn{Decimal Floating Point}) types using the following length modifiers
20835 together with a floating point specifier.
20840 @samp{H} for printing @code{Decimal32} types.
20843 @samp{D} for printing @code{Decimal64} types.
20846 @samp{DD} for printing @code{Decimal128} types.
20849 If the underlying @code{C} implementation used to build @value{GDBN} has
20850 support for the three length modifiers for DFP types, other modifiers
20851 such as width and precision will also be available for @value{GDBN} to use.
20853 In case there is no such @code{C} support, no additional modifiers will be
20854 available and the value will be printed in the standard way.
20856 Here's an example of printing DFP types using the above conversion letters:
20858 printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl
20862 @item eval @var{template}, @var{expressions}@dots{}
20863 Convert the values of one or more @var{expressions} under the control of
20864 the string @var{template} to a command line, and call it.
20869 @section Scripting @value{GDBN} using Python
20870 @cindex python scripting
20871 @cindex scripting with python
20873 You can script @value{GDBN} using the @uref{http://www.python.org/,
20874 Python programming language}. This feature is available only if
20875 @value{GDBN} was configured using @option{--with-python}.
20877 @cindex python directory
20878 Python scripts used by @value{GDBN} should be installed in
20879 @file{@var{data-directory}/python}, where @var{data-directory} is
20880 the data directory as determined at @value{GDBN} startup (@pxref{Data Files}).
20881 This directory, known as the @dfn{python directory},
20882 is automatically added to the Python Search Path in order to allow
20883 the Python interpreter to locate all scripts installed at this location.
20885 Additionally, @value{GDBN} commands and convenience functions which
20886 are written in Python and are located in the
20887 @file{@var{data-directory}/python/gdb/command} or
20888 @file{@var{data-directory}/python/gdb/function} directories are
20889 automatically imported when @value{GDBN} starts.
20892 * Python Commands:: Accessing Python from @value{GDBN}.
20893 * Python API:: Accessing @value{GDBN} from Python.
20894 * Auto-loading:: Automatically loading Python code.
20895 * Python modules:: Python modules provided by @value{GDBN}.
20898 @node Python Commands
20899 @subsection Python Commands
20900 @cindex python commands
20901 @cindex commands to access python
20903 @value{GDBN} provides one command for accessing the Python interpreter,
20904 and one related setting:
20908 @item python @r{[}@var{code}@r{]}
20909 The @code{python} command can be used to evaluate Python code.
20911 If given an argument, the @code{python} command will evaluate the
20912 argument as a Python command. For example:
20915 (@value{GDBP}) python print 23
20919 If you do not provide an argument to @code{python}, it will act as a
20920 multi-line command, like @code{define}. In this case, the Python
20921 script is made up of subsequent command lines, given after the
20922 @code{python} command. This command list is terminated using a line
20923 containing @code{end}. For example:
20926 (@value{GDBP}) python
20928 End with a line saying just "end".
20934 @kindex maint set python print-stack
20935 @item maint set python print-stack
20936 This command is now deprecated. Instead use @code{set python
20939 @kindex set python print-stack
20940 @item set python print-stack
20941 By default, @value{GDBN} will not print a stack trace when an error
20942 occurs in a Python script. This can be controlled using @code{set
20943 python print-stack}: if @code{on}, then Python stack printing is
20944 enabled; if @code{off}, the default, then Python stack printing is
20948 It is also possible to execute a Python script from the @value{GDBN}
20952 @item source @file{script-name}
20953 The script name must end with @samp{.py} and @value{GDBN} must be configured
20954 to recognize the script language based on filename extension using
20955 the @code{script-extension} setting. @xref{Extending GDB, ,Extending GDB}.
20957 @item python execfile ("script-name")
20958 This method is based on the @code{execfile} Python built-in function,
20959 and thus is always available.
20963 @subsection Python API
20965 @cindex programming in python
20967 @cindex python stdout
20968 @cindex python pagination
20969 At startup, @value{GDBN} overrides Python's @code{sys.stdout} and
20970 @code{sys.stderr} to print using @value{GDBN}'s output-paging streams.
20971 A Python program which outputs to one of these streams may have its
20972 output interrupted by the user (@pxref{Screen Size}). In this
20973 situation, a Python @code{KeyboardInterrupt} exception is thrown.
20976 * Basic Python:: Basic Python Functions.
20977 * Exception Handling:: How Python exceptions are translated.
20978 * Values From Inferior:: Python representation of values.
20979 * Types In Python:: Python representation of types.
20980 * Pretty Printing API:: Pretty-printing values.
20981 * Selecting Pretty-Printers:: How GDB chooses a pretty-printer.
20982 * Writing a Pretty-Printer:: Writing a Pretty-Printer.
20983 * Inferiors In Python:: Python representation of inferiors (processes)
20984 * Events In Python:: Listening for events from @value{GDBN}.
20985 * Threads In Python:: Accessing inferior threads from Python.
20986 * Commands In Python:: Implementing new commands in Python.
20987 * Parameters In Python:: Adding new @value{GDBN} parameters.
20988 * Functions In Python:: Writing new convenience functions.
20989 * Progspaces In Python:: Program spaces.
20990 * Objfiles In Python:: Object files.
20991 * Frames In Python:: Accessing inferior stack frames from Python.
20992 * Blocks In Python:: Accessing frame blocks from Python.
20993 * Symbols In Python:: Python representation of symbols.
20994 * Symbol Tables In Python:: Python representation of symbol tables.
20995 * Lazy Strings In Python:: Python representation of lazy strings.
20996 * Breakpoints In Python:: Manipulating breakpoints using Python.
21000 @subsubsection Basic Python
21002 @cindex python functions
21003 @cindex python module
21005 @value{GDBN} introduces a new Python module, named @code{gdb}. All
21006 methods and classes added by @value{GDBN} are placed in this module.
21007 @value{GDBN} automatically @code{import}s the @code{gdb} module for
21008 use in all scripts evaluated by the @code{python} command.
21010 @findex gdb.PYTHONDIR
21011 @defvar gdb.PYTHONDIR
21012 A string containing the python directory (@pxref{Python}).
21015 @findex gdb.execute
21016 @defun gdb.execute (command @r{[}, from_tty @r{[}, to_string@r{]]})
21017 Evaluate @var{command}, a string, as a @value{GDBN} CLI command.
21018 If a GDB exception happens while @var{command} runs, it is
21019 translated as described in @ref{Exception Handling,,Exception Handling}.
21021 @var{from_tty} specifies whether @value{GDBN} ought to consider this
21022 command as having originated from the user invoking it interactively.
21023 It must be a boolean value. If omitted, it defaults to @code{False}.
21025 By default, any output produced by @var{command} is sent to
21026 @value{GDBN}'s standard output. If the @var{to_string} parameter is
21027 @code{True}, then output will be collected by @code{gdb.execute} and
21028 returned as a string. The default is @code{False}, in which case the
21029 return value is @code{None}. If @var{to_string} is @code{True}, the
21030 @value{GDBN} virtual terminal will be temporarily set to unlimited width
21031 and height, and its pagination will be disabled; @pxref{Screen Size}.
21034 @findex gdb.breakpoints
21035 @defun gdb.breakpoints ()
21036 Return a sequence holding all of @value{GDBN}'s breakpoints.
21037 @xref{Breakpoints In Python}, for more information.
21040 @findex gdb.parameter
21041 @defun gdb.parameter (parameter)
21042 Return the value of a @value{GDBN} parameter. @var{parameter} is a
21043 string naming the parameter to look up; @var{parameter} may contain
21044 spaces if the parameter has a multi-part name. For example,
21045 @samp{print object} is a valid parameter name.
21047 If the named parameter does not exist, this function throws a
21048 @code{gdb.error} (@pxref{Exception Handling}). Otherwise, the
21049 parameter's value is converted to a Python value of the appropriate
21050 type, and returned.
21053 @findex gdb.history
21054 @defun gdb.history (number)
21055 Return a value from @value{GDBN}'s value history (@pxref{Value
21056 History}). @var{number} indicates which history element to return.
21057 If @var{number} is negative, then @value{GDBN} will take its absolute value
21058 and count backward from the last element (i.e., the most recent element) to
21059 find the value to return. If @var{number} is zero, then @value{GDBN} will
21060 return the most recent element. If the element specified by @var{number}
21061 doesn't exist in the value history, a @code{gdb.error} exception will be
21064 If no exception is raised, the return value is always an instance of
21065 @code{gdb.Value} (@pxref{Values From Inferior}).
21068 @findex gdb.parse_and_eval
21069 @defun gdb.parse_and_eval (expression)
21070 Parse @var{expression} as an expression in the current language,
21071 evaluate it, and return the result as a @code{gdb.Value}.
21072 @var{expression} must be a string.
21074 This function can be useful when implementing a new command
21075 (@pxref{Commands In Python}), as it provides a way to parse the
21076 command's argument as an expression. It is also useful simply to
21077 compute values, for example, it is the only way to get the value of a
21078 convenience variable (@pxref{Convenience Vars}) as a @code{gdb.Value}.
21081 @findex gdb.post_event
21082 @defun gdb.post_event (event)
21083 Put @var{event}, a callable object taking no arguments, into
21084 @value{GDBN}'s internal event queue. This callable will be invoked at
21085 some later point, during @value{GDBN}'s event processing. Events
21086 posted using @code{post_event} will be run in the order in which they
21087 were posted; however, there is no way to know when they will be
21088 processed relative to other events inside @value{GDBN}.
21090 @value{GDBN} is not thread-safe. If your Python program uses multiple
21091 threads, you must be careful to only call @value{GDBN}-specific
21092 functions in the main @value{GDBN} thread. @code{post_event} ensures
21096 (@value{GDBP}) python
21100 > def __init__(self, message):
21101 > self.message = message;
21102 > def __call__(self):
21103 > gdb.write(self.message)
21105 >class MyThread1 (threading.Thread):
21107 > gdb.post_event(Writer("Hello "))
21109 >class MyThread2 (threading.Thread):
21111 > gdb.post_event(Writer("World\n"))
21113 >MyThread1().start()
21114 >MyThread2().start()
21116 (@value{GDBP}) Hello World
21121 @defun gdb.write (string @r{[}, stream{]})
21122 Print a string to @value{GDBN}'s paginated output stream. The
21123 optional @var{stream} determines the stream to print to. The default
21124 stream is @value{GDBN}'s standard output stream. Possible stream
21131 @value{GDBN}'s standard output stream.
21136 @value{GDBN}'s standard error stream.
21141 @value{GDBN}'s log stream (@pxref{Logging Output}).
21144 Writing to @code{sys.stdout} or @code{sys.stderr} will automatically
21145 call this function and will automatically direct the output to the
21150 @defun gdb.flush ()
21151 Flush the buffer of a @value{GDBN} paginated stream so that the
21152 contents are displayed immediately. @value{GDBN} will flush the
21153 contents of a stream automatically when it encounters a newline in the
21154 buffer. The optional @var{stream} determines the stream to flush. The
21155 default stream is @value{GDBN}'s standard output stream. Possible
21162 @value{GDBN}'s standard output stream.
21167 @value{GDBN}'s standard error stream.
21172 @value{GDBN}'s log stream (@pxref{Logging Output}).
21176 Flushing @code{sys.stdout} or @code{sys.stderr} will automatically
21177 call this function for the relevant stream.
21180 @findex gdb.target_charset
21181 @defun gdb.target_charset ()
21182 Return the name of the current target character set (@pxref{Character
21183 Sets}). This differs from @code{gdb.parameter('target-charset')} in
21184 that @samp{auto} is never returned.
21187 @findex gdb.target_wide_charset
21188 @defun gdb.target_wide_charset ()
21189 Return the name of the current target wide character set
21190 (@pxref{Character Sets}). This differs from
21191 @code{gdb.parameter('target-wide-charset')} in that @samp{auto} is
21195 @findex gdb.solib_name
21196 @defun gdb.solib_name (address)
21197 Return the name of the shared library holding the given @var{address}
21198 as a string, or @code{None}.
21201 @findex gdb.decode_line
21202 @defun gdb.decode_line @r{[}expression@r{]}
21203 Return locations of the line specified by @var{expression}, or of the
21204 current line if no argument was given. This function returns a Python
21205 tuple containing two elements. The first element contains a string
21206 holding any unparsed section of @var{expression} (or @code{None} if
21207 the expression has been fully parsed). The second element contains
21208 either @code{None} or another tuple that contains all the locations
21209 that match the expression represented as @code{gdb.Symtab_and_line}
21210 objects (@pxref{Symbol Tables In Python}). If @var{expression} is
21211 provided, it is decoded the way that @value{GDBN}'s inbuilt
21212 @code{break} or @code{edit} commands do (@pxref{Specify Location}).
21215 @defun gdb.prompt_hook (current_prompt)
21216 @anchor{prompt_hook}
21218 If @var{prompt_hook} is callable, @value{GDBN} will call the method
21219 assigned to this operation before a prompt is displayed by
21222 The parameter @code{current_prompt} contains the current @value{GDBN}
21223 prompt. This method must return a Python string, or @code{None}. If
21224 a string is returned, the @value{GDBN} prompt will be set to that
21225 string. If @code{None} is returned, @value{GDBN} will continue to use
21226 the current prompt.
21228 Some prompts cannot be substituted in @value{GDBN}. Secondary prompts
21229 such as those used by readline for command input, and annotation
21230 related prompts are prohibited from being changed.
21233 @node Exception Handling
21234 @subsubsection Exception Handling
21235 @cindex python exceptions
21236 @cindex exceptions, python
21238 When executing the @code{python} command, Python exceptions
21239 uncaught within the Python code are translated to calls to
21240 @value{GDBN} error-reporting mechanism. If the command that called
21241 @code{python} does not handle the error, @value{GDBN} will
21242 terminate it and print an error message containing the Python
21243 exception name, the associated value, and the Python call stack
21244 backtrace at the point where the exception was raised. Example:
21247 (@value{GDBP}) python print foo
21248 Traceback (most recent call last):
21249 File "<string>", line 1, in <module>
21250 NameError: name 'foo' is not defined
21253 @value{GDBN} errors that happen in @value{GDBN} commands invoked by
21254 Python code are converted to Python exceptions. The type of the
21255 Python exception depends on the error.
21259 This is the base class for most exceptions generated by @value{GDBN}.
21260 It is derived from @code{RuntimeError}, for compatibility with earlier
21261 versions of @value{GDBN}.
21263 If an error occurring in @value{GDBN} does not fit into some more
21264 specific category, then the generated exception will have this type.
21266 @item gdb.MemoryError
21267 This is a subclass of @code{gdb.error} which is thrown when an
21268 operation tried to access invalid memory in the inferior.
21270 @item KeyboardInterrupt
21271 User interrupt (via @kbd{C-c} or by typing @kbd{q} at a pagination
21272 prompt) is translated to a Python @code{KeyboardInterrupt} exception.
21275 In all cases, your exception handler will see the @value{GDBN} error
21276 message as its value and the Python call stack backtrace at the Python
21277 statement closest to where the @value{GDBN} error occured as the
21280 @findex gdb.GdbError
21281 When implementing @value{GDBN} commands in Python via @code{gdb.Command},
21282 it is useful to be able to throw an exception that doesn't cause a
21283 traceback to be printed. For example, the user may have invoked the
21284 command incorrectly. Use the @code{gdb.GdbError} exception
21285 to handle this case. Example:
21289 >class HelloWorld (gdb.Command):
21290 > """Greet the whole world."""
21291 > def __init__ (self):
21292 > super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_OBSCURE)
21293 > def invoke (self, args, from_tty):
21294 > argv = gdb.string_to_argv (args)
21295 > if len (argv) != 0:
21296 > raise gdb.GdbError ("hello-world takes no arguments")
21297 > print "Hello, World!"
21300 (gdb) hello-world 42
21301 hello-world takes no arguments
21304 @node Values From Inferior
21305 @subsubsection Values From Inferior
21306 @cindex values from inferior, with Python
21307 @cindex python, working with values from inferior
21309 @cindex @code{gdb.Value}
21310 @value{GDBN} provides values it obtains from the inferior program in
21311 an object of type @code{gdb.Value}. @value{GDBN} uses this object
21312 for its internal bookkeeping of the inferior's values, and for
21313 fetching values when necessary.
21315 Inferior values that are simple scalars can be used directly in
21316 Python expressions that are valid for the value's data type. Here's
21317 an example for an integer or floating-point value @code{some_val}:
21324 As result of this, @code{bar} will also be a @code{gdb.Value} object
21325 whose values are of the same type as those of @code{some_val}.
21327 Inferior values that are structures or instances of some class can
21328 be accessed using the Python @dfn{dictionary syntax}. For example, if
21329 @code{some_val} is a @code{gdb.Value} instance holding a structure, you
21330 can access its @code{foo} element with:
21333 bar = some_val['foo']
21336 Again, @code{bar} will also be a @code{gdb.Value} object.
21338 A @code{gdb.Value} that represents a function can be executed via
21339 inferior function call. Any arguments provided to the call must match
21340 the function's prototype, and must be provided in the order specified
21343 For example, @code{some_val} is a @code{gdb.Value} instance
21344 representing a function that takes two integers as arguments. To
21345 execute this function, call it like so:
21348 result = some_val (10,20)
21351 Any values returned from a function call will be stored as a
21354 The following attributes are provided:
21357 @defvar Value.address
21358 If this object is addressable, this read-only attribute holds a
21359 @code{gdb.Value} object representing the address. Otherwise,
21360 this attribute holds @code{None}.
21363 @cindex optimized out value in Python
21364 @defvar Value.is_optimized_out
21365 This read-only boolean attribute is true if the compiler optimized out
21366 this value, thus it is not available for fetching from the inferior.
21370 The type of this @code{gdb.Value}. The value of this attribute is a
21371 @code{gdb.Type} object (@pxref{Types In Python}).
21374 @defvar Value.dynamic_type
21375 The dynamic type of this @code{gdb.Value}. This uses C@t{++} run-time
21376 type information (@acronym{RTTI}) to determine the dynamic type of the
21377 value. If this value is of class type, it will return the class in
21378 which the value is embedded, if any. If this value is of pointer or
21379 reference to a class type, it will compute the dynamic type of the
21380 referenced object, and return a pointer or reference to that type,
21381 respectively. In all other cases, it will return the value's static
21384 Note that this feature will only work when debugging a C@t{++} program
21385 that includes @acronym{RTTI} for the object in question. Otherwise,
21386 it will just return the static type of the value as in @kbd{ptype foo}
21387 (@pxref{Symbols, ptype}).
21391 The following methods are provided:
21394 @defun Value.__init__ (@var{val})
21395 Many Python values can be converted directly to a @code{gdb.Value} via
21396 this object initializer. Specifically:
21399 @item Python boolean
21400 A Python boolean is converted to the boolean type from the current
21403 @item Python integer
21404 A Python integer is converted to the C @code{long} type for the
21405 current architecture.
21408 A Python long is converted to the C @code{long long} type for the
21409 current architecture.
21412 A Python float is converted to the C @code{double} type for the
21413 current architecture.
21415 @item Python string
21416 A Python string is converted to a target string, using the current
21419 @item @code{gdb.Value}
21420 If @code{val} is a @code{gdb.Value}, then a copy of the value is made.
21422 @item @code{gdb.LazyString}
21423 If @code{val} is a @code{gdb.LazyString} (@pxref{Lazy Strings In
21424 Python}), then the lazy string's @code{value} method is called, and
21425 its result is used.
21429 @defun Value.cast (type)
21430 Return a new instance of @code{gdb.Value} that is the result of
21431 casting this instance to the type described by @var{type}, which must
21432 be a @code{gdb.Type} object. If the cast cannot be performed for some
21433 reason, this method throws an exception.
21436 @defun Value.dereference ()
21437 For pointer data types, this method returns a new @code{gdb.Value} object
21438 whose contents is the object pointed to by the pointer. For example, if
21439 @code{foo} is a C pointer to an @code{int}, declared in your C program as
21446 then you can use the corresponding @code{gdb.Value} to access what
21447 @code{foo} points to like this:
21450 bar = foo.dereference ()
21453 The result @code{bar} will be a @code{gdb.Value} object holding the
21454 value pointed to by @code{foo}.
21457 @defun Value.dynamic_cast (type)
21458 Like @code{Value.cast}, but works as if the C@t{++} @code{dynamic_cast}
21459 operator were used. Consult a C@t{++} reference for details.
21462 @defun Value.reinterpret_cast (type)
21463 Like @code{Value.cast}, but works as if the C@t{++} @code{reinterpret_cast}
21464 operator were used. Consult a C@t{++} reference for details.
21467 @defun Value.string (@r{[}encoding@r{[}, errors@r{[}, length@r{]]]})
21468 If this @code{gdb.Value} represents a string, then this method
21469 converts the contents to a Python string. Otherwise, this method will
21470 throw an exception.
21472 Strings are recognized in a language-specific way; whether a given
21473 @code{gdb.Value} represents a string is determined by the current
21476 For C-like languages, a value is a string if it is a pointer to or an
21477 array of characters or ints. The string is assumed to be terminated
21478 by a zero of the appropriate width. However if the optional length
21479 argument is given, the string will be converted to that given length,
21480 ignoring any embedded zeros that the string may contain.
21482 If the optional @var{encoding} argument is given, it must be a string
21483 naming the encoding of the string in the @code{gdb.Value}, such as
21484 @code{"ascii"}, @code{"iso-8859-6"} or @code{"utf-8"}. It accepts
21485 the same encodings as the corresponding argument to Python's
21486 @code{string.decode} method, and the Python codec machinery will be used
21487 to convert the string. If @var{encoding} is not given, or if
21488 @var{encoding} is the empty string, then either the @code{target-charset}
21489 (@pxref{Character Sets}) will be used, or a language-specific encoding
21490 will be used, if the current language is able to supply one.
21492 The optional @var{errors} argument is the same as the corresponding
21493 argument to Python's @code{string.decode} method.
21495 If the optional @var{length} argument is given, the string will be
21496 fetched and converted to the given length.
21499 @defun Value.lazy_string (@r{[}encoding @r{[}, length@r{]]})
21500 If this @code{gdb.Value} represents a string, then this method
21501 converts the contents to a @code{gdb.LazyString} (@pxref{Lazy Strings
21502 In Python}). Otherwise, this method will throw an exception.
21504 If the optional @var{encoding} argument is given, it must be a string
21505 naming the encoding of the @code{gdb.LazyString}. Some examples are:
21506 @samp{ascii}, @samp{iso-8859-6} or @samp{utf-8}. If the
21507 @var{encoding} argument is an encoding that @value{GDBN} does
21508 recognize, @value{GDBN} will raise an error.
21510 When a lazy string is printed, the @value{GDBN} encoding machinery is
21511 used to convert the string during printing. If the optional
21512 @var{encoding} argument is not provided, or is an empty string,
21513 @value{GDBN} will automatically select the encoding most suitable for
21514 the string type. For further information on encoding in @value{GDBN}
21515 please see @ref{Character Sets}.
21517 If the optional @var{length} argument is given, the string will be
21518 fetched and encoded to the length of characters specified. If
21519 the @var{length} argument is not provided, the string will be fetched
21520 and encoded until a null of appropriate width is found.
21524 @node Types In Python
21525 @subsubsection Types In Python
21526 @cindex types in Python
21527 @cindex Python, working with types
21530 @value{GDBN} represents types from the inferior using the class
21533 The following type-related functions are available in the @code{gdb}
21536 @findex gdb.lookup_type
21537 @defun gdb.lookup_type (name @r{[}, block@r{]})
21538 This function looks up a type by name. @var{name} is the name of the
21539 type to look up. It must be a string.
21541 If @var{block} is given, then @var{name} is looked up in that scope.
21542 Otherwise, it is searched for globally.
21544 Ordinarily, this function will return an instance of @code{gdb.Type}.
21545 If the named type cannot be found, it will throw an exception.
21548 If the type is a structure or class type, or an enum type, the fields
21549 of that type can be accessed using the Python @dfn{dictionary syntax}.
21550 For example, if @code{some_type} is a @code{gdb.Type} instance holding
21551 a structure type, you can access its @code{foo} field with:
21554 bar = some_type['foo']
21557 @code{bar} will be a @code{gdb.Field} object; see below under the
21558 description of the @code{Type.fields} method for a description of the
21559 @code{gdb.Field} class.
21561 An instance of @code{Type} has the following attributes:
21565 The type code for this type. The type code will be one of the
21566 @code{TYPE_CODE_} constants defined below.
21569 @defvar Type.sizeof
21570 The size of this type, in target @code{char} units. Usually, a
21571 target's @code{char} type will be an 8-bit byte. However, on some
21572 unusual platforms, this type may have a different size.
21576 The tag name for this type. The tag name is the name after
21577 @code{struct}, @code{union}, or @code{enum} in C and C@t{++}; not all
21578 languages have this concept. If this type has no tag name, then
21579 @code{None} is returned.
21583 The following methods are provided:
21586 @defun Type.fields ()
21587 For structure and union types, this method returns the fields. Range
21588 types have two fields, the minimum and maximum values. Enum types
21589 have one field per enum constant. Function and method types have one
21590 field per parameter. The base types of C@t{++} classes are also
21591 represented as fields. If the type has no fields, or does not fit
21592 into one of these categories, an empty sequence will be returned.
21594 Each field is a @code{gdb.Field} object, with some pre-defined attributes:
21597 This attribute is not available for @code{static} fields (as in
21598 C@t{++} or Java). For non-@code{static} fields, the value is the bit
21599 position of the field. For @code{enum} fields, the value is the
21600 enumeration member's integer representation.
21603 The name of the field, or @code{None} for anonymous fields.
21606 This is @code{True} if the field is artificial, usually meaning that
21607 it was provided by the compiler and not the user. This attribute is
21608 always provided, and is @code{False} if the field is not artificial.
21610 @item is_base_class
21611 This is @code{True} if the field represents a base class of a C@t{++}
21612 structure. This attribute is always provided, and is @code{False}
21613 if the field is not a base class of the type that is the argument of
21614 @code{fields}, or if that type was not a C@t{++} class.
21617 If the field is packed, or is a bitfield, then this will have a
21618 non-zero value, which is the size of the field in bits. Otherwise,
21619 this will be zero; in this case the field's size is given by its type.
21622 The type of the field. This is usually an instance of @code{Type},
21623 but it can be @code{None} in some situations.
21627 @defun Type.array (@var{n1} @r{[}, @var{n2}@r{]})
21628 Return a new @code{gdb.Type} object which represents an array of this
21629 type. If one argument is given, it is the inclusive upper bound of
21630 the array; in this case the lower bound is zero. If two arguments are
21631 given, the first argument is the lower bound of the array, and the
21632 second argument is the upper bound of the array. An array's length
21633 must not be negative, but the bounds can be.
21636 @defun Type.const ()
21637 Return a new @code{gdb.Type} object which represents a
21638 @code{const}-qualified variant of this type.
21641 @defun Type.volatile ()
21642 Return a new @code{gdb.Type} object which represents a
21643 @code{volatile}-qualified variant of this type.
21646 @defun Type.unqualified ()
21647 Return a new @code{gdb.Type} object which represents an unqualified
21648 variant of this type. That is, the result is neither @code{const} nor
21652 @defun Type.range ()
21653 Return a Python @code{Tuple} object that contains two elements: the
21654 low bound of the argument type and the high bound of that type. If
21655 the type does not have a range, @value{GDBN} will raise a
21656 @code{gdb.error} exception (@pxref{Exception Handling}).
21659 @defun Type.reference ()
21660 Return a new @code{gdb.Type} object which represents a reference to this
21664 @defun Type.pointer ()
21665 Return a new @code{gdb.Type} object which represents a pointer to this
21669 @defun Type.strip_typedefs ()
21670 Return a new @code{gdb.Type} that represents the real type,
21671 after removing all layers of typedefs.
21674 @defun Type.target ()
21675 Return a new @code{gdb.Type} object which represents the target type
21678 For a pointer type, the target type is the type of the pointed-to
21679 object. For an array type (meaning C-like arrays), the target type is
21680 the type of the elements of the array. For a function or method type,
21681 the target type is the type of the return value. For a complex type,
21682 the target type is the type of the elements. For a typedef, the
21683 target type is the aliased type.
21685 If the type does not have a target, this method will throw an
21689 @defun Type.template_argument (n @r{[}, block@r{]})
21690 If this @code{gdb.Type} is an instantiation of a template, this will
21691 return a new @code{gdb.Type} which represents the type of the
21692 @var{n}th template argument.
21694 If this @code{gdb.Type} is not a template type, this will throw an
21695 exception. Ordinarily, only C@t{++} code will have template types.
21697 If @var{block} is given, then @var{name} is looked up in that scope.
21698 Otherwise, it is searched for globally.
21703 Each type has a code, which indicates what category this type falls
21704 into. The available type categories are represented by constants
21705 defined in the @code{gdb} module:
21708 @findex TYPE_CODE_PTR
21709 @findex gdb.TYPE_CODE_PTR
21710 @item gdb.TYPE_CODE_PTR
21711 The type is a pointer.
21713 @findex TYPE_CODE_ARRAY
21714 @findex gdb.TYPE_CODE_ARRAY
21715 @item gdb.TYPE_CODE_ARRAY
21716 The type is an array.
21718 @findex TYPE_CODE_STRUCT
21719 @findex gdb.TYPE_CODE_STRUCT
21720 @item gdb.TYPE_CODE_STRUCT
21721 The type is a structure.
21723 @findex TYPE_CODE_UNION
21724 @findex gdb.TYPE_CODE_UNION
21725 @item gdb.TYPE_CODE_UNION
21726 The type is a union.
21728 @findex TYPE_CODE_ENUM
21729 @findex gdb.TYPE_CODE_ENUM
21730 @item gdb.TYPE_CODE_ENUM
21731 The type is an enum.
21733 @findex TYPE_CODE_FLAGS
21734 @findex gdb.TYPE_CODE_FLAGS
21735 @item gdb.TYPE_CODE_FLAGS
21736 A bit flags type, used for things such as status registers.
21738 @findex TYPE_CODE_FUNC
21739 @findex gdb.TYPE_CODE_FUNC
21740 @item gdb.TYPE_CODE_FUNC
21741 The type is a function.
21743 @findex TYPE_CODE_INT
21744 @findex gdb.TYPE_CODE_INT
21745 @item gdb.TYPE_CODE_INT
21746 The type is an integer type.
21748 @findex TYPE_CODE_FLT
21749 @findex gdb.TYPE_CODE_FLT
21750 @item gdb.TYPE_CODE_FLT
21751 A floating point type.
21753 @findex TYPE_CODE_VOID
21754 @findex gdb.TYPE_CODE_VOID
21755 @item gdb.TYPE_CODE_VOID
21756 The special type @code{void}.
21758 @findex TYPE_CODE_SET
21759 @findex gdb.TYPE_CODE_SET
21760 @item gdb.TYPE_CODE_SET
21763 @findex TYPE_CODE_RANGE
21764 @findex gdb.TYPE_CODE_RANGE
21765 @item gdb.TYPE_CODE_RANGE
21766 A range type, that is, an integer type with bounds.
21768 @findex TYPE_CODE_STRING
21769 @findex gdb.TYPE_CODE_STRING
21770 @item gdb.TYPE_CODE_STRING
21771 A string type. Note that this is only used for certain languages with
21772 language-defined string types; C strings are not represented this way.
21774 @findex TYPE_CODE_BITSTRING
21775 @findex gdb.TYPE_CODE_BITSTRING
21776 @item gdb.TYPE_CODE_BITSTRING
21779 @findex TYPE_CODE_ERROR
21780 @findex gdb.TYPE_CODE_ERROR
21781 @item gdb.TYPE_CODE_ERROR
21782 An unknown or erroneous type.
21784 @findex TYPE_CODE_METHOD
21785 @findex gdb.TYPE_CODE_METHOD
21786 @item gdb.TYPE_CODE_METHOD
21787 A method type, as found in C@t{++} or Java.
21789 @findex TYPE_CODE_METHODPTR
21790 @findex gdb.TYPE_CODE_METHODPTR
21791 @item gdb.TYPE_CODE_METHODPTR
21792 A pointer-to-member-function.
21794 @findex TYPE_CODE_MEMBERPTR
21795 @findex gdb.TYPE_CODE_MEMBERPTR
21796 @item gdb.TYPE_CODE_MEMBERPTR
21797 A pointer-to-member.
21799 @findex TYPE_CODE_REF
21800 @findex gdb.TYPE_CODE_REF
21801 @item gdb.TYPE_CODE_REF
21804 @findex TYPE_CODE_CHAR
21805 @findex gdb.TYPE_CODE_CHAR
21806 @item gdb.TYPE_CODE_CHAR
21809 @findex TYPE_CODE_BOOL
21810 @findex gdb.TYPE_CODE_BOOL
21811 @item gdb.TYPE_CODE_BOOL
21814 @findex TYPE_CODE_COMPLEX
21815 @findex gdb.TYPE_CODE_COMPLEX
21816 @item gdb.TYPE_CODE_COMPLEX
21817 A complex float type.
21819 @findex TYPE_CODE_TYPEDEF
21820 @findex gdb.TYPE_CODE_TYPEDEF
21821 @item gdb.TYPE_CODE_TYPEDEF
21822 A typedef to some other type.
21824 @findex TYPE_CODE_NAMESPACE
21825 @findex gdb.TYPE_CODE_NAMESPACE
21826 @item gdb.TYPE_CODE_NAMESPACE
21827 A C@t{++} namespace.
21829 @findex TYPE_CODE_DECFLOAT
21830 @findex gdb.TYPE_CODE_DECFLOAT
21831 @item gdb.TYPE_CODE_DECFLOAT
21832 A decimal floating point type.
21834 @findex TYPE_CODE_INTERNAL_FUNCTION
21835 @findex gdb.TYPE_CODE_INTERNAL_FUNCTION
21836 @item gdb.TYPE_CODE_INTERNAL_FUNCTION
21837 A function internal to @value{GDBN}. This is the type used to represent
21838 convenience functions.
21841 Further support for types is provided in the @code{gdb.types}
21842 Python module (@pxref{gdb.types}).
21844 @node Pretty Printing API
21845 @subsubsection Pretty Printing API
21847 An example output is provided (@pxref{Pretty Printing}).
21849 A pretty-printer is just an object that holds a value and implements a
21850 specific interface, defined here.
21852 @defun pretty_printer.children (self)
21853 @value{GDBN} will call this method on a pretty-printer to compute the
21854 children of the pretty-printer's value.
21856 This method must return an object conforming to the Python iterator
21857 protocol. Each item returned by the iterator must be a tuple holding
21858 two elements. The first element is the ``name'' of the child; the
21859 second element is the child's value. The value can be any Python
21860 object which is convertible to a @value{GDBN} value.
21862 This method is optional. If it does not exist, @value{GDBN} will act
21863 as though the value has no children.
21866 @defun pretty_printer.display_hint (self)
21867 The CLI may call this method and use its result to change the
21868 formatting of a value. The result will also be supplied to an MI
21869 consumer as a @samp{displayhint} attribute of the variable being
21872 This method is optional. If it does exist, this method must return a
21875 Some display hints are predefined by @value{GDBN}:
21879 Indicate that the object being printed is ``array-like''. The CLI
21880 uses this to respect parameters such as @code{set print elements} and
21881 @code{set print array}.
21884 Indicate that the object being printed is ``map-like'', and that the
21885 children of this value can be assumed to alternate between keys and
21889 Indicate that the object being printed is ``string-like''. If the
21890 printer's @code{to_string} method returns a Python string of some
21891 kind, then @value{GDBN} will call its internal language-specific
21892 string-printing function to format the string. For the CLI this means
21893 adding quotation marks, possibly escaping some characters, respecting
21894 @code{set print elements}, and the like.
21898 @defun pretty_printer.to_string (self)
21899 @value{GDBN} will call this method to display the string
21900 representation of the value passed to the object's constructor.
21902 When printing from the CLI, if the @code{to_string} method exists,
21903 then @value{GDBN} will prepend its result to the values returned by
21904 @code{children}. Exactly how this formatting is done is dependent on
21905 the display hint, and may change as more hints are added. Also,
21906 depending on the print settings (@pxref{Print Settings}), the CLI may
21907 print just the result of @code{to_string} in a stack trace, omitting
21908 the result of @code{children}.
21910 If this method returns a string, it is printed verbatim.
21912 Otherwise, if this method returns an instance of @code{gdb.Value},
21913 then @value{GDBN} prints this value. This may result in a call to
21914 another pretty-printer.
21916 If instead the method returns a Python value which is convertible to a
21917 @code{gdb.Value}, then @value{GDBN} performs the conversion and prints
21918 the resulting value. Again, this may result in a call to another
21919 pretty-printer. Python scalars (integers, floats, and booleans) and
21920 strings are convertible to @code{gdb.Value}; other types are not.
21922 Finally, if this method returns @code{None} then no further operations
21923 are peformed in this method and nothing is printed.
21925 If the result is not one of these types, an exception is raised.
21928 @value{GDBN} provides a function which can be used to look up the
21929 default pretty-printer for a @code{gdb.Value}:
21931 @findex gdb.default_visualizer
21932 @defun gdb.default_visualizer (value)
21933 This function takes a @code{gdb.Value} object as an argument. If a
21934 pretty-printer for this value exists, then it is returned. If no such
21935 printer exists, then this returns @code{None}.
21938 @node Selecting Pretty-Printers
21939 @subsubsection Selecting Pretty-Printers
21941 The Python list @code{gdb.pretty_printers} contains an array of
21942 functions or callable objects that have been registered via addition
21943 as a pretty-printer. Printers in this list are called @code{global}
21944 printers, they're available when debugging all inferiors.
21945 Each @code{gdb.Progspace} contains a @code{pretty_printers} attribute.
21946 Each @code{gdb.Objfile} also contains a @code{pretty_printers}
21949 Each function on these lists is passed a single @code{gdb.Value}
21950 argument and should return a pretty-printer object conforming to the
21951 interface definition above (@pxref{Pretty Printing API}). If a function
21952 cannot create a pretty-printer for the value, it should return
21955 @value{GDBN} first checks the @code{pretty_printers} attribute of each
21956 @code{gdb.Objfile} in the current program space and iteratively calls
21957 each enabled lookup routine in the list for that @code{gdb.Objfile}
21958 until it receives a pretty-printer object.
21959 If no pretty-printer is found in the objfile lists, @value{GDBN} then
21960 searches the pretty-printer list of the current program space,
21961 calling each enabled function until an object is returned.
21962 After these lists have been exhausted, it tries the global
21963 @code{gdb.pretty_printers} list, again calling each enabled function until an
21964 object is returned.
21966 The order in which the objfiles are searched is not specified. For a
21967 given list, functions are always invoked from the head of the list,
21968 and iterated over sequentially until the end of the list, or a printer
21969 object is returned.
21971 For various reasons a pretty-printer may not work.
21972 For example, the underlying data structure may have changed and
21973 the pretty-printer is out of date.
21975 The consequences of a broken pretty-printer are severe enough that
21976 @value{GDBN} provides support for enabling and disabling individual
21977 printers. For example, if @code{print frame-arguments} is on,
21978 a backtrace can become highly illegible if any argument is printed
21979 with a broken printer.
21981 Pretty-printers are enabled and disabled by attaching an @code{enabled}
21982 attribute to the registered function or callable object. If this attribute
21983 is present and its value is @code{False}, the printer is disabled, otherwise
21984 the printer is enabled.
21986 @node Writing a Pretty-Printer
21987 @subsubsection Writing a Pretty-Printer
21988 @cindex writing a pretty-printer
21990 A pretty-printer consists of two parts: a lookup function to detect
21991 if the type is supported, and the printer itself.
21993 Here is an example showing how a @code{std::string} printer might be
21994 written. @xref{Pretty Printing API}, for details on the API this class
21998 class StdStringPrinter(object):
21999 "Print a std::string"
22001 def __init__(self, val):
22004 def to_string(self):
22005 return self.val['_M_dataplus']['_M_p']
22007 def display_hint(self):
22011 And here is an example showing how a lookup function for the printer
22012 example above might be written.
22015 def str_lookup_function(val):
22016 lookup_tag = val.type.tag
22017 if lookup_tag == None:
22019 regex = re.compile("^std::basic_string<char,.*>$")
22020 if regex.match(lookup_tag):
22021 return StdStringPrinter(val)
22025 The example lookup function extracts the value's type, and attempts to
22026 match it to a type that it can pretty-print. If it is a type the
22027 printer can pretty-print, it will return a printer object. If not, it
22028 returns @code{None}.
22030 We recommend that you put your core pretty-printers into a Python
22031 package. If your pretty-printers are for use with a library, we
22032 further recommend embedding a version number into the package name.
22033 This practice will enable @value{GDBN} to load multiple versions of
22034 your pretty-printers at the same time, because they will have
22037 You should write auto-loaded code (@pxref{Auto-loading}) such that it
22038 can be evaluated multiple times without changing its meaning. An
22039 ideal auto-load file will consist solely of @code{import}s of your
22040 printer modules, followed by a call to a register pretty-printers with
22041 the current objfile.
22043 Taken as a whole, this approach will scale nicely to multiple
22044 inferiors, each potentially using a different library version.
22045 Embedding a version number in the Python package name will ensure that
22046 @value{GDBN} is able to load both sets of printers simultaneously.
22047 Then, because the search for pretty-printers is done by objfile, and
22048 because your auto-loaded code took care to register your library's
22049 printers with a specific objfile, @value{GDBN} will find the correct
22050 printers for the specific version of the library used by each
22053 To continue the @code{std::string} example (@pxref{Pretty Printing API}),
22054 this code might appear in @code{gdb.libstdcxx.v6}:
22057 def register_printers(objfile):
22058 objfile.pretty_printers.add(str_lookup_function)
22062 And then the corresponding contents of the auto-load file would be:
22065 import gdb.libstdcxx.v6
22066 gdb.libstdcxx.v6.register_printers(gdb.current_objfile())
22069 The previous example illustrates a basic pretty-printer.
22070 There are a few things that can be improved on.
22071 The printer doesn't have a name, making it hard to identify in a
22072 list of installed printers. The lookup function has a name, but
22073 lookup functions can have arbitrary, even identical, names.
22075 Second, the printer only handles one type, whereas a library typically has
22076 several types. One could install a lookup function for each desired type
22077 in the library, but one could also have a single lookup function recognize
22078 several types. The latter is the conventional way this is handled.
22079 If a pretty-printer can handle multiple data types, then its
22080 @dfn{subprinters} are the printers for the individual data types.
22082 The @code{gdb.printing} module provides a formal way of solving these
22083 problems (@pxref{gdb.printing}).
22084 Here is another example that handles multiple types.
22086 These are the types we are going to pretty-print:
22089 struct foo @{ int a, b; @};
22090 struct bar @{ struct foo x, y; @};
22093 Here are the printers:
22097 """Print a foo object."""
22099 def __init__(self, val):
22102 def to_string(self):
22103 return ("a=<" + str(self.val["a"]) +
22104 "> b=<" + str(self.val["b"]) + ">")
22107 """Print a bar object."""
22109 def __init__(self, val):
22112 def to_string(self):
22113 return ("x=<" + str(self.val["x"]) +
22114 "> y=<" + str(self.val["y"]) + ">")
22117 This example doesn't need a lookup function, that is handled by the
22118 @code{gdb.printing} module. Instead a function is provided to build up
22119 the object that handles the lookup.
22122 import gdb.printing
22124 def build_pretty_printer():
22125 pp = gdb.printing.RegexpCollectionPrettyPrinter(
22127 pp.add_printer('foo', '^foo$', fooPrinter)
22128 pp.add_printer('bar', '^bar$', barPrinter)
22132 And here is the autoload support:
22135 import gdb.printing
22137 gdb.printing.register_pretty_printer(
22138 gdb.current_objfile(),
22139 my_library.build_pretty_printer())
22142 Finally, when this printer is loaded into @value{GDBN}, here is the
22143 corresponding output of @samp{info pretty-printer}:
22146 (gdb) info pretty-printer
22153 @node Inferiors In Python
22154 @subsubsection Inferiors In Python
22155 @cindex inferiors in Python
22157 @findex gdb.Inferior
22158 Programs which are being run under @value{GDBN} are called inferiors
22159 (@pxref{Inferiors and Programs}). Python scripts can access
22160 information about and manipulate inferiors controlled by @value{GDBN}
22161 via objects of the @code{gdb.Inferior} class.
22163 The following inferior-related functions are available in the @code{gdb}
22166 @defun gdb.inferiors ()
22167 Return a tuple containing all inferior objects.
22170 @defun gdb.selected_inferior ()
22171 Return an object representing the current inferior.
22174 A @code{gdb.Inferior} object has the following attributes:
22177 @defvar Inferior.num
22178 ID of inferior, as assigned by GDB.
22181 @defvar Inferior.pid
22182 Process ID of the inferior, as assigned by the underlying operating
22186 @defvar Inferior.was_attached
22187 Boolean signaling whether the inferior was created using `attach', or
22188 started by @value{GDBN} itself.
22192 A @code{gdb.Inferior} object has the following methods:
22195 @defun Inferior.is_valid ()
22196 Returns @code{True} if the @code{gdb.Inferior} object is valid,
22197 @code{False} if not. A @code{gdb.Inferior} object will become invalid
22198 if the inferior no longer exists within @value{GDBN}. All other
22199 @code{gdb.Inferior} methods will throw an exception if it is invalid
22200 at the time the method is called.
22203 @defun Inferior.threads ()
22204 This method returns a tuple holding all the threads which are valid
22205 when it is called. If there are no valid threads, the method will
22206 return an empty tuple.
22209 @findex gdb.read_memory
22210 @defun Inferior.read_memory (address, length)
22211 Read @var{length} bytes of memory from the inferior, starting at
22212 @var{address}. Returns a buffer object, which behaves much like an array
22213 or a string. It can be modified and given to the @code{gdb.write_memory}
22217 @findex gdb.write_memory
22218 @defun Inferior.write_memory (address, buffer @r{[}, length@r{]})
22219 Write the contents of @var{buffer} to the inferior, starting at
22220 @var{address}. The @var{buffer} parameter must be a Python object
22221 which supports the buffer protocol, i.e., a string, an array or the
22222 object returned from @code{gdb.read_memory}. If given, @var{length}
22223 determines the number of bytes from @var{buffer} to be written.
22226 @findex gdb.search_memory
22227 @defun Inferior.search_memory (address, length, pattern)
22228 Search a region of the inferior memory starting at @var{address} with
22229 the given @var{length} using the search pattern supplied in
22230 @var{pattern}. The @var{pattern} parameter must be a Python object
22231 which supports the buffer protocol, i.e., a string, an array or the
22232 object returned from @code{gdb.read_memory}. Returns a Python @code{Long}
22233 containing the address where the pattern was found, or @code{None} if
22234 the pattern could not be found.
22238 @node Events In Python
22239 @subsubsection Events In Python
22240 @cindex inferior events in Python
22242 @value{GDBN} provides a general event facility so that Python code can be
22243 notified of various state changes, particularly changes that occur in
22246 An @dfn{event} is just an object that describes some state change. The
22247 type of the object and its attributes will vary depending on the details
22248 of the change. All the existing events are described below.
22250 In order to be notified of an event, you must register an event handler
22251 with an @dfn{event registry}. An event registry is an object in the
22252 @code{gdb.events} module which dispatches particular events. A registry
22253 provides methods to register and unregister event handlers:
22256 @defun EventRegistry.connect (object)
22257 Add the given callable @var{object} to the registry. This object will be
22258 called when an event corresponding to this registry occurs.
22261 @defun EventRegistry.disconnect (object)
22262 Remove the given @var{object} from the registry. Once removed, the object
22263 will no longer receive notifications of events.
22267 Here is an example:
22270 def exit_handler (event):
22271 print "event type: exit"
22272 print "exit code: %d" % (event.exit_code)
22274 gdb.events.exited.connect (exit_handler)
22277 In the above example we connect our handler @code{exit_handler} to the
22278 registry @code{events.exited}. Once connected, @code{exit_handler} gets
22279 called when the inferior exits. The argument @dfn{event} in this example is
22280 of type @code{gdb.ExitedEvent}. As you can see in the example the
22281 @code{ExitedEvent} object has an attribute which indicates the exit code of
22284 The following is a listing of the event registries that are available and
22285 details of the events they emit:
22290 Emits @code{gdb.ThreadEvent}.
22292 Some events can be thread specific when @value{GDBN} is running in non-stop
22293 mode. When represented in Python, these events all extend
22294 @code{gdb.ThreadEvent}. Note, this event is not emitted directly; instead,
22295 events which are emitted by this or other modules might extend this event.
22296 Examples of these events are @code{gdb.BreakpointEvent} and
22297 @code{gdb.ContinueEvent}.
22300 @defvar ThreadEvent.inferior_thread
22301 In non-stop mode this attribute will be set to the specific thread which was
22302 involved in the emitted event. Otherwise, it will be set to @code{None}.
22306 Emits @code{gdb.ContinueEvent} which extends @code{gdb.ThreadEvent}.
22308 This event indicates that the inferior has been continued after a stop. For
22309 inherited attribute refer to @code{gdb.ThreadEvent} above.
22311 @item events.exited
22312 Emits @code{events.ExitedEvent} which indicates that the inferior has exited.
22313 @code{events.ExitedEvent} has two attributes:
22315 @defvar ExitedEvent.exit_code
22316 An integer representing the exit code, if available, which the inferior
22317 has returned. (The exit code could be unavailable if, for example,
22318 @value{GDBN} detaches from the inferior.) If the exit code is unavailable,
22319 the attribute does not exist.
22321 @defvar ExitedEvent inferior
22322 A reference to the inferior which triggered the @code{exited} event.
22327 Emits @code{gdb.StopEvent} which extends @code{gdb.ThreadEvent}.
22329 Indicates that the inferior has stopped. All events emitted by this registry
22330 extend StopEvent. As a child of @code{gdb.ThreadEvent}, @code{gdb.StopEvent}
22331 will indicate the stopped thread when @value{GDBN} is running in non-stop
22332 mode. Refer to @code{gdb.ThreadEvent} above for more details.
22334 Emits @code{gdb.SignalEvent} which extends @code{gdb.StopEvent}.
22336 This event indicates that the inferior or one of its threads has received as
22337 signal. @code{gdb.SignalEvent} has the following attributes:
22340 @defvar SignalEvent.stop_signal
22341 A string representing the signal received by the inferior. A list of possible
22342 signal values can be obtained by running the command @code{info signals} in
22343 the @value{GDBN} command prompt.
22347 Also emits @code{gdb.BreakpointEvent} which extends @code{gdb.StopEvent}.
22349 @code{gdb.BreakpointEvent} event indicates that one or more breakpoints have
22350 been hit, and has the following attributes:
22353 @defvar BreakpointEvent.breakpoints
22354 A sequence containing references to all the breakpoints (type
22355 @code{gdb.Breakpoint}) that were hit.
22356 @xref{Breakpoints In Python}, for details of the @code{gdb.Breakpoint} object.
22358 @defvar BreakpointEvent.breakpoint
22359 A reference to the first breakpoint that was hit.
22360 This function is maintained for backward compatibility and is now deprecated
22361 in favor of the @code{gdb.BreakpointEvent.breakpoints} attribute.
22365 @item events.new_objfile
22366 Emits @code{gdb.NewObjFileEvent} which indicates that a new object file has
22367 been loaded by @value{GDBN}. @code{gdb.NewObjFileEvent} has one attribute:
22370 @defvar NewObjFileEvent.new_objfile
22371 A reference to the object file (@code{gdb.Objfile}) which has been loaded.
22372 @xref{Objfiles In Python}, for details of the @code{gdb.Objfile} object.
22378 @node Threads In Python
22379 @subsubsection Threads In Python
22380 @cindex threads in python
22382 @findex gdb.InferiorThread
22383 Python scripts can access information about, and manipulate inferior threads
22384 controlled by @value{GDBN}, via objects of the @code{gdb.InferiorThread} class.
22386 The following thread-related functions are available in the @code{gdb}
22389 @findex gdb.selected_thread
22390 @defun gdb.selected_thread ()
22391 This function returns the thread object for the selected thread. If there
22392 is no selected thread, this will return @code{None}.
22395 A @code{gdb.InferiorThread} object has the following attributes:
22398 @defvar InferiorThread.name
22399 The name of the thread. If the user specified a name using
22400 @code{thread name}, then this returns that name. Otherwise, if an
22401 OS-supplied name is available, then it is returned. Otherwise, this
22402 returns @code{None}.
22404 This attribute can be assigned to. The new value must be a string
22405 object, which sets the new name, or @code{None}, which removes any
22406 user-specified thread name.
22409 @defvar InferiorThread.num
22410 ID of the thread, as assigned by GDB.
22413 @defvar InferiorThread.ptid
22414 ID of the thread, as assigned by the operating system. This attribute is a
22415 tuple containing three integers. The first is the Process ID (PID); the second
22416 is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID).
22417 Either the LWPID or TID may be 0, which indicates that the operating system
22418 does not use that identifier.
22422 A @code{gdb.InferiorThread} object has the following methods:
22425 @defun InferiorThread.is_valid ()
22426 Returns @code{True} if the @code{gdb.InferiorThread} object is valid,
22427 @code{False} if not. A @code{gdb.InferiorThread} object will become
22428 invalid if the thread exits, or the inferior that the thread belongs
22429 is deleted. All other @code{gdb.InferiorThread} methods will throw an
22430 exception if it is invalid at the time the method is called.
22433 @defun InferiorThread.switch ()
22434 This changes @value{GDBN}'s currently selected thread to the one represented
22438 @defun InferiorThread.is_stopped ()
22439 Return a Boolean indicating whether the thread is stopped.
22442 @defun InferiorThread.is_running ()
22443 Return a Boolean indicating whether the thread is running.
22446 @defun InferiorThread.is_exited ()
22447 Return a Boolean indicating whether the thread is exited.
22451 @node Commands In Python
22452 @subsubsection Commands In Python
22454 @cindex commands in python
22455 @cindex python commands
22456 You can implement new @value{GDBN} CLI commands in Python. A CLI
22457 command is implemented using an instance of the @code{gdb.Command}
22458 class, most commonly using a subclass.
22460 @defun Command.__init__ (name, @var{command_class} @r{[}, var{completer_class} @r{[}, var{prefix}@r{]]})
22461 The object initializer for @code{Command} registers the new command
22462 with @value{GDBN}. This initializer is normally invoked from the
22463 subclass' own @code{__init__} method.
22465 @var{name} is the name of the command. If @var{name} consists of
22466 multiple words, then the initial words are looked for as prefix
22467 commands. In this case, if one of the prefix commands does not exist,
22468 an exception is raised.
22470 There is no support for multi-line commands.
22472 @var{command_class} should be one of the @samp{COMMAND_} constants
22473 defined below. This argument tells @value{GDBN} how to categorize the
22474 new command in the help system.
22476 @var{completer_class} is an optional argument. If given, it should be
22477 one of the @samp{COMPLETE_} constants defined below. This argument
22478 tells @value{GDBN} how to perform completion for this command. If not
22479 given, @value{GDBN} will attempt to complete using the object's
22480 @code{complete} method (see below); if no such method is found, an
22481 error will occur when completion is attempted.
22483 @var{prefix} is an optional argument. If @code{True}, then the new
22484 command is a prefix command; sub-commands of this command may be
22487 The help text for the new command is taken from the Python
22488 documentation string for the command's class, if there is one. If no
22489 documentation string is provided, the default value ``This command is
22490 not documented.'' is used.
22493 @cindex don't repeat Python command
22494 @defun Command.dont_repeat ()
22495 By default, a @value{GDBN} command is repeated when the user enters a
22496 blank line at the command prompt. A command can suppress this
22497 behavior by invoking the @code{dont_repeat} method. This is similar
22498 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
22501 @defun Command.invoke (argument, from_tty)
22502 This method is called by @value{GDBN} when this command is invoked.
22504 @var{argument} is a string. It is the argument to the command, after
22505 leading and trailing whitespace has been stripped.
22507 @var{from_tty} is a boolean argument. When true, this means that the
22508 command was entered by the user at the terminal; when false it means
22509 that the command came from elsewhere.
22511 If this method throws an exception, it is turned into a @value{GDBN}
22512 @code{error} call. Otherwise, the return value is ignored.
22514 @findex gdb.string_to_argv
22515 To break @var{argument} up into an argv-like string use
22516 @code{gdb.string_to_argv}. This function behaves identically to
22517 @value{GDBN}'s internal argument lexer @code{buildargv}.
22518 It is recommended to use this for consistency.
22519 Arguments are separated by spaces and may be quoted.
22523 print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
22524 ['1', '2 "3', '4 "5', "6 '7"]
22529 @cindex completion of Python commands
22530 @defun Command.complete (text, word)
22531 This method is called by @value{GDBN} when the user attempts
22532 completion on this command. All forms of completion are handled by
22533 this method, that is, the @key{TAB} and @key{M-?} key bindings
22534 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
22537 The arguments @var{text} and @var{word} are both strings. @var{text}
22538 holds the complete command line up to the cursor's location.
22539 @var{word} holds the last word of the command line; this is computed
22540 using a word-breaking heuristic.
22542 The @code{complete} method can return several values:
22545 If the return value is a sequence, the contents of the sequence are
22546 used as the completions. It is up to @code{complete} to ensure that the
22547 contents actually do complete the word. A zero-length sequence is
22548 allowed, it means that there were no completions available. Only
22549 string elements of the sequence are used; other elements in the
22550 sequence are ignored.
22553 If the return value is one of the @samp{COMPLETE_} constants defined
22554 below, then the corresponding @value{GDBN}-internal completion
22555 function is invoked, and its result is used.
22558 All other results are treated as though there were no available
22563 When a new command is registered, it must be declared as a member of
22564 some general class of commands. This is used to classify top-level
22565 commands in the on-line help system; note that prefix commands are not
22566 listed under their own category but rather that of their top-level
22567 command. The available classifications are represented by constants
22568 defined in the @code{gdb} module:
22571 @findex COMMAND_NONE
22572 @findex gdb.COMMAND_NONE
22573 @item gdb.COMMAND_NONE
22574 The command does not belong to any particular class. A command in
22575 this category will not be displayed in any of the help categories.
22577 @findex COMMAND_RUNNING
22578 @findex gdb.COMMAND_RUNNING
22579 @item gdb.COMMAND_RUNNING
22580 The command is related to running the inferior. For example,
22581 @code{start}, @code{step}, and @code{continue} are in this category.
22582 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
22583 commands in this category.
22585 @findex COMMAND_DATA
22586 @findex gdb.COMMAND_DATA
22587 @item gdb.COMMAND_DATA
22588 The command is related to data or variables. For example,
22589 @code{call}, @code{find}, and @code{print} are in this category. Type
22590 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
22593 @findex COMMAND_STACK
22594 @findex gdb.COMMAND_STACK
22595 @item gdb.COMMAND_STACK
22596 The command has to do with manipulation of the stack. For example,
22597 @code{backtrace}, @code{frame}, and @code{return} are in this
22598 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
22599 list of commands in this category.
22601 @findex COMMAND_FILES
22602 @findex gdb.COMMAND_FILES
22603 @item gdb.COMMAND_FILES
22604 This class is used for file-related commands. For example,
22605 @code{file}, @code{list} and @code{section} are in this category.
22606 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
22607 commands in this category.
22609 @findex COMMAND_SUPPORT
22610 @findex gdb.COMMAND_SUPPORT
22611 @item gdb.COMMAND_SUPPORT
22612 This should be used for ``support facilities'', generally meaning
22613 things that are useful to the user when interacting with @value{GDBN},
22614 but not related to the state of the inferior. For example,
22615 @code{help}, @code{make}, and @code{shell} are in this category. Type
22616 @kbd{help support} at the @value{GDBN} prompt to see a list of
22617 commands in this category.
22619 @findex COMMAND_STATUS
22620 @findex gdb.COMMAND_STATUS
22621 @item gdb.COMMAND_STATUS
22622 The command is an @samp{info}-related command, that is, related to the
22623 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
22624 and @code{show} are in this category. Type @kbd{help status} at the
22625 @value{GDBN} prompt to see a list of commands in this category.
22627 @findex COMMAND_BREAKPOINTS
22628 @findex gdb.COMMAND_BREAKPOINTS
22629 @item gdb.COMMAND_BREAKPOINTS
22630 The command has to do with breakpoints. For example, @code{break},
22631 @code{clear}, and @code{delete} are in this category. Type @kbd{help
22632 breakpoints} at the @value{GDBN} prompt to see a list of commands in
22635 @findex COMMAND_TRACEPOINTS
22636 @findex gdb.COMMAND_TRACEPOINTS
22637 @item gdb.COMMAND_TRACEPOINTS
22638 The command has to do with tracepoints. For example, @code{trace},
22639 @code{actions}, and @code{tfind} are in this category. Type
22640 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
22641 commands in this category.
22643 @findex COMMAND_OBSCURE
22644 @findex gdb.COMMAND_OBSCURE
22645 @item gdb.COMMAND_OBSCURE
22646 The command is only used in unusual circumstances, or is not of
22647 general interest to users. For example, @code{checkpoint},
22648 @code{fork}, and @code{stop} are in this category. Type @kbd{help
22649 obscure} at the @value{GDBN} prompt to see a list of commands in this
22652 @findex COMMAND_MAINTENANCE
22653 @findex gdb.COMMAND_MAINTENANCE
22654 @item gdb.COMMAND_MAINTENANCE
22655 The command is only useful to @value{GDBN} maintainers. The
22656 @code{maintenance} and @code{flushregs} commands are in this category.
22657 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
22658 commands in this category.
22661 A new command can use a predefined completion function, either by
22662 specifying it via an argument at initialization, or by returning it
22663 from the @code{complete} method. These predefined completion
22664 constants are all defined in the @code{gdb} module:
22667 @findex COMPLETE_NONE
22668 @findex gdb.COMPLETE_NONE
22669 @item gdb.COMPLETE_NONE
22670 This constant means that no completion should be done.
22672 @findex COMPLETE_FILENAME
22673 @findex gdb.COMPLETE_FILENAME
22674 @item gdb.COMPLETE_FILENAME
22675 This constant means that filename completion should be performed.
22677 @findex COMPLETE_LOCATION
22678 @findex gdb.COMPLETE_LOCATION
22679 @item gdb.COMPLETE_LOCATION
22680 This constant means that location completion should be done.
22681 @xref{Specify Location}.
22683 @findex COMPLETE_COMMAND
22684 @findex gdb.COMPLETE_COMMAND
22685 @item gdb.COMPLETE_COMMAND
22686 This constant means that completion should examine @value{GDBN}
22689 @findex COMPLETE_SYMBOL
22690 @findex gdb.COMPLETE_SYMBOL
22691 @item gdb.COMPLETE_SYMBOL
22692 This constant means that completion should be done using symbol names
22696 The following code snippet shows how a trivial CLI command can be
22697 implemented in Python:
22700 class HelloWorld (gdb.Command):
22701 """Greet the whole world."""
22703 def __init__ (self):
22704 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_OBSCURE)
22706 def invoke (self, arg, from_tty):
22707 print "Hello, World!"
22712 The last line instantiates the class, and is necessary to trigger the
22713 registration of the command with @value{GDBN}. Depending on how the
22714 Python code is read into @value{GDBN}, you may need to import the
22715 @code{gdb} module explicitly.
22717 @node Parameters In Python
22718 @subsubsection Parameters In Python
22720 @cindex parameters in python
22721 @cindex python parameters
22722 @tindex gdb.Parameter
22724 You can implement new @value{GDBN} parameters using Python. A new
22725 parameter is implemented as an instance of the @code{gdb.Parameter}
22728 Parameters are exposed to the user via the @code{set} and
22729 @code{show} commands. @xref{Help}.
22731 There are many parameters that already exist and can be set in
22732 @value{GDBN}. Two examples are: @code{set follow fork} and
22733 @code{set charset}. Setting these parameters influences certain
22734 behavior in @value{GDBN}. Similarly, you can define parameters that
22735 can be used to influence behavior in custom Python scripts and commands.
22737 @defun Parameter.__init__ (name, @var{command-class}, @var{parameter-class} @r{[}, @var{enum-sequence}@r{]})
22738 The object initializer for @code{Parameter} registers the new
22739 parameter with @value{GDBN}. This initializer is normally invoked
22740 from the subclass' own @code{__init__} method.
22742 @var{name} is the name of the new parameter. If @var{name} consists
22743 of multiple words, then the initial words are looked for as prefix
22744 parameters. An example of this can be illustrated with the
22745 @code{set print} set of parameters. If @var{name} is
22746 @code{print foo}, then @code{print} will be searched as the prefix
22747 parameter. In this case the parameter can subsequently be accessed in
22748 @value{GDBN} as @code{set print foo}.
22750 If @var{name} consists of multiple words, and no prefix parameter group
22751 can be found, an exception is raised.
22753 @var{command-class} should be one of the @samp{COMMAND_} constants
22754 (@pxref{Commands In Python}). This argument tells @value{GDBN} how to
22755 categorize the new parameter in the help system.
22757 @var{parameter-class} should be one of the @samp{PARAM_} constants
22758 defined below. This argument tells @value{GDBN} the type of the new
22759 parameter; this information is used for input validation and
22762 If @var{parameter-class} is @code{PARAM_ENUM}, then
22763 @var{enum-sequence} must be a sequence of strings. These strings
22764 represent the possible values for the parameter.
22766 If @var{parameter-class} is not @code{PARAM_ENUM}, then the presence
22767 of a fourth argument will cause an exception to be thrown.
22769 The help text for the new parameter is taken from the Python
22770 documentation string for the parameter's class, if there is one. If
22771 there is no documentation string, a default value is used.
22774 @defvar Parameter.set_doc
22775 If this attribute exists, and is a string, then its value is used as
22776 the help text for this parameter's @code{set} command. The value is
22777 examined when @code{Parameter.__init__} is invoked; subsequent changes
22781 @defvar Parameter.show_doc
22782 If this attribute exists, and is a string, then its value is used as
22783 the help text for this parameter's @code{show} command. The value is
22784 examined when @code{Parameter.__init__} is invoked; subsequent changes
22788 @defvar Parameter.value
22789 The @code{value} attribute holds the underlying value of the
22790 parameter. It can be read and assigned to just as any other
22791 attribute. @value{GDBN} does validation when assignments are made.
22794 There are two methods that should be implemented in any
22795 @code{Parameter} class. These are:
22797 @defun Parameter.get_set_string (self)
22798 @value{GDBN} will call this method when a @var{parameter}'s value has
22799 been changed via the @code{set} API (for example, @kbd{set foo off}).
22800 The @code{value} attribute has already been populated with the new
22801 value and may be used in output. This method must return a string.
22804 @defun Parameter.get_show_string (self, svalue)
22805 @value{GDBN} will call this method when a @var{parameter}'s
22806 @code{show} API has been invoked (for example, @kbd{show foo}). The
22807 argument @code{svalue} receives the string representation of the
22808 current value. This method must return a string.
22811 When a new parameter is defined, its type must be specified. The
22812 available types are represented by constants defined in the @code{gdb}
22816 @findex PARAM_BOOLEAN
22817 @findex gdb.PARAM_BOOLEAN
22818 @item gdb.PARAM_BOOLEAN
22819 The value is a plain boolean. The Python boolean values, @code{True}
22820 and @code{False} are the only valid values.
22822 @findex PARAM_AUTO_BOOLEAN
22823 @findex gdb.PARAM_AUTO_BOOLEAN
22824 @item gdb.PARAM_AUTO_BOOLEAN
22825 The value has three possible states: true, false, and @samp{auto}. In
22826 Python, true and false are represented using boolean constants, and
22827 @samp{auto} is represented using @code{None}.
22829 @findex PARAM_UINTEGER
22830 @findex gdb.PARAM_UINTEGER
22831 @item gdb.PARAM_UINTEGER
22832 The value is an unsigned integer. The value of 0 should be
22833 interpreted to mean ``unlimited''.
22835 @findex PARAM_INTEGER
22836 @findex gdb.PARAM_INTEGER
22837 @item gdb.PARAM_INTEGER
22838 The value is a signed integer. The value of 0 should be interpreted
22839 to mean ``unlimited''.
22841 @findex PARAM_STRING
22842 @findex gdb.PARAM_STRING
22843 @item gdb.PARAM_STRING
22844 The value is a string. When the user modifies the string, any escape
22845 sequences, such as @samp{\t}, @samp{\f}, and octal escapes, are
22846 translated into corresponding characters and encoded into the current
22849 @findex PARAM_STRING_NOESCAPE
22850 @findex gdb.PARAM_STRING_NOESCAPE
22851 @item gdb.PARAM_STRING_NOESCAPE
22852 The value is a string. When the user modifies the string, escapes are
22853 passed through untranslated.
22855 @findex PARAM_OPTIONAL_FILENAME
22856 @findex gdb.PARAM_OPTIONAL_FILENAME
22857 @item gdb.PARAM_OPTIONAL_FILENAME
22858 The value is a either a filename (a string), or @code{None}.
22860 @findex PARAM_FILENAME
22861 @findex gdb.PARAM_FILENAME
22862 @item gdb.PARAM_FILENAME
22863 The value is a filename. This is just like
22864 @code{PARAM_STRING_NOESCAPE}, but uses file names for completion.
22866 @findex PARAM_ZINTEGER
22867 @findex gdb.PARAM_ZINTEGER
22868 @item gdb.PARAM_ZINTEGER
22869 The value is an integer. This is like @code{PARAM_INTEGER}, except 0
22870 is interpreted as itself.
22873 @findex gdb.PARAM_ENUM
22874 @item gdb.PARAM_ENUM
22875 The value is a string, which must be one of a collection string
22876 constants provided when the parameter is created.
22879 @node Functions In Python
22880 @subsubsection Writing new convenience functions
22882 @cindex writing convenience functions
22883 @cindex convenience functions in python
22884 @cindex python convenience functions
22885 @tindex gdb.Function
22887 You can implement new convenience functions (@pxref{Convenience Vars})
22888 in Python. A convenience function is an instance of a subclass of the
22889 class @code{gdb.Function}.
22891 @defun Function.__init__ (name)
22892 The initializer for @code{Function} registers the new function with
22893 @value{GDBN}. The argument @var{name} is the name of the function,
22894 a string. The function will be visible to the user as a convenience
22895 variable of type @code{internal function}, whose name is the same as
22896 the given @var{name}.
22898 The documentation for the new function is taken from the documentation
22899 string for the new class.
22902 @defun Function.invoke (@var{*args})
22903 When a convenience function is evaluated, its arguments are converted
22904 to instances of @code{gdb.Value}, and then the function's
22905 @code{invoke} method is called. Note that @value{GDBN} does not
22906 predetermine the arity of convenience functions. Instead, all
22907 available arguments are passed to @code{invoke}, following the
22908 standard Python calling convention. In particular, a convenience
22909 function can have default values for parameters without ill effect.
22911 The return value of this method is used as its value in the enclosing
22912 expression. If an ordinary Python value is returned, it is converted
22913 to a @code{gdb.Value} following the usual rules.
22916 The following code snippet shows how a trivial convenience function can
22917 be implemented in Python:
22920 class Greet (gdb.Function):
22921 """Return string to greet someone.
22922 Takes a name as argument."""
22924 def __init__ (self):
22925 super (Greet, self).__init__ ("greet")
22927 def invoke (self, name):
22928 return "Hello, %s!" % name.string ()
22933 The last line instantiates the class, and is necessary to trigger the
22934 registration of the function with @value{GDBN}. Depending on how the
22935 Python code is read into @value{GDBN}, you may need to import the
22936 @code{gdb} module explicitly.
22938 @node Progspaces In Python
22939 @subsubsection Program Spaces In Python
22941 @cindex progspaces in python
22942 @tindex gdb.Progspace
22944 A program space, or @dfn{progspace}, represents a symbolic view
22945 of an address space.
22946 It consists of all of the objfiles of the program.
22947 @xref{Objfiles In Python}.
22948 @xref{Inferiors and Programs, program spaces}, for more details
22949 about program spaces.
22951 The following progspace-related functions are available in the
22954 @findex gdb.current_progspace
22955 @defun gdb.current_progspace ()
22956 This function returns the program space of the currently selected inferior.
22957 @xref{Inferiors and Programs}.
22960 @findex gdb.progspaces
22961 @defun gdb.progspaces ()
22962 Return a sequence of all the progspaces currently known to @value{GDBN}.
22965 Each progspace is represented by an instance of the @code{gdb.Progspace}
22968 @defvar Progspace.filename
22969 The file name of the progspace as a string.
22972 @defvar Progspace.pretty_printers
22973 The @code{pretty_printers} attribute is a list of functions. It is
22974 used to look up pretty-printers. A @code{Value} is passed to each
22975 function in order; if the function returns @code{None}, then the
22976 search continues. Otherwise, the return value should be an object
22977 which is used to format the value. @xref{Pretty Printing API}, for more
22981 @node Objfiles In Python
22982 @subsubsection Objfiles In Python
22984 @cindex objfiles in python
22985 @tindex gdb.Objfile
22987 @value{GDBN} loads symbols for an inferior from various
22988 symbol-containing files (@pxref{Files}). These include the primary
22989 executable file, any shared libraries used by the inferior, and any
22990 separate debug info files (@pxref{Separate Debug Files}).
22991 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
22993 The following objfile-related functions are available in the
22996 @findex gdb.current_objfile
22997 @defun gdb.current_objfile ()
22998 When auto-loading a Python script (@pxref{Auto-loading}), @value{GDBN}
22999 sets the ``current objfile'' to the corresponding objfile. This
23000 function returns the current objfile. If there is no current objfile,
23001 this function returns @code{None}.
23004 @findex gdb.objfiles
23005 @defun gdb.objfiles ()
23006 Return a sequence of all the objfiles current known to @value{GDBN}.
23007 @xref{Objfiles In Python}.
23010 Each objfile is represented by an instance of the @code{gdb.Objfile}
23013 @defvar Objfile.filename
23014 The file name of the objfile as a string.
23017 @defvar Objfile.pretty_printers
23018 The @code{pretty_printers} attribute is a list of functions. It is
23019 used to look up pretty-printers. A @code{Value} is passed to each
23020 function in order; if the function returns @code{None}, then the
23021 search continues. Otherwise, the return value should be an object
23022 which is used to format the value. @xref{Pretty Printing API}, for more
23026 A @code{gdb.Objfile} object has the following methods:
23028 @defun Objfile.is_valid ()
23029 Returns @code{True} if the @code{gdb.Objfile} object is valid,
23030 @code{False} if not. A @code{gdb.Objfile} object can become invalid
23031 if the object file it refers to is not loaded in @value{GDBN} any
23032 longer. All other @code{gdb.Objfile} methods will throw an exception
23033 if it is invalid at the time the method is called.
23036 @node Frames In Python
23037 @subsubsection Accessing inferior stack frames from Python.
23039 @cindex frames in python
23040 When the debugged program stops, @value{GDBN} is able to analyze its call
23041 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
23042 represents a frame in the stack. A @code{gdb.Frame} object is only valid
23043 while its corresponding frame exists in the inferior's stack. If you try
23044 to use an invalid frame object, @value{GDBN} will throw a @code{gdb.error}
23045 exception (@pxref{Exception Handling}).
23047 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
23051 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
23055 The following frame-related functions are available in the @code{gdb} module:
23057 @findex gdb.selected_frame
23058 @defun gdb.selected_frame ()
23059 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
23062 @findex gdb.newest_frame
23063 @defun gdb.newest_frame ()
23064 Return the newest frame object for the selected thread.
23067 @defun gdb.frame_stop_reason_string (reason)
23068 Return a string explaining the reason why @value{GDBN} stopped unwinding
23069 frames, as expressed by the given @var{reason} code (an integer, see the
23070 @code{unwind_stop_reason} method further down in this section).
23073 A @code{gdb.Frame} object has the following methods:
23076 @defun Frame.is_valid ()
23077 Returns true if the @code{gdb.Frame} object is valid, false if not.
23078 A frame object can become invalid if the frame it refers to doesn't
23079 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
23080 an exception if it is invalid at the time the method is called.
23083 @defun Frame.name ()
23084 Returns the function name of the frame, or @code{None} if it can't be
23088 @defun Frame.type ()
23089 Returns the type of the frame. The value can be one of:
23091 @item gdb.NORMAL_FRAME
23092 An ordinary stack frame.
23094 @item gdb.DUMMY_FRAME
23095 A fake stack frame that was created by @value{GDBN} when performing an
23096 inferior function call.
23098 @item gdb.INLINE_FRAME
23099 A frame representing an inlined function. The function was inlined
23100 into a @code{gdb.NORMAL_FRAME} that is older than this one.
23102 @item gdb.SIGTRAMP_FRAME
23103 A signal trampoline frame. This is the frame created by the OS when
23104 it calls into a signal handler.
23106 @item gdb.ARCH_FRAME
23107 A fake stack frame representing a cross-architecture call.
23109 @item gdb.SENTINEL_FRAME
23110 This is like @code{gdb.NORMAL_FRAME}, but it is only used for the
23115 @defun Frame.unwind_stop_reason ()
23116 Return an integer representing the reason why it's not possible to find
23117 more frames toward the outermost frame. Use
23118 @code{gdb.frame_stop_reason_string} to convert the value returned by this
23119 function to a string.
23123 Returns the frame's resume address.
23126 @defun Frame.block ()
23127 Return the frame's code block. @xref{Blocks In Python}.
23130 @defun Frame.function ()
23131 Return the symbol for the function corresponding to this frame.
23132 @xref{Symbols In Python}.
23135 @defun Frame.older ()
23136 Return the frame that called this frame.
23139 @defun Frame.newer ()
23140 Return the frame called by this frame.
23143 @defun Frame.find_sal ()
23144 Return the frame's symtab and line object.
23145 @xref{Symbol Tables In Python}.
23148 @defun Frame.read_var (variable @r{[}, block@r{]})
23149 Return the value of @var{variable} in this frame. If the optional
23150 argument @var{block} is provided, search for the variable from that
23151 block; otherwise start at the frame's current block (which is
23152 determined by the frame's current program counter). @var{variable}
23153 must be a string or a @code{gdb.Symbol} object. @var{block} must be a
23154 @code{gdb.Block} object.
23157 @defun Frame.select ()
23158 Set this frame to be the selected frame. @xref{Stack, ,Examining the
23163 @node Blocks In Python
23164 @subsubsection Accessing frame blocks from Python.
23166 @cindex blocks in python
23169 Within each frame, @value{GDBN} maintains information on each block
23170 stored in that frame. These blocks are organized hierarchically, and
23171 are represented individually in Python as a @code{gdb.Block}.
23172 Please see @ref{Frames In Python}, for a more in-depth discussion on
23173 frames. Furthermore, see @ref{Stack, ,Examining the Stack}, for more
23174 detailed technical information on @value{GDBN}'s book-keeping of the
23177 The following block-related functions are available in the @code{gdb}
23180 @findex gdb.block_for_pc
23181 @defun gdb.block_for_pc (pc)
23182 Return the @code{gdb.Block} containing the given @var{pc} value. If the
23183 block cannot be found for the @var{pc} value specified, the function
23184 will return @code{None}.
23187 A @code{gdb.Block} object has the following methods:
23190 @defun Block.is_valid ()
23191 Returns @code{True} if the @code{gdb.Block} object is valid,
23192 @code{False} if not. A block object can become invalid if the block it
23193 refers to doesn't exist anymore in the inferior. All other
23194 @code{gdb.Block} methods will throw an exception if it is invalid at
23195 the time the method is called. This method is also made available to
23196 the Python iterator object that @code{gdb.Block} provides in an iteration
23197 context and via the Python @code{iter} built-in function.
23201 A @code{gdb.Block} object has the following attributes:
23204 @defvar Block.start
23205 The start address of the block. This attribute is not writable.
23209 The end address of the block. This attribute is not writable.
23212 @defvar Block.function
23213 The name of the block represented as a @code{gdb.Symbol}. If the
23214 block is not named, then this attribute holds @code{None}. This
23215 attribute is not writable.
23218 @defvar Block.superblock
23219 The block containing this block. If this parent block does not exist,
23220 this attribute holds @code{None}. This attribute is not writable.
23224 @node Symbols In Python
23225 @subsubsection Python representation of Symbols.
23227 @cindex symbols in python
23230 @value{GDBN} represents every variable, function and type as an
23231 entry in a symbol table. @xref{Symbols, ,Examining the Symbol Table}.
23232 Similarly, Python represents these symbols in @value{GDBN} with the
23233 @code{gdb.Symbol} object.
23235 The following symbol-related functions are available in the @code{gdb}
23238 @findex gdb.lookup_symbol
23239 @defun gdb.lookup_symbol (name @r{[}, block @r{[}, domain@r{]]})
23240 This function searches for a symbol by name. The search scope can be
23241 restricted to the parameters defined in the optional domain and block
23244 @var{name} is the name of the symbol. It must be a string. The
23245 optional @var{block} argument restricts the search to symbols visible
23246 in that @var{block}. The @var{block} argument must be a
23247 @code{gdb.Block} object. If omitted, the block for the current frame
23248 is used. The optional @var{domain} argument restricts
23249 the search to the domain type. The @var{domain} argument must be a
23250 domain constant defined in the @code{gdb} module and described later
23253 The result is a tuple of two elements.
23254 The first element is a @code{gdb.Symbol} object or @code{None} if the symbol
23256 If the symbol is found, the second element is @code{True} if the symbol
23257 is a field of a method's object (e.g., @code{this} in C@t{++}),
23258 otherwise it is @code{False}.
23259 If the symbol is not found, the second element is @code{False}.
23262 @findex gdb.lookup_global_symbol
23263 @defun gdb.lookup_global_symbol (name @r{[}, domain@r{]})
23264 This function searches for a global symbol by name.
23265 The search scope can be restricted to by the domain argument.
23267 @var{name} is the name of the symbol. It must be a string.
23268 The optional @var{domain} argument restricts the search to the domain type.
23269 The @var{domain} argument must be a domain constant defined in the @code{gdb}
23270 module and described later in this chapter.
23272 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
23276 A @code{gdb.Symbol} object has the following attributes:
23279 @defvar Symbol.type
23280 The type of the symbol or @code{None} if no type is recorded.
23281 This attribute is represented as a @code{gdb.Type} object.
23282 @xref{Types In Python}. This attribute is not writable.
23285 @defvar Symbol.symtab
23286 The symbol table in which the symbol appears. This attribute is
23287 represented as a @code{gdb.Symtab} object. @xref{Symbol Tables In
23288 Python}. This attribute is not writable.
23291 @defvar Symbol.name
23292 The name of the symbol as a string. This attribute is not writable.
23295 @defvar Symbol.linkage_name
23296 The name of the symbol, as used by the linker (i.e., may be mangled).
23297 This attribute is not writable.
23300 @defvar Symbol.print_name
23301 The name of the symbol in a form suitable for output. This is either
23302 @code{name} or @code{linkage_name}, depending on whether the user
23303 asked @value{GDBN} to display demangled or mangled names.
23306 @defvar Symbol.addr_class
23307 The address class of the symbol. This classifies how to find the value
23308 of a symbol. Each address class is a constant defined in the
23309 @code{gdb} module and described later in this chapter.
23312 @defvar Symbol.is_argument
23313 @code{True} if the symbol is an argument of a function.
23316 @defvar Symbol.is_constant
23317 @code{True} if the symbol is a constant.
23320 @defvar Symbol.is_function
23321 @code{True} if the symbol is a function or a method.
23324 @defvar Symbol.is_variable
23325 @code{True} if the symbol is a variable.
23329 A @code{gdb.Symbol} object has the following methods:
23332 @defun Symbol.is_valid ()
23333 Returns @code{True} if the @code{gdb.Symbol} object is valid,
23334 @code{False} if not. A @code{gdb.Symbol} object can become invalid if
23335 the symbol it refers to does not exist in @value{GDBN} any longer.
23336 All other @code{gdb.Symbol} methods will throw an exception if it is
23337 invalid at the time the method is called.
23341 The available domain categories in @code{gdb.Symbol} are represented
23342 as constants in the @code{gdb} module:
23345 @findex SYMBOL_UNDEF_DOMAIN
23346 @findex gdb.SYMBOL_UNDEF_DOMAIN
23347 @item gdb.SYMBOL_UNDEF_DOMAIN
23348 This is used when a domain has not been discovered or none of the
23349 following domains apply. This usually indicates an error either
23350 in the symbol information or in @value{GDBN}'s handling of symbols.
23351 @findex SYMBOL_VAR_DOMAIN
23352 @findex gdb.SYMBOL_VAR_DOMAIN
23353 @item gdb.SYMBOL_VAR_DOMAIN
23354 This domain contains variables, function names, typedef names and enum
23356 @findex SYMBOL_STRUCT_DOMAIN
23357 @findex gdb.SYMBOL_STRUCT_DOMAIN
23358 @item gdb.SYMBOL_STRUCT_DOMAIN
23359 This domain holds struct, union and enum type names.
23360 @findex SYMBOL_LABEL_DOMAIN
23361 @findex gdb.SYMBOL_LABEL_DOMAIN
23362 @item gdb.SYMBOL_LABEL_DOMAIN
23363 This domain contains names of labels (for gotos).
23364 @findex SYMBOL_VARIABLES_DOMAIN
23365 @findex gdb.SYMBOL_VARIABLES_DOMAIN
23366 @item gdb.SYMBOL_VARIABLES_DOMAIN
23367 This domain holds a subset of the @code{SYMBOLS_VAR_DOMAIN}; it
23368 contains everything minus functions and types.
23369 @findex SYMBOL_FUNCTIONS_DOMAIN
23370 @findex gdb.SYMBOL_FUNCTIONS_DOMAIN
23371 @item gdb.SYMBOL_FUNCTION_DOMAIN
23372 This domain contains all functions.
23373 @findex SYMBOL_TYPES_DOMAIN
23374 @findex gdb.SYMBOL_TYPES_DOMAIN
23375 @item gdb.SYMBOL_TYPES_DOMAIN
23376 This domain contains all types.
23379 The available address class categories in @code{gdb.Symbol} are represented
23380 as constants in the @code{gdb} module:
23383 @findex SYMBOL_LOC_UNDEF
23384 @findex gdb.SYMBOL_LOC_UNDEF
23385 @item gdb.SYMBOL_LOC_UNDEF
23386 If this is returned by address class, it indicates an error either in
23387 the symbol information or in @value{GDBN}'s handling of symbols.
23388 @findex SYMBOL_LOC_CONST
23389 @findex gdb.SYMBOL_LOC_CONST
23390 @item gdb.SYMBOL_LOC_CONST
23391 Value is constant int.
23392 @findex SYMBOL_LOC_STATIC
23393 @findex gdb.SYMBOL_LOC_STATIC
23394 @item gdb.SYMBOL_LOC_STATIC
23395 Value is at a fixed address.
23396 @findex SYMBOL_LOC_REGISTER
23397 @findex gdb.SYMBOL_LOC_REGISTER
23398 @item gdb.SYMBOL_LOC_REGISTER
23399 Value is in a register.
23400 @findex SYMBOL_LOC_ARG
23401 @findex gdb.SYMBOL_LOC_ARG
23402 @item gdb.SYMBOL_LOC_ARG
23403 Value is an argument. This value is at the offset stored within the
23404 symbol inside the frame's argument list.
23405 @findex SYMBOL_LOC_REF_ARG
23406 @findex gdb.SYMBOL_LOC_REF_ARG
23407 @item gdb.SYMBOL_LOC_REF_ARG
23408 Value address is stored in the frame's argument list. Just like
23409 @code{LOC_ARG} except that the value's address is stored at the
23410 offset, not the value itself.
23411 @findex SYMBOL_LOC_REGPARM_ADDR
23412 @findex gdb.SYMBOL_LOC_REGPARM_ADDR
23413 @item gdb.SYMBOL_LOC_REGPARM_ADDR
23414 Value is a specified register. Just like @code{LOC_REGISTER} except
23415 the register holds the address of the argument instead of the argument
23417 @findex SYMBOL_LOC_LOCAL
23418 @findex gdb.SYMBOL_LOC_LOCAL
23419 @item gdb.SYMBOL_LOC_LOCAL
23420 Value is a local variable.
23421 @findex SYMBOL_LOC_TYPEDEF
23422 @findex gdb.SYMBOL_LOC_TYPEDEF
23423 @item gdb.SYMBOL_LOC_TYPEDEF
23424 Value not used. Symbols in the domain @code{SYMBOL_STRUCT_DOMAIN} all
23426 @findex SYMBOL_LOC_BLOCK
23427 @findex gdb.SYMBOL_LOC_BLOCK
23428 @item gdb.SYMBOL_LOC_BLOCK
23430 @findex SYMBOL_LOC_CONST_BYTES
23431 @findex gdb.SYMBOL_LOC_CONST_BYTES
23432 @item gdb.SYMBOL_LOC_CONST_BYTES
23433 Value is a byte-sequence.
23434 @findex SYMBOL_LOC_UNRESOLVED
23435 @findex gdb.SYMBOL_LOC_UNRESOLVED
23436 @item gdb.SYMBOL_LOC_UNRESOLVED
23437 Value is at a fixed address, but the address of the variable has to be
23438 determined from the minimal symbol table whenever the variable is
23440 @findex SYMBOL_LOC_OPTIMIZED_OUT
23441 @findex gdb.SYMBOL_LOC_OPTIMIZED_OUT
23442 @item gdb.SYMBOL_LOC_OPTIMIZED_OUT
23443 The value does not actually exist in the program.
23444 @findex SYMBOL_LOC_COMPUTED
23445 @findex gdb.SYMBOL_LOC_COMPUTED
23446 @item gdb.SYMBOL_LOC_COMPUTED
23447 The value's address is a computed location.
23450 @node Symbol Tables In Python
23451 @subsubsection Symbol table representation in Python.
23453 @cindex symbol tables in python
23455 @tindex gdb.Symtab_and_line
23457 Access to symbol table data maintained by @value{GDBN} on the inferior
23458 is exposed to Python via two objects: @code{gdb.Symtab_and_line} and
23459 @code{gdb.Symtab}. Symbol table and line data for a frame is returned
23460 from the @code{find_sal} method in @code{gdb.Frame} object.
23461 @xref{Frames In Python}.
23463 For more information on @value{GDBN}'s symbol table management, see
23464 @ref{Symbols, ,Examining the Symbol Table}, for more information.
23466 A @code{gdb.Symtab_and_line} object has the following attributes:
23469 @defvar Symtab_and_line.symtab
23470 The symbol table object (@code{gdb.Symtab}) for this frame.
23471 This attribute is not writable.
23474 @defvar Symtab_and_line.pc
23475 Indicates the current program counter address. This attribute is not
23479 @defvar Symtab_and_line.line
23480 Indicates the current line number for this object. This
23481 attribute is not writable.
23485 A @code{gdb.Symtab_and_line} object has the following methods:
23488 @defun Symtab_and_line.is_valid ()
23489 Returns @code{True} if the @code{gdb.Symtab_and_line} object is valid,
23490 @code{False} if not. A @code{gdb.Symtab_and_line} object can become
23491 invalid if the Symbol table and line object it refers to does not
23492 exist in @value{GDBN} any longer. All other
23493 @code{gdb.Symtab_and_line} methods will throw an exception if it is
23494 invalid at the time the method is called.
23498 A @code{gdb.Symtab} object has the following attributes:
23501 @defvar Symtab.filename
23502 The symbol table's source filename. This attribute is not writable.
23505 @defvar Symtab.objfile
23506 The symbol table's backing object file. @xref{Objfiles In Python}.
23507 This attribute is not writable.
23511 A @code{gdb.Symtab} object has the following methods:
23514 @defun Symtab.is_valid ()
23515 Returns @code{True} if the @code{gdb.Symtab} object is valid,
23516 @code{False} if not. A @code{gdb.Symtab} object can become invalid if
23517 the symbol table it refers to does not exist in @value{GDBN} any
23518 longer. All other @code{gdb.Symtab} methods will throw an exception
23519 if it is invalid at the time the method is called.
23522 @defun Symtab.fullname ()
23523 Return the symbol table's source absolute file name.
23527 @node Breakpoints In Python
23528 @subsubsection Manipulating breakpoints using Python
23530 @cindex breakpoints in python
23531 @tindex gdb.Breakpoint
23533 Python code can manipulate breakpoints via the @code{gdb.Breakpoint}
23536 @defun Breakpoint.__init__ (spec @r{[}, type @r{[}, wp_class @r{[},internal@r{]]]})
23537 Create a new breakpoint. @var{spec} is a string naming the
23538 location of the breakpoint, or an expression that defines a
23539 watchpoint. The contents can be any location recognized by the
23540 @code{break} command, or in the case of a watchpoint, by the @code{watch}
23541 command. The optional @var{type} denotes the breakpoint to create
23542 from the types defined later in this chapter. This argument can be
23543 either: @code{gdb.BP_BREAKPOINT} or @code{gdb.BP_WATCHPOINT}. @var{type}
23544 defaults to @code{gdb.BP_BREAKPOINT}. The optional @var{internal} argument
23545 allows the breakpoint to become invisible to the user. The breakpoint
23546 will neither be reported when created, nor will it be listed in the
23547 output from @code{info breakpoints} (but will be listed with the
23548 @code{maint info breakpoints} command). The optional @var{wp_class}
23549 argument defines the class of watchpoint to create, if @var{type} is
23550 @code{gdb.BP_WATCHPOINT}. If a watchpoint class is not provided, it is
23551 assumed to be a @code{gdb.WP_WRITE} class.
23554 @defun Breakpoint.stop (self)
23555 The @code{gdb.Breakpoint} class can be sub-classed and, in
23556 particular, you may choose to implement the @code{stop} method.
23557 If this method is defined as a sub-class of @code{gdb.Breakpoint},
23558 it will be called when the inferior reaches any location of a
23559 breakpoint which instantiates that sub-class. If the method returns
23560 @code{True}, the inferior will be stopped at the location of the
23561 breakpoint, otherwise the inferior will continue.
23563 If there are multiple breakpoints at the same location with a
23564 @code{stop} method, each one will be called regardless of the
23565 return status of the previous. This ensures that all @code{stop}
23566 methods have a chance to execute at that location. In this scenario
23567 if one of the methods returns @code{True} but the others return
23568 @code{False}, the inferior will still be stopped.
23570 You should not alter the execution state of the inferior (i.e.@:, step,
23571 next, etc.), alter the current frame context (i.e.@:, change the current
23572 active frame), or alter, add or delete any breakpoint. As a general
23573 rule, you should not alter any data within @value{GDBN} or the inferior
23576 Example @code{stop} implementation:
23579 class MyBreakpoint (gdb.Breakpoint):
23581 inf_val = gdb.parse_and_eval("foo")
23588 The available watchpoint types represented by constants are defined in the
23593 @findex gdb.WP_READ
23595 Read only watchpoint.
23598 @findex gdb.WP_WRITE
23600 Write only watchpoint.
23603 @findex gdb.WP_ACCESS
23604 @item gdb.WP_ACCESS
23605 Read/Write watchpoint.
23608 @defun Breakpoint.is_valid ()
23609 Return @code{True} if this @code{Breakpoint} object is valid,
23610 @code{False} otherwise. A @code{Breakpoint} object can become invalid
23611 if the user deletes the breakpoint. In this case, the object still
23612 exists, but the underlying breakpoint does not. In the cases of
23613 watchpoint scope, the watchpoint remains valid even if execution of the
23614 inferior leaves the scope of that watchpoint.
23617 @defun Breakpoint.delete
23618 Permanently deletes the @value{GDBN} breakpoint. This also
23619 invalidates the Python @code{Breakpoint} object. Any further access
23620 to this object's attributes or methods will raise an error.
23623 @defvar Breakpoint.enabled
23624 This attribute is @code{True} if the breakpoint is enabled, and
23625 @code{False} otherwise. This attribute is writable.
23628 @defvar Breakpoint.silent
23629 This attribute is @code{True} if the breakpoint is silent, and
23630 @code{False} otherwise. This attribute is writable.
23632 Note that a breakpoint can also be silent if it has commands and the
23633 first command is @code{silent}. This is not reported by the
23634 @code{silent} attribute.
23637 @defvar Breakpoint.thread
23638 If the breakpoint is thread-specific, this attribute holds the thread
23639 id. If the breakpoint is not thread-specific, this attribute is
23640 @code{None}. This attribute is writable.
23643 @defvar Breakpoint.task
23644 If the breakpoint is Ada task-specific, this attribute holds the Ada task
23645 id. If the breakpoint is not task-specific (or the underlying
23646 language is not Ada), this attribute is @code{None}. This attribute
23650 @defvar Breakpoint.ignore_count
23651 This attribute holds the ignore count for the breakpoint, an integer.
23652 This attribute is writable.
23655 @defvar Breakpoint.number
23656 This attribute holds the breakpoint's number --- the identifier used by
23657 the user to manipulate the breakpoint. This attribute is not writable.
23660 @defvar Breakpoint.type
23661 This attribute holds the breakpoint's type --- the identifier used to
23662 determine the actual breakpoint type or use-case. This attribute is not
23666 @defvar Breakpoint.visible
23667 This attribute tells whether the breakpoint is visible to the user
23668 when set, or when the @samp{info breakpoints} command is run. This
23669 attribute is not writable.
23672 The available types are represented by constants defined in the @code{gdb}
23676 @findex BP_BREAKPOINT
23677 @findex gdb.BP_BREAKPOINT
23678 @item gdb.BP_BREAKPOINT
23679 Normal code breakpoint.
23681 @findex BP_WATCHPOINT
23682 @findex gdb.BP_WATCHPOINT
23683 @item gdb.BP_WATCHPOINT
23684 Watchpoint breakpoint.
23686 @findex BP_HARDWARE_WATCHPOINT
23687 @findex gdb.BP_HARDWARE_WATCHPOINT
23688 @item gdb.BP_HARDWARE_WATCHPOINT
23689 Hardware assisted watchpoint.
23691 @findex BP_READ_WATCHPOINT
23692 @findex gdb.BP_READ_WATCHPOINT
23693 @item gdb.BP_READ_WATCHPOINT
23694 Hardware assisted read watchpoint.
23696 @findex BP_ACCESS_WATCHPOINT
23697 @findex gdb.BP_ACCESS_WATCHPOINT
23698 @item gdb.BP_ACCESS_WATCHPOINT
23699 Hardware assisted access watchpoint.
23702 @defvar Breakpoint.hit_count
23703 This attribute holds the hit count for the breakpoint, an integer.
23704 This attribute is writable, but currently it can only be set to zero.
23707 @defvar Breakpoint.location
23708 This attribute holds the location of the breakpoint, as specified by
23709 the user. It is a string. If the breakpoint does not have a location
23710 (that is, it is a watchpoint) the attribute's value is @code{None}. This
23711 attribute is not writable.
23714 @defvar Breakpoint.expression
23715 This attribute holds a breakpoint expression, as specified by
23716 the user. It is a string. If the breakpoint does not have an
23717 expression (the breakpoint is not a watchpoint) the attribute's value
23718 is @code{None}. This attribute is not writable.
23721 @defvar Breakpoint.condition
23722 This attribute holds the condition of the breakpoint, as specified by
23723 the user. It is a string. If there is no condition, this attribute's
23724 value is @code{None}. This attribute is writable.
23727 @defvar Breakpoint.commands
23728 This attribute holds the commands attached to the breakpoint. If
23729 there are commands, this attribute's value is a string holding all the
23730 commands, separated by newlines. If there are no commands, this
23731 attribute is @code{None}. This attribute is not writable.
23734 @node Lazy Strings In Python
23735 @subsubsection Python representation of lazy strings.
23737 @cindex lazy strings in python
23738 @tindex gdb.LazyString
23740 A @dfn{lazy string} is a string whose contents is not retrieved or
23741 encoded until it is needed.
23743 A @code{gdb.LazyString} is represented in @value{GDBN} as an
23744 @code{address} that points to a region of memory, an @code{encoding}
23745 that will be used to encode that region of memory, and a @code{length}
23746 to delimit the region of memory that represents the string. The
23747 difference between a @code{gdb.LazyString} and a string wrapped within
23748 a @code{gdb.Value} is that a @code{gdb.LazyString} will be treated
23749 differently by @value{GDBN} when printing. A @code{gdb.LazyString} is
23750 retrieved and encoded during printing, while a @code{gdb.Value}
23751 wrapping a string is immediately retrieved and encoded on creation.
23753 A @code{gdb.LazyString} object has the following functions:
23755 @defun LazyString.value ()
23756 Convert the @code{gdb.LazyString} to a @code{gdb.Value}. This value
23757 will point to the string in memory, but will lose all the delayed
23758 retrieval, encoding and handling that @value{GDBN} applies to a
23759 @code{gdb.LazyString}.
23762 @defvar LazyString.address
23763 This attribute holds the address of the string. This attribute is not
23767 @defvar LazyString.length
23768 This attribute holds the length of the string in characters. If the
23769 length is -1, then the string will be fetched and encoded up to the
23770 first null of appropriate width. This attribute is not writable.
23773 @defvar LazyString.encoding
23774 This attribute holds the encoding that will be applied to the string
23775 when the string is printed by @value{GDBN}. If the encoding is not
23776 set, or contains an empty string, then @value{GDBN} will select the
23777 most appropriate encoding when the string is printed. This attribute
23781 @defvar LazyString.type
23782 This attribute holds the type that is represented by the lazy string's
23783 type. For a lazy string this will always be a pointer type. To
23784 resolve this to the lazy string's character type, use the type's
23785 @code{target} method. @xref{Types In Python}. This attribute is not
23790 @subsection Auto-loading
23791 @cindex auto-loading, Python
23793 When a new object file is read (for example, due to the @code{file}
23794 command, or because the inferior has loaded a shared library),
23795 @value{GDBN} will look for Python support scripts in several ways:
23796 @file{@var{objfile}-gdb.py} and @code{.debug_gdb_scripts} section.
23799 * objfile-gdb.py file:: The @file{@var{objfile}-gdb.py} file
23800 * .debug_gdb_scripts section:: The @code{.debug_gdb_scripts} section
23801 * Which flavor to choose?::
23804 The auto-loading feature is useful for supplying application-specific
23805 debugging commands and scripts.
23807 Auto-loading can be enabled or disabled,
23808 and the list of auto-loaded scripts can be printed.
23811 @kindex set auto-load-scripts
23812 @item set auto-load-scripts [yes|no]
23813 Enable or disable the auto-loading of Python scripts.
23815 @kindex show auto-load-scripts
23816 @item show auto-load-scripts
23817 Show whether auto-loading of Python scripts is enabled or disabled.
23819 @kindex info auto-load-scripts
23820 @cindex print list of auto-loaded scripts
23821 @item info auto-load-scripts [@var{regexp}]
23822 Print the list of all scripts that @value{GDBN} auto-loaded.
23824 Also printed is the list of scripts that were mentioned in
23825 the @code{.debug_gdb_scripts} section and were not found
23826 (@pxref{.debug_gdb_scripts section}).
23827 This is useful because their names are not printed when @value{GDBN}
23828 tries to load them and fails. There may be many of them, and printing
23829 an error message for each one is problematic.
23831 If @var{regexp} is supplied only scripts with matching names are printed.
23836 (gdb) info auto-load-scripts
23838 Yes py-section-script.py
23839 full name: /tmp/py-section-script.py
23840 Missing my-foo-pretty-printers.py
23844 When reading an auto-loaded file, @value{GDBN} sets the
23845 @dfn{current objfile}. This is available via the @code{gdb.current_objfile}
23846 function (@pxref{Objfiles In Python}). This can be useful for
23847 registering objfile-specific pretty-printers.
23849 @node objfile-gdb.py file
23850 @subsubsection The @file{@var{objfile}-gdb.py} file
23851 @cindex @file{@var{objfile}-gdb.py}
23853 When a new object file is read, @value{GDBN} looks for
23854 a file named @file{@var{objfile}-gdb.py},
23855 where @var{objfile} is the object file's real name, formed by ensuring
23856 that the file name is absolute, following all symlinks, and resolving
23857 @code{.} and @code{..} components. If this file exists and is
23858 readable, @value{GDBN} will evaluate it as a Python script.
23860 If this file does not exist, and if the parameter
23861 @code{debug-file-directory} is set (@pxref{Separate Debug Files}),
23862 then @value{GDBN} will look for @var{real-name} in all of the
23863 directories mentioned in the value of @code{debug-file-directory}.
23865 Finally, if this file does not exist, then @value{GDBN} will look for
23866 a file named @file{@var{data-directory}/python/auto-load/@var{real-name}}, where
23867 @var{data-directory} is @value{GDBN}'s data directory (available via
23868 @code{show data-directory}, @pxref{Data Files}), and @var{real-name}
23869 is the object file's real name, as described above.
23871 @value{GDBN} does not track which files it has already auto-loaded this way.
23872 @value{GDBN} will load the associated script every time the corresponding
23873 @var{objfile} is opened.
23874 So your @file{-gdb.py} file should be careful to avoid errors if it
23875 is evaluated more than once.
23877 @node .debug_gdb_scripts section
23878 @subsubsection The @code{.debug_gdb_scripts} section
23879 @cindex @code{.debug_gdb_scripts} section
23881 For systems using file formats like ELF and COFF,
23882 when @value{GDBN} loads a new object file
23883 it will look for a special section named @samp{.debug_gdb_scripts}.
23884 If this section exists, its contents is a list of names of scripts to load.
23886 @value{GDBN} will look for each specified script file first in the
23887 current directory and then along the source search path
23888 (@pxref{Source Path, ,Specifying Source Directories}),
23889 except that @file{$cdir} is not searched, since the compilation
23890 directory is not relevant to scripts.
23892 Entries can be placed in section @code{.debug_gdb_scripts} with,
23893 for example, this GCC macro:
23896 /* Note: The "MS" section flags are to remove duplicates. */
23897 #define DEFINE_GDB_SCRIPT(script_name) \
23899 .pushsection \".debug_gdb_scripts\", \"MS\",@@progbits,1\n\
23901 .asciz \"" script_name "\"\n\
23907 Then one can reference the macro in a header or source file like this:
23910 DEFINE_GDB_SCRIPT ("my-app-scripts.py")
23913 The script name may include directories if desired.
23915 If the macro is put in a header, any application or library
23916 using this header will get a reference to the specified script.
23918 @node Which flavor to choose?
23919 @subsubsection Which flavor to choose?
23921 Given the multiple ways of auto-loading Python scripts, it might not always
23922 be clear which one to choose. This section provides some guidance.
23924 Benefits of the @file{-gdb.py} way:
23928 Can be used with file formats that don't support multiple sections.
23931 Ease of finding scripts for public libraries.
23933 Scripts specified in the @code{.debug_gdb_scripts} section are searched for
23934 in the source search path.
23935 For publicly installed libraries, e.g., @file{libstdc++}, there typically
23936 isn't a source directory in which to find the script.
23939 Doesn't require source code additions.
23942 Benefits of the @code{.debug_gdb_scripts} way:
23946 Works with static linking.
23948 Scripts for libraries done the @file{-gdb.py} way require an objfile to
23949 trigger their loading. When an application is statically linked the only
23950 objfile available is the executable, and it is cumbersome to attach all the
23951 scripts from all the input libraries to the executable's @file{-gdb.py} script.
23954 Works with classes that are entirely inlined.
23956 Some classes can be entirely inlined, and thus there may not be an associated
23957 shared library to attach a @file{-gdb.py} script to.
23960 Scripts needn't be copied out of the source tree.
23962 In some circumstances, apps can be built out of large collections of internal
23963 libraries, and the build infrastructure necessary to install the
23964 @file{-gdb.py} scripts in a place where @value{GDBN} can find them is
23965 cumbersome. It may be easier to specify the scripts in the
23966 @code{.debug_gdb_scripts} section as relative paths, and add a path to the
23967 top of the source tree to the source search path.
23970 @node Python modules
23971 @subsection Python modules
23972 @cindex python modules
23974 @value{GDBN} comes with several modules to assist writing Python code.
23977 * gdb.printing:: Building and registering pretty-printers.
23978 * gdb.types:: Utilities for working with types.
23979 * gdb.prompt:: Utilities for prompt value substitution.
23983 @subsubsection gdb.printing
23984 @cindex gdb.printing
23986 This module provides a collection of utilities for working with
23990 @item PrettyPrinter (@var{name}, @var{subprinters}=None)
23991 This class specifies the API that makes @samp{info pretty-printer},
23992 @samp{enable pretty-printer} and @samp{disable pretty-printer} work.
23993 Pretty-printers should generally inherit from this class.
23995 @item SubPrettyPrinter (@var{name})
23996 For printers that handle multiple types, this class specifies the
23997 corresponding API for the subprinters.
23999 @item RegexpCollectionPrettyPrinter (@var{name})
24000 Utility class for handling multiple printers, all recognized via
24001 regular expressions.
24002 @xref{Writing a Pretty-Printer}, for an example.
24004 @item register_pretty_printer (@var{obj}, @var{printer})
24005 Register @var{printer} with the pretty-printer list of @var{obj}.
24009 @subsubsection gdb.types
24012 This module provides a collection of utilities for working with
24013 @code{gdb.Types} objects.
24016 @item get_basic_type (@var{type})
24017 Return @var{type} with const and volatile qualifiers stripped,
24018 and with typedefs and C@t{++} references converted to the underlying type.
24023 typedef const int const_int;
24025 const_int& foo_ref (foo);
24026 int main () @{ return 0; @}
24033 (gdb) python import gdb.types
24034 (gdb) python foo_ref = gdb.parse_and_eval("foo_ref")
24035 (gdb) python print gdb.types.get_basic_type(foo_ref.type)
24039 @item has_field (@var{type}, @var{field})
24040 Return @code{True} if @var{type}, assumed to be a type with fields
24041 (e.g., a structure or union), has field @var{field}.
24043 @item make_enum_dict (@var{enum_type})
24044 Return a Python @code{dictionary} type produced from @var{enum_type}.
24048 @subsubsection gdb.prompt
24051 This module provides a method for prompt value-substitution.
24054 @item substitute_prompt (@var{string})
24055 Return @var{string} with escape sequences substituted by values. Some
24056 escape sequences take arguments. You can specify arguments inside
24057 ``@{@}'' immediately following the escape sequence.
24059 The escape sequences you can pass to this function are:
24063 Substitute a backslash.
24065 Substitute an ESC character.
24067 Substitute the selected frame; an argument names a frame parameter.
24069 Substitute a newline.
24071 Substitute a parameter's value; the argument names the parameter.
24073 Substitute a carriage return.
24075 Substitute the selected thread; an argument names a thread parameter.
24077 Substitute the version of GDB.
24079 Substitute the current working directory.
24081 Begin a sequence of non-printing characters. These sequences are
24082 typically used with the ESC character, and are not counted in the string
24083 length. Example: ``\[\e[0;34m\](gdb)\[\e[0m\]'' will return a
24084 blue-colored ``(gdb)'' prompt where the length is five.
24086 End a sequence of non-printing characters.
24092 substitute_prompt (``frame: \f,
24093 print arguments: \p@{print frame-arguments@}'')
24096 @exdent will return the string:
24099 "frame: main, print arguments: scalars"
24104 @chapter Command Interpreters
24105 @cindex command interpreters
24107 @value{GDBN} supports multiple command interpreters, and some command
24108 infrastructure to allow users or user interface writers to switch
24109 between interpreters or run commands in other interpreters.
24111 @value{GDBN} currently supports two command interpreters, the console
24112 interpreter (sometimes called the command-line interpreter or @sc{cli})
24113 and the machine interface interpreter (or @sc{gdb/mi}). This manual
24114 describes both of these interfaces in great detail.
24116 By default, @value{GDBN} will start with the console interpreter.
24117 However, the user may choose to start @value{GDBN} with another
24118 interpreter by specifying the @option{-i} or @option{--interpreter}
24119 startup options. Defined interpreters include:
24123 @cindex console interpreter
24124 The traditional console or command-line interpreter. This is the most often
24125 used interpreter with @value{GDBN}. With no interpreter specified at runtime,
24126 @value{GDBN} will use this interpreter.
24129 @cindex mi interpreter
24130 The newest @sc{gdb/mi} interface (currently @code{mi2}). Used primarily
24131 by programs wishing to use @value{GDBN} as a backend for a debugger GUI
24132 or an IDE. For more information, see @ref{GDB/MI, ,The @sc{gdb/mi}
24136 @cindex mi2 interpreter
24137 The current @sc{gdb/mi} interface.
24140 @cindex mi1 interpreter
24141 The @sc{gdb/mi} interface included in @value{GDBN} 5.1, 5.2, and 5.3.
24145 @cindex invoke another interpreter
24146 The interpreter being used by @value{GDBN} may not be dynamically
24147 switched at runtime. Although possible, this could lead to a very
24148 precarious situation. Consider an IDE using @sc{gdb/mi}. If a user
24149 enters the command "interpreter-set console" in a console view,
24150 @value{GDBN} would switch to using the console interpreter, rendering
24151 the IDE inoperable!
24153 @kindex interpreter-exec
24154 Although you may only choose a single interpreter at startup, you may execute
24155 commands in any interpreter from the current interpreter using the appropriate
24156 command. If you are running the console interpreter, simply use the
24157 @code{interpreter-exec} command:
24160 interpreter-exec mi "-data-list-register-names"
24163 @sc{gdb/mi} has a similar command, although it is only available in versions of
24164 @value{GDBN} which support @sc{gdb/mi} version 2 (or greater).
24167 @chapter @value{GDBN} Text User Interface
24169 @cindex Text User Interface
24172 * TUI Overview:: TUI overview
24173 * TUI Keys:: TUI key bindings
24174 * TUI Single Key Mode:: TUI single key mode
24175 * TUI Commands:: TUI-specific commands
24176 * TUI Configuration:: TUI configuration variables
24179 The @value{GDBN} Text User Interface (TUI) is a terminal
24180 interface which uses the @code{curses} library to show the source
24181 file, the assembly output, the program registers and @value{GDBN}
24182 commands in separate text windows. The TUI mode is supported only
24183 on platforms where a suitable version of the @code{curses} library
24186 @pindex @value{GDBTUI}
24187 The TUI mode is enabled by default when you invoke @value{GDBN} as
24188 either @samp{@value{GDBTUI}} or @samp{@value{GDBP} -tui}.
24189 You can also switch in and out of TUI mode while @value{GDBN} runs by
24190 using various TUI commands and key bindings, such as @kbd{C-x C-a}.
24191 @xref{TUI Keys, ,TUI Key Bindings}.
24194 @section TUI Overview
24196 In TUI mode, @value{GDBN} can display several text windows:
24200 This window is the @value{GDBN} command window with the @value{GDBN}
24201 prompt and the @value{GDBN} output. The @value{GDBN} input is still
24202 managed using readline.
24205 The source window shows the source file of the program. The current
24206 line and active breakpoints are displayed in this window.
24209 The assembly window shows the disassembly output of the program.
24212 This window shows the processor registers. Registers are highlighted
24213 when their values change.
24216 The source and assembly windows show the current program position
24217 by highlighting the current line and marking it with a @samp{>} marker.
24218 Breakpoints are indicated with two markers. The first marker
24219 indicates the breakpoint type:
24223 Breakpoint which was hit at least once.
24226 Breakpoint which was never hit.
24229 Hardware breakpoint which was hit at least once.
24232 Hardware breakpoint which was never hit.
24235 The second marker indicates whether the breakpoint is enabled or not:
24239 Breakpoint is enabled.
24242 Breakpoint is disabled.
24245 The source, assembly and register windows are updated when the current
24246 thread changes, when the frame changes, or when the program counter
24249 These windows are not all visible at the same time. The command
24250 window is always visible. The others can be arranged in several
24261 source and assembly,
24264 source and registers, or
24267 assembly and registers.
24270 A status line above the command window shows the following information:
24274 Indicates the current @value{GDBN} target.
24275 (@pxref{Targets, ,Specifying a Debugging Target}).
24278 Gives the current process or thread number.
24279 When no process is being debugged, this field is set to @code{No process}.
24282 Gives the current function name for the selected frame.
24283 The name is demangled if demangling is turned on (@pxref{Print Settings}).
24284 When there is no symbol corresponding to the current program counter,
24285 the string @code{??} is displayed.
24288 Indicates the current line number for the selected frame.
24289 When the current line number is not known, the string @code{??} is displayed.
24292 Indicates the current program counter address.
24296 @section TUI Key Bindings
24297 @cindex TUI key bindings
24299 The TUI installs several key bindings in the readline keymaps
24300 @ifset SYSTEM_READLINE
24301 (@pxref{Command Line Editing, , , rluserman, GNU Readline Library}).
24303 @ifclear SYSTEM_READLINE
24304 (@pxref{Command Line Editing}).
24306 The following key bindings are installed for both TUI mode and the
24307 @value{GDBN} standard mode.
24316 Enter or leave the TUI mode. When leaving the TUI mode,
24317 the curses window management stops and @value{GDBN} operates using
24318 its standard mode, writing on the terminal directly. When reentering
24319 the TUI mode, control is given back to the curses windows.
24320 The screen is then refreshed.
24324 Use a TUI layout with only one window. The layout will
24325 either be @samp{source} or @samp{assembly}. When the TUI mode
24326 is not active, it will switch to the TUI mode.
24328 Think of this key binding as the Emacs @kbd{C-x 1} binding.
24332 Use a TUI layout with at least two windows. When the current
24333 layout already has two windows, the next layout with two windows is used.
24334 When a new layout is chosen, one window will always be common to the
24335 previous layout and the new one.
24337 Think of it as the Emacs @kbd{C-x 2} binding.
24341 Change the active window. The TUI associates several key bindings
24342 (like scrolling and arrow keys) with the active window. This command
24343 gives the focus to the next TUI window.
24345 Think of it as the Emacs @kbd{C-x o} binding.
24349 Switch in and out of the TUI SingleKey mode that binds single
24350 keys to @value{GDBN} commands (@pxref{TUI Single Key Mode}).
24353 The following key bindings only work in the TUI mode:
24358 Scroll the active window one page up.
24362 Scroll the active window one page down.
24366 Scroll the active window one line up.
24370 Scroll the active window one line down.
24374 Scroll the active window one column left.
24378 Scroll the active window one column right.
24382 Refresh the screen.
24385 Because the arrow keys scroll the active window in the TUI mode, they
24386 are not available for their normal use by readline unless the command
24387 window has the focus. When another window is active, you must use
24388 other readline key bindings such as @kbd{C-p}, @kbd{C-n}, @kbd{C-b}
24389 and @kbd{C-f} to control the command window.
24391 @node TUI Single Key Mode
24392 @section TUI Single Key Mode
24393 @cindex TUI single key mode
24395 The TUI also provides a @dfn{SingleKey} mode, which binds several
24396 frequently used @value{GDBN} commands to single keys. Type @kbd{C-x s} to
24397 switch into this mode, where the following key bindings are used:
24400 @kindex c @r{(SingleKey TUI key)}
24404 @kindex d @r{(SingleKey TUI key)}
24408 @kindex f @r{(SingleKey TUI key)}
24412 @kindex n @r{(SingleKey TUI key)}
24416 @kindex q @r{(SingleKey TUI key)}
24418 exit the SingleKey mode.
24420 @kindex r @r{(SingleKey TUI key)}
24424 @kindex s @r{(SingleKey TUI key)}
24428 @kindex u @r{(SingleKey TUI key)}
24432 @kindex v @r{(SingleKey TUI key)}
24436 @kindex w @r{(SingleKey TUI key)}
24441 Other keys temporarily switch to the @value{GDBN} command prompt.
24442 The key that was pressed is inserted in the editing buffer so that
24443 it is possible to type most @value{GDBN} commands without interaction
24444 with the TUI SingleKey mode. Once the command is entered the TUI
24445 SingleKey mode is restored. The only way to permanently leave
24446 this mode is by typing @kbd{q} or @kbd{C-x s}.
24450 @section TUI-specific Commands
24451 @cindex TUI commands
24453 The TUI has specific commands to control the text windows.
24454 These commands are always available, even when @value{GDBN} is not in
24455 the TUI mode. When @value{GDBN} is in the standard mode, most
24456 of these commands will automatically switch to the TUI mode.
24458 Note that if @value{GDBN}'s @code{stdout} is not connected to a
24459 terminal, or @value{GDBN} has been started with the machine interface
24460 interpreter (@pxref{GDB/MI, ,The @sc{gdb/mi} Interface}), most of
24461 these commands will fail with an error, because it would not be
24462 possible or desirable to enable curses window management.
24467 List and give the size of all displayed windows.
24471 Display the next layout.
24474 Display the previous layout.
24477 Display the source window only.
24480 Display the assembly window only.
24483 Display the source and assembly window.
24486 Display the register window together with the source or assembly window.
24490 Make the next window active for scrolling.
24493 Make the previous window active for scrolling.
24496 Make the source window active for scrolling.
24499 Make the assembly window active for scrolling.
24502 Make the register window active for scrolling.
24505 Make the command window active for scrolling.
24509 Refresh the screen. This is similar to typing @kbd{C-L}.
24511 @item tui reg float
24513 Show the floating point registers in the register window.
24515 @item tui reg general
24516 Show the general registers in the register window.
24519 Show the next register group. The list of register groups as well as
24520 their order is target specific. The predefined register groups are the
24521 following: @code{general}, @code{float}, @code{system}, @code{vector},
24522 @code{all}, @code{save}, @code{restore}.
24524 @item tui reg system
24525 Show the system registers in the register window.
24529 Update the source window and the current execution point.
24531 @item winheight @var{name} +@var{count}
24532 @itemx winheight @var{name} -@var{count}
24534 Change the height of the window @var{name} by @var{count}
24535 lines. Positive counts increase the height, while negative counts
24538 @item tabset @var{nchars}
24540 Set the width of tab stops to be @var{nchars} characters.
24543 @node TUI Configuration
24544 @section TUI Configuration Variables
24545 @cindex TUI configuration variables
24547 Several configuration variables control the appearance of TUI windows.
24550 @item set tui border-kind @var{kind}
24551 @kindex set tui border-kind
24552 Select the border appearance for the source, assembly and register windows.
24553 The possible values are the following:
24556 Use a space character to draw the border.
24559 Use @sc{ascii} characters @samp{+}, @samp{-} and @samp{|} to draw the border.
24562 Use the Alternate Character Set to draw the border. The border is
24563 drawn using character line graphics if the terminal supports them.
24566 @item set tui border-mode @var{mode}
24567 @kindex set tui border-mode
24568 @itemx set tui active-border-mode @var{mode}
24569 @kindex set tui active-border-mode
24570 Select the display attributes for the borders of the inactive windows
24571 or the active window. The @var{mode} can be one of the following:
24574 Use normal attributes to display the border.
24580 Use reverse video mode.
24583 Use half bright mode.
24585 @item half-standout
24586 Use half bright and standout mode.
24589 Use extra bright or bold mode.
24591 @item bold-standout
24592 Use extra bright or bold and standout mode.
24597 @chapter Using @value{GDBN} under @sc{gnu} Emacs
24600 @cindex @sc{gnu} Emacs
24601 A special interface allows you to use @sc{gnu} Emacs to view (and
24602 edit) the source files for the program you are debugging with
24605 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
24606 executable file you want to debug as an argument. This command starts
24607 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
24608 created Emacs buffer.
24609 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
24611 Running @value{GDBN} under Emacs can be just like running @value{GDBN} normally except for two
24616 All ``terminal'' input and output goes through an Emacs buffer, called
24619 This applies both to @value{GDBN} commands and their output, and to the input
24620 and output done by the program you are debugging.
24622 This is useful because it means that you can copy the text of previous
24623 commands and input them again; you can even use parts of the output
24626 All the facilities of Emacs' Shell mode are available for interacting
24627 with your program. In particular, you can send signals the usual
24628 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
24632 @value{GDBN} displays source code through Emacs.
24634 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
24635 source file for that frame and puts an arrow (@samp{=>}) at the
24636 left margin of the current line. Emacs uses a separate buffer for
24637 source display, and splits the screen to show both your @value{GDBN} session
24640 Explicit @value{GDBN} @code{list} or search commands still produce output as
24641 usual, but you probably have no reason to use them from Emacs.
24644 We call this @dfn{text command mode}. Emacs 22.1, and later, also uses
24645 a graphical mode, enabled by default, which provides further buffers
24646 that can control the execution and describe the state of your program.
24647 @xref{GDB Graphical Interface,,, Emacs, The @sc{gnu} Emacs Manual}.
24649 If you specify an absolute file name when prompted for the @kbd{M-x
24650 gdb} argument, then Emacs sets your current working directory to where
24651 your program resides. If you only specify the file name, then Emacs
24652 sets your current working directory to the directory associated
24653 with the previous buffer. In this case, @value{GDBN} may find your
24654 program by searching your environment's @code{PATH} variable, but on
24655 some operating systems it might not find the source. So, although the
24656 @value{GDBN} input and output session proceeds normally, the auxiliary
24657 buffer does not display the current source and line of execution.
24659 The initial working directory of @value{GDBN} is printed on the top
24660 line of the GUD buffer and this serves as a default for the commands
24661 that specify files for @value{GDBN} to operate on. @xref{Files,
24662 ,Commands to Specify Files}.
24664 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If you
24665 need to call @value{GDBN} by a different name (for example, if you
24666 keep several configurations around, with different names) you can
24667 customize the Emacs variable @code{gud-gdb-command-name} to run the
24670 In the GUD buffer, you can use these special Emacs commands in
24671 addition to the standard Shell mode commands:
24675 Describe the features of Emacs' GUD Mode.
24678 Execute to another source line, like the @value{GDBN} @code{step} command; also
24679 update the display window to show the current file and location.
24682 Execute to next source line in this function, skipping all function
24683 calls, like the @value{GDBN} @code{next} command. Then update the display window
24684 to show the current file and location.
24687 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
24688 display window accordingly.
24691 Execute until exit from the selected stack frame, like the @value{GDBN}
24692 @code{finish} command.
24695 Continue execution of your program, like the @value{GDBN} @code{continue}
24699 Go up the number of frames indicated by the numeric argument
24700 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
24701 like the @value{GDBN} @code{up} command.
24704 Go down the number of frames indicated by the numeric argument, like the
24705 @value{GDBN} @code{down} command.
24708 In any source file, the Emacs command @kbd{C-x @key{SPC}} (@code{gud-break})
24709 tells @value{GDBN} to set a breakpoint on the source line point is on.
24711 In text command mode, if you type @kbd{M-x speedbar}, Emacs displays a
24712 separate frame which shows a backtrace when the GUD buffer is current.
24713 Move point to any frame in the stack and type @key{RET} to make it
24714 become the current frame and display the associated source in the
24715 source buffer. Alternatively, click @kbd{Mouse-2} to make the
24716 selected frame become the current one. In graphical mode, the
24717 speedbar displays watch expressions.
24719 If you accidentally delete the source-display buffer, an easy way to get
24720 it back is to type the command @code{f} in the @value{GDBN} buffer, to
24721 request a frame display; when you run under Emacs, this recreates
24722 the source buffer if necessary to show you the context of the current
24725 The source files displayed in Emacs are in ordinary Emacs buffers
24726 which are visiting the source files in the usual way. You can edit
24727 the files with these buffers if you wish; but keep in mind that @value{GDBN}
24728 communicates with Emacs in terms of line numbers. If you add or
24729 delete lines from the text, the line numbers that @value{GDBN} knows cease
24730 to correspond properly with the code.
24732 A more detailed description of Emacs' interaction with @value{GDBN} is
24733 given in the Emacs manual (@pxref{Debuggers,,, Emacs, The @sc{gnu}
24736 @c The following dropped because Epoch is nonstandard. Reactivate
24737 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
24739 @kindex Emacs Epoch environment
24743 Version 18 of @sc{gnu} Emacs has a built-in window system
24744 called the @code{epoch}
24745 environment. Users of this environment can use a new command,
24746 @code{inspect} which performs identically to @code{print} except that
24747 each value is printed in its own window.
24752 @chapter The @sc{gdb/mi} Interface
24754 @unnumberedsec Function and Purpose
24756 @cindex @sc{gdb/mi}, its purpose
24757 @sc{gdb/mi} is a line based machine oriented text interface to
24758 @value{GDBN} and is activated by specifying using the
24759 @option{--interpreter} command line option (@pxref{Mode Options}). It
24760 is specifically intended to support the development of systems which
24761 use the debugger as just one small component of a larger system.
24763 This chapter is a specification of the @sc{gdb/mi} interface. It is written
24764 in the form of a reference manual.
24766 Note that @sc{gdb/mi} is still under construction, so some of the
24767 features described below are incomplete and subject to change
24768 (@pxref{GDB/MI Development and Front Ends, , @sc{gdb/mi} Development and Front Ends}).
24770 @unnumberedsec Notation and Terminology
24772 @cindex notational conventions, for @sc{gdb/mi}
24773 This chapter uses the following notation:
24777 @code{|} separates two alternatives.
24780 @code{[ @var{something} ]} indicates that @var{something} is optional:
24781 it may or may not be given.
24784 @code{( @var{group} )*} means that @var{group} inside the parentheses
24785 may repeat zero or more times.
24788 @code{( @var{group} )+} means that @var{group} inside the parentheses
24789 may repeat one or more times.
24792 @code{"@var{string}"} means a literal @var{string}.
24796 @heading Dependencies
24800 * GDB/MI General Design::
24801 * GDB/MI Command Syntax::
24802 * GDB/MI Compatibility with CLI::
24803 * GDB/MI Development and Front Ends::
24804 * GDB/MI Output Records::
24805 * GDB/MI Simple Examples::
24806 * GDB/MI Command Description Format::
24807 * GDB/MI Breakpoint Commands::
24808 * GDB/MI Program Context::
24809 * GDB/MI Thread Commands::
24810 * GDB/MI Ada Tasking Commands::
24811 * GDB/MI Program Execution::
24812 * GDB/MI Stack Manipulation::
24813 * GDB/MI Variable Objects::
24814 * GDB/MI Data Manipulation::
24815 * GDB/MI Tracepoint Commands::
24816 * GDB/MI Symbol Query::
24817 * GDB/MI File Commands::
24819 * GDB/MI Kod Commands::
24820 * GDB/MI Memory Overlay Commands::
24821 * GDB/MI Signal Handling Commands::
24823 * GDB/MI Target Manipulation::
24824 * GDB/MI File Transfer Commands::
24825 * GDB/MI Miscellaneous Commands::
24828 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
24829 @node GDB/MI General Design
24830 @section @sc{gdb/mi} General Design
24831 @cindex GDB/MI General Design
24833 Interaction of a @sc{GDB/MI} frontend with @value{GDBN} involves three
24834 parts---commands sent to @value{GDBN}, responses to those commands
24835 and notifications. Each command results in exactly one response,
24836 indicating either successful completion of the command, or an error.
24837 For the commands that do not resume the target, the response contains the
24838 requested information. For the commands that resume the target, the
24839 response only indicates whether the target was successfully resumed.
24840 Notifications is the mechanism for reporting changes in the state of the
24841 target, or in @value{GDBN} state, that cannot conveniently be associated with
24842 a command and reported as part of that command response.
24844 The important examples of notifications are:
24848 Exec notifications. These are used to report changes in
24849 target state---when a target is resumed, or stopped. It would not
24850 be feasible to include this information in response of resuming
24851 commands, because one resume commands can result in multiple events in
24852 different threads. Also, quite some time may pass before any event
24853 happens in the target, while a frontend needs to know whether the resuming
24854 command itself was successfully executed.
24857 Console output, and status notifications. Console output
24858 notifications are used to report output of CLI commands, as well as
24859 diagnostics for other commands. Status notifications are used to
24860 report the progress of a long-running operation. Naturally, including
24861 this information in command response would mean no output is produced
24862 until the command is finished, which is undesirable.
24865 General notifications. Commands may have various side effects on
24866 the @value{GDBN} or target state beyond their official purpose. For example,
24867 a command may change the selected thread. Although such changes can
24868 be included in command response, using notification allows for more
24869 orthogonal frontend design.
24873 There's no guarantee that whenever an MI command reports an error,
24874 @value{GDBN} or the target are in any specific state, and especially,
24875 the state is not reverted to the state before the MI command was
24876 processed. Therefore, whenever an MI command results in an error,
24877 we recommend that the frontend refreshes all the information shown in
24878 the user interface.
24882 * Context management::
24883 * Asynchronous and non-stop modes::
24887 @node Context management
24888 @subsection Context management
24890 In most cases when @value{GDBN} accesses the target, this access is
24891 done in context of a specific thread and frame (@pxref{Frames}).
24892 Often, even when accessing global data, the target requires that a thread
24893 be specified. The CLI interface maintains the selected thread and frame,
24894 and supplies them to target on each command. This is convenient,
24895 because a command line user would not want to specify that information
24896 explicitly on each command, and because user interacts with
24897 @value{GDBN} via a single terminal, so no confusion is possible as
24898 to what thread and frame are the current ones.
24900 In the case of MI, the concept of selected thread and frame is less
24901 useful. First, a frontend can easily remember this information
24902 itself. Second, a graphical frontend can have more than one window,
24903 each one used for debugging a different thread, and the frontend might
24904 want to access additional threads for internal purposes. This
24905 increases the risk that by relying on implicitly selected thread, the
24906 frontend may be operating on a wrong one. Therefore, each MI command
24907 should explicitly specify which thread and frame to operate on. To
24908 make it possible, each MI command accepts the @samp{--thread} and
24909 @samp{--frame} options, the value to each is @value{GDBN} identifier
24910 for thread and frame to operate on.
24912 Usually, each top-level window in a frontend allows the user to select
24913 a thread and a frame, and remembers the user selection for further
24914 operations. However, in some cases @value{GDBN} may suggest that the
24915 current thread be changed. For example, when stopping on a breakpoint
24916 it is reasonable to switch to the thread where breakpoint is hit. For
24917 another example, if the user issues the CLI @samp{thread} command via
24918 the frontend, it is desirable to change the frontend's selected thread to the
24919 one specified by user. @value{GDBN} communicates the suggestion to
24920 change current thread using the @samp{=thread-selected} notification.
24921 No such notification is available for the selected frame at the moment.
24923 Note that historically, MI shares the selected thread with CLI, so
24924 frontends used the @code{-thread-select} to execute commands in the
24925 right context. However, getting this to work right is cumbersome. The
24926 simplest way is for frontend to emit @code{-thread-select} command
24927 before every command. This doubles the number of commands that need
24928 to be sent. The alternative approach is to suppress @code{-thread-select}
24929 if the selected thread in @value{GDBN} is supposed to be identical to the
24930 thread the frontend wants to operate on. However, getting this
24931 optimization right can be tricky. In particular, if the frontend
24932 sends several commands to @value{GDBN}, and one of the commands changes the
24933 selected thread, then the behaviour of subsequent commands will
24934 change. So, a frontend should either wait for response from such
24935 problematic commands, or explicitly add @code{-thread-select} for
24936 all subsequent commands. No frontend is known to do this exactly
24937 right, so it is suggested to just always pass the @samp{--thread} and
24938 @samp{--frame} options.
24940 @node Asynchronous and non-stop modes
24941 @subsection Asynchronous command execution and non-stop mode
24943 On some targets, @value{GDBN} is capable of processing MI commands
24944 even while the target is running. This is called @dfn{asynchronous
24945 command execution} (@pxref{Background Execution}). The frontend may
24946 specify a preferrence for asynchronous execution using the
24947 @code{-gdb-set target-async 1} command, which should be emitted before
24948 either running the executable or attaching to the target. After the
24949 frontend has started the executable or attached to the target, it can
24950 find if asynchronous execution is enabled using the
24951 @code{-list-target-features} command.
24953 Even if @value{GDBN} can accept a command while target is running,
24954 many commands that access the target do not work when the target is
24955 running. Therefore, asynchronous command execution is most useful
24956 when combined with non-stop mode (@pxref{Non-Stop Mode}). Then,
24957 it is possible to examine the state of one thread, while other threads
24960 When a given thread is running, MI commands that try to access the
24961 target in the context of that thread may not work, or may work only on
24962 some targets. In particular, commands that try to operate on thread's
24963 stack will not work, on any target. Commands that read memory, or
24964 modify breakpoints, may work or not work, depending on the target. Note
24965 that even commands that operate on global state, such as @code{print},
24966 @code{set}, and breakpoint commands, still access the target in the
24967 context of a specific thread, so frontend should try to find a
24968 stopped thread and perform the operation on that thread (using the
24969 @samp{--thread} option).
24971 Which commands will work in the context of a running thread is
24972 highly target dependent. However, the two commands
24973 @code{-exec-interrupt}, to stop a thread, and @code{-thread-info},
24974 to find the state of a thread, will always work.
24976 @node Thread groups
24977 @subsection Thread groups
24978 @value{GDBN} may be used to debug several processes at the same time.
24979 On some platfroms, @value{GDBN} may support debugging of several
24980 hardware systems, each one having several cores with several different
24981 processes running on each core. This section describes the MI
24982 mechanism to support such debugging scenarios.
24984 The key observation is that regardless of the structure of the
24985 target, MI can have a global list of threads, because most commands that
24986 accept the @samp{--thread} option do not need to know what process that
24987 thread belongs to. Therefore, it is not necessary to introduce
24988 neither additional @samp{--process} option, nor an notion of the
24989 current process in the MI interface. The only strictly new feature
24990 that is required is the ability to find how the threads are grouped
24993 To allow the user to discover such grouping, and to support arbitrary
24994 hierarchy of machines/cores/processes, MI introduces the concept of a
24995 @dfn{thread group}. Thread group is a collection of threads and other
24996 thread groups. A thread group always has a string identifier, a type,
24997 and may have additional attributes specific to the type. A new
24998 command, @code{-list-thread-groups}, returns the list of top-level
24999 thread groups, which correspond to processes that @value{GDBN} is
25000 debugging at the moment. By passing an identifier of a thread group
25001 to the @code{-list-thread-groups} command, it is possible to obtain
25002 the members of specific thread group.
25004 To allow the user to easily discover processes, and other objects, he
25005 wishes to debug, a concept of @dfn{available thread group} is
25006 introduced. Available thread group is an thread group that
25007 @value{GDBN} is not debugging, but that can be attached to, using the
25008 @code{-target-attach} command. The list of available top-level thread
25009 groups can be obtained using @samp{-list-thread-groups --available}.
25010 In general, the content of a thread group may be only retrieved only
25011 after attaching to that thread group.
25013 Thread groups are related to inferiors (@pxref{Inferiors and
25014 Programs}). Each inferior corresponds to a thread group of a special
25015 type @samp{process}, and some additional operations are permitted on
25016 such thread groups.
25018 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25019 @node GDB/MI Command Syntax
25020 @section @sc{gdb/mi} Command Syntax
25023 * GDB/MI Input Syntax::
25024 * GDB/MI Output Syntax::
25027 @node GDB/MI Input Syntax
25028 @subsection @sc{gdb/mi} Input Syntax
25030 @cindex input syntax for @sc{gdb/mi}
25031 @cindex @sc{gdb/mi}, input syntax
25033 @item @var{command} @expansion{}
25034 @code{@var{cli-command} | @var{mi-command}}
25036 @item @var{cli-command} @expansion{}
25037 @code{[ @var{token} ] @var{cli-command} @var{nl}}, where
25038 @var{cli-command} is any existing @value{GDBN} CLI command.
25040 @item @var{mi-command} @expansion{}
25041 @code{[ @var{token} ] "-" @var{operation} ( " " @var{option} )*
25042 @code{[} " --" @code{]} ( " " @var{parameter} )* @var{nl}}
25044 @item @var{token} @expansion{}
25045 "any sequence of digits"
25047 @item @var{option} @expansion{}
25048 @code{"-" @var{parameter} [ " " @var{parameter} ]}
25050 @item @var{parameter} @expansion{}
25051 @code{@var{non-blank-sequence} | @var{c-string}}
25053 @item @var{operation} @expansion{}
25054 @emph{any of the operations described in this chapter}
25056 @item @var{non-blank-sequence} @expansion{}
25057 @emph{anything, provided it doesn't contain special characters such as
25058 "-", @var{nl}, """ and of course " "}
25060 @item @var{c-string} @expansion{}
25061 @code{""" @var{seven-bit-iso-c-string-content} """}
25063 @item @var{nl} @expansion{}
25072 The CLI commands are still handled by the @sc{mi} interpreter; their
25073 output is described below.
25076 The @code{@var{token}}, when present, is passed back when the command
25080 Some @sc{mi} commands accept optional arguments as part of the parameter
25081 list. Each option is identified by a leading @samp{-} (dash) and may be
25082 followed by an optional argument parameter. Options occur first in the
25083 parameter list and can be delimited from normal parameters using
25084 @samp{--} (this is useful when some parameters begin with a dash).
25091 We want easy access to the existing CLI syntax (for debugging).
25094 We want it to be easy to spot a @sc{mi} operation.
25097 @node GDB/MI Output Syntax
25098 @subsection @sc{gdb/mi} Output Syntax
25100 @cindex output syntax of @sc{gdb/mi}
25101 @cindex @sc{gdb/mi}, output syntax
25102 The output from @sc{gdb/mi} consists of zero or more out-of-band records
25103 followed, optionally, by a single result record. This result record
25104 is for the most recent command. The sequence of output records is
25105 terminated by @samp{(gdb)}.
25107 If an input command was prefixed with a @code{@var{token}} then the
25108 corresponding output for that command will also be prefixed by that same
25112 @item @var{output} @expansion{}
25113 @code{( @var{out-of-band-record} )* [ @var{result-record} ] "(gdb)" @var{nl}}
25115 @item @var{result-record} @expansion{}
25116 @code{ [ @var{token} ] "^" @var{result-class} ( "," @var{result} )* @var{nl}}
25118 @item @var{out-of-band-record} @expansion{}
25119 @code{@var{async-record} | @var{stream-record}}
25121 @item @var{async-record} @expansion{}
25122 @code{@var{exec-async-output} | @var{status-async-output} | @var{notify-async-output}}
25124 @item @var{exec-async-output} @expansion{}
25125 @code{[ @var{token} ] "*" @var{async-output}}
25127 @item @var{status-async-output} @expansion{}
25128 @code{[ @var{token} ] "+" @var{async-output}}
25130 @item @var{notify-async-output} @expansion{}
25131 @code{[ @var{token} ] "=" @var{async-output}}
25133 @item @var{async-output} @expansion{}
25134 @code{@var{async-class} ( "," @var{result} )* @var{nl}}
25136 @item @var{result-class} @expansion{}
25137 @code{"done" | "running" | "connected" | "error" | "exit"}
25139 @item @var{async-class} @expansion{}
25140 @code{"stopped" | @var{others}} (where @var{others} will be added
25141 depending on the needs---this is still in development).
25143 @item @var{result} @expansion{}
25144 @code{ @var{variable} "=" @var{value}}
25146 @item @var{variable} @expansion{}
25147 @code{ @var{string} }
25149 @item @var{value} @expansion{}
25150 @code{ @var{const} | @var{tuple} | @var{list} }
25152 @item @var{const} @expansion{}
25153 @code{@var{c-string}}
25155 @item @var{tuple} @expansion{}
25156 @code{ "@{@}" | "@{" @var{result} ( "," @var{result} )* "@}" }
25158 @item @var{list} @expansion{}
25159 @code{ "[]" | "[" @var{value} ( "," @var{value} )* "]" | "["
25160 @var{result} ( "," @var{result} )* "]" }
25162 @item @var{stream-record} @expansion{}
25163 @code{@var{console-stream-output} | @var{target-stream-output} | @var{log-stream-output}}
25165 @item @var{console-stream-output} @expansion{}
25166 @code{"~" @var{c-string}}
25168 @item @var{target-stream-output} @expansion{}
25169 @code{"@@" @var{c-string}}
25171 @item @var{log-stream-output} @expansion{}
25172 @code{"&" @var{c-string}}
25174 @item @var{nl} @expansion{}
25177 @item @var{token} @expansion{}
25178 @emph{any sequence of digits}.
25186 All output sequences end in a single line containing a period.
25189 The @code{@var{token}} is from the corresponding request. Note that
25190 for all async output, while the token is allowed by the grammar and
25191 may be output by future versions of @value{GDBN} for select async
25192 output messages, it is generally omitted. Frontends should treat
25193 all async output as reporting general changes in the state of the
25194 target and there should be no need to associate async output to any
25198 @cindex status output in @sc{gdb/mi}
25199 @var{status-async-output} contains on-going status information about the
25200 progress of a slow operation. It can be discarded. All status output is
25201 prefixed by @samp{+}.
25204 @cindex async output in @sc{gdb/mi}
25205 @var{exec-async-output} contains asynchronous state change on the target
25206 (stopped, started, disappeared). All async output is prefixed by
25210 @cindex notify output in @sc{gdb/mi}
25211 @var{notify-async-output} contains supplementary information that the
25212 client should handle (e.g., a new breakpoint information). All notify
25213 output is prefixed by @samp{=}.
25216 @cindex console output in @sc{gdb/mi}
25217 @var{console-stream-output} is output that should be displayed as is in the
25218 console. It is the textual response to a CLI command. All the console
25219 output is prefixed by @samp{~}.
25222 @cindex target output in @sc{gdb/mi}
25223 @var{target-stream-output} is the output produced by the target program.
25224 All the target output is prefixed by @samp{@@}.
25227 @cindex log output in @sc{gdb/mi}
25228 @var{log-stream-output} is output text coming from @value{GDBN}'s internals, for
25229 instance messages that should be displayed as part of an error log. All
25230 the log output is prefixed by @samp{&}.
25233 @cindex list output in @sc{gdb/mi}
25234 New @sc{gdb/mi} commands should only output @var{lists} containing
25240 @xref{GDB/MI Stream Records, , @sc{gdb/mi} Stream Records}, for more
25241 details about the various output records.
25243 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25244 @node GDB/MI Compatibility with CLI
25245 @section @sc{gdb/mi} Compatibility with CLI
25247 @cindex compatibility, @sc{gdb/mi} and CLI
25248 @cindex @sc{gdb/mi}, compatibility with CLI
25250 For the developers convenience CLI commands can be entered directly,
25251 but there may be some unexpected behaviour. For example, commands
25252 that query the user will behave as if the user replied yes, breakpoint
25253 command lists are not executed and some CLI commands, such as
25254 @code{if}, @code{when} and @code{define}, prompt for further input with
25255 @samp{>}, which is not valid MI output.
25257 This feature may be removed at some stage in the future and it is
25258 recommended that front ends use the @code{-interpreter-exec} command
25259 (@pxref{-interpreter-exec}).
25261 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25262 @node GDB/MI Development and Front Ends
25263 @section @sc{gdb/mi} Development and Front Ends
25264 @cindex @sc{gdb/mi} development
25266 The application which takes the MI output and presents the state of the
25267 program being debugged to the user is called a @dfn{front end}.
25269 Although @sc{gdb/mi} is still incomplete, it is currently being used
25270 by a variety of front ends to @value{GDBN}. This makes it difficult
25271 to introduce new functionality without breaking existing usage. This
25272 section tries to minimize the problems by describing how the protocol
25275 Some changes in MI need not break a carefully designed front end, and
25276 for these the MI version will remain unchanged. The following is a
25277 list of changes that may occur within one level, so front ends should
25278 parse MI output in a way that can handle them:
25282 New MI commands may be added.
25285 New fields may be added to the output of any MI command.
25288 The range of values for fields with specified values, e.g.,
25289 @code{in_scope} (@pxref{-var-update}) may be extended.
25291 @c The format of field's content e.g type prefix, may change so parse it
25292 @c at your own risk. Yes, in general?
25294 @c The order of fields may change? Shouldn't really matter but it might
25295 @c resolve inconsistencies.
25298 If the changes are likely to break front ends, the MI version level
25299 will be increased by one. This will allow the front end to parse the
25300 output according to the MI version. Apart from mi0, new versions of
25301 @value{GDBN} will not support old versions of MI and it will be the
25302 responsibility of the front end to work with the new one.
25304 @c Starting with mi3, add a new command -mi-version that prints the MI
25307 The best way to avoid unexpected changes in MI that might break your front
25308 end is to make your project known to @value{GDBN} developers and
25309 follow development on @email{gdb@@sourceware.org} and
25310 @email{gdb-patches@@sourceware.org}.
25311 @cindex mailing lists
25313 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25314 @node GDB/MI Output Records
25315 @section @sc{gdb/mi} Output Records
25318 * GDB/MI Result Records::
25319 * GDB/MI Stream Records::
25320 * GDB/MI Async Records::
25321 * GDB/MI Frame Information::
25322 * GDB/MI Thread Information::
25323 * GDB/MI Ada Exception Information::
25326 @node GDB/MI Result Records
25327 @subsection @sc{gdb/mi} Result Records
25329 @cindex result records in @sc{gdb/mi}
25330 @cindex @sc{gdb/mi}, result records
25331 In addition to a number of out-of-band notifications, the response to a
25332 @sc{gdb/mi} command includes one of the following result indications:
25336 @item "^done" [ "," @var{results} ]
25337 The synchronous operation was successful, @code{@var{results}} are the return
25342 This result record is equivalent to @samp{^done}. Historically, it
25343 was output instead of @samp{^done} if the command has resumed the
25344 target. This behaviour is maintained for backward compatibility, but
25345 all frontends should treat @samp{^done} and @samp{^running}
25346 identically and rely on the @samp{*running} output record to determine
25347 which threads are resumed.
25351 @value{GDBN} has connected to a remote target.
25353 @item "^error" "," @var{c-string}
25355 The operation failed. The @code{@var{c-string}} contains the corresponding
25360 @value{GDBN} has terminated.
25364 @node GDB/MI Stream Records
25365 @subsection @sc{gdb/mi} Stream Records
25367 @cindex @sc{gdb/mi}, stream records
25368 @cindex stream records in @sc{gdb/mi}
25369 @value{GDBN} internally maintains a number of output streams: the console, the
25370 target, and the log. The output intended for each of these streams is
25371 funneled through the @sc{gdb/mi} interface using @dfn{stream records}.
25373 Each stream record begins with a unique @dfn{prefix character} which
25374 identifies its stream (@pxref{GDB/MI Output Syntax, , @sc{gdb/mi} Output
25375 Syntax}). In addition to the prefix, each stream record contains a
25376 @code{@var{string-output}}. This is either raw text (with an implicit new
25377 line) or a quoted C string (which does not contain an implicit newline).
25380 @item "~" @var{string-output}
25381 The console output stream contains text that should be displayed in the
25382 CLI console window. It contains the textual responses to CLI commands.
25384 @item "@@" @var{string-output}
25385 The target output stream contains any textual output from the running
25386 target. This is only present when GDB's event loop is truly
25387 asynchronous, which is currently only the case for remote targets.
25389 @item "&" @var{string-output}
25390 The log stream contains debugging messages being produced by @value{GDBN}'s
25394 @node GDB/MI Async Records
25395 @subsection @sc{gdb/mi} Async Records
25397 @cindex async records in @sc{gdb/mi}
25398 @cindex @sc{gdb/mi}, async records
25399 @dfn{Async} records are used to notify the @sc{gdb/mi} client of
25400 additional changes that have occurred. Those changes can either be a
25401 consequence of @sc{gdb/mi} commands (e.g., a breakpoint modified) or a result of
25402 target activity (e.g., target stopped).
25404 The following is the list of possible async records:
25408 @item *running,thread-id="@var{thread}"
25409 The target is now running. The @var{thread} field tells which
25410 specific thread is now running, and can be @samp{all} if all threads
25411 are running. The frontend should assume that no interaction with a
25412 running thread is possible after this notification is produced.
25413 The frontend should not assume that this notification is output
25414 only once for any command. @value{GDBN} may emit this notification
25415 several times, either for different threads, because it cannot resume
25416 all threads together, or even for a single thread, if the thread must
25417 be stepped though some code before letting it run freely.
25419 @item *stopped,reason="@var{reason}",thread-id="@var{id}",stopped-threads="@var{stopped}",core="@var{core}"
25420 The target has stopped. The @var{reason} field can have one of the
25424 @item breakpoint-hit
25425 A breakpoint was reached.
25426 @item watchpoint-trigger
25427 A watchpoint was triggered.
25428 @item read-watchpoint-trigger
25429 A read watchpoint was triggered.
25430 @item access-watchpoint-trigger
25431 An access watchpoint was triggered.
25432 @item function-finished
25433 An -exec-finish or similar CLI command was accomplished.
25434 @item location-reached
25435 An -exec-until or similar CLI command was accomplished.
25436 @item watchpoint-scope
25437 A watchpoint has gone out of scope.
25438 @item end-stepping-range
25439 An -exec-next, -exec-next-instruction, -exec-step, -exec-step-instruction or
25440 similar CLI command was accomplished.
25441 @item exited-signalled
25442 The inferior exited because of a signal.
25444 The inferior exited.
25445 @item exited-normally
25446 The inferior exited normally.
25447 @item signal-received
25448 A signal was received by the inferior.
25451 The @var{id} field identifies the thread that directly caused the stop
25452 -- for example by hitting a breakpoint. Depending on whether all-stop
25453 mode is in effect (@pxref{All-Stop Mode}), @value{GDBN} may either
25454 stop all threads, or only the thread that directly triggered the stop.
25455 If all threads are stopped, the @var{stopped} field will have the
25456 value of @code{"all"}. Otherwise, the value of the @var{stopped}
25457 field will be a list of thread identifiers. Presently, this list will
25458 always include a single thread, but frontend should be prepared to see
25459 several threads in the list. The @var{core} field reports the
25460 processor core on which the stop event has happened. This field may be absent
25461 if such information is not available.
25463 @item =thread-group-added,id="@var{id}"
25464 @itemx =thread-group-removed,id="@var{id}"
25465 A thread group was either added or removed. The @var{id} field
25466 contains the @value{GDBN} identifier of the thread group. When a thread
25467 group is added, it generally might not be associated with a running
25468 process. When a thread group is removed, its id becomes invalid and
25469 cannot be used in any way.
25471 @item =thread-group-started,id="@var{id}",pid="@var{pid}"
25472 A thread group became associated with a running program,
25473 either because the program was just started or the thread group
25474 was attached to a program. The @var{id} field contains the
25475 @value{GDBN} identifier of the thread group. The @var{pid} field
25476 contains process identifier, specific to the operating system.
25478 @item =thread-group-exited,id="@var{id}"[,exit-code="@var{code}"]
25479 A thread group is no longer associated with a running program,
25480 either because the program has exited, or because it was detached
25481 from. The @var{id} field contains the @value{GDBN} identifier of the
25482 thread group. @var{code} is the exit code of the inferior; it exists
25483 only when the inferior exited with some code.
25485 @item =thread-created,id="@var{id}",group-id="@var{gid}"
25486 @itemx =thread-exited,id="@var{id}",group-id="@var{gid}"
25487 A thread either was created, or has exited. The @var{id} field
25488 contains the @value{GDBN} identifier of the thread. The @var{gid}
25489 field identifies the thread group this thread belongs to.
25491 @item =thread-selected,id="@var{id}"
25492 Informs that the selected thread was changed as result of the last
25493 command. This notification is not emitted as result of @code{-thread-select}
25494 command but is emitted whenever an MI command that is not documented
25495 to change the selected thread actually changes it. In particular,
25496 invoking, directly or indirectly (via user-defined command), the CLI
25497 @code{thread} command, will generate this notification.
25499 We suggest that in response to this notification, front ends
25500 highlight the selected thread and cause subsequent commands to apply to
25503 @item =library-loaded,...
25504 Reports that a new library file was loaded by the program. This
25505 notification has 4 fields---@var{id}, @var{target-name},
25506 @var{host-name}, and @var{symbols-loaded}. The @var{id} field is an
25507 opaque identifier of the library. For remote debugging case,
25508 @var{target-name} and @var{host-name} fields give the name of the
25509 library file on the target, and on the host respectively. For native
25510 debugging, both those fields have the same value. The
25511 @var{symbols-loaded} field is emitted only for backward compatibility
25512 and should not be relied on to convey any useful information. The
25513 @var{thread-group} field, if present, specifies the id of the thread
25514 group in whose context the library was loaded. If the field is
25515 absent, it means the library was loaded in the context of all present
25518 @item =library-unloaded,...
25519 Reports that a library was unloaded by the program. This notification
25520 has 3 fields---@var{id}, @var{target-name} and @var{host-name} with
25521 the same meaning as for the @code{=library-loaded} notification.
25522 The @var{thread-group} field, if present, specifies the id of the
25523 thread group in whose context the library was unloaded. If the field is
25524 absent, it means the library was unloaded in the context of all present
25527 @item =breakpoint-created,bkpt=@{...@}
25528 @itemx =breakpoint-modified,bkpt=@{...@}
25529 @itemx =breakpoint-deleted,bkpt=@{...@}
25530 Reports that a breakpoint was created, modified, or deleted,
25531 respectively. Only user-visible breakpoints are reported to the MI
25534 The @var{bkpt} argument is of the same form as returned by the various
25535 breakpoint commands; @xref{GDB/MI Breakpoint Commands}.
25537 Note that if a breakpoint is emitted in the result record of a
25538 command, then it will not also be emitted in an async record.
25542 @node GDB/MI Frame Information
25543 @subsection @sc{gdb/mi} Frame Information
25545 Response from many MI commands includes an information about stack
25546 frame. This information is a tuple that may have the following
25551 The level of the stack frame. The innermost frame has the level of
25552 zero. This field is always present.
25555 The name of the function corresponding to the frame. This field may
25556 be absent if @value{GDBN} is unable to determine the function name.
25559 The code address for the frame. This field is always present.
25562 The name of the source files that correspond to the frame's code
25563 address. This field may be absent.
25566 The source line corresponding to the frames' code address. This field
25570 The name of the binary file (either executable or shared library) the
25571 corresponds to the frame's code address. This field may be absent.
25575 @node GDB/MI Thread Information
25576 @subsection @sc{gdb/mi} Thread Information
25578 Whenever @value{GDBN} has to report an information about a thread, it
25579 uses a tuple with the following fields:
25583 The numeric id assigned to the thread by @value{GDBN}. This field is
25587 Target-specific string identifying the thread. This field is always present.
25590 Additional information about the thread provided by the target.
25591 It is supposed to be human-readable and not interpreted by the
25592 frontend. This field is optional.
25595 Either @samp{stopped} or @samp{running}, depending on whether the
25596 thread is presently running. This field is always present.
25599 The value of this field is an integer number of the processor core the
25600 thread was last seen on. This field is optional.
25603 @node GDB/MI Ada Exception Information
25604 @subsection @sc{gdb/mi} Ada Exception Information
25606 Whenever a @code{*stopped} record is emitted because the program
25607 stopped after hitting an exception catchpoint (@pxref{Set Catchpoints}),
25608 @value{GDBN} provides the name of the exception that was raised via
25609 the @code{exception-name} field.
25611 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25612 @node GDB/MI Simple Examples
25613 @section Simple Examples of @sc{gdb/mi} Interaction
25614 @cindex @sc{gdb/mi}, simple examples
25616 This subsection presents several simple examples of interaction using
25617 the @sc{gdb/mi} interface. In these examples, @samp{->} means that the
25618 following line is passed to @sc{gdb/mi} as input, while @samp{<-} means
25619 the output received from @sc{gdb/mi}.
25621 Note the line breaks shown in the examples are here only for
25622 readability, they don't appear in the real output.
25624 @subheading Setting a Breakpoint
25626 Setting a breakpoint generates synchronous output which contains detailed
25627 information of the breakpoint.
25630 -> -break-insert main
25631 <- ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
25632 enabled="y",addr="0x08048564",func="main",file="myprog.c",
25633 fullname="/home/nickrob/myprog.c",line="68",times="0"@}
25637 @subheading Program Execution
25639 Program execution generates asynchronous records and MI gives the
25640 reason that execution stopped.
25646 <- *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0",
25647 frame=@{addr="0x08048564",func="main",
25648 args=[@{name="argc",value="1"@},@{name="argv",value="0xbfc4d4d4"@}],
25649 file="myprog.c",fullname="/home/nickrob/myprog.c",line="68"@}
25654 <- *stopped,reason="exited-normally"
25658 @subheading Quitting @value{GDBN}
25660 Quitting @value{GDBN} just prints the result class @samp{^exit}.
25668 Please note that @samp{^exit} is printed immediately, but it might
25669 take some time for @value{GDBN} to actually exit. During that time, @value{GDBN}
25670 performs necessary cleanups, including killing programs being debugged
25671 or disconnecting from debug hardware, so the frontend should wait till
25672 @value{GDBN} exits and should only forcibly kill @value{GDBN} if it
25673 fails to exit in reasonable time.
25675 @subheading A Bad Command
25677 Here's what happens if you pass a non-existent command:
25681 <- ^error,msg="Undefined MI command: rubbish"
25686 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25687 @node GDB/MI Command Description Format
25688 @section @sc{gdb/mi} Command Description Format
25690 The remaining sections describe blocks of commands. Each block of
25691 commands is laid out in a fashion similar to this section.
25693 @subheading Motivation
25695 The motivation for this collection of commands.
25697 @subheading Introduction
25699 A brief introduction to this collection of commands as a whole.
25701 @subheading Commands
25703 For each command in the block, the following is described:
25705 @subsubheading Synopsis
25708 -command @var{args}@dots{}
25711 @subsubheading Result
25713 @subsubheading @value{GDBN} Command
25715 The corresponding @value{GDBN} CLI command(s), if any.
25717 @subsubheading Example
25719 Example(s) formatted for readability. Some of the described commands have
25720 not been implemented yet and these are labeled N.A.@: (not available).
25723 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25724 @node GDB/MI Breakpoint Commands
25725 @section @sc{gdb/mi} Breakpoint Commands
25727 @cindex breakpoint commands for @sc{gdb/mi}
25728 @cindex @sc{gdb/mi}, breakpoint commands
25729 This section documents @sc{gdb/mi} commands for manipulating
25732 @subheading The @code{-break-after} Command
25733 @findex -break-after
25735 @subsubheading Synopsis
25738 -break-after @var{number} @var{count}
25741 The breakpoint number @var{number} is not in effect until it has been
25742 hit @var{count} times. To see how this is reflected in the output of
25743 the @samp{-break-list} command, see the description of the
25744 @samp{-break-list} command below.
25746 @subsubheading @value{GDBN} Command
25748 The corresponding @value{GDBN} command is @samp{ignore}.
25750 @subsubheading Example
25755 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
25756 enabled="y",addr="0x000100d0",func="main",file="hello.c",
25757 fullname="/home/foo/hello.c",line="5",times="0"@}
25764 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
25765 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
25766 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
25767 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
25768 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
25769 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
25770 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
25771 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
25772 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
25773 line="5",times="0",ignore="3"@}]@}
25778 @subheading The @code{-break-catch} Command
25779 @findex -break-catch
25782 @subheading The @code{-break-commands} Command
25783 @findex -break-commands
25785 @subsubheading Synopsis
25788 -break-commands @var{number} [ @var{command1} ... @var{commandN} ]
25791 Specifies the CLI commands that should be executed when breakpoint
25792 @var{number} is hit. The parameters @var{command1} to @var{commandN}
25793 are the commands. If no command is specified, any previously-set
25794 commands are cleared. @xref{Break Commands}. Typical use of this
25795 functionality is tracing a program, that is, printing of values of
25796 some variables whenever breakpoint is hit and then continuing.
25798 @subsubheading @value{GDBN} Command
25800 The corresponding @value{GDBN} command is @samp{commands}.
25802 @subsubheading Example
25807 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
25808 enabled="y",addr="0x000100d0",func="main",file="hello.c",
25809 fullname="/home/foo/hello.c",line="5",times="0"@}
25811 -break-commands 1 "print v" "continue"
25816 @subheading The @code{-break-condition} Command
25817 @findex -break-condition
25819 @subsubheading Synopsis
25822 -break-condition @var{number} @var{expr}
25825 Breakpoint @var{number} will stop the program only if the condition in
25826 @var{expr} is true. The condition becomes part of the
25827 @samp{-break-list} output (see the description of the @samp{-break-list}
25830 @subsubheading @value{GDBN} Command
25832 The corresponding @value{GDBN} command is @samp{condition}.
25834 @subsubheading Example
25838 -break-condition 1 1
25842 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
25843 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
25844 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
25845 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
25846 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
25847 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
25848 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
25849 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
25850 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
25851 line="5",cond="1",times="0",ignore="3"@}]@}
25855 @subheading The @code{-break-delete} Command
25856 @findex -break-delete
25858 @subsubheading Synopsis
25861 -break-delete ( @var{breakpoint} )+
25864 Delete the breakpoint(s) whose number(s) are specified in the argument
25865 list. This is obviously reflected in the breakpoint list.
25867 @subsubheading @value{GDBN} Command
25869 The corresponding @value{GDBN} command is @samp{delete}.
25871 @subsubheading Example
25879 ^done,BreakpointTable=@{nr_rows="0",nr_cols="6",
25880 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
25881 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
25882 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
25883 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
25884 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
25885 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
25890 @subheading The @code{-break-disable} Command
25891 @findex -break-disable
25893 @subsubheading Synopsis
25896 -break-disable ( @var{breakpoint} )+
25899 Disable the named @var{breakpoint}(s). The field @samp{enabled} in the
25900 break list is now set to @samp{n} for the named @var{breakpoint}(s).
25902 @subsubheading @value{GDBN} Command
25904 The corresponding @value{GDBN} command is @samp{disable}.
25906 @subsubheading Example
25914 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
25915 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
25916 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
25917 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
25918 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
25919 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
25920 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
25921 body=[bkpt=@{number="2",type="breakpoint",disp="keep",enabled="n",
25922 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
25923 line="5",times="0"@}]@}
25927 @subheading The @code{-break-enable} Command
25928 @findex -break-enable
25930 @subsubheading Synopsis
25933 -break-enable ( @var{breakpoint} )+
25936 Enable (previously disabled) @var{breakpoint}(s).
25938 @subsubheading @value{GDBN} Command
25940 The corresponding @value{GDBN} command is @samp{enable}.
25942 @subsubheading Example
25950 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
25951 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
25952 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
25953 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
25954 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
25955 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
25956 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
25957 body=[bkpt=@{number="2",type="breakpoint",disp="keep",enabled="y",
25958 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
25959 line="5",times="0"@}]@}
25963 @subheading The @code{-break-info} Command
25964 @findex -break-info
25966 @subsubheading Synopsis
25969 -break-info @var{breakpoint}
25973 Get information about a single breakpoint.
25975 @subsubheading @value{GDBN} Command
25977 The corresponding @value{GDBN} command is @samp{info break @var{breakpoint}}.
25979 @subsubheading Example
25982 @subheading The @code{-break-insert} Command
25983 @findex -break-insert
25985 @subsubheading Synopsis
25988 -break-insert [ -t ] [ -h ] [ -f ] [ -d ] [ -a ]
25989 [ -c @var{condition} ] [ -i @var{ignore-count} ]
25990 [ -p @var{thread} ] [ @var{location} ]
25994 If specified, @var{location}, can be one of:
26001 @item filename:linenum
26002 @item filename:function
26006 The possible optional parameters of this command are:
26010 Insert a temporary breakpoint.
26012 Insert a hardware breakpoint.
26013 @item -c @var{condition}
26014 Make the breakpoint conditional on @var{condition}.
26015 @item -i @var{ignore-count}
26016 Initialize the @var{ignore-count}.
26018 If @var{location} cannot be parsed (for example if it
26019 refers to unknown files or functions), create a pending
26020 breakpoint. Without this flag, @value{GDBN} will report
26021 an error, and won't create a breakpoint, if @var{location}
26024 Create a disabled breakpoint.
26026 Create a tracepoint. @xref{Tracepoints}. When this parameter
26027 is used together with @samp{-h}, a fast tracepoint is created.
26030 @subsubheading Result
26032 The result is in the form:
26035 ^done,bkpt=@{number="@var{number}",type="@var{type}",disp="del"|"keep",
26036 enabled="y"|"n",addr="@var{hex}",func="@var{funcname}",file="@var{filename}",
26037 fullname="@var{full_filename}",line="@var{lineno}",[thread="@var{threadno},]
26038 times="@var{times}"@}
26042 where @var{number} is the @value{GDBN} number for this breakpoint,
26043 @var{funcname} is the name of the function where the breakpoint was
26044 inserted, @var{filename} is the name of the source file which contains
26045 this function, @var{lineno} is the source line number within that file
26046 and @var{times} the number of times that the breakpoint has been hit
26047 (always 0 for -break-insert but may be greater for -break-info or -break-list
26048 which use the same output).
26050 Note: this format is open to change.
26051 @c An out-of-band breakpoint instead of part of the result?
26053 @subsubheading @value{GDBN} Command
26055 The corresponding @value{GDBN} commands are @samp{break}, @samp{tbreak},
26056 @samp{hbreak}, @samp{thbreak}, and @samp{rbreak}.
26058 @subsubheading Example
26063 ^done,bkpt=@{number="1",addr="0x0001072c",file="recursive2.c",
26064 fullname="/home/foo/recursive2.c,line="4",times="0"@}
26066 -break-insert -t foo
26067 ^done,bkpt=@{number="2",addr="0x00010774",file="recursive2.c",
26068 fullname="/home/foo/recursive2.c,line="11",times="0"@}
26071 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
26072 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
26073 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
26074 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
26075 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
26076 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
26077 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
26078 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
26079 addr="0x0001072c", func="main",file="recursive2.c",
26080 fullname="/home/foo/recursive2.c,"line="4",times="0"@},
26081 bkpt=@{number="2",type="breakpoint",disp="del",enabled="y",
26082 addr="0x00010774",func="foo",file="recursive2.c",
26083 fullname="/home/foo/recursive2.c",line="11",times="0"@}]@}
26085 -break-insert -r foo.*
26086 ~int foo(int, int);
26087 ^done,bkpt=@{number="3",addr="0x00010774",file="recursive2.c,
26088 "fullname="/home/foo/recursive2.c",line="11",times="0"@}
26092 @subheading The @code{-break-list} Command
26093 @findex -break-list
26095 @subsubheading Synopsis
26101 Displays the list of inserted breakpoints, showing the following fields:
26105 number of the breakpoint
26107 type of the breakpoint: @samp{breakpoint} or @samp{watchpoint}
26109 should the breakpoint be deleted or disabled when it is hit: @samp{keep}
26112 is the breakpoint enabled or no: @samp{y} or @samp{n}
26114 memory location at which the breakpoint is set
26116 logical location of the breakpoint, expressed by function name, file
26119 number of times the breakpoint has been hit
26122 If there are no breakpoints or watchpoints, the @code{BreakpointTable}
26123 @code{body} field is an empty list.
26125 @subsubheading @value{GDBN} Command
26127 The corresponding @value{GDBN} command is @samp{info break}.
26129 @subsubheading Example
26134 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
26135 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
26136 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
26137 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
26138 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
26139 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
26140 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
26141 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
26142 addr="0x000100d0",func="main",file="hello.c",line="5",times="0"@},
26143 bkpt=@{number="2",type="breakpoint",disp="keep",enabled="y",
26144 addr="0x00010114",func="foo",file="hello.c",fullname="/home/foo/hello.c",
26145 line="13",times="0"@}]@}
26149 Here's an example of the result when there are no breakpoints:
26154 ^done,BreakpointTable=@{nr_rows="0",nr_cols="6",
26155 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
26156 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
26157 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
26158 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
26159 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
26160 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
26165 @subheading The @code{-break-passcount} Command
26166 @findex -break-passcount
26168 @subsubheading Synopsis
26171 -break-passcount @var{tracepoint-number} @var{passcount}
26174 Set the passcount for tracepoint @var{tracepoint-number} to
26175 @var{passcount}. If the breakpoint referred to by @var{tracepoint-number}
26176 is not a tracepoint, error is emitted. This corresponds to CLI
26177 command @samp{passcount}.
26179 @subheading The @code{-break-watch} Command
26180 @findex -break-watch
26182 @subsubheading Synopsis
26185 -break-watch [ -a | -r ]
26188 Create a watchpoint. With the @samp{-a} option it will create an
26189 @dfn{access} watchpoint, i.e., a watchpoint that triggers either on a
26190 read from or on a write to the memory location. With the @samp{-r}
26191 option, the watchpoint created is a @dfn{read} watchpoint, i.e., it will
26192 trigger only when the memory location is accessed for reading. Without
26193 either of the options, the watchpoint created is a regular watchpoint,
26194 i.e., it will trigger when the memory location is accessed for writing.
26195 @xref{Set Watchpoints, , Setting Watchpoints}.
26197 Note that @samp{-break-list} will report a single list of watchpoints and
26198 breakpoints inserted.
26200 @subsubheading @value{GDBN} Command
26202 The corresponding @value{GDBN} commands are @samp{watch}, @samp{awatch}, and
26205 @subsubheading Example
26207 Setting a watchpoint on a variable in the @code{main} function:
26212 ^done,wpt=@{number="2",exp="x"@}
26217 *stopped,reason="watchpoint-trigger",wpt=@{number="2",exp="x"@},
26218 value=@{old="-268439212",new="55"@},
26219 frame=@{func="main",args=[],file="recursive2.c",
26220 fullname="/home/foo/bar/recursive2.c",line="5"@}
26224 Setting a watchpoint on a variable local to a function. @value{GDBN} will stop
26225 the program execution twice: first for the variable changing value, then
26226 for the watchpoint going out of scope.
26231 ^done,wpt=@{number="5",exp="C"@}
26236 *stopped,reason="watchpoint-trigger",
26237 wpt=@{number="5",exp="C"@},value=@{old="-276895068",new="3"@},
26238 frame=@{func="callee4",args=[],
26239 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
26240 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13"@}
26245 *stopped,reason="watchpoint-scope",wpnum="5",
26246 frame=@{func="callee3",args=[@{name="strarg",
26247 value="0x11940 \"A string argument.\""@}],
26248 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
26249 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
26253 Listing breakpoints and watchpoints, at different points in the program
26254 execution. Note that once the watchpoint goes out of scope, it is
26260 ^done,wpt=@{number="2",exp="C"@}
26263 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
26264 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
26265 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
26266 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
26267 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
26268 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
26269 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
26270 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
26271 addr="0x00010734",func="callee4",
26272 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
26273 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c"line="8",times="1"@},
26274 bkpt=@{number="2",type="watchpoint",disp="keep",
26275 enabled="y",addr="",what="C",times="0"@}]@}
26280 *stopped,reason="watchpoint-trigger",wpt=@{number="2",exp="C"@},
26281 value=@{old="-276895068",new="3"@},
26282 frame=@{func="callee4",args=[],
26283 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
26284 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13"@}
26287 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
26288 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
26289 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
26290 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
26291 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
26292 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
26293 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
26294 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
26295 addr="0x00010734",func="callee4",
26296 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
26297 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",times="1"@},
26298 bkpt=@{number="2",type="watchpoint",disp="keep",
26299 enabled="y",addr="",what="C",times="-5"@}]@}
26303 ^done,reason="watchpoint-scope",wpnum="2",
26304 frame=@{func="callee3",args=[@{name="strarg",
26305 value="0x11940 \"A string argument.\""@}],
26306 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
26307 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
26310 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
26311 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
26312 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
26313 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
26314 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
26315 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
26316 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
26317 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
26318 addr="0x00010734",func="callee4",
26319 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
26320 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",
26325 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
26326 @node GDB/MI Program Context
26327 @section @sc{gdb/mi} Program Context
26329 @subheading The @code{-exec-arguments} Command
26330 @findex -exec-arguments
26333 @subsubheading Synopsis
26336 -exec-arguments @var{args}
26339 Set the inferior program arguments, to be used in the next
26342 @subsubheading @value{GDBN} Command
26344 The corresponding @value{GDBN} command is @samp{set args}.
26346 @subsubheading Example
26350 -exec-arguments -v word
26357 @subheading The @code{-exec-show-arguments} Command
26358 @findex -exec-show-arguments
26360 @subsubheading Synopsis
26363 -exec-show-arguments
26366 Print the arguments of the program.
26368 @subsubheading @value{GDBN} Command
26370 The corresponding @value{GDBN} command is @samp{show args}.
26372 @subsubheading Example
26377 @subheading The @code{-environment-cd} Command
26378 @findex -environment-cd
26380 @subsubheading Synopsis
26383 -environment-cd @var{pathdir}
26386 Set @value{GDBN}'s working directory.
26388 @subsubheading @value{GDBN} Command
26390 The corresponding @value{GDBN} command is @samp{cd}.
26392 @subsubheading Example
26396 -environment-cd /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
26402 @subheading The @code{-environment-directory} Command
26403 @findex -environment-directory
26405 @subsubheading Synopsis
26408 -environment-directory [ -r ] [ @var{pathdir} ]+
26411 Add directories @var{pathdir} to beginning of search path for source files.
26412 If the @samp{-r} option is used, the search path is reset to the default
26413 search path. If directories @var{pathdir} are supplied in addition to the
26414 @samp{-r} option, the search path is first reset and then addition
26416 Multiple directories may be specified, separated by blanks. Specifying
26417 multiple directories in a single command
26418 results in the directories added to the beginning of the
26419 search path in the same order they were presented in the command.
26420 If blanks are needed as
26421 part of a directory name, double-quotes should be used around
26422 the name. In the command output, the path will show up separated
26423 by the system directory-separator character. The directory-separator
26424 character must not be used
26425 in any directory name.
26426 If no directories are specified, the current search path is displayed.
26428 @subsubheading @value{GDBN} Command
26430 The corresponding @value{GDBN} command is @samp{dir}.
26432 @subsubheading Example
26436 -environment-directory /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
26437 ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
26439 -environment-directory ""
26440 ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
26442 -environment-directory -r /home/jjohnstn/src/gdb /usr/src
26443 ^done,source-path="/home/jjohnstn/src/gdb:/usr/src:$cdir:$cwd"
26445 -environment-directory -r
26446 ^done,source-path="$cdir:$cwd"
26451 @subheading The @code{-environment-path} Command
26452 @findex -environment-path
26454 @subsubheading Synopsis
26457 -environment-path [ -r ] [ @var{pathdir} ]+
26460 Add directories @var{pathdir} to beginning of search path for object files.
26461 If the @samp{-r} option is used, the search path is reset to the original
26462 search path that existed at gdb start-up. If directories @var{pathdir} are
26463 supplied in addition to the
26464 @samp{-r} option, the search path is first reset and then addition
26466 Multiple directories may be specified, separated by blanks. Specifying
26467 multiple directories in a single command
26468 results in the directories added to the beginning of the
26469 search path in the same order they were presented in the command.
26470 If blanks are needed as
26471 part of a directory name, double-quotes should be used around
26472 the name. In the command output, the path will show up separated
26473 by the system directory-separator character. The directory-separator
26474 character must not be used
26475 in any directory name.
26476 If no directories are specified, the current path is displayed.
26479 @subsubheading @value{GDBN} Command
26481 The corresponding @value{GDBN} command is @samp{path}.
26483 @subsubheading Example
26488 ^done,path="/usr/bin"
26490 -environment-path /kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb /bin
26491 ^done,path="/kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb:/bin:/usr/bin"
26493 -environment-path -r /usr/local/bin
26494 ^done,path="/usr/local/bin:/usr/bin"
26499 @subheading The @code{-environment-pwd} Command
26500 @findex -environment-pwd
26502 @subsubheading Synopsis
26508 Show the current working directory.
26510 @subsubheading @value{GDBN} Command
26512 The corresponding @value{GDBN} command is @samp{pwd}.
26514 @subsubheading Example
26519 ^done,cwd="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb"
26523 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
26524 @node GDB/MI Thread Commands
26525 @section @sc{gdb/mi} Thread Commands
26528 @subheading The @code{-thread-info} Command
26529 @findex -thread-info
26531 @subsubheading Synopsis
26534 -thread-info [ @var{thread-id} ]
26537 Reports information about either a specific thread, if
26538 the @var{thread-id} parameter is present, or about all
26539 threads. When printing information about all threads,
26540 also reports the current thread.
26542 @subsubheading @value{GDBN} Command
26544 The @samp{info thread} command prints the same information
26547 @subsubheading Result
26549 The result is a list of threads. The following attributes are
26550 defined for a given thread:
26554 This field exists only for the current thread. It has the value @samp{*}.
26557 The identifier that @value{GDBN} uses to refer to the thread.
26560 The identifier that the target uses to refer to the thread.
26563 Extra information about the thread, in a target-specific format. This
26567 The name of the thread. If the user specified a name using the
26568 @code{thread name} command, then this name is given. Otherwise, if
26569 @value{GDBN} can extract the thread name from the target, then that
26570 name is given. If @value{GDBN} cannot find the thread name, then this
26574 The stack frame currently executing in the thread.
26577 The thread's state. The @samp{state} field may have the following
26582 The thread is stopped. Frame information is available for stopped
26586 The thread is running. There's no frame information for running
26592 If @value{GDBN} can find the CPU core on which this thread is running,
26593 then this field is the core identifier. This field is optional.
26597 @subsubheading Example
26602 @{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)",
26603 frame=@{level="0",addr="0xffffe410",func="__kernel_vsyscall",
26604 args=[]@},state="running"@},
26605 @{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
26606 frame=@{level="0",addr="0x0804891f",func="foo",
26607 args=[@{name="i",value="10"@}],
26608 file="/tmp/a.c",fullname="/tmp/a.c",line="158"@},
26609 state="running"@}],
26610 current-thread-id="1"
26614 @subheading The @code{-thread-list-ids} Command
26615 @findex -thread-list-ids
26617 @subsubheading Synopsis
26623 Produces a list of the currently known @value{GDBN} thread ids. At the
26624 end of the list it also prints the total number of such threads.
26626 This command is retained for historical reasons, the
26627 @code{-thread-info} command should be used instead.
26629 @subsubheading @value{GDBN} Command
26631 Part of @samp{info threads} supplies the same information.
26633 @subsubheading Example
26638 ^done,thread-ids=@{thread-id="3",thread-id="2",thread-id="1"@},
26639 current-thread-id="1",number-of-threads="3"
26644 @subheading The @code{-thread-select} Command
26645 @findex -thread-select
26647 @subsubheading Synopsis
26650 -thread-select @var{threadnum}
26653 Make @var{threadnum} the current thread. It prints the number of the new
26654 current thread, and the topmost frame for that thread.
26656 This command is deprecated in favor of explicitly using the
26657 @samp{--thread} option to each command.
26659 @subsubheading @value{GDBN} Command
26661 The corresponding @value{GDBN} command is @samp{thread}.
26663 @subsubheading Example
26670 *stopped,reason="end-stepping-range",thread-id="2",line="187",
26671 file="../../../devo/gdb/testsuite/gdb.threads/linux-dp.c"
26675 thread-ids=@{thread-id="3",thread-id="2",thread-id="1"@},
26676 number-of-threads="3"
26679 ^done,new-thread-id="3",
26680 frame=@{level="0",func="vprintf",
26681 args=[@{name="format",value="0x8048e9c \"%*s%c %d %c\\n\""@},
26682 @{name="arg",value="0x2"@}],file="vprintf.c",line="31"@}
26686 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
26687 @node GDB/MI Ada Tasking Commands
26688 @section @sc{gdb/mi} Ada Tasking Commands
26690 @subheading The @code{-ada-task-info} Command
26691 @findex -ada-task-info
26693 @subsubheading Synopsis
26696 -ada-task-info [ @var{task-id} ]
26699 Reports information about either a specific Ada task, if the
26700 @var{task-id} parameter is present, or about all Ada tasks.
26702 @subsubheading @value{GDBN} Command
26704 The @samp{info tasks} command prints the same information
26705 about all Ada tasks (@pxref{Ada Tasks}).
26707 @subsubheading Result
26709 The result is a table of Ada tasks. The following columns are
26710 defined for each Ada task:
26714 This field exists only for the current thread. It has the value @samp{*}.
26717 The identifier that @value{GDBN} uses to refer to the Ada task.
26720 The identifier that the target uses to refer to the Ada task.
26723 The identifier of the thread corresponding to the Ada task.
26725 This field should always exist, as Ada tasks are always implemented
26726 on top of a thread. But if @value{GDBN} cannot find this corresponding
26727 thread for any reason, the field is omitted.
26730 This field exists only when the task was created by another task.
26731 In this case, it provides the ID of the parent task.
26734 The base priority of the task.
26737 The current state of the task. For a detailed description of the
26738 possible states, see @ref{Ada Tasks}.
26741 The name of the task.
26745 @subsubheading Example
26749 ^done,tasks=@{nr_rows="3",nr_cols="8",
26750 hdr=[@{width="1",alignment="-1",col_name="current",colhdr=""@},
26751 @{width="3",alignment="1",col_name="id",colhdr="ID"@},
26752 @{width="9",alignment="1",col_name="task-id",colhdr="TID"@},
26753 @{width="4",alignment="1",col_name="thread-id",colhdr=""@},
26754 @{width="4",alignment="1",col_name="parent-id",colhdr="P-ID"@},
26755 @{width="3",alignment="1",col_name="priority",colhdr="Pri"@},
26756 @{width="22",alignment="-1",col_name="state",colhdr="State"@},
26757 @{width="1",alignment="2",col_name="name",colhdr="Name"@}],
26758 body=[@{current="*",id="1",task-id=" 644010",thread-id="1",priority="48",
26759 state="Child Termination Wait",name="main_task"@}]@}
26763 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
26764 @node GDB/MI Program Execution
26765 @section @sc{gdb/mi} Program Execution
26767 These are the asynchronous commands which generate the out-of-band
26768 record @samp{*stopped}. Currently @value{GDBN} only really executes
26769 asynchronously with remote targets and this interaction is mimicked in
26772 @subheading The @code{-exec-continue} Command
26773 @findex -exec-continue
26775 @subsubheading Synopsis
26778 -exec-continue [--reverse] [--all|--thread-group N]
26781 Resumes the execution of the inferior program, which will continue
26782 to execute until it reaches a debugger stop event. If the
26783 @samp{--reverse} option is specified, execution resumes in reverse until
26784 it reaches a stop event. Stop events may include
26787 breakpoints or watchpoints
26789 signals or exceptions
26791 the end of the process (or its beginning under @samp{--reverse})
26793 the end or beginning of a replay log if one is being used.
26795 In all-stop mode (@pxref{All-Stop
26796 Mode}), may resume only one thread, or all threads, depending on the
26797 value of the @samp{scheduler-locking} variable. If @samp{--all} is
26798 specified, all threads (in all inferiors) will be resumed. The @samp{--all} option is
26799 ignored in all-stop mode. If the @samp{--thread-group} options is
26800 specified, then all threads in that thread group are resumed.
26802 @subsubheading @value{GDBN} Command
26804 The corresponding @value{GDBN} corresponding is @samp{continue}.
26806 @subsubheading Example
26813 *stopped,reason="breakpoint-hit",disp="keep",bkptno="2",frame=@{
26814 func="foo",args=[],file="hello.c",fullname="/home/foo/bar/hello.c",
26820 @subheading The @code{-exec-finish} Command
26821 @findex -exec-finish
26823 @subsubheading Synopsis
26826 -exec-finish [--reverse]
26829 Resumes the execution of the inferior program until the current
26830 function is exited. Displays the results returned by the function.
26831 If the @samp{--reverse} option is specified, resumes the reverse
26832 execution of the inferior program until the point where current
26833 function was called.
26835 @subsubheading @value{GDBN} Command
26837 The corresponding @value{GDBN} command is @samp{finish}.
26839 @subsubheading Example
26841 Function returning @code{void}.
26848 *stopped,reason="function-finished",frame=@{func="main",args=[],
26849 file="hello.c",fullname="/home/foo/bar/hello.c",line="7"@}
26853 Function returning other than @code{void}. The name of the internal
26854 @value{GDBN} variable storing the result is printed, together with the
26861 *stopped,reason="function-finished",frame=@{addr="0x000107b0",func="foo",
26862 args=[@{name="a",value="1"],@{name="b",value="9"@}@},
26863 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
26864 gdb-result-var="$1",return-value="0"
26869 @subheading The @code{-exec-interrupt} Command
26870 @findex -exec-interrupt
26872 @subsubheading Synopsis
26875 -exec-interrupt [--all|--thread-group N]
26878 Interrupts the background execution of the target. Note how the token
26879 associated with the stop message is the one for the execution command
26880 that has been interrupted. The token for the interrupt itself only
26881 appears in the @samp{^done} output. If the user is trying to
26882 interrupt a non-running program, an error message will be printed.
26884 Note that when asynchronous execution is enabled, this command is
26885 asynchronous just like other execution commands. That is, first the
26886 @samp{^done} response will be printed, and the target stop will be
26887 reported after that using the @samp{*stopped} notification.
26889 In non-stop mode, only the context thread is interrupted by default.
26890 All threads (in all inferiors) will be interrupted if the
26891 @samp{--all} option is specified. If the @samp{--thread-group}
26892 option is specified, all threads in that group will be interrupted.
26894 @subsubheading @value{GDBN} Command
26896 The corresponding @value{GDBN} command is @samp{interrupt}.
26898 @subsubheading Example
26909 111*stopped,signal-name="SIGINT",signal-meaning="Interrupt",
26910 frame=@{addr="0x00010140",func="foo",args=[],file="try.c",
26911 fullname="/home/foo/bar/try.c",line="13"@}
26916 ^error,msg="mi_cmd_exec_interrupt: Inferior not executing."
26920 @subheading The @code{-exec-jump} Command
26923 @subsubheading Synopsis
26926 -exec-jump @var{location}
26929 Resumes execution of the inferior program at the location specified by
26930 parameter. @xref{Specify Location}, for a description of the
26931 different forms of @var{location}.
26933 @subsubheading @value{GDBN} Command
26935 The corresponding @value{GDBN} command is @samp{jump}.
26937 @subsubheading Example
26940 -exec-jump foo.c:10
26941 *running,thread-id="all"
26946 @subheading The @code{-exec-next} Command
26949 @subsubheading Synopsis
26952 -exec-next [--reverse]
26955 Resumes execution of the inferior program, stopping when the beginning
26956 of the next source line is reached.
26958 If the @samp{--reverse} option is specified, resumes reverse execution
26959 of the inferior program, stopping at the beginning of the previous
26960 source line. If you issue this command on the first line of a
26961 function, it will take you back to the caller of that function, to the
26962 source line where the function was called.
26965 @subsubheading @value{GDBN} Command
26967 The corresponding @value{GDBN} command is @samp{next}.
26969 @subsubheading Example
26975 *stopped,reason="end-stepping-range",line="8",file="hello.c"
26980 @subheading The @code{-exec-next-instruction} Command
26981 @findex -exec-next-instruction
26983 @subsubheading Synopsis
26986 -exec-next-instruction [--reverse]
26989 Executes one machine instruction. If the instruction is a function
26990 call, continues until the function returns. If the program stops at an
26991 instruction in the middle of a source line, the address will be
26994 If the @samp{--reverse} option is specified, resumes reverse execution
26995 of the inferior program, stopping at the previous instruction. If the
26996 previously executed instruction was a return from another function,
26997 it will continue to execute in reverse until the call to that function
26998 (from the current stack frame) is reached.
27000 @subsubheading @value{GDBN} Command
27002 The corresponding @value{GDBN} command is @samp{nexti}.
27004 @subsubheading Example
27008 -exec-next-instruction
27012 *stopped,reason="end-stepping-range",
27013 addr="0x000100d4",line="5",file="hello.c"
27018 @subheading The @code{-exec-return} Command
27019 @findex -exec-return
27021 @subsubheading Synopsis
27027 Makes current function return immediately. Doesn't execute the inferior.
27028 Displays the new current frame.
27030 @subsubheading @value{GDBN} Command
27032 The corresponding @value{GDBN} command is @samp{return}.
27034 @subsubheading Example
27038 200-break-insert callee4
27039 200^done,bkpt=@{number="1",addr="0x00010734",
27040 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8"@}
27045 000*stopped,reason="breakpoint-hit",disp="keep",bkptno="1",
27046 frame=@{func="callee4",args=[],
27047 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27048 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8"@}
27054 111^done,frame=@{level="0",func="callee3",
27055 args=[@{name="strarg",
27056 value="0x11940 \"A string argument.\""@}],
27057 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27058 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
27063 @subheading The @code{-exec-run} Command
27066 @subsubheading Synopsis
27069 -exec-run [--all | --thread-group N]
27072 Starts execution of the inferior from the beginning. The inferior
27073 executes until either a breakpoint is encountered or the program
27074 exits. In the latter case the output will include an exit code, if
27075 the program has exited exceptionally.
27077 When no option is specified, the current inferior is started. If the
27078 @samp{--thread-group} option is specified, it should refer to a thread
27079 group of type @samp{process}, and that thread group will be started.
27080 If the @samp{--all} option is specified, then all inferiors will be started.
27082 @subsubheading @value{GDBN} Command
27084 The corresponding @value{GDBN} command is @samp{run}.
27086 @subsubheading Examples
27091 ^done,bkpt=@{number="1",addr="0x0001072c",file="recursive2.c",line="4"@}
27096 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",
27097 frame=@{func="main",args=[],file="recursive2.c",
27098 fullname="/home/foo/bar/recursive2.c",line="4"@}
27103 Program exited normally:
27111 *stopped,reason="exited-normally"
27116 Program exited exceptionally:
27124 *stopped,reason="exited",exit-code="01"
27128 Another way the program can terminate is if it receives a signal such as
27129 @code{SIGINT}. In this case, @sc{gdb/mi} displays this:
27133 *stopped,reason="exited-signalled",signal-name="SIGINT",
27134 signal-meaning="Interrupt"
27138 @c @subheading -exec-signal
27141 @subheading The @code{-exec-step} Command
27144 @subsubheading Synopsis
27147 -exec-step [--reverse]
27150 Resumes execution of the inferior program, stopping when the beginning
27151 of the next source line is reached, if the next source line is not a
27152 function call. If it is, stop at the first instruction of the called
27153 function. If the @samp{--reverse} option is specified, resumes reverse
27154 execution of the inferior program, stopping at the beginning of the
27155 previously executed source line.
27157 @subsubheading @value{GDBN} Command
27159 The corresponding @value{GDBN} command is @samp{step}.
27161 @subsubheading Example
27163 Stepping into a function:
27169 *stopped,reason="end-stepping-range",
27170 frame=@{func="foo",args=[@{name="a",value="10"@},
27171 @{name="b",value="0"@}],file="recursive2.c",
27172 fullname="/home/foo/bar/recursive2.c",line="11"@}
27182 *stopped,reason="end-stepping-range",line="14",file="recursive2.c"
27187 @subheading The @code{-exec-step-instruction} Command
27188 @findex -exec-step-instruction
27190 @subsubheading Synopsis
27193 -exec-step-instruction [--reverse]
27196 Resumes the inferior which executes one machine instruction. If the
27197 @samp{--reverse} option is specified, resumes reverse execution of the
27198 inferior program, stopping at the previously executed instruction.
27199 The output, once @value{GDBN} has stopped, will vary depending on
27200 whether we have stopped in the middle of a source line or not. In the
27201 former case, the address at which the program stopped will be printed
27204 @subsubheading @value{GDBN} Command
27206 The corresponding @value{GDBN} command is @samp{stepi}.
27208 @subsubheading Example
27212 -exec-step-instruction
27216 *stopped,reason="end-stepping-range",
27217 frame=@{func="foo",args=[],file="try.c",
27218 fullname="/home/foo/bar/try.c",line="10"@}
27220 -exec-step-instruction
27224 *stopped,reason="end-stepping-range",
27225 frame=@{addr="0x000100f4",func="foo",args=[],file="try.c",
27226 fullname="/home/foo/bar/try.c",line="10"@}
27231 @subheading The @code{-exec-until} Command
27232 @findex -exec-until
27234 @subsubheading Synopsis
27237 -exec-until [ @var{location} ]
27240 Executes the inferior until the @var{location} specified in the
27241 argument is reached. If there is no argument, the inferior executes
27242 until a source line greater than the current one is reached. The
27243 reason for stopping in this case will be @samp{location-reached}.
27245 @subsubheading @value{GDBN} Command
27247 The corresponding @value{GDBN} command is @samp{until}.
27249 @subsubheading Example
27253 -exec-until recursive2.c:6
27257 *stopped,reason="location-reached",frame=@{func="main",args=[],
27258 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="6"@}
27263 @subheading -file-clear
27264 Is this going away????
27267 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
27268 @node GDB/MI Stack Manipulation
27269 @section @sc{gdb/mi} Stack Manipulation Commands
27272 @subheading The @code{-stack-info-frame} Command
27273 @findex -stack-info-frame
27275 @subsubheading Synopsis
27281 Get info on the selected frame.
27283 @subsubheading @value{GDBN} Command
27285 The corresponding @value{GDBN} command is @samp{info frame} or @samp{frame}
27286 (without arguments).
27288 @subsubheading Example
27293 ^done,frame=@{level="1",addr="0x0001076c",func="callee3",
27294 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27295 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17"@}
27299 @subheading The @code{-stack-info-depth} Command
27300 @findex -stack-info-depth
27302 @subsubheading Synopsis
27305 -stack-info-depth [ @var{max-depth} ]
27308 Return the depth of the stack. If the integer argument @var{max-depth}
27309 is specified, do not count beyond @var{max-depth} frames.
27311 @subsubheading @value{GDBN} Command
27313 There's no equivalent @value{GDBN} command.
27315 @subsubheading Example
27317 For a stack with frame levels 0 through 11:
27324 -stack-info-depth 4
27327 -stack-info-depth 12
27330 -stack-info-depth 11
27333 -stack-info-depth 13
27338 @subheading The @code{-stack-list-arguments} Command
27339 @findex -stack-list-arguments
27341 @subsubheading Synopsis
27344 -stack-list-arguments @var{print-values}
27345 [ @var{low-frame} @var{high-frame} ]
27348 Display a list of the arguments for the frames between @var{low-frame}
27349 and @var{high-frame} (inclusive). If @var{low-frame} and
27350 @var{high-frame} are not provided, list the arguments for the whole
27351 call stack. If the two arguments are equal, show the single frame
27352 at the corresponding level. It is an error if @var{low-frame} is
27353 larger than the actual number of frames. On the other hand,
27354 @var{high-frame} may be larger than the actual number of frames, in
27355 which case only existing frames will be returned.
27357 If @var{print-values} is 0 or @code{--no-values}, print only the names of
27358 the variables; if it is 1 or @code{--all-values}, print also their
27359 values; and if it is 2 or @code{--simple-values}, print the name,
27360 type and value for simple data types, and the name and type for arrays,
27361 structures and unions.
27363 Use of this command to obtain arguments in a single frame is
27364 deprecated in favor of the @samp{-stack-list-variables} command.
27366 @subsubheading @value{GDBN} Command
27368 @value{GDBN} does not have an equivalent command. @code{gdbtk} has a
27369 @samp{gdb_get_args} command which partially overlaps with the
27370 functionality of @samp{-stack-list-arguments}.
27372 @subsubheading Example
27379 frame=@{level="0",addr="0x00010734",func="callee4",
27380 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27381 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8"@},
27382 frame=@{level="1",addr="0x0001076c",func="callee3",
27383 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27384 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17"@},
27385 frame=@{level="2",addr="0x0001078c",func="callee2",
27386 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27387 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="22"@},
27388 frame=@{level="3",addr="0x000107b4",func="callee1",
27389 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27390 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="27"@},
27391 frame=@{level="4",addr="0x000107e0",func="main",
27392 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27393 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="32"@}]
27395 -stack-list-arguments 0
27398 frame=@{level="0",args=[]@},
27399 frame=@{level="1",args=[name="strarg"]@},
27400 frame=@{level="2",args=[name="intarg",name="strarg"]@},
27401 frame=@{level="3",args=[name="intarg",name="strarg",name="fltarg"]@},
27402 frame=@{level="4",args=[]@}]
27404 -stack-list-arguments 1
27407 frame=@{level="0",args=[]@},
27409 args=[@{name="strarg",value="0x11940 \"A string argument.\""@}]@},
27410 frame=@{level="2",args=[
27411 @{name="intarg",value="2"@},
27412 @{name="strarg",value="0x11940 \"A string argument.\""@}]@},
27413 @{frame=@{level="3",args=[
27414 @{name="intarg",value="2"@},
27415 @{name="strarg",value="0x11940 \"A string argument.\""@},
27416 @{name="fltarg",value="3.5"@}]@},
27417 frame=@{level="4",args=[]@}]
27419 -stack-list-arguments 0 2 2
27420 ^done,stack-args=[frame=@{level="2",args=[name="intarg",name="strarg"]@}]
27422 -stack-list-arguments 1 2 2
27423 ^done,stack-args=[frame=@{level="2",
27424 args=[@{name="intarg",value="2"@},
27425 @{name="strarg",value="0x11940 \"A string argument.\""@}]@}]
27429 @c @subheading -stack-list-exception-handlers
27432 @subheading The @code{-stack-list-frames} Command
27433 @findex -stack-list-frames
27435 @subsubheading Synopsis
27438 -stack-list-frames [ @var{low-frame} @var{high-frame} ]
27441 List the frames currently on the stack. For each frame it displays the
27446 The frame number, 0 being the topmost frame, i.e., the innermost function.
27448 The @code{$pc} value for that frame.
27452 File name of the source file where the function lives.
27453 @item @var{fullname}
27454 The full file name of the source file where the function lives.
27456 Line number corresponding to the @code{$pc}.
27458 The shared library where this function is defined. This is only given
27459 if the frame's function is not known.
27462 If invoked without arguments, this command prints a backtrace for the
27463 whole stack. If given two integer arguments, it shows the frames whose
27464 levels are between the two arguments (inclusive). If the two arguments
27465 are equal, it shows the single frame at the corresponding level. It is
27466 an error if @var{low-frame} is larger than the actual number of
27467 frames. On the other hand, @var{high-frame} may be larger than the
27468 actual number of frames, in which case only existing frames will be returned.
27470 @subsubheading @value{GDBN} Command
27472 The corresponding @value{GDBN} commands are @samp{backtrace} and @samp{where}.
27474 @subsubheading Example
27476 Full stack backtrace:
27482 [frame=@{level="0",addr="0x0001076c",func="foo",
27483 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="11"@},
27484 frame=@{level="1",addr="0x000107a4",func="foo",
27485 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
27486 frame=@{level="2",addr="0x000107a4",func="foo",
27487 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
27488 frame=@{level="3",addr="0x000107a4",func="foo",
27489 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
27490 frame=@{level="4",addr="0x000107a4",func="foo",
27491 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
27492 frame=@{level="5",addr="0x000107a4",func="foo",
27493 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
27494 frame=@{level="6",addr="0x000107a4",func="foo",
27495 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
27496 frame=@{level="7",addr="0x000107a4",func="foo",
27497 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
27498 frame=@{level="8",addr="0x000107a4",func="foo",
27499 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
27500 frame=@{level="9",addr="0x000107a4",func="foo",
27501 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
27502 frame=@{level="10",addr="0x000107a4",func="foo",
27503 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
27504 frame=@{level="11",addr="0x00010738",func="main",
27505 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="4"@}]
27509 Show frames between @var{low_frame} and @var{high_frame}:
27513 -stack-list-frames 3 5
27515 [frame=@{level="3",addr="0x000107a4",func="foo",
27516 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
27517 frame=@{level="4",addr="0x000107a4",func="foo",
27518 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
27519 frame=@{level="5",addr="0x000107a4",func="foo",
27520 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@}]
27524 Show a single frame:
27528 -stack-list-frames 3 3
27530 [frame=@{level="3",addr="0x000107a4",func="foo",
27531 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@}]
27536 @subheading The @code{-stack-list-locals} Command
27537 @findex -stack-list-locals
27539 @subsubheading Synopsis
27542 -stack-list-locals @var{print-values}
27545 Display the local variable names for the selected frame. If
27546 @var{print-values} is 0 or @code{--no-values}, print only the names of
27547 the variables; if it is 1 or @code{--all-values}, print also their
27548 values; and if it is 2 or @code{--simple-values}, print the name,
27549 type and value for simple data types, and the name and type for arrays,
27550 structures and unions. In this last case, a frontend can immediately
27551 display the value of simple data types and create variable objects for
27552 other data types when the user wishes to explore their values in
27555 This command is deprecated in favor of the
27556 @samp{-stack-list-variables} command.
27558 @subsubheading @value{GDBN} Command
27560 @samp{info locals} in @value{GDBN}, @samp{gdb_get_locals} in @code{gdbtk}.
27562 @subsubheading Example
27566 -stack-list-locals 0
27567 ^done,locals=[name="A",name="B",name="C"]
27569 -stack-list-locals --all-values
27570 ^done,locals=[@{name="A",value="1"@},@{name="B",value="2"@},
27571 @{name="C",value="@{1, 2, 3@}"@}]
27572 -stack-list-locals --simple-values
27573 ^done,locals=[@{name="A",type="int",value="1"@},
27574 @{name="B",type="int",value="2"@},@{name="C",type="int [3]"@}]
27578 @subheading The @code{-stack-list-variables} Command
27579 @findex -stack-list-variables
27581 @subsubheading Synopsis
27584 -stack-list-variables @var{print-values}
27587 Display the names of local variables and function arguments for the selected frame. If
27588 @var{print-values} is 0 or @code{--no-values}, print only the names of
27589 the variables; if it is 1 or @code{--all-values}, print also their
27590 values; and if it is 2 or @code{--simple-values}, print the name,
27591 type and value for simple data types, and the name and type for arrays,
27592 structures and unions.
27594 @subsubheading Example
27598 -stack-list-variables --thread 1 --frame 0 --all-values
27599 ^done,variables=[@{name="x",value="11"@},@{name="s",value="@{a = 1, b = 2@}"@}]
27604 @subheading The @code{-stack-select-frame} Command
27605 @findex -stack-select-frame
27607 @subsubheading Synopsis
27610 -stack-select-frame @var{framenum}
27613 Change the selected frame. Select a different frame @var{framenum} on
27616 This command in deprecated in favor of passing the @samp{--frame}
27617 option to every command.
27619 @subsubheading @value{GDBN} Command
27621 The corresponding @value{GDBN} commands are @samp{frame}, @samp{up},
27622 @samp{down}, @samp{select-frame}, @samp{up-silent}, and @samp{down-silent}.
27624 @subsubheading Example
27628 -stack-select-frame 2
27633 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
27634 @node GDB/MI Variable Objects
27635 @section @sc{gdb/mi} Variable Objects
27639 @subheading Motivation for Variable Objects in @sc{gdb/mi}
27641 For the implementation of a variable debugger window (locals, watched
27642 expressions, etc.), we are proposing the adaptation of the existing code
27643 used by @code{Insight}.
27645 The two main reasons for that are:
27649 It has been proven in practice (it is already on its second generation).
27652 It will shorten development time (needless to say how important it is
27656 The original interface was designed to be used by Tcl code, so it was
27657 slightly changed so it could be used through @sc{gdb/mi}. This section
27658 describes the @sc{gdb/mi} operations that will be available and gives some
27659 hints about their use.
27661 @emph{Note}: In addition to the set of operations described here, we
27662 expect the @sc{gui} implementation of a variable window to require, at
27663 least, the following operations:
27666 @item @code{-gdb-show} @code{output-radix}
27667 @item @code{-stack-list-arguments}
27668 @item @code{-stack-list-locals}
27669 @item @code{-stack-select-frame}
27674 @subheading Introduction to Variable Objects
27676 @cindex variable objects in @sc{gdb/mi}
27678 Variable objects are "object-oriented" MI interface for examining and
27679 changing values of expressions. Unlike some other MI interfaces that
27680 work with expressions, variable objects are specifically designed for
27681 simple and efficient presentation in the frontend. A variable object
27682 is identified by string name. When a variable object is created, the
27683 frontend specifies the expression for that variable object. The
27684 expression can be a simple variable, or it can be an arbitrary complex
27685 expression, and can even involve CPU registers. After creating a
27686 variable object, the frontend can invoke other variable object
27687 operations---for example to obtain or change the value of a variable
27688 object, or to change display format.
27690 Variable objects have hierarchical tree structure. Any variable object
27691 that corresponds to a composite type, such as structure in C, has
27692 a number of child variable objects, for example corresponding to each
27693 element of a structure. A child variable object can itself have
27694 children, recursively. Recursion ends when we reach
27695 leaf variable objects, which always have built-in types. Child variable
27696 objects are created only by explicit request, so if a frontend
27697 is not interested in the children of a particular variable object, no
27698 child will be created.
27700 For a leaf variable object it is possible to obtain its value as a
27701 string, or set the value from a string. String value can be also
27702 obtained for a non-leaf variable object, but it's generally a string
27703 that only indicates the type of the object, and does not list its
27704 contents. Assignment to a non-leaf variable object is not allowed.
27706 A frontend does not need to read the values of all variable objects each time
27707 the program stops. Instead, MI provides an update command that lists all
27708 variable objects whose values has changed since the last update
27709 operation. This considerably reduces the amount of data that must
27710 be transferred to the frontend. As noted above, children variable
27711 objects are created on demand, and only leaf variable objects have a
27712 real value. As result, gdb will read target memory only for leaf
27713 variables that frontend has created.
27715 The automatic update is not always desirable. For example, a frontend
27716 might want to keep a value of some expression for future reference,
27717 and never update it. For another example, fetching memory is
27718 relatively slow for embedded targets, so a frontend might want
27719 to disable automatic update for the variables that are either not
27720 visible on the screen, or ``closed''. This is possible using so
27721 called ``frozen variable objects''. Such variable objects are never
27722 implicitly updated.
27724 Variable objects can be either @dfn{fixed} or @dfn{floating}. For the
27725 fixed variable object, the expression is parsed when the variable
27726 object is created, including associating identifiers to specific
27727 variables. The meaning of expression never changes. For a floating
27728 variable object the values of variables whose names appear in the
27729 expressions are re-evaluated every time in the context of the current
27730 frame. Consider this example:
27735 struct work_state state;
27742 If a fixed variable object for the @code{state} variable is created in
27743 this function, and we enter the recursive call, the variable
27744 object will report the value of @code{state} in the top-level
27745 @code{do_work} invocation. On the other hand, a floating variable
27746 object will report the value of @code{state} in the current frame.
27748 If an expression specified when creating a fixed variable object
27749 refers to a local variable, the variable object becomes bound to the
27750 thread and frame in which the variable object is created. When such
27751 variable object is updated, @value{GDBN} makes sure that the
27752 thread/frame combination the variable object is bound to still exists,
27753 and re-evaluates the variable object in context of that thread/frame.
27755 The following is the complete set of @sc{gdb/mi} operations defined to
27756 access this functionality:
27758 @multitable @columnfractions .4 .6
27759 @item @strong{Operation}
27760 @tab @strong{Description}
27762 @item @code{-enable-pretty-printing}
27763 @tab enable Python-based pretty-printing
27764 @item @code{-var-create}
27765 @tab create a variable object
27766 @item @code{-var-delete}
27767 @tab delete the variable object and/or its children
27768 @item @code{-var-set-format}
27769 @tab set the display format of this variable
27770 @item @code{-var-show-format}
27771 @tab show the display format of this variable
27772 @item @code{-var-info-num-children}
27773 @tab tells how many children this object has
27774 @item @code{-var-list-children}
27775 @tab return a list of the object's children
27776 @item @code{-var-info-type}
27777 @tab show the type of this variable object
27778 @item @code{-var-info-expression}
27779 @tab print parent-relative expression that this variable object represents
27780 @item @code{-var-info-path-expression}
27781 @tab print full expression that this variable object represents
27782 @item @code{-var-show-attributes}
27783 @tab is this variable editable? does it exist here?
27784 @item @code{-var-evaluate-expression}
27785 @tab get the value of this variable
27786 @item @code{-var-assign}
27787 @tab set the value of this variable
27788 @item @code{-var-update}
27789 @tab update the variable and its children
27790 @item @code{-var-set-frozen}
27791 @tab set frozeness attribute
27792 @item @code{-var-set-update-range}
27793 @tab set range of children to display on update
27796 In the next subsection we describe each operation in detail and suggest
27797 how it can be used.
27799 @subheading Description And Use of Operations on Variable Objects
27801 @subheading The @code{-enable-pretty-printing} Command
27802 @findex -enable-pretty-printing
27805 -enable-pretty-printing
27808 @value{GDBN} allows Python-based visualizers to affect the output of the
27809 MI variable object commands. However, because there was no way to
27810 implement this in a fully backward-compatible way, a front end must
27811 request that this functionality be enabled.
27813 Once enabled, this feature cannot be disabled.
27815 Note that if Python support has not been compiled into @value{GDBN},
27816 this command will still succeed (and do nothing).
27818 This feature is currently (as of @value{GDBN} 7.0) experimental, and
27819 may work differently in future versions of @value{GDBN}.
27821 @subheading The @code{-var-create} Command
27822 @findex -var-create
27824 @subsubheading Synopsis
27827 -var-create @{@var{name} | "-"@}
27828 @{@var{frame-addr} | "*" | "@@"@} @var{expression}
27831 This operation creates a variable object, which allows the monitoring of
27832 a variable, the result of an expression, a memory cell or a CPU
27835 The @var{name} parameter is the string by which the object can be
27836 referenced. It must be unique. If @samp{-} is specified, the varobj
27837 system will generate a string ``varNNNNNN'' automatically. It will be
27838 unique provided that one does not specify @var{name} of that format.
27839 The command fails if a duplicate name is found.
27841 The frame under which the expression should be evaluated can be
27842 specified by @var{frame-addr}. A @samp{*} indicates that the current
27843 frame should be used. A @samp{@@} indicates that a floating variable
27844 object must be created.
27846 @var{expression} is any expression valid on the current language set (must not
27847 begin with a @samp{*}), or one of the following:
27851 @samp{*@var{addr}}, where @var{addr} is the address of a memory cell
27854 @samp{*@var{addr}-@var{addr}} --- a memory address range (TBD)
27857 @samp{$@var{regname}} --- a CPU register name
27860 @cindex dynamic varobj
27861 A varobj's contents may be provided by a Python-based pretty-printer. In this
27862 case the varobj is known as a @dfn{dynamic varobj}. Dynamic varobjs
27863 have slightly different semantics in some cases. If the
27864 @code{-enable-pretty-printing} command is not sent, then @value{GDBN}
27865 will never create a dynamic varobj. This ensures backward
27866 compatibility for existing clients.
27868 @subsubheading Result
27870 This operation returns attributes of the newly-created varobj. These
27875 The name of the varobj.
27878 The number of children of the varobj. This number is not necessarily
27879 reliable for a dynamic varobj. Instead, you must examine the
27880 @samp{has_more} attribute.
27883 The varobj's scalar value. For a varobj whose type is some sort of
27884 aggregate (e.g., a @code{struct}), or for a dynamic varobj, this value
27885 will not be interesting.
27888 The varobj's type. This is a string representation of the type, as
27889 would be printed by the @value{GDBN} CLI.
27892 If a variable object is bound to a specific thread, then this is the
27893 thread's identifier.
27896 For a dynamic varobj, this indicates whether there appear to be any
27897 children available. For a non-dynamic varobj, this will be 0.
27900 This attribute will be present and have the value @samp{1} if the
27901 varobj is a dynamic varobj. If the varobj is not a dynamic varobj,
27902 then this attribute will not be present.
27905 A dynamic varobj can supply a display hint to the front end. The
27906 value comes directly from the Python pretty-printer object's
27907 @code{display_hint} method. @xref{Pretty Printing API}.
27910 Typical output will look like this:
27913 name="@var{name}",numchild="@var{N}",type="@var{type}",thread-id="@var{M}",
27914 has_more="@var{has_more}"
27918 @subheading The @code{-var-delete} Command
27919 @findex -var-delete
27921 @subsubheading Synopsis
27924 -var-delete [ -c ] @var{name}
27927 Deletes a previously created variable object and all of its children.
27928 With the @samp{-c} option, just deletes the children.
27930 Returns an error if the object @var{name} is not found.
27933 @subheading The @code{-var-set-format} Command
27934 @findex -var-set-format
27936 @subsubheading Synopsis
27939 -var-set-format @var{name} @var{format-spec}
27942 Sets the output format for the value of the object @var{name} to be
27945 @anchor{-var-set-format}
27946 The syntax for the @var{format-spec} is as follows:
27949 @var{format-spec} @expansion{}
27950 @{binary | decimal | hexadecimal | octal | natural@}
27953 The natural format is the default format choosen automatically
27954 based on the variable type (like decimal for an @code{int}, hex
27955 for pointers, etc.).
27957 For a variable with children, the format is set only on the
27958 variable itself, and the children are not affected.
27960 @subheading The @code{-var-show-format} Command
27961 @findex -var-show-format
27963 @subsubheading Synopsis
27966 -var-show-format @var{name}
27969 Returns the format used to display the value of the object @var{name}.
27972 @var{format} @expansion{}
27977 @subheading The @code{-var-info-num-children} Command
27978 @findex -var-info-num-children
27980 @subsubheading Synopsis
27983 -var-info-num-children @var{name}
27986 Returns the number of children of a variable object @var{name}:
27992 Note that this number is not completely reliable for a dynamic varobj.
27993 It will return the current number of children, but more children may
27997 @subheading The @code{-var-list-children} Command
27998 @findex -var-list-children
28000 @subsubheading Synopsis
28003 -var-list-children [@var{print-values}] @var{name} [@var{from} @var{to}]
28005 @anchor{-var-list-children}
28007 Return a list of the children of the specified variable object and
28008 create variable objects for them, if they do not already exist. With
28009 a single argument or if @var{print-values} has a value of 0 or
28010 @code{--no-values}, print only the names of the variables; if
28011 @var{print-values} is 1 or @code{--all-values}, also print their
28012 values; and if it is 2 or @code{--simple-values} print the name and
28013 value for simple data types and just the name for arrays, structures
28016 @var{from} and @var{to}, if specified, indicate the range of children
28017 to report. If @var{from} or @var{to} is less than zero, the range is
28018 reset and all children will be reported. Otherwise, children starting
28019 at @var{from} (zero-based) and up to and excluding @var{to} will be
28022 If a child range is requested, it will only affect the current call to
28023 @code{-var-list-children}, but not future calls to @code{-var-update}.
28024 For this, you must instead use @code{-var-set-update-range}. The
28025 intent of this approach is to enable a front end to implement any
28026 update approach it likes; for example, scrolling a view may cause the
28027 front end to request more children with @code{-var-list-children}, and
28028 then the front end could call @code{-var-set-update-range} with a
28029 different range to ensure that future updates are restricted to just
28032 For each child the following results are returned:
28037 Name of the variable object created for this child.
28040 The expression to be shown to the user by the front end to designate this child.
28041 For example this may be the name of a structure member.
28043 For a dynamic varobj, this value cannot be used to form an
28044 expression. There is no way to do this at all with a dynamic varobj.
28046 For C/C@t{++} structures there are several pseudo children returned to
28047 designate access qualifiers. For these pseudo children @var{exp} is
28048 @samp{public}, @samp{private}, or @samp{protected}. In this case the
28049 type and value are not present.
28051 A dynamic varobj will not report the access qualifying
28052 pseudo-children, regardless of the language. This information is not
28053 available at all with a dynamic varobj.
28056 Number of children this child has. For a dynamic varobj, this will be
28060 The type of the child.
28063 If values were requested, this is the value.
28066 If this variable object is associated with a thread, this is the thread id.
28067 Otherwise this result is not present.
28070 If the variable object is frozen, this variable will be present with a value of 1.
28073 The result may have its own attributes:
28077 A dynamic varobj can supply a display hint to the front end. The
28078 value comes directly from the Python pretty-printer object's
28079 @code{display_hint} method. @xref{Pretty Printing API}.
28082 This is an integer attribute which is nonzero if there are children
28083 remaining after the end of the selected range.
28086 @subsubheading Example
28090 -var-list-children n
28091 ^done,numchild=@var{n},children=[child=@{name=@var{name},exp=@var{exp},
28092 numchild=@var{n},type=@var{type}@},@r{(repeats N times)}]
28094 -var-list-children --all-values n
28095 ^done,numchild=@var{n},children=[child=@{name=@var{name},exp=@var{exp},
28096 numchild=@var{n},value=@var{value},type=@var{type}@},@r{(repeats N times)}]
28100 @subheading The @code{-var-info-type} Command
28101 @findex -var-info-type
28103 @subsubheading Synopsis
28106 -var-info-type @var{name}
28109 Returns the type of the specified variable @var{name}. The type is
28110 returned as a string in the same format as it is output by the
28114 type=@var{typename}
28118 @subheading The @code{-var-info-expression} Command
28119 @findex -var-info-expression
28121 @subsubheading Synopsis
28124 -var-info-expression @var{name}
28127 Returns a string that is suitable for presenting this
28128 variable object in user interface. The string is generally
28129 not valid expression in the current language, and cannot be evaluated.
28131 For example, if @code{a} is an array, and variable object
28132 @code{A} was created for @code{a}, then we'll get this output:
28135 (gdb) -var-info-expression A.1
28136 ^done,lang="C",exp="1"
28140 Here, the values of @code{lang} can be @code{@{"C" | "C++" | "Java"@}}.
28142 Note that the output of the @code{-var-list-children} command also
28143 includes those expressions, so the @code{-var-info-expression} command
28146 @subheading The @code{-var-info-path-expression} Command
28147 @findex -var-info-path-expression
28149 @subsubheading Synopsis
28152 -var-info-path-expression @var{name}
28155 Returns an expression that can be evaluated in the current
28156 context and will yield the same value that a variable object has.
28157 Compare this with the @code{-var-info-expression} command, which
28158 result can be used only for UI presentation. Typical use of
28159 the @code{-var-info-path-expression} command is creating a
28160 watchpoint from a variable object.
28162 This command is currently not valid for children of a dynamic varobj,
28163 and will give an error when invoked on one.
28165 For example, suppose @code{C} is a C@t{++} class, derived from class
28166 @code{Base}, and that the @code{Base} class has a member called
28167 @code{m_size}. Assume a variable @code{c} is has the type of
28168 @code{C} and a variable object @code{C} was created for variable
28169 @code{c}. Then, we'll get this output:
28171 (gdb) -var-info-path-expression C.Base.public.m_size
28172 ^done,path_expr=((Base)c).m_size)
28175 @subheading The @code{-var-show-attributes} Command
28176 @findex -var-show-attributes
28178 @subsubheading Synopsis
28181 -var-show-attributes @var{name}
28184 List attributes of the specified variable object @var{name}:
28187 status=@var{attr} [ ( ,@var{attr} )* ]
28191 where @var{attr} is @code{@{ @{ editable | noneditable @} | TBD @}}.
28193 @subheading The @code{-var-evaluate-expression} Command
28194 @findex -var-evaluate-expression
28196 @subsubheading Synopsis
28199 -var-evaluate-expression [-f @var{format-spec}] @var{name}
28202 Evaluates the expression that is represented by the specified variable
28203 object and returns its value as a string. The format of the string
28204 can be specified with the @samp{-f} option. The possible values of
28205 this option are the same as for @code{-var-set-format}
28206 (@pxref{-var-set-format}). If the @samp{-f} option is not specified,
28207 the current display format will be used. The current display format
28208 can be changed using the @code{-var-set-format} command.
28214 Note that one must invoke @code{-var-list-children} for a variable
28215 before the value of a child variable can be evaluated.
28217 @subheading The @code{-var-assign} Command
28218 @findex -var-assign
28220 @subsubheading Synopsis
28223 -var-assign @var{name} @var{expression}
28226 Assigns the value of @var{expression} to the variable object specified
28227 by @var{name}. The object must be @samp{editable}. If the variable's
28228 value is altered by the assign, the variable will show up in any
28229 subsequent @code{-var-update} list.
28231 @subsubheading Example
28239 ^done,changelist=[@{name="var1",in_scope="true",type_changed="false"@}]
28243 @subheading The @code{-var-update} Command
28244 @findex -var-update
28246 @subsubheading Synopsis
28249 -var-update [@var{print-values}] @{@var{name} | "*"@}
28252 Reevaluate the expressions corresponding to the variable object
28253 @var{name} and all its direct and indirect children, and return the
28254 list of variable objects whose values have changed; @var{name} must
28255 be a root variable object. Here, ``changed'' means that the result of
28256 @code{-var-evaluate-expression} before and after the
28257 @code{-var-update} is different. If @samp{*} is used as the variable
28258 object names, all existing variable objects are updated, except
28259 for frozen ones (@pxref{-var-set-frozen}). The option
28260 @var{print-values} determines whether both names and values, or just
28261 names are printed. The possible values of this option are the same
28262 as for @code{-var-list-children} (@pxref{-var-list-children}). It is
28263 recommended to use the @samp{--all-values} option, to reduce the
28264 number of MI commands needed on each program stop.
28266 With the @samp{*} parameter, if a variable object is bound to a
28267 currently running thread, it will not be updated, without any
28270 If @code{-var-set-update-range} was previously used on a varobj, then
28271 only the selected range of children will be reported.
28273 @code{-var-update} reports all the changed varobjs in a tuple named
28276 Each item in the change list is itself a tuple holding:
28280 The name of the varobj.
28283 If values were requested for this update, then this field will be
28284 present and will hold the value of the varobj.
28287 @anchor{-var-update}
28288 This field is a string which may take one of three values:
28292 The variable object's current value is valid.
28295 The variable object does not currently hold a valid value but it may
28296 hold one in the future if its associated expression comes back into
28300 The variable object no longer holds a valid value.
28301 This can occur when the executable file being debugged has changed,
28302 either through recompilation or by using the @value{GDBN} @code{file}
28303 command. The front end should normally choose to delete these variable
28307 In the future new values may be added to this list so the front should
28308 be prepared for this possibility. @xref{GDB/MI Development and Front Ends, ,@sc{GDB/MI} Development and Front Ends}.
28311 This is only present if the varobj is still valid. If the type
28312 changed, then this will be the string @samp{true}; otherwise it will
28316 If the varobj's type changed, then this field will be present and will
28319 @item new_num_children
28320 For a dynamic varobj, if the number of children changed, or if the
28321 type changed, this will be the new number of children.
28323 The @samp{numchild} field in other varobj responses is generally not
28324 valid for a dynamic varobj -- it will show the number of children that
28325 @value{GDBN} knows about, but because dynamic varobjs lazily
28326 instantiate their children, this will not reflect the number of
28327 children which may be available.
28329 The @samp{new_num_children} attribute only reports changes to the
28330 number of children known by @value{GDBN}. This is the only way to
28331 detect whether an update has removed children (which necessarily can
28332 only happen at the end of the update range).
28335 The display hint, if any.
28338 This is an integer value, which will be 1 if there are more children
28339 available outside the varobj's update range.
28342 This attribute will be present and have the value @samp{1} if the
28343 varobj is a dynamic varobj. If the varobj is not a dynamic varobj,
28344 then this attribute will not be present.
28347 If new children were added to a dynamic varobj within the selected
28348 update range (as set by @code{-var-set-update-range}), then they will
28349 be listed in this attribute.
28352 @subsubheading Example
28359 -var-update --all-values var1
28360 ^done,changelist=[@{name="var1",value="3",in_scope="true",
28361 type_changed="false"@}]
28365 @subheading The @code{-var-set-frozen} Command
28366 @findex -var-set-frozen
28367 @anchor{-var-set-frozen}
28369 @subsubheading Synopsis
28372 -var-set-frozen @var{name} @var{flag}
28375 Set the frozenness flag on the variable object @var{name}. The
28376 @var{flag} parameter should be either @samp{1} to make the variable
28377 frozen or @samp{0} to make it unfrozen. If a variable object is
28378 frozen, then neither itself, nor any of its children, are
28379 implicitly updated by @code{-var-update} of
28380 a parent variable or by @code{-var-update *}. Only
28381 @code{-var-update} of the variable itself will update its value and
28382 values of its children. After a variable object is unfrozen, it is
28383 implicitly updated by all subsequent @code{-var-update} operations.
28384 Unfreezing a variable does not update it, only subsequent
28385 @code{-var-update} does.
28387 @subsubheading Example
28391 -var-set-frozen V 1
28396 @subheading The @code{-var-set-update-range} command
28397 @findex -var-set-update-range
28398 @anchor{-var-set-update-range}
28400 @subsubheading Synopsis
28403 -var-set-update-range @var{name} @var{from} @var{to}
28406 Set the range of children to be returned by future invocations of
28407 @code{-var-update}.
28409 @var{from} and @var{to} indicate the range of children to report. If
28410 @var{from} or @var{to} is less than zero, the range is reset and all
28411 children will be reported. Otherwise, children starting at @var{from}
28412 (zero-based) and up to and excluding @var{to} will be reported.
28414 @subsubheading Example
28418 -var-set-update-range V 1 2
28422 @subheading The @code{-var-set-visualizer} command
28423 @findex -var-set-visualizer
28424 @anchor{-var-set-visualizer}
28426 @subsubheading Synopsis
28429 -var-set-visualizer @var{name} @var{visualizer}
28432 Set a visualizer for the variable object @var{name}.
28434 @var{visualizer} is the visualizer to use. The special value
28435 @samp{None} means to disable any visualizer in use.
28437 If not @samp{None}, @var{visualizer} must be a Python expression.
28438 This expression must evaluate to a callable object which accepts a
28439 single argument. @value{GDBN} will call this object with the value of
28440 the varobj @var{name} as an argument (this is done so that the same
28441 Python pretty-printing code can be used for both the CLI and MI).
28442 When called, this object must return an object which conforms to the
28443 pretty-printing interface (@pxref{Pretty Printing API}).
28445 The pre-defined function @code{gdb.default_visualizer} may be used to
28446 select a visualizer by following the built-in process
28447 (@pxref{Selecting Pretty-Printers}). This is done automatically when
28448 a varobj is created, and so ordinarily is not needed.
28450 This feature is only available if Python support is enabled. The MI
28451 command @code{-list-features} (@pxref{GDB/MI Miscellaneous Commands})
28452 can be used to check this.
28454 @subsubheading Example
28456 Resetting the visualizer:
28460 -var-set-visualizer V None
28464 Reselecting the default (type-based) visualizer:
28468 -var-set-visualizer V gdb.default_visualizer
28472 Suppose @code{SomeClass} is a visualizer class. A lambda expression
28473 can be used to instantiate this class for a varobj:
28477 -var-set-visualizer V "lambda val: SomeClass()"
28481 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
28482 @node GDB/MI Data Manipulation
28483 @section @sc{gdb/mi} Data Manipulation
28485 @cindex data manipulation, in @sc{gdb/mi}
28486 @cindex @sc{gdb/mi}, data manipulation
28487 This section describes the @sc{gdb/mi} commands that manipulate data:
28488 examine memory and registers, evaluate expressions, etc.
28490 @c REMOVED FROM THE INTERFACE.
28491 @c @subheading -data-assign
28492 @c Change the value of a program variable. Plenty of side effects.
28493 @c @subsubheading GDB Command
28495 @c @subsubheading Example
28498 @subheading The @code{-data-disassemble} Command
28499 @findex -data-disassemble
28501 @subsubheading Synopsis
28505 [ -s @var{start-addr} -e @var{end-addr} ]
28506 | [ -f @var{filename} -l @var{linenum} [ -n @var{lines} ] ]
28514 @item @var{start-addr}
28515 is the beginning address (or @code{$pc})
28516 @item @var{end-addr}
28518 @item @var{filename}
28519 is the name of the file to disassemble
28520 @item @var{linenum}
28521 is the line number to disassemble around
28523 is the number of disassembly lines to be produced. If it is -1,
28524 the whole function will be disassembled, in case no @var{end-addr} is
28525 specified. If @var{end-addr} is specified as a non-zero value, and
28526 @var{lines} is lower than the number of disassembly lines between
28527 @var{start-addr} and @var{end-addr}, only @var{lines} lines are
28528 displayed; if @var{lines} is higher than the number of lines between
28529 @var{start-addr} and @var{end-addr}, only the lines up to @var{end-addr}
28532 is either 0 (meaning only disassembly), 1 (meaning mixed source and
28533 disassembly), 2 (meaning disassembly with raw opcodes), or 3 (meaning
28534 mixed source and disassembly with raw opcodes).
28537 @subsubheading Result
28539 The output for each instruction is composed of four fields:
28548 Note that whatever included in the instruction field, is not manipulated
28549 directly by @sc{gdb/mi}, i.e., it is not possible to adjust its format.
28551 @subsubheading @value{GDBN} Command
28553 There's no direct mapping from this command to the CLI.
28555 @subsubheading Example
28557 Disassemble from the current value of @code{$pc} to @code{$pc + 20}:
28561 -data-disassemble -s $pc -e "$pc + 20" -- 0
28564 @{address="0x000107c0",func-name="main",offset="4",
28565 inst="mov 2, %o0"@},
28566 @{address="0x000107c4",func-name="main",offset="8",
28567 inst="sethi %hi(0x11800), %o2"@},
28568 @{address="0x000107c8",func-name="main",offset="12",
28569 inst="or %o2, 0x140, %o1\t! 0x11940 <_lib_version+8>"@},
28570 @{address="0x000107cc",func-name="main",offset="16",
28571 inst="sethi %hi(0x11800), %o2"@},
28572 @{address="0x000107d0",func-name="main",offset="20",
28573 inst="or %o2, 0x168, %o4\t! 0x11968 <_lib_version+48>"@}]
28577 Disassemble the whole @code{main} function. Line 32 is part of
28581 -data-disassemble -f basics.c -l 32 -- 0
28583 @{address="0x000107bc",func-name="main",offset="0",
28584 inst="save %sp, -112, %sp"@},
28585 @{address="0x000107c0",func-name="main",offset="4",
28586 inst="mov 2, %o0"@},
28587 @{address="0x000107c4",func-name="main",offset="8",
28588 inst="sethi %hi(0x11800), %o2"@},
28590 @{address="0x0001081c",func-name="main",offset="96",inst="ret "@},
28591 @{address="0x00010820",func-name="main",offset="100",inst="restore "@}]
28595 Disassemble 3 instructions from the start of @code{main}:
28599 -data-disassemble -f basics.c -l 32 -n 3 -- 0
28601 @{address="0x000107bc",func-name="main",offset="0",
28602 inst="save %sp, -112, %sp"@},
28603 @{address="0x000107c0",func-name="main",offset="4",
28604 inst="mov 2, %o0"@},
28605 @{address="0x000107c4",func-name="main",offset="8",
28606 inst="sethi %hi(0x11800), %o2"@}]
28610 Disassemble 3 instructions from the start of @code{main} in mixed mode:
28614 -data-disassemble -f basics.c -l 32 -n 3 -- 1
28616 src_and_asm_line=@{line="31",
28617 file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \
28618 testsuite/gdb.mi/basics.c",line_asm_insn=[
28619 @{address="0x000107bc",func-name="main",offset="0",
28620 inst="save %sp, -112, %sp"@}]@},
28621 src_and_asm_line=@{line="32",
28622 file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \
28623 testsuite/gdb.mi/basics.c",line_asm_insn=[
28624 @{address="0x000107c0",func-name="main",offset="4",
28625 inst="mov 2, %o0"@},
28626 @{address="0x000107c4",func-name="main",offset="8",
28627 inst="sethi %hi(0x11800), %o2"@}]@}]
28632 @subheading The @code{-data-evaluate-expression} Command
28633 @findex -data-evaluate-expression
28635 @subsubheading Synopsis
28638 -data-evaluate-expression @var{expr}
28641 Evaluate @var{expr} as an expression. The expression could contain an
28642 inferior function call. The function call will execute synchronously.
28643 If the expression contains spaces, it must be enclosed in double quotes.
28645 @subsubheading @value{GDBN} Command
28647 The corresponding @value{GDBN} commands are @samp{print}, @samp{output}, and
28648 @samp{call}. In @code{gdbtk} only, there's a corresponding
28649 @samp{gdb_eval} command.
28651 @subsubheading Example
28653 In the following example, the numbers that precede the commands are the
28654 @dfn{tokens} described in @ref{GDB/MI Command Syntax, ,@sc{gdb/mi}
28655 Command Syntax}. Notice how @sc{gdb/mi} returns the same tokens in its
28659 211-data-evaluate-expression A
28662 311-data-evaluate-expression &A
28663 311^done,value="0xefffeb7c"
28665 411-data-evaluate-expression A+3
28668 511-data-evaluate-expression "A + 3"
28674 @subheading The @code{-data-list-changed-registers} Command
28675 @findex -data-list-changed-registers
28677 @subsubheading Synopsis
28680 -data-list-changed-registers
28683 Display a list of the registers that have changed.
28685 @subsubheading @value{GDBN} Command
28687 @value{GDBN} doesn't have a direct analog for this command; @code{gdbtk}
28688 has the corresponding command @samp{gdb_changed_register_list}.
28690 @subsubheading Example
28692 On a PPC MBX board:
28700 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",frame=@{
28701 func="main",args=[],file="try.c",fullname="/home/foo/bar/try.c",
28704 -data-list-changed-registers
28705 ^done,changed-registers=["0","1","2","4","5","6","7","8","9",
28706 "10","11","13","14","15","16","17","18","19","20","21","22","23",
28707 "24","25","26","27","28","30","31","64","65","66","67","69"]
28712 @subheading The @code{-data-list-register-names} Command
28713 @findex -data-list-register-names
28715 @subsubheading Synopsis
28718 -data-list-register-names [ ( @var{regno} )+ ]
28721 Show a list of register names for the current target. If no arguments
28722 are given, it shows a list of the names of all the registers. If
28723 integer numbers are given as arguments, it will print a list of the
28724 names of the registers corresponding to the arguments. To ensure
28725 consistency between a register name and its number, the output list may
28726 include empty register names.
28728 @subsubheading @value{GDBN} Command
28730 @value{GDBN} does not have a command which corresponds to
28731 @samp{-data-list-register-names}. In @code{gdbtk} there is a
28732 corresponding command @samp{gdb_regnames}.
28734 @subsubheading Example
28736 For the PPC MBX board:
28739 -data-list-register-names
28740 ^done,register-names=["r0","r1","r2","r3","r4","r5","r6","r7",
28741 "r8","r9","r10","r11","r12","r13","r14","r15","r16","r17","r18",
28742 "r19","r20","r21","r22","r23","r24","r25","r26","r27","r28","r29",
28743 "r30","r31","f0","f1","f2","f3","f4","f5","f6","f7","f8","f9",
28744 "f10","f11","f12","f13","f14","f15","f16","f17","f18","f19","f20",
28745 "f21","f22","f23","f24","f25","f26","f27","f28","f29","f30","f31",
28746 "", "pc","ps","cr","lr","ctr","xer"]
28748 -data-list-register-names 1 2 3
28749 ^done,register-names=["r1","r2","r3"]
28753 @subheading The @code{-data-list-register-values} Command
28754 @findex -data-list-register-values
28756 @subsubheading Synopsis
28759 -data-list-register-values @var{fmt} [ ( @var{regno} )*]
28762 Display the registers' contents. @var{fmt} is the format according to
28763 which the registers' contents are to be returned, followed by an optional
28764 list of numbers specifying the registers to display. A missing list of
28765 numbers indicates that the contents of all the registers must be returned.
28767 Allowed formats for @var{fmt} are:
28784 @subsubheading @value{GDBN} Command
28786 The corresponding @value{GDBN} commands are @samp{info reg}, @samp{info
28787 all-reg}, and (in @code{gdbtk}) @samp{gdb_fetch_registers}.
28789 @subsubheading Example
28791 For a PPC MBX board (note: line breaks are for readability only, they
28792 don't appear in the actual output):
28796 -data-list-register-values r 64 65
28797 ^done,register-values=[@{number="64",value="0xfe00a300"@},
28798 @{number="65",value="0x00029002"@}]
28800 -data-list-register-values x
28801 ^done,register-values=[@{number="0",value="0xfe0043c8"@},
28802 @{number="1",value="0x3fff88"@},@{number="2",value="0xfffffffe"@},
28803 @{number="3",value="0x0"@},@{number="4",value="0xa"@},
28804 @{number="5",value="0x3fff68"@},@{number="6",value="0x3fff58"@},
28805 @{number="7",value="0xfe011e98"@},@{number="8",value="0x2"@},
28806 @{number="9",value="0xfa202820"@},@{number="10",value="0xfa202808"@},
28807 @{number="11",value="0x1"@},@{number="12",value="0x0"@},
28808 @{number="13",value="0x4544"@},@{number="14",value="0xffdfffff"@},
28809 @{number="15",value="0xffffffff"@},@{number="16",value="0xfffffeff"@},
28810 @{number="17",value="0xefffffed"@},@{number="18",value="0xfffffffe"@},
28811 @{number="19",value="0xffffffff"@},@{number="20",value="0xffffffff"@},
28812 @{number="21",value="0xffffffff"@},@{number="22",value="0xfffffff7"@},
28813 @{number="23",value="0xffffffff"@},@{number="24",value="0xffffffff"@},
28814 @{number="25",value="0xffffffff"@},@{number="26",value="0xfffffffb"@},
28815 @{number="27",value="0xffffffff"@},@{number="28",value="0xf7bfffff"@},
28816 @{number="29",value="0x0"@},@{number="30",value="0xfe010000"@},
28817 @{number="31",value="0x0"@},@{number="32",value="0x0"@},
28818 @{number="33",value="0x0"@},@{number="34",value="0x0"@},
28819 @{number="35",value="0x0"@},@{number="36",value="0x0"@},
28820 @{number="37",value="0x0"@},@{number="38",value="0x0"@},
28821 @{number="39",value="0x0"@},@{number="40",value="0x0"@},
28822 @{number="41",value="0x0"@},@{number="42",value="0x0"@},
28823 @{number="43",value="0x0"@},@{number="44",value="0x0"@},
28824 @{number="45",value="0x0"@},@{number="46",value="0x0"@},
28825 @{number="47",value="0x0"@},@{number="48",value="0x0"@},
28826 @{number="49",value="0x0"@},@{number="50",value="0x0"@},
28827 @{number="51",value="0x0"@},@{number="52",value="0x0"@},
28828 @{number="53",value="0x0"@},@{number="54",value="0x0"@},
28829 @{number="55",value="0x0"@},@{number="56",value="0x0"@},
28830 @{number="57",value="0x0"@},@{number="58",value="0x0"@},
28831 @{number="59",value="0x0"@},@{number="60",value="0x0"@},
28832 @{number="61",value="0x0"@},@{number="62",value="0x0"@},
28833 @{number="63",value="0x0"@},@{number="64",value="0xfe00a300"@},
28834 @{number="65",value="0x29002"@},@{number="66",value="0x202f04b5"@},
28835 @{number="67",value="0xfe0043b0"@},@{number="68",value="0xfe00b3e4"@},
28836 @{number="69",value="0x20002b03"@}]
28841 @subheading The @code{-data-read-memory} Command
28842 @findex -data-read-memory
28844 This command is deprecated, use @code{-data-read-memory-bytes} instead.
28846 @subsubheading Synopsis
28849 -data-read-memory [ -o @var{byte-offset} ]
28850 @var{address} @var{word-format} @var{word-size}
28851 @var{nr-rows} @var{nr-cols} [ @var{aschar} ]
28858 @item @var{address}
28859 An expression specifying the address of the first memory word to be
28860 read. Complex expressions containing embedded white space should be
28861 quoted using the C convention.
28863 @item @var{word-format}
28864 The format to be used to print the memory words. The notation is the
28865 same as for @value{GDBN}'s @code{print} command (@pxref{Output Formats,
28868 @item @var{word-size}
28869 The size of each memory word in bytes.
28871 @item @var{nr-rows}
28872 The number of rows in the output table.
28874 @item @var{nr-cols}
28875 The number of columns in the output table.
28878 If present, indicates that each row should include an @sc{ascii} dump. The
28879 value of @var{aschar} is used as a padding character when a byte is not a
28880 member of the printable @sc{ascii} character set (printable @sc{ascii}
28881 characters are those whose code is between 32 and 126, inclusively).
28883 @item @var{byte-offset}
28884 An offset to add to the @var{address} before fetching memory.
28887 This command displays memory contents as a table of @var{nr-rows} by
28888 @var{nr-cols} words, each word being @var{word-size} bytes. In total,
28889 @code{@var{nr-rows} * @var{nr-cols} * @var{word-size}} bytes are read
28890 (returned as @samp{total-bytes}). Should less than the requested number
28891 of bytes be returned by the target, the missing words are identified
28892 using @samp{N/A}. The number of bytes read from the target is returned
28893 in @samp{nr-bytes} and the starting address used to read memory in
28896 The address of the next/previous row or page is available in
28897 @samp{next-row} and @samp{prev-row}, @samp{next-page} and
28900 @subsubheading @value{GDBN} Command
28902 The corresponding @value{GDBN} command is @samp{x}. @code{gdbtk} has
28903 @samp{gdb_get_mem} memory read command.
28905 @subsubheading Example
28907 Read six bytes of memory starting at @code{bytes+6} but then offset by
28908 @code{-6} bytes. Format as three rows of two columns. One byte per
28909 word. Display each word in hex.
28913 9-data-read-memory -o -6 -- bytes+6 x 1 3 2
28914 9^done,addr="0x00001390",nr-bytes="6",total-bytes="6",
28915 next-row="0x00001396",prev-row="0x0000138e",next-page="0x00001396",
28916 prev-page="0x0000138a",memory=[
28917 @{addr="0x00001390",data=["0x00","0x01"]@},
28918 @{addr="0x00001392",data=["0x02","0x03"]@},
28919 @{addr="0x00001394",data=["0x04","0x05"]@}]
28923 Read two bytes of memory starting at address @code{shorts + 64} and
28924 display as a single word formatted in decimal.
28928 5-data-read-memory shorts+64 d 2 1 1
28929 5^done,addr="0x00001510",nr-bytes="2",total-bytes="2",
28930 next-row="0x00001512",prev-row="0x0000150e",
28931 next-page="0x00001512",prev-page="0x0000150e",memory=[
28932 @{addr="0x00001510",data=["128"]@}]
28936 Read thirty two bytes of memory starting at @code{bytes+16} and format
28937 as eight rows of four columns. Include a string encoding with @samp{x}
28938 used as the non-printable character.
28942 4-data-read-memory bytes+16 x 1 8 4 x
28943 4^done,addr="0x000013a0",nr-bytes="32",total-bytes="32",
28944 next-row="0x000013c0",prev-row="0x0000139c",
28945 next-page="0x000013c0",prev-page="0x00001380",memory=[
28946 @{addr="0x000013a0",data=["0x10","0x11","0x12","0x13"],ascii="xxxx"@},
28947 @{addr="0x000013a4",data=["0x14","0x15","0x16","0x17"],ascii="xxxx"@},
28948 @{addr="0x000013a8",data=["0x18","0x19","0x1a","0x1b"],ascii="xxxx"@},
28949 @{addr="0x000013ac",data=["0x1c","0x1d","0x1e","0x1f"],ascii="xxxx"@},
28950 @{addr="0x000013b0",data=["0x20","0x21","0x22","0x23"],ascii=" !\"#"@},
28951 @{addr="0x000013b4",data=["0x24","0x25","0x26","0x27"],ascii="$%&'"@},
28952 @{addr="0x000013b8",data=["0x28","0x29","0x2a","0x2b"],ascii="()*+"@},
28953 @{addr="0x000013bc",data=["0x2c","0x2d","0x2e","0x2f"],ascii=",-./"@}]
28957 @subheading The @code{-data-read-memory-bytes} Command
28958 @findex -data-read-memory-bytes
28960 @subsubheading Synopsis
28963 -data-read-memory-bytes [ -o @var{byte-offset} ]
28964 @var{address} @var{count}
28971 @item @var{address}
28972 An expression specifying the address of the first memory word to be
28973 read. Complex expressions containing embedded white space should be
28974 quoted using the C convention.
28977 The number of bytes to read. This should be an integer literal.
28979 @item @var{byte-offset}
28980 The offsets in bytes relative to @var{address} at which to start
28981 reading. This should be an integer literal. This option is provided
28982 so that a frontend is not required to first evaluate address and then
28983 perform address arithmetics itself.
28987 This command attempts to read all accessible memory regions in the
28988 specified range. First, all regions marked as unreadable in the memory
28989 map (if one is defined) will be skipped. @xref{Memory Region
28990 Attributes}. Second, @value{GDBN} will attempt to read the remaining
28991 regions. For each one, if reading full region results in an errors,
28992 @value{GDBN} will try to read a subset of the region.
28994 In general, every single byte in the region may be readable or not,
28995 and the only way to read every readable byte is to try a read at
28996 every address, which is not practical. Therefore, @value{GDBN} will
28997 attempt to read all accessible bytes at either beginning or the end
28998 of the region, using a binary division scheme. This heuristic works
28999 well for reading accross a memory map boundary. Note that if a region
29000 has a readable range that is neither at the beginning or the end,
29001 @value{GDBN} will not read it.
29003 The result record (@pxref{GDB/MI Result Records}) that is output of
29004 the command includes a field named @samp{memory} whose content is a
29005 list of tuples. Each tuple represent a successfully read memory block
29006 and has the following fields:
29010 The start address of the memory block, as hexadecimal literal.
29013 The end address of the memory block, as hexadecimal literal.
29016 The offset of the memory block, as hexadecimal literal, relative to
29017 the start address passed to @code{-data-read-memory-bytes}.
29020 The contents of the memory block, in hex.
29026 @subsubheading @value{GDBN} Command
29028 The corresponding @value{GDBN} command is @samp{x}.
29030 @subsubheading Example
29034 -data-read-memory-bytes &a 10
29035 ^done,memory=[@{begin="0xbffff154",offset="0x00000000",
29037 contents="01000000020000000300"@}]
29042 @subheading The @code{-data-write-memory-bytes} Command
29043 @findex -data-write-memory-bytes
29045 @subsubheading Synopsis
29048 -data-write-memory-bytes @var{address} @var{contents}
29055 @item @var{address}
29056 An expression specifying the address of the first memory word to be
29057 read. Complex expressions containing embedded white space should be
29058 quoted using the C convention.
29060 @item @var{contents}
29061 The hex-encoded bytes to write.
29065 @subsubheading @value{GDBN} Command
29067 There's no corresponding @value{GDBN} command.
29069 @subsubheading Example
29073 -data-write-memory-bytes &a "aabbccdd"
29079 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
29080 @node GDB/MI Tracepoint Commands
29081 @section @sc{gdb/mi} Tracepoint Commands
29083 The commands defined in this section implement MI support for
29084 tracepoints. For detailed introduction, see @ref{Tracepoints}.
29086 @subheading The @code{-trace-find} Command
29087 @findex -trace-find
29089 @subsubheading Synopsis
29092 -trace-find @var{mode} [@var{parameters}@dots{}]
29095 Find a trace frame using criteria defined by @var{mode} and
29096 @var{parameters}. The following table lists permissible
29097 modes and their parameters. For details of operation, see @ref{tfind}.
29102 No parameters are required. Stops examining trace frames.
29105 An integer is required as parameter. Selects tracepoint frame with
29108 @item tracepoint-number
29109 An integer is required as parameter. Finds next
29110 trace frame that corresponds to tracepoint with the specified number.
29113 An address is required as parameter. Finds
29114 next trace frame that corresponds to any tracepoint at the specified
29117 @item pc-inside-range
29118 Two addresses are required as parameters. Finds next trace
29119 frame that corresponds to a tracepoint at an address inside the
29120 specified range. Both bounds are considered to be inside the range.
29122 @item pc-outside-range
29123 Two addresses are required as parameters. Finds
29124 next trace frame that corresponds to a tracepoint at an address outside
29125 the specified range. Both bounds are considered to be inside the range.
29128 Line specification is required as parameter. @xref{Specify Location}.
29129 Finds next trace frame that corresponds to a tracepoint at
29130 the specified location.
29134 If @samp{none} was passed as @var{mode}, the response does not
29135 have fields. Otherwise, the response may have the following fields:
29139 This field has either @samp{0} or @samp{1} as the value, depending
29140 on whether a matching tracepoint was found.
29143 The index of the found traceframe. This field is present iff
29144 the @samp{found} field has value of @samp{1}.
29147 The index of the found tracepoint. This field is present iff
29148 the @samp{found} field has value of @samp{1}.
29151 The information about the frame corresponding to the found trace
29152 frame. This field is present only if a trace frame was found.
29153 @xref{GDB/MI Frame Information}, for description of this field.
29157 @subsubheading @value{GDBN} Command
29159 The corresponding @value{GDBN} command is @samp{tfind}.
29161 @subheading -trace-define-variable
29162 @findex -trace-define-variable
29164 @subsubheading Synopsis
29167 -trace-define-variable @var{name} [ @var{value} ]
29170 Create trace variable @var{name} if it does not exist. If
29171 @var{value} is specified, sets the initial value of the specified
29172 trace variable to that value. Note that the @var{name} should start
29173 with the @samp{$} character.
29175 @subsubheading @value{GDBN} Command
29177 The corresponding @value{GDBN} command is @samp{tvariable}.
29179 @subheading -trace-list-variables
29180 @findex -trace-list-variables
29182 @subsubheading Synopsis
29185 -trace-list-variables
29188 Return a table of all defined trace variables. Each element of the
29189 table has the following fields:
29193 The name of the trace variable. This field is always present.
29196 The initial value. This is a 64-bit signed integer. This
29197 field is always present.
29200 The value the trace variable has at the moment. This is a 64-bit
29201 signed integer. This field is absent iff current value is
29202 not defined, for example if the trace was never run, or is
29207 @subsubheading @value{GDBN} Command
29209 The corresponding @value{GDBN} command is @samp{tvariables}.
29211 @subsubheading Example
29215 -trace-list-variables
29216 ^done,trace-variables=@{nr_rows="1",nr_cols="3",
29217 hdr=[@{width="15",alignment="-1",col_name="name",colhdr="Name"@},
29218 @{width="11",alignment="-1",col_name="initial",colhdr="Initial"@},
29219 @{width="11",alignment="-1",col_name="current",colhdr="Current"@}],
29220 body=[variable=@{name="$trace_timestamp",initial="0"@}
29221 variable=@{name="$foo",initial="10",current="15"@}]@}
29225 @subheading -trace-save
29226 @findex -trace-save
29228 @subsubheading Synopsis
29231 -trace-save [-r ] @var{filename}
29234 Saves the collected trace data to @var{filename}. Without the
29235 @samp{-r} option, the data is downloaded from the target and saved
29236 in a local file. With the @samp{-r} option the target is asked
29237 to perform the save.
29239 @subsubheading @value{GDBN} Command
29241 The corresponding @value{GDBN} command is @samp{tsave}.
29244 @subheading -trace-start
29245 @findex -trace-start
29247 @subsubheading Synopsis
29253 Starts a tracing experiments. The result of this command does not
29256 @subsubheading @value{GDBN} Command
29258 The corresponding @value{GDBN} command is @samp{tstart}.
29260 @subheading -trace-status
29261 @findex -trace-status
29263 @subsubheading Synopsis
29269 Obtains the status of a tracing experiment. The result may include
29270 the following fields:
29275 May have a value of either @samp{0}, when no tracing operations are
29276 supported, @samp{1}, when all tracing operations are supported, or
29277 @samp{file} when examining trace file. In the latter case, examining
29278 of trace frame is possible but new tracing experiement cannot be
29279 started. This field is always present.
29282 May have a value of either @samp{0} or @samp{1} depending on whether
29283 tracing experiement is in progress on target. This field is present
29284 if @samp{supported} field is not @samp{0}.
29287 Report the reason why the tracing was stopped last time. This field
29288 may be absent iff tracing was never stopped on target yet. The
29289 value of @samp{request} means the tracing was stopped as result of
29290 the @code{-trace-stop} command. The value of @samp{overflow} means
29291 the tracing buffer is full. The value of @samp{disconnection} means
29292 tracing was automatically stopped when @value{GDBN} has disconnected.
29293 The value of @samp{passcount} means tracing was stopped when a
29294 tracepoint was passed a maximal number of times for that tracepoint.
29295 This field is present if @samp{supported} field is not @samp{0}.
29297 @item stopping-tracepoint
29298 The number of tracepoint whose passcount as exceeded. This field is
29299 present iff the @samp{stop-reason} field has the value of
29303 @itemx frames-created
29304 The @samp{frames} field is a count of the total number of trace frames
29305 in the trace buffer, while @samp{frames-created} is the total created
29306 during the run, including ones that were discarded, such as when a
29307 circular trace buffer filled up. Both fields are optional.
29311 These fields tell the current size of the tracing buffer and the
29312 remaining space. These fields are optional.
29315 The value of the circular trace buffer flag. @code{1} means that the
29316 trace buffer is circular and old trace frames will be discarded if
29317 necessary to make room, @code{0} means that the trace buffer is linear
29321 The value of the disconnected tracing flag. @code{1} means that
29322 tracing will continue after @value{GDBN} disconnects, @code{0} means
29323 that the trace run will stop.
29327 @subsubheading @value{GDBN} Command
29329 The corresponding @value{GDBN} command is @samp{tstatus}.
29331 @subheading -trace-stop
29332 @findex -trace-stop
29334 @subsubheading Synopsis
29340 Stops a tracing experiment. The result of this command has the same
29341 fields as @code{-trace-status}, except that the @samp{supported} and
29342 @samp{running} fields are not output.
29344 @subsubheading @value{GDBN} Command
29346 The corresponding @value{GDBN} command is @samp{tstop}.
29349 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
29350 @node GDB/MI Symbol Query
29351 @section @sc{gdb/mi} Symbol Query Commands
29355 @subheading The @code{-symbol-info-address} Command
29356 @findex -symbol-info-address
29358 @subsubheading Synopsis
29361 -symbol-info-address @var{symbol}
29364 Describe where @var{symbol} is stored.
29366 @subsubheading @value{GDBN} Command
29368 The corresponding @value{GDBN} command is @samp{info address}.
29370 @subsubheading Example
29374 @subheading The @code{-symbol-info-file} Command
29375 @findex -symbol-info-file
29377 @subsubheading Synopsis
29383 Show the file for the symbol.
29385 @subsubheading @value{GDBN} Command
29387 There's no equivalent @value{GDBN} command. @code{gdbtk} has
29388 @samp{gdb_find_file}.
29390 @subsubheading Example
29394 @subheading The @code{-symbol-info-function} Command
29395 @findex -symbol-info-function
29397 @subsubheading Synopsis
29400 -symbol-info-function
29403 Show which function the symbol lives in.
29405 @subsubheading @value{GDBN} Command
29407 @samp{gdb_get_function} in @code{gdbtk}.
29409 @subsubheading Example
29413 @subheading The @code{-symbol-info-line} Command
29414 @findex -symbol-info-line
29416 @subsubheading Synopsis
29422 Show the core addresses of the code for a source line.
29424 @subsubheading @value{GDBN} Command
29426 The corresponding @value{GDBN} command is @samp{info line}.
29427 @code{gdbtk} has the @samp{gdb_get_line} and @samp{gdb_get_file} commands.
29429 @subsubheading Example
29433 @subheading The @code{-symbol-info-symbol} Command
29434 @findex -symbol-info-symbol
29436 @subsubheading Synopsis
29439 -symbol-info-symbol @var{addr}
29442 Describe what symbol is at location @var{addr}.
29444 @subsubheading @value{GDBN} Command
29446 The corresponding @value{GDBN} command is @samp{info symbol}.
29448 @subsubheading Example
29452 @subheading The @code{-symbol-list-functions} Command
29453 @findex -symbol-list-functions
29455 @subsubheading Synopsis
29458 -symbol-list-functions
29461 List the functions in the executable.
29463 @subsubheading @value{GDBN} Command
29465 @samp{info functions} in @value{GDBN}, @samp{gdb_listfunc} and
29466 @samp{gdb_search} in @code{gdbtk}.
29468 @subsubheading Example
29473 @subheading The @code{-symbol-list-lines} Command
29474 @findex -symbol-list-lines
29476 @subsubheading Synopsis
29479 -symbol-list-lines @var{filename}
29482 Print the list of lines that contain code and their associated program
29483 addresses for the given source filename. The entries are sorted in
29484 ascending PC order.
29486 @subsubheading @value{GDBN} Command
29488 There is no corresponding @value{GDBN} command.
29490 @subsubheading Example
29493 -symbol-list-lines basics.c
29494 ^done,lines=[@{pc="0x08048554",line="7"@},@{pc="0x0804855a",line="8"@}]
29500 @subheading The @code{-symbol-list-types} Command
29501 @findex -symbol-list-types
29503 @subsubheading Synopsis
29509 List all the type names.
29511 @subsubheading @value{GDBN} Command
29513 The corresponding commands are @samp{info types} in @value{GDBN},
29514 @samp{gdb_search} in @code{gdbtk}.
29516 @subsubheading Example
29520 @subheading The @code{-symbol-list-variables} Command
29521 @findex -symbol-list-variables
29523 @subsubheading Synopsis
29526 -symbol-list-variables
29529 List all the global and static variable names.
29531 @subsubheading @value{GDBN} Command
29533 @samp{info variables} in @value{GDBN}, @samp{gdb_search} in @code{gdbtk}.
29535 @subsubheading Example
29539 @subheading The @code{-symbol-locate} Command
29540 @findex -symbol-locate
29542 @subsubheading Synopsis
29548 @subsubheading @value{GDBN} Command
29550 @samp{gdb_loc} in @code{gdbtk}.
29552 @subsubheading Example
29556 @subheading The @code{-symbol-type} Command
29557 @findex -symbol-type
29559 @subsubheading Synopsis
29562 -symbol-type @var{variable}
29565 Show type of @var{variable}.
29567 @subsubheading @value{GDBN} Command
29569 The corresponding @value{GDBN} command is @samp{ptype}, @code{gdbtk} has
29570 @samp{gdb_obj_variable}.
29572 @subsubheading Example
29577 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
29578 @node GDB/MI File Commands
29579 @section @sc{gdb/mi} File Commands
29581 This section describes the GDB/MI commands to specify executable file names
29582 and to read in and obtain symbol table information.
29584 @subheading The @code{-file-exec-and-symbols} Command
29585 @findex -file-exec-and-symbols
29587 @subsubheading Synopsis
29590 -file-exec-and-symbols @var{file}
29593 Specify the executable file to be debugged. This file is the one from
29594 which the symbol table is also read. If no file is specified, the
29595 command clears the executable and symbol information. If breakpoints
29596 are set when using this command with no arguments, @value{GDBN} will produce
29597 error messages. Otherwise, no output is produced, except a completion
29600 @subsubheading @value{GDBN} Command
29602 The corresponding @value{GDBN} command is @samp{file}.
29604 @subsubheading Example
29608 -file-exec-and-symbols /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
29614 @subheading The @code{-file-exec-file} Command
29615 @findex -file-exec-file
29617 @subsubheading Synopsis
29620 -file-exec-file @var{file}
29623 Specify the executable file to be debugged. Unlike
29624 @samp{-file-exec-and-symbols}, the symbol table is @emph{not} read
29625 from this file. If used without argument, @value{GDBN} clears the information
29626 about the executable file. No output is produced, except a completion
29629 @subsubheading @value{GDBN} Command
29631 The corresponding @value{GDBN} command is @samp{exec-file}.
29633 @subsubheading Example
29637 -file-exec-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
29644 @subheading The @code{-file-list-exec-sections} Command
29645 @findex -file-list-exec-sections
29647 @subsubheading Synopsis
29650 -file-list-exec-sections
29653 List the sections of the current executable file.
29655 @subsubheading @value{GDBN} Command
29657 The @value{GDBN} command @samp{info file} shows, among the rest, the same
29658 information as this command. @code{gdbtk} has a corresponding command
29659 @samp{gdb_load_info}.
29661 @subsubheading Example
29666 @subheading The @code{-file-list-exec-source-file} Command
29667 @findex -file-list-exec-source-file
29669 @subsubheading Synopsis
29672 -file-list-exec-source-file
29675 List the line number, the current source file, and the absolute path
29676 to the current source file for the current executable. The macro
29677 information field has a value of @samp{1} or @samp{0} depending on
29678 whether or not the file includes preprocessor macro information.
29680 @subsubheading @value{GDBN} Command
29682 The @value{GDBN} equivalent is @samp{info source}
29684 @subsubheading Example
29688 123-file-list-exec-source-file
29689 123^done,line="1",file="foo.c",fullname="/home/bar/foo.c,macro-info="1"
29694 @subheading The @code{-file-list-exec-source-files} Command
29695 @findex -file-list-exec-source-files
29697 @subsubheading Synopsis
29700 -file-list-exec-source-files
29703 List the source files for the current executable.
29705 It will always output the filename, but only when @value{GDBN} can find
29706 the absolute file name of a source file, will it output the fullname.
29708 @subsubheading @value{GDBN} Command
29710 The @value{GDBN} equivalent is @samp{info sources}.
29711 @code{gdbtk} has an analogous command @samp{gdb_listfiles}.
29713 @subsubheading Example
29716 -file-list-exec-source-files
29718 @{file=foo.c,fullname=/home/foo.c@},
29719 @{file=/home/bar.c,fullname=/home/bar.c@},
29720 @{file=gdb_could_not_find_fullpath.c@}]
29725 @subheading The @code{-file-list-shared-libraries} Command
29726 @findex -file-list-shared-libraries
29728 @subsubheading Synopsis
29731 -file-list-shared-libraries
29734 List the shared libraries in the program.
29736 @subsubheading @value{GDBN} Command
29738 The corresponding @value{GDBN} command is @samp{info shared}.
29740 @subsubheading Example
29744 @subheading The @code{-file-list-symbol-files} Command
29745 @findex -file-list-symbol-files
29747 @subsubheading Synopsis
29750 -file-list-symbol-files
29755 @subsubheading @value{GDBN} Command
29757 The corresponding @value{GDBN} command is @samp{info file} (part of it).
29759 @subsubheading Example
29764 @subheading The @code{-file-symbol-file} Command
29765 @findex -file-symbol-file
29767 @subsubheading Synopsis
29770 -file-symbol-file @var{file}
29773 Read symbol table info from the specified @var{file} argument. When
29774 used without arguments, clears @value{GDBN}'s symbol table info. No output is
29775 produced, except for a completion notification.
29777 @subsubheading @value{GDBN} Command
29779 The corresponding @value{GDBN} command is @samp{symbol-file}.
29781 @subsubheading Example
29785 -file-symbol-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
29791 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
29792 @node GDB/MI Memory Overlay Commands
29793 @section @sc{gdb/mi} Memory Overlay Commands
29795 The memory overlay commands are not implemented.
29797 @c @subheading -overlay-auto
29799 @c @subheading -overlay-list-mapping-state
29801 @c @subheading -overlay-list-overlays
29803 @c @subheading -overlay-map
29805 @c @subheading -overlay-off
29807 @c @subheading -overlay-on
29809 @c @subheading -overlay-unmap
29811 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
29812 @node GDB/MI Signal Handling Commands
29813 @section @sc{gdb/mi} Signal Handling Commands
29815 Signal handling commands are not implemented.
29817 @c @subheading -signal-handle
29819 @c @subheading -signal-list-handle-actions
29821 @c @subheading -signal-list-signal-types
29825 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
29826 @node GDB/MI Target Manipulation
29827 @section @sc{gdb/mi} Target Manipulation Commands
29830 @subheading The @code{-target-attach} Command
29831 @findex -target-attach
29833 @subsubheading Synopsis
29836 -target-attach @var{pid} | @var{gid} | @var{file}
29839 Attach to a process @var{pid} or a file @var{file} outside of
29840 @value{GDBN}, or a thread group @var{gid}. If attaching to a thread
29841 group, the id previously returned by
29842 @samp{-list-thread-groups --available} must be used.
29844 @subsubheading @value{GDBN} Command
29846 The corresponding @value{GDBN} command is @samp{attach}.
29848 @subsubheading Example
29852 =thread-created,id="1"
29853 *stopped,thread-id="1",frame=@{addr="0xb7f7e410",func="bar",args=[]@}
29859 @subheading The @code{-target-compare-sections} Command
29860 @findex -target-compare-sections
29862 @subsubheading Synopsis
29865 -target-compare-sections [ @var{section} ]
29868 Compare data of section @var{section} on target to the exec file.
29869 Without the argument, all sections are compared.
29871 @subsubheading @value{GDBN} Command
29873 The @value{GDBN} equivalent is @samp{compare-sections}.
29875 @subsubheading Example
29880 @subheading The @code{-target-detach} Command
29881 @findex -target-detach
29883 @subsubheading Synopsis
29886 -target-detach [ @var{pid} | @var{gid} ]
29889 Detach from the remote target which normally resumes its execution.
29890 If either @var{pid} or @var{gid} is specified, detaches from either
29891 the specified process, or specified thread group. There's no output.
29893 @subsubheading @value{GDBN} Command
29895 The corresponding @value{GDBN} command is @samp{detach}.
29897 @subsubheading Example
29907 @subheading The @code{-target-disconnect} Command
29908 @findex -target-disconnect
29910 @subsubheading Synopsis
29916 Disconnect from the remote target. There's no output and the target is
29917 generally not resumed.
29919 @subsubheading @value{GDBN} Command
29921 The corresponding @value{GDBN} command is @samp{disconnect}.
29923 @subsubheading Example
29933 @subheading The @code{-target-download} Command
29934 @findex -target-download
29936 @subsubheading Synopsis
29942 Loads the executable onto the remote target.
29943 It prints out an update message every half second, which includes the fields:
29947 The name of the section.
29949 The size of what has been sent so far for that section.
29951 The size of the section.
29953 The total size of what was sent so far (the current and the previous sections).
29955 The size of the overall executable to download.
29959 Each message is sent as status record (@pxref{GDB/MI Output Syntax, ,
29960 @sc{gdb/mi} Output Syntax}).
29962 In addition, it prints the name and size of the sections, as they are
29963 downloaded. These messages include the following fields:
29967 The name of the section.
29969 The size of the section.
29971 The size of the overall executable to download.
29975 At the end, a summary is printed.
29977 @subsubheading @value{GDBN} Command
29979 The corresponding @value{GDBN} command is @samp{load}.
29981 @subsubheading Example
29983 Note: each status message appears on a single line. Here the messages
29984 have been broken down so that they can fit onto a page.
29989 +download,@{section=".text",section-size="6668",total-size="9880"@}
29990 +download,@{section=".text",section-sent="512",section-size="6668",
29991 total-sent="512",total-size="9880"@}
29992 +download,@{section=".text",section-sent="1024",section-size="6668",
29993 total-sent="1024",total-size="9880"@}
29994 +download,@{section=".text",section-sent="1536",section-size="6668",
29995 total-sent="1536",total-size="9880"@}
29996 +download,@{section=".text",section-sent="2048",section-size="6668",
29997 total-sent="2048",total-size="9880"@}
29998 +download,@{section=".text",section-sent="2560",section-size="6668",
29999 total-sent="2560",total-size="9880"@}
30000 +download,@{section=".text",section-sent="3072",section-size="6668",
30001 total-sent="3072",total-size="9880"@}
30002 +download,@{section=".text",section-sent="3584",section-size="6668",
30003 total-sent="3584",total-size="9880"@}
30004 +download,@{section=".text",section-sent="4096",section-size="6668",
30005 total-sent="4096",total-size="9880"@}
30006 +download,@{section=".text",section-sent="4608",section-size="6668",
30007 total-sent="4608",total-size="9880"@}
30008 +download,@{section=".text",section-sent="5120",section-size="6668",
30009 total-sent="5120",total-size="9880"@}
30010 +download,@{section=".text",section-sent="5632",section-size="6668",
30011 total-sent="5632",total-size="9880"@}
30012 +download,@{section=".text",section-sent="6144",section-size="6668",
30013 total-sent="6144",total-size="9880"@}
30014 +download,@{section=".text",section-sent="6656",section-size="6668",
30015 total-sent="6656",total-size="9880"@}
30016 +download,@{section=".init",section-size="28",total-size="9880"@}
30017 +download,@{section=".fini",section-size="28",total-size="9880"@}
30018 +download,@{section=".data",section-size="3156",total-size="9880"@}
30019 +download,@{section=".data",section-sent="512",section-size="3156",
30020 total-sent="7236",total-size="9880"@}
30021 +download,@{section=".data",section-sent="1024",section-size="3156",
30022 total-sent="7748",total-size="9880"@}
30023 +download,@{section=".data",section-sent="1536",section-size="3156",
30024 total-sent="8260",total-size="9880"@}
30025 +download,@{section=".data",section-sent="2048",section-size="3156",
30026 total-sent="8772",total-size="9880"@}
30027 +download,@{section=".data",section-sent="2560",section-size="3156",
30028 total-sent="9284",total-size="9880"@}
30029 +download,@{section=".data",section-sent="3072",section-size="3156",
30030 total-sent="9796",total-size="9880"@}
30031 ^done,address="0x10004",load-size="9880",transfer-rate="6586",
30038 @subheading The @code{-target-exec-status} Command
30039 @findex -target-exec-status
30041 @subsubheading Synopsis
30044 -target-exec-status
30047 Provide information on the state of the target (whether it is running or
30048 not, for instance).
30050 @subsubheading @value{GDBN} Command
30052 There's no equivalent @value{GDBN} command.
30054 @subsubheading Example
30058 @subheading The @code{-target-list-available-targets} Command
30059 @findex -target-list-available-targets
30061 @subsubheading Synopsis
30064 -target-list-available-targets
30067 List the possible targets to connect to.
30069 @subsubheading @value{GDBN} Command
30071 The corresponding @value{GDBN} command is @samp{help target}.
30073 @subsubheading Example
30077 @subheading The @code{-target-list-current-targets} Command
30078 @findex -target-list-current-targets
30080 @subsubheading Synopsis
30083 -target-list-current-targets
30086 Describe the current target.
30088 @subsubheading @value{GDBN} Command
30090 The corresponding information is printed by @samp{info file} (among
30093 @subsubheading Example
30097 @subheading The @code{-target-list-parameters} Command
30098 @findex -target-list-parameters
30100 @subsubheading Synopsis
30103 -target-list-parameters
30109 @subsubheading @value{GDBN} Command
30113 @subsubheading Example
30117 @subheading The @code{-target-select} Command
30118 @findex -target-select
30120 @subsubheading Synopsis
30123 -target-select @var{type} @var{parameters @dots{}}
30126 Connect @value{GDBN} to the remote target. This command takes two args:
30130 The type of target, for instance @samp{remote}, etc.
30131 @item @var{parameters}
30132 Device names, host names and the like. @xref{Target Commands, ,
30133 Commands for Managing Targets}, for more details.
30136 The output is a connection notification, followed by the address at
30137 which the target program is, in the following form:
30140 ^connected,addr="@var{address}",func="@var{function name}",
30141 args=[@var{arg list}]
30144 @subsubheading @value{GDBN} Command
30146 The corresponding @value{GDBN} command is @samp{target}.
30148 @subsubheading Example
30152 -target-select remote /dev/ttya
30153 ^connected,addr="0xfe00a300",func="??",args=[]
30157 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
30158 @node GDB/MI File Transfer Commands
30159 @section @sc{gdb/mi} File Transfer Commands
30162 @subheading The @code{-target-file-put} Command
30163 @findex -target-file-put
30165 @subsubheading Synopsis
30168 -target-file-put @var{hostfile} @var{targetfile}
30171 Copy file @var{hostfile} from the host system (the machine running
30172 @value{GDBN}) to @var{targetfile} on the target system.
30174 @subsubheading @value{GDBN} Command
30176 The corresponding @value{GDBN} command is @samp{remote put}.
30178 @subsubheading Example
30182 -target-file-put localfile remotefile
30188 @subheading The @code{-target-file-get} Command
30189 @findex -target-file-get
30191 @subsubheading Synopsis
30194 -target-file-get @var{targetfile} @var{hostfile}
30197 Copy file @var{targetfile} from the target system to @var{hostfile}
30198 on the host system.
30200 @subsubheading @value{GDBN} Command
30202 The corresponding @value{GDBN} command is @samp{remote get}.
30204 @subsubheading Example
30208 -target-file-get remotefile localfile
30214 @subheading The @code{-target-file-delete} Command
30215 @findex -target-file-delete
30217 @subsubheading Synopsis
30220 -target-file-delete @var{targetfile}
30223 Delete @var{targetfile} from the target system.
30225 @subsubheading @value{GDBN} Command
30227 The corresponding @value{GDBN} command is @samp{remote delete}.
30229 @subsubheading Example
30233 -target-file-delete remotefile
30239 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
30240 @node GDB/MI Miscellaneous Commands
30241 @section Miscellaneous @sc{gdb/mi} Commands
30243 @c @subheading -gdb-complete
30245 @subheading The @code{-gdb-exit} Command
30248 @subsubheading Synopsis
30254 Exit @value{GDBN} immediately.
30256 @subsubheading @value{GDBN} Command
30258 Approximately corresponds to @samp{quit}.
30260 @subsubheading Example
30270 @subheading The @code{-exec-abort} Command
30271 @findex -exec-abort
30273 @subsubheading Synopsis
30279 Kill the inferior running program.
30281 @subsubheading @value{GDBN} Command
30283 The corresponding @value{GDBN} command is @samp{kill}.
30285 @subsubheading Example
30290 @subheading The @code{-gdb-set} Command
30293 @subsubheading Synopsis
30299 Set an internal @value{GDBN} variable.
30300 @c IS THIS A DOLLAR VARIABLE? OR SOMETHING LIKE ANNOTATE ?????
30302 @subsubheading @value{GDBN} Command
30304 The corresponding @value{GDBN} command is @samp{set}.
30306 @subsubheading Example
30316 @subheading The @code{-gdb-show} Command
30319 @subsubheading Synopsis
30325 Show the current value of a @value{GDBN} variable.
30327 @subsubheading @value{GDBN} Command
30329 The corresponding @value{GDBN} command is @samp{show}.
30331 @subsubheading Example
30340 @c @subheading -gdb-source
30343 @subheading The @code{-gdb-version} Command
30344 @findex -gdb-version
30346 @subsubheading Synopsis
30352 Show version information for @value{GDBN}. Used mostly in testing.
30354 @subsubheading @value{GDBN} Command
30356 The @value{GDBN} equivalent is @samp{show version}. @value{GDBN} by
30357 default shows this information when you start an interactive session.
30359 @subsubheading Example
30361 @c This example modifies the actual output from GDB to avoid overfull
30367 ~Copyright 2000 Free Software Foundation, Inc.
30368 ~GDB is free software, covered by the GNU General Public License, and
30369 ~you are welcome to change it and/or distribute copies of it under
30370 ~ certain conditions.
30371 ~Type "show copying" to see the conditions.
30372 ~There is absolutely no warranty for GDB. Type "show warranty" for
30374 ~This GDB was configured as
30375 "--host=sparc-sun-solaris2.5.1 --target=ppc-eabi".
30380 @subheading The @code{-list-features} Command
30381 @findex -list-features
30383 Returns a list of particular features of the MI protocol that
30384 this version of gdb implements. A feature can be a command,
30385 or a new field in an output of some command, or even an
30386 important bugfix. While a frontend can sometimes detect presence
30387 of a feature at runtime, it is easier to perform detection at debugger
30390 The command returns a list of strings, with each string naming an
30391 available feature. Each returned string is just a name, it does not
30392 have any internal structure. The list of possible feature names
30398 (gdb) -list-features
30399 ^done,result=["feature1","feature2"]
30402 The current list of features is:
30405 @item frozen-varobjs
30406 Indicates support for the @code{-var-set-frozen} command, as well
30407 as possible presense of the @code{frozen} field in the output
30408 of @code{-varobj-create}.
30409 @item pending-breakpoints
30410 Indicates support for the @option{-f} option to the @code{-break-insert}
30413 Indicates Python scripting support, Python-based
30414 pretty-printing commands, and possible presence of the
30415 @samp{display_hint} field in the output of @code{-var-list-children}
30417 Indicates support for the @code{-thread-info} command.
30418 @item data-read-memory-bytes
30419 Indicates support for the @code{-data-read-memory-bytes} and the
30420 @code{-data-write-memory-bytes} commands.
30421 @item breakpoint-notifications
30422 Indicates that changes to breakpoints and breakpoints created via the
30423 CLI will be announced via async records.
30424 @item ada-task-info
30425 Indicates support for the @code{-ada-task-info} command.
30428 @subheading The @code{-list-target-features} Command
30429 @findex -list-target-features
30431 Returns a list of particular features that are supported by the
30432 target. Those features affect the permitted MI commands, but
30433 unlike the features reported by the @code{-list-features} command, the
30434 features depend on which target GDB is using at the moment. Whenever
30435 a target can change, due to commands such as @code{-target-select},
30436 @code{-target-attach} or @code{-exec-run}, the list of target features
30437 may change, and the frontend should obtain it again.
30441 (gdb) -list-features
30442 ^done,result=["async"]
30445 The current list of features is:
30449 Indicates that the target is capable of asynchronous command
30450 execution, which means that @value{GDBN} will accept further commands
30451 while the target is running.
30454 Indicates that the target is capable of reverse execution.
30455 @xref{Reverse Execution}, for more information.
30459 @subheading The @code{-list-thread-groups} Command
30460 @findex -list-thread-groups
30462 @subheading Synopsis
30465 -list-thread-groups [ --available ] [ --recurse 1 ] [ @var{group} ... ]
30468 Lists thread groups (@pxref{Thread groups}). When a single thread
30469 group is passed as the argument, lists the children of that group.
30470 When several thread group are passed, lists information about those
30471 thread groups. Without any parameters, lists information about all
30472 top-level thread groups.
30474 Normally, thread groups that are being debugged are reported.
30475 With the @samp{--available} option, @value{GDBN} reports thread groups
30476 available on the target.
30478 The output of this command may have either a @samp{threads} result or
30479 a @samp{groups} result. The @samp{thread} result has a list of tuples
30480 as value, with each tuple describing a thread (@pxref{GDB/MI Thread
30481 Information}). The @samp{groups} result has a list of tuples as value,
30482 each tuple describing a thread group. If top-level groups are
30483 requested (that is, no parameter is passed), or when several groups
30484 are passed, the output always has a @samp{groups} result. The format
30485 of the @samp{group} result is described below.
30487 To reduce the number of roundtrips it's possible to list thread groups
30488 together with their children, by passing the @samp{--recurse} option
30489 and the recursion depth. Presently, only recursion depth of 1 is
30490 permitted. If this option is present, then every reported thread group
30491 will also include its children, either as @samp{group} or
30492 @samp{threads} field.
30494 In general, any combination of option and parameters is permitted, with
30495 the following caveats:
30499 When a single thread group is passed, the output will typically
30500 be the @samp{threads} result. Because threads may not contain
30501 anything, the @samp{recurse} option will be ignored.
30504 When the @samp{--available} option is passed, limited information may
30505 be available. In particular, the list of threads of a process might
30506 be inaccessible. Further, specifying specific thread groups might
30507 not give any performance advantage over listing all thread groups.
30508 The frontend should assume that @samp{-list-thread-groups --available}
30509 is always an expensive operation and cache the results.
30513 The @samp{groups} result is a list of tuples, where each tuple may
30514 have the following fields:
30518 Identifier of the thread group. This field is always present.
30519 The identifier is an opaque string; frontends should not try to
30520 convert it to an integer, even though it might look like one.
30523 The type of the thread group. At present, only @samp{process} is a
30527 The target-specific process identifier. This field is only present
30528 for thread groups of type @samp{process} and only if the process exists.
30531 The number of children this thread group has. This field may be
30532 absent for an available thread group.
30535 This field has a list of tuples as value, each tuple describing a
30536 thread. It may be present if the @samp{--recurse} option is
30537 specified, and it's actually possible to obtain the threads.
30540 This field is a list of integers, each identifying a core that one
30541 thread of the group is running on. This field may be absent if
30542 such information is not available.
30545 The name of the executable file that corresponds to this thread group.
30546 The field is only present for thread groups of type @samp{process},
30547 and only if there is a corresponding executable file.
30551 @subheading Example
30555 -list-thread-groups
30556 ^done,groups=[@{id="17",type="process",pid="yyy",num_children="2"@}]
30557 -list-thread-groups 17
30558 ^done,threads=[@{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)",
30559 frame=@{level="0",addr="0xffffe410",func="__kernel_vsyscall",args=[]@},state="running"@},
30560 @{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
30561 frame=@{level="0",addr="0x0804891f",func="foo",args=[@{name="i",value="10"@}],
30562 file="/tmp/a.c",fullname="/tmp/a.c",line="158"@},state="running"@}]]
30563 -list-thread-groups --available
30564 ^done,groups=[@{id="17",type="process",pid="yyy",num_children="2",cores=[1,2]@}]
30565 -list-thread-groups --available --recurse 1
30566 ^done,groups=[@{id="17", types="process",pid="yyy",num_children="2",cores=[1,2],
30567 threads=[@{id="1",target-id="Thread 0xb7e14b90",cores=[1]@},
30568 @{id="2",target-id="Thread 0xb7e14b90",cores=[2]@}]@},..]
30569 -list-thread-groups --available --recurse 1 17 18
30570 ^done,groups=[@{id="17", types="process",pid="yyy",num_children="2",cores=[1,2],
30571 threads=[@{id="1",target-id="Thread 0xb7e14b90",cores=[1]@},
30572 @{id="2",target-id="Thread 0xb7e14b90",cores=[2]@}]@},...]
30576 @subheading The @code{-add-inferior} Command
30577 @findex -add-inferior
30579 @subheading Synopsis
30585 Creates a new inferior (@pxref{Inferiors and Programs}). The created
30586 inferior is not associated with any executable. Such association may
30587 be established with the @samp{-file-exec-and-symbols} command
30588 (@pxref{GDB/MI File Commands}). The command response has a single
30589 field, @samp{thread-group}, whose value is the identifier of the
30590 thread group corresponding to the new inferior.
30592 @subheading Example
30597 ^done,thread-group="i3"
30600 @subheading The @code{-interpreter-exec} Command
30601 @findex -interpreter-exec
30603 @subheading Synopsis
30606 -interpreter-exec @var{interpreter} @var{command}
30608 @anchor{-interpreter-exec}
30610 Execute the specified @var{command} in the given @var{interpreter}.
30612 @subheading @value{GDBN} Command
30614 The corresponding @value{GDBN} command is @samp{interpreter-exec}.
30616 @subheading Example
30620 -interpreter-exec console "break main"
30621 &"During symbol reading, couldn't parse type; debugger out of date?.\n"
30622 &"During symbol reading, bad structure-type format.\n"
30623 ~"Breakpoint 1 at 0x8074fc6: file ../../src/gdb/main.c, line 743.\n"
30628 @subheading The @code{-inferior-tty-set} Command
30629 @findex -inferior-tty-set
30631 @subheading Synopsis
30634 -inferior-tty-set /dev/pts/1
30637 Set terminal for future runs of the program being debugged.
30639 @subheading @value{GDBN} Command
30641 The corresponding @value{GDBN} command is @samp{set inferior-tty} /dev/pts/1.
30643 @subheading Example
30647 -inferior-tty-set /dev/pts/1
30652 @subheading The @code{-inferior-tty-show} Command
30653 @findex -inferior-tty-show
30655 @subheading Synopsis
30661 Show terminal for future runs of program being debugged.
30663 @subheading @value{GDBN} Command
30665 The corresponding @value{GDBN} command is @samp{show inferior-tty}.
30667 @subheading Example
30671 -inferior-tty-set /dev/pts/1
30675 ^done,inferior_tty_terminal="/dev/pts/1"
30679 @subheading The @code{-enable-timings} Command
30680 @findex -enable-timings
30682 @subheading Synopsis
30685 -enable-timings [yes | no]
30688 Toggle the printing of the wallclock, user and system times for an MI
30689 command as a field in its output. This command is to help frontend
30690 developers optimize the performance of their code. No argument is
30691 equivalent to @samp{yes}.
30693 @subheading @value{GDBN} Command
30697 @subheading Example
30705 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
30706 addr="0x080484ed",func="main",file="myprog.c",
30707 fullname="/home/nickrob/myprog.c",line="73",times="0"@},
30708 time=@{wallclock="0.05185",user="0.00800",system="0.00000"@}
30716 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0",
30717 frame=@{addr="0x080484ed",func="main",args=[@{name="argc",value="1"@},
30718 @{name="argv",value="0xbfb60364"@}],file="myprog.c",
30719 fullname="/home/nickrob/myprog.c",line="73"@}
30724 @chapter @value{GDBN} Annotations
30726 This chapter describes annotations in @value{GDBN}. Annotations were
30727 designed to interface @value{GDBN} to graphical user interfaces or other
30728 similar programs which want to interact with @value{GDBN} at a
30729 relatively high level.
30731 The annotation mechanism has largely been superseded by @sc{gdb/mi}
30735 This is Edition @value{EDITION}, @value{DATE}.
30739 * Annotations Overview:: What annotations are; the general syntax.
30740 * Server Prefix:: Issuing a command without affecting user state.
30741 * Prompting:: Annotations marking @value{GDBN}'s need for input.
30742 * Errors:: Annotations for error messages.
30743 * Invalidation:: Some annotations describe things now invalid.
30744 * Annotations for Running::
30745 Whether the program is running, how it stopped, etc.
30746 * Source Annotations:: Annotations describing source code.
30749 @node Annotations Overview
30750 @section What is an Annotation?
30751 @cindex annotations
30753 Annotations start with a newline character, two @samp{control-z}
30754 characters, and the name of the annotation. If there is no additional
30755 information associated with this annotation, the name of the annotation
30756 is followed immediately by a newline. If there is additional
30757 information, the name of the annotation is followed by a space, the
30758 additional information, and a newline. The additional information
30759 cannot contain newline characters.
30761 Any output not beginning with a newline and two @samp{control-z}
30762 characters denotes literal output from @value{GDBN}. Currently there is
30763 no need for @value{GDBN} to output a newline followed by two
30764 @samp{control-z} characters, but if there was such a need, the
30765 annotations could be extended with an @samp{escape} annotation which
30766 means those three characters as output.
30768 The annotation @var{level}, which is specified using the
30769 @option{--annotate} command line option (@pxref{Mode Options}), controls
30770 how much information @value{GDBN} prints together with its prompt,
30771 values of expressions, source lines, and other types of output. Level 0
30772 is for no annotations, level 1 is for use when @value{GDBN} is run as a
30773 subprocess of @sc{gnu} Emacs, level 3 is the maximum annotation suitable
30774 for programs that control @value{GDBN}, and level 2 annotations have
30775 been made obsolete (@pxref{Limitations, , Limitations of the Annotation
30776 Interface, annotate, GDB's Obsolete Annotations}).
30779 @kindex set annotate
30780 @item set annotate @var{level}
30781 The @value{GDBN} command @code{set annotate} sets the level of
30782 annotations to the specified @var{level}.
30784 @item show annotate
30785 @kindex show annotate
30786 Show the current annotation level.
30789 This chapter describes level 3 annotations.
30791 A simple example of starting up @value{GDBN} with annotations is:
30794 $ @kbd{gdb --annotate=3}
30796 Copyright 2003 Free Software Foundation, Inc.
30797 GDB is free software, covered by the GNU General Public License,
30798 and you are welcome to change it and/or distribute copies of it
30799 under certain conditions.
30800 Type "show copying" to see the conditions.
30801 There is absolutely no warranty for GDB. Type "show warranty"
30803 This GDB was configured as "i386-pc-linux-gnu"
30814 Here @samp{quit} is input to @value{GDBN}; the rest is output from
30815 @value{GDBN}. The three lines beginning @samp{^Z^Z} (where @samp{^Z}
30816 denotes a @samp{control-z} character) are annotations; the rest is
30817 output from @value{GDBN}.
30819 @node Server Prefix
30820 @section The Server Prefix
30821 @cindex server prefix
30823 If you prefix a command with @samp{server } then it will not affect
30824 the command history, nor will it affect @value{GDBN}'s notion of which
30825 command to repeat if @key{RET} is pressed on a line by itself. This
30826 means that commands can be run behind a user's back by a front-end in
30827 a transparent manner.
30829 The @code{server } prefix does not affect the recording of values into
30830 the value history; to print a value without recording it into the
30831 value history, use the @code{output} command instead of the
30832 @code{print} command.
30834 Using this prefix also disables confirmation requests
30835 (@pxref{confirmation requests}).
30838 @section Annotation for @value{GDBN} Input
30840 @cindex annotations for prompts
30841 When @value{GDBN} prompts for input, it annotates this fact so it is possible
30842 to know when to send output, when the output from a given command is
30845 Different kinds of input each have a different @dfn{input type}. Each
30846 input type has three annotations: a @code{pre-} annotation, which
30847 denotes the beginning of any prompt which is being output, a plain
30848 annotation, which denotes the end of the prompt, and then a @code{post-}
30849 annotation which denotes the end of any echo which may (or may not) be
30850 associated with the input. For example, the @code{prompt} input type
30851 features the following annotations:
30859 The input types are
30862 @findex pre-prompt annotation
30863 @findex prompt annotation
30864 @findex post-prompt annotation
30866 When @value{GDBN} is prompting for a command (the main @value{GDBN} prompt).
30868 @findex pre-commands annotation
30869 @findex commands annotation
30870 @findex post-commands annotation
30872 When @value{GDBN} prompts for a set of commands, like in the @code{commands}
30873 command. The annotations are repeated for each command which is input.
30875 @findex pre-overload-choice annotation
30876 @findex overload-choice annotation
30877 @findex post-overload-choice annotation
30878 @item overload-choice
30879 When @value{GDBN} wants the user to select between various overloaded functions.
30881 @findex pre-query annotation
30882 @findex query annotation
30883 @findex post-query annotation
30885 When @value{GDBN} wants the user to confirm a potentially dangerous operation.
30887 @findex pre-prompt-for-continue annotation
30888 @findex prompt-for-continue annotation
30889 @findex post-prompt-for-continue annotation
30890 @item prompt-for-continue
30891 When @value{GDBN} is asking the user to press return to continue. Note: Don't
30892 expect this to work well; instead use @code{set height 0} to disable
30893 prompting. This is because the counting of lines is buggy in the
30894 presence of annotations.
30899 @cindex annotations for errors, warnings and interrupts
30901 @findex quit annotation
30906 This annotation occurs right before @value{GDBN} responds to an interrupt.
30908 @findex error annotation
30913 This annotation occurs right before @value{GDBN} responds to an error.
30915 Quit and error annotations indicate that any annotations which @value{GDBN} was
30916 in the middle of may end abruptly. For example, if a
30917 @code{value-history-begin} annotation is followed by a @code{error}, one
30918 cannot expect to receive the matching @code{value-history-end}. One
30919 cannot expect not to receive it either, however; an error annotation
30920 does not necessarily mean that @value{GDBN} is immediately returning all the way
30923 @findex error-begin annotation
30924 A quit or error annotation may be preceded by
30930 Any output between that and the quit or error annotation is the error
30933 Warning messages are not yet annotated.
30934 @c If we want to change that, need to fix warning(), type_error(),
30935 @c range_error(), and possibly other places.
30938 @section Invalidation Notices
30940 @cindex annotations for invalidation messages
30941 The following annotations say that certain pieces of state may have
30945 @findex frames-invalid annotation
30946 @item ^Z^Zframes-invalid
30948 The frames (for example, output from the @code{backtrace} command) may
30951 @findex breakpoints-invalid annotation
30952 @item ^Z^Zbreakpoints-invalid
30954 The breakpoints may have changed. For example, the user just added or
30955 deleted a breakpoint.
30958 @node Annotations for Running
30959 @section Running the Program
30960 @cindex annotations for running programs
30962 @findex starting annotation
30963 @findex stopping annotation
30964 When the program starts executing due to a @value{GDBN} command such as
30965 @code{step} or @code{continue},
30971 is output. When the program stops,
30977 is output. Before the @code{stopped} annotation, a variety of
30978 annotations describe how the program stopped.
30981 @findex exited annotation
30982 @item ^Z^Zexited @var{exit-status}
30983 The program exited, and @var{exit-status} is the exit status (zero for
30984 successful exit, otherwise nonzero).
30986 @findex signalled annotation
30987 @findex signal-name annotation
30988 @findex signal-name-end annotation
30989 @findex signal-string annotation
30990 @findex signal-string-end annotation
30991 @item ^Z^Zsignalled
30992 The program exited with a signal. After the @code{^Z^Zsignalled}, the
30993 annotation continues:
30999 ^Z^Zsignal-name-end
31003 ^Z^Zsignal-string-end
31008 where @var{name} is the name of the signal, such as @code{SIGILL} or
31009 @code{SIGSEGV}, and @var{string} is the explanation of the signal, such
31010 as @code{Illegal Instruction} or @code{Segmentation fault}.
31011 @var{intro-text}, @var{middle-text}, and @var{end-text} are for the
31012 user's benefit and have no particular format.
31014 @findex signal annotation
31016 The syntax of this annotation is just like @code{signalled}, but @value{GDBN} is
31017 just saying that the program received the signal, not that it was
31018 terminated with it.
31020 @findex breakpoint annotation
31021 @item ^Z^Zbreakpoint @var{number}
31022 The program hit breakpoint number @var{number}.
31024 @findex watchpoint annotation
31025 @item ^Z^Zwatchpoint @var{number}
31026 The program hit watchpoint number @var{number}.
31029 @node Source Annotations
31030 @section Displaying Source
31031 @cindex annotations for source display
31033 @findex source annotation
31034 The following annotation is used instead of displaying source code:
31037 ^Z^Zsource @var{filename}:@var{line}:@var{character}:@var{middle}:@var{addr}
31040 where @var{filename} is an absolute file name indicating which source
31041 file, @var{line} is the line number within that file (where 1 is the
31042 first line in the file), @var{character} is the character position
31043 within the file (where 0 is the first character in the file) (for most
31044 debug formats this will necessarily point to the beginning of a line),
31045 @var{middle} is @samp{middle} if @var{addr} is in the middle of the
31046 line, or @samp{beg} if @var{addr} is at the beginning of the line, and
31047 @var{addr} is the address in the target program associated with the
31048 source which is being displayed. @var{addr} is in the form @samp{0x}
31049 followed by one or more lowercase hex digits (note that this does not
31050 depend on the language).
31052 @node JIT Interface
31053 @chapter JIT Compilation Interface
31054 @cindex just-in-time compilation
31055 @cindex JIT compilation interface
31057 This chapter documents @value{GDBN}'s @dfn{just-in-time} (JIT) compilation
31058 interface. A JIT compiler is a program or library that generates native
31059 executable code at runtime and executes it, usually in order to achieve good
31060 performance while maintaining platform independence.
31062 Programs that use JIT compilation are normally difficult to debug because
31063 portions of their code are generated at runtime, instead of being loaded from
31064 object files, which is where @value{GDBN} normally finds the program's symbols
31065 and debug information. In order to debug programs that use JIT compilation,
31066 @value{GDBN} has an interface that allows the program to register in-memory
31067 symbol files with @value{GDBN} at runtime.
31069 If you are using @value{GDBN} to debug a program that uses this interface, then
31070 it should work transparently so long as you have not stripped the binary. If
31071 you are developing a JIT compiler, then the interface is documented in the rest
31072 of this chapter. At this time, the only known client of this interface is the
31075 Broadly speaking, the JIT interface mirrors the dynamic loader interface. The
31076 JIT compiler communicates with @value{GDBN} by writing data into a global
31077 variable and calling a fuction at a well-known symbol. When @value{GDBN}
31078 attaches, it reads a linked list of symbol files from the global variable to
31079 find existing code, and puts a breakpoint in the function so that it can find
31080 out about additional code.
31083 * Declarations:: Relevant C struct declarations
31084 * Registering Code:: Steps to register code
31085 * Unregistering Code:: Steps to unregister code
31089 @section JIT Declarations
31091 These are the relevant struct declarations that a C program should include to
31092 implement the interface:
31102 struct jit_code_entry
31104 struct jit_code_entry *next_entry;
31105 struct jit_code_entry *prev_entry;
31106 const char *symfile_addr;
31107 uint64_t symfile_size;
31110 struct jit_descriptor
31113 /* This type should be jit_actions_t, but we use uint32_t
31114 to be explicit about the bitwidth. */
31115 uint32_t action_flag;
31116 struct jit_code_entry *relevant_entry;
31117 struct jit_code_entry *first_entry;
31120 /* GDB puts a breakpoint in this function. */
31121 void __attribute__((noinline)) __jit_debug_register_code() @{ @};
31123 /* Make sure to specify the version statically, because the
31124 debugger may check the version before we can set it. */
31125 struct jit_descriptor __jit_debug_descriptor = @{ 1, 0, 0, 0 @};
31128 If the JIT is multi-threaded, then it is important that the JIT synchronize any
31129 modifications to this global data properly, which can easily be done by putting
31130 a global mutex around modifications to these structures.
31132 @node Registering Code
31133 @section Registering Code
31135 To register code with @value{GDBN}, the JIT should follow this protocol:
31139 Generate an object file in memory with symbols and other desired debug
31140 information. The file must include the virtual addresses of the sections.
31143 Create a code entry for the file, which gives the start and size of the symbol
31147 Add it to the linked list in the JIT descriptor.
31150 Point the relevant_entry field of the descriptor at the entry.
31153 Set @code{action_flag} to @code{JIT_REGISTER} and call
31154 @code{__jit_debug_register_code}.
31157 When @value{GDBN} is attached and the breakpoint fires, @value{GDBN} uses the
31158 @code{relevant_entry} pointer so it doesn't have to walk the list looking for
31159 new code. However, the linked list must still be maintained in order to allow
31160 @value{GDBN} to attach to a running process and still find the symbol files.
31162 @node Unregistering Code
31163 @section Unregistering Code
31165 If code is freed, then the JIT should use the following protocol:
31169 Remove the code entry corresponding to the code from the linked list.
31172 Point the @code{relevant_entry} field of the descriptor at the code entry.
31175 Set @code{action_flag} to @code{JIT_UNREGISTER} and call
31176 @code{__jit_debug_register_code}.
31179 If the JIT frees or recompiles code without unregistering it, then @value{GDBN}
31180 and the JIT will leak the memory used for the associated symbol files.
31183 @chapter Reporting Bugs in @value{GDBN}
31184 @cindex bugs in @value{GDBN}
31185 @cindex reporting bugs in @value{GDBN}
31187 Your bug reports play an essential role in making @value{GDBN} reliable.
31189 Reporting a bug may help you by bringing a solution to your problem, or it
31190 may not. But in any case the principal function of a bug report is to help
31191 the entire community by making the next version of @value{GDBN} work better. Bug
31192 reports are your contribution to the maintenance of @value{GDBN}.
31194 In order for a bug report to serve its purpose, you must include the
31195 information that enables us to fix the bug.
31198 * Bug Criteria:: Have you found a bug?
31199 * Bug Reporting:: How to report bugs
31203 @section Have You Found a Bug?
31204 @cindex bug criteria
31206 If you are not sure whether you have found a bug, here are some guidelines:
31209 @cindex fatal signal
31210 @cindex debugger crash
31211 @cindex crash of debugger
31213 If the debugger gets a fatal signal, for any input whatever, that is a
31214 @value{GDBN} bug. Reliable debuggers never crash.
31216 @cindex error on valid input
31218 If @value{GDBN} produces an error message for valid input, that is a
31219 bug. (Note that if you're cross debugging, the problem may also be
31220 somewhere in the connection to the target.)
31222 @cindex invalid input
31224 If @value{GDBN} does not produce an error message for invalid input,
31225 that is a bug. However, you should note that your idea of
31226 ``invalid input'' might be our idea of ``an extension'' or ``support
31227 for traditional practice''.
31230 If you are an experienced user of debugging tools, your suggestions
31231 for improvement of @value{GDBN} are welcome in any case.
31234 @node Bug Reporting
31235 @section How to Report Bugs
31236 @cindex bug reports
31237 @cindex @value{GDBN} bugs, reporting
31239 A number of companies and individuals offer support for @sc{gnu} products.
31240 If you obtained @value{GDBN} from a support organization, we recommend you
31241 contact that organization first.
31243 You can find contact information for many support companies and
31244 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
31246 @c should add a web page ref...
31249 @ifset BUGURL_DEFAULT
31250 In any event, we also recommend that you submit bug reports for
31251 @value{GDBN}. The preferred method is to submit them directly using
31252 @uref{http://www.gnu.org/software/gdb/bugs/, @value{GDBN}'s Bugs web
31253 page}. Alternatively, the @email{bug-gdb@@gnu.org, e-mail gateway} can
31256 @strong{Do not send bug reports to @samp{info-gdb}, or to
31257 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
31258 not want to receive bug reports. Those that do have arranged to receive
31261 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
31262 serves as a repeater. The mailing list and the newsgroup carry exactly
31263 the same messages. Often people think of posting bug reports to the
31264 newsgroup instead of mailing them. This appears to work, but it has one
31265 problem which can be crucial: a newsgroup posting often lacks a mail
31266 path back to the sender. Thus, if we need to ask for more information,
31267 we may be unable to reach you. For this reason, it is better to send
31268 bug reports to the mailing list.
31270 @ifclear BUGURL_DEFAULT
31271 In any event, we also recommend that you submit bug reports for
31272 @value{GDBN} to @value{BUGURL}.
31276 The fundamental principle of reporting bugs usefully is this:
31277 @strong{report all the facts}. If you are not sure whether to state a
31278 fact or leave it out, state it!
31280 Often people omit facts because they think they know what causes the
31281 problem and assume that some details do not matter. Thus, you might
31282 assume that the name of the variable you use in an example does not matter.
31283 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
31284 stray memory reference which happens to fetch from the location where that
31285 name is stored in memory; perhaps, if the name were different, the contents
31286 of that location would fool the debugger into doing the right thing despite
31287 the bug. Play it safe and give a specific, complete example. That is the
31288 easiest thing for you to do, and the most helpful.
31290 Keep in mind that the purpose of a bug report is to enable us to fix the
31291 bug. It may be that the bug has been reported previously, but neither
31292 you nor we can know that unless your bug report is complete and
31295 Sometimes people give a few sketchy facts and ask, ``Does this ring a
31296 bell?'' Those bug reports are useless, and we urge everyone to
31297 @emph{refuse to respond to them} except to chide the sender to report
31300 To enable us to fix the bug, you should include all these things:
31304 The version of @value{GDBN}. @value{GDBN} announces it if you start
31305 with no arguments; you can also print it at any time using @code{show
31308 Without this, we will not know whether there is any point in looking for
31309 the bug in the current version of @value{GDBN}.
31312 The type of machine you are using, and the operating system name and
31316 What compiler (and its version) was used to compile @value{GDBN}---e.g.@:
31317 ``@value{GCC}--2.8.1''.
31320 What compiler (and its version) was used to compile the program you are
31321 debugging---e.g.@: ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
31322 C Compiler''. For @value{NGCC}, you can say @kbd{@value{GCC} --version}
31323 to get this information; for other compilers, see the documentation for
31327 The command arguments you gave the compiler to compile your example and
31328 observe the bug. For example, did you use @samp{-O}? To guarantee
31329 you will not omit something important, list them all. A copy of the
31330 Makefile (or the output from make) is sufficient.
31332 If we were to try to guess the arguments, we would probably guess wrong
31333 and then we might not encounter the bug.
31336 A complete input script, and all necessary source files, that will
31340 A description of what behavior you observe that you believe is
31341 incorrect. For example, ``It gets a fatal signal.''
31343 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
31344 will certainly notice it. But if the bug is incorrect output, we might
31345 not notice unless it is glaringly wrong. You might as well not give us
31346 a chance to make a mistake.
31348 Even if the problem you experience is a fatal signal, you should still
31349 say so explicitly. Suppose something strange is going on, such as, your
31350 copy of @value{GDBN} is out of synch, or you have encountered a bug in
31351 the C library on your system. (This has happened!) Your copy might
31352 crash and ours would not. If you told us to expect a crash, then when
31353 ours fails to crash, we would know that the bug was not happening for
31354 us. If you had not told us to expect a crash, then we would not be able
31355 to draw any conclusion from our observations.
31358 @cindex recording a session script
31359 To collect all this information, you can use a session recording program
31360 such as @command{script}, which is available on many Unix systems.
31361 Just run your @value{GDBN} session inside @command{script} and then
31362 include the @file{typescript} file with your bug report.
31364 Another way to record a @value{GDBN} session is to run @value{GDBN}
31365 inside Emacs and then save the entire buffer to a file.
31368 If you wish to suggest changes to the @value{GDBN} source, send us context
31369 diffs. If you even discuss something in the @value{GDBN} source, refer to
31370 it by context, not by line number.
31372 The line numbers in our development sources will not match those in your
31373 sources. Your line numbers would convey no useful information to us.
31377 Here are some things that are not necessary:
31381 A description of the envelope of the bug.
31383 Often people who encounter a bug spend a lot of time investigating
31384 which changes to the input file will make the bug go away and which
31385 changes will not affect it.
31387 This is often time consuming and not very useful, because the way we
31388 will find the bug is by running a single example under the debugger
31389 with breakpoints, not by pure deduction from a series of examples.
31390 We recommend that you save your time for something else.
31392 Of course, if you can find a simpler example to report @emph{instead}
31393 of the original one, that is a convenience for us. Errors in the
31394 output will be easier to spot, running under the debugger will take
31395 less time, and so on.
31397 However, simplification is not vital; if you do not want to do this,
31398 report the bug anyway and send us the entire test case you used.
31401 A patch for the bug.
31403 A patch for the bug does help us if it is a good one. But do not omit
31404 the necessary information, such as the test case, on the assumption that
31405 a patch is all we need. We might see problems with your patch and decide
31406 to fix the problem another way, or we might not understand it at all.
31408 Sometimes with a program as complicated as @value{GDBN} it is very hard to
31409 construct an example that will make the program follow a certain path
31410 through the code. If you do not send us the example, we will not be able
31411 to construct one, so we will not be able to verify that the bug is fixed.
31413 And if we cannot understand what bug you are trying to fix, or why your
31414 patch should be an improvement, we will not install it. A test case will
31415 help us to understand.
31418 A guess about what the bug is or what it depends on.
31420 Such guesses are usually wrong. Even we cannot guess right about such
31421 things without first using the debugger to find the facts.
31424 @c The readline documentation is distributed with the readline code
31425 @c and consists of the two following files:
31428 @c Use -I with makeinfo to point to the appropriate directory,
31429 @c environment var TEXINPUTS with TeX.
31430 @ifclear SYSTEM_READLINE
31431 @include rluser.texi
31432 @include hsuser.texi
31436 @appendix In Memoriam
31438 The @value{GDBN} project mourns the loss of the following long-time
31443 Fred was a long-standing contributor to @value{GDBN} (1991-2006), and
31444 to Free Software in general. Outside of @value{GDBN}, he was known in
31445 the Amiga world for his series of Fish Disks, and the GeekGadget project.
31447 @item Michael Snyder
31448 Michael was one of the Global Maintainers of the @value{GDBN} project,
31449 with contributions recorded as early as 1996, until 2011. In addition
31450 to his day to day participation, he was a large driving force behind
31451 adding Reverse Debugging to @value{GDBN}.
31454 Beyond their technical contributions to the project, they were also
31455 enjoyable members of the Free Software Community. We will miss them.
31457 @node Formatting Documentation
31458 @appendix Formatting Documentation
31460 @cindex @value{GDBN} reference card
31461 @cindex reference card
31462 The @value{GDBN} 4 release includes an already-formatted reference card, ready
31463 for printing with PostScript or Ghostscript, in the @file{gdb}
31464 subdirectory of the main source directory@footnote{In
31465 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
31466 release.}. If you can use PostScript or Ghostscript with your printer,
31467 you can print the reference card immediately with @file{refcard.ps}.
31469 The release also includes the source for the reference card. You
31470 can format it, using @TeX{}, by typing:
31476 The @value{GDBN} reference card is designed to print in @dfn{landscape}
31477 mode on US ``letter'' size paper;
31478 that is, on a sheet 11 inches wide by 8.5 inches
31479 high. You will need to specify this form of printing as an option to
31480 your @sc{dvi} output program.
31482 @cindex documentation
31484 All the documentation for @value{GDBN} comes as part of the machine-readable
31485 distribution. The documentation is written in Texinfo format, which is
31486 a documentation system that uses a single source file to produce both
31487 on-line information and a printed manual. You can use one of the Info
31488 formatting commands to create the on-line version of the documentation
31489 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
31491 @value{GDBN} includes an already formatted copy of the on-line Info
31492 version of this manual in the @file{gdb} subdirectory. The main Info
31493 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
31494 subordinate files matching @samp{gdb.info*} in the same directory. If
31495 necessary, you can print out these files, or read them with any editor;
31496 but they are easier to read using the @code{info} subsystem in @sc{gnu}
31497 Emacs or the standalone @code{info} program, available as part of the
31498 @sc{gnu} Texinfo distribution.
31500 If you want to format these Info files yourself, you need one of the
31501 Info formatting programs, such as @code{texinfo-format-buffer} or
31504 If you have @code{makeinfo} installed, and are in the top level
31505 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
31506 version @value{GDBVN}), you can make the Info file by typing:
31513 If you want to typeset and print copies of this manual, you need @TeX{},
31514 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
31515 Texinfo definitions file.
31517 @TeX{} is a typesetting program; it does not print files directly, but
31518 produces output files called @sc{dvi} files. To print a typeset
31519 document, you need a program to print @sc{dvi} files. If your system
31520 has @TeX{} installed, chances are it has such a program. The precise
31521 command to use depends on your system; @kbd{lpr -d} is common; another
31522 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
31523 require a file name without any extension or a @samp{.dvi} extension.
31525 @TeX{} also requires a macro definitions file called
31526 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
31527 written in Texinfo format. On its own, @TeX{} cannot either read or
31528 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
31529 and is located in the @file{gdb-@var{version-number}/texinfo}
31532 If you have @TeX{} and a @sc{dvi} printer program installed, you can
31533 typeset and print this manual. First switch to the @file{gdb}
31534 subdirectory of the main source directory (for example, to
31535 @file{gdb-@value{GDBVN}/gdb}) and type:
31541 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
31543 @node Installing GDB
31544 @appendix Installing @value{GDBN}
31545 @cindex installation
31548 * Requirements:: Requirements for building @value{GDBN}
31549 * Running Configure:: Invoking the @value{GDBN} @file{configure} script
31550 * Separate Objdir:: Compiling @value{GDBN} in another directory
31551 * Config Names:: Specifying names for hosts and targets
31552 * Configure Options:: Summary of options for configure
31553 * System-wide configuration:: Having a system-wide init file
31557 @section Requirements for Building @value{GDBN}
31558 @cindex building @value{GDBN}, requirements for
31560 Building @value{GDBN} requires various tools and packages to be available.
31561 Other packages will be used only if they are found.
31563 @heading Tools/Packages Necessary for Building @value{GDBN}
31565 @item ISO C90 compiler
31566 @value{GDBN} is written in ISO C90. It should be buildable with any
31567 working C90 compiler, e.g.@: GCC.
31571 @heading Tools/Packages Optional for Building @value{GDBN}
31575 @value{GDBN} can use the Expat XML parsing library. This library may be
31576 included with your operating system distribution; if it is not, you
31577 can get the latest version from @url{http://expat.sourceforge.net}.
31578 The @file{configure} script will search for this library in several
31579 standard locations; if it is installed in an unusual path, you can
31580 use the @option{--with-libexpat-prefix} option to specify its location.
31586 Remote protocol memory maps (@pxref{Memory Map Format})
31588 Target descriptions (@pxref{Target Descriptions})
31590 Remote shared library lists (@pxref{Library List Format})
31592 MS-Windows shared libraries (@pxref{Shared Libraries})
31594 Traceframe info (@pxref{Traceframe Info Format})
31598 @cindex compressed debug sections
31599 @value{GDBN} will use the @samp{zlib} library, if available, to read
31600 compressed debug sections. Some linkers, such as GNU gold, are capable
31601 of producing binaries with compressed debug sections. If @value{GDBN}
31602 is compiled with @samp{zlib}, it will be able to read the debug
31603 information in such binaries.
31605 The @samp{zlib} library is likely included with your operating system
31606 distribution; if it is not, you can get the latest version from
31607 @url{http://zlib.net}.
31610 @value{GDBN}'s features related to character sets (@pxref{Character
31611 Sets}) require a functioning @code{iconv} implementation. If you are
31612 on a GNU system, then this is provided by the GNU C Library. Some
31613 other systems also provide a working @code{iconv}.
31615 If @value{GDBN} is using the @code{iconv} program which is installed
31616 in a non-standard place, you will need to tell @value{GDBN} where to find it.
31617 This is done with @option{--with-iconv-bin} which specifies the
31618 directory that contains the @code{iconv} program.
31620 On systems without @code{iconv}, you can install GNU Libiconv. If you
31621 have previously installed Libiconv, you can use the
31622 @option{--with-libiconv-prefix} option to configure.
31624 @value{GDBN}'s top-level @file{configure} and @file{Makefile} will
31625 arrange to build Libiconv if a directory named @file{libiconv} appears
31626 in the top-most source directory. If Libiconv is built this way, and
31627 if the operating system does not provide a suitable @code{iconv}
31628 implementation, then the just-built library will automatically be used
31629 by @value{GDBN}. One easy way to set this up is to download GNU
31630 Libiconv, unpack it, and then rename the directory holding the
31631 Libiconv source code to @samp{libiconv}.
31634 @node Running Configure
31635 @section Invoking the @value{GDBN} @file{configure} Script
31636 @cindex configuring @value{GDBN}
31637 @value{GDBN} comes with a @file{configure} script that automates the process
31638 of preparing @value{GDBN} for installation; you can then use @code{make} to
31639 build the @code{gdb} program.
31641 @c irrelevant in info file; it's as current as the code it lives with.
31642 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
31643 look at the @file{README} file in the sources; we may have improved the
31644 installation procedures since publishing this manual.}
31647 The @value{GDBN} distribution includes all the source code you need for
31648 @value{GDBN} in a single directory, whose name is usually composed by
31649 appending the version number to @samp{gdb}.
31651 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
31652 @file{gdb-@value{GDBVN}} directory. That directory contains:
31655 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
31656 script for configuring @value{GDBN} and all its supporting libraries
31658 @item gdb-@value{GDBVN}/gdb
31659 the source specific to @value{GDBN} itself
31661 @item gdb-@value{GDBVN}/bfd
31662 source for the Binary File Descriptor library
31664 @item gdb-@value{GDBVN}/include
31665 @sc{gnu} include files
31667 @item gdb-@value{GDBVN}/libiberty
31668 source for the @samp{-liberty} free software library
31670 @item gdb-@value{GDBVN}/opcodes
31671 source for the library of opcode tables and disassemblers
31673 @item gdb-@value{GDBVN}/readline
31674 source for the @sc{gnu} command-line interface
31676 @item gdb-@value{GDBVN}/glob
31677 source for the @sc{gnu} filename pattern-matching subroutine
31679 @item gdb-@value{GDBVN}/mmalloc
31680 source for the @sc{gnu} memory-mapped malloc package
31683 The simplest way to configure and build @value{GDBN} is to run @file{configure}
31684 from the @file{gdb-@var{version-number}} source directory, which in
31685 this example is the @file{gdb-@value{GDBVN}} directory.
31687 First switch to the @file{gdb-@var{version-number}} source directory
31688 if you are not already in it; then run @file{configure}. Pass the
31689 identifier for the platform on which @value{GDBN} will run as an
31695 cd gdb-@value{GDBVN}
31696 ./configure @var{host}
31701 where @var{host} is an identifier such as @samp{sun4} or
31702 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
31703 (You can often leave off @var{host}; @file{configure} tries to guess the
31704 correct value by examining your system.)
31706 Running @samp{configure @var{host}} and then running @code{make} builds the
31707 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
31708 libraries, then @code{gdb} itself. The configured source files, and the
31709 binaries, are left in the corresponding source directories.
31712 @file{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
31713 system does not recognize this automatically when you run a different
31714 shell, you may need to run @code{sh} on it explicitly:
31717 sh configure @var{host}
31720 If you run @file{configure} from a directory that contains source
31721 directories for multiple libraries or programs, such as the
31722 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN},
31724 creates configuration files for every directory level underneath (unless
31725 you tell it not to, with the @samp{--norecursion} option).
31727 You should run the @file{configure} script from the top directory in the
31728 source tree, the @file{gdb-@var{version-number}} directory. If you run
31729 @file{configure} from one of the subdirectories, you will configure only
31730 that subdirectory. That is usually not what you want. In particular,
31731 if you run the first @file{configure} from the @file{gdb} subdirectory
31732 of the @file{gdb-@var{version-number}} directory, you will omit the
31733 configuration of @file{bfd}, @file{readline}, and other sibling
31734 directories of the @file{gdb} subdirectory. This leads to build errors
31735 about missing include files such as @file{bfd/bfd.h}.
31737 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
31738 However, you should make sure that the shell on your path (named by
31739 the @samp{SHELL} environment variable) is publicly readable. Remember
31740 that @value{GDBN} uses the shell to start your program---some systems refuse to
31741 let @value{GDBN} debug child processes whose programs are not readable.
31743 @node Separate Objdir
31744 @section Compiling @value{GDBN} in Another Directory
31746 If you want to run @value{GDBN} versions for several host or target machines,
31747 you need a different @code{gdb} compiled for each combination of
31748 host and target. @file{configure} is designed to make this easy by
31749 allowing you to generate each configuration in a separate subdirectory,
31750 rather than in the source directory. If your @code{make} program
31751 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
31752 @code{make} in each of these directories builds the @code{gdb}
31753 program specified there.
31755 To build @code{gdb} in a separate directory, run @file{configure}
31756 with the @samp{--srcdir} option to specify where to find the source.
31757 (You also need to specify a path to find @file{configure}
31758 itself from your working directory. If the path to @file{configure}
31759 would be the same as the argument to @samp{--srcdir}, you can leave out
31760 the @samp{--srcdir} option; it is assumed.)
31762 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
31763 separate directory for a Sun 4 like this:
31767 cd gdb-@value{GDBVN}
31770 ../gdb-@value{GDBVN}/configure sun4
31775 When @file{configure} builds a configuration using a remote source
31776 directory, it creates a tree for the binaries with the same structure
31777 (and using the same names) as the tree under the source directory. In
31778 the example, you'd find the Sun 4 library @file{libiberty.a} in the
31779 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
31780 @file{gdb-sun4/gdb}.
31782 Make sure that your path to the @file{configure} script has just one
31783 instance of @file{gdb} in it. If your path to @file{configure} looks
31784 like @file{../gdb-@value{GDBVN}/gdb/configure}, you are configuring only
31785 one subdirectory of @value{GDBN}, not the whole package. This leads to
31786 build errors about missing include files such as @file{bfd/bfd.h}.
31788 One popular reason to build several @value{GDBN} configurations in separate
31789 directories is to configure @value{GDBN} for cross-compiling (where
31790 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
31791 programs that run on another machine---the @dfn{target}).
31792 You specify a cross-debugging target by
31793 giving the @samp{--target=@var{target}} option to @file{configure}.
31795 When you run @code{make} to build a program or library, you must run
31796 it in a configured directory---whatever directory you were in when you
31797 called @file{configure} (or one of its subdirectories).
31799 The @code{Makefile} that @file{configure} generates in each source
31800 directory also runs recursively. If you type @code{make} in a source
31801 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
31802 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
31803 will build all the required libraries, and then build GDB.
31805 When you have multiple hosts or targets configured in separate
31806 directories, you can run @code{make} on them in parallel (for example,
31807 if they are NFS-mounted on each of the hosts); they will not interfere
31811 @section Specifying Names for Hosts and Targets
31813 The specifications used for hosts and targets in the @file{configure}
31814 script are based on a three-part naming scheme, but some short predefined
31815 aliases are also supported. The full naming scheme encodes three pieces
31816 of information in the following pattern:
31819 @var{architecture}-@var{vendor}-@var{os}
31822 For example, you can use the alias @code{sun4} as a @var{host} argument,
31823 or as the value for @var{target} in a @code{--target=@var{target}}
31824 option. The equivalent full name is @samp{sparc-sun-sunos4}.
31826 The @file{configure} script accompanying @value{GDBN} does not provide
31827 any query facility to list all supported host and target names or
31828 aliases. @file{configure} calls the Bourne shell script
31829 @code{config.sub} to map abbreviations to full names; you can read the
31830 script, if you wish, or you can use it to test your guesses on
31831 abbreviations---for example:
31834 % sh config.sub i386-linux
31836 % sh config.sub alpha-linux
31837 alpha-unknown-linux-gnu
31838 % sh config.sub hp9k700
31840 % sh config.sub sun4
31841 sparc-sun-sunos4.1.1
31842 % sh config.sub sun3
31843 m68k-sun-sunos4.1.1
31844 % sh config.sub i986v
31845 Invalid configuration `i986v': machine `i986v' not recognized
31849 @code{config.sub} is also distributed in the @value{GDBN} source
31850 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
31852 @node Configure Options
31853 @section @file{configure} Options
31855 Here is a summary of the @file{configure} options and arguments that
31856 are most often useful for building @value{GDBN}. @file{configure} also has
31857 several other options not listed here. @inforef{What Configure
31858 Does,,configure.info}, for a full explanation of @file{configure}.
31861 configure @r{[}--help@r{]}
31862 @r{[}--prefix=@var{dir}@r{]}
31863 @r{[}--exec-prefix=@var{dir}@r{]}
31864 @r{[}--srcdir=@var{dirname}@r{]}
31865 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
31866 @r{[}--target=@var{target}@r{]}
31871 You may introduce options with a single @samp{-} rather than
31872 @samp{--} if you prefer; but you may abbreviate option names if you use
31877 Display a quick summary of how to invoke @file{configure}.
31879 @item --prefix=@var{dir}
31880 Configure the source to install programs and files under directory
31883 @item --exec-prefix=@var{dir}
31884 Configure the source to install programs under directory
31887 @c avoid splitting the warning from the explanation:
31889 @item --srcdir=@var{dirname}
31890 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
31891 @code{make} that implements the @code{VPATH} feature.}@*
31892 Use this option to make configurations in directories separate from the
31893 @value{GDBN} source directories. Among other things, you can use this to
31894 build (or maintain) several configurations simultaneously, in separate
31895 directories. @file{configure} writes configuration-specific files in
31896 the current directory, but arranges for them to use the source in the
31897 directory @var{dirname}. @file{configure} creates directories under
31898 the working directory in parallel to the source directories below
31901 @item --norecursion
31902 Configure only the directory level where @file{configure} is executed; do not
31903 propagate configuration to subdirectories.
31905 @item --target=@var{target}
31906 Configure @value{GDBN} for cross-debugging programs running on the specified
31907 @var{target}. Without this option, @value{GDBN} is configured to debug
31908 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
31910 There is no convenient way to generate a list of all available targets.
31912 @item @var{host} @dots{}
31913 Configure @value{GDBN} to run on the specified @var{host}.
31915 There is no convenient way to generate a list of all available hosts.
31918 There are many other options available as well, but they are generally
31919 needed for special purposes only.
31921 @node System-wide configuration
31922 @section System-wide configuration and settings
31923 @cindex system-wide init file
31925 @value{GDBN} can be configured to have a system-wide init file;
31926 this file will be read and executed at startup (@pxref{Startup, , What
31927 @value{GDBN} does during startup}).
31929 Here is the corresponding configure option:
31932 @item --with-system-gdbinit=@var{file}
31933 Specify that the default location of the system-wide init file is
31937 If @value{GDBN} has been configured with the option @option{--prefix=$prefix},
31938 it may be subject to relocation. Two possible cases:
31942 If the default location of this init file contains @file{$prefix},
31943 it will be subject to relocation. Suppose that the configure options
31944 are @option{--prefix=$prefix --with-system-gdbinit=$prefix/etc/gdbinit};
31945 if @value{GDBN} is moved from @file{$prefix} to @file{$install}, the system
31946 init file is looked for as @file{$install/etc/gdbinit} instead of
31947 @file{$prefix/etc/gdbinit}.
31950 By contrast, if the default location does not contain the prefix,
31951 it will not be relocated. E.g.@: if @value{GDBN} has been configured with
31952 @option{--prefix=/usr/local --with-system-gdbinit=/usr/share/gdb/gdbinit},
31953 then @value{GDBN} will always look for @file{/usr/share/gdb/gdbinit},
31954 wherever @value{GDBN} is installed.
31957 @node Maintenance Commands
31958 @appendix Maintenance Commands
31959 @cindex maintenance commands
31960 @cindex internal commands
31962 In addition to commands intended for @value{GDBN} users, @value{GDBN}
31963 includes a number of commands intended for @value{GDBN} developers,
31964 that are not documented elsewhere in this manual. These commands are
31965 provided here for reference. (For commands that turn on debugging
31966 messages, see @ref{Debugging Output}.)
31969 @kindex maint agent
31970 @kindex maint agent-eval
31971 @item maint agent @var{expression}
31972 @itemx maint agent-eval @var{expression}
31973 Translate the given @var{expression} into remote agent bytecodes.
31974 This command is useful for debugging the Agent Expression mechanism
31975 (@pxref{Agent Expressions}). The @samp{agent} version produces an
31976 expression useful for data collection, such as by tracepoints, while
31977 @samp{maint agent-eval} produces an expression that evaluates directly
31978 to a result. For instance, a collection expression for @code{globa +
31979 globb} will include bytecodes to record four bytes of memory at each
31980 of the addresses of @code{globa} and @code{globb}, while discarding
31981 the result of the addition, while an evaluation expression will do the
31982 addition and return the sum.
31984 @kindex maint info breakpoints
31985 @item @anchor{maint info breakpoints}maint info breakpoints
31986 Using the same format as @samp{info breakpoints}, display both the
31987 breakpoints you've set explicitly, and those @value{GDBN} is using for
31988 internal purposes. Internal breakpoints are shown with negative
31989 breakpoint numbers. The type column identifies what kind of breakpoint
31994 Normal, explicitly set breakpoint.
31997 Normal, explicitly set watchpoint.
32000 Internal breakpoint, used to handle correctly stepping through
32001 @code{longjmp} calls.
32003 @item longjmp resume
32004 Internal breakpoint at the target of a @code{longjmp}.
32007 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
32010 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
32013 Shared library events.
32017 @kindex set displaced-stepping
32018 @kindex show displaced-stepping
32019 @cindex displaced stepping support
32020 @cindex out-of-line single-stepping
32021 @item set displaced-stepping
32022 @itemx show displaced-stepping
32023 Control whether or not @value{GDBN} will do @dfn{displaced stepping}
32024 if the target supports it. Displaced stepping is a way to single-step
32025 over breakpoints without removing them from the inferior, by executing
32026 an out-of-line copy of the instruction that was originally at the
32027 breakpoint location. It is also known as out-of-line single-stepping.
32030 @item set displaced-stepping on
32031 If the target architecture supports it, @value{GDBN} will use
32032 displaced stepping to step over breakpoints.
32034 @item set displaced-stepping off
32035 @value{GDBN} will not use displaced stepping to step over breakpoints,
32036 even if such is supported by the target architecture.
32038 @cindex non-stop mode, and @samp{set displaced-stepping}
32039 @item set displaced-stepping auto
32040 This is the default mode. @value{GDBN} will use displaced stepping
32041 only if non-stop mode is active (@pxref{Non-Stop Mode}) and the target
32042 architecture supports displaced stepping.
32045 @kindex maint check-symtabs
32046 @item maint check-symtabs
32047 Check the consistency of psymtabs and symtabs.
32049 @kindex maint cplus first_component
32050 @item maint cplus first_component @var{name}
32051 Print the first C@t{++} class/namespace component of @var{name}.
32053 @kindex maint cplus namespace
32054 @item maint cplus namespace
32055 Print the list of possible C@t{++} namespaces.
32057 @kindex maint demangle
32058 @item maint demangle @var{name}
32059 Demangle a C@t{++} or Objective-C mangled @var{name}.
32061 @kindex maint deprecate
32062 @kindex maint undeprecate
32063 @cindex deprecated commands
32064 @item maint deprecate @var{command} @r{[}@var{replacement}@r{]}
32065 @itemx maint undeprecate @var{command}
32066 Deprecate or undeprecate the named @var{command}. Deprecated commands
32067 cause @value{GDBN} to issue a warning when you use them. The optional
32068 argument @var{replacement} says which newer command should be used in
32069 favor of the deprecated one; if it is given, @value{GDBN} will mention
32070 the replacement as part of the warning.
32072 @kindex maint dump-me
32073 @item maint dump-me
32074 @cindex @code{SIGQUIT} signal, dump core of @value{GDBN}
32075 Cause a fatal signal in the debugger and force it to dump its core.
32076 This is supported only on systems which support aborting a program
32077 with the @code{SIGQUIT} signal.
32079 @kindex maint internal-error
32080 @kindex maint internal-warning
32081 @item maint internal-error @r{[}@var{message-text}@r{]}
32082 @itemx maint internal-warning @r{[}@var{message-text}@r{]}
32083 Cause @value{GDBN} to call the internal function @code{internal_error}
32084 or @code{internal_warning} and hence behave as though an internal error
32085 or internal warning has been detected. In addition to reporting the
32086 internal problem, these functions give the user the opportunity to
32087 either quit @value{GDBN} or create a core file of the current
32088 @value{GDBN} session.
32090 These commands take an optional parameter @var{message-text} that is
32091 used as the text of the error or warning message.
32093 Here's an example of using @code{internal-error}:
32096 (@value{GDBP}) @kbd{maint internal-error testing, 1, 2}
32097 @dots{}/maint.c:121: internal-error: testing, 1, 2
32098 A problem internal to GDB has been detected. Further
32099 debugging may prove unreliable.
32100 Quit this debugging session? (y or n) @kbd{n}
32101 Create a core file? (y or n) @kbd{n}
32105 @cindex @value{GDBN} internal error
32106 @cindex internal errors, control of @value{GDBN} behavior
32108 @kindex maint set internal-error
32109 @kindex maint show internal-error
32110 @kindex maint set internal-warning
32111 @kindex maint show internal-warning
32112 @item maint set internal-error @var{action} [ask|yes|no]
32113 @itemx maint show internal-error @var{action}
32114 @itemx maint set internal-warning @var{action} [ask|yes|no]
32115 @itemx maint show internal-warning @var{action}
32116 When @value{GDBN} reports an internal problem (error or warning) it
32117 gives the user the opportunity to both quit @value{GDBN} and create a
32118 core file of the current @value{GDBN} session. These commands let you
32119 override the default behaviour for each particular @var{action},
32120 described in the table below.
32124 You can specify that @value{GDBN} should always (yes) or never (no)
32125 quit. The default is to ask the user what to do.
32128 You can specify that @value{GDBN} should always (yes) or never (no)
32129 create a core file. The default is to ask the user what to do.
32132 @kindex maint packet
32133 @item maint packet @var{text}
32134 If @value{GDBN} is talking to an inferior via the serial protocol,
32135 then this command sends the string @var{text} to the inferior, and
32136 displays the response packet. @value{GDBN} supplies the initial
32137 @samp{$} character, the terminating @samp{#} character, and the
32140 @kindex maint print architecture
32141 @item maint print architecture @r{[}@var{file}@r{]}
32142 Print the entire architecture configuration. The optional argument
32143 @var{file} names the file where the output goes.
32145 @kindex maint print c-tdesc
32146 @item maint print c-tdesc
32147 Print the current target description (@pxref{Target Descriptions}) as
32148 a C source file. The created source file can be used in @value{GDBN}
32149 when an XML parser is not available to parse the description.
32151 @kindex maint print dummy-frames
32152 @item maint print dummy-frames
32153 Prints the contents of @value{GDBN}'s internal dummy-frame stack.
32156 (@value{GDBP}) @kbd{b add}
32158 (@value{GDBP}) @kbd{print add(2,3)}
32159 Breakpoint 2, add (a=2, b=3) at @dots{}
32161 The program being debugged stopped while in a function called from GDB.
32163 (@value{GDBP}) @kbd{maint print dummy-frames}
32164 0x1a57c80: pc=0x01014068 fp=0x0200bddc sp=0x0200bdd6
32165 top=0x0200bdd4 id=@{stack=0x200bddc,code=0x101405c@}
32166 call_lo=0x01014000 call_hi=0x01014001
32170 Takes an optional file parameter.
32172 @kindex maint print registers
32173 @kindex maint print raw-registers
32174 @kindex maint print cooked-registers
32175 @kindex maint print register-groups
32176 @kindex maint print remote-registers
32177 @item maint print registers @r{[}@var{file}@r{]}
32178 @itemx maint print raw-registers @r{[}@var{file}@r{]}
32179 @itemx maint print cooked-registers @r{[}@var{file}@r{]}
32180 @itemx maint print register-groups @r{[}@var{file}@r{]}
32181 @itemx maint print remote-registers @r{[}@var{file}@r{]}
32182 Print @value{GDBN}'s internal register data structures.
32184 The command @code{maint print raw-registers} includes the contents of
32185 the raw register cache; the command @code{maint print
32186 cooked-registers} includes the (cooked) value of all registers,
32187 including registers which aren't available on the target nor visible
32188 to user; the command @code{maint print register-groups} includes the
32189 groups that each register is a member of; and the command @code{maint
32190 print remote-registers} includes the remote target's register numbers
32191 and offsets in the `G' packets. @xref{Registers,, Registers, gdbint,
32192 @value{GDBN} Internals}.
32194 These commands take an optional parameter, a file name to which to
32195 write the information.
32197 @kindex maint print reggroups
32198 @item maint print reggroups @r{[}@var{file}@r{]}
32199 Print @value{GDBN}'s internal register group data structures. The
32200 optional argument @var{file} tells to what file to write the
32203 The register groups info looks like this:
32206 (@value{GDBP}) @kbd{maint print reggroups}
32219 This command forces @value{GDBN} to flush its internal register cache.
32221 @kindex maint print objfiles
32222 @cindex info for known object files
32223 @item maint print objfiles
32224 Print a dump of all known object files. For each object file, this
32225 command prints its name, address in memory, and all of its psymtabs
32228 @kindex maint print section-scripts
32229 @cindex info for known .debug_gdb_scripts-loaded scripts
32230 @item maint print section-scripts [@var{regexp}]
32231 Print a dump of scripts specified in the @code{.debug_gdb_section} section.
32232 If @var{regexp} is specified, only print scripts loaded by object files
32233 matching @var{regexp}.
32234 For each script, this command prints its name as specified in the objfile,
32235 and the full path if known.
32236 @xref{.debug_gdb_scripts section}.
32238 @kindex maint print statistics
32239 @cindex bcache statistics
32240 @item maint print statistics
32241 This command prints, for each object file in the program, various data
32242 about that object file followed by the byte cache (@dfn{bcache})
32243 statistics for the object file. The objfile data includes the number
32244 of minimal, partial, full, and stabs symbols, the number of types
32245 defined by the objfile, the number of as yet unexpanded psym tables,
32246 the number of line tables and string tables, and the amount of memory
32247 used by the various tables. The bcache statistics include the counts,
32248 sizes, and counts of duplicates of all and unique objects, max,
32249 average, and median entry size, total memory used and its overhead and
32250 savings, and various measures of the hash table size and chain
32253 @kindex maint print target-stack
32254 @cindex target stack description
32255 @item maint print target-stack
32256 A @dfn{target} is an interface between the debugger and a particular
32257 kind of file or process. Targets can be stacked in @dfn{strata},
32258 so that more than one target can potentially respond to a request.
32259 In particular, memory accesses will walk down the stack of targets
32260 until they find a target that is interested in handling that particular
32263 This command prints a short description of each layer that was pushed on
32264 the @dfn{target stack}, starting from the top layer down to the bottom one.
32266 @kindex maint print type
32267 @cindex type chain of a data type
32268 @item maint print type @var{expr}
32269 Print the type chain for a type specified by @var{expr}. The argument
32270 can be either a type name or a symbol. If it is a symbol, the type of
32271 that symbol is described. The type chain produced by this command is
32272 a recursive definition of the data type as stored in @value{GDBN}'s
32273 data structures, including its flags and contained types.
32275 @kindex maint set dwarf2 always-disassemble
32276 @kindex maint show dwarf2 always-disassemble
32277 @item maint set dwarf2 always-disassemble
32278 @item maint show dwarf2 always-disassemble
32279 Control the behavior of @code{info address} when using DWARF debugging
32282 The default is @code{off}, which means that @value{GDBN} should try to
32283 describe a variable's location in an easily readable format. When
32284 @code{on}, @value{GDBN} will instead display the DWARF location
32285 expression in an assembly-like format. Note that some locations are
32286 too complex for @value{GDBN} to describe simply; in this case you will
32287 always see the disassembly form.
32289 Here is an example of the resulting disassembly:
32292 (gdb) info addr argc
32293 Symbol "argc" is a complex DWARF expression:
32297 For more information on these expressions, see
32298 @uref{http://www.dwarfstd.org/, the DWARF standard}.
32300 @kindex maint set dwarf2 max-cache-age
32301 @kindex maint show dwarf2 max-cache-age
32302 @item maint set dwarf2 max-cache-age
32303 @itemx maint show dwarf2 max-cache-age
32304 Control the DWARF 2 compilation unit cache.
32306 @cindex DWARF 2 compilation units cache
32307 In object files with inter-compilation-unit references, such as those
32308 produced by the GCC option @samp{-feliminate-dwarf2-dups}, the DWARF 2
32309 reader needs to frequently refer to previously read compilation units.
32310 This setting controls how long a compilation unit will remain in the
32311 cache if it is not referenced. A higher limit means that cached
32312 compilation units will be stored in memory longer, and more total
32313 memory will be used. Setting it to zero disables caching, which will
32314 slow down @value{GDBN} startup, but reduce memory consumption.
32316 @kindex maint set profile
32317 @kindex maint show profile
32318 @cindex profiling GDB
32319 @item maint set profile
32320 @itemx maint show profile
32321 Control profiling of @value{GDBN}.
32323 Profiling will be disabled until you use the @samp{maint set profile}
32324 command to enable it. When you enable profiling, the system will begin
32325 collecting timing and execution count data; when you disable profiling or
32326 exit @value{GDBN}, the results will be written to a log file. Remember that
32327 if you use profiling, @value{GDBN} will overwrite the profiling log file
32328 (often called @file{gmon.out}). If you have a record of important profiling
32329 data in a @file{gmon.out} file, be sure to move it to a safe location.
32331 Configuring with @samp{--enable-profiling} arranges for @value{GDBN} to be
32332 compiled with the @samp{-pg} compiler option.
32334 @kindex maint set show-debug-regs
32335 @kindex maint show show-debug-regs
32336 @cindex hardware debug registers
32337 @item maint set show-debug-regs
32338 @itemx maint show show-debug-regs
32339 Control whether to show variables that mirror the hardware debug
32340 registers. Use @code{ON} to enable, @code{OFF} to disable. If
32341 enabled, the debug registers values are shown when @value{GDBN} inserts or
32342 removes a hardware breakpoint or watchpoint, and when the inferior
32343 triggers a hardware-assisted breakpoint or watchpoint.
32345 @kindex maint set show-all-tib
32346 @kindex maint show show-all-tib
32347 @item maint set show-all-tib
32348 @itemx maint show show-all-tib
32349 Control whether to show all non zero areas within a 1k block starting
32350 at thread local base, when using the @samp{info w32 thread-information-block}
32353 @kindex maint space
32354 @cindex memory used by commands
32356 Control whether to display memory usage for each command. If set to a
32357 nonzero value, @value{GDBN} will display how much memory each command
32358 took, following the command's own output. This can also be requested
32359 by invoking @value{GDBN} with the @option{--statistics} command-line
32360 switch (@pxref{Mode Options}).
32363 @cindex time of command execution
32365 Control whether to display the execution time for each command. If
32366 set to a nonzero value, @value{GDBN} will display how much time it
32367 took to execute each command, following the command's own output.
32368 The time is not printed for the commands that run the target, since
32369 there's no mechanism currently to compute how much time was spend
32370 by @value{GDBN} and how much time was spend by the program been debugged.
32371 it's not possibly currently
32372 This can also be requested by invoking @value{GDBN} with the
32373 @option{--statistics} command-line switch (@pxref{Mode Options}).
32375 @kindex maint translate-address
32376 @item maint translate-address @r{[}@var{section}@r{]} @var{addr}
32377 Find the symbol stored at the location specified by the address
32378 @var{addr} and an optional section name @var{section}. If found,
32379 @value{GDBN} prints the name of the closest symbol and an offset from
32380 the symbol's location to the specified address. This is similar to
32381 the @code{info address} command (@pxref{Symbols}), except that this
32382 command also allows to find symbols in other sections.
32384 If section was not specified, the section in which the symbol was found
32385 is also printed. For dynamically linked executables, the name of
32386 executable or shared library containing the symbol is printed as well.
32390 The following command is useful for non-interactive invocations of
32391 @value{GDBN}, such as in the test suite.
32394 @item set watchdog @var{nsec}
32395 @kindex set watchdog
32396 @cindex watchdog timer
32397 @cindex timeout for commands
32398 Set the maximum number of seconds @value{GDBN} will wait for the
32399 target operation to finish. If this time expires, @value{GDBN}
32400 reports and error and the command is aborted.
32402 @item show watchdog
32403 Show the current setting of the target wait timeout.
32406 @node Remote Protocol
32407 @appendix @value{GDBN} Remote Serial Protocol
32412 * Stop Reply Packets::
32413 * General Query Packets::
32414 * Architecture-Specific Protocol Details::
32415 * Tracepoint Packets::
32416 * Host I/O Packets::
32418 * Notification Packets::
32419 * Remote Non-Stop::
32420 * Packet Acknowledgment::
32422 * File-I/O Remote Protocol Extension::
32423 * Library List Format::
32424 * Memory Map Format::
32425 * Thread List Format::
32426 * Traceframe Info Format::
32432 There may be occasions when you need to know something about the
32433 protocol---for example, if there is only one serial port to your target
32434 machine, you might want your program to do something special if it
32435 recognizes a packet meant for @value{GDBN}.
32437 In the examples below, @samp{->} and @samp{<-} are used to indicate
32438 transmitted and received data, respectively.
32440 @cindex protocol, @value{GDBN} remote serial
32441 @cindex serial protocol, @value{GDBN} remote
32442 @cindex remote serial protocol
32443 All @value{GDBN} commands and responses (other than acknowledgments
32444 and notifications, see @ref{Notification Packets}) are sent as a
32445 @var{packet}. A @var{packet} is introduced with the character
32446 @samp{$}, the actual @var{packet-data}, and the terminating character
32447 @samp{#} followed by a two-digit @var{checksum}:
32450 @code{$}@var{packet-data}@code{#}@var{checksum}
32454 @cindex checksum, for @value{GDBN} remote
32456 The two-digit @var{checksum} is computed as the modulo 256 sum of all
32457 characters between the leading @samp{$} and the trailing @samp{#} (an
32458 eight bit unsigned checksum).
32460 Implementors should note that prior to @value{GDBN} 5.0 the protocol
32461 specification also included an optional two-digit @var{sequence-id}:
32464 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
32467 @cindex sequence-id, for @value{GDBN} remote
32469 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
32470 has never output @var{sequence-id}s. Stubs that handle packets added
32471 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
32473 When either the host or the target machine receives a packet, the first
32474 response expected is an acknowledgment: either @samp{+} (to indicate
32475 the package was received correctly) or @samp{-} (to request
32479 -> @code{$}@var{packet-data}@code{#}@var{checksum}
32484 The @samp{+}/@samp{-} acknowledgments can be disabled
32485 once a connection is established.
32486 @xref{Packet Acknowledgment}, for details.
32488 The host (@value{GDBN}) sends @var{command}s, and the target (the
32489 debugging stub incorporated in your program) sends a @var{response}. In
32490 the case of step and continue @var{command}s, the response is only sent
32491 when the operation has completed, and the target has again stopped all
32492 threads in all attached processes. This is the default all-stop mode
32493 behavior, but the remote protocol also supports @value{GDBN}'s non-stop
32494 execution mode; see @ref{Remote Non-Stop}, for details.
32496 @var{packet-data} consists of a sequence of characters with the
32497 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
32500 @cindex remote protocol, field separator
32501 Fields within the packet should be separated using @samp{,} @samp{;} or
32502 @samp{:}. Except where otherwise noted all numbers are represented in
32503 @sc{hex} with leading zeros suppressed.
32505 Implementors should note that prior to @value{GDBN} 5.0, the character
32506 @samp{:} could not appear as the third character in a packet (as it
32507 would potentially conflict with the @var{sequence-id}).
32509 @cindex remote protocol, binary data
32510 @anchor{Binary Data}
32511 Binary data in most packets is encoded either as two hexadecimal
32512 digits per byte of binary data. This allowed the traditional remote
32513 protocol to work over connections which were only seven-bit clean.
32514 Some packets designed more recently assume an eight-bit clean
32515 connection, and use a more efficient encoding to send and receive
32518 The binary data representation uses @code{7d} (@sc{ascii} @samp{@}})
32519 as an escape character. Any escaped byte is transmitted as the escape
32520 character followed by the original character XORed with @code{0x20}.
32521 For example, the byte @code{0x7d} would be transmitted as the two
32522 bytes @code{0x7d 0x5d}. The bytes @code{0x23} (@sc{ascii} @samp{#}),
32523 @code{0x24} (@sc{ascii} @samp{$}), and @code{0x7d} (@sc{ascii}
32524 @samp{@}}) must always be escaped. Responses sent by the stub
32525 must also escape @code{0x2a} (@sc{ascii} @samp{*}), so that it
32526 is not interpreted as the start of a run-length encoded sequence
32529 Response @var{data} can be run-length encoded to save space.
32530 Run-length encoding replaces runs of identical characters with one
32531 instance of the repeated character, followed by a @samp{*} and a
32532 repeat count. The repeat count is itself sent encoded, to avoid
32533 binary characters in @var{data}: a value of @var{n} is sent as
32534 @code{@var{n}+29}. For a repeat count greater or equal to 3, this
32535 produces a printable @sc{ascii} character, e.g.@: a space (@sc{ascii}
32536 code 32) for a repeat count of 3. (This is because run-length
32537 encoding starts to win for counts 3 or more.) Thus, for example,
32538 @samp{0* } is a run-length encoding of ``0000'': the space character
32539 after @samp{*} means repeat the leading @code{0} @w{@code{32 - 29 =
32542 The printable characters @samp{#} and @samp{$} or with a numeric value
32543 greater than 126 must not be used. Runs of six repeats (@samp{#}) or
32544 seven repeats (@samp{$}) can be expanded using a repeat count of only
32545 five (@samp{"}). For example, @samp{00000000} can be encoded as
32548 The error response returned for some packets includes a two character
32549 error number. That number is not well defined.
32551 @cindex empty response, for unsupported packets
32552 For any @var{command} not supported by the stub, an empty response
32553 (@samp{$#00}) should be returned. That way it is possible to extend the
32554 protocol. A newer @value{GDBN} can tell if a packet is supported based
32557 At a minimum, a stub is required to support the @samp{g} and @samp{G}
32558 commands for register access, and the @samp{m} and @samp{M} commands
32559 for memory access. Stubs that only control single-threaded targets
32560 can implement run control with the @samp{c} (continue), and @samp{s}
32561 (step) commands. Stubs that support multi-threading targets should
32562 support the @samp{vCont} command. All other commands are optional.
32567 The following table provides a complete list of all currently defined
32568 @var{command}s and their corresponding response @var{data}.
32569 @xref{File-I/O Remote Protocol Extension}, for details about the File
32570 I/O extension of the remote protocol.
32572 Each packet's description has a template showing the packet's overall
32573 syntax, followed by an explanation of the packet's meaning. We
32574 include spaces in some of the templates for clarity; these are not
32575 part of the packet's syntax. No @value{GDBN} packet uses spaces to
32576 separate its components. For example, a template like @samp{foo
32577 @var{bar} @var{baz}} describes a packet beginning with the three ASCII
32578 bytes @samp{foo}, followed by a @var{bar}, followed directly by a
32579 @var{baz}. @value{GDBN} does not transmit a space character between the
32580 @samp{foo} and the @var{bar}, or between the @var{bar} and the
32583 @cindex @var{thread-id}, in remote protocol
32584 @anchor{thread-id syntax}
32585 Several packets and replies include a @var{thread-id} field to identify
32586 a thread. Normally these are positive numbers with a target-specific
32587 interpretation, formatted as big-endian hex strings. A @var{thread-id}
32588 can also be a literal @samp{-1} to indicate all threads, or @samp{0} to
32591 In addition, the remote protocol supports a multiprocess feature in
32592 which the @var{thread-id} syntax is extended to optionally include both
32593 process and thread ID fields, as @samp{p@var{pid}.@var{tid}}.
32594 The @var{pid} (process) and @var{tid} (thread) components each have the
32595 format described above: a positive number with target-specific
32596 interpretation formatted as a big-endian hex string, literal @samp{-1}
32597 to indicate all processes or threads (respectively), or @samp{0} to
32598 indicate an arbitrary process or thread. Specifying just a process, as
32599 @samp{p@var{pid}}, is equivalent to @samp{p@var{pid}.-1}. It is an
32600 error to specify all processes but a specific thread, such as
32601 @samp{p-1.@var{tid}}. Note that the @samp{p} prefix is @emph{not} used
32602 for those packets and replies explicitly documented to include a process
32603 ID, rather than a @var{thread-id}.
32605 The multiprocess @var{thread-id} syntax extensions are only used if both
32606 @value{GDBN} and the stub report support for the @samp{multiprocess}
32607 feature using @samp{qSupported}. @xref{multiprocess extensions}, for
32610 Note that all packet forms beginning with an upper- or lower-case
32611 letter, other than those described here, are reserved for future use.
32613 Here are the packet descriptions.
32618 @cindex @samp{!} packet
32619 @anchor{extended mode}
32620 Enable extended mode. In extended mode, the remote server is made
32621 persistent. The @samp{R} packet is used to restart the program being
32627 The remote target both supports and has enabled extended mode.
32631 @cindex @samp{?} packet
32632 Indicate the reason the target halted. The reply is the same as for
32633 step and continue. This packet has a special interpretation when the
32634 target is in non-stop mode; see @ref{Remote Non-Stop}.
32637 @xref{Stop Reply Packets}, for the reply specifications.
32639 @item A @var{arglen},@var{argnum},@var{arg},@dots{}
32640 @cindex @samp{A} packet
32641 Initialized @code{argv[]} array passed into program. @var{arglen}
32642 specifies the number of bytes in the hex encoded byte stream
32643 @var{arg}. See @code{gdbserver} for more details.
32648 The arguments were set.
32654 @cindex @samp{b} packet
32655 (Don't use this packet; its behavior is not well-defined.)
32656 Change the serial line speed to @var{baud}.
32658 JTC: @emph{When does the transport layer state change? When it's
32659 received, or after the ACK is transmitted. In either case, there are
32660 problems if the command or the acknowledgment packet is dropped.}
32662 Stan: @emph{If people really wanted to add something like this, and get
32663 it working for the first time, they ought to modify ser-unix.c to send
32664 some kind of out-of-band message to a specially-setup stub and have the
32665 switch happen "in between" packets, so that from remote protocol's point
32666 of view, nothing actually happened.}
32668 @item B @var{addr},@var{mode}
32669 @cindex @samp{B} packet
32670 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
32671 breakpoint at @var{addr}.
32673 Don't use this packet. Use the @samp{Z} and @samp{z} packets instead
32674 (@pxref{insert breakpoint or watchpoint packet}).
32676 @cindex @samp{bc} packet
32679 Backward continue. Execute the target system in reverse. No parameter.
32680 @xref{Reverse Execution}, for more information.
32683 @xref{Stop Reply Packets}, for the reply specifications.
32685 @cindex @samp{bs} packet
32688 Backward single step. Execute one instruction in reverse. No parameter.
32689 @xref{Reverse Execution}, for more information.
32692 @xref{Stop Reply Packets}, for the reply specifications.
32694 @item c @r{[}@var{addr}@r{]}
32695 @cindex @samp{c} packet
32696 Continue. @var{addr} is address to resume. If @var{addr} is omitted,
32697 resume at current address.
32699 This packet is deprecated for multi-threading support. @xref{vCont
32703 @xref{Stop Reply Packets}, for the reply specifications.
32705 @item C @var{sig}@r{[};@var{addr}@r{]}
32706 @cindex @samp{C} packet
32707 Continue with signal @var{sig} (hex signal number). If
32708 @samp{;@var{addr}} is omitted, resume at same address.
32710 This packet is deprecated for multi-threading support. @xref{vCont
32714 @xref{Stop Reply Packets}, for the reply specifications.
32717 @cindex @samp{d} packet
32720 Don't use this packet; instead, define a general set packet
32721 (@pxref{General Query Packets}).
32725 @cindex @samp{D} packet
32726 The first form of the packet is used to detach @value{GDBN} from the
32727 remote system. It is sent to the remote target
32728 before @value{GDBN} disconnects via the @code{detach} command.
32730 The second form, including a process ID, is used when multiprocess
32731 protocol extensions are enabled (@pxref{multiprocess extensions}), to
32732 detach only a specific process. The @var{pid} is specified as a
32733 big-endian hex string.
32743 @item F @var{RC},@var{EE},@var{CF};@var{XX}
32744 @cindex @samp{F} packet
32745 A reply from @value{GDBN} to an @samp{F} packet sent by the target.
32746 This is part of the File-I/O protocol extension. @xref{File-I/O
32747 Remote Protocol Extension}, for the specification.
32750 @anchor{read registers packet}
32751 @cindex @samp{g} packet
32752 Read general registers.
32756 @item @var{XX@dots{}}
32757 Each byte of register data is described by two hex digits. The bytes
32758 with the register are transmitted in target byte order. The size of
32759 each register and their position within the @samp{g} packet are
32760 determined by the @value{GDBN} internal gdbarch functions
32761 @code{DEPRECATED_REGISTER_RAW_SIZE} and @code{gdbarch_register_name}. The
32762 specification of several standard @samp{g} packets is specified below.
32764 When reading registers from a trace frame (@pxref{Analyze Collected
32765 Data,,Using the Collected Data}), the stub may also return a string of
32766 literal @samp{x}'s in place of the register data digits, to indicate
32767 that the corresponding register has not been collected, thus its value
32768 is unavailable. For example, for an architecture with 4 registers of
32769 4 bytes each, the following reply indicates to @value{GDBN} that
32770 registers 0 and 2 have not been collected, while registers 1 and 3
32771 have been collected, and both have zero value:
32775 <- @code{xxxxxxxx00000000xxxxxxxx00000000}
32782 @item G @var{XX@dots{}}
32783 @cindex @samp{G} packet
32784 Write general registers. @xref{read registers packet}, for a
32785 description of the @var{XX@dots{}} data.
32795 @item H @var{op} @var{thread-id}
32796 @cindex @samp{H} packet
32797 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
32798 @samp{G}, et.al.). @var{op} depends on the operation to be performed:
32799 it should be @samp{c} for step and continue operations (note that this
32800 is deprecated, supporting the @samp{vCont} command is a better
32801 option), @samp{g} for other operations. The thread designator
32802 @var{thread-id} has the format and interpretation described in
32803 @ref{thread-id syntax}.
32814 @c 'H': How restrictive (or permissive) is the thread model. If a
32815 @c thread is selected and stopped, are other threads allowed
32816 @c to continue to execute? As I mentioned above, I think the
32817 @c semantics of each command when a thread is selected must be
32818 @c described. For example:
32820 @c 'g': If the stub supports threads and a specific thread is
32821 @c selected, returns the register block from that thread;
32822 @c otherwise returns current registers.
32824 @c 'G' If the stub supports threads and a specific thread is
32825 @c selected, sets the registers of the register block of
32826 @c that thread; otherwise sets current registers.
32828 @item i @r{[}@var{addr}@r{[},@var{nnn}@r{]]}
32829 @anchor{cycle step packet}
32830 @cindex @samp{i} packet
32831 Step the remote target by a single clock cycle. If @samp{,@var{nnn}} is
32832 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
32833 step starting at that address.
32836 @cindex @samp{I} packet
32837 Signal, then cycle step. @xref{step with signal packet}. @xref{cycle
32841 @cindex @samp{k} packet
32844 FIXME: @emph{There is no description of how to operate when a specific
32845 thread context has been selected (i.e.@: does 'k' kill only that
32848 @item m @var{addr},@var{length}
32849 @cindex @samp{m} packet
32850 Read @var{length} bytes of memory starting at address @var{addr}.
32851 Note that @var{addr} may not be aligned to any particular boundary.
32853 The stub need not use any particular size or alignment when gathering
32854 data from memory for the response; even if @var{addr} is word-aligned
32855 and @var{length} is a multiple of the word size, the stub is free to
32856 use byte accesses, or not. For this reason, this packet may not be
32857 suitable for accessing memory-mapped I/O devices.
32858 @cindex alignment of remote memory accesses
32859 @cindex size of remote memory accesses
32860 @cindex memory, alignment and size of remote accesses
32864 @item @var{XX@dots{}}
32865 Memory contents; each byte is transmitted as a two-digit hexadecimal
32866 number. The reply may contain fewer bytes than requested if the
32867 server was able to read only part of the region of memory.
32872 @item M @var{addr},@var{length}:@var{XX@dots{}}
32873 @cindex @samp{M} packet
32874 Write @var{length} bytes of memory starting at address @var{addr}.
32875 @var{XX@dots{}} is the data; each byte is transmitted as a two-digit
32876 hexadecimal number.
32883 for an error (this includes the case where only part of the data was
32888 @cindex @samp{p} packet
32889 Read the value of register @var{n}; @var{n} is in hex.
32890 @xref{read registers packet}, for a description of how the returned
32891 register value is encoded.
32895 @item @var{XX@dots{}}
32896 the register's value
32900 Indicating an unrecognized @var{query}.
32903 @item P @var{n@dots{}}=@var{r@dots{}}
32904 @anchor{write register packet}
32905 @cindex @samp{P} packet
32906 Write register @var{n@dots{}} with value @var{r@dots{}}. The register
32907 number @var{n} is in hexadecimal, and @var{r@dots{}} contains two hex
32908 digits for each byte in the register (target byte order).
32918 @item q @var{name} @var{params}@dots{}
32919 @itemx Q @var{name} @var{params}@dots{}
32920 @cindex @samp{q} packet
32921 @cindex @samp{Q} packet
32922 General query (@samp{q}) and set (@samp{Q}). These packets are
32923 described fully in @ref{General Query Packets}.
32926 @cindex @samp{r} packet
32927 Reset the entire system.
32929 Don't use this packet; use the @samp{R} packet instead.
32932 @cindex @samp{R} packet
32933 Restart the program being debugged. @var{XX}, while needed, is ignored.
32934 This packet is only available in extended mode (@pxref{extended mode}).
32936 The @samp{R} packet has no reply.
32938 @item s @r{[}@var{addr}@r{]}
32939 @cindex @samp{s} packet
32940 Single step. @var{addr} is the address at which to resume. If
32941 @var{addr} is omitted, resume at same address.
32943 This packet is deprecated for multi-threading support. @xref{vCont
32947 @xref{Stop Reply Packets}, for the reply specifications.
32949 @item S @var{sig}@r{[};@var{addr}@r{]}
32950 @anchor{step with signal packet}
32951 @cindex @samp{S} packet
32952 Step with signal. This is analogous to the @samp{C} packet, but
32953 requests a single-step, rather than a normal resumption of execution.
32955 This packet is deprecated for multi-threading support. @xref{vCont
32959 @xref{Stop Reply Packets}, for the reply specifications.
32961 @item t @var{addr}:@var{PP},@var{MM}
32962 @cindex @samp{t} packet
32963 Search backwards starting at address @var{addr} for a match with pattern
32964 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4 bytes.
32965 @var{addr} must be at least 3 digits.
32967 @item T @var{thread-id}
32968 @cindex @samp{T} packet
32969 Find out if the thread @var{thread-id} is alive. @xref{thread-id syntax}.
32974 thread is still alive
32980 Packets starting with @samp{v} are identified by a multi-letter name,
32981 up to the first @samp{;} or @samp{?} (or the end of the packet).
32983 @item vAttach;@var{pid}
32984 @cindex @samp{vAttach} packet
32985 Attach to a new process with the specified process ID @var{pid}.
32986 The process ID is a
32987 hexadecimal integer identifying the process. In all-stop mode, all
32988 threads in the attached process are stopped; in non-stop mode, it may be
32989 attached without being stopped if that is supported by the target.
32991 @c In non-stop mode, on a successful vAttach, the stub should set the
32992 @c current thread to a thread of the newly-attached process. After
32993 @c attaching, GDB queries for the attached process's thread ID with qC.
32994 @c Also note that, from a user perspective, whether or not the
32995 @c target is stopped on attach in non-stop mode depends on whether you
32996 @c use the foreground or background version of the attach command, not
32997 @c on what vAttach does; GDB does the right thing with respect to either
32998 @c stopping or restarting threads.
33000 This packet is only available in extended mode (@pxref{extended mode}).
33006 @item @r{Any stop packet}
33007 for success in all-stop mode (@pxref{Stop Reply Packets})
33009 for success in non-stop mode (@pxref{Remote Non-Stop})
33012 @item vCont@r{[};@var{action}@r{[}:@var{thread-id}@r{]]}@dots{}
33013 @cindex @samp{vCont} packet
33014 @anchor{vCont packet}
33015 Resume the inferior, specifying different actions for each thread.
33016 If an action is specified with no @var{thread-id}, then it is applied to any
33017 threads that don't have a specific action specified; if no default action is
33018 specified then other threads should remain stopped in all-stop mode and
33019 in their current state in non-stop mode.
33020 Specifying multiple
33021 default actions is an error; specifying no actions is also an error.
33022 Thread IDs are specified using the syntax described in @ref{thread-id syntax}.
33024 Currently supported actions are:
33030 Continue with signal @var{sig}. The signal @var{sig} should be two hex digits.
33034 Step with signal @var{sig}. The signal @var{sig} should be two hex digits.
33039 The optional argument @var{addr} normally associated with the
33040 @samp{c}, @samp{C}, @samp{s}, and @samp{S} packets is
33041 not supported in @samp{vCont}.
33043 The @samp{t} action is only relevant in non-stop mode
33044 (@pxref{Remote Non-Stop}) and may be ignored by the stub otherwise.
33045 A stop reply should be generated for any affected thread not already stopped.
33046 When a thread is stopped by means of a @samp{t} action,
33047 the corresponding stop reply should indicate that the thread has stopped with
33048 signal @samp{0}, regardless of whether the target uses some other signal
33049 as an implementation detail.
33052 @xref{Stop Reply Packets}, for the reply specifications.
33055 @cindex @samp{vCont?} packet
33056 Request a list of actions supported by the @samp{vCont} packet.
33060 @item vCont@r{[};@var{action}@dots{}@r{]}
33061 The @samp{vCont} packet is supported. Each @var{action} is a supported
33062 command in the @samp{vCont} packet.
33064 The @samp{vCont} packet is not supported.
33067 @item vFile:@var{operation}:@var{parameter}@dots{}
33068 @cindex @samp{vFile} packet
33069 Perform a file operation on the target system. For details,
33070 see @ref{Host I/O Packets}.
33072 @item vFlashErase:@var{addr},@var{length}
33073 @cindex @samp{vFlashErase} packet
33074 Direct the stub to erase @var{length} bytes of flash starting at
33075 @var{addr}. The region may enclose any number of flash blocks, but
33076 its start and end must fall on block boundaries, as indicated by the
33077 flash block size appearing in the memory map (@pxref{Memory Map
33078 Format}). @value{GDBN} groups flash memory programming operations
33079 together, and sends a @samp{vFlashDone} request after each group; the
33080 stub is allowed to delay erase operation until the @samp{vFlashDone}
33081 packet is received.
33083 The stub must support @samp{vCont} if it reports support for
33084 multiprocess extensions (@pxref{multiprocess extensions}). Note that in
33085 this case @samp{vCont} actions can be specified to apply to all threads
33086 in a process by using the @samp{p@var{pid}.-1} form of the
33097 @item vFlashWrite:@var{addr}:@var{XX@dots{}}
33098 @cindex @samp{vFlashWrite} packet
33099 Direct the stub to write data to flash address @var{addr}. The data
33100 is passed in binary form using the same encoding as for the @samp{X}
33101 packet (@pxref{Binary Data}). The memory ranges specified by
33102 @samp{vFlashWrite} packets preceding a @samp{vFlashDone} packet must
33103 not overlap, and must appear in order of increasing addresses
33104 (although @samp{vFlashErase} packets for higher addresses may already
33105 have been received; the ordering is guaranteed only between
33106 @samp{vFlashWrite} packets). If a packet writes to an address that was
33107 neither erased by a preceding @samp{vFlashErase} packet nor by some other
33108 target-specific method, the results are unpredictable.
33116 for vFlashWrite addressing non-flash memory
33122 @cindex @samp{vFlashDone} packet
33123 Indicate to the stub that flash programming operation is finished.
33124 The stub is permitted to delay or batch the effects of a group of
33125 @samp{vFlashErase} and @samp{vFlashWrite} packets until a
33126 @samp{vFlashDone} packet is received. The contents of the affected
33127 regions of flash memory are unpredictable until the @samp{vFlashDone}
33128 request is completed.
33130 @item vKill;@var{pid}
33131 @cindex @samp{vKill} packet
33132 Kill the process with the specified process ID. @var{pid} is a
33133 hexadecimal integer identifying the process. This packet is used in
33134 preference to @samp{k} when multiprocess protocol extensions are
33135 supported; see @ref{multiprocess extensions}.
33145 @item vRun;@var{filename}@r{[};@var{argument}@r{]}@dots{}
33146 @cindex @samp{vRun} packet
33147 Run the program @var{filename}, passing it each @var{argument} on its
33148 command line. The file and arguments are hex-encoded strings. If
33149 @var{filename} is an empty string, the stub may use a default program
33150 (e.g.@: the last program run). The program is created in the stopped
33153 @c FIXME: What about non-stop mode?
33155 This packet is only available in extended mode (@pxref{extended mode}).
33161 @item @r{Any stop packet}
33162 for success (@pxref{Stop Reply Packets})
33166 @anchor{vStopped packet}
33167 @cindex @samp{vStopped} packet
33169 In non-stop mode (@pxref{Remote Non-Stop}), acknowledge a previous stop
33170 reply and prompt for the stub to report another one.
33174 @item @r{Any stop packet}
33175 if there is another unreported stop event (@pxref{Stop Reply Packets})
33177 if there are no unreported stop events
33180 @item X @var{addr},@var{length}:@var{XX@dots{}}
33182 @cindex @samp{X} packet
33183 Write data to memory, where the data is transmitted in binary.
33184 @var{addr} is address, @var{length} is number of bytes,
33185 @samp{@var{XX}@dots{}} is binary data (@pxref{Binary Data}).
33195 @item z @var{type},@var{addr},@var{kind}
33196 @itemx Z @var{type},@var{addr},@var{kind}
33197 @anchor{insert breakpoint or watchpoint packet}
33198 @cindex @samp{z} packet
33199 @cindex @samp{Z} packets
33200 Insert (@samp{Z}) or remove (@samp{z}) a @var{type} breakpoint or
33201 watchpoint starting at address @var{address} of kind @var{kind}.
33203 Each breakpoint and watchpoint packet @var{type} is documented
33206 @emph{Implementation notes: A remote target shall return an empty string
33207 for an unrecognized breakpoint or watchpoint packet @var{type}. A
33208 remote target shall support either both or neither of a given
33209 @samp{Z@var{type}@dots{}} and @samp{z@var{type}@dots{}} packet pair. To
33210 avoid potential problems with duplicate packets, the operations should
33211 be implemented in an idempotent way.}
33213 @item z0,@var{addr},@var{kind}
33214 @itemx Z0,@var{addr},@var{kind}
33215 @cindex @samp{z0} packet
33216 @cindex @samp{Z0} packet
33217 Insert (@samp{Z0}) or remove (@samp{z0}) a memory breakpoint at address
33218 @var{addr} of type @var{kind}.
33220 A memory breakpoint is implemented by replacing the instruction at
33221 @var{addr} with a software breakpoint or trap instruction. The
33222 @var{kind} is target-specific and typically indicates the size of
33223 the breakpoint in bytes that should be inserted. E.g., the @sc{arm}
33224 and @sc{mips} can insert either a 2 or 4 byte breakpoint. Some
33225 architectures have additional meanings for @var{kind};
33226 see @ref{Architecture-Specific Protocol Details}.
33228 @emph{Implementation note: It is possible for a target to copy or move
33229 code that contains memory breakpoints (e.g., when implementing
33230 overlays). The behavior of this packet, in the presence of such a
33231 target, is not defined.}
33243 @item z1,@var{addr},@var{kind}
33244 @itemx Z1,@var{addr},@var{kind}
33245 @cindex @samp{z1} packet
33246 @cindex @samp{Z1} packet
33247 Insert (@samp{Z1}) or remove (@samp{z1}) a hardware breakpoint at
33248 address @var{addr}.
33250 A hardware breakpoint is implemented using a mechanism that is not
33251 dependant on being able to modify the target's memory. @var{kind}
33252 has the same meaning as in @samp{Z0} packets.
33254 @emph{Implementation note: A hardware breakpoint is not affected by code
33267 @item z2,@var{addr},@var{kind}
33268 @itemx Z2,@var{addr},@var{kind}
33269 @cindex @samp{z2} packet
33270 @cindex @samp{Z2} packet
33271 Insert (@samp{Z2}) or remove (@samp{z2}) a write watchpoint at @var{addr}.
33272 @var{kind} is interpreted as the number of bytes to watch.
33284 @item z3,@var{addr},@var{kind}
33285 @itemx Z3,@var{addr},@var{kind}
33286 @cindex @samp{z3} packet
33287 @cindex @samp{Z3} packet
33288 Insert (@samp{Z3}) or remove (@samp{z3}) a read watchpoint at @var{addr}.
33289 @var{kind} is interpreted as the number of bytes to watch.
33301 @item z4,@var{addr},@var{kind}
33302 @itemx Z4,@var{addr},@var{kind}
33303 @cindex @samp{z4} packet
33304 @cindex @samp{Z4} packet
33305 Insert (@samp{Z4}) or remove (@samp{z4}) an access watchpoint at @var{addr}.
33306 @var{kind} is interpreted as the number of bytes to watch.
33320 @node Stop Reply Packets
33321 @section Stop Reply Packets
33322 @cindex stop reply packets
33324 The @samp{C}, @samp{c}, @samp{S}, @samp{s}, @samp{vCont},
33325 @samp{vAttach}, @samp{vRun}, @samp{vStopped}, and @samp{?} packets can
33326 receive any of the below as a reply. Except for @samp{?}
33327 and @samp{vStopped}, that reply is only returned
33328 when the target halts. In the below the exact meaning of @dfn{signal
33329 number} is defined by the header @file{include/gdb/signals.h} in the
33330 @value{GDBN} source code.
33332 As in the description of request packets, we include spaces in the
33333 reply templates for clarity; these are not part of the reply packet's
33334 syntax. No @value{GDBN} stop reply packet uses spaces to separate its
33340 The program received signal number @var{AA} (a two-digit hexadecimal
33341 number). This is equivalent to a @samp{T} response with no
33342 @var{n}:@var{r} pairs.
33344 @item T @var{AA} @var{n1}:@var{r1};@var{n2}:@var{r2};@dots{}
33345 @cindex @samp{T} packet reply
33346 The program received signal number @var{AA} (a two-digit hexadecimal
33347 number). This is equivalent to an @samp{S} response, except that the
33348 @samp{@var{n}:@var{r}} pairs can carry values of important registers
33349 and other information directly in the stop reply packet, reducing
33350 round-trip latency. Single-step and breakpoint traps are reported
33351 this way. Each @samp{@var{n}:@var{r}} pair is interpreted as follows:
33355 If @var{n} is a hexadecimal number, it is a register number, and the
33356 corresponding @var{r} gives that register's value. @var{r} is a
33357 series of bytes in target byte order, with each byte given by a
33358 two-digit hex number.
33361 If @var{n} is @samp{thread}, then @var{r} is the @var{thread-id} of
33362 the stopped thread, as specified in @ref{thread-id syntax}.
33365 If @var{n} is @samp{core}, then @var{r} is the hexadecimal number of
33366 the core on which the stop event was detected.
33369 If @var{n} is a recognized @dfn{stop reason}, it describes a more
33370 specific event that stopped the target. The currently defined stop
33371 reasons are listed below. @var{aa} should be @samp{05}, the trap
33372 signal. At most one stop reason should be present.
33375 Otherwise, @value{GDBN} should ignore this @samp{@var{n}:@var{r}} pair
33376 and go on to the next; this allows us to extend the protocol in the
33380 The currently defined stop reasons are:
33386 The packet indicates a watchpoint hit, and @var{r} is the data address, in
33389 @cindex shared library events, remote reply
33391 The packet indicates that the loaded libraries have changed.
33392 @value{GDBN} should use @samp{qXfer:libraries:read} to fetch a new
33393 list of loaded libraries. @var{r} is ignored.
33395 @cindex replay log events, remote reply
33397 The packet indicates that the target cannot continue replaying
33398 logged execution events, because it has reached the end (or the
33399 beginning when executing backward) of the log. The value of @var{r}
33400 will be either @samp{begin} or @samp{end}. @xref{Reverse Execution},
33401 for more information.
33405 @itemx W @var{AA} ; process:@var{pid}
33406 The process exited, and @var{AA} is the exit status. This is only
33407 applicable to certain targets.
33409 The second form of the response, including the process ID of the exited
33410 process, can be used only when @value{GDBN} has reported support for
33411 multiprocess protocol extensions; see @ref{multiprocess extensions}.
33412 The @var{pid} is formatted as a big-endian hex string.
33415 @itemx X @var{AA} ; process:@var{pid}
33416 The process terminated with signal @var{AA}.
33418 The second form of the response, including the process ID of the
33419 terminated process, can be used only when @value{GDBN} has reported
33420 support for multiprocess protocol extensions; see @ref{multiprocess
33421 extensions}. The @var{pid} is formatted as a big-endian hex string.
33423 @item O @var{XX}@dots{}
33424 @samp{@var{XX}@dots{}} is hex encoding of @sc{ascii} data, to be
33425 written as the program's console output. This can happen at any time
33426 while the program is running and the debugger should continue to wait
33427 for @samp{W}, @samp{T}, etc. This reply is not permitted in non-stop mode.
33429 @item F @var{call-id},@var{parameter}@dots{}
33430 @var{call-id} is the identifier which says which host system call should
33431 be called. This is just the name of the function. Translation into the
33432 correct system call is only applicable as it's defined in @value{GDBN}.
33433 @xref{File-I/O Remote Protocol Extension}, for a list of implemented
33436 @samp{@var{parameter}@dots{}} is a list of parameters as defined for
33437 this very system call.
33439 The target replies with this packet when it expects @value{GDBN} to
33440 call a host system call on behalf of the target. @value{GDBN} replies
33441 with an appropriate @samp{F} packet and keeps up waiting for the next
33442 reply packet from the target. The latest @samp{C}, @samp{c}, @samp{S}
33443 or @samp{s} action is expected to be continued. @xref{File-I/O Remote
33444 Protocol Extension}, for more details.
33448 @node General Query Packets
33449 @section General Query Packets
33450 @cindex remote query requests
33452 Packets starting with @samp{q} are @dfn{general query packets};
33453 packets starting with @samp{Q} are @dfn{general set packets}. General
33454 query and set packets are a semi-unified form for retrieving and
33455 sending information to and from the stub.
33457 The initial letter of a query or set packet is followed by a name
33458 indicating what sort of thing the packet applies to. For example,
33459 @value{GDBN} may use a @samp{qSymbol} packet to exchange symbol
33460 definitions with the stub. These packet names follow some
33465 The name must not contain commas, colons or semicolons.
33467 Most @value{GDBN} query and set packets have a leading upper case
33470 The names of custom vendor packets should use a company prefix, in
33471 lower case, followed by a period. For example, packets designed at
33472 the Acme Corporation might begin with @samp{qacme.foo} (for querying
33473 foos) or @samp{Qacme.bar} (for setting bars).
33476 The name of a query or set packet should be separated from any
33477 parameters by a @samp{:}; the parameters themselves should be
33478 separated by @samp{,} or @samp{;}. Stubs must be careful to match the
33479 full packet name, and check for a separator or the end of the packet,
33480 in case two packet names share a common prefix. New packets should not begin
33481 with @samp{qC}, @samp{qP}, or @samp{qL}@footnote{The @samp{qP} and @samp{qL}
33482 packets predate these conventions, and have arguments without any terminator
33483 for the packet name; we suspect they are in widespread use in places that
33484 are difficult to upgrade. The @samp{qC} packet has no arguments, but some
33485 existing stubs (e.g.@: RedBoot) are known to not check for the end of the
33488 Like the descriptions of the other packets, each description here
33489 has a template showing the packet's overall syntax, followed by an
33490 explanation of the packet's meaning. We include spaces in some of the
33491 templates for clarity; these are not part of the packet's syntax. No
33492 @value{GDBN} packet uses spaces to separate its components.
33494 Here are the currently defined query and set packets:
33498 @item QAllow:@var{op}:@var{val}@dots{}
33499 @cindex @samp{QAllow} packet
33500 Specify which operations @value{GDBN} expects to request of the
33501 target, as a semicolon-separated list of operation name and value
33502 pairs. Possible values for @var{op} include @samp{WriteReg},
33503 @samp{WriteMem}, @samp{InsertBreak}, @samp{InsertTrace},
33504 @samp{InsertFastTrace}, and @samp{Stop}. @var{val} is either 0,
33505 indicating that @value{GDBN} will not request the operation, or 1,
33506 indicating that it may. (The target can then use this to set up its
33507 own internals optimally, for instance if the debugger never expects to
33508 insert breakpoints, it may not need to install its own trap handler.)
33511 @cindex current thread, remote request
33512 @cindex @samp{qC} packet
33513 Return the current thread ID.
33517 @item QC @var{thread-id}
33518 Where @var{thread-id} is a thread ID as documented in
33519 @ref{thread-id syntax}.
33520 @item @r{(anything else)}
33521 Any other reply implies the old thread ID.
33524 @item qCRC:@var{addr},@var{length}
33525 @cindex CRC of memory block, remote request
33526 @cindex @samp{qCRC} packet
33527 Compute the CRC checksum of a block of memory using CRC-32 defined in
33528 IEEE 802.3. The CRC is computed byte at a time, taking the most
33529 significant bit of each byte first. The initial pattern code
33530 @code{0xffffffff} is used to ensure leading zeros affect the CRC.
33532 @emph{Note:} This is the same CRC used in validating separate debug
33533 files (@pxref{Separate Debug Files, , Debugging Information in Separate
33534 Files}). However the algorithm is slightly different. When validating
33535 separate debug files, the CRC is computed taking the @emph{least}
33536 significant bit of each byte first, and the final result is inverted to
33537 detect trailing zeros.
33542 An error (such as memory fault)
33543 @item C @var{crc32}
33544 The specified memory region's checksum is @var{crc32}.
33547 @item QDisableRandomization:@var{value}
33548 @cindex disable address space randomization, remote request
33549 @cindex @samp{QDisableRandomization} packet
33550 Some target operating systems will randomize the virtual address space
33551 of the inferior process as a security feature, but provide a feature
33552 to disable such randomization, e.g.@: to allow for a more deterministic
33553 debugging experience. On such systems, this packet with a @var{value}
33554 of 1 directs the target to disable address space randomization for
33555 processes subsequently started via @samp{vRun} packets, while a packet
33556 with a @var{value} of 0 tells the target to enable address space
33559 This packet is only available in extended mode (@pxref{extended mode}).
33564 The request succeeded.
33567 An error occurred. @var{nn} are hex digits.
33570 An empty reply indicates that @samp{QDisableRandomization} is not supported
33574 This packet is not probed by default; the remote stub must request it,
33575 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
33576 This should only be done on targets that actually support disabling
33577 address space randomization.
33580 @itemx qsThreadInfo
33581 @cindex list active threads, remote request
33582 @cindex @samp{qfThreadInfo} packet
33583 @cindex @samp{qsThreadInfo} packet
33584 Obtain a list of all active thread IDs from the target (OS). Since there
33585 may be too many active threads to fit into one reply packet, this query
33586 works iteratively: it may require more than one query/reply sequence to
33587 obtain the entire list of threads. The first query of the sequence will
33588 be the @samp{qfThreadInfo} query; subsequent queries in the
33589 sequence will be the @samp{qsThreadInfo} query.
33591 NOTE: This packet replaces the @samp{qL} query (see below).
33595 @item m @var{thread-id}
33597 @item m @var{thread-id},@var{thread-id}@dots{}
33598 a comma-separated list of thread IDs
33600 (lower case letter @samp{L}) denotes end of list.
33603 In response to each query, the target will reply with a list of one or
33604 more thread IDs, separated by commas.
33605 @value{GDBN} will respond to each reply with a request for more thread
33606 ids (using the @samp{qs} form of the query), until the target responds
33607 with @samp{l} (lower-case ell, for @dfn{last}).
33608 Refer to @ref{thread-id syntax}, for the format of the @var{thread-id}
33611 @item qGetTLSAddr:@var{thread-id},@var{offset},@var{lm}
33612 @cindex get thread-local storage address, remote request
33613 @cindex @samp{qGetTLSAddr} packet
33614 Fetch the address associated with thread local storage specified
33615 by @var{thread-id}, @var{offset}, and @var{lm}.
33617 @var{thread-id} is the thread ID associated with the
33618 thread for which to fetch the TLS address. @xref{thread-id syntax}.
33620 @var{offset} is the (big endian, hex encoded) offset associated with the
33621 thread local variable. (This offset is obtained from the debug
33622 information associated with the variable.)
33624 @var{lm} is the (big endian, hex encoded) OS/ABI-specific encoding of the
33625 load module associated with the thread local storage. For example,
33626 a @sc{gnu}/Linux system will pass the link map address of the shared
33627 object associated with the thread local storage under consideration.
33628 Other operating environments may choose to represent the load module
33629 differently, so the precise meaning of this parameter will vary.
33633 @item @var{XX}@dots{}
33634 Hex encoded (big endian) bytes representing the address of the thread
33635 local storage requested.
33638 An error occurred. @var{nn} are hex digits.
33641 An empty reply indicates that @samp{qGetTLSAddr} is not supported by the stub.
33644 @item qGetTIBAddr:@var{thread-id}
33645 @cindex get thread information block address
33646 @cindex @samp{qGetTIBAddr} packet
33647 Fetch address of the Windows OS specific Thread Information Block.
33649 @var{thread-id} is the thread ID associated with the thread.
33653 @item @var{XX}@dots{}
33654 Hex encoded (big endian) bytes representing the linear address of the
33655 thread information block.
33658 An error occured. This means that either the thread was not found, or the
33659 address could not be retrieved.
33662 An empty reply indicates that @samp{qGetTIBAddr} is not supported by the stub.
33665 @item qL @var{startflag} @var{threadcount} @var{nextthread}
33666 Obtain thread information from RTOS. Where: @var{startflag} (one hex
33667 digit) is one to indicate the first query and zero to indicate a
33668 subsequent query; @var{threadcount} (two hex digits) is the maximum
33669 number of threads the response packet can contain; and @var{nextthread}
33670 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
33671 returned in the response as @var{argthread}.
33673 Don't use this packet; use the @samp{qfThreadInfo} query instead (see above).
33677 @item qM @var{count} @var{done} @var{argthread} @var{thread}@dots{}
33678 Where: @var{count} (two hex digits) is the number of threads being
33679 returned; @var{done} (one hex digit) is zero to indicate more threads
33680 and one indicates no further threads; @var{argthreadid} (eight hex
33681 digits) is @var{nextthread} from the request packet; @var{thread}@dots{}
33682 is a sequence of thread IDs from the target. @var{threadid} (eight hex
33683 digits). See @code{remote.c:parse_threadlist_response()}.
33687 @cindex section offsets, remote request
33688 @cindex @samp{qOffsets} packet
33689 Get section offsets that the target used when relocating the downloaded
33694 @item Text=@var{xxx};Data=@var{yyy}@r{[};Bss=@var{zzz}@r{]}
33695 Relocate the @code{Text} section by @var{xxx} from its original address.
33696 Relocate the @code{Data} section by @var{yyy} from its original address.
33697 If the object file format provides segment information (e.g.@: @sc{elf}
33698 @samp{PT_LOAD} program headers), @value{GDBN} will relocate entire
33699 segments by the supplied offsets.
33701 @emph{Note: while a @code{Bss} offset may be included in the response,
33702 @value{GDBN} ignores this and instead applies the @code{Data} offset
33703 to the @code{Bss} section.}
33705 @item TextSeg=@var{xxx}@r{[};DataSeg=@var{yyy}@r{]}
33706 Relocate the first segment of the object file, which conventionally
33707 contains program code, to a starting address of @var{xxx}. If
33708 @samp{DataSeg} is specified, relocate the second segment, which
33709 conventionally contains modifiable data, to a starting address of
33710 @var{yyy}. @value{GDBN} will report an error if the object file
33711 does not contain segment information, or does not contain at least
33712 as many segments as mentioned in the reply. Extra segments are
33713 kept at fixed offsets relative to the last relocated segment.
33716 @item qP @var{mode} @var{thread-id}
33717 @cindex thread information, remote request
33718 @cindex @samp{qP} packet
33719 Returns information on @var{thread-id}. Where: @var{mode} is a hex
33720 encoded 32 bit mode; @var{thread-id} is a thread ID
33721 (@pxref{thread-id syntax}).
33723 Don't use this packet; use the @samp{qThreadExtraInfo} query instead
33726 Reply: see @code{remote.c:remote_unpack_thread_info_response()}.
33730 @cindex non-stop mode, remote request
33731 @cindex @samp{QNonStop} packet
33733 Enter non-stop (@samp{QNonStop:1}) or all-stop (@samp{QNonStop:0}) mode.
33734 @xref{Remote Non-Stop}, for more information.
33739 The request succeeded.
33742 An error occurred. @var{nn} are hex digits.
33745 An empty reply indicates that @samp{QNonStop} is not supported by
33749 This packet is not probed by default; the remote stub must request it,
33750 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
33751 Use of this packet is controlled by the @code{set non-stop} command;
33752 @pxref{Non-Stop Mode}.
33754 @item QPassSignals: @var{signal} @r{[};@var{signal}@r{]}@dots{}
33755 @cindex pass signals to inferior, remote request
33756 @cindex @samp{QPassSignals} packet
33757 @anchor{QPassSignals}
33758 Each listed @var{signal} should be passed directly to the inferior process.
33759 Signals are numbered identically to continue packets and stop replies
33760 (@pxref{Stop Reply Packets}). Each @var{signal} list item should be
33761 strictly greater than the previous item. These signals do not need to stop
33762 the inferior, or be reported to @value{GDBN}. All other signals should be
33763 reported to @value{GDBN}. Multiple @samp{QPassSignals} packets do not
33764 combine; any earlier @samp{QPassSignals} list is completely replaced by the
33765 new list. This packet improves performance when using @samp{handle
33766 @var{signal} nostop noprint pass}.
33771 The request succeeded.
33774 An error occurred. @var{nn} are hex digits.
33777 An empty reply indicates that @samp{QPassSignals} is not supported by
33781 Use of this packet is controlled by the @code{set remote pass-signals}
33782 command (@pxref{Remote Configuration, set remote pass-signals}).
33783 This packet is not probed by default; the remote stub must request it,
33784 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
33786 @item qRcmd,@var{command}
33787 @cindex execute remote command, remote request
33788 @cindex @samp{qRcmd} packet
33789 @var{command} (hex encoded) is passed to the local interpreter for
33790 execution. Invalid commands should be reported using the output
33791 string. Before the final result packet, the target may also respond
33792 with a number of intermediate @samp{O@var{output}} console output
33793 packets. @emph{Implementors should note that providing access to a
33794 stubs's interpreter may have security implications}.
33799 A command response with no output.
33801 A command response with the hex encoded output string @var{OUTPUT}.
33803 Indicate a badly formed request.
33805 An empty reply indicates that @samp{qRcmd} is not recognized.
33808 (Note that the @code{qRcmd} packet's name is separated from the
33809 command by a @samp{,}, not a @samp{:}, contrary to the naming
33810 conventions above. Please don't use this packet as a model for new
33813 @item qSearch:memory:@var{address};@var{length};@var{search-pattern}
33814 @cindex searching memory, in remote debugging
33815 @cindex @samp{qSearch:memory} packet
33816 @anchor{qSearch memory}
33817 Search @var{length} bytes at @var{address} for @var{search-pattern}.
33818 @var{address} and @var{length} are encoded in hex.
33819 @var{search-pattern} is a sequence of bytes, hex encoded.
33824 The pattern was not found.
33826 The pattern was found at @var{address}.
33828 A badly formed request or an error was encountered while searching memory.
33830 An empty reply indicates that @samp{qSearch:memory} is not recognized.
33833 @item QStartNoAckMode
33834 @cindex @samp{QStartNoAckMode} packet
33835 @anchor{QStartNoAckMode}
33836 Request that the remote stub disable the normal @samp{+}/@samp{-}
33837 protocol acknowledgments (@pxref{Packet Acknowledgment}).
33842 The stub has switched to no-acknowledgment mode.
33843 @value{GDBN} acknowledges this reponse,
33844 but neither the stub nor @value{GDBN} shall send or expect further
33845 @samp{+}/@samp{-} acknowledgments in the current connection.
33847 An empty reply indicates that the stub does not support no-acknowledgment mode.
33850 @item qSupported @r{[}:@var{gdbfeature} @r{[};@var{gdbfeature}@r{]}@dots{} @r{]}
33851 @cindex supported packets, remote query
33852 @cindex features of the remote protocol
33853 @cindex @samp{qSupported} packet
33854 @anchor{qSupported}
33855 Tell the remote stub about features supported by @value{GDBN}, and
33856 query the stub for features it supports. This packet allows
33857 @value{GDBN} and the remote stub to take advantage of each others'
33858 features. @samp{qSupported} also consolidates multiple feature probes
33859 at startup, to improve @value{GDBN} performance---a single larger
33860 packet performs better than multiple smaller probe packets on
33861 high-latency links. Some features may enable behavior which must not
33862 be on by default, e.g.@: because it would confuse older clients or
33863 stubs. Other features may describe packets which could be
33864 automatically probed for, but are not. These features must be
33865 reported before @value{GDBN} will use them. This ``default
33866 unsupported'' behavior is not appropriate for all packets, but it
33867 helps to keep the initial connection time under control with new
33868 versions of @value{GDBN} which support increasing numbers of packets.
33872 @item @var{stubfeature} @r{[};@var{stubfeature}@r{]}@dots{}
33873 The stub supports or does not support each returned @var{stubfeature},
33874 depending on the form of each @var{stubfeature} (see below for the
33877 An empty reply indicates that @samp{qSupported} is not recognized,
33878 or that no features needed to be reported to @value{GDBN}.
33881 The allowed forms for each feature (either a @var{gdbfeature} in the
33882 @samp{qSupported} packet, or a @var{stubfeature} in the response)
33886 @item @var{name}=@var{value}
33887 The remote protocol feature @var{name} is supported, and associated
33888 with the specified @var{value}. The format of @var{value} depends
33889 on the feature, but it must not include a semicolon.
33891 The remote protocol feature @var{name} is supported, and does not
33892 need an associated value.
33894 The remote protocol feature @var{name} is not supported.
33896 The remote protocol feature @var{name} may be supported, and
33897 @value{GDBN} should auto-detect support in some other way when it is
33898 needed. This form will not be used for @var{gdbfeature} notifications,
33899 but may be used for @var{stubfeature} responses.
33902 Whenever the stub receives a @samp{qSupported} request, the
33903 supplied set of @value{GDBN} features should override any previous
33904 request. This allows @value{GDBN} to put the stub in a known
33905 state, even if the stub had previously been communicating with
33906 a different version of @value{GDBN}.
33908 The following values of @var{gdbfeature} (for the packet sent by @value{GDBN})
33913 This feature indicates whether @value{GDBN} supports multiprocess
33914 extensions to the remote protocol. @value{GDBN} does not use such
33915 extensions unless the stub also reports that it supports them by
33916 including @samp{multiprocess+} in its @samp{qSupported} reply.
33917 @xref{multiprocess extensions}, for details.
33920 This feature indicates that @value{GDBN} supports the XML target
33921 description. If the stub sees @samp{xmlRegisters=} with target
33922 specific strings separated by a comma, it will report register
33926 This feature indicates whether @value{GDBN} supports the
33927 @samp{qRelocInsn} packet (@pxref{Tracepoint Packets,,Relocate
33928 instruction reply packet}).
33931 Stubs should ignore any unknown values for
33932 @var{gdbfeature}. Any @value{GDBN} which sends a @samp{qSupported}
33933 packet supports receiving packets of unlimited length (earlier
33934 versions of @value{GDBN} may reject overly long responses). Additional values
33935 for @var{gdbfeature} may be defined in the future to let the stub take
33936 advantage of new features in @value{GDBN}, e.g.@: incompatible
33937 improvements in the remote protocol---the @samp{multiprocess} feature is
33938 an example of such a feature. The stub's reply should be independent
33939 of the @var{gdbfeature} entries sent by @value{GDBN}; first @value{GDBN}
33940 describes all the features it supports, and then the stub replies with
33941 all the features it supports.
33943 Similarly, @value{GDBN} will silently ignore unrecognized stub feature
33944 responses, as long as each response uses one of the standard forms.
33946 Some features are flags. A stub which supports a flag feature
33947 should respond with a @samp{+} form response. Other features
33948 require values, and the stub should respond with an @samp{=}
33951 Each feature has a default value, which @value{GDBN} will use if
33952 @samp{qSupported} is not available or if the feature is not mentioned
33953 in the @samp{qSupported} response. The default values are fixed; a
33954 stub is free to omit any feature responses that match the defaults.
33956 Not all features can be probed, but for those which can, the probing
33957 mechanism is useful: in some cases, a stub's internal
33958 architecture may not allow the protocol layer to know some information
33959 about the underlying target in advance. This is especially common in
33960 stubs which may be configured for multiple targets.
33962 These are the currently defined stub features and their properties:
33964 @multitable @columnfractions 0.35 0.2 0.12 0.2
33965 @c NOTE: The first row should be @headitem, but we do not yet require
33966 @c a new enough version of Texinfo (4.7) to use @headitem.
33968 @tab Value Required
33972 @item @samp{PacketSize}
33977 @item @samp{qXfer:auxv:read}
33982 @item @samp{qXfer:features:read}
33987 @item @samp{qXfer:libraries:read}
33992 @item @samp{qXfer:memory-map:read}
33997 @item @samp{qXfer:sdata:read}
34002 @item @samp{qXfer:spu:read}
34007 @item @samp{qXfer:spu:write}
34012 @item @samp{qXfer:siginfo:read}
34017 @item @samp{qXfer:siginfo:write}
34022 @item @samp{qXfer:threads:read}
34027 @item @samp{qXfer:traceframe-info:read}
34032 @item @samp{qXfer:fdpic:read}
34037 @item @samp{QNonStop}
34042 @item @samp{QPassSignals}
34047 @item @samp{QStartNoAckMode}
34052 @item @samp{multiprocess}
34057 @item @samp{ConditionalTracepoints}
34062 @item @samp{ReverseContinue}
34067 @item @samp{ReverseStep}
34072 @item @samp{TracepointSource}
34077 @item @samp{QAllow}
34082 @item @samp{QDisableRandomization}
34087 @item @samp{EnableDisableTracepoints}
34094 These are the currently defined stub features, in more detail:
34097 @cindex packet size, remote protocol
34098 @item PacketSize=@var{bytes}
34099 The remote stub can accept packets up to at least @var{bytes} in
34100 length. @value{GDBN} will send packets up to this size for bulk
34101 transfers, and will never send larger packets. This is a limit on the
34102 data characters in the packet, including the frame and checksum.
34103 There is no trailing NUL byte in a remote protocol packet; if the stub
34104 stores packets in a NUL-terminated format, it should allow an extra
34105 byte in its buffer for the NUL. If this stub feature is not supported,
34106 @value{GDBN} guesses based on the size of the @samp{g} packet response.
34108 @item qXfer:auxv:read
34109 The remote stub understands the @samp{qXfer:auxv:read} packet
34110 (@pxref{qXfer auxiliary vector read}).
34112 @item qXfer:features:read
34113 The remote stub understands the @samp{qXfer:features:read} packet
34114 (@pxref{qXfer target description read}).
34116 @item qXfer:libraries:read
34117 The remote stub understands the @samp{qXfer:libraries:read} packet
34118 (@pxref{qXfer library list read}).
34120 @item qXfer:memory-map:read
34121 The remote stub understands the @samp{qXfer:memory-map:read} packet
34122 (@pxref{qXfer memory map read}).
34124 @item qXfer:sdata:read
34125 The remote stub understands the @samp{qXfer:sdata:read} packet
34126 (@pxref{qXfer sdata read}).
34128 @item qXfer:spu:read
34129 The remote stub understands the @samp{qXfer:spu:read} packet
34130 (@pxref{qXfer spu read}).
34132 @item qXfer:spu:write
34133 The remote stub understands the @samp{qXfer:spu:write} packet
34134 (@pxref{qXfer spu write}).
34136 @item qXfer:siginfo:read
34137 The remote stub understands the @samp{qXfer:siginfo:read} packet
34138 (@pxref{qXfer siginfo read}).
34140 @item qXfer:siginfo:write
34141 The remote stub understands the @samp{qXfer:siginfo:write} packet
34142 (@pxref{qXfer siginfo write}).
34144 @item qXfer:threads:read
34145 The remote stub understands the @samp{qXfer:threads:read} packet
34146 (@pxref{qXfer threads read}).
34148 @item qXfer:traceframe-info:read
34149 The remote stub understands the @samp{qXfer:traceframe-info:read}
34150 packet (@pxref{qXfer traceframe info read}).
34152 @item qXfer:fdpic:read
34153 The remote stub understands the @samp{qXfer:fdpic:read}
34154 packet (@pxref{qXfer fdpic loadmap read}).
34157 The remote stub understands the @samp{QNonStop} packet
34158 (@pxref{QNonStop}).
34161 The remote stub understands the @samp{QPassSignals} packet
34162 (@pxref{QPassSignals}).
34164 @item QStartNoAckMode
34165 The remote stub understands the @samp{QStartNoAckMode} packet and
34166 prefers to operate in no-acknowledgment mode. @xref{Packet Acknowledgment}.
34169 @anchor{multiprocess extensions}
34170 @cindex multiprocess extensions, in remote protocol
34171 The remote stub understands the multiprocess extensions to the remote
34172 protocol syntax. The multiprocess extensions affect the syntax of
34173 thread IDs in both packets and replies (@pxref{thread-id syntax}), and
34174 add process IDs to the @samp{D} packet and @samp{W} and @samp{X}
34175 replies. Note that reporting this feature indicates support for the
34176 syntactic extensions only, not that the stub necessarily supports
34177 debugging of more than one process at a time. The stub must not use
34178 multiprocess extensions in packet replies unless @value{GDBN} has also
34179 indicated it supports them in its @samp{qSupported} request.
34181 @item qXfer:osdata:read
34182 The remote stub understands the @samp{qXfer:osdata:read} packet
34183 ((@pxref{qXfer osdata read}).
34185 @item ConditionalTracepoints
34186 The remote stub accepts and implements conditional expressions defined
34187 for tracepoints (@pxref{Tracepoint Conditions}).
34189 @item ReverseContinue
34190 The remote stub accepts and implements the reverse continue packet
34194 The remote stub accepts and implements the reverse step packet
34197 @item TracepointSource
34198 The remote stub understands the @samp{QTDPsrc} packet that supplies
34199 the source form of tracepoint definitions.
34202 The remote stub understands the @samp{QAllow} packet.
34204 @item QDisableRandomization
34205 The remote stub understands the @samp{QDisableRandomization} packet.
34207 @item StaticTracepoint
34208 @cindex static tracepoints, in remote protocol
34209 The remote stub supports static tracepoints.
34211 @item EnableDisableTracepoints
34212 The remote stub supports the @samp{QTEnable} (@pxref{QTEnable}) and
34213 @samp{QTDisable} (@pxref{QTDisable}) packets that allow tracepoints
34214 to be enabled and disabled while a trace experiment is running.
34219 @cindex symbol lookup, remote request
34220 @cindex @samp{qSymbol} packet
34221 Notify the target that @value{GDBN} is prepared to serve symbol lookup
34222 requests. Accept requests from the target for the values of symbols.
34227 The target does not need to look up any (more) symbols.
34228 @item qSymbol:@var{sym_name}
34229 The target requests the value of symbol @var{sym_name} (hex encoded).
34230 @value{GDBN} may provide the value by using the
34231 @samp{qSymbol:@var{sym_value}:@var{sym_name}} message, described
34235 @item qSymbol:@var{sym_value}:@var{sym_name}
34236 Set the value of @var{sym_name} to @var{sym_value}.
34238 @var{sym_name} (hex encoded) is the name of a symbol whose value the
34239 target has previously requested.
34241 @var{sym_value} (hex) is the value for symbol @var{sym_name}. If
34242 @value{GDBN} cannot supply a value for @var{sym_name}, then this field
34248 The target does not need to look up any (more) symbols.
34249 @item qSymbol:@var{sym_name}
34250 The target requests the value of a new symbol @var{sym_name} (hex
34251 encoded). @value{GDBN} will continue to supply the values of symbols
34252 (if available), until the target ceases to request them.
34257 @item QTDisconnected
34264 @xref{Tracepoint Packets}.
34266 @item qThreadExtraInfo,@var{thread-id}
34267 @cindex thread attributes info, remote request
34268 @cindex @samp{qThreadExtraInfo} packet
34269 Obtain a printable string description of a thread's attributes from
34270 the target OS. @var{thread-id} is a thread ID;
34271 see @ref{thread-id syntax}. This
34272 string may contain anything that the target OS thinks is interesting
34273 for @value{GDBN} to tell the user about the thread. The string is
34274 displayed in @value{GDBN}'s @code{info threads} display. Some
34275 examples of possible thread extra info strings are @samp{Runnable}, or
34276 @samp{Blocked on Mutex}.
34280 @item @var{XX}@dots{}
34281 Where @samp{@var{XX}@dots{}} is a hex encoding of @sc{ascii} data,
34282 comprising the printable string containing the extra information about
34283 the thread's attributes.
34286 (Note that the @code{qThreadExtraInfo} packet's name is separated from
34287 the command by a @samp{,}, not a @samp{:}, contrary to the naming
34288 conventions above. Please don't use this packet as a model for new
34305 @xref{Tracepoint Packets}.
34307 @item qXfer:@var{object}:read:@var{annex}:@var{offset},@var{length}
34308 @cindex read special object, remote request
34309 @cindex @samp{qXfer} packet
34310 @anchor{qXfer read}
34311 Read uninterpreted bytes from the target's special data area
34312 identified by the keyword @var{object}. Request @var{length} bytes
34313 starting at @var{offset} bytes into the data. The content and
34314 encoding of @var{annex} is specific to @var{object}; it can supply
34315 additional details about what data to access.
34317 Here are the specific requests of this form defined so far. All
34318 @samp{qXfer:@var{object}:read:@dots{}} requests use the same reply
34319 formats, listed below.
34322 @item qXfer:auxv:read::@var{offset},@var{length}
34323 @anchor{qXfer auxiliary vector read}
34324 Access the target's @dfn{auxiliary vector}. @xref{OS Information,
34325 auxiliary vector}. Note @var{annex} must be empty.
34327 This packet is not probed by default; the remote stub must request it,
34328 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
34330 @item qXfer:features:read:@var{annex}:@var{offset},@var{length}
34331 @anchor{qXfer target description read}
34332 Access the @dfn{target description}. @xref{Target Descriptions}. The
34333 annex specifies which XML document to access. The main description is
34334 always loaded from the @samp{target.xml} annex.
34336 This packet is not probed by default; the remote stub must request it,
34337 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
34339 @item qXfer:libraries:read:@var{annex}:@var{offset},@var{length}
34340 @anchor{qXfer library list read}
34341 Access the target's list of loaded libraries. @xref{Library List Format}.
34342 The annex part of the generic @samp{qXfer} packet must be empty
34343 (@pxref{qXfer read}).
34345 Targets which maintain a list of libraries in the program's memory do
34346 not need to implement this packet; it is designed for platforms where
34347 the operating system manages the list of loaded libraries.
34349 This packet is not probed by default; the remote stub must request it,
34350 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
34352 @item qXfer:memory-map:read::@var{offset},@var{length}
34353 @anchor{qXfer memory map read}
34354 Access the target's @dfn{memory-map}. @xref{Memory Map Format}. The
34355 annex part of the generic @samp{qXfer} packet must be empty
34356 (@pxref{qXfer read}).
34358 This packet is not probed by default; the remote stub must request it,
34359 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
34361 @item qXfer:sdata:read::@var{offset},@var{length}
34362 @anchor{qXfer sdata read}
34364 Read contents of the extra collected static tracepoint marker
34365 information. The annex part of the generic @samp{qXfer} packet must
34366 be empty (@pxref{qXfer read}). @xref{Tracepoint Actions,,Tracepoint
34369 This packet is not probed by default; the remote stub must request it,
34370 by supplying an appropriate @samp{qSupported} response
34371 (@pxref{qSupported}).
34373 @item qXfer:siginfo:read::@var{offset},@var{length}
34374 @anchor{qXfer siginfo read}
34375 Read contents of the extra signal information on the target
34376 system. The annex part of the generic @samp{qXfer} packet must be
34377 empty (@pxref{qXfer read}).
34379 This packet is not probed by default; the remote stub must request it,
34380 by supplying an appropriate @samp{qSupported} response
34381 (@pxref{qSupported}).
34383 @item qXfer:spu:read:@var{annex}:@var{offset},@var{length}
34384 @anchor{qXfer spu read}
34385 Read contents of an @code{spufs} file on the target system. The
34386 annex specifies which file to read; it must be of the form
34387 @file{@var{id}/@var{name}}, where @var{id} specifies an SPU context ID
34388 in the target process, and @var{name} identifes the @code{spufs} file
34389 in that context to be accessed.
34391 This packet is not probed by default; the remote stub must request it,
34392 by supplying an appropriate @samp{qSupported} response
34393 (@pxref{qSupported}).
34395 @item qXfer:threads:read::@var{offset},@var{length}
34396 @anchor{qXfer threads read}
34397 Access the list of threads on target. @xref{Thread List Format}. The
34398 annex part of the generic @samp{qXfer} packet must be empty
34399 (@pxref{qXfer read}).
34401 This packet is not probed by default; the remote stub must request it,
34402 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
34404 @item qXfer:traceframe-info:read::@var{offset},@var{length}
34405 @anchor{qXfer traceframe info read}
34407 Return a description of the current traceframe's contents.
34408 @xref{Traceframe Info Format}. The annex part of the generic
34409 @samp{qXfer} packet must be empty (@pxref{qXfer read}).
34411 This packet is not probed by default; the remote stub must request it,
34412 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
34414 @item qXfer:fdpic:read:@var{annex}:@var{offset},@var{length}
34415 @anchor{qXfer fdpic loadmap read}
34416 Read contents of @code{loadmap}s on the target system. The
34417 annex, either @samp{exec} or @samp{interp}, specifies which @code{loadmap},
34418 executable @code{loadmap} or interpreter @code{loadmap} to read.
34420 This packet is not probed by default; the remote stub must request it,
34421 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
34423 @item qXfer:osdata:read::@var{offset},@var{length}
34424 @anchor{qXfer osdata read}
34425 Access the target's @dfn{operating system information}.
34426 @xref{Operating System Information}.
34433 Data @var{data} (@pxref{Binary Data}) has been read from the
34434 target. There may be more data at a higher address (although
34435 it is permitted to return @samp{m} even for the last valid
34436 block of data, as long as at least one byte of data was read).
34437 @var{data} may have fewer bytes than the @var{length} in the
34441 Data @var{data} (@pxref{Binary Data}) has been read from the target.
34442 There is no more data to be read. @var{data} may have fewer bytes
34443 than the @var{length} in the request.
34446 The @var{offset} in the request is at the end of the data.
34447 There is no more data to be read.
34450 The request was malformed, or @var{annex} was invalid.
34453 The offset was invalid, or there was an error encountered reading the data.
34454 @var{nn} is a hex-encoded @code{errno} value.
34457 An empty reply indicates the @var{object} string was not recognized by
34458 the stub, or that the object does not support reading.
34461 @item qXfer:@var{object}:write:@var{annex}:@var{offset}:@var{data}@dots{}
34462 @cindex write data into object, remote request
34463 @anchor{qXfer write}
34464 Write uninterpreted bytes into the target's special data area
34465 identified by the keyword @var{object}, starting at @var{offset} bytes
34466 into the data. @var{data}@dots{} is the binary-encoded data
34467 (@pxref{Binary Data}) to be written. The content and encoding of @var{annex}
34468 is specific to @var{object}; it can supply additional details about what data
34471 Here are the specific requests of this form defined so far. All
34472 @samp{qXfer:@var{object}:write:@dots{}} requests use the same reply
34473 formats, listed below.
34476 @item qXfer:siginfo:write::@var{offset}:@var{data}@dots{}
34477 @anchor{qXfer siginfo write}
34478 Write @var{data} to the extra signal information on the target system.
34479 The annex part of the generic @samp{qXfer} packet must be
34480 empty (@pxref{qXfer write}).
34482 This packet is not probed by default; the remote stub must request it,
34483 by supplying an appropriate @samp{qSupported} response
34484 (@pxref{qSupported}).
34486 @item qXfer:spu:write:@var{annex}:@var{offset}:@var{data}@dots{}
34487 @anchor{qXfer spu write}
34488 Write @var{data} to an @code{spufs} file on the target system. The
34489 annex specifies which file to write; it must be of the form
34490 @file{@var{id}/@var{name}}, where @var{id} specifies an SPU context ID
34491 in the target process, and @var{name} identifes the @code{spufs} file
34492 in that context to be accessed.
34494 This packet is not probed by default; the remote stub must request it,
34495 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
34501 @var{nn} (hex encoded) is the number of bytes written.
34502 This may be fewer bytes than supplied in the request.
34505 The request was malformed, or @var{annex} was invalid.
34508 The offset was invalid, or there was an error encountered writing the data.
34509 @var{nn} is a hex-encoded @code{errno} value.
34512 An empty reply indicates the @var{object} string was not
34513 recognized by the stub, or that the object does not support writing.
34516 @item qXfer:@var{object}:@var{operation}:@dots{}
34517 Requests of this form may be added in the future. When a stub does
34518 not recognize the @var{object} keyword, or its support for
34519 @var{object} does not recognize the @var{operation} keyword, the stub
34520 must respond with an empty packet.
34522 @item qAttached:@var{pid}
34523 @cindex query attached, remote request
34524 @cindex @samp{qAttached} packet
34525 Return an indication of whether the remote server attached to an
34526 existing process or created a new process. When the multiprocess
34527 protocol extensions are supported (@pxref{multiprocess extensions}),
34528 @var{pid} is an integer in hexadecimal format identifying the target
34529 process. Otherwise, @value{GDBN} will omit the @var{pid} field and
34530 the query packet will be simplified as @samp{qAttached}.
34532 This query is used, for example, to know whether the remote process
34533 should be detached or killed when a @value{GDBN} session is ended with
34534 the @code{quit} command.
34539 The remote server attached to an existing process.
34541 The remote server created a new process.
34543 A badly formed request or an error was encountered.
34548 @node Architecture-Specific Protocol Details
34549 @section Architecture-Specific Protocol Details
34551 This section describes how the remote protocol is applied to specific
34552 target architectures. Also see @ref{Standard Target Features}, for
34553 details of XML target descriptions for each architecture.
34557 @subsubsection Breakpoint Kinds
34559 These breakpoint kinds are defined for the @samp{Z0} and @samp{Z1} packets.
34564 16-bit Thumb mode breakpoint.
34567 32-bit Thumb mode (Thumb-2) breakpoint.
34570 32-bit ARM mode breakpoint.
34576 @subsubsection Register Packet Format
34578 The following @code{g}/@code{G} packets have previously been defined.
34579 In the below, some thirty-two bit registers are transferred as
34580 sixty-four bits. Those registers should be zero/sign extended (which?)
34581 to fill the space allocated. Register bytes are transferred in target
34582 byte order. The two nibbles within a register byte are transferred
34583 most-significant - least-significant.
34589 All registers are transferred as thirty-two bit quantities in the order:
34590 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
34591 registers; fsr; fir; fp.
34595 All registers are transferred as sixty-four bit quantities (including
34596 thirty-two bit registers such as @code{sr}). The ordering is the same
34601 @node Tracepoint Packets
34602 @section Tracepoint Packets
34603 @cindex tracepoint packets
34604 @cindex packets, tracepoint
34606 Here we describe the packets @value{GDBN} uses to implement
34607 tracepoints (@pxref{Tracepoints}).
34611 @item QTDP:@var{n}:@var{addr}:@var{ena}:@var{step}:@var{pass}[:F@var{flen}][:X@var{len},@var{bytes}]@r{[}-@r{]}
34612 Create a new tracepoint, number @var{n}, at @var{addr}. If @var{ena}
34613 is @samp{E}, then the tracepoint is enabled; if it is @samp{D}, then
34614 the tracepoint is disabled. @var{step} is the tracepoint's step
34615 count, and @var{pass} is its pass count. If an @samp{F} is present,
34616 then the tracepoint is to be a fast tracepoint, and the @var{flen} is
34617 the number of bytes that the target should copy elsewhere to make room
34618 for the tracepoint. If an @samp{X} is present, it introduces a
34619 tracepoint condition, which consists of a hexadecimal length, followed
34620 by a comma and hex-encoded bytes, in a manner similar to action
34621 encodings as described below. If the trailing @samp{-} is present,
34622 further @samp{QTDP} packets will follow to specify this tracepoint's
34628 The packet was understood and carried out.
34630 @xref{Tracepoint Packets,,Relocate instruction reply packet}.
34632 The packet was not recognized.
34635 @item QTDP:-@var{n}:@var{addr}:@r{[}S@r{]}@var{action}@dots{}@r{[}-@r{]}
34636 Define actions to be taken when a tracepoint is hit. @var{n} and
34637 @var{addr} must be the same as in the initial @samp{QTDP} packet for
34638 this tracepoint. This packet may only be sent immediately after
34639 another @samp{QTDP} packet that ended with a @samp{-}. If the
34640 trailing @samp{-} is present, further @samp{QTDP} packets will follow,
34641 specifying more actions for this tracepoint.
34643 In the series of action packets for a given tracepoint, at most one
34644 can have an @samp{S} before its first @var{action}. If such a packet
34645 is sent, it and the following packets define ``while-stepping''
34646 actions. Any prior packets define ordinary actions --- that is, those
34647 taken when the tracepoint is first hit. If no action packet has an
34648 @samp{S}, then all the packets in the series specify ordinary
34649 tracepoint actions.
34651 The @samp{@var{action}@dots{}} portion of the packet is a series of
34652 actions, concatenated without separators. Each action has one of the
34658 Collect the registers whose bits are set in @var{mask}. @var{mask} is
34659 a hexadecimal number whose @var{i}'th bit is set if register number
34660 @var{i} should be collected. (The least significant bit is numbered
34661 zero.) Note that @var{mask} may be any number of digits long; it may
34662 not fit in a 32-bit word.
34664 @item M @var{basereg},@var{offset},@var{len}
34665 Collect @var{len} bytes of memory starting at the address in register
34666 number @var{basereg}, plus @var{offset}. If @var{basereg} is
34667 @samp{-1}, then the range has a fixed address: @var{offset} is the
34668 address of the lowest byte to collect. The @var{basereg},
34669 @var{offset}, and @var{len} parameters are all unsigned hexadecimal
34670 values (the @samp{-1} value for @var{basereg} is a special case).
34672 @item X @var{len},@var{expr}
34673 Evaluate @var{expr}, whose length is @var{len}, and collect memory as
34674 it directs. @var{expr} is an agent expression, as described in
34675 @ref{Agent Expressions}. Each byte of the expression is encoded as a
34676 two-digit hex number in the packet; @var{len} is the number of bytes
34677 in the expression (and thus one-half the number of hex digits in the
34682 Any number of actions may be packed together in a single @samp{QTDP}
34683 packet, as long as the packet does not exceed the maximum packet
34684 length (400 bytes, for many stubs). There may be only one @samp{R}
34685 action per tracepoint, and it must precede any @samp{M} or @samp{X}
34686 actions. Any registers referred to by @samp{M} and @samp{X} actions
34687 must be collected by a preceding @samp{R} action. (The
34688 ``while-stepping'' actions are treated as if they were attached to a
34689 separate tracepoint, as far as these restrictions are concerned.)
34694 The packet was understood and carried out.
34696 @xref{Tracepoint Packets,,Relocate instruction reply packet}.
34698 The packet was not recognized.
34701 @item QTDPsrc:@var{n}:@var{addr}:@var{type}:@var{start}:@var{slen}:@var{bytes}
34702 @cindex @samp{QTDPsrc} packet
34703 Specify a source string of tracepoint @var{n} at address @var{addr}.
34704 This is useful to get accurate reproduction of the tracepoints
34705 originally downloaded at the beginning of the trace run. @var{type}
34706 is the name of the tracepoint part, such as @samp{cond} for the
34707 tracepoint's conditional expression (see below for a list of types), while
34708 @var{bytes} is the string, encoded in hexadecimal.
34710 @var{start} is the offset of the @var{bytes} within the overall source
34711 string, while @var{slen} is the total length of the source string.
34712 This is intended for handling source strings that are longer than will
34713 fit in a single packet.
34714 @c Add detailed example when this info is moved into a dedicated
34715 @c tracepoint descriptions section.
34717 The available string types are @samp{at} for the location,
34718 @samp{cond} for the conditional, and @samp{cmd} for an action command.
34719 @value{GDBN} sends a separate packet for each command in the action
34720 list, in the same order in which the commands are stored in the list.
34722 The target does not need to do anything with source strings except
34723 report them back as part of the replies to the @samp{qTfP}/@samp{qTsP}
34726 Although this packet is optional, and @value{GDBN} will only send it
34727 if the target replies with @samp{TracepointSource} @xref{General
34728 Query Packets}, it makes both disconnected tracing and trace files
34729 much easier to use. Otherwise the user must be careful that the
34730 tracepoints in effect while looking at trace frames are identical to
34731 the ones in effect during the trace run; even a small discrepancy
34732 could cause @samp{tdump} not to work, or a particular trace frame not
34735 @item QTDV:@var{n}:@var{value}
34736 @cindex define trace state variable, remote request
34737 @cindex @samp{QTDV} packet
34738 Create a new trace state variable, number @var{n}, with an initial
34739 value of @var{value}, which is a 64-bit signed integer. Both @var{n}
34740 and @var{value} are encoded as hexadecimal values. @value{GDBN} has
34741 the option of not using this packet for initial values of zero; the
34742 target should simply create the trace state variables as they are
34743 mentioned in expressions.
34745 @item QTFrame:@var{n}
34746 Select the @var{n}'th tracepoint frame from the buffer, and use the
34747 register and memory contents recorded there to answer subsequent
34748 request packets from @value{GDBN}.
34750 A successful reply from the stub indicates that the stub has found the
34751 requested frame. The response is a series of parts, concatenated
34752 without separators, describing the frame we selected. Each part has
34753 one of the following forms:
34757 The selected frame is number @var{n} in the trace frame buffer;
34758 @var{f} is a hexadecimal number. If @var{f} is @samp{-1}, then there
34759 was no frame matching the criteria in the request packet.
34762 The selected trace frame records a hit of tracepoint number @var{t};
34763 @var{t} is a hexadecimal number.
34767 @item QTFrame:pc:@var{addr}
34768 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
34769 currently selected frame whose PC is @var{addr};
34770 @var{addr} is a hexadecimal number.
34772 @item QTFrame:tdp:@var{t}
34773 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
34774 currently selected frame that is a hit of tracepoint @var{t}; @var{t}
34775 is a hexadecimal number.
34777 @item QTFrame:range:@var{start}:@var{end}
34778 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
34779 currently selected frame whose PC is between @var{start} (inclusive)
34780 and @var{end} (inclusive); @var{start} and @var{end} are hexadecimal
34783 @item QTFrame:outside:@var{start}:@var{end}
34784 Like @samp{QTFrame:range:@var{start}:@var{end}}, but select the first
34785 frame @emph{outside} the given range of addresses (exclusive).
34788 Begin the tracepoint experiment. Begin collecting data from
34789 tracepoint hits in the trace frame buffer. This packet supports the
34790 @samp{qRelocInsn} reply (@pxref{Tracepoint Packets,,Relocate
34791 instruction reply packet}).
34794 End the tracepoint experiment. Stop collecting trace frames.
34796 @item QTEnable:@var{n}:@var{addr}
34798 Enable tracepoint @var{n} at address @var{addr} in a started tracepoint
34799 experiment. If the tracepoint was previously disabled, then collection
34800 of data from it will resume.
34802 @item QTDisable:@var{n}:@var{addr}
34804 Disable tracepoint @var{n} at address @var{addr} in a started tracepoint
34805 experiment. No more data will be collected from the tracepoint unless
34806 @samp{QTEnable:@var{n}:@var{addr}} is subsequently issued.
34809 Clear the table of tracepoints, and empty the trace frame buffer.
34811 @item QTro:@var{start1},@var{end1}:@var{start2},@var{end2}:@dots{}
34812 Establish the given ranges of memory as ``transparent''. The stub
34813 will answer requests for these ranges from memory's current contents,
34814 if they were not collected as part of the tracepoint hit.
34816 @value{GDBN} uses this to mark read-only regions of memory, like those
34817 containing program code. Since these areas never change, they should
34818 still have the same contents they did when the tracepoint was hit, so
34819 there's no reason for the stub to refuse to provide their contents.
34821 @item QTDisconnected:@var{value}
34822 Set the choice to what to do with the tracing run when @value{GDBN}
34823 disconnects from the target. A @var{value} of 1 directs the target to
34824 continue the tracing run, while 0 tells the target to stop tracing if
34825 @value{GDBN} is no longer in the picture.
34828 Ask the stub if there is a trace experiment running right now.
34830 The reply has the form:
34834 @item T@var{running}@r{[};@var{field}@r{]}@dots{}
34835 @var{running} is a single digit @code{1} if the trace is presently
34836 running, or @code{0} if not. It is followed by semicolon-separated
34837 optional fields that an agent may use to report additional status.
34841 If the trace is not running, the agent may report any of several
34842 explanations as one of the optional fields:
34847 No trace has been run yet.
34850 The trace was stopped by a user-originated stop command.
34853 The trace stopped because the trace buffer filled up.
34855 @item tdisconnected:0
34856 The trace stopped because @value{GDBN} disconnected from the target.
34858 @item tpasscount:@var{tpnum}
34859 The trace stopped because tracepoint @var{tpnum} exceeded its pass count.
34861 @item terror:@var{text}:@var{tpnum}
34862 The trace stopped because tracepoint @var{tpnum} had an error. The
34863 string @var{text} is available to describe the nature of the error
34864 (for instance, a divide by zero in the condition expression).
34865 @var{text} is hex encoded.
34868 The trace stopped for some other reason.
34872 Additional optional fields supply statistical and other information.
34873 Although not required, they are extremely useful for users monitoring
34874 the progress of a trace run. If a trace has stopped, and these
34875 numbers are reported, they must reflect the state of the just-stopped
34880 @item tframes:@var{n}
34881 The number of trace frames in the buffer.
34883 @item tcreated:@var{n}
34884 The total number of trace frames created during the run. This may
34885 be larger than the trace frame count, if the buffer is circular.
34887 @item tsize:@var{n}
34888 The total size of the trace buffer, in bytes.
34890 @item tfree:@var{n}
34891 The number of bytes still unused in the buffer.
34893 @item circular:@var{n}
34894 The value of the circular trace buffer flag. @code{1} means that the
34895 trace buffer is circular and old trace frames will be discarded if
34896 necessary to make room, @code{0} means that the trace buffer is linear
34899 @item disconn:@var{n}
34900 The value of the disconnected tracing flag. @code{1} means that
34901 tracing will continue after @value{GDBN} disconnects, @code{0} means
34902 that the trace run will stop.
34906 @item qTV:@var{var}
34907 @cindex trace state variable value, remote request
34908 @cindex @samp{qTV} packet
34909 Ask the stub for the value of the trace state variable number @var{var}.
34914 The value of the variable is @var{value}. This will be the current
34915 value of the variable if the user is examining a running target, or a
34916 saved value if the variable was collected in the trace frame that the
34917 user is looking at. Note that multiple requests may result in
34918 different reply values, such as when requesting values while the
34919 program is running.
34922 The value of the variable is unknown. This would occur, for example,
34923 if the user is examining a trace frame in which the requested variable
34929 These packets request data about tracepoints that are being used by
34930 the target. @value{GDBN} sends @code{qTfP} to get the first piece
34931 of data, and multiple @code{qTsP} to get additional pieces. Replies
34932 to these packets generally take the form of the @code{QTDP} packets
34933 that define tracepoints. (FIXME add detailed syntax)
34937 These packets request data about trace state variables that are on the
34938 target. @value{GDBN} sends @code{qTfV} to get the first vari of data,
34939 and multiple @code{qTsV} to get additional variables. Replies to
34940 these packets follow the syntax of the @code{QTDV} packets that define
34941 trace state variables.
34945 These packets request data about static tracepoint markers that exist
34946 in the target program. @value{GDBN} sends @code{qTfSTM} to get the
34947 first piece of data, and multiple @code{qTsSTM} to get additional
34948 pieces. Replies to these packets take the following form:
34952 @item m @var{address}:@var{id}:@var{extra}
34954 @item m @var{address}:@var{id}:@var{extra},@var{address}:@var{id}:@var{extra}@dots{}
34955 a comma-separated list of markers
34957 (lower case letter @samp{L}) denotes end of list.
34959 An error occurred. @var{nn} are hex digits.
34961 An empty reply indicates that the request is not supported by the
34965 @var{address} is encoded in hex.
34966 @var{id} and @var{extra} are strings encoded in hex.
34968 In response to each query, the target will reply with a list of one or
34969 more markers, separated by commas. @value{GDBN} will respond to each
34970 reply with a request for more markers (using the @samp{qs} form of the
34971 query), until the target responds with @samp{l} (lower-case ell, for
34974 @item qTSTMat:@var{address}
34975 This packets requests data about static tracepoint markers in the
34976 target program at @var{address}. Replies to this packet follow the
34977 syntax of the @samp{qTfSTM} and @code{qTsSTM} packets that list static
34978 tracepoint markers.
34980 @item QTSave:@var{filename}
34981 This packet directs the target to save trace data to the file name
34982 @var{filename} in the target's filesystem. @var{filename} is encoded
34983 as a hex string; the interpretation of the file name (relative vs
34984 absolute, wild cards, etc) is up to the target.
34986 @item qTBuffer:@var{offset},@var{len}
34987 Return up to @var{len} bytes of the current contents of trace buffer,
34988 starting at @var{offset}. The trace buffer is treated as if it were
34989 a contiguous collection of traceframes, as per the trace file format.
34990 The reply consists as many hex-encoded bytes as the target can deliver
34991 in a packet; it is not an error to return fewer than were asked for.
34992 A reply consisting of just @code{l} indicates that no bytes are
34995 @item QTBuffer:circular:@var{value}
34996 This packet directs the target to use a circular trace buffer if
34997 @var{value} is 1, or a linear buffer if the value is 0.
35001 @subsection Relocate instruction reply packet
35002 When installing fast tracepoints in memory, the target may need to
35003 relocate the instruction currently at the tracepoint address to a
35004 different address in memory. For most instructions, a simple copy is
35005 enough, but, for example, call instructions that implicitly push the
35006 return address on the stack, and relative branches or other
35007 PC-relative instructions require offset adjustment, so that the effect
35008 of executing the instruction at a different address is the same as if
35009 it had executed in the original location.
35011 In response to several of the tracepoint packets, the target may also
35012 respond with a number of intermediate @samp{qRelocInsn} request
35013 packets before the final result packet, to have @value{GDBN} handle
35014 this relocation operation. If a packet supports this mechanism, its
35015 documentation will explicitly say so. See for example the above
35016 descriptions for the @samp{QTStart} and @samp{QTDP} packets. The
35017 format of the request is:
35020 @item qRelocInsn:@var{from};@var{to}
35022 This requests @value{GDBN} to copy instruction at address @var{from}
35023 to address @var{to}, possibly adjusted so that executing the
35024 instruction at @var{to} has the same effect as executing it at
35025 @var{from}. @value{GDBN} writes the adjusted instruction to target
35026 memory starting at @var{to}.
35031 @item qRelocInsn:@var{adjusted_size}
35032 Informs the stub the relocation is complete. @var{adjusted_size} is
35033 the length in bytes of resulting relocated instruction sequence.
35035 A badly formed request was detected, or an error was encountered while
35036 relocating the instruction.
35039 @node Host I/O Packets
35040 @section Host I/O Packets
35041 @cindex Host I/O, remote protocol
35042 @cindex file transfer, remote protocol
35044 The @dfn{Host I/O} packets allow @value{GDBN} to perform I/O
35045 operations on the far side of a remote link. For example, Host I/O is
35046 used to upload and download files to a remote target with its own
35047 filesystem. Host I/O uses the same constant values and data structure
35048 layout as the target-initiated File-I/O protocol. However, the
35049 Host I/O packets are structured differently. The target-initiated
35050 protocol relies on target memory to store parameters and buffers.
35051 Host I/O requests are initiated by @value{GDBN}, and the
35052 target's memory is not involved. @xref{File-I/O Remote Protocol
35053 Extension}, for more details on the target-initiated protocol.
35055 The Host I/O request packets all encode a single operation along with
35056 its arguments. They have this format:
35060 @item vFile:@var{operation}: @var{parameter}@dots{}
35061 @var{operation} is the name of the particular request; the target
35062 should compare the entire packet name up to the second colon when checking
35063 for a supported operation. The format of @var{parameter} depends on
35064 the operation. Numbers are always passed in hexadecimal. Negative
35065 numbers have an explicit minus sign (i.e.@: two's complement is not
35066 used). Strings (e.g.@: filenames) are encoded as a series of
35067 hexadecimal bytes. The last argument to a system call may be a
35068 buffer of escaped binary data (@pxref{Binary Data}).
35072 The valid responses to Host I/O packets are:
35076 @item F @var{result} [, @var{errno}] [; @var{attachment}]
35077 @var{result} is the integer value returned by this operation, usually
35078 non-negative for success and -1 for errors. If an error has occured,
35079 @var{errno} will be included in the result. @var{errno} will have a
35080 value defined by the File-I/O protocol (@pxref{Errno Values}). For
35081 operations which return data, @var{attachment} supplies the data as a
35082 binary buffer. Binary buffers in response packets are escaped in the
35083 normal way (@pxref{Binary Data}). See the individual packet
35084 documentation for the interpretation of @var{result} and
35088 An empty response indicates that this operation is not recognized.
35092 These are the supported Host I/O operations:
35095 @item vFile:open: @var{pathname}, @var{flags}, @var{mode}
35096 Open a file at @var{pathname} and return a file descriptor for it, or
35097 return -1 if an error occurs. @var{pathname} is a string,
35098 @var{flags} is an integer indicating a mask of open flags
35099 (@pxref{Open Flags}), and @var{mode} is an integer indicating a mask
35100 of mode bits to use if the file is created (@pxref{mode_t Values}).
35101 @xref{open}, for details of the open flags and mode values.
35103 @item vFile:close: @var{fd}
35104 Close the open file corresponding to @var{fd} and return 0, or
35105 -1 if an error occurs.
35107 @item vFile:pread: @var{fd}, @var{count}, @var{offset}
35108 Read data from the open file corresponding to @var{fd}. Up to
35109 @var{count} bytes will be read from the file, starting at @var{offset}
35110 relative to the start of the file. The target may read fewer bytes;
35111 common reasons include packet size limits and an end-of-file
35112 condition. The number of bytes read is returned. Zero should only be
35113 returned for a successful read at the end of the file, or if
35114 @var{count} was zero.
35116 The data read should be returned as a binary attachment on success.
35117 If zero bytes were read, the response should include an empty binary
35118 attachment (i.e.@: a trailing semicolon). The return value is the
35119 number of target bytes read; the binary attachment may be longer if
35120 some characters were escaped.
35122 @item vFile:pwrite: @var{fd}, @var{offset}, @var{data}
35123 Write @var{data} (a binary buffer) to the open file corresponding
35124 to @var{fd}. Start the write at @var{offset} from the start of the
35125 file. Unlike many @code{write} system calls, there is no
35126 separate @var{count} argument; the length of @var{data} in the
35127 packet is used. @samp{vFile:write} returns the number of bytes written,
35128 which may be shorter than the length of @var{data}, or -1 if an
35131 @item vFile:unlink: @var{pathname}
35132 Delete the file at @var{pathname} on the target. Return 0,
35133 or -1 if an error occurs. @var{pathname} is a string.
35138 @section Interrupts
35139 @cindex interrupts (remote protocol)
35141 When a program on the remote target is running, @value{GDBN} may
35142 attempt to interrupt it by sending a @samp{Ctrl-C}, @code{BREAK} or
35143 a @code{BREAK} followed by @code{g},
35144 control of which is specified via @value{GDBN}'s @samp{interrupt-sequence}.
35146 The precise meaning of @code{BREAK} is defined by the transport
35147 mechanism and may, in fact, be undefined. @value{GDBN} does not
35148 currently define a @code{BREAK} mechanism for any of the network
35149 interfaces except for TCP, in which case @value{GDBN} sends the
35150 @code{telnet} BREAK sequence.
35152 @samp{Ctrl-C}, on the other hand, is defined and implemented for all
35153 transport mechanisms. It is represented by sending the single byte
35154 @code{0x03} without any of the usual packet overhead described in
35155 the Overview section (@pxref{Overview}). When a @code{0x03} byte is
35156 transmitted as part of a packet, it is considered to be packet data
35157 and does @emph{not} represent an interrupt. E.g., an @samp{X} packet
35158 (@pxref{X packet}), used for binary downloads, may include an unescaped
35159 @code{0x03} as part of its packet.
35161 @code{BREAK} followed by @code{g} is also known as Magic SysRq g.
35162 When Linux kernel receives this sequence from serial port,
35163 it stops execution and connects to gdb.
35165 Stubs are not required to recognize these interrupt mechanisms and the
35166 precise meaning associated with receipt of the interrupt is
35167 implementation defined. If the target supports debugging of multiple
35168 threads and/or processes, it should attempt to interrupt all
35169 currently-executing threads and processes.
35170 If the stub is successful at interrupting the
35171 running program, it should send one of the stop
35172 reply packets (@pxref{Stop Reply Packets}) to @value{GDBN} as a result
35173 of successfully stopping the program in all-stop mode, and a stop reply
35174 for each stopped thread in non-stop mode.
35175 Interrupts received while the
35176 program is stopped are discarded.
35178 @node Notification Packets
35179 @section Notification Packets
35180 @cindex notification packets
35181 @cindex packets, notification
35183 The @value{GDBN} remote serial protocol includes @dfn{notifications},
35184 packets that require no acknowledgment. Both the GDB and the stub
35185 may send notifications (although the only notifications defined at
35186 present are sent by the stub). Notifications carry information
35187 without incurring the round-trip latency of an acknowledgment, and so
35188 are useful for low-impact communications where occasional packet loss
35191 A notification packet has the form @samp{% @var{data} #
35192 @var{checksum}}, where @var{data} is the content of the notification,
35193 and @var{checksum} is a checksum of @var{data}, computed and formatted
35194 as for ordinary @value{GDBN} packets. A notification's @var{data}
35195 never contains @samp{$}, @samp{%} or @samp{#} characters. Upon
35196 receiving a notification, the recipient sends no @samp{+} or @samp{-}
35197 to acknowledge the notification's receipt or to report its corruption.
35199 Every notification's @var{data} begins with a name, which contains no
35200 colon characters, followed by a colon character.
35202 Recipients should silently ignore corrupted notifications and
35203 notifications they do not understand. Recipients should restart
35204 timeout periods on receipt of a well-formed notification, whether or
35205 not they understand it.
35207 Senders should only send the notifications described here when this
35208 protocol description specifies that they are permitted. In the
35209 future, we may extend the protocol to permit existing notifications in
35210 new contexts; this rule helps older senders avoid confusing newer
35213 (Older versions of @value{GDBN} ignore bytes received until they see
35214 the @samp{$} byte that begins an ordinary packet, so new stubs may
35215 transmit notifications without fear of confusing older clients. There
35216 are no notifications defined for @value{GDBN} to send at the moment, but we
35217 assume that most older stubs would ignore them, as well.)
35219 The following notification packets from the stub to @value{GDBN} are
35223 @item Stop: @var{reply}
35224 Report an asynchronous stop event in non-stop mode.
35225 The @var{reply} has the form of a stop reply, as
35226 described in @ref{Stop Reply Packets}. Refer to @ref{Remote Non-Stop},
35227 for information on how these notifications are acknowledged by
35231 @node Remote Non-Stop
35232 @section Remote Protocol Support for Non-Stop Mode
35234 @value{GDBN}'s remote protocol supports non-stop debugging of
35235 multi-threaded programs, as described in @ref{Non-Stop Mode}. If the stub
35236 supports non-stop mode, it should report that to @value{GDBN} by including
35237 @samp{QNonStop+} in its @samp{qSupported} response (@pxref{qSupported}).
35239 @value{GDBN} typically sends a @samp{QNonStop} packet only when
35240 establishing a new connection with the stub. Entering non-stop mode
35241 does not alter the state of any currently-running threads, but targets
35242 must stop all threads in any already-attached processes when entering
35243 all-stop mode. @value{GDBN} uses the @samp{?} packet as necessary to
35244 probe the target state after a mode change.
35246 In non-stop mode, when an attached process encounters an event that
35247 would otherwise be reported with a stop reply, it uses the
35248 asynchronous notification mechanism (@pxref{Notification Packets}) to
35249 inform @value{GDBN}. In contrast to all-stop mode, where all threads
35250 in all processes are stopped when a stop reply is sent, in non-stop
35251 mode only the thread reporting the stop event is stopped. That is,
35252 when reporting a @samp{S} or @samp{T} response to indicate completion
35253 of a step operation, hitting a breakpoint, or a fault, only the
35254 affected thread is stopped; any other still-running threads continue
35255 to run. When reporting a @samp{W} or @samp{X} response, all running
35256 threads belonging to other attached processes continue to run.
35258 Only one stop reply notification at a time may be pending; if
35259 additional stop events occur before @value{GDBN} has acknowledged the
35260 previous notification, they must be queued by the stub for later
35261 synchronous transmission in response to @samp{vStopped} packets from
35262 @value{GDBN}. Because the notification mechanism is unreliable,
35263 the stub is permitted to resend a stop reply notification
35264 if it believes @value{GDBN} may not have received it. @value{GDBN}
35265 ignores additional stop reply notifications received before it has
35266 finished processing a previous notification and the stub has completed
35267 sending any queued stop events.
35269 Otherwise, @value{GDBN} must be prepared to receive a stop reply
35270 notification at any time. Specifically, they may appear when
35271 @value{GDBN} is not otherwise reading input from the stub, or when
35272 @value{GDBN} is expecting to read a normal synchronous response or a
35273 @samp{+}/@samp{-} acknowledgment to a packet it has sent.
35274 Notification packets are distinct from any other communication from
35275 the stub so there is no ambiguity.
35277 After receiving a stop reply notification, @value{GDBN} shall
35278 acknowledge it by sending a @samp{vStopped} packet (@pxref{vStopped packet})
35279 as a regular, synchronous request to the stub. Such acknowledgment
35280 is not required to happen immediately, as @value{GDBN} is permitted to
35281 send other, unrelated packets to the stub first, which the stub should
35284 Upon receiving a @samp{vStopped} packet, if the stub has other queued
35285 stop events to report to @value{GDBN}, it shall respond by sending a
35286 normal stop reply response. @value{GDBN} shall then send another
35287 @samp{vStopped} packet to solicit further responses; again, it is
35288 permitted to send other, unrelated packets as well which the stub
35289 should process normally.
35291 If the stub receives a @samp{vStopped} packet and there are no
35292 additional stop events to report, the stub shall return an @samp{OK}
35293 response. At this point, if further stop events occur, the stub shall
35294 send a new stop reply notification, @value{GDBN} shall accept the
35295 notification, and the process shall be repeated.
35297 In non-stop mode, the target shall respond to the @samp{?} packet as
35298 follows. First, any incomplete stop reply notification/@samp{vStopped}
35299 sequence in progress is abandoned. The target must begin a new
35300 sequence reporting stop events for all stopped threads, whether or not
35301 it has previously reported those events to @value{GDBN}. The first
35302 stop reply is sent as a synchronous reply to the @samp{?} packet, and
35303 subsequent stop replies are sent as responses to @samp{vStopped} packets
35304 using the mechanism described above. The target must not send
35305 asynchronous stop reply notifications until the sequence is complete.
35306 If all threads are running when the target receives the @samp{?} packet,
35307 or if the target is not attached to any process, it shall respond
35310 @node Packet Acknowledgment
35311 @section Packet Acknowledgment
35313 @cindex acknowledgment, for @value{GDBN} remote
35314 @cindex packet acknowledgment, for @value{GDBN} remote
35315 By default, when either the host or the target machine receives a packet,
35316 the first response expected is an acknowledgment: either @samp{+} (to indicate
35317 the package was received correctly) or @samp{-} (to request retransmission).
35318 This mechanism allows the @value{GDBN} remote protocol to operate over
35319 unreliable transport mechanisms, such as a serial line.
35321 In cases where the transport mechanism is itself reliable (such as a pipe or
35322 TCP connection), the @samp{+}/@samp{-} acknowledgments are redundant.
35323 It may be desirable to disable them in that case to reduce communication
35324 overhead, or for other reasons. This can be accomplished by means of the
35325 @samp{QStartNoAckMode} packet; @pxref{QStartNoAckMode}.
35327 When in no-acknowledgment mode, neither the stub nor @value{GDBN} shall send or
35328 expect @samp{+}/@samp{-} protocol acknowledgments. The packet
35329 and response format still includes the normal checksum, as described in
35330 @ref{Overview}, but the checksum may be ignored by the receiver.
35332 If the stub supports @samp{QStartNoAckMode} and prefers to operate in
35333 no-acknowledgment mode, it should report that to @value{GDBN}
35334 by including @samp{QStartNoAckMode+} in its response to @samp{qSupported};
35335 @pxref{qSupported}.
35336 If @value{GDBN} also supports @samp{QStartNoAckMode} and it has not been
35337 disabled via the @code{set remote noack-packet off} command
35338 (@pxref{Remote Configuration}),
35339 @value{GDBN} may then send a @samp{QStartNoAckMode} packet to the stub.
35340 Only then may the stub actually turn off packet acknowledgments.
35341 @value{GDBN} sends a final @samp{+} acknowledgment of the stub's @samp{OK}
35342 response, which can be safely ignored by the stub.
35344 Note that @code{set remote noack-packet} command only affects negotiation
35345 between @value{GDBN} and the stub when subsequent connections are made;
35346 it does not affect the protocol acknowledgment state for any current
35348 Since @samp{+}/@samp{-} acknowledgments are enabled by default when a
35349 new connection is established,
35350 there is also no protocol request to re-enable the acknowledgments
35351 for the current connection, once disabled.
35356 Example sequence of a target being re-started. Notice how the restart
35357 does not get any direct output:
35362 @emph{target restarts}
35365 <- @code{T001:1234123412341234}
35369 Example sequence of a target being stepped by a single instruction:
35372 -> @code{G1445@dots{}}
35377 <- @code{T001:1234123412341234}
35381 <- @code{1455@dots{}}
35385 @node File-I/O Remote Protocol Extension
35386 @section File-I/O Remote Protocol Extension
35387 @cindex File-I/O remote protocol extension
35390 * File-I/O Overview::
35391 * Protocol Basics::
35392 * The F Request Packet::
35393 * The F Reply Packet::
35394 * The Ctrl-C Message::
35396 * List of Supported Calls::
35397 * Protocol-specific Representation of Datatypes::
35399 * File-I/O Examples::
35402 @node File-I/O Overview
35403 @subsection File-I/O Overview
35404 @cindex file-i/o overview
35406 The @dfn{File I/O remote protocol extension} (short: File-I/O) allows the
35407 target to use the host's file system and console I/O to perform various
35408 system calls. System calls on the target system are translated into a
35409 remote protocol packet to the host system, which then performs the needed
35410 actions and returns a response packet to the target system.
35411 This simulates file system operations even on targets that lack file systems.
35413 The protocol is defined to be independent of both the host and target systems.
35414 It uses its own internal representation of datatypes and values. Both
35415 @value{GDBN} and the target's @value{GDBN} stub are responsible for
35416 translating the system-dependent value representations into the internal
35417 protocol representations when data is transmitted.
35419 The communication is synchronous. A system call is possible only when
35420 @value{GDBN} is waiting for a response from the @samp{C}, @samp{c}, @samp{S}
35421 or @samp{s} packets. While @value{GDBN} handles the request for a system call,
35422 the target is stopped to allow deterministic access to the target's
35423 memory. Therefore File-I/O is not interruptible by target signals. On
35424 the other hand, it is possible to interrupt File-I/O by a user interrupt
35425 (@samp{Ctrl-C}) within @value{GDBN}.
35427 The target's request to perform a host system call does not finish
35428 the latest @samp{C}, @samp{c}, @samp{S} or @samp{s} action. That means,
35429 after finishing the system call, the target returns to continuing the
35430 previous activity (continue, step). No additional continue or step
35431 request from @value{GDBN} is required.
35434 (@value{GDBP}) continue
35435 <- target requests 'system call X'
35436 target is stopped, @value{GDBN} executes system call
35437 -> @value{GDBN} returns result
35438 ... target continues, @value{GDBN} returns to wait for the target
35439 <- target hits breakpoint and sends a Txx packet
35442 The protocol only supports I/O on the console and to regular files on
35443 the host file system. Character or block special devices, pipes,
35444 named pipes, sockets or any other communication method on the host
35445 system are not supported by this protocol.
35447 File I/O is not supported in non-stop mode.
35449 @node Protocol Basics
35450 @subsection Protocol Basics
35451 @cindex protocol basics, file-i/o
35453 The File-I/O protocol uses the @code{F} packet as the request as well
35454 as reply packet. Since a File-I/O system call can only occur when
35455 @value{GDBN} is waiting for a response from the continuing or stepping target,
35456 the File-I/O request is a reply that @value{GDBN} has to expect as a result
35457 of a previous @samp{C}, @samp{c}, @samp{S} or @samp{s} packet.
35458 This @code{F} packet contains all information needed to allow @value{GDBN}
35459 to call the appropriate host system call:
35463 A unique identifier for the requested system call.
35466 All parameters to the system call. Pointers are given as addresses
35467 in the target memory address space. Pointers to strings are given as
35468 pointer/length pair. Numerical values are given as they are.
35469 Numerical control flags are given in a protocol-specific representation.
35473 At this point, @value{GDBN} has to perform the following actions.
35477 If the parameters include pointer values to data needed as input to a
35478 system call, @value{GDBN} requests this data from the target with a
35479 standard @code{m} packet request. This additional communication has to be
35480 expected by the target implementation and is handled as any other @code{m}
35484 @value{GDBN} translates all value from protocol representation to host
35485 representation as needed. Datatypes are coerced into the host types.
35488 @value{GDBN} calls the system call.
35491 It then coerces datatypes back to protocol representation.
35494 If the system call is expected to return data in buffer space specified
35495 by pointer parameters to the call, the data is transmitted to the
35496 target using a @code{M} or @code{X} packet. This packet has to be expected
35497 by the target implementation and is handled as any other @code{M} or @code{X}
35502 Eventually @value{GDBN} replies with another @code{F} packet which contains all
35503 necessary information for the target to continue. This at least contains
35510 @code{errno}, if has been changed by the system call.
35517 After having done the needed type and value coercion, the target continues
35518 the latest continue or step action.
35520 @node The F Request Packet
35521 @subsection The @code{F} Request Packet
35522 @cindex file-i/o request packet
35523 @cindex @code{F} request packet
35525 The @code{F} request packet has the following format:
35528 @item F@var{call-id},@var{parameter@dots{}}
35530 @var{call-id} is the identifier to indicate the host system call to be called.
35531 This is just the name of the function.
35533 @var{parameter@dots{}} are the parameters to the system call.
35534 Parameters are hexadecimal integer values, either the actual values in case
35535 of scalar datatypes, pointers to target buffer space in case of compound
35536 datatypes and unspecified memory areas, or pointer/length pairs in case
35537 of string parameters. These are appended to the @var{call-id} as a
35538 comma-delimited list. All values are transmitted in ASCII
35539 string representation, pointer/length pairs separated by a slash.
35545 @node The F Reply Packet
35546 @subsection The @code{F} Reply Packet
35547 @cindex file-i/o reply packet
35548 @cindex @code{F} reply packet
35550 The @code{F} reply packet has the following format:
35554 @item F@var{retcode},@var{errno},@var{Ctrl-C flag};@var{call-specific attachment}
35556 @var{retcode} is the return code of the system call as hexadecimal value.
35558 @var{errno} is the @code{errno} set by the call, in protocol-specific
35560 This parameter can be omitted if the call was successful.
35562 @var{Ctrl-C flag} is only sent if the user requested a break. In this
35563 case, @var{errno} must be sent as well, even if the call was successful.
35564 The @var{Ctrl-C flag} itself consists of the character @samp{C}:
35571 or, if the call was interrupted before the host call has been performed:
35578 assuming 4 is the protocol-specific representation of @code{EINTR}.
35583 @node The Ctrl-C Message
35584 @subsection The @samp{Ctrl-C} Message
35585 @cindex ctrl-c message, in file-i/o protocol
35587 If the @samp{Ctrl-C} flag is set in the @value{GDBN}
35588 reply packet (@pxref{The F Reply Packet}),
35589 the target should behave as if it had
35590 gotten a break message. The meaning for the target is ``system call
35591 interrupted by @code{SIGINT}''. Consequentially, the target should actually stop
35592 (as with a break message) and return to @value{GDBN} with a @code{T02}
35595 It's important for the target to know in which
35596 state the system call was interrupted. There are two possible cases:
35600 The system call hasn't been performed on the host yet.
35603 The system call on the host has been finished.
35607 These two states can be distinguished by the target by the value of the
35608 returned @code{errno}. If it's the protocol representation of @code{EINTR}, the system
35609 call hasn't been performed. This is equivalent to the @code{EINTR} handling
35610 on POSIX systems. In any other case, the target may presume that the
35611 system call has been finished --- successfully or not --- and should behave
35612 as if the break message arrived right after the system call.
35614 @value{GDBN} must behave reliably. If the system call has not been called
35615 yet, @value{GDBN} may send the @code{F} reply immediately, setting @code{EINTR} as
35616 @code{errno} in the packet. If the system call on the host has been finished
35617 before the user requests a break, the full action must be finished by
35618 @value{GDBN}. This requires sending @code{M} or @code{X} packets as necessary.
35619 The @code{F} packet may only be sent when either nothing has happened
35620 or the full action has been completed.
35623 @subsection Console I/O
35624 @cindex console i/o as part of file-i/o
35626 By default and if not explicitly closed by the target system, the file
35627 descriptors 0, 1 and 2 are connected to the @value{GDBN} console. Output
35628 on the @value{GDBN} console is handled as any other file output operation
35629 (@code{write(1, @dots{})} or @code{write(2, @dots{})}). Console input is handled
35630 by @value{GDBN} so that after the target read request from file descriptor
35631 0 all following typing is buffered until either one of the following
35636 The user types @kbd{Ctrl-c}. The behaviour is as explained above, and the
35638 system call is treated as finished.
35641 The user presses @key{RET}. This is treated as end of input with a trailing
35645 The user types @kbd{Ctrl-d}. This is treated as end of input. No trailing
35646 character (neither newline nor @samp{Ctrl-D}) is appended to the input.
35650 If the user has typed more characters than fit in the buffer given to
35651 the @code{read} call, the trailing characters are buffered in @value{GDBN} until
35652 either another @code{read(0, @dots{})} is requested by the target, or debugging
35653 is stopped at the user's request.
35656 @node List of Supported Calls
35657 @subsection List of Supported Calls
35658 @cindex list of supported file-i/o calls
35675 @unnumberedsubsubsec open
35676 @cindex open, file-i/o system call
35681 int open(const char *pathname, int flags);
35682 int open(const char *pathname, int flags, mode_t mode);
35686 @samp{Fopen,@var{pathptr}/@var{len},@var{flags},@var{mode}}
35689 @var{flags} is the bitwise @code{OR} of the following values:
35693 If the file does not exist it will be created. The host
35694 rules apply as far as file ownership and time stamps
35698 When used with @code{O_CREAT}, if the file already exists it is
35699 an error and open() fails.
35702 If the file already exists and the open mode allows
35703 writing (@code{O_RDWR} or @code{O_WRONLY} is given) it will be
35704 truncated to zero length.
35707 The file is opened in append mode.
35710 The file is opened for reading only.
35713 The file is opened for writing only.
35716 The file is opened for reading and writing.
35720 Other bits are silently ignored.
35724 @var{mode} is the bitwise @code{OR} of the following values:
35728 User has read permission.
35731 User has write permission.
35734 Group has read permission.
35737 Group has write permission.
35740 Others have read permission.
35743 Others have write permission.
35747 Other bits are silently ignored.
35750 @item Return value:
35751 @code{open} returns the new file descriptor or -1 if an error
35758 @var{pathname} already exists and @code{O_CREAT} and @code{O_EXCL} were used.
35761 @var{pathname} refers to a directory.
35764 The requested access is not allowed.
35767 @var{pathname} was too long.
35770 A directory component in @var{pathname} does not exist.
35773 @var{pathname} refers to a device, pipe, named pipe or socket.
35776 @var{pathname} refers to a file on a read-only filesystem and
35777 write access was requested.
35780 @var{pathname} is an invalid pointer value.
35783 No space on device to create the file.
35786 The process already has the maximum number of files open.
35789 The limit on the total number of files open on the system
35793 The call was interrupted by the user.
35799 @unnumberedsubsubsec close
35800 @cindex close, file-i/o system call
35809 @samp{Fclose,@var{fd}}
35811 @item Return value:
35812 @code{close} returns zero on success, or -1 if an error occurred.
35818 @var{fd} isn't a valid open file descriptor.
35821 The call was interrupted by the user.
35827 @unnumberedsubsubsec read
35828 @cindex read, file-i/o system call
35833 int read(int fd, void *buf, unsigned int count);
35837 @samp{Fread,@var{fd},@var{bufptr},@var{count}}
35839 @item Return value:
35840 On success, the number of bytes read is returned.
35841 Zero indicates end of file. If count is zero, read
35842 returns zero as well. On error, -1 is returned.
35848 @var{fd} is not a valid file descriptor or is not open for
35852 @var{bufptr} is an invalid pointer value.
35855 The call was interrupted by the user.
35861 @unnumberedsubsubsec write
35862 @cindex write, file-i/o system call
35867 int write(int fd, const void *buf, unsigned int count);
35871 @samp{Fwrite,@var{fd},@var{bufptr},@var{count}}
35873 @item Return value:
35874 On success, the number of bytes written are returned.
35875 Zero indicates nothing was written. On error, -1
35882 @var{fd} is not a valid file descriptor or is not open for
35886 @var{bufptr} is an invalid pointer value.
35889 An attempt was made to write a file that exceeds the
35890 host-specific maximum file size allowed.
35893 No space on device to write the data.
35896 The call was interrupted by the user.
35902 @unnumberedsubsubsec lseek
35903 @cindex lseek, file-i/o system call
35908 long lseek (int fd, long offset, int flag);
35912 @samp{Flseek,@var{fd},@var{offset},@var{flag}}
35914 @var{flag} is one of:
35918 The offset is set to @var{offset} bytes.
35921 The offset is set to its current location plus @var{offset}
35925 The offset is set to the size of the file plus @var{offset}
35929 @item Return value:
35930 On success, the resulting unsigned offset in bytes from
35931 the beginning of the file is returned. Otherwise, a
35932 value of -1 is returned.
35938 @var{fd} is not a valid open file descriptor.
35941 @var{fd} is associated with the @value{GDBN} console.
35944 @var{flag} is not a proper value.
35947 The call was interrupted by the user.
35953 @unnumberedsubsubsec rename
35954 @cindex rename, file-i/o system call
35959 int rename(const char *oldpath, const char *newpath);
35963 @samp{Frename,@var{oldpathptr}/@var{len},@var{newpathptr}/@var{len}}
35965 @item Return value:
35966 On success, zero is returned. On error, -1 is returned.
35972 @var{newpath} is an existing directory, but @var{oldpath} is not a
35976 @var{newpath} is a non-empty directory.
35979 @var{oldpath} or @var{newpath} is a directory that is in use by some
35983 An attempt was made to make a directory a subdirectory
35987 A component used as a directory in @var{oldpath} or new
35988 path is not a directory. Or @var{oldpath} is a directory
35989 and @var{newpath} exists but is not a directory.
35992 @var{oldpathptr} or @var{newpathptr} are invalid pointer values.
35995 No access to the file or the path of the file.
35999 @var{oldpath} or @var{newpath} was too long.
36002 A directory component in @var{oldpath} or @var{newpath} does not exist.
36005 The file is on a read-only filesystem.
36008 The device containing the file has no room for the new
36012 The call was interrupted by the user.
36018 @unnumberedsubsubsec unlink
36019 @cindex unlink, file-i/o system call
36024 int unlink(const char *pathname);
36028 @samp{Funlink,@var{pathnameptr}/@var{len}}
36030 @item Return value:
36031 On success, zero is returned. On error, -1 is returned.
36037 No access to the file or the path of the file.
36040 The system does not allow unlinking of directories.
36043 The file @var{pathname} cannot be unlinked because it's
36044 being used by another process.
36047 @var{pathnameptr} is an invalid pointer value.
36050 @var{pathname} was too long.
36053 A directory component in @var{pathname} does not exist.
36056 A component of the path is not a directory.
36059 The file is on a read-only filesystem.
36062 The call was interrupted by the user.
36068 @unnumberedsubsubsec stat/fstat
36069 @cindex fstat, file-i/o system call
36070 @cindex stat, file-i/o system call
36075 int stat(const char *pathname, struct stat *buf);
36076 int fstat(int fd, struct stat *buf);
36080 @samp{Fstat,@var{pathnameptr}/@var{len},@var{bufptr}}@*
36081 @samp{Ffstat,@var{fd},@var{bufptr}}
36083 @item Return value:
36084 On success, zero is returned. On error, -1 is returned.
36090 @var{fd} is not a valid open file.
36093 A directory component in @var{pathname} does not exist or the
36094 path is an empty string.
36097 A component of the path is not a directory.
36100 @var{pathnameptr} is an invalid pointer value.
36103 No access to the file or the path of the file.
36106 @var{pathname} was too long.
36109 The call was interrupted by the user.
36115 @unnumberedsubsubsec gettimeofday
36116 @cindex gettimeofday, file-i/o system call
36121 int gettimeofday(struct timeval *tv, void *tz);
36125 @samp{Fgettimeofday,@var{tvptr},@var{tzptr}}
36127 @item Return value:
36128 On success, 0 is returned, -1 otherwise.
36134 @var{tz} is a non-NULL pointer.
36137 @var{tvptr} and/or @var{tzptr} is an invalid pointer value.
36143 @unnumberedsubsubsec isatty
36144 @cindex isatty, file-i/o system call
36149 int isatty(int fd);
36153 @samp{Fisatty,@var{fd}}
36155 @item Return value:
36156 Returns 1 if @var{fd} refers to the @value{GDBN} console, 0 otherwise.
36162 The call was interrupted by the user.
36167 Note that the @code{isatty} call is treated as a special case: it returns
36168 1 to the target if the file descriptor is attached
36169 to the @value{GDBN} console, 0 otherwise. Implementing through system calls
36170 would require implementing @code{ioctl} and would be more complex than
36175 @unnumberedsubsubsec system
36176 @cindex system, file-i/o system call
36181 int system(const char *command);
36185 @samp{Fsystem,@var{commandptr}/@var{len}}
36187 @item Return value:
36188 If @var{len} is zero, the return value indicates whether a shell is
36189 available. A zero return value indicates a shell is not available.
36190 For non-zero @var{len}, the value returned is -1 on error and the
36191 return status of the command otherwise. Only the exit status of the
36192 command is returned, which is extracted from the host's @code{system}
36193 return value by calling @code{WEXITSTATUS(retval)}. In case
36194 @file{/bin/sh} could not be executed, 127 is returned.
36200 The call was interrupted by the user.
36205 @value{GDBN} takes over the full task of calling the necessary host calls
36206 to perform the @code{system} call. The return value of @code{system} on
36207 the host is simplified before it's returned
36208 to the target. Any termination signal information from the child process
36209 is discarded, and the return value consists
36210 entirely of the exit status of the called command.
36212 Due to security concerns, the @code{system} call is by default refused
36213 by @value{GDBN}. The user has to allow this call explicitly with the
36214 @code{set remote system-call-allowed 1} command.
36217 @item set remote system-call-allowed
36218 @kindex set remote system-call-allowed
36219 Control whether to allow the @code{system} calls in the File I/O
36220 protocol for the remote target. The default is zero (disabled).
36222 @item show remote system-call-allowed
36223 @kindex show remote system-call-allowed
36224 Show whether the @code{system} calls are allowed in the File I/O
36228 @node Protocol-specific Representation of Datatypes
36229 @subsection Protocol-specific Representation of Datatypes
36230 @cindex protocol-specific representation of datatypes, in file-i/o protocol
36233 * Integral Datatypes::
36235 * Memory Transfer::
36240 @node Integral Datatypes
36241 @unnumberedsubsubsec Integral Datatypes
36242 @cindex integral datatypes, in file-i/o protocol
36244 The integral datatypes used in the system calls are @code{int},
36245 @code{unsigned int}, @code{long}, @code{unsigned long},
36246 @code{mode_t}, and @code{time_t}.
36248 @code{int}, @code{unsigned int}, @code{mode_t} and @code{time_t} are
36249 implemented as 32 bit values in this protocol.
36251 @code{long} and @code{unsigned long} are implemented as 64 bit types.
36253 @xref{Limits}, for corresponding MIN and MAX values (similar to those
36254 in @file{limits.h}) to allow range checking on host and target.
36256 @code{time_t} datatypes are defined as seconds since the Epoch.
36258 All integral datatypes transferred as part of a memory read or write of a
36259 structured datatype e.g.@: a @code{struct stat} have to be given in big endian
36262 @node Pointer Values
36263 @unnumberedsubsubsec Pointer Values
36264 @cindex pointer values, in file-i/o protocol
36266 Pointers to target data are transmitted as they are. An exception
36267 is made for pointers to buffers for which the length isn't
36268 transmitted as part of the function call, namely strings. Strings
36269 are transmitted as a pointer/length pair, both as hex values, e.g.@:
36276 which is a pointer to data of length 18 bytes at position 0x1aaf.
36277 The length is defined as the full string length in bytes, including
36278 the trailing null byte. For example, the string @code{"hello world"}
36279 at address 0x123456 is transmitted as
36285 @node Memory Transfer
36286 @unnumberedsubsubsec Memory Transfer
36287 @cindex memory transfer, in file-i/o protocol
36289 Structured data which is transferred using a memory read or write (for
36290 example, a @code{struct stat}) is expected to be in a protocol-specific format
36291 with all scalar multibyte datatypes being big endian. Translation to
36292 this representation needs to be done both by the target before the @code{F}
36293 packet is sent, and by @value{GDBN} before
36294 it transfers memory to the target. Transferred pointers to structured
36295 data should point to the already-coerced data at any time.
36299 @unnumberedsubsubsec struct stat
36300 @cindex struct stat, in file-i/o protocol
36302 The buffer of type @code{struct stat} used by the target and @value{GDBN}
36303 is defined as follows:
36307 unsigned int st_dev; /* device */
36308 unsigned int st_ino; /* inode */
36309 mode_t st_mode; /* protection */
36310 unsigned int st_nlink; /* number of hard links */
36311 unsigned int st_uid; /* user ID of owner */
36312 unsigned int st_gid; /* group ID of owner */
36313 unsigned int st_rdev; /* device type (if inode device) */
36314 unsigned long st_size; /* total size, in bytes */
36315 unsigned long st_blksize; /* blocksize for filesystem I/O */
36316 unsigned long st_blocks; /* number of blocks allocated */
36317 time_t st_atime; /* time of last access */
36318 time_t st_mtime; /* time of last modification */
36319 time_t st_ctime; /* time of last change */
36323 The integral datatypes conform to the definitions given in the
36324 appropriate section (see @ref{Integral Datatypes}, for details) so this
36325 structure is of size 64 bytes.
36327 The values of several fields have a restricted meaning and/or
36333 A value of 0 represents a file, 1 the console.
36336 No valid meaning for the target. Transmitted unchanged.
36339 Valid mode bits are described in @ref{Constants}. Any other
36340 bits have currently no meaning for the target.
36345 No valid meaning for the target. Transmitted unchanged.
36350 These values have a host and file system dependent
36351 accuracy. Especially on Windows hosts, the file system may not
36352 support exact timing values.
36355 The target gets a @code{struct stat} of the above representation and is
36356 responsible for coercing it to the target representation before
36359 Note that due to size differences between the host, target, and protocol
36360 representations of @code{struct stat} members, these members could eventually
36361 get truncated on the target.
36363 @node struct timeval
36364 @unnumberedsubsubsec struct timeval
36365 @cindex struct timeval, in file-i/o protocol
36367 The buffer of type @code{struct timeval} used by the File-I/O protocol
36368 is defined as follows:
36372 time_t tv_sec; /* second */
36373 long tv_usec; /* microsecond */
36377 The integral datatypes conform to the definitions given in the
36378 appropriate section (see @ref{Integral Datatypes}, for details) so this
36379 structure is of size 8 bytes.
36382 @subsection Constants
36383 @cindex constants, in file-i/o protocol
36385 The following values are used for the constants inside of the
36386 protocol. @value{GDBN} and target are responsible for translating these
36387 values before and after the call as needed.
36398 @unnumberedsubsubsec Open Flags
36399 @cindex open flags, in file-i/o protocol
36401 All values are given in hexadecimal representation.
36413 @node mode_t Values
36414 @unnumberedsubsubsec mode_t Values
36415 @cindex mode_t values, in file-i/o protocol
36417 All values are given in octal representation.
36434 @unnumberedsubsubsec Errno Values
36435 @cindex errno values, in file-i/o protocol
36437 All values are given in decimal representation.
36462 @code{EUNKNOWN} is used as a fallback error value if a host system returns
36463 any error value not in the list of supported error numbers.
36466 @unnumberedsubsubsec Lseek Flags
36467 @cindex lseek flags, in file-i/o protocol
36476 @unnumberedsubsubsec Limits
36477 @cindex limits, in file-i/o protocol
36479 All values are given in decimal representation.
36482 INT_MIN -2147483648
36484 UINT_MAX 4294967295
36485 LONG_MIN -9223372036854775808
36486 LONG_MAX 9223372036854775807
36487 ULONG_MAX 18446744073709551615
36490 @node File-I/O Examples
36491 @subsection File-I/O Examples
36492 @cindex file-i/o examples
36494 Example sequence of a write call, file descriptor 3, buffer is at target
36495 address 0x1234, 6 bytes should be written:
36498 <- @code{Fwrite,3,1234,6}
36499 @emph{request memory read from target}
36502 @emph{return "6 bytes written"}
36506 Example sequence of a read call, file descriptor 3, buffer is at target
36507 address 0x1234, 6 bytes should be read:
36510 <- @code{Fread,3,1234,6}
36511 @emph{request memory write to target}
36512 -> @code{X1234,6:XXXXXX}
36513 @emph{return "6 bytes read"}
36517 Example sequence of a read call, call fails on the host due to invalid
36518 file descriptor (@code{EBADF}):
36521 <- @code{Fread,3,1234,6}
36525 Example sequence of a read call, user presses @kbd{Ctrl-c} before syscall on
36529 <- @code{Fread,3,1234,6}
36534 Example sequence of a read call, user presses @kbd{Ctrl-c} after syscall on
36538 <- @code{Fread,3,1234,6}
36539 -> @code{X1234,6:XXXXXX}
36543 @node Library List Format
36544 @section Library List Format
36545 @cindex library list format, remote protocol
36547 On some platforms, a dynamic loader (e.g.@: @file{ld.so}) runs in the
36548 same process as your application to manage libraries. In this case,
36549 @value{GDBN} can use the loader's symbol table and normal memory
36550 operations to maintain a list of shared libraries. On other
36551 platforms, the operating system manages loaded libraries.
36552 @value{GDBN} can not retrieve the list of currently loaded libraries
36553 through memory operations, so it uses the @samp{qXfer:libraries:read}
36554 packet (@pxref{qXfer library list read}) instead. The remote stub
36555 queries the target's operating system and reports which libraries
36558 The @samp{qXfer:libraries:read} packet returns an XML document which
36559 lists loaded libraries and their offsets. Each library has an
36560 associated name and one or more segment or section base addresses,
36561 which report where the library was loaded in memory.
36563 For the common case of libraries that are fully linked binaries, the
36564 library should have a list of segments. If the target supports
36565 dynamic linking of a relocatable object file, its library XML element
36566 should instead include a list of allocated sections. The segment or
36567 section bases are start addresses, not relocation offsets; they do not
36568 depend on the library's link-time base addresses.
36570 @value{GDBN} must be linked with the Expat library to support XML
36571 library lists. @xref{Expat}.
36573 A simple memory map, with one loaded library relocated by a single
36574 offset, looks like this:
36578 <library name="/lib/libc.so.6">
36579 <segment address="0x10000000"/>
36584 Another simple memory map, with one loaded library with three
36585 allocated sections (.text, .data, .bss), looks like this:
36589 <library name="sharedlib.o">
36590 <section address="0x10000000"/>
36591 <section address="0x20000000"/>
36592 <section address="0x30000000"/>
36597 The format of a library list is described by this DTD:
36600 <!-- library-list: Root element with versioning -->
36601 <!ELEMENT library-list (library)*>
36602 <!ATTLIST library-list version CDATA #FIXED "1.0">
36603 <!ELEMENT library (segment*, section*)>
36604 <!ATTLIST library name CDATA #REQUIRED>
36605 <!ELEMENT segment EMPTY>
36606 <!ATTLIST segment address CDATA #REQUIRED>
36607 <!ELEMENT section EMPTY>
36608 <!ATTLIST section address CDATA #REQUIRED>
36611 In addition, segments and section descriptors cannot be mixed within a
36612 single library element, and you must supply at least one segment or
36613 section for each library.
36615 @node Memory Map Format
36616 @section Memory Map Format
36617 @cindex memory map format
36619 To be able to write into flash memory, @value{GDBN} needs to obtain a
36620 memory map from the target. This section describes the format of the
36623 The memory map is obtained using the @samp{qXfer:memory-map:read}
36624 (@pxref{qXfer memory map read}) packet and is an XML document that
36625 lists memory regions.
36627 @value{GDBN} must be linked with the Expat library to support XML
36628 memory maps. @xref{Expat}.
36630 The top-level structure of the document is shown below:
36633 <?xml version="1.0"?>
36634 <!DOCTYPE memory-map
36635 PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN"
36636 "http://sourceware.org/gdb/gdb-memory-map.dtd">
36642 Each region can be either:
36647 A region of RAM starting at @var{addr} and extending for @var{length}
36651 <memory type="ram" start="@var{addr}" length="@var{length}"/>
36656 A region of read-only memory:
36659 <memory type="rom" start="@var{addr}" length="@var{length}"/>
36664 A region of flash memory, with erasure blocks @var{blocksize}
36668 <memory type="flash" start="@var{addr}" length="@var{length}">
36669 <property name="blocksize">@var{blocksize}</property>
36675 Regions must not overlap. @value{GDBN} assumes that areas of memory not covered
36676 by the memory map are RAM, and uses the ordinary @samp{M} and @samp{X}
36677 packets to write to addresses in such ranges.
36679 The formal DTD for memory map format is given below:
36682 <!-- ................................................... -->
36683 <!-- Memory Map XML DTD ................................ -->
36684 <!-- File: memory-map.dtd .............................. -->
36685 <!-- .................................... .............. -->
36686 <!-- memory-map.dtd -->
36687 <!-- memory-map: Root element with versioning -->
36688 <!ELEMENT memory-map (memory | property)>
36689 <!ATTLIST memory-map version CDATA #FIXED "1.0.0">
36690 <!ELEMENT memory (property)>
36691 <!-- memory: Specifies a memory region,
36692 and its type, or device. -->
36693 <!ATTLIST memory type CDATA #REQUIRED
36694 start CDATA #REQUIRED
36695 length CDATA #REQUIRED
36696 device CDATA #IMPLIED>
36697 <!-- property: Generic attribute tag -->
36698 <!ELEMENT property (#PCDATA | property)*>
36699 <!ATTLIST property name CDATA #REQUIRED>
36702 @node Thread List Format
36703 @section Thread List Format
36704 @cindex thread list format
36706 To efficiently update the list of threads and their attributes,
36707 @value{GDBN} issues the @samp{qXfer:threads:read} packet
36708 (@pxref{qXfer threads read}) and obtains the XML document with
36709 the following structure:
36712 <?xml version="1.0"?>
36714 <thread id="id" core="0">
36715 ... description ...
36720 Each @samp{thread} element must have the @samp{id} attribute that
36721 identifies the thread (@pxref{thread-id syntax}). The
36722 @samp{core} attribute, if present, specifies which processor core
36723 the thread was last executing on. The content of the of @samp{thread}
36724 element is interpreted as human-readable auxilliary information.
36726 @node Traceframe Info Format
36727 @section Traceframe Info Format
36728 @cindex traceframe info format
36730 To be able to know which objects in the inferior can be examined when
36731 inspecting a tracepoint hit, @value{GDBN} needs to obtain the list of
36732 memory ranges, registers and trace state variables that have been
36733 collected in a traceframe.
36735 This list is obtained using the @samp{qXfer:traceframe-info:read}
36736 (@pxref{qXfer traceframe info read}) packet and is an XML document.
36738 @value{GDBN} must be linked with the Expat library to support XML
36739 traceframe info discovery. @xref{Expat}.
36741 The top-level structure of the document is shown below:
36744 <?xml version="1.0"?>
36745 <!DOCTYPE traceframe-info
36746 PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN"
36747 "http://sourceware.org/gdb/gdb-traceframe-info.dtd">
36753 Each traceframe block can be either:
36758 A region of collected memory starting at @var{addr} and extending for
36759 @var{length} bytes from there:
36762 <memory start="@var{addr}" length="@var{length}"/>
36767 The formal DTD for the traceframe info format is given below:
36770 <!ELEMENT traceframe-info (memory)* >
36771 <!ATTLIST traceframe-info version CDATA #FIXED "1.0">
36773 <!ELEMENT memory EMPTY>
36774 <!ATTLIST memory start CDATA #REQUIRED
36775 length CDATA #REQUIRED>
36778 @include agentexpr.texi
36780 @node Target Descriptions
36781 @appendix Target Descriptions
36782 @cindex target descriptions
36784 One of the challenges of using @value{GDBN} to debug embedded systems
36785 is that there are so many minor variants of each processor
36786 architecture in use. It is common practice for vendors to start with
36787 a standard processor core --- ARM, PowerPC, or MIPS, for example ---
36788 and then make changes to adapt it to a particular market niche. Some
36789 architectures have hundreds of variants, available from dozens of
36790 vendors. This leads to a number of problems:
36794 With so many different customized processors, it is difficult for
36795 the @value{GDBN} maintainers to keep up with the changes.
36797 Since individual variants may have short lifetimes or limited
36798 audiences, it may not be worthwhile to carry information about every
36799 variant in the @value{GDBN} source tree.
36801 When @value{GDBN} does support the architecture of the embedded system
36802 at hand, the task of finding the correct architecture name to give the
36803 @command{set architecture} command can be error-prone.
36806 To address these problems, the @value{GDBN} remote protocol allows a
36807 target system to not only identify itself to @value{GDBN}, but to
36808 actually describe its own features. This lets @value{GDBN} support
36809 processor variants it has never seen before --- to the extent that the
36810 descriptions are accurate, and that @value{GDBN} understands them.
36812 @value{GDBN} must be linked with the Expat library to support XML
36813 target descriptions. @xref{Expat}.
36816 * Retrieving Descriptions:: How descriptions are fetched from a target.
36817 * Target Description Format:: The contents of a target description.
36818 * Predefined Target Types:: Standard types available for target
36820 * Standard Target Features:: Features @value{GDBN} knows about.
36823 @node Retrieving Descriptions
36824 @section Retrieving Descriptions
36826 Target descriptions can be read from the target automatically, or
36827 specified by the user manually. The default behavior is to read the
36828 description from the target. @value{GDBN} retrieves it via the remote
36829 protocol using @samp{qXfer} requests (@pxref{General Query Packets,
36830 qXfer}). The @var{annex} in the @samp{qXfer} packet will be
36831 @samp{target.xml}. The contents of the @samp{target.xml} annex are an
36832 XML document, of the form described in @ref{Target Description
36835 Alternatively, you can specify a file to read for the target description.
36836 If a file is set, the target will not be queried. The commands to
36837 specify a file are:
36840 @cindex set tdesc filename
36841 @item set tdesc filename @var{path}
36842 Read the target description from @var{path}.
36844 @cindex unset tdesc filename
36845 @item unset tdesc filename
36846 Do not read the XML target description from a file. @value{GDBN}
36847 will use the description supplied by the current target.
36849 @cindex show tdesc filename
36850 @item show tdesc filename
36851 Show the filename to read for a target description, if any.
36855 @node Target Description Format
36856 @section Target Description Format
36857 @cindex target descriptions, XML format
36859 A target description annex is an @uref{http://www.w3.org/XML/, XML}
36860 document which complies with the Document Type Definition provided in
36861 the @value{GDBN} sources in @file{gdb/features/gdb-target.dtd}. This
36862 means you can use generally available tools like @command{xmllint} to
36863 check that your feature descriptions are well-formed and valid.
36864 However, to help people unfamiliar with XML write descriptions for
36865 their targets, we also describe the grammar here.
36867 Target descriptions can identify the architecture of the remote target
36868 and (for some architectures) provide information about custom register
36869 sets. They can also identify the OS ABI of the remote target.
36870 @value{GDBN} can use this information to autoconfigure for your
36871 target, or to warn you if you connect to an unsupported target.
36873 Here is a simple target description:
36876 <target version="1.0">
36877 <architecture>i386:x86-64</architecture>
36882 This minimal description only says that the target uses
36883 the x86-64 architecture.
36885 A target description has the following overall form, with [ ] marking
36886 optional elements and @dots{} marking repeatable elements. The elements
36887 are explained further below.
36890 <?xml version="1.0"?>
36891 <!DOCTYPE target SYSTEM "gdb-target.dtd">
36892 <target version="1.0">
36893 @r{[}@var{architecture}@r{]}
36894 @r{[}@var{osabi}@r{]}
36895 @r{[}@var{compatible}@r{]}
36896 @r{[}@var{feature}@dots{}@r{]}
36901 The description is generally insensitive to whitespace and line
36902 breaks, under the usual common-sense rules. The XML version
36903 declaration and document type declaration can generally be omitted
36904 (@value{GDBN} does not require them), but specifying them may be
36905 useful for XML validation tools. The @samp{version} attribute for
36906 @samp{<target>} may also be omitted, but we recommend
36907 including it; if future versions of @value{GDBN} use an incompatible
36908 revision of @file{gdb-target.dtd}, they will detect and report
36909 the version mismatch.
36911 @subsection Inclusion
36912 @cindex target descriptions, inclusion
36915 @cindex <xi:include>
36918 It can sometimes be valuable to split a target description up into
36919 several different annexes, either for organizational purposes, or to
36920 share files between different possible target descriptions. You can
36921 divide a description into multiple files by replacing any element of
36922 the target description with an inclusion directive of the form:
36925 <xi:include href="@var{document}"/>
36929 When @value{GDBN} encounters an element of this form, it will retrieve
36930 the named XML @var{document}, and replace the inclusion directive with
36931 the contents of that document. If the current description was read
36932 using @samp{qXfer}, then so will be the included document;
36933 @var{document} will be interpreted as the name of an annex. If the
36934 current description was read from a file, @value{GDBN} will look for
36935 @var{document} as a file in the same directory where it found the
36936 original description.
36938 @subsection Architecture
36939 @cindex <architecture>
36941 An @samp{<architecture>} element has this form:
36944 <architecture>@var{arch}</architecture>
36947 @var{arch} is one of the architectures from the set accepted by
36948 @code{set architecture} (@pxref{Targets, ,Specifying a Debugging Target}).
36951 @cindex @code{<osabi>}
36953 This optional field was introduced in @value{GDBN} version 7.0.
36954 Previous versions of @value{GDBN} ignore it.
36956 An @samp{<osabi>} element has this form:
36959 <osabi>@var{abi-name}</osabi>
36962 @var{abi-name} is an OS ABI name from the same selection accepted by
36963 @w{@code{set osabi}} (@pxref{ABI, ,Configuring the Current ABI}).
36965 @subsection Compatible Architecture
36966 @cindex @code{<compatible>}
36968 This optional field was introduced in @value{GDBN} version 7.0.
36969 Previous versions of @value{GDBN} ignore it.
36971 A @samp{<compatible>} element has this form:
36974 <compatible>@var{arch}</compatible>
36977 @var{arch} is one of the architectures from the set accepted by
36978 @code{set architecture} (@pxref{Targets, ,Specifying a Debugging Target}).
36980 A @samp{<compatible>} element is used to specify that the target
36981 is able to run binaries in some other than the main target architecture
36982 given by the @samp{<architecture>} element. For example, on the
36983 Cell Broadband Engine, the main architecture is @code{powerpc:common}
36984 or @code{powerpc:common64}, but the system is able to run binaries
36985 in the @code{spu} architecture as well. The way to describe this
36986 capability with @samp{<compatible>} is as follows:
36989 <architecture>powerpc:common</architecture>
36990 <compatible>spu</compatible>
36993 @subsection Features
36996 Each @samp{<feature>} describes some logical portion of the target
36997 system. Features are currently used to describe available CPU
36998 registers and the types of their contents. A @samp{<feature>} element
37002 <feature name="@var{name}">
37003 @r{[}@var{type}@dots{}@r{]}
37009 Each feature's name should be unique within the description. The name
37010 of a feature does not matter unless @value{GDBN} has some special
37011 knowledge of the contents of that feature; if it does, the feature
37012 should have its standard name. @xref{Standard Target Features}.
37016 Any register's value is a collection of bits which @value{GDBN} must
37017 interpret. The default interpretation is a two's complement integer,
37018 but other types can be requested by name in the register description.
37019 Some predefined types are provided by @value{GDBN} (@pxref{Predefined
37020 Target Types}), and the description can define additional composite types.
37022 Each type element must have an @samp{id} attribute, which gives
37023 a unique (within the containing @samp{<feature>}) name to the type.
37024 Types must be defined before they are used.
37027 Some targets offer vector registers, which can be treated as arrays
37028 of scalar elements. These types are written as @samp{<vector>} elements,
37029 specifying the array element type, @var{type}, and the number of elements,
37033 <vector id="@var{id}" type="@var{type}" count="@var{count}"/>
37037 If a register's value is usefully viewed in multiple ways, define it
37038 with a union type containing the useful representations. The
37039 @samp{<union>} element contains one or more @samp{<field>} elements,
37040 each of which has a @var{name} and a @var{type}:
37043 <union id="@var{id}">
37044 <field name="@var{name}" type="@var{type}"/>
37050 If a register's value is composed from several separate values, define
37051 it with a structure type. There are two forms of the @samp{<struct>}
37052 element; a @samp{<struct>} element must either contain only bitfields
37053 or contain no bitfields. If the structure contains only bitfields,
37054 its total size in bytes must be specified, each bitfield must have an
37055 explicit start and end, and bitfields are automatically assigned an
37056 integer type. The field's @var{start} should be less than or
37057 equal to its @var{end}, and zero represents the least significant bit.
37060 <struct id="@var{id}" size="@var{size}">
37061 <field name="@var{name}" start="@var{start}" end="@var{end}"/>
37066 If the structure contains no bitfields, then each field has an
37067 explicit type, and no implicit padding is added.
37070 <struct id="@var{id}">
37071 <field name="@var{name}" type="@var{type}"/>
37077 If a register's value is a series of single-bit flags, define it with
37078 a flags type. The @samp{<flags>} element has an explicit @var{size}
37079 and contains one or more @samp{<field>} elements. Each field has a
37080 @var{name}, a @var{start}, and an @var{end}. Only single-bit flags
37084 <flags id="@var{id}" size="@var{size}">
37085 <field name="@var{name}" start="@var{start}" end="@var{end}"/>
37090 @subsection Registers
37093 Each register is represented as an element with this form:
37096 <reg name="@var{name}"
37097 bitsize="@var{size}"
37098 @r{[}regnum="@var{num}"@r{]}
37099 @r{[}save-restore="@var{save-restore}"@r{]}
37100 @r{[}type="@var{type}"@r{]}
37101 @r{[}group="@var{group}"@r{]}/>
37105 The components are as follows:
37110 The register's name; it must be unique within the target description.
37113 The register's size, in bits.
37116 The register's number. If omitted, a register's number is one greater
37117 than that of the previous register (either in the current feature or in
37118 a preceding feature); the first register in the target description
37119 defaults to zero. This register number is used to read or write
37120 the register; e.g.@: it is used in the remote @code{p} and @code{P}
37121 packets, and registers appear in the @code{g} and @code{G} packets
37122 in order of increasing register number.
37125 Whether the register should be preserved across inferior function
37126 calls; this must be either @code{yes} or @code{no}. The default is
37127 @code{yes}, which is appropriate for most registers except for
37128 some system control registers; this is not related to the target's
37132 The type of the register. @var{type} may be a predefined type, a type
37133 defined in the current feature, or one of the special types @code{int}
37134 and @code{float}. @code{int} is an integer type of the correct size
37135 for @var{bitsize}, and @code{float} is a floating point type (in the
37136 architecture's normal floating point format) of the correct size for
37137 @var{bitsize}. The default is @code{int}.
37140 The register group to which this register belongs. @var{group} must
37141 be either @code{general}, @code{float}, or @code{vector}. If no
37142 @var{group} is specified, @value{GDBN} will not display the register
37143 in @code{info registers}.
37147 @node Predefined Target Types
37148 @section Predefined Target Types
37149 @cindex target descriptions, predefined types
37151 Type definitions in the self-description can build up composite types
37152 from basic building blocks, but can not define fundamental types. Instead,
37153 standard identifiers are provided by @value{GDBN} for the fundamental
37154 types. The currently supported types are:
37163 Signed integer types holding the specified number of bits.
37170 Unsigned integer types holding the specified number of bits.
37174 Pointers to unspecified code and data. The program counter and
37175 any dedicated return address register may be marked as code
37176 pointers; printing a code pointer converts it into a symbolic
37177 address. The stack pointer and any dedicated address registers
37178 may be marked as data pointers.
37181 Single precision IEEE floating point.
37184 Double precision IEEE floating point.
37187 The 12-byte extended precision format used by ARM FPA registers.
37190 The 10-byte extended precision format used by x87 registers.
37193 32bit @sc{eflags} register used by x86.
37196 32bit @sc{mxcsr} register used by x86.
37200 @node Standard Target Features
37201 @section Standard Target Features
37202 @cindex target descriptions, standard features
37204 A target description must contain either no registers or all the
37205 target's registers. If the description contains no registers, then
37206 @value{GDBN} will assume a default register layout, selected based on
37207 the architecture. If the description contains any registers, the
37208 default layout will not be used; the standard registers must be
37209 described in the target description, in such a way that @value{GDBN}
37210 can recognize them.
37212 This is accomplished by giving specific names to feature elements
37213 which contain standard registers. @value{GDBN} will look for features
37214 with those names and verify that they contain the expected registers;
37215 if any known feature is missing required registers, or if any required
37216 feature is missing, @value{GDBN} will reject the target
37217 description. You can add additional registers to any of the
37218 standard features --- @value{GDBN} will display them just as if
37219 they were added to an unrecognized feature.
37221 This section lists the known features and their expected contents.
37222 Sample XML documents for these features are included in the
37223 @value{GDBN} source tree, in the directory @file{gdb/features}.
37225 Names recognized by @value{GDBN} should include the name of the
37226 company or organization which selected the name, and the overall
37227 architecture to which the feature applies; so e.g.@: the feature
37228 containing ARM core registers is named @samp{org.gnu.gdb.arm.core}.
37230 The names of registers are not case sensitive for the purpose
37231 of recognizing standard features, but @value{GDBN} will only display
37232 registers using the capitalization used in the description.
37239 * PowerPC Features::
37245 @subsection ARM Features
37246 @cindex target descriptions, ARM features
37248 The @samp{org.gnu.gdb.arm.core} feature is required for non-M-profile
37250 It should contain registers @samp{r0} through @samp{r13}, @samp{sp},
37251 @samp{lr}, @samp{pc}, and @samp{cpsr}.
37253 For M-profile targets (e.g. Cortex-M3), the @samp{org.gnu.gdb.arm.core}
37254 feature is replaced by @samp{org.gnu.gdb.arm.m-profile}. It should contain
37255 registers @samp{r0} through @samp{r13}, @samp{sp}, @samp{lr}, @samp{pc},
37258 The @samp{org.gnu.gdb.arm.fpa} feature is optional. If present, it
37259 should contain registers @samp{f0} through @samp{f7} and @samp{fps}.
37261 The @samp{org.gnu.gdb.xscale.iwmmxt} feature is optional. If present,
37262 it should contain at least registers @samp{wR0} through @samp{wR15} and
37263 @samp{wCGR0} through @samp{wCGR3}. The @samp{wCID}, @samp{wCon},
37264 @samp{wCSSF}, and @samp{wCASF} registers are optional.
37266 The @samp{org.gnu.gdb.arm.vfp} feature is optional. If present, it
37267 should contain at least registers @samp{d0} through @samp{d15}. If
37268 they are present, @samp{d16} through @samp{d31} should also be included.
37269 @value{GDBN} will synthesize the single-precision registers from
37270 halves of the double-precision registers.
37272 The @samp{org.gnu.gdb.arm.neon} feature is optional. It does not
37273 need to contain registers; it instructs @value{GDBN} to display the
37274 VFP double-precision registers as vectors and to synthesize the
37275 quad-precision registers from pairs of double-precision registers.
37276 If this feature is present, @samp{org.gnu.gdb.arm.vfp} must also
37277 be present and include 32 double-precision registers.
37279 @node i386 Features
37280 @subsection i386 Features
37281 @cindex target descriptions, i386 features
37283 The @samp{org.gnu.gdb.i386.core} feature is required for i386/amd64
37284 targets. It should describe the following registers:
37288 @samp{eax} through @samp{edi} plus @samp{eip} for i386
37290 @samp{rax} through @samp{r15} plus @samp{rip} for amd64
37292 @samp{eflags}, @samp{cs}, @samp{ss}, @samp{ds}, @samp{es},
37293 @samp{fs}, @samp{gs}
37295 @samp{st0} through @samp{st7}
37297 @samp{fctrl}, @samp{fstat}, @samp{ftag}, @samp{fiseg}, @samp{fioff},
37298 @samp{foseg}, @samp{fooff} and @samp{fop}
37301 The register sets may be different, depending on the target.
37303 The @samp{org.gnu.gdb.i386.sse} feature is optional. It should
37304 describe registers:
37308 @samp{xmm0} through @samp{xmm7} for i386
37310 @samp{xmm0} through @samp{xmm15} for amd64
37315 The @samp{org.gnu.gdb.i386.avx} feature is optional and requires the
37316 @samp{org.gnu.gdb.i386.sse} feature. It should
37317 describe the upper 128 bits of @sc{ymm} registers:
37321 @samp{ymm0h} through @samp{ymm7h} for i386
37323 @samp{ymm0h} through @samp{ymm15h} for amd64
37326 The @samp{org.gnu.gdb.i386.linux} feature is optional. It should
37327 describe a single register, @samp{orig_eax}.
37329 @node MIPS Features
37330 @subsection MIPS Features
37331 @cindex target descriptions, MIPS features
37333 The @samp{org.gnu.gdb.mips.cpu} feature is required for MIPS targets.
37334 It should contain registers @samp{r0} through @samp{r31}, @samp{lo},
37335 @samp{hi}, and @samp{pc}. They may be 32-bit or 64-bit depending
37338 The @samp{org.gnu.gdb.mips.cp0} feature is also required. It should
37339 contain at least the @samp{status}, @samp{badvaddr}, and @samp{cause}
37340 registers. They may be 32-bit or 64-bit depending on the target.
37342 The @samp{org.gnu.gdb.mips.fpu} feature is currently required, though
37343 it may be optional in a future version of @value{GDBN}. It should
37344 contain registers @samp{f0} through @samp{f31}, @samp{fcsr}, and
37345 @samp{fir}. They may be 32-bit or 64-bit depending on the target.
37347 The @samp{org.gnu.gdb.mips.linux} feature is optional. It should
37348 contain a single register, @samp{restart}, which is used by the
37349 Linux kernel to control restartable syscalls.
37351 @node M68K Features
37352 @subsection M68K Features
37353 @cindex target descriptions, M68K features
37356 @item @samp{org.gnu.gdb.m68k.core}
37357 @itemx @samp{org.gnu.gdb.coldfire.core}
37358 @itemx @samp{org.gnu.gdb.fido.core}
37359 One of those features must be always present.
37360 The feature that is present determines which flavor of m68k is
37361 used. The feature that is present should contain registers
37362 @samp{d0} through @samp{d7}, @samp{a0} through @samp{a5}, @samp{fp},
37363 @samp{sp}, @samp{ps} and @samp{pc}.
37365 @item @samp{org.gnu.gdb.coldfire.fp}
37366 This feature is optional. If present, it should contain registers
37367 @samp{fp0} through @samp{fp7}, @samp{fpcontrol}, @samp{fpstatus} and
37371 @node PowerPC Features
37372 @subsection PowerPC Features
37373 @cindex target descriptions, PowerPC features
37375 The @samp{org.gnu.gdb.power.core} feature is required for PowerPC
37376 targets. It should contain registers @samp{r0} through @samp{r31},
37377 @samp{pc}, @samp{msr}, @samp{cr}, @samp{lr}, @samp{ctr}, and
37378 @samp{xer}. They may be 32-bit or 64-bit depending on the target.
37380 The @samp{org.gnu.gdb.power.fpu} feature is optional. It should
37381 contain registers @samp{f0} through @samp{f31} and @samp{fpscr}.
37383 The @samp{org.gnu.gdb.power.altivec} feature is optional. It should
37384 contain registers @samp{vr0} through @samp{vr31}, @samp{vscr},
37387 The @samp{org.gnu.gdb.power.vsx} feature is optional. It should
37388 contain registers @samp{vs0h} through @samp{vs31h}. @value{GDBN}
37389 will combine these registers with the floating point registers
37390 (@samp{f0} through @samp{f31}) and the altivec registers (@samp{vr0}
37391 through @samp{vr31}) to present the 128-bit wide registers @samp{vs0}
37392 through @samp{vs63}, the set of vector registers for POWER7.
37394 The @samp{org.gnu.gdb.power.spe} feature is optional. It should
37395 contain registers @samp{ev0h} through @samp{ev31h}, @samp{acc}, and
37396 @samp{spefscr}. SPE targets should provide 32-bit registers in
37397 @samp{org.gnu.gdb.power.core} and provide the upper halves in
37398 @samp{ev0h} through @samp{ev31h}. @value{GDBN} will combine
37399 these to present registers @samp{ev0} through @samp{ev31} to the
37402 @node TIC6x Features
37403 @subsection TMS320C6x Features
37404 @cindex target descriptions, TIC6x features
37405 @cindex target descriptions, TMS320C6x features
37406 The @samp{org.gnu.gdb.tic6x.core} feature is required for TMS320C6x
37407 targets. It should contain registers @samp{A0} through @samp{A15},
37408 registers @samp{B0} through @samp{B15}, @samp{CSR} and @samp{PC}.
37410 The @samp{org.gnu.gdb.tic6x.gp} feature is optional. It should
37411 contain registers @samp{A16} through @samp{A31} and @samp{B16}
37412 through @samp{B31}.
37414 The @samp{org.gnu.gdb.tic6x.c6xp} feature is optional. It should
37415 contain registers @samp{TSR}, @samp{ILC} and @samp{RILC}.
37417 @node Operating System Information
37418 @appendix Operating System Information
37419 @cindex operating system information
37425 Users of @value{GDBN} often wish to obtain information about the state of
37426 the operating system running on the target---for example the list of
37427 processes, or the list of open files. This section describes the
37428 mechanism that makes it possible. This mechanism is similar to the
37429 target features mechanism (@pxref{Target Descriptions}), but focuses
37430 on a different aspect of target.
37432 Operating system information is retrived from the target via the
37433 remote protocol, using @samp{qXfer} requests (@pxref{qXfer osdata
37434 read}). The object name in the request should be @samp{osdata}, and
37435 the @var{annex} identifies the data to be fetched.
37438 @appendixsection Process list
37439 @cindex operating system information, process list
37441 When requesting the process list, the @var{annex} field in the
37442 @samp{qXfer} request should be @samp{processes}. The returned data is
37443 an XML document. The formal syntax of this document is defined in
37444 @file{gdb/features/osdata.dtd}.
37446 An example document is:
37449 <?xml version="1.0"?>
37450 <!DOCTYPE target SYSTEM "osdata.dtd">
37451 <osdata type="processes">
37453 <column name="pid">1</column>
37454 <column name="user">root</column>
37455 <column name="command">/sbin/init</column>
37456 <column name="cores">1,2,3</column>
37461 Each item should include a column whose name is @samp{pid}. The value
37462 of that column should identify the process on the target. The
37463 @samp{user} and @samp{command} columns are optional, and will be
37464 displayed by @value{GDBN}. The @samp{cores} column, if present,
37465 should contain a comma-separated list of cores that this process
37466 is running on. Target may provide additional columns,
37467 which @value{GDBN} currently ignores.
37469 @node Trace File Format
37470 @appendix Trace File Format
37471 @cindex trace file format
37473 The trace file comes in three parts: a header, a textual description
37474 section, and a trace frame section with binary data.
37476 The header has the form @code{\x7fTRACE0\n}. The first byte is
37477 @code{0x7f} so as to indicate that the file contains binary data,
37478 while the @code{0} is a version number that may have different values
37481 The description section consists of multiple lines of @sc{ascii} text
37482 separated by newline characters (@code{0xa}). The lines may include a
37483 variety of optional descriptive or context-setting information, such
37484 as tracepoint definitions or register set size. @value{GDBN} will
37485 ignore any line that it does not recognize. An empty line marks the end
37488 @c FIXME add some specific types of data
37490 The trace frame section consists of a number of consecutive frames.
37491 Each frame begins with a two-byte tracepoint number, followed by a
37492 four-byte size giving the amount of data in the frame. The data in
37493 the frame consists of a number of blocks, each introduced by a
37494 character indicating its type (at least register, memory, and trace
37495 state variable). The data in this section is raw binary, not a
37496 hexadecimal or other encoding; its endianness matches the target's
37499 @c FIXME bi-arch may require endianness/arch info in description section
37502 @item R @var{bytes}
37503 Register block. The number and ordering of bytes matches that of a
37504 @code{g} packet in the remote protocol. Note that these are the
37505 actual bytes, in target order and @value{GDBN} register order, not a
37506 hexadecimal encoding.
37508 @item M @var{address} @var{length} @var{bytes}...
37509 Memory block. This is a contiguous block of memory, at the 8-byte
37510 address @var{address}, with a 2-byte length @var{length}, followed by
37511 @var{length} bytes.
37513 @item V @var{number} @var{value}
37514 Trace state variable block. This records the 8-byte signed value
37515 @var{value} of trace state variable numbered @var{number}.
37519 Future enhancements of the trace file format may include additional types
37522 @node Index Section Format
37523 @appendix @code{.gdb_index} section format
37524 @cindex .gdb_index section format
37525 @cindex index section format
37527 This section documents the index section that is created by @code{save
37528 gdb-index} (@pxref{Index Files}). The index section is
37529 DWARF-specific; some knowledge of DWARF is assumed in this
37532 The mapped index file format is designed to be directly
37533 @code{mmap}able on any architecture. In most cases, a datum is
37534 represented using a little-endian 32-bit integer value, called an
37535 @code{offset_type}. Big endian machines must byte-swap the values
37536 before using them. Exceptions to this rule are noted. The data is
37537 laid out such that alignment is always respected.
37539 A mapped index consists of several areas, laid out in order.
37543 The file header. This is a sequence of values, of @code{offset_type}
37544 unless otherwise noted:
37548 The version number, currently 5. Versions 1, 2 and 3 are obsolete.
37549 Version 4 differs by its hashing function.
37552 The offset, from the start of the file, of the CU list.
37555 The offset, from the start of the file, of the types CU list. Note
37556 that this area can be empty, in which case this offset will be equal
37557 to the next offset.
37560 The offset, from the start of the file, of the address area.
37563 The offset, from the start of the file, of the symbol table.
37566 The offset, from the start of the file, of the constant pool.
37570 The CU list. This is a sequence of pairs of 64-bit little-endian
37571 values, sorted by the CU offset. The first element in each pair is
37572 the offset of a CU in the @code{.debug_info} section. The second
37573 element in each pair is the length of that CU. References to a CU
37574 elsewhere in the map are done using a CU index, which is just the
37575 0-based index into this table. Note that if there are type CUs, then
37576 conceptually CUs and type CUs form a single list for the purposes of
37580 The types CU list. This is a sequence of triplets of 64-bit
37581 little-endian values. In a triplet, the first value is the CU offset,
37582 the second value is the type offset in the CU, and the third value is
37583 the type signature. The types CU list is not sorted.
37586 The address area. The address area consists of a sequence of address
37587 entries. Each address entry has three elements:
37591 The low address. This is a 64-bit little-endian value.
37594 The high address. This is a 64-bit little-endian value. Like
37595 @code{DW_AT_high_pc}, the value is one byte beyond the end.
37598 The CU index. This is an @code{offset_type} value.
37602 The symbol table. This is an open-addressed hash table. The size of
37603 the hash table is always a power of 2.
37605 Each slot in the hash table consists of a pair of @code{offset_type}
37606 values. The first value is the offset of the symbol's name in the
37607 constant pool. The second value is the offset of the CU vector in the
37610 If both values are 0, then this slot in the hash table is empty. This
37611 is ok because while 0 is a valid constant pool index, it cannot be a
37612 valid index for both a string and a CU vector.
37614 The hash value for a table entry is computed by applying an
37615 iterative hash function to the symbol's name. Starting with an
37616 initial value of @code{r = 0}, each (unsigned) character @samp{c} in
37617 the string is incorporated into the hash using the formula depending on the
37622 The formula is @code{r = r * 67 + c - 113}.
37625 The formula is @code{r = r * 67 + tolower (c) - 113}.
37628 The terminating @samp{\0} is not incorporated into the hash.
37630 The step size used in the hash table is computed via
37631 @code{((hash * 17) & (size - 1)) | 1}, where @samp{hash} is the hash
37632 value, and @samp{size} is the size of the hash table. The step size
37633 is used to find the next candidate slot when handling a hash
37636 The names of C@t{++} symbols in the hash table are canonicalized. We
37637 don't currently have a simple description of the canonicalization
37638 algorithm; if you intend to create new index sections, you must read
37642 The constant pool. This is simply a bunch of bytes. It is organized
37643 so that alignment is correct: CU vectors are stored first, followed by
37646 A CU vector in the constant pool is a sequence of @code{offset_type}
37647 values. The first value is the number of CU indices in the vector.
37648 Each subsequent value is the index of a CU in the CU list. This
37649 element in the hash table is used to indicate which CUs define the
37652 A string in the constant pool is zero-terminated.
37657 @node GNU Free Documentation License
37658 @appendix GNU Free Documentation License
37667 % I think something like @colophon should be in texinfo. In the
37669 \long\def\colophon{\hbox to0pt{}\vfill
37670 \centerline{The body of this manual is set in}
37671 \centerline{\fontname\tenrm,}
37672 \centerline{with headings in {\bf\fontname\tenbf}}
37673 \centerline{and examples in {\tt\fontname\tentt}.}
37674 \centerline{{\it\fontname\tenit\/},}
37675 \centerline{{\bf\fontname\tenbf}, and}
37676 \centerline{{\sl\fontname\tensl\/}}
37677 \centerline{are used for emphasis.}\vfill}
37679 % Blame: doc@cygnus.com, 1991.