1 \input texinfo @c -*-texinfo-*-
2 @c Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,
3 @c 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
4 @c 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 1.1 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 1-882114-77-9 @*
104 This edition of the GDB manual is dedicated to the memory of Fred
105 Fish. Fred was a long-standing contributor to GDB and to Free
106 software in general. We will miss him.
111 @node Top, Summary, (dir), (dir)
113 @top Debugging with @value{GDBN}
115 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
117 This is the @value{EDITION} Edition, for @value{GDBN}
118 @ifset VERSION_PACKAGE
119 @value{VERSION_PACKAGE}
121 Version @value{GDBVN}.
123 Copyright (C) 1988-2010 Free Software Foundation, Inc.
125 This edition of the GDB manual is dedicated to the memory of Fred
126 Fish. Fred was a long-standing contributor to GDB and to Free
127 software in general. We will miss him.
130 * Summary:: Summary of @value{GDBN}
131 * Sample Session:: A sample @value{GDBN} session
133 * Invocation:: Getting in and out of @value{GDBN}
134 * Commands:: @value{GDBN} commands
135 * Running:: Running programs under @value{GDBN}
136 * Stopping:: Stopping and continuing
137 * Reverse Execution:: Running programs backward
138 * Process Record and Replay:: Recording inferior's execution and replaying it
139 * Stack:: Examining the stack
140 * Source:: Examining source files
141 * Data:: Examining data
142 * Optimized Code:: Debugging optimized code
143 * Macros:: Preprocessor Macros
144 * Tracepoints:: Debugging remote targets non-intrusively
145 * Overlays:: Debugging programs that use overlays
147 * Languages:: Using @value{GDBN} with different languages
149 * Symbols:: Examining the symbol table
150 * Altering:: Altering execution
151 * GDB Files:: @value{GDBN} files
152 * Targets:: Specifying a debugging target
153 * Remote Debugging:: Debugging remote programs
154 * Configurations:: Configuration-specific information
155 * Controlling GDB:: Controlling @value{GDBN}
156 * Extending GDB:: Extending @value{GDBN}
157 * Interpreters:: Command Interpreters
158 * TUI:: @value{GDBN} Text User Interface
159 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
160 * GDB/MI:: @value{GDBN}'s Machine Interface.
161 * Annotations:: @value{GDBN}'s annotation interface.
162 * JIT Interface:: Using the JIT debugging interface.
164 * GDB Bugs:: Reporting bugs in @value{GDBN}
166 * Command Line Editing:: Command Line Editing
167 * Using History Interactively:: Using History Interactively
168 * Formatting Documentation:: How to format and print @value{GDBN} documentation
169 * Installing GDB:: Installing GDB
170 * Maintenance Commands:: Maintenance Commands
171 * Remote Protocol:: GDB Remote Serial Protocol
172 * Agent Expressions:: The GDB Agent Expression Mechanism
173 * Target Descriptions:: How targets can describe themselves to
175 * Operating System Information:: Getting additional information from
177 * Trace File Format:: GDB trace file format
178 * Copying:: GNU General Public License says
179 how you can copy and share GDB
180 * GNU Free Documentation License:: The license for this documentation
189 @unnumbered Summary of @value{GDBN}
191 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
192 going on ``inside'' another program while it executes---or what another
193 program was doing at the moment it crashed.
195 @value{GDBN} can do four main kinds of things (plus other things in support of
196 these) to help you catch bugs in the act:
200 Start your program, specifying anything that might affect its behavior.
203 Make your program stop on specified conditions.
206 Examine what has happened, when your program has stopped.
209 Change things in your program, so you can experiment with correcting the
210 effects of one bug and go on to learn about another.
213 You can use @value{GDBN} to debug programs written in C and C@t{++}.
214 For more information, see @ref{Supported Languages,,Supported Languages}.
215 For more information, see @ref{C,,C and C++}.
218 Support for Modula-2 is partial. For information on Modula-2, see
219 @ref{Modula-2,,Modula-2}.
222 Debugging Pascal programs which use sets, subranges, file variables, or
223 nested functions does not currently work. @value{GDBN} does not support
224 entering expressions, printing values, or similar features using Pascal
228 @value{GDBN} can be used to debug programs written in Fortran, although
229 it may be necessary to refer to some variables with a trailing
232 @value{GDBN} can be used to debug programs written in Objective-C,
233 using either the Apple/NeXT or the GNU Objective-C runtime.
236 * Free Software:: Freely redistributable software
237 * Contributors:: Contributors to GDB
241 @unnumberedsec Free Software
243 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
244 General Public License
245 (GPL). The GPL gives you the freedom to copy or adapt a licensed
246 program---but every person getting a copy also gets with it the
247 freedom to modify that copy (which means that they must get access to
248 the source code), and the freedom to distribute further copies.
249 Typical software companies use copyrights to limit your freedoms; the
250 Free Software Foundation uses the GPL to preserve these freedoms.
252 Fundamentally, the General Public License is a license which says that
253 you have these freedoms and that you cannot take these freedoms away
256 @unnumberedsec Free Software Needs Free Documentation
258 The biggest deficiency in the free software community today is not in
259 the software---it is the lack of good free documentation that we can
260 include with the free software. Many of our most important
261 programs do not come with free reference manuals and free introductory
262 texts. Documentation is an essential part of any software package;
263 when an important free software package does not come with a free
264 manual and a free tutorial, that is a major gap. We have many such
267 Consider Perl, for instance. The tutorial manuals that people
268 normally use are non-free. How did this come about? Because the
269 authors of those manuals published them with restrictive terms---no
270 copying, no modification, source files not available---which exclude
271 them from the free software world.
273 That wasn't the first time this sort of thing happened, and it was far
274 from the last. Many times we have heard a GNU user eagerly describe a
275 manual that he is writing, his intended contribution to the community,
276 only to learn that he had ruined everything by signing a publication
277 contract to make it non-free.
279 Free documentation, like free software, is a matter of freedom, not
280 price. The problem with the non-free manual is not that publishers
281 charge a price for printed copies---that in itself is fine. (The Free
282 Software Foundation sells printed copies of manuals, too.) The
283 problem is the restrictions on the use of the manual. Free manuals
284 are available in source code form, and give you permission to copy and
285 modify. Non-free manuals do not allow this.
287 The criteria of freedom for a free manual are roughly the same as for
288 free software. Redistribution (including the normal kinds of
289 commercial redistribution) must be permitted, so that the manual can
290 accompany every copy of the program, both on-line and on paper.
292 Permission for modification of the technical content is crucial too.
293 When people modify the software, adding or changing features, if they
294 are conscientious they will change the manual too---so they can
295 provide accurate and clear documentation for the modified program. A
296 manual that leaves you no choice but to write a new manual to document
297 a changed version of the program is not really available to our
300 Some kinds of limits on the way modification is handled are
301 acceptable. For example, requirements to preserve the original
302 author's copyright notice, the distribution terms, or the list of
303 authors, are ok. It is also no problem to require modified versions
304 to include notice that they were modified. Even entire sections that
305 may not be deleted or changed are acceptable, as long as they deal
306 with nontechnical topics (like this one). These kinds of restrictions
307 are acceptable because they don't obstruct the community's normal use
310 However, it must be possible to modify all the @emph{technical}
311 content of the manual, and then distribute the result in all the usual
312 media, through all the usual channels. Otherwise, the restrictions
313 obstruct the use of the manual, it is not free, and we need another
314 manual to replace it.
316 Please spread the word about this issue. Our community continues to
317 lose manuals to proprietary publishing. If we spread the word that
318 free software needs free reference manuals and free tutorials, perhaps
319 the next person who wants to contribute by writing documentation will
320 realize, before it is too late, that only free manuals contribute to
321 the free software community.
323 If you are writing documentation, please insist on publishing it under
324 the GNU Free Documentation License or another free documentation
325 license. Remember that this decision requires your approval---you
326 don't have to let the publisher decide. Some commercial publishers
327 will use a free license if you insist, but they will not propose the
328 option; it is up to you to raise the issue and say firmly that this is
329 what you want. If the publisher you are dealing with refuses, please
330 try other publishers. If you're not sure whether a proposed license
331 is free, write to @email{licensing@@gnu.org}.
333 You can encourage commercial publishers to sell more free, copylefted
334 manuals and tutorials by buying them, and particularly by buying
335 copies from the publishers that paid for their writing or for major
336 improvements. Meanwhile, try to avoid buying non-free documentation
337 at all. Check the distribution terms of a manual before you buy it,
338 and insist that whoever seeks your business must respect your freedom.
339 Check the history of the book, and try to reward the publishers that
340 have paid or pay the authors to work on it.
342 The Free Software Foundation maintains a list of free documentation
343 published by other publishers, at
344 @url{http://www.fsf.org/doc/other-free-books.html}.
347 @unnumberedsec Contributors to @value{GDBN}
349 Richard Stallman was the original author of @value{GDBN}, and of many
350 other @sc{gnu} programs. Many others have contributed to its
351 development. This section attempts to credit major contributors. One
352 of the virtues of free software is that everyone is free to contribute
353 to it; with regret, we cannot actually acknowledge everyone here. The
354 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
355 blow-by-blow account.
357 Changes much prior to version 2.0 are lost in the mists of time.
360 @emph{Plea:} Additions to this section are particularly welcome. If you
361 or your friends (or enemies, to be evenhanded) have been unfairly
362 omitted from this list, we would like to add your names!
365 So that they may not regard their many labors as thankless, we
366 particularly thank those who shepherded @value{GDBN} through major
368 Andrew Cagney (releases 6.3, 6.2, 6.1, 6.0, 5.3, 5.2, 5.1 and 5.0);
369 Jim Blandy (release 4.18);
370 Jason Molenda (release 4.17);
371 Stan Shebs (release 4.14);
372 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
373 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
374 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
375 Jim Kingdon (releases 3.5, 3.4, and 3.3);
376 and Randy Smith (releases 3.2, 3.1, and 3.0).
378 Richard Stallman, assisted at various times by Peter TerMaat, Chris
379 Hanson, and Richard Mlynarik, handled releases through 2.8.
381 Michael Tiemann is the author of most of the @sc{gnu} C@t{++} support
382 in @value{GDBN}, with significant additional contributions from Per
383 Bothner and Daniel Berlin. James Clark wrote the @sc{gnu} C@t{++}
384 demangler. Early work on C@t{++} was by Peter TerMaat (who also did
385 much general update work leading to release 3.0).
387 @value{GDBN} uses the BFD subroutine library to examine multiple
388 object-file formats; BFD was a joint project of David V.
389 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
391 David Johnson wrote the original COFF support; Pace Willison did
392 the original support for encapsulated COFF.
394 Brent Benson of Harris Computer Systems contributed DWARF 2 support.
396 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
397 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
399 Jean-Daniel Fekete contributed Sun 386i support.
400 Chris Hanson improved the HP9000 support.
401 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
402 David Johnson contributed Encore Umax support.
403 Jyrki Kuoppala contributed Altos 3068 support.
404 Jeff Law contributed HP PA and SOM support.
405 Keith Packard contributed NS32K support.
406 Doug Rabson contributed Acorn Risc Machine support.
407 Bob Rusk contributed Harris Nighthawk CX-UX support.
408 Chris Smith contributed Convex support (and Fortran debugging).
409 Jonathan Stone contributed Pyramid support.
410 Michael Tiemann contributed SPARC support.
411 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
412 Pace Willison contributed Intel 386 support.
413 Jay Vosburgh contributed Symmetry support.
414 Marko Mlinar contributed OpenRISC 1000 support.
416 Andreas Schwab contributed M68K @sc{gnu}/Linux support.
418 Rich Schaefer and Peter Schauer helped with support of SunOS shared
421 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
422 about several machine instruction sets.
424 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
425 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
426 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
427 and RDI targets, respectively.
429 Brian Fox is the author of the readline libraries providing
430 command-line editing and command history.
432 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
433 Modula-2 support, and contributed the Languages chapter of this manual.
435 Fred Fish wrote most of the support for Unix System Vr4.
436 He also enhanced the command-completion support to cover C@t{++} overloaded
439 Hitachi America (now Renesas America), Ltd. sponsored the support for
440 H8/300, H8/500, and Super-H processors.
442 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
444 Mitsubishi (now Renesas) sponsored the support for D10V, D30V, and M32R/D
447 Toshiba sponsored the support for the TX39 Mips processor.
449 Matsushita sponsored the support for the MN10200 and MN10300 processors.
451 Fujitsu sponsored the support for SPARClite and FR30 processors.
453 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
456 Michael Snyder added support for tracepoints.
458 Stu Grossman wrote gdbserver.
460 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
461 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
463 The following people at the Hewlett-Packard Company contributed
464 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
465 (narrow mode), HP's implementation of kernel threads, HP's aC@t{++}
466 compiler, and the Text User Interface (nee Terminal User Interface):
467 Ben Krepp, Richard Title, John Bishop, Susan Macchia, Kathy Mann,
468 Satish Pai, India Paul, Steve Rehrauer, and Elena Zannoni. Kim Haase
469 provided HP-specific information in this manual.
471 DJ Delorie ported @value{GDBN} to MS-DOS, for the DJGPP project.
472 Robert Hoehne made significant contributions to the DJGPP port.
474 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
475 development since 1991. Cygnus engineers who have worked on @value{GDBN}
476 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
477 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
478 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
479 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
480 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
481 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
482 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
483 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
484 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
485 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
486 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
487 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
488 Zuhn have made contributions both large and small.
490 Andrew Cagney, Fernando Nasser, and Elena Zannoni, while working for
491 Cygnus Solutions, implemented the original @sc{gdb/mi} interface.
493 Jim Blandy added support for preprocessor macros, while working for Red
496 Andrew Cagney designed @value{GDBN}'s architecture vector. Many
497 people including Andrew Cagney, Stephane Carrez, Randolph Chung, Nick
498 Duffek, Richard Henderson, Mark Kettenis, Grace Sainsbury, Kei
499 Sakamoto, Yoshinori Sato, Michael Snyder, Andreas Schwab, Jason
500 Thorpe, Corinna Vinschen, Ulrich Weigand, and Elena Zannoni, helped
501 with the migration of old architectures to this new framework.
503 Andrew Cagney completely re-designed and re-implemented @value{GDBN}'s
504 unwinder framework, this consisting of a fresh new design featuring
505 frame IDs, independent frame sniffers, and the sentinel frame. Mark
506 Kettenis implemented the @sc{dwarf 2} unwinder, Jeff Johnston the
507 libunwind unwinder, and Andrew Cagney the dummy, sentinel, tramp, and
508 trad unwinders. The architecture-specific changes, each involving a
509 complete rewrite of the architecture's frame code, were carried out by
510 Jim Blandy, Joel Brobecker, Kevin Buettner, Andrew Cagney, Stephane
511 Carrez, Randolph Chung, Orjan Friberg, Richard Henderson, Daniel
512 Jacobowitz, Jeff Johnston, Mark Kettenis, Theodore A. Roth, Kei
513 Sakamoto, Yoshinori Sato, Michael Snyder, Corinna Vinschen, and Ulrich
516 Christian Zankel, Ross Morley, Bob Wilson, and Maxim Grigoriev from
517 Tensilica, Inc.@: contributed support for Xtensa processors. Others
518 who have worked on the Xtensa port of @value{GDBN} in the past include
519 Steve Tjiang, John Newlin, and Scott Foehner.
521 Michael Eager and staff of Xilinx, Inc., contributed support for the
522 Xilinx MicroBlaze architecture.
525 @chapter A Sample @value{GDBN} Session
527 You can use this manual at your leisure to read all about @value{GDBN}.
528 However, a handful of commands are enough to get started using the
529 debugger. This chapter illustrates those commands.
532 In this sample session, we emphasize user input like this: @b{input},
533 to make it easier to pick out from the surrounding output.
536 @c FIXME: this example may not be appropriate for some configs, where
537 @c FIXME...primary interest is in remote use.
539 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
540 processor) exhibits the following bug: sometimes, when we change its
541 quote strings from the default, the commands used to capture one macro
542 definition within another stop working. In the following short @code{m4}
543 session, we define a macro @code{foo} which expands to @code{0000}; we
544 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
545 same thing. However, when we change the open quote string to
546 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
547 procedure fails to define a new synonym @code{baz}:
556 @b{define(bar,defn(`foo'))}
560 @b{changequote(<QUOTE>,<UNQUOTE>)}
562 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
565 m4: End of input: 0: fatal error: EOF in string
569 Let us use @value{GDBN} to try to see what is going on.
572 $ @b{@value{GDBP} m4}
573 @c FIXME: this falsifies the exact text played out, to permit smallbook
574 @c FIXME... format to come out better.
575 @value{GDBN} is free software and you are welcome to distribute copies
576 of it under certain conditions; type "show copying" to see
578 There is absolutely no warranty for @value{GDBN}; type "show warranty"
581 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
586 @value{GDBN} reads only enough symbol data to know where to find the
587 rest when needed; as a result, the first prompt comes up very quickly.
588 We now tell @value{GDBN} to use a narrower display width than usual, so
589 that examples fit in this manual.
592 (@value{GDBP}) @b{set width 70}
596 We need to see how the @code{m4} built-in @code{changequote} works.
597 Having looked at the source, we know the relevant subroutine is
598 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
599 @code{break} command.
602 (@value{GDBP}) @b{break m4_changequote}
603 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
607 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
608 control; as long as control does not reach the @code{m4_changequote}
609 subroutine, the program runs as usual:
612 (@value{GDBP}) @b{run}
613 Starting program: /work/Editorial/gdb/gnu/m4/m4
621 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
622 suspends execution of @code{m4}, displaying information about the
623 context where it stops.
626 @b{changequote(<QUOTE>,<UNQUOTE>)}
628 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
630 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
634 Now we use the command @code{n} (@code{next}) to advance execution to
635 the next line of the current function.
639 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
644 @code{set_quotes} looks like a promising subroutine. We can go into it
645 by using the command @code{s} (@code{step}) instead of @code{next}.
646 @code{step} goes to the next line to be executed in @emph{any}
647 subroutine, so it steps into @code{set_quotes}.
651 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
653 530 if (lquote != def_lquote)
657 The display that shows the subroutine where @code{m4} is now
658 suspended (and its arguments) is called a stack frame display. It
659 shows a summary of the stack. We can use the @code{backtrace}
660 command (which can also be spelled @code{bt}), to see where we are
661 in the stack as a whole: the @code{backtrace} command displays a
662 stack frame for each active subroutine.
665 (@value{GDBP}) @b{bt}
666 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
668 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
670 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
671 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
673 #4 0x79dc in expand_input () at macro.c:40
674 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
678 We step through a few more lines to see what happens. The first two
679 times, we can use @samp{s}; the next two times we use @code{n} to avoid
680 falling into the @code{xstrdup} subroutine.
684 0x3b5c 532 if (rquote != def_rquote)
686 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
687 def_lquote : xstrdup(lq);
689 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
692 538 len_lquote = strlen(rquote);
696 The last line displayed looks a little odd; we can examine the variables
697 @code{lquote} and @code{rquote} to see if they are in fact the new left
698 and right quotes we specified. We use the command @code{p}
699 (@code{print}) to see their values.
702 (@value{GDBP}) @b{p lquote}
703 $1 = 0x35d40 "<QUOTE>"
704 (@value{GDBP}) @b{p rquote}
705 $2 = 0x35d50 "<UNQUOTE>"
709 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
710 To look at some context, we can display ten lines of source
711 surrounding the current line with the @code{l} (@code{list}) command.
717 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
719 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
722 538 len_lquote = strlen(rquote);
723 539 len_rquote = strlen(lquote);
730 Let us step past the two lines that set @code{len_lquote} and
731 @code{len_rquote}, and then examine the values of those variables.
735 539 len_rquote = strlen(lquote);
738 (@value{GDBP}) @b{p len_lquote}
740 (@value{GDBP}) @b{p len_rquote}
745 That certainly looks wrong, assuming @code{len_lquote} and
746 @code{len_rquote} are meant to be the lengths of @code{lquote} and
747 @code{rquote} respectively. We can set them to better values using
748 the @code{p} command, since it can print the value of
749 any expression---and that expression can include subroutine calls and
753 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
755 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
760 Is that enough to fix the problem of using the new quotes with the
761 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
762 executing with the @code{c} (@code{continue}) command, and then try the
763 example that caused trouble initially:
769 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
776 Success! The new quotes now work just as well as the default ones. The
777 problem seems to have been just the two typos defining the wrong
778 lengths. We allow @code{m4} exit by giving it an EOF as input:
782 Program exited normally.
786 The message @samp{Program exited normally.} is from @value{GDBN}; it
787 indicates @code{m4} has finished executing. We can end our @value{GDBN}
788 session with the @value{GDBN} @code{quit} command.
791 (@value{GDBP}) @b{quit}
795 @chapter Getting In and Out of @value{GDBN}
797 This chapter discusses how to start @value{GDBN}, and how to get out of it.
801 type @samp{@value{GDBP}} to start @value{GDBN}.
803 type @kbd{quit} or @kbd{Ctrl-d} to exit.
807 * Invoking GDB:: How to start @value{GDBN}
808 * Quitting GDB:: How to quit @value{GDBN}
809 * Shell Commands:: How to use shell commands inside @value{GDBN}
810 * Logging Output:: How to log @value{GDBN}'s output to a file
814 @section Invoking @value{GDBN}
816 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
817 @value{GDBN} reads commands from the terminal until you tell it to exit.
819 You can also run @code{@value{GDBP}} with a variety of arguments and options,
820 to specify more of your debugging environment at the outset.
822 The command-line options described here are designed
823 to cover a variety of situations; in some environments, some of these
824 options may effectively be unavailable.
826 The most usual way to start @value{GDBN} is with one argument,
827 specifying an executable program:
830 @value{GDBP} @var{program}
834 You can also start with both an executable program and a core file
838 @value{GDBP} @var{program} @var{core}
841 You can, instead, specify a process ID as a second argument, if you want
842 to debug a running process:
845 @value{GDBP} @var{program} 1234
849 would attach @value{GDBN} to process @code{1234} (unless you also have a file
850 named @file{1234}; @value{GDBN} does check for a core file first).
852 Taking advantage of the second command-line argument requires a fairly
853 complete operating system; when you use @value{GDBN} as a remote
854 debugger attached to a bare board, there may not be any notion of
855 ``process'', and there is often no way to get a core dump. @value{GDBN}
856 will warn you if it is unable to attach or to read core dumps.
858 You can optionally have @code{@value{GDBP}} pass any arguments after the
859 executable file to the inferior using @code{--args}. This option stops
862 @value{GDBP} --args gcc -O2 -c foo.c
864 This will cause @code{@value{GDBP}} to debug @code{gcc}, and to set
865 @code{gcc}'s command-line arguments (@pxref{Arguments}) to @samp{-O2 -c foo.c}.
867 You can run @code{@value{GDBP}} without printing the front material, which describes
868 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
875 You can further control how @value{GDBN} starts up by using command-line
876 options. @value{GDBN} itself can remind you of the options available.
886 to display all available options and briefly describe their use
887 (@samp{@value{GDBP} -h} is a shorter equivalent).
889 All options and command line arguments you give are processed
890 in sequential order. The order makes a difference when the
891 @samp{-x} option is used.
895 * File Options:: Choosing files
896 * Mode Options:: Choosing modes
897 * Startup:: What @value{GDBN} does during startup
901 @subsection Choosing Files
903 When @value{GDBN} starts, it reads any arguments other than options as
904 specifying an executable file and core file (or process ID). This is
905 the same as if the arguments were specified by the @samp{-se} and
906 @samp{-c} (or @samp{-p}) options respectively. (@value{GDBN} reads the
907 first argument that does not have an associated option flag as
908 equivalent to the @samp{-se} option followed by that argument; and the
909 second argument that does not have an associated option flag, if any, as
910 equivalent to the @samp{-c}/@samp{-p} option followed by that argument.)
911 If the second argument begins with a decimal digit, @value{GDBN} will
912 first attempt to attach to it as a process, and if that fails, attempt
913 to open it as a corefile. If you have a corefile whose name begins with
914 a digit, you can prevent @value{GDBN} from treating it as a pid by
915 prefixing it with @file{./}, e.g.@: @file{./12345}.
917 If @value{GDBN} has not been configured to included core file support,
918 such as for most embedded targets, then it will complain about a second
919 argument and ignore it.
921 Many options have both long and short forms; both are shown in the
922 following list. @value{GDBN} also recognizes the long forms if you truncate
923 them, so long as enough of the option is present to be unambiguous.
924 (If you prefer, you can flag option arguments with @samp{--} rather
925 than @samp{-}, though we illustrate the more usual convention.)
927 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
928 @c way, both those who look for -foo and --foo in the index, will find
932 @item -symbols @var{file}
934 @cindex @code{--symbols}
936 Read symbol table from file @var{file}.
938 @item -exec @var{file}
940 @cindex @code{--exec}
942 Use file @var{file} as the executable file to execute when appropriate,
943 and for examining pure data in conjunction with a core dump.
947 Read symbol table from file @var{file} and use it as the executable
950 @item -core @var{file}
952 @cindex @code{--core}
954 Use file @var{file} as a core dump to examine.
956 @item -pid @var{number}
957 @itemx -p @var{number}
960 Connect to process ID @var{number}, as with the @code{attach} command.
962 @item -command @var{file}
964 @cindex @code{--command}
966 Execute commands from file @var{file}. The contents of this file is
967 evaluated exactly as the @code{source} command would.
968 @xref{Command Files,, Command files}.
970 @item -eval-command @var{command}
971 @itemx -ex @var{command}
972 @cindex @code{--eval-command}
974 Execute a single @value{GDBN} command.
976 This option may be used multiple times to call multiple commands. It may
977 also be interleaved with @samp{-command} as required.
980 @value{GDBP} -ex 'target sim' -ex 'load' \
981 -x setbreakpoints -ex 'run' a.out
984 @item -directory @var{directory}
985 @itemx -d @var{directory}
986 @cindex @code{--directory}
988 Add @var{directory} to the path to search for source and script files.
992 @cindex @code{--readnow}
994 Read each symbol file's entire symbol table immediately, rather than
995 the default, which is to read it incrementally as it is needed.
996 This makes startup slower, but makes future operations faster.
1001 @subsection Choosing Modes
1003 You can run @value{GDBN} in various alternative modes---for example, in
1004 batch mode or quiet mode.
1011 Do not execute commands found in any initialization files. Normally,
1012 @value{GDBN} executes the commands in these files after all the command
1013 options and arguments have been processed. @xref{Command Files,,Command
1019 @cindex @code{--quiet}
1020 @cindex @code{--silent}
1022 ``Quiet''. Do not print the introductory and copyright messages. These
1023 messages are also suppressed in batch mode.
1026 @cindex @code{--batch}
1027 Run in batch mode. Exit with status @code{0} after processing all the
1028 command files specified with @samp{-x} (and all commands from
1029 initialization files, if not inhibited with @samp{-n}). Exit with
1030 nonzero status if an error occurs in executing the @value{GDBN} commands
1031 in the command files. Batch mode also disables pagination;
1032 @pxref{Screen Size} and acts as if @kbd{set confirm off} were in
1033 effect (@pxref{Messages/Warnings}).
1035 Batch mode may be useful for running @value{GDBN} as a filter, for
1036 example to download and run a program on another computer; in order to
1037 make this more useful, the message
1040 Program exited normally.
1044 (which is ordinarily issued whenever a program running under
1045 @value{GDBN} control terminates) is not issued when running in batch
1049 @cindex @code{--batch-silent}
1050 Run in batch mode exactly like @samp{-batch}, but totally silently. All
1051 @value{GDBN} output to @code{stdout} is prevented (@code{stderr} is
1052 unaffected). This is much quieter than @samp{-silent} and would be useless
1053 for an interactive session.
1055 This is particularly useful when using targets that give @samp{Loading section}
1056 messages, for example.
1058 Note that targets that give their output via @value{GDBN}, as opposed to
1059 writing directly to @code{stdout}, will also be made silent.
1061 @item -return-child-result
1062 @cindex @code{--return-child-result}
1063 The return code from @value{GDBN} will be the return code from the child
1064 process (the process being debugged), with the following exceptions:
1068 @value{GDBN} exits abnormally. E.g., due to an incorrect argument or an
1069 internal error. In this case the exit code is the same as it would have been
1070 without @samp{-return-child-result}.
1072 The user quits with an explicit value. E.g., @samp{quit 1}.
1074 The child process never runs, or is not allowed to terminate, in which case
1075 the exit code will be -1.
1078 This option is useful in conjunction with @samp{-batch} or @samp{-batch-silent},
1079 when @value{GDBN} is being used as a remote program loader or simulator
1084 @cindex @code{--nowindows}
1086 ``No windows''. If @value{GDBN} comes with a graphical user interface
1087 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
1088 interface. If no GUI is available, this option has no effect.
1092 @cindex @code{--windows}
1094 If @value{GDBN} includes a GUI, then this option requires it to be
1097 @item -cd @var{directory}
1099 Run @value{GDBN} using @var{directory} as its working directory,
1100 instead of the current directory.
1104 @cindex @code{--fullname}
1106 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
1107 subprocess. It tells @value{GDBN} to output the full file name and line
1108 number in a standard, recognizable fashion each time a stack frame is
1109 displayed (which includes each time your program stops). This
1110 recognizable format looks like two @samp{\032} characters, followed by
1111 the file name, line number and character position separated by colons,
1112 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
1113 @samp{\032} characters as a signal to display the source code for the
1117 @cindex @code{--epoch}
1118 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
1119 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
1120 routines so as to allow Epoch to display values of expressions in a
1123 @item -annotate @var{level}
1124 @cindex @code{--annotate}
1125 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
1126 effect is identical to using @samp{set annotate @var{level}}
1127 (@pxref{Annotations}). The annotation @var{level} controls how much
1128 information @value{GDBN} prints together with its prompt, values of
1129 expressions, source lines, and other types of output. Level 0 is the
1130 normal, level 1 is for use when @value{GDBN} is run as a subprocess of
1131 @sc{gnu} Emacs, level 3 is the maximum annotation suitable for programs
1132 that control @value{GDBN}, and level 2 has been deprecated.
1134 The annotation mechanism has largely been superseded by @sc{gdb/mi}
1138 @cindex @code{--args}
1139 Change interpretation of command line so that arguments following the
1140 executable file are passed as command line arguments to the inferior.
1141 This option stops option processing.
1143 @item -baud @var{bps}
1145 @cindex @code{--baud}
1147 Set the line speed (baud rate or bits per second) of any serial
1148 interface used by @value{GDBN} for remote debugging.
1150 @item -l @var{timeout}
1152 Set the timeout (in seconds) of any communication used by @value{GDBN}
1153 for remote debugging.
1155 @item -tty @var{device}
1156 @itemx -t @var{device}
1157 @cindex @code{--tty}
1159 Run using @var{device} for your program's standard input and output.
1160 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1162 @c resolve the situation of these eventually
1164 @cindex @code{--tui}
1165 Activate the @dfn{Text User Interface} when starting. The Text User
1166 Interface manages several text windows on the terminal, showing
1167 source, assembly, registers and @value{GDBN} command outputs
1168 (@pxref{TUI, ,@value{GDBN} Text User Interface}). Alternatively, the
1169 Text User Interface can be enabled by invoking the program
1170 @samp{@value{GDBTUI}}. Do not use this option if you run @value{GDBN} from
1171 Emacs (@pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}).
1174 @c @cindex @code{--xdb}
1175 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1176 @c For information, see the file @file{xdb_trans.html}, which is usually
1177 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1180 @item -interpreter @var{interp}
1181 @cindex @code{--interpreter}
1182 Use the interpreter @var{interp} for interface with the controlling
1183 program or device. This option is meant to be set by programs which
1184 communicate with @value{GDBN} using it as a back end.
1185 @xref{Interpreters, , Command Interpreters}.
1187 @samp{--interpreter=mi} (or @samp{--interpreter=mi2}) causes
1188 @value{GDBN} to use the @dfn{@sc{gdb/mi} interface} (@pxref{GDB/MI, ,
1189 The @sc{gdb/mi} Interface}) included since @value{GDBN} version 6.0. The
1190 previous @sc{gdb/mi} interface, included in @value{GDBN} version 5.3 and
1191 selected with @samp{--interpreter=mi1}, is deprecated. Earlier
1192 @sc{gdb/mi} interfaces are no longer supported.
1195 @cindex @code{--write}
1196 Open the executable and core files for both reading and writing. This
1197 is equivalent to the @samp{set write on} command inside @value{GDBN}
1201 @cindex @code{--statistics}
1202 This option causes @value{GDBN} to print statistics about time and
1203 memory usage after it completes each command and returns to the prompt.
1206 @cindex @code{--version}
1207 This option causes @value{GDBN} to print its version number and
1208 no-warranty blurb, and exit.
1213 @subsection What @value{GDBN} Does During Startup
1214 @cindex @value{GDBN} startup
1216 Here's the description of what @value{GDBN} does during session startup:
1220 Sets up the command interpreter as specified by the command line
1221 (@pxref{Mode Options, interpreter}).
1225 Reads the system-wide @dfn{init file} (if @option{--with-system-gdbinit} was
1226 used when building @value{GDBN}; @pxref{System-wide configuration,
1227 ,System-wide configuration and settings}) and executes all the commands in
1231 Reads the init file (if any) in your home directory@footnote{On
1232 DOS/Windows systems, the home directory is the one pointed to by the
1233 @code{HOME} environment variable.} and executes all the commands in
1237 Processes command line options and operands.
1240 Reads and executes the commands from init file (if any) in the current
1241 working directory. This is only done if the current directory is
1242 different from your home directory. Thus, you can have more than one
1243 init file, one generic in your home directory, and another, specific
1244 to the program you are debugging, in the directory where you invoke
1248 Reads command files specified by the @samp{-x} option. @xref{Command
1249 Files}, for more details about @value{GDBN} command files.
1252 Reads the command history recorded in the @dfn{history file}.
1253 @xref{Command History}, for more details about the command history and the
1254 files where @value{GDBN} records it.
1257 Init files use the same syntax as @dfn{command files} (@pxref{Command
1258 Files}) and are processed by @value{GDBN} in the same way. The init
1259 file in your home directory can set options (such as @samp{set
1260 complaints}) that affect subsequent processing of command line options
1261 and operands. Init files are not executed if you use the @samp{-nx}
1262 option (@pxref{Mode Options, ,Choosing Modes}).
1264 To display the list of init files loaded by gdb at startup, you
1265 can use @kbd{gdb --help}.
1267 @cindex init file name
1268 @cindex @file{.gdbinit}
1269 @cindex @file{gdb.ini}
1270 The @value{GDBN} init files are normally called @file{.gdbinit}.
1271 The DJGPP port of @value{GDBN} uses the name @file{gdb.ini}, due to
1272 the limitations of file names imposed by DOS filesystems. The Windows
1273 ports of @value{GDBN} use the standard name, but if they find a
1274 @file{gdb.ini} file, they warn you about that and suggest to rename
1275 the file to the standard name.
1279 @section Quitting @value{GDBN}
1280 @cindex exiting @value{GDBN}
1281 @cindex leaving @value{GDBN}
1284 @kindex quit @r{[}@var{expression}@r{]}
1285 @kindex q @r{(@code{quit})}
1286 @item quit @r{[}@var{expression}@r{]}
1288 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1289 @code{q}), or type an end-of-file character (usually @kbd{Ctrl-d}). If you
1290 do not supply @var{expression}, @value{GDBN} will terminate normally;
1291 otherwise it will terminate using the result of @var{expression} as the
1296 An interrupt (often @kbd{Ctrl-c}) does not exit from @value{GDBN}, but rather
1297 terminates the action of any @value{GDBN} command that is in progress and
1298 returns to @value{GDBN} command level. It is safe to type the interrupt
1299 character at any time because @value{GDBN} does not allow it to take effect
1300 until a time when it is safe.
1302 If you have been using @value{GDBN} to control an attached process or
1303 device, you can release it with the @code{detach} command
1304 (@pxref{Attach, ,Debugging an Already-running Process}).
1306 @node Shell Commands
1307 @section Shell Commands
1309 If you need to execute occasional shell commands during your
1310 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1311 just use the @code{shell} command.
1315 @cindex shell escape
1316 @item shell @var{command string}
1317 Invoke a standard shell to execute @var{command string}.
1318 If it exists, the environment variable @code{SHELL} determines which
1319 shell to run. Otherwise @value{GDBN} uses the default shell
1320 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1323 The utility @code{make} is often needed in development environments.
1324 You do not have to use the @code{shell} command for this purpose in
1329 @cindex calling make
1330 @item make @var{make-args}
1331 Execute the @code{make} program with the specified
1332 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1335 @node Logging Output
1336 @section Logging Output
1337 @cindex logging @value{GDBN} output
1338 @cindex save @value{GDBN} output to a file
1340 You may want to save the output of @value{GDBN} commands to a file.
1341 There are several commands to control @value{GDBN}'s logging.
1345 @item set logging on
1347 @item set logging off
1349 @cindex logging file name
1350 @item set logging file @var{file}
1351 Change the name of the current logfile. The default logfile is @file{gdb.txt}.
1352 @item set logging overwrite [on|off]
1353 By default, @value{GDBN} will append to the logfile. Set @code{overwrite} if
1354 you want @code{set logging on} to overwrite the logfile instead.
1355 @item set logging redirect [on|off]
1356 By default, @value{GDBN} output will go to both the terminal and the logfile.
1357 Set @code{redirect} if you want output to go only to the log file.
1358 @kindex show logging
1360 Show the current values of the logging settings.
1364 @chapter @value{GDBN} Commands
1366 You can abbreviate a @value{GDBN} command to the first few letters of the command
1367 name, if that abbreviation is unambiguous; and you can repeat certain
1368 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1369 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1370 show you the alternatives available, if there is more than one possibility).
1373 * Command Syntax:: How to give commands to @value{GDBN}
1374 * Completion:: Command completion
1375 * Help:: How to ask @value{GDBN} for help
1378 @node Command Syntax
1379 @section Command Syntax
1381 A @value{GDBN} command is a single line of input. There is no limit on
1382 how long it can be. It starts with a command name, which is followed by
1383 arguments whose meaning depends on the command name. For example, the
1384 command @code{step} accepts an argument which is the number of times to
1385 step, as in @samp{step 5}. You can also use the @code{step} command
1386 with no arguments. Some commands do not allow any arguments.
1388 @cindex abbreviation
1389 @value{GDBN} command names may always be truncated if that abbreviation is
1390 unambiguous. Other possible command abbreviations are listed in the
1391 documentation for individual commands. In some cases, even ambiguous
1392 abbreviations are allowed; for example, @code{s} is specially defined as
1393 equivalent to @code{step} even though there are other commands whose
1394 names start with @code{s}. You can test abbreviations by using them as
1395 arguments to the @code{help} command.
1397 @cindex repeating commands
1398 @kindex RET @r{(repeat last command)}
1399 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1400 repeat the previous command. Certain commands (for example, @code{run})
1401 will not repeat this way; these are commands whose unintentional
1402 repetition might cause trouble and which you are unlikely to want to
1403 repeat. User-defined commands can disable this feature; see
1404 @ref{Define, dont-repeat}.
1406 The @code{list} and @code{x} commands, when you repeat them with
1407 @key{RET}, construct new arguments rather than repeating
1408 exactly as typed. This permits easy scanning of source or memory.
1410 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1411 output, in a way similar to the common utility @code{more}
1412 (@pxref{Screen Size,,Screen Size}). Since it is easy to press one
1413 @key{RET} too many in this situation, @value{GDBN} disables command
1414 repetition after any command that generates this sort of display.
1416 @kindex # @r{(a comment)}
1418 Any text from a @kbd{#} to the end of the line is a comment; it does
1419 nothing. This is useful mainly in command files (@pxref{Command
1420 Files,,Command Files}).
1422 @cindex repeating command sequences
1423 @kindex Ctrl-o @r{(operate-and-get-next)}
1424 The @kbd{Ctrl-o} binding is useful for repeating a complex sequence of
1425 commands. This command accepts the current line, like @key{RET}, and
1426 then fetches the next line relative to the current line from the history
1430 @section Command Completion
1433 @cindex word completion
1434 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1435 only one possibility; it can also show you what the valid possibilities
1436 are for the next word in a command, at any time. This works for @value{GDBN}
1437 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1439 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1440 of a word. If there is only one possibility, @value{GDBN} fills in the
1441 word, and waits for you to finish the command (or press @key{RET} to
1442 enter it). For example, if you type
1444 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1445 @c complete accuracy in these examples; space introduced for clarity.
1446 @c If texinfo enhancements make it unnecessary, it would be nice to
1447 @c replace " @key" by "@key" in the following...
1449 (@value{GDBP}) info bre @key{TAB}
1453 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1454 the only @code{info} subcommand beginning with @samp{bre}:
1457 (@value{GDBP}) info breakpoints
1461 You can either press @key{RET} at this point, to run the @code{info
1462 breakpoints} command, or backspace and enter something else, if
1463 @samp{breakpoints} does not look like the command you expected. (If you
1464 were sure you wanted @code{info breakpoints} in the first place, you
1465 might as well just type @key{RET} immediately after @samp{info bre},
1466 to exploit command abbreviations rather than command completion).
1468 If there is more than one possibility for the next word when you press
1469 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1470 characters and try again, or just press @key{TAB} a second time;
1471 @value{GDBN} displays all the possible completions for that word. For
1472 example, you might want to set a breakpoint on a subroutine whose name
1473 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1474 just sounds the bell. Typing @key{TAB} again displays all the
1475 function names in your program that begin with those characters, for
1479 (@value{GDBP}) b make_ @key{TAB}
1480 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1481 make_a_section_from_file make_environ
1482 make_abs_section make_function_type
1483 make_blockvector make_pointer_type
1484 make_cleanup make_reference_type
1485 make_command make_symbol_completion_list
1486 (@value{GDBP}) b make_
1490 After displaying the available possibilities, @value{GDBN} copies your
1491 partial input (@samp{b make_} in the example) so you can finish the
1494 If you just want to see the list of alternatives in the first place, you
1495 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1496 means @kbd{@key{META} ?}. You can type this either by holding down a
1497 key designated as the @key{META} shift on your keyboard (if there is
1498 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1500 @cindex quotes in commands
1501 @cindex completion of quoted strings
1502 Sometimes the string you need, while logically a ``word'', may contain
1503 parentheses or other characters that @value{GDBN} normally excludes from
1504 its notion of a word. To permit word completion to work in this
1505 situation, you may enclose words in @code{'} (single quote marks) in
1506 @value{GDBN} commands.
1508 The most likely situation where you might need this is in typing the
1509 name of a C@t{++} function. This is because C@t{++} allows function
1510 overloading (multiple definitions of the same function, distinguished
1511 by argument type). For example, when you want to set a breakpoint you
1512 may need to distinguish whether you mean the version of @code{name}
1513 that takes an @code{int} parameter, @code{name(int)}, or the version
1514 that takes a @code{float} parameter, @code{name(float)}. To use the
1515 word-completion facilities in this situation, type a single quote
1516 @code{'} at the beginning of the function name. This alerts
1517 @value{GDBN} that it may need to consider more information than usual
1518 when you press @key{TAB} or @kbd{M-?} to request word completion:
1521 (@value{GDBP}) b 'bubble( @kbd{M-?}
1522 bubble(double,double) bubble(int,int)
1523 (@value{GDBP}) b 'bubble(
1526 In some cases, @value{GDBN} can tell that completing a name requires using
1527 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1528 completing as much as it can) if you do not type the quote in the first
1532 (@value{GDBP}) b bub @key{TAB}
1533 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1534 (@value{GDBP}) b 'bubble(
1538 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1539 you have not yet started typing the argument list when you ask for
1540 completion on an overloaded symbol.
1542 For more information about overloaded functions, see @ref{C Plus Plus
1543 Expressions, ,C@t{++} Expressions}. You can use the command @code{set
1544 overload-resolution off} to disable overload resolution;
1545 see @ref{Debugging C Plus Plus, ,@value{GDBN} Features for C@t{++}}.
1547 @cindex completion of structure field names
1548 @cindex structure field name completion
1549 @cindex completion of union field names
1550 @cindex union field name completion
1551 When completing in an expression which looks up a field in a
1552 structure, @value{GDBN} also tries@footnote{The completer can be
1553 confused by certain kinds of invalid expressions. Also, it only
1554 examines the static type of the expression, not the dynamic type.} to
1555 limit completions to the field names available in the type of the
1559 (@value{GDBP}) p gdb_stdout.@kbd{M-?}
1560 magic to_delete to_fputs to_put to_rewind
1561 to_data to_flush to_isatty to_read to_write
1565 This is because the @code{gdb_stdout} is a variable of the type
1566 @code{struct ui_file} that is defined in @value{GDBN} sources as
1573 ui_file_flush_ftype *to_flush;
1574 ui_file_write_ftype *to_write;
1575 ui_file_fputs_ftype *to_fputs;
1576 ui_file_read_ftype *to_read;
1577 ui_file_delete_ftype *to_delete;
1578 ui_file_isatty_ftype *to_isatty;
1579 ui_file_rewind_ftype *to_rewind;
1580 ui_file_put_ftype *to_put;
1587 @section Getting Help
1588 @cindex online documentation
1591 You can always ask @value{GDBN} itself for information on its commands,
1592 using the command @code{help}.
1595 @kindex h @r{(@code{help})}
1598 You can use @code{help} (abbreviated @code{h}) with no arguments to
1599 display a short list of named classes of commands:
1603 List of classes of commands:
1605 aliases -- Aliases of other commands
1606 breakpoints -- Making program stop at certain points
1607 data -- Examining data
1608 files -- Specifying and examining files
1609 internals -- Maintenance commands
1610 obscure -- Obscure features
1611 running -- Running the program
1612 stack -- Examining the stack
1613 status -- Status inquiries
1614 support -- Support facilities
1615 tracepoints -- Tracing of program execution without
1616 stopping the program
1617 user-defined -- User-defined commands
1619 Type "help" followed by a class name for a list of
1620 commands in that class.
1621 Type "help" followed by command name for full
1623 Command name abbreviations are allowed if unambiguous.
1626 @c the above line break eliminates huge line overfull...
1628 @item help @var{class}
1629 Using one of the general help classes as an argument, you can get a
1630 list of the individual commands in that class. For example, here is the
1631 help display for the class @code{status}:
1634 (@value{GDBP}) help status
1639 @c Line break in "show" line falsifies real output, but needed
1640 @c to fit in smallbook page size.
1641 info -- Generic command for showing things
1642 about the program being debugged
1643 show -- Generic command for showing things
1646 Type "help" followed by command name for full
1648 Command name abbreviations are allowed if unambiguous.
1652 @item help @var{command}
1653 With a command name as @code{help} argument, @value{GDBN} displays a
1654 short paragraph on how to use that command.
1657 @item apropos @var{args}
1658 The @code{apropos} command searches through all of the @value{GDBN}
1659 commands, and their documentation, for the regular expression specified in
1660 @var{args}. It prints out all matches found. For example:
1671 set symbol-reloading -- Set dynamic symbol table reloading
1672 multiple times in one run
1673 show symbol-reloading -- Show dynamic symbol table reloading
1674 multiple times in one run
1679 @item complete @var{args}
1680 The @code{complete @var{args}} command lists all the possible completions
1681 for the beginning of a command. Use @var{args} to specify the beginning of the
1682 command you want completed. For example:
1688 @noindent results in:
1699 @noindent This is intended for use by @sc{gnu} Emacs.
1702 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1703 and @code{show} to inquire about the state of your program, or the state
1704 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1705 manual introduces each of them in the appropriate context. The listings
1706 under @code{info} and under @code{show} in the Index point to
1707 all the sub-commands. @xref{Index}.
1712 @kindex i @r{(@code{info})}
1714 This command (abbreviated @code{i}) is for describing the state of your
1715 program. For example, you can show the arguments passed to a function
1716 with @code{info args}, list the registers currently in use with @code{info
1717 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1718 You can get a complete list of the @code{info} sub-commands with
1719 @w{@code{help info}}.
1723 You can assign the result of an expression to an environment variable with
1724 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1725 @code{set prompt $}.
1729 In contrast to @code{info}, @code{show} is for describing the state of
1730 @value{GDBN} itself.
1731 You can change most of the things you can @code{show}, by using the
1732 related command @code{set}; for example, you can control what number
1733 system is used for displays with @code{set radix}, or simply inquire
1734 which is currently in use with @code{show radix}.
1737 To display all the settable parameters and their current
1738 values, you can use @code{show} with no arguments; you may also use
1739 @code{info set}. Both commands produce the same display.
1740 @c FIXME: "info set" violates the rule that "info" is for state of
1741 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1742 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1746 Here are three miscellaneous @code{show} subcommands, all of which are
1747 exceptional in lacking corresponding @code{set} commands:
1750 @kindex show version
1751 @cindex @value{GDBN} version number
1753 Show what version of @value{GDBN} is running. You should include this
1754 information in @value{GDBN} bug-reports. If multiple versions of
1755 @value{GDBN} are in use at your site, you may need to determine which
1756 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1757 commands are introduced, and old ones may wither away. Also, many
1758 system vendors ship variant versions of @value{GDBN}, and there are
1759 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1760 The version number is the same as the one announced when you start
1763 @kindex show copying
1764 @kindex info copying
1765 @cindex display @value{GDBN} copyright
1768 Display information about permission for copying @value{GDBN}.
1770 @kindex show warranty
1771 @kindex info warranty
1773 @itemx info warranty
1774 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1775 if your version of @value{GDBN} comes with one.
1780 @chapter Running Programs Under @value{GDBN}
1782 When you run a program under @value{GDBN}, you must first generate
1783 debugging information when you compile it.
1785 You may start @value{GDBN} with its arguments, if any, in an environment
1786 of your choice. If you are doing native debugging, you may redirect
1787 your program's input and output, debug an already running process, or
1788 kill a child process.
1791 * Compilation:: Compiling for debugging
1792 * Starting:: Starting your program
1793 * Arguments:: Your program's arguments
1794 * Environment:: Your program's environment
1796 * Working Directory:: Your program's working directory
1797 * Input/Output:: Your program's input and output
1798 * Attach:: Debugging an already-running process
1799 * Kill Process:: Killing the child process
1801 * Inferiors and Programs:: Debugging multiple inferiors and programs
1802 * Threads:: Debugging programs with multiple threads
1803 * Forks:: Debugging forks
1804 * Checkpoint/Restart:: Setting a @emph{bookmark} to return to later
1808 @section Compiling for Debugging
1810 In order to debug a program effectively, you need to generate
1811 debugging information when you compile it. This debugging information
1812 is stored in the object file; it describes the data type of each
1813 variable or function and the correspondence between source line numbers
1814 and addresses in the executable code.
1816 To request debugging information, specify the @samp{-g} option when you run
1819 Programs that are to be shipped to your customers are compiled with
1820 optimizations, using the @samp{-O} compiler option. However, some
1821 compilers are unable to handle the @samp{-g} and @samp{-O} options
1822 together. Using those compilers, you cannot generate optimized
1823 executables containing debugging information.
1825 @value{NGCC}, the @sc{gnu} C/C@t{++} compiler, supports @samp{-g} with or
1826 without @samp{-O}, making it possible to debug optimized code. We
1827 recommend that you @emph{always} use @samp{-g} whenever you compile a
1828 program. You may think your program is correct, but there is no sense
1829 in pushing your luck. For more information, see @ref{Optimized Code}.
1831 Older versions of the @sc{gnu} C compiler permitted a variant option
1832 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1833 format; if your @sc{gnu} C compiler has this option, do not use it.
1835 @value{GDBN} knows about preprocessor macros and can show you their
1836 expansion (@pxref{Macros}). Most compilers do not include information
1837 about preprocessor macros in the debugging information if you specify
1838 the @option{-g} flag alone, because this information is rather large.
1839 Version 3.1 and later of @value{NGCC}, the @sc{gnu} C compiler,
1840 provides macro information if you specify the options
1841 @option{-gdwarf-2} and @option{-g3}; the former option requests
1842 debugging information in the Dwarf 2 format, and the latter requests
1843 ``extra information''. In the future, we hope to find more compact
1844 ways to represent macro information, so that it can be included with
1849 @section Starting your Program
1855 @kindex r @r{(@code{run})}
1858 Use the @code{run} command to start your program under @value{GDBN}.
1859 You must first specify the program name (except on VxWorks) with an
1860 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1861 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1862 (@pxref{Files, ,Commands to Specify Files}).
1866 If you are running your program in an execution environment that
1867 supports processes, @code{run} creates an inferior process and makes
1868 that process run your program. In some environments without processes,
1869 @code{run} jumps to the start of your program. Other targets,
1870 like @samp{remote}, are always running. If you get an error
1871 message like this one:
1874 The "remote" target does not support "run".
1875 Try "help target" or "continue".
1879 then use @code{continue} to run your program. You may need @code{load}
1880 first (@pxref{load}).
1882 The execution of a program is affected by certain information it
1883 receives from its superior. @value{GDBN} provides ways to specify this
1884 information, which you must do @emph{before} starting your program. (You
1885 can change it after starting your program, but such changes only affect
1886 your program the next time you start it.) This information may be
1887 divided into four categories:
1890 @item The @emph{arguments.}
1891 Specify the arguments to give your program as the arguments of the
1892 @code{run} command. If a shell is available on your target, the shell
1893 is used to pass the arguments, so that you may use normal conventions
1894 (such as wildcard expansion or variable substitution) in describing
1896 In Unix systems, you can control which shell is used with the
1897 @code{SHELL} environment variable.
1898 @xref{Arguments, ,Your Program's Arguments}.
1900 @item The @emph{environment.}
1901 Your program normally inherits its environment from @value{GDBN}, but you can
1902 use the @value{GDBN} commands @code{set environment} and @code{unset
1903 environment} to change parts of the environment that affect
1904 your program. @xref{Environment, ,Your Program's Environment}.
1906 @item The @emph{working directory.}
1907 Your program inherits its working directory from @value{GDBN}. You can set
1908 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1909 @xref{Working Directory, ,Your Program's Working Directory}.
1911 @item The @emph{standard input and output.}
1912 Your program normally uses the same device for standard input and
1913 standard output as @value{GDBN} is using. You can redirect input and output
1914 in the @code{run} command line, or you can use the @code{tty} command to
1915 set a different device for your program.
1916 @xref{Input/Output, ,Your Program's Input and Output}.
1919 @emph{Warning:} While input and output redirection work, you cannot use
1920 pipes to pass the output of the program you are debugging to another
1921 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1925 When you issue the @code{run} command, your program begins to execute
1926 immediately. @xref{Stopping, ,Stopping and Continuing}, for discussion
1927 of how to arrange for your program to stop. Once your program has
1928 stopped, you may call functions in your program, using the @code{print}
1929 or @code{call} commands. @xref{Data, ,Examining Data}.
1931 If the modification time of your symbol file has changed since the last
1932 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1933 table, and reads it again. When it does this, @value{GDBN} tries to retain
1934 your current breakpoints.
1939 @cindex run to main procedure
1940 The name of the main procedure can vary from language to language.
1941 With C or C@t{++}, the main procedure name is always @code{main}, but
1942 other languages such as Ada do not require a specific name for their
1943 main procedure. The debugger provides a convenient way to start the
1944 execution of the program and to stop at the beginning of the main
1945 procedure, depending on the language used.
1947 The @samp{start} command does the equivalent of setting a temporary
1948 breakpoint at the beginning of the main procedure and then invoking
1949 the @samp{run} command.
1951 @cindex elaboration phase
1952 Some programs contain an @dfn{elaboration} phase where some startup code is
1953 executed before the main procedure is called. This depends on the
1954 languages used to write your program. In C@t{++}, for instance,
1955 constructors for static and global objects are executed before
1956 @code{main} is called. It is therefore possible that the debugger stops
1957 before reaching the main procedure. However, the temporary breakpoint
1958 will remain to halt execution.
1960 Specify the arguments to give to your program as arguments to the
1961 @samp{start} command. These arguments will be given verbatim to the
1962 underlying @samp{run} command. Note that the same arguments will be
1963 reused if no argument is provided during subsequent calls to
1964 @samp{start} or @samp{run}.
1966 It is sometimes necessary to debug the program during elaboration. In
1967 these cases, using the @code{start} command would stop the execution of
1968 your program too late, as the program would have already completed the
1969 elaboration phase. Under these circumstances, insert breakpoints in your
1970 elaboration code before running your program.
1972 @kindex set exec-wrapper
1973 @item set exec-wrapper @var{wrapper}
1974 @itemx show exec-wrapper
1975 @itemx unset exec-wrapper
1976 When @samp{exec-wrapper} is set, the specified wrapper is used to
1977 launch programs for debugging. @value{GDBN} starts your program
1978 with a shell command of the form @kbd{exec @var{wrapper}
1979 @var{program}}. Quoting is added to @var{program} and its
1980 arguments, but not to @var{wrapper}, so you should add quotes if
1981 appropriate for your shell. The wrapper runs until it executes
1982 your program, and then @value{GDBN} takes control.
1984 You can use any program that eventually calls @code{execve} with
1985 its arguments as a wrapper. Several standard Unix utilities do
1986 this, e.g.@: @code{env} and @code{nohup}. Any Unix shell script ending
1987 with @code{exec "$@@"} will also work.
1989 For example, you can use @code{env} to pass an environment variable to
1990 the debugged program, without setting the variable in your shell's
1994 (@value{GDBP}) set exec-wrapper env 'LD_PRELOAD=libtest.so'
1998 This command is available when debugging locally on most targets, excluding
1999 @sc{djgpp}, Cygwin, MS Windows, and QNX Neutrino.
2001 @kindex set disable-randomization
2002 @item set disable-randomization
2003 @itemx set disable-randomization on
2004 This option (enabled by default in @value{GDBN}) will turn off the native
2005 randomization of the virtual address space of the started program. This option
2006 is useful for multiple debugging sessions to make the execution better
2007 reproducible and memory addresses reusable across debugging sessions.
2009 This feature is implemented only on @sc{gnu}/Linux. You can get the same
2013 (@value{GDBP}) set exec-wrapper setarch `uname -m` -R
2016 @item set disable-randomization off
2017 Leave the behavior of the started executable unchanged. Some bugs rear their
2018 ugly heads only when the program is loaded at certain addresses. If your bug
2019 disappears when you run the program under @value{GDBN}, that might be because
2020 @value{GDBN} by default disables the address randomization on platforms, such
2021 as @sc{gnu}/Linux, which do that for stand-alone programs. Use @kbd{set
2022 disable-randomization off} to try to reproduce such elusive bugs.
2024 The virtual address space randomization is implemented only on @sc{gnu}/Linux.
2025 It protects the programs against some kinds of security attacks. In these
2026 cases the attacker needs to know the exact location of a concrete executable
2027 code. Randomizing its location makes it impossible to inject jumps misusing
2028 a code at its expected addresses.
2030 Prelinking shared libraries provides a startup performance advantage but it
2031 makes addresses in these libraries predictable for privileged processes by
2032 having just unprivileged access at the target system. Reading the shared
2033 library binary gives enough information for assembling the malicious code
2034 misusing it. Still even a prelinked shared library can get loaded at a new
2035 random address just requiring the regular relocation process during the
2036 startup. Shared libraries not already prelinked are always loaded at
2037 a randomly chosen address.
2039 Position independent executables (PIE) contain position independent code
2040 similar to the shared libraries and therefore such executables get loaded at
2041 a randomly chosen address upon startup. PIE executables always load even
2042 already prelinked shared libraries at a random address. You can build such
2043 executable using @command{gcc -fPIE -pie}.
2045 Heap (malloc storage), stack and custom mmap areas are always placed randomly
2046 (as long as the randomization is enabled).
2048 @item show disable-randomization
2049 Show the current setting of the explicit disable of the native randomization of
2050 the virtual address space of the started program.
2055 @section Your Program's Arguments
2057 @cindex arguments (to your program)
2058 The arguments to your program can be specified by the arguments of the
2060 They are passed to a shell, which expands wildcard characters and
2061 performs redirection of I/O, and thence to your program. Your
2062 @code{SHELL} environment variable (if it exists) specifies what shell
2063 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
2064 the default shell (@file{/bin/sh} on Unix).
2066 On non-Unix systems, the program is usually invoked directly by
2067 @value{GDBN}, which emulates I/O redirection via the appropriate system
2068 calls, and the wildcard characters are expanded by the startup code of
2069 the program, not by the shell.
2071 @code{run} with no arguments uses the same arguments used by the previous
2072 @code{run}, or those set by the @code{set args} command.
2077 Specify the arguments to be used the next time your program is run. If
2078 @code{set args} has no arguments, @code{run} executes your program
2079 with no arguments. Once you have run your program with arguments,
2080 using @code{set args} before the next @code{run} is the only way to run
2081 it again without arguments.
2085 Show the arguments to give your program when it is started.
2089 @section Your Program's Environment
2091 @cindex environment (of your program)
2092 The @dfn{environment} consists of a set of environment variables and
2093 their values. Environment variables conventionally record such things as
2094 your user name, your home directory, your terminal type, and your search
2095 path for programs to run. Usually you set up environment variables with
2096 the shell and they are inherited by all the other programs you run. When
2097 debugging, it can be useful to try running your program with a modified
2098 environment without having to start @value{GDBN} over again.
2102 @item path @var{directory}
2103 Add @var{directory} to the front of the @code{PATH} environment variable
2104 (the search path for executables) that will be passed to your program.
2105 The value of @code{PATH} used by @value{GDBN} does not change.
2106 You may specify several directory names, separated by whitespace or by a
2107 system-dependent separator character (@samp{:} on Unix, @samp{;} on
2108 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
2109 is moved to the front, so it is searched sooner.
2111 You can use the string @samp{$cwd} to refer to whatever is the current
2112 working directory at the time @value{GDBN} searches the path. If you
2113 use @samp{.} instead, it refers to the directory where you executed the
2114 @code{path} command. @value{GDBN} replaces @samp{.} in the
2115 @var{directory} argument (with the current path) before adding
2116 @var{directory} to the search path.
2117 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
2118 @c document that, since repeating it would be a no-op.
2122 Display the list of search paths for executables (the @code{PATH}
2123 environment variable).
2125 @kindex show environment
2126 @item show environment @r{[}@var{varname}@r{]}
2127 Print the value of environment variable @var{varname} to be given to
2128 your program when it starts. If you do not supply @var{varname},
2129 print the names and values of all environment variables to be given to
2130 your program. You can abbreviate @code{environment} as @code{env}.
2132 @kindex set environment
2133 @item set environment @var{varname} @r{[}=@var{value}@r{]}
2134 Set environment variable @var{varname} to @var{value}. The value
2135 changes for your program only, not for @value{GDBN} itself. @var{value} may
2136 be any string; the values of environment variables are just strings, and
2137 any interpretation is supplied by your program itself. The @var{value}
2138 parameter is optional; if it is eliminated, the variable is set to a
2140 @c "any string" here does not include leading, trailing
2141 @c blanks. Gnu asks: does anyone care?
2143 For example, this command:
2150 tells the debugged program, when subsequently run, that its user is named
2151 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
2152 are not actually required.)
2154 @kindex unset environment
2155 @item unset environment @var{varname}
2156 Remove variable @var{varname} from the environment to be passed to your
2157 program. This is different from @samp{set env @var{varname} =};
2158 @code{unset environment} removes the variable from the environment,
2159 rather than assigning it an empty value.
2162 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
2164 by your @code{SHELL} environment variable if it exists (or
2165 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
2166 that runs an initialization file---such as @file{.cshrc} for C-shell, or
2167 @file{.bashrc} for BASH---any variables you set in that file affect
2168 your program. You may wish to move setting of environment variables to
2169 files that are only run when you sign on, such as @file{.login} or
2172 @node Working Directory
2173 @section Your Program's Working Directory
2175 @cindex working directory (of your program)
2176 Each time you start your program with @code{run}, it inherits its
2177 working directory from the current working directory of @value{GDBN}.
2178 The @value{GDBN} working directory is initially whatever it inherited
2179 from its parent process (typically the shell), but you can specify a new
2180 working directory in @value{GDBN} with the @code{cd} command.
2182 The @value{GDBN} working directory also serves as a default for the commands
2183 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
2188 @cindex change working directory
2189 @item cd @var{directory}
2190 Set the @value{GDBN} working directory to @var{directory}.
2194 Print the @value{GDBN} working directory.
2197 It is generally impossible to find the current working directory of
2198 the process being debugged (since a program can change its directory
2199 during its run). If you work on a system where @value{GDBN} is
2200 configured with the @file{/proc} support, you can use the @code{info
2201 proc} command (@pxref{SVR4 Process Information}) to find out the
2202 current working directory of the debuggee.
2205 @section Your Program's Input and Output
2210 By default, the program you run under @value{GDBN} does input and output to
2211 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
2212 to its own terminal modes to interact with you, but it records the terminal
2213 modes your program was using and switches back to them when you continue
2214 running your program.
2217 @kindex info terminal
2219 Displays information recorded by @value{GDBN} about the terminal modes your
2223 You can redirect your program's input and/or output using shell
2224 redirection with the @code{run} command. For example,
2231 starts your program, diverting its output to the file @file{outfile}.
2234 @cindex controlling terminal
2235 Another way to specify where your program should do input and output is
2236 with the @code{tty} command. This command accepts a file name as
2237 argument, and causes this file to be the default for future @code{run}
2238 commands. It also resets the controlling terminal for the child
2239 process, for future @code{run} commands. For example,
2246 directs that processes started with subsequent @code{run} commands
2247 default to do input and output on the terminal @file{/dev/ttyb} and have
2248 that as their controlling terminal.
2250 An explicit redirection in @code{run} overrides the @code{tty} command's
2251 effect on the input/output device, but not its effect on the controlling
2254 When you use the @code{tty} command or redirect input in the @code{run}
2255 command, only the input @emph{for your program} is affected. The input
2256 for @value{GDBN} still comes from your terminal. @code{tty} is an alias
2257 for @code{set inferior-tty}.
2259 @cindex inferior tty
2260 @cindex set inferior controlling terminal
2261 You can use the @code{show inferior-tty} command to tell @value{GDBN} to
2262 display the name of the terminal that will be used for future runs of your
2266 @item set inferior-tty /dev/ttyb
2267 @kindex set inferior-tty
2268 Set the tty for the program being debugged to /dev/ttyb.
2270 @item show inferior-tty
2271 @kindex show inferior-tty
2272 Show the current tty for the program being debugged.
2276 @section Debugging an Already-running Process
2281 @item attach @var{process-id}
2282 This command attaches to a running process---one that was started
2283 outside @value{GDBN}. (@code{info files} shows your active
2284 targets.) The command takes as argument a process ID. The usual way to
2285 find out the @var{process-id} of a Unix process is with the @code{ps} utility,
2286 or with the @samp{jobs -l} shell command.
2288 @code{attach} does not repeat if you press @key{RET} a second time after
2289 executing the command.
2292 To use @code{attach}, your program must be running in an environment
2293 which supports processes; for example, @code{attach} does not work for
2294 programs on bare-board targets that lack an operating system. You must
2295 also have permission to send the process a signal.
2297 When you use @code{attach}, the debugger finds the program running in
2298 the process first by looking in the current working directory, then (if
2299 the program is not found) by using the source file search path
2300 (@pxref{Source Path, ,Specifying Source Directories}). You can also use
2301 the @code{file} command to load the program. @xref{Files, ,Commands to
2304 The first thing @value{GDBN} does after arranging to debug the specified
2305 process is to stop it. You can examine and modify an attached process
2306 with all the @value{GDBN} commands that are ordinarily available when
2307 you start processes with @code{run}. You can insert breakpoints; you
2308 can step and continue; you can modify storage. If you would rather the
2309 process continue running, you may use the @code{continue} command after
2310 attaching @value{GDBN} to the process.
2315 When you have finished debugging the attached process, you can use the
2316 @code{detach} command to release it from @value{GDBN} control. Detaching
2317 the process continues its execution. After the @code{detach} command,
2318 that process and @value{GDBN} become completely independent once more, and you
2319 are ready to @code{attach} another process or start one with @code{run}.
2320 @code{detach} does not repeat if you press @key{RET} again after
2321 executing the command.
2324 If you exit @value{GDBN} while you have an attached process, you detach
2325 that process. If you use the @code{run} command, you kill that process.
2326 By default, @value{GDBN} asks for confirmation if you try to do either of these
2327 things; you can control whether or not you need to confirm by using the
2328 @code{set confirm} command (@pxref{Messages/Warnings, ,Optional Warnings and
2332 @section Killing the Child Process
2337 Kill the child process in which your program is running under @value{GDBN}.
2340 This command is useful if you wish to debug a core dump instead of a
2341 running process. @value{GDBN} ignores any core dump file while your program
2344 On some operating systems, a program cannot be executed outside @value{GDBN}
2345 while you have breakpoints set on it inside @value{GDBN}. You can use the
2346 @code{kill} command in this situation to permit running your program
2347 outside the debugger.
2349 The @code{kill} command is also useful if you wish to recompile and
2350 relink your program, since on many systems it is impossible to modify an
2351 executable file while it is running in a process. In this case, when you
2352 next type @code{run}, @value{GDBN} notices that the file has changed, and
2353 reads the symbol table again (while trying to preserve your current
2354 breakpoint settings).
2356 @node Inferiors and Programs
2357 @section Debugging Multiple Inferiors and Programs
2359 @value{GDBN} lets you run and debug multiple programs in a single
2360 session. In addition, @value{GDBN} on some systems may let you run
2361 several programs simultaneously (otherwise you have to exit from one
2362 before starting another). In the most general case, you can have
2363 multiple threads of execution in each of multiple processes, launched
2364 from multiple executables.
2367 @value{GDBN} represents the state of each program execution with an
2368 object called an @dfn{inferior}. An inferior typically corresponds to
2369 a process, but is more general and applies also to targets that do not
2370 have processes. Inferiors may be created before a process runs, and
2371 may be retained after a process exits. Inferiors have unique
2372 identifiers that are different from process ids. Usually each
2373 inferior will also have its own distinct address space, although some
2374 embedded targets may have several inferiors running in different parts
2375 of a single address space. Each inferior may in turn have multiple
2376 threads running in it.
2378 To find out what inferiors exist at any moment, use @w{@code{info
2382 @kindex info inferiors
2383 @item info inferiors
2384 Print a list of all inferiors currently being managed by @value{GDBN}.
2386 @value{GDBN} displays for each inferior (in this order):
2390 the inferior number assigned by @value{GDBN}
2393 the target system's inferior identifier
2396 the name of the executable the inferior is running.
2401 An asterisk @samp{*} preceding the @value{GDBN} inferior number
2402 indicates the current inferior.
2406 @c end table here to get a little more width for example
2409 (@value{GDBP}) info inferiors
2410 Num Description Executable
2411 2 process 2307 hello
2412 * 1 process 3401 goodbye
2415 To switch focus between inferiors, use the @code{inferior} command:
2418 @kindex inferior @var{infno}
2419 @item inferior @var{infno}
2420 Make inferior number @var{infno} the current inferior. The argument
2421 @var{infno} is the inferior number assigned by @value{GDBN}, as shown
2422 in the first field of the @samp{info inferiors} display.
2426 You can get multiple executables into a debugging session via the
2427 @code{add-inferior} and @w{@code{clone-inferior}} commands. On some
2428 systems @value{GDBN} can add inferiors to the debug session
2429 automatically by following calls to @code{fork} and @code{exec}. To
2430 remove inferiors from the debugging session use the
2431 @w{@code{remove-inferior}} command.
2434 @kindex add-inferior
2435 @item add-inferior [ -copies @var{n} ] [ -exec @var{executable} ]
2436 Adds @var{n} inferiors to be run using @var{executable} as the
2437 executable. @var{n} defaults to 1. If no executable is specified,
2438 the inferiors begins empty, with no program. You can still assign or
2439 change the program assigned to the inferior at any time by using the
2440 @code{file} command with the executable name as its argument.
2442 @kindex clone-inferior
2443 @item clone-inferior [ -copies @var{n} ] [ @var{infno} ]
2444 Adds @var{n} inferiors ready to execute the same program as inferior
2445 @var{infno}. @var{n} defaults to 1. @var{infno} defaults to the
2446 number of the current inferior. This is a convenient command when you
2447 want to run another instance of the inferior you are debugging.
2450 (@value{GDBP}) info inferiors
2451 Num Description Executable
2452 * 1 process 29964 helloworld
2453 (@value{GDBP}) clone-inferior
2456 (@value{GDBP}) info inferiors
2457 Num Description Executable
2459 * 1 process 29964 helloworld
2462 You can now simply switch focus to inferior 2 and run it.
2464 @kindex remove-inferior
2465 @item remove-inferior @var{infno}
2466 Removes the inferior @var{infno}. It is not possible to remove an
2467 inferior that is running with this command. For those, use the
2468 @code{kill} or @code{detach} command first.
2472 To quit debugging one of the running inferiors that is not the current
2473 inferior, you can either detach from it by using the @w{@code{detach
2474 inferior}} command (allowing it to run independently), or kill it
2475 using the @w{@code{kill inferior}} command:
2478 @kindex detach inferior @var{infno}
2479 @item detach inferior @var{infno}
2480 Detach from the inferior identified by @value{GDBN} inferior number
2481 @var{infno}, and remove it from the inferior list.
2483 @kindex kill inferior @var{infno}
2484 @item kill inferior @var{infno}
2485 Kill the inferior identified by @value{GDBN} inferior number
2486 @var{infno}, and remove it from the inferior list.
2489 After the successful completion of a command such as @code{detach},
2490 @code{detach inferior}, @code{kill} or @code{kill inferior}, or after
2491 a normal process exit, the inferior is still valid and listed with
2492 @code{info inferiors}, ready to be restarted.
2495 To be notified when inferiors are started or exit under @value{GDBN}'s
2496 control use @w{@code{set print inferior-events}}:
2499 @kindex set print inferior-events
2500 @cindex print messages on inferior start and exit
2501 @item set print inferior-events
2502 @itemx set print inferior-events on
2503 @itemx set print inferior-events off
2504 The @code{set print inferior-events} command allows you to enable or
2505 disable printing of messages when @value{GDBN} notices that new
2506 inferiors have started or that inferiors have exited or have been
2507 detached. By default, these messages will not be printed.
2509 @kindex show print inferior-events
2510 @item show print inferior-events
2511 Show whether messages will be printed when @value{GDBN} detects that
2512 inferiors have started, exited or have been detached.
2515 Many commands will work the same with multiple programs as with a
2516 single program: e.g., @code{print myglobal} will simply display the
2517 value of @code{myglobal} in the current inferior.
2520 Occasionaly, when debugging @value{GDBN} itself, it may be useful to
2521 get more info about the relationship of inferiors, programs, address
2522 spaces in a debug session. You can do that with the @w{@code{maint
2523 info program-spaces}} command.
2526 @kindex maint info program-spaces
2527 @item maint info program-spaces
2528 Print a list of all program spaces currently being managed by
2531 @value{GDBN} displays for each program space (in this order):
2535 the program space number assigned by @value{GDBN}
2538 the name of the executable loaded into the program space, with e.g.,
2539 the @code{file} command.
2544 An asterisk @samp{*} preceding the @value{GDBN} program space number
2545 indicates the current program space.
2547 In addition, below each program space line, @value{GDBN} prints extra
2548 information that isn't suitable to display in tabular form. For
2549 example, the list of inferiors bound to the program space.
2552 (@value{GDBP}) maint info program-spaces
2555 Bound inferiors: ID 1 (process 21561)
2559 Here we can see that no inferior is running the program @code{hello},
2560 while @code{process 21561} is running the program @code{goodbye}. On
2561 some targets, it is possible that multiple inferiors are bound to the
2562 same program space. The most common example is that of debugging both
2563 the parent and child processes of a @code{vfork} call. For example,
2566 (@value{GDBP}) maint info program-spaces
2569 Bound inferiors: ID 2 (process 18050), ID 1 (process 18045)
2572 Here, both inferior 2 and inferior 1 are running in the same program
2573 space as a result of inferior 1 having executed a @code{vfork} call.
2577 @section Debugging Programs with Multiple Threads
2579 @cindex threads of execution
2580 @cindex multiple threads
2581 @cindex switching threads
2582 In some operating systems, such as HP-UX and Solaris, a single program
2583 may have more than one @dfn{thread} of execution. The precise semantics
2584 of threads differ from one operating system to another, but in general
2585 the threads of a single program are akin to multiple processes---except
2586 that they share one address space (that is, they can all examine and
2587 modify the same variables). On the other hand, each thread has its own
2588 registers and execution stack, and perhaps private memory.
2590 @value{GDBN} provides these facilities for debugging multi-thread
2594 @item automatic notification of new threads
2595 @item @samp{thread @var{threadno}}, a command to switch among threads
2596 @item @samp{info threads}, a command to inquire about existing threads
2597 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
2598 a command to apply a command to a list of threads
2599 @item thread-specific breakpoints
2600 @item @samp{set print thread-events}, which controls printing of
2601 messages on thread start and exit.
2602 @item @samp{set libthread-db-search-path @var{path}}, which lets
2603 the user specify which @code{libthread_db} to use if the default choice
2604 isn't compatible with the program.
2608 @emph{Warning:} These facilities are not yet available on every
2609 @value{GDBN} configuration where the operating system supports threads.
2610 If your @value{GDBN} does not support threads, these commands have no
2611 effect. For example, a system without thread support shows no output
2612 from @samp{info threads}, and always rejects the @code{thread} command,
2616 (@value{GDBP}) info threads
2617 (@value{GDBP}) thread 1
2618 Thread ID 1 not known. Use the "info threads" command to
2619 see the IDs of currently known threads.
2621 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
2622 @c doesn't support threads"?
2625 @cindex focus of debugging
2626 @cindex current thread
2627 The @value{GDBN} thread debugging facility allows you to observe all
2628 threads while your program runs---but whenever @value{GDBN} takes
2629 control, one thread in particular is always the focus of debugging.
2630 This thread is called the @dfn{current thread}. Debugging commands show
2631 program information from the perspective of the current thread.
2633 @cindex @code{New} @var{systag} message
2634 @cindex thread identifier (system)
2635 @c FIXME-implementors!! It would be more helpful if the [New...] message
2636 @c included GDB's numeric thread handle, so you could just go to that
2637 @c thread without first checking `info threads'.
2638 Whenever @value{GDBN} detects a new thread in your program, it displays
2639 the target system's identification for the thread with a message in the
2640 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2641 whose form varies depending on the particular system. For example, on
2642 @sc{gnu}/Linux, you might see
2645 [New Thread 46912507313328 (LWP 25582)]
2649 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
2650 the @var{systag} is simply something like @samp{process 368}, with no
2653 @c FIXME!! (1) Does the [New...] message appear even for the very first
2654 @c thread of a program, or does it only appear for the
2655 @c second---i.e.@: when it becomes obvious we have a multithread
2657 @c (2) *Is* there necessarily a first thread always? Or do some
2658 @c multithread systems permit starting a program with multiple
2659 @c threads ab initio?
2661 @cindex thread number
2662 @cindex thread identifier (GDB)
2663 For debugging purposes, @value{GDBN} associates its own thread
2664 number---always a single integer---with each thread in your program.
2667 @kindex info threads
2669 Display a summary of all threads currently in your
2670 program. @value{GDBN} displays for each thread (in this order):
2674 the thread number assigned by @value{GDBN}
2677 the target system's thread identifier (@var{systag})
2680 the current stack frame summary for that thread
2684 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2685 indicates the current thread.
2689 @c end table here to get a little more width for example
2692 (@value{GDBP}) info threads
2693 3 process 35 thread 27 0x34e5 in sigpause ()
2694 2 process 35 thread 23 0x34e5 in sigpause ()
2695 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2701 @cindex debugging multithreaded programs (on HP-UX)
2702 @cindex thread identifier (GDB), on HP-UX
2703 For debugging purposes, @value{GDBN} associates its own thread
2704 number---a small integer assigned in thread-creation order---with each
2705 thread in your program.
2707 @cindex @code{New} @var{systag} message, on HP-UX
2708 @cindex thread identifier (system), on HP-UX
2709 @c FIXME-implementors!! It would be more helpful if the [New...] message
2710 @c included GDB's numeric thread handle, so you could just go to that
2711 @c thread without first checking `info threads'.
2712 Whenever @value{GDBN} detects a new thread in your program, it displays
2713 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2714 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2715 whose form varies depending on the particular system. For example, on
2719 [New thread 2 (system thread 26594)]
2723 when @value{GDBN} notices a new thread.
2726 @kindex info threads (HP-UX)
2728 Display a summary of all threads currently in your
2729 program. @value{GDBN} displays for each thread (in this order):
2732 @item the thread number assigned by @value{GDBN}
2734 @item the target system's thread identifier (@var{systag})
2736 @item the current stack frame summary for that thread
2740 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2741 indicates the current thread.
2745 @c end table here to get a little more width for example
2748 (@value{GDBP}) info threads
2749 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2751 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2752 from /usr/lib/libc.2
2753 1 system thread 27905 0x7b003498 in _brk () \@*
2754 from /usr/lib/libc.2
2757 On Solaris, you can display more information about user threads with a
2758 Solaris-specific command:
2761 @item maint info sol-threads
2762 @kindex maint info sol-threads
2763 @cindex thread info (Solaris)
2764 Display info on Solaris user threads.
2768 @kindex thread @var{threadno}
2769 @item thread @var{threadno}
2770 Make thread number @var{threadno} the current thread. The command
2771 argument @var{threadno} is the internal @value{GDBN} thread number, as
2772 shown in the first field of the @samp{info threads} display.
2773 @value{GDBN} responds by displaying the system identifier of the thread
2774 you selected, and its current stack frame summary:
2777 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2778 (@value{GDBP}) thread 2
2779 [Switching to process 35 thread 23]
2780 0x34e5 in sigpause ()
2784 As with the @samp{[New @dots{}]} message, the form of the text after
2785 @samp{Switching to} depends on your system's conventions for identifying
2788 @kindex thread apply
2789 @cindex apply command to several threads
2790 @item thread apply [@var{threadno}] [@var{all}] @var{command}
2791 The @code{thread apply} command allows you to apply the named
2792 @var{command} to one or more threads. Specify the numbers of the
2793 threads that you want affected with the command argument
2794 @var{threadno}. It can be a single thread number, one of the numbers
2795 shown in the first field of the @samp{info threads} display; or it
2796 could be a range of thread numbers, as in @code{2-4}. To apply a
2797 command to all threads, type @kbd{thread apply all @var{command}}.
2799 @kindex set print thread-events
2800 @cindex print messages on thread start and exit
2801 @item set print thread-events
2802 @itemx set print thread-events on
2803 @itemx set print thread-events off
2804 The @code{set print thread-events} command allows you to enable or
2805 disable printing of messages when @value{GDBN} notices that new threads have
2806 started or that threads have exited. By default, these messages will
2807 be printed if detection of these events is supported by the target.
2808 Note that these messages cannot be disabled on all targets.
2810 @kindex show print thread-events
2811 @item show print thread-events
2812 Show whether messages will be printed when @value{GDBN} detects that threads
2813 have started and exited.
2816 @xref{Thread Stops,,Stopping and Starting Multi-thread Programs}, for
2817 more information about how @value{GDBN} behaves when you stop and start
2818 programs with multiple threads.
2820 @xref{Set Watchpoints,,Setting Watchpoints}, for information about
2821 watchpoints in programs with multiple threads.
2824 @kindex set libthread-db-search-path
2825 @cindex search path for @code{libthread_db}
2826 @item set libthread-db-search-path @r{[}@var{path}@r{]}
2827 If this variable is set, @var{path} is a colon-separated list of
2828 directories @value{GDBN} will use to search for @code{libthread_db}.
2829 If you omit @var{path}, @samp{libthread-db-search-path} will be reset to
2832 On @sc{gnu}/Linux and Solaris systems, @value{GDBN} uses a ``helper''
2833 @code{libthread_db} library to obtain information about threads in the
2834 inferior process. @value{GDBN} will use @samp{libthread-db-search-path}
2835 to find @code{libthread_db}. If that fails, @value{GDBN} will continue
2836 with default system shared library directories, and finally the directory
2837 from which @code{libpthread} was loaded in the inferior process.
2839 For any @code{libthread_db} library @value{GDBN} finds in above directories,
2840 @value{GDBN} attempts to initialize it with the current inferior process.
2841 If this initialization fails (which could happen because of a version
2842 mismatch between @code{libthread_db} and @code{libpthread}), @value{GDBN}
2843 will unload @code{libthread_db}, and continue with the next directory.
2844 If none of @code{libthread_db} libraries initialize successfully,
2845 @value{GDBN} will issue a warning and thread debugging will be disabled.
2847 Setting @code{libthread-db-search-path} is currently implemented
2848 only on some platforms.
2850 @kindex show libthread-db-search-path
2851 @item show libthread-db-search-path
2852 Display current libthread_db search path.
2856 @section Debugging Forks
2858 @cindex fork, debugging programs which call
2859 @cindex multiple processes
2860 @cindex processes, multiple
2861 On most systems, @value{GDBN} has no special support for debugging
2862 programs which create additional processes using the @code{fork}
2863 function. When a program forks, @value{GDBN} will continue to debug the
2864 parent process and the child process will run unimpeded. If you have
2865 set a breakpoint in any code which the child then executes, the child
2866 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2867 will cause it to terminate.
2869 However, if you want to debug the child process there is a workaround
2870 which isn't too painful. Put a call to @code{sleep} in the code which
2871 the child process executes after the fork. It may be useful to sleep
2872 only if a certain environment variable is set, or a certain file exists,
2873 so that the delay need not occur when you don't want to run @value{GDBN}
2874 on the child. While the child is sleeping, use the @code{ps} program to
2875 get its process ID. Then tell @value{GDBN} (a new invocation of
2876 @value{GDBN} if you are also debugging the parent process) to attach to
2877 the child process (@pxref{Attach}). From that point on you can debug
2878 the child process just like any other process which you attached to.
2880 On some systems, @value{GDBN} provides support for debugging programs that
2881 create additional processes using the @code{fork} or @code{vfork} functions.
2882 Currently, the only platforms with this feature are HP-UX (11.x and later
2883 only?) and @sc{gnu}/Linux (kernel version 2.5.60 and later).
2885 By default, when a program forks, @value{GDBN} will continue to debug
2886 the parent process and the child process will run unimpeded.
2888 If you want to follow the child process instead of the parent process,
2889 use the command @w{@code{set follow-fork-mode}}.
2892 @kindex set follow-fork-mode
2893 @item set follow-fork-mode @var{mode}
2894 Set the debugger response to a program call of @code{fork} or
2895 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2896 process. The @var{mode} argument can be:
2900 The original process is debugged after a fork. The child process runs
2901 unimpeded. This is the default.
2904 The new process is debugged after a fork. The parent process runs
2909 @kindex show follow-fork-mode
2910 @item show follow-fork-mode
2911 Display the current debugger response to a @code{fork} or @code{vfork} call.
2914 @cindex debugging multiple processes
2915 On Linux, if you want to debug both the parent and child processes, use the
2916 command @w{@code{set detach-on-fork}}.
2919 @kindex set detach-on-fork
2920 @item set detach-on-fork @var{mode}
2921 Tells gdb whether to detach one of the processes after a fork, or
2922 retain debugger control over them both.
2926 The child process (or parent process, depending on the value of
2927 @code{follow-fork-mode}) will be detached and allowed to run
2928 independently. This is the default.
2931 Both processes will be held under the control of @value{GDBN}.
2932 One process (child or parent, depending on the value of
2933 @code{follow-fork-mode}) is debugged as usual, while the other
2938 @kindex show detach-on-fork
2939 @item show detach-on-fork
2940 Show whether detach-on-fork mode is on/off.
2943 If you choose to set @samp{detach-on-fork} mode off, then @value{GDBN}
2944 will retain control of all forked processes (including nested forks).
2945 You can list the forked processes under the control of @value{GDBN} by
2946 using the @w{@code{info inferiors}} command, and switch from one fork
2947 to another by using the @code{inferior} command (@pxref{Inferiors and
2948 Programs, ,Debugging Multiple Inferiors and Programs}).
2950 To quit debugging one of the forked processes, you can either detach
2951 from it by using the @w{@code{detach inferior}} command (allowing it
2952 to run independently), or kill it using the @w{@code{kill inferior}}
2953 command. @xref{Inferiors and Programs, ,Debugging Multiple Inferiors
2956 If you ask to debug a child process and a @code{vfork} is followed by an
2957 @code{exec}, @value{GDBN} executes the new target up to the first
2958 breakpoint in the new target. If you have a breakpoint set on
2959 @code{main} in your original program, the breakpoint will also be set on
2960 the child process's @code{main}.
2962 On some systems, when a child process is spawned by @code{vfork}, you
2963 cannot debug the child or parent until an @code{exec} call completes.
2965 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2966 call executes, the new target restarts. To restart the parent
2967 process, use the @code{file} command with the parent executable name
2968 as its argument. By default, after an @code{exec} call executes,
2969 @value{GDBN} discards the symbols of the previous executable image.
2970 You can change this behaviour with the @w{@code{set follow-exec-mode}}
2974 @kindex set follow-exec-mode
2975 @item set follow-exec-mode @var{mode}
2977 Set debugger response to a program call of @code{exec}. An
2978 @code{exec} call replaces the program image of a process.
2980 @code{follow-exec-mode} can be:
2984 @value{GDBN} creates a new inferior and rebinds the process to this
2985 new inferior. The program the process was running before the
2986 @code{exec} call can be restarted afterwards by restarting the
2992 (@value{GDBP}) info inferiors
2994 Id Description Executable
2997 process 12020 is executing new program: prog2
2998 Program exited normally.
2999 (@value{GDBP}) info inferiors
3000 Id Description Executable
3006 @value{GDBN} keeps the process bound to the same inferior. The new
3007 executable image replaces the previous executable loaded in the
3008 inferior. Restarting the inferior after the @code{exec} call, with
3009 e.g., the @code{run} command, restarts the executable the process was
3010 running after the @code{exec} call. This is the default mode.
3015 (@value{GDBP}) info inferiors
3016 Id Description Executable
3019 process 12020 is executing new program: prog2
3020 Program exited normally.
3021 (@value{GDBP}) info inferiors
3022 Id Description Executable
3029 You can use the @code{catch} command to make @value{GDBN} stop whenever
3030 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
3031 Catchpoints, ,Setting Catchpoints}.
3033 @node Checkpoint/Restart
3034 @section Setting a @emph{Bookmark} to Return to Later
3039 @cindex snapshot of a process
3040 @cindex rewind program state
3042 On certain operating systems@footnote{Currently, only
3043 @sc{gnu}/Linux.}, @value{GDBN} is able to save a @dfn{snapshot} of a
3044 program's state, called a @dfn{checkpoint}, and come back to it
3047 Returning to a checkpoint effectively undoes everything that has
3048 happened in the program since the @code{checkpoint} was saved. This
3049 includes changes in memory, registers, and even (within some limits)
3050 system state. Effectively, it is like going back in time to the
3051 moment when the checkpoint was saved.
3053 Thus, if you're stepping thru a program and you think you're
3054 getting close to the point where things go wrong, you can save
3055 a checkpoint. Then, if you accidentally go too far and miss
3056 the critical statement, instead of having to restart your program
3057 from the beginning, you can just go back to the checkpoint and
3058 start again from there.
3060 This can be especially useful if it takes a lot of time or
3061 steps to reach the point where you think the bug occurs.
3063 To use the @code{checkpoint}/@code{restart} method of debugging:
3068 Save a snapshot of the debugged program's current execution state.
3069 The @code{checkpoint} command takes no arguments, but each checkpoint
3070 is assigned a small integer id, similar to a breakpoint id.
3072 @kindex info checkpoints
3073 @item info checkpoints
3074 List the checkpoints that have been saved in the current debugging
3075 session. For each checkpoint, the following information will be
3082 @item Source line, or label
3085 @kindex restart @var{checkpoint-id}
3086 @item restart @var{checkpoint-id}
3087 Restore the program state that was saved as checkpoint number
3088 @var{checkpoint-id}. All program variables, registers, stack frames
3089 etc.@: will be returned to the values that they had when the checkpoint
3090 was saved. In essence, gdb will ``wind back the clock'' to the point
3091 in time when the checkpoint was saved.
3093 Note that breakpoints, @value{GDBN} variables, command history etc.
3094 are not affected by restoring a checkpoint. In general, a checkpoint
3095 only restores things that reside in the program being debugged, not in
3098 @kindex delete checkpoint @var{checkpoint-id}
3099 @item delete checkpoint @var{checkpoint-id}
3100 Delete the previously-saved checkpoint identified by @var{checkpoint-id}.
3104 Returning to a previously saved checkpoint will restore the user state
3105 of the program being debugged, plus a significant subset of the system
3106 (OS) state, including file pointers. It won't ``un-write'' data from
3107 a file, but it will rewind the file pointer to the previous location,
3108 so that the previously written data can be overwritten. For files
3109 opened in read mode, the pointer will also be restored so that the
3110 previously read data can be read again.
3112 Of course, characters that have been sent to a printer (or other
3113 external device) cannot be ``snatched back'', and characters received
3114 from eg.@: a serial device can be removed from internal program buffers,
3115 but they cannot be ``pushed back'' into the serial pipeline, ready to
3116 be received again. Similarly, the actual contents of files that have
3117 been changed cannot be restored (at this time).
3119 However, within those constraints, you actually can ``rewind'' your
3120 program to a previously saved point in time, and begin debugging it
3121 again --- and you can change the course of events so as to debug a
3122 different execution path this time.
3124 @cindex checkpoints and process id
3125 Finally, there is one bit of internal program state that will be
3126 different when you return to a checkpoint --- the program's process
3127 id. Each checkpoint will have a unique process id (or @var{pid}),
3128 and each will be different from the program's original @var{pid}.
3129 If your program has saved a local copy of its process id, this could
3130 potentially pose a problem.
3132 @subsection A Non-obvious Benefit of Using Checkpoints
3134 On some systems such as @sc{gnu}/Linux, address space randomization
3135 is performed on new processes for security reasons. This makes it
3136 difficult or impossible to set a breakpoint, or watchpoint, on an
3137 absolute address if you have to restart the program, since the
3138 absolute location of a symbol will change from one execution to the
3141 A checkpoint, however, is an @emph{identical} copy of a process.
3142 Therefore if you create a checkpoint at (eg.@:) the start of main,
3143 and simply return to that checkpoint instead of restarting the
3144 process, you can avoid the effects of address randomization and
3145 your symbols will all stay in the same place.
3148 @chapter Stopping and Continuing
3150 The principal purposes of using a debugger are so that you can stop your
3151 program before it terminates; or so that, if your program runs into
3152 trouble, you can investigate and find out why.
3154 Inside @value{GDBN}, your program may stop for any of several reasons,
3155 such as a signal, a breakpoint, or reaching a new line after a
3156 @value{GDBN} command such as @code{step}. You may then examine and
3157 change variables, set new breakpoints or remove old ones, and then
3158 continue execution. Usually, the messages shown by @value{GDBN} provide
3159 ample explanation of the status of your program---but you can also
3160 explicitly request this information at any time.
3163 @kindex info program
3165 Display information about the status of your program: whether it is
3166 running or not, what process it is, and why it stopped.
3170 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
3171 * Continuing and Stepping:: Resuming execution
3173 * Thread Stops:: Stopping and starting multi-thread programs
3177 @section Breakpoints, Watchpoints, and Catchpoints
3180 A @dfn{breakpoint} makes your program stop whenever a certain point in
3181 the program is reached. For each breakpoint, you can add conditions to
3182 control in finer detail whether your program stops. You can set
3183 breakpoints with the @code{break} command and its variants (@pxref{Set
3184 Breaks, ,Setting Breakpoints}), to specify the place where your program
3185 should stop by line number, function name or exact address in the
3188 On some systems, you can set breakpoints in shared libraries before
3189 the executable is run. There is a minor limitation on HP-UX systems:
3190 you must wait until the executable is run in order to set breakpoints
3191 in shared library routines that are not called directly by the program
3192 (for example, routines that are arguments in a @code{pthread_create}
3196 @cindex data breakpoints
3197 @cindex memory tracing
3198 @cindex breakpoint on memory address
3199 @cindex breakpoint on variable modification
3200 A @dfn{watchpoint} is a special breakpoint that stops your program
3201 when the value of an expression changes. The expression may be a value
3202 of a variable, or it could involve values of one or more variables
3203 combined by operators, such as @samp{a + b}. This is sometimes called
3204 @dfn{data breakpoints}. You must use a different command to set
3205 watchpoints (@pxref{Set Watchpoints, ,Setting Watchpoints}), but aside
3206 from that, you can manage a watchpoint like any other breakpoint: you
3207 enable, disable, and delete both breakpoints and watchpoints using the
3210 You can arrange to have values from your program displayed automatically
3211 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
3215 @cindex breakpoint on events
3216 A @dfn{catchpoint} is another special breakpoint that stops your program
3217 when a certain kind of event occurs, such as the throwing of a C@t{++}
3218 exception or the loading of a library. As with watchpoints, you use a
3219 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
3220 Catchpoints}), but aside from that, you can manage a catchpoint like any
3221 other breakpoint. (To stop when your program receives a signal, use the
3222 @code{handle} command; see @ref{Signals, ,Signals}.)
3224 @cindex breakpoint numbers
3225 @cindex numbers for breakpoints
3226 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
3227 catchpoint when you create it; these numbers are successive integers
3228 starting with one. In many of the commands for controlling various
3229 features of breakpoints you use the breakpoint number to say which
3230 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
3231 @dfn{disabled}; if disabled, it has no effect on your program until you
3234 @cindex breakpoint ranges
3235 @cindex ranges of breakpoints
3236 Some @value{GDBN} commands accept a range of breakpoints on which to
3237 operate. A breakpoint range is either a single breakpoint number, like
3238 @samp{5}, or two such numbers, in increasing order, separated by a
3239 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
3240 all breakpoints in that range are operated on.
3243 * Set Breaks:: Setting breakpoints
3244 * Set Watchpoints:: Setting watchpoints
3245 * Set Catchpoints:: Setting catchpoints
3246 * Delete Breaks:: Deleting breakpoints
3247 * Disabling:: Disabling breakpoints
3248 * Conditions:: Break conditions
3249 * Break Commands:: Breakpoint command lists
3250 * Save Breakpoints:: How to save breakpoints in a file
3251 * Error in Breakpoints:: ``Cannot insert breakpoints''
3252 * Breakpoint-related Warnings:: ``Breakpoint address adjusted...''
3256 @subsection Setting Breakpoints
3258 @c FIXME LMB what does GDB do if no code on line of breakpt?
3259 @c consider in particular declaration with/without initialization.
3261 @c FIXME 2 is there stuff on this already? break at fun start, already init?
3264 @kindex b @r{(@code{break})}
3265 @vindex $bpnum@r{, convenience variable}
3266 @cindex latest breakpoint
3267 Breakpoints are set with the @code{break} command (abbreviated
3268 @code{b}). The debugger convenience variable @samp{$bpnum} records the
3269 number of the breakpoint you've set most recently; see @ref{Convenience
3270 Vars,, Convenience Variables}, for a discussion of what you can do with
3271 convenience variables.
3274 @item break @var{location}
3275 Set a breakpoint at the given @var{location}, which can specify a
3276 function name, a line number, or an address of an instruction.
3277 (@xref{Specify Location}, for a list of all the possible ways to
3278 specify a @var{location}.) The breakpoint will stop your program just
3279 before it executes any of the code in the specified @var{location}.
3281 When using source languages that permit overloading of symbols, such as
3282 C@t{++}, a function name may refer to more than one possible place to break.
3283 @xref{Ambiguous Expressions,,Ambiguous Expressions}, for a discussion of
3286 It is also possible to insert a breakpoint that will stop the program
3287 only if a specific thread (@pxref{Thread-Specific Breakpoints})
3288 or a specific task (@pxref{Ada Tasks}) hits that breakpoint.
3291 When called without any arguments, @code{break} sets a breakpoint at
3292 the next instruction to be executed in the selected stack frame
3293 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
3294 innermost, this makes your program stop as soon as control
3295 returns to that frame. This is similar to the effect of a
3296 @code{finish} command in the frame inside the selected frame---except
3297 that @code{finish} does not leave an active breakpoint. If you use
3298 @code{break} without an argument in the innermost frame, @value{GDBN} stops
3299 the next time it reaches the current location; this may be useful
3302 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
3303 least one instruction has been executed. If it did not do this, you
3304 would be unable to proceed past a breakpoint without first disabling the
3305 breakpoint. This rule applies whether or not the breakpoint already
3306 existed when your program stopped.
3308 @item break @dots{} if @var{cond}
3309 Set a breakpoint with condition @var{cond}; evaluate the expression
3310 @var{cond} each time the breakpoint is reached, and stop only if the
3311 value is nonzero---that is, if @var{cond} evaluates as true.
3312 @samp{@dots{}} stands for one of the possible arguments described
3313 above (or no argument) specifying where to break. @xref{Conditions,
3314 ,Break Conditions}, for more information on breakpoint conditions.
3317 @item tbreak @var{args}
3318 Set a breakpoint enabled only for one stop. @var{args} are the
3319 same as for the @code{break} command, and the breakpoint is set in the same
3320 way, but the breakpoint is automatically deleted after the first time your
3321 program stops there. @xref{Disabling, ,Disabling Breakpoints}.
3324 @cindex hardware breakpoints
3325 @item hbreak @var{args}
3326 Set a hardware-assisted breakpoint. @var{args} are the same as for the
3327 @code{break} command and the breakpoint is set in the same way, but the
3328 breakpoint requires hardware support and some target hardware may not
3329 have this support. The main purpose of this is EPROM/ROM code
3330 debugging, so you can set a breakpoint at an instruction without
3331 changing the instruction. This can be used with the new trap-generation
3332 provided by SPARClite DSU and most x86-based targets. These targets
3333 will generate traps when a program accesses some data or instruction
3334 address that is assigned to the debug registers. However the hardware
3335 breakpoint registers can take a limited number of breakpoints. For
3336 example, on the DSU, only two data breakpoints can be set at a time, and
3337 @value{GDBN} will reject this command if more than two are used. Delete
3338 or disable unused hardware breakpoints before setting new ones
3339 (@pxref{Disabling, ,Disabling Breakpoints}).
3340 @xref{Conditions, ,Break Conditions}.
3341 For remote targets, you can restrict the number of hardware
3342 breakpoints @value{GDBN} will use, see @ref{set remote
3343 hardware-breakpoint-limit}.
3346 @item thbreak @var{args}
3347 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
3348 are the same as for the @code{hbreak} command and the breakpoint is set in
3349 the same way. However, like the @code{tbreak} command,
3350 the breakpoint is automatically deleted after the
3351 first time your program stops there. Also, like the @code{hbreak}
3352 command, the breakpoint requires hardware support and some target hardware
3353 may not have this support. @xref{Disabling, ,Disabling Breakpoints}.
3354 See also @ref{Conditions, ,Break Conditions}.
3357 @cindex regular expression
3358 @cindex breakpoints in functions matching a regexp
3359 @cindex set breakpoints in many functions
3360 @item rbreak @var{regex}
3361 Set breakpoints on all functions matching the regular expression
3362 @var{regex}. This command sets an unconditional breakpoint on all
3363 matches, printing a list of all breakpoints it set. Once these
3364 breakpoints are set, they are treated just like the breakpoints set with
3365 the @code{break} command. You can delete them, disable them, or make
3366 them conditional the same way as any other breakpoint.
3368 The syntax of the regular expression is the standard one used with tools
3369 like @file{grep}. Note that this is different from the syntax used by
3370 shells, so for instance @code{foo*} matches all functions that include
3371 an @code{fo} followed by zero or more @code{o}s. There is an implicit
3372 @code{.*} leading and trailing the regular expression you supply, so to
3373 match only functions that begin with @code{foo}, use @code{^foo}.
3375 @cindex non-member C@t{++} functions, set breakpoint in
3376 When debugging C@t{++} programs, @code{rbreak} is useful for setting
3377 breakpoints on overloaded functions that are not members of any special
3380 @cindex set breakpoints on all functions
3381 The @code{rbreak} command can be used to set breakpoints in
3382 @strong{all} the functions in a program, like this:
3385 (@value{GDBP}) rbreak .
3388 @kindex info breakpoints
3389 @cindex @code{$_} and @code{info breakpoints}
3390 @item info breakpoints @r{[}@var{n}@r{]}
3391 @itemx info break @r{[}@var{n}@r{]}
3392 Print a table of all breakpoints, watchpoints, and catchpoints set and
3393 not deleted. Optional argument @var{n} means print information only
3394 about the specified breakpoint (or watchpoint or catchpoint). For
3395 each breakpoint, following columns are printed:
3398 @item Breakpoint Numbers
3400 Breakpoint, watchpoint, or catchpoint.
3402 Whether the breakpoint is marked to be disabled or deleted when hit.
3403 @item Enabled or Disabled
3404 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
3405 that are not enabled.
3407 Where the breakpoint is in your program, as a memory address. For a
3408 pending breakpoint whose address is not yet known, this field will
3409 contain @samp{<PENDING>}. Such breakpoint won't fire until a shared
3410 library that has the symbol or line referred by breakpoint is loaded.
3411 See below for details. A breakpoint with several locations will
3412 have @samp{<MULTIPLE>} in this field---see below for details.
3414 Where the breakpoint is in the source for your program, as a file and
3415 line number. For a pending breakpoint, the original string passed to
3416 the breakpoint command will be listed as it cannot be resolved until
3417 the appropriate shared library is loaded in the future.
3421 If a breakpoint is conditional, @code{info break} shows the condition on
3422 the line following the affected breakpoint; breakpoint commands, if any,
3423 are listed after that. A pending breakpoint is allowed to have a condition
3424 specified for it. The condition is not parsed for validity until a shared
3425 library is loaded that allows the pending breakpoint to resolve to a
3429 @code{info break} with a breakpoint
3430 number @var{n} as argument lists only that breakpoint. The
3431 convenience variable @code{$_} and the default examining-address for
3432 the @code{x} command are set to the address of the last breakpoint
3433 listed (@pxref{Memory, ,Examining Memory}).
3436 @code{info break} displays a count of the number of times the breakpoint
3437 has been hit. This is especially useful in conjunction with the
3438 @code{ignore} command. You can ignore a large number of breakpoint
3439 hits, look at the breakpoint info to see how many times the breakpoint
3440 was hit, and then run again, ignoring one less than that number. This
3441 will get you quickly to the last hit of that breakpoint.
3444 @value{GDBN} allows you to set any number of breakpoints at the same place in
3445 your program. There is nothing silly or meaningless about this. When
3446 the breakpoints are conditional, this is even useful
3447 (@pxref{Conditions, ,Break Conditions}).
3449 @cindex multiple locations, breakpoints
3450 @cindex breakpoints, multiple locations
3451 It is possible that a breakpoint corresponds to several locations
3452 in your program. Examples of this situation are:
3456 For a C@t{++} constructor, the @value{NGCC} compiler generates several
3457 instances of the function body, used in different cases.
3460 For a C@t{++} template function, a given line in the function can
3461 correspond to any number of instantiations.
3464 For an inlined function, a given source line can correspond to
3465 several places where that function is inlined.
3468 In all those cases, @value{GDBN} will insert a breakpoint at all
3469 the relevant locations@footnote{
3470 As of this writing, multiple-location breakpoints work only if there's
3471 line number information for all the locations. This means that they
3472 will generally not work in system libraries, unless you have debug
3473 info with line numbers for them.}.
3475 A breakpoint with multiple locations is displayed in the breakpoint
3476 table using several rows---one header row, followed by one row for
3477 each breakpoint location. The header row has @samp{<MULTIPLE>} in the
3478 address column. The rows for individual locations contain the actual
3479 addresses for locations, and show the functions to which those
3480 locations belong. The number column for a location is of the form
3481 @var{breakpoint-number}.@var{location-number}.
3486 Num Type Disp Enb Address What
3487 1 breakpoint keep y <MULTIPLE>
3489 breakpoint already hit 1 time
3490 1.1 y 0x080486a2 in void foo<int>() at t.cc:8
3491 1.2 y 0x080486ca in void foo<double>() at t.cc:8
3494 Each location can be individually enabled or disabled by passing
3495 @var{breakpoint-number}.@var{location-number} as argument to the
3496 @code{enable} and @code{disable} commands. Note that you cannot
3497 delete the individual locations from the list, you can only delete the
3498 entire list of locations that belong to their parent breakpoint (with
3499 the @kbd{delete @var{num}} command, where @var{num} is the number of
3500 the parent breakpoint, 1 in the above example). Disabling or enabling
3501 the parent breakpoint (@pxref{Disabling}) affects all of the locations
3502 that belong to that breakpoint.
3504 @cindex pending breakpoints
3505 It's quite common to have a breakpoint inside a shared library.
3506 Shared libraries can be loaded and unloaded explicitly,
3507 and possibly repeatedly, as the program is executed. To support
3508 this use case, @value{GDBN} updates breakpoint locations whenever
3509 any shared library is loaded or unloaded. Typically, you would
3510 set a breakpoint in a shared library at the beginning of your
3511 debugging session, when the library is not loaded, and when the
3512 symbols from the library are not available. When you try to set
3513 breakpoint, @value{GDBN} will ask you if you want to set
3514 a so called @dfn{pending breakpoint}---breakpoint whose address
3515 is not yet resolved.
3517 After the program is run, whenever a new shared library is loaded,
3518 @value{GDBN} reevaluates all the breakpoints. When a newly loaded
3519 shared library contains the symbol or line referred to by some
3520 pending breakpoint, that breakpoint is resolved and becomes an
3521 ordinary breakpoint. When a library is unloaded, all breakpoints
3522 that refer to its symbols or source lines become pending again.
3524 This logic works for breakpoints with multiple locations, too. For
3525 example, if you have a breakpoint in a C@t{++} template function, and
3526 a newly loaded shared library has an instantiation of that template,
3527 a new location is added to the list of locations for the breakpoint.
3529 Except for having unresolved address, pending breakpoints do not
3530 differ from regular breakpoints. You can set conditions or commands,
3531 enable and disable them and perform other breakpoint operations.
3533 @value{GDBN} provides some additional commands for controlling what
3534 happens when the @samp{break} command cannot resolve breakpoint
3535 address specification to an address:
3537 @kindex set breakpoint pending
3538 @kindex show breakpoint pending
3540 @item set breakpoint pending auto
3541 This is the default behavior. When @value{GDBN} cannot find the breakpoint
3542 location, it queries you whether a pending breakpoint should be created.
3544 @item set breakpoint pending on
3545 This indicates that an unrecognized breakpoint location should automatically
3546 result in a pending breakpoint being created.
3548 @item set breakpoint pending off
3549 This indicates that pending breakpoints are not to be created. Any
3550 unrecognized breakpoint location results in an error. This setting does
3551 not affect any pending breakpoints previously created.
3553 @item show breakpoint pending
3554 Show the current behavior setting for creating pending breakpoints.
3557 The settings above only affect the @code{break} command and its
3558 variants. Once breakpoint is set, it will be automatically updated
3559 as shared libraries are loaded and unloaded.
3561 @cindex automatic hardware breakpoints
3562 For some targets, @value{GDBN} can automatically decide if hardware or
3563 software breakpoints should be used, depending on whether the
3564 breakpoint address is read-only or read-write. This applies to
3565 breakpoints set with the @code{break} command as well as to internal
3566 breakpoints set by commands like @code{next} and @code{finish}. For
3567 breakpoints set with @code{hbreak}, @value{GDBN} will always use hardware
3570 You can control this automatic behaviour with the following commands::
3572 @kindex set breakpoint auto-hw
3573 @kindex show breakpoint auto-hw
3575 @item set breakpoint auto-hw on
3576 This is the default behavior. When @value{GDBN} sets a breakpoint, it
3577 will try to use the target memory map to decide if software or hardware
3578 breakpoint must be used.
3580 @item set breakpoint auto-hw off
3581 This indicates @value{GDBN} should not automatically select breakpoint
3582 type. If the target provides a memory map, @value{GDBN} will warn when
3583 trying to set software breakpoint at a read-only address.
3586 @value{GDBN} normally implements breakpoints by replacing the program code
3587 at the breakpoint address with a special instruction, which, when
3588 executed, given control to the debugger. By default, the program
3589 code is so modified only when the program is resumed. As soon as
3590 the program stops, @value{GDBN} restores the original instructions. This
3591 behaviour guards against leaving breakpoints inserted in the
3592 target should gdb abrubptly disconnect. However, with slow remote
3593 targets, inserting and removing breakpoint can reduce the performance.
3594 This behavior can be controlled with the following commands::
3596 @kindex set breakpoint always-inserted
3597 @kindex show breakpoint always-inserted
3599 @item set breakpoint always-inserted off
3600 All breakpoints, including newly added by the user, are inserted in
3601 the target only when the target is resumed. All breakpoints are
3602 removed from the target when it stops.
3604 @item set breakpoint always-inserted on
3605 Causes all breakpoints to be inserted in the target at all times. If
3606 the user adds a new breakpoint, or changes an existing breakpoint, the
3607 breakpoints in the target are updated immediately. A breakpoint is
3608 removed from the target only when breakpoint itself is removed.
3610 @cindex non-stop mode, and @code{breakpoint always-inserted}
3611 @item set breakpoint always-inserted auto
3612 This is the default mode. If @value{GDBN} is controlling the inferior
3613 in non-stop mode (@pxref{Non-Stop Mode}), gdb behaves as if
3614 @code{breakpoint always-inserted} mode is on. If @value{GDBN} is
3615 controlling the inferior in all-stop mode, @value{GDBN} behaves as if
3616 @code{breakpoint always-inserted} mode is off.
3619 @cindex negative breakpoint numbers
3620 @cindex internal @value{GDBN} breakpoints
3621 @value{GDBN} itself sometimes sets breakpoints in your program for
3622 special purposes, such as proper handling of @code{longjmp} (in C
3623 programs). These internal breakpoints are assigned negative numbers,
3624 starting with @code{-1}; @samp{info breakpoints} does not display them.
3625 You can see these breakpoints with the @value{GDBN} maintenance command
3626 @samp{maint info breakpoints} (@pxref{maint info breakpoints}).
3629 @node Set Watchpoints
3630 @subsection Setting Watchpoints
3632 @cindex setting watchpoints
3633 You can use a watchpoint to stop execution whenever the value of an
3634 expression changes, without having to predict a particular place where
3635 this may happen. (This is sometimes called a @dfn{data breakpoint}.)
3636 The expression may be as simple as the value of a single variable, or
3637 as complex as many variables combined by operators. Examples include:
3641 A reference to the value of a single variable.
3644 An address cast to an appropriate data type. For example,
3645 @samp{*(int *)0x12345678} will watch a 4-byte region at the specified
3646 address (assuming an @code{int} occupies 4 bytes).
3649 An arbitrarily complex expression, such as @samp{a*b + c/d}. The
3650 expression can use any operators valid in the program's native
3651 language (@pxref{Languages}).
3654 You can set a watchpoint on an expression even if the expression can
3655 not be evaluated yet. For instance, you can set a watchpoint on
3656 @samp{*global_ptr} before @samp{global_ptr} is initialized.
3657 @value{GDBN} will stop when your program sets @samp{global_ptr} and
3658 the expression produces a valid value. If the expression becomes
3659 valid in some other way than changing a variable (e.g.@: if the memory
3660 pointed to by @samp{*global_ptr} becomes readable as the result of a
3661 @code{malloc} call), @value{GDBN} may not stop until the next time
3662 the expression changes.
3664 @cindex software watchpoints
3665 @cindex hardware watchpoints
3666 Depending on your system, watchpoints may be implemented in software or
3667 hardware. @value{GDBN} does software watchpointing by single-stepping your
3668 program and testing the variable's value each time, which is hundreds of
3669 times slower than normal execution. (But this may still be worth it, to
3670 catch errors where you have no clue what part of your program is the
3673 On some systems, such as HP-UX, PowerPC, @sc{gnu}/Linux and most other
3674 x86-based targets, @value{GDBN} includes support for hardware
3675 watchpoints, which do not slow down the running of your program.
3679 @item watch @var{expr} @r{[}thread @var{threadnum}@r{]}
3680 Set a watchpoint for an expression. @value{GDBN} will break when the
3681 expression @var{expr} is written into by the program and its value
3682 changes. The simplest (and the most popular) use of this command is
3683 to watch the value of a single variable:
3686 (@value{GDBP}) watch foo
3689 If the command includes a @code{@r{[}thread @var{threadnum}@r{]}}
3690 clause, @value{GDBN} breaks only when the thread identified by
3691 @var{threadnum} changes the value of @var{expr}. If any other threads
3692 change the value of @var{expr}, @value{GDBN} will not break. Note
3693 that watchpoints restricted to a single thread in this way only work
3694 with Hardware Watchpoints.
3697 @item rwatch @var{expr} @r{[}thread @var{threadnum}@r{]}
3698 Set a watchpoint that will break when the value of @var{expr} is read
3702 @item awatch @var{expr} @r{[}thread @var{threadnum}@r{]}
3703 Set a watchpoint that will break when @var{expr} is either read from
3704 or written into by the program.
3706 @kindex info watchpoints @r{[}@var{n}@r{]}
3707 @item info watchpoints
3708 This command prints a list of watchpoints, using the same format as
3709 @code{info break} (@pxref{Set Breaks}).
3712 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
3713 watchpoints execute very quickly, and the debugger reports a change in
3714 value at the exact instruction where the change occurs. If @value{GDBN}
3715 cannot set a hardware watchpoint, it sets a software watchpoint, which
3716 executes more slowly and reports the change in value at the next
3717 @emph{statement}, not the instruction, after the change occurs.
3719 @cindex use only software watchpoints
3720 You can force @value{GDBN} to use only software watchpoints with the
3721 @kbd{set can-use-hw-watchpoints 0} command. With this variable set to
3722 zero, @value{GDBN} will never try to use hardware watchpoints, even if
3723 the underlying system supports them. (Note that hardware-assisted
3724 watchpoints that were set @emph{before} setting
3725 @code{can-use-hw-watchpoints} to zero will still use the hardware
3726 mechanism of watching expression values.)
3729 @item set can-use-hw-watchpoints
3730 @kindex set can-use-hw-watchpoints
3731 Set whether or not to use hardware watchpoints.
3733 @item show can-use-hw-watchpoints
3734 @kindex show can-use-hw-watchpoints
3735 Show the current mode of using hardware watchpoints.
3738 For remote targets, you can restrict the number of hardware
3739 watchpoints @value{GDBN} will use, see @ref{set remote
3740 hardware-breakpoint-limit}.
3742 When you issue the @code{watch} command, @value{GDBN} reports
3745 Hardware watchpoint @var{num}: @var{expr}
3749 if it was able to set a hardware watchpoint.
3751 Currently, the @code{awatch} and @code{rwatch} commands can only set
3752 hardware watchpoints, because accesses to data that don't change the
3753 value of the watched expression cannot be detected without examining
3754 every instruction as it is being executed, and @value{GDBN} does not do
3755 that currently. If @value{GDBN} finds that it is unable to set a
3756 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
3757 will print a message like this:
3760 Expression cannot be implemented with read/access watchpoint.
3763 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
3764 data type of the watched expression is wider than what a hardware
3765 watchpoint on the target machine can handle. For example, some systems
3766 can only watch regions that are up to 4 bytes wide; on such systems you
3767 cannot set hardware watchpoints for an expression that yields a
3768 double-precision floating-point number (which is typically 8 bytes
3769 wide). As a work-around, it might be possible to break the large region
3770 into a series of smaller ones and watch them with separate watchpoints.
3772 If you set too many hardware watchpoints, @value{GDBN} might be unable
3773 to insert all of them when you resume the execution of your program.
3774 Since the precise number of active watchpoints is unknown until such
3775 time as the program is about to be resumed, @value{GDBN} might not be
3776 able to warn you about this when you set the watchpoints, and the
3777 warning will be printed only when the program is resumed:
3780 Hardware watchpoint @var{num}: Could not insert watchpoint
3784 If this happens, delete or disable some of the watchpoints.
3786 Watching complex expressions that reference many variables can also
3787 exhaust the resources available for hardware-assisted watchpoints.
3788 That's because @value{GDBN} needs to watch every variable in the
3789 expression with separately allocated resources.
3791 If you call a function interactively using @code{print} or @code{call},
3792 any watchpoints you have set will be inactive until @value{GDBN} reaches another
3793 kind of breakpoint or the call completes.
3795 @value{GDBN} automatically deletes watchpoints that watch local
3796 (automatic) variables, or expressions that involve such variables, when
3797 they go out of scope, that is, when the execution leaves the block in
3798 which these variables were defined. In particular, when the program
3799 being debugged terminates, @emph{all} local variables go out of scope,
3800 and so only watchpoints that watch global variables remain set. If you
3801 rerun the program, you will need to set all such watchpoints again. One
3802 way of doing that would be to set a code breakpoint at the entry to the
3803 @code{main} function and when it breaks, set all the watchpoints.
3805 @cindex watchpoints and threads
3806 @cindex threads and watchpoints
3807 In multi-threaded programs, watchpoints will detect changes to the
3808 watched expression from every thread.
3811 @emph{Warning:} In multi-threaded programs, software watchpoints
3812 have only limited usefulness. If @value{GDBN} creates a software
3813 watchpoint, it can only watch the value of an expression @emph{in a
3814 single thread}. If you are confident that the expression can only
3815 change due to the current thread's activity (and if you are also
3816 confident that no other thread can become current), then you can use
3817 software watchpoints as usual. However, @value{GDBN} may not notice
3818 when a non-current thread's activity changes the expression. (Hardware
3819 watchpoints, in contrast, watch an expression in all threads.)
3822 @xref{set remote hardware-watchpoint-limit}.
3824 @node Set Catchpoints
3825 @subsection Setting Catchpoints
3826 @cindex catchpoints, setting
3827 @cindex exception handlers
3828 @cindex event handling
3830 You can use @dfn{catchpoints} to cause the debugger to stop for certain
3831 kinds of program events, such as C@t{++} exceptions or the loading of a
3832 shared library. Use the @code{catch} command to set a catchpoint.
3836 @item catch @var{event}
3837 Stop when @var{event} occurs. @var{event} can be any of the following:
3840 @cindex stop on C@t{++} exceptions
3841 The throwing of a C@t{++} exception.
3844 The catching of a C@t{++} exception.
3847 @cindex Ada exception catching
3848 @cindex catch Ada exceptions
3849 An Ada exception being raised. If an exception name is specified
3850 at the end of the command (eg @code{catch exception Program_Error}),
3851 the debugger will stop only when this specific exception is raised.
3852 Otherwise, the debugger stops execution when any Ada exception is raised.
3854 When inserting an exception catchpoint on a user-defined exception whose
3855 name is identical to one of the exceptions defined by the language, the
3856 fully qualified name must be used as the exception name. Otherwise,
3857 @value{GDBN} will assume that it should stop on the pre-defined exception
3858 rather than the user-defined one. For instance, assuming an exception
3859 called @code{Constraint_Error} is defined in package @code{Pck}, then
3860 the command to use to catch such exceptions is @kbd{catch exception
3861 Pck.Constraint_Error}.
3863 @item exception unhandled
3864 An exception that was raised but is not handled by the program.
3867 A failed Ada assertion.
3870 @cindex break on fork/exec
3871 A call to @code{exec}. This is currently only available for HP-UX
3875 @itemx syscall @r{[}@var{name} @r{|} @var{number}@r{]} @dots{}
3876 @cindex break on a system call.
3877 A call to or return from a system call, a.k.a.@: @dfn{syscall}. A
3878 syscall is a mechanism for application programs to request a service
3879 from the operating system (OS) or one of the OS system services.
3880 @value{GDBN} can catch some or all of the syscalls issued by the
3881 debuggee, and show the related information for each syscall. If no
3882 argument is specified, calls to and returns from all system calls
3885 @var{name} can be any system call name that is valid for the
3886 underlying OS. Just what syscalls are valid depends on the OS. On
3887 GNU and Unix systems, you can find the full list of valid syscall
3888 names on @file{/usr/include/asm/unistd.h}.
3890 @c For MS-Windows, the syscall names and the corresponding numbers
3891 @c can be found, e.g., on this URL:
3892 @c http://www.metasploit.com/users/opcode/syscalls.html
3893 @c but we don't support Windows syscalls yet.
3895 Normally, @value{GDBN} knows in advance which syscalls are valid for
3896 each OS, so you can use the @value{GDBN} command-line completion
3897 facilities (@pxref{Completion,, command completion}) to list the
3900 You may also specify the system call numerically. A syscall's
3901 number is the value passed to the OS's syscall dispatcher to
3902 identify the requested service. When you specify the syscall by its
3903 name, @value{GDBN} uses its database of syscalls to convert the name
3904 into the corresponding numeric code, but using the number directly
3905 may be useful if @value{GDBN}'s database does not have the complete
3906 list of syscalls on your system (e.g., because @value{GDBN} lags
3907 behind the OS upgrades).
3909 The example below illustrates how this command works if you don't provide
3913 (@value{GDBP}) catch syscall
3914 Catchpoint 1 (syscall)
3916 Starting program: /tmp/catch-syscall
3918 Catchpoint 1 (call to syscall 'close'), \
3919 0xffffe424 in __kernel_vsyscall ()
3923 Catchpoint 1 (returned from syscall 'close'), \
3924 0xffffe424 in __kernel_vsyscall ()
3928 Here is an example of catching a system call by name:
3931 (@value{GDBP}) catch syscall chroot
3932 Catchpoint 1 (syscall 'chroot' [61])
3934 Starting program: /tmp/catch-syscall
3936 Catchpoint 1 (call to syscall 'chroot'), \
3937 0xffffe424 in __kernel_vsyscall ()
3941 Catchpoint 1 (returned from syscall 'chroot'), \
3942 0xffffe424 in __kernel_vsyscall ()
3946 An example of specifying a system call numerically. In the case
3947 below, the syscall number has a corresponding entry in the XML
3948 file, so @value{GDBN} finds its name and prints it:
3951 (@value{GDBP}) catch syscall 252
3952 Catchpoint 1 (syscall(s) 'exit_group')
3954 Starting program: /tmp/catch-syscall
3956 Catchpoint 1 (call to syscall 'exit_group'), \
3957 0xffffe424 in __kernel_vsyscall ()
3961 Program exited normally.
3965 However, there can be situations when there is no corresponding name
3966 in XML file for that syscall number. In this case, @value{GDBN} prints
3967 a warning message saying that it was not able to find the syscall name,
3968 but the catchpoint will be set anyway. See the example below:
3971 (@value{GDBP}) catch syscall 764
3972 warning: The number '764' does not represent a known syscall.
3973 Catchpoint 2 (syscall 764)
3977 If you configure @value{GDBN} using the @samp{--without-expat} option,
3978 it will not be able to display syscall names. Also, if your
3979 architecture does not have an XML file describing its system calls,
3980 you will not be able to see the syscall names. It is important to
3981 notice that these two features are used for accessing the syscall
3982 name database. In either case, you will see a warning like this:
3985 (@value{GDBP}) catch syscall
3986 warning: Could not open "syscalls/i386-linux.xml"
3987 warning: Could not load the syscall XML file 'syscalls/i386-linux.xml'.
3988 GDB will not be able to display syscall names.
3989 Catchpoint 1 (syscall)
3993 Of course, the file name will change depending on your architecture and system.
3995 Still using the example above, you can also try to catch a syscall by its
3996 number. In this case, you would see something like:
3999 (@value{GDBP}) catch syscall 252
4000 Catchpoint 1 (syscall(s) 252)
4003 Again, in this case @value{GDBN} would not be able to display syscall's names.
4006 A call to @code{fork}. This is currently only available for HP-UX
4010 A call to @code{vfork}. This is currently only available for HP-UX
4015 @item tcatch @var{event}
4016 Set a catchpoint that is enabled only for one stop. The catchpoint is
4017 automatically deleted after the first time the event is caught.
4021 Use the @code{info break} command to list the current catchpoints.
4023 There are currently some limitations to C@t{++} exception handling
4024 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
4028 If you call a function interactively, @value{GDBN} normally returns
4029 control to you when the function has finished executing. If the call
4030 raises an exception, however, the call may bypass the mechanism that
4031 returns control to you and cause your program either to abort or to
4032 simply continue running until it hits a breakpoint, catches a signal
4033 that @value{GDBN} is listening for, or exits. This is the case even if
4034 you set a catchpoint for the exception; catchpoints on exceptions are
4035 disabled within interactive calls.
4038 You cannot raise an exception interactively.
4041 You cannot install an exception handler interactively.
4044 @cindex raise exceptions
4045 Sometimes @code{catch} is not the best way to debug exception handling:
4046 if you need to know exactly where an exception is raised, it is better to
4047 stop @emph{before} the exception handler is called, since that way you
4048 can see the stack before any unwinding takes place. If you set a
4049 breakpoint in an exception handler instead, it may not be easy to find
4050 out where the exception was raised.
4052 To stop just before an exception handler is called, you need some
4053 knowledge of the implementation. In the case of @sc{gnu} C@t{++}, exceptions are
4054 raised by calling a library function named @code{__raise_exception}
4055 which has the following ANSI C interface:
4058 /* @var{addr} is where the exception identifier is stored.
4059 @var{id} is the exception identifier. */
4060 void __raise_exception (void **addr, void *id);
4064 To make the debugger catch all exceptions before any stack
4065 unwinding takes place, set a breakpoint on @code{__raise_exception}
4066 (@pxref{Breakpoints, ,Breakpoints; Watchpoints; and Exceptions}).
4068 With a conditional breakpoint (@pxref{Conditions, ,Break Conditions})
4069 that depends on the value of @var{id}, you can stop your program when
4070 a specific exception is raised. You can use multiple conditional
4071 breakpoints to stop your program when any of a number of exceptions are
4076 @subsection Deleting Breakpoints
4078 @cindex clearing breakpoints, watchpoints, catchpoints
4079 @cindex deleting breakpoints, watchpoints, catchpoints
4080 It is often necessary to eliminate a breakpoint, watchpoint, or
4081 catchpoint once it has done its job and you no longer want your program
4082 to stop there. This is called @dfn{deleting} the breakpoint. A
4083 breakpoint that has been deleted no longer exists; it is forgotten.
4085 With the @code{clear} command you can delete breakpoints according to
4086 where they are in your program. With the @code{delete} command you can
4087 delete individual breakpoints, watchpoints, or catchpoints by specifying
4088 their breakpoint numbers.
4090 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
4091 automatically ignores breakpoints on the first instruction to be executed
4092 when you continue execution without changing the execution address.
4097 Delete any breakpoints at the next instruction to be executed in the
4098 selected stack frame (@pxref{Selection, ,Selecting a Frame}). When
4099 the innermost frame is selected, this is a good way to delete a
4100 breakpoint where your program just stopped.
4102 @item clear @var{location}
4103 Delete any breakpoints set at the specified @var{location}.
4104 @xref{Specify Location}, for the various forms of @var{location}; the
4105 most useful ones are listed below:
4108 @item clear @var{function}
4109 @itemx clear @var{filename}:@var{function}
4110 Delete any breakpoints set at entry to the named @var{function}.
4112 @item clear @var{linenum}
4113 @itemx clear @var{filename}:@var{linenum}
4114 Delete any breakpoints set at or within the code of the specified
4115 @var{linenum} of the specified @var{filename}.
4118 @cindex delete breakpoints
4120 @kindex d @r{(@code{delete})}
4121 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
4122 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
4123 ranges specified as arguments. If no argument is specified, delete all
4124 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
4125 confirm off}). You can abbreviate this command as @code{d}.
4129 @subsection Disabling Breakpoints
4131 @cindex enable/disable a breakpoint
4132 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
4133 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
4134 it had been deleted, but remembers the information on the breakpoint so
4135 that you can @dfn{enable} it again later.
4137 You disable and enable breakpoints, watchpoints, and catchpoints with
4138 the @code{enable} and @code{disable} commands, optionally specifying
4139 one or more breakpoint numbers as arguments. Use @code{info break} to
4140 print a list of all breakpoints, watchpoints, and catchpoints if you
4141 do not know which numbers to use.
4143 Disabling and enabling a breakpoint that has multiple locations
4144 affects all of its locations.
4146 A breakpoint, watchpoint, or catchpoint can have any of four different
4147 states of enablement:
4151 Enabled. The breakpoint stops your program. A breakpoint set
4152 with the @code{break} command starts out in this state.
4154 Disabled. The breakpoint has no effect on your program.
4156 Enabled once. The breakpoint stops your program, but then becomes
4159 Enabled for deletion. The breakpoint stops your program, but
4160 immediately after it does so it is deleted permanently. A breakpoint
4161 set with the @code{tbreak} command starts out in this state.
4164 You can use the following commands to enable or disable breakpoints,
4165 watchpoints, and catchpoints:
4169 @kindex dis @r{(@code{disable})}
4170 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
4171 Disable the specified breakpoints---or all breakpoints, if none are
4172 listed. A disabled breakpoint has no effect but is not forgotten. All
4173 options such as ignore-counts, conditions and commands are remembered in
4174 case the breakpoint is enabled again later. You may abbreviate
4175 @code{disable} as @code{dis}.
4178 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
4179 Enable the specified breakpoints (or all defined breakpoints). They
4180 become effective once again in stopping your program.
4182 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
4183 Enable the specified breakpoints temporarily. @value{GDBN} disables any
4184 of these breakpoints immediately after stopping your program.
4186 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
4187 Enable the specified breakpoints to work once, then die. @value{GDBN}
4188 deletes any of these breakpoints as soon as your program stops there.
4189 Breakpoints set by the @code{tbreak} command start out in this state.
4192 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
4193 @c confusing: tbreak is also initially enabled.
4194 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
4195 ,Setting Breakpoints}), breakpoints that you set are initially enabled;
4196 subsequently, they become disabled or enabled only when you use one of
4197 the commands above. (The command @code{until} can set and delete a
4198 breakpoint of its own, but it does not change the state of your other
4199 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
4203 @subsection Break Conditions
4204 @cindex conditional breakpoints
4205 @cindex breakpoint conditions
4207 @c FIXME what is scope of break condition expr? Context where wanted?
4208 @c in particular for a watchpoint?
4209 The simplest sort of breakpoint breaks every time your program reaches a
4210 specified place. You can also specify a @dfn{condition} for a
4211 breakpoint. A condition is just a Boolean expression in your
4212 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
4213 a condition evaluates the expression each time your program reaches it,
4214 and your program stops only if the condition is @emph{true}.
4216 This is the converse of using assertions for program validation; in that
4217 situation, you want to stop when the assertion is violated---that is,
4218 when the condition is false. In C, if you want to test an assertion expressed
4219 by the condition @var{assert}, you should set the condition
4220 @samp{! @var{assert}} on the appropriate breakpoint.
4222 Conditions are also accepted for watchpoints; you may not need them,
4223 since a watchpoint is inspecting the value of an expression anyhow---but
4224 it might be simpler, say, to just set a watchpoint on a variable name,
4225 and specify a condition that tests whether the new value is an interesting
4228 Break conditions can have side effects, and may even call functions in
4229 your program. This can be useful, for example, to activate functions
4230 that log program progress, or to use your own print functions to
4231 format special data structures. The effects are completely predictable
4232 unless there is another enabled breakpoint at the same address. (In
4233 that case, @value{GDBN} might see the other breakpoint first and stop your
4234 program without checking the condition of this one.) Note that
4235 breakpoint commands are usually more convenient and flexible than break
4237 purpose of performing side effects when a breakpoint is reached
4238 (@pxref{Break Commands, ,Breakpoint Command Lists}).
4240 Break conditions can be specified when a breakpoint is set, by using
4241 @samp{if} in the arguments to the @code{break} command. @xref{Set
4242 Breaks, ,Setting Breakpoints}. They can also be changed at any time
4243 with the @code{condition} command.
4245 You can also use the @code{if} keyword with the @code{watch} command.
4246 The @code{catch} command does not recognize the @code{if} keyword;
4247 @code{condition} is the only way to impose a further condition on a
4252 @item condition @var{bnum} @var{expression}
4253 Specify @var{expression} as the break condition for breakpoint,
4254 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
4255 breakpoint @var{bnum} stops your program only if the value of
4256 @var{expression} is true (nonzero, in C). When you use
4257 @code{condition}, @value{GDBN} checks @var{expression} immediately for
4258 syntactic correctness, and to determine whether symbols in it have
4259 referents in the context of your breakpoint. If @var{expression} uses
4260 symbols not referenced in the context of the breakpoint, @value{GDBN}
4261 prints an error message:
4264 No symbol "foo" in current context.
4269 not actually evaluate @var{expression} at the time the @code{condition}
4270 command (or a command that sets a breakpoint with a condition, like
4271 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
4273 @item condition @var{bnum}
4274 Remove the condition from breakpoint number @var{bnum}. It becomes
4275 an ordinary unconditional breakpoint.
4278 @cindex ignore count (of breakpoint)
4279 A special case of a breakpoint condition is to stop only when the
4280 breakpoint has been reached a certain number of times. This is so
4281 useful that there is a special way to do it, using the @dfn{ignore
4282 count} of the breakpoint. Every breakpoint has an ignore count, which
4283 is an integer. Most of the time, the ignore count is zero, and
4284 therefore has no effect. But if your program reaches a breakpoint whose
4285 ignore count is positive, then instead of stopping, it just decrements
4286 the ignore count by one and continues. As a result, if the ignore count
4287 value is @var{n}, the breakpoint does not stop the next @var{n} times
4288 your program reaches it.
4292 @item ignore @var{bnum} @var{count}
4293 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
4294 The next @var{count} times the breakpoint is reached, your program's
4295 execution does not stop; other than to decrement the ignore count, @value{GDBN}
4298 To make the breakpoint stop the next time it is reached, specify
4301 When you use @code{continue} to resume execution of your program from a
4302 breakpoint, you can specify an ignore count directly as an argument to
4303 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
4304 Stepping,,Continuing and Stepping}.
4306 If a breakpoint has a positive ignore count and a condition, the
4307 condition is not checked. Once the ignore count reaches zero,
4308 @value{GDBN} resumes checking the condition.
4310 You could achieve the effect of the ignore count with a condition such
4311 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
4312 is decremented each time. @xref{Convenience Vars, ,Convenience
4316 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
4319 @node Break Commands
4320 @subsection Breakpoint Command Lists
4322 @cindex breakpoint commands
4323 You can give any breakpoint (or watchpoint or catchpoint) a series of
4324 commands to execute when your program stops due to that breakpoint. For
4325 example, you might want to print the values of certain expressions, or
4326 enable other breakpoints.
4330 @kindex end@r{ (breakpoint commands)}
4331 @item commands @r{[}@var{range}@dots{}@r{]}
4332 @itemx @dots{} @var{command-list} @dots{}
4334 Specify a list of commands for the given breakpoints. The commands
4335 themselves appear on the following lines. Type a line containing just
4336 @code{end} to terminate the commands.
4338 To remove all commands from a breakpoint, type @code{commands} and
4339 follow it immediately with @code{end}; that is, give no commands.
4341 With no argument, @code{commands} refers to the last breakpoint,
4342 watchpoint, or catchpoint set (not to the breakpoint most recently
4343 encountered). If the most recent breakpoints were set with a single
4344 command, then the @code{commands} will apply to all the breakpoints
4345 set by that command. This applies to breakpoints set by
4346 @code{rbreak}, and also applies when a single @code{break} command
4347 creates multiple breakpoints (@pxref{Ambiguous Expressions,,Ambiguous
4351 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
4352 disabled within a @var{command-list}.
4354 You can use breakpoint commands to start your program up again. Simply
4355 use the @code{continue} command, or @code{step}, or any other command
4356 that resumes execution.
4358 Any other commands in the command list, after a command that resumes
4359 execution, are ignored. This is because any time you resume execution
4360 (even with a simple @code{next} or @code{step}), you may encounter
4361 another breakpoint---which could have its own command list, leading to
4362 ambiguities about which list to execute.
4365 If the first command you specify in a command list is @code{silent}, the
4366 usual message about stopping at a breakpoint is not printed. This may
4367 be desirable for breakpoints that are to print a specific message and
4368 then continue. If none of the remaining commands print anything, you
4369 see no sign that the breakpoint was reached. @code{silent} is
4370 meaningful only at the beginning of a breakpoint command list.
4372 The commands @code{echo}, @code{output}, and @code{printf} allow you to
4373 print precisely controlled output, and are often useful in silent
4374 breakpoints. @xref{Output, ,Commands for Controlled Output}.
4376 For example, here is how you could use breakpoint commands to print the
4377 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
4383 printf "x is %d\n",x
4388 One application for breakpoint commands is to compensate for one bug so
4389 you can test for another. Put a breakpoint just after the erroneous line
4390 of code, give it a condition to detect the case in which something
4391 erroneous has been done, and give it commands to assign correct values
4392 to any variables that need them. End with the @code{continue} command
4393 so that your program does not stop, and start with the @code{silent}
4394 command so that no output is produced. Here is an example:
4405 @node Save Breakpoints
4406 @subsection How to save breakpoints to a file
4408 To save breakpoint definitions to a file use the @w{@code{save
4409 breakpoints}} command.
4412 @kindex save breakpoints
4413 @cindex save breakpoints to a file for future sessions
4414 @item save breakpoints [@var{filename}]
4415 This command saves all current breakpoint definitions together with
4416 their commands and ignore counts, into a file @file{@var{filename}}
4417 suitable for use in a later debugging session. This includes all
4418 types of breakpoints (breakpoints, watchpoints, catchpoints,
4419 tracepoints). To read the saved breakpoint definitions, use the
4420 @code{source} command (@pxref{Command Files}). Note that watchpoints
4421 with expressions involving local variables may fail to be recreated
4422 because it may not be possible to access the context where the
4423 watchpoint is valid anymore. Because the saved breakpoint definitions
4424 are simply a sequence of @value{GDBN} commands that recreate the
4425 breakpoints, you can edit the file in your favorite editing program,
4426 and remove the breakpoint definitions you're not interested in, or
4427 that can no longer be recreated.
4430 @c @ifclear BARETARGET
4431 @node Error in Breakpoints
4432 @subsection ``Cannot insert breakpoints''
4434 If you request too many active hardware-assisted breakpoints and
4435 watchpoints, you will see this error message:
4437 @c FIXME: the precise wording of this message may change; the relevant
4438 @c source change is not committed yet (Sep 3, 1999).
4440 Stopped; cannot insert breakpoints.
4441 You may have requested too many hardware breakpoints and watchpoints.
4445 This message is printed when you attempt to resume the program, since
4446 only then @value{GDBN} knows exactly how many hardware breakpoints and
4447 watchpoints it needs to insert.
4449 When this message is printed, you need to disable or remove some of the
4450 hardware-assisted breakpoints and watchpoints, and then continue.
4452 @node Breakpoint-related Warnings
4453 @subsection ``Breakpoint address adjusted...''
4454 @cindex breakpoint address adjusted
4456 Some processor architectures place constraints on the addresses at
4457 which breakpoints may be placed. For architectures thus constrained,
4458 @value{GDBN} will attempt to adjust the breakpoint's address to comply
4459 with the constraints dictated by the architecture.
4461 One example of such an architecture is the Fujitsu FR-V. The FR-V is
4462 a VLIW architecture in which a number of RISC-like instructions may be
4463 bundled together for parallel execution. The FR-V architecture
4464 constrains the location of a breakpoint instruction within such a
4465 bundle to the instruction with the lowest address. @value{GDBN}
4466 honors this constraint by adjusting a breakpoint's address to the
4467 first in the bundle.
4469 It is not uncommon for optimized code to have bundles which contain
4470 instructions from different source statements, thus it may happen that
4471 a breakpoint's address will be adjusted from one source statement to
4472 another. Since this adjustment may significantly alter @value{GDBN}'s
4473 breakpoint related behavior from what the user expects, a warning is
4474 printed when the breakpoint is first set and also when the breakpoint
4477 A warning like the one below is printed when setting a breakpoint
4478 that's been subject to address adjustment:
4481 warning: Breakpoint address adjusted from 0x00010414 to 0x00010410.
4484 Such warnings are printed both for user settable and @value{GDBN}'s
4485 internal breakpoints. If you see one of these warnings, you should
4486 verify that a breakpoint set at the adjusted address will have the
4487 desired affect. If not, the breakpoint in question may be removed and
4488 other breakpoints may be set which will have the desired behavior.
4489 E.g., it may be sufficient to place the breakpoint at a later
4490 instruction. A conditional breakpoint may also be useful in some
4491 cases to prevent the breakpoint from triggering too often.
4493 @value{GDBN} will also issue a warning when stopping at one of these
4494 adjusted breakpoints:
4497 warning: Breakpoint 1 address previously adjusted from 0x00010414
4501 When this warning is encountered, it may be too late to take remedial
4502 action except in cases where the breakpoint is hit earlier or more
4503 frequently than expected.
4505 @node Continuing and Stepping
4506 @section Continuing and Stepping
4510 @cindex resuming execution
4511 @dfn{Continuing} means resuming program execution until your program
4512 completes normally. In contrast, @dfn{stepping} means executing just
4513 one more ``step'' of your program, where ``step'' may mean either one
4514 line of source code, or one machine instruction (depending on what
4515 particular command you use). Either when continuing or when stepping,
4516 your program may stop even sooner, due to a breakpoint or a signal. (If
4517 it stops due to a signal, you may want to use @code{handle}, or use
4518 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
4522 @kindex c @r{(@code{continue})}
4523 @kindex fg @r{(resume foreground execution)}
4524 @item continue @r{[}@var{ignore-count}@r{]}
4525 @itemx c @r{[}@var{ignore-count}@r{]}
4526 @itemx fg @r{[}@var{ignore-count}@r{]}
4527 Resume program execution, at the address where your program last stopped;
4528 any breakpoints set at that address are bypassed. The optional argument
4529 @var{ignore-count} allows you to specify a further number of times to
4530 ignore a breakpoint at this location; its effect is like that of
4531 @code{ignore} (@pxref{Conditions, ,Break Conditions}).
4533 The argument @var{ignore-count} is meaningful only when your program
4534 stopped due to a breakpoint. At other times, the argument to
4535 @code{continue} is ignored.
4537 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
4538 debugged program is deemed to be the foreground program) are provided
4539 purely for convenience, and have exactly the same behavior as
4543 To resume execution at a different place, you can use @code{return}
4544 (@pxref{Returning, ,Returning from a Function}) to go back to the
4545 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
4546 Different Address}) to go to an arbitrary location in your program.
4548 A typical technique for using stepping is to set a breakpoint
4549 (@pxref{Breakpoints, ,Breakpoints; Watchpoints; and Catchpoints}) at the
4550 beginning of the function or the section of your program where a problem
4551 is believed to lie, run your program until it stops at that breakpoint,
4552 and then step through the suspect area, examining the variables that are
4553 interesting, until you see the problem happen.
4557 @kindex s @r{(@code{step})}
4559 Continue running your program until control reaches a different source
4560 line, then stop it and return control to @value{GDBN}. This command is
4561 abbreviated @code{s}.
4564 @c "without debugging information" is imprecise; actually "without line
4565 @c numbers in the debugging information". (gcc -g1 has debugging info but
4566 @c not line numbers). But it seems complex to try to make that
4567 @c distinction here.
4568 @emph{Warning:} If you use the @code{step} command while control is
4569 within a function that was compiled without debugging information,
4570 execution proceeds until control reaches a function that does have
4571 debugging information. Likewise, it will not step into a function which
4572 is compiled without debugging information. To step through functions
4573 without debugging information, use the @code{stepi} command, described
4577 The @code{step} command only stops at the first instruction of a source
4578 line. This prevents the multiple stops that could otherwise occur in
4579 @code{switch} statements, @code{for} loops, etc. @code{step} continues
4580 to stop if a function that has debugging information is called within
4581 the line. In other words, @code{step} @emph{steps inside} any functions
4582 called within the line.
4584 Also, the @code{step} command only enters a function if there is line
4585 number information for the function. Otherwise it acts like the
4586 @code{next} command. This avoids problems when using @code{cc -gl}
4587 on MIPS machines. Previously, @code{step} entered subroutines if there
4588 was any debugging information about the routine.
4590 @item step @var{count}
4591 Continue running as in @code{step}, but do so @var{count} times. If a
4592 breakpoint is reached, or a signal not related to stepping occurs before
4593 @var{count} steps, stepping stops right away.
4596 @kindex n @r{(@code{next})}
4597 @item next @r{[}@var{count}@r{]}
4598 Continue to the next source line in the current (innermost) stack frame.
4599 This is similar to @code{step}, but function calls that appear within
4600 the line of code are executed without stopping. Execution stops when
4601 control reaches a different line of code at the original stack level
4602 that was executing when you gave the @code{next} command. This command
4603 is abbreviated @code{n}.
4605 An argument @var{count} is a repeat count, as for @code{step}.
4608 @c FIX ME!! Do we delete this, or is there a way it fits in with
4609 @c the following paragraph? --- Vctoria
4611 @c @code{next} within a function that lacks debugging information acts like
4612 @c @code{step}, but any function calls appearing within the code of the
4613 @c function are executed without stopping.
4615 The @code{next} command only stops at the first instruction of a
4616 source line. This prevents multiple stops that could otherwise occur in
4617 @code{switch} statements, @code{for} loops, etc.
4619 @kindex set step-mode
4621 @cindex functions without line info, and stepping
4622 @cindex stepping into functions with no line info
4623 @itemx set step-mode on
4624 The @code{set step-mode on} command causes the @code{step} command to
4625 stop at the first instruction of a function which contains no debug line
4626 information rather than stepping over it.
4628 This is useful in cases where you may be interested in inspecting the
4629 machine instructions of a function which has no symbolic info and do not
4630 want @value{GDBN} to automatically skip over this function.
4632 @item set step-mode off
4633 Causes the @code{step} command to step over any functions which contains no
4634 debug information. This is the default.
4636 @item show step-mode
4637 Show whether @value{GDBN} will stop in or step over functions without
4638 source line debug information.
4641 @kindex fin @r{(@code{finish})}
4643 Continue running until just after function in the selected stack frame
4644 returns. Print the returned value (if any). This command can be
4645 abbreviated as @code{fin}.
4647 Contrast this with the @code{return} command (@pxref{Returning,
4648 ,Returning from a Function}).
4651 @kindex u @r{(@code{until})}
4652 @cindex run until specified location
4655 Continue running until a source line past the current line, in the
4656 current stack frame, is reached. This command is used to avoid single
4657 stepping through a loop more than once. It is like the @code{next}
4658 command, except that when @code{until} encounters a jump, it
4659 automatically continues execution until the program counter is greater
4660 than the address of the jump.
4662 This means that when you reach the end of a loop after single stepping
4663 though it, @code{until} makes your program continue execution until it
4664 exits the loop. In contrast, a @code{next} command at the end of a loop
4665 simply steps back to the beginning of the loop, which forces you to step
4666 through the next iteration.
4668 @code{until} always stops your program if it attempts to exit the current
4671 @code{until} may produce somewhat counterintuitive results if the order
4672 of machine code does not match the order of the source lines. For
4673 example, in the following excerpt from a debugging session, the @code{f}
4674 (@code{frame}) command shows that execution is stopped at line
4675 @code{206}; yet when we use @code{until}, we get to line @code{195}:
4679 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
4681 (@value{GDBP}) until
4682 195 for ( ; argc > 0; NEXTARG) @{
4685 This happened because, for execution efficiency, the compiler had
4686 generated code for the loop closure test at the end, rather than the
4687 start, of the loop---even though the test in a C @code{for}-loop is
4688 written before the body of the loop. The @code{until} command appeared
4689 to step back to the beginning of the loop when it advanced to this
4690 expression; however, it has not really gone to an earlier
4691 statement---not in terms of the actual machine code.
4693 @code{until} with no argument works by means of single
4694 instruction stepping, and hence is slower than @code{until} with an
4697 @item until @var{location}
4698 @itemx u @var{location}
4699 Continue running your program until either the specified location is
4700 reached, or the current stack frame returns. @var{location} is any of
4701 the forms described in @ref{Specify Location}.
4702 This form of the command uses temporary breakpoints, and
4703 hence is quicker than @code{until} without an argument. The specified
4704 location is actually reached only if it is in the current frame. This
4705 implies that @code{until} can be used to skip over recursive function
4706 invocations. For instance in the code below, if the current location is
4707 line @code{96}, issuing @code{until 99} will execute the program up to
4708 line @code{99} in the same invocation of factorial, i.e., after the inner
4709 invocations have returned.
4712 94 int factorial (int value)
4714 96 if (value > 1) @{
4715 97 value *= factorial (value - 1);
4722 @kindex advance @var{location}
4723 @itemx advance @var{location}
4724 Continue running the program up to the given @var{location}. An argument is
4725 required, which should be of one of the forms described in
4726 @ref{Specify Location}.
4727 Execution will also stop upon exit from the current stack
4728 frame. This command is similar to @code{until}, but @code{advance} will
4729 not skip over recursive function calls, and the target location doesn't
4730 have to be in the same frame as the current one.
4734 @kindex si @r{(@code{stepi})}
4736 @itemx stepi @var{arg}
4738 Execute one machine instruction, then stop and return to the debugger.
4740 It is often useful to do @samp{display/i $pc} when stepping by machine
4741 instructions. This makes @value{GDBN} automatically display the next
4742 instruction to be executed, each time your program stops. @xref{Auto
4743 Display,, Automatic Display}.
4745 An argument is a repeat count, as in @code{step}.
4749 @kindex ni @r{(@code{nexti})}
4751 @itemx nexti @var{arg}
4753 Execute one machine instruction, but if it is a function call,
4754 proceed until the function returns.
4756 An argument is a repeat count, as in @code{next}.
4763 A signal is an asynchronous event that can happen in a program. The
4764 operating system defines the possible kinds of signals, and gives each
4765 kind a name and a number. For example, in Unix @code{SIGINT} is the
4766 signal a program gets when you type an interrupt character (often @kbd{Ctrl-c});
4767 @code{SIGSEGV} is the signal a program gets from referencing a place in
4768 memory far away from all the areas in use; @code{SIGALRM} occurs when
4769 the alarm clock timer goes off (which happens only if your program has
4770 requested an alarm).
4772 @cindex fatal signals
4773 Some signals, including @code{SIGALRM}, are a normal part of the
4774 functioning of your program. Others, such as @code{SIGSEGV}, indicate
4775 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
4776 program has not specified in advance some other way to handle the signal.
4777 @code{SIGINT} does not indicate an error in your program, but it is normally
4778 fatal so it can carry out the purpose of the interrupt: to kill the program.
4780 @value{GDBN} has the ability to detect any occurrence of a signal in your
4781 program. You can tell @value{GDBN} in advance what to do for each kind of
4784 @cindex handling signals
4785 Normally, @value{GDBN} is set up to let the non-erroneous signals like
4786 @code{SIGALRM} be silently passed to your program
4787 (so as not to interfere with their role in the program's functioning)
4788 but to stop your program immediately whenever an error signal happens.
4789 You can change these settings with the @code{handle} command.
4792 @kindex info signals
4796 Print a table of all the kinds of signals and how @value{GDBN} has been told to
4797 handle each one. You can use this to see the signal numbers of all
4798 the defined types of signals.
4800 @item info signals @var{sig}
4801 Similar, but print information only about the specified signal number.
4803 @code{info handle} is an alias for @code{info signals}.
4806 @item handle @var{signal} @r{[}@var{keywords}@dots{}@r{]}
4807 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
4808 can be the number of a signal or its name (with or without the
4809 @samp{SIG} at the beginning); a list of signal numbers of the form
4810 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
4811 known signals. Optional arguments @var{keywords}, described below,
4812 say what change to make.
4816 The keywords allowed by the @code{handle} command can be abbreviated.
4817 Their full names are:
4821 @value{GDBN} should not stop your program when this signal happens. It may
4822 still print a message telling you that the signal has come in.
4825 @value{GDBN} should stop your program when this signal happens. This implies
4826 the @code{print} keyword as well.
4829 @value{GDBN} should print a message when this signal happens.
4832 @value{GDBN} should not mention the occurrence of the signal at all. This
4833 implies the @code{nostop} keyword as well.
4837 @value{GDBN} should allow your program to see this signal; your program
4838 can handle the signal, or else it may terminate if the signal is fatal
4839 and not handled. @code{pass} and @code{noignore} are synonyms.
4843 @value{GDBN} should not allow your program to see this signal.
4844 @code{nopass} and @code{ignore} are synonyms.
4848 When a signal stops your program, the signal is not visible to the
4850 continue. Your program sees the signal then, if @code{pass} is in
4851 effect for the signal in question @emph{at that time}. In other words,
4852 after @value{GDBN} reports a signal, you can use the @code{handle}
4853 command with @code{pass} or @code{nopass} to control whether your
4854 program sees that signal when you continue.
4856 The default is set to @code{nostop}, @code{noprint}, @code{pass} for
4857 non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and
4858 @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the
4861 You can also use the @code{signal} command to prevent your program from
4862 seeing a signal, or cause it to see a signal it normally would not see,
4863 or to give it any signal at any time. For example, if your program stopped
4864 due to some sort of memory reference error, you might store correct
4865 values into the erroneous variables and continue, hoping to see more
4866 execution; but your program would probably terminate immediately as
4867 a result of the fatal signal once it saw the signal. To prevent this,
4868 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
4871 @cindex extra signal information
4872 @anchor{extra signal information}
4874 On some targets, @value{GDBN} can inspect extra signal information
4875 associated with the intercepted signal, before it is actually
4876 delivered to the program being debugged. This information is exported
4877 by the convenience variable @code{$_siginfo}, and consists of data
4878 that is passed by the kernel to the signal handler at the time of the
4879 receipt of a signal. The data type of the information itself is
4880 target dependent. You can see the data type using the @code{ptype
4881 $_siginfo} command. On Unix systems, it typically corresponds to the
4882 standard @code{siginfo_t} type, as defined in the @file{signal.h}
4885 Here's an example, on a @sc{gnu}/Linux system, printing the stray
4886 referenced address that raised a segmentation fault.
4890 (@value{GDBP}) continue
4891 Program received signal SIGSEGV, Segmentation fault.
4892 0x0000000000400766 in main ()
4894 (@value{GDBP}) ptype $_siginfo
4901 struct @{...@} _kill;
4902 struct @{...@} _timer;
4904 struct @{...@} _sigchld;
4905 struct @{...@} _sigfault;
4906 struct @{...@} _sigpoll;
4909 (@value{GDBP}) ptype $_siginfo._sifields._sigfault
4913 (@value{GDBP}) p $_siginfo._sifields._sigfault.si_addr
4914 $1 = (void *) 0x7ffff7ff7000
4918 Depending on target support, @code{$_siginfo} may also be writable.
4921 @section Stopping and Starting Multi-thread Programs
4923 @cindex stopped threads
4924 @cindex threads, stopped
4926 @cindex continuing threads
4927 @cindex threads, continuing
4929 @value{GDBN} supports debugging programs with multiple threads
4930 (@pxref{Threads,, Debugging Programs with Multiple Threads}). There
4931 are two modes of controlling execution of your program within the
4932 debugger. In the default mode, referred to as @dfn{all-stop mode},
4933 when any thread in your program stops (for example, at a breakpoint
4934 or while being stepped), all other threads in the program are also stopped by
4935 @value{GDBN}. On some targets, @value{GDBN} also supports
4936 @dfn{non-stop mode}, in which other threads can continue to run freely while
4937 you examine the stopped thread in the debugger.
4940 * All-Stop Mode:: All threads stop when GDB takes control
4941 * Non-Stop Mode:: Other threads continue to execute
4942 * Background Execution:: Running your program asynchronously
4943 * Thread-Specific Breakpoints:: Controlling breakpoints
4944 * Interrupted System Calls:: GDB may interfere with system calls
4948 @subsection All-Stop Mode
4950 @cindex all-stop mode
4952 In all-stop mode, whenever your program stops under @value{GDBN} for any reason,
4953 @emph{all} threads of execution stop, not just the current thread. This
4954 allows you to examine the overall state of the program, including
4955 switching between threads, without worrying that things may change
4958 Conversely, whenever you restart the program, @emph{all} threads start
4959 executing. @emph{This is true even when single-stepping} with commands
4960 like @code{step} or @code{next}.
4962 In particular, @value{GDBN} cannot single-step all threads in lockstep.
4963 Since thread scheduling is up to your debugging target's operating
4964 system (not controlled by @value{GDBN}), other threads may
4965 execute more than one statement while the current thread completes a
4966 single step. Moreover, in general other threads stop in the middle of a
4967 statement, rather than at a clean statement boundary, when the program
4970 You might even find your program stopped in another thread after
4971 continuing or even single-stepping. This happens whenever some other
4972 thread runs into a breakpoint, a signal, or an exception before the
4973 first thread completes whatever you requested.
4975 @cindex automatic thread selection
4976 @cindex switching threads automatically
4977 @cindex threads, automatic switching
4978 Whenever @value{GDBN} stops your program, due to a breakpoint or a
4979 signal, it automatically selects the thread where that breakpoint or
4980 signal happened. @value{GDBN} alerts you to the context switch with a
4981 message such as @samp{[Switching to Thread @var{n}]} to identify the
4984 On some OSes, you can modify @value{GDBN}'s default behavior by
4985 locking the OS scheduler to allow only a single thread to run.
4988 @item set scheduler-locking @var{mode}
4989 @cindex scheduler locking mode
4990 @cindex lock scheduler
4991 Set the scheduler locking mode. If it is @code{off}, then there is no
4992 locking and any thread may run at any time. If @code{on}, then only the
4993 current thread may run when the inferior is resumed. The @code{step}
4994 mode optimizes for single-stepping; it prevents other threads
4995 from preempting the current thread while you are stepping, so that
4996 the focus of debugging does not change unexpectedly.
4997 Other threads only rarely (or never) get a chance to run
4998 when you step. They are more likely to run when you @samp{next} over a
4999 function call, and they are completely free to run when you use commands
5000 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
5001 thread hits a breakpoint during its timeslice, @value{GDBN} does not change
5002 the current thread away from the thread that you are debugging.
5004 @item show scheduler-locking
5005 Display the current scheduler locking mode.
5008 @cindex resume threads of multiple processes simultaneously
5009 By default, when you issue one of the execution commands such as
5010 @code{continue}, @code{next} or @code{step}, @value{GDBN} allows only
5011 threads of the current inferior to run. For example, if @value{GDBN}
5012 is attached to two inferiors, each with two threads, the
5013 @code{continue} command resumes only the two threads of the current
5014 inferior. This is useful, for example, when you debug a program that
5015 forks and you want to hold the parent stopped (so that, for instance,
5016 it doesn't run to exit), while you debug the child. In other
5017 situations, you may not be interested in inspecting the current state
5018 of any of the processes @value{GDBN} is attached to, and you may want
5019 to resume them all until some breakpoint is hit. In the latter case,
5020 you can instruct @value{GDBN} to allow all threads of all the
5021 inferiors to run with the @w{@code{set schedule-multiple}} command.
5024 @kindex set schedule-multiple
5025 @item set schedule-multiple
5026 Set the mode for allowing threads of multiple processes to be resumed
5027 when an execution command is issued. When @code{on}, all threads of
5028 all processes are allowed to run. When @code{off}, only the threads
5029 of the current process are resumed. The default is @code{off}. The
5030 @code{scheduler-locking} mode takes precedence when set to @code{on},
5031 or while you are stepping and set to @code{step}.
5033 @item show schedule-multiple
5034 Display the current mode for resuming the execution of threads of
5039 @subsection Non-Stop Mode
5041 @cindex non-stop mode
5043 @c This section is really only a place-holder, and needs to be expanded
5044 @c with more details.
5046 For some multi-threaded targets, @value{GDBN} supports an optional
5047 mode of operation in which you can examine stopped program threads in
5048 the debugger while other threads continue to execute freely. This
5049 minimizes intrusion when debugging live systems, such as programs
5050 where some threads have real-time constraints or must continue to
5051 respond to external events. This is referred to as @dfn{non-stop} mode.
5053 In non-stop mode, when a thread stops to report a debugging event,
5054 @emph{only} that thread is stopped; @value{GDBN} does not stop other
5055 threads as well, in contrast to the all-stop mode behavior. Additionally,
5056 execution commands such as @code{continue} and @code{step} apply by default
5057 only to the current thread in non-stop mode, rather than all threads as
5058 in all-stop mode. This allows you to control threads explicitly in
5059 ways that are not possible in all-stop mode --- for example, stepping
5060 one thread while allowing others to run freely, stepping
5061 one thread while holding all others stopped, or stepping several threads
5062 independently and simultaneously.
5064 To enter non-stop mode, use this sequence of commands before you run
5065 or attach to your program:
5068 # Enable the async interface.
5071 # If using the CLI, pagination breaks non-stop.
5074 # Finally, turn it on!
5078 You can use these commands to manipulate the non-stop mode setting:
5081 @kindex set non-stop
5082 @item set non-stop on
5083 Enable selection of non-stop mode.
5084 @item set non-stop off
5085 Disable selection of non-stop mode.
5086 @kindex show non-stop
5088 Show the current non-stop enablement setting.
5091 Note these commands only reflect whether non-stop mode is enabled,
5092 not whether the currently-executing program is being run in non-stop mode.
5093 In particular, the @code{set non-stop} preference is only consulted when
5094 @value{GDBN} starts or connects to the target program, and it is generally
5095 not possible to switch modes once debugging has started. Furthermore,
5096 since not all targets support non-stop mode, even when you have enabled
5097 non-stop mode, @value{GDBN} may still fall back to all-stop operation by
5100 In non-stop mode, all execution commands apply only to the current thread
5101 by default. That is, @code{continue} only continues one thread.
5102 To continue all threads, issue @code{continue -a} or @code{c -a}.
5104 You can use @value{GDBN}'s background execution commands
5105 (@pxref{Background Execution}) to run some threads in the background
5106 while you continue to examine or step others from @value{GDBN}.
5107 The MI execution commands (@pxref{GDB/MI Program Execution}) are
5108 always executed asynchronously in non-stop mode.
5110 Suspending execution is done with the @code{interrupt} command when
5111 running in the background, or @kbd{Ctrl-c} during foreground execution.
5112 In all-stop mode, this stops the whole process;
5113 but in non-stop mode the interrupt applies only to the current thread.
5114 To stop the whole program, use @code{interrupt -a}.
5116 Other execution commands do not currently support the @code{-a} option.
5118 In non-stop mode, when a thread stops, @value{GDBN} doesn't automatically make
5119 that thread current, as it does in all-stop mode. This is because the
5120 thread stop notifications are asynchronous with respect to @value{GDBN}'s
5121 command interpreter, and it would be confusing if @value{GDBN} unexpectedly
5122 changed to a different thread just as you entered a command to operate on the
5123 previously current thread.
5125 @node Background Execution
5126 @subsection Background Execution
5128 @cindex foreground execution
5129 @cindex background execution
5130 @cindex asynchronous execution
5131 @cindex execution, foreground, background and asynchronous
5133 @value{GDBN}'s execution commands have two variants: the normal
5134 foreground (synchronous) behavior, and a background
5135 (asynchronous) behavior. In foreground execution, @value{GDBN} waits for
5136 the program to report that some thread has stopped before prompting for
5137 another command. In background execution, @value{GDBN} immediately gives
5138 a command prompt so that you can issue other commands while your program runs.
5140 You need to explicitly enable asynchronous mode before you can use
5141 background execution commands. You can use these commands to
5142 manipulate the asynchronous mode setting:
5145 @kindex set target-async
5146 @item set target-async on
5147 Enable asynchronous mode.
5148 @item set target-async off
5149 Disable asynchronous mode.
5150 @kindex show target-async
5151 @item show target-async
5152 Show the current target-async setting.
5155 If the target doesn't support async mode, @value{GDBN} issues an error
5156 message if you attempt to use the background execution commands.
5158 To specify background execution, add a @code{&} to the command. For example,
5159 the background form of the @code{continue} command is @code{continue&}, or
5160 just @code{c&}. The execution commands that accept background execution
5166 @xref{Starting, , Starting your Program}.
5170 @xref{Attach, , Debugging an Already-running Process}.
5174 @xref{Continuing and Stepping, step}.
5178 @xref{Continuing and Stepping, stepi}.
5182 @xref{Continuing and Stepping, next}.
5186 @xref{Continuing and Stepping, nexti}.
5190 @xref{Continuing and Stepping, continue}.
5194 @xref{Continuing and Stepping, finish}.
5198 @xref{Continuing and Stepping, until}.
5202 Background execution is especially useful in conjunction with non-stop
5203 mode for debugging programs with multiple threads; see @ref{Non-Stop Mode}.
5204 However, you can also use these commands in the normal all-stop mode with
5205 the restriction that you cannot issue another execution command until the
5206 previous one finishes. Examples of commands that are valid in all-stop
5207 mode while the program is running include @code{help} and @code{info break}.
5209 You can interrupt your program while it is running in the background by
5210 using the @code{interrupt} command.
5217 Suspend execution of the running program. In all-stop mode,
5218 @code{interrupt} stops the whole process, but in non-stop mode, it stops
5219 only the current thread. To stop the whole program in non-stop mode,
5220 use @code{interrupt -a}.
5223 @node Thread-Specific Breakpoints
5224 @subsection Thread-Specific Breakpoints
5226 When your program has multiple threads (@pxref{Threads,, Debugging
5227 Programs with Multiple Threads}), you can choose whether to set
5228 breakpoints on all threads, or on a particular thread.
5231 @cindex breakpoints and threads
5232 @cindex thread breakpoints
5233 @kindex break @dots{} thread @var{threadno}
5234 @item break @var{linespec} thread @var{threadno}
5235 @itemx break @var{linespec} thread @var{threadno} if @dots{}
5236 @var{linespec} specifies source lines; there are several ways of
5237 writing them (@pxref{Specify Location}), but the effect is always to
5238 specify some source line.
5240 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
5241 to specify that you only want @value{GDBN} to stop the program when a
5242 particular thread reaches this breakpoint. @var{threadno} is one of the
5243 numeric thread identifiers assigned by @value{GDBN}, shown in the first
5244 column of the @samp{info threads} display.
5246 If you do not specify @samp{thread @var{threadno}} when you set a
5247 breakpoint, the breakpoint applies to @emph{all} threads of your
5250 You can use the @code{thread} qualifier on conditional breakpoints as
5251 well; in this case, place @samp{thread @var{threadno}} before or
5252 after the breakpoint condition, like this:
5255 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
5260 @node Interrupted System Calls
5261 @subsection Interrupted System Calls
5263 @cindex thread breakpoints and system calls
5264 @cindex system calls and thread breakpoints
5265 @cindex premature return from system calls
5266 There is an unfortunate side effect when using @value{GDBN} to debug
5267 multi-threaded programs. If one thread stops for a
5268 breakpoint, or for some other reason, and another thread is blocked in a
5269 system call, then the system call may return prematurely. This is a
5270 consequence of the interaction between multiple threads and the signals
5271 that @value{GDBN} uses to implement breakpoints and other events that
5274 To handle this problem, your program should check the return value of
5275 each system call and react appropriately. This is good programming
5278 For example, do not write code like this:
5284 The call to @code{sleep} will return early if a different thread stops
5285 at a breakpoint or for some other reason.
5287 Instead, write this:
5292 unslept = sleep (unslept);
5295 A system call is allowed to return early, so the system is still
5296 conforming to its specification. But @value{GDBN} does cause your
5297 multi-threaded program to behave differently than it would without
5300 Also, @value{GDBN} uses internal breakpoints in the thread library to
5301 monitor certain events such as thread creation and thread destruction.
5302 When such an event happens, a system call in another thread may return
5303 prematurely, even though your program does not appear to stop.
5306 @node Reverse Execution
5307 @chapter Running programs backward
5308 @cindex reverse execution
5309 @cindex running programs backward
5311 When you are debugging a program, it is not unusual to realize that
5312 you have gone too far, and some event of interest has already happened.
5313 If the target environment supports it, @value{GDBN} can allow you to
5314 ``rewind'' the program by running it backward.
5316 A target environment that supports reverse execution should be able
5317 to ``undo'' the changes in machine state that have taken place as the
5318 program was executing normally. Variables, registers etc.@: should
5319 revert to their previous values. Obviously this requires a great
5320 deal of sophistication on the part of the target environment; not
5321 all target environments can support reverse execution.
5323 When a program is executed in reverse, the instructions that
5324 have most recently been executed are ``un-executed'', in reverse
5325 order. The program counter runs backward, following the previous
5326 thread of execution in reverse. As each instruction is ``un-executed'',
5327 the values of memory and/or registers that were changed by that
5328 instruction are reverted to their previous states. After executing
5329 a piece of source code in reverse, all side effects of that code
5330 should be ``undone'', and all variables should be returned to their
5331 prior values@footnote{
5332 Note that some side effects are easier to undo than others. For instance,
5333 memory and registers are relatively easy, but device I/O is hard. Some
5334 targets may be able undo things like device I/O, and some may not.
5336 The contract between @value{GDBN} and the reverse executing target
5337 requires only that the target do something reasonable when
5338 @value{GDBN} tells it to execute backwards, and then report the
5339 results back to @value{GDBN}. Whatever the target reports back to
5340 @value{GDBN}, @value{GDBN} will report back to the user. @value{GDBN}
5341 assumes that the memory and registers that the target reports are in a
5342 consistant state, but @value{GDBN} accepts whatever it is given.
5345 If you are debugging in a target environment that supports
5346 reverse execution, @value{GDBN} provides the following commands.
5349 @kindex reverse-continue
5350 @kindex rc @r{(@code{reverse-continue})}
5351 @item reverse-continue @r{[}@var{ignore-count}@r{]}
5352 @itemx rc @r{[}@var{ignore-count}@r{]}
5353 Beginning at the point where your program last stopped, start executing
5354 in reverse. Reverse execution will stop for breakpoints and synchronous
5355 exceptions (signals), just like normal execution. Behavior of
5356 asynchronous signals depends on the target environment.
5358 @kindex reverse-step
5359 @kindex rs @r{(@code{step})}
5360 @item reverse-step @r{[}@var{count}@r{]}
5361 Run the program backward until control reaches the start of a
5362 different source line; then stop it, and return control to @value{GDBN}.
5364 Like the @code{step} command, @code{reverse-step} will only stop
5365 at the beginning of a source line. It ``un-executes'' the previously
5366 executed source line. If the previous source line included calls to
5367 debuggable functions, @code{reverse-step} will step (backward) into
5368 the called function, stopping at the beginning of the @emph{last}
5369 statement in the called function (typically a return statement).
5371 Also, as with the @code{step} command, if non-debuggable functions are
5372 called, @code{reverse-step} will run thru them backward without stopping.
5374 @kindex reverse-stepi
5375 @kindex rsi @r{(@code{reverse-stepi})}
5376 @item reverse-stepi @r{[}@var{count}@r{]}
5377 Reverse-execute one machine instruction. Note that the instruction
5378 to be reverse-executed is @emph{not} the one pointed to by the program
5379 counter, but the instruction executed prior to that one. For instance,
5380 if the last instruction was a jump, @code{reverse-stepi} will take you
5381 back from the destination of the jump to the jump instruction itself.
5383 @kindex reverse-next
5384 @kindex rn @r{(@code{reverse-next})}
5385 @item reverse-next @r{[}@var{count}@r{]}
5386 Run backward to the beginning of the previous line executed in
5387 the current (innermost) stack frame. If the line contains function
5388 calls, they will be ``un-executed'' without stopping. Starting from
5389 the first line of a function, @code{reverse-next} will take you back
5390 to the caller of that function, @emph{before} the function was called,
5391 just as the normal @code{next} command would take you from the last
5392 line of a function back to its return to its caller
5393 @footnote{Unless the code is too heavily optimized.}.
5395 @kindex reverse-nexti
5396 @kindex rni @r{(@code{reverse-nexti})}
5397 @item reverse-nexti @r{[}@var{count}@r{]}
5398 Like @code{nexti}, @code{reverse-nexti} executes a single instruction
5399 in reverse, except that called functions are ``un-executed'' atomically.
5400 That is, if the previously executed instruction was a return from
5401 another function, @code{reverse-nexti} will continue to execute
5402 in reverse until the call to that function (from the current stack
5405 @kindex reverse-finish
5406 @item reverse-finish
5407 Just as the @code{finish} command takes you to the point where the
5408 current function returns, @code{reverse-finish} takes you to the point
5409 where it was called. Instead of ending up at the end of the current
5410 function invocation, you end up at the beginning.
5412 @kindex set exec-direction
5413 @item set exec-direction
5414 Set the direction of target execution.
5415 @itemx set exec-direction reverse
5416 @cindex execute forward or backward in time
5417 @value{GDBN} will perform all execution commands in reverse, until the
5418 exec-direction mode is changed to ``forward''. Affected commands include
5419 @code{step, stepi, next, nexti, continue, and finish}. The @code{return}
5420 command cannot be used in reverse mode.
5421 @item set exec-direction forward
5422 @value{GDBN} will perform all execution commands in the normal fashion.
5423 This is the default.
5427 @node Process Record and Replay
5428 @chapter Recording Inferior's Execution and Replaying It
5429 @cindex process record and replay
5430 @cindex recording inferior's execution and replaying it
5432 On some platforms, @value{GDBN} provides a special @dfn{process record
5433 and replay} target that can record a log of the process execution, and
5434 replay it later with both forward and reverse execution commands.
5437 When this target is in use, if the execution log includes the record
5438 for the next instruction, @value{GDBN} will debug in @dfn{replay
5439 mode}. In the replay mode, the inferior does not really execute code
5440 instructions. Instead, all the events that normally happen during
5441 code execution are taken from the execution log. While code is not
5442 really executed in replay mode, the values of registers (including the
5443 program counter register) and the memory of the inferior are still
5444 changed as they normally would. Their contents are taken from the
5448 If the record for the next instruction is not in the execution log,
5449 @value{GDBN} will debug in @dfn{record mode}. In this mode, the
5450 inferior executes normally, and @value{GDBN} records the execution log
5453 The process record and replay target supports reverse execution
5454 (@pxref{Reverse Execution}), even if the platform on which the
5455 inferior runs does not. However, the reverse execution is limited in
5456 this case by the range of the instructions recorded in the execution
5457 log. In other words, reverse execution on platforms that don't
5458 support it directly can only be done in the replay mode.
5460 When debugging in the reverse direction, @value{GDBN} will work in
5461 replay mode as long as the execution log includes the record for the
5462 previous instruction; otherwise, it will work in record mode, if the
5463 platform supports reverse execution, or stop if not.
5465 For architecture environments that support process record and replay,
5466 @value{GDBN} provides the following commands:
5469 @kindex target record
5473 This command starts the process record and replay target. The process
5474 record and replay target can only debug a process that is already
5475 running. Therefore, you need first to start the process with the
5476 @kbd{run} or @kbd{start} commands, and then start the recording with
5477 the @kbd{target record} command.
5479 Both @code{record} and @code{rec} are aliases of @code{target record}.
5481 @cindex displaced stepping, and process record and replay
5482 Displaced stepping (@pxref{Maintenance Commands,, displaced stepping})
5483 will be automatically disabled when process record and replay target
5484 is started. That's because the process record and replay target
5485 doesn't support displaced stepping.
5487 @cindex non-stop mode, and process record and replay
5488 @cindex asynchronous execution, and process record and replay
5489 If the inferior is in the non-stop mode (@pxref{Non-Stop Mode}) or in
5490 the asynchronous execution mode (@pxref{Background Execution}), the
5491 process record and replay target cannot be started because it doesn't
5492 support these two modes.
5497 Stop the process record and replay target. When process record and
5498 replay target stops, the entire execution log will be deleted and the
5499 inferior will either be terminated, or will remain in its final state.
5501 When you stop the process record and replay target in record mode (at
5502 the end of the execution log), the inferior will be stopped at the
5503 next instruction that would have been recorded. In other words, if
5504 you record for a while and then stop recording, the inferior process
5505 will be left in the same state as if the recording never happened.
5507 On the other hand, if the process record and replay target is stopped
5508 while in replay mode (that is, not at the end of the execution log,
5509 but at some earlier point), the inferior process will become ``live''
5510 at that earlier state, and it will then be possible to continue the
5511 usual ``live'' debugging of the process from that state.
5513 When the inferior process exits, or @value{GDBN} detaches from it,
5514 process record and replay target will automatically stop itself.
5516 @kindex set record insn-number-max
5517 @item set record insn-number-max @var{limit}
5518 Set the limit of instructions to be recorded. Default value is 200000.
5520 If @var{limit} is a positive number, then @value{GDBN} will start
5521 deleting instructions from the log once the number of the record
5522 instructions becomes greater than @var{limit}. For every new recorded
5523 instruction, @value{GDBN} will delete the earliest recorded
5524 instruction to keep the number of recorded instructions at the limit.
5525 (Since deleting recorded instructions loses information, @value{GDBN}
5526 lets you control what happens when the limit is reached, by means of
5527 the @code{stop-at-limit} option, described below.)
5529 If @var{limit} is zero, @value{GDBN} will never delete recorded
5530 instructions from the execution log. The number of recorded
5531 instructions is unlimited in this case.
5533 @kindex show record insn-number-max
5534 @item show record insn-number-max
5535 Show the limit of instructions to be recorded.
5537 @kindex set record stop-at-limit
5538 @item set record stop-at-limit
5539 Control the behavior when the number of recorded instructions reaches
5540 the limit. If ON (the default), @value{GDBN} will stop when the limit
5541 is reached for the first time and ask you whether you want to stop the
5542 inferior or continue running it and recording the execution log. If
5543 you decide to continue recording, each new recorded instruction will
5544 cause the oldest one to be deleted.
5546 If this option is OFF, @value{GDBN} will automatically delete the
5547 oldest record to make room for each new one, without asking.
5549 @kindex show record stop-at-limit
5550 @item show record stop-at-limit
5551 Show the current setting of @code{stop-at-limit}.
5555 Show various statistics about the state of process record and its
5556 in-memory execution log buffer, including:
5560 Whether in record mode or replay mode.
5562 Lowest recorded instruction number (counting from when the current execution log started recording instructions).
5564 Highest recorded instruction number.
5566 Current instruction about to be replayed (if in replay mode).
5568 Number of instructions contained in the execution log.
5570 Maximum number of instructions that may be contained in the execution log.
5573 @kindex record delete
5576 When record target runs in replay mode (``in the past''), delete the
5577 subsequent execution log and begin to record a new execution log starting
5578 from the current address. This means you will abandon the previously
5579 recorded ``future'' and begin recording a new ``future''.
5584 @chapter Examining the Stack
5586 When your program has stopped, the first thing you need to know is where it
5587 stopped and how it got there.
5590 Each time your program performs a function call, information about the call
5592 That information includes the location of the call in your program,
5593 the arguments of the call,
5594 and the local variables of the function being called.
5595 The information is saved in a block of data called a @dfn{stack frame}.
5596 The stack frames are allocated in a region of memory called the @dfn{call
5599 When your program stops, the @value{GDBN} commands for examining the
5600 stack allow you to see all of this information.
5602 @cindex selected frame
5603 One of the stack frames is @dfn{selected} by @value{GDBN} and many
5604 @value{GDBN} commands refer implicitly to the selected frame. In
5605 particular, whenever you ask @value{GDBN} for the value of a variable in
5606 your program, the value is found in the selected frame. There are
5607 special @value{GDBN} commands to select whichever frame you are
5608 interested in. @xref{Selection, ,Selecting a Frame}.
5610 When your program stops, @value{GDBN} automatically selects the
5611 currently executing frame and describes it briefly, similar to the
5612 @code{frame} command (@pxref{Frame Info, ,Information about a Frame}).
5615 * Frames:: Stack frames
5616 * Backtrace:: Backtraces
5617 * Selection:: Selecting a frame
5618 * Frame Info:: Information on a frame
5623 @section Stack Frames
5625 @cindex frame, definition
5627 The call stack is divided up into contiguous pieces called @dfn{stack
5628 frames}, or @dfn{frames} for short; each frame is the data associated
5629 with one call to one function. The frame contains the arguments given
5630 to the function, the function's local variables, and the address at
5631 which the function is executing.
5633 @cindex initial frame
5634 @cindex outermost frame
5635 @cindex innermost frame
5636 When your program is started, the stack has only one frame, that of the
5637 function @code{main}. This is called the @dfn{initial} frame or the
5638 @dfn{outermost} frame. Each time a function is called, a new frame is
5639 made. Each time a function returns, the frame for that function invocation
5640 is eliminated. If a function is recursive, there can be many frames for
5641 the same function. The frame for the function in which execution is
5642 actually occurring is called the @dfn{innermost} frame. This is the most
5643 recently created of all the stack frames that still exist.
5645 @cindex frame pointer
5646 Inside your program, stack frames are identified by their addresses. A
5647 stack frame consists of many bytes, each of which has its own address; each
5648 kind of computer has a convention for choosing one byte whose
5649 address serves as the address of the frame. Usually this address is kept
5650 in a register called the @dfn{frame pointer register}
5651 (@pxref{Registers, $fp}) while execution is going on in that frame.
5653 @cindex frame number
5654 @value{GDBN} assigns numbers to all existing stack frames, starting with
5655 zero for the innermost frame, one for the frame that called it,
5656 and so on upward. These numbers do not really exist in your program;
5657 they are assigned by @value{GDBN} to give you a way of designating stack
5658 frames in @value{GDBN} commands.
5660 @c The -fomit-frame-pointer below perennially causes hbox overflow
5661 @c underflow problems.
5662 @cindex frameless execution
5663 Some compilers provide a way to compile functions so that they operate
5664 without stack frames. (For example, the @value{NGCC} option
5666 @samp{-fomit-frame-pointer}
5668 generates functions without a frame.)
5669 This is occasionally done with heavily used library functions to save
5670 the frame setup time. @value{GDBN} has limited facilities for dealing
5671 with these function invocations. If the innermost function invocation
5672 has no stack frame, @value{GDBN} nevertheless regards it as though
5673 it had a separate frame, which is numbered zero as usual, allowing
5674 correct tracing of the function call chain. However, @value{GDBN} has
5675 no provision for frameless functions elsewhere in the stack.
5678 @kindex frame@r{, command}
5679 @cindex current stack frame
5680 @item frame @var{args}
5681 The @code{frame} command allows you to move from one stack frame to another,
5682 and to print the stack frame you select. @var{args} may be either the
5683 address of the frame or the stack frame number. Without an argument,
5684 @code{frame} prints the current stack frame.
5686 @kindex select-frame
5687 @cindex selecting frame silently
5689 The @code{select-frame} command allows you to move from one stack frame
5690 to another without printing the frame. This is the silent version of
5698 @cindex call stack traces
5699 A backtrace is a summary of how your program got where it is. It shows one
5700 line per frame, for many frames, starting with the currently executing
5701 frame (frame zero), followed by its caller (frame one), and on up the
5706 @kindex bt @r{(@code{backtrace})}
5709 Print a backtrace of the entire stack: one line per frame for all
5710 frames in the stack.
5712 You can stop the backtrace at any time by typing the system interrupt
5713 character, normally @kbd{Ctrl-c}.
5715 @item backtrace @var{n}
5717 Similar, but print only the innermost @var{n} frames.
5719 @item backtrace -@var{n}
5721 Similar, but print only the outermost @var{n} frames.
5723 @item backtrace full
5725 @itemx bt full @var{n}
5726 @itemx bt full -@var{n}
5727 Print the values of the local variables also. @var{n} specifies the
5728 number of frames to print, as described above.
5733 The names @code{where} and @code{info stack} (abbreviated @code{info s})
5734 are additional aliases for @code{backtrace}.
5736 @cindex multiple threads, backtrace
5737 In a multi-threaded program, @value{GDBN} by default shows the
5738 backtrace only for the current thread. To display the backtrace for
5739 several or all of the threads, use the command @code{thread apply}
5740 (@pxref{Threads, thread apply}). For example, if you type @kbd{thread
5741 apply all backtrace}, @value{GDBN} will display the backtrace for all
5742 the threads; this is handy when you debug a core dump of a
5743 multi-threaded program.
5745 Each line in the backtrace shows the frame number and the function name.
5746 The program counter value is also shown---unless you use @code{set
5747 print address off}. The backtrace also shows the source file name and
5748 line number, as well as the arguments to the function. The program
5749 counter value is omitted if it is at the beginning of the code for that
5752 Here is an example of a backtrace. It was made with the command
5753 @samp{bt 3}, so it shows the innermost three frames.
5757 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
5759 #1 0x6e38 in expand_macro (sym=0x2b600, data=...) at macro.c:242
5760 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
5762 (More stack frames follow...)
5767 The display for frame zero does not begin with a program counter
5768 value, indicating that your program has stopped at the beginning of the
5769 code for line @code{993} of @code{builtin.c}.
5772 The value of parameter @code{data} in frame 1 has been replaced by
5773 @code{@dots{}}. By default, @value{GDBN} prints the value of a parameter
5774 only if it is a scalar (integer, pointer, enumeration, etc). See command
5775 @kbd{set print frame-arguments} in @ref{Print Settings} for more details
5776 on how to configure the way function parameter values are printed.
5778 @cindex value optimized out, in backtrace
5779 @cindex function call arguments, optimized out
5780 If your program was compiled with optimizations, some compilers will
5781 optimize away arguments passed to functions if those arguments are
5782 never used after the call. Such optimizations generate code that
5783 passes arguments through registers, but doesn't store those arguments
5784 in the stack frame. @value{GDBN} has no way of displaying such
5785 arguments in stack frames other than the innermost one. Here's what
5786 such a backtrace might look like:
5790 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
5792 #1 0x6e38 in expand_macro (sym=<value optimized out>) at macro.c:242
5793 #2 0x6840 in expand_token (obs=0x0, t=<value optimized out>, td=0xf7fffb08)
5795 (More stack frames follow...)
5800 The values of arguments that were not saved in their stack frames are
5801 shown as @samp{<value optimized out>}.
5803 If you need to display the values of such optimized-out arguments,
5804 either deduce that from other variables whose values depend on the one
5805 you are interested in, or recompile without optimizations.
5807 @cindex backtrace beyond @code{main} function
5808 @cindex program entry point
5809 @cindex startup code, and backtrace
5810 Most programs have a standard user entry point---a place where system
5811 libraries and startup code transition into user code. For C this is
5812 @code{main}@footnote{
5813 Note that embedded programs (the so-called ``free-standing''
5814 environment) are not required to have a @code{main} function as the
5815 entry point. They could even have multiple entry points.}.
5816 When @value{GDBN} finds the entry function in a backtrace
5817 it will terminate the backtrace, to avoid tracing into highly
5818 system-specific (and generally uninteresting) code.
5820 If you need to examine the startup code, or limit the number of levels
5821 in a backtrace, you can change this behavior:
5824 @item set backtrace past-main
5825 @itemx set backtrace past-main on
5826 @kindex set backtrace
5827 Backtraces will continue past the user entry point.
5829 @item set backtrace past-main off
5830 Backtraces will stop when they encounter the user entry point. This is the
5833 @item show backtrace past-main
5834 @kindex show backtrace
5835 Display the current user entry point backtrace policy.
5837 @item set backtrace past-entry
5838 @itemx set backtrace past-entry on
5839 Backtraces will continue past the internal entry point of an application.
5840 This entry point is encoded by the linker when the application is built,
5841 and is likely before the user entry point @code{main} (or equivalent) is called.
5843 @item set backtrace past-entry off
5844 Backtraces will stop when they encounter the internal entry point of an
5845 application. This is the default.
5847 @item show backtrace past-entry
5848 Display the current internal entry point backtrace policy.
5850 @item set backtrace limit @var{n}
5851 @itemx set backtrace limit 0
5852 @cindex backtrace limit
5853 Limit the backtrace to @var{n} levels. A value of zero means
5856 @item show backtrace limit
5857 Display the current limit on backtrace levels.
5861 @section Selecting a Frame
5863 Most commands for examining the stack and other data in your program work on
5864 whichever stack frame is selected at the moment. Here are the commands for
5865 selecting a stack frame; all of them finish by printing a brief description
5866 of the stack frame just selected.
5869 @kindex frame@r{, selecting}
5870 @kindex f @r{(@code{frame})}
5873 Select frame number @var{n}. Recall that frame zero is the innermost
5874 (currently executing) frame, frame one is the frame that called the
5875 innermost one, and so on. The highest-numbered frame is the one for
5878 @item frame @var{addr}
5880 Select the frame at address @var{addr}. This is useful mainly if the
5881 chaining of stack frames has been damaged by a bug, making it
5882 impossible for @value{GDBN} to assign numbers properly to all frames. In
5883 addition, this can be useful when your program has multiple stacks and
5884 switches between them.
5886 On the SPARC architecture, @code{frame} needs two addresses to
5887 select an arbitrary frame: a frame pointer and a stack pointer.
5889 On the MIPS and Alpha architecture, it needs two addresses: a stack
5890 pointer and a program counter.
5892 On the 29k architecture, it needs three addresses: a register stack
5893 pointer, a program counter, and a memory stack pointer.
5897 Move @var{n} frames up the stack. For positive numbers @var{n}, this
5898 advances toward the outermost frame, to higher frame numbers, to frames
5899 that have existed longer. @var{n} defaults to one.
5902 @kindex do @r{(@code{down})}
5904 Move @var{n} frames down the stack. For positive numbers @var{n}, this
5905 advances toward the innermost frame, to lower frame numbers, to frames
5906 that were created more recently. @var{n} defaults to one. You may
5907 abbreviate @code{down} as @code{do}.
5910 All of these commands end by printing two lines of output describing the
5911 frame. The first line shows the frame number, the function name, the
5912 arguments, and the source file and line number of execution in that
5913 frame. The second line shows the text of that source line.
5921 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
5923 10 read_input_file (argv[i]);
5927 After such a printout, the @code{list} command with no arguments
5928 prints ten lines centered on the point of execution in the frame.
5929 You can also edit the program at the point of execution with your favorite
5930 editing program by typing @code{edit}.
5931 @xref{List, ,Printing Source Lines},
5935 @kindex down-silently
5937 @item up-silently @var{n}
5938 @itemx down-silently @var{n}
5939 These two commands are variants of @code{up} and @code{down},
5940 respectively; they differ in that they do their work silently, without
5941 causing display of the new frame. They are intended primarily for use
5942 in @value{GDBN} command scripts, where the output might be unnecessary and
5947 @section Information About a Frame
5949 There are several other commands to print information about the selected
5955 When used without any argument, this command does not change which
5956 frame is selected, but prints a brief description of the currently
5957 selected stack frame. It can be abbreviated @code{f}. With an
5958 argument, this command is used to select a stack frame.
5959 @xref{Selection, ,Selecting a Frame}.
5962 @kindex info f @r{(@code{info frame})}
5965 This command prints a verbose description of the selected stack frame,
5970 the address of the frame
5972 the address of the next frame down (called by this frame)
5974 the address of the next frame up (caller of this frame)
5976 the language in which the source code corresponding to this frame is written
5978 the address of the frame's arguments
5980 the address of the frame's local variables
5982 the program counter saved in it (the address of execution in the caller frame)
5984 which registers were saved in the frame
5987 @noindent The verbose description is useful when
5988 something has gone wrong that has made the stack format fail to fit
5989 the usual conventions.
5991 @item info frame @var{addr}
5992 @itemx info f @var{addr}
5993 Print a verbose description of the frame at address @var{addr}, without
5994 selecting that frame. The selected frame remains unchanged by this
5995 command. This requires the same kind of address (more than one for some
5996 architectures) that you specify in the @code{frame} command.
5997 @xref{Selection, ,Selecting a Frame}.
6001 Print the arguments of the selected frame, each on a separate line.
6005 Print the local variables of the selected frame, each on a separate
6006 line. These are all variables (declared either static or automatic)
6007 accessible at the point of execution of the selected frame.
6010 @cindex catch exceptions, list active handlers
6011 @cindex exception handlers, how to list
6013 Print a list of all the exception handlers that are active in the
6014 current stack frame at the current point of execution. To see other
6015 exception handlers, visit the associated frame (using the @code{up},
6016 @code{down}, or @code{frame} commands); then type @code{info catch}.
6017 @xref{Set Catchpoints, , Setting Catchpoints}.
6023 @chapter Examining Source Files
6025 @value{GDBN} can print parts of your program's source, since the debugging
6026 information recorded in the program tells @value{GDBN} what source files were
6027 used to build it. When your program stops, @value{GDBN} spontaneously prints
6028 the line where it stopped. Likewise, when you select a stack frame
6029 (@pxref{Selection, ,Selecting a Frame}), @value{GDBN} prints the line where
6030 execution in that frame has stopped. You can print other portions of
6031 source files by explicit command.
6033 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
6034 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
6035 @value{GDBN} under @sc{gnu} Emacs}.
6038 * List:: Printing source lines
6039 * Specify Location:: How to specify code locations
6040 * Edit:: Editing source files
6041 * Search:: Searching source files
6042 * Source Path:: Specifying source directories
6043 * Machine Code:: Source and machine code
6047 @section Printing Source Lines
6050 @kindex l @r{(@code{list})}
6051 To print lines from a source file, use the @code{list} command
6052 (abbreviated @code{l}). By default, ten lines are printed.
6053 There are several ways to specify what part of the file you want to
6054 print; see @ref{Specify Location}, for the full list.
6056 Here are the forms of the @code{list} command most commonly used:
6059 @item list @var{linenum}
6060 Print lines centered around line number @var{linenum} in the
6061 current source file.
6063 @item list @var{function}
6064 Print lines centered around the beginning of function
6068 Print more lines. If the last lines printed were printed with a
6069 @code{list} command, this prints lines following the last lines
6070 printed; however, if the last line printed was a solitary line printed
6071 as part of displaying a stack frame (@pxref{Stack, ,Examining the
6072 Stack}), this prints lines centered around that line.
6075 Print lines just before the lines last printed.
6078 @cindex @code{list}, how many lines to display
6079 By default, @value{GDBN} prints ten source lines with any of these forms of
6080 the @code{list} command. You can change this using @code{set listsize}:
6083 @kindex set listsize
6084 @item set listsize @var{count}
6085 Make the @code{list} command display @var{count} source lines (unless
6086 the @code{list} argument explicitly specifies some other number).
6088 @kindex show listsize
6090 Display the number of lines that @code{list} prints.
6093 Repeating a @code{list} command with @key{RET} discards the argument,
6094 so it is equivalent to typing just @code{list}. This is more useful
6095 than listing the same lines again. An exception is made for an
6096 argument of @samp{-}; that argument is preserved in repetition so that
6097 each repetition moves up in the source file.
6099 In general, the @code{list} command expects you to supply zero, one or two
6100 @dfn{linespecs}. Linespecs specify source lines; there are several ways
6101 of writing them (@pxref{Specify Location}), but the effect is always
6102 to specify some source line.
6104 Here is a complete description of the possible arguments for @code{list}:
6107 @item list @var{linespec}
6108 Print lines centered around the line specified by @var{linespec}.
6110 @item list @var{first},@var{last}
6111 Print lines from @var{first} to @var{last}. Both arguments are
6112 linespecs. When a @code{list} command has two linespecs, and the
6113 source file of the second linespec is omitted, this refers to
6114 the same source file as the first linespec.
6116 @item list ,@var{last}
6117 Print lines ending with @var{last}.
6119 @item list @var{first},
6120 Print lines starting with @var{first}.
6123 Print lines just after the lines last printed.
6126 Print lines just before the lines last printed.
6129 As described in the preceding table.
6132 @node Specify Location
6133 @section Specifying a Location
6134 @cindex specifying location
6137 Several @value{GDBN} commands accept arguments that specify a location
6138 of your program's code. Since @value{GDBN} is a source-level
6139 debugger, a location usually specifies some line in the source code;
6140 for that reason, locations are also known as @dfn{linespecs}.
6142 Here are all the different ways of specifying a code location that
6143 @value{GDBN} understands:
6147 Specifies the line number @var{linenum} of the current source file.
6150 @itemx +@var{offset}
6151 Specifies the line @var{offset} lines before or after the @dfn{current
6152 line}. For the @code{list} command, the current line is the last one
6153 printed; for the breakpoint commands, this is the line at which
6154 execution stopped in the currently selected @dfn{stack frame}
6155 (@pxref{Frames, ,Frames}, for a description of stack frames.) When
6156 used as the second of the two linespecs in a @code{list} command,
6157 this specifies the line @var{offset} lines up or down from the first
6160 @item @var{filename}:@var{linenum}
6161 Specifies the line @var{linenum} in the source file @var{filename}.
6163 @item @var{function}
6164 Specifies the line that begins the body of the function @var{function}.
6165 For example, in C, this is the line with the open brace.
6167 @item @var{filename}:@var{function}
6168 Specifies the line that begins the body of the function @var{function}
6169 in the file @var{filename}. You only need the file name with a
6170 function name to avoid ambiguity when there are identically named
6171 functions in different source files.
6173 @item *@var{address}
6174 Specifies the program address @var{address}. For line-oriented
6175 commands, such as @code{list} and @code{edit}, this specifies a source
6176 line that contains @var{address}. For @code{break} and other
6177 breakpoint oriented commands, this can be used to set breakpoints in
6178 parts of your program which do not have debugging information or
6181 Here @var{address} may be any expression valid in the current working
6182 language (@pxref{Languages, working language}) that specifies a code
6183 address. In addition, as a convenience, @value{GDBN} extends the
6184 semantics of expressions used in locations to cover the situations
6185 that frequently happen during debugging. Here are the various forms
6189 @item @var{expression}
6190 Any expression valid in the current working language.
6192 @item @var{funcaddr}
6193 An address of a function or procedure derived from its name. In C,
6194 C@t{++}, Java, Objective-C, Fortran, minimal, and assembly, this is
6195 simply the function's name @var{function} (and actually a special case
6196 of a valid expression). In Pascal and Modula-2, this is
6197 @code{&@var{function}}. In Ada, this is @code{@var{function}'Address}
6198 (although the Pascal form also works).
6200 This form specifies the address of the function's first instruction,
6201 before the stack frame and arguments have been set up.
6203 @item '@var{filename}'::@var{funcaddr}
6204 Like @var{funcaddr} above, but also specifies the name of the source
6205 file explicitly. This is useful if the name of the function does not
6206 specify the function unambiguously, e.g., if there are several
6207 functions with identical names in different source files.
6214 @section Editing Source Files
6215 @cindex editing source files
6218 @kindex e @r{(@code{edit})}
6219 To edit the lines in a source file, use the @code{edit} command.
6220 The editing program of your choice
6221 is invoked with the current line set to
6222 the active line in the program.
6223 Alternatively, there are several ways to specify what part of the file you
6224 want to print if you want to see other parts of the program:
6227 @item edit @var{location}
6228 Edit the source file specified by @code{location}. Editing starts at
6229 that @var{location}, e.g., at the specified source line of the
6230 specified file. @xref{Specify Location}, for all the possible forms
6231 of the @var{location} argument; here are the forms of the @code{edit}
6232 command most commonly used:
6235 @item edit @var{number}
6236 Edit the current source file with @var{number} as the active line number.
6238 @item edit @var{function}
6239 Edit the file containing @var{function} at the beginning of its definition.
6244 @subsection Choosing your Editor
6245 You can customize @value{GDBN} to use any editor you want
6247 The only restriction is that your editor (say @code{ex}), recognizes the
6248 following command-line syntax:
6250 ex +@var{number} file
6252 The optional numeric value +@var{number} specifies the number of the line in
6253 the file where to start editing.}.
6254 By default, it is @file{@value{EDITOR}}, but you can change this
6255 by setting the environment variable @code{EDITOR} before using
6256 @value{GDBN}. For example, to configure @value{GDBN} to use the
6257 @code{vi} editor, you could use these commands with the @code{sh} shell:
6263 or in the @code{csh} shell,
6265 setenv EDITOR /usr/bin/vi
6270 @section Searching Source Files
6271 @cindex searching source files
6273 There are two commands for searching through the current source file for a
6278 @kindex forward-search
6279 @item forward-search @var{regexp}
6280 @itemx search @var{regexp}
6281 The command @samp{forward-search @var{regexp}} checks each line,
6282 starting with the one following the last line listed, for a match for
6283 @var{regexp}. It lists the line that is found. You can use the
6284 synonym @samp{search @var{regexp}} or abbreviate the command name as
6287 @kindex reverse-search
6288 @item reverse-search @var{regexp}
6289 The command @samp{reverse-search @var{regexp}} checks each line, starting
6290 with the one before the last line listed and going backward, for a match
6291 for @var{regexp}. It lists the line that is found. You can abbreviate
6292 this command as @code{rev}.
6296 @section Specifying Source Directories
6299 @cindex directories for source files
6300 Executable programs sometimes do not record the directories of the source
6301 files from which they were compiled, just the names. Even when they do,
6302 the directories could be moved between the compilation and your debugging
6303 session. @value{GDBN} has a list of directories to search for source files;
6304 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
6305 it tries all the directories in the list, in the order they are present
6306 in the list, until it finds a file with the desired name.
6308 For example, suppose an executable references the file
6309 @file{/usr/src/foo-1.0/lib/foo.c}, and our source path is
6310 @file{/mnt/cross}. The file is first looked up literally; if this
6311 fails, @file{/mnt/cross/usr/src/foo-1.0/lib/foo.c} is tried; if this
6312 fails, @file{/mnt/cross/foo.c} is opened; if this fails, an error
6313 message is printed. @value{GDBN} does not look up the parts of the
6314 source file name, such as @file{/mnt/cross/src/foo-1.0/lib/foo.c}.
6315 Likewise, the subdirectories of the source path are not searched: if
6316 the source path is @file{/mnt/cross}, and the binary refers to
6317 @file{foo.c}, @value{GDBN} would not find it under
6318 @file{/mnt/cross/usr/src/foo-1.0/lib}.
6320 Plain file names, relative file names with leading directories, file
6321 names containing dots, etc.@: are all treated as described above; for
6322 instance, if the source path is @file{/mnt/cross}, and the source file
6323 is recorded as @file{../lib/foo.c}, @value{GDBN} would first try
6324 @file{../lib/foo.c}, then @file{/mnt/cross/../lib/foo.c}, and after
6325 that---@file{/mnt/cross/foo.c}.
6327 Note that the executable search path is @emph{not} used to locate the
6330 Whenever you reset or rearrange the source path, @value{GDBN} clears out
6331 any information it has cached about where source files are found and where
6332 each line is in the file.
6336 When you start @value{GDBN}, its source path includes only @samp{cdir}
6337 and @samp{cwd}, in that order.
6338 To add other directories, use the @code{directory} command.
6340 The search path is used to find both program source files and @value{GDBN}
6341 script files (read using the @samp{-command} option and @samp{source} command).
6343 In addition to the source path, @value{GDBN} provides a set of commands
6344 that manage a list of source path substitution rules. A @dfn{substitution
6345 rule} specifies how to rewrite source directories stored in the program's
6346 debug information in case the sources were moved to a different
6347 directory between compilation and debugging. A rule is made of
6348 two strings, the first specifying what needs to be rewritten in
6349 the path, and the second specifying how it should be rewritten.
6350 In @ref{set substitute-path}, we name these two parts @var{from} and
6351 @var{to} respectively. @value{GDBN} does a simple string replacement
6352 of @var{from} with @var{to} at the start of the directory part of the
6353 source file name, and uses that result instead of the original file
6354 name to look up the sources.
6356 Using the previous example, suppose the @file{foo-1.0} tree has been
6357 moved from @file{/usr/src} to @file{/mnt/cross}, then you can tell
6358 @value{GDBN} to replace @file{/usr/src} in all source path names with
6359 @file{/mnt/cross}. The first lookup will then be
6360 @file{/mnt/cross/foo-1.0/lib/foo.c} in place of the original location
6361 of @file{/usr/src/foo-1.0/lib/foo.c}. To define a source path
6362 substitution rule, use the @code{set substitute-path} command
6363 (@pxref{set substitute-path}).
6365 To avoid unexpected substitution results, a rule is applied only if the
6366 @var{from} part of the directory name ends at a directory separator.
6367 For instance, a rule substituting @file{/usr/source} into
6368 @file{/mnt/cross} will be applied to @file{/usr/source/foo-1.0} but
6369 not to @file{/usr/sourceware/foo-2.0}. And because the substitution
6370 is applied only at the beginning of the directory name, this rule will
6371 not be applied to @file{/root/usr/source/baz.c} either.
6373 In many cases, you can achieve the same result using the @code{directory}
6374 command. However, @code{set substitute-path} can be more efficient in
6375 the case where the sources are organized in a complex tree with multiple
6376 subdirectories. With the @code{directory} command, you need to add each
6377 subdirectory of your project. If you moved the entire tree while
6378 preserving its internal organization, then @code{set substitute-path}
6379 allows you to direct the debugger to all the sources with one single
6382 @code{set substitute-path} is also more than just a shortcut command.
6383 The source path is only used if the file at the original location no
6384 longer exists. On the other hand, @code{set substitute-path} modifies
6385 the debugger behavior to look at the rewritten location instead. So, if
6386 for any reason a source file that is not relevant to your executable is
6387 located at the original location, a substitution rule is the only
6388 method available to point @value{GDBN} at the new location.
6390 @cindex @samp{--with-relocated-sources}
6391 @cindex default source path substitution
6392 You can configure a default source path substitution rule by
6393 configuring @value{GDBN} with the
6394 @samp{--with-relocated-sources=@var{dir}} option. The @var{dir}
6395 should be the name of a directory under @value{GDBN}'s configured
6396 prefix (set with @samp{--prefix} or @samp{--exec-prefix}), and
6397 directory names in debug information under @var{dir} will be adjusted
6398 automatically if the installed @value{GDBN} is moved to a new
6399 location. This is useful if @value{GDBN}, libraries or executables
6400 with debug information and corresponding source code are being moved
6404 @item directory @var{dirname} @dots{}
6405 @item dir @var{dirname} @dots{}
6406 Add directory @var{dirname} to the front of the source path. Several
6407 directory names may be given to this command, separated by @samp{:}
6408 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
6409 part of absolute file names) or
6410 whitespace. You may specify a directory that is already in the source
6411 path; this moves it forward, so @value{GDBN} searches it sooner.
6415 @vindex $cdir@r{, convenience variable}
6416 @vindex $cwd@r{, convenience variable}
6417 @cindex compilation directory
6418 @cindex current directory
6419 @cindex working directory
6420 @cindex directory, current
6421 @cindex directory, compilation
6422 You can use the string @samp{$cdir} to refer to the compilation
6423 directory (if one is recorded), and @samp{$cwd} to refer to the current
6424 working directory. @samp{$cwd} is not the same as @samp{.}---the former
6425 tracks the current working directory as it changes during your @value{GDBN}
6426 session, while the latter is immediately expanded to the current
6427 directory at the time you add an entry to the source path.
6430 Reset the source path to its default value (@samp{$cdir:$cwd} on Unix systems). This requires confirmation.
6432 @c RET-repeat for @code{directory} is explicitly disabled, but since
6433 @c repeating it would be a no-op we do not say that. (thanks to RMS)
6435 @item show directories
6436 @kindex show directories
6437 Print the source path: show which directories it contains.
6439 @anchor{set substitute-path}
6440 @item set substitute-path @var{from} @var{to}
6441 @kindex set substitute-path
6442 Define a source path substitution rule, and add it at the end of the
6443 current list of existing substitution rules. If a rule with the same
6444 @var{from} was already defined, then the old rule is also deleted.
6446 For example, if the file @file{/foo/bar/baz.c} was moved to
6447 @file{/mnt/cross/baz.c}, then the command
6450 (@value{GDBP}) set substitute-path /usr/src /mnt/cross
6454 will tell @value{GDBN} to replace @samp{/usr/src} with
6455 @samp{/mnt/cross}, which will allow @value{GDBN} to find the file
6456 @file{baz.c} even though it was moved.
6458 In the case when more than one substitution rule have been defined,
6459 the rules are evaluated one by one in the order where they have been
6460 defined. The first one matching, if any, is selected to perform
6463 For instance, if we had entered the following commands:
6466 (@value{GDBP}) set substitute-path /usr/src/include /mnt/include
6467 (@value{GDBP}) set substitute-path /usr/src /mnt/src
6471 @value{GDBN} would then rewrite @file{/usr/src/include/defs.h} into
6472 @file{/mnt/include/defs.h} by using the first rule. However, it would
6473 use the second rule to rewrite @file{/usr/src/lib/foo.c} into
6474 @file{/mnt/src/lib/foo.c}.
6477 @item unset substitute-path [path]
6478 @kindex unset substitute-path
6479 If a path is specified, search the current list of substitution rules
6480 for a rule that would rewrite that path. Delete that rule if found.
6481 A warning is emitted by the debugger if no rule could be found.
6483 If no path is specified, then all substitution rules are deleted.
6485 @item show substitute-path [path]
6486 @kindex show substitute-path
6487 If a path is specified, then print the source path substitution rule
6488 which would rewrite that path, if any.
6490 If no path is specified, then print all existing source path substitution
6495 If your source path is cluttered with directories that are no longer of
6496 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
6497 versions of source. You can correct the situation as follows:
6501 Use @code{directory} with no argument to reset the source path to its default value.
6504 Use @code{directory} with suitable arguments to reinstall the
6505 directories you want in the source path. You can add all the
6506 directories in one command.
6510 @section Source and Machine Code
6511 @cindex source line and its code address
6513 You can use the command @code{info line} to map source lines to program
6514 addresses (and vice versa), and the command @code{disassemble} to display
6515 a range of addresses as machine instructions. You can use the command
6516 @code{set disassemble-next-line} to set whether to disassemble next
6517 source line when execution stops. When run under @sc{gnu} Emacs
6518 mode, the @code{info line} command causes the arrow to point to the
6519 line specified. Also, @code{info line} prints addresses in symbolic form as
6524 @item info line @var{linespec}
6525 Print the starting and ending addresses of the compiled code for
6526 source line @var{linespec}. You can specify source lines in any of
6527 the ways documented in @ref{Specify Location}.
6530 For example, we can use @code{info line} to discover the location of
6531 the object code for the first line of function
6532 @code{m4_changequote}:
6534 @c FIXME: I think this example should also show the addresses in
6535 @c symbolic form, as they usually would be displayed.
6537 (@value{GDBP}) info line m4_changequote
6538 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
6542 @cindex code address and its source line
6543 We can also inquire (using @code{*@var{addr}} as the form for
6544 @var{linespec}) what source line covers a particular address:
6546 (@value{GDBP}) info line *0x63ff
6547 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
6550 @cindex @code{$_} and @code{info line}
6551 @cindex @code{x} command, default address
6552 @kindex x@r{(examine), and} info line
6553 After @code{info line}, the default address for the @code{x} command
6554 is changed to the starting address of the line, so that @samp{x/i} is
6555 sufficient to begin examining the machine code (@pxref{Memory,
6556 ,Examining Memory}). Also, this address is saved as the value of the
6557 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
6562 @cindex assembly instructions
6563 @cindex instructions, assembly
6564 @cindex machine instructions
6565 @cindex listing machine instructions
6567 @itemx disassemble /m
6568 @itemx disassemble /r
6569 This specialized command dumps a range of memory as machine
6570 instructions. It can also print mixed source+disassembly by specifying
6571 the @code{/m} modifier and print the raw instructions in hex as well as
6572 in symbolic form by specifying the @code{/r}.
6573 The default memory range is the function surrounding the
6574 program counter of the selected frame. A single argument to this
6575 command is a program counter value; @value{GDBN} dumps the function
6576 surrounding this value. When two arguments are given, they should
6577 be separated by a comma, possibly surrounded by whitespace. The
6578 arguments specify a range of addresses (first inclusive, second exclusive)
6579 to dump. In that case, the name of the function is also printed (since
6580 there could be several functions in the given range).
6582 The argument(s) can be any expression yielding a numeric value, such as
6583 @samp{0x32c4}, @samp{&main+10} or @samp{$pc - 8}.
6585 If the range of memory being disassembled contains current program counter,
6586 the instruction at that location is shown with a @code{=>} marker.
6589 The following example shows the disassembly of a range of addresses of
6590 HP PA-RISC 2.0 code:
6593 (@value{GDBP}) disas 0x32c4, 0x32e4
6594 Dump of assembler code from 0x32c4 to 0x32e4:
6595 0x32c4 <main+204>: addil 0,dp
6596 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
6597 0x32cc <main+212>: ldil 0x3000,r31
6598 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
6599 0x32d4 <main+220>: ldo 0(r31),rp
6600 0x32d8 <main+224>: addil -0x800,dp
6601 0x32dc <main+228>: ldo 0x588(r1),r26
6602 0x32e0 <main+232>: ldil 0x3000,r31
6603 End of assembler dump.
6606 Here is an example showing mixed source+assembly for Intel x86, when the
6607 program is stopped just after function prologue:
6610 (@value{GDBP}) disas /m main
6611 Dump of assembler code for function main:
6613 0x08048330 <+0>: push %ebp
6614 0x08048331 <+1>: mov %esp,%ebp
6615 0x08048333 <+3>: sub $0x8,%esp
6616 0x08048336 <+6>: and $0xfffffff0,%esp
6617 0x08048339 <+9>: sub $0x10,%esp
6619 6 printf ("Hello.\n");
6620 => 0x0804833c <+12>: movl $0x8048440,(%esp)
6621 0x08048343 <+19>: call 0x8048284 <puts@@plt>
6625 0x08048348 <+24>: mov $0x0,%eax
6626 0x0804834d <+29>: leave
6627 0x0804834e <+30>: ret
6629 End of assembler dump.
6632 Some architectures have more than one commonly-used set of instruction
6633 mnemonics or other syntax.
6635 For programs that were dynamically linked and use shared libraries,
6636 instructions that call functions or branch to locations in the shared
6637 libraries might show a seemingly bogus location---it's actually a
6638 location of the relocation table. On some architectures, @value{GDBN}
6639 might be able to resolve these to actual function names.
6642 @kindex set disassembly-flavor
6643 @cindex Intel disassembly flavor
6644 @cindex AT&T disassembly flavor
6645 @item set disassembly-flavor @var{instruction-set}
6646 Select the instruction set to use when disassembling the
6647 program via the @code{disassemble} or @code{x/i} commands.
6649 Currently this command is only defined for the Intel x86 family. You
6650 can set @var{instruction-set} to either @code{intel} or @code{att}.
6651 The default is @code{att}, the AT&T flavor used by default by Unix
6652 assemblers for x86-based targets.
6654 @kindex show disassembly-flavor
6655 @item show disassembly-flavor
6656 Show the current setting of the disassembly flavor.
6660 @kindex set disassemble-next-line
6661 @kindex show disassemble-next-line
6662 @item set disassemble-next-line
6663 @itemx show disassemble-next-line
6664 Control whether or not @value{GDBN} will disassemble the next source
6665 line or instruction when execution stops. If ON, @value{GDBN} will
6666 display disassembly of the next source line when execution of the
6667 program being debugged stops. This is @emph{in addition} to
6668 displaying the source line itself, which @value{GDBN} always does if
6669 possible. If the next source line cannot be displayed for some reason
6670 (e.g., if @value{GDBN} cannot find the source file, or there's no line
6671 info in the debug info), @value{GDBN} will display disassembly of the
6672 next @emph{instruction} instead of showing the next source line. If
6673 AUTO, @value{GDBN} will display disassembly of next instruction only
6674 if the source line cannot be displayed. This setting causes
6675 @value{GDBN} to display some feedback when you step through a function
6676 with no line info or whose source file is unavailable. The default is
6677 OFF, which means never display the disassembly of the next line or
6683 @chapter Examining Data
6685 @cindex printing data
6686 @cindex examining data
6689 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
6690 @c document because it is nonstandard... Under Epoch it displays in a
6691 @c different window or something like that.
6692 The usual way to examine data in your program is with the @code{print}
6693 command (abbreviated @code{p}), or its synonym @code{inspect}. It
6694 evaluates and prints the value of an expression of the language your
6695 program is written in (@pxref{Languages, ,Using @value{GDBN} with
6696 Different Languages}). It may also print the expression using a
6697 Python-based pretty-printer (@pxref{Pretty Printing}).
6700 @item print @var{expr}
6701 @itemx print /@var{f} @var{expr}
6702 @var{expr} is an expression (in the source language). By default the
6703 value of @var{expr} is printed in a format appropriate to its data type;
6704 you can choose a different format by specifying @samp{/@var{f}}, where
6705 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
6709 @itemx print /@var{f}
6710 @cindex reprint the last value
6711 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
6712 @dfn{value history}; @pxref{Value History, ,Value History}). This allows you to
6713 conveniently inspect the same value in an alternative format.
6716 A more low-level way of examining data is with the @code{x} command.
6717 It examines data in memory at a specified address and prints it in a
6718 specified format. @xref{Memory, ,Examining Memory}.
6720 If you are interested in information about types, or about how the
6721 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
6722 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
6726 * Expressions:: Expressions
6727 * Ambiguous Expressions:: Ambiguous Expressions
6728 * Variables:: Program variables
6729 * Arrays:: Artificial arrays
6730 * Output Formats:: Output formats
6731 * Memory:: Examining memory
6732 * Auto Display:: Automatic display
6733 * Print Settings:: Print settings
6734 * Value History:: Value history
6735 * Convenience Vars:: Convenience variables
6736 * Registers:: Registers
6737 * Floating Point Hardware:: Floating point hardware
6738 * Vector Unit:: Vector Unit
6739 * OS Information:: Auxiliary data provided by operating system
6740 * Memory Region Attributes:: Memory region attributes
6741 * Dump/Restore Files:: Copy between memory and a file
6742 * Core File Generation:: Cause a program dump its core
6743 * Character Sets:: Debugging programs that use a different
6744 character set than GDB does
6745 * Caching Remote Data:: Data caching for remote targets
6746 * Searching Memory:: Searching memory for a sequence of bytes
6750 @section Expressions
6753 @code{print} and many other @value{GDBN} commands accept an expression and
6754 compute its value. Any kind of constant, variable or operator defined
6755 by the programming language you are using is valid in an expression in
6756 @value{GDBN}. This includes conditional expressions, function calls,
6757 casts, and string constants. It also includes preprocessor macros, if
6758 you compiled your program to include this information; see
6761 @cindex arrays in expressions
6762 @value{GDBN} supports array constants in expressions input by
6763 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
6764 you can use the command @code{print @{1, 2, 3@}} to create an array
6765 of three integers. If you pass an array to a function or assign it
6766 to a program variable, @value{GDBN} copies the array to memory that
6767 is @code{malloc}ed in the target program.
6769 Because C is so widespread, most of the expressions shown in examples in
6770 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
6771 Languages}, for information on how to use expressions in other
6774 In this section, we discuss operators that you can use in @value{GDBN}
6775 expressions regardless of your programming language.
6777 @cindex casts, in expressions
6778 Casts are supported in all languages, not just in C, because it is so
6779 useful to cast a number into a pointer in order to examine a structure
6780 at that address in memory.
6781 @c FIXME: casts supported---Mod2 true?
6783 @value{GDBN} supports these operators, in addition to those common
6784 to programming languages:
6788 @samp{@@} is a binary operator for treating parts of memory as arrays.
6789 @xref{Arrays, ,Artificial Arrays}, for more information.
6792 @samp{::} allows you to specify a variable in terms of the file or
6793 function where it is defined. @xref{Variables, ,Program Variables}.
6795 @cindex @{@var{type}@}
6796 @cindex type casting memory
6797 @cindex memory, viewing as typed object
6798 @cindex casts, to view memory
6799 @item @{@var{type}@} @var{addr}
6800 Refers to an object of type @var{type} stored at address @var{addr} in
6801 memory. @var{addr} may be any expression whose value is an integer or
6802 pointer (but parentheses are required around binary operators, just as in
6803 a cast). This construct is allowed regardless of what kind of data is
6804 normally supposed to reside at @var{addr}.
6807 @node Ambiguous Expressions
6808 @section Ambiguous Expressions
6809 @cindex ambiguous expressions
6811 Expressions can sometimes contain some ambiguous elements. For instance,
6812 some programming languages (notably Ada, C@t{++} and Objective-C) permit
6813 a single function name to be defined several times, for application in
6814 different contexts. This is called @dfn{overloading}. Another example
6815 involving Ada is generics. A @dfn{generic package} is similar to C@t{++}
6816 templates and is typically instantiated several times, resulting in
6817 the same function name being defined in different contexts.
6819 In some cases and depending on the language, it is possible to adjust
6820 the expression to remove the ambiguity. For instance in C@t{++}, you
6821 can specify the signature of the function you want to break on, as in
6822 @kbd{break @var{function}(@var{types})}. In Ada, using the fully
6823 qualified name of your function often makes the expression unambiguous
6826 When an ambiguity that needs to be resolved is detected, the debugger
6827 has the capability to display a menu of numbered choices for each
6828 possibility, and then waits for the selection with the prompt @samp{>}.
6829 The first option is always @samp{[0] cancel}, and typing @kbd{0 @key{RET}}
6830 aborts the current command. If the command in which the expression was
6831 used allows more than one choice to be selected, the next option in the
6832 menu is @samp{[1] all}, and typing @kbd{1 @key{RET}} selects all possible
6835 For example, the following session excerpt shows an attempt to set a
6836 breakpoint at the overloaded symbol @code{String::after}.
6837 We choose three particular definitions of that function name:
6839 @c FIXME! This is likely to change to show arg type lists, at least
6842 (@value{GDBP}) b String::after
6845 [2] file:String.cc; line number:867
6846 [3] file:String.cc; line number:860
6847 [4] file:String.cc; line number:875
6848 [5] file:String.cc; line number:853
6849 [6] file:String.cc; line number:846
6850 [7] file:String.cc; line number:735
6852 Breakpoint 1 at 0xb26c: file String.cc, line 867.
6853 Breakpoint 2 at 0xb344: file String.cc, line 875.
6854 Breakpoint 3 at 0xafcc: file String.cc, line 846.
6855 Multiple breakpoints were set.
6856 Use the "delete" command to delete unwanted
6863 @kindex set multiple-symbols
6864 @item set multiple-symbols @var{mode}
6865 @cindex multiple-symbols menu
6867 This option allows you to adjust the debugger behavior when an expression
6870 By default, @var{mode} is set to @code{all}. If the command with which
6871 the expression is used allows more than one choice, then @value{GDBN}
6872 automatically selects all possible choices. For instance, inserting
6873 a breakpoint on a function using an ambiguous name results in a breakpoint
6874 inserted on each possible match. However, if a unique choice must be made,
6875 then @value{GDBN} uses the menu to help you disambiguate the expression.
6876 For instance, printing the address of an overloaded function will result
6877 in the use of the menu.
6879 When @var{mode} is set to @code{ask}, the debugger always uses the menu
6880 when an ambiguity is detected.
6882 Finally, when @var{mode} is set to @code{cancel}, the debugger reports
6883 an error due to the ambiguity and the command is aborted.
6885 @kindex show multiple-symbols
6886 @item show multiple-symbols
6887 Show the current value of the @code{multiple-symbols} setting.
6891 @section Program Variables
6893 The most common kind of expression to use is the name of a variable
6896 Variables in expressions are understood in the selected stack frame
6897 (@pxref{Selection, ,Selecting a Frame}); they must be either:
6901 global (or file-static)
6908 visible according to the scope rules of the
6909 programming language from the point of execution in that frame
6912 @noindent This means that in the function
6927 you can examine and use the variable @code{a} whenever your program is
6928 executing within the function @code{foo}, but you can only use or
6929 examine the variable @code{b} while your program is executing inside
6930 the block where @code{b} is declared.
6932 @cindex variable name conflict
6933 There is an exception: you can refer to a variable or function whose
6934 scope is a single source file even if the current execution point is not
6935 in this file. But it is possible to have more than one such variable or
6936 function with the same name (in different source files). If that
6937 happens, referring to that name has unpredictable effects. If you wish,
6938 you can specify a static variable in a particular function or file,
6939 using the colon-colon (@code{::}) notation:
6941 @cindex colon-colon, context for variables/functions
6943 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
6944 @cindex @code{::}, context for variables/functions
6947 @var{file}::@var{variable}
6948 @var{function}::@var{variable}
6952 Here @var{file} or @var{function} is the name of the context for the
6953 static @var{variable}. In the case of file names, you can use quotes to
6954 make sure @value{GDBN} parses the file name as a single word---for example,
6955 to print a global value of @code{x} defined in @file{f2.c}:
6958 (@value{GDBP}) p 'f2.c'::x
6961 @cindex C@t{++} scope resolution
6962 This use of @samp{::} is very rarely in conflict with the very similar
6963 use of the same notation in C@t{++}. @value{GDBN} also supports use of the C@t{++}
6964 scope resolution operator in @value{GDBN} expressions.
6965 @c FIXME: Um, so what happens in one of those rare cases where it's in
6968 @cindex wrong values
6969 @cindex variable values, wrong
6970 @cindex function entry/exit, wrong values of variables
6971 @cindex optimized code, wrong values of variables
6973 @emph{Warning:} Occasionally, a local variable may appear to have the
6974 wrong value at certain points in a function---just after entry to a new
6975 scope, and just before exit.
6977 You may see this problem when you are stepping by machine instructions.
6978 This is because, on most machines, it takes more than one instruction to
6979 set up a stack frame (including local variable definitions); if you are
6980 stepping by machine instructions, variables may appear to have the wrong
6981 values until the stack frame is completely built. On exit, it usually
6982 also takes more than one machine instruction to destroy a stack frame;
6983 after you begin stepping through that group of instructions, local
6984 variable definitions may be gone.
6986 This may also happen when the compiler does significant optimizations.
6987 To be sure of always seeing accurate values, turn off all optimization
6990 @cindex ``No symbol "foo" in current context''
6991 Another possible effect of compiler optimizations is to optimize
6992 unused variables out of existence, or assign variables to registers (as
6993 opposed to memory addresses). Depending on the support for such cases
6994 offered by the debug info format used by the compiler, @value{GDBN}
6995 might not be able to display values for such local variables. If that
6996 happens, @value{GDBN} will print a message like this:
6999 No symbol "foo" in current context.
7002 To solve such problems, either recompile without optimizations, or use a
7003 different debug info format, if the compiler supports several such
7004 formats. For example, @value{NGCC}, the @sc{gnu} C/C@t{++} compiler,
7005 usually supports the @option{-gstabs+} option. @option{-gstabs+}
7006 produces debug info in a format that is superior to formats such as
7007 COFF. You may be able to use DWARF 2 (@option{-gdwarf-2}), which is also
7008 an effective form for debug info. @xref{Debugging Options,,Options
7009 for Debugging Your Program or GCC, gcc.info, Using the @sc{gnu}
7010 Compiler Collection (GCC)}.
7011 @xref{C, ,C and C@t{++}}, for more information about debug info formats
7012 that are best suited to C@t{++} programs.
7014 If you ask to print an object whose contents are unknown to
7015 @value{GDBN}, e.g., because its data type is not completely specified
7016 by the debug information, @value{GDBN} will say @samp{<incomplete
7017 type>}. @xref{Symbols, incomplete type}, for more about this.
7019 Strings are identified as arrays of @code{char} values without specified
7020 signedness. Arrays of either @code{signed char} or @code{unsigned char} get
7021 printed as arrays of 1 byte sized integers. @code{-fsigned-char} or
7022 @code{-funsigned-char} @value{NGCC} options have no effect as @value{GDBN}
7023 defines literal string type @code{"char"} as @code{char} without a sign.
7028 signed char var1[] = "A";
7031 You get during debugging
7036 $2 = @{65 'A', 0 '\0'@}
7040 @section Artificial Arrays
7042 @cindex artificial array
7044 @kindex @@@r{, referencing memory as an array}
7045 It is often useful to print out several successive objects of the
7046 same type in memory; a section of an array, or an array of
7047 dynamically determined size for which only a pointer exists in the
7050 You can do this by referring to a contiguous span of memory as an
7051 @dfn{artificial array}, using the binary operator @samp{@@}. The left
7052 operand of @samp{@@} should be the first element of the desired array
7053 and be an individual object. The right operand should be the desired length
7054 of the array. The result is an array value whose elements are all of
7055 the type of the left argument. The first element is actually the left
7056 argument; the second element comes from bytes of memory immediately
7057 following those that hold the first element, and so on. Here is an
7058 example. If a program says
7061 int *array = (int *) malloc (len * sizeof (int));
7065 you can print the contents of @code{array} with
7071 The left operand of @samp{@@} must reside in memory. Array values made
7072 with @samp{@@} in this way behave just like other arrays in terms of
7073 subscripting, and are coerced to pointers when used in expressions.
7074 Artificial arrays most often appear in expressions via the value history
7075 (@pxref{Value History, ,Value History}), after printing one out.
7077 Another way to create an artificial array is to use a cast.
7078 This re-interprets a value as if it were an array.
7079 The value need not be in memory:
7081 (@value{GDBP}) p/x (short[2])0x12345678
7082 $1 = @{0x1234, 0x5678@}
7085 As a convenience, if you leave the array length out (as in
7086 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
7087 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
7089 (@value{GDBP}) p/x (short[])0x12345678
7090 $2 = @{0x1234, 0x5678@}
7093 Sometimes the artificial array mechanism is not quite enough; in
7094 moderately complex data structures, the elements of interest may not
7095 actually be adjacent---for example, if you are interested in the values
7096 of pointers in an array. One useful work-around in this situation is
7097 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
7098 Variables}) as a counter in an expression that prints the first
7099 interesting value, and then repeat that expression via @key{RET}. For
7100 instance, suppose you have an array @code{dtab} of pointers to
7101 structures, and you are interested in the values of a field @code{fv}
7102 in each structure. Here is an example of what you might type:
7112 @node Output Formats
7113 @section Output Formats
7115 @cindex formatted output
7116 @cindex output formats
7117 By default, @value{GDBN} prints a value according to its data type. Sometimes
7118 this is not what you want. For example, you might want to print a number
7119 in hex, or a pointer in decimal. Or you might want to view data in memory
7120 at a certain address as a character string or as an instruction. To do
7121 these things, specify an @dfn{output format} when you print a value.
7123 The simplest use of output formats is to say how to print a value
7124 already computed. This is done by starting the arguments of the
7125 @code{print} command with a slash and a format letter. The format
7126 letters supported are:
7130 Regard the bits of the value as an integer, and print the integer in
7134 Print as integer in signed decimal.
7137 Print as integer in unsigned decimal.
7140 Print as integer in octal.
7143 Print as integer in binary. The letter @samp{t} stands for ``two''.
7144 @footnote{@samp{b} cannot be used because these format letters are also
7145 used with the @code{x} command, where @samp{b} stands for ``byte'';
7146 see @ref{Memory,,Examining Memory}.}
7149 @cindex unknown address, locating
7150 @cindex locate address
7151 Print as an address, both absolute in hexadecimal and as an offset from
7152 the nearest preceding symbol. You can use this format used to discover
7153 where (in what function) an unknown address is located:
7156 (@value{GDBP}) p/a 0x54320
7157 $3 = 0x54320 <_initialize_vx+396>
7161 The command @code{info symbol 0x54320} yields similar results.
7162 @xref{Symbols, info symbol}.
7165 Regard as an integer and print it as a character constant. This
7166 prints both the numerical value and its character representation. The
7167 character representation is replaced with the octal escape @samp{\nnn}
7168 for characters outside the 7-bit @sc{ascii} range.
7170 Without this format, @value{GDBN} displays @code{char},
7171 @w{@code{unsigned char}}, and @w{@code{signed char}} data as character
7172 constants. Single-byte members of vectors are displayed as integer
7176 Regard the bits of the value as a floating point number and print
7177 using typical floating point syntax.
7180 @cindex printing strings
7181 @cindex printing byte arrays
7182 Regard as a string, if possible. With this format, pointers to single-byte
7183 data are displayed as null-terminated strings and arrays of single-byte data
7184 are displayed as fixed-length strings. Other values are displayed in their
7187 Without this format, @value{GDBN} displays pointers to and arrays of
7188 @code{char}, @w{@code{unsigned char}}, and @w{@code{signed char}} as
7189 strings. Single-byte members of a vector are displayed as an integer
7193 @cindex raw printing
7194 Print using the @samp{raw} formatting. By default, @value{GDBN} will
7195 use a Python-based pretty-printer, if one is available (@pxref{Pretty
7196 Printing}). This typically results in a higher-level display of the
7197 value's contents. The @samp{r} format bypasses any Python
7198 pretty-printer which might exist.
7201 For example, to print the program counter in hex (@pxref{Registers}), type
7208 Note that no space is required before the slash; this is because command
7209 names in @value{GDBN} cannot contain a slash.
7211 To reprint the last value in the value history with a different format,
7212 you can use the @code{print} command with just a format and no
7213 expression. For example, @samp{p/x} reprints the last value in hex.
7216 @section Examining Memory
7218 You can use the command @code{x} (for ``examine'') to examine memory in
7219 any of several formats, independently of your program's data types.
7221 @cindex examining memory
7223 @kindex x @r{(examine memory)}
7224 @item x/@var{nfu} @var{addr}
7227 Use the @code{x} command to examine memory.
7230 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
7231 much memory to display and how to format it; @var{addr} is an
7232 expression giving the address where you want to start displaying memory.
7233 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
7234 Several commands set convenient defaults for @var{addr}.
7237 @item @var{n}, the repeat count
7238 The repeat count is a decimal integer; the default is 1. It specifies
7239 how much memory (counting by units @var{u}) to display.
7240 @c This really is **decimal**; unaffected by 'set radix' as of GDB
7243 @item @var{f}, the display format
7244 The display format is one of the formats used by @code{print}
7245 (@samp{x}, @samp{d}, @samp{u}, @samp{o}, @samp{t}, @samp{a}, @samp{c},
7246 @samp{f}, @samp{s}), and in addition @samp{i} (for machine instructions).
7247 The default is @samp{x} (hexadecimal) initially. The default changes
7248 each time you use either @code{x} or @code{print}.
7250 @item @var{u}, the unit size
7251 The unit size is any of
7257 Halfwords (two bytes).
7259 Words (four bytes). This is the initial default.
7261 Giant words (eight bytes).
7264 Each time you specify a unit size with @code{x}, that size becomes the
7265 default unit the next time you use @code{x}. For the @samp{i} format,
7266 the unit size is ignored and is normally not written. For the @samp{s} format,
7267 the unit size defaults to @samp{b}, unless it is explicitly given.
7268 Use @kbd{x /hs} to display 16-bit char strings and @kbd{x /ws} to display
7269 32-bit strings. The next use of @kbd{x /s} will again display 8-bit strings.
7270 Note that the results depend on the programming language of the
7271 current compilation unit. If the language is C, the @samp{s}
7272 modifier will use the UTF-16 encoding while @samp{w} will use
7273 UTF-32. The encoding is set by the programming language and cannot
7276 @item @var{addr}, starting display address
7277 @var{addr} is the address where you want @value{GDBN} to begin displaying
7278 memory. The expression need not have a pointer value (though it may);
7279 it is always interpreted as an integer address of a byte of memory.
7280 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
7281 @var{addr} is usually just after the last address examined---but several
7282 other commands also set the default address: @code{info breakpoints} (to
7283 the address of the last breakpoint listed), @code{info line} (to the
7284 starting address of a line), and @code{print} (if you use it to display
7285 a value from memory).
7288 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
7289 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
7290 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
7291 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
7292 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
7294 Since the letters indicating unit sizes are all distinct from the
7295 letters specifying output formats, you do not have to remember whether
7296 unit size or format comes first; either order works. The output
7297 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
7298 (However, the count @var{n} must come first; @samp{wx4} does not work.)
7300 Even though the unit size @var{u} is ignored for the formats @samp{s}
7301 and @samp{i}, you might still want to use a count @var{n}; for example,
7302 @samp{3i} specifies that you want to see three machine instructions,
7303 including any operands. For convenience, especially when used with
7304 the @code{display} command, the @samp{i} format also prints branch delay
7305 slot instructions, if any, beyond the count specified, which immediately
7306 follow the last instruction that is within the count. The command
7307 @code{disassemble} gives an alternative way of inspecting machine
7308 instructions; see @ref{Machine Code,,Source and Machine Code}.
7310 All the defaults for the arguments to @code{x} are designed to make it
7311 easy to continue scanning memory with minimal specifications each time
7312 you use @code{x}. For example, after you have inspected three machine
7313 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
7314 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
7315 the repeat count @var{n} is used again; the other arguments default as
7316 for successive uses of @code{x}.
7318 When examining machine instructions, the instruction at current program
7319 counter is shown with a @code{=>} marker. For example:
7322 (@value{GDBP}) x/5i $pc-6
7323 0x804837f <main+11>: mov %esp,%ebp
7324 0x8048381 <main+13>: push %ecx
7325 0x8048382 <main+14>: sub $0x4,%esp
7326 => 0x8048385 <main+17>: movl $0x8048460,(%esp)
7327 0x804838c <main+24>: call 0x80482d4 <puts@@plt>
7330 @cindex @code{$_}, @code{$__}, and value history
7331 The addresses and contents printed by the @code{x} command are not saved
7332 in the value history because there is often too much of them and they
7333 would get in the way. Instead, @value{GDBN} makes these values available for
7334 subsequent use in expressions as values of the convenience variables
7335 @code{$_} and @code{$__}. After an @code{x} command, the last address
7336 examined is available for use in expressions in the convenience variable
7337 @code{$_}. The contents of that address, as examined, are available in
7338 the convenience variable @code{$__}.
7340 If the @code{x} command has a repeat count, the address and contents saved
7341 are from the last memory unit printed; this is not the same as the last
7342 address printed if several units were printed on the last line of output.
7344 @cindex remote memory comparison
7345 @cindex verify remote memory image
7346 When you are debugging a program running on a remote target machine
7347 (@pxref{Remote Debugging}), you may wish to verify the program's image in the
7348 remote machine's memory against the executable file you downloaded to
7349 the target. The @code{compare-sections} command is provided for such
7353 @kindex compare-sections
7354 @item compare-sections @r{[}@var{section-name}@r{]}
7355 Compare the data of a loadable section @var{section-name} in the
7356 executable file of the program being debugged with the same section in
7357 the remote machine's memory, and report any mismatches. With no
7358 arguments, compares all loadable sections. This command's
7359 availability depends on the target's support for the @code{"qCRC"}
7364 @section Automatic Display
7365 @cindex automatic display
7366 @cindex display of expressions
7368 If you find that you want to print the value of an expression frequently
7369 (to see how it changes), you might want to add it to the @dfn{automatic
7370 display list} so that @value{GDBN} prints its value each time your program stops.
7371 Each expression added to the list is given a number to identify it;
7372 to remove an expression from the list, you specify that number.
7373 The automatic display looks like this:
7377 3: bar[5] = (struct hack *) 0x3804
7381 This display shows item numbers, expressions and their current values. As with
7382 displays you request manually using @code{x} or @code{print}, you can
7383 specify the output format you prefer; in fact, @code{display} decides
7384 whether to use @code{print} or @code{x} depending your format
7385 specification---it uses @code{x} if you specify either the @samp{i}
7386 or @samp{s} format, or a unit size; otherwise it uses @code{print}.
7390 @item display @var{expr}
7391 Add the expression @var{expr} to the list of expressions to display
7392 each time your program stops. @xref{Expressions, ,Expressions}.
7394 @code{display} does not repeat if you press @key{RET} again after using it.
7396 @item display/@var{fmt} @var{expr}
7397 For @var{fmt} specifying only a display format and not a size or
7398 count, add the expression @var{expr} to the auto-display list but
7399 arrange to display it each time in the specified format @var{fmt}.
7400 @xref{Output Formats,,Output Formats}.
7402 @item display/@var{fmt} @var{addr}
7403 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
7404 number of units, add the expression @var{addr} as a memory address to
7405 be examined each time your program stops. Examining means in effect
7406 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining Memory}.
7409 For example, @samp{display/i $pc} can be helpful, to see the machine
7410 instruction about to be executed each time execution stops (@samp{$pc}
7411 is a common name for the program counter; @pxref{Registers, ,Registers}).
7414 @kindex delete display
7416 @item undisplay @var{dnums}@dots{}
7417 @itemx delete display @var{dnums}@dots{}
7418 Remove item numbers @var{dnums} from the list of expressions to display.
7420 @code{undisplay} does not repeat if you press @key{RET} after using it.
7421 (Otherwise you would just get the error @samp{No display number @dots{}}.)
7423 @kindex disable display
7424 @item disable display @var{dnums}@dots{}
7425 Disable the display of item numbers @var{dnums}. A disabled display
7426 item is not printed automatically, but is not forgotten. It may be
7427 enabled again later.
7429 @kindex enable display
7430 @item enable display @var{dnums}@dots{}
7431 Enable display of item numbers @var{dnums}. It becomes effective once
7432 again in auto display of its expression, until you specify otherwise.
7435 Display the current values of the expressions on the list, just as is
7436 done when your program stops.
7438 @kindex info display
7440 Print the list of expressions previously set up to display
7441 automatically, each one with its item number, but without showing the
7442 values. This includes disabled expressions, which are marked as such.
7443 It also includes expressions which would not be displayed right now
7444 because they refer to automatic variables not currently available.
7447 @cindex display disabled out of scope
7448 If a display expression refers to local variables, then it does not make
7449 sense outside the lexical context for which it was set up. Such an
7450 expression is disabled when execution enters a context where one of its
7451 variables is not defined. For example, if you give the command
7452 @code{display last_char} while inside a function with an argument
7453 @code{last_char}, @value{GDBN} displays this argument while your program
7454 continues to stop inside that function. When it stops elsewhere---where
7455 there is no variable @code{last_char}---the display is disabled
7456 automatically. The next time your program stops where @code{last_char}
7457 is meaningful, you can enable the display expression once again.
7459 @node Print Settings
7460 @section Print Settings
7462 @cindex format options
7463 @cindex print settings
7464 @value{GDBN} provides the following ways to control how arrays, structures,
7465 and symbols are printed.
7468 These settings are useful for debugging programs in any language:
7472 @item set print address
7473 @itemx set print address on
7474 @cindex print/don't print memory addresses
7475 @value{GDBN} prints memory addresses showing the location of stack
7476 traces, structure values, pointer values, breakpoints, and so forth,
7477 even when it also displays the contents of those addresses. The default
7478 is @code{on}. For example, this is what a stack frame display looks like with
7479 @code{set print address on}:
7484 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
7486 530 if (lquote != def_lquote)
7490 @item set print address off
7491 Do not print addresses when displaying their contents. For example,
7492 this is the same stack frame displayed with @code{set print address off}:
7496 (@value{GDBP}) set print addr off
7498 #0 set_quotes (lq="<<", rq=">>") at input.c:530
7499 530 if (lquote != def_lquote)
7503 You can use @samp{set print address off} to eliminate all machine
7504 dependent displays from the @value{GDBN} interface. For example, with
7505 @code{print address off}, you should get the same text for backtraces on
7506 all machines---whether or not they involve pointer arguments.
7509 @item show print address
7510 Show whether or not addresses are to be printed.
7513 When @value{GDBN} prints a symbolic address, it normally prints the
7514 closest earlier symbol plus an offset. If that symbol does not uniquely
7515 identify the address (for example, it is a name whose scope is a single
7516 source file), you may need to clarify. One way to do this is with
7517 @code{info line}, for example @samp{info line *0x4537}. Alternately,
7518 you can set @value{GDBN} to print the source file and line number when
7519 it prints a symbolic address:
7522 @item set print symbol-filename on
7523 @cindex source file and line of a symbol
7524 @cindex symbol, source file and line
7525 Tell @value{GDBN} to print the source file name and line number of a
7526 symbol in the symbolic form of an address.
7528 @item set print symbol-filename off
7529 Do not print source file name and line number of a symbol. This is the
7532 @item show print symbol-filename
7533 Show whether or not @value{GDBN} will print the source file name and
7534 line number of a symbol in the symbolic form of an address.
7537 Another situation where it is helpful to show symbol filenames and line
7538 numbers is when disassembling code; @value{GDBN} shows you the line
7539 number and source file that corresponds to each instruction.
7541 Also, you may wish to see the symbolic form only if the address being
7542 printed is reasonably close to the closest earlier symbol:
7545 @item set print max-symbolic-offset @var{max-offset}
7546 @cindex maximum value for offset of closest symbol
7547 Tell @value{GDBN} to only display the symbolic form of an address if the
7548 offset between the closest earlier symbol and the address is less than
7549 @var{max-offset}. The default is 0, which tells @value{GDBN}
7550 to always print the symbolic form of an address if any symbol precedes it.
7552 @item show print max-symbolic-offset
7553 Ask how large the maximum offset is that @value{GDBN} prints in a
7557 @cindex wild pointer, interpreting
7558 @cindex pointer, finding referent
7559 If you have a pointer and you are not sure where it points, try
7560 @samp{set print symbol-filename on}. Then you can determine the name
7561 and source file location of the variable where it points, using
7562 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
7563 For example, here @value{GDBN} shows that a variable @code{ptt} points
7564 at another variable @code{t}, defined in @file{hi2.c}:
7567 (@value{GDBP}) set print symbol-filename on
7568 (@value{GDBP}) p/a ptt
7569 $4 = 0xe008 <t in hi2.c>
7573 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
7574 does not show the symbol name and filename of the referent, even with
7575 the appropriate @code{set print} options turned on.
7578 Other settings control how different kinds of objects are printed:
7581 @item set print array
7582 @itemx set print array on
7583 @cindex pretty print arrays
7584 Pretty print arrays. This format is more convenient to read,
7585 but uses more space. The default is off.
7587 @item set print array off
7588 Return to compressed format for arrays.
7590 @item show print array
7591 Show whether compressed or pretty format is selected for displaying
7594 @cindex print array indexes
7595 @item set print array-indexes
7596 @itemx set print array-indexes on
7597 Print the index of each element when displaying arrays. May be more
7598 convenient to locate a given element in the array or quickly find the
7599 index of a given element in that printed array. The default is off.
7601 @item set print array-indexes off
7602 Stop printing element indexes when displaying arrays.
7604 @item show print array-indexes
7605 Show whether the index of each element is printed when displaying
7608 @item set print elements @var{number-of-elements}
7609 @cindex number of array elements to print
7610 @cindex limit on number of printed array elements
7611 Set a limit on how many elements of an array @value{GDBN} will print.
7612 If @value{GDBN} is printing a large array, it stops printing after it has
7613 printed the number of elements set by the @code{set print elements} command.
7614 This limit also applies to the display of strings.
7615 When @value{GDBN} starts, this limit is set to 200.
7616 Setting @var{number-of-elements} to zero means that the printing is unlimited.
7618 @item show print elements
7619 Display the number of elements of a large array that @value{GDBN} will print.
7620 If the number is 0, then the printing is unlimited.
7622 @item set print frame-arguments @var{value}
7623 @kindex set print frame-arguments
7624 @cindex printing frame argument values
7625 @cindex print all frame argument values
7626 @cindex print frame argument values for scalars only
7627 @cindex do not print frame argument values
7628 This command allows to control how the values of arguments are printed
7629 when the debugger prints a frame (@pxref{Frames}). The possible
7634 The values of all arguments are printed.
7637 Print the value of an argument only if it is a scalar. The value of more
7638 complex arguments such as arrays, structures, unions, etc, is replaced
7639 by @code{@dots{}}. This is the default. Here is an example where
7640 only scalar arguments are shown:
7643 #1 0x08048361 in call_me (i=3, s=@dots{}, ss=0xbf8d508c, u=@dots{}, e=green)
7648 None of the argument values are printed. Instead, the value of each argument
7649 is replaced by @code{@dots{}}. In this case, the example above now becomes:
7652 #1 0x08048361 in call_me (i=@dots{}, s=@dots{}, ss=@dots{}, u=@dots{}, e=@dots{})
7657 By default, only scalar arguments are printed. This command can be used
7658 to configure the debugger to print the value of all arguments, regardless
7659 of their type. However, it is often advantageous to not print the value
7660 of more complex parameters. For instance, it reduces the amount of
7661 information printed in each frame, making the backtrace more readable.
7662 Also, it improves performance when displaying Ada frames, because
7663 the computation of large arguments can sometimes be CPU-intensive,
7664 especially in large applications. Setting @code{print frame-arguments}
7665 to @code{scalars} (the default) or @code{none} avoids this computation,
7666 thus speeding up the display of each Ada frame.
7668 @item show print frame-arguments
7669 Show how the value of arguments should be displayed when printing a frame.
7671 @item set print repeats
7672 @cindex repeated array elements
7673 Set the threshold for suppressing display of repeated array
7674 elements. When the number of consecutive identical elements of an
7675 array exceeds the threshold, @value{GDBN} prints the string
7676 @code{"<repeats @var{n} times>"}, where @var{n} is the number of
7677 identical repetitions, instead of displaying the identical elements
7678 themselves. Setting the threshold to zero will cause all elements to
7679 be individually printed. The default threshold is 10.
7681 @item show print repeats
7682 Display the current threshold for printing repeated identical
7685 @item set print null-stop
7686 @cindex @sc{null} elements in arrays
7687 Cause @value{GDBN} to stop printing the characters of an array when the first
7688 @sc{null} is encountered. This is useful when large arrays actually
7689 contain only short strings.
7692 @item show print null-stop
7693 Show whether @value{GDBN} stops printing an array on the first
7694 @sc{null} character.
7696 @item set print pretty on
7697 @cindex print structures in indented form
7698 @cindex indentation in structure display
7699 Cause @value{GDBN} to print structures in an indented format with one member
7700 per line, like this:
7715 @item set print pretty off
7716 Cause @value{GDBN} to print structures in a compact format, like this:
7720 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
7721 meat = 0x54 "Pork"@}
7726 This is the default format.
7728 @item show print pretty
7729 Show which format @value{GDBN} is using to print structures.
7731 @item set print sevenbit-strings on
7732 @cindex eight-bit characters in strings
7733 @cindex octal escapes in strings
7734 Print using only seven-bit characters; if this option is set,
7735 @value{GDBN} displays any eight-bit characters (in strings or
7736 character values) using the notation @code{\}@var{nnn}. This setting is
7737 best if you are working in English (@sc{ascii}) and you use the
7738 high-order bit of characters as a marker or ``meta'' bit.
7740 @item set print sevenbit-strings off
7741 Print full eight-bit characters. This allows the use of more
7742 international character sets, and is the default.
7744 @item show print sevenbit-strings
7745 Show whether or not @value{GDBN} is printing only seven-bit characters.
7747 @item set print union on
7748 @cindex unions in structures, printing
7749 Tell @value{GDBN} to print unions which are contained in structures
7750 and other unions. This is the default setting.
7752 @item set print union off
7753 Tell @value{GDBN} not to print unions which are contained in
7754 structures and other unions. @value{GDBN} will print @code{"@{...@}"}
7757 @item show print union
7758 Ask @value{GDBN} whether or not it will print unions which are contained in
7759 structures and other unions.
7761 For example, given the declarations
7764 typedef enum @{Tree, Bug@} Species;
7765 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
7766 typedef enum @{Caterpillar, Cocoon, Butterfly@}
7777 struct thing foo = @{Tree, @{Acorn@}@};
7781 with @code{set print union on} in effect @samp{p foo} would print
7784 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
7788 and with @code{set print union off} in effect it would print
7791 $1 = @{it = Tree, form = @{...@}@}
7795 @code{set print union} affects programs written in C-like languages
7801 These settings are of interest when debugging C@t{++} programs:
7804 @cindex demangling C@t{++} names
7805 @item set print demangle
7806 @itemx set print demangle on
7807 Print C@t{++} names in their source form rather than in the encoded
7808 (``mangled'') form passed to the assembler and linker for type-safe
7809 linkage. The default is on.
7811 @item show print demangle
7812 Show whether C@t{++} names are printed in mangled or demangled form.
7814 @item set print asm-demangle
7815 @itemx set print asm-demangle on
7816 Print C@t{++} names in their source form rather than their mangled form, even
7817 in assembler code printouts such as instruction disassemblies.
7820 @item show print asm-demangle
7821 Show whether C@t{++} names in assembly listings are printed in mangled
7824 @cindex C@t{++} symbol decoding style
7825 @cindex symbol decoding style, C@t{++}
7826 @kindex set demangle-style
7827 @item set demangle-style @var{style}
7828 Choose among several encoding schemes used by different compilers to
7829 represent C@t{++} names. The choices for @var{style} are currently:
7833 Allow @value{GDBN} to choose a decoding style by inspecting your program.
7836 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
7837 This is the default.
7840 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
7843 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
7846 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
7847 @strong{Warning:} this setting alone is not sufficient to allow
7848 debugging @code{cfront}-generated executables. @value{GDBN} would
7849 require further enhancement to permit that.
7852 If you omit @var{style}, you will see a list of possible formats.
7854 @item show demangle-style
7855 Display the encoding style currently in use for decoding C@t{++} symbols.
7857 @item set print object
7858 @itemx set print object on
7859 @cindex derived type of an object, printing
7860 @cindex display derived types
7861 When displaying a pointer to an object, identify the @emph{actual}
7862 (derived) type of the object rather than the @emph{declared} type, using
7863 the virtual function table.
7865 @item set print object off
7866 Display only the declared type of objects, without reference to the
7867 virtual function table. This is the default setting.
7869 @item show print object
7870 Show whether actual, or declared, object types are displayed.
7872 @item set print static-members
7873 @itemx set print static-members on
7874 @cindex static members of C@t{++} objects
7875 Print static members when displaying a C@t{++} object. The default is on.
7877 @item set print static-members off
7878 Do not print static members when displaying a C@t{++} object.
7880 @item show print static-members
7881 Show whether C@t{++} static members are printed or not.
7883 @item set print pascal_static-members
7884 @itemx set print pascal_static-members on
7885 @cindex static members of Pascal objects
7886 @cindex Pascal objects, static members display
7887 Print static members when displaying a Pascal object. The default is on.
7889 @item set print pascal_static-members off
7890 Do not print static members when displaying a Pascal object.
7892 @item show print pascal_static-members
7893 Show whether Pascal static members are printed or not.
7895 @c These don't work with HP ANSI C++ yet.
7896 @item set print vtbl
7897 @itemx set print vtbl on
7898 @cindex pretty print C@t{++} virtual function tables
7899 @cindex virtual functions (C@t{++}) display
7900 @cindex VTBL display
7901 Pretty print C@t{++} virtual function tables. The default is off.
7902 (The @code{vtbl} commands do not work on programs compiled with the HP
7903 ANSI C@t{++} compiler (@code{aCC}).)
7905 @item set print vtbl off
7906 Do not pretty print C@t{++} virtual function tables.
7908 @item show print vtbl
7909 Show whether C@t{++} virtual function tables are pretty printed, or not.
7913 @section Value History
7915 @cindex value history
7916 @cindex history of values printed by @value{GDBN}
7917 Values printed by the @code{print} command are saved in the @value{GDBN}
7918 @dfn{value history}. This allows you to refer to them in other expressions.
7919 Values are kept until the symbol table is re-read or discarded
7920 (for example with the @code{file} or @code{symbol-file} commands).
7921 When the symbol table changes, the value history is discarded,
7922 since the values may contain pointers back to the types defined in the
7927 @cindex history number
7928 The values printed are given @dfn{history numbers} by which you can
7929 refer to them. These are successive integers starting with one.
7930 @code{print} shows you the history number assigned to a value by
7931 printing @samp{$@var{num} = } before the value; here @var{num} is the
7934 To refer to any previous value, use @samp{$} followed by the value's
7935 history number. The way @code{print} labels its output is designed to
7936 remind you of this. Just @code{$} refers to the most recent value in
7937 the history, and @code{$$} refers to the value before that.
7938 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
7939 is the value just prior to @code{$$}, @code{$$1} is equivalent to
7940 @code{$$}, and @code{$$0} is equivalent to @code{$}.
7942 For example, suppose you have just printed a pointer to a structure and
7943 want to see the contents of the structure. It suffices to type
7949 If you have a chain of structures where the component @code{next} points
7950 to the next one, you can print the contents of the next one with this:
7957 You can print successive links in the chain by repeating this
7958 command---which you can do by just typing @key{RET}.
7960 Note that the history records values, not expressions. If the value of
7961 @code{x} is 4 and you type these commands:
7969 then the value recorded in the value history by the @code{print} command
7970 remains 4 even though the value of @code{x} has changed.
7975 Print the last ten values in the value history, with their item numbers.
7976 This is like @samp{p@ $$9} repeated ten times, except that @code{show
7977 values} does not change the history.
7979 @item show values @var{n}
7980 Print ten history values centered on history item number @var{n}.
7983 Print ten history values just after the values last printed. If no more
7984 values are available, @code{show values +} produces no display.
7987 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
7988 same effect as @samp{show values +}.
7990 @node Convenience Vars
7991 @section Convenience Variables
7993 @cindex convenience variables
7994 @cindex user-defined variables
7995 @value{GDBN} provides @dfn{convenience variables} that you can use within
7996 @value{GDBN} to hold on to a value and refer to it later. These variables
7997 exist entirely within @value{GDBN}; they are not part of your program, and
7998 setting a convenience variable has no direct effect on further execution
7999 of your program. That is why you can use them freely.
8001 Convenience variables are prefixed with @samp{$}. Any name preceded by
8002 @samp{$} can be used for a convenience variable, unless it is one of
8003 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
8004 (Value history references, in contrast, are @emph{numbers} preceded
8005 by @samp{$}. @xref{Value History, ,Value History}.)
8007 You can save a value in a convenience variable with an assignment
8008 expression, just as you would set a variable in your program.
8012 set $foo = *object_ptr
8016 would save in @code{$foo} the value contained in the object pointed to by
8019 Using a convenience variable for the first time creates it, but its
8020 value is @code{void} until you assign a new value. You can alter the
8021 value with another assignment at any time.
8023 Convenience variables have no fixed types. You can assign a convenience
8024 variable any type of value, including structures and arrays, even if
8025 that variable already has a value of a different type. The convenience
8026 variable, when used as an expression, has the type of its current value.
8029 @kindex show convenience
8030 @cindex show all user variables
8031 @item show convenience
8032 Print a list of convenience variables used so far, and their values.
8033 Abbreviated @code{show conv}.
8035 @kindex init-if-undefined
8036 @cindex convenience variables, initializing
8037 @item init-if-undefined $@var{variable} = @var{expression}
8038 Set a convenience variable if it has not already been set. This is useful
8039 for user-defined commands that keep some state. It is similar, in concept,
8040 to using local static variables with initializers in C (except that
8041 convenience variables are global). It can also be used to allow users to
8042 override default values used in a command script.
8044 If the variable is already defined then the expression is not evaluated so
8045 any side-effects do not occur.
8048 One of the ways to use a convenience variable is as a counter to be
8049 incremented or a pointer to be advanced. For example, to print
8050 a field from successive elements of an array of structures:
8054 print bar[$i++]->contents
8058 Repeat that command by typing @key{RET}.
8060 Some convenience variables are created automatically by @value{GDBN} and given
8061 values likely to be useful.
8064 @vindex $_@r{, convenience variable}
8066 The variable @code{$_} is automatically set by the @code{x} command to
8067 the last address examined (@pxref{Memory, ,Examining Memory}). Other
8068 commands which provide a default address for @code{x} to examine also
8069 set @code{$_} to that address; these commands include @code{info line}
8070 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
8071 except when set by the @code{x} command, in which case it is a pointer
8072 to the type of @code{$__}.
8074 @vindex $__@r{, convenience variable}
8076 The variable @code{$__} is automatically set by the @code{x} command
8077 to the value found in the last address examined. Its type is chosen
8078 to match the format in which the data was printed.
8081 @vindex $_exitcode@r{, convenience variable}
8082 The variable @code{$_exitcode} is automatically set to the exit code when
8083 the program being debugged terminates.
8086 @vindex $_siginfo@r{, convenience variable}
8087 The variable @code{$_siginfo} contains extra signal information
8088 (@pxref{extra signal information}). Note that @code{$_siginfo}
8089 could be empty, if the application has not yet received any signals.
8090 For example, it will be empty before you execute the @code{run} command.
8093 @vindex $_tlb@r{, convenience variable}
8094 The variable @code{$_tlb} is automatically set when debugging
8095 applications running on MS-Windows in native mode or connected to
8096 gdbserver that supports the @code{qGetTIBAddr} request.
8097 @xref{General Query Packets}.
8098 This variable contains the address of the thread information block.
8102 On HP-UX systems, if you refer to a function or variable name that
8103 begins with a dollar sign, @value{GDBN} searches for a user or system
8104 name first, before it searches for a convenience variable.
8106 @cindex convenience functions
8107 @value{GDBN} also supplies some @dfn{convenience functions}. These
8108 have a syntax similar to convenience variables. A convenience
8109 function can be used in an expression just like an ordinary function;
8110 however, a convenience function is implemented internally to
8115 @kindex help function
8116 @cindex show all convenience functions
8117 Print a list of all convenience functions.
8124 You can refer to machine register contents, in expressions, as variables
8125 with names starting with @samp{$}. The names of registers are different
8126 for each machine; use @code{info registers} to see the names used on
8130 @kindex info registers
8131 @item info registers
8132 Print the names and values of all registers except floating-point
8133 and vector registers (in the selected stack frame).
8135 @kindex info all-registers
8136 @cindex floating point registers
8137 @item info all-registers
8138 Print the names and values of all registers, including floating-point
8139 and vector registers (in the selected stack frame).
8141 @item info registers @var{regname} @dots{}
8142 Print the @dfn{relativized} value of each specified register @var{regname}.
8143 As discussed in detail below, register values are normally relative to
8144 the selected stack frame. @var{regname} may be any register name valid on
8145 the machine you are using, with or without the initial @samp{$}.
8148 @cindex stack pointer register
8149 @cindex program counter register
8150 @cindex process status register
8151 @cindex frame pointer register
8152 @cindex standard registers
8153 @value{GDBN} has four ``standard'' register names that are available (in
8154 expressions) on most machines---whenever they do not conflict with an
8155 architecture's canonical mnemonics for registers. The register names
8156 @code{$pc} and @code{$sp} are used for the program counter register and
8157 the stack pointer. @code{$fp} is used for a register that contains a
8158 pointer to the current stack frame, and @code{$ps} is used for a
8159 register that contains the processor status. For example,
8160 you could print the program counter in hex with
8167 or print the instruction to be executed next with
8174 or add four to the stack pointer@footnote{This is a way of removing
8175 one word from the stack, on machines where stacks grow downward in
8176 memory (most machines, nowadays). This assumes that the innermost
8177 stack frame is selected; setting @code{$sp} is not allowed when other
8178 stack frames are selected. To pop entire frames off the stack,
8179 regardless of machine architecture, use @code{return};
8180 see @ref{Returning, ,Returning from a Function}.} with
8186 Whenever possible, these four standard register names are available on
8187 your machine even though the machine has different canonical mnemonics,
8188 so long as there is no conflict. The @code{info registers} command
8189 shows the canonical names. For example, on the SPARC, @code{info
8190 registers} displays the processor status register as @code{$psr} but you
8191 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
8192 is an alias for the @sc{eflags} register.
8194 @value{GDBN} always considers the contents of an ordinary register as an
8195 integer when the register is examined in this way. Some machines have
8196 special registers which can hold nothing but floating point; these
8197 registers are considered to have floating point values. There is no way
8198 to refer to the contents of an ordinary register as floating point value
8199 (although you can @emph{print} it as a floating point value with
8200 @samp{print/f $@var{regname}}).
8202 Some registers have distinct ``raw'' and ``virtual'' data formats. This
8203 means that the data format in which the register contents are saved by
8204 the operating system is not the same one that your program normally
8205 sees. For example, the registers of the 68881 floating point
8206 coprocessor are always saved in ``extended'' (raw) format, but all C
8207 programs expect to work with ``double'' (virtual) format. In such
8208 cases, @value{GDBN} normally works with the virtual format only (the format
8209 that makes sense for your program), but the @code{info registers} command
8210 prints the data in both formats.
8212 @cindex SSE registers (x86)
8213 @cindex MMX registers (x86)
8214 Some machines have special registers whose contents can be interpreted
8215 in several different ways. For example, modern x86-based machines
8216 have SSE and MMX registers that can hold several values packed
8217 together in several different formats. @value{GDBN} refers to such
8218 registers in @code{struct} notation:
8221 (@value{GDBP}) print $xmm1
8223 v4_float = @{0, 3.43859137e-038, 1.54142831e-044, 1.821688e-044@},
8224 v2_double = @{9.92129282474342e-303, 2.7585945287983262e-313@},
8225 v16_int8 = "\000\000\000\000\3706;\001\v\000\000\000\r\000\000",
8226 v8_int16 = @{0, 0, 14072, 315, 11, 0, 13, 0@},
8227 v4_int32 = @{0, 20657912, 11, 13@},
8228 v2_int64 = @{88725056443645952, 55834574859@},
8229 uint128 = 0x0000000d0000000b013b36f800000000
8234 To set values of such registers, you need to tell @value{GDBN} which
8235 view of the register you wish to change, as if you were assigning
8236 value to a @code{struct} member:
8239 (@value{GDBP}) set $xmm1.uint128 = 0x000000000000000000000000FFFFFFFF
8242 Normally, register values are relative to the selected stack frame
8243 (@pxref{Selection, ,Selecting a Frame}). This means that you get the
8244 value that the register would contain if all stack frames farther in
8245 were exited and their saved registers restored. In order to see the
8246 true contents of hardware registers, you must select the innermost
8247 frame (with @samp{frame 0}).
8249 However, @value{GDBN} must deduce where registers are saved, from the machine
8250 code generated by your compiler. If some registers are not saved, or if
8251 @value{GDBN} is unable to locate the saved registers, the selected stack
8252 frame makes no difference.
8254 @node Floating Point Hardware
8255 @section Floating Point Hardware
8256 @cindex floating point
8258 Depending on the configuration, @value{GDBN} may be able to give
8259 you more information about the status of the floating point hardware.
8264 Display hardware-dependent information about the floating
8265 point unit. The exact contents and layout vary depending on the
8266 floating point chip. Currently, @samp{info float} is supported on
8267 the ARM and x86 machines.
8271 @section Vector Unit
8274 Depending on the configuration, @value{GDBN} may be able to give you
8275 more information about the status of the vector unit.
8280 Display information about the vector unit. The exact contents and
8281 layout vary depending on the hardware.
8284 @node OS Information
8285 @section Operating System Auxiliary Information
8286 @cindex OS information
8288 @value{GDBN} provides interfaces to useful OS facilities that can help
8289 you debug your program.
8291 @cindex @code{ptrace} system call
8292 @cindex @code{struct user} contents
8293 When @value{GDBN} runs on a @dfn{Posix system} (such as GNU or Unix
8294 machines), it interfaces with the inferior via the @code{ptrace}
8295 system call. The operating system creates a special sata structure,
8296 called @code{struct user}, for this interface. You can use the
8297 command @code{info udot} to display the contents of this data
8303 Display the contents of the @code{struct user} maintained by the OS
8304 kernel for the program being debugged. @value{GDBN} displays the
8305 contents of @code{struct user} as a list of hex numbers, similar to
8306 the @code{examine} command.
8309 @cindex auxiliary vector
8310 @cindex vector, auxiliary
8311 Some operating systems supply an @dfn{auxiliary vector} to programs at
8312 startup. This is akin to the arguments and environment that you
8313 specify for a program, but contains a system-dependent variety of
8314 binary values that tell system libraries important details about the
8315 hardware, operating system, and process. Each value's purpose is
8316 identified by an integer tag; the meanings are well-known but system-specific.
8317 Depending on the configuration and operating system facilities,
8318 @value{GDBN} may be able to show you this information. For remote
8319 targets, this functionality may further depend on the remote stub's
8320 support of the @samp{qXfer:auxv:read} packet, see
8321 @ref{qXfer auxiliary vector read}.
8326 Display the auxiliary vector of the inferior, which can be either a
8327 live process or a core dump file. @value{GDBN} prints each tag value
8328 numerically, and also shows names and text descriptions for recognized
8329 tags. Some values in the vector are numbers, some bit masks, and some
8330 pointers to strings or other data. @value{GDBN} displays each value in the
8331 most appropriate form for a recognized tag, and in hexadecimal for
8332 an unrecognized tag.
8335 On some targets, @value{GDBN} can access operating-system-specific information
8336 and display it to user, without interpretation. For remote targets,
8337 this functionality depends on the remote stub's support of the
8338 @samp{qXfer:osdata:read} packet, see @ref{qXfer osdata read}.
8341 @kindex info os processes
8342 @item info os processes
8343 Display the list of processes on the target. For each process,
8344 @value{GDBN} prints the process identifier, the name of the user, and
8345 the command corresponding to the process.
8348 @node Memory Region Attributes
8349 @section Memory Region Attributes
8350 @cindex memory region attributes
8352 @dfn{Memory region attributes} allow you to describe special handling
8353 required by regions of your target's memory. @value{GDBN} uses
8354 attributes to determine whether to allow certain types of memory
8355 accesses; whether to use specific width accesses; and whether to cache
8356 target memory. By default the description of memory regions is
8357 fetched from the target (if the current target supports this), but the
8358 user can override the fetched regions.
8360 Defined memory regions can be individually enabled and disabled. When a
8361 memory region is disabled, @value{GDBN} uses the default attributes when
8362 accessing memory in that region. Similarly, if no memory regions have
8363 been defined, @value{GDBN} uses the default attributes when accessing
8366 When a memory region is defined, it is given a number to identify it;
8367 to enable, disable, or remove a memory region, you specify that number.
8371 @item mem @var{lower} @var{upper} @var{attributes}@dots{}
8372 Define a memory region bounded by @var{lower} and @var{upper} with
8373 attributes @var{attributes}@dots{}, and add it to the list of regions
8374 monitored by @value{GDBN}. Note that @var{upper} == 0 is a special
8375 case: it is treated as the target's maximum memory address.
8376 (0xffff on 16 bit targets, 0xffffffff on 32 bit targets, etc.)
8379 Discard any user changes to the memory regions and use target-supplied
8380 regions, if available, or no regions if the target does not support.
8383 @item delete mem @var{nums}@dots{}
8384 Remove memory regions @var{nums}@dots{} from the list of regions
8385 monitored by @value{GDBN}.
8388 @item disable mem @var{nums}@dots{}
8389 Disable monitoring of memory regions @var{nums}@dots{}.
8390 A disabled memory region is not forgotten.
8391 It may be enabled again later.
8394 @item enable mem @var{nums}@dots{}
8395 Enable monitoring of memory regions @var{nums}@dots{}.
8399 Print a table of all defined memory regions, with the following columns
8403 @item Memory Region Number
8404 @item Enabled or Disabled.
8405 Enabled memory regions are marked with @samp{y}.
8406 Disabled memory regions are marked with @samp{n}.
8409 The address defining the inclusive lower bound of the memory region.
8412 The address defining the exclusive upper bound of the memory region.
8415 The list of attributes set for this memory region.
8420 @subsection Attributes
8422 @subsubsection Memory Access Mode
8423 The access mode attributes set whether @value{GDBN} may make read or
8424 write accesses to a memory region.
8426 While these attributes prevent @value{GDBN} from performing invalid
8427 memory accesses, they do nothing to prevent the target system, I/O DMA,
8428 etc.@: from accessing memory.
8432 Memory is read only.
8434 Memory is write only.
8436 Memory is read/write. This is the default.
8439 @subsubsection Memory Access Size
8440 The access size attribute tells @value{GDBN} to use specific sized
8441 accesses in the memory region. Often memory mapped device registers
8442 require specific sized accesses. If no access size attribute is
8443 specified, @value{GDBN} may use accesses of any size.
8447 Use 8 bit memory accesses.
8449 Use 16 bit memory accesses.
8451 Use 32 bit memory accesses.
8453 Use 64 bit memory accesses.
8456 @c @subsubsection Hardware/Software Breakpoints
8457 @c The hardware/software breakpoint attributes set whether @value{GDBN}
8458 @c will use hardware or software breakpoints for the internal breakpoints
8459 @c used by the step, next, finish, until, etc. commands.
8463 @c Always use hardware breakpoints
8464 @c @item swbreak (default)
8467 @subsubsection Data Cache
8468 The data cache attributes set whether @value{GDBN} will cache target
8469 memory. While this generally improves performance by reducing debug
8470 protocol overhead, it can lead to incorrect results because @value{GDBN}
8471 does not know about volatile variables or memory mapped device
8476 Enable @value{GDBN} to cache target memory.
8478 Disable @value{GDBN} from caching target memory. This is the default.
8481 @subsection Memory Access Checking
8482 @value{GDBN} can be instructed to refuse accesses to memory that is
8483 not explicitly described. This can be useful if accessing such
8484 regions has undesired effects for a specific target, or to provide
8485 better error checking. The following commands control this behaviour.
8488 @kindex set mem inaccessible-by-default
8489 @item set mem inaccessible-by-default [on|off]
8490 If @code{on} is specified, make @value{GDBN} treat memory not
8491 explicitly described by the memory ranges as non-existent and refuse accesses
8492 to such memory. The checks are only performed if there's at least one
8493 memory range defined. If @code{off} is specified, make @value{GDBN}
8494 treat the memory not explicitly described by the memory ranges as RAM.
8495 The default value is @code{on}.
8496 @kindex show mem inaccessible-by-default
8497 @item show mem inaccessible-by-default
8498 Show the current handling of accesses to unknown memory.
8502 @c @subsubsection Memory Write Verification
8503 @c The memory write verification attributes set whether @value{GDBN}
8504 @c will re-reads data after each write to verify the write was successful.
8508 @c @item noverify (default)
8511 @node Dump/Restore Files
8512 @section Copy Between Memory and a File
8513 @cindex dump/restore files
8514 @cindex append data to a file
8515 @cindex dump data to a file
8516 @cindex restore data from a file
8518 You can use the commands @code{dump}, @code{append}, and
8519 @code{restore} to copy data between target memory and a file. The
8520 @code{dump} and @code{append} commands write data to a file, and the
8521 @code{restore} command reads data from a file back into the inferior's
8522 memory. Files may be in binary, Motorola S-record, Intel hex, or
8523 Tektronix Hex format; however, @value{GDBN} can only append to binary
8529 @item dump @r{[}@var{format}@r{]} memory @var{filename} @var{start_addr} @var{end_addr}
8530 @itemx dump @r{[}@var{format}@r{]} value @var{filename} @var{expr}
8531 Dump the contents of memory from @var{start_addr} to @var{end_addr},
8532 or the value of @var{expr}, to @var{filename} in the given format.
8534 The @var{format} parameter may be any one of:
8541 Motorola S-record format.
8543 Tektronix Hex format.
8546 @value{GDBN} uses the same definitions of these formats as the
8547 @sc{gnu} binary utilities, like @samp{objdump} and @samp{objcopy}. If
8548 @var{format} is omitted, @value{GDBN} dumps the data in raw binary
8552 @item append @r{[}binary@r{]} memory @var{filename} @var{start_addr} @var{end_addr}
8553 @itemx append @r{[}binary@r{]} value @var{filename} @var{expr}
8554 Append the contents of memory from @var{start_addr} to @var{end_addr},
8555 or the value of @var{expr}, to the file @var{filename}, in raw binary form.
8556 (@value{GDBN} can only append data to files in raw binary form.)
8559 @item restore @var{filename} @r{[}binary@r{]} @var{bias} @var{start} @var{end}
8560 Restore the contents of file @var{filename} into memory. The
8561 @code{restore} command can automatically recognize any known @sc{bfd}
8562 file format, except for raw binary. To restore a raw binary file you
8563 must specify the optional keyword @code{binary} after the filename.
8565 If @var{bias} is non-zero, its value will be added to the addresses
8566 contained in the file. Binary files always start at address zero, so
8567 they will be restored at address @var{bias}. Other bfd files have
8568 a built-in location; they will be restored at offset @var{bias}
8571 If @var{start} and/or @var{end} are non-zero, then only data between
8572 file offset @var{start} and file offset @var{end} will be restored.
8573 These offsets are relative to the addresses in the file, before
8574 the @var{bias} argument is applied.
8578 @node Core File Generation
8579 @section How to Produce a Core File from Your Program
8580 @cindex dump core from inferior
8582 A @dfn{core file} or @dfn{core dump} is a file that records the memory
8583 image of a running process and its process status (register values
8584 etc.). Its primary use is post-mortem debugging of a program that
8585 crashed while it ran outside a debugger. A program that crashes
8586 automatically produces a core file, unless this feature is disabled by
8587 the user. @xref{Files}, for information on invoking @value{GDBN} in
8588 the post-mortem debugging mode.
8590 Occasionally, you may wish to produce a core file of the program you
8591 are debugging in order to preserve a snapshot of its state.
8592 @value{GDBN} has a special command for that.
8596 @kindex generate-core-file
8597 @item generate-core-file [@var{file}]
8598 @itemx gcore [@var{file}]
8599 Produce a core dump of the inferior process. The optional argument
8600 @var{file} specifies the file name where to put the core dump. If not
8601 specified, the file name defaults to @file{core.@var{pid}}, where
8602 @var{pid} is the inferior process ID.
8604 Note that this command is implemented only for some systems (as of
8605 this writing, @sc{gnu}/Linux, FreeBSD, Solaris, Unixware, and S390).
8608 @node Character Sets
8609 @section Character Sets
8610 @cindex character sets
8612 @cindex translating between character sets
8613 @cindex host character set
8614 @cindex target character set
8616 If the program you are debugging uses a different character set to
8617 represent characters and strings than the one @value{GDBN} uses itself,
8618 @value{GDBN} can automatically translate between the character sets for
8619 you. The character set @value{GDBN} uses we call the @dfn{host
8620 character set}; the one the inferior program uses we call the
8621 @dfn{target character set}.
8623 For example, if you are running @value{GDBN} on a @sc{gnu}/Linux system, which
8624 uses the ISO Latin 1 character set, but you are using @value{GDBN}'s
8625 remote protocol (@pxref{Remote Debugging}) to debug a program
8626 running on an IBM mainframe, which uses the @sc{ebcdic} character set,
8627 then the host character set is Latin-1, and the target character set is
8628 @sc{ebcdic}. If you give @value{GDBN} the command @code{set
8629 target-charset EBCDIC-US}, then @value{GDBN} translates between
8630 @sc{ebcdic} and Latin 1 as you print character or string values, or use
8631 character and string literals in expressions.
8633 @value{GDBN} has no way to automatically recognize which character set
8634 the inferior program uses; you must tell it, using the @code{set
8635 target-charset} command, described below.
8637 Here are the commands for controlling @value{GDBN}'s character set
8641 @item set target-charset @var{charset}
8642 @kindex set target-charset
8643 Set the current target character set to @var{charset}. To display the
8644 list of supported target character sets, type
8645 @kbd{@w{set target-charset @key{TAB}@key{TAB}}}.
8647 @item set host-charset @var{charset}
8648 @kindex set host-charset
8649 Set the current host character set to @var{charset}.
8651 By default, @value{GDBN} uses a host character set appropriate to the
8652 system it is running on; you can override that default using the
8653 @code{set host-charset} command. On some systems, @value{GDBN} cannot
8654 automatically determine the appropriate host character set. In this
8655 case, @value{GDBN} uses @samp{UTF-8}.
8657 @value{GDBN} can only use certain character sets as its host character
8658 set. If you type @kbd{@w{set target-charset @key{TAB}@key{TAB}}},
8659 @value{GDBN} will list the host character sets it supports.
8661 @item set charset @var{charset}
8663 Set the current host and target character sets to @var{charset}. As
8664 above, if you type @kbd{@w{set charset @key{TAB}@key{TAB}}},
8665 @value{GDBN} will list the names of the character sets that can be used
8666 for both host and target.
8669 @kindex show charset
8670 Show the names of the current host and target character sets.
8672 @item show host-charset
8673 @kindex show host-charset
8674 Show the name of the current host character set.
8676 @item show target-charset
8677 @kindex show target-charset
8678 Show the name of the current target character set.
8680 @item set target-wide-charset @var{charset}
8681 @kindex set target-wide-charset
8682 Set the current target's wide character set to @var{charset}. This is
8683 the character set used by the target's @code{wchar_t} type. To
8684 display the list of supported wide character sets, type
8685 @kbd{@w{set target-wide-charset @key{TAB}@key{TAB}}}.
8687 @item show target-wide-charset
8688 @kindex show target-wide-charset
8689 Show the name of the current target's wide character set.
8692 Here is an example of @value{GDBN}'s character set support in action.
8693 Assume that the following source code has been placed in the file
8694 @file{charset-test.c}:
8700 = @{72, 101, 108, 108, 111, 44, 32, 119,
8701 111, 114, 108, 100, 33, 10, 0@};
8702 char ibm1047_hello[]
8703 = @{200, 133, 147, 147, 150, 107, 64, 166,
8704 150, 153, 147, 132, 90, 37, 0@};
8708 printf ("Hello, world!\n");
8712 In this program, @code{ascii_hello} and @code{ibm1047_hello} are arrays
8713 containing the string @samp{Hello, world!} followed by a newline,
8714 encoded in the @sc{ascii} and @sc{ibm1047} character sets.
8716 We compile the program, and invoke the debugger on it:
8719 $ gcc -g charset-test.c -o charset-test
8720 $ gdb -nw charset-test
8721 GNU gdb 2001-12-19-cvs
8722 Copyright 2001 Free Software Foundation, Inc.
8727 We can use the @code{show charset} command to see what character sets
8728 @value{GDBN} is currently using to interpret and display characters and
8732 (@value{GDBP}) show charset
8733 The current host and target character set is `ISO-8859-1'.
8737 For the sake of printing this manual, let's use @sc{ascii} as our
8738 initial character set:
8740 (@value{GDBP}) set charset ASCII
8741 (@value{GDBP}) show charset
8742 The current host and target character set is `ASCII'.
8746 Let's assume that @sc{ascii} is indeed the correct character set for our
8747 host system --- in other words, let's assume that if @value{GDBN} prints
8748 characters using the @sc{ascii} character set, our terminal will display
8749 them properly. Since our current target character set is also
8750 @sc{ascii}, the contents of @code{ascii_hello} print legibly:
8753 (@value{GDBP}) print ascii_hello
8754 $1 = 0x401698 "Hello, world!\n"
8755 (@value{GDBP}) print ascii_hello[0]
8760 @value{GDBN} uses the target character set for character and string
8761 literals you use in expressions:
8764 (@value{GDBP}) print '+'
8769 The @sc{ascii} character set uses the number 43 to encode the @samp{+}
8772 @value{GDBN} relies on the user to tell it which character set the
8773 target program uses. If we print @code{ibm1047_hello} while our target
8774 character set is still @sc{ascii}, we get jibberish:
8777 (@value{GDBP}) print ibm1047_hello
8778 $4 = 0x4016a8 "\310\205\223\223\226k@@\246\226\231\223\204Z%"
8779 (@value{GDBP}) print ibm1047_hello[0]
8784 If we invoke the @code{set target-charset} followed by @key{TAB}@key{TAB},
8785 @value{GDBN} tells us the character sets it supports:
8788 (@value{GDBP}) set target-charset
8789 ASCII EBCDIC-US IBM1047 ISO-8859-1
8790 (@value{GDBP}) set target-charset
8793 We can select @sc{ibm1047} as our target character set, and examine the
8794 program's strings again. Now the @sc{ascii} string is wrong, but
8795 @value{GDBN} translates the contents of @code{ibm1047_hello} from the
8796 target character set, @sc{ibm1047}, to the host character set,
8797 @sc{ascii}, and they display correctly:
8800 (@value{GDBP}) set target-charset IBM1047
8801 (@value{GDBP}) show charset
8802 The current host character set is `ASCII'.
8803 The current target character set is `IBM1047'.
8804 (@value{GDBP}) print ascii_hello
8805 $6 = 0x401698 "\110\145%%?\054\040\167?\162%\144\041\012"
8806 (@value{GDBP}) print ascii_hello[0]
8808 (@value{GDBP}) print ibm1047_hello
8809 $8 = 0x4016a8 "Hello, world!\n"
8810 (@value{GDBP}) print ibm1047_hello[0]
8815 As above, @value{GDBN} uses the target character set for character and
8816 string literals you use in expressions:
8819 (@value{GDBP}) print '+'
8824 The @sc{ibm1047} character set uses the number 78 to encode the @samp{+}
8827 @node Caching Remote Data
8828 @section Caching Data of Remote Targets
8829 @cindex caching data of remote targets
8831 @value{GDBN} caches data exchanged between the debugger and a
8832 remote target (@pxref{Remote Debugging}). Such caching generally improves
8833 performance, because it reduces the overhead of the remote protocol by
8834 bundling memory reads and writes into large chunks. Unfortunately, simply
8835 caching everything would lead to incorrect results, since @value{GDBN}
8836 does not necessarily know anything about volatile values, memory-mapped I/O
8837 addresses, etc. Furthermore, in non-stop mode (@pxref{Non-Stop Mode})
8838 memory can be changed @emph{while} a gdb command is executing.
8839 Therefore, by default, @value{GDBN} only caches data
8840 known to be on the stack@footnote{In non-stop mode, it is moderately
8841 rare for a running thread to modify the stack of a stopped thread
8842 in a way that would interfere with a backtrace, and caching of
8843 stack reads provides a significant speed up of remote backtraces.}.
8844 Other regions of memory can be explicitly marked as
8845 cacheable; see @pxref{Memory Region Attributes}.
8848 @kindex set remotecache
8849 @item set remotecache on
8850 @itemx set remotecache off
8851 This option no longer does anything; it exists for compatibility
8854 @kindex show remotecache
8855 @item show remotecache
8856 Show the current state of the obsolete remotecache flag.
8858 @kindex set stack-cache
8859 @item set stack-cache on
8860 @itemx set stack-cache off
8861 Enable or disable caching of stack accesses. When @code{ON}, use
8862 caching. By default, this option is @code{ON}.
8864 @kindex show stack-cache
8865 @item show stack-cache
8866 Show the current state of data caching for memory accesses.
8869 @item info dcache @r{[}line@r{]}
8870 Print the information about the data cache performance. The
8871 information displayed includes the dcache width and depth, and for
8872 each cache line, its number, address, and how many times it was
8873 referenced. This command is useful for debugging the data cache
8876 If a line number is specified, the contents of that line will be
8880 @node Searching Memory
8881 @section Search Memory
8882 @cindex searching memory
8884 Memory can be searched for a particular sequence of bytes with the
8885 @code{find} command.
8889 @item find @r{[}/@var{sn}@r{]} @var{start_addr}, +@var{len}, @var{val1} @r{[}, @var{val2}, @dots{}@r{]}
8890 @itemx find @r{[}/@var{sn}@r{]} @var{start_addr}, @var{end_addr}, @var{val1} @r{[}, @var{val2}, @dots{}@r{]}
8891 Search memory for the sequence of bytes specified by @var{val1}, @var{val2},
8892 etc. The search begins at address @var{start_addr} and continues for either
8893 @var{len} bytes or through to @var{end_addr} inclusive.
8896 @var{s} and @var{n} are optional parameters.
8897 They may be specified in either order, apart or together.
8900 @item @var{s}, search query size
8901 The size of each search query value.
8907 halfwords (two bytes)
8911 giant words (eight bytes)
8914 All values are interpreted in the current language.
8915 This means, for example, that if the current source language is C/C@t{++}
8916 then searching for the string ``hello'' includes the trailing '\0'.
8918 If the value size is not specified, it is taken from the
8919 value's type in the current language.
8920 This is useful when one wants to specify the search
8921 pattern as a mixture of types.
8922 Note that this means, for example, that in the case of C-like languages
8923 a search for an untyped 0x42 will search for @samp{(int) 0x42}
8924 which is typically four bytes.
8926 @item @var{n}, maximum number of finds
8927 The maximum number of matches to print. The default is to print all finds.
8930 You can use strings as search values. Quote them with double-quotes
8932 The string value is copied into the search pattern byte by byte,
8933 regardless of the endianness of the target and the size specification.
8935 The address of each match found is printed as well as a count of the
8936 number of matches found.
8938 The address of the last value found is stored in convenience variable
8940 A count of the number of matches is stored in @samp{$numfound}.
8942 For example, if stopped at the @code{printf} in this function:
8948 static char hello[] = "hello-hello";
8949 static struct @{ char c; short s; int i; @}
8950 __attribute__ ((packed)) mixed
8951 = @{ 'c', 0x1234, 0x87654321 @};
8952 printf ("%s\n", hello);
8957 you get during debugging:
8960 (gdb) find &hello[0], +sizeof(hello), "hello"
8961 0x804956d <hello.1620+6>
8963 (gdb) find &hello[0], +sizeof(hello), 'h', 'e', 'l', 'l', 'o'
8964 0x8049567 <hello.1620>
8965 0x804956d <hello.1620+6>
8967 (gdb) find /b1 &hello[0], +sizeof(hello), 'h', 0x65, 'l'
8968 0x8049567 <hello.1620>
8970 (gdb) find &mixed, +sizeof(mixed), (char) 'c', (short) 0x1234, (int) 0x87654321
8971 0x8049560 <mixed.1625>
8973 (gdb) print $numfound
8976 $2 = (void *) 0x8049560
8979 @node Optimized Code
8980 @chapter Debugging Optimized Code
8981 @cindex optimized code, debugging
8982 @cindex debugging optimized code
8984 Almost all compilers support optimization. With optimization
8985 disabled, the compiler generates assembly code that corresponds
8986 directly to your source code, in a simplistic way. As the compiler
8987 applies more powerful optimizations, the generated assembly code
8988 diverges from your original source code. With help from debugging
8989 information generated by the compiler, @value{GDBN} can map from
8990 the running program back to constructs from your original source.
8992 @value{GDBN} is more accurate with optimization disabled. If you
8993 can recompile without optimization, it is easier to follow the
8994 progress of your program during debugging. But, there are many cases
8995 where you may need to debug an optimized version.
8997 When you debug a program compiled with @samp{-g -O}, remember that the
8998 optimizer has rearranged your code; the debugger shows you what is
8999 really there. Do not be too surprised when the execution path does not
9000 exactly match your source file! An extreme example: if you define a
9001 variable, but never use it, @value{GDBN} never sees that
9002 variable---because the compiler optimizes it out of existence.
9004 Some things do not work as well with @samp{-g -O} as with just
9005 @samp{-g}, particularly on machines with instruction scheduling. If in
9006 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
9007 please report it to us as a bug (including a test case!).
9008 @xref{Variables}, for more information about debugging optimized code.
9011 * Inline Functions:: How @value{GDBN} presents inlining
9014 @node Inline Functions
9015 @section Inline Functions
9016 @cindex inline functions, debugging
9018 @dfn{Inlining} is an optimization that inserts a copy of the function
9019 body directly at each call site, instead of jumping to a shared
9020 routine. @value{GDBN} displays inlined functions just like
9021 non-inlined functions. They appear in backtraces. You can view their
9022 arguments and local variables, step into them with @code{step}, skip
9023 them with @code{next}, and escape from them with @code{finish}.
9024 You can check whether a function was inlined by using the
9025 @code{info frame} command.
9027 For @value{GDBN} to support inlined functions, the compiler must
9028 record information about inlining in the debug information ---
9029 @value{NGCC} using the @sc{dwarf 2} format does this, and several
9030 other compilers do also. @value{GDBN} only supports inlined functions
9031 when using @sc{dwarf 2}. Versions of @value{NGCC} before 4.1
9032 do not emit two required attributes (@samp{DW_AT_call_file} and
9033 @samp{DW_AT_call_line}); @value{GDBN} does not display inlined
9034 function calls with earlier versions of @value{NGCC}. It instead
9035 displays the arguments and local variables of inlined functions as
9036 local variables in the caller.
9038 The body of an inlined function is directly included at its call site;
9039 unlike a non-inlined function, there are no instructions devoted to
9040 the call. @value{GDBN} still pretends that the call site and the
9041 start of the inlined function are different instructions. Stepping to
9042 the call site shows the call site, and then stepping again shows
9043 the first line of the inlined function, even though no additional
9044 instructions are executed.
9046 This makes source-level debugging much clearer; you can see both the
9047 context of the call and then the effect of the call. Only stepping by
9048 a single instruction using @code{stepi} or @code{nexti} does not do
9049 this; single instruction steps always show the inlined body.
9051 There are some ways that @value{GDBN} does not pretend that inlined
9052 function calls are the same as normal calls:
9056 You cannot set breakpoints on inlined functions. @value{GDBN}
9057 either reports that there is no symbol with that name, or else sets the
9058 breakpoint only on non-inlined copies of the function. This limitation
9059 will be removed in a future version of @value{GDBN}; until then,
9060 set a breakpoint by line number on the first line of the inlined
9064 Setting breakpoints at the call site of an inlined function may not
9065 work, because the call site does not contain any code. @value{GDBN}
9066 may incorrectly move the breakpoint to the next line of the enclosing
9067 function, after the call. This limitation will be removed in a future
9068 version of @value{GDBN}; until then, set a breakpoint on an earlier line
9069 or inside the inlined function instead.
9072 @value{GDBN} cannot locate the return value of inlined calls after
9073 using the @code{finish} command. This is a limitation of compiler-generated
9074 debugging information; after @code{finish}, you can step to the next line
9075 and print a variable where your program stored the return value.
9081 @chapter C Preprocessor Macros
9083 Some languages, such as C and C@t{++}, provide a way to define and invoke
9084 ``preprocessor macros'' which expand into strings of tokens.
9085 @value{GDBN} can evaluate expressions containing macro invocations, show
9086 the result of macro expansion, and show a macro's definition, including
9087 where it was defined.
9089 You may need to compile your program specially to provide @value{GDBN}
9090 with information about preprocessor macros. Most compilers do not
9091 include macros in their debugging information, even when you compile
9092 with the @option{-g} flag. @xref{Compilation}.
9094 A program may define a macro at one point, remove that definition later,
9095 and then provide a different definition after that. Thus, at different
9096 points in the program, a macro may have different definitions, or have
9097 no definition at all. If there is a current stack frame, @value{GDBN}
9098 uses the macros in scope at that frame's source code line. Otherwise,
9099 @value{GDBN} uses the macros in scope at the current listing location;
9102 Whenever @value{GDBN} evaluates an expression, it always expands any
9103 macro invocations present in the expression. @value{GDBN} also provides
9104 the following commands for working with macros explicitly.
9108 @kindex macro expand
9109 @cindex macro expansion, showing the results of preprocessor
9110 @cindex preprocessor macro expansion, showing the results of
9111 @cindex expanding preprocessor macros
9112 @item macro expand @var{expression}
9113 @itemx macro exp @var{expression}
9114 Show the results of expanding all preprocessor macro invocations in
9115 @var{expression}. Since @value{GDBN} simply expands macros, but does
9116 not parse the result, @var{expression} need not be a valid expression;
9117 it can be any string of tokens.
9120 @item macro expand-once @var{expression}
9121 @itemx macro exp1 @var{expression}
9122 @cindex expand macro once
9123 @i{(This command is not yet implemented.)} Show the results of
9124 expanding those preprocessor macro invocations that appear explicitly in
9125 @var{expression}. Macro invocations appearing in that expansion are
9126 left unchanged. This command allows you to see the effect of a
9127 particular macro more clearly, without being confused by further
9128 expansions. Since @value{GDBN} simply expands macros, but does not
9129 parse the result, @var{expression} need not be a valid expression; it
9130 can be any string of tokens.
9133 @cindex macro definition, showing
9134 @cindex definition, showing a macro's
9135 @item info macro @var{macro}
9136 Show the definition of the macro named @var{macro}, and describe the
9137 source location or compiler command-line where that definition was established.
9139 @kindex macro define
9140 @cindex user-defined macros
9141 @cindex defining macros interactively
9142 @cindex macros, user-defined
9143 @item macro define @var{macro} @var{replacement-list}
9144 @itemx macro define @var{macro}(@var{arglist}) @var{replacement-list}
9145 Introduce a definition for a preprocessor macro named @var{macro},
9146 invocations of which are replaced by the tokens given in
9147 @var{replacement-list}. The first form of this command defines an
9148 ``object-like'' macro, which takes no arguments; the second form
9149 defines a ``function-like'' macro, which takes the arguments given in
9152 A definition introduced by this command is in scope in every
9153 expression evaluated in @value{GDBN}, until it is removed with the
9154 @code{macro undef} command, described below. The definition overrides
9155 all definitions for @var{macro} present in the program being debugged,
9156 as well as any previous user-supplied definition.
9159 @item macro undef @var{macro}
9160 Remove any user-supplied definition for the macro named @var{macro}.
9161 This command only affects definitions provided with the @code{macro
9162 define} command, described above; it cannot remove definitions present
9163 in the program being debugged.
9167 List all the macros defined using the @code{macro define} command.
9170 @cindex macros, example of debugging with
9171 Here is a transcript showing the above commands in action. First, we
9172 show our source files:
9180 #define ADD(x) (M + x)
9185 printf ("Hello, world!\n");
9187 printf ("We're so creative.\n");
9189 printf ("Goodbye, world!\n");
9196 Now, we compile the program using the @sc{gnu} C compiler, @value{NGCC}.
9197 We pass the @option{-gdwarf-2} and @option{-g3} flags to ensure the
9198 compiler includes information about preprocessor macros in the debugging
9202 $ gcc -gdwarf-2 -g3 sample.c -o sample
9206 Now, we start @value{GDBN} on our sample program:
9210 GNU gdb 2002-05-06-cvs
9211 Copyright 2002 Free Software Foundation, Inc.
9212 GDB is free software, @dots{}
9216 We can expand macros and examine their definitions, even when the
9217 program is not running. @value{GDBN} uses the current listing position
9218 to decide which macro definitions are in scope:
9221 (@value{GDBP}) list main
9224 5 #define ADD(x) (M + x)
9229 10 printf ("Hello, world!\n");
9231 12 printf ("We're so creative.\n");
9232 (@value{GDBP}) info macro ADD
9233 Defined at /home/jimb/gdb/macros/play/sample.c:5
9234 #define ADD(x) (M + x)
9235 (@value{GDBP}) info macro Q
9236 Defined at /home/jimb/gdb/macros/play/sample.h:1
9237 included at /home/jimb/gdb/macros/play/sample.c:2
9239 (@value{GDBP}) macro expand ADD(1)
9240 expands to: (42 + 1)
9241 (@value{GDBP}) macro expand-once ADD(1)
9242 expands to: once (M + 1)
9246 In the example above, note that @code{macro expand-once} expands only
9247 the macro invocation explicit in the original text --- the invocation of
9248 @code{ADD} --- but does not expand the invocation of the macro @code{M},
9249 which was introduced by @code{ADD}.
9251 Once the program is running, @value{GDBN} uses the macro definitions in
9252 force at the source line of the current stack frame:
9255 (@value{GDBP}) break main
9256 Breakpoint 1 at 0x8048370: file sample.c, line 10.
9258 Starting program: /home/jimb/gdb/macros/play/sample
9260 Breakpoint 1, main () at sample.c:10
9261 10 printf ("Hello, world!\n");
9265 At line 10, the definition of the macro @code{N} at line 9 is in force:
9268 (@value{GDBP}) info macro N
9269 Defined at /home/jimb/gdb/macros/play/sample.c:9
9271 (@value{GDBP}) macro expand N Q M
9273 (@value{GDBP}) print N Q M
9278 As we step over directives that remove @code{N}'s definition, and then
9279 give it a new definition, @value{GDBN} finds the definition (or lack
9280 thereof) in force at each point:
9285 12 printf ("We're so creative.\n");
9286 (@value{GDBP}) info macro N
9287 The symbol `N' has no definition as a C/C++ preprocessor macro
9288 at /home/jimb/gdb/macros/play/sample.c:12
9291 14 printf ("Goodbye, world!\n");
9292 (@value{GDBP}) info macro N
9293 Defined at /home/jimb/gdb/macros/play/sample.c:13
9295 (@value{GDBP}) macro expand N Q M
9296 expands to: 1729 < 42
9297 (@value{GDBP}) print N Q M
9302 In addition to source files, macros can be defined on the compilation command
9303 line using the @option{-D@var{name}=@var{value}} syntax. For macros defined in
9304 such a way, @value{GDBN} displays the location of their definition as line zero
9305 of the source file submitted to the compiler.
9308 (@value{GDBP}) info macro __STDC__
9309 Defined at /home/jimb/gdb/macros/play/sample.c:0
9316 @chapter Tracepoints
9317 @c This chapter is based on the documentation written by Michael
9318 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
9321 In some applications, it is not feasible for the debugger to interrupt
9322 the program's execution long enough for the developer to learn
9323 anything helpful about its behavior. If the program's correctness
9324 depends on its real-time behavior, delays introduced by a debugger
9325 might cause the program to change its behavior drastically, or perhaps
9326 fail, even when the code itself is correct. It is useful to be able
9327 to observe the program's behavior without interrupting it.
9329 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
9330 specify locations in the program, called @dfn{tracepoints}, and
9331 arbitrary expressions to evaluate when those tracepoints are reached.
9332 Later, using the @code{tfind} command, you can examine the values
9333 those expressions had when the program hit the tracepoints. The
9334 expressions may also denote objects in memory---structures or arrays,
9335 for example---whose values @value{GDBN} should record; while visiting
9336 a particular tracepoint, you may inspect those objects as if they were
9337 in memory at that moment. However, because @value{GDBN} records these
9338 values without interacting with you, it can do so quickly and
9339 unobtrusively, hopefully not disturbing the program's behavior.
9341 The tracepoint facility is currently available only for remote
9342 targets. @xref{Targets}. In addition, your remote target must know
9343 how to collect trace data. This functionality is implemented in the
9344 remote stub; however, none of the stubs distributed with @value{GDBN}
9345 support tracepoints as of this writing. The format of the remote
9346 packets used to implement tracepoints are described in @ref{Tracepoint
9349 It is also possible to get trace data from a file, in a manner reminiscent
9350 of corefiles; you specify the filename, and use @code{tfind} to search
9351 through the file. @xref{Trace Files}, for more details.
9353 This chapter describes the tracepoint commands and features.
9357 * Analyze Collected Data::
9358 * Tracepoint Variables::
9362 @node Set Tracepoints
9363 @section Commands to Set Tracepoints
9365 Before running such a @dfn{trace experiment}, an arbitrary number of
9366 tracepoints can be set. A tracepoint is actually a special type of
9367 breakpoint (@pxref{Set Breaks}), so you can manipulate it using
9368 standard breakpoint commands. For instance, as with breakpoints,
9369 tracepoint numbers are successive integers starting from one, and many
9370 of the commands associated with tracepoints take the tracepoint number
9371 as their argument, to identify which tracepoint to work on.
9373 For each tracepoint, you can specify, in advance, some arbitrary set
9374 of data that you want the target to collect in the trace buffer when
9375 it hits that tracepoint. The collected data can include registers,
9376 local variables, or global data. Later, you can use @value{GDBN}
9377 commands to examine the values these data had at the time the
9380 Tracepoints do not support every breakpoint feature. Ignore counts on
9381 tracepoints have no effect, and tracepoints cannot run @value{GDBN}
9382 commands when they are hit. Tracepoints may not be thread-specific
9385 @cindex fast tracepoints
9386 Some targets may support @dfn{fast tracepoints}, which are inserted in
9387 a different way (such as with a jump instead of a trap), that is
9388 faster but possibly restricted in where they may be installed.
9390 This section describes commands to set tracepoints and associated
9391 conditions and actions.
9394 * Create and Delete Tracepoints::
9395 * Enable and Disable Tracepoints::
9396 * Tracepoint Passcounts::
9397 * Tracepoint Conditions::
9398 * Trace State Variables::
9399 * Tracepoint Actions::
9400 * Listing Tracepoints::
9401 * Starting and Stopping Trace Experiments::
9402 * Tracepoint Restrictions::
9405 @node Create and Delete Tracepoints
9406 @subsection Create and Delete Tracepoints
9409 @cindex set tracepoint
9411 @item trace @var{location}
9412 The @code{trace} command is very similar to the @code{break} command.
9413 Its argument @var{location} can be a source line, a function name, or
9414 an address in the target program. @xref{Specify Location}. The
9415 @code{trace} command defines a tracepoint, which is a point in the
9416 target program where the debugger will briefly stop, collect some
9417 data, and then allow the program to continue. Setting a tracepoint or
9418 changing its actions doesn't take effect until the next @code{tstart}
9419 command, and once a trace experiment is running, further changes will
9420 not have any effect until the next trace experiment starts.
9422 Here are some examples of using the @code{trace} command:
9425 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
9427 (@value{GDBP}) @b{trace +2} // 2 lines forward
9429 (@value{GDBP}) @b{trace my_function} // first source line of function
9431 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
9433 (@value{GDBP}) @b{trace *0x2117c4} // an address
9437 You can abbreviate @code{trace} as @code{tr}.
9439 @item trace @var{location} if @var{cond}
9440 Set a tracepoint with condition @var{cond}; evaluate the expression
9441 @var{cond} each time the tracepoint is reached, and collect data only
9442 if the value is nonzero---that is, if @var{cond} evaluates as true.
9443 @xref{Tracepoint Conditions, ,Tracepoint Conditions}, for more
9444 information on tracepoint conditions.
9446 @item ftrace @var{location} [ if @var{cond} ]
9447 @cindex set fast tracepoint
9449 The @code{ftrace} command sets a fast tracepoint. For targets that
9450 support them, fast tracepoints will use a more efficient but possibly
9451 less general technique to trigger data collection, such as a jump
9452 instruction instead of a trap, or some sort of hardware support. It
9453 may not be possible to create a fast tracepoint at the desired
9454 location, in which case the command will exit with an explanatory
9457 @value{GDBN} handles arguments to @code{ftrace} exactly as for
9461 @cindex last tracepoint number
9462 @cindex recent tracepoint number
9463 @cindex tracepoint number
9464 The convenience variable @code{$tpnum} records the tracepoint number
9465 of the most recently set tracepoint.
9467 @kindex delete tracepoint
9468 @cindex tracepoint deletion
9469 @item delete tracepoint @r{[}@var{num}@r{]}
9470 Permanently delete one or more tracepoints. With no argument, the
9471 default is to delete all tracepoints. Note that the regular
9472 @code{delete} command can remove tracepoints also.
9477 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
9479 (@value{GDBP}) @b{delete trace} // remove all tracepoints
9483 You can abbreviate this command as @code{del tr}.
9486 @node Enable and Disable Tracepoints
9487 @subsection Enable and Disable Tracepoints
9489 These commands are deprecated; they are equivalent to plain @code{disable} and @code{enable}.
9492 @kindex disable tracepoint
9493 @item disable tracepoint @r{[}@var{num}@r{]}
9494 Disable tracepoint @var{num}, or all tracepoints if no argument
9495 @var{num} is given. A disabled tracepoint will have no effect during
9496 the next trace experiment, but it is not forgotten. You can re-enable
9497 a disabled tracepoint using the @code{enable tracepoint} command.
9499 @kindex enable tracepoint
9500 @item enable tracepoint @r{[}@var{num}@r{]}
9501 Enable tracepoint @var{num}, or all tracepoints. The enabled
9502 tracepoints will become effective the next time a trace experiment is
9506 @node Tracepoint Passcounts
9507 @subsection Tracepoint Passcounts
9511 @cindex tracepoint pass count
9512 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
9513 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
9514 automatically stop a trace experiment. If a tracepoint's passcount is
9515 @var{n}, then the trace experiment will be automatically stopped on
9516 the @var{n}'th time that tracepoint is hit. If the tracepoint number
9517 @var{num} is not specified, the @code{passcount} command sets the
9518 passcount of the most recently defined tracepoint. If no passcount is
9519 given, the trace experiment will run until stopped explicitly by the
9525 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of
9526 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// tracepoint 2}
9528 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
9529 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// most recently defined tracepoint.}
9530 (@value{GDBP}) @b{trace foo}
9531 (@value{GDBP}) @b{pass 3}
9532 (@value{GDBP}) @b{trace bar}
9533 (@value{GDBP}) @b{pass 2}
9534 (@value{GDBP}) @b{trace baz}
9535 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
9536 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// executed 3 times OR when bar has}
9537 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// been executed 2 times}
9538 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// OR when baz has been executed 1 time.}
9542 @node Tracepoint Conditions
9543 @subsection Tracepoint Conditions
9544 @cindex conditional tracepoints
9545 @cindex tracepoint conditions
9547 The simplest sort of tracepoint collects data every time your program
9548 reaches a specified place. You can also specify a @dfn{condition} for
9549 a tracepoint. A condition is just a Boolean expression in your
9550 programming language (@pxref{Expressions, ,Expressions}). A
9551 tracepoint with a condition evaluates the expression each time your
9552 program reaches it, and data collection happens only if the condition
9555 Tracepoint conditions can be specified when a tracepoint is set, by
9556 using @samp{if} in the arguments to the @code{trace} command.
9557 @xref{Create and Delete Tracepoints, ,Setting Tracepoints}. They can
9558 also be set or changed at any time with the @code{condition} command,
9559 just as with breakpoints.
9561 Unlike breakpoint conditions, @value{GDBN} does not actually evaluate
9562 the conditional expression itself. Instead, @value{GDBN} encodes the
9563 expression into an agent expression (@pxref{Agent Expressions}
9564 suitable for execution on the target, independently of @value{GDBN}.
9565 Global variables become raw memory locations, locals become stack
9566 accesses, and so forth.
9568 For instance, suppose you have a function that is usually called
9569 frequently, but should not be called after an error has occurred. You
9570 could use the following tracepoint command to collect data about calls
9571 of that function that happen while the error code is propagating
9572 through the program; an unconditional tracepoint could end up
9573 collecting thousands of useless trace frames that you would have to
9577 (@value{GDBP}) @kbd{trace normal_operation if errcode > 0}
9580 @node Trace State Variables
9581 @subsection Trace State Variables
9582 @cindex trace state variables
9584 A @dfn{trace state variable} is a special type of variable that is
9585 created and managed by target-side code. The syntax is the same as
9586 that for GDB's convenience variables (a string prefixed with ``$''),
9587 but they are stored on the target. They must be created explicitly,
9588 using a @code{tvariable} command. They are always 64-bit signed
9591 Trace state variables are remembered by @value{GDBN}, and downloaded
9592 to the target along with tracepoint information when the trace
9593 experiment starts. There are no intrinsic limits on the number of
9594 trace state variables, beyond memory limitations of the target.
9596 @cindex convenience variables, and trace state variables
9597 Although trace state variables are managed by the target, you can use
9598 them in print commands and expressions as if they were convenience
9599 variables; @value{GDBN} will get the current value from the target
9600 while the trace experiment is running. Trace state variables share
9601 the same namespace as other ``$'' variables, which means that you
9602 cannot have trace state variables with names like @code{$23} or
9603 @code{$pc}, nor can you have a trace state variable and a convenience
9604 variable with the same name.
9608 @item tvariable $@var{name} [ = @var{expression} ]
9610 The @code{tvariable} command creates a new trace state variable named
9611 @code{$@var{name}}, and optionally gives it an initial value of
9612 @var{expression}. @var{expression} is evaluated when this command is
9613 entered; the result will be converted to an integer if possible,
9614 otherwise @value{GDBN} will report an error. A subsequent
9615 @code{tvariable} command specifying the same name does not create a
9616 variable, but instead assigns the supplied initial value to the
9617 existing variable of that name, overwriting any previous initial
9618 value. The default initial value is 0.
9620 @item info tvariables
9621 @kindex info tvariables
9622 List all the trace state variables along with their initial values.
9623 Their current values may also be displayed, if the trace experiment is
9626 @item delete tvariable @r{[} $@var{name} @dots{} @r{]}
9627 @kindex delete tvariable
9628 Delete the given trace state variables, or all of them if no arguments
9633 @node Tracepoint Actions
9634 @subsection Tracepoint Action Lists
9638 @cindex tracepoint actions
9639 @item actions @r{[}@var{num}@r{]}
9640 This command will prompt for a list of actions to be taken when the
9641 tracepoint is hit. If the tracepoint number @var{num} is not
9642 specified, this command sets the actions for the one that was most
9643 recently defined (so that you can define a tracepoint and then say
9644 @code{actions} without bothering about its number). You specify the
9645 actions themselves on the following lines, one action at a time, and
9646 terminate the actions list with a line containing just @code{end}. So
9647 far, the only defined actions are @code{collect}, @code{teval}, and
9648 @code{while-stepping}.
9650 @cindex remove actions from a tracepoint
9651 To remove all actions from a tracepoint, type @samp{actions @var{num}}
9652 and follow it immediately with @samp{end}.
9655 (@value{GDBP}) @b{collect @var{data}} // collect some data
9657 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times, collect data
9659 (@value{GDBP}) @b{end} // signals the end of actions.
9662 In the following example, the action list begins with @code{collect}
9663 commands indicating the things to be collected when the tracepoint is
9664 hit. Then, in order to single-step and collect additional data
9665 following the tracepoint, a @code{while-stepping} command is used,
9666 followed by the list of things to be collected after each step in a
9667 sequence of single steps. The @code{while-stepping} command is
9668 terminated by its own separate @code{end} command. Lastly, the action
9669 list is terminated by an @code{end} command.
9672 (@value{GDBP}) @b{trace foo}
9673 (@value{GDBP}) @b{actions}
9674 Enter actions for tracepoint 1, one per line:
9683 @kindex collect @r{(tracepoints)}
9684 @item collect @var{expr1}, @var{expr2}, @dots{}
9685 Collect values of the given expressions when the tracepoint is hit.
9686 This command accepts a comma-separated list of any valid expressions.
9687 In addition to global, static, or local variables, the following
9688 special arguments are supported:
9692 collect all registers
9695 collect all function arguments
9698 collect all local variables.
9701 You can give several consecutive @code{collect} commands, each one
9702 with a single argument, or one @code{collect} command with several
9703 arguments separated by commas: the effect is the same.
9705 The command @code{info scope} (@pxref{Symbols, info scope}) is
9706 particularly useful for figuring out what data to collect.
9708 @kindex teval @r{(tracepoints)}
9709 @item teval @var{expr1}, @var{expr2}, @dots{}
9710 Evaluate the given expressions when the tracepoint is hit. This
9711 command accepts a comma-separated list of expressions. The results
9712 are discarded, so this is mainly useful for assigning values to trace
9713 state variables (@pxref{Trace State Variables}) without adding those
9714 values to the trace buffer, as would be the case if the @code{collect}
9717 @kindex while-stepping @r{(tracepoints)}
9718 @item while-stepping @var{n}
9719 Perform @var{n} single-step instruction traces after the tracepoint,
9720 collecting new data after each step. The @code{while-stepping}
9721 command is followed by the list of what to collect while stepping
9722 (followed by its own @code{end} command):
9726 > collect $regs, myglobal
9732 Note that @code{$pc} is not automatically collected by
9733 @code{while-stepping}; you need to explicitly collect that register if
9734 you need it. You may abbreviate @code{while-stepping} as @code{ws} or
9737 @item set default-collect @var{expr1}, @var{expr2}, @dots{}
9738 @kindex set default-collect
9739 @cindex default collection action
9740 This variable is a list of expressions to collect at each tracepoint
9741 hit. It is effectively an additional @code{collect} action prepended
9742 to every tracepoint action list. The expressions are parsed
9743 individually for each tracepoint, so for instance a variable named
9744 @code{xyz} may be interpreted as a global for one tracepoint, and a
9745 local for another, as appropriate to the tracepoint's location.
9747 @item show default-collect
9748 @kindex show default-collect
9749 Show the list of expressions that are collected by default at each
9754 @node Listing Tracepoints
9755 @subsection Listing Tracepoints
9758 @kindex info tracepoints
9760 @cindex information about tracepoints
9761 @item info tracepoints @r{[}@var{num}@r{]}
9762 Display information about the tracepoint @var{num}. If you don't
9763 specify a tracepoint number, displays information about all the
9764 tracepoints defined so far. The format is similar to that used for
9765 @code{info breakpoints}; in fact, @code{info tracepoints} is the same
9766 command, simply restricting itself to tracepoints.
9768 A tracepoint's listing may include additional information specific to
9773 its passcount as given by the @code{passcount @var{n}} command
9775 its step count as given by the @code{while-stepping @var{n}} command
9777 its action list as given by the @code{actions} command. The actions
9778 are prefixed with an @samp{A} so as to distinguish them from commands.
9782 (@value{GDBP}) @b{info trace}
9783 Num Type Disp Enb Address What
9784 1 tracepoint keep y 0x0804ab57 in foo() at main.cxx:7
9788 A collect globfoo, $regs
9796 This command can be abbreviated @code{info tp}.
9799 @node Starting and Stopping Trace Experiments
9800 @subsection Starting and Stopping Trace Experiments
9804 @cindex start a new trace experiment
9805 @cindex collected data discarded
9807 This command takes no arguments. It starts the trace experiment, and
9808 begins collecting data. This has the side effect of discarding all
9809 the data collected in the trace buffer during the previous trace
9813 @cindex stop a running trace experiment
9815 This command takes no arguments. It ends the trace experiment, and
9816 stops collecting data.
9818 @strong{Note}: a trace experiment and data collection may stop
9819 automatically if any tracepoint's passcount is reached
9820 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
9823 @cindex status of trace data collection
9824 @cindex trace experiment, status of
9826 This command displays the status of the current trace data
9830 Here is an example of the commands we described so far:
9833 (@value{GDBP}) @b{trace gdb_c_test}
9834 (@value{GDBP}) @b{actions}
9835 Enter actions for tracepoint #1, one per line.
9836 > collect $regs,$locals,$args
9841 (@value{GDBP}) @b{tstart}
9842 [time passes @dots{}]
9843 (@value{GDBP}) @b{tstop}
9846 @cindex disconnected tracing
9847 You can choose to continue running the trace experiment even if
9848 @value{GDBN} disconnects from the target, voluntarily or
9849 involuntarily. For commands such as @code{detach}, the debugger will
9850 ask what you want to do with the trace. But for unexpected
9851 terminations (@value{GDBN} crash, network outage), it would be
9852 unfortunate to lose hard-won trace data, so the variable
9853 @code{disconnected-tracing} lets you decide whether the trace should
9854 continue running without @value{GDBN}.
9857 @item set disconnected-tracing on
9858 @itemx set disconnected-tracing off
9859 @kindex set disconnected-tracing
9860 Choose whether a tracing run should continue to run if @value{GDBN}
9861 has disconnected from the target. Note that @code{detach} or
9862 @code{quit} will ask you directly what to do about a running trace no
9863 matter what this variable's setting, so the variable is mainly useful
9864 for handling unexpected situations, such as loss of the network.
9866 @item show disconnected-tracing
9867 @kindex show disconnected-tracing
9868 Show the current choice for disconnected tracing.
9872 When you reconnect to the target, the trace experiment may or may not
9873 still be running; it might have filled the trace buffer in the
9874 meantime, or stopped for one of the other reasons. If it is running,
9875 it will continue after reconnection.
9877 Upon reconnection, the target will upload information about the
9878 tracepoints in effect. @value{GDBN} will then compare that
9879 information to the set of tracepoints currently defined, and attempt
9880 to match them up, allowing for the possibility that the numbers may
9881 have changed due to creation and deletion in the meantime. If one of
9882 the target's tracepoints does not match any in @value{GDBN}, the
9883 debugger will create a new tracepoint, so that you have a number with
9884 which to specify that tracepoint. This matching-up process is
9885 necessarily heuristic, and it may result in useless tracepoints being
9886 created; you may simply delete them if they are of no use.
9888 @cindex circular trace buffer
9889 If your target agent supports a @dfn{circular trace buffer}, then you
9890 can run a trace experiment indefinitely without filling the trace
9891 buffer; when space runs out, the agent deletes already-collected trace
9892 frames, oldest first, until there is enough room to continue
9893 collecting. This is especially useful if your tracepoints are being
9894 hit too often, and your trace gets terminated prematurely because the
9895 buffer is full. To ask for a circular trace buffer, simply set
9896 @samp{circular_trace_buffer} to on. You can set this at any time,
9897 including during tracing; if the agent can do it, it will change
9898 buffer handling on the fly, otherwise it will not take effect until
9902 @item set circular-trace-buffer on
9903 @itemx set circular-trace-buffer off
9904 @kindex set circular-trace-buffer
9905 Choose whether a tracing run should use a linear or circular buffer
9906 for trace data. A linear buffer will not lose any trace data, but may
9907 fill up prematurely, while a circular buffer will discard old trace
9908 data, but it will have always room for the latest tracepoint hits.
9910 @item show circular-trace-buffer
9911 @kindex show circular-trace-buffer
9912 Show the current choice for the trace buffer. Note that this may not
9913 match the agent's current buffer handling, nor is it guaranteed to
9914 match the setting that might have been in effect during a past run,
9915 for instance if you are looking at frames from a trace file.
9919 @node Tracepoint Restrictions
9920 @subsection Tracepoint Restrictions
9922 @cindex tracepoint restrictions
9923 There are a number of restrictions on the use of tracepoints. As
9924 described above, tracepoint data gathering occurs on the target
9925 without interaction from @value{GDBN}. Thus the full capabilities of
9926 the debugger are not available during data gathering, and then at data
9927 examination time, you will be limited by only having what was
9928 collected. The following items describe some common problems, but it
9929 is not exhaustive, and you may run into additional difficulties not
9935 Tracepoint expressions are intended to gather objects (lvalues). Thus
9936 the full flexibility of GDB's expression evaluator is not available.
9937 You cannot call functions, cast objects to aggregate types, access
9938 convenience variables or modify values (except by assignment to trace
9939 state variables). Some language features may implicitly call
9940 functions (for instance Objective-C fields with accessors), and therefore
9941 cannot be collected either.
9944 Collection of local variables, either individually or in bulk with
9945 @code{$locals} or @code{$args}, during @code{while-stepping} may
9946 behave erratically. The stepping action may enter a new scope (for
9947 instance by stepping into a function), or the location of the variable
9948 may change (for instance it is loaded into a register). The
9949 tracepoint data recorded uses the location information for the
9950 variables that is correct for the tracepoint location. When the
9951 tracepoint is created, it is not possible, in general, to determine
9952 where the steps of a @code{while-stepping} sequence will advance the
9953 program---particularly if a conditional branch is stepped.
9956 Collection of an incompletely-initialized or partially-destroyed object
9957 may result in something that @value{GDBN} cannot display, or displays
9958 in a misleading way.
9961 When @value{GDBN} displays a pointer to character it automatically
9962 dereferences the pointer to also display characters of the string
9963 being pointed to. However, collecting the pointer during tracing does
9964 not automatically collect the string. You need to explicitly
9965 dereference the pointer and provide size information if you want to
9966 collect not only the pointer, but the memory pointed to. For example,
9967 @code{*ptr@@50} can be used to collect the 50 element array pointed to
9971 It is not possible to collect a complete stack backtrace at a
9972 tracepoint. Instead, you may collect the registers and a few hundred
9973 bytes from the stack pointer with something like @code{*$esp@@300}
9974 (adjust to use the name of the actual stack pointer register on your
9975 target architecture, and the amount of stack you wish to capture).
9976 Then the @code{backtrace} command will show a partial backtrace when
9977 using a trace frame. The number of stack frames that can be examined
9978 depends on the sizes of the frames in the collected stack. Note that
9979 if you ask for a block so large that it goes past the bottom of the
9980 stack, the target agent may report an error trying to read from an
9984 If you do not collect registers at a tracepoint, @value{GDBN} can
9985 infer that the value of @code{$pc} must be the same as the address of
9986 the tracepoint and use that when you are looking at a trace frame
9987 for that tracepoint. However, this cannot work if the tracepoint has
9988 multiple locations (for instance if it was set in a function that was
9989 inlined), or if it has a @code{while-stepping} loop. In those cases
9990 @value{GDBN} will warn you that it can't infer @code{$pc}, and default
9995 @node Analyze Collected Data
9996 @section Using the Collected Data
9998 After the tracepoint experiment ends, you use @value{GDBN} commands
9999 for examining the trace data. The basic idea is that each tracepoint
10000 collects a trace @dfn{snapshot} every time it is hit and another
10001 snapshot every time it single-steps. All these snapshots are
10002 consecutively numbered from zero and go into a buffer, and you can
10003 examine them later. The way you examine them is to @dfn{focus} on a
10004 specific trace snapshot. When the remote stub is focused on a trace
10005 snapshot, it will respond to all @value{GDBN} requests for memory and
10006 registers by reading from the buffer which belongs to that snapshot,
10007 rather than from @emph{real} memory or registers of the program being
10008 debugged. This means that @strong{all} @value{GDBN} commands
10009 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
10010 behave as if we were currently debugging the program state as it was
10011 when the tracepoint occurred. Any requests for data that are not in
10012 the buffer will fail.
10015 * tfind:: How to select a trace snapshot
10016 * tdump:: How to display all data for a snapshot
10017 * save tracepoints:: How to save tracepoints for a future run
10021 @subsection @code{tfind @var{n}}
10024 @cindex select trace snapshot
10025 @cindex find trace snapshot
10026 The basic command for selecting a trace snapshot from the buffer is
10027 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
10028 counting from zero. If no argument @var{n} is given, the next
10029 snapshot is selected.
10031 Here are the various forms of using the @code{tfind} command.
10035 Find the first snapshot in the buffer. This is a synonym for
10036 @code{tfind 0} (since 0 is the number of the first snapshot).
10039 Stop debugging trace snapshots, resume @emph{live} debugging.
10042 Same as @samp{tfind none}.
10045 No argument means find the next trace snapshot.
10048 Find the previous trace snapshot before the current one. This permits
10049 retracing earlier steps.
10051 @item tfind tracepoint @var{num}
10052 Find the next snapshot associated with tracepoint @var{num}. Search
10053 proceeds forward from the last examined trace snapshot. If no
10054 argument @var{num} is given, it means find the next snapshot collected
10055 for the same tracepoint as the current snapshot.
10057 @item tfind pc @var{addr}
10058 Find the next snapshot associated with the value @var{addr} of the
10059 program counter. Search proceeds forward from the last examined trace
10060 snapshot. If no argument @var{addr} is given, it means find the next
10061 snapshot with the same value of PC as the current snapshot.
10063 @item tfind outside @var{addr1}, @var{addr2}
10064 Find the next snapshot whose PC is outside the given range of
10065 addresses (exclusive).
10067 @item tfind range @var{addr1}, @var{addr2}
10068 Find the next snapshot whose PC is between @var{addr1} and
10069 @var{addr2} (inclusive).
10071 @item tfind line @r{[}@var{file}:@r{]}@var{n}
10072 Find the next snapshot associated with the source line @var{n}. If
10073 the optional argument @var{file} is given, refer to line @var{n} in
10074 that source file. Search proceeds forward from the last examined
10075 trace snapshot. If no argument @var{n} is given, it means find the
10076 next line other than the one currently being examined; thus saying
10077 @code{tfind line} repeatedly can appear to have the same effect as
10078 stepping from line to line in a @emph{live} debugging session.
10081 The default arguments for the @code{tfind} commands are specifically
10082 designed to make it easy to scan through the trace buffer. For
10083 instance, @code{tfind} with no argument selects the next trace
10084 snapshot, and @code{tfind -} with no argument selects the previous
10085 trace snapshot. So, by giving one @code{tfind} command, and then
10086 simply hitting @key{RET} repeatedly you can examine all the trace
10087 snapshots in order. Or, by saying @code{tfind -} and then hitting
10088 @key{RET} repeatedly you can examine the snapshots in reverse order.
10089 The @code{tfind line} command with no argument selects the snapshot
10090 for the next source line executed. The @code{tfind pc} command with
10091 no argument selects the next snapshot with the same program counter
10092 (PC) as the current frame. The @code{tfind tracepoint} command with
10093 no argument selects the next trace snapshot collected by the same
10094 tracepoint as the current one.
10096 In addition to letting you scan through the trace buffer manually,
10097 these commands make it easy to construct @value{GDBN} scripts that
10098 scan through the trace buffer and print out whatever collected data
10099 you are interested in. Thus, if we want to examine the PC, FP, and SP
10100 registers from each trace frame in the buffer, we can say this:
10103 (@value{GDBP}) @b{tfind start}
10104 (@value{GDBP}) @b{while ($trace_frame != -1)}
10105 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
10106 $trace_frame, $pc, $sp, $fp
10110 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
10111 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
10112 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
10113 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
10114 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
10115 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
10116 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
10117 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
10118 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
10119 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
10120 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
10123 Or, if we want to examine the variable @code{X} at each source line in
10127 (@value{GDBP}) @b{tfind start}
10128 (@value{GDBP}) @b{while ($trace_frame != -1)}
10129 > printf "Frame %d, X == %d\n", $trace_frame, X
10139 @subsection @code{tdump}
10141 @cindex dump all data collected at tracepoint
10142 @cindex tracepoint data, display
10144 This command takes no arguments. It prints all the data collected at
10145 the current trace snapshot.
10148 (@value{GDBP}) @b{trace 444}
10149 (@value{GDBP}) @b{actions}
10150 Enter actions for tracepoint #2, one per line:
10151 > collect $regs, $locals, $args, gdb_long_test
10154 (@value{GDBP}) @b{tstart}
10156 (@value{GDBP}) @b{tfind line 444}
10157 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
10159 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
10161 (@value{GDBP}) @b{tdump}
10162 Data collected at tracepoint 2, trace frame 1:
10163 d0 0xc4aa0085 -995491707
10167 d4 0x71aea3d 119204413
10170 d7 0x380035 3670069
10171 a0 0x19e24a 1696330
10172 a1 0x3000668 50333288
10174 a3 0x322000 3284992
10175 a4 0x3000698 50333336
10176 a5 0x1ad3cc 1758156
10177 fp 0x30bf3c 0x30bf3c
10178 sp 0x30bf34 0x30bf34
10180 pc 0x20b2c8 0x20b2c8
10184 p = 0x20e5b4 "gdb-test"
10191 gdb_long_test = 17 '\021'
10196 @code{tdump} works by scanning the tracepoint's current collection
10197 actions and printing the value of each expression listed. So
10198 @code{tdump} can fail, if after a run, you change the tracepoint's
10199 actions to mention variables that were not collected during the run.
10201 Also, for tracepoints with @code{while-stepping} loops, @code{tdump}
10202 uses the collected value of @code{$pc} to distinguish between trace
10203 frames that were collected at the tracepoint hit, and frames that were
10204 collected while stepping. This allows it to correctly choose whether
10205 to display the basic list of collections, or the collections from the
10206 body of the while-stepping loop. However, if @code{$pc} was not collected,
10207 then @code{tdump} will always attempt to dump using the basic collection
10208 list, and may fail if a while-stepping frame does not include all the
10209 same data that is collected at the tracepoint hit.
10210 @c This is getting pretty arcane, example would be good.
10212 @node save tracepoints
10213 @subsection @code{save tracepoints @var{filename}}
10214 @kindex save tracepoints
10215 @kindex save-tracepoints
10216 @cindex save tracepoints for future sessions
10218 This command saves all current tracepoint definitions together with
10219 their actions and passcounts, into a file @file{@var{filename}}
10220 suitable for use in a later debugging session. To read the saved
10221 tracepoint definitions, use the @code{source} command (@pxref{Command
10222 Files}). The @w{@code{save-tracepoints}} command is a deprecated
10223 alias for @w{@code{save tracepoints}}
10225 @node Tracepoint Variables
10226 @section Convenience Variables for Tracepoints
10227 @cindex tracepoint variables
10228 @cindex convenience variables for tracepoints
10231 @vindex $trace_frame
10232 @item (int) $trace_frame
10233 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
10234 snapshot is selected.
10236 @vindex $tracepoint
10237 @item (int) $tracepoint
10238 The tracepoint for the current trace snapshot.
10240 @vindex $trace_line
10241 @item (int) $trace_line
10242 The line number for the current trace snapshot.
10244 @vindex $trace_file
10245 @item (char []) $trace_file
10246 The source file for the current trace snapshot.
10248 @vindex $trace_func
10249 @item (char []) $trace_func
10250 The name of the function containing @code{$tracepoint}.
10253 Note: @code{$trace_file} is not suitable for use in @code{printf},
10254 use @code{output} instead.
10256 Here's a simple example of using these convenience variables for
10257 stepping through all the trace snapshots and printing some of their
10258 data. Note that these are not the same as trace state variables,
10259 which are managed by the target.
10262 (@value{GDBP}) @b{tfind start}
10264 (@value{GDBP}) @b{while $trace_frame != -1}
10265 > output $trace_file
10266 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
10272 @section Using Trace Files
10273 @cindex trace files
10275 In some situations, the target running a trace experiment may no
10276 longer be available; perhaps it crashed, or the hardware was needed
10277 for a different activity. To handle these cases, you can arrange to
10278 dump the trace data into a file, and later use that file as a source
10279 of trace data, via the @code{target tfile} command.
10284 @item tsave [ -r ] @var{filename}
10285 Save the trace data to @var{filename}. By default, this command
10286 assumes that @var{filename} refers to the host filesystem, so if
10287 necessary @value{GDBN} will copy raw trace data up from the target and
10288 then save it. If the target supports it, you can also supply the
10289 optional argument @code{-r} (``remote'') to direct the target to save
10290 the data directly into @var{filename} in its own filesystem, which may be
10291 more efficient if the trace buffer is very large. (Note, however, that
10292 @code{target tfile} can only read from files accessible to the host.)
10294 @kindex target tfile
10296 @item target tfile @var{filename}
10297 Use the file named @var{filename} as a source of trace data. Commands
10298 that examine data work as they do with a live target, but it is not
10299 possible to run any new trace experiments. @code{tstatus} will report
10300 the state of the trace run at the moment the data was saved, as well
10301 as the current trace frame you are examining. @var{filename} must be
10302 on a filesystem accessible to the host.
10307 @chapter Debugging Programs That Use Overlays
10310 If your program is too large to fit completely in your target system's
10311 memory, you can sometimes use @dfn{overlays} to work around this
10312 problem. @value{GDBN} provides some support for debugging programs that
10316 * How Overlays Work:: A general explanation of overlays.
10317 * Overlay Commands:: Managing overlays in @value{GDBN}.
10318 * Automatic Overlay Debugging:: @value{GDBN} can find out which overlays are
10319 mapped by asking the inferior.
10320 * Overlay Sample Program:: A sample program using overlays.
10323 @node How Overlays Work
10324 @section How Overlays Work
10325 @cindex mapped overlays
10326 @cindex unmapped overlays
10327 @cindex load address, overlay's
10328 @cindex mapped address
10329 @cindex overlay area
10331 Suppose you have a computer whose instruction address space is only 64
10332 kilobytes long, but which has much more memory which can be accessed by
10333 other means: special instructions, segment registers, or memory
10334 management hardware, for example. Suppose further that you want to
10335 adapt a program which is larger than 64 kilobytes to run on this system.
10337 One solution is to identify modules of your program which are relatively
10338 independent, and need not call each other directly; call these modules
10339 @dfn{overlays}. Separate the overlays from the main program, and place
10340 their machine code in the larger memory. Place your main program in
10341 instruction memory, but leave at least enough space there to hold the
10342 largest overlay as well.
10344 Now, to call a function located in an overlay, you must first copy that
10345 overlay's machine code from the large memory into the space set aside
10346 for it in the instruction memory, and then jump to its entry point
10349 @c NB: In the below the mapped area's size is greater or equal to the
10350 @c size of all overlays. This is intentional to remind the developer
10351 @c that overlays don't necessarily need to be the same size.
10355 Data Instruction Larger
10356 Address Space Address Space Address Space
10357 +-----------+ +-----------+ +-----------+
10359 +-----------+ +-----------+ +-----------+<-- overlay 1
10360 | program | | main | .----| overlay 1 | load address
10361 | variables | | program | | +-----------+
10362 | and heap | | | | | |
10363 +-----------+ | | | +-----------+<-- overlay 2
10364 | | +-----------+ | | | load address
10365 +-----------+ | | | .-| overlay 2 |
10367 mapped --->+-----------+ | | +-----------+
10368 address | | | | | |
10369 | overlay | <-' | | |
10370 | area | <---' +-----------+<-- overlay 3
10371 | | <---. | | load address
10372 +-----------+ `--| overlay 3 |
10379 @anchor{A code overlay}A code overlay
10383 The diagram (@pxref{A code overlay}) shows a system with separate data
10384 and instruction address spaces. To map an overlay, the program copies
10385 its code from the larger address space to the instruction address space.
10386 Since the overlays shown here all use the same mapped address, only one
10387 may be mapped at a time. For a system with a single address space for
10388 data and instructions, the diagram would be similar, except that the
10389 program variables and heap would share an address space with the main
10390 program and the overlay area.
10392 An overlay loaded into instruction memory and ready for use is called a
10393 @dfn{mapped} overlay; its @dfn{mapped address} is its address in the
10394 instruction memory. An overlay not present (or only partially present)
10395 in instruction memory is called @dfn{unmapped}; its @dfn{load address}
10396 is its address in the larger memory. The mapped address is also called
10397 the @dfn{virtual memory address}, or @dfn{VMA}; the load address is also
10398 called the @dfn{load memory address}, or @dfn{LMA}.
10400 Unfortunately, overlays are not a completely transparent way to adapt a
10401 program to limited instruction memory. They introduce a new set of
10402 global constraints you must keep in mind as you design your program:
10407 Before calling or returning to a function in an overlay, your program
10408 must make sure that overlay is actually mapped. Otherwise, the call or
10409 return will transfer control to the right address, but in the wrong
10410 overlay, and your program will probably crash.
10413 If the process of mapping an overlay is expensive on your system, you
10414 will need to choose your overlays carefully to minimize their effect on
10415 your program's performance.
10418 The executable file you load onto your system must contain each
10419 overlay's instructions, appearing at the overlay's load address, not its
10420 mapped address. However, each overlay's instructions must be relocated
10421 and its symbols defined as if the overlay were at its mapped address.
10422 You can use GNU linker scripts to specify different load and relocation
10423 addresses for pieces of your program; see @ref{Overlay Description,,,
10424 ld.info, Using ld: the GNU linker}.
10427 The procedure for loading executable files onto your system must be able
10428 to load their contents into the larger address space as well as the
10429 instruction and data spaces.
10433 The overlay system described above is rather simple, and could be
10434 improved in many ways:
10439 If your system has suitable bank switch registers or memory management
10440 hardware, you could use those facilities to make an overlay's load area
10441 contents simply appear at their mapped address in instruction space.
10442 This would probably be faster than copying the overlay to its mapped
10443 area in the usual way.
10446 If your overlays are small enough, you could set aside more than one
10447 overlay area, and have more than one overlay mapped at a time.
10450 You can use overlays to manage data, as well as instructions. In
10451 general, data overlays are even less transparent to your design than
10452 code overlays: whereas code overlays only require care when you call or
10453 return to functions, data overlays require care every time you access
10454 the data. Also, if you change the contents of a data overlay, you
10455 must copy its contents back out to its load address before you can copy a
10456 different data overlay into the same mapped area.
10461 @node Overlay Commands
10462 @section Overlay Commands
10464 To use @value{GDBN}'s overlay support, each overlay in your program must
10465 correspond to a separate section of the executable file. The section's
10466 virtual memory address and load memory address must be the overlay's
10467 mapped and load addresses. Identifying overlays with sections allows
10468 @value{GDBN} to determine the appropriate address of a function or
10469 variable, depending on whether the overlay is mapped or not.
10471 @value{GDBN}'s overlay commands all start with the word @code{overlay};
10472 you can abbreviate this as @code{ov} or @code{ovly}. The commands are:
10477 Disable @value{GDBN}'s overlay support. When overlay support is
10478 disabled, @value{GDBN} assumes that all functions and variables are
10479 always present at their mapped addresses. By default, @value{GDBN}'s
10480 overlay support is disabled.
10482 @item overlay manual
10483 @cindex manual overlay debugging
10484 Enable @dfn{manual} overlay debugging. In this mode, @value{GDBN}
10485 relies on you to tell it which overlays are mapped, and which are not,
10486 using the @code{overlay map-overlay} and @code{overlay unmap-overlay}
10487 commands described below.
10489 @item overlay map-overlay @var{overlay}
10490 @itemx overlay map @var{overlay}
10491 @cindex map an overlay
10492 Tell @value{GDBN} that @var{overlay} is now mapped; @var{overlay} must
10493 be the name of the object file section containing the overlay. When an
10494 overlay is mapped, @value{GDBN} assumes it can find the overlay's
10495 functions and variables at their mapped addresses. @value{GDBN} assumes
10496 that any other overlays whose mapped ranges overlap that of
10497 @var{overlay} are now unmapped.
10499 @item overlay unmap-overlay @var{overlay}
10500 @itemx overlay unmap @var{overlay}
10501 @cindex unmap an overlay
10502 Tell @value{GDBN} that @var{overlay} is no longer mapped; @var{overlay}
10503 must be the name of the object file section containing the overlay.
10504 When an overlay is unmapped, @value{GDBN} assumes it can find the
10505 overlay's functions and variables at their load addresses.
10508 Enable @dfn{automatic} overlay debugging. In this mode, @value{GDBN}
10509 consults a data structure the overlay manager maintains in the inferior
10510 to see which overlays are mapped. For details, see @ref{Automatic
10511 Overlay Debugging}.
10513 @item overlay load-target
10514 @itemx overlay load
10515 @cindex reloading the overlay table
10516 Re-read the overlay table from the inferior. Normally, @value{GDBN}
10517 re-reads the table @value{GDBN} automatically each time the inferior
10518 stops, so this command should only be necessary if you have changed the
10519 overlay mapping yourself using @value{GDBN}. This command is only
10520 useful when using automatic overlay debugging.
10522 @item overlay list-overlays
10523 @itemx overlay list
10524 @cindex listing mapped overlays
10525 Display a list of the overlays currently mapped, along with their mapped
10526 addresses, load addresses, and sizes.
10530 Normally, when @value{GDBN} prints a code address, it includes the name
10531 of the function the address falls in:
10534 (@value{GDBP}) print main
10535 $3 = @{int ()@} 0x11a0 <main>
10538 When overlay debugging is enabled, @value{GDBN} recognizes code in
10539 unmapped overlays, and prints the names of unmapped functions with
10540 asterisks around them. For example, if @code{foo} is a function in an
10541 unmapped overlay, @value{GDBN} prints it this way:
10544 (@value{GDBP}) overlay list
10545 No sections are mapped.
10546 (@value{GDBP}) print foo
10547 $5 = @{int (int)@} 0x100000 <*foo*>
10550 When @code{foo}'s overlay is mapped, @value{GDBN} prints the function's
10554 (@value{GDBP}) overlay list
10555 Section .ov.foo.text, loaded at 0x100000 - 0x100034,
10556 mapped at 0x1016 - 0x104a
10557 (@value{GDBP}) print foo
10558 $6 = @{int (int)@} 0x1016 <foo>
10561 When overlay debugging is enabled, @value{GDBN} can find the correct
10562 address for functions and variables in an overlay, whether or not the
10563 overlay is mapped. This allows most @value{GDBN} commands, like
10564 @code{break} and @code{disassemble}, to work normally, even on unmapped
10565 code. However, @value{GDBN}'s breakpoint support has some limitations:
10569 @cindex breakpoints in overlays
10570 @cindex overlays, setting breakpoints in
10571 You can set breakpoints in functions in unmapped overlays, as long as
10572 @value{GDBN} can write to the overlay at its load address.
10574 @value{GDBN} can not set hardware or simulator-based breakpoints in
10575 unmapped overlays. However, if you set a breakpoint at the end of your
10576 overlay manager (and tell @value{GDBN} which overlays are now mapped, if
10577 you are using manual overlay management), @value{GDBN} will re-set its
10578 breakpoints properly.
10582 @node Automatic Overlay Debugging
10583 @section Automatic Overlay Debugging
10584 @cindex automatic overlay debugging
10586 @value{GDBN} can automatically track which overlays are mapped and which
10587 are not, given some simple co-operation from the overlay manager in the
10588 inferior. If you enable automatic overlay debugging with the
10589 @code{overlay auto} command (@pxref{Overlay Commands}), @value{GDBN}
10590 looks in the inferior's memory for certain variables describing the
10591 current state of the overlays.
10593 Here are the variables your overlay manager must define to support
10594 @value{GDBN}'s automatic overlay debugging:
10598 @item @code{_ovly_table}:
10599 This variable must be an array of the following structures:
10604 /* The overlay's mapped address. */
10607 /* The size of the overlay, in bytes. */
10608 unsigned long size;
10610 /* The overlay's load address. */
10613 /* Non-zero if the overlay is currently mapped;
10615 unsigned long mapped;
10619 @item @code{_novlys}:
10620 This variable must be a four-byte signed integer, holding the total
10621 number of elements in @code{_ovly_table}.
10625 To decide whether a particular overlay is mapped or not, @value{GDBN}
10626 looks for an entry in @w{@code{_ovly_table}} whose @code{vma} and
10627 @code{lma} members equal the VMA and LMA of the overlay's section in the
10628 executable file. When @value{GDBN} finds a matching entry, it consults
10629 the entry's @code{mapped} member to determine whether the overlay is
10632 In addition, your overlay manager may define a function called
10633 @code{_ovly_debug_event}. If this function is defined, @value{GDBN}
10634 will silently set a breakpoint there. If the overlay manager then
10635 calls this function whenever it has changed the overlay table, this
10636 will enable @value{GDBN} to accurately keep track of which overlays
10637 are in program memory, and update any breakpoints that may be set
10638 in overlays. This will allow breakpoints to work even if the
10639 overlays are kept in ROM or other non-writable memory while they
10640 are not being executed.
10642 @node Overlay Sample Program
10643 @section Overlay Sample Program
10644 @cindex overlay example program
10646 When linking a program which uses overlays, you must place the overlays
10647 at their load addresses, while relocating them to run at their mapped
10648 addresses. To do this, you must write a linker script (@pxref{Overlay
10649 Description,,, ld.info, Using ld: the GNU linker}). Unfortunately,
10650 since linker scripts are specific to a particular host system, target
10651 architecture, and target memory layout, this manual cannot provide
10652 portable sample code demonstrating @value{GDBN}'s overlay support.
10654 However, the @value{GDBN} source distribution does contain an overlaid
10655 program, with linker scripts for a few systems, as part of its test
10656 suite. The program consists of the following files from
10657 @file{gdb/testsuite/gdb.base}:
10661 The main program file.
10663 A simple overlay manager, used by @file{overlays.c}.
10668 Overlay modules, loaded and used by @file{overlays.c}.
10671 Linker scripts for linking the test program on the @code{d10v-elf}
10672 and @code{m32r-elf} targets.
10675 You can build the test program using the @code{d10v-elf} GCC
10676 cross-compiler like this:
10679 $ d10v-elf-gcc -g -c overlays.c
10680 $ d10v-elf-gcc -g -c ovlymgr.c
10681 $ d10v-elf-gcc -g -c foo.c
10682 $ d10v-elf-gcc -g -c bar.c
10683 $ d10v-elf-gcc -g -c baz.c
10684 $ d10v-elf-gcc -g -c grbx.c
10685 $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
10686 baz.o grbx.o -Wl,-Td10v.ld -o overlays
10689 The build process is identical for any other architecture, except that
10690 you must substitute the appropriate compiler and linker script for the
10691 target system for @code{d10v-elf-gcc} and @code{d10v.ld}.
10695 @chapter Using @value{GDBN} with Different Languages
10698 Although programming languages generally have common aspects, they are
10699 rarely expressed in the same manner. For instance, in ANSI C,
10700 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
10701 Modula-2, it is accomplished by @code{p^}. Values can also be
10702 represented (and displayed) differently. Hex numbers in C appear as
10703 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
10705 @cindex working language
10706 Language-specific information is built into @value{GDBN} for some languages,
10707 allowing you to express operations like the above in your program's
10708 native language, and allowing @value{GDBN} to output values in a manner
10709 consistent with the syntax of your program's native language. The
10710 language you use to build expressions is called the @dfn{working
10714 * Setting:: Switching between source languages
10715 * Show:: Displaying the language
10716 * Checks:: Type and range checks
10717 * Supported Languages:: Supported languages
10718 * Unsupported Languages:: Unsupported languages
10722 @section Switching Between Source Languages
10724 There are two ways to control the working language---either have @value{GDBN}
10725 set it automatically, or select it manually yourself. You can use the
10726 @code{set language} command for either purpose. On startup, @value{GDBN}
10727 defaults to setting the language automatically. The working language is
10728 used to determine how expressions you type are interpreted, how values
10731 In addition to the working language, every source file that
10732 @value{GDBN} knows about has its own working language. For some object
10733 file formats, the compiler might indicate which language a particular
10734 source file is in. However, most of the time @value{GDBN} infers the
10735 language from the name of the file. The language of a source file
10736 controls whether C@t{++} names are demangled---this way @code{backtrace} can
10737 show each frame appropriately for its own language. There is no way to
10738 set the language of a source file from within @value{GDBN}, but you can
10739 set the language associated with a filename extension. @xref{Show, ,
10740 Displaying the Language}.
10742 This is most commonly a problem when you use a program, such
10743 as @code{cfront} or @code{f2c}, that generates C but is written in
10744 another language. In that case, make the
10745 program use @code{#line} directives in its C output; that way
10746 @value{GDBN} will know the correct language of the source code of the original
10747 program, and will display that source code, not the generated C code.
10750 * Filenames:: Filename extensions and languages.
10751 * Manually:: Setting the working language manually
10752 * Automatically:: Having @value{GDBN} infer the source language
10756 @subsection List of Filename Extensions and Languages
10758 If a source file name ends in one of the following extensions, then
10759 @value{GDBN} infers that its language is the one indicated.
10777 C@t{++} source file
10780 Objective-C source file
10784 Fortran source file
10787 Modula-2 source file
10791 Assembler source file. This actually behaves almost like C, but
10792 @value{GDBN} does not skip over function prologues when stepping.
10795 In addition, you may set the language associated with a filename
10796 extension. @xref{Show, , Displaying the Language}.
10799 @subsection Setting the Working Language
10801 If you allow @value{GDBN} to set the language automatically,
10802 expressions are interpreted the same way in your debugging session and
10805 @kindex set language
10806 If you wish, you may set the language manually. To do this, issue the
10807 command @samp{set language @var{lang}}, where @var{lang} is the name of
10808 a language, such as
10809 @code{c} or @code{modula-2}.
10810 For a list of the supported languages, type @samp{set language}.
10812 Setting the language manually prevents @value{GDBN} from updating the working
10813 language automatically. This can lead to confusion if you try
10814 to debug a program when the working language is not the same as the
10815 source language, when an expression is acceptable to both
10816 languages---but means different things. For instance, if the current
10817 source file were written in C, and @value{GDBN} was parsing Modula-2, a
10825 might not have the effect you intended. In C, this means to add
10826 @code{b} and @code{c} and place the result in @code{a}. The result
10827 printed would be the value of @code{a}. In Modula-2, this means to compare
10828 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
10830 @node Automatically
10831 @subsection Having @value{GDBN} Infer the Source Language
10833 To have @value{GDBN} set the working language automatically, use
10834 @samp{set language local} or @samp{set language auto}. @value{GDBN}
10835 then infers the working language. That is, when your program stops in a
10836 frame (usually by encountering a breakpoint), @value{GDBN} sets the
10837 working language to the language recorded for the function in that
10838 frame. If the language for a frame is unknown (that is, if the function
10839 or block corresponding to the frame was defined in a source file that
10840 does not have a recognized extension), the current working language is
10841 not changed, and @value{GDBN} issues a warning.
10843 This may not seem necessary for most programs, which are written
10844 entirely in one source language. However, program modules and libraries
10845 written in one source language can be used by a main program written in
10846 a different source language. Using @samp{set language auto} in this
10847 case frees you from having to set the working language manually.
10850 @section Displaying the Language
10852 The following commands help you find out which language is the
10853 working language, and also what language source files were written in.
10856 @item show language
10857 @kindex show language
10858 Display the current working language. This is the
10859 language you can use with commands such as @code{print} to
10860 build and compute expressions that may involve variables in your program.
10863 @kindex info frame@r{, show the source language}
10864 Display the source language for this frame. This language becomes the
10865 working language if you use an identifier from this frame.
10866 @xref{Frame Info, ,Information about a Frame}, to identify the other
10867 information listed here.
10870 @kindex info source@r{, show the source language}
10871 Display the source language of this source file.
10872 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
10873 information listed here.
10876 In unusual circumstances, you may have source files with extensions
10877 not in the standard list. You can then set the extension associated
10878 with a language explicitly:
10881 @item set extension-language @var{ext} @var{language}
10882 @kindex set extension-language
10883 Tell @value{GDBN} that source files with extension @var{ext} are to be
10884 assumed as written in the source language @var{language}.
10886 @item info extensions
10887 @kindex info extensions
10888 List all the filename extensions and the associated languages.
10892 @section Type and Range Checking
10895 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
10896 checking are included, but they do not yet have any effect. This
10897 section documents the intended facilities.
10899 @c FIXME remove warning when type/range code added
10901 Some languages are designed to guard you against making seemingly common
10902 errors through a series of compile- and run-time checks. These include
10903 checking the type of arguments to functions and operators, and making
10904 sure mathematical overflows are caught at run time. Checks such as
10905 these help to ensure a program's correctness once it has been compiled
10906 by eliminating type mismatches, and providing active checks for range
10907 errors when your program is running.
10909 @value{GDBN} can check for conditions like the above if you wish.
10910 Although @value{GDBN} does not check the statements in your program,
10911 it can check expressions entered directly into @value{GDBN} for
10912 evaluation via the @code{print} command, for example. As with the
10913 working language, @value{GDBN} can also decide whether or not to check
10914 automatically based on your program's source language.
10915 @xref{Supported Languages, ,Supported Languages}, for the default
10916 settings of supported languages.
10919 * Type Checking:: An overview of type checking
10920 * Range Checking:: An overview of range checking
10923 @cindex type checking
10924 @cindex checks, type
10925 @node Type Checking
10926 @subsection An Overview of Type Checking
10928 Some languages, such as Modula-2, are strongly typed, meaning that the
10929 arguments to operators and functions have to be of the correct type,
10930 otherwise an error occurs. These checks prevent type mismatch
10931 errors from ever causing any run-time problems. For example,
10939 The second example fails because the @code{CARDINAL} 1 is not
10940 type-compatible with the @code{REAL} 2.3.
10942 For the expressions you use in @value{GDBN} commands, you can tell the
10943 @value{GDBN} type checker to skip checking;
10944 to treat any mismatches as errors and abandon the expression;
10945 or to only issue warnings when type mismatches occur,
10946 but evaluate the expression anyway. When you choose the last of
10947 these, @value{GDBN} evaluates expressions like the second example above, but
10948 also issues a warning.
10950 Even if you turn type checking off, there may be other reasons
10951 related to type that prevent @value{GDBN} from evaluating an expression.
10952 For instance, @value{GDBN} does not know how to add an @code{int} and
10953 a @code{struct foo}. These particular type errors have nothing to do
10954 with the language in use, and usually arise from expressions, such as
10955 the one described above, which make little sense to evaluate anyway.
10957 Each language defines to what degree it is strict about type. For
10958 instance, both Modula-2 and C require the arguments to arithmetical
10959 operators to be numbers. In C, enumerated types and pointers can be
10960 represented as numbers, so that they are valid arguments to mathematical
10961 operators. @xref{Supported Languages, ,Supported Languages}, for further
10962 details on specific languages.
10964 @value{GDBN} provides some additional commands for controlling the type checker:
10966 @kindex set check type
10967 @kindex show check type
10969 @item set check type auto
10970 Set type checking on or off based on the current working language.
10971 @xref{Supported Languages, ,Supported Languages}, for the default settings for
10974 @item set check type on
10975 @itemx set check type off
10976 Set type checking on or off, overriding the default setting for the
10977 current working language. Issue a warning if the setting does not
10978 match the language default. If any type mismatches occur in
10979 evaluating an expression while type checking is on, @value{GDBN} prints a
10980 message and aborts evaluation of the expression.
10982 @item set check type warn
10983 Cause the type checker to issue warnings, but to always attempt to
10984 evaluate the expression. Evaluating the expression may still
10985 be impossible for other reasons. For example, @value{GDBN} cannot add
10986 numbers and structures.
10989 Show the current setting of the type checker, and whether or not @value{GDBN}
10990 is setting it automatically.
10993 @cindex range checking
10994 @cindex checks, range
10995 @node Range Checking
10996 @subsection An Overview of Range Checking
10998 In some languages (such as Modula-2), it is an error to exceed the
10999 bounds of a type; this is enforced with run-time checks. Such range
11000 checking is meant to ensure program correctness by making sure
11001 computations do not overflow, or indices on an array element access do
11002 not exceed the bounds of the array.
11004 For expressions you use in @value{GDBN} commands, you can tell
11005 @value{GDBN} to treat range errors in one of three ways: ignore them,
11006 always treat them as errors and abandon the expression, or issue
11007 warnings but evaluate the expression anyway.
11009 A range error can result from numerical overflow, from exceeding an
11010 array index bound, or when you type a constant that is not a member
11011 of any type. Some languages, however, do not treat overflows as an
11012 error. In many implementations of C, mathematical overflow causes the
11013 result to ``wrap around'' to lower values---for example, if @var{m} is
11014 the largest integer value, and @var{s} is the smallest, then
11017 @var{m} + 1 @result{} @var{s}
11020 This, too, is specific to individual languages, and in some cases
11021 specific to individual compilers or machines. @xref{Supported Languages, ,
11022 Supported Languages}, for further details on specific languages.
11024 @value{GDBN} provides some additional commands for controlling the range checker:
11026 @kindex set check range
11027 @kindex show check range
11029 @item set check range auto
11030 Set range checking on or off based on the current working language.
11031 @xref{Supported Languages, ,Supported Languages}, for the default settings for
11034 @item set check range on
11035 @itemx set check range off
11036 Set range checking on or off, overriding the default setting for the
11037 current working language. A warning is issued if the setting does not
11038 match the language default. If a range error occurs and range checking is on,
11039 then a message is printed and evaluation of the expression is aborted.
11041 @item set check range warn
11042 Output messages when the @value{GDBN} range checker detects a range error,
11043 but attempt to evaluate the expression anyway. Evaluating the
11044 expression may still be impossible for other reasons, such as accessing
11045 memory that the process does not own (a typical example from many Unix
11049 Show the current setting of the range checker, and whether or not it is
11050 being set automatically by @value{GDBN}.
11053 @node Supported Languages
11054 @section Supported Languages
11056 @value{GDBN} supports C, C@t{++}, Objective-C, Fortran, Java, Pascal,
11057 assembly, Modula-2, and Ada.
11058 @c This is false ...
11059 Some @value{GDBN} features may be used in expressions regardless of the
11060 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
11061 and the @samp{@{type@}addr} construct (@pxref{Expressions,
11062 ,Expressions}) can be used with the constructs of any supported
11065 The following sections detail to what degree each source language is
11066 supported by @value{GDBN}. These sections are not meant to be language
11067 tutorials or references, but serve only as a reference guide to what the
11068 @value{GDBN} expression parser accepts, and what input and output
11069 formats should look like for different languages. There are many good
11070 books written on each of these languages; please look to these for a
11071 language reference or tutorial.
11074 * C:: C and C@t{++}
11075 * Objective-C:: Objective-C
11076 * Fortran:: Fortran
11078 * Modula-2:: Modula-2
11083 @subsection C and C@t{++}
11085 @cindex C and C@t{++}
11086 @cindex expressions in C or C@t{++}
11088 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
11089 to both languages. Whenever this is the case, we discuss those languages
11093 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
11094 @cindex @sc{gnu} C@t{++}
11095 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
11096 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
11097 effectively, you must compile your C@t{++} programs with a supported
11098 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
11099 compiler (@code{aCC}).
11101 For best results when using @sc{gnu} C@t{++}, use the DWARF 2 debugging
11102 format; if it doesn't work on your system, try the stabs+ debugging
11103 format. You can select those formats explicitly with the @code{g++}
11104 command-line options @option{-gdwarf-2} and @option{-gstabs+}.
11105 @xref{Debugging Options,,Options for Debugging Your Program or GCC,
11106 gcc.info, Using the @sc{gnu} Compiler Collection (GCC)}.
11109 * C Operators:: C and C@t{++} operators
11110 * C Constants:: C and C@t{++} constants
11111 * C Plus Plus Expressions:: C@t{++} expressions
11112 * C Defaults:: Default settings for C and C@t{++}
11113 * C Checks:: C and C@t{++} type and range checks
11114 * Debugging C:: @value{GDBN} and C
11115 * Debugging C Plus Plus:: @value{GDBN} features for C@t{++}
11116 * Decimal Floating Point:: Numbers in Decimal Floating Point format
11120 @subsubsection C and C@t{++} Operators
11122 @cindex C and C@t{++} operators
11124 Operators must be defined on values of specific types. For instance,
11125 @code{+} is defined on numbers, but not on structures. Operators are
11126 often defined on groups of types.
11128 For the purposes of C and C@t{++}, the following definitions hold:
11133 @emph{Integral types} include @code{int} with any of its storage-class
11134 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
11137 @emph{Floating-point types} include @code{float}, @code{double}, and
11138 @code{long double} (if supported by the target platform).
11141 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
11144 @emph{Scalar types} include all of the above.
11149 The following operators are supported. They are listed here
11150 in order of increasing precedence:
11154 The comma or sequencing operator. Expressions in a comma-separated list
11155 are evaluated from left to right, with the result of the entire
11156 expression being the last expression evaluated.
11159 Assignment. The value of an assignment expression is the value
11160 assigned. Defined on scalar types.
11163 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
11164 and translated to @w{@code{@var{a} = @var{a op b}}}.
11165 @w{@code{@var{op}=}} and @code{=} have the same precedence.
11166 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
11167 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
11170 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
11171 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
11175 Logical @sc{or}. Defined on integral types.
11178 Logical @sc{and}. Defined on integral types.
11181 Bitwise @sc{or}. Defined on integral types.
11184 Bitwise exclusive-@sc{or}. Defined on integral types.
11187 Bitwise @sc{and}. Defined on integral types.
11190 Equality and inequality. Defined on scalar types. The value of these
11191 expressions is 0 for false and non-zero for true.
11193 @item <@r{, }>@r{, }<=@r{, }>=
11194 Less than, greater than, less than or equal, greater than or equal.
11195 Defined on scalar types. The value of these expressions is 0 for false
11196 and non-zero for true.
11199 left shift, and right shift. Defined on integral types.
11202 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
11205 Addition and subtraction. Defined on integral types, floating-point types and
11208 @item *@r{, }/@r{, }%
11209 Multiplication, division, and modulus. Multiplication and division are
11210 defined on integral and floating-point types. Modulus is defined on
11214 Increment and decrement. When appearing before a variable, the
11215 operation is performed before the variable is used in an expression;
11216 when appearing after it, the variable's value is used before the
11217 operation takes place.
11220 Pointer dereferencing. Defined on pointer types. Same precedence as
11224 Address operator. Defined on variables. Same precedence as @code{++}.
11226 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
11227 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
11228 to examine the address
11229 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
11233 Negative. Defined on integral and floating-point types. Same
11234 precedence as @code{++}.
11237 Logical negation. Defined on integral types. Same precedence as
11241 Bitwise complement operator. Defined on integral types. Same precedence as
11246 Structure member, and pointer-to-structure member. For convenience,
11247 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
11248 pointer based on the stored type information.
11249 Defined on @code{struct} and @code{union} data.
11252 Dereferences of pointers to members.
11255 Array indexing. @code{@var{a}[@var{i}]} is defined as
11256 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
11259 Function parameter list. Same precedence as @code{->}.
11262 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
11263 and @code{class} types.
11266 Doubled colons also represent the @value{GDBN} scope operator
11267 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
11271 If an operator is redefined in the user code, @value{GDBN} usually
11272 attempts to invoke the redefined version instead of using the operator's
11273 predefined meaning.
11276 @subsubsection C and C@t{++} Constants
11278 @cindex C and C@t{++} constants
11280 @value{GDBN} allows you to express the constants of C and C@t{++} in the
11285 Integer constants are a sequence of digits. Octal constants are
11286 specified by a leading @samp{0} (i.e.@: zero), and hexadecimal constants
11287 by a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
11288 @samp{l}, specifying that the constant should be treated as a
11292 Floating point constants are a sequence of digits, followed by a decimal
11293 point, followed by a sequence of digits, and optionally followed by an
11294 exponent. An exponent is of the form:
11295 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
11296 sequence of digits. The @samp{+} is optional for positive exponents.
11297 A floating-point constant may also end with a letter @samp{f} or
11298 @samp{F}, specifying that the constant should be treated as being of
11299 the @code{float} (as opposed to the default @code{double}) type; or with
11300 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
11304 Enumerated constants consist of enumerated identifiers, or their
11305 integral equivalents.
11308 Character constants are a single character surrounded by single quotes
11309 (@code{'}), or a number---the ordinal value of the corresponding character
11310 (usually its @sc{ascii} value). Within quotes, the single character may
11311 be represented by a letter or by @dfn{escape sequences}, which are of
11312 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
11313 of the character's ordinal value; or of the form @samp{\@var{x}}, where
11314 @samp{@var{x}} is a predefined special character---for example,
11315 @samp{\n} for newline.
11318 String constants are a sequence of character constants surrounded by
11319 double quotes (@code{"}). Any valid character constant (as described
11320 above) may appear. Double quotes within the string must be preceded by
11321 a backslash, so for instance @samp{"a\"b'c"} is a string of five
11325 Pointer constants are an integral value. You can also write pointers
11326 to constants using the C operator @samp{&}.
11329 Array constants are comma-separated lists surrounded by braces @samp{@{}
11330 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
11331 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
11332 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
11335 @node C Plus Plus Expressions
11336 @subsubsection C@t{++} Expressions
11338 @cindex expressions in C@t{++}
11339 @value{GDBN} expression handling can interpret most C@t{++} expressions.
11341 @cindex debugging C@t{++} programs
11342 @cindex C@t{++} compilers
11343 @cindex debug formats and C@t{++}
11344 @cindex @value{NGCC} and C@t{++}
11346 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the
11347 proper compiler and the proper debug format. Currently, @value{GDBN}
11348 works best when debugging C@t{++} code that is compiled with
11349 @value{NGCC} 2.95.3 or with @value{NGCC} 3.1 or newer, using the options
11350 @option{-gdwarf-2} or @option{-gstabs+}. DWARF 2 is preferred over
11351 stabs+. Most configurations of @value{NGCC} emit either DWARF 2 or
11352 stabs+ as their default debug format, so you usually don't need to
11353 specify a debug format explicitly. Other compilers and/or debug formats
11354 are likely to work badly or not at all when using @value{GDBN} to debug
11360 @cindex member functions
11362 Member function calls are allowed; you can use expressions like
11365 count = aml->GetOriginal(x, y)
11368 @vindex this@r{, inside C@t{++} member functions}
11369 @cindex namespace in C@t{++}
11371 While a member function is active (in the selected stack frame), your
11372 expressions have the same namespace available as the member function;
11373 that is, @value{GDBN} allows implicit references to the class instance
11374 pointer @code{this} following the same rules as C@t{++}.
11376 @cindex call overloaded functions
11377 @cindex overloaded functions, calling
11378 @cindex type conversions in C@t{++}
11380 You can call overloaded functions; @value{GDBN} resolves the function
11381 call to the right definition, with some restrictions. @value{GDBN} does not
11382 perform overload resolution involving user-defined type conversions,
11383 calls to constructors, or instantiations of templates that do not exist
11384 in the program. It also cannot handle ellipsis argument lists or
11387 It does perform integral conversions and promotions, floating-point
11388 promotions, arithmetic conversions, pointer conversions, conversions of
11389 class objects to base classes, and standard conversions such as those of
11390 functions or arrays to pointers; it requires an exact match on the
11391 number of function arguments.
11393 Overload resolution is always performed, unless you have specified
11394 @code{set overload-resolution off}. @xref{Debugging C Plus Plus,
11395 ,@value{GDBN} Features for C@t{++}}.
11397 You must specify @code{set overload-resolution off} in order to use an
11398 explicit function signature to call an overloaded function, as in
11400 p 'foo(char,int)'('x', 13)
11403 The @value{GDBN} command-completion facility can simplify this;
11404 see @ref{Completion, ,Command Completion}.
11406 @cindex reference declarations
11408 @value{GDBN} understands variables declared as C@t{++} references; you can use
11409 them in expressions just as you do in C@t{++} source---they are automatically
11412 In the parameter list shown when @value{GDBN} displays a frame, the values of
11413 reference variables are not displayed (unlike other variables); this
11414 avoids clutter, since references are often used for large structures.
11415 The @emph{address} of a reference variable is always shown, unless
11416 you have specified @samp{set print address off}.
11419 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
11420 expressions can use it just as expressions in your program do. Since
11421 one scope may be defined in another, you can use @code{::} repeatedly if
11422 necessary, for example in an expression like
11423 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
11424 resolving name scope by reference to source files, in both C and C@t{++}
11425 debugging (@pxref{Variables, ,Program Variables}).
11428 In addition, when used with HP's C@t{++} compiler, @value{GDBN} supports
11429 calling virtual functions correctly, printing out virtual bases of
11430 objects, calling functions in a base subobject, casting objects, and
11431 invoking user-defined operators.
11434 @subsubsection C and C@t{++} Defaults
11436 @cindex C and C@t{++} defaults
11438 If you allow @value{GDBN} to set type and range checking automatically, they
11439 both default to @code{off} whenever the working language changes to
11440 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
11441 selects the working language.
11443 If you allow @value{GDBN} to set the language automatically, it
11444 recognizes source files whose names end with @file{.c}, @file{.C}, or
11445 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
11446 these files, it sets the working language to C or C@t{++}.
11447 @xref{Automatically, ,Having @value{GDBN} Infer the Source Language},
11448 for further details.
11450 @c Type checking is (a) primarily motivated by Modula-2, and (b)
11451 @c unimplemented. If (b) changes, it might make sense to let this node
11452 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
11455 @subsubsection C and C@t{++} Type and Range Checks
11457 @cindex C and C@t{++} checks
11459 By default, when @value{GDBN} parses C or C@t{++} expressions, type checking
11460 is not used. However, if you turn type checking on, @value{GDBN}
11461 considers two variables type equivalent if:
11465 The two variables are structured and have the same structure, union, or
11469 The two variables have the same type name, or types that have been
11470 declared equivalent through @code{typedef}.
11473 @c leaving this out because neither J Gilmore nor R Pesch understand it.
11476 The two @code{struct}, @code{union}, or @code{enum} variables are
11477 declared in the same declaration. (Note: this may not be true for all C
11482 Range checking, if turned on, is done on mathematical operations. Array
11483 indices are not checked, since they are often used to index a pointer
11484 that is not itself an array.
11487 @subsubsection @value{GDBN} and C
11489 The @code{set print union} and @code{show print union} commands apply to
11490 the @code{union} type. When set to @samp{on}, any @code{union} that is
11491 inside a @code{struct} or @code{class} is also printed. Otherwise, it
11492 appears as @samp{@{...@}}.
11494 The @code{@@} operator aids in the debugging of dynamic arrays, formed
11495 with pointers and a memory allocation function. @xref{Expressions,
11498 @node Debugging C Plus Plus
11499 @subsubsection @value{GDBN} Features for C@t{++}
11501 @cindex commands for C@t{++}
11503 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
11504 designed specifically for use with C@t{++}. Here is a summary:
11507 @cindex break in overloaded functions
11508 @item @r{breakpoint menus}
11509 When you want a breakpoint in a function whose name is overloaded,
11510 @value{GDBN} has the capability to display a menu of possible breakpoint
11511 locations to help you specify which function definition you want.
11512 @xref{Ambiguous Expressions,,Ambiguous Expressions}.
11514 @cindex overloading in C@t{++}
11515 @item rbreak @var{regex}
11516 Setting breakpoints using regular expressions is helpful for setting
11517 breakpoints on overloaded functions that are not members of any special
11519 @xref{Set Breaks, ,Setting Breakpoints}.
11521 @cindex C@t{++} exception handling
11524 Debug C@t{++} exception handling using these commands. @xref{Set
11525 Catchpoints, , Setting Catchpoints}.
11527 @cindex inheritance
11528 @item ptype @var{typename}
11529 Print inheritance relationships as well as other information for type
11531 @xref{Symbols, ,Examining the Symbol Table}.
11533 @cindex C@t{++} symbol display
11534 @item set print demangle
11535 @itemx show print demangle
11536 @itemx set print asm-demangle
11537 @itemx show print asm-demangle
11538 Control whether C@t{++} symbols display in their source form, both when
11539 displaying code as C@t{++} source and when displaying disassemblies.
11540 @xref{Print Settings, ,Print Settings}.
11542 @item set print object
11543 @itemx show print object
11544 Choose whether to print derived (actual) or declared types of objects.
11545 @xref{Print Settings, ,Print Settings}.
11547 @item set print vtbl
11548 @itemx show print vtbl
11549 Control the format for printing virtual function tables.
11550 @xref{Print Settings, ,Print Settings}.
11551 (The @code{vtbl} commands do not work on programs compiled with the HP
11552 ANSI C@t{++} compiler (@code{aCC}).)
11554 @kindex set overload-resolution
11555 @cindex overloaded functions, overload resolution
11556 @item set overload-resolution on
11557 Enable overload resolution for C@t{++} expression evaluation. The default
11558 is on. For overloaded functions, @value{GDBN} evaluates the arguments
11559 and searches for a function whose signature matches the argument types,
11560 using the standard C@t{++} conversion rules (see @ref{C Plus Plus
11561 Expressions, ,C@t{++} Expressions}, for details).
11562 If it cannot find a match, it emits a message.
11564 @item set overload-resolution off
11565 Disable overload resolution for C@t{++} expression evaluation. For
11566 overloaded functions that are not class member functions, @value{GDBN}
11567 chooses the first function of the specified name that it finds in the
11568 symbol table, whether or not its arguments are of the correct type. For
11569 overloaded functions that are class member functions, @value{GDBN}
11570 searches for a function whose signature @emph{exactly} matches the
11573 @kindex show overload-resolution
11574 @item show overload-resolution
11575 Show the current setting of overload resolution.
11577 @item @r{Overloaded symbol names}
11578 You can specify a particular definition of an overloaded symbol, using
11579 the same notation that is used to declare such symbols in C@t{++}: type
11580 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
11581 also use the @value{GDBN} command-line word completion facilities to list the
11582 available choices, or to finish the type list for you.
11583 @xref{Completion,, Command Completion}, for details on how to do this.
11586 @node Decimal Floating Point
11587 @subsubsection Decimal Floating Point format
11588 @cindex decimal floating point format
11590 @value{GDBN} can examine, set and perform computations with numbers in
11591 decimal floating point format, which in the C language correspond to the
11592 @code{_Decimal32}, @code{_Decimal64} and @code{_Decimal128} types as
11593 specified by the extension to support decimal floating-point arithmetic.
11595 There are two encodings in use, depending on the architecture: BID (Binary
11596 Integer Decimal) for x86 and x86-64, and DPD (Densely Packed Decimal) for
11597 PowerPC. @value{GDBN} will use the appropriate encoding for the configured
11600 Because of a limitation in @file{libdecnumber}, the library used by @value{GDBN}
11601 to manipulate decimal floating point numbers, it is not possible to convert
11602 (using a cast, for example) integers wider than 32-bit to decimal float.
11604 In addition, in order to imitate @value{GDBN}'s behaviour with binary floating
11605 point computations, error checking in decimal float operations ignores
11606 underflow, overflow and divide by zero exceptions.
11608 In the PowerPC architecture, @value{GDBN} provides a set of pseudo-registers
11609 to inspect @code{_Decimal128} values stored in floating point registers.
11610 See @ref{PowerPC,,PowerPC} for more details.
11613 @subsection Objective-C
11615 @cindex Objective-C
11616 This section provides information about some commands and command
11617 options that are useful for debugging Objective-C code. See also
11618 @ref{Symbols, info classes}, and @ref{Symbols, info selectors}, for a
11619 few more commands specific to Objective-C support.
11622 * Method Names in Commands::
11623 * The Print Command with Objective-C::
11626 @node Method Names in Commands
11627 @subsubsection Method Names in Commands
11629 The following commands have been extended to accept Objective-C method
11630 names as line specifications:
11632 @kindex clear@r{, and Objective-C}
11633 @kindex break@r{, and Objective-C}
11634 @kindex info line@r{, and Objective-C}
11635 @kindex jump@r{, and Objective-C}
11636 @kindex list@r{, and Objective-C}
11640 @item @code{info line}
11645 A fully qualified Objective-C method name is specified as
11648 -[@var{Class} @var{methodName}]
11651 where the minus sign is used to indicate an instance method and a
11652 plus sign (not shown) is used to indicate a class method. The class
11653 name @var{Class} and method name @var{methodName} are enclosed in
11654 brackets, similar to the way messages are specified in Objective-C
11655 source code. For example, to set a breakpoint at the @code{create}
11656 instance method of class @code{Fruit} in the program currently being
11660 break -[Fruit create]
11663 To list ten program lines around the @code{initialize} class method,
11667 list +[NSText initialize]
11670 In the current version of @value{GDBN}, the plus or minus sign is
11671 required. In future versions of @value{GDBN}, the plus or minus
11672 sign will be optional, but you can use it to narrow the search. It
11673 is also possible to specify just a method name:
11679 You must specify the complete method name, including any colons. If
11680 your program's source files contain more than one @code{create} method,
11681 you'll be presented with a numbered list of classes that implement that
11682 method. Indicate your choice by number, or type @samp{0} to exit if
11685 As another example, to clear a breakpoint established at the
11686 @code{makeKeyAndOrderFront:} method of the @code{NSWindow} class, enter:
11689 clear -[NSWindow makeKeyAndOrderFront:]
11692 @node The Print Command with Objective-C
11693 @subsubsection The Print Command With Objective-C
11694 @cindex Objective-C, print objects
11695 @kindex print-object
11696 @kindex po @r{(@code{print-object})}
11698 The print command has also been extended to accept methods. For example:
11701 print -[@var{object} hash]
11704 @cindex print an Objective-C object description
11705 @cindex @code{_NSPrintForDebugger}, and printing Objective-C objects
11707 will tell @value{GDBN} to send the @code{hash} message to @var{object}
11708 and print the result. Also, an additional command has been added,
11709 @code{print-object} or @code{po} for short, which is meant to print
11710 the description of an object. However, this command may only work
11711 with certain Objective-C libraries that have a particular hook
11712 function, @code{_NSPrintForDebugger}, defined.
11715 @subsection Fortran
11716 @cindex Fortran-specific support in @value{GDBN}
11718 @value{GDBN} can be used to debug programs written in Fortran, but it
11719 currently supports only the features of Fortran 77 language.
11721 @cindex trailing underscore, in Fortran symbols
11722 Some Fortran compilers (@sc{gnu} Fortran 77 and Fortran 95 compilers
11723 among them) append an underscore to the names of variables and
11724 functions. When you debug programs compiled by those compilers, you
11725 will need to refer to variables and functions with a trailing
11729 * Fortran Operators:: Fortran operators and expressions
11730 * Fortran Defaults:: Default settings for Fortran
11731 * Special Fortran Commands:: Special @value{GDBN} commands for Fortran
11734 @node Fortran Operators
11735 @subsubsection Fortran Operators and Expressions
11737 @cindex Fortran operators and expressions
11739 Operators must be defined on values of specific types. For instance,
11740 @code{+} is defined on numbers, but not on characters or other non-
11741 arithmetic types. Operators are often defined on groups of types.
11745 The exponentiation operator. It raises the first operand to the power
11749 The range operator. Normally used in the form of array(low:high) to
11750 represent a section of array.
11753 The access component operator. Normally used to access elements in derived
11754 types. Also suitable for unions. As unions aren't part of regular Fortran,
11755 this can only happen when accessing a register that uses a gdbarch-defined
11759 @node Fortran Defaults
11760 @subsubsection Fortran Defaults
11762 @cindex Fortran Defaults
11764 Fortran symbols are usually case-insensitive, so @value{GDBN} by
11765 default uses case-insensitive matches for Fortran symbols. You can
11766 change that with the @samp{set case-insensitive} command, see
11767 @ref{Symbols}, for the details.
11769 @node Special Fortran Commands
11770 @subsubsection Special Fortran Commands
11772 @cindex Special Fortran commands
11774 @value{GDBN} has some commands to support Fortran-specific features,
11775 such as displaying common blocks.
11778 @cindex @code{COMMON} blocks, Fortran
11779 @kindex info common
11780 @item info common @r{[}@var{common-name}@r{]}
11781 This command prints the values contained in the Fortran @code{COMMON}
11782 block whose name is @var{common-name}. With no argument, the names of
11783 all @code{COMMON} blocks visible at the current program location are
11790 @cindex Pascal support in @value{GDBN}, limitations
11791 Debugging Pascal programs which use sets, subranges, file variables, or
11792 nested functions does not currently work. @value{GDBN} does not support
11793 entering expressions, printing values, or similar features using Pascal
11796 The Pascal-specific command @code{set print pascal_static-members}
11797 controls whether static members of Pascal objects are displayed.
11798 @xref{Print Settings, pascal_static-members}.
11801 @subsection Modula-2
11803 @cindex Modula-2, @value{GDBN} support
11805 The extensions made to @value{GDBN} to support Modula-2 only support
11806 output from the @sc{gnu} Modula-2 compiler (which is currently being
11807 developed). Other Modula-2 compilers are not currently supported, and
11808 attempting to debug executables produced by them is most likely
11809 to give an error as @value{GDBN} reads in the executable's symbol
11812 @cindex expressions in Modula-2
11814 * M2 Operators:: Built-in operators
11815 * Built-In Func/Proc:: Built-in functions and procedures
11816 * M2 Constants:: Modula-2 constants
11817 * M2 Types:: Modula-2 types
11818 * M2 Defaults:: Default settings for Modula-2
11819 * Deviations:: Deviations from standard Modula-2
11820 * M2 Checks:: Modula-2 type and range checks
11821 * M2 Scope:: The scope operators @code{::} and @code{.}
11822 * GDB/M2:: @value{GDBN} and Modula-2
11826 @subsubsection Operators
11827 @cindex Modula-2 operators
11829 Operators must be defined on values of specific types. For instance,
11830 @code{+} is defined on numbers, but not on structures. Operators are
11831 often defined on groups of types. For the purposes of Modula-2, the
11832 following definitions hold:
11837 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
11841 @emph{Character types} consist of @code{CHAR} and its subranges.
11844 @emph{Floating-point types} consist of @code{REAL}.
11847 @emph{Pointer types} consist of anything declared as @code{POINTER TO
11851 @emph{Scalar types} consist of all of the above.
11854 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
11857 @emph{Boolean types} consist of @code{BOOLEAN}.
11861 The following operators are supported, and appear in order of
11862 increasing precedence:
11866 Function argument or array index separator.
11869 Assignment. The value of @var{var} @code{:=} @var{value} is
11873 Less than, greater than on integral, floating-point, or enumerated
11877 Less than or equal to, greater than or equal to
11878 on integral, floating-point and enumerated types, or set inclusion on
11879 set types. Same precedence as @code{<}.
11881 @item =@r{, }<>@r{, }#
11882 Equality and two ways of expressing inequality, valid on scalar types.
11883 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
11884 available for inequality, since @code{#} conflicts with the script
11888 Set membership. Defined on set types and the types of their members.
11889 Same precedence as @code{<}.
11892 Boolean disjunction. Defined on boolean types.
11895 Boolean conjunction. Defined on boolean types.
11898 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
11901 Addition and subtraction on integral and floating-point types, or union
11902 and difference on set types.
11905 Multiplication on integral and floating-point types, or set intersection
11909 Division on floating-point types, or symmetric set difference on set
11910 types. Same precedence as @code{*}.
11913 Integer division and remainder. Defined on integral types. Same
11914 precedence as @code{*}.
11917 Negative. Defined on @code{INTEGER} and @code{REAL} data.
11920 Pointer dereferencing. Defined on pointer types.
11923 Boolean negation. Defined on boolean types. Same precedence as
11927 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
11928 precedence as @code{^}.
11931 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
11934 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
11938 @value{GDBN} and Modula-2 scope operators.
11942 @emph{Warning:} Set expressions and their operations are not yet supported, so @value{GDBN}
11943 treats the use of the operator @code{IN}, or the use of operators
11944 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
11945 @code{<=}, and @code{>=} on sets as an error.
11949 @node Built-In Func/Proc
11950 @subsubsection Built-in Functions and Procedures
11951 @cindex Modula-2 built-ins
11953 Modula-2 also makes available several built-in procedures and functions.
11954 In describing these, the following metavariables are used:
11959 represents an @code{ARRAY} variable.
11962 represents a @code{CHAR} constant or variable.
11965 represents a variable or constant of integral type.
11968 represents an identifier that belongs to a set. Generally used in the
11969 same function with the metavariable @var{s}. The type of @var{s} should
11970 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
11973 represents a variable or constant of integral or floating-point type.
11976 represents a variable or constant of floating-point type.
11982 represents a variable.
11985 represents a variable or constant of one of many types. See the
11986 explanation of the function for details.
11989 All Modula-2 built-in procedures also return a result, described below.
11993 Returns the absolute value of @var{n}.
11996 If @var{c} is a lower case letter, it returns its upper case
11997 equivalent, otherwise it returns its argument.
12000 Returns the character whose ordinal value is @var{i}.
12003 Decrements the value in the variable @var{v} by one. Returns the new value.
12005 @item DEC(@var{v},@var{i})
12006 Decrements the value in the variable @var{v} by @var{i}. Returns the
12009 @item EXCL(@var{m},@var{s})
12010 Removes the element @var{m} from the set @var{s}. Returns the new
12013 @item FLOAT(@var{i})
12014 Returns the floating point equivalent of the integer @var{i}.
12016 @item HIGH(@var{a})
12017 Returns the index of the last member of @var{a}.
12020 Increments the value in the variable @var{v} by one. Returns the new value.
12022 @item INC(@var{v},@var{i})
12023 Increments the value in the variable @var{v} by @var{i}. Returns the
12026 @item INCL(@var{m},@var{s})
12027 Adds the element @var{m} to the set @var{s} if it is not already
12028 there. Returns the new set.
12031 Returns the maximum value of the type @var{t}.
12034 Returns the minimum value of the type @var{t}.
12037 Returns boolean TRUE if @var{i} is an odd number.
12040 Returns the ordinal value of its argument. For example, the ordinal
12041 value of a character is its @sc{ascii} value (on machines supporting the
12042 @sc{ascii} character set). @var{x} must be of an ordered type, which include
12043 integral, character and enumerated types.
12045 @item SIZE(@var{x})
12046 Returns the size of its argument. @var{x} can be a variable or a type.
12048 @item TRUNC(@var{r})
12049 Returns the integral part of @var{r}.
12051 @item TSIZE(@var{x})
12052 Returns the size of its argument. @var{x} can be a variable or a type.
12054 @item VAL(@var{t},@var{i})
12055 Returns the member of the type @var{t} whose ordinal value is @var{i}.
12059 @emph{Warning:} Sets and their operations are not yet supported, so
12060 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
12064 @cindex Modula-2 constants
12066 @subsubsection Constants
12068 @value{GDBN} allows you to express the constants of Modula-2 in the following
12074 Integer constants are simply a sequence of digits. When used in an
12075 expression, a constant is interpreted to be type-compatible with the
12076 rest of the expression. Hexadecimal integers are specified by a
12077 trailing @samp{H}, and octal integers by a trailing @samp{B}.
12080 Floating point constants appear as a sequence of digits, followed by a
12081 decimal point and another sequence of digits. An optional exponent can
12082 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
12083 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
12084 digits of the floating point constant must be valid decimal (base 10)
12088 Character constants consist of a single character enclosed by a pair of
12089 like quotes, either single (@code{'}) or double (@code{"}). They may
12090 also be expressed by their ordinal value (their @sc{ascii} value, usually)
12091 followed by a @samp{C}.
12094 String constants consist of a sequence of characters enclosed by a
12095 pair of like quotes, either single (@code{'}) or double (@code{"}).
12096 Escape sequences in the style of C are also allowed. @xref{C
12097 Constants, ,C and C@t{++} Constants}, for a brief explanation of escape
12101 Enumerated constants consist of an enumerated identifier.
12104 Boolean constants consist of the identifiers @code{TRUE} and
12108 Pointer constants consist of integral values only.
12111 Set constants are not yet supported.
12115 @subsubsection Modula-2 Types
12116 @cindex Modula-2 types
12118 Currently @value{GDBN} can print the following data types in Modula-2
12119 syntax: array types, record types, set types, pointer types, procedure
12120 types, enumerated types, subrange types and base types. You can also
12121 print the contents of variables declared using these type.
12122 This section gives a number of simple source code examples together with
12123 sample @value{GDBN} sessions.
12125 The first example contains the following section of code:
12134 and you can request @value{GDBN} to interrogate the type and value of
12135 @code{r} and @code{s}.
12138 (@value{GDBP}) print s
12140 (@value{GDBP}) ptype s
12142 (@value{GDBP}) print r
12144 (@value{GDBP}) ptype r
12149 Likewise if your source code declares @code{s} as:
12153 s: SET ['A'..'Z'] ;
12157 then you may query the type of @code{s} by:
12160 (@value{GDBP}) ptype s
12161 type = SET ['A'..'Z']
12165 Note that at present you cannot interactively manipulate set
12166 expressions using the debugger.
12168 The following example shows how you might declare an array in Modula-2
12169 and how you can interact with @value{GDBN} to print its type and contents:
12173 s: ARRAY [-10..10] OF CHAR ;
12177 (@value{GDBP}) ptype s
12178 ARRAY [-10..10] OF CHAR
12181 Note that the array handling is not yet complete and although the type
12182 is printed correctly, expression handling still assumes that all
12183 arrays have a lower bound of zero and not @code{-10} as in the example
12186 Here are some more type related Modula-2 examples:
12190 colour = (blue, red, yellow, green) ;
12191 t = [blue..yellow] ;
12199 The @value{GDBN} interaction shows how you can query the data type
12200 and value of a variable.
12203 (@value{GDBP}) print s
12205 (@value{GDBP}) ptype t
12206 type = [blue..yellow]
12210 In this example a Modula-2 array is declared and its contents
12211 displayed. Observe that the contents are written in the same way as
12212 their @code{C} counterparts.
12216 s: ARRAY [1..5] OF CARDINAL ;
12222 (@value{GDBP}) print s
12223 $1 = @{1, 0, 0, 0, 0@}
12224 (@value{GDBP}) ptype s
12225 type = ARRAY [1..5] OF CARDINAL
12228 The Modula-2 language interface to @value{GDBN} also understands
12229 pointer types as shown in this example:
12233 s: POINTER TO ARRAY [1..5] OF CARDINAL ;
12240 and you can request that @value{GDBN} describes the type of @code{s}.
12243 (@value{GDBP}) ptype s
12244 type = POINTER TO ARRAY [1..5] OF CARDINAL
12247 @value{GDBN} handles compound types as we can see in this example.
12248 Here we combine array types, record types, pointer types and subrange
12259 myarray = ARRAY myrange OF CARDINAL ;
12260 myrange = [-2..2] ;
12262 s: POINTER TO ARRAY myrange OF foo ;
12266 and you can ask @value{GDBN} to describe the type of @code{s} as shown
12270 (@value{GDBP}) ptype s
12271 type = POINTER TO ARRAY [-2..2] OF foo = RECORD
12274 f3 : ARRAY [-2..2] OF CARDINAL;
12279 @subsubsection Modula-2 Defaults
12280 @cindex Modula-2 defaults
12282 If type and range checking are set automatically by @value{GDBN}, they
12283 both default to @code{on} whenever the working language changes to
12284 Modula-2. This happens regardless of whether you or @value{GDBN}
12285 selected the working language.
12287 If you allow @value{GDBN} to set the language automatically, then entering
12288 code compiled from a file whose name ends with @file{.mod} sets the
12289 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN}
12290 Infer the Source Language}, for further details.
12293 @subsubsection Deviations from Standard Modula-2
12294 @cindex Modula-2, deviations from
12296 A few changes have been made to make Modula-2 programs easier to debug.
12297 This is done primarily via loosening its type strictness:
12301 Unlike in standard Modula-2, pointer constants can be formed by
12302 integers. This allows you to modify pointer variables during
12303 debugging. (In standard Modula-2, the actual address contained in a
12304 pointer variable is hidden from you; it can only be modified
12305 through direct assignment to another pointer variable or expression that
12306 returned a pointer.)
12309 C escape sequences can be used in strings and characters to represent
12310 non-printable characters. @value{GDBN} prints out strings with these
12311 escape sequences embedded. Single non-printable characters are
12312 printed using the @samp{CHR(@var{nnn})} format.
12315 The assignment operator (@code{:=}) returns the value of its right-hand
12319 All built-in procedures both modify @emph{and} return their argument.
12323 @subsubsection Modula-2 Type and Range Checks
12324 @cindex Modula-2 checks
12327 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
12330 @c FIXME remove warning when type/range checks added
12332 @value{GDBN} considers two Modula-2 variables type equivalent if:
12336 They are of types that have been declared equivalent via a @code{TYPE
12337 @var{t1} = @var{t2}} statement
12340 They have been declared on the same line. (Note: This is true of the
12341 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
12344 As long as type checking is enabled, any attempt to combine variables
12345 whose types are not equivalent is an error.
12347 Range checking is done on all mathematical operations, assignment, array
12348 index bounds, and all built-in functions and procedures.
12351 @subsubsection The Scope Operators @code{::} and @code{.}
12353 @cindex @code{.}, Modula-2 scope operator
12354 @cindex colon, doubled as scope operator
12356 @vindex colon-colon@r{, in Modula-2}
12357 @c Info cannot handle :: but TeX can.
12360 @vindex ::@r{, in Modula-2}
12363 There are a few subtle differences between the Modula-2 scope operator
12364 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
12369 @var{module} . @var{id}
12370 @var{scope} :: @var{id}
12374 where @var{scope} is the name of a module or a procedure,
12375 @var{module} the name of a module, and @var{id} is any declared
12376 identifier within your program, except another module.
12378 Using the @code{::} operator makes @value{GDBN} search the scope
12379 specified by @var{scope} for the identifier @var{id}. If it is not
12380 found in the specified scope, then @value{GDBN} searches all scopes
12381 enclosing the one specified by @var{scope}.
12383 Using the @code{.} operator makes @value{GDBN} search the current scope for
12384 the identifier specified by @var{id} that was imported from the
12385 definition module specified by @var{module}. With this operator, it is
12386 an error if the identifier @var{id} was not imported from definition
12387 module @var{module}, or if @var{id} is not an identifier in
12391 @subsubsection @value{GDBN} and Modula-2
12393 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
12394 Five subcommands of @code{set print} and @code{show print} apply
12395 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
12396 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
12397 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
12398 analogue in Modula-2.
12400 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
12401 with any language, is not useful with Modula-2. Its
12402 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
12403 created in Modula-2 as they can in C or C@t{++}. However, because an
12404 address can be specified by an integral constant, the construct
12405 @samp{@{@var{type}@}@var{adrexp}} is still useful.
12407 @cindex @code{#} in Modula-2
12408 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
12409 interpreted as the beginning of a comment. Use @code{<>} instead.
12415 The extensions made to @value{GDBN} for Ada only support
12416 output from the @sc{gnu} Ada (GNAT) compiler.
12417 Other Ada compilers are not currently supported, and
12418 attempting to debug executables produced by them is most likely
12422 @cindex expressions in Ada
12424 * Ada Mode Intro:: General remarks on the Ada syntax
12425 and semantics supported by Ada mode
12427 * Omissions from Ada:: Restrictions on the Ada expression syntax.
12428 * Additions to Ada:: Extensions of the Ada expression syntax.
12429 * Stopping Before Main Program:: Debugging the program during elaboration.
12430 * Ada Tasks:: Listing and setting breakpoints in tasks.
12431 * Ada Tasks and Core Files:: Tasking Support when Debugging Core Files
12432 * Ada Glitches:: Known peculiarities of Ada mode.
12435 @node Ada Mode Intro
12436 @subsubsection Introduction
12437 @cindex Ada mode, general
12439 The Ada mode of @value{GDBN} supports a fairly large subset of Ada expression
12440 syntax, with some extensions.
12441 The philosophy behind the design of this subset is
12445 That @value{GDBN} should provide basic literals and access to operations for
12446 arithmetic, dereferencing, field selection, indexing, and subprogram calls,
12447 leaving more sophisticated computations to subprograms written into the
12448 program (which therefore may be called from @value{GDBN}).
12451 That type safety and strict adherence to Ada language restrictions
12452 are not particularly important to the @value{GDBN} user.
12455 That brevity is important to the @value{GDBN} user.
12458 Thus, for brevity, the debugger acts as if all names declared in
12459 user-written packages are directly visible, even if they are not visible
12460 according to Ada rules, thus making it unnecessary to fully qualify most
12461 names with their packages, regardless of context. Where this causes
12462 ambiguity, @value{GDBN} asks the user's intent.
12464 The debugger will start in Ada mode if it detects an Ada main program.
12465 As for other languages, it will enter Ada mode when stopped in a program that
12466 was translated from an Ada source file.
12468 While in Ada mode, you may use `@t{--}' for comments. This is useful
12469 mostly for documenting command files. The standard @value{GDBN} comment
12470 (@samp{#}) still works at the beginning of a line in Ada mode, but not in the
12471 middle (to allow based literals).
12473 The debugger supports limited overloading. Given a subprogram call in which
12474 the function symbol has multiple definitions, it will use the number of
12475 actual parameters and some information about their types to attempt to narrow
12476 the set of definitions. It also makes very limited use of context, preferring
12477 procedures to functions in the context of the @code{call} command, and
12478 functions to procedures elsewhere.
12480 @node Omissions from Ada
12481 @subsubsection Omissions from Ada
12482 @cindex Ada, omissions from
12484 Here are the notable omissions from the subset:
12488 Only a subset of the attributes are supported:
12492 @t{'First}, @t{'Last}, and @t{'Length}
12493 on array objects (not on types and subtypes).
12496 @t{'Min} and @t{'Max}.
12499 @t{'Pos} and @t{'Val}.
12505 @t{'Range} on array objects (not subtypes), but only as the right
12506 operand of the membership (@code{in}) operator.
12509 @t{'Access}, @t{'Unchecked_Access}, and
12510 @t{'Unrestricted_Access} (a GNAT extension).
12518 @code{Characters.Latin_1} are not available and
12519 concatenation is not implemented. Thus, escape characters in strings are
12520 not currently available.
12523 Equality tests (@samp{=} and @samp{/=}) on arrays test for bitwise
12524 equality of representations. They will generally work correctly
12525 for strings and arrays whose elements have integer or enumeration types.
12526 They may not work correctly for arrays whose element
12527 types have user-defined equality, for arrays of real values
12528 (in particular, IEEE-conformant floating point, because of negative
12529 zeroes and NaNs), and for arrays whose elements contain unused bits with
12530 indeterminate values.
12533 The other component-by-component array operations (@code{and}, @code{or},
12534 @code{xor}, @code{not}, and relational tests other than equality)
12535 are not implemented.
12538 @cindex array aggregates (Ada)
12539 @cindex record aggregates (Ada)
12540 @cindex aggregates (Ada)
12541 There is limited support for array and record aggregates. They are
12542 permitted only on the right sides of assignments, as in these examples:
12545 (@value{GDBP}) set An_Array := (1, 2, 3, 4, 5, 6)
12546 (@value{GDBP}) set An_Array := (1, others => 0)
12547 (@value{GDBP}) set An_Array := (0|4 => 1, 1..3 => 2, 5 => 6)
12548 (@value{GDBP}) set A_2D_Array := ((1, 2, 3), (4, 5, 6), (7, 8, 9))
12549 (@value{GDBP}) set A_Record := (1, "Peter", True);
12550 (@value{GDBP}) set A_Record := (Name => "Peter", Id => 1, Alive => True)
12554 discriminant's value by assigning an aggregate has an
12555 undefined effect if that discriminant is used within the record.
12556 However, you can first modify discriminants by directly assigning to
12557 them (which normally would not be allowed in Ada), and then performing an
12558 aggregate assignment. For example, given a variable @code{A_Rec}
12559 declared to have a type such as:
12562 type Rec (Len : Small_Integer := 0) is record
12564 Vals : IntArray (1 .. Len);
12568 you can assign a value with a different size of @code{Vals} with two
12572 (@value{GDBP}) set A_Rec.Len := 4
12573 (@value{GDBP}) set A_Rec := (Id => 42, Vals => (1, 2, 3, 4))
12576 As this example also illustrates, @value{GDBN} is very loose about the usual
12577 rules concerning aggregates. You may leave out some of the
12578 components of an array or record aggregate (such as the @code{Len}
12579 component in the assignment to @code{A_Rec} above); they will retain their
12580 original values upon assignment. You may freely use dynamic values as
12581 indices in component associations. You may even use overlapping or
12582 redundant component associations, although which component values are
12583 assigned in such cases is not defined.
12586 Calls to dispatching subprograms are not implemented.
12589 The overloading algorithm is much more limited (i.e., less selective)
12590 than that of real Ada. It makes only limited use of the context in
12591 which a subexpression appears to resolve its meaning, and it is much
12592 looser in its rules for allowing type matches. As a result, some
12593 function calls will be ambiguous, and the user will be asked to choose
12594 the proper resolution.
12597 The @code{new} operator is not implemented.
12600 Entry calls are not implemented.
12603 Aside from printing, arithmetic operations on the native VAX floating-point
12604 formats are not supported.
12607 It is not possible to slice a packed array.
12610 The names @code{True} and @code{False}, when not part of a qualified name,
12611 are interpreted as if implicitly prefixed by @code{Standard}, regardless of
12613 Should your program
12614 redefine these names in a package or procedure (at best a dubious practice),
12615 you will have to use fully qualified names to access their new definitions.
12618 @node Additions to Ada
12619 @subsubsection Additions to Ada
12620 @cindex Ada, deviations from
12622 As it does for other languages, @value{GDBN} makes certain generic
12623 extensions to Ada (@pxref{Expressions}):
12627 If the expression @var{E} is a variable residing in memory (typically
12628 a local variable or array element) and @var{N} is a positive integer,
12629 then @code{@var{E}@@@var{N}} displays the values of @var{E} and the
12630 @var{N}-1 adjacent variables following it in memory as an array. In
12631 Ada, this operator is generally not necessary, since its prime use is
12632 in displaying parts of an array, and slicing will usually do this in
12633 Ada. However, there are occasional uses when debugging programs in
12634 which certain debugging information has been optimized away.
12637 @code{@var{B}::@var{var}} means ``the variable named @var{var} that
12638 appears in function or file @var{B}.'' When @var{B} is a file name,
12639 you must typically surround it in single quotes.
12642 The expression @code{@{@var{type}@} @var{addr}} means ``the variable of type
12643 @var{type} that appears at address @var{addr}.''
12646 A name starting with @samp{$} is a convenience variable
12647 (@pxref{Convenience Vars}) or a machine register (@pxref{Registers}).
12650 In addition, @value{GDBN} provides a few other shortcuts and outright
12651 additions specific to Ada:
12655 The assignment statement is allowed as an expression, returning
12656 its right-hand operand as its value. Thus, you may enter
12659 (@value{GDBP}) set x := y + 3
12660 (@value{GDBP}) print A(tmp := y + 1)
12664 The semicolon is allowed as an ``operator,'' returning as its value
12665 the value of its right-hand operand.
12666 This allows, for example,
12667 complex conditional breaks:
12670 (@value{GDBP}) break f
12671 (@value{GDBP}) condition 1 (report(i); k += 1; A(k) > 100)
12675 Rather than use catenation and symbolic character names to introduce special
12676 characters into strings, one may instead use a special bracket notation,
12677 which is also used to print strings. A sequence of characters of the form
12678 @samp{["@var{XX}"]} within a string or character literal denotes the
12679 (single) character whose numeric encoding is @var{XX} in hexadecimal. The
12680 sequence of characters @samp{["""]} also denotes a single quotation mark
12681 in strings. For example,
12683 "One line.["0a"]Next line.["0a"]"
12686 contains an ASCII newline character (@code{Ada.Characters.Latin_1.LF})
12690 The subtype used as a prefix for the attributes @t{'Pos}, @t{'Min}, and
12691 @t{'Max} is optional (and is ignored in any case). For example, it is valid
12695 (@value{GDBP}) print 'max(x, y)
12699 When printing arrays, @value{GDBN} uses positional notation when the
12700 array has a lower bound of 1, and uses a modified named notation otherwise.
12701 For example, a one-dimensional array of three integers with a lower bound
12702 of 3 might print as
12709 That is, in contrast to valid Ada, only the first component has a @code{=>}
12713 You may abbreviate attributes in expressions with any unique,
12714 multi-character subsequence of
12715 their names (an exact match gets preference).
12716 For example, you may use @t{a'len}, @t{a'gth}, or @t{a'lh}
12717 in place of @t{a'length}.
12720 @cindex quoting Ada internal identifiers
12721 Since Ada is case-insensitive, the debugger normally maps identifiers you type
12722 to lower case. The GNAT compiler uses upper-case characters for
12723 some of its internal identifiers, which are normally of no interest to users.
12724 For the rare occasions when you actually have to look at them,
12725 enclose them in angle brackets to avoid the lower-case mapping.
12728 (@value{GDBP}) print <JMPBUF_SAVE>[0]
12732 Printing an object of class-wide type or dereferencing an
12733 access-to-class-wide value will display all the components of the object's
12734 specific type (as indicated by its run-time tag). Likewise, component
12735 selection on such a value will operate on the specific type of the
12740 @node Stopping Before Main Program
12741 @subsubsection Stopping at the Very Beginning
12743 @cindex breakpointing Ada elaboration code
12744 It is sometimes necessary to debug the program during elaboration, and
12745 before reaching the main procedure.
12746 As defined in the Ada Reference
12747 Manual, the elaboration code is invoked from a procedure called
12748 @code{adainit}. To run your program up to the beginning of
12749 elaboration, simply use the following two commands:
12750 @code{tbreak adainit} and @code{run}.
12753 @subsubsection Extensions for Ada Tasks
12754 @cindex Ada, tasking
12756 Support for Ada tasks is analogous to that for threads (@pxref{Threads}).
12757 @value{GDBN} provides the following task-related commands:
12762 This command shows a list of current Ada tasks, as in the following example:
12769 (@value{GDBP}) info tasks
12770 ID TID P-ID Pri State Name
12771 1 8088000 0 15 Child Activation Wait main_task
12772 2 80a4000 1 15 Accept Statement b
12773 3 809a800 1 15 Child Activation Wait a
12774 * 4 80ae800 3 15 Runnable c
12779 In this listing, the asterisk before the last task indicates it to be the
12780 task currently being inspected.
12784 Represents @value{GDBN}'s internal task number.
12790 The parent's task ID (@value{GDBN}'s internal task number).
12793 The base priority of the task.
12796 Current state of the task.
12800 The task has been created but has not been activated. It cannot be
12804 The task is not blocked for any reason known to Ada. (It may be waiting
12805 for a mutex, though.) It is conceptually "executing" in normal mode.
12808 The task is terminated, in the sense of ARM 9.3 (5). Any dependents
12809 that were waiting on terminate alternatives have been awakened and have
12810 terminated themselves.
12812 @item Child Activation Wait
12813 The task is waiting for created tasks to complete activation.
12815 @item Accept Statement
12816 The task is waiting on an accept or selective wait statement.
12818 @item Waiting on entry call
12819 The task is waiting on an entry call.
12821 @item Async Select Wait
12822 The task is waiting to start the abortable part of an asynchronous
12826 The task is waiting on a select statement with only a delay
12829 @item Child Termination Wait
12830 The task is sleeping having completed a master within itself, and is
12831 waiting for the tasks dependent on that master to become terminated or
12832 waiting on a terminate Phase.
12834 @item Wait Child in Term Alt
12835 The task is sleeping waiting for tasks on terminate alternatives to
12836 finish terminating.
12838 @item Accepting RV with @var{taskno}
12839 The task is accepting a rendez-vous with the task @var{taskno}.
12843 Name of the task in the program.
12847 @kindex info task @var{taskno}
12848 @item info task @var{taskno}
12849 This command shows detailled informations on the specified task, as in
12850 the following example:
12855 (@value{GDBP}) info tasks
12856 ID TID P-ID Pri State Name
12857 1 8077880 0 15 Child Activation Wait main_task
12858 * 2 807c468 1 15 Runnable task_1
12859 (@value{GDBP}) info task 2
12860 Ada Task: 0x807c468
12863 Parent: 1 (main_task)
12869 @kindex task@r{ (Ada)}
12870 @cindex current Ada task ID
12871 This command prints the ID of the current task.
12877 (@value{GDBP}) info tasks
12878 ID TID P-ID Pri State Name
12879 1 8077870 0 15 Child Activation Wait main_task
12880 * 2 807c458 1 15 Runnable t
12881 (@value{GDBP}) task
12882 [Current task is 2]
12885 @item task @var{taskno}
12886 @cindex Ada task switching
12887 This command is like the @code{thread @var{threadno}}
12888 command (@pxref{Threads}). It switches the context of debugging
12889 from the current task to the given task.
12895 (@value{GDBP}) info tasks
12896 ID TID P-ID Pri State Name
12897 1 8077870 0 15 Child Activation Wait main_task
12898 * 2 807c458 1 15 Runnable t
12899 (@value{GDBP}) task 1
12900 [Switching to task 1]
12901 #0 0x8067726 in pthread_cond_wait ()
12903 #0 0x8067726 in pthread_cond_wait ()
12904 #1 0x8056714 in system.os_interface.pthread_cond_wait ()
12905 #2 0x805cb63 in system.task_primitives.operations.sleep ()
12906 #3 0x806153e in system.tasking.stages.activate_tasks ()
12907 #4 0x804aacc in un () at un.adb:5
12910 @item break @var{linespec} task @var{taskno}
12911 @itemx break @var{linespec} task @var{taskno} if @dots{}
12912 @cindex breakpoints and tasks, in Ada
12913 @cindex task breakpoints, in Ada
12914 @kindex break @dots{} task @var{taskno}@r{ (Ada)}
12915 These commands are like the @code{break @dots{} thread @dots{}}
12916 command (@pxref{Thread Stops}).
12917 @var{linespec} specifies source lines, as described
12918 in @ref{Specify Location}.
12920 Use the qualifier @samp{task @var{taskno}} with a breakpoint command
12921 to specify that you only want @value{GDBN} to stop the program when a
12922 particular Ada task reaches this breakpoint. @var{taskno} is one of the
12923 numeric task identifiers assigned by @value{GDBN}, shown in the first
12924 column of the @samp{info tasks} display.
12926 If you do not specify @samp{task @var{taskno}} when you set a
12927 breakpoint, the breakpoint applies to @emph{all} tasks of your
12930 You can use the @code{task} qualifier on conditional breakpoints as
12931 well; in this case, place @samp{task @var{taskno}} before the
12932 breakpoint condition (before the @code{if}).
12940 (@value{GDBP}) info tasks
12941 ID TID P-ID Pri State Name
12942 1 140022020 0 15 Child Activation Wait main_task
12943 2 140045060 1 15 Accept/Select Wait t2
12944 3 140044840 1 15 Runnable t1
12945 * 4 140056040 1 15 Runnable t3
12946 (@value{GDBP}) b 15 task 2
12947 Breakpoint 5 at 0x120044cb0: file test_task_debug.adb, line 15.
12948 (@value{GDBP}) cont
12953 Breakpoint 5, test_task_debug () at test_task_debug.adb:15
12955 (@value{GDBP}) info tasks
12956 ID TID P-ID Pri State Name
12957 1 140022020 0 15 Child Activation Wait main_task
12958 * 2 140045060 1 15 Runnable t2
12959 3 140044840 1 15 Runnable t1
12960 4 140056040 1 15 Delay Sleep t3
12964 @node Ada Tasks and Core Files
12965 @subsubsection Tasking Support when Debugging Core Files
12966 @cindex Ada tasking and core file debugging
12968 When inspecting a core file, as opposed to debugging a live program,
12969 tasking support may be limited or even unavailable, depending on
12970 the platform being used.
12971 For instance, on x86-linux, the list of tasks is available, but task
12972 switching is not supported. On Tru64, however, task switching will work
12975 On certain platforms, including Tru64, the debugger needs to perform some
12976 memory writes in order to provide Ada tasking support. When inspecting
12977 a core file, this means that the core file must be opened with read-write
12978 privileges, using the command @samp{"set write on"} (@pxref{Patching}).
12979 Under these circumstances, you should make a backup copy of the core
12980 file before inspecting it with @value{GDBN}.
12983 @subsubsection Known Peculiarities of Ada Mode
12984 @cindex Ada, problems
12986 Besides the omissions listed previously (@pxref{Omissions from Ada}),
12987 we know of several problems with and limitations of Ada mode in
12989 some of which will be fixed with planned future releases of the debugger
12990 and the GNU Ada compiler.
12994 Currently, the debugger
12995 has insufficient information to determine whether certain pointers represent
12996 pointers to objects or the objects themselves.
12997 Thus, the user may have to tack an extra @code{.all} after an expression
12998 to get it printed properly.
13001 Static constants that the compiler chooses not to materialize as objects in
13002 storage are invisible to the debugger.
13005 Named parameter associations in function argument lists are ignored (the
13006 argument lists are treated as positional).
13009 Many useful library packages are currently invisible to the debugger.
13012 Fixed-point arithmetic, conversions, input, and output is carried out using
13013 floating-point arithmetic, and may give results that only approximate those on
13017 The GNAT compiler never generates the prefix @code{Standard} for any of
13018 the standard symbols defined by the Ada language. @value{GDBN} knows about
13019 this: it will strip the prefix from names when you use it, and will never
13020 look for a name you have so qualified among local symbols, nor match against
13021 symbols in other packages or subprograms. If you have
13022 defined entities anywhere in your program other than parameters and
13023 local variables whose simple names match names in @code{Standard},
13024 GNAT's lack of qualification here can cause confusion. When this happens,
13025 you can usually resolve the confusion
13026 by qualifying the problematic names with package
13027 @code{Standard} explicitly.
13030 Older versions of the compiler sometimes generate erroneous debugging
13031 information, resulting in the debugger incorrectly printing the value
13032 of affected entities. In some cases, the debugger is able to work
13033 around an issue automatically. In other cases, the debugger is able
13034 to work around the issue, but the work-around has to be specifically
13037 @kindex set ada trust-PAD-over-XVS
13038 @kindex show ada trust-PAD-over-XVS
13041 @item set ada trust-PAD-over-XVS on
13042 Configure GDB to strictly follow the GNAT encoding when computing the
13043 value of Ada entities, particularly when @code{PAD} and @code{PAD___XVS}
13044 types are involved (see @code{ada/exp_dbug.ads} in the GCC sources for
13045 a complete description of the encoding used by the GNAT compiler).
13046 This is the default.
13048 @item set ada trust-PAD-over-XVS off
13049 This is related to the encoding using by the GNAT compiler. If @value{GDBN}
13050 sometimes prints the wrong value for certain entities, changing @code{ada
13051 trust-PAD-over-XVS} to @code{off} activates a work-around which may fix
13052 the issue. It is always safe to set @code{ada trust-PAD-over-XVS} to
13053 @code{off}, but this incurs a slight performance penalty, so it is
13054 recommended to leave this setting to @code{on} unless necessary.
13058 @node Unsupported Languages
13059 @section Unsupported Languages
13061 @cindex unsupported languages
13062 @cindex minimal language
13063 In addition to the other fully-supported programming languages,
13064 @value{GDBN} also provides a pseudo-language, called @code{minimal}.
13065 It does not represent a real programming language, but provides a set
13066 of capabilities close to what the C or assembly languages provide.
13067 This should allow most simple operations to be performed while debugging
13068 an application that uses a language currently not supported by @value{GDBN}.
13070 If the language is set to @code{auto}, @value{GDBN} will automatically
13071 select this language if the current frame corresponds to an unsupported
13075 @chapter Examining the Symbol Table
13077 The commands described in this chapter allow you to inquire about the
13078 symbols (names of variables, functions and types) defined in your
13079 program. This information is inherent in the text of your program and
13080 does not change as your program executes. @value{GDBN} finds it in your
13081 program's symbol table, in the file indicated when you started @value{GDBN}
13082 (@pxref{File Options, ,Choosing Files}), or by one of the
13083 file-management commands (@pxref{Files, ,Commands to Specify Files}).
13085 @cindex symbol names
13086 @cindex names of symbols
13087 @cindex quoting names
13088 Occasionally, you may need to refer to symbols that contain unusual
13089 characters, which @value{GDBN} ordinarily treats as word delimiters. The
13090 most frequent case is in referring to static variables in other
13091 source files (@pxref{Variables,,Program Variables}). File names
13092 are recorded in object files as debugging symbols, but @value{GDBN} would
13093 ordinarily parse a typical file name, like @file{foo.c}, as the three words
13094 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
13095 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
13102 looks up the value of @code{x} in the scope of the file @file{foo.c}.
13105 @cindex case-insensitive symbol names
13106 @cindex case sensitivity in symbol names
13107 @kindex set case-sensitive
13108 @item set case-sensitive on
13109 @itemx set case-sensitive off
13110 @itemx set case-sensitive auto
13111 Normally, when @value{GDBN} looks up symbols, it matches their names
13112 with case sensitivity determined by the current source language.
13113 Occasionally, you may wish to control that. The command @code{set
13114 case-sensitive} lets you do that by specifying @code{on} for
13115 case-sensitive matches or @code{off} for case-insensitive ones. If
13116 you specify @code{auto}, case sensitivity is reset to the default
13117 suitable for the source language. The default is case-sensitive
13118 matches for all languages except for Fortran, for which the default is
13119 case-insensitive matches.
13121 @kindex show case-sensitive
13122 @item show case-sensitive
13123 This command shows the current setting of case sensitivity for symbols
13126 @kindex info address
13127 @cindex address of a symbol
13128 @item info address @var{symbol}
13129 Describe where the data for @var{symbol} is stored. For a register
13130 variable, this says which register it is kept in. For a non-register
13131 local variable, this prints the stack-frame offset at which the variable
13134 Note the contrast with @samp{print &@var{symbol}}, which does not work
13135 at all for a register variable, and for a stack local variable prints
13136 the exact address of the current instantiation of the variable.
13138 @kindex info symbol
13139 @cindex symbol from address
13140 @cindex closest symbol and offset for an address
13141 @item info symbol @var{addr}
13142 Print the name of a symbol which is stored at the address @var{addr}.
13143 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
13144 nearest symbol and an offset from it:
13147 (@value{GDBP}) info symbol 0x54320
13148 _initialize_vx + 396 in section .text
13152 This is the opposite of the @code{info address} command. You can use
13153 it to find out the name of a variable or a function given its address.
13155 For dynamically linked executables, the name of executable or shared
13156 library containing the symbol is also printed:
13159 (@value{GDBP}) info symbol 0x400225
13160 _start + 5 in section .text of /tmp/a.out
13161 (@value{GDBP}) info symbol 0x2aaaac2811cf
13162 __read_nocancel + 6 in section .text of /usr/lib64/libc.so.6
13166 @item whatis [@var{arg}]
13167 Print the data type of @var{arg}, which can be either an expression or
13168 a data type. With no argument, print the data type of @code{$}, the
13169 last value in the value history. If @var{arg} is an expression, it is
13170 not actually evaluated, and any side-effecting operations (such as
13171 assignments or function calls) inside it do not take place. If
13172 @var{arg} is a type name, it may be the name of a type or typedef, or
13173 for C code it may have the form @samp{class @var{class-name}},
13174 @samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or
13175 @samp{enum @var{enum-tag}}.
13176 @xref{Expressions, ,Expressions}.
13179 @item ptype [@var{arg}]
13180 @code{ptype} accepts the same arguments as @code{whatis}, but prints a
13181 detailed description of the type, instead of just the name of the type.
13182 @xref{Expressions, ,Expressions}.
13184 For example, for this variable declaration:
13187 struct complex @{double real; double imag;@} v;
13191 the two commands give this output:
13195 (@value{GDBP}) whatis v
13196 type = struct complex
13197 (@value{GDBP}) ptype v
13198 type = struct complex @{
13206 As with @code{whatis}, using @code{ptype} without an argument refers to
13207 the type of @code{$}, the last value in the value history.
13209 @cindex incomplete type
13210 Sometimes, programs use opaque data types or incomplete specifications
13211 of complex data structure. If the debug information included in the
13212 program does not allow @value{GDBN} to display a full declaration of
13213 the data type, it will say @samp{<incomplete type>}. For example,
13214 given these declarations:
13218 struct foo *fooptr;
13222 but no definition for @code{struct foo} itself, @value{GDBN} will say:
13225 (@value{GDBP}) ptype foo
13226 $1 = <incomplete type>
13230 ``Incomplete type'' is C terminology for data types that are not
13231 completely specified.
13234 @item info types @var{regexp}
13236 Print a brief description of all types whose names match the regular
13237 expression @var{regexp} (or all types in your program, if you supply
13238 no argument). Each complete typename is matched as though it were a
13239 complete line; thus, @samp{i type value} gives information on all
13240 types in your program whose names include the string @code{value}, but
13241 @samp{i type ^value$} gives information only on types whose complete
13242 name is @code{value}.
13244 This command differs from @code{ptype} in two ways: first, like
13245 @code{whatis}, it does not print a detailed description; second, it
13246 lists all source files where a type is defined.
13249 @cindex local variables
13250 @item info scope @var{location}
13251 List all the variables local to a particular scope. This command
13252 accepts a @var{location} argument---a function name, a source line, or
13253 an address preceded by a @samp{*}, and prints all the variables local
13254 to the scope defined by that location. (@xref{Specify Location}, for
13255 details about supported forms of @var{location}.) For example:
13258 (@value{GDBP}) @b{info scope command_line_handler}
13259 Scope for command_line_handler:
13260 Symbol rl is an argument at stack/frame offset 8, length 4.
13261 Symbol linebuffer is in static storage at address 0x150a18, length 4.
13262 Symbol linelength is in static storage at address 0x150a1c, length 4.
13263 Symbol p is a local variable in register $esi, length 4.
13264 Symbol p1 is a local variable in register $ebx, length 4.
13265 Symbol nline is a local variable in register $edx, length 4.
13266 Symbol repeat is a local variable at frame offset -8, length 4.
13270 This command is especially useful for determining what data to collect
13271 during a @dfn{trace experiment}, see @ref{Tracepoint Actions,
13274 @kindex info source
13276 Show information about the current source file---that is, the source file for
13277 the function containing the current point of execution:
13280 the name of the source file, and the directory containing it,
13282 the directory it was compiled in,
13284 its length, in lines,
13286 which programming language it is written in,
13288 whether the executable includes debugging information for that file, and
13289 if so, what format the information is in (e.g., STABS, Dwarf 2, etc.), and
13291 whether the debugging information includes information about
13292 preprocessor macros.
13296 @kindex info sources
13298 Print the names of all source files in your program for which there is
13299 debugging information, organized into two lists: files whose symbols
13300 have already been read, and files whose symbols will be read when needed.
13302 @kindex info functions
13303 @item info functions
13304 Print the names and data types of all defined functions.
13306 @item info functions @var{regexp}
13307 Print the names and data types of all defined functions
13308 whose names contain a match for regular expression @var{regexp}.
13309 Thus, @samp{info fun step} finds all functions whose names
13310 include @code{step}; @samp{info fun ^step} finds those whose names
13311 start with @code{step}. If a function name contains characters
13312 that conflict with the regular expression language (e.g.@:
13313 @samp{operator*()}), they may be quoted with a backslash.
13315 @kindex info variables
13316 @item info variables
13317 Print the names and data types of all variables that are defined
13318 outside of functions (i.e.@: excluding local variables).
13320 @item info variables @var{regexp}
13321 Print the names and data types of all variables (except for local
13322 variables) whose names contain a match for regular expression
13325 @kindex info classes
13326 @cindex Objective-C, classes and selectors
13328 @itemx info classes @var{regexp}
13329 Display all Objective-C classes in your program, or
13330 (with the @var{regexp} argument) all those matching a particular regular
13333 @kindex info selectors
13334 @item info selectors
13335 @itemx info selectors @var{regexp}
13336 Display all Objective-C selectors in your program, or
13337 (with the @var{regexp} argument) all those matching a particular regular
13341 This was never implemented.
13342 @kindex info methods
13344 @itemx info methods @var{regexp}
13345 The @code{info methods} command permits the user to examine all defined
13346 methods within C@t{++} program, or (with the @var{regexp} argument) a
13347 specific set of methods found in the various C@t{++} classes. Many
13348 C@t{++} classes provide a large number of methods. Thus, the output
13349 from the @code{ptype} command can be overwhelming and hard to use. The
13350 @code{info-methods} command filters the methods, printing only those
13351 which match the regular-expression @var{regexp}.
13354 @cindex reloading symbols
13355 Some systems allow individual object files that make up your program to
13356 be replaced without stopping and restarting your program. For example,
13357 in VxWorks you can simply recompile a defective object file and keep on
13358 running. If you are running on one of these systems, you can allow
13359 @value{GDBN} to reload the symbols for automatically relinked modules:
13362 @kindex set symbol-reloading
13363 @item set symbol-reloading on
13364 Replace symbol definitions for the corresponding source file when an
13365 object file with a particular name is seen again.
13367 @item set symbol-reloading off
13368 Do not replace symbol definitions when encountering object files of the
13369 same name more than once. This is the default state; if you are not
13370 running on a system that permits automatic relinking of modules, you
13371 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
13372 may discard symbols when linking large programs, that may contain
13373 several modules (from different directories or libraries) with the same
13376 @kindex show symbol-reloading
13377 @item show symbol-reloading
13378 Show the current @code{on} or @code{off} setting.
13381 @cindex opaque data types
13382 @kindex set opaque-type-resolution
13383 @item set opaque-type-resolution on
13384 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
13385 declared as a pointer to a @code{struct}, @code{class}, or
13386 @code{union}---for example, @code{struct MyType *}---that is used in one
13387 source file although the full declaration of @code{struct MyType} is in
13388 another source file. The default is on.
13390 A change in the setting of this subcommand will not take effect until
13391 the next time symbols for a file are loaded.
13393 @item set opaque-type-resolution off
13394 Tell @value{GDBN} not to resolve opaque types. In this case, the type
13395 is printed as follows:
13397 @{<no data fields>@}
13400 @kindex show opaque-type-resolution
13401 @item show opaque-type-resolution
13402 Show whether opaque types are resolved or not.
13404 @kindex maint print symbols
13405 @cindex symbol dump
13406 @kindex maint print psymbols
13407 @cindex partial symbol dump
13408 @item maint print symbols @var{filename}
13409 @itemx maint print psymbols @var{filename}
13410 @itemx maint print msymbols @var{filename}
13411 Write a dump of debugging symbol data into the file @var{filename}.
13412 These commands are used to debug the @value{GDBN} symbol-reading code. Only
13413 symbols with debugging data are included. If you use @samp{maint print
13414 symbols}, @value{GDBN} includes all the symbols for which it has already
13415 collected full details: that is, @var{filename} reflects symbols for
13416 only those files whose symbols @value{GDBN} has read. You can use the
13417 command @code{info sources} to find out which files these are. If you
13418 use @samp{maint print psymbols} instead, the dump shows information about
13419 symbols that @value{GDBN} only knows partially---that is, symbols defined in
13420 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
13421 @samp{maint print msymbols} dumps just the minimal symbol information
13422 required for each object file from which @value{GDBN} has read some symbols.
13423 @xref{Files, ,Commands to Specify Files}, for a discussion of how
13424 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
13426 @kindex maint info symtabs
13427 @kindex maint info psymtabs
13428 @cindex listing @value{GDBN}'s internal symbol tables
13429 @cindex symbol tables, listing @value{GDBN}'s internal
13430 @cindex full symbol tables, listing @value{GDBN}'s internal
13431 @cindex partial symbol tables, listing @value{GDBN}'s internal
13432 @item maint info symtabs @r{[} @var{regexp} @r{]}
13433 @itemx maint info psymtabs @r{[} @var{regexp} @r{]}
13435 List the @code{struct symtab} or @code{struct partial_symtab}
13436 structures whose names match @var{regexp}. If @var{regexp} is not
13437 given, list them all. The output includes expressions which you can
13438 copy into a @value{GDBN} debugging this one to examine a particular
13439 structure in more detail. For example:
13442 (@value{GDBP}) maint info psymtabs dwarf2read
13443 @{ objfile /home/gnu/build/gdb/gdb
13444 ((struct objfile *) 0x82e69d0)
13445 @{ psymtab /home/gnu/src/gdb/dwarf2read.c
13446 ((struct partial_symtab *) 0x8474b10)
13449 text addresses 0x814d3c8 -- 0x8158074
13450 globals (* (struct partial_symbol **) 0x8507a08 @@ 9)
13451 statics (* (struct partial_symbol **) 0x40e95b78 @@ 2882)
13452 dependencies (none)
13455 (@value{GDBP}) maint info symtabs
13459 We see that there is one partial symbol table whose filename contains
13460 the string @samp{dwarf2read}, belonging to the @samp{gdb} executable;
13461 and we see that @value{GDBN} has not read in any symtabs yet at all.
13462 If we set a breakpoint on a function, that will cause @value{GDBN} to
13463 read the symtab for the compilation unit containing that function:
13466 (@value{GDBP}) break dwarf2_psymtab_to_symtab
13467 Breakpoint 1 at 0x814e5da: file /home/gnu/src/gdb/dwarf2read.c,
13469 (@value{GDBP}) maint info symtabs
13470 @{ objfile /home/gnu/build/gdb/gdb
13471 ((struct objfile *) 0x82e69d0)
13472 @{ symtab /home/gnu/src/gdb/dwarf2read.c
13473 ((struct symtab *) 0x86c1f38)
13476 blockvector ((struct blockvector *) 0x86c1bd0) (primary)
13477 linetable ((struct linetable *) 0x8370fa0)
13478 debugformat DWARF 2
13487 @chapter Altering Execution
13489 Once you think you have found an error in your program, you might want to
13490 find out for certain whether correcting the apparent error would lead to
13491 correct results in the rest of the run. You can find the answer by
13492 experiment, using the @value{GDBN} features for altering execution of the
13495 For example, you can store new values into variables or memory
13496 locations, give your program a signal, restart it at a different
13497 address, or even return prematurely from a function.
13500 * Assignment:: Assignment to variables
13501 * Jumping:: Continuing at a different address
13502 * Signaling:: Giving your program a signal
13503 * Returning:: Returning from a function
13504 * Calling:: Calling your program's functions
13505 * Patching:: Patching your program
13509 @section Assignment to Variables
13512 @cindex setting variables
13513 To alter the value of a variable, evaluate an assignment expression.
13514 @xref{Expressions, ,Expressions}. For example,
13521 stores the value 4 into the variable @code{x}, and then prints the
13522 value of the assignment expression (which is 4).
13523 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
13524 information on operators in supported languages.
13526 @kindex set variable
13527 @cindex variables, setting
13528 If you are not interested in seeing the value of the assignment, use the
13529 @code{set} command instead of the @code{print} command. @code{set} is
13530 really the same as @code{print} except that the expression's value is
13531 not printed and is not put in the value history (@pxref{Value History,
13532 ,Value History}). The expression is evaluated only for its effects.
13534 If the beginning of the argument string of the @code{set} command
13535 appears identical to a @code{set} subcommand, use the @code{set
13536 variable} command instead of just @code{set}. This command is identical
13537 to @code{set} except for its lack of subcommands. For example, if your
13538 program has a variable @code{width}, you get an error if you try to set
13539 a new value with just @samp{set width=13}, because @value{GDBN} has the
13540 command @code{set width}:
13543 (@value{GDBP}) whatis width
13545 (@value{GDBP}) p width
13547 (@value{GDBP}) set width=47
13548 Invalid syntax in expression.
13552 The invalid expression, of course, is @samp{=47}. In
13553 order to actually set the program's variable @code{width}, use
13556 (@value{GDBP}) set var width=47
13559 Because the @code{set} command has many subcommands that can conflict
13560 with the names of program variables, it is a good idea to use the
13561 @code{set variable} command instead of just @code{set}. For example, if
13562 your program has a variable @code{g}, you run into problems if you try
13563 to set a new value with just @samp{set g=4}, because @value{GDBN} has
13564 the command @code{set gnutarget}, abbreviated @code{set g}:
13568 (@value{GDBP}) whatis g
13572 (@value{GDBP}) set g=4
13576 The program being debugged has been started already.
13577 Start it from the beginning? (y or n) y
13578 Starting program: /home/smith/cc_progs/a.out
13579 "/home/smith/cc_progs/a.out": can't open to read symbols:
13580 Invalid bfd target.
13581 (@value{GDBP}) show g
13582 The current BFD target is "=4".
13587 The program variable @code{g} did not change, and you silently set the
13588 @code{gnutarget} to an invalid value. In order to set the variable
13592 (@value{GDBP}) set var g=4
13595 @value{GDBN} allows more implicit conversions in assignments than C; you can
13596 freely store an integer value into a pointer variable or vice versa,
13597 and you can convert any structure to any other structure that is the
13598 same length or shorter.
13599 @comment FIXME: how do structs align/pad in these conversions?
13600 @comment /doc@cygnus.com 18dec1990
13602 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
13603 construct to generate a value of specified type at a specified address
13604 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
13605 to memory location @code{0x83040} as an integer (which implies a certain size
13606 and representation in memory), and
13609 set @{int@}0x83040 = 4
13613 stores the value 4 into that memory location.
13616 @section Continuing at a Different Address
13618 Ordinarily, when you continue your program, you do so at the place where
13619 it stopped, with the @code{continue} command. You can instead continue at
13620 an address of your own choosing, with the following commands:
13624 @item jump @var{linespec}
13625 @itemx jump @var{location}
13626 Resume execution at line @var{linespec} or at address given by
13627 @var{location}. Execution stops again immediately if there is a
13628 breakpoint there. @xref{Specify Location}, for a description of the
13629 different forms of @var{linespec} and @var{location}. It is common
13630 practice to use the @code{tbreak} command in conjunction with
13631 @code{jump}. @xref{Set Breaks, ,Setting Breakpoints}.
13633 The @code{jump} command does not change the current stack frame, or
13634 the stack pointer, or the contents of any memory location or any
13635 register other than the program counter. If line @var{linespec} is in
13636 a different function from the one currently executing, the results may
13637 be bizarre if the two functions expect different patterns of arguments or
13638 of local variables. For this reason, the @code{jump} command requests
13639 confirmation if the specified line is not in the function currently
13640 executing. However, even bizarre results are predictable if you are
13641 well acquainted with the machine-language code of your program.
13644 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
13645 On many systems, you can get much the same effect as the @code{jump}
13646 command by storing a new value into the register @code{$pc}. The
13647 difference is that this does not start your program running; it only
13648 changes the address of where it @emph{will} run when you continue. For
13656 makes the next @code{continue} command or stepping command execute at
13657 address @code{0x485}, rather than at the address where your program stopped.
13658 @xref{Continuing and Stepping, ,Continuing and Stepping}.
13660 The most common occasion to use the @code{jump} command is to back
13661 up---perhaps with more breakpoints set---over a portion of a program
13662 that has already executed, in order to examine its execution in more
13667 @section Giving your Program a Signal
13668 @cindex deliver a signal to a program
13672 @item signal @var{signal}
13673 Resume execution where your program stopped, but immediately give it the
13674 signal @var{signal}. @var{signal} can be the name or the number of a
13675 signal. For example, on many systems @code{signal 2} and @code{signal
13676 SIGINT} are both ways of sending an interrupt signal.
13678 Alternatively, if @var{signal} is zero, continue execution without
13679 giving a signal. This is useful when your program stopped on account of
13680 a signal and would ordinary see the signal when resumed with the
13681 @code{continue} command; @samp{signal 0} causes it to resume without a
13684 @code{signal} does not repeat when you press @key{RET} a second time
13685 after executing the command.
13689 Invoking the @code{signal} command is not the same as invoking the
13690 @code{kill} utility from the shell. Sending a signal with @code{kill}
13691 causes @value{GDBN} to decide what to do with the signal depending on
13692 the signal handling tables (@pxref{Signals}). The @code{signal} command
13693 passes the signal directly to your program.
13697 @section Returning from a Function
13700 @cindex returning from a function
13703 @itemx return @var{expression}
13704 You can cancel execution of a function call with the @code{return}
13705 command. If you give an
13706 @var{expression} argument, its value is used as the function's return
13710 When you use @code{return}, @value{GDBN} discards the selected stack frame
13711 (and all frames within it). You can think of this as making the
13712 discarded frame return prematurely. If you wish to specify a value to
13713 be returned, give that value as the argument to @code{return}.
13715 This pops the selected stack frame (@pxref{Selection, ,Selecting a
13716 Frame}), and any other frames inside of it, leaving its caller as the
13717 innermost remaining frame. That frame becomes selected. The
13718 specified value is stored in the registers used for returning values
13721 The @code{return} command does not resume execution; it leaves the
13722 program stopped in the state that would exist if the function had just
13723 returned. In contrast, the @code{finish} command (@pxref{Continuing
13724 and Stepping, ,Continuing and Stepping}) resumes execution until the
13725 selected stack frame returns naturally.
13727 @value{GDBN} needs to know how the @var{expression} argument should be set for
13728 the inferior. The concrete registers assignment depends on the OS ABI and the
13729 type being returned by the selected stack frame. For example it is common for
13730 OS ABI to return floating point values in FPU registers while integer values in
13731 CPU registers. Still some ABIs return even floating point values in CPU
13732 registers. Larger integer widths (such as @code{long long int}) also have
13733 specific placement rules. @value{GDBN} already knows the OS ABI from its
13734 current target so it needs to find out also the type being returned to make the
13735 assignment into the right register(s).
13737 Normally, the selected stack frame has debug info. @value{GDBN} will always
13738 use the debug info instead of the implicit type of @var{expression} when the
13739 debug info is available. For example, if you type @kbd{return -1}, and the
13740 function in the current stack frame is declared to return a @code{long long
13741 int}, @value{GDBN} transparently converts the implicit @code{int} value of -1
13742 into a @code{long long int}:
13745 Breakpoint 1, func () at gdb.base/return-nodebug.c:29
13747 (@value{GDBP}) return -1
13748 Make func return now? (y or n) y
13749 #0 0x004004f6 in main () at gdb.base/return-nodebug.c:43
13750 43 printf ("result=%lld\n", func ());
13754 However, if the selected stack frame does not have a debug info, e.g., if the
13755 function was compiled without debug info, @value{GDBN} has to find out the type
13756 to return from user. Specifying a different type by mistake may set the value
13757 in different inferior registers than the caller code expects. For example,
13758 typing @kbd{return -1} with its implicit type @code{int} would set only a part
13759 of a @code{long long int} result for a debug info less function (on 32-bit
13760 architectures). Therefore the user is required to specify the return type by
13761 an appropriate cast explicitly:
13764 Breakpoint 2, 0x0040050b in func ()
13765 (@value{GDBP}) return -1
13766 Return value type not available for selected stack frame.
13767 Please use an explicit cast of the value to return.
13768 (@value{GDBP}) return (long long int) -1
13769 Make selected stack frame return now? (y or n) y
13770 #0 0x00400526 in main ()
13775 @section Calling Program Functions
13778 @cindex calling functions
13779 @cindex inferior functions, calling
13780 @item print @var{expr}
13781 Evaluate the expression @var{expr} and display the resulting value.
13782 @var{expr} may include calls to functions in the program being
13786 @item call @var{expr}
13787 Evaluate the expression @var{expr} without displaying @code{void}
13790 You can use this variant of the @code{print} command if you want to
13791 execute a function from your program that does not return anything
13792 (a.k.a.@: @dfn{a void function}), but without cluttering the output
13793 with @code{void} returned values that @value{GDBN} will otherwise
13794 print. If the result is not void, it is printed and saved in the
13798 It is possible for the function you call via the @code{print} or
13799 @code{call} command to generate a signal (e.g., if there's a bug in
13800 the function, or if you passed it incorrect arguments). What happens
13801 in that case is controlled by the @code{set unwindonsignal} command.
13803 Similarly, with a C@t{++} program it is possible for the function you
13804 call via the @code{print} or @code{call} command to generate an
13805 exception that is not handled due to the constraints of the dummy
13806 frame. In this case, any exception that is raised in the frame, but has
13807 an out-of-frame exception handler will not be found. GDB builds a
13808 dummy-frame for the inferior function call, and the unwinder cannot
13809 seek for exception handlers outside of this dummy-frame. What happens
13810 in that case is controlled by the
13811 @code{set unwind-on-terminating-exception} command.
13814 @item set unwindonsignal
13815 @kindex set unwindonsignal
13816 @cindex unwind stack in called functions
13817 @cindex call dummy stack unwinding
13818 Set unwinding of the stack if a signal is received while in a function
13819 that @value{GDBN} called in the program being debugged. If set to on,
13820 @value{GDBN} unwinds the stack it created for the call and restores
13821 the context to what it was before the call. If set to off (the
13822 default), @value{GDBN} stops in the frame where the signal was
13825 @item show unwindonsignal
13826 @kindex show unwindonsignal
13827 Show the current setting of stack unwinding in the functions called by
13830 @item set unwind-on-terminating-exception
13831 @kindex set unwind-on-terminating-exception
13832 @cindex unwind stack in called functions with unhandled exceptions
13833 @cindex call dummy stack unwinding on unhandled exception.
13834 Set unwinding of the stack if a C@t{++} exception is raised, but left
13835 unhandled while in a function that @value{GDBN} called in the program being
13836 debugged. If set to on (the default), @value{GDBN} unwinds the stack
13837 it created for the call and restores the context to what it was before
13838 the call. If set to off, @value{GDBN} the exception is delivered to
13839 the default C@t{++} exception handler and the inferior terminated.
13841 @item show unwind-on-terminating-exception
13842 @kindex show unwind-on-terminating-exception
13843 Show the current setting of stack unwinding in the functions called by
13848 @cindex weak alias functions
13849 Sometimes, a function you wish to call is actually a @dfn{weak alias}
13850 for another function. In such case, @value{GDBN} might not pick up
13851 the type information, including the types of the function arguments,
13852 which causes @value{GDBN} to call the inferior function incorrectly.
13853 As a result, the called function will function erroneously and may
13854 even crash. A solution to that is to use the name of the aliased
13858 @section Patching Programs
13860 @cindex patching binaries
13861 @cindex writing into executables
13862 @cindex writing into corefiles
13864 By default, @value{GDBN} opens the file containing your program's
13865 executable code (or the corefile) read-only. This prevents accidental
13866 alterations to machine code; but it also prevents you from intentionally
13867 patching your program's binary.
13869 If you'd like to be able to patch the binary, you can specify that
13870 explicitly with the @code{set write} command. For example, you might
13871 want to turn on internal debugging flags, or even to make emergency
13877 @itemx set write off
13878 If you specify @samp{set write on}, @value{GDBN} opens executable and
13879 core files for both reading and writing; if you specify @kbd{set write
13880 off} (the default), @value{GDBN} opens them read-only.
13882 If you have already loaded a file, you must load it again (using the
13883 @code{exec-file} or @code{core-file} command) after changing @code{set
13884 write}, for your new setting to take effect.
13888 Display whether executable files and core files are opened for writing
13889 as well as reading.
13893 @chapter @value{GDBN} Files
13895 @value{GDBN} needs to know the file name of the program to be debugged,
13896 both in order to read its symbol table and in order to start your
13897 program. To debug a core dump of a previous run, you must also tell
13898 @value{GDBN} the name of the core dump file.
13901 * Files:: Commands to specify files
13902 * Separate Debug Files:: Debugging information in separate files
13903 * Symbol Errors:: Errors reading symbol files
13904 * Data Files:: GDB data files
13908 @section Commands to Specify Files
13910 @cindex symbol table
13911 @cindex core dump file
13913 You may want to specify executable and core dump file names. The usual
13914 way to do this is at start-up time, using the arguments to
13915 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
13916 Out of @value{GDBN}}).
13918 Occasionally it is necessary to change to a different file during a
13919 @value{GDBN} session. Or you may run @value{GDBN} and forget to
13920 specify a file you want to use. Or you are debugging a remote target
13921 via @code{gdbserver} (@pxref{Server, file, Using the @code{gdbserver}
13922 Program}). In these situations the @value{GDBN} commands to specify
13923 new files are useful.
13926 @cindex executable file
13928 @item file @var{filename}
13929 Use @var{filename} as the program to be debugged. It is read for its
13930 symbols and for the contents of pure memory. It is also the program
13931 executed when you use the @code{run} command. If you do not specify a
13932 directory and the file is not found in the @value{GDBN} working directory,
13933 @value{GDBN} uses the environment variable @code{PATH} as a list of
13934 directories to search, just as the shell does when looking for a program
13935 to run. You can change the value of this variable, for both @value{GDBN}
13936 and your program, using the @code{path} command.
13938 @cindex unlinked object files
13939 @cindex patching object files
13940 You can load unlinked object @file{.o} files into @value{GDBN} using
13941 the @code{file} command. You will not be able to ``run'' an object
13942 file, but you can disassemble functions and inspect variables. Also,
13943 if the underlying BFD functionality supports it, you could use
13944 @kbd{gdb -write} to patch object files using this technique. Note
13945 that @value{GDBN} can neither interpret nor modify relocations in this
13946 case, so branches and some initialized variables will appear to go to
13947 the wrong place. But this feature is still handy from time to time.
13950 @code{file} with no argument makes @value{GDBN} discard any information it
13951 has on both executable file and the symbol table.
13954 @item exec-file @r{[} @var{filename} @r{]}
13955 Specify that the program to be run (but not the symbol table) is found
13956 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
13957 if necessary to locate your program. Omitting @var{filename} means to
13958 discard information on the executable file.
13960 @kindex symbol-file
13961 @item symbol-file @r{[} @var{filename} @r{]}
13962 Read symbol table information from file @var{filename}. @code{PATH} is
13963 searched when necessary. Use the @code{file} command to get both symbol
13964 table and program to run from the same file.
13966 @code{symbol-file} with no argument clears out @value{GDBN} information on your
13967 program's symbol table.
13969 The @code{symbol-file} command causes @value{GDBN} to forget the contents of
13970 some breakpoints and auto-display expressions. This is because they may
13971 contain pointers to the internal data recording symbols and data types,
13972 which are part of the old symbol table data being discarded inside
13975 @code{symbol-file} does not repeat if you press @key{RET} again after
13978 When @value{GDBN} is configured for a particular environment, it
13979 understands debugging information in whatever format is the standard
13980 generated for that environment; you may use either a @sc{gnu} compiler, or
13981 other compilers that adhere to the local conventions.
13982 Best results are usually obtained from @sc{gnu} compilers; for example,
13983 using @code{@value{NGCC}} you can generate debugging information for
13986 For most kinds of object files, with the exception of old SVR3 systems
13987 using COFF, the @code{symbol-file} command does not normally read the
13988 symbol table in full right away. Instead, it scans the symbol table
13989 quickly to find which source files and which symbols are present. The
13990 details are read later, one source file at a time, as they are needed.
13992 The purpose of this two-stage reading strategy is to make @value{GDBN}
13993 start up faster. For the most part, it is invisible except for
13994 occasional pauses while the symbol table details for a particular source
13995 file are being read. (The @code{set verbose} command can turn these
13996 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
13997 Warnings and Messages}.)
13999 We have not implemented the two-stage strategy for COFF yet. When the
14000 symbol table is stored in COFF format, @code{symbol-file} reads the
14001 symbol table data in full right away. Note that ``stabs-in-COFF''
14002 still does the two-stage strategy, since the debug info is actually
14006 @cindex reading symbols immediately
14007 @cindex symbols, reading immediately
14008 @item symbol-file @r{[} -readnow @r{]} @var{filename}
14009 @itemx file @r{[} -readnow @r{]} @var{filename}
14010 You can override the @value{GDBN} two-stage strategy for reading symbol
14011 tables by using the @samp{-readnow} option with any of the commands that
14012 load symbol table information, if you want to be sure @value{GDBN} has the
14013 entire symbol table available.
14015 @c FIXME: for now no mention of directories, since this seems to be in
14016 @c flux. 13mar1992 status is that in theory GDB would look either in
14017 @c current dir or in same dir as myprog; but issues like competing
14018 @c GDB's, or clutter in system dirs, mean that in practice right now
14019 @c only current dir is used. FFish says maybe a special GDB hierarchy
14020 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
14024 @item core-file @r{[}@var{filename}@r{]}
14026 Specify the whereabouts of a core dump file to be used as the ``contents
14027 of memory''. Traditionally, core files contain only some parts of the
14028 address space of the process that generated them; @value{GDBN} can access the
14029 executable file itself for other parts.
14031 @code{core-file} with no argument specifies that no core file is
14034 Note that the core file is ignored when your program is actually running
14035 under @value{GDBN}. So, if you have been running your program and you
14036 wish to debug a core file instead, you must kill the subprocess in which
14037 the program is running. To do this, use the @code{kill} command
14038 (@pxref{Kill Process, ,Killing the Child Process}).
14040 @kindex add-symbol-file
14041 @cindex dynamic linking
14042 @item add-symbol-file @var{filename} @var{address}
14043 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]}
14044 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address} @dots{}
14045 The @code{add-symbol-file} command reads additional symbol table
14046 information from the file @var{filename}. You would use this command
14047 when @var{filename} has been dynamically loaded (by some other means)
14048 into the program that is running. @var{address} should be the memory
14049 address at which the file has been loaded; @value{GDBN} cannot figure
14050 this out for itself. You can additionally specify an arbitrary number
14051 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
14052 section name and base address for that section. You can specify any
14053 @var{address} as an expression.
14055 The symbol table of the file @var{filename} is added to the symbol table
14056 originally read with the @code{symbol-file} command. You can use the
14057 @code{add-symbol-file} command any number of times; the new symbol data
14058 thus read keeps adding to the old. To discard all old symbol data
14059 instead, use the @code{symbol-file} command without any arguments.
14061 @cindex relocatable object files, reading symbols from
14062 @cindex object files, relocatable, reading symbols from
14063 @cindex reading symbols from relocatable object files
14064 @cindex symbols, reading from relocatable object files
14065 @cindex @file{.o} files, reading symbols from
14066 Although @var{filename} is typically a shared library file, an
14067 executable file, or some other object file which has been fully
14068 relocated for loading into a process, you can also load symbolic
14069 information from relocatable @file{.o} files, as long as:
14073 the file's symbolic information refers only to linker symbols defined in
14074 that file, not to symbols defined by other object files,
14076 every section the file's symbolic information refers to has actually
14077 been loaded into the inferior, as it appears in the file, and
14079 you can determine the address at which every section was loaded, and
14080 provide these to the @code{add-symbol-file} command.
14084 Some embedded operating systems, like Sun Chorus and VxWorks, can load
14085 relocatable files into an already running program; such systems
14086 typically make the requirements above easy to meet. However, it's
14087 important to recognize that many native systems use complex link
14088 procedures (@code{.linkonce} section factoring and C@t{++} constructor table
14089 assembly, for example) that make the requirements difficult to meet. In
14090 general, one cannot assume that using @code{add-symbol-file} to read a
14091 relocatable object file's symbolic information will have the same effect
14092 as linking the relocatable object file into the program in the normal
14095 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
14097 @kindex add-symbol-file-from-memory
14098 @cindex @code{syscall DSO}
14099 @cindex load symbols from memory
14100 @item add-symbol-file-from-memory @var{address}
14101 Load symbols from the given @var{address} in a dynamically loaded
14102 object file whose image is mapped directly into the inferior's memory.
14103 For example, the Linux kernel maps a @code{syscall DSO} into each
14104 process's address space; this DSO provides kernel-specific code for
14105 some system calls. The argument can be any expression whose
14106 evaluation yields the address of the file's shared object file header.
14107 For this command to work, you must have used @code{symbol-file} or
14108 @code{exec-file} commands in advance.
14110 @kindex add-shared-symbol-files
14112 @item add-shared-symbol-files @var{library-file}
14113 @itemx assf @var{library-file}
14114 The @code{add-shared-symbol-files} command can currently be used only
14115 in the Cygwin build of @value{GDBN} on MS-Windows OS, where it is an
14116 alias for the @code{dll-symbols} command (@pxref{Cygwin Native}).
14117 @value{GDBN} automatically looks for shared libraries, however if
14118 @value{GDBN} does not find yours, you can invoke
14119 @code{add-shared-symbol-files}. It takes one argument: the shared
14120 library's file name. @code{assf} is a shorthand alias for
14121 @code{add-shared-symbol-files}.
14124 @item section @var{section} @var{addr}
14125 The @code{section} command changes the base address of the named
14126 @var{section} of the exec file to @var{addr}. This can be used if the
14127 exec file does not contain section addresses, (such as in the
14128 @code{a.out} format), or when the addresses specified in the file
14129 itself are wrong. Each section must be changed separately. The
14130 @code{info files} command, described below, lists all the sections and
14134 @kindex info target
14137 @code{info files} and @code{info target} are synonymous; both print the
14138 current target (@pxref{Targets, ,Specifying a Debugging Target}),
14139 including the names of the executable and core dump files currently in
14140 use by @value{GDBN}, and the files from which symbols were loaded. The
14141 command @code{help target} lists all possible targets rather than
14144 @kindex maint info sections
14145 @item maint info sections
14146 Another command that can give you extra information about program sections
14147 is @code{maint info sections}. In addition to the section information
14148 displayed by @code{info files}, this command displays the flags and file
14149 offset of each section in the executable and core dump files. In addition,
14150 @code{maint info sections} provides the following command options (which
14151 may be arbitrarily combined):
14155 Display sections for all loaded object files, including shared libraries.
14156 @item @var{sections}
14157 Display info only for named @var{sections}.
14158 @item @var{section-flags}
14159 Display info only for sections for which @var{section-flags} are true.
14160 The section flags that @value{GDBN} currently knows about are:
14163 Section will have space allocated in the process when loaded.
14164 Set for all sections except those containing debug information.
14166 Section will be loaded from the file into the child process memory.
14167 Set for pre-initialized code and data, clear for @code{.bss} sections.
14169 Section needs to be relocated before loading.
14171 Section cannot be modified by the child process.
14173 Section contains executable code only.
14175 Section contains data only (no executable code).
14177 Section will reside in ROM.
14179 Section contains data for constructor/destructor lists.
14181 Section is not empty.
14183 An instruction to the linker to not output the section.
14184 @item COFF_SHARED_LIBRARY
14185 A notification to the linker that the section contains
14186 COFF shared library information.
14188 Section contains common symbols.
14191 @kindex set trust-readonly-sections
14192 @cindex read-only sections
14193 @item set trust-readonly-sections on
14194 Tell @value{GDBN} that readonly sections in your object file
14195 really are read-only (i.e.@: that their contents will not change).
14196 In that case, @value{GDBN} can fetch values from these sections
14197 out of the object file, rather than from the target program.
14198 For some targets (notably embedded ones), this can be a significant
14199 enhancement to debugging performance.
14201 The default is off.
14203 @item set trust-readonly-sections off
14204 Tell @value{GDBN} not to trust readonly sections. This means that
14205 the contents of the section might change while the program is running,
14206 and must therefore be fetched from the target when needed.
14208 @item show trust-readonly-sections
14209 Show the current setting of trusting readonly sections.
14212 All file-specifying commands allow both absolute and relative file names
14213 as arguments. @value{GDBN} always converts the file name to an absolute file
14214 name and remembers it that way.
14216 @cindex shared libraries
14217 @anchor{Shared Libraries}
14218 @value{GDBN} supports @sc{gnu}/Linux, MS-Windows, HP-UX, SunOS, SVr4, Irix,
14219 and IBM RS/6000 AIX shared libraries.
14221 On MS-Windows @value{GDBN} must be linked with the Expat library to support
14222 shared libraries. @xref{Expat}.
14224 @value{GDBN} automatically loads symbol definitions from shared libraries
14225 when you use the @code{run} command, or when you examine a core file.
14226 (Before you issue the @code{run} command, @value{GDBN} does not understand
14227 references to a function in a shared library, however---unless you are
14228 debugging a core file).
14230 On HP-UX, if the program loads a library explicitly, @value{GDBN}
14231 automatically loads the symbols at the time of the @code{shl_load} call.
14233 @c FIXME: some @value{GDBN} release may permit some refs to undef
14234 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
14235 @c FIXME...lib; check this from time to time when updating manual
14237 There are times, however, when you may wish to not automatically load
14238 symbol definitions from shared libraries, such as when they are
14239 particularly large or there are many of them.
14241 To control the automatic loading of shared library symbols, use the
14245 @kindex set auto-solib-add
14246 @item set auto-solib-add @var{mode}
14247 If @var{mode} is @code{on}, symbols from all shared object libraries
14248 will be loaded automatically when the inferior begins execution, you
14249 attach to an independently started inferior, or when the dynamic linker
14250 informs @value{GDBN} that a new library has been loaded. If @var{mode}
14251 is @code{off}, symbols must be loaded manually, using the
14252 @code{sharedlibrary} command. The default value is @code{on}.
14254 @cindex memory used for symbol tables
14255 If your program uses lots of shared libraries with debug info that
14256 takes large amounts of memory, you can decrease the @value{GDBN}
14257 memory footprint by preventing it from automatically loading the
14258 symbols from shared libraries. To that end, type @kbd{set
14259 auto-solib-add off} before running the inferior, then load each
14260 library whose debug symbols you do need with @kbd{sharedlibrary
14261 @var{regexp}}, where @var{regexp} is a regular expression that matches
14262 the libraries whose symbols you want to be loaded.
14264 @kindex show auto-solib-add
14265 @item show auto-solib-add
14266 Display the current autoloading mode.
14269 @cindex load shared library
14270 To explicitly load shared library symbols, use the @code{sharedlibrary}
14274 @kindex info sharedlibrary
14276 @item info share @var{regex}
14277 @itemx info sharedlibrary @var{regex}
14278 Print the names of the shared libraries which are currently loaded
14279 that match @var{regex}. If @var{regex} is omitted then print
14280 all shared libraries that are loaded.
14282 @kindex sharedlibrary
14284 @item sharedlibrary @var{regex}
14285 @itemx share @var{regex}
14286 Load shared object library symbols for files matching a
14287 Unix regular expression.
14288 As with files loaded automatically, it only loads shared libraries
14289 required by your program for a core file or after typing @code{run}. If
14290 @var{regex} is omitted all shared libraries required by your program are
14293 @item nosharedlibrary
14294 @kindex nosharedlibrary
14295 @cindex unload symbols from shared libraries
14296 Unload all shared object library symbols. This discards all symbols
14297 that have been loaded from all shared libraries. Symbols from shared
14298 libraries that were loaded by explicit user requests are not
14302 Sometimes you may wish that @value{GDBN} stops and gives you control
14303 when any of shared library events happen. Use the @code{set
14304 stop-on-solib-events} command for this:
14307 @item set stop-on-solib-events
14308 @kindex set stop-on-solib-events
14309 This command controls whether @value{GDBN} should give you control
14310 when the dynamic linker notifies it about some shared library event.
14311 The most common event of interest is loading or unloading of a new
14314 @item show stop-on-solib-events
14315 @kindex show stop-on-solib-events
14316 Show whether @value{GDBN} stops and gives you control when shared
14317 library events happen.
14320 Shared libraries are also supported in many cross or remote debugging
14321 configurations. @value{GDBN} needs to have access to the target's libraries;
14322 this can be accomplished either by providing copies of the libraries
14323 on the host system, or by asking @value{GDBN} to automatically retrieve the
14324 libraries from the target. If copies of the target libraries are
14325 provided, they need to be the same as the target libraries, although the
14326 copies on the target can be stripped as long as the copies on the host are
14329 @cindex where to look for shared libraries
14330 For remote debugging, you need to tell @value{GDBN} where the target
14331 libraries are, so that it can load the correct copies---otherwise, it
14332 may try to load the host's libraries. @value{GDBN} has two variables
14333 to specify the search directories for target libraries.
14336 @cindex prefix for shared library file names
14337 @cindex system root, alternate
14338 @kindex set solib-absolute-prefix
14339 @kindex set sysroot
14340 @item set sysroot @var{path}
14341 Use @var{path} as the system root for the program being debugged. Any
14342 absolute shared library paths will be prefixed with @var{path}; many
14343 runtime loaders store the absolute paths to the shared library in the
14344 target program's memory. If you use @code{set sysroot} to find shared
14345 libraries, they need to be laid out in the same way that they are on
14346 the target, with e.g.@: a @file{/lib} and @file{/usr/lib} hierarchy
14349 If @var{path} starts with the sequence @file{remote:}, @value{GDBN} will
14350 retrieve the target libraries from the remote system. This is only
14351 supported when using a remote target that supports the @code{remote get}
14352 command (@pxref{File Transfer,,Sending files to a remote system}).
14353 The part of @var{path} following the initial @file{remote:}
14354 (if present) is used as system root prefix on the remote file system.
14355 @footnote{If you want to specify a local system root using a directory
14356 that happens to be named @file{remote:}, you need to use some equivalent
14357 variant of the name like @file{./remote:}.}
14359 The @code{set solib-absolute-prefix} command is an alias for @code{set
14362 @cindex default system root
14363 @cindex @samp{--with-sysroot}
14364 You can set the default system root by using the configure-time
14365 @samp{--with-sysroot} option. If the system root is inside
14366 @value{GDBN}'s configured binary prefix (set with @samp{--prefix} or
14367 @samp{--exec-prefix}), then the default system root will be updated
14368 automatically if the installed @value{GDBN} is moved to a new
14371 @kindex show sysroot
14373 Display the current shared library prefix.
14375 @kindex set solib-search-path
14376 @item set solib-search-path @var{path}
14377 If this variable is set, @var{path} is a colon-separated list of
14378 directories to search for shared libraries. @samp{solib-search-path}
14379 is used after @samp{sysroot} fails to locate the library, or if the
14380 path to the library is relative instead of absolute. If you want to
14381 use @samp{solib-search-path} instead of @samp{sysroot}, be sure to set
14382 @samp{sysroot} to a nonexistent directory to prevent @value{GDBN} from
14383 finding your host's libraries. @samp{sysroot} is preferred; setting
14384 it to a nonexistent directory may interfere with automatic loading
14385 of shared library symbols.
14387 @kindex show solib-search-path
14388 @item show solib-search-path
14389 Display the current shared library search path.
14393 @node Separate Debug Files
14394 @section Debugging Information in Separate Files
14395 @cindex separate debugging information files
14396 @cindex debugging information in separate files
14397 @cindex @file{.debug} subdirectories
14398 @cindex debugging information directory, global
14399 @cindex global debugging information directory
14400 @cindex build ID, and separate debugging files
14401 @cindex @file{.build-id} directory
14403 @value{GDBN} allows you to put a program's debugging information in a
14404 file separate from the executable itself, in a way that allows
14405 @value{GDBN} to find and load the debugging information automatically.
14406 Since debugging information can be very large---sometimes larger
14407 than the executable code itself---some systems distribute debugging
14408 information for their executables in separate files, which users can
14409 install only when they need to debug a problem.
14411 @value{GDBN} supports two ways of specifying the separate debug info
14416 The executable contains a @dfn{debug link} that specifies the name of
14417 the separate debug info file. The separate debug file's name is
14418 usually @file{@var{executable}.debug}, where @var{executable} is the
14419 name of the corresponding executable file without leading directories
14420 (e.g., @file{ls.debug} for @file{/usr/bin/ls}). In addition, the
14421 debug link specifies a 32-bit @dfn{Cyclic Redundancy Check} (CRC)
14422 checksum for the debug file, which @value{GDBN} uses to validate that
14423 the executable and the debug file came from the same build.
14426 The executable contains a @dfn{build ID}, a unique bit string that is
14427 also present in the corresponding debug info file. (This is supported
14428 only on some operating systems, notably those which use the ELF format
14429 for binary files and the @sc{gnu} Binutils.) For more details about
14430 this feature, see the description of the @option{--build-id}
14431 command-line option in @ref{Options, , Command Line Options, ld.info,
14432 The GNU Linker}. The debug info file's name is not specified
14433 explicitly by the build ID, but can be computed from the build ID, see
14437 Depending on the way the debug info file is specified, @value{GDBN}
14438 uses two different methods of looking for the debug file:
14442 For the ``debug link'' method, @value{GDBN} looks up the named file in
14443 the directory of the executable file, then in a subdirectory of that
14444 directory named @file{.debug}, and finally under the global debug
14445 directory, in a subdirectory whose name is identical to the leading
14446 directories of the executable's absolute file name.
14449 For the ``build ID'' method, @value{GDBN} looks in the
14450 @file{.build-id} subdirectory of the global debug directory for a file
14451 named @file{@var{nn}/@var{nnnnnnnn}.debug}, where @var{nn} are the
14452 first 2 hex characters of the build ID bit string, and @var{nnnnnnnn}
14453 are the rest of the bit string. (Real build ID strings are 32 or more
14454 hex characters, not 10.)
14457 So, for example, suppose you ask @value{GDBN} to debug
14458 @file{/usr/bin/ls}, which has a debug link that specifies the
14459 file @file{ls.debug}, and a build ID whose value in hex is
14460 @code{abcdef1234}. If the global debug directory is
14461 @file{/usr/lib/debug}, then @value{GDBN} will look for the following
14462 debug information files, in the indicated order:
14466 @file{/usr/lib/debug/.build-id/ab/cdef1234.debug}
14468 @file{/usr/bin/ls.debug}
14470 @file{/usr/bin/.debug/ls.debug}
14472 @file{/usr/lib/debug/usr/bin/ls.debug}.
14475 You can set the global debugging info directory's name, and view the
14476 name @value{GDBN} is currently using.
14480 @kindex set debug-file-directory
14481 @item set debug-file-directory @var{directories}
14482 Set the directories which @value{GDBN} searches for separate debugging
14483 information files to @var{directory}. Multiple directory components can be set
14484 concatenating them by a directory separator.
14486 @kindex show debug-file-directory
14487 @item show debug-file-directory
14488 Show the directories @value{GDBN} searches for separate debugging
14493 @cindex @code{.gnu_debuglink} sections
14494 @cindex debug link sections
14495 A debug link is a special section of the executable file named
14496 @code{.gnu_debuglink}. The section must contain:
14500 A filename, with any leading directory components removed, followed by
14503 zero to three bytes of padding, as needed to reach the next four-byte
14504 boundary within the section, and
14506 a four-byte CRC checksum, stored in the same endianness used for the
14507 executable file itself. The checksum is computed on the debugging
14508 information file's full contents by the function given below, passing
14509 zero as the @var{crc} argument.
14512 Any executable file format can carry a debug link, as long as it can
14513 contain a section named @code{.gnu_debuglink} with the contents
14516 @cindex @code{.note.gnu.build-id} sections
14517 @cindex build ID sections
14518 The build ID is a special section in the executable file (and in other
14519 ELF binary files that @value{GDBN} may consider). This section is
14520 often named @code{.note.gnu.build-id}, but that name is not mandatory.
14521 It contains unique identification for the built files---the ID remains
14522 the same across multiple builds of the same build tree. The default
14523 algorithm SHA1 produces 160 bits (40 hexadecimal characters) of the
14524 content for the build ID string. The same section with an identical
14525 value is present in the original built binary with symbols, in its
14526 stripped variant, and in the separate debugging information file.
14528 The debugging information file itself should be an ordinary
14529 executable, containing a full set of linker symbols, sections, and
14530 debugging information. The sections of the debugging information file
14531 should have the same names, addresses, and sizes as the original file,
14532 but they need not contain any data---much like a @code{.bss} section
14533 in an ordinary executable.
14535 The @sc{gnu} binary utilities (Binutils) package includes the
14536 @samp{objcopy} utility that can produce
14537 the separated executable / debugging information file pairs using the
14538 following commands:
14541 @kbd{objcopy --only-keep-debug foo foo.debug}
14546 These commands remove the debugging
14547 information from the executable file @file{foo} and place it in the file
14548 @file{foo.debug}. You can use the first, second or both methods to link the
14553 The debug link method needs the following additional command to also leave
14554 behind a debug link in @file{foo}:
14557 @kbd{objcopy --add-gnu-debuglink=foo.debug foo}
14560 Ulrich Drepper's @file{elfutils} package, starting with version 0.53, contains
14561 a version of the @code{strip} command such that the command @kbd{strip foo -f
14562 foo.debug} has the same functionality as the two @code{objcopy} commands and
14563 the @code{ln -s} command above, together.
14566 Build ID gets embedded into the main executable using @code{ld --build-id} or
14567 the @value{NGCC} counterpart @code{gcc -Wl,--build-id}. Build ID support plus
14568 compatibility fixes for debug files separation are present in @sc{gnu} binary
14569 utilities (Binutils) package since version 2.18.
14574 @cindex CRC algorithm definition
14575 The CRC used in @code{.gnu_debuglink} is the CRC-32 defined in
14576 IEEE 802.3 using the polynomial:
14578 @c TexInfo requires naked braces for multi-digit exponents for Tex
14579 @c output, but this causes HTML output to barf. HTML has to be set using
14580 @c raw commands. So we end up having to specify this equation in 2
14585 <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>
14586 + <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
14592 @math{x^{32} + x^{26} + x^{23} + x^{22} + x^{16} + x^{12} + x^{11}}
14593 @math{+ x^{10} + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1}
14597 The function is computed byte at a time, taking the least
14598 significant bit of each byte first. The initial pattern
14599 @code{0xffffffff} is used, to ensure leading zeros affect the CRC and
14600 the final result is inverted to ensure trailing zeros also affect the
14603 @emph{Note:} This is the same CRC polynomial as used in handling the
14604 @dfn{Remote Serial Protocol} @code{qCRC} packet (@pxref{Remote Protocol,
14605 , @value{GDBN} Remote Serial Protocol}). However in the
14606 case of the Remote Serial Protocol, the CRC is computed @emph{most}
14607 significant bit first, and the result is not inverted, so trailing
14608 zeros have no effect on the CRC value.
14610 To complete the description, we show below the code of the function
14611 which produces the CRC used in @code{.gnu_debuglink}. Inverting the
14612 initially supplied @code{crc} argument means that an initial call to
14613 this function passing in zero will start computing the CRC using
14616 @kindex gnu_debuglink_crc32
14619 gnu_debuglink_crc32 (unsigned long crc,
14620 unsigned char *buf, size_t len)
14622 static const unsigned long crc32_table[256] =
14624 0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419,
14625 0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4,
14626 0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07,
14627 0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
14628 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856,
14629 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
14630 0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4,
14631 0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
14632 0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3,
14633 0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a,
14634 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599,
14635 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
14636 0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190,
14637 0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f,
14638 0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e,
14639 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
14640 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed,
14641 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
14642 0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3,
14643 0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
14644 0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a,
14645 0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5,
14646 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010,
14647 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
14648 0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17,
14649 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6,
14650 0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615,
14651 0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
14652 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344,
14653 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
14654 0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a,
14655 0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
14656 0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1,
14657 0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c,
14658 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef,
14659 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
14660 0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe,
14661 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31,
14662 0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c,
14663 0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
14664 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b,
14665 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
14666 0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1,
14667 0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
14668 0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278,
14669 0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7,
14670 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66,
14671 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
14672 0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605,
14673 0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8,
14674 0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b,
14677 unsigned char *end;
14679 crc = ~crc & 0xffffffff;
14680 for (end = buf + len; buf < end; ++buf)
14681 crc = crc32_table[(crc ^ *buf) & 0xff] ^ (crc >> 8);
14682 return ~crc & 0xffffffff;
14687 This computation does not apply to the ``build ID'' method.
14690 @node Symbol Errors
14691 @section Errors Reading Symbol Files
14693 While reading a symbol file, @value{GDBN} occasionally encounters problems,
14694 such as symbol types it does not recognize, or known bugs in compiler
14695 output. By default, @value{GDBN} does not notify you of such problems, since
14696 they are relatively common and primarily of interest to people
14697 debugging compilers. If you are interested in seeing information
14698 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
14699 only one message about each such type of problem, no matter how many
14700 times the problem occurs; or you can ask @value{GDBN} to print more messages,
14701 to see how many times the problems occur, with the @code{set
14702 complaints} command (@pxref{Messages/Warnings, ,Optional Warnings and
14705 The messages currently printed, and their meanings, include:
14708 @item inner block not inside outer block in @var{symbol}
14710 The symbol information shows where symbol scopes begin and end
14711 (such as at the start of a function or a block of statements). This
14712 error indicates that an inner scope block is not fully contained
14713 in its outer scope blocks.
14715 @value{GDBN} circumvents the problem by treating the inner block as if it had
14716 the same scope as the outer block. In the error message, @var{symbol}
14717 may be shown as ``@code{(don't know)}'' if the outer block is not a
14720 @item block at @var{address} out of order
14722 The symbol information for symbol scope blocks should occur in
14723 order of increasing addresses. This error indicates that it does not
14726 @value{GDBN} does not circumvent this problem, and has trouble
14727 locating symbols in the source file whose symbols it is reading. (You
14728 can often determine what source file is affected by specifying
14729 @code{set verbose on}. @xref{Messages/Warnings, ,Optional Warnings and
14732 @item bad block start address patched
14734 The symbol information for a symbol scope block has a start address
14735 smaller than the address of the preceding source line. This is known
14736 to occur in the SunOS 4.1.1 (and earlier) C compiler.
14738 @value{GDBN} circumvents the problem by treating the symbol scope block as
14739 starting on the previous source line.
14741 @item bad string table offset in symbol @var{n}
14744 Symbol number @var{n} contains a pointer into the string table which is
14745 larger than the size of the string table.
14747 @value{GDBN} circumvents the problem by considering the symbol to have the
14748 name @code{foo}, which may cause other problems if many symbols end up
14751 @item unknown symbol type @code{0x@var{nn}}
14753 The symbol information contains new data types that @value{GDBN} does
14754 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
14755 uncomprehended information, in hexadecimal.
14757 @value{GDBN} circumvents the error by ignoring this symbol information.
14758 This usually allows you to debug your program, though certain symbols
14759 are not accessible. If you encounter such a problem and feel like
14760 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
14761 on @code{complain}, then go up to the function @code{read_dbx_symtab}
14762 and examine @code{*bufp} to see the symbol.
14764 @item stub type has NULL name
14766 @value{GDBN} could not find the full definition for a struct or class.
14768 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
14769 The symbol information for a C@t{++} member function is missing some
14770 information that recent versions of the compiler should have output for
14773 @item info mismatch between compiler and debugger
14775 @value{GDBN} could not parse a type specification output by the compiler.
14780 @section GDB Data Files
14782 @cindex prefix for data files
14783 @value{GDBN} will sometimes read an auxiliary data file. These files
14784 are kept in a directory known as the @dfn{data directory}.
14786 You can set the data directory's name, and view the name @value{GDBN}
14787 is currently using.
14790 @kindex set data-directory
14791 @item set data-directory @var{directory}
14792 Set the directory which @value{GDBN} searches for auxiliary data files
14793 to @var{directory}.
14795 @kindex show data-directory
14796 @item show data-directory
14797 Show the directory @value{GDBN} searches for auxiliary data files.
14800 @cindex default data directory
14801 @cindex @samp{--with-gdb-datadir}
14802 You can set the default data directory by using the configure-time
14803 @samp{--with-gdb-datadir} option. If the data directory is inside
14804 @value{GDBN}'s configured binary prefix (set with @samp{--prefix} or
14805 @samp{--exec-prefix}), then the default data directory will be updated
14806 automatically if the installed @value{GDBN} is moved to a new
14810 @chapter Specifying a Debugging Target
14812 @cindex debugging target
14813 A @dfn{target} is the execution environment occupied by your program.
14815 Often, @value{GDBN} runs in the same host environment as your program;
14816 in that case, the debugging target is specified as a side effect when
14817 you use the @code{file} or @code{core} commands. When you need more
14818 flexibility---for example, running @value{GDBN} on a physically separate
14819 host, or controlling a standalone system over a serial port or a
14820 realtime system over a TCP/IP connection---you can use the @code{target}
14821 command to specify one of the target types configured for @value{GDBN}
14822 (@pxref{Target Commands, ,Commands for Managing Targets}).
14824 @cindex target architecture
14825 It is possible to build @value{GDBN} for several different @dfn{target
14826 architectures}. When @value{GDBN} is built like that, you can choose
14827 one of the available architectures with the @kbd{set architecture}
14831 @kindex set architecture
14832 @kindex show architecture
14833 @item set architecture @var{arch}
14834 This command sets the current target architecture to @var{arch}. The
14835 value of @var{arch} can be @code{"auto"}, in addition to one of the
14836 supported architectures.
14838 @item show architecture
14839 Show the current target architecture.
14841 @item set processor
14843 @kindex set processor
14844 @kindex show processor
14845 These are alias commands for, respectively, @code{set architecture}
14846 and @code{show architecture}.
14850 * Active Targets:: Active targets
14851 * Target Commands:: Commands for managing targets
14852 * Byte Order:: Choosing target byte order
14855 @node Active Targets
14856 @section Active Targets
14858 @cindex stacking targets
14859 @cindex active targets
14860 @cindex multiple targets
14862 There are three classes of targets: processes, core files, and
14863 executable files. @value{GDBN} can work concurrently on up to three
14864 active targets, one in each class. This allows you to (for example)
14865 start a process and inspect its activity without abandoning your work on
14868 For example, if you execute @samp{gdb a.out}, then the executable file
14869 @code{a.out} is the only active target. If you designate a core file as
14870 well---presumably from a prior run that crashed and coredumped---then
14871 @value{GDBN} has two active targets and uses them in tandem, looking
14872 first in the corefile target, then in the executable file, to satisfy
14873 requests for memory addresses. (Typically, these two classes of target
14874 are complementary, since core files contain only a program's
14875 read-write memory---variables and so on---plus machine status, while
14876 executable files contain only the program text and initialized data.)
14878 When you type @code{run}, your executable file becomes an active process
14879 target as well. When a process target is active, all @value{GDBN}
14880 commands requesting memory addresses refer to that target; addresses in
14881 an active core file or executable file target are obscured while the
14882 process target is active.
14884 Use the @code{core-file} and @code{exec-file} commands to select a new
14885 core file or executable target (@pxref{Files, ,Commands to Specify
14886 Files}). To specify as a target a process that is already running, use
14887 the @code{attach} command (@pxref{Attach, ,Debugging an Already-running
14890 @node Target Commands
14891 @section Commands for Managing Targets
14894 @item target @var{type} @var{parameters}
14895 Connects the @value{GDBN} host environment to a target machine or
14896 process. A target is typically a protocol for talking to debugging
14897 facilities. You use the argument @var{type} to specify the type or
14898 protocol of the target machine.
14900 Further @var{parameters} are interpreted by the target protocol, but
14901 typically include things like device names or host names to connect
14902 with, process numbers, and baud rates.
14904 The @code{target} command does not repeat if you press @key{RET} again
14905 after executing the command.
14907 @kindex help target
14909 Displays the names of all targets available. To display targets
14910 currently selected, use either @code{info target} or @code{info files}
14911 (@pxref{Files, ,Commands to Specify Files}).
14913 @item help target @var{name}
14914 Describe a particular target, including any parameters necessary to
14917 @kindex set gnutarget
14918 @item set gnutarget @var{args}
14919 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
14920 knows whether it is reading an @dfn{executable},
14921 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
14922 with the @code{set gnutarget} command. Unlike most @code{target} commands,
14923 with @code{gnutarget} the @code{target} refers to a program, not a machine.
14926 @emph{Warning:} To specify a file format with @code{set gnutarget},
14927 you must know the actual BFD name.
14931 @xref{Files, , Commands to Specify Files}.
14933 @kindex show gnutarget
14934 @item show gnutarget
14935 Use the @code{show gnutarget} command to display what file format
14936 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
14937 @value{GDBN} will determine the file format for each file automatically,
14938 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
14941 @cindex common targets
14942 Here are some common targets (available, or not, depending on the GDB
14947 @item target exec @var{program}
14948 @cindex executable file target
14949 An executable file. @samp{target exec @var{program}} is the same as
14950 @samp{exec-file @var{program}}.
14952 @item target core @var{filename}
14953 @cindex core dump file target
14954 A core dump file. @samp{target core @var{filename}} is the same as
14955 @samp{core-file @var{filename}}.
14957 @item target remote @var{medium}
14958 @cindex remote target
14959 A remote system connected to @value{GDBN} via a serial line or network
14960 connection. This command tells @value{GDBN} to use its own remote
14961 protocol over @var{medium} for debugging. @xref{Remote Debugging}.
14963 For example, if you have a board connected to @file{/dev/ttya} on the
14964 machine running @value{GDBN}, you could say:
14967 target remote /dev/ttya
14970 @code{target remote} supports the @code{load} command. This is only
14971 useful if you have some other way of getting the stub to the target
14972 system, and you can put it somewhere in memory where it won't get
14973 clobbered by the download.
14975 @item target sim @r{[}@var{simargs}@r{]} @dots{}
14976 @cindex built-in simulator target
14977 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
14985 works; however, you cannot assume that a specific memory map, device
14986 drivers, or even basic I/O is available, although some simulators do
14987 provide these. For info about any processor-specific simulator details,
14988 see the appropriate section in @ref{Embedded Processors, ,Embedded
14993 Some configurations may include these targets as well:
14997 @item target nrom @var{dev}
14998 @cindex NetROM ROM emulator target
14999 NetROM ROM emulator. This target only supports downloading.
15003 Different targets are available on different configurations of @value{GDBN};
15004 your configuration may have more or fewer targets.
15006 Many remote targets require you to download the executable's code once
15007 you've successfully established a connection. You may wish to control
15008 various aspects of this process.
15013 @kindex set hash@r{, for remote monitors}
15014 @cindex hash mark while downloading
15015 This command controls whether a hash mark @samp{#} is displayed while
15016 downloading a file to the remote monitor. If on, a hash mark is
15017 displayed after each S-record is successfully downloaded to the
15021 @kindex show hash@r{, for remote monitors}
15022 Show the current status of displaying the hash mark.
15024 @item set debug monitor
15025 @kindex set debug monitor
15026 @cindex display remote monitor communications
15027 Enable or disable display of communications messages between
15028 @value{GDBN} and the remote monitor.
15030 @item show debug monitor
15031 @kindex show debug monitor
15032 Show the current status of displaying communications between
15033 @value{GDBN} and the remote monitor.
15038 @kindex load @var{filename}
15039 @item load @var{filename}
15041 Depending on what remote debugging facilities are configured into
15042 @value{GDBN}, the @code{load} command may be available. Where it exists, it
15043 is meant to make @var{filename} (an executable) available for debugging
15044 on the remote system---by downloading, or dynamic linking, for example.
15045 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
15046 the @code{add-symbol-file} command.
15048 If your @value{GDBN} does not have a @code{load} command, attempting to
15049 execute it gets the error message ``@code{You can't do that when your
15050 target is @dots{}}''
15052 The file is loaded at whatever address is specified in the executable.
15053 For some object file formats, you can specify the load address when you
15054 link the program; for other formats, like a.out, the object file format
15055 specifies a fixed address.
15056 @c FIXME! This would be a good place for an xref to the GNU linker doc.
15058 Depending on the remote side capabilities, @value{GDBN} may be able to
15059 load programs into flash memory.
15061 @code{load} does not repeat if you press @key{RET} again after using it.
15065 @section Choosing Target Byte Order
15067 @cindex choosing target byte order
15068 @cindex target byte order
15070 Some types of processors, such as the MIPS, PowerPC, and Renesas SH,
15071 offer the ability to run either big-endian or little-endian byte
15072 orders. Usually the executable or symbol will include a bit to
15073 designate the endian-ness, and you will not need to worry about
15074 which to use. However, you may still find it useful to adjust
15075 @value{GDBN}'s idea of processor endian-ness manually.
15079 @item set endian big
15080 Instruct @value{GDBN} to assume the target is big-endian.
15082 @item set endian little
15083 Instruct @value{GDBN} to assume the target is little-endian.
15085 @item set endian auto
15086 Instruct @value{GDBN} to use the byte order associated with the
15090 Display @value{GDBN}'s current idea of the target byte order.
15094 Note that these commands merely adjust interpretation of symbolic
15095 data on the host, and that they have absolutely no effect on the
15099 @node Remote Debugging
15100 @chapter Debugging Remote Programs
15101 @cindex remote debugging
15103 If you are trying to debug a program running on a machine that cannot run
15104 @value{GDBN} in the usual way, it is often useful to use remote debugging.
15105 For example, you might use remote debugging on an operating system kernel,
15106 or on a small system which does not have a general purpose operating system
15107 powerful enough to run a full-featured debugger.
15109 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
15110 to make this work with particular debugging targets. In addition,
15111 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
15112 but not specific to any particular target system) which you can use if you
15113 write the remote stubs---the code that runs on the remote system to
15114 communicate with @value{GDBN}.
15116 Other remote targets may be available in your
15117 configuration of @value{GDBN}; use @code{help target} to list them.
15120 * Connecting:: Connecting to a remote target
15121 * File Transfer:: Sending files to a remote system
15122 * Server:: Using the gdbserver program
15123 * Remote Configuration:: Remote configuration
15124 * Remote Stub:: Implementing a remote stub
15128 @section Connecting to a Remote Target
15130 On the @value{GDBN} host machine, you will need an unstripped copy of
15131 your program, since @value{GDBN} needs symbol and debugging information.
15132 Start up @value{GDBN} as usual, using the name of the local copy of your
15133 program as the first argument.
15135 @cindex @code{target remote}
15136 @value{GDBN} can communicate with the target over a serial line, or
15137 over an @acronym{IP} network using @acronym{TCP} or @acronym{UDP}. In
15138 each case, @value{GDBN} uses the same protocol for debugging your
15139 program; only the medium carrying the debugging packets varies. The
15140 @code{target remote} command establishes a connection to the target.
15141 Its arguments indicate which medium to use:
15145 @item target remote @var{serial-device}
15146 @cindex serial line, @code{target remote}
15147 Use @var{serial-device} to communicate with the target. For example,
15148 to use a serial line connected to the device named @file{/dev/ttyb}:
15151 target remote /dev/ttyb
15154 If you're using a serial line, you may want to give @value{GDBN} the
15155 @w{@samp{--baud}} option, or use the @code{set remotebaud} command
15156 (@pxref{Remote Configuration, set remotebaud}) before the
15157 @code{target} command.
15159 @item target remote @code{@var{host}:@var{port}}
15160 @itemx target remote @code{tcp:@var{host}:@var{port}}
15161 @cindex @acronym{TCP} port, @code{target remote}
15162 Debug using a @acronym{TCP} connection to @var{port} on @var{host}.
15163 The @var{host} may be either a host name or a numeric @acronym{IP}
15164 address; @var{port} must be a decimal number. The @var{host} could be
15165 the target machine itself, if it is directly connected to the net, or
15166 it might be a terminal server which in turn has a serial line to the
15169 For example, to connect to port 2828 on a terminal server named
15173 target remote manyfarms:2828
15176 If your remote target is actually running on the same machine as your
15177 debugger session (e.g.@: a simulator for your target running on the
15178 same host), you can omit the hostname. For example, to connect to
15179 port 1234 on your local machine:
15182 target remote :1234
15186 Note that the colon is still required here.
15188 @item target remote @code{udp:@var{host}:@var{port}}
15189 @cindex @acronym{UDP} port, @code{target remote}
15190 Debug using @acronym{UDP} packets to @var{port} on @var{host}. For example, to
15191 connect to @acronym{UDP} port 2828 on a terminal server named @code{manyfarms}:
15194 target remote udp:manyfarms:2828
15197 When using a @acronym{UDP} connection for remote debugging, you should
15198 keep in mind that the `U' stands for ``Unreliable''. @acronym{UDP}
15199 can silently drop packets on busy or unreliable networks, which will
15200 cause havoc with your debugging session.
15202 @item target remote | @var{command}
15203 @cindex pipe, @code{target remote} to
15204 Run @var{command} in the background and communicate with it using a
15205 pipe. The @var{command} is a shell command, to be parsed and expanded
15206 by the system's command shell, @code{/bin/sh}; it should expect remote
15207 protocol packets on its standard input, and send replies on its
15208 standard output. You could use this to run a stand-alone simulator
15209 that speaks the remote debugging protocol, to make net connections
15210 using programs like @code{ssh}, or for other similar tricks.
15212 If @var{command} closes its standard output (perhaps by exiting),
15213 @value{GDBN} will try to send it a @code{SIGTERM} signal. (If the
15214 program has already exited, this will have no effect.)
15218 Once the connection has been established, you can use all the usual
15219 commands to examine and change data. The remote program is already
15220 running; you can use @kbd{step} and @kbd{continue}, and you do not
15221 need to use @kbd{run}.
15223 @cindex interrupting remote programs
15224 @cindex remote programs, interrupting
15225 Whenever @value{GDBN} is waiting for the remote program, if you type the
15226 interrupt character (often @kbd{Ctrl-c}), @value{GDBN} attempts to stop the
15227 program. This may or may not succeed, depending in part on the hardware
15228 and the serial drivers the remote system uses. If you type the
15229 interrupt character once again, @value{GDBN} displays this prompt:
15232 Interrupted while waiting for the program.
15233 Give up (and stop debugging it)? (y or n)
15236 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
15237 (If you decide you want to try again later, you can use @samp{target
15238 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
15239 goes back to waiting.
15242 @kindex detach (remote)
15244 When you have finished debugging the remote program, you can use the
15245 @code{detach} command to release it from @value{GDBN} control.
15246 Detaching from the target normally resumes its execution, but the results
15247 will depend on your particular remote stub. After the @code{detach}
15248 command, @value{GDBN} is free to connect to another target.
15252 The @code{disconnect} command behaves like @code{detach}, except that
15253 the target is generally not resumed. It will wait for @value{GDBN}
15254 (this instance or another one) to connect and continue debugging. After
15255 the @code{disconnect} command, @value{GDBN} is again free to connect to
15258 @cindex send command to remote monitor
15259 @cindex extend @value{GDBN} for remote targets
15260 @cindex add new commands for external monitor
15262 @item monitor @var{cmd}
15263 This command allows you to send arbitrary commands directly to the
15264 remote monitor. Since @value{GDBN} doesn't care about the commands it
15265 sends like this, this command is the way to extend @value{GDBN}---you
15266 can add new commands that only the external monitor will understand
15270 @node File Transfer
15271 @section Sending files to a remote system
15272 @cindex remote target, file transfer
15273 @cindex file transfer
15274 @cindex sending files to remote systems
15276 Some remote targets offer the ability to transfer files over the same
15277 connection used to communicate with @value{GDBN}. This is convenient
15278 for targets accessible through other means, e.g.@: @sc{gnu}/Linux systems
15279 running @code{gdbserver} over a network interface. For other targets,
15280 e.g.@: embedded devices with only a single serial port, this may be
15281 the only way to upload or download files.
15283 Not all remote targets support these commands.
15287 @item remote put @var{hostfile} @var{targetfile}
15288 Copy file @var{hostfile} from the host system (the machine running
15289 @value{GDBN}) to @var{targetfile} on the target system.
15292 @item remote get @var{targetfile} @var{hostfile}
15293 Copy file @var{targetfile} from the target system to @var{hostfile}
15294 on the host system.
15296 @kindex remote delete
15297 @item remote delete @var{targetfile}
15298 Delete @var{targetfile} from the target system.
15303 @section Using the @code{gdbserver} Program
15306 @cindex remote connection without stubs
15307 @code{gdbserver} is a control program for Unix-like systems, which
15308 allows you to connect your program with a remote @value{GDBN} via
15309 @code{target remote}---but without linking in the usual debugging stub.
15311 @code{gdbserver} is not a complete replacement for the debugging stubs,
15312 because it requires essentially the same operating-system facilities
15313 that @value{GDBN} itself does. In fact, a system that can run
15314 @code{gdbserver} to connect to a remote @value{GDBN} could also run
15315 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
15316 because it is a much smaller program than @value{GDBN} itself. It is
15317 also easier to port than all of @value{GDBN}, so you may be able to get
15318 started more quickly on a new system by using @code{gdbserver}.
15319 Finally, if you develop code for real-time systems, you may find that
15320 the tradeoffs involved in real-time operation make it more convenient to
15321 do as much development work as possible on another system, for example
15322 by cross-compiling. You can use @code{gdbserver} to make a similar
15323 choice for debugging.
15325 @value{GDBN} and @code{gdbserver} communicate via either a serial line
15326 or a TCP connection, using the standard @value{GDBN} remote serial
15330 @emph{Warning:} @code{gdbserver} does not have any built-in security.
15331 Do not run @code{gdbserver} connected to any public network; a
15332 @value{GDBN} connection to @code{gdbserver} provides access to the
15333 target system with the same privileges as the user running
15337 @subsection Running @code{gdbserver}
15338 @cindex arguments, to @code{gdbserver}
15340 Run @code{gdbserver} on the target system. You need a copy of the
15341 program you want to debug, including any libraries it requires.
15342 @code{gdbserver} does not need your program's symbol table, so you can
15343 strip the program if necessary to save space. @value{GDBN} on the host
15344 system does all the symbol handling.
15346 To use the server, you must tell it how to communicate with @value{GDBN};
15347 the name of your program; and the arguments for your program. The usual
15351 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
15354 @var{comm} is either a device name (to use a serial line) or a TCP
15355 hostname and portnumber. For example, to debug Emacs with the argument
15356 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
15360 target> gdbserver /dev/com1 emacs foo.txt
15363 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
15366 To use a TCP connection instead of a serial line:
15369 target> gdbserver host:2345 emacs foo.txt
15372 The only difference from the previous example is the first argument,
15373 specifying that you are communicating with the host @value{GDBN} via
15374 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
15375 expect a TCP connection from machine @samp{host} to local TCP port 2345.
15376 (Currently, the @samp{host} part is ignored.) You can choose any number
15377 you want for the port number as long as it does not conflict with any
15378 TCP ports already in use on the target system (for example, @code{23} is
15379 reserved for @code{telnet}).@footnote{If you choose a port number that
15380 conflicts with another service, @code{gdbserver} prints an error message
15381 and exits.} You must use the same port number with the host @value{GDBN}
15382 @code{target remote} command.
15384 @subsubsection Attaching to a Running Program
15386 On some targets, @code{gdbserver} can also attach to running programs.
15387 This is accomplished via the @code{--attach} argument. The syntax is:
15390 target> gdbserver --attach @var{comm} @var{pid}
15393 @var{pid} is the process ID of a currently running process. It isn't necessary
15394 to point @code{gdbserver} at a binary for the running process.
15397 @cindex attach to a program by name
15398 You can debug processes by name instead of process ID if your target has the
15399 @code{pidof} utility:
15402 target> gdbserver --attach @var{comm} `pidof @var{program}`
15405 In case more than one copy of @var{program} is running, or @var{program}
15406 has multiple threads, most versions of @code{pidof} support the
15407 @code{-s} option to only return the first process ID.
15409 @subsubsection Multi-Process Mode for @code{gdbserver}
15410 @cindex gdbserver, multiple processes
15411 @cindex multiple processes with gdbserver
15413 When you connect to @code{gdbserver} using @code{target remote},
15414 @code{gdbserver} debugs the specified program only once. When the
15415 program exits, or you detach from it, @value{GDBN} closes the connection
15416 and @code{gdbserver} exits.
15418 If you connect using @kbd{target extended-remote}, @code{gdbserver}
15419 enters multi-process mode. When the debugged program exits, or you
15420 detach from it, @value{GDBN} stays connected to @code{gdbserver} even
15421 though no program is running. The @code{run} and @code{attach}
15422 commands instruct @code{gdbserver} to run or attach to a new program.
15423 The @code{run} command uses @code{set remote exec-file} (@pxref{set
15424 remote exec-file}) to select the program to run. Command line
15425 arguments are supported, except for wildcard expansion and I/O
15426 redirection (@pxref{Arguments}).
15428 To start @code{gdbserver} without supplying an initial command to run
15429 or process ID to attach, use the @option{--multi} command line option.
15430 Then you can connect using @kbd{target extended-remote} and start
15431 the program you want to debug.
15433 @code{gdbserver} does not automatically exit in multi-process mode.
15434 You can terminate it by using @code{monitor exit}
15435 (@pxref{Monitor Commands for gdbserver}).
15437 @subsubsection Other Command-Line Arguments for @code{gdbserver}
15439 The @option{--debug} option tells @code{gdbserver} to display extra
15440 status information about the debugging process. The
15441 @option{--remote-debug} option tells @code{gdbserver} to display
15442 remote protocol debug output. These options are intended for
15443 @code{gdbserver} development and for bug reports to the developers.
15445 The @option{--wrapper} option specifies a wrapper to launch programs
15446 for debugging. The option should be followed by the name of the
15447 wrapper, then any command-line arguments to pass to the wrapper, then
15448 @kbd{--} indicating the end of the wrapper arguments.
15450 @code{gdbserver} runs the specified wrapper program with a combined
15451 command line including the wrapper arguments, then the name of the
15452 program to debug, then any arguments to the program. The wrapper
15453 runs until it executes your program, and then @value{GDBN} gains control.
15455 You can use any program that eventually calls @code{execve} with
15456 its arguments as a wrapper. Several standard Unix utilities do
15457 this, e.g.@: @code{env} and @code{nohup}. Any Unix shell script ending
15458 with @code{exec "$@@"} will also work.
15460 For example, you can use @code{env} to pass an environment variable to
15461 the debugged program, without setting the variable in @code{gdbserver}'s
15465 $ gdbserver --wrapper env LD_PRELOAD=libtest.so -- :2222 ./testprog
15468 @subsection Connecting to @code{gdbserver}
15470 Run @value{GDBN} on the host system.
15472 First make sure you have the necessary symbol files. Load symbols for
15473 your application using the @code{file} command before you connect. Use
15474 @code{set sysroot} to locate target libraries (unless your @value{GDBN}
15475 was compiled with the correct sysroot using @code{--with-sysroot}).
15477 The symbol file and target libraries must exactly match the executable
15478 and libraries on the target, with one exception: the files on the host
15479 system should not be stripped, even if the files on the target system
15480 are. Mismatched or missing files will lead to confusing results
15481 during debugging. On @sc{gnu}/Linux targets, mismatched or missing
15482 files may also prevent @code{gdbserver} from debugging multi-threaded
15485 Connect to your target (@pxref{Connecting,,Connecting to a Remote Target}).
15486 For TCP connections, you must start up @code{gdbserver} prior to using
15487 the @code{target remote} command. Otherwise you may get an error whose
15488 text depends on the host system, but which usually looks something like
15489 @samp{Connection refused}. Don't use the @code{load}
15490 command in @value{GDBN} when using @code{gdbserver}, since the program is
15491 already on the target.
15493 @subsection Monitor Commands for @code{gdbserver}
15494 @cindex monitor commands, for @code{gdbserver}
15495 @anchor{Monitor Commands for gdbserver}
15497 During a @value{GDBN} session using @code{gdbserver}, you can use the
15498 @code{monitor} command to send special requests to @code{gdbserver}.
15499 Here are the available commands.
15503 List the available monitor commands.
15505 @item monitor set debug 0
15506 @itemx monitor set debug 1
15507 Disable or enable general debugging messages.
15509 @item monitor set remote-debug 0
15510 @itemx monitor set remote-debug 1
15511 Disable or enable specific debugging messages associated with the remote
15512 protocol (@pxref{Remote Protocol}).
15514 @item monitor set libthread-db-search-path [PATH]
15515 @cindex gdbserver, search path for @code{libthread_db}
15516 When this command is issued, @var{path} is a colon-separated list of
15517 directories to search for @code{libthread_db} (@pxref{Threads,,set
15518 libthread-db-search-path}). If you omit @var{path},
15519 @samp{libthread-db-search-path} will be reset to an empty list.
15522 Tell gdbserver to exit immediately. This command should be followed by
15523 @code{disconnect} to close the debugging session. @code{gdbserver} will
15524 detach from any attached processes and kill any processes it created.
15525 Use @code{monitor exit} to terminate @code{gdbserver} at the end
15526 of a multi-process mode debug session.
15530 @node Remote Configuration
15531 @section Remote Configuration
15534 @kindex show remote
15535 This section documents the configuration options available when
15536 debugging remote programs. For the options related to the File I/O
15537 extensions of the remote protocol, see @ref{system,
15538 system-call-allowed}.
15541 @item set remoteaddresssize @var{bits}
15542 @cindex address size for remote targets
15543 @cindex bits in remote address
15544 Set the maximum size of address in a memory packet to the specified
15545 number of bits. @value{GDBN} will mask off the address bits above
15546 that number, when it passes addresses to the remote target. The
15547 default value is the number of bits in the target's address.
15549 @item show remoteaddresssize
15550 Show the current value of remote address size in bits.
15552 @item set remotebaud @var{n}
15553 @cindex baud rate for remote targets
15554 Set the baud rate for the remote serial I/O to @var{n} baud. The
15555 value is used to set the speed of the serial port used for debugging
15558 @item show remotebaud
15559 Show the current speed of the remote connection.
15561 @item set remotebreak
15562 @cindex interrupt remote programs
15563 @cindex BREAK signal instead of Ctrl-C
15564 @anchor{set remotebreak}
15565 If set to on, @value{GDBN} sends a @code{BREAK} signal to the remote
15566 when you type @kbd{Ctrl-c} to interrupt the program running
15567 on the remote. If set to off, @value{GDBN} sends the @samp{Ctrl-C}
15568 character instead. The default is off, since most remote systems
15569 expect to see @samp{Ctrl-C} as the interrupt signal.
15571 @item show remotebreak
15572 Show whether @value{GDBN} sends @code{BREAK} or @samp{Ctrl-C} to
15573 interrupt the remote program.
15575 @item set remoteflow on
15576 @itemx set remoteflow off
15577 @kindex set remoteflow
15578 Enable or disable hardware flow control (@code{RTS}/@code{CTS})
15579 on the serial port used to communicate to the remote target.
15581 @item show remoteflow
15582 @kindex show remoteflow
15583 Show the current setting of hardware flow control.
15585 @item set remotelogbase @var{base}
15586 Set the base (a.k.a.@: radix) of logging serial protocol
15587 communications to @var{base}. Supported values of @var{base} are:
15588 @code{ascii}, @code{octal}, and @code{hex}. The default is
15591 @item show remotelogbase
15592 Show the current setting of the radix for logging remote serial
15595 @item set remotelogfile @var{file}
15596 @cindex record serial communications on file
15597 Record remote serial communications on the named @var{file}. The
15598 default is not to record at all.
15600 @item show remotelogfile.
15601 Show the current setting of the file name on which to record the
15602 serial communications.
15604 @item set remotetimeout @var{num}
15605 @cindex timeout for serial communications
15606 @cindex remote timeout
15607 Set the timeout limit to wait for the remote target to respond to
15608 @var{num} seconds. The default is 2 seconds.
15610 @item show remotetimeout
15611 Show the current number of seconds to wait for the remote target
15614 @cindex limit hardware breakpoints and watchpoints
15615 @cindex remote target, limit break- and watchpoints
15616 @anchor{set remote hardware-watchpoint-limit}
15617 @anchor{set remote hardware-breakpoint-limit}
15618 @item set remote hardware-watchpoint-limit @var{limit}
15619 @itemx set remote hardware-breakpoint-limit @var{limit}
15620 Restrict @value{GDBN} to using @var{limit} remote hardware breakpoint or
15621 watchpoints. A limit of -1, the default, is treated as unlimited.
15623 @item set remote exec-file @var{filename}
15624 @itemx show remote exec-file
15625 @anchor{set remote exec-file}
15626 @cindex executable file, for remote target
15627 Select the file used for @code{run} with @code{target
15628 extended-remote}. This should be set to a filename valid on the
15629 target system. If it is not set, the target will use a default
15630 filename (e.g.@: the last program run).
15632 @item set remote interrupt-sequence
15633 @cindex interrupt remote programs
15634 @cindex select Ctrl-C, BREAK or BREAK-g
15635 Allow the user to select one of @samp{Ctrl-C}, a @code{BREAK} or
15636 @samp{BREAK-g} as the
15637 sequence to the remote target in order to interrupt the execution.
15638 @samp{Ctrl-C} is a default. Some system prefers @code{BREAK} which
15639 is high level of serial line for some certain time.
15640 Linux kernel prefers @samp{BREAK-g}, a.k.a Magic SysRq g.
15641 It is @code{BREAK} signal followed by character @code{g}.
15643 @item show interrupt-sequence
15644 Show which of @samp{Ctrl-C}, @code{BREAK} or @code{BREAK-g}
15645 is sent by @value{GDBN} to interrupt the remote program.
15646 @code{BREAK-g} is BREAK signal followed by @code{g} and
15647 also known as Magic SysRq g.
15649 @item set remote interrupt-on-connect
15650 @cindex send interrupt-sequence on start
15651 Specify whether interrupt-sequence is sent to remote target when
15652 @value{GDBN} connects to it. This is mostly needed when you debug
15653 Linux kernel. Linux kernel expects @code{BREAK} followed by @code{g}
15654 which is known as Magic SysRq g in order to connect @value{GDBN}.
15656 @item show interrupt-on-connect
15657 Show whether interrupt-sequence is sent
15658 to remote target when @value{GDBN} connects to it.
15662 @item set tcp auto-retry on
15663 @cindex auto-retry, for remote TCP target
15664 Enable auto-retry for remote TCP connections. This is useful if the remote
15665 debugging agent is launched in parallel with @value{GDBN}; there is a race
15666 condition because the agent may not become ready to accept the connection
15667 before @value{GDBN} attempts to connect. When auto-retry is
15668 enabled, if the initial attempt to connect fails, @value{GDBN} reattempts
15669 to establish the connection using the timeout specified by
15670 @code{set tcp connect-timeout}.
15672 @item set tcp auto-retry off
15673 Do not auto-retry failed TCP connections.
15675 @item show tcp auto-retry
15676 Show the current auto-retry setting.
15678 @item set tcp connect-timeout @var{seconds}
15679 @cindex connection timeout, for remote TCP target
15680 @cindex timeout, for remote target connection
15681 Set the timeout for establishing a TCP connection to the remote target to
15682 @var{seconds}. The timeout affects both polling to retry failed connections
15683 (enabled by @code{set tcp auto-retry on}) and waiting for connections
15684 that are merely slow to complete, and represents an approximate cumulative
15687 @item show tcp connect-timeout
15688 Show the current connection timeout setting.
15691 @cindex remote packets, enabling and disabling
15692 The @value{GDBN} remote protocol autodetects the packets supported by
15693 your debugging stub. If you need to override the autodetection, you
15694 can use these commands to enable or disable individual packets. Each
15695 packet can be set to @samp{on} (the remote target supports this
15696 packet), @samp{off} (the remote target does not support this packet),
15697 or @samp{auto} (detect remote target support for this packet). They
15698 all default to @samp{auto}. For more information about each packet,
15699 see @ref{Remote Protocol}.
15701 During normal use, you should not have to use any of these commands.
15702 If you do, that may be a bug in your remote debugging stub, or a bug
15703 in @value{GDBN}. You may want to report the problem to the
15704 @value{GDBN} developers.
15706 For each packet @var{name}, the command to enable or disable the
15707 packet is @code{set remote @var{name}-packet}. The available settings
15710 @multitable @columnfractions 0.28 0.32 0.25
15713 @tab Related Features
15715 @item @code{fetch-register}
15717 @tab @code{info registers}
15719 @item @code{set-register}
15723 @item @code{binary-download}
15725 @tab @code{load}, @code{set}
15727 @item @code{read-aux-vector}
15728 @tab @code{qXfer:auxv:read}
15729 @tab @code{info auxv}
15731 @item @code{symbol-lookup}
15732 @tab @code{qSymbol}
15733 @tab Detecting multiple threads
15735 @item @code{attach}
15736 @tab @code{vAttach}
15739 @item @code{verbose-resume}
15741 @tab Stepping or resuming multiple threads
15747 @item @code{software-breakpoint}
15751 @item @code{hardware-breakpoint}
15755 @item @code{write-watchpoint}
15759 @item @code{read-watchpoint}
15763 @item @code{access-watchpoint}
15767 @item @code{target-features}
15768 @tab @code{qXfer:features:read}
15769 @tab @code{set architecture}
15771 @item @code{library-info}
15772 @tab @code{qXfer:libraries:read}
15773 @tab @code{info sharedlibrary}
15775 @item @code{memory-map}
15776 @tab @code{qXfer:memory-map:read}
15777 @tab @code{info mem}
15779 @item @code{read-spu-object}
15780 @tab @code{qXfer:spu:read}
15781 @tab @code{info spu}
15783 @item @code{write-spu-object}
15784 @tab @code{qXfer:spu:write}
15785 @tab @code{info spu}
15787 @item @code{read-siginfo-object}
15788 @tab @code{qXfer:siginfo:read}
15789 @tab @code{print $_siginfo}
15791 @item @code{write-siginfo-object}
15792 @tab @code{qXfer:siginfo:write}
15793 @tab @code{set $_siginfo}
15795 @item @code{threads}
15796 @tab @code{qXfer:threads:read}
15797 @tab @code{info threads}
15799 @item @code{get-thread-local-@*storage-address}
15800 @tab @code{qGetTLSAddr}
15801 @tab Displaying @code{__thread} variables
15803 @item @code{get-thread-information-block-address}
15804 @tab @code{qGetTIBAddr}
15805 @tab Display MS-Windows Thread Information Block.
15807 @item @code{search-memory}
15808 @tab @code{qSearch:memory}
15811 @item @code{supported-packets}
15812 @tab @code{qSupported}
15813 @tab Remote communications parameters
15815 @item @code{pass-signals}
15816 @tab @code{QPassSignals}
15817 @tab @code{handle @var{signal}}
15819 @item @code{hostio-close-packet}
15820 @tab @code{vFile:close}
15821 @tab @code{remote get}, @code{remote put}
15823 @item @code{hostio-open-packet}
15824 @tab @code{vFile:open}
15825 @tab @code{remote get}, @code{remote put}
15827 @item @code{hostio-pread-packet}
15828 @tab @code{vFile:pread}
15829 @tab @code{remote get}, @code{remote put}
15831 @item @code{hostio-pwrite-packet}
15832 @tab @code{vFile:pwrite}
15833 @tab @code{remote get}, @code{remote put}
15835 @item @code{hostio-unlink-packet}
15836 @tab @code{vFile:unlink}
15837 @tab @code{remote delete}
15839 @item @code{noack-packet}
15840 @tab @code{QStartNoAckMode}
15841 @tab Packet acknowledgment
15843 @item @code{osdata}
15844 @tab @code{qXfer:osdata:read}
15845 @tab @code{info os}
15847 @item @code{query-attached}
15848 @tab @code{qAttached}
15849 @tab Querying remote process attach state.
15853 @section Implementing a Remote Stub
15855 @cindex debugging stub, example
15856 @cindex remote stub, example
15857 @cindex stub example, remote debugging
15858 The stub files provided with @value{GDBN} implement the target side of the
15859 communication protocol, and the @value{GDBN} side is implemented in the
15860 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
15861 these subroutines to communicate, and ignore the details. (If you're
15862 implementing your own stub file, you can still ignore the details: start
15863 with one of the existing stub files. @file{sparc-stub.c} is the best
15864 organized, and therefore the easiest to read.)
15866 @cindex remote serial debugging, overview
15867 To debug a program running on another machine (the debugging
15868 @dfn{target} machine), you must first arrange for all the usual
15869 prerequisites for the program to run by itself. For example, for a C
15874 A startup routine to set up the C runtime environment; these usually
15875 have a name like @file{crt0}. The startup routine may be supplied by
15876 your hardware supplier, or you may have to write your own.
15879 A C subroutine library to support your program's
15880 subroutine calls, notably managing input and output.
15883 A way of getting your program to the other machine---for example, a
15884 download program. These are often supplied by the hardware
15885 manufacturer, but you may have to write your own from hardware
15889 The next step is to arrange for your program to use a serial port to
15890 communicate with the machine where @value{GDBN} is running (the @dfn{host}
15891 machine). In general terms, the scheme looks like this:
15895 @value{GDBN} already understands how to use this protocol; when everything
15896 else is set up, you can simply use the @samp{target remote} command
15897 (@pxref{Targets,,Specifying a Debugging Target}).
15899 @item On the target,
15900 you must link with your program a few special-purpose subroutines that
15901 implement the @value{GDBN} remote serial protocol. The file containing these
15902 subroutines is called a @dfn{debugging stub}.
15904 On certain remote targets, you can use an auxiliary program
15905 @code{gdbserver} instead of linking a stub into your program.
15906 @xref{Server,,Using the @code{gdbserver} Program}, for details.
15909 The debugging stub is specific to the architecture of the remote
15910 machine; for example, use @file{sparc-stub.c} to debug programs on
15913 @cindex remote serial stub list
15914 These working remote stubs are distributed with @value{GDBN}:
15919 @cindex @file{i386-stub.c}
15922 For Intel 386 and compatible architectures.
15925 @cindex @file{m68k-stub.c}
15926 @cindex Motorola 680x0
15928 For Motorola 680x0 architectures.
15931 @cindex @file{sh-stub.c}
15934 For Renesas SH architectures.
15937 @cindex @file{sparc-stub.c}
15939 For @sc{sparc} architectures.
15941 @item sparcl-stub.c
15942 @cindex @file{sparcl-stub.c}
15945 For Fujitsu @sc{sparclite} architectures.
15949 The @file{README} file in the @value{GDBN} distribution may list other
15950 recently added stubs.
15953 * Stub Contents:: What the stub can do for you
15954 * Bootstrapping:: What you must do for the stub
15955 * Debug Session:: Putting it all together
15958 @node Stub Contents
15959 @subsection What the Stub Can Do for You
15961 @cindex remote serial stub
15962 The debugging stub for your architecture supplies these three
15966 @item set_debug_traps
15967 @findex set_debug_traps
15968 @cindex remote serial stub, initialization
15969 This routine arranges for @code{handle_exception} to run when your
15970 program stops. You must call this subroutine explicitly near the
15971 beginning of your program.
15973 @item handle_exception
15974 @findex handle_exception
15975 @cindex remote serial stub, main routine
15976 This is the central workhorse, but your program never calls it
15977 explicitly---the setup code arranges for @code{handle_exception} to
15978 run when a trap is triggered.
15980 @code{handle_exception} takes control when your program stops during
15981 execution (for example, on a breakpoint), and mediates communications
15982 with @value{GDBN} on the host machine. This is where the communications
15983 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
15984 representative on the target machine. It begins by sending summary
15985 information on the state of your program, then continues to execute,
15986 retrieving and transmitting any information @value{GDBN} needs, until you
15987 execute a @value{GDBN} command that makes your program resume; at that point,
15988 @code{handle_exception} returns control to your own code on the target
15992 @cindex @code{breakpoint} subroutine, remote
15993 Use this auxiliary subroutine to make your program contain a
15994 breakpoint. Depending on the particular situation, this may be the only
15995 way for @value{GDBN} to get control. For instance, if your target
15996 machine has some sort of interrupt button, you won't need to call this;
15997 pressing the interrupt button transfers control to
15998 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
15999 simply receiving characters on the serial port may also trigger a trap;
16000 again, in that situation, you don't need to call @code{breakpoint} from
16001 your own program---simply running @samp{target remote} from the host
16002 @value{GDBN} session gets control.
16004 Call @code{breakpoint} if none of these is true, or if you simply want
16005 to make certain your program stops at a predetermined point for the
16006 start of your debugging session.
16009 @node Bootstrapping
16010 @subsection What You Must Do for the Stub
16012 @cindex remote stub, support routines
16013 The debugging stubs that come with @value{GDBN} are set up for a particular
16014 chip architecture, but they have no information about the rest of your
16015 debugging target machine.
16017 First of all you need to tell the stub how to communicate with the
16021 @item int getDebugChar()
16022 @findex getDebugChar
16023 Write this subroutine to read a single character from the serial port.
16024 It may be identical to @code{getchar} for your target system; a
16025 different name is used to allow you to distinguish the two if you wish.
16027 @item void putDebugChar(int)
16028 @findex putDebugChar
16029 Write this subroutine to write a single character to the serial port.
16030 It may be identical to @code{putchar} for your target system; a
16031 different name is used to allow you to distinguish the two if you wish.
16034 @cindex control C, and remote debugging
16035 @cindex interrupting remote targets
16036 If you want @value{GDBN} to be able to stop your program while it is
16037 running, you need to use an interrupt-driven serial driver, and arrange
16038 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
16039 character). That is the character which @value{GDBN} uses to tell the
16040 remote system to stop.
16042 Getting the debugging target to return the proper status to @value{GDBN}
16043 probably requires changes to the standard stub; one quick and dirty way
16044 is to just execute a breakpoint instruction (the ``dirty'' part is that
16045 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
16047 Other routines you need to supply are:
16050 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
16051 @findex exceptionHandler
16052 Write this function to install @var{exception_address} in the exception
16053 handling tables. You need to do this because the stub does not have any
16054 way of knowing what the exception handling tables on your target system
16055 are like (for example, the processor's table might be in @sc{rom},
16056 containing entries which point to a table in @sc{ram}).
16057 @var{exception_number} is the exception number which should be changed;
16058 its meaning is architecture-dependent (for example, different numbers
16059 might represent divide by zero, misaligned access, etc). When this
16060 exception occurs, control should be transferred directly to
16061 @var{exception_address}, and the processor state (stack, registers,
16062 and so on) should be just as it is when a processor exception occurs. So if
16063 you want to use a jump instruction to reach @var{exception_address}, it
16064 should be a simple jump, not a jump to subroutine.
16066 For the 386, @var{exception_address} should be installed as an interrupt
16067 gate so that interrupts are masked while the handler runs. The gate
16068 should be at privilege level 0 (the most privileged level). The
16069 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
16070 help from @code{exceptionHandler}.
16072 @item void flush_i_cache()
16073 @findex flush_i_cache
16074 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
16075 instruction cache, if any, on your target machine. If there is no
16076 instruction cache, this subroutine may be a no-op.
16078 On target machines that have instruction caches, @value{GDBN} requires this
16079 function to make certain that the state of your program is stable.
16083 You must also make sure this library routine is available:
16086 @item void *memset(void *, int, int)
16088 This is the standard library function @code{memset} that sets an area of
16089 memory to a known value. If you have one of the free versions of
16090 @code{libc.a}, @code{memset} can be found there; otherwise, you must
16091 either obtain it from your hardware manufacturer, or write your own.
16094 If you do not use the GNU C compiler, you may need other standard
16095 library subroutines as well; this varies from one stub to another,
16096 but in general the stubs are likely to use any of the common library
16097 subroutines which @code{@value{NGCC}} generates as inline code.
16100 @node Debug Session
16101 @subsection Putting it All Together
16103 @cindex remote serial debugging summary
16104 In summary, when your program is ready to debug, you must follow these
16109 Make sure you have defined the supporting low-level routines
16110 (@pxref{Bootstrapping,,What You Must Do for the Stub}):
16112 @code{getDebugChar}, @code{putDebugChar},
16113 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
16117 Insert these lines near the top of your program:
16125 For the 680x0 stub only, you need to provide a variable called
16126 @code{exceptionHook}. Normally you just use:
16129 void (*exceptionHook)() = 0;
16133 but if before calling @code{set_debug_traps}, you set it to point to a
16134 function in your program, that function is called when
16135 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
16136 error). The function indicated by @code{exceptionHook} is called with
16137 one parameter: an @code{int} which is the exception number.
16140 Compile and link together: your program, the @value{GDBN} debugging stub for
16141 your target architecture, and the supporting subroutines.
16144 Make sure you have a serial connection between your target machine and
16145 the @value{GDBN} host, and identify the serial port on the host.
16148 @c The "remote" target now provides a `load' command, so we should
16149 @c document that. FIXME.
16150 Download your program to your target machine (or get it there by
16151 whatever means the manufacturer provides), and start it.
16154 Start @value{GDBN} on the host, and connect to the target
16155 (@pxref{Connecting,,Connecting to a Remote Target}).
16159 @node Configurations
16160 @chapter Configuration-Specific Information
16162 While nearly all @value{GDBN} commands are available for all native and
16163 cross versions of the debugger, there are some exceptions. This chapter
16164 describes things that are only available in certain configurations.
16166 There are three major categories of configurations: native
16167 configurations, where the host and target are the same, embedded
16168 operating system configurations, which are usually the same for several
16169 different processor architectures, and bare embedded processors, which
16170 are quite different from each other.
16175 * Embedded Processors::
16182 This section describes details specific to particular native
16187 * BSD libkvm Interface:: Debugging BSD kernel memory images
16188 * SVR4 Process Information:: SVR4 process information
16189 * DJGPP Native:: Features specific to the DJGPP port
16190 * Cygwin Native:: Features specific to the Cygwin port
16191 * Hurd Native:: Features specific to @sc{gnu} Hurd
16192 * Neutrino:: Features specific to QNX Neutrino
16193 * Darwin:: Features specific to Darwin
16199 On HP-UX systems, if you refer to a function or variable name that
16200 begins with a dollar sign, @value{GDBN} searches for a user or system
16201 name first, before it searches for a convenience variable.
16204 @node BSD libkvm Interface
16205 @subsection BSD libkvm Interface
16208 @cindex kernel memory image
16209 @cindex kernel crash dump
16211 BSD-derived systems (FreeBSD/NetBSD/OpenBSD) have a kernel memory
16212 interface that provides a uniform interface for accessing kernel virtual
16213 memory images, including live systems and crash dumps. @value{GDBN}
16214 uses this interface to allow you to debug live kernels and kernel crash
16215 dumps on many native BSD configurations. This is implemented as a
16216 special @code{kvm} debugging target. For debugging a live system, load
16217 the currently running kernel into @value{GDBN} and connect to the
16221 (@value{GDBP}) @b{target kvm}
16224 For debugging crash dumps, provide the file name of the crash dump as an
16228 (@value{GDBP}) @b{target kvm /var/crash/bsd.0}
16231 Once connected to the @code{kvm} target, the following commands are
16237 Set current context from the @dfn{Process Control Block} (PCB) address.
16240 Set current context from proc address. This command isn't available on
16241 modern FreeBSD systems.
16244 @node SVR4 Process Information
16245 @subsection SVR4 Process Information
16247 @cindex examine process image
16248 @cindex process info via @file{/proc}
16250 Many versions of SVR4 and compatible systems provide a facility called
16251 @samp{/proc} that can be used to examine the image of a running
16252 process using file-system subroutines. If @value{GDBN} is configured
16253 for an operating system with this facility, the command @code{info
16254 proc} is available to report information about the process running
16255 your program, or about any process running on your system. @code{info
16256 proc} works only on SVR4 systems that include the @code{procfs} code.
16257 This includes, as of this writing, @sc{gnu}/Linux, OSF/1 (Digital
16258 Unix), Solaris, Irix, and Unixware, but not HP-UX, for example.
16264 @itemx info proc @var{process-id}
16265 Summarize available information about any running process. If a
16266 process ID is specified by @var{process-id}, display information about
16267 that process; otherwise display information about the program being
16268 debugged. The summary includes the debugged process ID, the command
16269 line used to invoke it, its current working directory, and its
16270 executable file's absolute file name.
16272 On some systems, @var{process-id} can be of the form
16273 @samp{[@var{pid}]/@var{tid}} which specifies a certain thread ID
16274 within a process. If the optional @var{pid} part is missing, it means
16275 a thread from the process being debugged (the leading @samp{/} still
16276 needs to be present, or else @value{GDBN} will interpret the number as
16277 a process ID rather than a thread ID).
16279 @item info proc mappings
16280 @cindex memory address space mappings
16281 Report the memory address space ranges accessible in the program, with
16282 information on whether the process has read, write, or execute access
16283 rights to each range. On @sc{gnu}/Linux systems, each memory range
16284 includes the object file which is mapped to that range, instead of the
16285 memory access rights to that range.
16287 @item info proc stat
16288 @itemx info proc status
16289 @cindex process detailed status information
16290 These subcommands are specific to @sc{gnu}/Linux systems. They show
16291 the process-related information, including the user ID and group ID;
16292 how many threads are there in the process; its virtual memory usage;
16293 the signals that are pending, blocked, and ignored; its TTY; its
16294 consumption of system and user time; its stack size; its @samp{nice}
16295 value; etc. For more information, see the @samp{proc} man page
16296 (type @kbd{man 5 proc} from your shell prompt).
16298 @item info proc all
16299 Show all the information about the process described under all of the
16300 above @code{info proc} subcommands.
16303 @comment These sub-options of 'info proc' were not included when
16304 @comment procfs.c was re-written. Keep their descriptions around
16305 @comment against the day when someone finds the time to put them back in.
16306 @kindex info proc times
16307 @item info proc times
16308 Starting time, user CPU time, and system CPU time for your program and
16311 @kindex info proc id
16313 Report on the process IDs related to your program: its own process ID,
16314 the ID of its parent, the process group ID, and the session ID.
16317 @item set procfs-trace
16318 @kindex set procfs-trace
16319 @cindex @code{procfs} API calls
16320 This command enables and disables tracing of @code{procfs} API calls.
16322 @item show procfs-trace
16323 @kindex show procfs-trace
16324 Show the current state of @code{procfs} API call tracing.
16326 @item set procfs-file @var{file}
16327 @kindex set procfs-file
16328 Tell @value{GDBN} to write @code{procfs} API trace to the named
16329 @var{file}. @value{GDBN} appends the trace info to the previous
16330 contents of the file. The default is to display the trace on the
16333 @item show procfs-file
16334 @kindex show procfs-file
16335 Show the file to which @code{procfs} API trace is written.
16337 @item proc-trace-entry
16338 @itemx proc-trace-exit
16339 @itemx proc-untrace-entry
16340 @itemx proc-untrace-exit
16341 @kindex proc-trace-entry
16342 @kindex proc-trace-exit
16343 @kindex proc-untrace-entry
16344 @kindex proc-untrace-exit
16345 These commands enable and disable tracing of entries into and exits
16346 from the @code{syscall} interface.
16349 @kindex info pidlist
16350 @cindex process list, QNX Neutrino
16351 For QNX Neutrino only, this command displays the list of all the
16352 processes and all the threads within each process.
16355 @kindex info meminfo
16356 @cindex mapinfo list, QNX Neutrino
16357 For QNX Neutrino only, this command displays the list of all mapinfos.
16361 @subsection Features for Debugging @sc{djgpp} Programs
16362 @cindex @sc{djgpp} debugging
16363 @cindex native @sc{djgpp} debugging
16364 @cindex MS-DOS-specific commands
16367 @sc{djgpp} is a port of the @sc{gnu} development tools to MS-DOS and
16368 MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs
16369 that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on
16370 top of real-mode DOS systems and their emulations.
16372 @value{GDBN} supports native debugging of @sc{djgpp} programs, and
16373 defines a few commands specific to the @sc{djgpp} port. This
16374 subsection describes those commands.
16379 This is a prefix of @sc{djgpp}-specific commands which print
16380 information about the target system and important OS structures.
16383 @cindex MS-DOS system info
16384 @cindex free memory information (MS-DOS)
16385 @item info dos sysinfo
16386 This command displays assorted information about the underlying
16387 platform: the CPU type and features, the OS version and flavor, the
16388 DPMI version, and the available conventional and DPMI memory.
16393 @cindex segment descriptor tables
16394 @cindex descriptor tables display
16396 @itemx info dos ldt
16397 @itemx info dos idt
16398 These 3 commands display entries from, respectively, Global, Local,
16399 and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor
16400 tables are data structures which store a descriptor for each segment
16401 that is currently in use. The segment's selector is an index into a
16402 descriptor table; the table entry for that index holds the
16403 descriptor's base address and limit, and its attributes and access
16406 A typical @sc{djgpp} program uses 3 segments: a code segment, a data
16407 segment (used for both data and the stack), and a DOS segment (which
16408 allows access to DOS/BIOS data structures and absolute addresses in
16409 conventional memory). However, the DPMI host will usually define
16410 additional segments in order to support the DPMI environment.
16412 @cindex garbled pointers
16413 These commands allow to display entries from the descriptor tables.
16414 Without an argument, all entries from the specified table are
16415 displayed. An argument, which should be an integer expression, means
16416 display a single entry whose index is given by the argument. For
16417 example, here's a convenient way to display information about the
16418 debugged program's data segment:
16421 @exdent @code{(@value{GDBP}) info dos ldt $ds}
16422 @exdent @code{0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)}
16426 This comes in handy when you want to see whether a pointer is outside
16427 the data segment's limit (i.e.@: @dfn{garbled}).
16429 @cindex page tables display (MS-DOS)
16431 @itemx info dos pte
16432 These two commands display entries from, respectively, the Page
16433 Directory and the Page Tables. Page Directories and Page Tables are
16434 data structures which control how virtual memory addresses are mapped
16435 into physical addresses. A Page Table includes an entry for every
16436 page of memory that is mapped into the program's address space; there
16437 may be several Page Tables, each one holding up to 4096 entries. A
16438 Page Directory has up to 4096 entries, one each for every Page Table
16439 that is currently in use.
16441 Without an argument, @kbd{info dos pde} displays the entire Page
16442 Directory, and @kbd{info dos pte} displays all the entries in all of
16443 the Page Tables. An argument, an integer expression, given to the
16444 @kbd{info dos pde} command means display only that entry from the Page
16445 Directory table. An argument given to the @kbd{info dos pte} command
16446 means display entries from a single Page Table, the one pointed to by
16447 the specified entry in the Page Directory.
16449 @cindex direct memory access (DMA) on MS-DOS
16450 These commands are useful when your program uses @dfn{DMA} (Direct
16451 Memory Access), which needs physical addresses to program the DMA
16454 These commands are supported only with some DPMI servers.
16456 @cindex physical address from linear address
16457 @item info dos address-pte @var{addr}
16458 This command displays the Page Table entry for a specified linear
16459 address. The argument @var{addr} is a linear address which should
16460 already have the appropriate segment's base address added to it,
16461 because this command accepts addresses which may belong to @emph{any}
16462 segment. For example, here's how to display the Page Table entry for
16463 the page where a variable @code{i} is stored:
16466 @exdent @code{(@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i}
16467 @exdent @code{Page Table entry for address 0x11a00d30:}
16468 @exdent @code{Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30}
16472 This says that @code{i} is stored at offset @code{0xd30} from the page
16473 whose physical base address is @code{0x02698000}, and shows all the
16474 attributes of that page.
16476 Note that you must cast the addresses of variables to a @code{char *},
16477 since otherwise the value of @code{__djgpp_base_address}, the base
16478 address of all variables and functions in a @sc{djgpp} program, will
16479 be added using the rules of C pointer arithmetics: if @code{i} is
16480 declared an @code{int}, @value{GDBN} will add 4 times the value of
16481 @code{__djgpp_base_address} to the address of @code{i}.
16483 Here's another example, it displays the Page Table entry for the
16487 @exdent @code{(@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)}
16488 @exdent @code{Page Table entry for address 0x29110:}
16489 @exdent @code{Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110}
16493 (The @code{+ 3} offset is because the transfer buffer's address is the
16494 3rd member of the @code{_go32_info_block} structure.) The output
16495 clearly shows that this DPMI server maps the addresses in conventional
16496 memory 1:1, i.e.@: the physical (@code{0x00029000} + @code{0x110}) and
16497 linear (@code{0x29110}) addresses are identical.
16499 This command is supported only with some DPMI servers.
16502 @cindex DOS serial data link, remote debugging
16503 In addition to native debugging, the DJGPP port supports remote
16504 debugging via a serial data link. The following commands are specific
16505 to remote serial debugging in the DJGPP port of @value{GDBN}.
16508 @kindex set com1base
16509 @kindex set com1irq
16510 @kindex set com2base
16511 @kindex set com2irq
16512 @kindex set com3base
16513 @kindex set com3irq
16514 @kindex set com4base
16515 @kindex set com4irq
16516 @item set com1base @var{addr}
16517 This command sets the base I/O port address of the @file{COM1} serial
16520 @item set com1irq @var{irq}
16521 This command sets the @dfn{Interrupt Request} (@code{IRQ}) line to use
16522 for the @file{COM1} serial port.
16524 There are similar commands @samp{set com2base}, @samp{set com3irq},
16525 etc.@: for setting the port address and the @code{IRQ} lines for the
16528 @kindex show com1base
16529 @kindex show com1irq
16530 @kindex show com2base
16531 @kindex show com2irq
16532 @kindex show com3base
16533 @kindex show com3irq
16534 @kindex show com4base
16535 @kindex show com4irq
16536 The related commands @samp{show com1base}, @samp{show com1irq} etc.@:
16537 display the current settings of the base address and the @code{IRQ}
16538 lines used by the COM ports.
16541 @kindex info serial
16542 @cindex DOS serial port status
16543 This command prints the status of the 4 DOS serial ports. For each
16544 port, it prints whether it's active or not, its I/O base address and
16545 IRQ number, whether it uses a 16550-style FIFO, its baudrate, and the
16546 counts of various errors encountered so far.
16550 @node Cygwin Native
16551 @subsection Features for Debugging MS Windows PE Executables
16552 @cindex MS Windows debugging
16553 @cindex native Cygwin debugging
16554 @cindex Cygwin-specific commands
16556 @value{GDBN} supports native debugging of MS Windows programs, including
16557 DLLs with and without symbolic debugging information.
16559 @cindex Ctrl-BREAK, MS-Windows
16560 @cindex interrupt debuggee on MS-Windows
16561 MS-Windows programs that call @code{SetConsoleMode} to switch off the
16562 special meaning of the @samp{Ctrl-C} keystroke cannot be interrupted
16563 by typing @kbd{C-c}. For this reason, @value{GDBN} on MS-Windows
16564 supports @kbd{C-@key{BREAK}} as an alternative interrupt key
16565 sequence, which can be used to interrupt the debuggee even if it
16568 There are various additional Cygwin-specific commands, described in
16569 this section. Working with DLLs that have no debugging symbols is
16570 described in @ref{Non-debug DLL Symbols}.
16575 This is a prefix of MS Windows-specific commands which print
16576 information about the target system and important OS structures.
16578 @item info w32 selector
16579 This command displays information returned by
16580 the Win32 API @code{GetThreadSelectorEntry} function.
16581 It takes an optional argument that is evaluated to
16582 a long value to give the information about this given selector.
16583 Without argument, this command displays information
16584 about the six segment registers.
16586 @item info w32 thread-information-block
16587 This command displays thread specific information stored in the
16588 Thread Information Block (readable on the X86 CPU family using @code{$fs}
16589 selector for 32-bit programs and @code{$gs} for 64-bit programs).
16593 This is a Cygwin-specific alias of @code{info shared}.
16595 @kindex dll-symbols
16597 This command loads symbols from a dll similarly to
16598 add-sym command but without the need to specify a base address.
16600 @kindex set cygwin-exceptions
16601 @cindex debugging the Cygwin DLL
16602 @cindex Cygwin DLL, debugging
16603 @item set cygwin-exceptions @var{mode}
16604 If @var{mode} is @code{on}, @value{GDBN} will break on exceptions that
16605 happen inside the Cygwin DLL. If @var{mode} is @code{off},
16606 @value{GDBN} will delay recognition of exceptions, and may ignore some
16607 exceptions which seem to be caused by internal Cygwin DLL
16608 ``bookkeeping''. This option is meant primarily for debugging the
16609 Cygwin DLL itself; the default value is @code{off} to avoid annoying
16610 @value{GDBN} users with false @code{SIGSEGV} signals.
16612 @kindex show cygwin-exceptions
16613 @item show cygwin-exceptions
16614 Displays whether @value{GDBN} will break on exceptions that happen
16615 inside the Cygwin DLL itself.
16617 @kindex set new-console
16618 @item set new-console @var{mode}
16619 If @var{mode} is @code{on} the debuggee will
16620 be started in a new console on next start.
16621 If @var{mode} is @code{off}, the debuggee will
16622 be started in the same console as the debugger.
16624 @kindex show new-console
16625 @item show new-console
16626 Displays whether a new console is used
16627 when the debuggee is started.
16629 @kindex set new-group
16630 @item set new-group @var{mode}
16631 This boolean value controls whether the debuggee should
16632 start a new group or stay in the same group as the debugger.
16633 This affects the way the Windows OS handles
16636 @kindex show new-group
16637 @item show new-group
16638 Displays current value of new-group boolean.
16640 @kindex set debugevents
16641 @item set debugevents
16642 This boolean value adds debug output concerning kernel events related
16643 to the debuggee seen by the debugger. This includes events that
16644 signal thread and process creation and exit, DLL loading and
16645 unloading, console interrupts, and debugging messages produced by the
16646 Windows @code{OutputDebugString} API call.
16648 @kindex set debugexec
16649 @item set debugexec
16650 This boolean value adds debug output concerning execute events
16651 (such as resume thread) seen by the debugger.
16653 @kindex set debugexceptions
16654 @item set debugexceptions
16655 This boolean value adds debug output concerning exceptions in the
16656 debuggee seen by the debugger.
16658 @kindex set debugmemory
16659 @item set debugmemory
16660 This boolean value adds debug output concerning debuggee memory reads
16661 and writes by the debugger.
16665 This boolean values specifies whether the debuggee is called
16666 via a shell or directly (default value is on).
16670 Displays if the debuggee will be started with a shell.
16675 * Non-debug DLL Symbols:: Support for DLLs without debugging symbols
16678 @node Non-debug DLL Symbols
16679 @subsubsection Support for DLLs without Debugging Symbols
16680 @cindex DLLs with no debugging symbols
16681 @cindex Minimal symbols and DLLs
16683 Very often on windows, some of the DLLs that your program relies on do
16684 not include symbolic debugging information (for example,
16685 @file{kernel32.dll}). When @value{GDBN} doesn't recognize any debugging
16686 symbols in a DLL, it relies on the minimal amount of symbolic
16687 information contained in the DLL's export table. This section
16688 describes working with such symbols, known internally to @value{GDBN} as
16689 ``minimal symbols''.
16691 Note that before the debugged program has started execution, no DLLs
16692 will have been loaded. The easiest way around this problem is simply to
16693 start the program --- either by setting a breakpoint or letting the
16694 program run once to completion. It is also possible to force
16695 @value{GDBN} to load a particular DLL before starting the executable ---
16696 see the shared library information in @ref{Files}, or the
16697 @code{dll-symbols} command in @ref{Cygwin Native}. Currently,
16698 explicitly loading symbols from a DLL with no debugging information will
16699 cause the symbol names to be duplicated in @value{GDBN}'s lookup table,
16700 which may adversely affect symbol lookup performance.
16702 @subsubsection DLL Name Prefixes
16704 In keeping with the naming conventions used by the Microsoft debugging
16705 tools, DLL export symbols are made available with a prefix based on the
16706 DLL name, for instance @code{KERNEL32!CreateFileA}. The plain name is
16707 also entered into the symbol table, so @code{CreateFileA} is often
16708 sufficient. In some cases there will be name clashes within a program
16709 (particularly if the executable itself includes full debugging symbols)
16710 necessitating the use of the fully qualified name when referring to the
16711 contents of the DLL. Use single-quotes around the name to avoid the
16712 exclamation mark (``!'') being interpreted as a language operator.
16714 Note that the internal name of the DLL may be all upper-case, even
16715 though the file name of the DLL is lower-case, or vice-versa. Since
16716 symbols within @value{GDBN} are @emph{case-sensitive} this may cause
16717 some confusion. If in doubt, try the @code{info functions} and
16718 @code{info variables} commands or even @code{maint print msymbols}
16719 (@pxref{Symbols}). Here's an example:
16722 (@value{GDBP}) info function CreateFileA
16723 All functions matching regular expression "CreateFileA":
16725 Non-debugging symbols:
16726 0x77e885f4 CreateFileA
16727 0x77e885f4 KERNEL32!CreateFileA
16731 (@value{GDBP}) info function !
16732 All functions matching regular expression "!":
16734 Non-debugging symbols:
16735 0x6100114c cygwin1!__assert
16736 0x61004034 cygwin1!_dll_crt0@@0
16737 0x61004240 cygwin1!dll_crt0(per_process *)
16741 @subsubsection Working with Minimal Symbols
16743 Symbols extracted from a DLL's export table do not contain very much
16744 type information. All that @value{GDBN} can do is guess whether a symbol
16745 refers to a function or variable depending on the linker section that
16746 contains the symbol. Also note that the actual contents of the memory
16747 contained in a DLL are not available unless the program is running. This
16748 means that you cannot examine the contents of a variable or disassemble
16749 a function within a DLL without a running program.
16751 Variables are generally treated as pointers and dereferenced
16752 automatically. For this reason, it is often necessary to prefix a
16753 variable name with the address-of operator (``&'') and provide explicit
16754 type information in the command. Here's an example of the type of
16758 (@value{GDBP}) print 'cygwin1!__argv'
16763 (@value{GDBP}) x 'cygwin1!__argv'
16764 0x10021610: "\230y\""
16767 And two possible solutions:
16770 (@value{GDBP}) print ((char **)'cygwin1!__argv')[0]
16771 $2 = 0x22fd98 "/cygdrive/c/mydirectory/myprogram"
16775 (@value{GDBP}) x/2x &'cygwin1!__argv'
16776 0x610c0aa8 <cygwin1!__argv>: 0x10021608 0x00000000
16777 (@value{GDBP}) x/x 0x10021608
16778 0x10021608: 0x0022fd98
16779 (@value{GDBP}) x/s 0x0022fd98
16780 0x22fd98: "/cygdrive/c/mydirectory/myprogram"
16783 Setting a break point within a DLL is possible even before the program
16784 starts execution. However, under these circumstances, @value{GDBN} can't
16785 examine the initial instructions of the function in order to skip the
16786 function's frame set-up code. You can work around this by using ``*&''
16787 to set the breakpoint at a raw memory address:
16790 (@value{GDBP}) break *&'python22!PyOS_Readline'
16791 Breakpoint 1 at 0x1e04eff0
16794 The author of these extensions is not entirely convinced that setting a
16795 break point within a shared DLL like @file{kernel32.dll} is completely
16799 @subsection Commands Specific to @sc{gnu} Hurd Systems
16800 @cindex @sc{gnu} Hurd debugging
16802 This subsection describes @value{GDBN} commands specific to the
16803 @sc{gnu} Hurd native debugging.
16808 @kindex set signals@r{, Hurd command}
16809 @kindex set sigs@r{, Hurd command}
16810 This command toggles the state of inferior signal interception by
16811 @value{GDBN}. Mach exceptions, such as breakpoint traps, are not
16812 affected by this command. @code{sigs} is a shorthand alias for
16817 @kindex show signals@r{, Hurd command}
16818 @kindex show sigs@r{, Hurd command}
16819 Show the current state of intercepting inferior's signals.
16821 @item set signal-thread
16822 @itemx set sigthread
16823 @kindex set signal-thread
16824 @kindex set sigthread
16825 This command tells @value{GDBN} which thread is the @code{libc} signal
16826 thread. That thread is run when a signal is delivered to a running
16827 process. @code{set sigthread} is the shorthand alias of @code{set
16830 @item show signal-thread
16831 @itemx show sigthread
16832 @kindex show signal-thread
16833 @kindex show sigthread
16834 These two commands show which thread will run when the inferior is
16835 delivered a signal.
16838 @kindex set stopped@r{, Hurd command}
16839 This commands tells @value{GDBN} that the inferior process is stopped,
16840 as with the @code{SIGSTOP} signal. The stopped process can be
16841 continued by delivering a signal to it.
16844 @kindex show stopped@r{, Hurd command}
16845 This command shows whether @value{GDBN} thinks the debuggee is
16848 @item set exceptions
16849 @kindex set exceptions@r{, Hurd command}
16850 Use this command to turn off trapping of exceptions in the inferior.
16851 When exception trapping is off, neither breakpoints nor
16852 single-stepping will work. To restore the default, set exception
16855 @item show exceptions
16856 @kindex show exceptions@r{, Hurd command}
16857 Show the current state of trapping exceptions in the inferior.
16859 @item set task pause
16860 @kindex set task@r{, Hurd commands}
16861 @cindex task attributes (@sc{gnu} Hurd)
16862 @cindex pause current task (@sc{gnu} Hurd)
16863 This command toggles task suspension when @value{GDBN} has control.
16864 Setting it to on takes effect immediately, and the task is suspended
16865 whenever @value{GDBN} gets control. Setting it to off will take
16866 effect the next time the inferior is continued. If this option is set
16867 to off, you can use @code{set thread default pause on} or @code{set
16868 thread pause on} (see below) to pause individual threads.
16870 @item show task pause
16871 @kindex show task@r{, Hurd commands}
16872 Show the current state of task suspension.
16874 @item set task detach-suspend-count
16875 @cindex task suspend count
16876 @cindex detach from task, @sc{gnu} Hurd
16877 This command sets the suspend count the task will be left with when
16878 @value{GDBN} detaches from it.
16880 @item show task detach-suspend-count
16881 Show the suspend count the task will be left with when detaching.
16883 @item set task exception-port
16884 @itemx set task excp
16885 @cindex task exception port, @sc{gnu} Hurd
16886 This command sets the task exception port to which @value{GDBN} will
16887 forward exceptions. The argument should be the value of the @dfn{send
16888 rights} of the task. @code{set task excp} is a shorthand alias.
16890 @item set noninvasive
16891 @cindex noninvasive task options
16892 This command switches @value{GDBN} to a mode that is the least
16893 invasive as far as interfering with the inferior is concerned. This
16894 is the same as using @code{set task pause}, @code{set exceptions}, and
16895 @code{set signals} to values opposite to the defaults.
16897 @item info send-rights
16898 @itemx info receive-rights
16899 @itemx info port-rights
16900 @itemx info port-sets
16901 @itemx info dead-names
16904 @cindex send rights, @sc{gnu} Hurd
16905 @cindex receive rights, @sc{gnu} Hurd
16906 @cindex port rights, @sc{gnu} Hurd
16907 @cindex port sets, @sc{gnu} Hurd
16908 @cindex dead names, @sc{gnu} Hurd
16909 These commands display information about, respectively, send rights,
16910 receive rights, port rights, port sets, and dead names of a task.
16911 There are also shorthand aliases: @code{info ports} for @code{info
16912 port-rights} and @code{info psets} for @code{info port-sets}.
16914 @item set thread pause
16915 @kindex set thread@r{, Hurd command}
16916 @cindex thread properties, @sc{gnu} Hurd
16917 @cindex pause current thread (@sc{gnu} Hurd)
16918 This command toggles current thread suspension when @value{GDBN} has
16919 control. Setting it to on takes effect immediately, and the current
16920 thread is suspended whenever @value{GDBN} gets control. Setting it to
16921 off will take effect the next time the inferior is continued.
16922 Normally, this command has no effect, since when @value{GDBN} has
16923 control, the whole task is suspended. However, if you used @code{set
16924 task pause off} (see above), this command comes in handy to suspend
16925 only the current thread.
16927 @item show thread pause
16928 @kindex show thread@r{, Hurd command}
16929 This command shows the state of current thread suspension.
16931 @item set thread run
16932 This command sets whether the current thread is allowed to run.
16934 @item show thread run
16935 Show whether the current thread is allowed to run.
16937 @item set thread detach-suspend-count
16938 @cindex thread suspend count, @sc{gnu} Hurd
16939 @cindex detach from thread, @sc{gnu} Hurd
16940 This command sets the suspend count @value{GDBN} will leave on a
16941 thread when detaching. This number is relative to the suspend count
16942 found by @value{GDBN} when it notices the thread; use @code{set thread
16943 takeover-suspend-count} to force it to an absolute value.
16945 @item show thread detach-suspend-count
16946 Show the suspend count @value{GDBN} will leave on the thread when
16949 @item set thread exception-port
16950 @itemx set thread excp
16951 Set the thread exception port to which to forward exceptions. This
16952 overrides the port set by @code{set task exception-port} (see above).
16953 @code{set thread excp} is the shorthand alias.
16955 @item set thread takeover-suspend-count
16956 Normally, @value{GDBN}'s thread suspend counts are relative to the
16957 value @value{GDBN} finds when it notices each thread. This command
16958 changes the suspend counts to be absolute instead.
16960 @item set thread default
16961 @itemx show thread default
16962 @cindex thread default settings, @sc{gnu} Hurd
16963 Each of the above @code{set thread} commands has a @code{set thread
16964 default} counterpart (e.g., @code{set thread default pause}, @code{set
16965 thread default exception-port}, etc.). The @code{thread default}
16966 variety of commands sets the default thread properties for all
16967 threads; you can then change the properties of individual threads with
16968 the non-default commands.
16973 @subsection QNX Neutrino
16974 @cindex QNX Neutrino
16976 @value{GDBN} provides the following commands specific to the QNX
16980 @item set debug nto-debug
16981 @kindex set debug nto-debug
16982 When set to on, enables debugging messages specific to the QNX
16985 @item show debug nto-debug
16986 @kindex show debug nto-debug
16987 Show the current state of QNX Neutrino messages.
16994 @value{GDBN} provides the following commands specific to the Darwin target:
16997 @item set debug darwin @var{num}
16998 @kindex set debug darwin
16999 When set to a non zero value, enables debugging messages specific to
17000 the Darwin support. Higher values produce more verbose output.
17002 @item show debug darwin
17003 @kindex show debug darwin
17004 Show the current state of Darwin messages.
17006 @item set debug mach-o @var{num}
17007 @kindex set debug mach-o
17008 When set to a non zero value, enables debugging messages while
17009 @value{GDBN} is reading Darwin object files. (@dfn{Mach-O} is the
17010 file format used on Darwin for object and executable files.) Higher
17011 values produce more verbose output. This is a command to diagnose
17012 problems internal to @value{GDBN} and should not be needed in normal
17015 @item show debug mach-o
17016 @kindex show debug mach-o
17017 Show the current state of Mach-O file messages.
17019 @item set mach-exceptions on
17020 @itemx set mach-exceptions off
17021 @kindex set mach-exceptions
17022 On Darwin, faults are first reported as a Mach exception and are then
17023 mapped to a Posix signal. Use this command to turn on trapping of
17024 Mach exceptions in the inferior. This might be sometimes useful to
17025 better understand the cause of a fault. The default is off.
17027 @item show mach-exceptions
17028 @kindex show mach-exceptions
17029 Show the current state of exceptions trapping.
17034 @section Embedded Operating Systems
17036 This section describes configurations involving the debugging of
17037 embedded operating systems that are available for several different
17041 * VxWorks:: Using @value{GDBN} with VxWorks
17044 @value{GDBN} includes the ability to debug programs running on
17045 various real-time operating systems.
17048 @subsection Using @value{GDBN} with VxWorks
17054 @kindex target vxworks
17055 @item target vxworks @var{machinename}
17056 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
17057 is the target system's machine name or IP address.
17061 On VxWorks, @code{load} links @var{filename} dynamically on the
17062 current target system as well as adding its symbols in @value{GDBN}.
17064 @value{GDBN} enables developers to spawn and debug tasks running on networked
17065 VxWorks targets from a Unix host. Already-running tasks spawned from
17066 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
17067 both the Unix host and on the VxWorks target. The program
17068 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
17069 installed with the name @code{vxgdb}, to distinguish it from a
17070 @value{GDBN} for debugging programs on the host itself.)
17073 @item VxWorks-timeout @var{args}
17074 @kindex vxworks-timeout
17075 All VxWorks-based targets now support the option @code{vxworks-timeout}.
17076 This option is set by the user, and @var{args} represents the number of
17077 seconds @value{GDBN} waits for responses to rpc's. You might use this if
17078 your VxWorks target is a slow software simulator or is on the far side
17079 of a thin network line.
17082 The following information on connecting to VxWorks was current when
17083 this manual was produced; newer releases of VxWorks may use revised
17086 @findex INCLUDE_RDB
17087 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
17088 to include the remote debugging interface routines in the VxWorks
17089 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
17090 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
17091 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
17092 source debugging task @code{tRdbTask} when VxWorks is booted. For more
17093 information on configuring and remaking VxWorks, see the manufacturer's
17095 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
17097 Once you have included @file{rdb.a} in your VxWorks system image and set
17098 your Unix execution search path to find @value{GDBN}, you are ready to
17099 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
17100 @code{vxgdb}, depending on your installation).
17102 @value{GDBN} comes up showing the prompt:
17109 * VxWorks Connection:: Connecting to VxWorks
17110 * VxWorks Download:: VxWorks download
17111 * VxWorks Attach:: Running tasks
17114 @node VxWorks Connection
17115 @subsubsection Connecting to VxWorks
17117 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
17118 network. To connect to a target whose host name is ``@code{tt}'', type:
17121 (vxgdb) target vxworks tt
17125 @value{GDBN} displays messages like these:
17128 Attaching remote machine across net...
17133 @value{GDBN} then attempts to read the symbol tables of any object modules
17134 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
17135 these files by searching the directories listed in the command search
17136 path (@pxref{Environment, ,Your Program's Environment}); if it fails
17137 to find an object file, it displays a message such as:
17140 prog.o: No such file or directory.
17143 When this happens, add the appropriate directory to the search path with
17144 the @value{GDBN} command @code{path}, and execute the @code{target}
17147 @node VxWorks Download
17148 @subsubsection VxWorks Download
17150 @cindex download to VxWorks
17151 If you have connected to the VxWorks target and you want to debug an
17152 object that has not yet been loaded, you can use the @value{GDBN}
17153 @code{load} command to download a file from Unix to VxWorks
17154 incrementally. The object file given as an argument to the @code{load}
17155 command is actually opened twice: first by the VxWorks target in order
17156 to download the code, then by @value{GDBN} in order to read the symbol
17157 table. This can lead to problems if the current working directories on
17158 the two systems differ. If both systems have NFS mounted the same
17159 filesystems, you can avoid these problems by using absolute paths.
17160 Otherwise, it is simplest to set the working directory on both systems
17161 to the directory in which the object file resides, and then to reference
17162 the file by its name, without any path. For instance, a program
17163 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
17164 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
17165 program, type this on VxWorks:
17168 -> cd "@var{vxpath}/vw/demo/rdb"
17172 Then, in @value{GDBN}, type:
17175 (vxgdb) cd @var{hostpath}/vw/demo/rdb
17176 (vxgdb) load prog.o
17179 @value{GDBN} displays a response similar to this:
17182 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
17185 You can also use the @code{load} command to reload an object module
17186 after editing and recompiling the corresponding source file. Note that
17187 this makes @value{GDBN} delete all currently-defined breakpoints,
17188 auto-displays, and convenience variables, and to clear the value
17189 history. (This is necessary in order to preserve the integrity of
17190 debugger's data structures that reference the target system's symbol
17193 @node VxWorks Attach
17194 @subsubsection Running Tasks
17196 @cindex running VxWorks tasks
17197 You can also attach to an existing task using the @code{attach} command as
17201 (vxgdb) attach @var{task}
17205 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
17206 or suspended when you attach to it. Running tasks are suspended at
17207 the time of attachment.
17209 @node Embedded Processors
17210 @section Embedded Processors
17212 This section goes into details specific to particular embedded
17215 @cindex send command to simulator
17216 Whenever a specific embedded processor has a simulator, @value{GDBN}
17217 allows to send an arbitrary command to the simulator.
17220 @item sim @var{command}
17221 @kindex sim@r{, a command}
17222 Send an arbitrary @var{command} string to the simulator. Consult the
17223 documentation for the specific simulator in use for information about
17224 acceptable commands.
17230 * M32R/D:: Renesas M32R/D
17231 * M68K:: Motorola M68K
17232 * MicroBlaze:: Xilinx MicroBlaze
17233 * MIPS Embedded:: MIPS Embedded
17234 * OpenRISC 1000:: OpenRisc 1000
17235 * PA:: HP PA Embedded
17236 * PowerPC Embedded:: PowerPC Embedded
17237 * Sparclet:: Tsqware Sparclet
17238 * Sparclite:: Fujitsu Sparclite
17239 * Z8000:: Zilog Z8000
17242 * Super-H:: Renesas Super-H
17251 @item target rdi @var{dev}
17252 ARM Angel monitor, via RDI library interface to ADP protocol. You may
17253 use this target to communicate with both boards running the Angel
17254 monitor, or with the EmbeddedICE JTAG debug device.
17257 @item target rdp @var{dev}
17262 @value{GDBN} provides the following ARM-specific commands:
17265 @item set arm disassembler
17267 This commands selects from a list of disassembly styles. The
17268 @code{"std"} style is the standard style.
17270 @item show arm disassembler
17272 Show the current disassembly style.
17274 @item set arm apcs32
17275 @cindex ARM 32-bit mode
17276 This command toggles ARM operation mode between 32-bit and 26-bit.
17278 @item show arm apcs32
17279 Display the current usage of the ARM 32-bit mode.
17281 @item set arm fpu @var{fputype}
17282 This command sets the ARM floating-point unit (FPU) type. The
17283 argument @var{fputype} can be one of these:
17287 Determine the FPU type by querying the OS ABI.
17289 Software FPU, with mixed-endian doubles on little-endian ARM
17292 GCC-compiled FPA co-processor.
17294 Software FPU with pure-endian doubles.
17300 Show the current type of the FPU.
17303 This command forces @value{GDBN} to use the specified ABI.
17306 Show the currently used ABI.
17308 @item set arm fallback-mode (arm|thumb|auto)
17309 @value{GDBN} uses the symbol table, when available, to determine
17310 whether instructions are ARM or Thumb. This command controls
17311 @value{GDBN}'s default behavior when the symbol table is not
17312 available. The default is @samp{auto}, which causes @value{GDBN} to
17313 use the current execution mode (from the @code{T} bit in the @code{CPSR}
17316 @item show arm fallback-mode
17317 Show the current fallback instruction mode.
17319 @item set arm force-mode (arm|thumb|auto)
17320 This command overrides use of the symbol table to determine whether
17321 instructions are ARM or Thumb. The default is @samp{auto}, which
17322 causes @value{GDBN} to use the symbol table and then the setting
17323 of @samp{set arm fallback-mode}.
17325 @item show arm force-mode
17326 Show the current forced instruction mode.
17328 @item set debug arm
17329 Toggle whether to display ARM-specific debugging messages from the ARM
17330 target support subsystem.
17332 @item show debug arm
17333 Show whether ARM-specific debugging messages are enabled.
17336 The following commands are available when an ARM target is debugged
17337 using the RDI interface:
17340 @item rdilogfile @r{[}@var{file}@r{]}
17342 @cindex ADP (Angel Debugger Protocol) logging
17343 Set the filename for the ADP (Angel Debugger Protocol) packet log.
17344 With an argument, sets the log file to the specified @var{file}. With
17345 no argument, show the current log file name. The default log file is
17348 @item rdilogenable @r{[}@var{arg}@r{]}
17349 @kindex rdilogenable
17350 Control logging of ADP packets. With an argument of 1 or @code{"yes"}
17351 enables logging, with an argument 0 or @code{"no"} disables it. With
17352 no arguments displays the current setting. When logging is enabled,
17353 ADP packets exchanged between @value{GDBN} and the RDI target device
17354 are logged to a file.
17356 @item set rdiromatzero
17357 @kindex set rdiromatzero
17358 @cindex ROM at zero address, RDI
17359 Tell @value{GDBN} whether the target has ROM at address 0. If on,
17360 vector catching is disabled, so that zero address can be used. If off
17361 (the default), vector catching is enabled. For this command to take
17362 effect, it needs to be invoked prior to the @code{target rdi} command.
17364 @item show rdiromatzero
17365 @kindex show rdiromatzero
17366 Show the current setting of ROM at zero address.
17368 @item set rdiheartbeat
17369 @kindex set rdiheartbeat
17370 @cindex RDI heartbeat
17371 Enable or disable RDI heartbeat packets. It is not recommended to
17372 turn on this option, since it confuses ARM and EPI JTAG interface, as
17373 well as the Angel monitor.
17375 @item show rdiheartbeat
17376 @kindex show rdiheartbeat
17377 Show the setting of RDI heartbeat packets.
17381 @item target sim @r{[}@var{simargs}@r{]} @dots{}
17382 The @value{GDBN} ARM simulator accepts the following optional arguments.
17385 @item --swi-support=@var{type}
17386 Tell the simulator which SWI interfaces to support.
17387 @var{type} may be a comma separated list of the following values.
17388 The default value is @code{all}.
17401 @subsection Renesas M32R/D and M32R/SDI
17404 @kindex target m32r
17405 @item target m32r @var{dev}
17406 Renesas M32R/D ROM monitor.
17408 @kindex target m32rsdi
17409 @item target m32rsdi @var{dev}
17410 Renesas M32R SDI server, connected via parallel port to the board.
17413 The following @value{GDBN} commands are specific to the M32R monitor:
17416 @item set download-path @var{path}
17417 @kindex set download-path
17418 @cindex find downloadable @sc{srec} files (M32R)
17419 Set the default path for finding downloadable @sc{srec} files.
17421 @item show download-path
17422 @kindex show download-path
17423 Show the default path for downloadable @sc{srec} files.
17425 @item set board-address @var{addr}
17426 @kindex set board-address
17427 @cindex M32-EVA target board address
17428 Set the IP address for the M32R-EVA target board.
17430 @item show board-address
17431 @kindex show board-address
17432 Show the current IP address of the target board.
17434 @item set server-address @var{addr}
17435 @kindex set server-address
17436 @cindex download server address (M32R)
17437 Set the IP address for the download server, which is the @value{GDBN}'s
17440 @item show server-address
17441 @kindex show server-address
17442 Display the IP address of the download server.
17444 @item upload @r{[}@var{file}@r{]}
17445 @kindex upload@r{, M32R}
17446 Upload the specified @sc{srec} @var{file} via the monitor's Ethernet
17447 upload capability. If no @var{file} argument is given, the current
17448 executable file is uploaded.
17450 @item tload @r{[}@var{file}@r{]}
17451 @kindex tload@r{, M32R}
17452 Test the @code{upload} command.
17455 The following commands are available for M32R/SDI:
17460 @cindex reset SDI connection, M32R
17461 This command resets the SDI connection.
17465 This command shows the SDI connection status.
17468 @kindex debug_chaos
17469 @cindex M32R/Chaos debugging
17470 Instructs the remote that M32R/Chaos debugging is to be used.
17472 @item use_debug_dma
17473 @kindex use_debug_dma
17474 Instructs the remote to use the DEBUG_DMA method of accessing memory.
17477 @kindex use_mon_code
17478 Instructs the remote to use the MON_CODE method of accessing memory.
17481 @kindex use_ib_break
17482 Instructs the remote to set breakpoints by IB break.
17484 @item use_dbt_break
17485 @kindex use_dbt_break
17486 Instructs the remote to set breakpoints by DBT.
17492 The Motorola m68k configuration includes ColdFire support, and a
17493 target command for the following ROM monitor.
17497 @kindex target dbug
17498 @item target dbug @var{dev}
17499 dBUG ROM monitor for Motorola ColdFire.
17504 @subsection MicroBlaze
17505 @cindex Xilinx MicroBlaze
17506 @cindex XMD, Xilinx Microprocessor Debugger
17508 The MicroBlaze is a soft-core processor supported on various Xilinx
17509 FPGAs, such as Spartan or Virtex series. Boards with these processors
17510 usually have JTAG ports which connect to a host system running the Xilinx
17511 Embedded Development Kit (EDK) or Software Development Kit (SDK).
17512 This host system is used to download the configuration bitstream to
17513 the target FPGA. The Xilinx Microprocessor Debugger (XMD) program
17514 communicates with the target board using the JTAG interface and
17515 presents a @code{gdbserver} interface to the board. By default
17516 @code{xmd} uses port @code{1234}. (While it is possible to change
17517 this default port, it requires the use of undocumented @code{xmd}
17518 commands. Contact Xilinx support if you need to do this.)
17520 Use these GDB commands to connect to the MicroBlaze target processor.
17523 @item target remote :1234
17524 Use this command to connect to the target if you are running @value{GDBN}
17525 on the same system as @code{xmd}.
17527 @item target remote @var{xmd-host}:1234
17528 Use this command to connect to the target if it is connected to @code{xmd}
17529 running on a different system named @var{xmd-host}.
17532 Use this command to download a program to the MicroBlaze target.
17534 @item set debug microblaze @var{n}
17535 Enable MicroBlaze-specific debugging messages if non-zero.
17537 @item show debug microblaze @var{n}
17538 Show MicroBlaze-specific debugging level.
17541 @node MIPS Embedded
17542 @subsection MIPS Embedded
17544 @cindex MIPS boards
17545 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
17546 MIPS board attached to a serial line. This is available when
17547 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
17550 Use these @value{GDBN} commands to specify the connection to your target board:
17553 @item target mips @var{port}
17554 @kindex target mips @var{port}
17555 To run a program on the board, start up @code{@value{GDBP}} with the
17556 name of your program as the argument. To connect to the board, use the
17557 command @samp{target mips @var{port}}, where @var{port} is the name of
17558 the serial port connected to the board. If the program has not already
17559 been downloaded to the board, you may use the @code{load} command to
17560 download it. You can then use all the usual @value{GDBN} commands.
17562 For example, this sequence connects to the target board through a serial
17563 port, and loads and runs a program called @var{prog} through the
17567 host$ @value{GDBP} @var{prog}
17568 @value{GDBN} is free software and @dots{}
17569 (@value{GDBP}) target mips /dev/ttyb
17570 (@value{GDBP}) load @var{prog}
17574 @item target mips @var{hostname}:@var{portnumber}
17575 On some @value{GDBN} host configurations, you can specify a TCP
17576 connection (for instance, to a serial line managed by a terminal
17577 concentrator) instead of a serial port, using the syntax
17578 @samp{@var{hostname}:@var{portnumber}}.
17580 @item target pmon @var{port}
17581 @kindex target pmon @var{port}
17584 @item target ddb @var{port}
17585 @kindex target ddb @var{port}
17586 NEC's DDB variant of PMON for Vr4300.
17588 @item target lsi @var{port}
17589 @kindex target lsi @var{port}
17590 LSI variant of PMON.
17592 @kindex target r3900
17593 @item target r3900 @var{dev}
17594 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
17596 @kindex target array
17597 @item target array @var{dev}
17598 Array Tech LSI33K RAID controller board.
17604 @value{GDBN} also supports these special commands for MIPS targets:
17607 @item set mipsfpu double
17608 @itemx set mipsfpu single
17609 @itemx set mipsfpu none
17610 @itemx set mipsfpu auto
17611 @itemx show mipsfpu
17612 @kindex set mipsfpu
17613 @kindex show mipsfpu
17614 @cindex MIPS remote floating point
17615 @cindex floating point, MIPS remote
17616 If your target board does not support the MIPS floating point
17617 coprocessor, you should use the command @samp{set mipsfpu none} (if you
17618 need this, you may wish to put the command in your @value{GDBN} init
17619 file). This tells @value{GDBN} how to find the return value of
17620 functions which return floating point values. It also allows
17621 @value{GDBN} to avoid saving the floating point registers when calling
17622 functions on the board. If you are using a floating point coprocessor
17623 with only single precision floating point support, as on the @sc{r4650}
17624 processor, use the command @samp{set mipsfpu single}. The default
17625 double precision floating point coprocessor may be selected using
17626 @samp{set mipsfpu double}.
17628 In previous versions the only choices were double precision or no
17629 floating point, so @samp{set mipsfpu on} will select double precision
17630 and @samp{set mipsfpu off} will select no floating point.
17632 As usual, you can inquire about the @code{mipsfpu} variable with
17633 @samp{show mipsfpu}.
17635 @item set timeout @var{seconds}
17636 @itemx set retransmit-timeout @var{seconds}
17637 @itemx show timeout
17638 @itemx show retransmit-timeout
17639 @cindex @code{timeout}, MIPS protocol
17640 @cindex @code{retransmit-timeout}, MIPS protocol
17641 @kindex set timeout
17642 @kindex show timeout
17643 @kindex set retransmit-timeout
17644 @kindex show retransmit-timeout
17645 You can control the timeout used while waiting for a packet, in the MIPS
17646 remote protocol, with the @code{set timeout @var{seconds}} command. The
17647 default is 5 seconds. Similarly, you can control the timeout used while
17648 waiting for an acknowledgment of a packet with the @code{set
17649 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
17650 You can inspect both values with @code{show timeout} and @code{show
17651 retransmit-timeout}. (These commands are @emph{only} available when
17652 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
17654 The timeout set by @code{set timeout} does not apply when @value{GDBN}
17655 is waiting for your program to stop. In that case, @value{GDBN} waits
17656 forever because it has no way of knowing how long the program is going
17657 to run before stopping.
17659 @item set syn-garbage-limit @var{num}
17660 @kindex set syn-garbage-limit@r{, MIPS remote}
17661 @cindex synchronize with remote MIPS target
17662 Limit the maximum number of characters @value{GDBN} should ignore when
17663 it tries to synchronize with the remote target. The default is 10
17664 characters. Setting the limit to -1 means there's no limit.
17666 @item show syn-garbage-limit
17667 @kindex show syn-garbage-limit@r{, MIPS remote}
17668 Show the current limit on the number of characters to ignore when
17669 trying to synchronize with the remote system.
17671 @item set monitor-prompt @var{prompt}
17672 @kindex set monitor-prompt@r{, MIPS remote}
17673 @cindex remote monitor prompt
17674 Tell @value{GDBN} to expect the specified @var{prompt} string from the
17675 remote monitor. The default depends on the target:
17685 @item show monitor-prompt
17686 @kindex show monitor-prompt@r{, MIPS remote}
17687 Show the current strings @value{GDBN} expects as the prompt from the
17690 @item set monitor-warnings
17691 @kindex set monitor-warnings@r{, MIPS remote}
17692 Enable or disable monitor warnings about hardware breakpoints. This
17693 has effect only for the @code{lsi} target. When on, @value{GDBN} will
17694 display warning messages whose codes are returned by the @code{lsi}
17695 PMON monitor for breakpoint commands.
17697 @item show monitor-warnings
17698 @kindex show monitor-warnings@r{, MIPS remote}
17699 Show the current setting of printing monitor warnings.
17701 @item pmon @var{command}
17702 @kindex pmon@r{, MIPS remote}
17703 @cindex send PMON command
17704 This command allows sending an arbitrary @var{command} string to the
17705 monitor. The monitor must be in debug mode for this to work.
17708 @node OpenRISC 1000
17709 @subsection OpenRISC 1000
17710 @cindex OpenRISC 1000
17712 @cindex or1k boards
17713 See OR1k Architecture document (@uref{www.opencores.org}) for more information
17714 about platform and commands.
17718 @kindex target jtag
17719 @item target jtag jtag://@var{host}:@var{port}
17721 Connects to remote JTAG server.
17722 JTAG remote server can be either an or1ksim or JTAG server,
17723 connected via parallel port to the board.
17725 Example: @code{target jtag jtag://localhost:9999}
17728 @item or1ksim @var{command}
17729 If connected to @code{or1ksim} OpenRISC 1000 Architectural
17730 Simulator, proprietary commands can be executed.
17732 @kindex info or1k spr
17733 @item info or1k spr
17734 Displays spr groups.
17736 @item info or1k spr @var{group}
17737 @itemx info or1k spr @var{groupno}
17738 Displays register names in selected group.
17740 @item info or1k spr @var{group} @var{register}
17741 @itemx info or1k spr @var{register}
17742 @itemx info or1k spr @var{groupno} @var{registerno}
17743 @itemx info or1k spr @var{registerno}
17744 Shows information about specified spr register.
17747 @item spr @var{group} @var{register} @var{value}
17748 @itemx spr @var{register @var{value}}
17749 @itemx spr @var{groupno} @var{registerno @var{value}}
17750 @itemx spr @var{registerno @var{value}}
17751 Writes @var{value} to specified spr register.
17754 Some implementations of OpenRISC 1000 Architecture also have hardware trace.
17755 It is very similar to @value{GDBN} trace, except it does not interfere with normal
17756 program execution and is thus much faster. Hardware breakpoints/watchpoint
17757 triggers can be set using:
17760 Load effective address/data
17762 Store effective address/data
17764 Access effective address ($SEA or $LEA) or data ($SDATA/$LDATA)
17769 When triggered, it can capture low level data, like: @code{PC}, @code{LSEA},
17770 @code{LDATA}, @code{SDATA}, @code{READSPR}, @code{WRITESPR}, @code{INSTR}.
17772 @code{htrace} commands:
17773 @cindex OpenRISC 1000 htrace
17776 @item hwatch @var{conditional}
17777 Set hardware watchpoint on combination of Load/Store Effective Address(es)
17778 or Data. For example:
17780 @code{hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)}
17782 @code{hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)}
17786 Display information about current HW trace configuration.
17788 @item htrace trigger @var{conditional}
17789 Set starting criteria for HW trace.
17791 @item htrace qualifier @var{conditional}
17792 Set acquisition qualifier for HW trace.
17794 @item htrace stop @var{conditional}
17795 Set HW trace stopping criteria.
17797 @item htrace record [@var{data}]*
17798 Selects the data to be recorded, when qualifier is met and HW trace was
17801 @item htrace enable
17802 @itemx htrace disable
17803 Enables/disables the HW trace.
17805 @item htrace rewind [@var{filename}]
17806 Clears currently recorded trace data.
17808 If filename is specified, new trace file is made and any newly collected data
17809 will be written there.
17811 @item htrace print [@var{start} [@var{len}]]
17812 Prints trace buffer, using current record configuration.
17814 @item htrace mode continuous
17815 Set continuous trace mode.
17817 @item htrace mode suspend
17818 Set suspend trace mode.
17822 @node PowerPC Embedded
17823 @subsection PowerPC Embedded
17825 @value{GDBN} provides the following PowerPC-specific commands:
17828 @kindex set powerpc
17829 @item set powerpc soft-float
17830 @itemx show powerpc soft-float
17831 Force @value{GDBN} to use (or not use) a software floating point calling
17832 convention. By default, @value{GDBN} selects the calling convention based
17833 on the selected architecture and the provided executable file.
17835 @item set powerpc vector-abi
17836 @itemx show powerpc vector-abi
17837 Force @value{GDBN} to use the specified calling convention for vector
17838 arguments and return values. The valid options are @samp{auto};
17839 @samp{generic}, to avoid vector registers even if they are present;
17840 @samp{altivec}, to use AltiVec registers; and @samp{spe} to use SPE
17841 registers. By default, @value{GDBN} selects the calling convention
17842 based on the selected architecture and the provided executable file.
17844 @kindex target dink32
17845 @item target dink32 @var{dev}
17846 DINK32 ROM monitor.
17848 @kindex target ppcbug
17849 @item target ppcbug @var{dev}
17850 @kindex target ppcbug1
17851 @item target ppcbug1 @var{dev}
17852 PPCBUG ROM monitor for PowerPC.
17855 @item target sds @var{dev}
17856 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
17859 @cindex SDS protocol
17860 The following commands specific to the SDS protocol are supported
17864 @item set sdstimeout @var{nsec}
17865 @kindex set sdstimeout
17866 Set the timeout for SDS protocol reads to be @var{nsec} seconds. The
17867 default is 2 seconds.
17869 @item show sdstimeout
17870 @kindex show sdstimeout
17871 Show the current value of the SDS timeout.
17873 @item sds @var{command}
17874 @kindex sds@r{, a command}
17875 Send the specified @var{command} string to the SDS monitor.
17880 @subsection HP PA Embedded
17884 @kindex target op50n
17885 @item target op50n @var{dev}
17886 OP50N monitor, running on an OKI HPPA board.
17888 @kindex target w89k
17889 @item target w89k @var{dev}
17890 W89K monitor, running on a Winbond HPPA board.
17895 @subsection Tsqware Sparclet
17899 @value{GDBN} enables developers to debug tasks running on
17900 Sparclet targets from a Unix host.
17901 @value{GDBN} uses code that runs on
17902 both the Unix host and on the Sparclet target. The program
17903 @code{@value{GDBP}} is installed and executed on the Unix host.
17906 @item remotetimeout @var{args}
17907 @kindex remotetimeout
17908 @value{GDBN} supports the option @code{remotetimeout}.
17909 This option is set by the user, and @var{args} represents the number of
17910 seconds @value{GDBN} waits for responses.
17913 @cindex compiling, on Sparclet
17914 When compiling for debugging, include the options @samp{-g} to get debug
17915 information and @samp{-Ttext} to relocate the program to where you wish to
17916 load it on the target. You may also want to add the options @samp{-n} or
17917 @samp{-N} in order to reduce the size of the sections. Example:
17920 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
17923 You can use @code{objdump} to verify that the addresses are what you intended:
17926 sparclet-aout-objdump --headers --syms prog
17929 @cindex running, on Sparclet
17931 your Unix execution search path to find @value{GDBN}, you are ready to
17932 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
17933 (or @code{sparclet-aout-gdb}, depending on your installation).
17935 @value{GDBN} comes up showing the prompt:
17942 * Sparclet File:: Setting the file to debug
17943 * Sparclet Connection:: Connecting to Sparclet
17944 * Sparclet Download:: Sparclet download
17945 * Sparclet Execution:: Running and debugging
17948 @node Sparclet File
17949 @subsubsection Setting File to Debug
17951 The @value{GDBN} command @code{file} lets you choose with program to debug.
17954 (gdbslet) file prog
17958 @value{GDBN} then attempts to read the symbol table of @file{prog}.
17959 @value{GDBN} locates
17960 the file by searching the directories listed in the command search
17962 If the file was compiled with debug information (option @samp{-g}), source
17963 files will be searched as well.
17964 @value{GDBN} locates
17965 the source files by searching the directories listed in the directory search
17966 path (@pxref{Environment, ,Your Program's Environment}).
17968 to find a file, it displays a message such as:
17971 prog: No such file or directory.
17974 When this happens, add the appropriate directories to the search paths with
17975 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
17976 @code{target} command again.
17978 @node Sparclet Connection
17979 @subsubsection Connecting to Sparclet
17981 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
17982 To connect to a target on serial port ``@code{ttya}'', type:
17985 (gdbslet) target sparclet /dev/ttya
17986 Remote target sparclet connected to /dev/ttya
17987 main () at ../prog.c:3
17991 @value{GDBN} displays messages like these:
17997 @node Sparclet Download
17998 @subsubsection Sparclet Download
18000 @cindex download to Sparclet
18001 Once connected to the Sparclet target,
18002 you can use the @value{GDBN}
18003 @code{load} command to download the file from the host to the target.
18004 The file name and load offset should be given as arguments to the @code{load}
18006 Since the file format is aout, the program must be loaded to the starting
18007 address. You can use @code{objdump} to find out what this value is. The load
18008 offset is an offset which is added to the VMA (virtual memory address)
18009 of each of the file's sections.
18010 For instance, if the program
18011 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
18012 and bss at 0x12010170, in @value{GDBN}, type:
18015 (gdbslet) load prog 0x12010000
18016 Loading section .text, size 0xdb0 vma 0x12010000
18019 If the code is loaded at a different address then what the program was linked
18020 to, you may need to use the @code{section} and @code{add-symbol-file} commands
18021 to tell @value{GDBN} where to map the symbol table.
18023 @node Sparclet Execution
18024 @subsubsection Running and Debugging
18026 @cindex running and debugging Sparclet programs
18027 You can now begin debugging the task using @value{GDBN}'s execution control
18028 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
18029 manual for the list of commands.
18033 Breakpoint 1 at 0x12010000: file prog.c, line 3.
18035 Starting program: prog
18036 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
18037 3 char *symarg = 0;
18039 4 char *execarg = "hello!";
18044 @subsection Fujitsu Sparclite
18048 @kindex target sparclite
18049 @item target sparclite @var{dev}
18050 Fujitsu sparclite boards, used only for the purpose of loading.
18051 You must use an additional command to debug the program.
18052 For example: target remote @var{dev} using @value{GDBN} standard
18058 @subsection Zilog Z8000
18061 @cindex simulator, Z8000
18062 @cindex Zilog Z8000 simulator
18064 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
18067 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
18068 unsegmented variant of the Z8000 architecture) or the Z8001 (the
18069 segmented variant). The simulator recognizes which architecture is
18070 appropriate by inspecting the object code.
18073 @item target sim @var{args}
18075 @kindex target sim@r{, with Z8000}
18076 Debug programs on a simulated CPU. If the simulator supports setup
18077 options, specify them via @var{args}.
18081 After specifying this target, you can debug programs for the simulated
18082 CPU in the same style as programs for your host computer; use the
18083 @code{file} command to load a new program image, the @code{run} command
18084 to run your program, and so on.
18086 As well as making available all the usual machine registers
18087 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
18088 additional items of information as specially named registers:
18093 Counts clock-ticks in the simulator.
18096 Counts instructions run in the simulator.
18099 Execution time in 60ths of a second.
18103 You can refer to these values in @value{GDBN} expressions with the usual
18104 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
18105 conditional breakpoint that suspends only after at least 5000
18106 simulated clock ticks.
18109 @subsection Atmel AVR
18112 When configured for debugging the Atmel AVR, @value{GDBN} supports the
18113 following AVR-specific commands:
18116 @item info io_registers
18117 @kindex info io_registers@r{, AVR}
18118 @cindex I/O registers (Atmel AVR)
18119 This command displays information about the AVR I/O registers. For
18120 each register, @value{GDBN} prints its number and value.
18127 When configured for debugging CRIS, @value{GDBN} provides the
18128 following CRIS-specific commands:
18131 @item set cris-version @var{ver}
18132 @cindex CRIS version
18133 Set the current CRIS version to @var{ver}, either @samp{10} or @samp{32}.
18134 The CRIS version affects register names and sizes. This command is useful in
18135 case autodetection of the CRIS version fails.
18137 @item show cris-version
18138 Show the current CRIS version.
18140 @item set cris-dwarf2-cfi
18141 @cindex DWARF-2 CFI and CRIS
18142 Set the usage of DWARF-2 CFI for CRIS debugging. The default is @samp{on}.
18143 Change to @samp{off} when using @code{gcc-cris} whose version is below
18146 @item show cris-dwarf2-cfi
18147 Show the current state of using DWARF-2 CFI.
18149 @item set cris-mode @var{mode}
18151 Set the current CRIS mode to @var{mode}. It should only be changed when
18152 debugging in guru mode, in which case it should be set to
18153 @samp{guru} (the default is @samp{normal}).
18155 @item show cris-mode
18156 Show the current CRIS mode.
18160 @subsection Renesas Super-H
18163 For the Renesas Super-H processor, @value{GDBN} provides these
18168 @kindex regs@r{, Super-H}
18169 Show the values of all Super-H registers.
18171 @item set sh calling-convention @var{convention}
18172 @kindex set sh calling-convention
18173 Set the calling-convention used when calling functions from @value{GDBN}.
18174 Allowed values are @samp{gcc}, which is the default setting, and @samp{renesas}.
18175 With the @samp{gcc} setting, functions are called using the @value{NGCC} calling
18176 convention. If the DWARF-2 information of the called function specifies
18177 that the function follows the Renesas calling convention, the function
18178 is called using the Renesas calling convention. If the calling convention
18179 is set to @samp{renesas}, the Renesas calling convention is always used,
18180 regardless of the DWARF-2 information. This can be used to override the
18181 default of @samp{gcc} if debug information is missing, or the compiler
18182 does not emit the DWARF-2 calling convention entry for a function.
18184 @item show sh calling-convention
18185 @kindex show sh calling-convention
18186 Show the current calling convention setting.
18191 @node Architectures
18192 @section Architectures
18194 This section describes characteristics of architectures that affect
18195 all uses of @value{GDBN} with the architecture, both native and cross.
18202 * HPPA:: HP PA architecture
18203 * SPU:: Cell Broadband Engine SPU architecture
18208 @subsection x86 Architecture-specific Issues
18211 @item set struct-convention @var{mode}
18212 @kindex set struct-convention
18213 @cindex struct return convention
18214 @cindex struct/union returned in registers
18215 Set the convention used by the inferior to return @code{struct}s and
18216 @code{union}s from functions to @var{mode}. Possible values of
18217 @var{mode} are @code{"pcc"}, @code{"reg"}, and @code{"default"} (the
18218 default). @code{"default"} or @code{"pcc"} means that @code{struct}s
18219 are returned on the stack, while @code{"reg"} means that a
18220 @code{struct} or a @code{union} whose size is 1, 2, 4, or 8 bytes will
18221 be returned in a register.
18223 @item show struct-convention
18224 @kindex show struct-convention
18225 Show the current setting of the convention to return @code{struct}s
18234 @kindex set rstack_high_address
18235 @cindex AMD 29K register stack
18236 @cindex register stack, AMD29K
18237 @item set rstack_high_address @var{address}
18238 On AMD 29000 family processors, registers are saved in a separate
18239 @dfn{register stack}. There is no way for @value{GDBN} to determine the
18240 extent of this stack. Normally, @value{GDBN} just assumes that the
18241 stack is ``large enough''. This may result in @value{GDBN} referencing
18242 memory locations that do not exist. If necessary, you can get around
18243 this problem by specifying the ending address of the register stack with
18244 the @code{set rstack_high_address} command. The argument should be an
18245 address, which you probably want to precede with @samp{0x} to specify in
18248 @kindex show rstack_high_address
18249 @item show rstack_high_address
18250 Display the current limit of the register stack, on AMD 29000 family
18258 See the following section.
18263 @cindex stack on Alpha
18264 @cindex stack on MIPS
18265 @cindex Alpha stack
18267 Alpha- and MIPS-based computers use an unusual stack frame, which
18268 sometimes requires @value{GDBN} to search backward in the object code to
18269 find the beginning of a function.
18271 @cindex response time, MIPS debugging
18272 To improve response time (especially for embedded applications, where
18273 @value{GDBN} may be restricted to a slow serial line for this search)
18274 you may want to limit the size of this search, using one of these
18278 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
18279 @item set heuristic-fence-post @var{limit}
18280 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
18281 search for the beginning of a function. A value of @var{0} (the
18282 default) means there is no limit. However, except for @var{0}, the
18283 larger the limit the more bytes @code{heuristic-fence-post} must search
18284 and therefore the longer it takes to run. You should only need to use
18285 this command when debugging a stripped executable.
18287 @item show heuristic-fence-post
18288 Display the current limit.
18292 These commands are available @emph{only} when @value{GDBN} is configured
18293 for debugging programs on Alpha or MIPS processors.
18295 Several MIPS-specific commands are available when debugging MIPS
18299 @item set mips abi @var{arg}
18300 @kindex set mips abi
18301 @cindex set ABI for MIPS
18302 Tell @value{GDBN} which MIPS ABI is used by the inferior. Possible
18303 values of @var{arg} are:
18307 The default ABI associated with the current binary (this is the
18318 @item show mips abi
18319 @kindex show mips abi
18320 Show the MIPS ABI used by @value{GDBN} to debug the inferior.
18323 @itemx show mipsfpu
18324 @xref{MIPS Embedded, set mipsfpu}.
18326 @item set mips mask-address @var{arg}
18327 @kindex set mips mask-address
18328 @cindex MIPS addresses, masking
18329 This command determines whether the most-significant 32 bits of 64-bit
18330 MIPS addresses are masked off. The argument @var{arg} can be
18331 @samp{on}, @samp{off}, or @samp{auto}. The latter is the default
18332 setting, which lets @value{GDBN} determine the correct value.
18334 @item show mips mask-address
18335 @kindex show mips mask-address
18336 Show whether the upper 32 bits of MIPS addresses are masked off or
18339 @item set remote-mips64-transfers-32bit-regs
18340 @kindex set remote-mips64-transfers-32bit-regs
18341 This command controls compatibility with 64-bit MIPS targets that
18342 transfer data in 32-bit quantities. If you have an old MIPS 64 target
18343 that transfers 32 bits for some registers, like @sc{sr} and @sc{fsr},
18344 and 64 bits for other registers, set this option to @samp{on}.
18346 @item show remote-mips64-transfers-32bit-regs
18347 @kindex show remote-mips64-transfers-32bit-regs
18348 Show the current setting of compatibility with older MIPS 64 targets.
18350 @item set debug mips
18351 @kindex set debug mips
18352 This command turns on and off debugging messages for the MIPS-specific
18353 target code in @value{GDBN}.
18355 @item show debug mips
18356 @kindex show debug mips
18357 Show the current setting of MIPS debugging messages.
18363 @cindex HPPA support
18365 When @value{GDBN} is debugging the HP PA architecture, it provides the
18366 following special commands:
18369 @item set debug hppa
18370 @kindex set debug hppa
18371 This command determines whether HPPA architecture-specific debugging
18372 messages are to be displayed.
18374 @item show debug hppa
18375 Show whether HPPA debugging messages are displayed.
18377 @item maint print unwind @var{address}
18378 @kindex maint print unwind@r{, HPPA}
18379 This command displays the contents of the unwind table entry at the
18380 given @var{address}.
18386 @subsection Cell Broadband Engine SPU architecture
18387 @cindex Cell Broadband Engine
18390 When @value{GDBN} is debugging the Cell Broadband Engine SPU architecture,
18391 it provides the following special commands:
18394 @item info spu event
18396 Display SPU event facility status. Shows current event mask
18397 and pending event status.
18399 @item info spu signal
18400 Display SPU signal notification facility status. Shows pending
18401 signal-control word and signal notification mode of both signal
18402 notification channels.
18404 @item info spu mailbox
18405 Display SPU mailbox facility status. Shows all pending entries,
18406 in order of processing, in each of the SPU Write Outbound,
18407 SPU Write Outbound Interrupt, and SPU Read Inbound mailboxes.
18410 Display MFC DMA status. Shows all pending commands in the MFC
18411 DMA queue. For each entry, opcode, tag, class IDs, effective
18412 and local store addresses and transfer size are shown.
18414 @item info spu proxydma
18415 Display MFC Proxy-DMA status. Shows all pending commands in the MFC
18416 Proxy-DMA queue. For each entry, opcode, tag, class IDs, effective
18417 and local store addresses and transfer size are shown.
18421 When @value{GDBN} is debugging a combined PowerPC/SPU application
18422 on the Cell Broadband Engine, it provides in addition the following
18426 @item set spu stop-on-load @var{arg}
18428 Set whether to stop for new SPE threads. When set to @code{on}, @value{GDBN}
18429 will give control to the user when a new SPE thread enters its @code{main}
18430 function. The default is @code{off}.
18432 @item show spu stop-on-load
18434 Show whether to stop for new SPE threads.
18436 @item set spu auto-flush-cache @var{arg}
18437 Set whether to automatically flush the software-managed cache. When set to
18438 @code{on}, @value{GDBN} will automatically cause the SPE software-managed
18439 cache to be flushed whenever SPE execution stops. This provides a consistent
18440 view of PowerPC memory that is accessed via the cache. If an application
18441 does not use the software-managed cache, this option has no effect.
18443 @item show spu auto-flush-cache
18444 Show whether to automatically flush the software-managed cache.
18449 @subsection PowerPC
18450 @cindex PowerPC architecture
18452 When @value{GDBN} is debugging the PowerPC architecture, it provides a set of
18453 pseudo-registers to enable inspection of 128-bit wide Decimal Floating Point
18454 numbers stored in the floating point registers. These values must be stored
18455 in two consecutive registers, always starting at an even register like
18456 @code{f0} or @code{f2}.
18458 The pseudo-registers go from @code{$dl0} through @code{$dl15}, and are formed
18459 by joining the even/odd register pairs @code{f0} and @code{f1} for @code{$dl0},
18460 @code{f2} and @code{f3} for @code{$dl1} and so on.
18462 For POWER7 processors, @value{GDBN} provides a set of pseudo-registers, the 64-bit
18463 wide Extended Floating Point Registers (@samp{f32} through @samp{f63}).
18466 @node Controlling GDB
18467 @chapter Controlling @value{GDBN}
18469 You can alter the way @value{GDBN} interacts with you by using the
18470 @code{set} command. For commands controlling how @value{GDBN} displays
18471 data, see @ref{Print Settings, ,Print Settings}. Other settings are
18476 * Editing:: Command editing
18477 * Command History:: Command history
18478 * Screen Size:: Screen size
18479 * Numbers:: Numbers
18480 * ABI:: Configuring the current ABI
18481 * Messages/Warnings:: Optional warnings and messages
18482 * Debugging Output:: Optional messages about internal happenings
18483 * Other Misc Settings:: Other Miscellaneous Settings
18491 @value{GDBN} indicates its readiness to read a command by printing a string
18492 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
18493 can change the prompt string with the @code{set prompt} command. For
18494 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
18495 the prompt in one of the @value{GDBN} sessions so that you can always tell
18496 which one you are talking to.
18498 @emph{Note:} @code{set prompt} does not add a space for you after the
18499 prompt you set. This allows you to set a prompt which ends in a space
18500 or a prompt that does not.
18504 @item set prompt @var{newprompt}
18505 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
18507 @kindex show prompt
18509 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
18513 @section Command Editing
18515 @cindex command line editing
18517 @value{GDBN} reads its input commands via the @dfn{Readline} interface. This
18518 @sc{gnu} library provides consistent behavior for programs which provide a
18519 command line interface to the user. Advantages are @sc{gnu} Emacs-style
18520 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
18521 substitution, and a storage and recall of command history across
18522 debugging sessions.
18524 You may control the behavior of command line editing in @value{GDBN} with the
18525 command @code{set}.
18528 @kindex set editing
18531 @itemx set editing on
18532 Enable command line editing (enabled by default).
18534 @item set editing off
18535 Disable command line editing.
18537 @kindex show editing
18539 Show whether command line editing is enabled.
18542 @xref{Command Line Editing}, for more details about the Readline
18543 interface. Users unfamiliar with @sc{gnu} Emacs or @code{vi} are
18544 encouraged to read that chapter.
18546 @node Command History
18547 @section Command History
18548 @cindex command history
18550 @value{GDBN} can keep track of the commands you type during your
18551 debugging sessions, so that you can be certain of precisely what
18552 happened. Use these commands to manage the @value{GDBN} command
18555 @value{GDBN} uses the @sc{gnu} History library, a part of the Readline
18556 package, to provide the history facility. @xref{Using History
18557 Interactively}, for the detailed description of the History library.
18559 To issue a command to @value{GDBN} without affecting certain aspects of
18560 the state which is seen by users, prefix it with @samp{server }
18561 (@pxref{Server Prefix}). This
18562 means that this command will not affect the command history, nor will it
18563 affect @value{GDBN}'s notion of which command to repeat if @key{RET} is
18564 pressed on a line by itself.
18566 @cindex @code{server}, command prefix
18567 The server prefix does not affect the recording of values into the value
18568 history; to print a value without recording it into the value history,
18569 use the @code{output} command instead of the @code{print} command.
18571 Here is the description of @value{GDBN} commands related to command
18575 @cindex history substitution
18576 @cindex history file
18577 @kindex set history filename
18578 @cindex @env{GDBHISTFILE}, environment variable
18579 @item set history filename @var{fname}
18580 Set the name of the @value{GDBN} command history file to @var{fname}.
18581 This is the file where @value{GDBN} reads an initial command history
18582 list, and where it writes the command history from this session when it
18583 exits. You can access this list through history expansion or through
18584 the history command editing characters listed below. This file defaults
18585 to the value of the environment variable @code{GDBHISTFILE}, or to
18586 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
18589 @cindex save command history
18590 @kindex set history save
18591 @item set history save
18592 @itemx set history save on
18593 Record command history in a file, whose name may be specified with the
18594 @code{set history filename} command. By default, this option is disabled.
18596 @item set history save off
18597 Stop recording command history in a file.
18599 @cindex history size
18600 @kindex set history size
18601 @cindex @env{HISTSIZE}, environment variable
18602 @item set history size @var{size}
18603 Set the number of commands which @value{GDBN} keeps in its history list.
18604 This defaults to the value of the environment variable
18605 @code{HISTSIZE}, or to 256 if this variable is not set.
18608 History expansion assigns special meaning to the character @kbd{!}.
18609 @xref{Event Designators}, for more details.
18611 @cindex history expansion, turn on/off
18612 Since @kbd{!} is also the logical not operator in C, history expansion
18613 is off by default. If you decide to enable history expansion with the
18614 @code{set history expansion on} command, you may sometimes need to
18615 follow @kbd{!} (when it is used as logical not, in an expression) with
18616 a space or a tab to prevent it from being expanded. The readline
18617 history facilities do not attempt substitution on the strings
18618 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
18620 The commands to control history expansion are:
18623 @item set history expansion on
18624 @itemx set history expansion
18625 @kindex set history expansion
18626 Enable history expansion. History expansion is off by default.
18628 @item set history expansion off
18629 Disable history expansion.
18632 @kindex show history
18634 @itemx show history filename
18635 @itemx show history save
18636 @itemx show history size
18637 @itemx show history expansion
18638 These commands display the state of the @value{GDBN} history parameters.
18639 @code{show history} by itself displays all four states.
18644 @kindex show commands
18645 @cindex show last commands
18646 @cindex display command history
18647 @item show commands
18648 Display the last ten commands in the command history.
18650 @item show commands @var{n}
18651 Print ten commands centered on command number @var{n}.
18653 @item show commands +
18654 Print ten commands just after the commands last printed.
18658 @section Screen Size
18659 @cindex size of screen
18660 @cindex pauses in output
18662 Certain commands to @value{GDBN} may produce large amounts of
18663 information output to the screen. To help you read all of it,
18664 @value{GDBN} pauses and asks you for input at the end of each page of
18665 output. Type @key{RET} when you want to continue the output, or @kbd{q}
18666 to discard the remaining output. Also, the screen width setting
18667 determines when to wrap lines of output. Depending on what is being
18668 printed, @value{GDBN} tries to break the line at a readable place,
18669 rather than simply letting it overflow onto the following line.
18671 Normally @value{GDBN} knows the size of the screen from the terminal
18672 driver software. For example, on Unix @value{GDBN} uses the termcap data base
18673 together with the value of the @code{TERM} environment variable and the
18674 @code{stty rows} and @code{stty cols} settings. If this is not correct,
18675 you can override it with the @code{set height} and @code{set
18682 @kindex show height
18683 @item set height @var{lpp}
18685 @itemx set width @var{cpl}
18687 These @code{set} commands specify a screen height of @var{lpp} lines and
18688 a screen width of @var{cpl} characters. The associated @code{show}
18689 commands display the current settings.
18691 If you specify a height of zero lines, @value{GDBN} does not pause during
18692 output no matter how long the output is. This is useful if output is to a
18693 file or to an editor buffer.
18695 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
18696 from wrapping its output.
18698 @item set pagination on
18699 @itemx set pagination off
18700 @kindex set pagination
18701 Turn the output pagination on or off; the default is on. Turning
18702 pagination off is the alternative to @code{set height 0}. Note that
18703 running @value{GDBN} with the @option{--batch} option (@pxref{Mode
18704 Options, -batch}) also automatically disables pagination.
18706 @item show pagination
18707 @kindex show pagination
18708 Show the current pagination mode.
18713 @cindex number representation
18714 @cindex entering numbers
18716 You can always enter numbers in octal, decimal, or hexadecimal in
18717 @value{GDBN} by the usual conventions: octal numbers begin with
18718 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
18719 begin with @samp{0x}. Numbers that neither begin with @samp{0} or
18720 @samp{0x}, nor end with a @samp{.} are, by default, entered in base
18721 10; likewise, the default display for numbers---when no particular
18722 format is specified---is base 10. You can change the default base for
18723 both input and output with the commands described below.
18726 @kindex set input-radix
18727 @item set input-radix @var{base}
18728 Set the default base for numeric input. Supported choices
18729 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
18730 specified either unambiguously or using the current input radix; for
18734 set input-radix 012
18735 set input-radix 10.
18736 set input-radix 0xa
18740 sets the input base to decimal. On the other hand, @samp{set input-radix 10}
18741 leaves the input radix unchanged, no matter what it was, since
18742 @samp{10}, being without any leading or trailing signs of its base, is
18743 interpreted in the current radix. Thus, if the current radix is 16,
18744 @samp{10} is interpreted in hex, i.e.@: as 16 decimal, which doesn't
18747 @kindex set output-radix
18748 @item set output-radix @var{base}
18749 Set the default base for numeric display. Supported choices
18750 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
18751 specified either unambiguously or using the current input radix.
18753 @kindex show input-radix
18754 @item show input-radix
18755 Display the current default base for numeric input.
18757 @kindex show output-radix
18758 @item show output-radix
18759 Display the current default base for numeric display.
18761 @item set radix @r{[}@var{base}@r{]}
18765 These commands set and show the default base for both input and output
18766 of numbers. @code{set radix} sets the radix of input and output to
18767 the same base; without an argument, it resets the radix back to its
18768 default value of 10.
18773 @section Configuring the Current ABI
18775 @value{GDBN} can determine the @dfn{ABI} (Application Binary Interface) of your
18776 application automatically. However, sometimes you need to override its
18777 conclusions. Use these commands to manage @value{GDBN}'s view of the
18784 One @value{GDBN} configuration can debug binaries for multiple operating
18785 system targets, either via remote debugging or native emulation.
18786 @value{GDBN} will autodetect the @dfn{OS ABI} (Operating System ABI) in use,
18787 but you can override its conclusion using the @code{set osabi} command.
18788 One example where this is useful is in debugging of binaries which use
18789 an alternate C library (e.g.@: @sc{uClibc} for @sc{gnu}/Linux) which does
18790 not have the same identifying marks that the standard C library for your
18795 Show the OS ABI currently in use.
18798 With no argument, show the list of registered available OS ABI's.
18800 @item set osabi @var{abi}
18801 Set the current OS ABI to @var{abi}.
18804 @cindex float promotion
18806 Generally, the way that an argument of type @code{float} is passed to a
18807 function depends on whether the function is prototyped. For a prototyped
18808 (i.e.@: ANSI/ISO style) function, @code{float} arguments are passed unchanged,
18809 according to the architecture's convention for @code{float}. For unprototyped
18810 (i.e.@: K&R style) functions, @code{float} arguments are first promoted to type
18811 @code{double} and then passed.
18813 Unfortunately, some forms of debug information do not reliably indicate whether
18814 a function is prototyped. If @value{GDBN} calls a function that is not marked
18815 as prototyped, it consults @kbd{set coerce-float-to-double}.
18818 @kindex set coerce-float-to-double
18819 @item set coerce-float-to-double
18820 @itemx set coerce-float-to-double on
18821 Arguments of type @code{float} will be promoted to @code{double} when passed
18822 to an unprototyped function. This is the default setting.
18824 @item set coerce-float-to-double off
18825 Arguments of type @code{float} will be passed directly to unprototyped
18828 @kindex show coerce-float-to-double
18829 @item show coerce-float-to-double
18830 Show the current setting of promoting @code{float} to @code{double}.
18834 @kindex show cp-abi
18835 @value{GDBN} needs to know the ABI used for your program's C@t{++}
18836 objects. The correct C@t{++} ABI depends on which C@t{++} compiler was
18837 used to build your application. @value{GDBN} only fully supports
18838 programs with a single C@t{++} ABI; if your program contains code using
18839 multiple C@t{++} ABI's or if @value{GDBN} can not identify your
18840 program's ABI correctly, you can tell @value{GDBN} which ABI to use.
18841 Currently supported ABI's include ``gnu-v2'', for @code{g++} versions
18842 before 3.0, ``gnu-v3'', for @code{g++} versions 3.0 and later, and
18843 ``hpaCC'' for the HP ANSI C@t{++} compiler. Other C@t{++} compilers may
18844 use the ``gnu-v2'' or ``gnu-v3'' ABI's as well. The default setting is
18849 Show the C@t{++} ABI currently in use.
18852 With no argument, show the list of supported C@t{++} ABI's.
18854 @item set cp-abi @var{abi}
18855 @itemx set cp-abi auto
18856 Set the current C@t{++} ABI to @var{abi}, or return to automatic detection.
18859 @node Messages/Warnings
18860 @section Optional Warnings and Messages
18862 @cindex verbose operation
18863 @cindex optional warnings
18864 By default, @value{GDBN} is silent about its inner workings. If you are
18865 running on a slow machine, you may want to use the @code{set verbose}
18866 command. This makes @value{GDBN} tell you when it does a lengthy
18867 internal operation, so you will not think it has crashed.
18869 Currently, the messages controlled by @code{set verbose} are those
18870 which announce that the symbol table for a source file is being read;
18871 see @code{symbol-file} in @ref{Files, ,Commands to Specify Files}.
18874 @kindex set verbose
18875 @item set verbose on
18876 Enables @value{GDBN} output of certain informational messages.
18878 @item set verbose off
18879 Disables @value{GDBN} output of certain informational messages.
18881 @kindex show verbose
18883 Displays whether @code{set verbose} is on or off.
18886 By default, if @value{GDBN} encounters bugs in the symbol table of an
18887 object file, it is silent; but if you are debugging a compiler, you may
18888 find this information useful (@pxref{Symbol Errors, ,Errors Reading
18893 @kindex set complaints
18894 @item set complaints @var{limit}
18895 Permits @value{GDBN} to output @var{limit} complaints about each type of
18896 unusual symbols before becoming silent about the problem. Set
18897 @var{limit} to zero to suppress all complaints; set it to a large number
18898 to prevent complaints from being suppressed.
18900 @kindex show complaints
18901 @item show complaints
18902 Displays how many symbol complaints @value{GDBN} is permitted to produce.
18906 @anchor{confirmation requests}
18907 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
18908 lot of stupid questions to confirm certain commands. For example, if
18909 you try to run a program which is already running:
18913 The program being debugged has been started already.
18914 Start it from the beginning? (y or n)
18917 If you are willing to unflinchingly face the consequences of your own
18918 commands, you can disable this ``feature'':
18922 @kindex set confirm
18924 @cindex confirmation
18925 @cindex stupid questions
18926 @item set confirm off
18927 Disables confirmation requests. Note that running @value{GDBN} with
18928 the @option{--batch} option (@pxref{Mode Options, -batch}) also
18929 automatically disables confirmation requests.
18931 @item set confirm on
18932 Enables confirmation requests (the default).
18934 @kindex show confirm
18936 Displays state of confirmation requests.
18940 @cindex command tracing
18941 If you need to debug user-defined commands or sourced files you may find it
18942 useful to enable @dfn{command tracing}. In this mode each command will be
18943 printed as it is executed, prefixed with one or more @samp{+} symbols, the
18944 quantity denoting the call depth of each command.
18947 @kindex set trace-commands
18948 @cindex command scripts, debugging
18949 @item set trace-commands on
18950 Enable command tracing.
18951 @item set trace-commands off
18952 Disable command tracing.
18953 @item show trace-commands
18954 Display the current state of command tracing.
18957 @node Debugging Output
18958 @section Optional Messages about Internal Happenings
18959 @cindex optional debugging messages
18961 @value{GDBN} has commands that enable optional debugging messages from
18962 various @value{GDBN} subsystems; normally these commands are of
18963 interest to @value{GDBN} maintainers, or when reporting a bug. This
18964 section documents those commands.
18967 @kindex set exec-done-display
18968 @item set exec-done-display
18969 Turns on or off the notification of asynchronous commands'
18970 completion. When on, @value{GDBN} will print a message when an
18971 asynchronous command finishes its execution. The default is off.
18972 @kindex show exec-done-display
18973 @item show exec-done-display
18974 Displays the current setting of asynchronous command completion
18977 @cindex gdbarch debugging info
18978 @cindex architecture debugging info
18979 @item set debug arch
18980 Turns on or off display of gdbarch debugging info. The default is off
18982 @item show debug arch
18983 Displays the current state of displaying gdbarch debugging info.
18984 @item set debug aix-thread
18985 @cindex AIX threads
18986 Display debugging messages about inner workings of the AIX thread
18988 @item show debug aix-thread
18989 Show the current state of AIX thread debugging info display.
18990 @item set debug dwarf2-die
18991 @cindex DWARF2 DIEs
18992 Dump DWARF2 DIEs after they are read in.
18993 The value is the number of nesting levels to print.
18994 A value of zero turns off the display.
18995 @item show debug dwarf2-die
18996 Show the current state of DWARF2 DIE debugging.
18997 @item set debug displaced
18998 @cindex displaced stepping debugging info
18999 Turns on or off display of @value{GDBN} debugging info for the
19000 displaced stepping support. The default is off.
19001 @item show debug displaced
19002 Displays the current state of displaying @value{GDBN} debugging info
19003 related to displaced stepping.
19004 @item set debug event
19005 @cindex event debugging info
19006 Turns on or off display of @value{GDBN} event debugging info. The
19008 @item show debug event
19009 Displays the current state of displaying @value{GDBN} event debugging
19011 @item set debug expression
19012 @cindex expression debugging info
19013 Turns on or off display of debugging info about @value{GDBN}
19014 expression parsing. The default is off.
19015 @item show debug expression
19016 Displays the current state of displaying debugging info about
19017 @value{GDBN} expression parsing.
19018 @item set debug frame
19019 @cindex frame debugging info
19020 Turns on or off display of @value{GDBN} frame debugging info. The
19022 @item show debug frame
19023 Displays the current state of displaying @value{GDBN} frame debugging
19025 @item set debug gnu-nat
19026 @cindex @sc{gnu}/Hurd debug messages
19027 Turns on or off debugging messages from the @sc{gnu}/Hurd debug support.
19028 @item show debug gnu-nat
19029 Show the current state of @sc{gnu}/Hurd debugging messages.
19030 @item set debug infrun
19031 @cindex inferior debugging info
19032 Turns on or off display of @value{GDBN} debugging info for running the inferior.
19033 The default is off. @file{infrun.c} contains GDB's runtime state machine used
19034 for implementing operations such as single-stepping the inferior.
19035 @item show debug infrun
19036 Displays the current state of @value{GDBN} inferior debugging.
19037 @item set debug lin-lwp
19038 @cindex @sc{gnu}/Linux LWP debug messages
19039 @cindex Linux lightweight processes
19040 Turns on or off debugging messages from the Linux LWP debug support.
19041 @item show debug lin-lwp
19042 Show the current state of Linux LWP debugging messages.
19043 @item set debug lin-lwp-async
19044 @cindex @sc{gnu}/Linux LWP async debug messages
19045 @cindex Linux lightweight processes
19046 Turns on or off debugging messages from the Linux LWP async debug support.
19047 @item show debug lin-lwp-async
19048 Show the current state of Linux LWP async debugging messages.
19049 @item set debug observer
19050 @cindex observer debugging info
19051 Turns on or off display of @value{GDBN} observer debugging. This
19052 includes info such as the notification of observable events.
19053 @item show debug observer
19054 Displays the current state of observer debugging.
19055 @item set debug overload
19056 @cindex C@t{++} overload debugging info
19057 Turns on or off display of @value{GDBN} C@t{++} overload debugging
19058 info. This includes info such as ranking of functions, etc. The default
19060 @item show debug overload
19061 Displays the current state of displaying @value{GDBN} C@t{++} overload
19063 @cindex expression parser, debugging info
19064 @cindex debug expression parser
19065 @item set debug parser
19066 Turns on or off the display of expression parser debugging output.
19067 Internally, this sets the @code{yydebug} variable in the expression
19068 parser. @xref{Tracing, , Tracing Your Parser, bison, Bison}, for
19069 details. The default is off.
19070 @item show debug parser
19071 Show the current state of expression parser debugging.
19072 @cindex packets, reporting on stdout
19073 @cindex serial connections, debugging
19074 @cindex debug remote protocol
19075 @cindex remote protocol debugging
19076 @cindex display remote packets
19077 @item set debug remote
19078 Turns on or off display of reports on all packets sent back and forth across
19079 the serial line to the remote machine. The info is printed on the
19080 @value{GDBN} standard output stream. The default is off.
19081 @item show debug remote
19082 Displays the state of display of remote packets.
19083 @item set debug serial
19084 Turns on or off display of @value{GDBN} serial debugging info. The
19086 @item show debug serial
19087 Displays the current state of displaying @value{GDBN} serial debugging
19089 @item set debug solib-frv
19090 @cindex FR-V shared-library debugging
19091 Turns on or off debugging messages for FR-V shared-library code.
19092 @item show debug solib-frv
19093 Display the current state of FR-V shared-library code debugging
19095 @item set debug target
19096 @cindex target debugging info
19097 Turns on or off display of @value{GDBN} target debugging info. This info
19098 includes what is going on at the target level of GDB, as it happens. The
19099 default is 0. Set it to 1 to track events, and to 2 to also track the
19100 value of large memory transfers. Changes to this flag do not take effect
19101 until the next time you connect to a target or use the @code{run} command.
19102 @item show debug target
19103 Displays the current state of displaying @value{GDBN} target debugging
19105 @item set debug timestamp
19106 @cindex timestampping debugging info
19107 Turns on or off display of timestamps with @value{GDBN} debugging info.
19108 When enabled, seconds and microseconds are displayed before each debugging
19110 @item show debug timestamp
19111 Displays the current state of displaying timestamps with @value{GDBN}
19113 @item set debugvarobj
19114 @cindex variable object debugging info
19115 Turns on or off display of @value{GDBN} variable object debugging
19116 info. The default is off.
19117 @item show debugvarobj
19118 Displays the current state of displaying @value{GDBN} variable object
19120 @item set debug xml
19121 @cindex XML parser debugging
19122 Turns on or off debugging messages for built-in XML parsers.
19123 @item show debug xml
19124 Displays the current state of XML debugging messages.
19127 @node Other Misc Settings
19128 @section Other Miscellaneous Settings
19129 @cindex miscellaneous settings
19132 @kindex set interactive-mode
19133 @item set interactive-mode
19134 If @code{on}, forces @value{GDBN} to operate interactively.
19135 If @code{off}, forces @value{GDBN} to operate non-interactively,
19136 If @code{auto} (the default), @value{GDBN} guesses which mode to use,
19137 based on whether the debugger was started in a terminal or not.
19139 In the vast majority of cases, the debugger should be able to guess
19140 correctly which mode should be used. But this setting can be useful
19141 in certain specific cases, such as running a MinGW @value{GDBN}
19142 inside a cygwin window.
19144 @kindex show interactive-mode
19145 @item show interactive-mode
19146 Displays whether the debugger is operating in interactive mode or not.
19149 @node Extending GDB
19150 @chapter Extending @value{GDBN}
19151 @cindex extending GDB
19153 @value{GDBN} provides two mechanisms for extension. The first is based
19154 on composition of @value{GDBN} commands, and the second is based on the
19155 Python scripting language.
19157 To facilitate the use of these extensions, @value{GDBN} is capable
19158 of evaluating the contents of a file. When doing so, @value{GDBN}
19159 can recognize which scripting language is being used by looking at
19160 the filename extension. Files with an unrecognized filename extension
19161 are always treated as a @value{GDBN} Command Files.
19162 @xref{Command Files,, Command files}.
19164 You can control how @value{GDBN} evaluates these files with the following
19168 @kindex set script-extension
19169 @kindex show script-extension
19170 @item set script-extension off
19171 All scripts are always evaluated as @value{GDBN} Command Files.
19173 @item set script-extension soft
19174 The debugger determines the scripting language based on filename
19175 extension. If this scripting language is supported, @value{GDBN}
19176 evaluates the script using that language. Otherwise, it evaluates
19177 the file as a @value{GDBN} Command File.
19179 @item set script-extension strict
19180 The debugger determines the scripting language based on filename
19181 extension, and evaluates the script using that language. If the
19182 language is not supported, then the evaluation fails.
19184 @item show script-extension
19185 Display the current value of the @code{script-extension} option.
19190 * Sequences:: Canned Sequences of Commands
19191 * Python:: Scripting @value{GDBN} using Python
19195 @section Canned Sequences of Commands
19197 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
19198 Command Lists}), @value{GDBN} provides two ways to store sequences of
19199 commands for execution as a unit: user-defined commands and command
19203 * Define:: How to define your own commands
19204 * Hooks:: Hooks for user-defined commands
19205 * Command Files:: How to write scripts of commands to be stored in a file
19206 * Output:: Commands for controlled output
19210 @subsection User-defined Commands
19212 @cindex user-defined command
19213 @cindex arguments, to user-defined commands
19214 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
19215 which you assign a new name as a command. This is done with the
19216 @code{define} command. User commands may accept up to 10 arguments
19217 separated by whitespace. Arguments are accessed within the user command
19218 via @code{$arg0@dots{}$arg9}. A trivial example:
19222 print $arg0 + $arg1 + $arg2
19227 To execute the command use:
19234 This defines the command @code{adder}, which prints the sum of
19235 its three arguments. Note the arguments are text substitutions, so they may
19236 reference variables, use complex expressions, or even perform inferior
19239 @cindex argument count in user-defined commands
19240 @cindex how many arguments (user-defined commands)
19241 In addition, @code{$argc} may be used to find out how many arguments have
19242 been passed. This expands to a number in the range 0@dots{}10.
19247 print $arg0 + $arg1
19250 print $arg0 + $arg1 + $arg2
19258 @item define @var{commandname}
19259 Define a command named @var{commandname}. If there is already a command
19260 by that name, you are asked to confirm that you want to redefine it.
19261 @var{commandname} may be a bare command name consisting of letters,
19262 numbers, dashes, and underscores. It may also start with any predefined
19263 prefix command. For example, @samp{define target my-target} creates
19264 a user-defined @samp{target my-target} command.
19266 The definition of the command is made up of other @value{GDBN} command lines,
19267 which are given following the @code{define} command. The end of these
19268 commands is marked by a line containing @code{end}.
19271 @kindex end@r{ (user-defined commands)}
19272 @item document @var{commandname}
19273 Document the user-defined command @var{commandname}, so that it can be
19274 accessed by @code{help}. The command @var{commandname} must already be
19275 defined. This command reads lines of documentation just as @code{define}
19276 reads the lines of the command definition, ending with @code{end}.
19277 After the @code{document} command is finished, @code{help} on command
19278 @var{commandname} displays the documentation you have written.
19280 You may use the @code{document} command again to change the
19281 documentation of a command. Redefining the command with @code{define}
19282 does not change the documentation.
19284 @kindex dont-repeat
19285 @cindex don't repeat command
19287 Used inside a user-defined command, this tells @value{GDBN} that this
19288 command should not be repeated when the user hits @key{RET}
19289 (@pxref{Command Syntax, repeat last command}).
19291 @kindex help user-defined
19292 @item help user-defined
19293 List all user-defined commands, with the first line of the documentation
19298 @itemx show user @var{commandname}
19299 Display the @value{GDBN} commands used to define @var{commandname} (but
19300 not its documentation). If no @var{commandname} is given, display the
19301 definitions for all user-defined commands.
19303 @cindex infinite recursion in user-defined commands
19304 @kindex show max-user-call-depth
19305 @kindex set max-user-call-depth
19306 @item show max-user-call-depth
19307 @itemx set max-user-call-depth
19308 The value of @code{max-user-call-depth} controls how many recursion
19309 levels are allowed in user-defined commands before @value{GDBN} suspects an
19310 infinite recursion and aborts the command.
19313 In addition to the above commands, user-defined commands frequently
19314 use control flow commands, described in @ref{Command Files}.
19316 When user-defined commands are executed, the
19317 commands of the definition are not printed. An error in any command
19318 stops execution of the user-defined command.
19320 If used interactively, commands that would ask for confirmation proceed
19321 without asking when used inside a user-defined command. Many @value{GDBN}
19322 commands that normally print messages to say what they are doing omit the
19323 messages when used in a user-defined command.
19326 @subsection User-defined Command Hooks
19327 @cindex command hooks
19328 @cindex hooks, for commands
19329 @cindex hooks, pre-command
19332 You may define @dfn{hooks}, which are a special kind of user-defined
19333 command. Whenever you run the command @samp{foo}, if the user-defined
19334 command @samp{hook-foo} exists, it is executed (with no arguments)
19335 before that command.
19337 @cindex hooks, post-command
19339 A hook may also be defined which is run after the command you executed.
19340 Whenever you run the command @samp{foo}, if the user-defined command
19341 @samp{hookpost-foo} exists, it is executed (with no arguments) after
19342 that command. Post-execution hooks may exist simultaneously with
19343 pre-execution hooks, for the same command.
19345 It is valid for a hook to call the command which it hooks. If this
19346 occurs, the hook is not re-executed, thereby avoiding infinite recursion.
19348 @c It would be nice if hookpost could be passed a parameter indicating
19349 @c if the command it hooks executed properly or not. FIXME!
19351 @kindex stop@r{, a pseudo-command}
19352 In addition, a pseudo-command, @samp{stop} exists. Defining
19353 (@samp{hook-stop}) makes the associated commands execute every time
19354 execution stops in your program: before breakpoint commands are run,
19355 displays are printed, or the stack frame is printed.
19357 For example, to ignore @code{SIGALRM} signals while
19358 single-stepping, but treat them normally during normal execution,
19363 handle SIGALRM nopass
19367 handle SIGALRM pass
19370 define hook-continue
19371 handle SIGALRM pass
19375 As a further example, to hook at the beginning and end of the @code{echo}
19376 command, and to add extra text to the beginning and end of the message,
19384 define hookpost-echo
19388 (@value{GDBP}) echo Hello World
19389 <<<---Hello World--->>>
19394 You can define a hook for any single-word command in @value{GDBN}, but
19395 not for command aliases; you should define a hook for the basic command
19396 name, e.g.@: @code{backtrace} rather than @code{bt}.
19397 @c FIXME! So how does Joe User discover whether a command is an alias
19399 You can hook a multi-word command by adding @code{hook-} or
19400 @code{hookpost-} to the last word of the command, e.g.@:
19401 @samp{define target hook-remote} to add a hook to @samp{target remote}.
19403 If an error occurs during the execution of your hook, execution of
19404 @value{GDBN} commands stops and @value{GDBN} issues a prompt
19405 (before the command that you actually typed had a chance to run).
19407 If you try to define a hook which does not match any known command, you
19408 get a warning from the @code{define} command.
19410 @node Command Files
19411 @subsection Command Files
19413 @cindex command files
19414 @cindex scripting commands
19415 A command file for @value{GDBN} is a text file made of lines that are
19416 @value{GDBN} commands. Comments (lines starting with @kbd{#}) may
19417 also be included. An empty line in a command file does nothing; it
19418 does not mean to repeat the last command, as it would from the
19421 You can request the execution of a command file with the @code{source}
19422 command. Note that the @code{source} command is also used to evaluate
19423 scripts that are not Command Files. The exact behavior can be configured
19424 using the @code{script-extension} setting.
19425 @xref{Extending GDB,, Extending GDB}.
19429 @cindex execute commands from a file
19430 @item source [-s] [-v] @var{filename}
19431 Execute the command file @var{filename}.
19434 The lines in a command file are generally executed sequentially,
19435 unless the order of execution is changed by one of the
19436 @emph{flow-control commands} described below. The commands are not
19437 printed as they are executed. An error in any command terminates
19438 execution of the command file and control is returned to the console.
19440 @value{GDBN} first searches for @var{filename} in the current directory.
19441 If the file is not found there, and @var{filename} does not specify a
19442 directory, then @value{GDBN} also looks for the file on the source search path
19443 (specified with the @samp{directory} command);
19444 except that @file{$cdir} is not searched because the compilation directory
19445 is not relevant to scripts.
19447 If @code{-s} is specified, then @value{GDBN} searches for @var{filename}
19448 on the search path even if @var{filename} specifies a directory.
19449 The search is done by appending @var{filename} to each element of the
19450 search path. So, for example, if @var{filename} is @file{mylib/myscript}
19451 and the search path contains @file{/home/user} then @value{GDBN} will
19452 look for the script @file{/home/user/mylib/myscript}.
19453 The search is also done if @var{filename} is an absolute path.
19454 For example, if @var{filename} is @file{/tmp/myscript} and
19455 the search path contains @file{/home/user} then @value{GDBN} will
19456 look for the script @file{/home/user/tmp/myscript}.
19457 For DOS-like systems, if @var{filename} contains a drive specification,
19458 it is stripped before concatenation. For example, if @var{filename} is
19459 @file{d:myscript} and the search path contains @file{c:/tmp} then @value{GDBN}
19460 will look for the script @file{c:/tmp/myscript}.
19462 If @code{-v}, for verbose mode, is given then @value{GDBN} displays
19463 each command as it is executed. The option must be given before
19464 @var{filename}, and is interpreted as part of the filename anywhere else.
19466 Commands that would ask for confirmation if used interactively proceed
19467 without asking when used in a command file. Many @value{GDBN} commands that
19468 normally print messages to say what they are doing omit the messages
19469 when called from command files.
19471 @value{GDBN} also accepts command input from standard input. In this
19472 mode, normal output goes to standard output and error output goes to
19473 standard error. Errors in a command file supplied on standard input do
19474 not terminate execution of the command file---execution continues with
19478 gdb < cmds > log 2>&1
19481 (The syntax above will vary depending on the shell used.) This example
19482 will execute commands from the file @file{cmds}. All output and errors
19483 would be directed to @file{log}.
19485 Since commands stored on command files tend to be more general than
19486 commands typed interactively, they frequently need to deal with
19487 complicated situations, such as different or unexpected values of
19488 variables and symbols, changes in how the program being debugged is
19489 built, etc. @value{GDBN} provides a set of flow-control commands to
19490 deal with these complexities. Using these commands, you can write
19491 complex scripts that loop over data structures, execute commands
19492 conditionally, etc.
19499 This command allows to include in your script conditionally executed
19500 commands. The @code{if} command takes a single argument, which is an
19501 expression to evaluate. It is followed by a series of commands that
19502 are executed only if the expression is true (its value is nonzero).
19503 There can then optionally be an @code{else} line, followed by a series
19504 of commands that are only executed if the expression was false. The
19505 end of the list is marked by a line containing @code{end}.
19509 This command allows to write loops. Its syntax is similar to
19510 @code{if}: the command takes a single argument, which is an expression
19511 to evaluate, and must be followed by the commands to execute, one per
19512 line, terminated by an @code{end}. These commands are called the
19513 @dfn{body} of the loop. The commands in the body of @code{while} are
19514 executed repeatedly as long as the expression evaluates to true.
19518 This command exits the @code{while} loop in whose body it is included.
19519 Execution of the script continues after that @code{while}s @code{end}
19522 @kindex loop_continue
19523 @item loop_continue
19524 This command skips the execution of the rest of the body of commands
19525 in the @code{while} loop in whose body it is included. Execution
19526 branches to the beginning of the @code{while} loop, where it evaluates
19527 the controlling expression.
19529 @kindex end@r{ (if/else/while commands)}
19531 Terminate the block of commands that are the body of @code{if},
19532 @code{else}, or @code{while} flow-control commands.
19537 @subsection Commands for Controlled Output
19539 During the execution of a command file or a user-defined command, normal
19540 @value{GDBN} output is suppressed; the only output that appears is what is
19541 explicitly printed by the commands in the definition. This section
19542 describes three commands useful for generating exactly the output you
19547 @item echo @var{text}
19548 @c I do not consider backslash-space a standard C escape sequence
19549 @c because it is not in ANSI.
19550 Print @var{text}. Nonprinting characters can be included in
19551 @var{text} using C escape sequences, such as @samp{\n} to print a
19552 newline. @strong{No newline is printed unless you specify one.}
19553 In addition to the standard C escape sequences, a backslash followed
19554 by a space stands for a space. This is useful for displaying a
19555 string with spaces at the beginning or the end, since leading and
19556 trailing spaces are otherwise trimmed from all arguments.
19557 To print @samp{@w{ }and foo =@w{ }}, use the command
19558 @samp{echo \@w{ }and foo = \@w{ }}.
19560 A backslash at the end of @var{text} can be used, as in C, to continue
19561 the command onto subsequent lines. For example,
19564 echo This is some text\n\
19565 which is continued\n\
19566 onto several lines.\n
19569 produces the same output as
19572 echo This is some text\n
19573 echo which is continued\n
19574 echo onto several lines.\n
19578 @item output @var{expression}
19579 Print the value of @var{expression} and nothing but that value: no
19580 newlines, no @samp{$@var{nn} = }. The value is not entered in the
19581 value history either. @xref{Expressions, ,Expressions}, for more information
19584 @item output/@var{fmt} @var{expression}
19585 Print the value of @var{expression} in format @var{fmt}. You can use
19586 the same formats as for @code{print}. @xref{Output Formats,,Output
19587 Formats}, for more information.
19590 @item printf @var{template}, @var{expressions}@dots{}
19591 Print the values of one or more @var{expressions} under the control of
19592 the string @var{template}. To print several values, make
19593 @var{expressions} be a comma-separated list of individual expressions,
19594 which may be either numbers or pointers. Their values are printed as
19595 specified by @var{template}, exactly as a C program would do by
19596 executing the code below:
19599 printf (@var{template}, @var{expressions}@dots{});
19602 As in @code{C} @code{printf}, ordinary characters in @var{template}
19603 are printed verbatim, while @dfn{conversion specification} introduced
19604 by the @samp{%} character cause subsequent @var{expressions} to be
19605 evaluated, their values converted and formatted according to type and
19606 style information encoded in the conversion specifications, and then
19609 For example, you can print two values in hex like this:
19612 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
19615 @code{printf} supports all the standard @code{C} conversion
19616 specifications, including the flags and modifiers between the @samp{%}
19617 character and the conversion letter, with the following exceptions:
19621 The argument-ordering modifiers, such as @samp{2$}, are not supported.
19624 The modifier @samp{*} is not supported for specifying precision or
19628 The @samp{'} flag (for separation of digits into groups according to
19629 @code{LC_NUMERIC'}) is not supported.
19632 The type modifiers @samp{hh}, @samp{j}, @samp{t}, and @samp{z} are not
19636 The conversion letter @samp{n} (as in @samp{%n}) is not supported.
19639 The conversion letters @samp{a} and @samp{A} are not supported.
19643 Note that the @samp{ll} type modifier is supported only if the
19644 underlying @code{C} implementation used to build @value{GDBN} supports
19645 the @code{long long int} type, and the @samp{L} type modifier is
19646 supported only if @code{long double} type is available.
19648 As in @code{C}, @code{printf} supports simple backslash-escape
19649 sequences, such as @code{\n}, @samp{\t}, @samp{\\}, @samp{\"},
19650 @samp{\a}, and @samp{\f}, that consist of backslash followed by a
19651 single character. Octal and hexadecimal escape sequences are not
19654 Additionally, @code{printf} supports conversion specifications for DFP
19655 (@dfn{Decimal Floating Point}) types using the following length modifiers
19656 together with a floating point specifier.
19661 @samp{H} for printing @code{Decimal32} types.
19664 @samp{D} for printing @code{Decimal64} types.
19667 @samp{DD} for printing @code{Decimal128} types.
19670 If the underlying @code{C} implementation used to build @value{GDBN} has
19671 support for the three length modifiers for DFP types, other modifiers
19672 such as width and precision will also be available for @value{GDBN} to use.
19674 In case there is no such @code{C} support, no additional modifiers will be
19675 available and the value will be printed in the standard way.
19677 Here's an example of printing DFP types using the above conversion letters:
19679 printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl
19685 @section Scripting @value{GDBN} using Python
19686 @cindex python scripting
19687 @cindex scripting with python
19689 You can script @value{GDBN} using the @uref{http://www.python.org/,
19690 Python programming language}. This feature is available only if
19691 @value{GDBN} was configured using @option{--with-python}.
19694 * Python Commands:: Accessing Python from @value{GDBN}.
19695 * Python API:: Accessing @value{GDBN} from Python.
19698 @node Python Commands
19699 @subsection Python Commands
19700 @cindex python commands
19701 @cindex commands to access python
19703 @value{GDBN} provides one command for accessing the Python interpreter,
19704 and one related setting:
19708 @item python @r{[}@var{code}@r{]}
19709 The @code{python} command can be used to evaluate Python code.
19711 If given an argument, the @code{python} command will evaluate the
19712 argument as a Python command. For example:
19715 (@value{GDBP}) python print 23
19719 If you do not provide an argument to @code{python}, it will act as a
19720 multi-line command, like @code{define}. In this case, the Python
19721 script is made up of subsequent command lines, given after the
19722 @code{python} command. This command list is terminated using a line
19723 containing @code{end}. For example:
19726 (@value{GDBP}) python
19728 End with a line saying just "end".
19734 @kindex maint set python print-stack
19735 @item maint set python print-stack
19736 By default, @value{GDBN} will print a stack trace when an error occurs
19737 in a Python script. This can be controlled using @code{maint set
19738 python print-stack}: if @code{on}, the default, then Python stack
19739 printing is enabled; if @code{off}, then Python stack printing is
19743 It is also possible to execute a Python script from the @value{GDBN}
19747 @item source @file{script-name}
19748 The script name must end with @samp{.py} and @value{GDBN} must be configured
19749 to recognize the script language based on filename extension using
19750 the @code{script-extension} setting. @xref{Extending GDB, ,Extending GDB}.
19752 @item python execfile ("script-name")
19753 This method is based on the @code{execfile} Python built-in function,
19754 and thus is always available.
19758 @subsection Python API
19760 @cindex programming in python
19762 @cindex python stdout
19763 @cindex python pagination
19764 At startup, @value{GDBN} overrides Python's @code{sys.stdout} and
19765 @code{sys.stderr} to print using @value{GDBN}'s output-paging streams.
19766 A Python program which outputs to one of these streams may have its
19767 output interrupted by the user (@pxref{Screen Size}). In this
19768 situation, a Python @code{KeyboardInterrupt} exception is thrown.
19771 * Basic Python:: Basic Python Functions.
19772 * Exception Handling::
19773 * Auto-loading:: Automatically loading Python code.
19774 * Values From Inferior::
19775 * Types In Python:: Python representation of types.
19776 * Pretty Printing:: Pretty-printing values.
19777 * Selecting Pretty-Printers:: How GDB chooses a pretty-printer.
19778 * Commands In Python:: Implementing new commands in Python.
19779 * Functions In Python:: Writing new convenience functions.
19780 * Progspaces In Python:: Program spaces.
19781 * Objfiles In Python:: Object files.
19782 * Frames In Python:: Accessing inferior stack frames from Python.
19783 * Blocks In Python:: Accessing frame blocks from Python.
19784 * Symbols In Python:: Python representation of symbols.
19785 * Symbol Tables In Python:: Python representation of symbol tables.
19786 * Lazy Strings In Python:: Python representation of lazy strings.
19787 * Breakpoints In Python:: Manipulating breakpoints using Python.
19791 @subsubsection Basic Python
19793 @cindex python functions
19794 @cindex python module
19796 @value{GDBN} introduces a new Python module, named @code{gdb}. All
19797 methods and classes added by @value{GDBN} are placed in this module.
19798 @value{GDBN} automatically @code{import}s the @code{gdb} module for
19799 use in all scripts evaluated by the @code{python} command.
19801 @findex gdb.execute
19802 @defun execute command [from_tty]
19803 Evaluate @var{command}, a string, as a @value{GDBN} CLI command.
19804 If a GDB exception happens while @var{command} runs, it is
19805 translated as described in @ref{Exception Handling,,Exception Handling}.
19806 If no exceptions occur, this function returns @code{None}.
19808 @var{from_tty} specifies whether @value{GDBN} ought to consider this
19809 command as having originated from the user invoking it interactively.
19810 It must be a boolean value. If omitted, it defaults to @code{False}.
19813 @findex gdb.breakpoints
19815 Return a sequence holding all of @value{GDBN}'s breakpoints.
19816 @xref{Breakpoints In Python}, for more information.
19819 @findex gdb.parameter
19820 @defun parameter parameter
19821 Return the value of a @value{GDBN} parameter. @var{parameter} is a
19822 string naming the parameter to look up; @var{parameter} may contain
19823 spaces if the parameter has a multi-part name. For example,
19824 @samp{print object} is a valid parameter name.
19826 If the named parameter does not exist, this function throws a
19827 @code{RuntimeError}. Otherwise, the parameter's value is converted to
19828 a Python value of the appropriate type, and returned.
19831 @findex gdb.history
19832 @defun history number
19833 Return a value from @value{GDBN}'s value history (@pxref{Value
19834 History}). @var{number} indicates which history element to return.
19835 If @var{number} is negative, then @value{GDBN} will take its absolute value
19836 and count backward from the last element (i.e., the most recent element) to
19837 find the value to return. If @var{number} is zero, then @value{GDBN} will
19838 return the most recent element. If the element specified by @var{number}
19839 doesn't exist in the value history, a @code{RuntimeError} exception will be
19842 If no exception is raised, the return value is always an instance of
19843 @code{gdb.Value} (@pxref{Values From Inferior}).
19846 @findex gdb.parse_and_eval
19847 @defun parse_and_eval expression
19848 Parse @var{expression} as an expression in the current language,
19849 evaluate it, and return the result as a @code{gdb.Value}.
19850 @var{expression} must be a string.
19852 This function can be useful when implementing a new command
19853 (@pxref{Commands In Python}), as it provides a way to parse the
19854 command's argument as an expression. It is also useful simply to
19855 compute values, for example, it is the only way to get the value of a
19856 convenience variable (@pxref{Convenience Vars}) as a @code{gdb.Value}.
19860 @defun write string
19861 Print a string to @value{GDBN}'s paginated standard output stream.
19862 Writing to @code{sys.stdout} or @code{sys.stderr} will automatically
19863 call this function.
19868 Flush @value{GDBN}'s paginated standard output stream. Flushing
19869 @code{sys.stdout} or @code{sys.stderr} will automatically call this
19873 @findex gdb.target_charset
19874 @defun target_charset
19875 Return the name of the current target character set (@pxref{Character
19876 Sets}). This differs from @code{gdb.parameter('target-charset')} in
19877 that @samp{auto} is never returned.
19880 @findex gdb.target_wide_charset
19881 @defun target_wide_charset
19882 Return the name of the current target wide character set
19883 (@pxref{Character Sets}). This differs from
19884 @code{gdb.parameter('target-wide-charset')} in that @samp{auto} is
19888 @node Exception Handling
19889 @subsubsection Exception Handling
19890 @cindex python exceptions
19891 @cindex exceptions, python
19893 When executing the @code{python} command, Python exceptions
19894 uncaught within the Python code are translated to calls to
19895 @value{GDBN} error-reporting mechanism. If the command that called
19896 @code{python} does not handle the error, @value{GDBN} will
19897 terminate it and print an error message containing the Python
19898 exception name, the associated value, and the Python call stack
19899 backtrace at the point where the exception was raised. Example:
19902 (@value{GDBP}) python print foo
19903 Traceback (most recent call last):
19904 File "<string>", line 1, in <module>
19905 NameError: name 'foo' is not defined
19908 @value{GDBN} errors that happen in @value{GDBN} commands invoked by Python
19909 code are converted to Python @code{RuntimeError} exceptions. User
19910 interrupt (via @kbd{C-c} or by typing @kbd{q} at a pagination
19911 prompt) is translated to a Python @code{KeyboardInterrupt}
19912 exception. If you catch these exceptions in your Python code, your
19913 exception handler will see @code{RuntimeError} or
19914 @code{KeyboardInterrupt} as the exception type, the @value{GDBN} error
19915 message as its value, and the Python call stack backtrace at the
19916 Python statement closest to where the @value{GDBN} error occured as the
19920 @subsubsection Auto-loading
19921 @cindex auto-loading, Python
19923 When a new object file is read (for example, due to the @code{file}
19924 command, or because the inferior has loaded a shared library),
19925 @value{GDBN} will look for a file named @file{@var{objfile}-gdb.py},
19926 where @var{objfile} is the object file's real name, formed by ensuring
19927 that the file name is absolute, following all symlinks, and resolving
19928 @code{.} and @code{..} components. If this file exists and is
19929 readable, @value{GDBN} will evaluate it as a Python script.
19931 If this file does not exist, and if the parameter
19932 @code{debug-file-directory} is set (@pxref{Separate Debug Files}),
19933 then @value{GDBN} will use for its each separated directory component
19934 @code{component} the file named @file{@code{component}/@var{real-name}}, where
19935 @var{real-name} is the object file's real name, as described above.
19937 Finally, if this file does not exist, then @value{GDBN} will look for
19938 a file named @file{@var{data-directory}/python/auto-load/@var{real-name}}, where
19939 @var{data-directory} is @value{GDBN}'s data directory (available via
19940 @code{show data-directory}, @pxref{Data Files}), and @var{real-name}
19941 is the object file's real name, as described above.
19943 When reading an auto-loaded file, @value{GDBN} sets the ``current
19944 objfile''. This is available via the @code{gdb.current_objfile}
19945 function (@pxref{Objfiles In Python}). This can be useful for
19946 registering objfile-specific pretty-printers.
19948 The auto-loading feature is useful for supplying application-specific
19949 debugging commands and scripts. You can enable or disable this
19950 feature, and view its current state.
19953 @kindex maint set python auto-load
19954 @item maint set python auto-load [yes|no]
19955 Enable or disable the Python auto-loading feature.
19957 @kindex maint show python auto-load
19958 @item maint show python auto-load
19959 Show whether Python auto-loading is enabled or disabled.
19962 @value{GDBN} does not track which files it has already auto-loaded.
19963 So, your @samp{-gdb.py} file should take care to ensure that it may be
19964 evaluated multiple times without error.
19966 @node Values From Inferior
19967 @subsubsection Values From Inferior
19968 @cindex values from inferior, with Python
19969 @cindex python, working with values from inferior
19971 @cindex @code{gdb.Value}
19972 @value{GDBN} provides values it obtains from the inferior program in
19973 an object of type @code{gdb.Value}. @value{GDBN} uses this object
19974 for its internal bookkeeping of the inferior's values, and for
19975 fetching values when necessary.
19977 Inferior values that are simple scalars can be used directly in
19978 Python expressions that are valid for the value's data type. Here's
19979 an example for an integer or floating-point value @code{some_val}:
19986 As result of this, @code{bar} will also be a @code{gdb.Value} object
19987 whose values are of the same type as those of @code{some_val}.
19989 Inferior values that are structures or instances of some class can
19990 be accessed using the Python @dfn{dictionary syntax}. For example, if
19991 @code{some_val} is a @code{gdb.Value} instance holding a structure, you
19992 can access its @code{foo} element with:
19995 bar = some_val['foo']
19998 Again, @code{bar} will also be a @code{gdb.Value} object.
20000 The following attributes are provided:
20003 @defivar Value address
20004 If this object is addressable, this read-only attribute holds a
20005 @code{gdb.Value} object representing the address. Otherwise,
20006 this attribute holds @code{None}.
20009 @cindex optimized out value in Python
20010 @defivar Value is_optimized_out
20011 This read-only boolean attribute is true if the compiler optimized out
20012 this value, thus it is not available for fetching from the inferior.
20015 @defivar Value type
20016 The type of this @code{gdb.Value}. The value of this attribute is a
20017 @code{gdb.Type} object.
20021 The following methods are provided:
20024 @defmethod Value cast type
20025 Return a new instance of @code{gdb.Value} that is the result of
20026 casting this instance to the type described by @var{type}, which must
20027 be a @code{gdb.Type} object. If the cast cannot be performed for some
20028 reason, this method throws an exception.
20031 @defmethod Value dereference
20032 For pointer data types, this method returns a new @code{gdb.Value} object
20033 whose contents is the object pointed to by the pointer. For example, if
20034 @code{foo} is a C pointer to an @code{int}, declared in your C program as
20041 then you can use the corresponding @code{gdb.Value} to access what
20042 @code{foo} points to like this:
20045 bar = foo.dereference ()
20048 The result @code{bar} will be a @code{gdb.Value} object holding the
20049 value pointed to by @code{foo}.
20052 @defmethod Value string @r{[}encoding@r{]} @r{[}errors@r{]} @r{[}length@r{]}
20053 If this @code{gdb.Value} represents a string, then this method
20054 converts the contents to a Python string. Otherwise, this method will
20055 throw an exception.
20057 Strings are recognized in a language-specific way; whether a given
20058 @code{gdb.Value} represents a string is determined by the current
20061 For C-like languages, a value is a string if it is a pointer to or an
20062 array of characters or ints. The string is assumed to be terminated
20063 by a zero of the appropriate width. However if the optional length
20064 argument is given, the string will be converted to that given length,
20065 ignoring any embedded zeros that the string may contain.
20067 If the optional @var{encoding} argument is given, it must be a string
20068 naming the encoding of the string in the @code{gdb.Value}, such as
20069 @code{"ascii"}, @code{"iso-8859-6"} or @code{"utf-8"}. It accepts
20070 the same encodings as the corresponding argument to Python's
20071 @code{string.decode} method, and the Python codec machinery will be used
20072 to convert the string. If @var{encoding} is not given, or if
20073 @var{encoding} is the empty string, then either the @code{target-charset}
20074 (@pxref{Character Sets}) will be used, or a language-specific encoding
20075 will be used, if the current language is able to supply one.
20077 The optional @var{errors} argument is the same as the corresponding
20078 argument to Python's @code{string.decode} method.
20080 If the optional @var{length} argument is given, the string will be
20081 fetched and converted to the given length.
20084 @defmethod Value lazy_string @r{[}encoding@r{]} @r{[}length@r{]}
20085 If this @code{gdb.Value} represents a string, then this method
20086 converts the contents to a @code{gdb.LazyString} (@pxref{Lazy Strings
20087 In Python}). Otherwise, this method will throw an exception.
20089 If the optional @var{encoding} argument is given, it must be a string
20090 naming the encoding of the @code{gdb.LazyString}. Some examples are:
20091 @samp{ascii}, @samp{iso-8859-6} or @samp{utf-8}. If the
20092 @var{encoding} argument is an encoding that @value{GDBN} does
20093 recognize, @value{GDBN} will raise an error.
20095 When a lazy string is printed, the @value{GDBN} encoding machinery is
20096 used to convert the string during printing. If the optional
20097 @var{encoding} argument is not provided, or is an empty string,
20098 @value{GDBN} will automatically select the encoding most suitable for
20099 the string type. For further information on encoding in @value{GDBN}
20100 please see @ref{Character Sets}.
20102 If the optional @var{length} argument is given, the string will be
20103 fetched and encoded to the length of characters specified. If
20104 the @var{length} argument is not provided, the string will be fetched
20105 and encoded until a null of appropriate width is found.
20109 @node Types In Python
20110 @subsubsection Types In Python
20111 @cindex types in Python
20112 @cindex Python, working with types
20115 @value{GDBN} represents types from the inferior using the class
20118 The following type-related functions are available in the @code{gdb}
20121 @findex gdb.lookup_type
20122 @defun lookup_type name [block]
20123 This function looks up a type by name. @var{name} is the name of the
20124 type to look up. It must be a string.
20126 If @var{block} is given, then @var{name} is looked up in that scope.
20127 Otherwise, it is searched for globally.
20129 Ordinarily, this function will return an instance of @code{gdb.Type}.
20130 If the named type cannot be found, it will throw an exception.
20133 An instance of @code{Type} has the following attributes:
20137 The type code for this type. The type code will be one of the
20138 @code{TYPE_CODE_} constants defined below.
20141 @defivar Type sizeof
20142 The size of this type, in target @code{char} units. Usually, a
20143 target's @code{char} type will be an 8-bit byte. However, on some
20144 unusual platforms, this type may have a different size.
20148 The tag name for this type. The tag name is the name after
20149 @code{struct}, @code{union}, or @code{enum} in C and C@t{++}; not all
20150 languages have this concept. If this type has no tag name, then
20151 @code{None} is returned.
20155 The following methods are provided:
20158 @defmethod Type fields
20159 For structure and union types, this method returns the fields. Range
20160 types have two fields, the minimum and maximum values. Enum types
20161 have one field per enum constant. Function and method types have one
20162 field per parameter. The base types of C@t{++} classes are also
20163 represented as fields. If the type has no fields, or does not fit
20164 into one of these categories, an empty sequence will be returned.
20166 Each field is an object, with some pre-defined attributes:
20169 This attribute is not available for @code{static} fields (as in
20170 C@t{++} or Java). For non-@code{static} fields, the value is the bit
20171 position of the field.
20174 The name of the field, or @code{None} for anonymous fields.
20177 This is @code{True} if the field is artificial, usually meaning that
20178 it was provided by the compiler and not the user. This attribute is
20179 always provided, and is @code{False} if the field is not artificial.
20181 @item is_base_class
20182 This is @code{True} if the field represents a base class of a C@t{++}
20183 structure. This attribute is always provided, and is @code{False}
20184 if the field is not a base class of the type that is the argument of
20185 @code{fields}, or if that type was not a C@t{++} class.
20188 If the field is packed, or is a bitfield, then this will have a
20189 non-zero value, which is the size of the field in bits. Otherwise,
20190 this will be zero; in this case the field's size is given by its type.
20193 The type of the field. This is usually an instance of @code{Type},
20194 but it can be @code{None} in some situations.
20198 @defmethod Type const
20199 Return a new @code{gdb.Type} object which represents a
20200 @code{const}-qualified variant of this type.
20203 @defmethod Type volatile
20204 Return a new @code{gdb.Type} object which represents a
20205 @code{volatile}-qualified variant of this type.
20208 @defmethod Type unqualified
20209 Return a new @code{gdb.Type} object which represents an unqualified
20210 variant of this type. That is, the result is neither @code{const} nor
20214 @defmethod Type range
20215 Return a Python @code{Tuple} object that contains two elements: the
20216 low bound of the argument type and the high bound of that type. If
20217 the type does not have a range, @value{GDBN} will raise a
20218 @code{RuntimeError} exception.
20221 @defmethod Type reference
20222 Return a new @code{gdb.Type} object which represents a reference to this
20226 @defmethod Type pointer
20227 Return a new @code{gdb.Type} object which represents a pointer to this
20231 @defmethod Type strip_typedefs
20232 Return a new @code{gdb.Type} that represents the real type,
20233 after removing all layers of typedefs.
20236 @defmethod Type target
20237 Return a new @code{gdb.Type} object which represents the target type
20240 For a pointer type, the target type is the type of the pointed-to
20241 object. For an array type (meaning C-like arrays), the target type is
20242 the type of the elements of the array. For a function or method type,
20243 the target type is the type of the return value. For a complex type,
20244 the target type is the type of the elements. For a typedef, the
20245 target type is the aliased type.
20247 If the type does not have a target, this method will throw an
20251 @defmethod Type template_argument n [block]
20252 If this @code{gdb.Type} is an instantiation of a template, this will
20253 return a new @code{gdb.Type} which represents the type of the
20254 @var{n}th template argument.
20256 If this @code{gdb.Type} is not a template type, this will throw an
20257 exception. Ordinarily, only C@t{++} code will have template types.
20259 If @var{block} is given, then @var{name} is looked up in that scope.
20260 Otherwise, it is searched for globally.
20265 Each type has a code, which indicates what category this type falls
20266 into. The available type categories are represented by constants
20267 defined in the @code{gdb} module:
20270 @findex TYPE_CODE_PTR
20271 @findex gdb.TYPE_CODE_PTR
20272 @item TYPE_CODE_PTR
20273 The type is a pointer.
20275 @findex TYPE_CODE_ARRAY
20276 @findex gdb.TYPE_CODE_ARRAY
20277 @item TYPE_CODE_ARRAY
20278 The type is an array.
20280 @findex TYPE_CODE_STRUCT
20281 @findex gdb.TYPE_CODE_STRUCT
20282 @item TYPE_CODE_STRUCT
20283 The type is a structure.
20285 @findex TYPE_CODE_UNION
20286 @findex gdb.TYPE_CODE_UNION
20287 @item TYPE_CODE_UNION
20288 The type is a union.
20290 @findex TYPE_CODE_ENUM
20291 @findex gdb.TYPE_CODE_ENUM
20292 @item TYPE_CODE_ENUM
20293 The type is an enum.
20295 @findex TYPE_CODE_FLAGS
20296 @findex gdb.TYPE_CODE_FLAGS
20297 @item TYPE_CODE_FLAGS
20298 A bit flags type, used for things such as status registers.
20300 @findex TYPE_CODE_FUNC
20301 @findex gdb.TYPE_CODE_FUNC
20302 @item TYPE_CODE_FUNC
20303 The type is a function.
20305 @findex TYPE_CODE_INT
20306 @findex gdb.TYPE_CODE_INT
20307 @item TYPE_CODE_INT
20308 The type is an integer type.
20310 @findex TYPE_CODE_FLT
20311 @findex gdb.TYPE_CODE_FLT
20312 @item TYPE_CODE_FLT
20313 A floating point type.
20315 @findex TYPE_CODE_VOID
20316 @findex gdb.TYPE_CODE_VOID
20317 @item TYPE_CODE_VOID
20318 The special type @code{void}.
20320 @findex TYPE_CODE_SET
20321 @findex gdb.TYPE_CODE_SET
20322 @item TYPE_CODE_SET
20325 @findex TYPE_CODE_RANGE
20326 @findex gdb.TYPE_CODE_RANGE
20327 @item TYPE_CODE_RANGE
20328 A range type, that is, an integer type with bounds.
20330 @findex TYPE_CODE_STRING
20331 @findex gdb.TYPE_CODE_STRING
20332 @item TYPE_CODE_STRING
20333 A string type. Note that this is only used for certain languages with
20334 language-defined string types; C strings are not represented this way.
20336 @findex TYPE_CODE_BITSTRING
20337 @findex gdb.TYPE_CODE_BITSTRING
20338 @item TYPE_CODE_BITSTRING
20341 @findex TYPE_CODE_ERROR
20342 @findex gdb.TYPE_CODE_ERROR
20343 @item TYPE_CODE_ERROR
20344 An unknown or erroneous type.
20346 @findex TYPE_CODE_METHOD
20347 @findex gdb.TYPE_CODE_METHOD
20348 @item TYPE_CODE_METHOD
20349 A method type, as found in C@t{++} or Java.
20351 @findex TYPE_CODE_METHODPTR
20352 @findex gdb.TYPE_CODE_METHODPTR
20353 @item TYPE_CODE_METHODPTR
20354 A pointer-to-member-function.
20356 @findex TYPE_CODE_MEMBERPTR
20357 @findex gdb.TYPE_CODE_MEMBERPTR
20358 @item TYPE_CODE_MEMBERPTR
20359 A pointer-to-member.
20361 @findex TYPE_CODE_REF
20362 @findex gdb.TYPE_CODE_REF
20363 @item TYPE_CODE_REF
20366 @findex TYPE_CODE_CHAR
20367 @findex gdb.TYPE_CODE_CHAR
20368 @item TYPE_CODE_CHAR
20371 @findex TYPE_CODE_BOOL
20372 @findex gdb.TYPE_CODE_BOOL
20373 @item TYPE_CODE_BOOL
20376 @findex TYPE_CODE_COMPLEX
20377 @findex gdb.TYPE_CODE_COMPLEX
20378 @item TYPE_CODE_COMPLEX
20379 A complex float type.
20381 @findex TYPE_CODE_TYPEDEF
20382 @findex gdb.TYPE_CODE_TYPEDEF
20383 @item TYPE_CODE_TYPEDEF
20384 A typedef to some other type.
20386 @findex TYPE_CODE_NAMESPACE
20387 @findex gdb.TYPE_CODE_NAMESPACE
20388 @item TYPE_CODE_NAMESPACE
20389 A C@t{++} namespace.
20391 @findex TYPE_CODE_DECFLOAT
20392 @findex gdb.TYPE_CODE_DECFLOAT
20393 @item TYPE_CODE_DECFLOAT
20394 A decimal floating point type.
20396 @findex TYPE_CODE_INTERNAL_FUNCTION
20397 @findex gdb.TYPE_CODE_INTERNAL_FUNCTION
20398 @item TYPE_CODE_INTERNAL_FUNCTION
20399 A function internal to @value{GDBN}. This is the type used to represent
20400 convenience functions.
20403 @node Pretty Printing
20404 @subsubsection Pretty Printing
20406 @value{GDBN} provides a mechanism to allow pretty-printing of values
20407 using Python code. The pretty-printer API allows application-specific
20408 code to greatly simplify the display of complex objects. This
20409 mechanism works for both MI and the CLI.
20411 For example, here is how a C@t{++} @code{std::string} looks without a
20415 (@value{GDBP}) print s
20417 static npos = 4294967295,
20419 <std::allocator<char>> = @{
20420 <__gnu_cxx::new_allocator<char>> = @{<No data fields>@}, <No data fields>@},
20421 members of std::basic_string<char, std::char_traits<char>, std::allocator<char> >::_Alloc_hider:
20422 _M_p = 0x804a014 "abcd"
20427 After a pretty-printer for @code{std::string} has been installed, only
20428 the contents are printed:
20431 (@value{GDBP}) print s
20435 A pretty-printer is just an object that holds a value and implements a
20436 specific interface, defined here.
20438 @defop Operation {pretty printer} children (self)
20439 @value{GDBN} will call this method on a pretty-printer to compute the
20440 children of the pretty-printer's value.
20442 This method must return an object conforming to the Python iterator
20443 protocol. Each item returned by the iterator must be a tuple holding
20444 two elements. The first element is the ``name'' of the child; the
20445 second element is the child's value. The value can be any Python
20446 object which is convertible to a @value{GDBN} value.
20448 This method is optional. If it does not exist, @value{GDBN} will act
20449 as though the value has no children.
20452 @defop Operation {pretty printer} display_hint (self)
20453 The CLI may call this method and use its result to change the
20454 formatting of a value. The result will also be supplied to an MI
20455 consumer as a @samp{displayhint} attribute of the variable being
20458 This method is optional. If it does exist, this method must return a
20461 Some display hints are predefined by @value{GDBN}:
20465 Indicate that the object being printed is ``array-like''. The CLI
20466 uses this to respect parameters such as @code{set print elements} and
20467 @code{set print array}.
20470 Indicate that the object being printed is ``map-like'', and that the
20471 children of this value can be assumed to alternate between keys and
20475 Indicate that the object being printed is ``string-like''. If the
20476 printer's @code{to_string} method returns a Python string of some
20477 kind, then @value{GDBN} will call its internal language-specific
20478 string-printing function to format the string. For the CLI this means
20479 adding quotation marks, possibly escaping some characters, respecting
20480 @code{set print elements}, and the like.
20484 @defop Operation {pretty printer} to_string (self)
20485 @value{GDBN} will call this method to display the string
20486 representation of the value passed to the object's constructor.
20488 When printing from the CLI, if the @code{to_string} method exists,
20489 then @value{GDBN} will prepend its result to the values returned by
20490 @code{children}. Exactly how this formatting is done is dependent on
20491 the display hint, and may change as more hints are added. Also,
20492 depending on the print settings (@pxref{Print Settings}), the CLI may
20493 print just the result of @code{to_string} in a stack trace, omitting
20494 the result of @code{children}.
20496 If this method returns a string, it is printed verbatim.
20498 Otherwise, if this method returns an instance of @code{gdb.Value},
20499 then @value{GDBN} prints this value. This may result in a call to
20500 another pretty-printer.
20502 If instead the method returns a Python value which is convertible to a
20503 @code{gdb.Value}, then @value{GDBN} performs the conversion and prints
20504 the resulting value. Again, this may result in a call to another
20505 pretty-printer. Python scalars (integers, floats, and booleans) and
20506 strings are convertible to @code{gdb.Value}; other types are not.
20508 Finally, if this method returns @code{None} then no further operations
20509 are peformed in this method and nothing is printed.
20511 If the result is not one of these types, an exception is raised.
20514 @node Selecting Pretty-Printers
20515 @subsubsection Selecting Pretty-Printers
20517 The Python list @code{gdb.pretty_printers} contains an array of
20518 functions that have been registered via addition as a pretty-printer.
20519 Each @code{gdb.Progspace} contains a @code{pretty_printers} attribute.
20520 Each @code{gdb.Objfile} also contains a @code{pretty_printers}
20523 A function on one of these lists is passed a single @code{gdb.Value}
20524 argument and should return a pretty-printer object conforming to the
20525 interface definition above (@pxref{Pretty Printing}). If a function
20526 cannot create a pretty-printer for the value, it should return
20529 @value{GDBN} first checks the @code{pretty_printers} attribute of each
20530 @code{gdb.Objfile} in the current program space and iteratively calls
20531 each function in the list for that @code{gdb.Objfile} until it receives
20532 a pretty-printer object.
20533 If no pretty-printer is found in the objfile lists, @value{GDBN} then
20534 searches the pretty-printer list of the current program space,
20535 calling each function until an object is returned.
20536 After these lists have been exhausted, it tries the global
20537 @code{gdb.pretty-printers} list, again calling each function until an
20538 object is returned.
20540 The order in which the objfiles are searched is not specified. For a
20541 given list, functions are always invoked from the head of the list,
20542 and iterated over sequentially until the end of the list, or a printer
20543 object is returned.
20545 Here is an example showing how a @code{std::string} printer might be
20549 class StdStringPrinter:
20550 "Print a std::string"
20552 def __init__ (self, val):
20555 def to_string (self):
20556 return self.val['_M_dataplus']['_M_p']
20558 def display_hint (self):
20562 And here is an example showing how a lookup function for the printer
20563 example above might be written.
20566 def str_lookup_function (val):
20568 lookup_tag = val.type.tag
20569 regex = re.compile ("^std::basic_string<char,.*>$")
20570 if lookup_tag == None:
20572 if regex.match (lookup_tag):
20573 return StdStringPrinter (val)
20578 The example lookup function extracts the value's type, and attempts to
20579 match it to a type that it can pretty-print. If it is a type the
20580 printer can pretty-print, it will return a printer object. If not, it
20581 returns @code{None}.
20583 We recommend that you put your core pretty-printers into a Python
20584 package. If your pretty-printers are for use with a library, we
20585 further recommend embedding a version number into the package name.
20586 This practice will enable @value{GDBN} to load multiple versions of
20587 your pretty-printers at the same time, because they will have
20590 You should write auto-loaded code (@pxref{Auto-loading}) such that it
20591 can be evaluated multiple times without changing its meaning. An
20592 ideal auto-load file will consist solely of @code{import}s of your
20593 printer modules, followed by a call to a register pretty-printers with
20594 the current objfile.
20596 Taken as a whole, this approach will scale nicely to multiple
20597 inferiors, each potentially using a different library version.
20598 Embedding a version number in the Python package name will ensure that
20599 @value{GDBN} is able to load both sets of printers simultaneously.
20600 Then, because the search for pretty-printers is done by objfile, and
20601 because your auto-loaded code took care to register your library's
20602 printers with a specific objfile, @value{GDBN} will find the correct
20603 printers for the specific version of the library used by each
20606 To continue the @code{std::string} example (@pxref{Pretty Printing}),
20607 this code might appear in @code{gdb.libstdcxx.v6}:
20610 def register_printers (objfile):
20611 objfile.pretty_printers.add (str_lookup_function)
20615 And then the corresponding contents of the auto-load file would be:
20618 import gdb.libstdcxx.v6
20619 gdb.libstdcxx.v6.register_printers (gdb.current_objfile ())
20622 @node Commands In Python
20623 @subsubsection Commands In Python
20625 @cindex commands in python
20626 @cindex python commands
20627 You can implement new @value{GDBN} CLI commands in Python. A CLI
20628 command is implemented using an instance of the @code{gdb.Command}
20629 class, most commonly using a subclass.
20631 @defmethod Command __init__ name @var{command_class} @r{[}@var{completer_class}@r{]} @r{[}@var{prefix}@r{]}
20632 The object initializer for @code{Command} registers the new command
20633 with @value{GDBN}. This initializer is normally invoked from the
20634 subclass' own @code{__init__} method.
20636 @var{name} is the name of the command. If @var{name} consists of
20637 multiple words, then the initial words are looked for as prefix
20638 commands. In this case, if one of the prefix commands does not exist,
20639 an exception is raised.
20641 There is no support for multi-line commands.
20643 @var{command_class} should be one of the @samp{COMMAND_} constants
20644 defined below. This argument tells @value{GDBN} how to categorize the
20645 new command in the help system.
20647 @var{completer_class} is an optional argument. If given, it should be
20648 one of the @samp{COMPLETE_} constants defined below. This argument
20649 tells @value{GDBN} how to perform completion for this command. If not
20650 given, @value{GDBN} will attempt to complete using the object's
20651 @code{complete} method (see below); if no such method is found, an
20652 error will occur when completion is attempted.
20654 @var{prefix} is an optional argument. If @code{True}, then the new
20655 command is a prefix command; sub-commands of this command may be
20658 The help text for the new command is taken from the Python
20659 documentation string for the command's class, if there is one. If no
20660 documentation string is provided, the default value ``This command is
20661 not documented.'' is used.
20664 @cindex don't repeat Python command
20665 @defmethod Command dont_repeat
20666 By default, a @value{GDBN} command is repeated when the user enters a
20667 blank line at the command prompt. A command can suppress this
20668 behavior by invoking the @code{dont_repeat} method. This is similar
20669 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
20672 @defmethod Command invoke argument from_tty
20673 This method is called by @value{GDBN} when this command is invoked.
20675 @var{argument} is a string. It is the argument to the command, after
20676 leading and trailing whitespace has been stripped.
20678 @var{from_tty} is a boolean argument. When true, this means that the
20679 command was entered by the user at the terminal; when false it means
20680 that the command came from elsewhere.
20682 If this method throws an exception, it is turned into a @value{GDBN}
20683 @code{error} call. Otherwise, the return value is ignored.
20686 @cindex completion of Python commands
20687 @defmethod Command complete text word
20688 This method is called by @value{GDBN} when the user attempts
20689 completion on this command. All forms of completion are handled by
20690 this method, that is, the @key{TAB} and @key{M-?} key bindings
20691 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
20694 The arguments @var{text} and @var{word} are both strings. @var{text}
20695 holds the complete command line up to the cursor's location.
20696 @var{word} holds the last word of the command line; this is computed
20697 using a word-breaking heuristic.
20699 The @code{complete} method can return several values:
20702 If the return value is a sequence, the contents of the sequence are
20703 used as the completions. It is up to @code{complete} to ensure that the
20704 contents actually do complete the word. A zero-length sequence is
20705 allowed, it means that there were no completions available. Only
20706 string elements of the sequence are used; other elements in the
20707 sequence are ignored.
20710 If the return value is one of the @samp{COMPLETE_} constants defined
20711 below, then the corresponding @value{GDBN}-internal completion
20712 function is invoked, and its result is used.
20715 All other results are treated as though there were no available
20720 When a new command is registered, it must be declared as a member of
20721 some general class of commands. This is used to classify top-level
20722 commands in the on-line help system; note that prefix commands are not
20723 listed under their own category but rather that of their top-level
20724 command. The available classifications are represented by constants
20725 defined in the @code{gdb} module:
20728 @findex COMMAND_NONE
20729 @findex gdb.COMMAND_NONE
20731 The command does not belong to any particular class. A command in
20732 this category will not be displayed in any of the help categories.
20734 @findex COMMAND_RUNNING
20735 @findex gdb.COMMAND_RUNNING
20736 @item COMMAND_RUNNING
20737 The command is related to running the inferior. For example,
20738 @code{start}, @code{step}, and @code{continue} are in this category.
20739 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
20740 commands in this category.
20742 @findex COMMAND_DATA
20743 @findex gdb.COMMAND_DATA
20745 The command is related to data or variables. For example,
20746 @code{call}, @code{find}, and @code{print} are in this category. Type
20747 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
20750 @findex COMMAND_STACK
20751 @findex gdb.COMMAND_STACK
20752 @item COMMAND_STACK
20753 The command has to do with manipulation of the stack. For example,
20754 @code{backtrace}, @code{frame}, and @code{return} are in this
20755 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
20756 list of commands in this category.
20758 @findex COMMAND_FILES
20759 @findex gdb.COMMAND_FILES
20760 @item COMMAND_FILES
20761 This class is used for file-related commands. For example,
20762 @code{file}, @code{list} and @code{section} are in this category.
20763 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
20764 commands in this category.
20766 @findex COMMAND_SUPPORT
20767 @findex gdb.COMMAND_SUPPORT
20768 @item COMMAND_SUPPORT
20769 This should be used for ``support facilities'', generally meaning
20770 things that are useful to the user when interacting with @value{GDBN},
20771 but not related to the state of the inferior. For example,
20772 @code{help}, @code{make}, and @code{shell} are in this category. Type
20773 @kbd{help support} at the @value{GDBN} prompt to see a list of
20774 commands in this category.
20776 @findex COMMAND_STATUS
20777 @findex gdb.COMMAND_STATUS
20778 @item COMMAND_STATUS
20779 The command is an @samp{info}-related command, that is, related to the
20780 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
20781 and @code{show} are in this category. Type @kbd{help status} at the
20782 @value{GDBN} prompt to see a list of commands in this category.
20784 @findex COMMAND_BREAKPOINTS
20785 @findex gdb.COMMAND_BREAKPOINTS
20786 @item COMMAND_BREAKPOINTS
20787 The command has to do with breakpoints. For example, @code{break},
20788 @code{clear}, and @code{delete} are in this category. Type @kbd{help
20789 breakpoints} at the @value{GDBN} prompt to see a list of commands in
20792 @findex COMMAND_TRACEPOINTS
20793 @findex gdb.COMMAND_TRACEPOINTS
20794 @item COMMAND_TRACEPOINTS
20795 The command has to do with tracepoints. For example, @code{trace},
20796 @code{actions}, and @code{tfind} are in this category. Type
20797 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
20798 commands in this category.
20800 @findex COMMAND_OBSCURE
20801 @findex gdb.COMMAND_OBSCURE
20802 @item COMMAND_OBSCURE
20803 The command is only used in unusual circumstances, or is not of
20804 general interest to users. For example, @code{checkpoint},
20805 @code{fork}, and @code{stop} are in this category. Type @kbd{help
20806 obscure} at the @value{GDBN} prompt to see a list of commands in this
20809 @findex COMMAND_MAINTENANCE
20810 @findex gdb.COMMAND_MAINTENANCE
20811 @item COMMAND_MAINTENANCE
20812 The command is only useful to @value{GDBN} maintainers. The
20813 @code{maintenance} and @code{flushregs} commands are in this category.
20814 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
20815 commands in this category.
20818 A new command can use a predefined completion function, either by
20819 specifying it via an argument at initialization, or by returning it
20820 from the @code{complete} method. These predefined completion
20821 constants are all defined in the @code{gdb} module:
20824 @findex COMPLETE_NONE
20825 @findex gdb.COMPLETE_NONE
20826 @item COMPLETE_NONE
20827 This constant means that no completion should be done.
20829 @findex COMPLETE_FILENAME
20830 @findex gdb.COMPLETE_FILENAME
20831 @item COMPLETE_FILENAME
20832 This constant means that filename completion should be performed.
20834 @findex COMPLETE_LOCATION
20835 @findex gdb.COMPLETE_LOCATION
20836 @item COMPLETE_LOCATION
20837 This constant means that location completion should be done.
20838 @xref{Specify Location}.
20840 @findex COMPLETE_COMMAND
20841 @findex gdb.COMPLETE_COMMAND
20842 @item COMPLETE_COMMAND
20843 This constant means that completion should examine @value{GDBN}
20846 @findex COMPLETE_SYMBOL
20847 @findex gdb.COMPLETE_SYMBOL
20848 @item COMPLETE_SYMBOL
20849 This constant means that completion should be done using symbol names
20853 The following code snippet shows how a trivial CLI command can be
20854 implemented in Python:
20857 class HelloWorld (gdb.Command):
20858 """Greet the whole world."""
20860 def __init__ (self):
20861 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_OBSCURE)
20863 def invoke (self, arg, from_tty):
20864 print "Hello, World!"
20869 The last line instantiates the class, and is necessary to trigger the
20870 registration of the command with @value{GDBN}. Depending on how the
20871 Python code is read into @value{GDBN}, you may need to import the
20872 @code{gdb} module explicitly.
20874 @node Functions In Python
20875 @subsubsection Writing new convenience functions
20877 @cindex writing convenience functions
20878 @cindex convenience functions in python
20879 @cindex python convenience functions
20880 @tindex gdb.Function
20882 You can implement new convenience functions (@pxref{Convenience Vars})
20883 in Python. A convenience function is an instance of a subclass of the
20884 class @code{gdb.Function}.
20886 @defmethod Function __init__ name
20887 The initializer for @code{Function} registers the new function with
20888 @value{GDBN}. The argument @var{name} is the name of the function,
20889 a string. The function will be visible to the user as a convenience
20890 variable of type @code{internal function}, whose name is the same as
20891 the given @var{name}.
20893 The documentation for the new function is taken from the documentation
20894 string for the new class.
20897 @defmethod Function invoke @var{*args}
20898 When a convenience function is evaluated, its arguments are converted
20899 to instances of @code{gdb.Value}, and then the function's
20900 @code{invoke} method is called. Note that @value{GDBN} does not
20901 predetermine the arity of convenience functions. Instead, all
20902 available arguments are passed to @code{invoke}, following the
20903 standard Python calling convention. In particular, a convenience
20904 function can have default values for parameters without ill effect.
20906 The return value of this method is used as its value in the enclosing
20907 expression. If an ordinary Python value is returned, it is converted
20908 to a @code{gdb.Value} following the usual rules.
20911 The following code snippet shows how a trivial convenience function can
20912 be implemented in Python:
20915 class Greet (gdb.Function):
20916 """Return string to greet someone.
20917 Takes a name as argument."""
20919 def __init__ (self):
20920 super (Greet, self).__init__ ("greet")
20922 def invoke (self, name):
20923 return "Hello, %s!" % name.string ()
20928 The last line instantiates the class, and is necessary to trigger the
20929 registration of the function with @value{GDBN}. Depending on how the
20930 Python code is read into @value{GDBN}, you may need to import the
20931 @code{gdb} module explicitly.
20933 @node Progspaces In Python
20934 @subsubsection Program Spaces In Python
20936 @cindex progspaces in python
20937 @tindex gdb.Progspace
20939 A program space, or @dfn{progspace}, represents a symbolic view
20940 of an address space.
20941 It consists of all of the objfiles of the program.
20942 @xref{Objfiles In Python}.
20943 @xref{Inferiors and Programs, program spaces}, for more details
20944 about program spaces.
20946 The following progspace-related functions are available in the
20949 @findex gdb.current_progspace
20950 @defun current_progspace
20951 This function returns the program space of the currently selected inferior.
20952 @xref{Inferiors and Programs}.
20955 @findex gdb.progspaces
20957 Return a sequence of all the progspaces currently known to @value{GDBN}.
20960 Each progspace is represented by an instance of the @code{gdb.Progspace}
20963 @defivar Progspace filename
20964 The file name of the progspace as a string.
20967 @defivar Progspace pretty_printers
20968 The @code{pretty_printers} attribute is a list of functions. It is
20969 used to look up pretty-printers. A @code{Value} is passed to each
20970 function in order; if the function returns @code{None}, then the
20971 search continues. Otherwise, the return value should be an object
20972 which is used to format the value. @xref{Pretty Printing}, for more
20976 @node Objfiles In Python
20977 @subsubsection Objfiles In Python
20979 @cindex objfiles in python
20980 @tindex gdb.Objfile
20982 @value{GDBN} loads symbols for an inferior from various
20983 symbol-containing files (@pxref{Files}). These include the primary
20984 executable file, any shared libraries used by the inferior, and any
20985 separate debug info files (@pxref{Separate Debug Files}).
20986 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
20988 The following objfile-related functions are available in the
20991 @findex gdb.current_objfile
20992 @defun current_objfile
20993 When auto-loading a Python script (@pxref{Auto-loading}), @value{GDBN}
20994 sets the ``current objfile'' to the corresponding objfile. This
20995 function returns the current objfile. If there is no current objfile,
20996 this function returns @code{None}.
20999 @findex gdb.objfiles
21001 Return a sequence of all the objfiles current known to @value{GDBN}.
21002 @xref{Objfiles In Python}.
21005 Each objfile is represented by an instance of the @code{gdb.Objfile}
21008 @defivar Objfile filename
21009 The file name of the objfile as a string.
21012 @defivar Objfile pretty_printers
21013 The @code{pretty_printers} attribute is a list of functions. It is
21014 used to look up pretty-printers. A @code{Value} is passed to each
21015 function in order; if the function returns @code{None}, then the
21016 search continues. Otherwise, the return value should be an object
21017 which is used to format the value. @xref{Pretty Printing}, for more
21021 @node Frames In Python
21022 @subsubsection Accessing inferior stack frames from Python.
21024 @cindex frames in python
21025 When the debugged program stops, @value{GDBN} is able to analyze its call
21026 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
21027 represents a frame in the stack. A @code{gdb.Frame} object is only valid
21028 while its corresponding frame exists in the inferior's stack. If you try
21029 to use an invalid frame object, @value{GDBN} will throw a @code{RuntimeError}
21032 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
21036 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
21040 The following frame-related functions are available in the @code{gdb} module:
21042 @findex gdb.selected_frame
21043 @defun selected_frame
21044 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
21047 @defun frame_stop_reason_string reason
21048 Return a string explaining the reason why @value{GDBN} stopped unwinding
21049 frames, as expressed by the given @var{reason} code (an integer, see the
21050 @code{unwind_stop_reason} method further down in this section).
21053 A @code{gdb.Frame} object has the following methods:
21056 @defmethod Frame is_valid
21057 Returns true if the @code{gdb.Frame} object is valid, false if not.
21058 A frame object can become invalid if the frame it refers to doesn't
21059 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
21060 an exception if it is invalid at the time the method is called.
21063 @defmethod Frame name
21064 Returns the function name of the frame, or @code{None} if it can't be
21068 @defmethod Frame type
21069 Returns the type of the frame. The value can be one of
21070 @code{gdb.NORMAL_FRAME}, @code{gdb.DUMMY_FRAME}, @code{gdb.SIGTRAMP_FRAME}
21071 or @code{gdb.SENTINEL_FRAME}.
21074 @defmethod Frame unwind_stop_reason
21075 Return an integer representing the reason why it's not possible to find
21076 more frames toward the outermost frame. Use
21077 @code{gdb.frame_stop_reason_string} to convert the value returned by this
21078 function to a string.
21081 @defmethod Frame pc
21082 Returns the frame's resume address.
21085 @defmethod Frame block
21086 Return the frame's code block. @xref{Blocks In Python}.
21089 @defmethod Frame function
21090 Return the symbol for the function corresponding to this frame.
21091 @xref{Symbols In Python}.
21094 @defmethod Frame older
21095 Return the frame that called this frame.
21098 @defmethod Frame newer
21099 Return the frame called by this frame.
21102 @defmethod Frame find_sal
21103 Return the frame's symtab and line object.
21104 @xref{Symbol Tables In Python}.
21107 @defmethod Frame read_var variable @r{[}block@r{]}
21108 Return the value of @var{variable} in this frame. If the optional
21109 argument @var{block} is provided, search for the variable from that
21110 block; otherwise start at the frame's current block (which is
21111 determined by the frame's current program counter). @var{variable}
21112 must be a string or a @code{gdb.Symbol} object. @var{block} must be a
21113 @code{gdb.Block} object.
21116 @defmethod Frame select
21117 Set this frame to be the selected frame. @xref{Stack, ,Examining the
21122 @node Blocks In Python
21123 @subsubsection Accessing frame blocks from Python.
21125 @cindex blocks in python
21128 Within each frame, @value{GDBN} maintains information on each block
21129 stored in that frame. These blocks are organized hierarchically, and
21130 are represented individually in Python as a @code{gdb.Block}.
21131 Please see @ref{Frames In Python}, for a more in-depth discussion on
21132 frames. Furthermore, see @ref{Stack, ,Examining the Stack}, for more
21133 detailed technical information on @value{GDBN}'s book-keeping of the
21136 The following block-related functions are available in the @code{gdb}
21139 @findex gdb.block_for_pc
21140 @defun block_for_pc pc
21141 Return the @code{gdb.Block} containing the given @var{pc} value. If the
21142 block cannot be found for the @var{pc} value specified, the function
21143 will return @code{None}.
21146 A @code{gdb.Block} object has the following attributes:
21149 @defivar Block start
21150 The start address of the block. This attribute is not writable.
21154 The end address of the block. This attribute is not writable.
21157 @defivar Block function
21158 The name of the block represented as a @code{gdb.Symbol}. If the
21159 block is not named, then this attribute holds @code{None}. This
21160 attribute is not writable.
21163 @defivar Block superblock
21164 The block containing this block. If this parent block does not exist,
21165 this attribute holds @code{None}. This attribute is not writable.
21169 @node Symbols In Python
21170 @subsubsection Python representation of Symbols.
21172 @cindex symbols in python
21175 @value{GDBN} represents every variable, function and type as an
21176 entry in a symbol table. @xref{Symbols, ,Examining the Symbol Table}.
21177 Similarly, Python represents these symbols in @value{GDBN} with the
21178 @code{gdb.Symbol} object.
21180 The following symbol-related functions are available in the @code{gdb}
21183 @findex gdb.lookup_symbol
21184 @defun lookup_symbol name [block] [domain]
21185 This function searches for a symbol by name. The search scope can be
21186 restricted to the parameters defined in the optional domain and block
21189 @var{name} is the name of the symbol. It must be a string. The
21190 optional @var{block} argument restricts the search to symbols visible
21191 in that @var{block}. The @var{block} argument must be a
21192 @code{gdb.Block} object. The optional @var{domain} argument restricts
21193 the search to the domain type. The @var{domain} argument must be a
21194 domain constant defined in the @code{gdb} module and described later
21198 A @code{gdb.Symbol} object has the following attributes:
21201 @defivar Symbol symtab
21202 The symbol table in which the symbol appears. This attribute is
21203 represented as a @code{gdb.Symtab} object. @xref{Symbol Tables In
21204 Python}. This attribute is not writable.
21207 @defivar Symbol name
21208 The name of the symbol as a string. This attribute is not writable.
21211 @defivar Symbol linkage_name
21212 The name of the symbol, as used by the linker (i.e., may be mangled).
21213 This attribute is not writable.
21216 @defivar Symbol print_name
21217 The name of the symbol in a form suitable for output. This is either
21218 @code{name} or @code{linkage_name}, depending on whether the user
21219 asked @value{GDBN} to display demangled or mangled names.
21222 @defivar Symbol addr_class
21223 The address class of the symbol. This classifies how to find the value
21224 of a symbol. Each address class is a constant defined in the
21225 @code{gdb} module and described later in this chapter.
21228 @defivar Symbol is_argument
21229 @code{True} if the symbol is an argument of a function.
21232 @defivar Symbol is_constant
21233 @code{True} if the symbol is a constant.
21236 @defivar Symbol is_function
21237 @code{True} if the symbol is a function or a method.
21240 @defivar Symbol is_variable
21241 @code{True} if the symbol is a variable.
21245 The available domain categories in @code{gdb.Symbol} are represented
21246 as constants in the @code{gdb} module:
21249 @findex SYMBOL_UNDEF_DOMAIN
21250 @findex gdb.SYMBOL_UNDEF_DOMAIN
21251 @item SYMBOL_UNDEF_DOMAIN
21252 This is used when a domain has not been discovered or none of the
21253 following domains apply. This usually indicates an error either
21254 in the symbol information or in @value{GDBN}'s handling of symbols.
21255 @findex SYMBOL_VAR_DOMAIN
21256 @findex gdb.SYMBOL_VAR_DOMAIN
21257 @item SYMBOL_VAR_DOMAIN
21258 This domain contains variables, function names, typedef names and enum
21260 @findex SYMBOL_STRUCT_DOMAIN
21261 @findex gdb.SYMBOL_STRUCT_DOMAIN
21262 @item SYMBOL_STRUCT_DOMAIN
21263 This domain holds struct, union and enum type names.
21264 @findex SYMBOL_LABEL_DOMAIN
21265 @findex gdb.SYMBOL_LABEL_DOMAIN
21266 @item SYMBOL_LABEL_DOMAIN
21267 This domain contains names of labels (for gotos).
21268 @findex SYMBOL_VARIABLES_DOMAIN
21269 @findex gdb.SYMBOL_VARIABLES_DOMAIN
21270 @item SYMBOL_VARIABLES_DOMAIN
21271 This domain holds a subset of the @code{SYMBOLS_VAR_DOMAIN}; it
21272 contains everything minus functions and types.
21273 @findex SYMBOL_FUNCTIONS_DOMAIN
21274 @findex gdb.SYMBOL_FUNCTIONS_DOMAIN
21275 @item SYMBOL_FUNCTION_DOMAIN
21276 This domain contains all functions.
21277 @findex SYMBOL_TYPES_DOMAIN
21278 @findex gdb.SYMBOL_TYPES_DOMAIN
21279 @item SYMBOL_TYPES_DOMAIN
21280 This domain contains all types.
21283 The available address class categories in @code{gdb.Symbol} are represented
21284 as constants in the @code{gdb} module:
21287 @findex SYMBOL_LOC_UNDEF
21288 @findex gdb.SYMBOL_LOC_UNDEF
21289 @item SYMBOL_LOC_UNDEF
21290 If this is returned by address class, it indicates an error either in
21291 the symbol information or in @value{GDBN}'s handling of symbols.
21292 @findex SYMBOL_LOC_CONST
21293 @findex gdb.SYMBOL_LOC_CONST
21294 @item SYMBOL_LOC_CONST
21295 Value is constant int.
21296 @findex SYMBOL_LOC_STATIC
21297 @findex gdb.SYMBOL_LOC_STATIC
21298 @item SYMBOL_LOC_STATIC
21299 Value is at a fixed address.
21300 @findex SYMBOL_LOC_REGISTER
21301 @findex gdb.SYMBOL_LOC_REGISTER
21302 @item SYMBOL_LOC_REGISTER
21303 Value is in a register.
21304 @findex SYMBOL_LOC_ARG
21305 @findex gdb.SYMBOL_LOC_ARG
21306 @item SYMBOL_LOC_ARG
21307 Value is an argument. This value is at the offset stored within the
21308 symbol inside the frame's argument list.
21309 @findex SYMBOL_LOC_REF_ARG
21310 @findex gdb.SYMBOL_LOC_REF_ARG
21311 @item SYMBOL_LOC_REF_ARG
21312 Value address is stored in the frame's argument list. Just like
21313 @code{LOC_ARG} except that the value's address is stored at the
21314 offset, not the value itself.
21315 @findex SYMBOL_LOC_REGPARM_ADDR
21316 @findex gdb.SYMBOL_LOC_REGPARM_ADDR
21317 @item SYMBOL_LOC_REGPARM_ADDR
21318 Value is a specified register. Just like @code{LOC_REGISTER} except
21319 the register holds the address of the argument instead of the argument
21321 @findex SYMBOL_LOC_LOCAL
21322 @findex gdb.SYMBOL_LOC_LOCAL
21323 @item SYMBOL_LOC_LOCAL
21324 Value is a local variable.
21325 @findex SYMBOL_LOC_TYPEDEF
21326 @findex gdb.SYMBOL_LOC_TYPEDEF
21327 @item SYMBOL_LOC_TYPEDEF
21328 Value not used. Symbols in the domain @code{SYMBOL_STRUCT_DOMAIN} all
21330 @findex SYMBOL_LOC_BLOCK
21331 @findex gdb.SYMBOL_LOC_BLOCK
21332 @item SYMBOL_LOC_BLOCK
21334 @findex SYMBOL_LOC_CONST_BYTES
21335 @findex gdb.SYMBOL_LOC_CONST_BYTES
21336 @item SYMBOL_LOC_CONST_BYTES
21337 Value is a byte-sequence.
21338 @findex SYMBOL_LOC_UNRESOLVED
21339 @findex gdb.SYMBOL_LOC_UNRESOLVED
21340 @item SYMBOL_LOC_UNRESOLVED
21341 Value is at a fixed address, but the address of the variable has to be
21342 determined from the minimal symbol table whenever the variable is
21344 @findex SYMBOL_LOC_OPTIMIZED_OUT
21345 @findex gdb.SYMBOL_LOC_OPTIMIZED_OUT
21346 @item SYMBOL_LOC_OPTIMIZED_OUT
21347 The value does not actually exist in the program.
21348 @findex SYMBOL_LOC_COMPUTED
21349 @findex gdb.SYMBOL_LOC_COMPUTED
21350 @item SYMBOL_LOC_COMPUTED
21351 The value's address is a computed location.
21354 @node Symbol Tables In Python
21355 @subsubsection Symbol table representation in Python.
21357 @cindex symbol tables in python
21359 @tindex gdb.Symtab_and_line
21361 Access to symbol table data maintained by @value{GDBN} on the inferior
21362 is exposed to Python via two objects: @code{gdb.Symtab_and_line} and
21363 @code{gdb.Symtab}. Symbol table and line data for a frame is returned
21364 from the @code{find_sal} method in @code{gdb.Frame} object.
21365 @xref{Frames In Python}.
21367 For more information on @value{GDBN}'s symbol table management, see
21368 @ref{Symbols, ,Examining the Symbol Table}, for more information.
21370 A @code{gdb.Symtab_and_line} object has the following attributes:
21373 @defivar Symtab_and_line symtab
21374 The symbol table object (@code{gdb.Symtab}) for this frame.
21375 This attribute is not writable.
21378 @defivar Symtab_and_line pc
21379 Indicates the current program counter address. This attribute is not
21383 @defivar Symtab_and_line line
21384 Indicates the current line number for this object. This
21385 attribute is not writable.
21389 A @code{gdb.Symtab} object has the following attributes:
21392 @defivar Symtab filename
21393 The symbol table's source filename. This attribute is not writable.
21396 @defivar Symtab objfile
21397 The symbol table's backing object file. @xref{Objfiles In Python}.
21398 This attribute is not writable.
21402 The following methods are provided:
21405 @defmethod Symtab fullname
21406 Return the symbol table's source absolute file name.
21410 @node Breakpoints In Python
21411 @subsubsection Manipulating breakpoints using Python
21413 @cindex breakpoints in python
21414 @tindex gdb.Breakpoint
21416 Python code can manipulate breakpoints via the @code{gdb.Breakpoint}
21419 @defmethod Breakpoint __init__ spec @r{[}type@r{]} @r{[}wp_class@r{]}
21420 Create a new breakpoint. @var{spec} is a string naming the
21421 location of the breakpoint, or an expression that defines a
21422 watchpoint. The contents can be any location recognized by the
21423 @code{break} command, or in the case of a watchpoint, by the @code{watch}
21424 command. The optional @var{type} denotes the breakpoint to create
21425 from the types defined later in this chapter. This argument can be
21426 either: @code{BP_BREAKPOINT} or @code{BP_WATCHPOINT}. @var{type}
21427 defaults to @code{BP_BREAKPOINT}. The optional @var{wp_class}
21428 argument defines the class of watchpoint to create, if @var{type} is
21429 defined as @code{BP_WATCHPOINT}. If a watchpoint class is not
21430 provided, it is assumed to be a @var{WP_WRITE} class.
21433 The available watchpoint types represented by constants are defined in the
21438 @findex gdb.WP_READ
21440 Read only watchpoint.
21443 @findex gdb.WP_WRITE
21445 Write only watchpoint.
21448 @findex gdb.WP_ACCESS
21450 Read/Write watchpoint.
21453 @defmethod Breakpoint is_valid
21454 Return @code{True} if this @code{Breakpoint} object is valid,
21455 @code{False} otherwise. A @code{Breakpoint} object can become invalid
21456 if the user deletes the breakpoint. In this case, the object still
21457 exists, but the underlying breakpoint does not. In the cases of
21458 watchpoint scope, the watchpoint remains valid even if execution of the
21459 inferior leaves the scope of that watchpoint.
21462 @defivar Breakpoint enabled
21463 This attribute is @code{True} if the breakpoint is enabled, and
21464 @code{False} otherwise. This attribute is writable.
21467 @defivar Breakpoint silent
21468 This attribute is @code{True} if the breakpoint is silent, and
21469 @code{False} otherwise. This attribute is writable.
21471 Note that a breakpoint can also be silent if it has commands and the
21472 first command is @code{silent}. This is not reported by the
21473 @code{silent} attribute.
21476 @defivar Breakpoint thread
21477 If the breakpoint is thread-specific, this attribute holds the thread
21478 id. If the breakpoint is not thread-specific, this attribute is
21479 @code{None}. This attribute is writable.
21482 @defivar Breakpoint task
21483 If the breakpoint is Ada task-specific, this attribute holds the Ada task
21484 id. If the breakpoint is not task-specific (or the underlying
21485 language is not Ada), this attribute is @code{None}. This attribute
21489 @defivar Breakpoint ignore_count
21490 This attribute holds the ignore count for the breakpoint, an integer.
21491 This attribute is writable.
21494 @defivar Breakpoint number
21495 This attribute holds the breakpoint's number --- the identifier used by
21496 the user to manipulate the breakpoint. This attribute is not writable.
21499 @defivar Breakpoint type
21500 This attribute holds the breakpoint's type --- the identifier used to
21501 determine the actual breakpoint type or use-case. This attribute is not
21505 The available types are represented by constants defined in the @code{gdb}
21509 @findex BP_BREAKPOINT
21510 @findex gdb.BP_BREAKPOINT
21511 @item BP_BREAKPOINT
21512 Normal code breakpoint.
21514 @findex BP_WATCHPOINT
21515 @findex gdb.BP_WATCHPOINT
21516 @item BP_WATCHPOINT
21517 Watchpoint breakpoint.
21519 @findex BP_HARDWARE_WATCHPOINT
21520 @findex gdb.BP_HARDWARE_WATCHPOINT
21521 @item BP_HARDWARE_WATCHPOINT
21522 Hardware assisted watchpoint.
21524 @findex BP_READ_WATCHPOINT
21525 @findex gdb.BP_READ_WATCHPOINT
21526 @item BP_READ_WATCHPOINT
21527 Hardware assisted read watchpoint.
21529 @findex BP_ACCESS_WATCHPOINT
21530 @findex gdb.BP_ACCESS_WATCHPOINT
21531 @item BP_ACCESS_WATCHPOINT
21532 Hardware assisted access watchpoint.
21535 @defivar Breakpoint hit_count
21536 This attribute holds the hit count for the breakpoint, an integer.
21537 This attribute is writable, but currently it can only be set to zero.
21540 @defivar Breakpoint location
21541 This attribute holds the location of the breakpoint, as specified by
21542 the user. It is a string. If the breakpoint does not have a location
21543 (that is, it is a watchpoint) the attribute's value is @code{None}. This
21544 attribute is not writable.
21547 @defivar Breakpoint expression
21548 This attribute holds a breakpoint expression, as specified by
21549 the user. It is a string. If the breakpoint does not have an
21550 expression (the breakpoint is not a watchpoint) the attribute's value
21551 is @code{None}. This attribute is not writable.
21554 @defivar Breakpoint condition
21555 This attribute holds the condition of the breakpoint, as specified by
21556 the user. It is a string. If there is no condition, this attribute's
21557 value is @code{None}. This attribute is writable.
21560 @defivar Breakpoint commands
21561 This attribute holds the commands attached to the breakpoint. If
21562 there are commands, this attribute's value is a string holding all the
21563 commands, separated by newlines. If there are no commands, this
21564 attribute is @code{None}. This attribute is not writable.
21567 @node Lazy Strings In Python
21568 @subsubsection Python representation of lazy strings.
21570 @cindex lazy strings in python
21571 @tindex gdb.LazyString
21573 A @dfn{lazy string} is a string whose contents is not retrieved or
21574 encoded until it is needed.
21576 A @code{gdb.LazyString} is represented in @value{GDBN} as an
21577 @code{address} that points to a region of memory, an @code{encoding}
21578 that will be used to encode that region of memory, and a @code{length}
21579 to delimit the region of memory that represents the string. The
21580 difference between a @code{gdb.LazyString} and a string wrapped within
21581 a @code{gdb.Value} is that a @code{gdb.LazyString} will be treated
21582 differently by @value{GDBN} when printing. A @code{gdb.LazyString} is
21583 retrieved and encoded during printing, while a @code{gdb.Value}
21584 wrapping a string is immediately retrieved and encoded on creation.
21586 A @code{gdb.LazyString} object has the following functions:
21588 @defmethod LazyString value
21589 Convert the @code{gdb.LazyString} to a @code{gdb.Value}. This value
21590 will point to the string in memory, but will lose all the delayed
21591 retrieval, encoding and handling that @value{GDBN} applies to a
21592 @code{gdb.LazyString}.
21595 @defivar LazyString address
21596 This attribute holds the address of the string. This attribute is not
21600 @defivar LazyString length
21601 This attribute holds the length of the string in characters. If the
21602 length is -1, then the string will be fetched and encoded up to the
21603 first null of appropriate width. This attribute is not writable.
21606 @defivar LazyString encoding
21607 This attribute holds the encoding that will be applied to the string
21608 when the string is printed by @value{GDBN}. If the encoding is not
21609 set, or contains an empty string, then @value{GDBN} will select the
21610 most appropriate encoding when the string is printed. This attribute
21614 @defivar LazyString type
21615 This attribute holds the type that is represented by the lazy string's
21616 type. For a lazy string this will always be a pointer type. To
21617 resolve this to the lazy string's character type, use the type's
21618 @code{target} method. @xref{Types In Python}. This attribute is not
21623 @chapter Command Interpreters
21624 @cindex command interpreters
21626 @value{GDBN} supports multiple command interpreters, and some command
21627 infrastructure to allow users or user interface writers to switch
21628 between interpreters or run commands in other interpreters.
21630 @value{GDBN} currently supports two command interpreters, the console
21631 interpreter (sometimes called the command-line interpreter or @sc{cli})
21632 and the machine interface interpreter (or @sc{gdb/mi}). This manual
21633 describes both of these interfaces in great detail.
21635 By default, @value{GDBN} will start with the console interpreter.
21636 However, the user may choose to start @value{GDBN} with another
21637 interpreter by specifying the @option{-i} or @option{--interpreter}
21638 startup options. Defined interpreters include:
21642 @cindex console interpreter
21643 The traditional console or command-line interpreter. This is the most often
21644 used interpreter with @value{GDBN}. With no interpreter specified at runtime,
21645 @value{GDBN} will use this interpreter.
21648 @cindex mi interpreter
21649 The newest @sc{gdb/mi} interface (currently @code{mi2}). Used primarily
21650 by programs wishing to use @value{GDBN} as a backend for a debugger GUI
21651 or an IDE. For more information, see @ref{GDB/MI, ,The @sc{gdb/mi}
21655 @cindex mi2 interpreter
21656 The current @sc{gdb/mi} interface.
21659 @cindex mi1 interpreter
21660 The @sc{gdb/mi} interface included in @value{GDBN} 5.1, 5.2, and 5.3.
21664 @cindex invoke another interpreter
21665 The interpreter being used by @value{GDBN} may not be dynamically
21666 switched at runtime. Although possible, this could lead to a very
21667 precarious situation. Consider an IDE using @sc{gdb/mi}. If a user
21668 enters the command "interpreter-set console" in a console view,
21669 @value{GDBN} would switch to using the console interpreter, rendering
21670 the IDE inoperable!
21672 @kindex interpreter-exec
21673 Although you may only choose a single interpreter at startup, you may execute
21674 commands in any interpreter from the current interpreter using the appropriate
21675 command. If you are running the console interpreter, simply use the
21676 @code{interpreter-exec} command:
21679 interpreter-exec mi "-data-list-register-names"
21682 @sc{gdb/mi} has a similar command, although it is only available in versions of
21683 @value{GDBN} which support @sc{gdb/mi} version 2 (or greater).
21686 @chapter @value{GDBN} Text User Interface
21688 @cindex Text User Interface
21691 * TUI Overview:: TUI overview
21692 * TUI Keys:: TUI key bindings
21693 * TUI Single Key Mode:: TUI single key mode
21694 * TUI Commands:: TUI-specific commands
21695 * TUI Configuration:: TUI configuration variables
21698 The @value{GDBN} Text User Interface (TUI) is a terminal
21699 interface which uses the @code{curses} library to show the source
21700 file, the assembly output, the program registers and @value{GDBN}
21701 commands in separate text windows. The TUI mode is supported only
21702 on platforms where a suitable version of the @code{curses} library
21705 @pindex @value{GDBTUI}
21706 The TUI mode is enabled by default when you invoke @value{GDBN} as
21707 either @samp{@value{GDBTUI}} or @samp{@value{GDBP} -tui}.
21708 You can also switch in and out of TUI mode while @value{GDBN} runs by
21709 using various TUI commands and key bindings, such as @kbd{C-x C-a}.
21710 @xref{TUI Keys, ,TUI Key Bindings}.
21713 @section TUI Overview
21715 In TUI mode, @value{GDBN} can display several text windows:
21719 This window is the @value{GDBN} command window with the @value{GDBN}
21720 prompt and the @value{GDBN} output. The @value{GDBN} input is still
21721 managed using readline.
21724 The source window shows the source file of the program. The current
21725 line and active breakpoints are displayed in this window.
21728 The assembly window shows the disassembly output of the program.
21731 This window shows the processor registers. Registers are highlighted
21732 when their values change.
21735 The source and assembly windows show the current program position
21736 by highlighting the current line and marking it with a @samp{>} marker.
21737 Breakpoints are indicated with two markers. The first marker
21738 indicates the breakpoint type:
21742 Breakpoint which was hit at least once.
21745 Breakpoint which was never hit.
21748 Hardware breakpoint which was hit at least once.
21751 Hardware breakpoint which was never hit.
21754 The second marker indicates whether the breakpoint is enabled or not:
21758 Breakpoint is enabled.
21761 Breakpoint is disabled.
21764 The source, assembly and register windows are updated when the current
21765 thread changes, when the frame changes, or when the program counter
21768 These windows are not all visible at the same time. The command
21769 window is always visible. The others can be arranged in several
21780 source and assembly,
21783 source and registers, or
21786 assembly and registers.
21789 A status line above the command window shows the following information:
21793 Indicates the current @value{GDBN} target.
21794 (@pxref{Targets, ,Specifying a Debugging Target}).
21797 Gives the current process or thread number.
21798 When no process is being debugged, this field is set to @code{No process}.
21801 Gives the current function name for the selected frame.
21802 The name is demangled if demangling is turned on (@pxref{Print Settings}).
21803 When there is no symbol corresponding to the current program counter,
21804 the string @code{??} is displayed.
21807 Indicates the current line number for the selected frame.
21808 When the current line number is not known, the string @code{??} is displayed.
21811 Indicates the current program counter address.
21815 @section TUI Key Bindings
21816 @cindex TUI key bindings
21818 The TUI installs several key bindings in the readline keymaps
21819 (@pxref{Command Line Editing}). The following key bindings
21820 are installed for both TUI mode and the @value{GDBN} standard mode.
21829 Enter or leave the TUI mode. When leaving the TUI mode,
21830 the curses window management stops and @value{GDBN} operates using
21831 its standard mode, writing on the terminal directly. When reentering
21832 the TUI mode, control is given back to the curses windows.
21833 The screen is then refreshed.
21837 Use a TUI layout with only one window. The layout will
21838 either be @samp{source} or @samp{assembly}. When the TUI mode
21839 is not active, it will switch to the TUI mode.
21841 Think of this key binding as the Emacs @kbd{C-x 1} binding.
21845 Use a TUI layout with at least two windows. When the current
21846 layout already has two windows, the next layout with two windows is used.
21847 When a new layout is chosen, one window will always be common to the
21848 previous layout and the new one.
21850 Think of it as the Emacs @kbd{C-x 2} binding.
21854 Change the active window. The TUI associates several key bindings
21855 (like scrolling and arrow keys) with the active window. This command
21856 gives the focus to the next TUI window.
21858 Think of it as the Emacs @kbd{C-x o} binding.
21862 Switch in and out of the TUI SingleKey mode that binds single
21863 keys to @value{GDBN} commands (@pxref{TUI Single Key Mode}).
21866 The following key bindings only work in the TUI mode:
21871 Scroll the active window one page up.
21875 Scroll the active window one page down.
21879 Scroll the active window one line up.
21883 Scroll the active window one line down.
21887 Scroll the active window one column left.
21891 Scroll the active window one column right.
21895 Refresh the screen.
21898 Because the arrow keys scroll the active window in the TUI mode, they
21899 are not available for their normal use by readline unless the command
21900 window has the focus. When another window is active, you must use
21901 other readline key bindings such as @kbd{C-p}, @kbd{C-n}, @kbd{C-b}
21902 and @kbd{C-f} to control the command window.
21904 @node TUI Single Key Mode
21905 @section TUI Single Key Mode
21906 @cindex TUI single key mode
21908 The TUI also provides a @dfn{SingleKey} mode, which binds several
21909 frequently used @value{GDBN} commands to single keys. Type @kbd{C-x s} to
21910 switch into this mode, where the following key bindings are used:
21913 @kindex c @r{(SingleKey TUI key)}
21917 @kindex d @r{(SingleKey TUI key)}
21921 @kindex f @r{(SingleKey TUI key)}
21925 @kindex n @r{(SingleKey TUI key)}
21929 @kindex q @r{(SingleKey TUI key)}
21931 exit the SingleKey mode.
21933 @kindex r @r{(SingleKey TUI key)}
21937 @kindex s @r{(SingleKey TUI key)}
21941 @kindex u @r{(SingleKey TUI key)}
21945 @kindex v @r{(SingleKey TUI key)}
21949 @kindex w @r{(SingleKey TUI key)}
21954 Other keys temporarily switch to the @value{GDBN} command prompt.
21955 The key that was pressed is inserted in the editing buffer so that
21956 it is possible to type most @value{GDBN} commands without interaction
21957 with the TUI SingleKey mode. Once the command is entered the TUI
21958 SingleKey mode is restored. The only way to permanently leave
21959 this mode is by typing @kbd{q} or @kbd{C-x s}.
21963 @section TUI-specific Commands
21964 @cindex TUI commands
21966 The TUI has specific commands to control the text windows.
21967 These commands are always available, even when @value{GDBN} is not in
21968 the TUI mode. When @value{GDBN} is in the standard mode, most
21969 of these commands will automatically switch to the TUI mode.
21971 Note that if @value{GDBN}'s @code{stdout} is not connected to a
21972 terminal, or @value{GDBN} has been started with the machine interface
21973 interpreter (@pxref{GDB/MI, ,The @sc{gdb/mi} Interface}), most of
21974 these commands will fail with an error, because it would not be
21975 possible or desirable to enable curses window management.
21980 List and give the size of all displayed windows.
21984 Display the next layout.
21987 Display the previous layout.
21990 Display the source window only.
21993 Display the assembly window only.
21996 Display the source and assembly window.
21999 Display the register window together with the source or assembly window.
22003 Make the next window active for scrolling.
22006 Make the previous window active for scrolling.
22009 Make the source window active for scrolling.
22012 Make the assembly window active for scrolling.
22015 Make the register window active for scrolling.
22018 Make the command window active for scrolling.
22022 Refresh the screen. This is similar to typing @kbd{C-L}.
22024 @item tui reg float
22026 Show the floating point registers in the register window.
22028 @item tui reg general
22029 Show the general registers in the register window.
22032 Show the next register group. The list of register groups as well as
22033 their order is target specific. The predefined register groups are the
22034 following: @code{general}, @code{float}, @code{system}, @code{vector},
22035 @code{all}, @code{save}, @code{restore}.
22037 @item tui reg system
22038 Show the system registers in the register window.
22042 Update the source window and the current execution point.
22044 @item winheight @var{name} +@var{count}
22045 @itemx winheight @var{name} -@var{count}
22047 Change the height of the window @var{name} by @var{count}
22048 lines. Positive counts increase the height, while negative counts
22051 @item tabset @var{nchars}
22053 Set the width of tab stops to be @var{nchars} characters.
22056 @node TUI Configuration
22057 @section TUI Configuration Variables
22058 @cindex TUI configuration variables
22060 Several configuration variables control the appearance of TUI windows.
22063 @item set tui border-kind @var{kind}
22064 @kindex set tui border-kind
22065 Select the border appearance for the source, assembly and register windows.
22066 The possible values are the following:
22069 Use a space character to draw the border.
22072 Use @sc{ascii} characters @samp{+}, @samp{-} and @samp{|} to draw the border.
22075 Use the Alternate Character Set to draw the border. The border is
22076 drawn using character line graphics if the terminal supports them.
22079 @item set tui border-mode @var{mode}
22080 @kindex set tui border-mode
22081 @itemx set tui active-border-mode @var{mode}
22082 @kindex set tui active-border-mode
22083 Select the display attributes for the borders of the inactive windows
22084 or the active window. The @var{mode} can be one of the following:
22087 Use normal attributes to display the border.
22093 Use reverse video mode.
22096 Use half bright mode.
22098 @item half-standout
22099 Use half bright and standout mode.
22102 Use extra bright or bold mode.
22104 @item bold-standout
22105 Use extra bright or bold and standout mode.
22110 @chapter Using @value{GDBN} under @sc{gnu} Emacs
22113 @cindex @sc{gnu} Emacs
22114 A special interface allows you to use @sc{gnu} Emacs to view (and
22115 edit) the source files for the program you are debugging with
22118 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
22119 executable file you want to debug as an argument. This command starts
22120 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
22121 created Emacs buffer.
22122 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
22124 Running @value{GDBN} under Emacs can be just like running @value{GDBN} normally except for two
22129 All ``terminal'' input and output goes through an Emacs buffer, called
22132 This applies both to @value{GDBN} commands and their output, and to the input
22133 and output done by the program you are debugging.
22135 This is useful because it means that you can copy the text of previous
22136 commands and input them again; you can even use parts of the output
22139 All the facilities of Emacs' Shell mode are available for interacting
22140 with your program. In particular, you can send signals the usual
22141 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
22145 @value{GDBN} displays source code through Emacs.
22147 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
22148 source file for that frame and puts an arrow (@samp{=>}) at the
22149 left margin of the current line. Emacs uses a separate buffer for
22150 source display, and splits the screen to show both your @value{GDBN} session
22153 Explicit @value{GDBN} @code{list} or search commands still produce output as
22154 usual, but you probably have no reason to use them from Emacs.
22157 We call this @dfn{text command mode}. Emacs 22.1, and later, also uses
22158 a graphical mode, enabled by default, which provides further buffers
22159 that can control the execution and describe the state of your program.
22160 @xref{GDB Graphical Interface,,, Emacs, The @sc{gnu} Emacs Manual}.
22162 If you specify an absolute file name when prompted for the @kbd{M-x
22163 gdb} argument, then Emacs sets your current working directory to where
22164 your program resides. If you only specify the file name, then Emacs
22165 sets your current working directory to to the directory associated
22166 with the previous buffer. In this case, @value{GDBN} may find your
22167 program by searching your environment's @code{PATH} variable, but on
22168 some operating systems it might not find the source. So, although the
22169 @value{GDBN} input and output session proceeds normally, the auxiliary
22170 buffer does not display the current source and line of execution.
22172 The initial working directory of @value{GDBN} is printed on the top
22173 line of the GUD buffer and this serves as a default for the commands
22174 that specify files for @value{GDBN} to operate on. @xref{Files,
22175 ,Commands to Specify Files}.
22177 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If you
22178 need to call @value{GDBN} by a different name (for example, if you
22179 keep several configurations around, with different names) you can
22180 customize the Emacs variable @code{gud-gdb-command-name} to run the
22183 In the GUD buffer, you can use these special Emacs commands in
22184 addition to the standard Shell mode commands:
22188 Describe the features of Emacs' GUD Mode.
22191 Execute to another source line, like the @value{GDBN} @code{step} command; also
22192 update the display window to show the current file and location.
22195 Execute to next source line in this function, skipping all function
22196 calls, like the @value{GDBN} @code{next} command. Then update the display window
22197 to show the current file and location.
22200 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
22201 display window accordingly.
22204 Execute until exit from the selected stack frame, like the @value{GDBN}
22205 @code{finish} command.
22208 Continue execution of your program, like the @value{GDBN} @code{continue}
22212 Go up the number of frames indicated by the numeric argument
22213 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
22214 like the @value{GDBN} @code{up} command.
22217 Go down the number of frames indicated by the numeric argument, like the
22218 @value{GDBN} @code{down} command.
22221 In any source file, the Emacs command @kbd{C-x @key{SPC}} (@code{gud-break})
22222 tells @value{GDBN} to set a breakpoint on the source line point is on.
22224 In text command mode, if you type @kbd{M-x speedbar}, Emacs displays a
22225 separate frame which shows a backtrace when the GUD buffer is current.
22226 Move point to any frame in the stack and type @key{RET} to make it
22227 become the current frame and display the associated source in the
22228 source buffer. Alternatively, click @kbd{Mouse-2} to make the
22229 selected frame become the current one. In graphical mode, the
22230 speedbar displays watch expressions.
22232 If you accidentally delete the source-display buffer, an easy way to get
22233 it back is to type the command @code{f} in the @value{GDBN} buffer, to
22234 request a frame display; when you run under Emacs, this recreates
22235 the source buffer if necessary to show you the context of the current
22238 The source files displayed in Emacs are in ordinary Emacs buffers
22239 which are visiting the source files in the usual way. You can edit
22240 the files with these buffers if you wish; but keep in mind that @value{GDBN}
22241 communicates with Emacs in terms of line numbers. If you add or
22242 delete lines from the text, the line numbers that @value{GDBN} knows cease
22243 to correspond properly with the code.
22245 A more detailed description of Emacs' interaction with @value{GDBN} is
22246 given in the Emacs manual (@pxref{Debuggers,,, Emacs, The @sc{gnu}
22249 @c The following dropped because Epoch is nonstandard. Reactivate
22250 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
22252 @kindex Emacs Epoch environment
22256 Version 18 of @sc{gnu} Emacs has a built-in window system
22257 called the @code{epoch}
22258 environment. Users of this environment can use a new command,
22259 @code{inspect} which performs identically to @code{print} except that
22260 each value is printed in its own window.
22265 @chapter The @sc{gdb/mi} Interface
22267 @unnumberedsec Function and Purpose
22269 @cindex @sc{gdb/mi}, its purpose
22270 @sc{gdb/mi} is a line based machine oriented text interface to
22271 @value{GDBN} and is activated by specifying using the
22272 @option{--interpreter} command line option (@pxref{Mode Options}). It
22273 is specifically intended to support the development of systems which
22274 use the debugger as just one small component of a larger system.
22276 This chapter is a specification of the @sc{gdb/mi} interface. It is written
22277 in the form of a reference manual.
22279 Note that @sc{gdb/mi} is still under construction, so some of the
22280 features described below are incomplete and subject to change
22281 (@pxref{GDB/MI Development and Front Ends, , @sc{gdb/mi} Development and Front Ends}).
22283 @unnumberedsec Notation and Terminology
22285 @cindex notational conventions, for @sc{gdb/mi}
22286 This chapter uses the following notation:
22290 @code{|} separates two alternatives.
22293 @code{[ @var{something} ]} indicates that @var{something} is optional:
22294 it may or may not be given.
22297 @code{( @var{group} )*} means that @var{group} inside the parentheses
22298 may repeat zero or more times.
22301 @code{( @var{group} )+} means that @var{group} inside the parentheses
22302 may repeat one or more times.
22305 @code{"@var{string}"} means a literal @var{string}.
22309 @heading Dependencies
22313 * GDB/MI General Design::
22314 * GDB/MI Command Syntax::
22315 * GDB/MI Compatibility with CLI::
22316 * GDB/MI Development and Front Ends::
22317 * GDB/MI Output Records::
22318 * GDB/MI Simple Examples::
22319 * GDB/MI Command Description Format::
22320 * GDB/MI Breakpoint Commands::
22321 * GDB/MI Program Context::
22322 * GDB/MI Thread Commands::
22323 * GDB/MI Program Execution::
22324 * GDB/MI Stack Manipulation::
22325 * GDB/MI Variable Objects::
22326 * GDB/MI Data Manipulation::
22327 * GDB/MI Tracepoint Commands::
22328 * GDB/MI Symbol Query::
22329 * GDB/MI File Commands::
22331 * GDB/MI Kod Commands::
22332 * GDB/MI Memory Overlay Commands::
22333 * GDB/MI Signal Handling Commands::
22335 * GDB/MI Target Manipulation::
22336 * GDB/MI File Transfer Commands::
22337 * GDB/MI Miscellaneous Commands::
22340 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
22341 @node GDB/MI General Design
22342 @section @sc{gdb/mi} General Design
22343 @cindex GDB/MI General Design
22345 Interaction of a @sc{GDB/MI} frontend with @value{GDBN} involves three
22346 parts---commands sent to @value{GDBN}, responses to those commands
22347 and notifications. Each command results in exactly one response,
22348 indicating either successful completion of the command, or an error.
22349 For the commands that do not resume the target, the response contains the
22350 requested information. For the commands that resume the target, the
22351 response only indicates whether the target was successfully resumed.
22352 Notifications is the mechanism for reporting changes in the state of the
22353 target, or in @value{GDBN} state, that cannot conveniently be associated with
22354 a command and reported as part of that command response.
22356 The important examples of notifications are:
22360 Exec notifications. These are used to report changes in
22361 target state---when a target is resumed, or stopped. It would not
22362 be feasible to include this information in response of resuming
22363 commands, because one resume commands can result in multiple events in
22364 different threads. Also, quite some time may pass before any event
22365 happens in the target, while a frontend needs to know whether the resuming
22366 command itself was successfully executed.
22369 Console output, and status notifications. Console output
22370 notifications are used to report output of CLI commands, as well as
22371 diagnostics for other commands. Status notifications are used to
22372 report the progress of a long-running operation. Naturally, including
22373 this information in command response would mean no output is produced
22374 until the command is finished, which is undesirable.
22377 General notifications. Commands may have various side effects on
22378 the @value{GDBN} or target state beyond their official purpose. For example,
22379 a command may change the selected thread. Although such changes can
22380 be included in command response, using notification allows for more
22381 orthogonal frontend design.
22385 There's no guarantee that whenever an MI command reports an error,
22386 @value{GDBN} or the target are in any specific state, and especially,
22387 the state is not reverted to the state before the MI command was
22388 processed. Therefore, whenever an MI command results in an error,
22389 we recommend that the frontend refreshes all the information shown in
22390 the user interface.
22394 * Context management::
22395 * Asynchronous and non-stop modes::
22399 @node Context management
22400 @subsection Context management
22402 In most cases when @value{GDBN} accesses the target, this access is
22403 done in context of a specific thread and frame (@pxref{Frames}).
22404 Often, even when accessing global data, the target requires that a thread
22405 be specified. The CLI interface maintains the selected thread and frame,
22406 and supplies them to target on each command. This is convenient,
22407 because a command line user would not want to specify that information
22408 explicitly on each command, and because user interacts with
22409 @value{GDBN} via a single terminal, so no confusion is possible as
22410 to what thread and frame are the current ones.
22412 In the case of MI, the concept of selected thread and frame is less
22413 useful. First, a frontend can easily remember this information
22414 itself. Second, a graphical frontend can have more than one window,
22415 each one used for debugging a different thread, and the frontend might
22416 want to access additional threads for internal purposes. This
22417 increases the risk that by relying on implicitly selected thread, the
22418 frontend may be operating on a wrong one. Therefore, each MI command
22419 should explicitly specify which thread and frame to operate on. To
22420 make it possible, each MI command accepts the @samp{--thread} and
22421 @samp{--frame} options, the value to each is @value{GDBN} identifier
22422 for thread and frame to operate on.
22424 Usually, each top-level window in a frontend allows the user to select
22425 a thread and a frame, and remembers the user selection for further
22426 operations. However, in some cases @value{GDBN} may suggest that the
22427 current thread be changed. For example, when stopping on a breakpoint
22428 it is reasonable to switch to the thread where breakpoint is hit. For
22429 another example, if the user issues the CLI @samp{thread} command via
22430 the frontend, it is desirable to change the frontend's selected thread to the
22431 one specified by user. @value{GDBN} communicates the suggestion to
22432 change current thread using the @samp{=thread-selected} notification.
22433 No such notification is available for the selected frame at the moment.
22435 Note that historically, MI shares the selected thread with CLI, so
22436 frontends used the @code{-thread-select} to execute commands in the
22437 right context. However, getting this to work right is cumbersome. The
22438 simplest way is for frontend to emit @code{-thread-select} command
22439 before every command. This doubles the number of commands that need
22440 to be sent. The alternative approach is to suppress @code{-thread-select}
22441 if the selected thread in @value{GDBN} is supposed to be identical to the
22442 thread the frontend wants to operate on. However, getting this
22443 optimization right can be tricky. In particular, if the frontend
22444 sends several commands to @value{GDBN}, and one of the commands changes the
22445 selected thread, then the behaviour of subsequent commands will
22446 change. So, a frontend should either wait for response from such
22447 problematic commands, or explicitly add @code{-thread-select} for
22448 all subsequent commands. No frontend is known to do this exactly
22449 right, so it is suggested to just always pass the @samp{--thread} and
22450 @samp{--frame} options.
22452 @node Asynchronous and non-stop modes
22453 @subsection Asynchronous command execution and non-stop mode
22455 On some targets, @value{GDBN} is capable of processing MI commands
22456 even while the target is running. This is called @dfn{asynchronous
22457 command execution} (@pxref{Background Execution}). The frontend may
22458 specify a preferrence for asynchronous execution using the
22459 @code{-gdb-set target-async 1} command, which should be emitted before
22460 either running the executable or attaching to the target. After the
22461 frontend has started the executable or attached to the target, it can
22462 find if asynchronous execution is enabled using the
22463 @code{-list-target-features} command.
22465 Even if @value{GDBN} can accept a command while target is running,
22466 many commands that access the target do not work when the target is
22467 running. Therefore, asynchronous command execution is most useful
22468 when combined with non-stop mode (@pxref{Non-Stop Mode}). Then,
22469 it is possible to examine the state of one thread, while other threads
22472 When a given thread is running, MI commands that try to access the
22473 target in the context of that thread may not work, or may work only on
22474 some targets. In particular, commands that try to operate on thread's
22475 stack will not work, on any target. Commands that read memory, or
22476 modify breakpoints, may work or not work, depending on the target. Note
22477 that even commands that operate on global state, such as @code{print},
22478 @code{set}, and breakpoint commands, still access the target in the
22479 context of a specific thread, so frontend should try to find a
22480 stopped thread and perform the operation on that thread (using the
22481 @samp{--thread} option).
22483 Which commands will work in the context of a running thread is
22484 highly target dependent. However, the two commands
22485 @code{-exec-interrupt}, to stop a thread, and @code{-thread-info},
22486 to find the state of a thread, will always work.
22488 @node Thread groups
22489 @subsection Thread groups
22490 @value{GDBN} may be used to debug several processes at the same time.
22491 On some platfroms, @value{GDBN} may support debugging of several
22492 hardware systems, each one having several cores with several different
22493 processes running on each core. This section describes the MI
22494 mechanism to support such debugging scenarios.
22496 The key observation is that regardless of the structure of the
22497 target, MI can have a global list of threads, because most commands that
22498 accept the @samp{--thread} option do not need to know what process that
22499 thread belongs to. Therefore, it is not necessary to introduce
22500 neither additional @samp{--process} option, nor an notion of the
22501 current process in the MI interface. The only strictly new feature
22502 that is required is the ability to find how the threads are grouped
22505 To allow the user to discover such grouping, and to support arbitrary
22506 hierarchy of machines/cores/processes, MI introduces the concept of a
22507 @dfn{thread group}. Thread group is a collection of threads and other
22508 thread groups. A thread group always has a string identifier, a type,
22509 and may have additional attributes specific to the type. A new
22510 command, @code{-list-thread-groups}, returns the list of top-level
22511 thread groups, which correspond to processes that @value{GDBN} is
22512 debugging at the moment. By passing an identifier of a thread group
22513 to the @code{-list-thread-groups} command, it is possible to obtain
22514 the members of specific thread group.
22516 To allow the user to easily discover processes, and other objects, he
22517 wishes to debug, a concept of @dfn{available thread group} is
22518 introduced. Available thread group is an thread group that
22519 @value{GDBN} is not debugging, but that can be attached to, using the
22520 @code{-target-attach} command. The list of available top-level thread
22521 groups can be obtained using @samp{-list-thread-groups --available}.
22522 In general, the content of a thread group may be only retrieved only
22523 after attaching to that thread group.
22525 Thread groups are related to inferiors (@pxref{Inferiors and
22526 Programs}). Each inferior corresponds to a thread group of a special
22527 type @samp{process}, and some additional operations are permitted on
22528 such thread groups.
22530 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
22531 @node GDB/MI Command Syntax
22532 @section @sc{gdb/mi} Command Syntax
22535 * GDB/MI Input Syntax::
22536 * GDB/MI Output Syntax::
22539 @node GDB/MI Input Syntax
22540 @subsection @sc{gdb/mi} Input Syntax
22542 @cindex input syntax for @sc{gdb/mi}
22543 @cindex @sc{gdb/mi}, input syntax
22545 @item @var{command} @expansion{}
22546 @code{@var{cli-command} | @var{mi-command}}
22548 @item @var{cli-command} @expansion{}
22549 @code{[ @var{token} ] @var{cli-command} @var{nl}}, where
22550 @var{cli-command} is any existing @value{GDBN} CLI command.
22552 @item @var{mi-command} @expansion{}
22553 @code{[ @var{token} ] "-" @var{operation} ( " " @var{option} )*
22554 @code{[} " --" @code{]} ( " " @var{parameter} )* @var{nl}}
22556 @item @var{token} @expansion{}
22557 "any sequence of digits"
22559 @item @var{option} @expansion{}
22560 @code{"-" @var{parameter} [ " " @var{parameter} ]}
22562 @item @var{parameter} @expansion{}
22563 @code{@var{non-blank-sequence} | @var{c-string}}
22565 @item @var{operation} @expansion{}
22566 @emph{any of the operations described in this chapter}
22568 @item @var{non-blank-sequence} @expansion{}
22569 @emph{anything, provided it doesn't contain special characters such as
22570 "-", @var{nl}, """ and of course " "}
22572 @item @var{c-string} @expansion{}
22573 @code{""" @var{seven-bit-iso-c-string-content} """}
22575 @item @var{nl} @expansion{}
22584 The CLI commands are still handled by the @sc{mi} interpreter; their
22585 output is described below.
22588 The @code{@var{token}}, when present, is passed back when the command
22592 Some @sc{mi} commands accept optional arguments as part of the parameter
22593 list. Each option is identified by a leading @samp{-} (dash) and may be
22594 followed by an optional argument parameter. Options occur first in the
22595 parameter list and can be delimited from normal parameters using
22596 @samp{--} (this is useful when some parameters begin with a dash).
22603 We want easy access to the existing CLI syntax (for debugging).
22606 We want it to be easy to spot a @sc{mi} operation.
22609 @node GDB/MI Output Syntax
22610 @subsection @sc{gdb/mi} Output Syntax
22612 @cindex output syntax of @sc{gdb/mi}
22613 @cindex @sc{gdb/mi}, output syntax
22614 The output from @sc{gdb/mi} consists of zero or more out-of-band records
22615 followed, optionally, by a single result record. This result record
22616 is for the most recent command. The sequence of output records is
22617 terminated by @samp{(gdb)}.
22619 If an input command was prefixed with a @code{@var{token}} then the
22620 corresponding output for that command will also be prefixed by that same
22624 @item @var{output} @expansion{}
22625 @code{( @var{out-of-band-record} )* [ @var{result-record} ] "(gdb)" @var{nl}}
22627 @item @var{result-record} @expansion{}
22628 @code{ [ @var{token} ] "^" @var{result-class} ( "," @var{result} )* @var{nl}}
22630 @item @var{out-of-band-record} @expansion{}
22631 @code{@var{async-record} | @var{stream-record}}
22633 @item @var{async-record} @expansion{}
22634 @code{@var{exec-async-output} | @var{status-async-output} | @var{notify-async-output}}
22636 @item @var{exec-async-output} @expansion{}
22637 @code{[ @var{token} ] "*" @var{async-output}}
22639 @item @var{status-async-output} @expansion{}
22640 @code{[ @var{token} ] "+" @var{async-output}}
22642 @item @var{notify-async-output} @expansion{}
22643 @code{[ @var{token} ] "=" @var{async-output}}
22645 @item @var{async-output} @expansion{}
22646 @code{@var{async-class} ( "," @var{result} )* @var{nl}}
22648 @item @var{result-class} @expansion{}
22649 @code{"done" | "running" | "connected" | "error" | "exit"}
22651 @item @var{async-class} @expansion{}
22652 @code{"stopped" | @var{others}} (where @var{others} will be added
22653 depending on the needs---this is still in development).
22655 @item @var{result} @expansion{}
22656 @code{ @var{variable} "=" @var{value}}
22658 @item @var{variable} @expansion{}
22659 @code{ @var{string} }
22661 @item @var{value} @expansion{}
22662 @code{ @var{const} | @var{tuple} | @var{list} }
22664 @item @var{const} @expansion{}
22665 @code{@var{c-string}}
22667 @item @var{tuple} @expansion{}
22668 @code{ "@{@}" | "@{" @var{result} ( "," @var{result} )* "@}" }
22670 @item @var{list} @expansion{}
22671 @code{ "[]" | "[" @var{value} ( "," @var{value} )* "]" | "["
22672 @var{result} ( "," @var{result} )* "]" }
22674 @item @var{stream-record} @expansion{}
22675 @code{@var{console-stream-output} | @var{target-stream-output} | @var{log-stream-output}}
22677 @item @var{console-stream-output} @expansion{}
22678 @code{"~" @var{c-string}}
22680 @item @var{target-stream-output} @expansion{}
22681 @code{"@@" @var{c-string}}
22683 @item @var{log-stream-output} @expansion{}
22684 @code{"&" @var{c-string}}
22686 @item @var{nl} @expansion{}
22689 @item @var{token} @expansion{}
22690 @emph{any sequence of digits}.
22698 All output sequences end in a single line containing a period.
22701 The @code{@var{token}} is from the corresponding request. Note that
22702 for all async output, while the token is allowed by the grammar and
22703 may be output by future versions of @value{GDBN} for select async
22704 output messages, it is generally omitted. Frontends should treat
22705 all async output as reporting general changes in the state of the
22706 target and there should be no need to associate async output to any
22710 @cindex status output in @sc{gdb/mi}
22711 @var{status-async-output} contains on-going status information about the
22712 progress of a slow operation. It can be discarded. All status output is
22713 prefixed by @samp{+}.
22716 @cindex async output in @sc{gdb/mi}
22717 @var{exec-async-output} contains asynchronous state change on the target
22718 (stopped, started, disappeared). All async output is prefixed by
22722 @cindex notify output in @sc{gdb/mi}
22723 @var{notify-async-output} contains supplementary information that the
22724 client should handle (e.g., a new breakpoint information). All notify
22725 output is prefixed by @samp{=}.
22728 @cindex console output in @sc{gdb/mi}
22729 @var{console-stream-output} is output that should be displayed as is in the
22730 console. It is the textual response to a CLI command. All the console
22731 output is prefixed by @samp{~}.
22734 @cindex target output in @sc{gdb/mi}
22735 @var{target-stream-output} is the output produced by the target program.
22736 All the target output is prefixed by @samp{@@}.
22739 @cindex log output in @sc{gdb/mi}
22740 @var{log-stream-output} is output text coming from @value{GDBN}'s internals, for
22741 instance messages that should be displayed as part of an error log. All
22742 the log output is prefixed by @samp{&}.
22745 @cindex list output in @sc{gdb/mi}
22746 New @sc{gdb/mi} commands should only output @var{lists} containing
22752 @xref{GDB/MI Stream Records, , @sc{gdb/mi} Stream Records}, for more
22753 details about the various output records.
22755 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
22756 @node GDB/MI Compatibility with CLI
22757 @section @sc{gdb/mi} Compatibility with CLI
22759 @cindex compatibility, @sc{gdb/mi} and CLI
22760 @cindex @sc{gdb/mi}, compatibility with CLI
22762 For the developers convenience CLI commands can be entered directly,
22763 but there may be some unexpected behaviour. For example, commands
22764 that query the user will behave as if the user replied yes, breakpoint
22765 command lists are not executed and some CLI commands, such as
22766 @code{if}, @code{when} and @code{define}, prompt for further input with
22767 @samp{>}, which is not valid MI output.
22769 This feature may be removed at some stage in the future and it is
22770 recommended that front ends use the @code{-interpreter-exec} command
22771 (@pxref{-interpreter-exec}).
22773 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
22774 @node GDB/MI Development and Front Ends
22775 @section @sc{gdb/mi} Development and Front Ends
22776 @cindex @sc{gdb/mi} development
22778 The application which takes the MI output and presents the state of the
22779 program being debugged to the user is called a @dfn{front end}.
22781 Although @sc{gdb/mi} is still incomplete, it is currently being used
22782 by a variety of front ends to @value{GDBN}. This makes it difficult
22783 to introduce new functionality without breaking existing usage. This
22784 section tries to minimize the problems by describing how the protocol
22787 Some changes in MI need not break a carefully designed front end, and
22788 for these the MI version will remain unchanged. The following is a
22789 list of changes that may occur within one level, so front ends should
22790 parse MI output in a way that can handle them:
22794 New MI commands may be added.
22797 New fields may be added to the output of any MI command.
22800 The range of values for fields with specified values, e.g.,
22801 @code{in_scope} (@pxref{-var-update}) may be extended.
22803 @c The format of field's content e.g type prefix, may change so parse it
22804 @c at your own risk. Yes, in general?
22806 @c The order of fields may change? Shouldn't really matter but it might
22807 @c resolve inconsistencies.
22810 If the changes are likely to break front ends, the MI version level
22811 will be increased by one. This will allow the front end to parse the
22812 output according to the MI version. Apart from mi0, new versions of
22813 @value{GDBN} will not support old versions of MI and it will be the
22814 responsibility of the front end to work with the new one.
22816 @c Starting with mi3, add a new command -mi-version that prints the MI
22819 The best way to avoid unexpected changes in MI that might break your front
22820 end is to make your project known to @value{GDBN} developers and
22821 follow development on @email{gdb@@sourceware.org} and
22822 @email{gdb-patches@@sourceware.org}.
22823 @cindex mailing lists
22825 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
22826 @node GDB/MI Output Records
22827 @section @sc{gdb/mi} Output Records
22830 * GDB/MI Result Records::
22831 * GDB/MI Stream Records::
22832 * GDB/MI Async Records::
22833 * GDB/MI Frame Information::
22834 * GDB/MI Thread Information::
22837 @node GDB/MI Result Records
22838 @subsection @sc{gdb/mi} Result Records
22840 @cindex result records in @sc{gdb/mi}
22841 @cindex @sc{gdb/mi}, result records
22842 In addition to a number of out-of-band notifications, the response to a
22843 @sc{gdb/mi} command includes one of the following result indications:
22847 @item "^done" [ "," @var{results} ]
22848 The synchronous operation was successful, @code{@var{results}} are the return
22853 This result record is equivalent to @samp{^done}. Historically, it
22854 was output instead of @samp{^done} if the command has resumed the
22855 target. This behaviour is maintained for backward compatibility, but
22856 all frontends should treat @samp{^done} and @samp{^running}
22857 identically and rely on the @samp{*running} output record to determine
22858 which threads are resumed.
22862 @value{GDBN} has connected to a remote target.
22864 @item "^error" "," @var{c-string}
22866 The operation failed. The @code{@var{c-string}} contains the corresponding
22871 @value{GDBN} has terminated.
22875 @node GDB/MI Stream Records
22876 @subsection @sc{gdb/mi} Stream Records
22878 @cindex @sc{gdb/mi}, stream records
22879 @cindex stream records in @sc{gdb/mi}
22880 @value{GDBN} internally maintains a number of output streams: the console, the
22881 target, and the log. The output intended for each of these streams is
22882 funneled through the @sc{gdb/mi} interface using @dfn{stream records}.
22884 Each stream record begins with a unique @dfn{prefix character} which
22885 identifies its stream (@pxref{GDB/MI Output Syntax, , @sc{gdb/mi} Output
22886 Syntax}). In addition to the prefix, each stream record contains a
22887 @code{@var{string-output}}. This is either raw text (with an implicit new
22888 line) or a quoted C string (which does not contain an implicit newline).
22891 @item "~" @var{string-output}
22892 The console output stream contains text that should be displayed in the
22893 CLI console window. It contains the textual responses to CLI commands.
22895 @item "@@" @var{string-output}
22896 The target output stream contains any textual output from the running
22897 target. This is only present when GDB's event loop is truly
22898 asynchronous, which is currently only the case for remote targets.
22900 @item "&" @var{string-output}
22901 The log stream contains debugging messages being produced by @value{GDBN}'s
22905 @node GDB/MI Async Records
22906 @subsection @sc{gdb/mi} Async Records
22908 @cindex async records in @sc{gdb/mi}
22909 @cindex @sc{gdb/mi}, async records
22910 @dfn{Async} records are used to notify the @sc{gdb/mi} client of
22911 additional changes that have occurred. Those changes can either be a
22912 consequence of @sc{gdb/mi} commands (e.g., a breakpoint modified) or a result of
22913 target activity (e.g., target stopped).
22915 The following is the list of possible async records:
22919 @item *running,thread-id="@var{thread}"
22920 The target is now running. The @var{thread} field tells which
22921 specific thread is now running, and can be @samp{all} if all threads
22922 are running. The frontend should assume that no interaction with a
22923 running thread is possible after this notification is produced.
22924 The frontend should not assume that this notification is output
22925 only once for any command. @value{GDBN} may emit this notification
22926 several times, either for different threads, because it cannot resume
22927 all threads together, or even for a single thread, if the thread must
22928 be stepped though some code before letting it run freely.
22930 @item *stopped,reason="@var{reason}",thread-id="@var{id}",stopped-threads="@var{stopped}",core="@var{core}"
22931 The target has stopped. The @var{reason} field can have one of the
22935 @item breakpoint-hit
22936 A breakpoint was reached.
22937 @item watchpoint-trigger
22938 A watchpoint was triggered.
22939 @item read-watchpoint-trigger
22940 A read watchpoint was triggered.
22941 @item access-watchpoint-trigger
22942 An access watchpoint was triggered.
22943 @item function-finished
22944 An -exec-finish or similar CLI command was accomplished.
22945 @item location-reached
22946 An -exec-until or similar CLI command was accomplished.
22947 @item watchpoint-scope
22948 A watchpoint has gone out of scope.
22949 @item end-stepping-range
22950 An -exec-next, -exec-next-instruction, -exec-step, -exec-step-instruction or
22951 similar CLI command was accomplished.
22952 @item exited-signalled
22953 The inferior exited because of a signal.
22955 The inferior exited.
22956 @item exited-normally
22957 The inferior exited normally.
22958 @item signal-received
22959 A signal was received by the inferior.
22962 The @var{id} field identifies the thread that directly caused the stop
22963 -- for example by hitting a breakpoint. Depending on whether all-stop
22964 mode is in effect (@pxref{All-Stop Mode}), @value{GDBN} may either
22965 stop all threads, or only the thread that directly triggered the stop.
22966 If all threads are stopped, the @var{stopped} field will have the
22967 value of @code{"all"}. Otherwise, the value of the @var{stopped}
22968 field will be a list of thread identifiers. Presently, this list will
22969 always include a single thread, but frontend should be prepared to see
22970 several threads in the list. The @var{core} field reports the
22971 processor core on which the stop event has happened. This field may be absent
22972 if such information is not available.
22974 @item =thread-group-added,id="@var{id}"
22975 @itemx =thread-group-removed,id="@var{id}"
22976 A thread group was either added or removed. The @var{id} field
22977 contains the @value{GDBN} identifier of the thread group. When a thread
22978 group is added, it generally might not be associated with a running
22979 process. When a thread group is removed, its id becomes invalid and
22980 cannot be used in any way.
22982 @item =thread-group-started,id="@var{id}",pid="@var{pid}"
22983 A thread group became associated with a running program,
22984 either because the program was just started or the thread group
22985 was attached to a program. The @var{id} field contains the
22986 @value{GDBN} identifier of the thread group. The @var{pid} field
22987 contains process identifier, specific to the operating system.
22989 @itemx =thread-group-exited,id="@var{id}"
22990 A thread group is no longer associated with a running program,
22991 either because the program has exited, or because it was detached
22992 from. The @var{id} field contains the @value{GDBN} identifier of the
22995 @item =thread-created,id="@var{id}",group-id="@var{gid}"
22996 @itemx =thread-exited,id="@var{id}",group-id="@var{gid}"
22997 A thread either was created, or has exited. The @var{id} field
22998 contains the @value{GDBN} identifier of the thread. The @var{gid}
22999 field identifies the thread group this thread belongs to.
23001 @item =thread-selected,id="@var{id}"
23002 Informs that the selected thread was changed as result of the last
23003 command. This notification is not emitted as result of @code{-thread-select}
23004 command but is emitted whenever an MI command that is not documented
23005 to change the selected thread actually changes it. In particular,
23006 invoking, directly or indirectly (via user-defined command), the CLI
23007 @code{thread} command, will generate this notification.
23009 We suggest that in response to this notification, front ends
23010 highlight the selected thread and cause subsequent commands to apply to
23013 @item =library-loaded,...
23014 Reports that a new library file was loaded by the program. This
23015 notification has 4 fields---@var{id}, @var{target-name},
23016 @var{host-name}, and @var{symbols-loaded}. The @var{id} field is an
23017 opaque identifier of the library. For remote debugging case,
23018 @var{target-name} and @var{host-name} fields give the name of the
23019 library file on the target, and on the host respectively. For native
23020 debugging, both those fields have the same value. The
23021 @var{symbols-loaded} field reports if the debug symbols for this
23022 library are loaded. The @var{thread-group} field, if present,
23023 specifies the id of the thread group in whose context the library was loaded.
23024 If the field is absent, it means the library was loaded in the context
23025 of all present thread groups.
23027 @item =library-unloaded,...
23028 Reports that a library was unloaded by the program. This notification
23029 has 3 fields---@var{id}, @var{target-name} and @var{host-name} with
23030 the same meaning as for the @code{=library-loaded} notification.
23031 The @var{thread-group} field, if present, specifies the id of the
23032 thread group in whose context the library was unloaded. If the field is
23033 absent, it means the library was unloaded in the context of all present
23038 @node GDB/MI Frame Information
23039 @subsection @sc{gdb/mi} Frame Information
23041 Response from many MI commands includes an information about stack
23042 frame. This information is a tuple that may have the following
23047 The level of the stack frame. The innermost frame has the level of
23048 zero. This field is always present.
23051 The name of the function corresponding to the frame. This field may
23052 be absent if @value{GDBN} is unable to determine the function name.
23055 The code address for the frame. This field is always present.
23058 The name of the source files that correspond to the frame's code
23059 address. This field may be absent.
23062 The source line corresponding to the frames' code address. This field
23066 The name of the binary file (either executable or shared library) the
23067 corresponds to the frame's code address. This field may be absent.
23071 @node GDB/MI Thread Information
23072 @subsection @sc{gdb/mi} Thread Information
23074 Whenever @value{GDBN} has to report an information about a thread, it
23075 uses a tuple with the following fields:
23079 The numeric id assigned to the thread by @value{GDBN}. This field is
23083 Target-specific string identifying the thread. This field is always present.
23086 Additional information about the thread provided by the target.
23087 It is supposed to be human-readable and not interpreted by the
23088 frontend. This field is optional.
23091 Either @samp{stopped} or @samp{running}, depending on whether the
23092 thread is presently running. This field is always present.
23095 The value of this field is an integer number of the processor core the
23096 thread was last seen on. This field is optional.
23100 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
23101 @node GDB/MI Simple Examples
23102 @section Simple Examples of @sc{gdb/mi} Interaction
23103 @cindex @sc{gdb/mi}, simple examples
23105 This subsection presents several simple examples of interaction using
23106 the @sc{gdb/mi} interface. In these examples, @samp{->} means that the
23107 following line is passed to @sc{gdb/mi} as input, while @samp{<-} means
23108 the output received from @sc{gdb/mi}.
23110 Note the line breaks shown in the examples are here only for
23111 readability, they don't appear in the real output.
23113 @subheading Setting a Breakpoint
23115 Setting a breakpoint generates synchronous output which contains detailed
23116 information of the breakpoint.
23119 -> -break-insert main
23120 <- ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
23121 enabled="y",addr="0x08048564",func="main",file="myprog.c",
23122 fullname="/home/nickrob/myprog.c",line="68",times="0"@}
23126 @subheading Program Execution
23128 Program execution generates asynchronous records and MI gives the
23129 reason that execution stopped.
23135 <- *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0",
23136 frame=@{addr="0x08048564",func="main",
23137 args=[@{name="argc",value="1"@},@{name="argv",value="0xbfc4d4d4"@}],
23138 file="myprog.c",fullname="/home/nickrob/myprog.c",line="68"@}
23143 <- *stopped,reason="exited-normally"
23147 @subheading Quitting @value{GDBN}
23149 Quitting @value{GDBN} just prints the result class @samp{^exit}.
23157 Please note that @samp{^exit} is printed immediately, but it might
23158 take some time for @value{GDBN} to actually exit. During that time, @value{GDBN}
23159 performs necessary cleanups, including killing programs being debugged
23160 or disconnecting from debug hardware, so the frontend should wait till
23161 @value{GDBN} exits and should only forcibly kill @value{GDBN} if it
23162 fails to exit in reasonable time.
23164 @subheading A Bad Command
23166 Here's what happens if you pass a non-existent command:
23170 <- ^error,msg="Undefined MI command: rubbish"
23175 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
23176 @node GDB/MI Command Description Format
23177 @section @sc{gdb/mi} Command Description Format
23179 The remaining sections describe blocks of commands. Each block of
23180 commands is laid out in a fashion similar to this section.
23182 @subheading Motivation
23184 The motivation for this collection of commands.
23186 @subheading Introduction
23188 A brief introduction to this collection of commands as a whole.
23190 @subheading Commands
23192 For each command in the block, the following is described:
23194 @subsubheading Synopsis
23197 -command @var{args}@dots{}
23200 @subsubheading Result
23202 @subsubheading @value{GDBN} Command
23204 The corresponding @value{GDBN} CLI command(s), if any.
23206 @subsubheading Example
23208 Example(s) formatted for readability. Some of the described commands have
23209 not been implemented yet and these are labeled N.A.@: (not available).
23212 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
23213 @node GDB/MI Breakpoint Commands
23214 @section @sc{gdb/mi} Breakpoint Commands
23216 @cindex breakpoint commands for @sc{gdb/mi}
23217 @cindex @sc{gdb/mi}, breakpoint commands
23218 This section documents @sc{gdb/mi} commands for manipulating
23221 @subheading The @code{-break-after} Command
23222 @findex -break-after
23224 @subsubheading Synopsis
23227 -break-after @var{number} @var{count}
23230 The breakpoint number @var{number} is not in effect until it has been
23231 hit @var{count} times. To see how this is reflected in the output of
23232 the @samp{-break-list} command, see the description of the
23233 @samp{-break-list} command below.
23235 @subsubheading @value{GDBN} Command
23237 The corresponding @value{GDBN} command is @samp{ignore}.
23239 @subsubheading Example
23244 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
23245 enabled="y",addr="0x000100d0",func="main",file="hello.c",
23246 fullname="/home/foo/hello.c",line="5",times="0"@}
23253 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
23254 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
23255 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
23256 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
23257 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
23258 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
23259 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
23260 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
23261 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
23262 line="5",times="0",ignore="3"@}]@}
23267 @subheading The @code{-break-catch} Command
23268 @findex -break-catch
23271 @subheading The @code{-break-commands} Command
23272 @findex -break-commands
23274 @subsubheading Synopsis
23277 -break-commands @var{number} [ @var{command1} ... @var{commandN} ]
23280 Specifies the CLI commands that should be executed when breakpoint
23281 @var{number} is hit. The parameters @var{command1} to @var{commandN}
23282 are the commands. If no command is specified, any previously-set
23283 commands are cleared. @xref{Break Commands}. Typical use of this
23284 functionality is tracing a program, that is, printing of values of
23285 some variables whenever breakpoint is hit and then continuing.
23287 @subsubheading @value{GDBN} Command
23289 The corresponding @value{GDBN} command is @samp{commands}.
23291 @subsubheading Example
23296 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
23297 enabled="y",addr="0x000100d0",func="main",file="hello.c",
23298 fullname="/home/foo/hello.c",line="5",times="0"@}
23300 -break-commands 1 "print v" "continue"
23305 @subheading The @code{-break-condition} Command
23306 @findex -break-condition
23308 @subsubheading Synopsis
23311 -break-condition @var{number} @var{expr}
23314 Breakpoint @var{number} will stop the program only if the condition in
23315 @var{expr} is true. The condition becomes part of the
23316 @samp{-break-list} output (see the description of the @samp{-break-list}
23319 @subsubheading @value{GDBN} Command
23321 The corresponding @value{GDBN} command is @samp{condition}.
23323 @subsubheading Example
23327 -break-condition 1 1
23331 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
23332 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
23333 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
23334 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
23335 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
23336 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
23337 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
23338 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
23339 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
23340 line="5",cond="1",times="0",ignore="3"@}]@}
23344 @subheading The @code{-break-delete} Command
23345 @findex -break-delete
23347 @subsubheading Synopsis
23350 -break-delete ( @var{breakpoint} )+
23353 Delete the breakpoint(s) whose number(s) are specified in the argument
23354 list. This is obviously reflected in the breakpoint list.
23356 @subsubheading @value{GDBN} Command
23358 The corresponding @value{GDBN} command is @samp{delete}.
23360 @subsubheading Example
23368 ^done,BreakpointTable=@{nr_rows="0",nr_cols="6",
23369 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
23370 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
23371 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
23372 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
23373 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
23374 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
23379 @subheading The @code{-break-disable} Command
23380 @findex -break-disable
23382 @subsubheading Synopsis
23385 -break-disable ( @var{breakpoint} )+
23388 Disable the named @var{breakpoint}(s). The field @samp{enabled} in the
23389 break list is now set to @samp{n} for the named @var{breakpoint}(s).
23391 @subsubheading @value{GDBN} Command
23393 The corresponding @value{GDBN} command is @samp{disable}.
23395 @subsubheading Example
23403 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
23404 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
23405 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
23406 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
23407 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
23408 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
23409 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
23410 body=[bkpt=@{number="2",type="breakpoint",disp="keep",enabled="n",
23411 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
23412 line="5",times="0"@}]@}
23416 @subheading The @code{-break-enable} Command
23417 @findex -break-enable
23419 @subsubheading Synopsis
23422 -break-enable ( @var{breakpoint} )+
23425 Enable (previously disabled) @var{breakpoint}(s).
23427 @subsubheading @value{GDBN} Command
23429 The corresponding @value{GDBN} command is @samp{enable}.
23431 @subsubheading Example
23439 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
23440 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
23441 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
23442 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
23443 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
23444 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
23445 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
23446 body=[bkpt=@{number="2",type="breakpoint",disp="keep",enabled="y",
23447 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
23448 line="5",times="0"@}]@}
23452 @subheading The @code{-break-info} Command
23453 @findex -break-info
23455 @subsubheading Synopsis
23458 -break-info @var{breakpoint}
23462 Get information about a single breakpoint.
23464 @subsubheading @value{GDBN} Command
23466 The corresponding @value{GDBN} command is @samp{info break @var{breakpoint}}.
23468 @subsubheading Example
23471 @subheading The @code{-break-insert} Command
23472 @findex -break-insert
23474 @subsubheading Synopsis
23477 -break-insert [ -t ] [ -h ] [ -f ] [ -d ] [ -a ]
23478 [ -c @var{condition} ] [ -i @var{ignore-count} ]
23479 [ -p @var{thread} ] [ @var{location} ]
23483 If specified, @var{location}, can be one of:
23490 @item filename:linenum
23491 @item filename:function
23495 The possible optional parameters of this command are:
23499 Insert a temporary breakpoint.
23501 Insert a hardware breakpoint.
23502 @item -c @var{condition}
23503 Make the breakpoint conditional on @var{condition}.
23504 @item -i @var{ignore-count}
23505 Initialize the @var{ignore-count}.
23507 If @var{location} cannot be parsed (for example if it
23508 refers to unknown files or functions), create a pending
23509 breakpoint. Without this flag, @value{GDBN} will report
23510 an error, and won't create a breakpoint, if @var{location}
23513 Create a disabled breakpoint.
23515 Create a tracepoint. @xref{Tracepoints}. When this parameter
23516 is used together with @samp{-h}, a fast tracepoint is created.
23519 @subsubheading Result
23521 The result is in the form:
23524 ^done,bkpt=@{number="@var{number}",type="@var{type}",disp="del"|"keep",
23525 enabled="y"|"n",addr="@var{hex}",func="@var{funcname}",file="@var{filename}",
23526 fullname="@var{full_filename}",line="@var{lineno}",[thread="@var{threadno},]
23527 times="@var{times}"@}
23531 where @var{number} is the @value{GDBN} number for this breakpoint,
23532 @var{funcname} is the name of the function where the breakpoint was
23533 inserted, @var{filename} is the name of the source file which contains
23534 this function, @var{lineno} is the source line number within that file
23535 and @var{times} the number of times that the breakpoint has been hit
23536 (always 0 for -break-insert but may be greater for -break-info or -break-list
23537 which use the same output).
23539 Note: this format is open to change.
23540 @c An out-of-band breakpoint instead of part of the result?
23542 @subsubheading @value{GDBN} Command
23544 The corresponding @value{GDBN} commands are @samp{break}, @samp{tbreak},
23545 @samp{hbreak}, @samp{thbreak}, and @samp{rbreak}.
23547 @subsubheading Example
23552 ^done,bkpt=@{number="1",addr="0x0001072c",file="recursive2.c",
23553 fullname="/home/foo/recursive2.c,line="4",times="0"@}
23555 -break-insert -t foo
23556 ^done,bkpt=@{number="2",addr="0x00010774",file="recursive2.c",
23557 fullname="/home/foo/recursive2.c,line="11",times="0"@}
23560 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
23561 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
23562 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
23563 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
23564 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
23565 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
23566 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
23567 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
23568 addr="0x0001072c", func="main",file="recursive2.c",
23569 fullname="/home/foo/recursive2.c,"line="4",times="0"@},
23570 bkpt=@{number="2",type="breakpoint",disp="del",enabled="y",
23571 addr="0x00010774",func="foo",file="recursive2.c",
23572 fullname="/home/foo/recursive2.c",line="11",times="0"@}]@}
23574 -break-insert -r foo.*
23575 ~int foo(int, int);
23576 ^done,bkpt=@{number="3",addr="0x00010774",file="recursive2.c,
23577 "fullname="/home/foo/recursive2.c",line="11",times="0"@}
23581 @subheading The @code{-break-list} Command
23582 @findex -break-list
23584 @subsubheading Synopsis
23590 Displays the list of inserted breakpoints, showing the following fields:
23594 number of the breakpoint
23596 type of the breakpoint: @samp{breakpoint} or @samp{watchpoint}
23598 should the breakpoint be deleted or disabled when it is hit: @samp{keep}
23601 is the breakpoint enabled or no: @samp{y} or @samp{n}
23603 memory location at which the breakpoint is set
23605 logical location of the breakpoint, expressed by function name, file
23608 number of times the breakpoint has been hit
23611 If there are no breakpoints or watchpoints, the @code{BreakpointTable}
23612 @code{body} field is an empty list.
23614 @subsubheading @value{GDBN} Command
23616 The corresponding @value{GDBN} command is @samp{info break}.
23618 @subsubheading Example
23623 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
23624 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
23625 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
23626 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
23627 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
23628 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
23629 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
23630 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
23631 addr="0x000100d0",func="main",file="hello.c",line="5",times="0"@},
23632 bkpt=@{number="2",type="breakpoint",disp="keep",enabled="y",
23633 addr="0x00010114",func="foo",file="hello.c",fullname="/home/foo/hello.c",
23634 line="13",times="0"@}]@}
23638 Here's an example of the result when there are no breakpoints:
23643 ^done,BreakpointTable=@{nr_rows="0",nr_cols="6",
23644 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
23645 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
23646 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
23647 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
23648 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
23649 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
23654 @subheading The @code{-break-passcount} Command
23655 @findex -break-passcount
23657 @subsubheading Synopsis
23660 -break-passcount @var{tracepoint-number} @var{passcount}
23663 Set the passcount for tracepoint @var{tracepoint-number} to
23664 @var{passcount}. If the breakpoint referred to by @var{tracepoint-number}
23665 is not a tracepoint, error is emitted. This corresponds to CLI
23666 command @samp{passcount}.
23668 @subheading The @code{-break-watch} Command
23669 @findex -break-watch
23671 @subsubheading Synopsis
23674 -break-watch [ -a | -r ]
23677 Create a watchpoint. With the @samp{-a} option it will create an
23678 @dfn{access} watchpoint, i.e., a watchpoint that triggers either on a
23679 read from or on a write to the memory location. With the @samp{-r}
23680 option, the watchpoint created is a @dfn{read} watchpoint, i.e., it will
23681 trigger only when the memory location is accessed for reading. Without
23682 either of the options, the watchpoint created is a regular watchpoint,
23683 i.e., it will trigger when the memory location is accessed for writing.
23684 @xref{Set Watchpoints, , Setting Watchpoints}.
23686 Note that @samp{-break-list} will report a single list of watchpoints and
23687 breakpoints inserted.
23689 @subsubheading @value{GDBN} Command
23691 The corresponding @value{GDBN} commands are @samp{watch}, @samp{awatch}, and
23694 @subsubheading Example
23696 Setting a watchpoint on a variable in the @code{main} function:
23701 ^done,wpt=@{number="2",exp="x"@}
23706 *stopped,reason="watchpoint-trigger",wpt=@{number="2",exp="x"@},
23707 value=@{old="-268439212",new="55"@},
23708 frame=@{func="main",args=[],file="recursive2.c",
23709 fullname="/home/foo/bar/recursive2.c",line="5"@}
23713 Setting a watchpoint on a variable local to a function. @value{GDBN} will stop
23714 the program execution twice: first for the variable changing value, then
23715 for the watchpoint going out of scope.
23720 ^done,wpt=@{number="5",exp="C"@}
23725 *stopped,reason="watchpoint-trigger",
23726 wpt=@{number="5",exp="C"@},value=@{old="-276895068",new="3"@},
23727 frame=@{func="callee4",args=[],
23728 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
23729 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13"@}
23734 *stopped,reason="watchpoint-scope",wpnum="5",
23735 frame=@{func="callee3",args=[@{name="strarg",
23736 value="0x11940 \"A string argument.\""@}],
23737 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
23738 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
23742 Listing breakpoints and watchpoints, at different points in the program
23743 execution. Note that once the watchpoint goes out of scope, it is
23749 ^done,wpt=@{number="2",exp="C"@}
23752 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
23753 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
23754 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
23755 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
23756 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
23757 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
23758 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
23759 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
23760 addr="0x00010734",func="callee4",
23761 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
23762 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c"line="8",times="1"@},
23763 bkpt=@{number="2",type="watchpoint",disp="keep",
23764 enabled="y",addr="",what="C",times="0"@}]@}
23769 *stopped,reason="watchpoint-trigger",wpt=@{number="2",exp="C"@},
23770 value=@{old="-276895068",new="3"@},
23771 frame=@{func="callee4",args=[],
23772 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
23773 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13"@}
23776 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
23777 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
23778 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
23779 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
23780 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
23781 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
23782 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
23783 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
23784 addr="0x00010734",func="callee4",
23785 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
23786 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",times="1"@},
23787 bkpt=@{number="2",type="watchpoint",disp="keep",
23788 enabled="y",addr="",what="C",times="-5"@}]@}
23792 ^done,reason="watchpoint-scope",wpnum="2",
23793 frame=@{func="callee3",args=[@{name="strarg",
23794 value="0x11940 \"A string argument.\""@}],
23795 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
23796 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
23799 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
23800 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
23801 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
23802 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
23803 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
23804 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
23805 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
23806 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
23807 addr="0x00010734",func="callee4",
23808 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
23809 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",
23814 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
23815 @node GDB/MI Program Context
23816 @section @sc{gdb/mi} Program Context
23818 @subheading The @code{-exec-arguments} Command
23819 @findex -exec-arguments
23822 @subsubheading Synopsis
23825 -exec-arguments @var{args}
23828 Set the inferior program arguments, to be used in the next
23831 @subsubheading @value{GDBN} Command
23833 The corresponding @value{GDBN} command is @samp{set args}.
23835 @subsubheading Example
23839 -exec-arguments -v word
23846 @subheading The @code{-exec-show-arguments} Command
23847 @findex -exec-show-arguments
23849 @subsubheading Synopsis
23852 -exec-show-arguments
23855 Print the arguments of the program.
23857 @subsubheading @value{GDBN} Command
23859 The corresponding @value{GDBN} command is @samp{show args}.
23861 @subsubheading Example
23866 @subheading The @code{-environment-cd} Command
23867 @findex -environment-cd
23869 @subsubheading Synopsis
23872 -environment-cd @var{pathdir}
23875 Set @value{GDBN}'s working directory.
23877 @subsubheading @value{GDBN} Command
23879 The corresponding @value{GDBN} command is @samp{cd}.
23881 @subsubheading Example
23885 -environment-cd /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
23891 @subheading The @code{-environment-directory} Command
23892 @findex -environment-directory
23894 @subsubheading Synopsis
23897 -environment-directory [ -r ] [ @var{pathdir} ]+
23900 Add directories @var{pathdir} to beginning of search path for source files.
23901 If the @samp{-r} option is used, the search path is reset to the default
23902 search path. If directories @var{pathdir} are supplied in addition to the
23903 @samp{-r} option, the search path is first reset and then addition
23905 Multiple directories may be specified, separated by blanks. Specifying
23906 multiple directories in a single command
23907 results in the directories added to the beginning of the
23908 search path in the same order they were presented in the command.
23909 If blanks are needed as
23910 part of a directory name, double-quotes should be used around
23911 the name. In the command output, the path will show up separated
23912 by the system directory-separator character. The directory-separator
23913 character must not be used
23914 in any directory name.
23915 If no directories are specified, the current search path is displayed.
23917 @subsubheading @value{GDBN} Command
23919 The corresponding @value{GDBN} command is @samp{dir}.
23921 @subsubheading Example
23925 -environment-directory /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
23926 ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
23928 -environment-directory ""
23929 ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
23931 -environment-directory -r /home/jjohnstn/src/gdb /usr/src
23932 ^done,source-path="/home/jjohnstn/src/gdb:/usr/src:$cdir:$cwd"
23934 -environment-directory -r
23935 ^done,source-path="$cdir:$cwd"
23940 @subheading The @code{-environment-path} Command
23941 @findex -environment-path
23943 @subsubheading Synopsis
23946 -environment-path [ -r ] [ @var{pathdir} ]+
23949 Add directories @var{pathdir} to beginning of search path for object files.
23950 If the @samp{-r} option is used, the search path is reset to the original
23951 search path that existed at gdb start-up. If directories @var{pathdir} are
23952 supplied in addition to the
23953 @samp{-r} option, the search path is first reset and then addition
23955 Multiple directories may be specified, separated by blanks. Specifying
23956 multiple directories in a single command
23957 results in the directories added to the beginning of the
23958 search path in the same order they were presented in the command.
23959 If blanks are needed as
23960 part of a directory name, double-quotes should be used around
23961 the name. In the command output, the path will show up separated
23962 by the system directory-separator character. The directory-separator
23963 character must not be used
23964 in any directory name.
23965 If no directories are specified, the current path is displayed.
23968 @subsubheading @value{GDBN} Command
23970 The corresponding @value{GDBN} command is @samp{path}.
23972 @subsubheading Example
23977 ^done,path="/usr/bin"
23979 -environment-path /kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb /bin
23980 ^done,path="/kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb:/bin:/usr/bin"
23982 -environment-path -r /usr/local/bin
23983 ^done,path="/usr/local/bin:/usr/bin"
23988 @subheading The @code{-environment-pwd} Command
23989 @findex -environment-pwd
23991 @subsubheading Synopsis
23997 Show the current working directory.
23999 @subsubheading @value{GDBN} Command
24001 The corresponding @value{GDBN} command is @samp{pwd}.
24003 @subsubheading Example
24008 ^done,cwd="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb"
24012 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
24013 @node GDB/MI Thread Commands
24014 @section @sc{gdb/mi} Thread Commands
24017 @subheading The @code{-thread-info} Command
24018 @findex -thread-info
24020 @subsubheading Synopsis
24023 -thread-info [ @var{thread-id} ]
24026 Reports information about either a specific thread, if
24027 the @var{thread-id} parameter is present, or about all
24028 threads. When printing information about all threads,
24029 also reports the current thread.
24031 @subsubheading @value{GDBN} Command
24033 The @samp{info thread} command prints the same information
24036 @subsubheading Example
24041 @{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)",
24042 frame=@{level="0",addr="0xffffe410",func="__kernel_vsyscall",args=[]@},state="running"@},
24043 @{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
24044 frame=@{level="0",addr="0x0804891f",func="foo",args=[@{name="i",value="10"@}],
24045 file="/tmp/a.c",fullname="/tmp/a.c",line="158"@},state="running"@}],
24046 current-thread-id="1"
24050 The @samp{state} field may have the following values:
24054 The thread is stopped. Frame information is available for stopped
24058 The thread is running. There's no frame information for running
24063 @subheading The @code{-thread-list-ids} Command
24064 @findex -thread-list-ids
24066 @subsubheading Synopsis
24072 Produces a list of the currently known @value{GDBN} thread ids. At the
24073 end of the list it also prints the total number of such threads.
24075 This command is retained for historical reasons, the
24076 @code{-thread-info} command should be used instead.
24078 @subsubheading @value{GDBN} Command
24080 Part of @samp{info threads} supplies the same information.
24082 @subsubheading Example
24087 ^done,thread-ids=@{thread-id="3",thread-id="2",thread-id="1"@},
24088 current-thread-id="1",number-of-threads="3"
24093 @subheading The @code{-thread-select} Command
24094 @findex -thread-select
24096 @subsubheading Synopsis
24099 -thread-select @var{threadnum}
24102 Make @var{threadnum} the current thread. It prints the number of the new
24103 current thread, and the topmost frame for that thread.
24105 This command is deprecated in favor of explicitly using the
24106 @samp{--thread} option to each command.
24108 @subsubheading @value{GDBN} Command
24110 The corresponding @value{GDBN} command is @samp{thread}.
24112 @subsubheading Example
24119 *stopped,reason="end-stepping-range",thread-id="2",line="187",
24120 file="../../../devo/gdb/testsuite/gdb.threads/linux-dp.c"
24124 thread-ids=@{thread-id="3",thread-id="2",thread-id="1"@},
24125 number-of-threads="3"
24128 ^done,new-thread-id="3",
24129 frame=@{level="0",func="vprintf",
24130 args=[@{name="format",value="0x8048e9c \"%*s%c %d %c\\n\""@},
24131 @{name="arg",value="0x2"@}],file="vprintf.c",line="31"@}
24135 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
24136 @node GDB/MI Program Execution
24137 @section @sc{gdb/mi} Program Execution
24139 These are the asynchronous commands which generate the out-of-band
24140 record @samp{*stopped}. Currently @value{GDBN} only really executes
24141 asynchronously with remote targets and this interaction is mimicked in
24144 @subheading The @code{-exec-continue} Command
24145 @findex -exec-continue
24147 @subsubheading Synopsis
24150 -exec-continue [--reverse] [--all|--thread-group N]
24153 Resumes the execution of the inferior program, which will continue
24154 to execute until it reaches a debugger stop event. If the
24155 @samp{--reverse} option is specified, execution resumes in reverse until
24156 it reaches a stop event. Stop events may include
24159 breakpoints or watchpoints
24161 signals or exceptions
24163 the end of the process (or its beginning under @samp{--reverse})
24165 the end or beginning of a replay log if one is being used.
24167 In all-stop mode (@pxref{All-Stop
24168 Mode}), may resume only one thread, or all threads, depending on the
24169 value of the @samp{scheduler-locking} variable. If @samp{--all} is
24170 specified, all threads (in all inferiors) will be resumed. The @samp{--all} option is
24171 ignored in all-stop mode. If the @samp{--thread-group} options is
24172 specified, then all threads in that thread group are resumed.
24174 @subsubheading @value{GDBN} Command
24176 The corresponding @value{GDBN} corresponding is @samp{continue}.
24178 @subsubheading Example
24185 *stopped,reason="breakpoint-hit",disp="keep",bkptno="2",frame=@{
24186 func="foo",args=[],file="hello.c",fullname="/home/foo/bar/hello.c",
24192 @subheading The @code{-exec-finish} Command
24193 @findex -exec-finish
24195 @subsubheading Synopsis
24198 -exec-finish [--reverse]
24201 Resumes the execution of the inferior program until the current
24202 function is exited. Displays the results returned by the function.
24203 If the @samp{--reverse} option is specified, resumes the reverse
24204 execution of the inferior program until the point where current
24205 function was called.
24207 @subsubheading @value{GDBN} Command
24209 The corresponding @value{GDBN} command is @samp{finish}.
24211 @subsubheading Example
24213 Function returning @code{void}.
24220 *stopped,reason="function-finished",frame=@{func="main",args=[],
24221 file="hello.c",fullname="/home/foo/bar/hello.c",line="7"@}
24225 Function returning other than @code{void}. The name of the internal
24226 @value{GDBN} variable storing the result is printed, together with the
24233 *stopped,reason="function-finished",frame=@{addr="0x000107b0",func="foo",
24234 args=[@{name="a",value="1"],@{name="b",value="9"@}@},
24235 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
24236 gdb-result-var="$1",return-value="0"
24241 @subheading The @code{-exec-interrupt} Command
24242 @findex -exec-interrupt
24244 @subsubheading Synopsis
24247 -exec-interrupt [--all|--thread-group N]
24250 Interrupts the background execution of the target. Note how the token
24251 associated with the stop message is the one for the execution command
24252 that has been interrupted. The token for the interrupt itself only
24253 appears in the @samp{^done} output. If the user is trying to
24254 interrupt a non-running program, an error message will be printed.
24256 Note that when asynchronous execution is enabled, this command is
24257 asynchronous just like other execution commands. That is, first the
24258 @samp{^done} response will be printed, and the target stop will be
24259 reported after that using the @samp{*stopped} notification.
24261 In non-stop mode, only the context thread is interrupted by default.
24262 All threads (in all inferiors) will be interrupted if the
24263 @samp{--all} option is specified. If the @samp{--thread-group}
24264 option is specified, all threads in that group will be interrupted.
24266 @subsubheading @value{GDBN} Command
24268 The corresponding @value{GDBN} command is @samp{interrupt}.
24270 @subsubheading Example
24281 111*stopped,signal-name="SIGINT",signal-meaning="Interrupt",
24282 frame=@{addr="0x00010140",func="foo",args=[],file="try.c",
24283 fullname="/home/foo/bar/try.c",line="13"@}
24288 ^error,msg="mi_cmd_exec_interrupt: Inferior not executing."
24292 @subheading The @code{-exec-jump} Command
24295 @subsubheading Synopsis
24298 -exec-jump @var{location}
24301 Resumes execution of the inferior program at the location specified by
24302 parameter. @xref{Specify Location}, for a description of the
24303 different forms of @var{location}.
24305 @subsubheading @value{GDBN} Command
24307 The corresponding @value{GDBN} command is @samp{jump}.
24309 @subsubheading Example
24312 -exec-jump foo.c:10
24313 *running,thread-id="all"
24318 @subheading The @code{-exec-next} Command
24321 @subsubheading Synopsis
24324 -exec-next [--reverse]
24327 Resumes execution of the inferior program, stopping when the beginning
24328 of the next source line is reached.
24330 If the @samp{--reverse} option is specified, resumes reverse execution
24331 of the inferior program, stopping at the beginning of the previous
24332 source line. If you issue this command on the first line of a
24333 function, it will take you back to the caller of that function, to the
24334 source line where the function was called.
24337 @subsubheading @value{GDBN} Command
24339 The corresponding @value{GDBN} command is @samp{next}.
24341 @subsubheading Example
24347 *stopped,reason="end-stepping-range",line="8",file="hello.c"
24352 @subheading The @code{-exec-next-instruction} Command
24353 @findex -exec-next-instruction
24355 @subsubheading Synopsis
24358 -exec-next-instruction [--reverse]
24361 Executes one machine instruction. If the instruction is a function
24362 call, continues until the function returns. If the program stops at an
24363 instruction in the middle of a source line, the address will be
24366 If the @samp{--reverse} option is specified, resumes reverse execution
24367 of the inferior program, stopping at the previous instruction. If the
24368 previously executed instruction was a return from another function,
24369 it will continue to execute in reverse until the call to that function
24370 (from the current stack frame) is reached.
24372 @subsubheading @value{GDBN} Command
24374 The corresponding @value{GDBN} command is @samp{nexti}.
24376 @subsubheading Example
24380 -exec-next-instruction
24384 *stopped,reason="end-stepping-range",
24385 addr="0x000100d4",line="5",file="hello.c"
24390 @subheading The @code{-exec-return} Command
24391 @findex -exec-return
24393 @subsubheading Synopsis
24399 Makes current function return immediately. Doesn't execute the inferior.
24400 Displays the new current frame.
24402 @subsubheading @value{GDBN} Command
24404 The corresponding @value{GDBN} command is @samp{return}.
24406 @subsubheading Example
24410 200-break-insert callee4
24411 200^done,bkpt=@{number="1",addr="0x00010734",
24412 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8"@}
24417 000*stopped,reason="breakpoint-hit",disp="keep",bkptno="1",
24418 frame=@{func="callee4",args=[],
24419 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
24420 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8"@}
24426 111^done,frame=@{level="0",func="callee3",
24427 args=[@{name="strarg",
24428 value="0x11940 \"A string argument.\""@}],
24429 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
24430 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
24435 @subheading The @code{-exec-run} Command
24438 @subsubheading Synopsis
24441 -exec-run [--all | --thread-group N]
24444 Starts execution of the inferior from the beginning. The inferior
24445 executes until either a breakpoint is encountered or the program
24446 exits. In the latter case the output will include an exit code, if
24447 the program has exited exceptionally.
24449 When no option is specified, the current inferior is started. If the
24450 @samp{--thread-group} option is specified, it should refer to a thread
24451 group of type @samp{process}, and that thread group will be started.
24452 If the @samp{--all} option is specified, then all inferiors will be started.
24454 @subsubheading @value{GDBN} Command
24456 The corresponding @value{GDBN} command is @samp{run}.
24458 @subsubheading Examples
24463 ^done,bkpt=@{number="1",addr="0x0001072c",file="recursive2.c",line="4"@}
24468 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",
24469 frame=@{func="main",args=[],file="recursive2.c",
24470 fullname="/home/foo/bar/recursive2.c",line="4"@}
24475 Program exited normally:
24483 *stopped,reason="exited-normally"
24488 Program exited exceptionally:
24496 *stopped,reason="exited",exit-code="01"
24500 Another way the program can terminate is if it receives a signal such as
24501 @code{SIGINT}. In this case, @sc{gdb/mi} displays this:
24505 *stopped,reason="exited-signalled",signal-name="SIGINT",
24506 signal-meaning="Interrupt"
24510 @c @subheading -exec-signal
24513 @subheading The @code{-exec-step} Command
24516 @subsubheading Synopsis
24519 -exec-step [--reverse]
24522 Resumes execution of the inferior program, stopping when the beginning
24523 of the next source line is reached, if the next source line is not a
24524 function call. If it is, stop at the first instruction of the called
24525 function. If the @samp{--reverse} option is specified, resumes reverse
24526 execution of the inferior program, stopping at the beginning of the
24527 previously executed source line.
24529 @subsubheading @value{GDBN} Command
24531 The corresponding @value{GDBN} command is @samp{step}.
24533 @subsubheading Example
24535 Stepping into a function:
24541 *stopped,reason="end-stepping-range",
24542 frame=@{func="foo",args=[@{name="a",value="10"@},
24543 @{name="b",value="0"@}],file="recursive2.c",
24544 fullname="/home/foo/bar/recursive2.c",line="11"@}
24554 *stopped,reason="end-stepping-range",line="14",file="recursive2.c"
24559 @subheading The @code{-exec-step-instruction} Command
24560 @findex -exec-step-instruction
24562 @subsubheading Synopsis
24565 -exec-step-instruction [--reverse]
24568 Resumes the inferior which executes one machine instruction. If the
24569 @samp{--reverse} option is specified, resumes reverse execution of the
24570 inferior program, stopping at the previously executed instruction.
24571 The output, once @value{GDBN} has stopped, will vary depending on
24572 whether we have stopped in the middle of a source line or not. In the
24573 former case, the address at which the program stopped will be printed
24576 @subsubheading @value{GDBN} Command
24578 The corresponding @value{GDBN} command is @samp{stepi}.
24580 @subsubheading Example
24584 -exec-step-instruction
24588 *stopped,reason="end-stepping-range",
24589 frame=@{func="foo",args=[],file="try.c",
24590 fullname="/home/foo/bar/try.c",line="10"@}
24592 -exec-step-instruction
24596 *stopped,reason="end-stepping-range",
24597 frame=@{addr="0x000100f4",func="foo",args=[],file="try.c",
24598 fullname="/home/foo/bar/try.c",line="10"@}
24603 @subheading The @code{-exec-until} Command
24604 @findex -exec-until
24606 @subsubheading Synopsis
24609 -exec-until [ @var{location} ]
24612 Executes the inferior until the @var{location} specified in the
24613 argument is reached. If there is no argument, the inferior executes
24614 until a source line greater than the current one is reached. The
24615 reason for stopping in this case will be @samp{location-reached}.
24617 @subsubheading @value{GDBN} Command
24619 The corresponding @value{GDBN} command is @samp{until}.
24621 @subsubheading Example
24625 -exec-until recursive2.c:6
24629 *stopped,reason="location-reached",frame=@{func="main",args=[],
24630 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="6"@}
24635 @subheading -file-clear
24636 Is this going away????
24639 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
24640 @node GDB/MI Stack Manipulation
24641 @section @sc{gdb/mi} Stack Manipulation Commands
24644 @subheading The @code{-stack-info-frame} Command
24645 @findex -stack-info-frame
24647 @subsubheading Synopsis
24653 Get info on the selected frame.
24655 @subsubheading @value{GDBN} Command
24657 The corresponding @value{GDBN} command is @samp{info frame} or @samp{frame}
24658 (without arguments).
24660 @subsubheading Example
24665 ^done,frame=@{level="1",addr="0x0001076c",func="callee3",
24666 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
24667 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17"@}
24671 @subheading The @code{-stack-info-depth} Command
24672 @findex -stack-info-depth
24674 @subsubheading Synopsis
24677 -stack-info-depth [ @var{max-depth} ]
24680 Return the depth of the stack. If the integer argument @var{max-depth}
24681 is specified, do not count beyond @var{max-depth} frames.
24683 @subsubheading @value{GDBN} Command
24685 There's no equivalent @value{GDBN} command.
24687 @subsubheading Example
24689 For a stack with frame levels 0 through 11:
24696 -stack-info-depth 4
24699 -stack-info-depth 12
24702 -stack-info-depth 11
24705 -stack-info-depth 13
24710 @subheading The @code{-stack-list-arguments} Command
24711 @findex -stack-list-arguments
24713 @subsubheading Synopsis
24716 -stack-list-arguments @var{print-values}
24717 [ @var{low-frame} @var{high-frame} ]
24720 Display a list of the arguments for the frames between @var{low-frame}
24721 and @var{high-frame} (inclusive). If @var{low-frame} and
24722 @var{high-frame} are not provided, list the arguments for the whole
24723 call stack. If the two arguments are equal, show the single frame
24724 at the corresponding level. It is an error if @var{low-frame} is
24725 larger than the actual number of frames. On the other hand,
24726 @var{high-frame} may be larger than the actual number of frames, in
24727 which case only existing frames will be returned.
24729 If @var{print-values} is 0 or @code{--no-values}, print only the names of
24730 the variables; if it is 1 or @code{--all-values}, print also their
24731 values; and if it is 2 or @code{--simple-values}, print the name,
24732 type and value for simple data types, and the name and type for arrays,
24733 structures and unions.
24735 Use of this command to obtain arguments in a single frame is
24736 deprecated in favor of the @samp{-stack-list-variables} command.
24738 @subsubheading @value{GDBN} Command
24740 @value{GDBN} does not have an equivalent command. @code{gdbtk} has a
24741 @samp{gdb_get_args} command which partially overlaps with the
24742 functionality of @samp{-stack-list-arguments}.
24744 @subsubheading Example
24751 frame=@{level="0",addr="0x00010734",func="callee4",
24752 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
24753 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8"@},
24754 frame=@{level="1",addr="0x0001076c",func="callee3",
24755 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
24756 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17"@},
24757 frame=@{level="2",addr="0x0001078c",func="callee2",
24758 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
24759 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="22"@},
24760 frame=@{level="3",addr="0x000107b4",func="callee1",
24761 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
24762 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="27"@},
24763 frame=@{level="4",addr="0x000107e0",func="main",
24764 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
24765 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="32"@}]
24767 -stack-list-arguments 0
24770 frame=@{level="0",args=[]@},
24771 frame=@{level="1",args=[name="strarg"]@},
24772 frame=@{level="2",args=[name="intarg",name="strarg"]@},
24773 frame=@{level="3",args=[name="intarg",name="strarg",name="fltarg"]@},
24774 frame=@{level="4",args=[]@}]
24776 -stack-list-arguments 1
24779 frame=@{level="0",args=[]@},
24781 args=[@{name="strarg",value="0x11940 \"A string argument.\""@}]@},
24782 frame=@{level="2",args=[
24783 @{name="intarg",value="2"@},
24784 @{name="strarg",value="0x11940 \"A string argument.\""@}]@},
24785 @{frame=@{level="3",args=[
24786 @{name="intarg",value="2"@},
24787 @{name="strarg",value="0x11940 \"A string argument.\""@},
24788 @{name="fltarg",value="3.5"@}]@},
24789 frame=@{level="4",args=[]@}]
24791 -stack-list-arguments 0 2 2
24792 ^done,stack-args=[frame=@{level="2",args=[name="intarg",name="strarg"]@}]
24794 -stack-list-arguments 1 2 2
24795 ^done,stack-args=[frame=@{level="2",
24796 args=[@{name="intarg",value="2"@},
24797 @{name="strarg",value="0x11940 \"A string argument.\""@}]@}]
24801 @c @subheading -stack-list-exception-handlers
24804 @subheading The @code{-stack-list-frames} Command
24805 @findex -stack-list-frames
24807 @subsubheading Synopsis
24810 -stack-list-frames [ @var{low-frame} @var{high-frame} ]
24813 List the frames currently on the stack. For each frame it displays the
24818 The frame number, 0 being the topmost frame, i.e., the innermost function.
24820 The @code{$pc} value for that frame.
24824 File name of the source file where the function lives.
24826 Line number corresponding to the @code{$pc}.
24829 If invoked without arguments, this command prints a backtrace for the
24830 whole stack. If given two integer arguments, it shows the frames whose
24831 levels are between the two arguments (inclusive). If the two arguments
24832 are equal, it shows the single frame at the corresponding level. It is
24833 an error if @var{low-frame} is larger than the actual number of
24834 frames. On the other hand, @var{high-frame} may be larger than the
24835 actual number of frames, in which case only existing frames will be returned.
24837 @subsubheading @value{GDBN} Command
24839 The corresponding @value{GDBN} commands are @samp{backtrace} and @samp{where}.
24841 @subsubheading Example
24843 Full stack backtrace:
24849 [frame=@{level="0",addr="0x0001076c",func="foo",
24850 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="11"@},
24851 frame=@{level="1",addr="0x000107a4",func="foo",
24852 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
24853 frame=@{level="2",addr="0x000107a4",func="foo",
24854 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
24855 frame=@{level="3",addr="0x000107a4",func="foo",
24856 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
24857 frame=@{level="4",addr="0x000107a4",func="foo",
24858 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
24859 frame=@{level="5",addr="0x000107a4",func="foo",
24860 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
24861 frame=@{level="6",addr="0x000107a4",func="foo",
24862 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
24863 frame=@{level="7",addr="0x000107a4",func="foo",
24864 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
24865 frame=@{level="8",addr="0x000107a4",func="foo",
24866 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
24867 frame=@{level="9",addr="0x000107a4",func="foo",
24868 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
24869 frame=@{level="10",addr="0x000107a4",func="foo",
24870 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
24871 frame=@{level="11",addr="0x00010738",func="main",
24872 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="4"@}]
24876 Show frames between @var{low_frame} and @var{high_frame}:
24880 -stack-list-frames 3 5
24882 [frame=@{level="3",addr="0x000107a4",func="foo",
24883 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
24884 frame=@{level="4",addr="0x000107a4",func="foo",
24885 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
24886 frame=@{level="5",addr="0x000107a4",func="foo",
24887 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@}]
24891 Show a single frame:
24895 -stack-list-frames 3 3
24897 [frame=@{level="3",addr="0x000107a4",func="foo",
24898 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@}]
24903 @subheading The @code{-stack-list-locals} Command
24904 @findex -stack-list-locals
24906 @subsubheading Synopsis
24909 -stack-list-locals @var{print-values}
24912 Display the local variable names for the selected frame. If
24913 @var{print-values} is 0 or @code{--no-values}, print only the names of
24914 the variables; if it is 1 or @code{--all-values}, print also their
24915 values; and if it is 2 or @code{--simple-values}, print the name,
24916 type and value for simple data types, and the name and type for arrays,
24917 structures and unions. In this last case, a frontend can immediately
24918 display the value of simple data types and create variable objects for
24919 other data types when the user wishes to explore their values in
24922 This command is deprecated in favor of the
24923 @samp{-stack-list-variables} command.
24925 @subsubheading @value{GDBN} Command
24927 @samp{info locals} in @value{GDBN}, @samp{gdb_get_locals} in @code{gdbtk}.
24929 @subsubheading Example
24933 -stack-list-locals 0
24934 ^done,locals=[name="A",name="B",name="C"]
24936 -stack-list-locals --all-values
24937 ^done,locals=[@{name="A",value="1"@},@{name="B",value="2"@},
24938 @{name="C",value="@{1, 2, 3@}"@}]
24939 -stack-list-locals --simple-values
24940 ^done,locals=[@{name="A",type="int",value="1"@},
24941 @{name="B",type="int",value="2"@},@{name="C",type="int [3]"@}]
24945 @subheading The @code{-stack-list-variables} Command
24946 @findex -stack-list-variables
24948 @subsubheading Synopsis
24951 -stack-list-variables @var{print-values}
24954 Display the names of local variables and function arguments for the selected frame. If
24955 @var{print-values} is 0 or @code{--no-values}, print only the names of
24956 the variables; if it is 1 or @code{--all-values}, print also their
24957 values; and if it is 2 or @code{--simple-values}, print the name,
24958 type and value for simple data types, and the name and type for arrays,
24959 structures and unions.
24961 @subsubheading Example
24965 -stack-list-variables --thread 1 --frame 0 --all-values
24966 ^done,variables=[@{name="x",value="11"@},@{name="s",value="@{a = 1, b = 2@}"@}]
24971 @subheading The @code{-stack-select-frame} Command
24972 @findex -stack-select-frame
24974 @subsubheading Synopsis
24977 -stack-select-frame @var{framenum}
24980 Change the selected frame. Select a different frame @var{framenum} on
24983 This command in deprecated in favor of passing the @samp{--frame}
24984 option to every command.
24986 @subsubheading @value{GDBN} Command
24988 The corresponding @value{GDBN} commands are @samp{frame}, @samp{up},
24989 @samp{down}, @samp{select-frame}, @samp{up-silent}, and @samp{down-silent}.
24991 @subsubheading Example
24995 -stack-select-frame 2
25000 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25001 @node GDB/MI Variable Objects
25002 @section @sc{gdb/mi} Variable Objects
25006 @subheading Motivation for Variable Objects in @sc{gdb/mi}
25008 For the implementation of a variable debugger window (locals, watched
25009 expressions, etc.), we are proposing the adaptation of the existing code
25010 used by @code{Insight}.
25012 The two main reasons for that are:
25016 It has been proven in practice (it is already on its second generation).
25019 It will shorten development time (needless to say how important it is
25023 The original interface was designed to be used by Tcl code, so it was
25024 slightly changed so it could be used through @sc{gdb/mi}. This section
25025 describes the @sc{gdb/mi} operations that will be available and gives some
25026 hints about their use.
25028 @emph{Note}: In addition to the set of operations described here, we
25029 expect the @sc{gui} implementation of a variable window to require, at
25030 least, the following operations:
25033 @item @code{-gdb-show} @code{output-radix}
25034 @item @code{-stack-list-arguments}
25035 @item @code{-stack-list-locals}
25036 @item @code{-stack-select-frame}
25041 @subheading Introduction to Variable Objects
25043 @cindex variable objects in @sc{gdb/mi}
25045 Variable objects are "object-oriented" MI interface for examining and
25046 changing values of expressions. Unlike some other MI interfaces that
25047 work with expressions, variable objects are specifically designed for
25048 simple and efficient presentation in the frontend. A variable object
25049 is identified by string name. When a variable object is created, the
25050 frontend specifies the expression for that variable object. The
25051 expression can be a simple variable, or it can be an arbitrary complex
25052 expression, and can even involve CPU registers. After creating a
25053 variable object, the frontend can invoke other variable object
25054 operations---for example to obtain or change the value of a variable
25055 object, or to change display format.
25057 Variable objects have hierarchical tree structure. Any variable object
25058 that corresponds to a composite type, such as structure in C, has
25059 a number of child variable objects, for example corresponding to each
25060 element of a structure. A child variable object can itself have
25061 children, recursively. Recursion ends when we reach
25062 leaf variable objects, which always have built-in types. Child variable
25063 objects are created only by explicit request, so if a frontend
25064 is not interested in the children of a particular variable object, no
25065 child will be created.
25067 For a leaf variable object it is possible to obtain its value as a
25068 string, or set the value from a string. String value can be also
25069 obtained for a non-leaf variable object, but it's generally a string
25070 that only indicates the type of the object, and does not list its
25071 contents. Assignment to a non-leaf variable object is not allowed.
25073 A frontend does not need to read the values of all variable objects each time
25074 the program stops. Instead, MI provides an update command that lists all
25075 variable objects whose values has changed since the last update
25076 operation. This considerably reduces the amount of data that must
25077 be transferred to the frontend. As noted above, children variable
25078 objects are created on demand, and only leaf variable objects have a
25079 real value. As result, gdb will read target memory only for leaf
25080 variables that frontend has created.
25082 The automatic update is not always desirable. For example, a frontend
25083 might want to keep a value of some expression for future reference,
25084 and never update it. For another example, fetching memory is
25085 relatively slow for embedded targets, so a frontend might want
25086 to disable automatic update for the variables that are either not
25087 visible on the screen, or ``closed''. This is possible using so
25088 called ``frozen variable objects''. Such variable objects are never
25089 implicitly updated.
25091 Variable objects can be either @dfn{fixed} or @dfn{floating}. For the
25092 fixed variable object, the expression is parsed when the variable
25093 object is created, including associating identifiers to specific
25094 variables. The meaning of expression never changes. For a floating
25095 variable object the values of variables whose names appear in the
25096 expressions are re-evaluated every time in the context of the current
25097 frame. Consider this example:
25102 struct work_state state;
25109 If a fixed variable object for the @code{state} variable is created in
25110 this function, and we enter the recursive call, the the variable
25111 object will report the value of @code{state} in the top-level
25112 @code{do_work} invocation. On the other hand, a floating variable
25113 object will report the value of @code{state} in the current frame.
25115 If an expression specified when creating a fixed variable object
25116 refers to a local variable, the variable object becomes bound to the
25117 thread and frame in which the variable object is created. When such
25118 variable object is updated, @value{GDBN} makes sure that the
25119 thread/frame combination the variable object is bound to still exists,
25120 and re-evaluates the variable object in context of that thread/frame.
25122 The following is the complete set of @sc{gdb/mi} operations defined to
25123 access this functionality:
25125 @multitable @columnfractions .4 .6
25126 @item @strong{Operation}
25127 @tab @strong{Description}
25129 @item @code{-enable-pretty-printing}
25130 @tab enable Python-based pretty-printing
25131 @item @code{-var-create}
25132 @tab create a variable object
25133 @item @code{-var-delete}
25134 @tab delete the variable object and/or its children
25135 @item @code{-var-set-format}
25136 @tab set the display format of this variable
25137 @item @code{-var-show-format}
25138 @tab show the display format of this variable
25139 @item @code{-var-info-num-children}
25140 @tab tells how many children this object has
25141 @item @code{-var-list-children}
25142 @tab return a list of the object's children
25143 @item @code{-var-info-type}
25144 @tab show the type of this variable object
25145 @item @code{-var-info-expression}
25146 @tab print parent-relative expression that this variable object represents
25147 @item @code{-var-info-path-expression}
25148 @tab print full expression that this variable object represents
25149 @item @code{-var-show-attributes}
25150 @tab is this variable editable? does it exist here?
25151 @item @code{-var-evaluate-expression}
25152 @tab get the value of this variable
25153 @item @code{-var-assign}
25154 @tab set the value of this variable
25155 @item @code{-var-update}
25156 @tab update the variable and its children
25157 @item @code{-var-set-frozen}
25158 @tab set frozeness attribute
25159 @item @code{-var-set-update-range}
25160 @tab set range of children to display on update
25163 In the next subsection we describe each operation in detail and suggest
25164 how it can be used.
25166 @subheading Description And Use of Operations on Variable Objects
25168 @subheading The @code{-enable-pretty-printing} Command
25169 @findex -enable-pretty-printing
25172 -enable-pretty-printing
25175 @value{GDBN} allows Python-based visualizers to affect the output of the
25176 MI variable object commands. However, because there was no way to
25177 implement this in a fully backward-compatible way, a front end must
25178 request that this functionality be enabled.
25180 Once enabled, this feature cannot be disabled.
25182 Note that if Python support has not been compiled into @value{GDBN},
25183 this command will still succeed (and do nothing).
25185 This feature is currently (as of @value{GDBN} 7.0) experimental, and
25186 may work differently in future versions of @value{GDBN}.
25188 @subheading The @code{-var-create} Command
25189 @findex -var-create
25191 @subsubheading Synopsis
25194 -var-create @{@var{name} | "-"@}
25195 @{@var{frame-addr} | "*" | "@@"@} @var{expression}
25198 This operation creates a variable object, which allows the monitoring of
25199 a variable, the result of an expression, a memory cell or a CPU
25202 The @var{name} parameter is the string by which the object can be
25203 referenced. It must be unique. If @samp{-} is specified, the varobj
25204 system will generate a string ``varNNNNNN'' automatically. It will be
25205 unique provided that one does not specify @var{name} of that format.
25206 The command fails if a duplicate name is found.
25208 The frame under which the expression should be evaluated can be
25209 specified by @var{frame-addr}. A @samp{*} indicates that the current
25210 frame should be used. A @samp{@@} indicates that a floating variable
25211 object must be created.
25213 @var{expression} is any expression valid on the current language set (must not
25214 begin with a @samp{*}), or one of the following:
25218 @samp{*@var{addr}}, where @var{addr} is the address of a memory cell
25221 @samp{*@var{addr}-@var{addr}} --- a memory address range (TBD)
25224 @samp{$@var{regname}} --- a CPU register name
25227 @cindex dynamic varobj
25228 A varobj's contents may be provided by a Python-based pretty-printer. In this
25229 case the varobj is known as a @dfn{dynamic varobj}. Dynamic varobjs
25230 have slightly different semantics in some cases. If the
25231 @code{-enable-pretty-printing} command is not sent, then @value{GDBN}
25232 will never create a dynamic varobj. This ensures backward
25233 compatibility for existing clients.
25235 @subsubheading Result
25237 This operation returns attributes of the newly-created varobj. These
25242 The name of the varobj.
25245 The number of children of the varobj. This number is not necessarily
25246 reliable for a dynamic varobj. Instead, you must examine the
25247 @samp{has_more} attribute.
25250 The varobj's scalar value. For a varobj whose type is some sort of
25251 aggregate (e.g., a @code{struct}), or for a dynamic varobj, this value
25252 will not be interesting.
25255 The varobj's type. This is a string representation of the type, as
25256 would be printed by the @value{GDBN} CLI.
25259 If a variable object is bound to a specific thread, then this is the
25260 thread's identifier.
25263 For a dynamic varobj, this indicates whether there appear to be any
25264 children available. For a non-dynamic varobj, this will be 0.
25267 This attribute will be present and have the value @samp{1} if the
25268 varobj is a dynamic varobj. If the varobj is not a dynamic varobj,
25269 then this attribute will not be present.
25272 A dynamic varobj can supply a display hint to the front end. The
25273 value comes directly from the Python pretty-printer object's
25274 @code{display_hint} method. @xref{Pretty Printing}.
25277 Typical output will look like this:
25280 name="@var{name}",numchild="@var{N}",type="@var{type}",thread-id="@var{M}",
25281 has_more="@var{has_more}"
25285 @subheading The @code{-var-delete} Command
25286 @findex -var-delete
25288 @subsubheading Synopsis
25291 -var-delete [ -c ] @var{name}
25294 Deletes a previously created variable object and all of its children.
25295 With the @samp{-c} option, just deletes the children.
25297 Returns an error if the object @var{name} is not found.
25300 @subheading The @code{-var-set-format} Command
25301 @findex -var-set-format
25303 @subsubheading Synopsis
25306 -var-set-format @var{name} @var{format-spec}
25309 Sets the output format for the value of the object @var{name} to be
25312 @anchor{-var-set-format}
25313 The syntax for the @var{format-spec} is as follows:
25316 @var{format-spec} @expansion{}
25317 @{binary | decimal | hexadecimal | octal | natural@}
25320 The natural format is the default format choosen automatically
25321 based on the variable type (like decimal for an @code{int}, hex
25322 for pointers, etc.).
25324 For a variable with children, the format is set only on the
25325 variable itself, and the children are not affected.
25327 @subheading The @code{-var-show-format} Command
25328 @findex -var-show-format
25330 @subsubheading Synopsis
25333 -var-show-format @var{name}
25336 Returns the format used to display the value of the object @var{name}.
25339 @var{format} @expansion{}
25344 @subheading The @code{-var-info-num-children} Command
25345 @findex -var-info-num-children
25347 @subsubheading Synopsis
25350 -var-info-num-children @var{name}
25353 Returns the number of children of a variable object @var{name}:
25359 Note that this number is not completely reliable for a dynamic varobj.
25360 It will return the current number of children, but more children may
25364 @subheading The @code{-var-list-children} Command
25365 @findex -var-list-children
25367 @subsubheading Synopsis
25370 -var-list-children [@var{print-values}] @var{name} [@var{from} @var{to}]
25372 @anchor{-var-list-children}
25374 Return a list of the children of the specified variable object and
25375 create variable objects for them, if they do not already exist. With
25376 a single argument or if @var{print-values} has a value for of 0 or
25377 @code{--no-values}, print only the names of the variables; if
25378 @var{print-values} is 1 or @code{--all-values}, also print their
25379 values; and if it is 2 or @code{--simple-values} print the name and
25380 value for simple data types and just the name for arrays, structures
25383 @var{from} and @var{to}, if specified, indicate the range of children
25384 to report. If @var{from} or @var{to} is less than zero, the range is
25385 reset and all children will be reported. Otherwise, children starting
25386 at @var{from} (zero-based) and up to and excluding @var{to} will be
25389 If a child range is requested, it will only affect the current call to
25390 @code{-var-list-children}, but not future calls to @code{-var-update}.
25391 For this, you must instead use @code{-var-set-update-range}. The
25392 intent of this approach is to enable a front end to implement any
25393 update approach it likes; for example, scrolling a view may cause the
25394 front end to request more children with @code{-var-list-children}, and
25395 then the front end could call @code{-var-set-update-range} with a
25396 different range to ensure that future updates are restricted to just
25399 For each child the following results are returned:
25404 Name of the variable object created for this child.
25407 The expression to be shown to the user by the front end to designate this child.
25408 For example this may be the name of a structure member.
25410 For a dynamic varobj, this value cannot be used to form an
25411 expression. There is no way to do this at all with a dynamic varobj.
25413 For C/C@t{++} structures there are several pseudo children returned to
25414 designate access qualifiers. For these pseudo children @var{exp} is
25415 @samp{public}, @samp{private}, or @samp{protected}. In this case the
25416 type and value are not present.
25418 A dynamic varobj will not report the access qualifying
25419 pseudo-children, regardless of the language. This information is not
25420 available at all with a dynamic varobj.
25423 Number of children this child has. For a dynamic varobj, this will be
25427 The type of the child.
25430 If values were requested, this is the value.
25433 If this variable object is associated with a thread, this is the thread id.
25434 Otherwise this result is not present.
25437 If the variable object is frozen, this variable will be present with a value of 1.
25440 The result may have its own attributes:
25444 A dynamic varobj can supply a display hint to the front end. The
25445 value comes directly from the Python pretty-printer object's
25446 @code{display_hint} method. @xref{Pretty Printing}.
25449 This is an integer attribute which is nonzero if there are children
25450 remaining after the end of the selected range.
25453 @subsubheading Example
25457 -var-list-children n
25458 ^done,numchild=@var{n},children=[child=@{name=@var{name},exp=@var{exp},
25459 numchild=@var{n},type=@var{type}@},@r{(repeats N times)}]
25461 -var-list-children --all-values n
25462 ^done,numchild=@var{n},children=[child=@{name=@var{name},exp=@var{exp},
25463 numchild=@var{n},value=@var{value},type=@var{type}@},@r{(repeats N times)}]
25467 @subheading The @code{-var-info-type} Command
25468 @findex -var-info-type
25470 @subsubheading Synopsis
25473 -var-info-type @var{name}
25476 Returns the type of the specified variable @var{name}. The type is
25477 returned as a string in the same format as it is output by the
25481 type=@var{typename}
25485 @subheading The @code{-var-info-expression} Command
25486 @findex -var-info-expression
25488 @subsubheading Synopsis
25491 -var-info-expression @var{name}
25494 Returns a string that is suitable for presenting this
25495 variable object in user interface. The string is generally
25496 not valid expression in the current language, and cannot be evaluated.
25498 For example, if @code{a} is an array, and variable object
25499 @code{A} was created for @code{a}, then we'll get this output:
25502 (gdb) -var-info-expression A.1
25503 ^done,lang="C",exp="1"
25507 Here, the values of @code{lang} can be @code{@{"C" | "C++" | "Java"@}}.
25509 Note that the output of the @code{-var-list-children} command also
25510 includes those expressions, so the @code{-var-info-expression} command
25513 @subheading The @code{-var-info-path-expression} Command
25514 @findex -var-info-path-expression
25516 @subsubheading Synopsis
25519 -var-info-path-expression @var{name}
25522 Returns an expression that can be evaluated in the current
25523 context and will yield the same value that a variable object has.
25524 Compare this with the @code{-var-info-expression} command, which
25525 result can be used only for UI presentation. Typical use of
25526 the @code{-var-info-path-expression} command is creating a
25527 watchpoint from a variable object.
25529 This command is currently not valid for children of a dynamic varobj,
25530 and will give an error when invoked on one.
25532 For example, suppose @code{C} is a C@t{++} class, derived from class
25533 @code{Base}, and that the @code{Base} class has a member called
25534 @code{m_size}. Assume a variable @code{c} is has the type of
25535 @code{C} and a variable object @code{C} was created for variable
25536 @code{c}. Then, we'll get this output:
25538 (gdb) -var-info-path-expression C.Base.public.m_size
25539 ^done,path_expr=((Base)c).m_size)
25542 @subheading The @code{-var-show-attributes} Command
25543 @findex -var-show-attributes
25545 @subsubheading Synopsis
25548 -var-show-attributes @var{name}
25551 List attributes of the specified variable object @var{name}:
25554 status=@var{attr} [ ( ,@var{attr} )* ]
25558 where @var{attr} is @code{@{ @{ editable | noneditable @} | TBD @}}.
25560 @subheading The @code{-var-evaluate-expression} Command
25561 @findex -var-evaluate-expression
25563 @subsubheading Synopsis
25566 -var-evaluate-expression [-f @var{format-spec}] @var{name}
25569 Evaluates the expression that is represented by the specified variable
25570 object and returns its value as a string. The format of the string
25571 can be specified with the @samp{-f} option. The possible values of
25572 this option are the same as for @code{-var-set-format}
25573 (@pxref{-var-set-format}). If the @samp{-f} option is not specified,
25574 the current display format will be used. The current display format
25575 can be changed using the @code{-var-set-format} command.
25581 Note that one must invoke @code{-var-list-children} for a variable
25582 before the value of a child variable can be evaluated.
25584 @subheading The @code{-var-assign} Command
25585 @findex -var-assign
25587 @subsubheading Synopsis
25590 -var-assign @var{name} @var{expression}
25593 Assigns the value of @var{expression} to the variable object specified
25594 by @var{name}. The object must be @samp{editable}. If the variable's
25595 value is altered by the assign, the variable will show up in any
25596 subsequent @code{-var-update} list.
25598 @subsubheading Example
25606 ^done,changelist=[@{name="var1",in_scope="true",type_changed="false"@}]
25610 @subheading The @code{-var-update} Command
25611 @findex -var-update
25613 @subsubheading Synopsis
25616 -var-update [@var{print-values}] @{@var{name} | "*"@}
25619 Reevaluate the expressions corresponding to the variable object
25620 @var{name} and all its direct and indirect children, and return the
25621 list of variable objects whose values have changed; @var{name} must
25622 be a root variable object. Here, ``changed'' means that the result of
25623 @code{-var-evaluate-expression} before and after the
25624 @code{-var-update} is different. If @samp{*} is used as the variable
25625 object names, all existing variable objects are updated, except
25626 for frozen ones (@pxref{-var-set-frozen}). The option
25627 @var{print-values} determines whether both names and values, or just
25628 names are printed. The possible values of this option are the same
25629 as for @code{-var-list-children} (@pxref{-var-list-children}). It is
25630 recommended to use the @samp{--all-values} option, to reduce the
25631 number of MI commands needed on each program stop.
25633 With the @samp{*} parameter, if a variable object is bound to a
25634 currently running thread, it will not be updated, without any
25637 If @code{-var-set-update-range} was previously used on a varobj, then
25638 only the selected range of children will be reported.
25640 @code{-var-update} reports all the changed varobjs in a tuple named
25643 Each item in the change list is itself a tuple holding:
25647 The name of the varobj.
25650 If values were requested for this update, then this field will be
25651 present and will hold the value of the varobj.
25654 @anchor{-var-update}
25655 This field is a string which may take one of three values:
25659 The variable object's current value is valid.
25662 The variable object does not currently hold a valid value but it may
25663 hold one in the future if its associated expression comes back into
25667 The variable object no longer holds a valid value.
25668 This can occur when the executable file being debugged has changed,
25669 either through recompilation or by using the @value{GDBN} @code{file}
25670 command. The front end should normally choose to delete these variable
25674 In the future new values may be added to this list so the front should
25675 be prepared for this possibility. @xref{GDB/MI Development and Front Ends, ,@sc{GDB/MI} Development and Front Ends}.
25678 This is only present if the varobj is still valid. If the type
25679 changed, then this will be the string @samp{true}; otherwise it will
25683 If the varobj's type changed, then this field will be present and will
25686 @item new_num_children
25687 For a dynamic varobj, if the number of children changed, or if the
25688 type changed, this will be the new number of children.
25690 The @samp{numchild} field in other varobj responses is generally not
25691 valid for a dynamic varobj -- it will show the number of children that
25692 @value{GDBN} knows about, but because dynamic varobjs lazily
25693 instantiate their children, this will not reflect the number of
25694 children which may be available.
25696 The @samp{new_num_children} attribute only reports changes to the
25697 number of children known by @value{GDBN}. This is the only way to
25698 detect whether an update has removed children (which necessarily can
25699 only happen at the end of the update range).
25702 The display hint, if any.
25705 This is an integer value, which will be 1 if there are more children
25706 available outside the varobj's update range.
25709 This attribute will be present and have the value @samp{1} if the
25710 varobj is a dynamic varobj. If the varobj is not a dynamic varobj,
25711 then this attribute will not be present.
25714 If new children were added to a dynamic varobj within the selected
25715 update range (as set by @code{-var-set-update-range}), then they will
25716 be listed in this attribute.
25719 @subsubheading Example
25726 -var-update --all-values var1
25727 ^done,changelist=[@{name="var1",value="3",in_scope="true",
25728 type_changed="false"@}]
25732 @subheading The @code{-var-set-frozen} Command
25733 @findex -var-set-frozen
25734 @anchor{-var-set-frozen}
25736 @subsubheading Synopsis
25739 -var-set-frozen @var{name} @var{flag}
25742 Set the frozenness flag on the variable object @var{name}. The
25743 @var{flag} parameter should be either @samp{1} to make the variable
25744 frozen or @samp{0} to make it unfrozen. If a variable object is
25745 frozen, then neither itself, nor any of its children, are
25746 implicitly updated by @code{-var-update} of
25747 a parent variable or by @code{-var-update *}. Only
25748 @code{-var-update} of the variable itself will update its value and
25749 values of its children. After a variable object is unfrozen, it is
25750 implicitly updated by all subsequent @code{-var-update} operations.
25751 Unfreezing a variable does not update it, only subsequent
25752 @code{-var-update} does.
25754 @subsubheading Example
25758 -var-set-frozen V 1
25763 @subheading The @code{-var-set-update-range} command
25764 @findex -var-set-update-range
25765 @anchor{-var-set-update-range}
25767 @subsubheading Synopsis
25770 -var-set-update-range @var{name} @var{from} @var{to}
25773 Set the range of children to be returned by future invocations of
25774 @code{-var-update}.
25776 @var{from} and @var{to} indicate the range of children to report. If
25777 @var{from} or @var{to} is less than zero, the range is reset and all
25778 children will be reported. Otherwise, children starting at @var{from}
25779 (zero-based) and up to and excluding @var{to} will be reported.
25781 @subsubheading Example
25785 -var-set-update-range V 1 2
25789 @subheading The @code{-var-set-visualizer} command
25790 @findex -var-set-visualizer
25791 @anchor{-var-set-visualizer}
25793 @subsubheading Synopsis
25796 -var-set-visualizer @var{name} @var{visualizer}
25799 Set a visualizer for the variable object @var{name}.
25801 @var{visualizer} is the visualizer to use. The special value
25802 @samp{None} means to disable any visualizer in use.
25804 If not @samp{None}, @var{visualizer} must be a Python expression.
25805 This expression must evaluate to a callable object which accepts a
25806 single argument. @value{GDBN} will call this object with the value of
25807 the varobj @var{name} as an argument (this is done so that the same
25808 Python pretty-printing code can be used for both the CLI and MI).
25809 When called, this object must return an object which conforms to the
25810 pretty-printing interface (@pxref{Pretty Printing}).
25812 The pre-defined function @code{gdb.default_visualizer} may be used to
25813 select a visualizer by following the built-in process
25814 (@pxref{Selecting Pretty-Printers}). This is done automatically when
25815 a varobj is created, and so ordinarily is not needed.
25817 This feature is only available if Python support is enabled. The MI
25818 command @code{-list-features} (@pxref{GDB/MI Miscellaneous Commands})
25819 can be used to check this.
25821 @subsubheading Example
25823 Resetting the visualizer:
25827 -var-set-visualizer V None
25831 Reselecting the default (type-based) visualizer:
25835 -var-set-visualizer V gdb.default_visualizer
25839 Suppose @code{SomeClass} is a visualizer class. A lambda expression
25840 can be used to instantiate this class for a varobj:
25844 -var-set-visualizer V "lambda val: SomeClass()"
25848 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25849 @node GDB/MI Data Manipulation
25850 @section @sc{gdb/mi} Data Manipulation
25852 @cindex data manipulation, in @sc{gdb/mi}
25853 @cindex @sc{gdb/mi}, data manipulation
25854 This section describes the @sc{gdb/mi} commands that manipulate data:
25855 examine memory and registers, evaluate expressions, etc.
25857 @c REMOVED FROM THE INTERFACE.
25858 @c @subheading -data-assign
25859 @c Change the value of a program variable. Plenty of side effects.
25860 @c @subsubheading GDB Command
25862 @c @subsubheading Example
25865 @subheading The @code{-data-disassemble} Command
25866 @findex -data-disassemble
25868 @subsubheading Synopsis
25872 [ -s @var{start-addr} -e @var{end-addr} ]
25873 | [ -f @var{filename} -l @var{linenum} [ -n @var{lines} ] ]
25881 @item @var{start-addr}
25882 is the beginning address (or @code{$pc})
25883 @item @var{end-addr}
25885 @item @var{filename}
25886 is the name of the file to disassemble
25887 @item @var{linenum}
25888 is the line number to disassemble around
25890 is the number of disassembly lines to be produced. If it is -1,
25891 the whole function will be disassembled, in case no @var{end-addr} is
25892 specified. If @var{end-addr} is specified as a non-zero value, and
25893 @var{lines} is lower than the number of disassembly lines between
25894 @var{start-addr} and @var{end-addr}, only @var{lines} lines are
25895 displayed; if @var{lines} is higher than the number of lines between
25896 @var{start-addr} and @var{end-addr}, only the lines up to @var{end-addr}
25899 is either 0 (meaning only disassembly) or 1 (meaning mixed source and
25903 @subsubheading Result
25905 The output for each instruction is composed of four fields:
25914 Note that whatever included in the instruction field, is not manipulated
25915 directly by @sc{gdb/mi}, i.e., it is not possible to adjust its format.
25917 @subsubheading @value{GDBN} Command
25919 There's no direct mapping from this command to the CLI.
25921 @subsubheading Example
25923 Disassemble from the current value of @code{$pc} to @code{$pc + 20}:
25927 -data-disassemble -s $pc -e "$pc + 20" -- 0
25930 @{address="0x000107c0",func-name="main",offset="4",
25931 inst="mov 2, %o0"@},
25932 @{address="0x000107c4",func-name="main",offset="8",
25933 inst="sethi %hi(0x11800), %o2"@},
25934 @{address="0x000107c8",func-name="main",offset="12",
25935 inst="or %o2, 0x140, %o1\t! 0x11940 <_lib_version+8>"@},
25936 @{address="0x000107cc",func-name="main",offset="16",
25937 inst="sethi %hi(0x11800), %o2"@},
25938 @{address="0x000107d0",func-name="main",offset="20",
25939 inst="or %o2, 0x168, %o4\t! 0x11968 <_lib_version+48>"@}]
25943 Disassemble the whole @code{main} function. Line 32 is part of
25947 -data-disassemble -f basics.c -l 32 -- 0
25949 @{address="0x000107bc",func-name="main",offset="0",
25950 inst="save %sp, -112, %sp"@},
25951 @{address="0x000107c0",func-name="main",offset="4",
25952 inst="mov 2, %o0"@},
25953 @{address="0x000107c4",func-name="main",offset="8",
25954 inst="sethi %hi(0x11800), %o2"@},
25956 @{address="0x0001081c",func-name="main",offset="96",inst="ret "@},
25957 @{address="0x00010820",func-name="main",offset="100",inst="restore "@}]
25961 Disassemble 3 instructions from the start of @code{main}:
25965 -data-disassemble -f basics.c -l 32 -n 3 -- 0
25967 @{address="0x000107bc",func-name="main",offset="0",
25968 inst="save %sp, -112, %sp"@},
25969 @{address="0x000107c0",func-name="main",offset="4",
25970 inst="mov 2, %o0"@},
25971 @{address="0x000107c4",func-name="main",offset="8",
25972 inst="sethi %hi(0x11800), %o2"@}]
25976 Disassemble 3 instructions from the start of @code{main} in mixed mode:
25980 -data-disassemble -f basics.c -l 32 -n 3 -- 1
25982 src_and_asm_line=@{line="31",
25983 file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \
25984 testsuite/gdb.mi/basics.c",line_asm_insn=[
25985 @{address="0x000107bc",func-name="main",offset="0",
25986 inst="save %sp, -112, %sp"@}]@},
25987 src_and_asm_line=@{line="32",
25988 file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \
25989 testsuite/gdb.mi/basics.c",line_asm_insn=[
25990 @{address="0x000107c0",func-name="main",offset="4",
25991 inst="mov 2, %o0"@},
25992 @{address="0x000107c4",func-name="main",offset="8",
25993 inst="sethi %hi(0x11800), %o2"@}]@}]
25998 @subheading The @code{-data-evaluate-expression} Command
25999 @findex -data-evaluate-expression
26001 @subsubheading Synopsis
26004 -data-evaluate-expression @var{expr}
26007 Evaluate @var{expr} as an expression. The expression could contain an
26008 inferior function call. The function call will execute synchronously.
26009 If the expression contains spaces, it must be enclosed in double quotes.
26011 @subsubheading @value{GDBN} Command
26013 The corresponding @value{GDBN} commands are @samp{print}, @samp{output}, and
26014 @samp{call}. In @code{gdbtk} only, there's a corresponding
26015 @samp{gdb_eval} command.
26017 @subsubheading Example
26019 In the following example, the numbers that precede the commands are the
26020 @dfn{tokens} described in @ref{GDB/MI Command Syntax, ,@sc{gdb/mi}
26021 Command Syntax}. Notice how @sc{gdb/mi} returns the same tokens in its
26025 211-data-evaluate-expression A
26028 311-data-evaluate-expression &A
26029 311^done,value="0xefffeb7c"
26031 411-data-evaluate-expression A+3
26034 511-data-evaluate-expression "A + 3"
26040 @subheading The @code{-data-list-changed-registers} Command
26041 @findex -data-list-changed-registers
26043 @subsubheading Synopsis
26046 -data-list-changed-registers
26049 Display a list of the registers that have changed.
26051 @subsubheading @value{GDBN} Command
26053 @value{GDBN} doesn't have a direct analog for this command; @code{gdbtk}
26054 has the corresponding command @samp{gdb_changed_register_list}.
26056 @subsubheading Example
26058 On a PPC MBX board:
26066 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",frame=@{
26067 func="main",args=[],file="try.c",fullname="/home/foo/bar/try.c",
26070 -data-list-changed-registers
26071 ^done,changed-registers=["0","1","2","4","5","6","7","8","9",
26072 "10","11","13","14","15","16","17","18","19","20","21","22","23",
26073 "24","25","26","27","28","30","31","64","65","66","67","69"]
26078 @subheading The @code{-data-list-register-names} Command
26079 @findex -data-list-register-names
26081 @subsubheading Synopsis
26084 -data-list-register-names [ ( @var{regno} )+ ]
26087 Show a list of register names for the current target. If no arguments
26088 are given, it shows a list of the names of all the registers. If
26089 integer numbers are given as arguments, it will print a list of the
26090 names of the registers corresponding to the arguments. To ensure
26091 consistency between a register name and its number, the output list may
26092 include empty register names.
26094 @subsubheading @value{GDBN} Command
26096 @value{GDBN} does not have a command which corresponds to
26097 @samp{-data-list-register-names}. In @code{gdbtk} there is a
26098 corresponding command @samp{gdb_regnames}.
26100 @subsubheading Example
26102 For the PPC MBX board:
26105 -data-list-register-names
26106 ^done,register-names=["r0","r1","r2","r3","r4","r5","r6","r7",
26107 "r8","r9","r10","r11","r12","r13","r14","r15","r16","r17","r18",
26108 "r19","r20","r21","r22","r23","r24","r25","r26","r27","r28","r29",
26109 "r30","r31","f0","f1","f2","f3","f4","f5","f6","f7","f8","f9",
26110 "f10","f11","f12","f13","f14","f15","f16","f17","f18","f19","f20",
26111 "f21","f22","f23","f24","f25","f26","f27","f28","f29","f30","f31",
26112 "", "pc","ps","cr","lr","ctr","xer"]
26114 -data-list-register-names 1 2 3
26115 ^done,register-names=["r1","r2","r3"]
26119 @subheading The @code{-data-list-register-values} Command
26120 @findex -data-list-register-values
26122 @subsubheading Synopsis
26125 -data-list-register-values @var{fmt} [ ( @var{regno} )*]
26128 Display the registers' contents. @var{fmt} is the format according to
26129 which the registers' contents are to be returned, followed by an optional
26130 list of numbers specifying the registers to display. A missing list of
26131 numbers indicates that the contents of all the registers must be returned.
26133 Allowed formats for @var{fmt} are:
26150 @subsubheading @value{GDBN} Command
26152 The corresponding @value{GDBN} commands are @samp{info reg}, @samp{info
26153 all-reg}, and (in @code{gdbtk}) @samp{gdb_fetch_registers}.
26155 @subsubheading Example
26157 For a PPC MBX board (note: line breaks are for readability only, they
26158 don't appear in the actual output):
26162 -data-list-register-values r 64 65
26163 ^done,register-values=[@{number="64",value="0xfe00a300"@},
26164 @{number="65",value="0x00029002"@}]
26166 -data-list-register-values x
26167 ^done,register-values=[@{number="0",value="0xfe0043c8"@},
26168 @{number="1",value="0x3fff88"@},@{number="2",value="0xfffffffe"@},
26169 @{number="3",value="0x0"@},@{number="4",value="0xa"@},
26170 @{number="5",value="0x3fff68"@},@{number="6",value="0x3fff58"@},
26171 @{number="7",value="0xfe011e98"@},@{number="8",value="0x2"@},
26172 @{number="9",value="0xfa202820"@},@{number="10",value="0xfa202808"@},
26173 @{number="11",value="0x1"@},@{number="12",value="0x0"@},
26174 @{number="13",value="0x4544"@},@{number="14",value="0xffdfffff"@},
26175 @{number="15",value="0xffffffff"@},@{number="16",value="0xfffffeff"@},
26176 @{number="17",value="0xefffffed"@},@{number="18",value="0xfffffffe"@},
26177 @{number="19",value="0xffffffff"@},@{number="20",value="0xffffffff"@},
26178 @{number="21",value="0xffffffff"@},@{number="22",value="0xfffffff7"@},
26179 @{number="23",value="0xffffffff"@},@{number="24",value="0xffffffff"@},
26180 @{number="25",value="0xffffffff"@},@{number="26",value="0xfffffffb"@},
26181 @{number="27",value="0xffffffff"@},@{number="28",value="0xf7bfffff"@},
26182 @{number="29",value="0x0"@},@{number="30",value="0xfe010000"@},
26183 @{number="31",value="0x0"@},@{number="32",value="0x0"@},
26184 @{number="33",value="0x0"@},@{number="34",value="0x0"@},
26185 @{number="35",value="0x0"@},@{number="36",value="0x0"@},
26186 @{number="37",value="0x0"@},@{number="38",value="0x0"@},
26187 @{number="39",value="0x0"@},@{number="40",value="0x0"@},
26188 @{number="41",value="0x0"@},@{number="42",value="0x0"@},
26189 @{number="43",value="0x0"@},@{number="44",value="0x0"@},
26190 @{number="45",value="0x0"@},@{number="46",value="0x0"@},
26191 @{number="47",value="0x0"@},@{number="48",value="0x0"@},
26192 @{number="49",value="0x0"@},@{number="50",value="0x0"@},
26193 @{number="51",value="0x0"@},@{number="52",value="0x0"@},
26194 @{number="53",value="0x0"@},@{number="54",value="0x0"@},
26195 @{number="55",value="0x0"@},@{number="56",value="0x0"@},
26196 @{number="57",value="0x0"@},@{number="58",value="0x0"@},
26197 @{number="59",value="0x0"@},@{number="60",value="0x0"@},
26198 @{number="61",value="0x0"@},@{number="62",value="0x0"@},
26199 @{number="63",value="0x0"@},@{number="64",value="0xfe00a300"@},
26200 @{number="65",value="0x29002"@},@{number="66",value="0x202f04b5"@},
26201 @{number="67",value="0xfe0043b0"@},@{number="68",value="0xfe00b3e4"@},
26202 @{number="69",value="0x20002b03"@}]
26207 @subheading The @code{-data-read-memory} Command
26208 @findex -data-read-memory
26210 @subsubheading Synopsis
26213 -data-read-memory [ -o @var{byte-offset} ]
26214 @var{address} @var{word-format} @var{word-size}
26215 @var{nr-rows} @var{nr-cols} [ @var{aschar} ]
26222 @item @var{address}
26223 An expression specifying the address of the first memory word to be
26224 read. Complex expressions containing embedded white space should be
26225 quoted using the C convention.
26227 @item @var{word-format}
26228 The format to be used to print the memory words. The notation is the
26229 same as for @value{GDBN}'s @code{print} command (@pxref{Output Formats,
26232 @item @var{word-size}
26233 The size of each memory word in bytes.
26235 @item @var{nr-rows}
26236 The number of rows in the output table.
26238 @item @var{nr-cols}
26239 The number of columns in the output table.
26242 If present, indicates that each row should include an @sc{ascii} dump. The
26243 value of @var{aschar} is used as a padding character when a byte is not a
26244 member of the printable @sc{ascii} character set (printable @sc{ascii}
26245 characters are those whose code is between 32 and 126, inclusively).
26247 @item @var{byte-offset}
26248 An offset to add to the @var{address} before fetching memory.
26251 This command displays memory contents as a table of @var{nr-rows} by
26252 @var{nr-cols} words, each word being @var{word-size} bytes. In total,
26253 @code{@var{nr-rows} * @var{nr-cols} * @var{word-size}} bytes are read
26254 (returned as @samp{total-bytes}). Should less than the requested number
26255 of bytes be returned by the target, the missing words are identified
26256 using @samp{N/A}. The number of bytes read from the target is returned
26257 in @samp{nr-bytes} and the starting address used to read memory in
26260 The address of the next/previous row or page is available in
26261 @samp{next-row} and @samp{prev-row}, @samp{next-page} and
26264 @subsubheading @value{GDBN} Command
26266 The corresponding @value{GDBN} command is @samp{x}. @code{gdbtk} has
26267 @samp{gdb_get_mem} memory read command.
26269 @subsubheading Example
26271 Read six bytes of memory starting at @code{bytes+6} but then offset by
26272 @code{-6} bytes. Format as three rows of two columns. One byte per
26273 word. Display each word in hex.
26277 9-data-read-memory -o -6 -- bytes+6 x 1 3 2
26278 9^done,addr="0x00001390",nr-bytes="6",total-bytes="6",
26279 next-row="0x00001396",prev-row="0x0000138e",next-page="0x00001396",
26280 prev-page="0x0000138a",memory=[
26281 @{addr="0x00001390",data=["0x00","0x01"]@},
26282 @{addr="0x00001392",data=["0x02","0x03"]@},
26283 @{addr="0x00001394",data=["0x04","0x05"]@}]
26287 Read two bytes of memory starting at address @code{shorts + 64} and
26288 display as a single word formatted in decimal.
26292 5-data-read-memory shorts+64 d 2 1 1
26293 5^done,addr="0x00001510",nr-bytes="2",total-bytes="2",
26294 next-row="0x00001512",prev-row="0x0000150e",
26295 next-page="0x00001512",prev-page="0x0000150e",memory=[
26296 @{addr="0x00001510",data=["128"]@}]
26300 Read thirty two bytes of memory starting at @code{bytes+16} and format
26301 as eight rows of four columns. Include a string encoding with @samp{x}
26302 used as the non-printable character.
26306 4-data-read-memory bytes+16 x 1 8 4 x
26307 4^done,addr="0x000013a0",nr-bytes="32",total-bytes="32",
26308 next-row="0x000013c0",prev-row="0x0000139c",
26309 next-page="0x000013c0",prev-page="0x00001380",memory=[
26310 @{addr="0x000013a0",data=["0x10","0x11","0x12","0x13"],ascii="xxxx"@},
26311 @{addr="0x000013a4",data=["0x14","0x15","0x16","0x17"],ascii="xxxx"@},
26312 @{addr="0x000013a8",data=["0x18","0x19","0x1a","0x1b"],ascii="xxxx"@},
26313 @{addr="0x000013ac",data=["0x1c","0x1d","0x1e","0x1f"],ascii="xxxx"@},
26314 @{addr="0x000013b0",data=["0x20","0x21","0x22","0x23"],ascii=" !\"#"@},
26315 @{addr="0x000013b4",data=["0x24","0x25","0x26","0x27"],ascii="$%&'"@},
26316 @{addr="0x000013b8",data=["0x28","0x29","0x2a","0x2b"],ascii="()*+"@},
26317 @{addr="0x000013bc",data=["0x2c","0x2d","0x2e","0x2f"],ascii=",-./"@}]
26321 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
26322 @node GDB/MI Tracepoint Commands
26323 @section @sc{gdb/mi} Tracepoint Commands
26325 The commands defined in this section implement MI support for
26326 tracepoints. For detailed introduction, see @ref{Tracepoints}.
26328 @subheading The @code{-trace-find} Command
26329 @findex -trace-find
26331 @subsubheading Synopsis
26334 -trace-find @var{mode} [@var{parameters}@dots{}]
26337 Find a trace frame using criteria defined by @var{mode} and
26338 @var{parameters}. The following table lists permissible
26339 modes and their parameters. For details of operation, see @ref{tfind}.
26344 No parameters are required. Stops examining trace frames.
26347 An integer is required as parameter. Selects tracepoint frame with
26350 @item tracepoint-number
26351 An integer is required as parameter. Finds next
26352 trace frame that corresponds to tracepoint with the specified number.
26355 An address is required as parameter. Finds
26356 next trace frame that corresponds to any tracepoint at the specified
26359 @item pc-inside-range
26360 Two addresses are required as parameters. Finds next trace
26361 frame that corresponds to a tracepoint at an address inside the
26362 specified range. Both bounds are considered to be inside the range.
26364 @item pc-outside-range
26365 Two addresses are required as parameters. Finds
26366 next trace frame that corresponds to a tracepoint at an address outside
26367 the specified range. Both bounds are considered to be inside the range.
26370 Line specification is required as parameter. @xref{Specify Location}.
26371 Finds next trace frame that corresponds to a tracepoint at
26372 the specified location.
26376 If @samp{none} was passed as @var{mode}, the response does not
26377 have fields. Otherwise, the response may have the following fields:
26381 This field has either @samp{0} or @samp{1} as the value, depending
26382 on whether a matching tracepoint was found.
26385 The index of the found traceframe. This field is present iff
26386 the @samp{found} field has value of @samp{1}.
26389 The index of the found tracepoint. This field is present iff
26390 the @samp{found} field has value of @samp{1}.
26393 The information about the frame corresponding to the found trace
26394 frame. This field is present only if a trace frame was found.
26395 @xref{GDB/MI Frame Information}, for description of this field.
26399 @subsubheading @value{GDBN} Command
26401 The corresponding @value{GDBN} command is @samp{tfind}.
26403 @subheading -trace-define-variable
26404 @findex -trace-define-variable
26406 @subsubheading Synopsis
26409 -trace-define-variable @var{name} [ @var{value} ]
26412 Create trace variable @var{name} if it does not exist. If
26413 @var{value} is specified, sets the initial value of the specified
26414 trace variable to that value. Note that the @var{name} should start
26415 with the @samp{$} character.
26417 @subsubheading @value{GDBN} Command
26419 The corresponding @value{GDBN} command is @samp{tvariable}.
26421 @subheading -trace-list-variables
26422 @findex -trace-list-variables
26424 @subsubheading Synopsis
26427 -trace-list-variables
26430 Return a table of all defined trace variables. Each element of the
26431 table has the following fields:
26435 The name of the trace variable. This field is always present.
26438 The initial value. This is a 64-bit signed integer. This
26439 field is always present.
26442 The value the trace variable has at the moment. This is a 64-bit
26443 signed integer. This field is absent iff current value is
26444 not defined, for example if the trace was never run, or is
26449 @subsubheading @value{GDBN} Command
26451 The corresponding @value{GDBN} command is @samp{tvariables}.
26453 @subsubheading Example
26457 -trace-list-variables
26458 ^done,trace-variables=@{nr_rows="1",nr_cols="3",
26459 hdr=[@{width="15",alignment="-1",col_name="name",colhdr="Name"@},
26460 @{width="11",alignment="-1",col_name="initial",colhdr="Initial"@},
26461 @{width="11",alignment="-1",col_name="current",colhdr="Current"@}],
26462 body=[variable=@{name="$trace_timestamp",initial="0"@}
26463 variable=@{name="$foo",initial="10",current="15"@}]@}
26467 @subheading -trace-save
26468 @findex -trace-save
26470 @subsubheading Synopsis
26473 -trace-save [-r ] @var{filename}
26476 Saves the collected trace data to @var{filename}. Without the
26477 @samp{-r} option, the data is downloaded from the target and saved
26478 in a local file. With the @samp{-r} option the target is asked
26479 to perform the save.
26481 @subsubheading @value{GDBN} Command
26483 The corresponding @value{GDBN} command is @samp{tsave}.
26486 @subheading -trace-start
26487 @findex -trace-start
26489 @subsubheading Synopsis
26495 Starts a tracing experiments. The result of this command does not
26498 @subsubheading @value{GDBN} Command
26500 The corresponding @value{GDBN} command is @samp{tstart}.
26502 @subheading -trace-status
26503 @findex -trace-status
26505 @subsubheading Synopsis
26511 Obtains the status of a tracing experiment. The result may include
26512 the following fields:
26517 May have a value of either @samp{0}, when no tracing operations are
26518 supported, @samp{1}, when all tracing operations are supported, or
26519 @samp{file} when examining trace file. In the latter case, examining
26520 of trace frame is possible but new tracing experiement cannot be
26521 started. This field is always present.
26524 May have a value of either @samp{0} or @samp{1} depending on whether
26525 tracing experiement is in progress on target. This field is present
26526 if @samp{supported} field is not @samp{0}.
26529 Report the reason why the tracing was stopped last time. This field
26530 may be absent iff tracing was never stopped on target yet. The
26531 value of @samp{request} means the tracing was stopped as result of
26532 the @code{-trace-stop} command. The value of @samp{overflow} means
26533 the tracing buffer is full. The value of @samp{disconnection} means
26534 tracing was automatically stopped when @value{GDBN} has disconnected.
26535 The value of @samp{passcount} means tracing was stopped when a
26536 tracepoint was passed a maximal number of times for that tracepoint.
26537 This field is present if @samp{supported} field is not @samp{0}.
26539 @item stopping-tracepoint
26540 The number of tracepoint whose passcount as exceeded. This field is
26541 present iff the @samp{stop-reason} field has the value of
26545 @itemx frames-created
26546 The @samp{frames} field is a count of the total number of trace frames
26547 in the trace buffer, while @samp{frames-created} is the total created
26548 during the run, including ones that were discarded, such as when a
26549 circular trace buffer filled up. Both fields are optional.
26553 These fields tell the current size of the tracing buffer and the
26554 remaining space. These fields are optional.
26557 The value of the circular trace buffer flag. @code{1} means that the
26558 trace buffer is circular and old trace frames will be discarded if
26559 necessary to make room, @code{0} means that the trace buffer is linear
26563 The value of the disconnected tracing flag. @code{1} means that
26564 tracing will continue after @value{GDBN} disconnects, @code{0} means
26565 that the trace run will stop.
26569 @subsubheading @value{GDBN} Command
26571 The corresponding @value{GDBN} command is @samp{tstatus}.
26573 @subheading -trace-stop
26574 @findex -trace-stop
26576 @subsubheading Synopsis
26582 Stops a tracing experiment. The result of this command has the same
26583 fields as @code{-trace-status}, except that the @samp{supported} and
26584 @samp{running} fields are not output.
26586 @subsubheading @value{GDBN} Command
26588 The corresponding @value{GDBN} command is @samp{tstop}.
26591 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
26592 @node GDB/MI Symbol Query
26593 @section @sc{gdb/mi} Symbol Query Commands
26597 @subheading The @code{-symbol-info-address} Command
26598 @findex -symbol-info-address
26600 @subsubheading Synopsis
26603 -symbol-info-address @var{symbol}
26606 Describe where @var{symbol} is stored.
26608 @subsubheading @value{GDBN} Command
26610 The corresponding @value{GDBN} command is @samp{info address}.
26612 @subsubheading Example
26616 @subheading The @code{-symbol-info-file} Command
26617 @findex -symbol-info-file
26619 @subsubheading Synopsis
26625 Show the file for the symbol.
26627 @subsubheading @value{GDBN} Command
26629 There's no equivalent @value{GDBN} command. @code{gdbtk} has
26630 @samp{gdb_find_file}.
26632 @subsubheading Example
26636 @subheading The @code{-symbol-info-function} Command
26637 @findex -symbol-info-function
26639 @subsubheading Synopsis
26642 -symbol-info-function
26645 Show which function the symbol lives in.
26647 @subsubheading @value{GDBN} Command
26649 @samp{gdb_get_function} in @code{gdbtk}.
26651 @subsubheading Example
26655 @subheading The @code{-symbol-info-line} Command
26656 @findex -symbol-info-line
26658 @subsubheading Synopsis
26664 Show the core addresses of the code for a source line.
26666 @subsubheading @value{GDBN} Command
26668 The corresponding @value{GDBN} command is @samp{info line}.
26669 @code{gdbtk} has the @samp{gdb_get_line} and @samp{gdb_get_file} commands.
26671 @subsubheading Example
26675 @subheading The @code{-symbol-info-symbol} Command
26676 @findex -symbol-info-symbol
26678 @subsubheading Synopsis
26681 -symbol-info-symbol @var{addr}
26684 Describe what symbol is at location @var{addr}.
26686 @subsubheading @value{GDBN} Command
26688 The corresponding @value{GDBN} command is @samp{info symbol}.
26690 @subsubheading Example
26694 @subheading The @code{-symbol-list-functions} Command
26695 @findex -symbol-list-functions
26697 @subsubheading Synopsis
26700 -symbol-list-functions
26703 List the functions in the executable.
26705 @subsubheading @value{GDBN} Command
26707 @samp{info functions} in @value{GDBN}, @samp{gdb_listfunc} and
26708 @samp{gdb_search} in @code{gdbtk}.
26710 @subsubheading Example
26715 @subheading The @code{-symbol-list-lines} Command
26716 @findex -symbol-list-lines
26718 @subsubheading Synopsis
26721 -symbol-list-lines @var{filename}
26724 Print the list of lines that contain code and their associated program
26725 addresses for the given source filename. The entries are sorted in
26726 ascending PC order.
26728 @subsubheading @value{GDBN} Command
26730 There is no corresponding @value{GDBN} command.
26732 @subsubheading Example
26735 -symbol-list-lines basics.c
26736 ^done,lines=[@{pc="0x08048554",line="7"@},@{pc="0x0804855a",line="8"@}]
26742 @subheading The @code{-symbol-list-types} Command
26743 @findex -symbol-list-types
26745 @subsubheading Synopsis
26751 List all the type names.
26753 @subsubheading @value{GDBN} Command
26755 The corresponding commands are @samp{info types} in @value{GDBN},
26756 @samp{gdb_search} in @code{gdbtk}.
26758 @subsubheading Example
26762 @subheading The @code{-symbol-list-variables} Command
26763 @findex -symbol-list-variables
26765 @subsubheading Synopsis
26768 -symbol-list-variables
26771 List all the global and static variable names.
26773 @subsubheading @value{GDBN} Command
26775 @samp{info variables} in @value{GDBN}, @samp{gdb_search} in @code{gdbtk}.
26777 @subsubheading Example
26781 @subheading The @code{-symbol-locate} Command
26782 @findex -symbol-locate
26784 @subsubheading Synopsis
26790 @subsubheading @value{GDBN} Command
26792 @samp{gdb_loc} in @code{gdbtk}.
26794 @subsubheading Example
26798 @subheading The @code{-symbol-type} Command
26799 @findex -symbol-type
26801 @subsubheading Synopsis
26804 -symbol-type @var{variable}
26807 Show type of @var{variable}.
26809 @subsubheading @value{GDBN} Command
26811 The corresponding @value{GDBN} command is @samp{ptype}, @code{gdbtk} has
26812 @samp{gdb_obj_variable}.
26814 @subsubheading Example
26819 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
26820 @node GDB/MI File Commands
26821 @section @sc{gdb/mi} File Commands
26823 This section describes the GDB/MI commands to specify executable file names
26824 and to read in and obtain symbol table information.
26826 @subheading The @code{-file-exec-and-symbols} Command
26827 @findex -file-exec-and-symbols
26829 @subsubheading Synopsis
26832 -file-exec-and-symbols @var{file}
26835 Specify the executable file to be debugged. This file is the one from
26836 which the symbol table is also read. If no file is specified, the
26837 command clears the executable and symbol information. If breakpoints
26838 are set when using this command with no arguments, @value{GDBN} will produce
26839 error messages. Otherwise, no output is produced, except a completion
26842 @subsubheading @value{GDBN} Command
26844 The corresponding @value{GDBN} command is @samp{file}.
26846 @subsubheading Example
26850 -file-exec-and-symbols /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
26856 @subheading The @code{-file-exec-file} Command
26857 @findex -file-exec-file
26859 @subsubheading Synopsis
26862 -file-exec-file @var{file}
26865 Specify the executable file to be debugged. Unlike
26866 @samp{-file-exec-and-symbols}, the symbol table is @emph{not} read
26867 from this file. If used without argument, @value{GDBN} clears the information
26868 about the executable file. No output is produced, except a completion
26871 @subsubheading @value{GDBN} Command
26873 The corresponding @value{GDBN} command is @samp{exec-file}.
26875 @subsubheading Example
26879 -file-exec-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
26886 @subheading The @code{-file-list-exec-sections} Command
26887 @findex -file-list-exec-sections
26889 @subsubheading Synopsis
26892 -file-list-exec-sections
26895 List the sections of the current executable file.
26897 @subsubheading @value{GDBN} Command
26899 The @value{GDBN} command @samp{info file} shows, among the rest, the same
26900 information as this command. @code{gdbtk} has a corresponding command
26901 @samp{gdb_load_info}.
26903 @subsubheading Example
26908 @subheading The @code{-file-list-exec-source-file} Command
26909 @findex -file-list-exec-source-file
26911 @subsubheading Synopsis
26914 -file-list-exec-source-file
26917 List the line number, the current source file, and the absolute path
26918 to the current source file for the current executable. The macro
26919 information field has a value of @samp{1} or @samp{0} depending on
26920 whether or not the file includes preprocessor macro information.
26922 @subsubheading @value{GDBN} Command
26924 The @value{GDBN} equivalent is @samp{info source}
26926 @subsubheading Example
26930 123-file-list-exec-source-file
26931 123^done,line="1",file="foo.c",fullname="/home/bar/foo.c,macro-info="1"
26936 @subheading The @code{-file-list-exec-source-files} Command
26937 @findex -file-list-exec-source-files
26939 @subsubheading Synopsis
26942 -file-list-exec-source-files
26945 List the source files for the current executable.
26947 It will always output the filename, but only when @value{GDBN} can find
26948 the absolute file name of a source file, will it output the fullname.
26950 @subsubheading @value{GDBN} Command
26952 The @value{GDBN} equivalent is @samp{info sources}.
26953 @code{gdbtk} has an analogous command @samp{gdb_listfiles}.
26955 @subsubheading Example
26958 -file-list-exec-source-files
26960 @{file=foo.c,fullname=/home/foo.c@},
26961 @{file=/home/bar.c,fullname=/home/bar.c@},
26962 @{file=gdb_could_not_find_fullpath.c@}]
26967 @subheading The @code{-file-list-shared-libraries} Command
26968 @findex -file-list-shared-libraries
26970 @subsubheading Synopsis
26973 -file-list-shared-libraries
26976 List the shared libraries in the program.
26978 @subsubheading @value{GDBN} Command
26980 The corresponding @value{GDBN} command is @samp{info shared}.
26982 @subsubheading Example
26986 @subheading The @code{-file-list-symbol-files} Command
26987 @findex -file-list-symbol-files
26989 @subsubheading Synopsis
26992 -file-list-symbol-files
26997 @subsubheading @value{GDBN} Command
26999 The corresponding @value{GDBN} command is @samp{info file} (part of it).
27001 @subsubheading Example
27006 @subheading The @code{-file-symbol-file} Command
27007 @findex -file-symbol-file
27009 @subsubheading Synopsis
27012 -file-symbol-file @var{file}
27015 Read symbol table info from the specified @var{file} argument. When
27016 used without arguments, clears @value{GDBN}'s symbol table info. No output is
27017 produced, except for a completion notification.
27019 @subsubheading @value{GDBN} Command
27021 The corresponding @value{GDBN} command is @samp{symbol-file}.
27023 @subsubheading Example
27027 -file-symbol-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
27033 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
27034 @node GDB/MI Memory Overlay Commands
27035 @section @sc{gdb/mi} Memory Overlay Commands
27037 The memory overlay commands are not implemented.
27039 @c @subheading -overlay-auto
27041 @c @subheading -overlay-list-mapping-state
27043 @c @subheading -overlay-list-overlays
27045 @c @subheading -overlay-map
27047 @c @subheading -overlay-off
27049 @c @subheading -overlay-on
27051 @c @subheading -overlay-unmap
27053 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
27054 @node GDB/MI Signal Handling Commands
27055 @section @sc{gdb/mi} Signal Handling Commands
27057 Signal handling commands are not implemented.
27059 @c @subheading -signal-handle
27061 @c @subheading -signal-list-handle-actions
27063 @c @subheading -signal-list-signal-types
27067 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
27068 @node GDB/MI Target Manipulation
27069 @section @sc{gdb/mi} Target Manipulation Commands
27072 @subheading The @code{-target-attach} Command
27073 @findex -target-attach
27075 @subsubheading Synopsis
27078 -target-attach @var{pid} | @var{gid} | @var{file}
27081 Attach to a process @var{pid} or a file @var{file} outside of
27082 @value{GDBN}, or a thread group @var{gid}. If attaching to a thread
27083 group, the id previously returned by
27084 @samp{-list-thread-groups --available} must be used.
27086 @subsubheading @value{GDBN} Command
27088 The corresponding @value{GDBN} command is @samp{attach}.
27090 @subsubheading Example
27094 =thread-created,id="1"
27095 *stopped,thread-id="1",frame=@{addr="0xb7f7e410",func="bar",args=[]@}
27101 @subheading The @code{-target-compare-sections} Command
27102 @findex -target-compare-sections
27104 @subsubheading Synopsis
27107 -target-compare-sections [ @var{section} ]
27110 Compare data of section @var{section} on target to the exec file.
27111 Without the argument, all sections are compared.
27113 @subsubheading @value{GDBN} Command
27115 The @value{GDBN} equivalent is @samp{compare-sections}.
27117 @subsubheading Example
27122 @subheading The @code{-target-detach} Command
27123 @findex -target-detach
27125 @subsubheading Synopsis
27128 -target-detach [ @var{pid} | @var{gid} ]
27131 Detach from the remote target which normally resumes its execution.
27132 If either @var{pid} or @var{gid} is specified, detaches from either
27133 the specified process, or specified thread group. There's no output.
27135 @subsubheading @value{GDBN} Command
27137 The corresponding @value{GDBN} command is @samp{detach}.
27139 @subsubheading Example
27149 @subheading The @code{-target-disconnect} Command
27150 @findex -target-disconnect
27152 @subsubheading Synopsis
27158 Disconnect from the remote target. There's no output and the target is
27159 generally not resumed.
27161 @subsubheading @value{GDBN} Command
27163 The corresponding @value{GDBN} command is @samp{disconnect}.
27165 @subsubheading Example
27175 @subheading The @code{-target-download} Command
27176 @findex -target-download
27178 @subsubheading Synopsis
27184 Loads the executable onto the remote target.
27185 It prints out an update message every half second, which includes the fields:
27189 The name of the section.
27191 The size of what has been sent so far for that section.
27193 The size of the section.
27195 The total size of what was sent so far (the current and the previous sections).
27197 The size of the overall executable to download.
27201 Each message is sent as status record (@pxref{GDB/MI Output Syntax, ,
27202 @sc{gdb/mi} Output Syntax}).
27204 In addition, it prints the name and size of the sections, as they are
27205 downloaded. These messages include the following fields:
27209 The name of the section.
27211 The size of the section.
27213 The size of the overall executable to download.
27217 At the end, a summary is printed.
27219 @subsubheading @value{GDBN} Command
27221 The corresponding @value{GDBN} command is @samp{load}.
27223 @subsubheading Example
27225 Note: each status message appears on a single line. Here the messages
27226 have been broken down so that they can fit onto a page.
27231 +download,@{section=".text",section-size="6668",total-size="9880"@}
27232 +download,@{section=".text",section-sent="512",section-size="6668",
27233 total-sent="512",total-size="9880"@}
27234 +download,@{section=".text",section-sent="1024",section-size="6668",
27235 total-sent="1024",total-size="9880"@}
27236 +download,@{section=".text",section-sent="1536",section-size="6668",
27237 total-sent="1536",total-size="9880"@}
27238 +download,@{section=".text",section-sent="2048",section-size="6668",
27239 total-sent="2048",total-size="9880"@}
27240 +download,@{section=".text",section-sent="2560",section-size="6668",
27241 total-sent="2560",total-size="9880"@}
27242 +download,@{section=".text",section-sent="3072",section-size="6668",
27243 total-sent="3072",total-size="9880"@}
27244 +download,@{section=".text",section-sent="3584",section-size="6668",
27245 total-sent="3584",total-size="9880"@}
27246 +download,@{section=".text",section-sent="4096",section-size="6668",
27247 total-sent="4096",total-size="9880"@}
27248 +download,@{section=".text",section-sent="4608",section-size="6668",
27249 total-sent="4608",total-size="9880"@}
27250 +download,@{section=".text",section-sent="5120",section-size="6668",
27251 total-sent="5120",total-size="9880"@}
27252 +download,@{section=".text",section-sent="5632",section-size="6668",
27253 total-sent="5632",total-size="9880"@}
27254 +download,@{section=".text",section-sent="6144",section-size="6668",
27255 total-sent="6144",total-size="9880"@}
27256 +download,@{section=".text",section-sent="6656",section-size="6668",
27257 total-sent="6656",total-size="9880"@}
27258 +download,@{section=".init",section-size="28",total-size="9880"@}
27259 +download,@{section=".fini",section-size="28",total-size="9880"@}
27260 +download,@{section=".data",section-size="3156",total-size="9880"@}
27261 +download,@{section=".data",section-sent="512",section-size="3156",
27262 total-sent="7236",total-size="9880"@}
27263 +download,@{section=".data",section-sent="1024",section-size="3156",
27264 total-sent="7748",total-size="9880"@}
27265 +download,@{section=".data",section-sent="1536",section-size="3156",
27266 total-sent="8260",total-size="9880"@}
27267 +download,@{section=".data",section-sent="2048",section-size="3156",
27268 total-sent="8772",total-size="9880"@}
27269 +download,@{section=".data",section-sent="2560",section-size="3156",
27270 total-sent="9284",total-size="9880"@}
27271 +download,@{section=".data",section-sent="3072",section-size="3156",
27272 total-sent="9796",total-size="9880"@}
27273 ^done,address="0x10004",load-size="9880",transfer-rate="6586",
27280 @subheading The @code{-target-exec-status} Command
27281 @findex -target-exec-status
27283 @subsubheading Synopsis
27286 -target-exec-status
27289 Provide information on the state of the target (whether it is running or
27290 not, for instance).
27292 @subsubheading @value{GDBN} Command
27294 There's no equivalent @value{GDBN} command.
27296 @subsubheading Example
27300 @subheading The @code{-target-list-available-targets} Command
27301 @findex -target-list-available-targets
27303 @subsubheading Synopsis
27306 -target-list-available-targets
27309 List the possible targets to connect to.
27311 @subsubheading @value{GDBN} Command
27313 The corresponding @value{GDBN} command is @samp{help target}.
27315 @subsubheading Example
27319 @subheading The @code{-target-list-current-targets} Command
27320 @findex -target-list-current-targets
27322 @subsubheading Synopsis
27325 -target-list-current-targets
27328 Describe the current target.
27330 @subsubheading @value{GDBN} Command
27332 The corresponding information is printed by @samp{info file} (among
27335 @subsubheading Example
27339 @subheading The @code{-target-list-parameters} Command
27340 @findex -target-list-parameters
27342 @subsubheading Synopsis
27345 -target-list-parameters
27351 @subsubheading @value{GDBN} Command
27355 @subsubheading Example
27359 @subheading The @code{-target-select} Command
27360 @findex -target-select
27362 @subsubheading Synopsis
27365 -target-select @var{type} @var{parameters @dots{}}
27368 Connect @value{GDBN} to the remote target. This command takes two args:
27372 The type of target, for instance @samp{remote}, etc.
27373 @item @var{parameters}
27374 Device names, host names and the like. @xref{Target Commands, ,
27375 Commands for Managing Targets}, for more details.
27378 The output is a connection notification, followed by the address at
27379 which the target program is, in the following form:
27382 ^connected,addr="@var{address}",func="@var{function name}",
27383 args=[@var{arg list}]
27386 @subsubheading @value{GDBN} Command
27388 The corresponding @value{GDBN} command is @samp{target}.
27390 @subsubheading Example
27394 -target-select remote /dev/ttya
27395 ^connected,addr="0xfe00a300",func="??",args=[]
27399 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
27400 @node GDB/MI File Transfer Commands
27401 @section @sc{gdb/mi} File Transfer Commands
27404 @subheading The @code{-target-file-put} Command
27405 @findex -target-file-put
27407 @subsubheading Synopsis
27410 -target-file-put @var{hostfile} @var{targetfile}
27413 Copy file @var{hostfile} from the host system (the machine running
27414 @value{GDBN}) to @var{targetfile} on the target system.
27416 @subsubheading @value{GDBN} Command
27418 The corresponding @value{GDBN} command is @samp{remote put}.
27420 @subsubheading Example
27424 -target-file-put localfile remotefile
27430 @subheading The @code{-target-file-get} Command
27431 @findex -target-file-get
27433 @subsubheading Synopsis
27436 -target-file-get @var{targetfile} @var{hostfile}
27439 Copy file @var{targetfile} from the target system to @var{hostfile}
27440 on the host system.
27442 @subsubheading @value{GDBN} Command
27444 The corresponding @value{GDBN} command is @samp{remote get}.
27446 @subsubheading Example
27450 -target-file-get remotefile localfile
27456 @subheading The @code{-target-file-delete} Command
27457 @findex -target-file-delete
27459 @subsubheading Synopsis
27462 -target-file-delete @var{targetfile}
27465 Delete @var{targetfile} from the target system.
27467 @subsubheading @value{GDBN} Command
27469 The corresponding @value{GDBN} command is @samp{remote delete}.
27471 @subsubheading Example
27475 -target-file-delete remotefile
27481 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
27482 @node GDB/MI Miscellaneous Commands
27483 @section Miscellaneous @sc{gdb/mi} Commands
27485 @c @subheading -gdb-complete
27487 @subheading The @code{-gdb-exit} Command
27490 @subsubheading Synopsis
27496 Exit @value{GDBN} immediately.
27498 @subsubheading @value{GDBN} Command
27500 Approximately corresponds to @samp{quit}.
27502 @subsubheading Example
27512 @subheading The @code{-exec-abort} Command
27513 @findex -exec-abort
27515 @subsubheading Synopsis
27521 Kill the inferior running program.
27523 @subsubheading @value{GDBN} Command
27525 The corresponding @value{GDBN} command is @samp{kill}.
27527 @subsubheading Example
27532 @subheading The @code{-gdb-set} Command
27535 @subsubheading Synopsis
27541 Set an internal @value{GDBN} variable.
27542 @c IS THIS A DOLLAR VARIABLE? OR SOMETHING LIKE ANNOTATE ?????
27544 @subsubheading @value{GDBN} Command
27546 The corresponding @value{GDBN} command is @samp{set}.
27548 @subsubheading Example
27558 @subheading The @code{-gdb-show} Command
27561 @subsubheading Synopsis
27567 Show the current value of a @value{GDBN} variable.
27569 @subsubheading @value{GDBN} Command
27571 The corresponding @value{GDBN} command is @samp{show}.
27573 @subsubheading Example
27582 @c @subheading -gdb-source
27585 @subheading The @code{-gdb-version} Command
27586 @findex -gdb-version
27588 @subsubheading Synopsis
27594 Show version information for @value{GDBN}. Used mostly in testing.
27596 @subsubheading @value{GDBN} Command
27598 The @value{GDBN} equivalent is @samp{show version}. @value{GDBN} by
27599 default shows this information when you start an interactive session.
27601 @subsubheading Example
27603 @c This example modifies the actual output from GDB to avoid overfull
27609 ~Copyright 2000 Free Software Foundation, Inc.
27610 ~GDB is free software, covered by the GNU General Public License, and
27611 ~you are welcome to change it and/or distribute copies of it under
27612 ~ certain conditions.
27613 ~Type "show copying" to see the conditions.
27614 ~There is absolutely no warranty for GDB. Type "show warranty" for
27616 ~This GDB was configured as
27617 "--host=sparc-sun-solaris2.5.1 --target=ppc-eabi".
27622 @subheading The @code{-list-features} Command
27623 @findex -list-features
27625 Returns a list of particular features of the MI protocol that
27626 this version of gdb implements. A feature can be a command,
27627 or a new field in an output of some command, or even an
27628 important bugfix. While a frontend can sometimes detect presence
27629 of a feature at runtime, it is easier to perform detection at debugger
27632 The command returns a list of strings, with each string naming an
27633 available feature. Each returned string is just a name, it does not
27634 have any internal structure. The list of possible feature names
27640 (gdb) -list-features
27641 ^done,result=["feature1","feature2"]
27644 The current list of features is:
27647 @item frozen-varobjs
27648 Indicates presence of the @code{-var-set-frozen} command, as well
27649 as possible presense of the @code{frozen} field in the output
27650 of @code{-varobj-create}.
27651 @item pending-breakpoints
27652 Indicates presence of the @option{-f} option to the @code{-break-insert} command.
27654 Indicates presence of Python scripting support, Python-based
27655 pretty-printing commands, and possible presence of the
27656 @samp{display_hint} field in the output of @code{-var-list-children}
27658 Indicates presence of the @code{-thread-info} command.
27662 @subheading The @code{-list-target-features} Command
27663 @findex -list-target-features
27665 Returns a list of particular features that are supported by the
27666 target. Those features affect the permitted MI commands, but
27667 unlike the features reported by the @code{-list-features} command, the
27668 features depend on which target GDB is using at the moment. Whenever
27669 a target can change, due to commands such as @code{-target-select},
27670 @code{-target-attach} or @code{-exec-run}, the list of target features
27671 may change, and the frontend should obtain it again.
27675 (gdb) -list-features
27676 ^done,result=["async"]
27679 The current list of features is:
27683 Indicates that the target is capable of asynchronous command
27684 execution, which means that @value{GDBN} will accept further commands
27685 while the target is running.
27689 @subheading The @code{-list-thread-groups} Command
27690 @findex -list-thread-groups
27692 @subheading Synopsis
27695 -list-thread-groups [ --available ] [ --recurse 1 ] [ @var{group} ... ]
27698 Lists thread groups (@pxref{Thread groups}). When a single thread
27699 group is passed as the argument, lists the children of that group.
27700 When several thread group are passed, lists information about those
27701 thread groups. Without any parameters, lists information about all
27702 top-level thread groups.
27704 Normally, thread groups that are being debugged are reported.
27705 With the @samp{--available} option, @value{GDBN} reports thread groups
27706 available on the target.
27708 The output of this command may have either a @samp{threads} result or
27709 a @samp{groups} result. The @samp{thread} result has a list of tuples
27710 as value, with each tuple describing a thread (@pxref{GDB/MI Thread
27711 Information}). The @samp{groups} result has a list of tuples as value,
27712 each tuple describing a thread group. If top-level groups are
27713 requested (that is, no parameter is passed), or when several groups
27714 are passed, the output always has a @samp{groups} result. The format
27715 of the @samp{group} result is described below.
27717 To reduce the number of roundtrips it's possible to list thread groups
27718 together with their children, by passing the @samp{--recurse} option
27719 and the recursion depth. Presently, only recursion depth of 1 is
27720 permitted. If this option is present, then every reported thread group
27721 will also include its children, either as @samp{group} or
27722 @samp{threads} field.
27724 In general, any combination of option and parameters is permitted, with
27725 the following caveats:
27729 When a single thread group is passed, the output will typically
27730 be the @samp{threads} result. Because threads may not contain
27731 anything, the @samp{recurse} option will be ignored.
27734 When the @samp{--available} option is passed, limited information may
27735 be available. In particular, the list of threads of a process might
27736 be inaccessible. Further, specifying specific thread groups might
27737 not give any performance advantage over listing all thread groups.
27738 The frontend should assume that @samp{-list-thread-groups --available}
27739 is always an expensive operation and cache the results.
27743 The @samp{groups} result is a list of tuples, where each tuple may
27744 have the following fields:
27748 Identifier of the thread group. This field is always present.
27749 The identifier is an opaque string; frontends should not try to
27750 convert it to an integer, even though it might look like one.
27753 The type of the thread group. At present, only @samp{process} is a
27757 The target-specific process identifier. This field is only present
27758 for thread groups of type @samp{process} and only if the process exists.
27761 The number of children this thread group has. This field may be
27762 absent for an available thread group.
27765 This field has a list of tuples as value, each tuple describing a
27766 thread. It may be present if the @samp{--recurse} option is
27767 specified, and it's actually possible to obtain the threads.
27770 This field is a list of integers, each identifying a core that one
27771 thread of the group is running on. This field may be absent if
27772 such information is not available.
27775 The name of the executable file that corresponds to this thread group.
27776 The field is only present for thread groups of type @samp{process},
27777 and only if there is a corresponding executable file.
27781 @subheading Example
27785 -list-thread-groups
27786 ^done,groups=[@{id="17",type="process",pid="yyy",num_children="2"@}]
27787 -list-thread-groups 17
27788 ^done,threads=[@{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)",
27789 frame=@{level="0",addr="0xffffe410",func="__kernel_vsyscall",args=[]@},state="running"@},
27790 @{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
27791 frame=@{level="0",addr="0x0804891f",func="foo",args=[@{name="i",value="10"@}],
27792 file="/tmp/a.c",fullname="/tmp/a.c",line="158"@},state="running"@}]]
27793 -list-thread-groups --available
27794 ^done,groups=[@{id="17",type="process",pid="yyy",num_children="2",cores=[1,2]@}]
27795 -list-thread-groups --available --recurse 1
27796 ^done,groups=[@{id="17", types="process",pid="yyy",num_children="2",cores=[1,2],
27797 threads=[@{id="1",target-id="Thread 0xb7e14b90",cores=[1]@},
27798 @{id="2",target-id="Thread 0xb7e14b90",cores=[2]@}]@},..]
27799 -list-thread-groups --available --recurse 1 17 18
27800 ^done,groups=[@{id="17", types="process",pid="yyy",num_children="2",cores=[1,2],
27801 threads=[@{id="1",target-id="Thread 0xb7e14b90",cores=[1]@},
27802 @{id="2",target-id="Thread 0xb7e14b90",cores=[2]@}]@},...]
27806 @subheading The @code{-add-inferior} Command
27807 @findex -add-inferior
27809 @subheading Synopsis
27815 Creates a new inferior (@pxref{Inferiors and Programs}). The created
27816 inferior is not associated with any executable. Such association may
27817 be established with the @samp{-file-exec-and-symbols} command
27818 (@pxref{GDB/MI File Commands}). The command response has a single
27819 field, @samp{thread-group}, whose value is the identifier of the
27820 thread group corresponding to the new inferior.
27822 @subheading Example
27827 ^done,thread-group="i3"
27830 @subheading The @code{-interpreter-exec} Command
27831 @findex -interpreter-exec
27833 @subheading Synopsis
27836 -interpreter-exec @var{interpreter} @var{command}
27838 @anchor{-interpreter-exec}
27840 Execute the specified @var{command} in the given @var{interpreter}.
27842 @subheading @value{GDBN} Command
27844 The corresponding @value{GDBN} command is @samp{interpreter-exec}.
27846 @subheading Example
27850 -interpreter-exec console "break main"
27851 &"During symbol reading, couldn't parse type; debugger out of date?.\n"
27852 &"During symbol reading, bad structure-type format.\n"
27853 ~"Breakpoint 1 at 0x8074fc6: file ../../src/gdb/main.c, line 743.\n"
27858 @subheading The @code{-inferior-tty-set} Command
27859 @findex -inferior-tty-set
27861 @subheading Synopsis
27864 -inferior-tty-set /dev/pts/1
27867 Set terminal for future runs of the program being debugged.
27869 @subheading @value{GDBN} Command
27871 The corresponding @value{GDBN} command is @samp{set inferior-tty} /dev/pts/1.
27873 @subheading Example
27877 -inferior-tty-set /dev/pts/1
27882 @subheading The @code{-inferior-tty-show} Command
27883 @findex -inferior-tty-show
27885 @subheading Synopsis
27891 Show terminal for future runs of program being debugged.
27893 @subheading @value{GDBN} Command
27895 The corresponding @value{GDBN} command is @samp{show inferior-tty}.
27897 @subheading Example
27901 -inferior-tty-set /dev/pts/1
27905 ^done,inferior_tty_terminal="/dev/pts/1"
27909 @subheading The @code{-enable-timings} Command
27910 @findex -enable-timings
27912 @subheading Synopsis
27915 -enable-timings [yes | no]
27918 Toggle the printing of the wallclock, user and system times for an MI
27919 command as a field in its output. This command is to help frontend
27920 developers optimize the performance of their code. No argument is
27921 equivalent to @samp{yes}.
27923 @subheading @value{GDBN} Command
27927 @subheading Example
27935 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
27936 addr="0x080484ed",func="main",file="myprog.c",
27937 fullname="/home/nickrob/myprog.c",line="73",times="0"@},
27938 time=@{wallclock="0.05185",user="0.00800",system="0.00000"@}
27946 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0",
27947 frame=@{addr="0x080484ed",func="main",args=[@{name="argc",value="1"@},
27948 @{name="argv",value="0xbfb60364"@}],file="myprog.c",
27949 fullname="/home/nickrob/myprog.c",line="73"@}
27954 @chapter @value{GDBN} Annotations
27956 This chapter describes annotations in @value{GDBN}. Annotations were
27957 designed to interface @value{GDBN} to graphical user interfaces or other
27958 similar programs which want to interact with @value{GDBN} at a
27959 relatively high level.
27961 The annotation mechanism has largely been superseded by @sc{gdb/mi}
27965 This is Edition @value{EDITION}, @value{DATE}.
27969 * Annotations Overview:: What annotations are; the general syntax.
27970 * Server Prefix:: Issuing a command without affecting user state.
27971 * Prompting:: Annotations marking @value{GDBN}'s need for input.
27972 * Errors:: Annotations for error messages.
27973 * Invalidation:: Some annotations describe things now invalid.
27974 * Annotations for Running::
27975 Whether the program is running, how it stopped, etc.
27976 * Source Annotations:: Annotations describing source code.
27979 @node Annotations Overview
27980 @section What is an Annotation?
27981 @cindex annotations
27983 Annotations start with a newline character, two @samp{control-z}
27984 characters, and the name of the annotation. If there is no additional
27985 information associated with this annotation, the name of the annotation
27986 is followed immediately by a newline. If there is additional
27987 information, the name of the annotation is followed by a space, the
27988 additional information, and a newline. The additional information
27989 cannot contain newline characters.
27991 Any output not beginning with a newline and two @samp{control-z}
27992 characters denotes literal output from @value{GDBN}. Currently there is
27993 no need for @value{GDBN} to output a newline followed by two
27994 @samp{control-z} characters, but if there was such a need, the
27995 annotations could be extended with an @samp{escape} annotation which
27996 means those three characters as output.
27998 The annotation @var{level}, which is specified using the
27999 @option{--annotate} command line option (@pxref{Mode Options}), controls
28000 how much information @value{GDBN} prints together with its prompt,
28001 values of expressions, source lines, and other types of output. Level 0
28002 is for no annotations, level 1 is for use when @value{GDBN} is run as a
28003 subprocess of @sc{gnu} Emacs, level 3 is the maximum annotation suitable
28004 for programs that control @value{GDBN}, and level 2 annotations have
28005 been made obsolete (@pxref{Limitations, , Limitations of the Annotation
28006 Interface, annotate, GDB's Obsolete Annotations}).
28009 @kindex set annotate
28010 @item set annotate @var{level}
28011 The @value{GDBN} command @code{set annotate} sets the level of
28012 annotations to the specified @var{level}.
28014 @item show annotate
28015 @kindex show annotate
28016 Show the current annotation level.
28019 This chapter describes level 3 annotations.
28021 A simple example of starting up @value{GDBN} with annotations is:
28024 $ @kbd{gdb --annotate=3}
28026 Copyright 2003 Free Software Foundation, Inc.
28027 GDB is free software, covered by the GNU General Public License,
28028 and you are welcome to change it and/or distribute copies of it
28029 under certain conditions.
28030 Type "show copying" to see the conditions.
28031 There is absolutely no warranty for GDB. Type "show warranty"
28033 This GDB was configured as "i386-pc-linux-gnu"
28044 Here @samp{quit} is input to @value{GDBN}; the rest is output from
28045 @value{GDBN}. The three lines beginning @samp{^Z^Z} (where @samp{^Z}
28046 denotes a @samp{control-z} character) are annotations; the rest is
28047 output from @value{GDBN}.
28049 @node Server Prefix
28050 @section The Server Prefix
28051 @cindex server prefix
28053 If you prefix a command with @samp{server } then it will not affect
28054 the command history, nor will it affect @value{GDBN}'s notion of which
28055 command to repeat if @key{RET} is pressed on a line by itself. This
28056 means that commands can be run behind a user's back by a front-end in
28057 a transparent manner.
28059 The @code{server } prefix does not affect the recording of values into
28060 the value history; to print a value without recording it into the
28061 value history, use the @code{output} command instead of the
28062 @code{print} command.
28064 Using this prefix also disables confirmation requests
28065 (@pxref{confirmation requests}).
28068 @section Annotation for @value{GDBN} Input
28070 @cindex annotations for prompts
28071 When @value{GDBN} prompts for input, it annotates this fact so it is possible
28072 to know when to send output, when the output from a given command is
28075 Different kinds of input each have a different @dfn{input type}. Each
28076 input type has three annotations: a @code{pre-} annotation, which
28077 denotes the beginning of any prompt which is being output, a plain
28078 annotation, which denotes the end of the prompt, and then a @code{post-}
28079 annotation which denotes the end of any echo which may (or may not) be
28080 associated with the input. For example, the @code{prompt} input type
28081 features the following annotations:
28089 The input types are
28092 @findex pre-prompt annotation
28093 @findex prompt annotation
28094 @findex post-prompt annotation
28096 When @value{GDBN} is prompting for a command (the main @value{GDBN} prompt).
28098 @findex pre-commands annotation
28099 @findex commands annotation
28100 @findex post-commands annotation
28102 When @value{GDBN} prompts for a set of commands, like in the @code{commands}
28103 command. The annotations are repeated for each command which is input.
28105 @findex pre-overload-choice annotation
28106 @findex overload-choice annotation
28107 @findex post-overload-choice annotation
28108 @item overload-choice
28109 When @value{GDBN} wants the user to select between various overloaded functions.
28111 @findex pre-query annotation
28112 @findex query annotation
28113 @findex post-query annotation
28115 When @value{GDBN} wants the user to confirm a potentially dangerous operation.
28117 @findex pre-prompt-for-continue annotation
28118 @findex prompt-for-continue annotation
28119 @findex post-prompt-for-continue annotation
28120 @item prompt-for-continue
28121 When @value{GDBN} is asking the user to press return to continue. Note: Don't
28122 expect this to work well; instead use @code{set height 0} to disable
28123 prompting. This is because the counting of lines is buggy in the
28124 presence of annotations.
28129 @cindex annotations for errors, warnings and interrupts
28131 @findex quit annotation
28136 This annotation occurs right before @value{GDBN} responds to an interrupt.
28138 @findex error annotation
28143 This annotation occurs right before @value{GDBN} responds to an error.
28145 Quit and error annotations indicate that any annotations which @value{GDBN} was
28146 in the middle of may end abruptly. For example, if a
28147 @code{value-history-begin} annotation is followed by a @code{error}, one
28148 cannot expect to receive the matching @code{value-history-end}. One
28149 cannot expect not to receive it either, however; an error annotation
28150 does not necessarily mean that @value{GDBN} is immediately returning all the way
28153 @findex error-begin annotation
28154 A quit or error annotation may be preceded by
28160 Any output between that and the quit or error annotation is the error
28163 Warning messages are not yet annotated.
28164 @c If we want to change that, need to fix warning(), type_error(),
28165 @c range_error(), and possibly other places.
28168 @section Invalidation Notices
28170 @cindex annotations for invalidation messages
28171 The following annotations say that certain pieces of state may have
28175 @findex frames-invalid annotation
28176 @item ^Z^Zframes-invalid
28178 The frames (for example, output from the @code{backtrace} command) may
28181 @findex breakpoints-invalid annotation
28182 @item ^Z^Zbreakpoints-invalid
28184 The breakpoints may have changed. For example, the user just added or
28185 deleted a breakpoint.
28188 @node Annotations for Running
28189 @section Running the Program
28190 @cindex annotations for running programs
28192 @findex starting annotation
28193 @findex stopping annotation
28194 When the program starts executing due to a @value{GDBN} command such as
28195 @code{step} or @code{continue},
28201 is output. When the program stops,
28207 is output. Before the @code{stopped} annotation, a variety of
28208 annotations describe how the program stopped.
28211 @findex exited annotation
28212 @item ^Z^Zexited @var{exit-status}
28213 The program exited, and @var{exit-status} is the exit status (zero for
28214 successful exit, otherwise nonzero).
28216 @findex signalled annotation
28217 @findex signal-name annotation
28218 @findex signal-name-end annotation
28219 @findex signal-string annotation
28220 @findex signal-string-end annotation
28221 @item ^Z^Zsignalled
28222 The program exited with a signal. After the @code{^Z^Zsignalled}, the
28223 annotation continues:
28229 ^Z^Zsignal-name-end
28233 ^Z^Zsignal-string-end
28238 where @var{name} is the name of the signal, such as @code{SIGILL} or
28239 @code{SIGSEGV}, and @var{string} is the explanation of the signal, such
28240 as @code{Illegal Instruction} or @code{Segmentation fault}.
28241 @var{intro-text}, @var{middle-text}, and @var{end-text} are for the
28242 user's benefit and have no particular format.
28244 @findex signal annotation
28246 The syntax of this annotation is just like @code{signalled}, but @value{GDBN} is
28247 just saying that the program received the signal, not that it was
28248 terminated with it.
28250 @findex breakpoint annotation
28251 @item ^Z^Zbreakpoint @var{number}
28252 The program hit breakpoint number @var{number}.
28254 @findex watchpoint annotation
28255 @item ^Z^Zwatchpoint @var{number}
28256 The program hit watchpoint number @var{number}.
28259 @node Source Annotations
28260 @section Displaying Source
28261 @cindex annotations for source display
28263 @findex source annotation
28264 The following annotation is used instead of displaying source code:
28267 ^Z^Zsource @var{filename}:@var{line}:@var{character}:@var{middle}:@var{addr}
28270 where @var{filename} is an absolute file name indicating which source
28271 file, @var{line} is the line number within that file (where 1 is the
28272 first line in the file), @var{character} is the character position
28273 within the file (where 0 is the first character in the file) (for most
28274 debug formats this will necessarily point to the beginning of a line),
28275 @var{middle} is @samp{middle} if @var{addr} is in the middle of the
28276 line, or @samp{beg} if @var{addr} is at the beginning of the line, and
28277 @var{addr} is the address in the target program associated with the
28278 source which is being displayed. @var{addr} is in the form @samp{0x}
28279 followed by one or more lowercase hex digits (note that this does not
28280 depend on the language).
28282 @node JIT Interface
28283 @chapter JIT Compilation Interface
28284 @cindex just-in-time compilation
28285 @cindex JIT compilation interface
28287 This chapter documents @value{GDBN}'s @dfn{just-in-time} (JIT) compilation
28288 interface. A JIT compiler is a program or library that generates native
28289 executable code at runtime and executes it, usually in order to achieve good
28290 performance while maintaining platform independence.
28292 Programs that use JIT compilation are normally difficult to debug because
28293 portions of their code are generated at runtime, instead of being loaded from
28294 object files, which is where @value{GDBN} normally finds the program's symbols
28295 and debug information. In order to debug programs that use JIT compilation,
28296 @value{GDBN} has an interface that allows the program to register in-memory
28297 symbol files with @value{GDBN} at runtime.
28299 If you are using @value{GDBN} to debug a program that uses this interface, then
28300 it should work transparently so long as you have not stripped the binary. If
28301 you are developing a JIT compiler, then the interface is documented in the rest
28302 of this chapter. At this time, the only known client of this interface is the
28305 Broadly speaking, the JIT interface mirrors the dynamic loader interface. The
28306 JIT compiler communicates with @value{GDBN} by writing data into a global
28307 variable and calling a fuction at a well-known symbol. When @value{GDBN}
28308 attaches, it reads a linked list of symbol files from the global variable to
28309 find existing code, and puts a breakpoint in the function so that it can find
28310 out about additional code.
28313 * Declarations:: Relevant C struct declarations
28314 * Registering Code:: Steps to register code
28315 * Unregistering Code:: Steps to unregister code
28319 @section JIT Declarations
28321 These are the relevant struct declarations that a C program should include to
28322 implement the interface:
28332 struct jit_code_entry
28334 struct jit_code_entry *next_entry;
28335 struct jit_code_entry *prev_entry;
28336 const char *symfile_addr;
28337 uint64_t symfile_size;
28340 struct jit_descriptor
28343 /* This type should be jit_actions_t, but we use uint32_t
28344 to be explicit about the bitwidth. */
28345 uint32_t action_flag;
28346 struct jit_code_entry *relevant_entry;
28347 struct jit_code_entry *first_entry;
28350 /* GDB puts a breakpoint in this function. */
28351 void __attribute__((noinline)) __jit_debug_register_code() @{ @};
28353 /* Make sure to specify the version statically, because the
28354 debugger may check the version before we can set it. */
28355 struct jit_descriptor __jit_debug_descriptor = @{ 1, 0, 0, 0 @};
28358 If the JIT is multi-threaded, then it is important that the JIT synchronize any
28359 modifications to this global data properly, which can easily be done by putting
28360 a global mutex around modifications to these structures.
28362 @node Registering Code
28363 @section Registering Code
28365 To register code with @value{GDBN}, the JIT should follow this protocol:
28369 Generate an object file in memory with symbols and other desired debug
28370 information. The file must include the virtual addresses of the sections.
28373 Create a code entry for the file, which gives the start and size of the symbol
28377 Add it to the linked list in the JIT descriptor.
28380 Point the relevant_entry field of the descriptor at the entry.
28383 Set @code{action_flag} to @code{JIT_REGISTER} and call
28384 @code{__jit_debug_register_code}.
28387 When @value{GDBN} is attached and the breakpoint fires, @value{GDBN} uses the
28388 @code{relevant_entry} pointer so it doesn't have to walk the list looking for
28389 new code. However, the linked list must still be maintained in order to allow
28390 @value{GDBN} to attach to a running process and still find the symbol files.
28392 @node Unregistering Code
28393 @section Unregistering Code
28395 If code is freed, then the JIT should use the following protocol:
28399 Remove the code entry corresponding to the code from the linked list.
28402 Point the @code{relevant_entry} field of the descriptor at the code entry.
28405 Set @code{action_flag} to @code{JIT_UNREGISTER} and call
28406 @code{__jit_debug_register_code}.
28409 If the JIT frees or recompiles code without unregistering it, then @value{GDBN}
28410 and the JIT will leak the memory used for the associated symbol files.
28413 @chapter Reporting Bugs in @value{GDBN}
28414 @cindex bugs in @value{GDBN}
28415 @cindex reporting bugs in @value{GDBN}
28417 Your bug reports play an essential role in making @value{GDBN} reliable.
28419 Reporting a bug may help you by bringing a solution to your problem, or it
28420 may not. But in any case the principal function of a bug report is to help
28421 the entire community by making the next version of @value{GDBN} work better. Bug
28422 reports are your contribution to the maintenance of @value{GDBN}.
28424 In order for a bug report to serve its purpose, you must include the
28425 information that enables us to fix the bug.
28428 * Bug Criteria:: Have you found a bug?
28429 * Bug Reporting:: How to report bugs
28433 @section Have You Found a Bug?
28434 @cindex bug criteria
28436 If you are not sure whether you have found a bug, here are some guidelines:
28439 @cindex fatal signal
28440 @cindex debugger crash
28441 @cindex crash of debugger
28443 If the debugger gets a fatal signal, for any input whatever, that is a
28444 @value{GDBN} bug. Reliable debuggers never crash.
28446 @cindex error on valid input
28448 If @value{GDBN} produces an error message for valid input, that is a
28449 bug. (Note that if you're cross debugging, the problem may also be
28450 somewhere in the connection to the target.)
28452 @cindex invalid input
28454 If @value{GDBN} does not produce an error message for invalid input,
28455 that is a bug. However, you should note that your idea of
28456 ``invalid input'' might be our idea of ``an extension'' or ``support
28457 for traditional practice''.
28460 If you are an experienced user of debugging tools, your suggestions
28461 for improvement of @value{GDBN} are welcome in any case.
28464 @node Bug Reporting
28465 @section How to Report Bugs
28466 @cindex bug reports
28467 @cindex @value{GDBN} bugs, reporting
28469 A number of companies and individuals offer support for @sc{gnu} products.
28470 If you obtained @value{GDBN} from a support organization, we recommend you
28471 contact that organization first.
28473 You can find contact information for many support companies and
28474 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
28476 @c should add a web page ref...
28479 @ifset BUGURL_DEFAULT
28480 In any event, we also recommend that you submit bug reports for
28481 @value{GDBN}. The preferred method is to submit them directly using
28482 @uref{http://www.gnu.org/software/gdb/bugs/, @value{GDBN}'s Bugs web
28483 page}. Alternatively, the @email{bug-gdb@@gnu.org, e-mail gateway} can
28486 @strong{Do not send bug reports to @samp{info-gdb}, or to
28487 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
28488 not want to receive bug reports. Those that do have arranged to receive
28491 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
28492 serves as a repeater. The mailing list and the newsgroup carry exactly
28493 the same messages. Often people think of posting bug reports to the
28494 newsgroup instead of mailing them. This appears to work, but it has one
28495 problem which can be crucial: a newsgroup posting often lacks a mail
28496 path back to the sender. Thus, if we need to ask for more information,
28497 we may be unable to reach you. For this reason, it is better to send
28498 bug reports to the mailing list.
28500 @ifclear BUGURL_DEFAULT
28501 In any event, we also recommend that you submit bug reports for
28502 @value{GDBN} to @value{BUGURL}.
28506 The fundamental principle of reporting bugs usefully is this:
28507 @strong{report all the facts}. If you are not sure whether to state a
28508 fact or leave it out, state it!
28510 Often people omit facts because they think they know what causes the
28511 problem and assume that some details do not matter. Thus, you might
28512 assume that the name of the variable you use in an example does not matter.
28513 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
28514 stray memory reference which happens to fetch from the location where that
28515 name is stored in memory; perhaps, if the name were different, the contents
28516 of that location would fool the debugger into doing the right thing despite
28517 the bug. Play it safe and give a specific, complete example. That is the
28518 easiest thing for you to do, and the most helpful.
28520 Keep in mind that the purpose of a bug report is to enable us to fix the
28521 bug. It may be that the bug has been reported previously, but neither
28522 you nor we can know that unless your bug report is complete and
28525 Sometimes people give a few sketchy facts and ask, ``Does this ring a
28526 bell?'' Those bug reports are useless, and we urge everyone to
28527 @emph{refuse to respond to them} except to chide the sender to report
28530 To enable us to fix the bug, you should include all these things:
28534 The version of @value{GDBN}. @value{GDBN} announces it if you start
28535 with no arguments; you can also print it at any time using @code{show
28538 Without this, we will not know whether there is any point in looking for
28539 the bug in the current version of @value{GDBN}.
28542 The type of machine you are using, and the operating system name and
28546 What compiler (and its version) was used to compile @value{GDBN}---e.g.@:
28547 ``@value{GCC}--2.8.1''.
28550 What compiler (and its version) was used to compile the program you are
28551 debugging---e.g.@: ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
28552 C Compiler''. For @value{NGCC}, you can say @kbd{@value{GCC} --version}
28553 to get this information; for other compilers, see the documentation for
28557 The command arguments you gave the compiler to compile your example and
28558 observe the bug. For example, did you use @samp{-O}? To guarantee
28559 you will not omit something important, list them all. A copy of the
28560 Makefile (or the output from make) is sufficient.
28562 If we were to try to guess the arguments, we would probably guess wrong
28563 and then we might not encounter the bug.
28566 A complete input script, and all necessary source files, that will
28570 A description of what behavior you observe that you believe is
28571 incorrect. For example, ``It gets a fatal signal.''
28573 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
28574 will certainly notice it. But if the bug is incorrect output, we might
28575 not notice unless it is glaringly wrong. You might as well not give us
28576 a chance to make a mistake.
28578 Even if the problem you experience is a fatal signal, you should still
28579 say so explicitly. Suppose something strange is going on, such as, your
28580 copy of @value{GDBN} is out of synch, or you have encountered a bug in
28581 the C library on your system. (This has happened!) Your copy might
28582 crash and ours would not. If you told us to expect a crash, then when
28583 ours fails to crash, we would know that the bug was not happening for
28584 us. If you had not told us to expect a crash, then we would not be able
28585 to draw any conclusion from our observations.
28588 @cindex recording a session script
28589 To collect all this information, you can use a session recording program
28590 such as @command{script}, which is available on many Unix systems.
28591 Just run your @value{GDBN} session inside @command{script} and then
28592 include the @file{typescript} file with your bug report.
28594 Another way to record a @value{GDBN} session is to run @value{GDBN}
28595 inside Emacs and then save the entire buffer to a file.
28598 If you wish to suggest changes to the @value{GDBN} source, send us context
28599 diffs. If you even discuss something in the @value{GDBN} source, refer to
28600 it by context, not by line number.
28602 The line numbers in our development sources will not match those in your
28603 sources. Your line numbers would convey no useful information to us.
28607 Here are some things that are not necessary:
28611 A description of the envelope of the bug.
28613 Often people who encounter a bug spend a lot of time investigating
28614 which changes to the input file will make the bug go away and which
28615 changes will not affect it.
28617 This is often time consuming and not very useful, because the way we
28618 will find the bug is by running a single example under the debugger
28619 with breakpoints, not by pure deduction from a series of examples.
28620 We recommend that you save your time for something else.
28622 Of course, if you can find a simpler example to report @emph{instead}
28623 of the original one, that is a convenience for us. Errors in the
28624 output will be easier to spot, running under the debugger will take
28625 less time, and so on.
28627 However, simplification is not vital; if you do not want to do this,
28628 report the bug anyway and send us the entire test case you used.
28631 A patch for the bug.
28633 A patch for the bug does help us if it is a good one. But do not omit
28634 the necessary information, such as the test case, on the assumption that
28635 a patch is all we need. We might see problems with your patch and decide
28636 to fix the problem another way, or we might not understand it at all.
28638 Sometimes with a program as complicated as @value{GDBN} it is very hard to
28639 construct an example that will make the program follow a certain path
28640 through the code. If you do not send us the example, we will not be able
28641 to construct one, so we will not be able to verify that the bug is fixed.
28643 And if we cannot understand what bug you are trying to fix, or why your
28644 patch should be an improvement, we will not install it. A test case will
28645 help us to understand.
28648 A guess about what the bug is or what it depends on.
28650 Such guesses are usually wrong. Even we cannot guess right about such
28651 things without first using the debugger to find the facts.
28654 @c The readline documentation is distributed with the readline code
28655 @c and consists of the two following files:
28657 @c inc-hist.texinfo
28658 @c Use -I with makeinfo to point to the appropriate directory,
28659 @c environment var TEXINPUTS with TeX.
28660 @include rluser.texi
28661 @include inc-hist.texinfo
28664 @node Formatting Documentation
28665 @appendix Formatting Documentation
28667 @cindex @value{GDBN} reference card
28668 @cindex reference card
28669 The @value{GDBN} 4 release includes an already-formatted reference card, ready
28670 for printing with PostScript or Ghostscript, in the @file{gdb}
28671 subdirectory of the main source directory@footnote{In
28672 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
28673 release.}. If you can use PostScript or Ghostscript with your printer,
28674 you can print the reference card immediately with @file{refcard.ps}.
28676 The release also includes the source for the reference card. You
28677 can format it, using @TeX{}, by typing:
28683 The @value{GDBN} reference card is designed to print in @dfn{landscape}
28684 mode on US ``letter'' size paper;
28685 that is, on a sheet 11 inches wide by 8.5 inches
28686 high. You will need to specify this form of printing as an option to
28687 your @sc{dvi} output program.
28689 @cindex documentation
28691 All the documentation for @value{GDBN} comes as part of the machine-readable
28692 distribution. The documentation is written in Texinfo format, which is
28693 a documentation system that uses a single source file to produce both
28694 on-line information and a printed manual. You can use one of the Info
28695 formatting commands to create the on-line version of the documentation
28696 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
28698 @value{GDBN} includes an already formatted copy of the on-line Info
28699 version of this manual in the @file{gdb} subdirectory. The main Info
28700 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
28701 subordinate files matching @samp{gdb.info*} in the same directory. If
28702 necessary, you can print out these files, or read them with any editor;
28703 but they are easier to read using the @code{info} subsystem in @sc{gnu}
28704 Emacs or the standalone @code{info} program, available as part of the
28705 @sc{gnu} Texinfo distribution.
28707 If you want to format these Info files yourself, you need one of the
28708 Info formatting programs, such as @code{texinfo-format-buffer} or
28711 If you have @code{makeinfo} installed, and are in the top level
28712 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
28713 version @value{GDBVN}), you can make the Info file by typing:
28720 If you want to typeset and print copies of this manual, you need @TeX{},
28721 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
28722 Texinfo definitions file.
28724 @TeX{} is a typesetting program; it does not print files directly, but
28725 produces output files called @sc{dvi} files. To print a typeset
28726 document, you need a program to print @sc{dvi} files. If your system
28727 has @TeX{} installed, chances are it has such a program. The precise
28728 command to use depends on your system; @kbd{lpr -d} is common; another
28729 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
28730 require a file name without any extension or a @samp{.dvi} extension.
28732 @TeX{} also requires a macro definitions file called
28733 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
28734 written in Texinfo format. On its own, @TeX{} cannot either read or
28735 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
28736 and is located in the @file{gdb-@var{version-number}/texinfo}
28739 If you have @TeX{} and a @sc{dvi} printer program installed, you can
28740 typeset and print this manual. First switch to the @file{gdb}
28741 subdirectory of the main source directory (for example, to
28742 @file{gdb-@value{GDBVN}/gdb}) and type:
28748 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
28750 @node Installing GDB
28751 @appendix Installing @value{GDBN}
28752 @cindex installation
28755 * Requirements:: Requirements for building @value{GDBN}
28756 * Running Configure:: Invoking the @value{GDBN} @file{configure} script
28757 * Separate Objdir:: Compiling @value{GDBN} in another directory
28758 * Config Names:: Specifying names for hosts and targets
28759 * Configure Options:: Summary of options for configure
28760 * System-wide configuration:: Having a system-wide init file
28764 @section Requirements for Building @value{GDBN}
28765 @cindex building @value{GDBN}, requirements for
28767 Building @value{GDBN} requires various tools and packages to be available.
28768 Other packages will be used only if they are found.
28770 @heading Tools/Packages Necessary for Building @value{GDBN}
28772 @item ISO C90 compiler
28773 @value{GDBN} is written in ISO C90. It should be buildable with any
28774 working C90 compiler, e.g.@: GCC.
28778 @heading Tools/Packages Optional for Building @value{GDBN}
28782 @value{GDBN} can use the Expat XML parsing library. This library may be
28783 included with your operating system distribution; if it is not, you
28784 can get the latest version from @url{http://expat.sourceforge.net}.
28785 The @file{configure} script will search for this library in several
28786 standard locations; if it is installed in an unusual path, you can
28787 use the @option{--with-libexpat-prefix} option to specify its location.
28793 Remote protocol memory maps (@pxref{Memory Map Format})
28795 Target descriptions (@pxref{Target Descriptions})
28797 Remote shared library lists (@pxref{Library List Format})
28799 MS-Windows shared libraries (@pxref{Shared Libraries})
28803 @cindex compressed debug sections
28804 @value{GDBN} will use the @samp{zlib} library, if available, to read
28805 compressed debug sections. Some linkers, such as GNU gold, are capable
28806 of producing binaries with compressed debug sections. If @value{GDBN}
28807 is compiled with @samp{zlib}, it will be able to read the debug
28808 information in such binaries.
28810 The @samp{zlib} library is likely included with your operating system
28811 distribution; if it is not, you can get the latest version from
28812 @url{http://zlib.net}.
28815 @value{GDBN}'s features related to character sets (@pxref{Character
28816 Sets}) require a functioning @code{iconv} implementation. If you are
28817 on a GNU system, then this is provided by the GNU C Library. Some
28818 other systems also provide a working @code{iconv}.
28820 On systems with @code{iconv}, you can install GNU Libiconv. If you
28821 have previously installed Libiconv, you can use the
28822 @option{--with-libiconv-prefix} option to configure.
28824 @value{GDBN}'s top-level @file{configure} and @file{Makefile} will
28825 arrange to build Libiconv if a directory named @file{libiconv} appears
28826 in the top-most source directory. If Libiconv is built this way, and
28827 if the operating system does not provide a suitable @code{iconv}
28828 implementation, then the just-built library will automatically be used
28829 by @value{GDBN}. One easy way to set this up is to download GNU
28830 Libiconv, unpack it, and then rename the directory holding the
28831 Libiconv source code to @samp{libiconv}.
28834 @node Running Configure
28835 @section Invoking the @value{GDBN} @file{configure} Script
28836 @cindex configuring @value{GDBN}
28837 @value{GDBN} comes with a @file{configure} script that automates the process
28838 of preparing @value{GDBN} for installation; you can then use @code{make} to
28839 build the @code{gdb} program.
28841 @c irrelevant in info file; it's as current as the code it lives with.
28842 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
28843 look at the @file{README} file in the sources; we may have improved the
28844 installation procedures since publishing this manual.}
28847 The @value{GDBN} distribution includes all the source code you need for
28848 @value{GDBN} in a single directory, whose name is usually composed by
28849 appending the version number to @samp{gdb}.
28851 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
28852 @file{gdb-@value{GDBVN}} directory. That directory contains:
28855 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
28856 script for configuring @value{GDBN} and all its supporting libraries
28858 @item gdb-@value{GDBVN}/gdb
28859 the source specific to @value{GDBN} itself
28861 @item gdb-@value{GDBVN}/bfd
28862 source for the Binary File Descriptor library
28864 @item gdb-@value{GDBVN}/include
28865 @sc{gnu} include files
28867 @item gdb-@value{GDBVN}/libiberty
28868 source for the @samp{-liberty} free software library
28870 @item gdb-@value{GDBVN}/opcodes
28871 source for the library of opcode tables and disassemblers
28873 @item gdb-@value{GDBVN}/readline
28874 source for the @sc{gnu} command-line interface
28876 @item gdb-@value{GDBVN}/glob
28877 source for the @sc{gnu} filename pattern-matching subroutine
28879 @item gdb-@value{GDBVN}/mmalloc
28880 source for the @sc{gnu} memory-mapped malloc package
28883 The simplest way to configure and build @value{GDBN} is to run @file{configure}
28884 from the @file{gdb-@var{version-number}} source directory, which in
28885 this example is the @file{gdb-@value{GDBVN}} directory.
28887 First switch to the @file{gdb-@var{version-number}} source directory
28888 if you are not already in it; then run @file{configure}. Pass the
28889 identifier for the platform on which @value{GDBN} will run as an
28895 cd gdb-@value{GDBVN}
28896 ./configure @var{host}
28901 where @var{host} is an identifier such as @samp{sun4} or
28902 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
28903 (You can often leave off @var{host}; @file{configure} tries to guess the
28904 correct value by examining your system.)
28906 Running @samp{configure @var{host}} and then running @code{make} builds the
28907 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
28908 libraries, then @code{gdb} itself. The configured source files, and the
28909 binaries, are left in the corresponding source directories.
28912 @file{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
28913 system does not recognize this automatically when you run a different
28914 shell, you may need to run @code{sh} on it explicitly:
28917 sh configure @var{host}
28920 If you run @file{configure} from a directory that contains source
28921 directories for multiple libraries or programs, such as the
28922 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN},
28924 creates configuration files for every directory level underneath (unless
28925 you tell it not to, with the @samp{--norecursion} option).
28927 You should run the @file{configure} script from the top directory in the
28928 source tree, the @file{gdb-@var{version-number}} directory. If you run
28929 @file{configure} from one of the subdirectories, you will configure only
28930 that subdirectory. That is usually not what you want. In particular,
28931 if you run the first @file{configure} from the @file{gdb} subdirectory
28932 of the @file{gdb-@var{version-number}} directory, you will omit the
28933 configuration of @file{bfd}, @file{readline}, and other sibling
28934 directories of the @file{gdb} subdirectory. This leads to build errors
28935 about missing include files such as @file{bfd/bfd.h}.
28937 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
28938 However, you should make sure that the shell on your path (named by
28939 the @samp{SHELL} environment variable) is publicly readable. Remember
28940 that @value{GDBN} uses the shell to start your program---some systems refuse to
28941 let @value{GDBN} debug child processes whose programs are not readable.
28943 @node Separate Objdir
28944 @section Compiling @value{GDBN} in Another Directory
28946 If you want to run @value{GDBN} versions for several host or target machines,
28947 you need a different @code{gdb} compiled for each combination of
28948 host and target. @file{configure} is designed to make this easy by
28949 allowing you to generate each configuration in a separate subdirectory,
28950 rather than in the source directory. If your @code{make} program
28951 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
28952 @code{make} in each of these directories builds the @code{gdb}
28953 program specified there.
28955 To build @code{gdb} in a separate directory, run @file{configure}
28956 with the @samp{--srcdir} option to specify where to find the source.
28957 (You also need to specify a path to find @file{configure}
28958 itself from your working directory. If the path to @file{configure}
28959 would be the same as the argument to @samp{--srcdir}, you can leave out
28960 the @samp{--srcdir} option; it is assumed.)
28962 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
28963 separate directory for a Sun 4 like this:
28967 cd gdb-@value{GDBVN}
28970 ../gdb-@value{GDBVN}/configure sun4
28975 When @file{configure} builds a configuration using a remote source
28976 directory, it creates a tree for the binaries with the same structure
28977 (and using the same names) as the tree under the source directory. In
28978 the example, you'd find the Sun 4 library @file{libiberty.a} in the
28979 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
28980 @file{gdb-sun4/gdb}.
28982 Make sure that your path to the @file{configure} script has just one
28983 instance of @file{gdb} in it. If your path to @file{configure} looks
28984 like @file{../gdb-@value{GDBVN}/gdb/configure}, you are configuring only
28985 one subdirectory of @value{GDBN}, not the whole package. This leads to
28986 build errors about missing include files such as @file{bfd/bfd.h}.
28988 One popular reason to build several @value{GDBN} configurations in separate
28989 directories is to configure @value{GDBN} for cross-compiling (where
28990 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
28991 programs that run on another machine---the @dfn{target}).
28992 You specify a cross-debugging target by
28993 giving the @samp{--target=@var{target}} option to @file{configure}.
28995 When you run @code{make} to build a program or library, you must run
28996 it in a configured directory---whatever directory you were in when you
28997 called @file{configure} (or one of its subdirectories).
28999 The @code{Makefile} that @file{configure} generates in each source
29000 directory also runs recursively. If you type @code{make} in a source
29001 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
29002 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
29003 will build all the required libraries, and then build GDB.
29005 When you have multiple hosts or targets configured in separate
29006 directories, you can run @code{make} on them in parallel (for example,
29007 if they are NFS-mounted on each of the hosts); they will not interfere
29011 @section Specifying Names for Hosts and Targets
29013 The specifications used for hosts and targets in the @file{configure}
29014 script are based on a three-part naming scheme, but some short predefined
29015 aliases are also supported. The full naming scheme encodes three pieces
29016 of information in the following pattern:
29019 @var{architecture}-@var{vendor}-@var{os}
29022 For example, you can use the alias @code{sun4} as a @var{host} argument,
29023 or as the value for @var{target} in a @code{--target=@var{target}}
29024 option. The equivalent full name is @samp{sparc-sun-sunos4}.
29026 The @file{configure} script accompanying @value{GDBN} does not provide
29027 any query facility to list all supported host and target names or
29028 aliases. @file{configure} calls the Bourne shell script
29029 @code{config.sub} to map abbreviations to full names; you can read the
29030 script, if you wish, or you can use it to test your guesses on
29031 abbreviations---for example:
29034 % sh config.sub i386-linux
29036 % sh config.sub alpha-linux
29037 alpha-unknown-linux-gnu
29038 % sh config.sub hp9k700
29040 % sh config.sub sun4
29041 sparc-sun-sunos4.1.1
29042 % sh config.sub sun3
29043 m68k-sun-sunos4.1.1
29044 % sh config.sub i986v
29045 Invalid configuration `i986v': machine `i986v' not recognized
29049 @code{config.sub} is also distributed in the @value{GDBN} source
29050 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
29052 @node Configure Options
29053 @section @file{configure} Options
29055 Here is a summary of the @file{configure} options and arguments that
29056 are most often useful for building @value{GDBN}. @file{configure} also has
29057 several other options not listed here. @inforef{What Configure
29058 Does,,configure.info}, for a full explanation of @file{configure}.
29061 configure @r{[}--help@r{]}
29062 @r{[}--prefix=@var{dir}@r{]}
29063 @r{[}--exec-prefix=@var{dir}@r{]}
29064 @r{[}--srcdir=@var{dirname}@r{]}
29065 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
29066 @r{[}--target=@var{target}@r{]}
29071 You may introduce options with a single @samp{-} rather than
29072 @samp{--} if you prefer; but you may abbreviate option names if you use
29077 Display a quick summary of how to invoke @file{configure}.
29079 @item --prefix=@var{dir}
29080 Configure the source to install programs and files under directory
29083 @item --exec-prefix=@var{dir}
29084 Configure the source to install programs under directory
29087 @c avoid splitting the warning from the explanation:
29089 @item --srcdir=@var{dirname}
29090 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
29091 @code{make} that implements the @code{VPATH} feature.}@*
29092 Use this option to make configurations in directories separate from the
29093 @value{GDBN} source directories. Among other things, you can use this to
29094 build (or maintain) several configurations simultaneously, in separate
29095 directories. @file{configure} writes configuration-specific files in
29096 the current directory, but arranges for them to use the source in the
29097 directory @var{dirname}. @file{configure} creates directories under
29098 the working directory in parallel to the source directories below
29101 @item --norecursion
29102 Configure only the directory level where @file{configure} is executed; do not
29103 propagate configuration to subdirectories.
29105 @item --target=@var{target}
29106 Configure @value{GDBN} for cross-debugging programs running on the specified
29107 @var{target}. Without this option, @value{GDBN} is configured to debug
29108 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
29110 There is no convenient way to generate a list of all available targets.
29112 @item @var{host} @dots{}
29113 Configure @value{GDBN} to run on the specified @var{host}.
29115 There is no convenient way to generate a list of all available hosts.
29118 There are many other options available as well, but they are generally
29119 needed for special purposes only.
29121 @node System-wide configuration
29122 @section System-wide configuration and settings
29123 @cindex system-wide init file
29125 @value{GDBN} can be configured to have a system-wide init file;
29126 this file will be read and executed at startup (@pxref{Startup, , What
29127 @value{GDBN} does during startup}).
29129 Here is the corresponding configure option:
29132 @item --with-system-gdbinit=@var{file}
29133 Specify that the default location of the system-wide init file is
29137 If @value{GDBN} has been configured with the option @option{--prefix=$prefix},
29138 it may be subject to relocation. Two possible cases:
29142 If the default location of this init file contains @file{$prefix},
29143 it will be subject to relocation. Suppose that the configure options
29144 are @option{--prefix=$prefix --with-system-gdbinit=$prefix/etc/gdbinit};
29145 if @value{GDBN} is moved from @file{$prefix} to @file{$install}, the system
29146 init file is looked for as @file{$install/etc/gdbinit} instead of
29147 @file{$prefix/etc/gdbinit}.
29150 By contrast, if the default location does not contain the prefix,
29151 it will not be relocated. E.g.@: if @value{GDBN} has been configured with
29152 @option{--prefix=/usr/local --with-system-gdbinit=/usr/share/gdb/gdbinit},
29153 then @value{GDBN} will always look for @file{/usr/share/gdb/gdbinit},
29154 wherever @value{GDBN} is installed.
29157 @node Maintenance Commands
29158 @appendix Maintenance Commands
29159 @cindex maintenance commands
29160 @cindex internal commands
29162 In addition to commands intended for @value{GDBN} users, @value{GDBN}
29163 includes a number of commands intended for @value{GDBN} developers,
29164 that are not documented elsewhere in this manual. These commands are
29165 provided here for reference. (For commands that turn on debugging
29166 messages, see @ref{Debugging Output}.)
29169 @kindex maint agent
29170 @kindex maint agent-eval
29171 @item maint agent @var{expression}
29172 @itemx maint agent-eval @var{expression}
29173 Translate the given @var{expression} into remote agent bytecodes.
29174 This command is useful for debugging the Agent Expression mechanism
29175 (@pxref{Agent Expressions}). The @samp{agent} version produces an
29176 expression useful for data collection, such as by tracepoints, while
29177 @samp{maint agent-eval} produces an expression that evaluates directly
29178 to a result. For instance, a collection expression for @code{globa +
29179 globb} will include bytecodes to record four bytes of memory at each
29180 of the addresses of @code{globa} and @code{globb}, while discarding
29181 the result of the addition, while an evaluation expression will do the
29182 addition and return the sum.
29184 @kindex maint info breakpoints
29185 @item @anchor{maint info breakpoints}maint info breakpoints
29186 Using the same format as @samp{info breakpoints}, display both the
29187 breakpoints you've set explicitly, and those @value{GDBN} is using for
29188 internal purposes. Internal breakpoints are shown with negative
29189 breakpoint numbers. The type column identifies what kind of breakpoint
29194 Normal, explicitly set breakpoint.
29197 Normal, explicitly set watchpoint.
29200 Internal breakpoint, used to handle correctly stepping through
29201 @code{longjmp} calls.
29203 @item longjmp resume
29204 Internal breakpoint at the target of a @code{longjmp}.
29207 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
29210 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
29213 Shared library events.
29217 @kindex set displaced-stepping
29218 @kindex show displaced-stepping
29219 @cindex displaced stepping support
29220 @cindex out-of-line single-stepping
29221 @item set displaced-stepping
29222 @itemx show displaced-stepping
29223 Control whether or not @value{GDBN} will do @dfn{displaced stepping}
29224 if the target supports it. Displaced stepping is a way to single-step
29225 over breakpoints without removing them from the inferior, by executing
29226 an out-of-line copy of the instruction that was originally at the
29227 breakpoint location. It is also known as out-of-line single-stepping.
29230 @item set displaced-stepping on
29231 If the target architecture supports it, @value{GDBN} will use
29232 displaced stepping to step over breakpoints.
29234 @item set displaced-stepping off
29235 @value{GDBN} will not use displaced stepping to step over breakpoints,
29236 even if such is supported by the target architecture.
29238 @cindex non-stop mode, and @samp{set displaced-stepping}
29239 @item set displaced-stepping auto
29240 This is the default mode. @value{GDBN} will use displaced stepping
29241 only if non-stop mode is active (@pxref{Non-Stop Mode}) and the target
29242 architecture supports displaced stepping.
29245 @kindex maint check-symtabs
29246 @item maint check-symtabs
29247 Check the consistency of psymtabs and symtabs.
29249 @kindex maint cplus first_component
29250 @item maint cplus first_component @var{name}
29251 Print the first C@t{++} class/namespace component of @var{name}.
29253 @kindex maint cplus namespace
29254 @item maint cplus namespace
29255 Print the list of possible C@t{++} namespaces.
29257 @kindex maint demangle
29258 @item maint demangle @var{name}
29259 Demangle a C@t{++} or Objective-C mangled @var{name}.
29261 @kindex maint deprecate
29262 @kindex maint undeprecate
29263 @cindex deprecated commands
29264 @item maint deprecate @var{command} @r{[}@var{replacement}@r{]}
29265 @itemx maint undeprecate @var{command}
29266 Deprecate or undeprecate the named @var{command}. Deprecated commands
29267 cause @value{GDBN} to issue a warning when you use them. The optional
29268 argument @var{replacement} says which newer command should be used in
29269 favor of the deprecated one; if it is given, @value{GDBN} will mention
29270 the replacement as part of the warning.
29272 @kindex maint dump-me
29273 @item maint dump-me
29274 @cindex @code{SIGQUIT} signal, dump core of @value{GDBN}
29275 Cause a fatal signal in the debugger and force it to dump its core.
29276 This is supported only on systems which support aborting a program
29277 with the @code{SIGQUIT} signal.
29279 @kindex maint internal-error
29280 @kindex maint internal-warning
29281 @item maint internal-error @r{[}@var{message-text}@r{]}
29282 @itemx maint internal-warning @r{[}@var{message-text}@r{]}
29283 Cause @value{GDBN} to call the internal function @code{internal_error}
29284 or @code{internal_warning} and hence behave as though an internal error
29285 or internal warning has been detected. In addition to reporting the
29286 internal problem, these functions give the user the opportunity to
29287 either quit @value{GDBN} or create a core file of the current
29288 @value{GDBN} session.
29290 These commands take an optional parameter @var{message-text} that is
29291 used as the text of the error or warning message.
29293 Here's an example of using @code{internal-error}:
29296 (@value{GDBP}) @kbd{maint internal-error testing, 1, 2}
29297 @dots{}/maint.c:121: internal-error: testing, 1, 2
29298 A problem internal to GDB has been detected. Further
29299 debugging may prove unreliable.
29300 Quit this debugging session? (y or n) @kbd{n}
29301 Create a core file? (y or n) @kbd{n}
29305 @cindex @value{GDBN} internal error
29306 @cindex internal errors, control of @value{GDBN} behavior
29308 @kindex maint set internal-error
29309 @kindex maint show internal-error
29310 @kindex maint set internal-warning
29311 @kindex maint show internal-warning
29312 @item maint set internal-error @var{action} [ask|yes|no]
29313 @itemx maint show internal-error @var{action}
29314 @itemx maint set internal-warning @var{action} [ask|yes|no]
29315 @itemx maint show internal-warning @var{action}
29316 When @value{GDBN} reports an internal problem (error or warning) it
29317 gives the user the opportunity to both quit @value{GDBN} and create a
29318 core file of the current @value{GDBN} session. These commands let you
29319 override the default behaviour for each particular @var{action},
29320 described in the table below.
29324 You can specify that @value{GDBN} should always (yes) or never (no)
29325 quit. The default is to ask the user what to do.
29328 You can specify that @value{GDBN} should always (yes) or never (no)
29329 create a core file. The default is to ask the user what to do.
29332 @kindex maint packet
29333 @item maint packet @var{text}
29334 If @value{GDBN} is talking to an inferior via the serial protocol,
29335 then this command sends the string @var{text} to the inferior, and
29336 displays the response packet. @value{GDBN} supplies the initial
29337 @samp{$} character, the terminating @samp{#} character, and the
29340 @kindex maint print architecture
29341 @item maint print architecture @r{[}@var{file}@r{]}
29342 Print the entire architecture configuration. The optional argument
29343 @var{file} names the file where the output goes.
29345 @kindex maint print c-tdesc
29346 @item maint print c-tdesc
29347 Print the current target description (@pxref{Target Descriptions}) as
29348 a C source file. The created source file can be used in @value{GDBN}
29349 when an XML parser is not available to parse the description.
29351 @kindex maint print dummy-frames
29352 @item maint print dummy-frames
29353 Prints the contents of @value{GDBN}'s internal dummy-frame stack.
29356 (@value{GDBP}) @kbd{b add}
29358 (@value{GDBP}) @kbd{print add(2,3)}
29359 Breakpoint 2, add (a=2, b=3) at @dots{}
29361 The program being debugged stopped while in a function called from GDB.
29363 (@value{GDBP}) @kbd{maint print dummy-frames}
29364 0x1a57c80: pc=0x01014068 fp=0x0200bddc sp=0x0200bdd6
29365 top=0x0200bdd4 id=@{stack=0x200bddc,code=0x101405c@}
29366 call_lo=0x01014000 call_hi=0x01014001
29370 Takes an optional file parameter.
29372 @kindex maint print registers
29373 @kindex maint print raw-registers
29374 @kindex maint print cooked-registers
29375 @kindex maint print register-groups
29376 @item maint print registers @r{[}@var{file}@r{]}
29377 @itemx maint print raw-registers @r{[}@var{file}@r{]}
29378 @itemx maint print cooked-registers @r{[}@var{file}@r{]}
29379 @itemx maint print register-groups @r{[}@var{file}@r{]}
29380 Print @value{GDBN}'s internal register data structures.
29382 The command @code{maint print raw-registers} includes the contents of
29383 the raw register cache; the command @code{maint print cooked-registers}
29384 includes the (cooked) value of all registers, including registers which
29385 aren't available on the target nor visible to user; and the
29386 command @code{maint print register-groups} includes the groups that each
29387 register is a member of. @xref{Registers,, Registers, gdbint,
29388 @value{GDBN} Internals}.
29390 These commands take an optional parameter, a file name to which to
29391 write the information.
29393 @kindex maint print reggroups
29394 @item maint print reggroups @r{[}@var{file}@r{]}
29395 Print @value{GDBN}'s internal register group data structures. The
29396 optional argument @var{file} tells to what file to write the
29399 The register groups info looks like this:
29402 (@value{GDBP}) @kbd{maint print reggroups}
29415 This command forces @value{GDBN} to flush its internal register cache.
29417 @kindex maint print objfiles
29418 @cindex info for known object files
29419 @item maint print objfiles
29420 Print a dump of all known object files. For each object file, this
29421 command prints its name, address in memory, and all of its psymtabs
29424 @kindex maint print statistics
29425 @cindex bcache statistics
29426 @item maint print statistics
29427 This command prints, for each object file in the program, various data
29428 about that object file followed by the byte cache (@dfn{bcache})
29429 statistics for the object file. The objfile data includes the number
29430 of minimal, partial, full, and stabs symbols, the number of types
29431 defined by the objfile, the number of as yet unexpanded psym tables,
29432 the number of line tables and string tables, and the amount of memory
29433 used by the various tables. The bcache statistics include the counts,
29434 sizes, and counts of duplicates of all and unique objects, max,
29435 average, and median entry size, total memory used and its overhead and
29436 savings, and various measures of the hash table size and chain
29439 @kindex maint print target-stack
29440 @cindex target stack description
29441 @item maint print target-stack
29442 A @dfn{target} is an interface between the debugger and a particular
29443 kind of file or process. Targets can be stacked in @dfn{strata},
29444 so that more than one target can potentially respond to a request.
29445 In particular, memory accesses will walk down the stack of targets
29446 until they find a target that is interested in handling that particular
29449 This command prints a short description of each layer that was pushed on
29450 the @dfn{target stack}, starting from the top layer down to the bottom one.
29452 @kindex maint print type
29453 @cindex type chain of a data type
29454 @item maint print type @var{expr}
29455 Print the type chain for a type specified by @var{expr}. The argument
29456 can be either a type name or a symbol. If it is a symbol, the type of
29457 that symbol is described. The type chain produced by this command is
29458 a recursive definition of the data type as stored in @value{GDBN}'s
29459 data structures, including its flags and contained types.
29461 @kindex maint set dwarf2 max-cache-age
29462 @kindex maint show dwarf2 max-cache-age
29463 @item maint set dwarf2 max-cache-age
29464 @itemx maint show dwarf2 max-cache-age
29465 Control the DWARF 2 compilation unit cache.
29467 @cindex DWARF 2 compilation units cache
29468 In object files with inter-compilation-unit references, such as those
29469 produced by the GCC option @samp{-feliminate-dwarf2-dups}, the DWARF 2
29470 reader needs to frequently refer to previously read compilation units.
29471 This setting controls how long a compilation unit will remain in the
29472 cache if it is not referenced. A higher limit means that cached
29473 compilation units will be stored in memory longer, and more total
29474 memory will be used. Setting it to zero disables caching, which will
29475 slow down @value{GDBN} startup, but reduce memory consumption.
29477 @kindex maint set profile
29478 @kindex maint show profile
29479 @cindex profiling GDB
29480 @item maint set profile
29481 @itemx maint show profile
29482 Control profiling of @value{GDBN}.
29484 Profiling will be disabled until you use the @samp{maint set profile}
29485 command to enable it. When you enable profiling, the system will begin
29486 collecting timing and execution count data; when you disable profiling or
29487 exit @value{GDBN}, the results will be written to a log file. Remember that
29488 if you use profiling, @value{GDBN} will overwrite the profiling log file
29489 (often called @file{gmon.out}). If you have a record of important profiling
29490 data in a @file{gmon.out} file, be sure to move it to a safe location.
29492 Configuring with @samp{--enable-profiling} arranges for @value{GDBN} to be
29493 compiled with the @samp{-pg} compiler option.
29495 @kindex maint set show-debug-regs
29496 @kindex maint show show-debug-regs
29497 @cindex hardware debug registers
29498 @item maint set show-debug-regs
29499 @itemx maint show show-debug-regs
29500 Control whether to show variables that mirror the hardware debug
29501 registers. Use @code{ON} to enable, @code{OFF} to disable. If
29502 enabled, the debug registers values are shown when @value{GDBN} inserts or
29503 removes a hardware breakpoint or watchpoint, and when the inferior
29504 triggers a hardware-assisted breakpoint or watchpoint.
29506 @kindex maint set show-all-tib
29507 @kindex maint show show-all-tib
29508 @item maint set show-all-tib
29509 @itemx maint show show-all-tib
29510 Control whether to show all non zero areas within a 1k block starting
29511 at thread local base, when using the @samp{info w32 thread-information-block}
29514 @kindex maint space
29515 @cindex memory used by commands
29517 Control whether to display memory usage for each command. If set to a
29518 nonzero value, @value{GDBN} will display how much memory each command
29519 took, following the command's own output. This can also be requested
29520 by invoking @value{GDBN} with the @option{--statistics} command-line
29521 switch (@pxref{Mode Options}).
29524 @cindex time of command execution
29526 Control whether to display the execution time for each command. If
29527 set to a nonzero value, @value{GDBN} will display how much time it
29528 took to execute each command, following the command's own output.
29529 The time is not printed for the commands that run the target, since
29530 there's no mechanism currently to compute how much time was spend
29531 by @value{GDBN} and how much time was spend by the program been debugged.
29532 it's not possibly currently
29533 This can also be requested by invoking @value{GDBN} with the
29534 @option{--statistics} command-line switch (@pxref{Mode Options}).
29536 @kindex maint translate-address
29537 @item maint translate-address @r{[}@var{section}@r{]} @var{addr}
29538 Find the symbol stored at the location specified by the address
29539 @var{addr} and an optional section name @var{section}. If found,
29540 @value{GDBN} prints the name of the closest symbol and an offset from
29541 the symbol's location to the specified address. This is similar to
29542 the @code{info address} command (@pxref{Symbols}), except that this
29543 command also allows to find symbols in other sections.
29545 If section was not specified, the section in which the symbol was found
29546 is also printed. For dynamically linked executables, the name of
29547 executable or shared library containing the symbol is printed as well.
29551 The following command is useful for non-interactive invocations of
29552 @value{GDBN}, such as in the test suite.
29555 @item set watchdog @var{nsec}
29556 @kindex set watchdog
29557 @cindex watchdog timer
29558 @cindex timeout for commands
29559 Set the maximum number of seconds @value{GDBN} will wait for the
29560 target operation to finish. If this time expires, @value{GDBN}
29561 reports and error and the command is aborted.
29563 @item show watchdog
29564 Show the current setting of the target wait timeout.
29567 @node Remote Protocol
29568 @appendix @value{GDBN} Remote Serial Protocol
29573 * Stop Reply Packets::
29574 * General Query Packets::
29575 * Architecture-Specific Protocol Details::
29576 * Tracepoint Packets::
29577 * Host I/O Packets::
29579 * Notification Packets::
29580 * Remote Non-Stop::
29581 * Packet Acknowledgment::
29583 * File-I/O Remote Protocol Extension::
29584 * Library List Format::
29585 * Memory Map Format::
29586 * Thread List Format::
29592 There may be occasions when you need to know something about the
29593 protocol---for example, if there is only one serial port to your target
29594 machine, you might want your program to do something special if it
29595 recognizes a packet meant for @value{GDBN}.
29597 In the examples below, @samp{->} and @samp{<-} are used to indicate
29598 transmitted and received data, respectively.
29600 @cindex protocol, @value{GDBN} remote serial
29601 @cindex serial protocol, @value{GDBN} remote
29602 @cindex remote serial protocol
29603 All @value{GDBN} commands and responses (other than acknowledgments
29604 and notifications, see @ref{Notification Packets}) are sent as a
29605 @var{packet}. A @var{packet} is introduced with the character
29606 @samp{$}, the actual @var{packet-data}, and the terminating character
29607 @samp{#} followed by a two-digit @var{checksum}:
29610 @code{$}@var{packet-data}@code{#}@var{checksum}
29614 @cindex checksum, for @value{GDBN} remote
29616 The two-digit @var{checksum} is computed as the modulo 256 sum of all
29617 characters between the leading @samp{$} and the trailing @samp{#} (an
29618 eight bit unsigned checksum).
29620 Implementors should note that prior to @value{GDBN} 5.0 the protocol
29621 specification also included an optional two-digit @var{sequence-id}:
29624 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
29627 @cindex sequence-id, for @value{GDBN} remote
29629 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
29630 has never output @var{sequence-id}s. Stubs that handle packets added
29631 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
29633 When either the host or the target machine receives a packet, the first
29634 response expected is an acknowledgment: either @samp{+} (to indicate
29635 the package was received correctly) or @samp{-} (to request
29639 -> @code{$}@var{packet-data}@code{#}@var{checksum}
29644 The @samp{+}/@samp{-} acknowledgments can be disabled
29645 once a connection is established.
29646 @xref{Packet Acknowledgment}, for details.
29648 The host (@value{GDBN}) sends @var{command}s, and the target (the
29649 debugging stub incorporated in your program) sends a @var{response}. In
29650 the case of step and continue @var{command}s, the response is only sent
29651 when the operation has completed, and the target has again stopped all
29652 threads in all attached processes. This is the default all-stop mode
29653 behavior, but the remote protocol also supports @value{GDBN}'s non-stop
29654 execution mode; see @ref{Remote Non-Stop}, for details.
29656 @var{packet-data} consists of a sequence of characters with the
29657 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
29660 @cindex remote protocol, field separator
29661 Fields within the packet should be separated using @samp{,} @samp{;} or
29662 @samp{:}. Except where otherwise noted all numbers are represented in
29663 @sc{hex} with leading zeros suppressed.
29665 Implementors should note that prior to @value{GDBN} 5.0, the character
29666 @samp{:} could not appear as the third character in a packet (as it
29667 would potentially conflict with the @var{sequence-id}).
29669 @cindex remote protocol, binary data
29670 @anchor{Binary Data}
29671 Binary data in most packets is encoded either as two hexadecimal
29672 digits per byte of binary data. This allowed the traditional remote
29673 protocol to work over connections which were only seven-bit clean.
29674 Some packets designed more recently assume an eight-bit clean
29675 connection, and use a more efficient encoding to send and receive
29678 The binary data representation uses @code{7d} (@sc{ascii} @samp{@}})
29679 as an escape character. Any escaped byte is transmitted as the escape
29680 character followed by the original character XORed with @code{0x20}.
29681 For example, the byte @code{0x7d} would be transmitted as the two
29682 bytes @code{0x7d 0x5d}. The bytes @code{0x23} (@sc{ascii} @samp{#}),
29683 @code{0x24} (@sc{ascii} @samp{$}), and @code{0x7d} (@sc{ascii}
29684 @samp{@}}) must always be escaped. Responses sent by the stub
29685 must also escape @code{0x2a} (@sc{ascii} @samp{*}), so that it
29686 is not interpreted as the start of a run-length encoded sequence
29689 Response @var{data} can be run-length encoded to save space.
29690 Run-length encoding replaces runs of identical characters with one
29691 instance of the repeated character, followed by a @samp{*} and a
29692 repeat count. The repeat count is itself sent encoded, to avoid
29693 binary characters in @var{data}: a value of @var{n} is sent as
29694 @code{@var{n}+29}. For a repeat count greater or equal to 3, this
29695 produces a printable @sc{ascii} character, e.g.@: a space (@sc{ascii}
29696 code 32) for a repeat count of 3. (This is because run-length
29697 encoding starts to win for counts 3 or more.) Thus, for example,
29698 @samp{0* } is a run-length encoding of ``0000'': the space character
29699 after @samp{*} means repeat the leading @code{0} @w{@code{32 - 29 =
29702 The printable characters @samp{#} and @samp{$} or with a numeric value
29703 greater than 126 must not be used. Runs of six repeats (@samp{#}) or
29704 seven repeats (@samp{$}) can be expanded using a repeat count of only
29705 five (@samp{"}). For example, @samp{00000000} can be encoded as
29708 The error response returned for some packets includes a two character
29709 error number. That number is not well defined.
29711 @cindex empty response, for unsupported packets
29712 For any @var{command} not supported by the stub, an empty response
29713 (@samp{$#00}) should be returned. That way it is possible to extend the
29714 protocol. A newer @value{GDBN} can tell if a packet is supported based
29717 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
29718 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
29724 The following table provides a complete list of all currently defined
29725 @var{command}s and their corresponding response @var{data}.
29726 @xref{File-I/O Remote Protocol Extension}, for details about the File
29727 I/O extension of the remote protocol.
29729 Each packet's description has a template showing the packet's overall
29730 syntax, followed by an explanation of the packet's meaning. We
29731 include spaces in some of the templates for clarity; these are not
29732 part of the packet's syntax. No @value{GDBN} packet uses spaces to
29733 separate its components. For example, a template like @samp{foo
29734 @var{bar} @var{baz}} describes a packet beginning with the three ASCII
29735 bytes @samp{foo}, followed by a @var{bar}, followed directly by a
29736 @var{baz}. @value{GDBN} does not transmit a space character between the
29737 @samp{foo} and the @var{bar}, or between the @var{bar} and the
29740 @cindex @var{thread-id}, in remote protocol
29741 @anchor{thread-id syntax}
29742 Several packets and replies include a @var{thread-id} field to identify
29743 a thread. Normally these are positive numbers with a target-specific
29744 interpretation, formatted as big-endian hex strings. A @var{thread-id}
29745 can also be a literal @samp{-1} to indicate all threads, or @samp{0} to
29748 In addition, the remote protocol supports a multiprocess feature in
29749 which the @var{thread-id} syntax is extended to optionally include both
29750 process and thread ID fields, as @samp{p@var{pid}.@var{tid}}.
29751 The @var{pid} (process) and @var{tid} (thread) components each have the
29752 format described above: a positive number with target-specific
29753 interpretation formatted as a big-endian hex string, literal @samp{-1}
29754 to indicate all processes or threads (respectively), or @samp{0} to
29755 indicate an arbitrary process or thread. Specifying just a process, as
29756 @samp{p@var{pid}}, is equivalent to @samp{p@var{pid}.-1}. It is an
29757 error to specify all processes but a specific thread, such as
29758 @samp{p-1.@var{tid}}. Note that the @samp{p} prefix is @emph{not} used
29759 for those packets and replies explicitly documented to include a process
29760 ID, rather than a @var{thread-id}.
29762 The multiprocess @var{thread-id} syntax extensions are only used if both
29763 @value{GDBN} and the stub report support for the @samp{multiprocess}
29764 feature using @samp{qSupported}. @xref{multiprocess extensions}, for
29767 Note that all packet forms beginning with an upper- or lower-case
29768 letter, other than those described here, are reserved for future use.
29770 Here are the packet descriptions.
29775 @cindex @samp{!} packet
29776 @anchor{extended mode}
29777 Enable extended mode. In extended mode, the remote server is made
29778 persistent. The @samp{R} packet is used to restart the program being
29784 The remote target both supports and has enabled extended mode.
29788 @cindex @samp{?} packet
29789 Indicate the reason the target halted. The reply is the same as for
29790 step and continue. This packet has a special interpretation when the
29791 target is in non-stop mode; see @ref{Remote Non-Stop}.
29794 @xref{Stop Reply Packets}, for the reply specifications.
29796 @item A @var{arglen},@var{argnum},@var{arg},@dots{}
29797 @cindex @samp{A} packet
29798 Initialized @code{argv[]} array passed into program. @var{arglen}
29799 specifies the number of bytes in the hex encoded byte stream
29800 @var{arg}. See @code{gdbserver} for more details.
29805 The arguments were set.
29811 @cindex @samp{b} packet
29812 (Don't use this packet; its behavior is not well-defined.)
29813 Change the serial line speed to @var{baud}.
29815 JTC: @emph{When does the transport layer state change? When it's
29816 received, or after the ACK is transmitted. In either case, there are
29817 problems if the command or the acknowledgment packet is dropped.}
29819 Stan: @emph{If people really wanted to add something like this, and get
29820 it working for the first time, they ought to modify ser-unix.c to send
29821 some kind of out-of-band message to a specially-setup stub and have the
29822 switch happen "in between" packets, so that from remote protocol's point
29823 of view, nothing actually happened.}
29825 @item B @var{addr},@var{mode}
29826 @cindex @samp{B} packet
29827 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
29828 breakpoint at @var{addr}.
29830 Don't use this packet. Use the @samp{Z} and @samp{z} packets instead
29831 (@pxref{insert breakpoint or watchpoint packet}).
29833 @cindex @samp{bc} packet
29836 Backward continue. Execute the target system in reverse. No parameter.
29837 @xref{Reverse Execution}, for more information.
29840 @xref{Stop Reply Packets}, for the reply specifications.
29842 @cindex @samp{bs} packet
29845 Backward single step. Execute one instruction in reverse. No parameter.
29846 @xref{Reverse Execution}, for more information.
29849 @xref{Stop Reply Packets}, for the reply specifications.
29851 @item c @r{[}@var{addr}@r{]}
29852 @cindex @samp{c} packet
29853 Continue. @var{addr} is address to resume. If @var{addr} is omitted,
29854 resume at current address.
29857 @xref{Stop Reply Packets}, for the reply specifications.
29859 @item C @var{sig}@r{[};@var{addr}@r{]}
29860 @cindex @samp{C} packet
29861 Continue with signal @var{sig} (hex signal number). If
29862 @samp{;@var{addr}} is omitted, resume at same address.
29865 @xref{Stop Reply Packets}, for the reply specifications.
29868 @cindex @samp{d} packet
29871 Don't use this packet; instead, define a general set packet
29872 (@pxref{General Query Packets}).
29876 @cindex @samp{D} packet
29877 The first form of the packet is used to detach @value{GDBN} from the
29878 remote system. It is sent to the remote target
29879 before @value{GDBN} disconnects via the @code{detach} command.
29881 The second form, including a process ID, is used when multiprocess
29882 protocol extensions are enabled (@pxref{multiprocess extensions}), to
29883 detach only a specific process. The @var{pid} is specified as a
29884 big-endian hex string.
29894 @item F @var{RC},@var{EE},@var{CF};@var{XX}
29895 @cindex @samp{F} packet
29896 A reply from @value{GDBN} to an @samp{F} packet sent by the target.
29897 This is part of the File-I/O protocol extension. @xref{File-I/O
29898 Remote Protocol Extension}, for the specification.
29901 @anchor{read registers packet}
29902 @cindex @samp{g} packet
29903 Read general registers.
29907 @item @var{XX@dots{}}
29908 Each byte of register data is described by two hex digits. The bytes
29909 with the register are transmitted in target byte order. The size of
29910 each register and their position within the @samp{g} packet are
29911 determined by the @value{GDBN} internal gdbarch functions
29912 @code{DEPRECATED_REGISTER_RAW_SIZE} and @code{gdbarch_register_name}. The
29913 specification of several standard @samp{g} packets is specified below.
29918 @item G @var{XX@dots{}}
29919 @cindex @samp{G} packet
29920 Write general registers. @xref{read registers packet}, for a
29921 description of the @var{XX@dots{}} data.
29931 @item H @var{c} @var{thread-id}
29932 @cindex @samp{H} packet
29933 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
29934 @samp{G}, et.al.). @var{c} depends on the operation to be performed: it
29935 should be @samp{c} for step and continue operations, @samp{g} for other
29936 operations. The thread designator @var{thread-id} has the format and
29937 interpretation described in @ref{thread-id syntax}.
29948 @c 'H': How restrictive (or permissive) is the thread model. If a
29949 @c thread is selected and stopped, are other threads allowed
29950 @c to continue to execute? As I mentioned above, I think the
29951 @c semantics of each command when a thread is selected must be
29952 @c described. For example:
29954 @c 'g': If the stub supports threads and a specific thread is
29955 @c selected, returns the register block from that thread;
29956 @c otherwise returns current registers.
29958 @c 'G' If the stub supports threads and a specific thread is
29959 @c selected, sets the registers of the register block of
29960 @c that thread; otherwise sets current registers.
29962 @item i @r{[}@var{addr}@r{[},@var{nnn}@r{]]}
29963 @anchor{cycle step packet}
29964 @cindex @samp{i} packet
29965 Step the remote target by a single clock cycle. If @samp{,@var{nnn}} is
29966 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
29967 step starting at that address.
29970 @cindex @samp{I} packet
29971 Signal, then cycle step. @xref{step with signal packet}. @xref{cycle
29975 @cindex @samp{k} packet
29978 FIXME: @emph{There is no description of how to operate when a specific
29979 thread context has been selected (i.e.@: does 'k' kill only that
29982 @item m @var{addr},@var{length}
29983 @cindex @samp{m} packet
29984 Read @var{length} bytes of memory starting at address @var{addr}.
29985 Note that @var{addr} may not be aligned to any particular boundary.
29987 The stub need not use any particular size or alignment when gathering
29988 data from memory for the response; even if @var{addr} is word-aligned
29989 and @var{length} is a multiple of the word size, the stub is free to
29990 use byte accesses, or not. For this reason, this packet may not be
29991 suitable for accessing memory-mapped I/O devices.
29992 @cindex alignment of remote memory accesses
29993 @cindex size of remote memory accesses
29994 @cindex memory, alignment and size of remote accesses
29998 @item @var{XX@dots{}}
29999 Memory contents; each byte is transmitted as a two-digit hexadecimal
30000 number. The reply may contain fewer bytes than requested if the
30001 server was able to read only part of the region of memory.
30006 @item M @var{addr},@var{length}:@var{XX@dots{}}
30007 @cindex @samp{M} packet
30008 Write @var{length} bytes of memory starting at address @var{addr}.
30009 @var{XX@dots{}} is the data; each byte is transmitted as a two-digit
30010 hexadecimal number.
30017 for an error (this includes the case where only part of the data was
30022 @cindex @samp{p} packet
30023 Read the value of register @var{n}; @var{n} is in hex.
30024 @xref{read registers packet}, for a description of how the returned
30025 register value is encoded.
30029 @item @var{XX@dots{}}
30030 the register's value
30034 Indicating an unrecognized @var{query}.
30037 @item P @var{n@dots{}}=@var{r@dots{}}
30038 @anchor{write register packet}
30039 @cindex @samp{P} packet
30040 Write register @var{n@dots{}} with value @var{r@dots{}}. The register
30041 number @var{n} is in hexadecimal, and @var{r@dots{}} contains two hex
30042 digits for each byte in the register (target byte order).
30052 @item q @var{name} @var{params}@dots{}
30053 @itemx Q @var{name} @var{params}@dots{}
30054 @cindex @samp{q} packet
30055 @cindex @samp{Q} packet
30056 General query (@samp{q}) and set (@samp{Q}). These packets are
30057 described fully in @ref{General Query Packets}.
30060 @cindex @samp{r} packet
30061 Reset the entire system.
30063 Don't use this packet; use the @samp{R} packet instead.
30066 @cindex @samp{R} packet
30067 Restart the program being debugged. @var{XX}, while needed, is ignored.
30068 This packet is only available in extended mode (@pxref{extended mode}).
30070 The @samp{R} packet has no reply.
30072 @item s @r{[}@var{addr}@r{]}
30073 @cindex @samp{s} packet
30074 Single step. @var{addr} is the address at which to resume. If
30075 @var{addr} is omitted, resume at same address.
30078 @xref{Stop Reply Packets}, for the reply specifications.
30080 @item S @var{sig}@r{[};@var{addr}@r{]}
30081 @anchor{step with signal packet}
30082 @cindex @samp{S} packet
30083 Step with signal. This is analogous to the @samp{C} packet, but
30084 requests a single-step, rather than a normal resumption of execution.
30087 @xref{Stop Reply Packets}, for the reply specifications.
30089 @item t @var{addr}:@var{PP},@var{MM}
30090 @cindex @samp{t} packet
30091 Search backwards starting at address @var{addr} for a match with pattern
30092 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4 bytes.
30093 @var{addr} must be at least 3 digits.
30095 @item T @var{thread-id}
30096 @cindex @samp{T} packet
30097 Find out if the thread @var{thread-id} is alive. @xref{thread-id syntax}.
30102 thread is still alive
30108 Packets starting with @samp{v} are identified by a multi-letter name,
30109 up to the first @samp{;} or @samp{?} (or the end of the packet).
30111 @item vAttach;@var{pid}
30112 @cindex @samp{vAttach} packet
30113 Attach to a new process with the specified process ID @var{pid}.
30114 The process ID is a
30115 hexadecimal integer identifying the process. In all-stop mode, all
30116 threads in the attached process are stopped; in non-stop mode, it may be
30117 attached without being stopped if that is supported by the target.
30119 @c In non-stop mode, on a successful vAttach, the stub should set the
30120 @c current thread to a thread of the newly-attached process. After
30121 @c attaching, GDB queries for the attached process's thread ID with qC.
30122 @c Also note that, from a user perspective, whether or not the
30123 @c target is stopped on attach in non-stop mode depends on whether you
30124 @c use the foreground or background version of the attach command, not
30125 @c on what vAttach does; GDB does the right thing with respect to either
30126 @c stopping or restarting threads.
30128 This packet is only available in extended mode (@pxref{extended mode}).
30134 @item @r{Any stop packet}
30135 for success in all-stop mode (@pxref{Stop Reply Packets})
30137 for success in non-stop mode (@pxref{Remote Non-Stop})
30140 @item vCont@r{[};@var{action}@r{[}:@var{thread-id}@r{]]}@dots{}
30141 @cindex @samp{vCont} packet
30142 Resume the inferior, specifying different actions for each thread.
30143 If an action is specified with no @var{thread-id}, then it is applied to any
30144 threads that don't have a specific action specified; if no default action is
30145 specified then other threads should remain stopped in all-stop mode and
30146 in their current state in non-stop mode.
30147 Specifying multiple
30148 default actions is an error; specifying no actions is also an error.
30149 Thread IDs are specified using the syntax described in @ref{thread-id syntax}.
30151 Currently supported actions are:
30157 Continue with signal @var{sig}. The signal @var{sig} should be two hex digits.
30161 Step with signal @var{sig}. The signal @var{sig} should be two hex digits.
30166 The optional argument @var{addr} normally associated with the
30167 @samp{c}, @samp{C}, @samp{s}, and @samp{S} packets is
30168 not supported in @samp{vCont}.
30170 The @samp{t} action is only relevant in non-stop mode
30171 (@pxref{Remote Non-Stop}) and may be ignored by the stub otherwise.
30172 A stop reply should be generated for any affected thread not already stopped.
30173 When a thread is stopped by means of a @samp{t} action,
30174 the corresponding stop reply should indicate that the thread has stopped with
30175 signal @samp{0}, regardless of whether the target uses some other signal
30176 as an implementation detail.
30179 @xref{Stop Reply Packets}, for the reply specifications.
30182 @cindex @samp{vCont?} packet
30183 Request a list of actions supported by the @samp{vCont} packet.
30187 @item vCont@r{[};@var{action}@dots{}@r{]}
30188 The @samp{vCont} packet is supported. Each @var{action} is a supported
30189 command in the @samp{vCont} packet.
30191 The @samp{vCont} packet is not supported.
30194 @item vFile:@var{operation}:@var{parameter}@dots{}
30195 @cindex @samp{vFile} packet
30196 Perform a file operation on the target system. For details,
30197 see @ref{Host I/O Packets}.
30199 @item vFlashErase:@var{addr},@var{length}
30200 @cindex @samp{vFlashErase} packet
30201 Direct the stub to erase @var{length} bytes of flash starting at
30202 @var{addr}. The region may enclose any number of flash blocks, but
30203 its start and end must fall on block boundaries, as indicated by the
30204 flash block size appearing in the memory map (@pxref{Memory Map
30205 Format}). @value{GDBN} groups flash memory programming operations
30206 together, and sends a @samp{vFlashDone} request after each group; the
30207 stub is allowed to delay erase operation until the @samp{vFlashDone}
30208 packet is received.
30210 The stub must support @samp{vCont} if it reports support for
30211 multiprocess extensions (@pxref{multiprocess extensions}). Note that in
30212 this case @samp{vCont} actions can be specified to apply to all threads
30213 in a process by using the @samp{p@var{pid}.-1} form of the
30224 @item vFlashWrite:@var{addr}:@var{XX@dots{}}
30225 @cindex @samp{vFlashWrite} packet
30226 Direct the stub to write data to flash address @var{addr}. The data
30227 is passed in binary form using the same encoding as for the @samp{X}
30228 packet (@pxref{Binary Data}). The memory ranges specified by
30229 @samp{vFlashWrite} packets preceding a @samp{vFlashDone} packet must
30230 not overlap, and must appear in order of increasing addresses
30231 (although @samp{vFlashErase} packets for higher addresses may already
30232 have been received; the ordering is guaranteed only between
30233 @samp{vFlashWrite} packets). If a packet writes to an address that was
30234 neither erased by a preceding @samp{vFlashErase} packet nor by some other
30235 target-specific method, the results are unpredictable.
30243 for vFlashWrite addressing non-flash memory
30249 @cindex @samp{vFlashDone} packet
30250 Indicate to the stub that flash programming operation is finished.
30251 The stub is permitted to delay or batch the effects of a group of
30252 @samp{vFlashErase} and @samp{vFlashWrite} packets until a
30253 @samp{vFlashDone} packet is received. The contents of the affected
30254 regions of flash memory are unpredictable until the @samp{vFlashDone}
30255 request is completed.
30257 @item vKill;@var{pid}
30258 @cindex @samp{vKill} packet
30259 Kill the process with the specified process ID. @var{pid} is a
30260 hexadecimal integer identifying the process. This packet is used in
30261 preference to @samp{k} when multiprocess protocol extensions are
30262 supported; see @ref{multiprocess extensions}.
30272 @item vRun;@var{filename}@r{[};@var{argument}@r{]}@dots{}
30273 @cindex @samp{vRun} packet
30274 Run the program @var{filename}, passing it each @var{argument} on its
30275 command line. The file and arguments are hex-encoded strings. If
30276 @var{filename} is an empty string, the stub may use a default program
30277 (e.g.@: the last program run). The program is created in the stopped
30280 @c FIXME: What about non-stop mode?
30282 This packet is only available in extended mode (@pxref{extended mode}).
30288 @item @r{Any stop packet}
30289 for success (@pxref{Stop Reply Packets})
30293 @anchor{vStopped packet}
30294 @cindex @samp{vStopped} packet
30296 In non-stop mode (@pxref{Remote Non-Stop}), acknowledge a previous stop
30297 reply and prompt for the stub to report another one.
30301 @item @r{Any stop packet}
30302 if there is another unreported stop event (@pxref{Stop Reply Packets})
30304 if there are no unreported stop events
30307 @item X @var{addr},@var{length}:@var{XX@dots{}}
30309 @cindex @samp{X} packet
30310 Write data to memory, where the data is transmitted in binary.
30311 @var{addr} is address, @var{length} is number of bytes,
30312 @samp{@var{XX}@dots{}} is binary data (@pxref{Binary Data}).
30322 @item z @var{type},@var{addr},@var{kind}
30323 @itemx Z @var{type},@var{addr},@var{kind}
30324 @anchor{insert breakpoint or watchpoint packet}
30325 @cindex @samp{z} packet
30326 @cindex @samp{Z} packets
30327 Insert (@samp{Z}) or remove (@samp{z}) a @var{type} breakpoint or
30328 watchpoint starting at address @var{address} of kind @var{kind}.
30330 Each breakpoint and watchpoint packet @var{type} is documented
30333 @emph{Implementation notes: A remote target shall return an empty string
30334 for an unrecognized breakpoint or watchpoint packet @var{type}. A
30335 remote target shall support either both or neither of a given
30336 @samp{Z@var{type}@dots{}} and @samp{z@var{type}@dots{}} packet pair. To
30337 avoid potential problems with duplicate packets, the operations should
30338 be implemented in an idempotent way.}
30340 @item z0,@var{addr},@var{kind}
30341 @itemx Z0,@var{addr},@var{kind}
30342 @cindex @samp{z0} packet
30343 @cindex @samp{Z0} packet
30344 Insert (@samp{Z0}) or remove (@samp{z0}) a memory breakpoint at address
30345 @var{addr} of type @var{kind}.
30347 A memory breakpoint is implemented by replacing the instruction at
30348 @var{addr} with a software breakpoint or trap instruction. The
30349 @var{kind} is target-specific and typically indicates the size of
30350 the breakpoint in bytes that should be inserted. E.g., the @sc{arm}
30351 and @sc{mips} can insert either a 2 or 4 byte breakpoint. Some
30352 architectures have additional meanings for @var{kind};
30353 see @ref{Architecture-Specific Protocol Details}.
30355 @emph{Implementation note: It is possible for a target to copy or move
30356 code that contains memory breakpoints (e.g., when implementing
30357 overlays). The behavior of this packet, in the presence of such a
30358 target, is not defined.}
30370 @item z1,@var{addr},@var{kind}
30371 @itemx Z1,@var{addr},@var{kind}
30372 @cindex @samp{z1} packet
30373 @cindex @samp{Z1} packet
30374 Insert (@samp{Z1}) or remove (@samp{z1}) a hardware breakpoint at
30375 address @var{addr}.
30377 A hardware breakpoint is implemented using a mechanism that is not
30378 dependant on being able to modify the target's memory. @var{kind}
30379 has the same meaning as in @samp{Z0} packets.
30381 @emph{Implementation note: A hardware breakpoint is not affected by code
30394 @item z2,@var{addr},@var{kind}
30395 @itemx Z2,@var{addr},@var{kind}
30396 @cindex @samp{z2} packet
30397 @cindex @samp{Z2} packet
30398 Insert (@samp{Z2}) or remove (@samp{z2}) a write watchpoint at @var{addr}.
30399 @var{kind} is interpreted as the number of bytes to watch.
30411 @item z3,@var{addr},@var{kind}
30412 @itemx Z3,@var{addr},@var{kind}
30413 @cindex @samp{z3} packet
30414 @cindex @samp{Z3} packet
30415 Insert (@samp{Z3}) or remove (@samp{z3}) a read watchpoint at @var{addr}.
30416 @var{kind} is interpreted as the number of bytes to watch.
30428 @item z4,@var{addr},@var{kind}
30429 @itemx Z4,@var{addr},@var{kind}
30430 @cindex @samp{z4} packet
30431 @cindex @samp{Z4} packet
30432 Insert (@samp{Z4}) or remove (@samp{z4}) an access watchpoint at @var{addr}.
30433 @var{kind} is interpreted as the number of bytes to watch.
30447 @node Stop Reply Packets
30448 @section Stop Reply Packets
30449 @cindex stop reply packets
30451 The @samp{C}, @samp{c}, @samp{S}, @samp{s}, @samp{vCont},
30452 @samp{vAttach}, @samp{vRun}, @samp{vStopped}, and @samp{?} packets can
30453 receive any of the below as a reply. Except for @samp{?}
30454 and @samp{vStopped}, that reply is only returned
30455 when the target halts. In the below the exact meaning of @dfn{signal
30456 number} is defined by the header @file{include/gdb/signals.h} in the
30457 @value{GDBN} source code.
30459 As in the description of request packets, we include spaces in the
30460 reply templates for clarity; these are not part of the reply packet's
30461 syntax. No @value{GDBN} stop reply packet uses spaces to separate its
30467 The program received signal number @var{AA} (a two-digit hexadecimal
30468 number). This is equivalent to a @samp{T} response with no
30469 @var{n}:@var{r} pairs.
30471 @item T @var{AA} @var{n1}:@var{r1};@var{n2}:@var{r2};@dots{}
30472 @cindex @samp{T} packet reply
30473 The program received signal number @var{AA} (a two-digit hexadecimal
30474 number). This is equivalent to an @samp{S} response, except that the
30475 @samp{@var{n}:@var{r}} pairs can carry values of important registers
30476 and other information directly in the stop reply packet, reducing
30477 round-trip latency. Single-step and breakpoint traps are reported
30478 this way. Each @samp{@var{n}:@var{r}} pair is interpreted as follows:
30482 If @var{n} is a hexadecimal number, it is a register number, and the
30483 corresponding @var{r} gives that register's value. @var{r} is a
30484 series of bytes in target byte order, with each byte given by a
30485 two-digit hex number.
30488 If @var{n} is @samp{thread}, then @var{r} is the @var{thread-id} of
30489 the stopped thread, as specified in @ref{thread-id syntax}.
30492 If @var{n} is @samp{core}, then @var{r} is the hexadecimal number of
30493 the core on which the stop event was detected.
30496 If @var{n} is a recognized @dfn{stop reason}, it describes a more
30497 specific event that stopped the target. The currently defined stop
30498 reasons are listed below. @var{aa} should be @samp{05}, the trap
30499 signal. At most one stop reason should be present.
30502 Otherwise, @value{GDBN} should ignore this @samp{@var{n}:@var{r}} pair
30503 and go on to the next; this allows us to extend the protocol in the
30507 The currently defined stop reasons are:
30513 The packet indicates a watchpoint hit, and @var{r} is the data address, in
30516 @cindex shared library events, remote reply
30518 The packet indicates that the loaded libraries have changed.
30519 @value{GDBN} should use @samp{qXfer:libraries:read} to fetch a new
30520 list of loaded libraries. @var{r} is ignored.
30522 @cindex replay log events, remote reply
30524 The packet indicates that the target cannot continue replaying
30525 logged execution events, because it has reached the end (or the
30526 beginning when executing backward) of the log. The value of @var{r}
30527 will be either @samp{begin} or @samp{end}. @xref{Reverse Execution},
30528 for more information.
30532 @itemx W @var{AA} ; process:@var{pid}
30533 The process exited, and @var{AA} is the exit status. This is only
30534 applicable to certain targets.
30536 The second form of the response, including the process ID of the exited
30537 process, can be used only when @value{GDBN} has reported support for
30538 multiprocess protocol extensions; see @ref{multiprocess extensions}.
30539 The @var{pid} is formatted as a big-endian hex string.
30542 @itemx X @var{AA} ; process:@var{pid}
30543 The process terminated with signal @var{AA}.
30545 The second form of the response, including the process ID of the
30546 terminated process, can be used only when @value{GDBN} has reported
30547 support for multiprocess protocol extensions; see @ref{multiprocess
30548 extensions}. The @var{pid} is formatted as a big-endian hex string.
30550 @item O @var{XX}@dots{}
30551 @samp{@var{XX}@dots{}} is hex encoding of @sc{ascii} data, to be
30552 written as the program's console output. This can happen at any time
30553 while the program is running and the debugger should continue to wait
30554 for @samp{W}, @samp{T}, etc. This reply is not permitted in non-stop mode.
30556 @item F @var{call-id},@var{parameter}@dots{}
30557 @var{call-id} is the identifier which says which host system call should
30558 be called. This is just the name of the function. Translation into the
30559 correct system call is only applicable as it's defined in @value{GDBN}.
30560 @xref{File-I/O Remote Protocol Extension}, for a list of implemented
30563 @samp{@var{parameter}@dots{}} is a list of parameters as defined for
30564 this very system call.
30566 The target replies with this packet when it expects @value{GDBN} to
30567 call a host system call on behalf of the target. @value{GDBN} replies
30568 with an appropriate @samp{F} packet and keeps up waiting for the next
30569 reply packet from the target. The latest @samp{C}, @samp{c}, @samp{S}
30570 or @samp{s} action is expected to be continued. @xref{File-I/O Remote
30571 Protocol Extension}, for more details.
30575 @node General Query Packets
30576 @section General Query Packets
30577 @cindex remote query requests
30579 Packets starting with @samp{q} are @dfn{general query packets};
30580 packets starting with @samp{Q} are @dfn{general set packets}. General
30581 query and set packets are a semi-unified form for retrieving and
30582 sending information to and from the stub.
30584 The initial letter of a query or set packet is followed by a name
30585 indicating what sort of thing the packet applies to. For example,
30586 @value{GDBN} may use a @samp{qSymbol} packet to exchange symbol
30587 definitions with the stub. These packet names follow some
30592 The name must not contain commas, colons or semicolons.
30594 Most @value{GDBN} query and set packets have a leading upper case
30597 The names of custom vendor packets should use a company prefix, in
30598 lower case, followed by a period. For example, packets designed at
30599 the Acme Corporation might begin with @samp{qacme.foo} (for querying
30600 foos) or @samp{Qacme.bar} (for setting bars).
30603 The name of a query or set packet should be separated from any
30604 parameters by a @samp{:}; the parameters themselves should be
30605 separated by @samp{,} or @samp{;}. Stubs must be careful to match the
30606 full packet name, and check for a separator or the end of the packet,
30607 in case two packet names share a common prefix. New packets should not begin
30608 with @samp{qC}, @samp{qP}, or @samp{qL}@footnote{The @samp{qP} and @samp{qL}
30609 packets predate these conventions, and have arguments without any terminator
30610 for the packet name; we suspect they are in widespread use in places that
30611 are difficult to upgrade. The @samp{qC} packet has no arguments, but some
30612 existing stubs (e.g.@: RedBoot) are known to not check for the end of the
30615 Like the descriptions of the other packets, each description here
30616 has a template showing the packet's overall syntax, followed by an
30617 explanation of the packet's meaning. We include spaces in some of the
30618 templates for clarity; these are not part of the packet's syntax. No
30619 @value{GDBN} packet uses spaces to separate its components.
30621 Here are the currently defined query and set packets:
30626 @cindex current thread, remote request
30627 @cindex @samp{qC} packet
30628 Return the current thread ID.
30632 @item QC @var{thread-id}
30633 Where @var{thread-id} is a thread ID as documented in
30634 @ref{thread-id syntax}.
30635 @item @r{(anything else)}
30636 Any other reply implies the old thread ID.
30639 @item qCRC:@var{addr},@var{length}
30640 @cindex CRC of memory block, remote request
30641 @cindex @samp{qCRC} packet
30642 Compute the CRC checksum of a block of memory using CRC-32 defined in
30643 IEEE 802.3. The CRC is computed byte at a time, taking the most
30644 significant bit of each byte first. The initial pattern code
30645 @code{0xffffffff} is used to ensure leading zeros affect the CRC.
30647 @emph{Note:} This is the same CRC used in validating separate debug
30648 files (@pxref{Separate Debug Files, , Debugging Information in Separate
30649 Files}). However the algorithm is slightly different. When validating
30650 separate debug files, the CRC is computed taking the @emph{least}
30651 significant bit of each byte first, and the final result is inverted to
30652 detect trailing zeros.
30657 An error (such as memory fault)
30658 @item C @var{crc32}
30659 The specified memory region's checksum is @var{crc32}.
30663 @itemx qsThreadInfo
30664 @cindex list active threads, remote request
30665 @cindex @samp{qfThreadInfo} packet
30666 @cindex @samp{qsThreadInfo} packet
30667 Obtain a list of all active thread IDs from the target (OS). Since there
30668 may be too many active threads to fit into one reply packet, this query
30669 works iteratively: it may require more than one query/reply sequence to
30670 obtain the entire list of threads. The first query of the sequence will
30671 be the @samp{qfThreadInfo} query; subsequent queries in the
30672 sequence will be the @samp{qsThreadInfo} query.
30674 NOTE: This packet replaces the @samp{qL} query (see below).
30678 @item m @var{thread-id}
30680 @item m @var{thread-id},@var{thread-id}@dots{}
30681 a comma-separated list of thread IDs
30683 (lower case letter @samp{L}) denotes end of list.
30686 In response to each query, the target will reply with a list of one or
30687 more thread IDs, separated by commas.
30688 @value{GDBN} will respond to each reply with a request for more thread
30689 ids (using the @samp{qs} form of the query), until the target responds
30690 with @samp{l} (lower-case el, for @dfn{last}).
30691 Refer to @ref{thread-id syntax}, for the format of the @var{thread-id}
30694 @item qGetTLSAddr:@var{thread-id},@var{offset},@var{lm}
30695 @cindex get thread-local storage address, remote request
30696 @cindex @samp{qGetTLSAddr} packet
30697 Fetch the address associated with thread local storage specified
30698 by @var{thread-id}, @var{offset}, and @var{lm}.
30700 @var{thread-id} is the thread ID associated with the
30701 thread for which to fetch the TLS address. @xref{thread-id syntax}.
30703 @var{offset} is the (big endian, hex encoded) offset associated with the
30704 thread local variable. (This offset is obtained from the debug
30705 information associated with the variable.)
30707 @var{lm} is the (big endian, hex encoded) OS/ABI-specific encoding of the
30708 the load module associated with the thread local storage. For example,
30709 a @sc{gnu}/Linux system will pass the link map address of the shared
30710 object associated with the thread local storage under consideration.
30711 Other operating environments may choose to represent the load module
30712 differently, so the precise meaning of this parameter will vary.
30716 @item @var{XX}@dots{}
30717 Hex encoded (big endian) bytes representing the address of the thread
30718 local storage requested.
30721 An error occurred. @var{nn} are hex digits.
30724 An empty reply indicates that @samp{qGetTLSAddr} is not supported by the stub.
30727 @item qGetTIBAddr:@var{thread-id}
30728 @cindex get thread information block address
30729 @cindex @samp{qGetTIBAddr} packet
30730 Fetch address of the Windows OS specific Thread Information Block.
30732 @var{thread-id} is the thread ID associated with the thread.
30736 @item @var{XX}@dots{}
30737 Hex encoded (big endian) bytes representing the linear address of the
30738 thread information block.
30741 An error occured. This means that either the thread was not found, or the
30742 address could not be retrieved.
30745 An empty reply indicates that @samp{qGetTIBAddr} is not supported by the stub.
30748 @item qL @var{startflag} @var{threadcount} @var{nextthread}
30749 Obtain thread information from RTOS. Where: @var{startflag} (one hex
30750 digit) is one to indicate the first query and zero to indicate a
30751 subsequent query; @var{threadcount} (two hex digits) is the maximum
30752 number of threads the response packet can contain; and @var{nextthread}
30753 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
30754 returned in the response as @var{argthread}.
30756 Don't use this packet; use the @samp{qfThreadInfo} query instead (see above).
30760 @item qM @var{count} @var{done} @var{argthread} @var{thread}@dots{}
30761 Where: @var{count} (two hex digits) is the number of threads being
30762 returned; @var{done} (one hex digit) is zero to indicate more threads
30763 and one indicates no further threads; @var{argthreadid} (eight hex
30764 digits) is @var{nextthread} from the request packet; @var{thread}@dots{}
30765 is a sequence of thread IDs from the target. @var{threadid} (eight hex
30766 digits). See @code{remote.c:parse_threadlist_response()}.
30770 @cindex section offsets, remote request
30771 @cindex @samp{qOffsets} packet
30772 Get section offsets that the target used when relocating the downloaded
30777 @item Text=@var{xxx};Data=@var{yyy}@r{[};Bss=@var{zzz}@r{]}
30778 Relocate the @code{Text} section by @var{xxx} from its original address.
30779 Relocate the @code{Data} section by @var{yyy} from its original address.
30780 If the object file format provides segment information (e.g.@: @sc{elf}
30781 @samp{PT_LOAD} program headers), @value{GDBN} will relocate entire
30782 segments by the supplied offsets.
30784 @emph{Note: while a @code{Bss} offset may be included in the response,
30785 @value{GDBN} ignores this and instead applies the @code{Data} offset
30786 to the @code{Bss} section.}
30788 @item TextSeg=@var{xxx}@r{[};DataSeg=@var{yyy}@r{]}
30789 Relocate the first segment of the object file, which conventionally
30790 contains program code, to a starting address of @var{xxx}. If
30791 @samp{DataSeg} is specified, relocate the second segment, which
30792 conventionally contains modifiable data, to a starting address of
30793 @var{yyy}. @value{GDBN} will report an error if the object file
30794 does not contain segment information, or does not contain at least
30795 as many segments as mentioned in the reply. Extra segments are
30796 kept at fixed offsets relative to the last relocated segment.
30799 @item qP @var{mode} @var{thread-id}
30800 @cindex thread information, remote request
30801 @cindex @samp{qP} packet
30802 Returns information on @var{thread-id}. Where: @var{mode} is a hex
30803 encoded 32 bit mode; @var{thread-id} is a thread ID
30804 (@pxref{thread-id syntax}).
30806 Don't use this packet; use the @samp{qThreadExtraInfo} query instead
30809 Reply: see @code{remote.c:remote_unpack_thread_info_response()}.
30813 @cindex non-stop mode, remote request
30814 @cindex @samp{QNonStop} packet
30816 Enter non-stop (@samp{QNonStop:1}) or all-stop (@samp{QNonStop:0}) mode.
30817 @xref{Remote Non-Stop}, for more information.
30822 The request succeeded.
30825 An error occurred. @var{nn} are hex digits.
30828 An empty reply indicates that @samp{QNonStop} is not supported by
30832 This packet is not probed by default; the remote stub must request it,
30833 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
30834 Use of this packet is controlled by the @code{set non-stop} command;
30835 @pxref{Non-Stop Mode}.
30837 @item QPassSignals: @var{signal} @r{[};@var{signal}@r{]}@dots{}
30838 @cindex pass signals to inferior, remote request
30839 @cindex @samp{QPassSignals} packet
30840 @anchor{QPassSignals}
30841 Each listed @var{signal} should be passed directly to the inferior process.
30842 Signals are numbered identically to continue packets and stop replies
30843 (@pxref{Stop Reply Packets}). Each @var{signal} list item should be
30844 strictly greater than the previous item. These signals do not need to stop
30845 the inferior, or be reported to @value{GDBN}. All other signals should be
30846 reported to @value{GDBN}. Multiple @samp{QPassSignals} packets do not
30847 combine; any earlier @samp{QPassSignals} list is completely replaced by the
30848 new list. This packet improves performance when using @samp{handle
30849 @var{signal} nostop noprint pass}.
30854 The request succeeded.
30857 An error occurred. @var{nn} are hex digits.
30860 An empty reply indicates that @samp{QPassSignals} is not supported by
30864 Use of this packet is controlled by the @code{set remote pass-signals}
30865 command (@pxref{Remote Configuration, set remote pass-signals}).
30866 This packet is not probed by default; the remote stub must request it,
30867 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
30869 @item qRcmd,@var{command}
30870 @cindex execute remote command, remote request
30871 @cindex @samp{qRcmd} packet
30872 @var{command} (hex encoded) is passed to the local interpreter for
30873 execution. Invalid commands should be reported using the output
30874 string. Before the final result packet, the target may also respond
30875 with a number of intermediate @samp{O@var{output}} console output
30876 packets. @emph{Implementors should note that providing access to a
30877 stubs's interpreter may have security implications}.
30882 A command response with no output.
30884 A command response with the hex encoded output string @var{OUTPUT}.
30886 Indicate a badly formed request.
30888 An empty reply indicates that @samp{qRcmd} is not recognized.
30891 (Note that the @code{qRcmd} packet's name is separated from the
30892 command by a @samp{,}, not a @samp{:}, contrary to the naming
30893 conventions above. Please don't use this packet as a model for new
30896 @item qSearch:memory:@var{address};@var{length};@var{search-pattern}
30897 @cindex searching memory, in remote debugging
30898 @cindex @samp{qSearch:memory} packet
30899 @anchor{qSearch memory}
30900 Search @var{length} bytes at @var{address} for @var{search-pattern}.
30901 @var{address} and @var{length} are encoded in hex.
30902 @var{search-pattern} is a sequence of bytes, hex encoded.
30907 The pattern was not found.
30909 The pattern was found at @var{address}.
30911 A badly formed request or an error was encountered while searching memory.
30913 An empty reply indicates that @samp{qSearch:memory} is not recognized.
30916 @item QStartNoAckMode
30917 @cindex @samp{QStartNoAckMode} packet
30918 @anchor{QStartNoAckMode}
30919 Request that the remote stub disable the normal @samp{+}/@samp{-}
30920 protocol acknowledgments (@pxref{Packet Acknowledgment}).
30925 The stub has switched to no-acknowledgment mode.
30926 @value{GDBN} acknowledges this reponse,
30927 but neither the stub nor @value{GDBN} shall send or expect further
30928 @samp{+}/@samp{-} acknowledgments in the current connection.
30930 An empty reply indicates that the stub does not support no-acknowledgment mode.
30933 @item qSupported @r{[}:@var{gdbfeature} @r{[};@var{gdbfeature}@r{]}@dots{} @r{]}
30934 @cindex supported packets, remote query
30935 @cindex features of the remote protocol
30936 @cindex @samp{qSupported} packet
30937 @anchor{qSupported}
30938 Tell the remote stub about features supported by @value{GDBN}, and
30939 query the stub for features it supports. This packet allows
30940 @value{GDBN} and the remote stub to take advantage of each others'
30941 features. @samp{qSupported} also consolidates multiple feature probes
30942 at startup, to improve @value{GDBN} performance---a single larger
30943 packet performs better than multiple smaller probe packets on
30944 high-latency links. Some features may enable behavior which must not
30945 be on by default, e.g.@: because it would confuse older clients or
30946 stubs. Other features may describe packets which could be
30947 automatically probed for, but are not. These features must be
30948 reported before @value{GDBN} will use them. This ``default
30949 unsupported'' behavior is not appropriate for all packets, but it
30950 helps to keep the initial connection time under control with new
30951 versions of @value{GDBN} which support increasing numbers of packets.
30955 @item @var{stubfeature} @r{[};@var{stubfeature}@r{]}@dots{}
30956 The stub supports or does not support each returned @var{stubfeature},
30957 depending on the form of each @var{stubfeature} (see below for the
30960 An empty reply indicates that @samp{qSupported} is not recognized,
30961 or that no features needed to be reported to @value{GDBN}.
30964 The allowed forms for each feature (either a @var{gdbfeature} in the
30965 @samp{qSupported} packet, or a @var{stubfeature} in the response)
30969 @item @var{name}=@var{value}
30970 The remote protocol feature @var{name} is supported, and associated
30971 with the specified @var{value}. The format of @var{value} depends
30972 on the feature, but it must not include a semicolon.
30974 The remote protocol feature @var{name} is supported, and does not
30975 need an associated value.
30977 The remote protocol feature @var{name} is not supported.
30979 The remote protocol feature @var{name} may be supported, and
30980 @value{GDBN} should auto-detect support in some other way when it is
30981 needed. This form will not be used for @var{gdbfeature} notifications,
30982 but may be used for @var{stubfeature} responses.
30985 Whenever the stub receives a @samp{qSupported} request, the
30986 supplied set of @value{GDBN} features should override any previous
30987 request. This allows @value{GDBN} to put the stub in a known
30988 state, even if the stub had previously been communicating with
30989 a different version of @value{GDBN}.
30991 The following values of @var{gdbfeature} (for the packet sent by @value{GDBN})
30996 This feature indicates whether @value{GDBN} supports multiprocess
30997 extensions to the remote protocol. @value{GDBN} does not use such
30998 extensions unless the stub also reports that it supports them by
30999 including @samp{multiprocess+} in its @samp{qSupported} reply.
31000 @xref{multiprocess extensions}, for details.
31003 This feature indicates that @value{GDBN} supports the XML target
31004 description. If the stub sees @samp{xmlRegisters=} with target
31005 specific strings separated by a comma, it will report register
31009 Stubs should ignore any unknown values for
31010 @var{gdbfeature}. Any @value{GDBN} which sends a @samp{qSupported}
31011 packet supports receiving packets of unlimited length (earlier
31012 versions of @value{GDBN} may reject overly long responses). Additional values
31013 for @var{gdbfeature} may be defined in the future to let the stub take
31014 advantage of new features in @value{GDBN}, e.g.@: incompatible
31015 improvements in the remote protocol---the @samp{multiprocess} feature is
31016 an example of such a feature. The stub's reply should be independent
31017 of the @var{gdbfeature} entries sent by @value{GDBN}; first @value{GDBN}
31018 describes all the features it supports, and then the stub replies with
31019 all the features it supports.
31021 Similarly, @value{GDBN} will silently ignore unrecognized stub feature
31022 responses, as long as each response uses one of the standard forms.
31024 Some features are flags. A stub which supports a flag feature
31025 should respond with a @samp{+} form response. Other features
31026 require values, and the stub should respond with an @samp{=}
31029 Each feature has a default value, which @value{GDBN} will use if
31030 @samp{qSupported} is not available or if the feature is not mentioned
31031 in the @samp{qSupported} response. The default values are fixed; a
31032 stub is free to omit any feature responses that match the defaults.
31034 Not all features can be probed, but for those which can, the probing
31035 mechanism is useful: in some cases, a stub's internal
31036 architecture may not allow the protocol layer to know some information
31037 about the underlying target in advance. This is especially common in
31038 stubs which may be configured for multiple targets.
31040 These are the currently defined stub features and their properties:
31042 @multitable @columnfractions 0.35 0.2 0.12 0.2
31043 @c NOTE: The first row should be @headitem, but we do not yet require
31044 @c a new enough version of Texinfo (4.7) to use @headitem.
31046 @tab Value Required
31050 @item @samp{PacketSize}
31055 @item @samp{qXfer:auxv:read}
31060 @item @samp{qXfer:features:read}
31065 @item @samp{qXfer:libraries:read}
31070 @item @samp{qXfer:memory-map:read}
31075 @item @samp{qXfer:spu:read}
31080 @item @samp{qXfer:spu:write}
31085 @item @samp{qXfer:siginfo:read}
31090 @item @samp{qXfer:siginfo:write}
31095 @item @samp{qXfer:threads:read}
31101 @item @samp{QNonStop}
31106 @item @samp{QPassSignals}
31111 @item @samp{QStartNoAckMode}
31116 @item @samp{multiprocess}
31121 @item @samp{ConditionalTracepoints}
31126 @item @samp{ReverseContinue}
31131 @item @samp{ReverseStep}
31136 @item @samp{TracepointSource}
31143 These are the currently defined stub features, in more detail:
31146 @cindex packet size, remote protocol
31147 @item PacketSize=@var{bytes}
31148 The remote stub can accept packets up to at least @var{bytes} in
31149 length. @value{GDBN} will send packets up to this size for bulk
31150 transfers, and will never send larger packets. This is a limit on the
31151 data characters in the packet, including the frame and checksum.
31152 There is no trailing NUL byte in a remote protocol packet; if the stub
31153 stores packets in a NUL-terminated format, it should allow an extra
31154 byte in its buffer for the NUL. If this stub feature is not supported,
31155 @value{GDBN} guesses based on the size of the @samp{g} packet response.
31157 @item qXfer:auxv:read
31158 The remote stub understands the @samp{qXfer:auxv:read} packet
31159 (@pxref{qXfer auxiliary vector read}).
31161 @item qXfer:features:read
31162 The remote stub understands the @samp{qXfer:features:read} packet
31163 (@pxref{qXfer target description read}).
31165 @item qXfer:libraries:read
31166 The remote stub understands the @samp{qXfer:libraries:read} packet
31167 (@pxref{qXfer library list read}).
31169 @item qXfer:memory-map:read
31170 The remote stub understands the @samp{qXfer:memory-map:read} packet
31171 (@pxref{qXfer memory map read}).
31173 @item qXfer:spu:read
31174 The remote stub understands the @samp{qXfer:spu:read} packet
31175 (@pxref{qXfer spu read}).
31177 @item qXfer:spu:write
31178 The remote stub understands the @samp{qXfer:spu:write} packet
31179 (@pxref{qXfer spu write}).
31181 @item qXfer:siginfo:read
31182 The remote stub understands the @samp{qXfer:siginfo:read} packet
31183 (@pxref{qXfer siginfo read}).
31185 @item qXfer:siginfo:write
31186 The remote stub understands the @samp{qXfer:siginfo:write} packet
31187 (@pxref{qXfer siginfo write}).
31189 @item qXfer:threads:read
31190 The remote stub understands the @samp{qXfer:threads:read} packet
31191 (@pxref{qXfer threads read}).
31194 The remote stub understands the @samp{QNonStop} packet
31195 (@pxref{QNonStop}).
31198 The remote stub understands the @samp{QPassSignals} packet
31199 (@pxref{QPassSignals}).
31201 @item QStartNoAckMode
31202 The remote stub understands the @samp{QStartNoAckMode} packet and
31203 prefers to operate in no-acknowledgment mode. @xref{Packet Acknowledgment}.
31206 @anchor{multiprocess extensions}
31207 @cindex multiprocess extensions, in remote protocol
31208 The remote stub understands the multiprocess extensions to the remote
31209 protocol syntax. The multiprocess extensions affect the syntax of
31210 thread IDs in both packets and replies (@pxref{thread-id syntax}), and
31211 add process IDs to the @samp{D} packet and @samp{W} and @samp{X}
31212 replies. Note that reporting this feature indicates support for the
31213 syntactic extensions only, not that the stub necessarily supports
31214 debugging of more than one process at a time. The stub must not use
31215 multiprocess extensions in packet replies unless @value{GDBN} has also
31216 indicated it supports them in its @samp{qSupported} request.
31218 @item qXfer:osdata:read
31219 The remote stub understands the @samp{qXfer:osdata:read} packet
31220 ((@pxref{qXfer osdata read}).
31222 @item ConditionalTracepoints
31223 The remote stub accepts and implements conditional expressions defined
31224 for tracepoints (@pxref{Tracepoint Conditions}).
31226 @item ReverseContinue
31227 The remote stub accepts and implements the reverse continue packet
31231 The remote stub accepts and implements the reverse step packet
31234 @item TracepointSource
31235 The remote stub understands the @samp{QTDPsrc} packet that supplies
31236 the source form of tracepoint definitions.
31241 @cindex symbol lookup, remote request
31242 @cindex @samp{qSymbol} packet
31243 Notify the target that @value{GDBN} is prepared to serve symbol lookup
31244 requests. Accept requests from the target for the values of symbols.
31249 The target does not need to look up any (more) symbols.
31250 @item qSymbol:@var{sym_name}
31251 The target requests the value of symbol @var{sym_name} (hex encoded).
31252 @value{GDBN} may provide the value by using the
31253 @samp{qSymbol:@var{sym_value}:@var{sym_name}} message, described
31257 @item qSymbol:@var{sym_value}:@var{sym_name}
31258 Set the value of @var{sym_name} to @var{sym_value}.
31260 @var{sym_name} (hex encoded) is the name of a symbol whose value the
31261 target has previously requested.
31263 @var{sym_value} (hex) is the value for symbol @var{sym_name}. If
31264 @value{GDBN} cannot supply a value for @var{sym_name}, then this field
31270 The target does not need to look up any (more) symbols.
31271 @item qSymbol:@var{sym_name}
31272 The target requests the value of a new symbol @var{sym_name} (hex
31273 encoded). @value{GDBN} will continue to supply the values of symbols
31274 (if available), until the target ceases to request them.
31279 @item QTDisconnected
31286 @xref{Tracepoint Packets}.
31288 @item qThreadExtraInfo,@var{thread-id}
31289 @cindex thread attributes info, remote request
31290 @cindex @samp{qThreadExtraInfo} packet
31291 Obtain a printable string description of a thread's attributes from
31292 the target OS. @var{thread-id} is a thread ID;
31293 see @ref{thread-id syntax}. This
31294 string may contain anything that the target OS thinks is interesting
31295 for @value{GDBN} to tell the user about the thread. The string is
31296 displayed in @value{GDBN}'s @code{info threads} display. Some
31297 examples of possible thread extra info strings are @samp{Runnable}, or
31298 @samp{Blocked on Mutex}.
31302 @item @var{XX}@dots{}
31303 Where @samp{@var{XX}@dots{}} is a hex encoding of @sc{ascii} data,
31304 comprising the printable string containing the extra information about
31305 the thread's attributes.
31308 (Note that the @code{qThreadExtraInfo} packet's name is separated from
31309 the command by a @samp{,}, not a @samp{:}, contrary to the naming
31310 conventions above. Please don't use this packet as a model for new
31322 @xref{Tracepoint Packets}.
31324 @item qXfer:@var{object}:read:@var{annex}:@var{offset},@var{length}
31325 @cindex read special object, remote request
31326 @cindex @samp{qXfer} packet
31327 @anchor{qXfer read}
31328 Read uninterpreted bytes from the target's special data area
31329 identified by the keyword @var{object}. Request @var{length} bytes
31330 starting at @var{offset} bytes into the data. The content and
31331 encoding of @var{annex} is specific to @var{object}; it can supply
31332 additional details about what data to access.
31334 Here are the specific requests of this form defined so far. All
31335 @samp{qXfer:@var{object}:read:@dots{}} requests use the same reply
31336 formats, listed below.
31339 @item qXfer:auxv:read::@var{offset},@var{length}
31340 @anchor{qXfer auxiliary vector read}
31341 Access the target's @dfn{auxiliary vector}. @xref{OS Information,
31342 auxiliary vector}. Note @var{annex} must be empty.
31344 This packet is not probed by default; the remote stub must request it,
31345 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
31347 @item qXfer:features:read:@var{annex}:@var{offset},@var{length}
31348 @anchor{qXfer target description read}
31349 Access the @dfn{target description}. @xref{Target Descriptions}. The
31350 annex specifies which XML document to access. The main description is
31351 always loaded from the @samp{target.xml} annex.
31353 This packet is not probed by default; the remote stub must request it,
31354 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
31356 @item qXfer:libraries:read:@var{annex}:@var{offset},@var{length}
31357 @anchor{qXfer library list read}
31358 Access the target's list of loaded libraries. @xref{Library List Format}.
31359 The annex part of the generic @samp{qXfer} packet must be empty
31360 (@pxref{qXfer read}).
31362 Targets which maintain a list of libraries in the program's memory do
31363 not need to implement this packet; it is designed for platforms where
31364 the operating system manages the list of loaded libraries.
31366 This packet is not probed by default; the remote stub must request it,
31367 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
31369 @item qXfer:memory-map:read::@var{offset},@var{length}
31370 @anchor{qXfer memory map read}
31371 Access the target's @dfn{memory-map}. @xref{Memory Map Format}. The
31372 annex part of the generic @samp{qXfer} packet must be empty
31373 (@pxref{qXfer read}).
31375 This packet is not probed by default; the remote stub must request it,
31376 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
31378 @item qXfer:siginfo:read::@var{offset},@var{length}
31379 @anchor{qXfer siginfo read}
31380 Read contents of the extra signal information on the target
31381 system. The annex part of the generic @samp{qXfer} packet must be
31382 empty (@pxref{qXfer read}).
31384 This packet is not probed by default; the remote stub must request it,
31385 by supplying an appropriate @samp{qSupported} response
31386 (@pxref{qSupported}).
31388 @item qXfer:spu:read:@var{annex}:@var{offset},@var{length}
31389 @anchor{qXfer spu read}
31390 Read contents of an @code{spufs} file on the target system. The
31391 annex specifies which file to read; it must be of the form
31392 @file{@var{id}/@var{name}}, where @var{id} specifies an SPU context ID
31393 in the target process, and @var{name} identifes the @code{spufs} file
31394 in that context to be accessed.
31396 This packet is not probed by default; the remote stub must request it,
31397 by supplying an appropriate @samp{qSupported} response
31398 (@pxref{qSupported}).
31400 @item qXfer:threads:read::@var{offset},@var{length}
31401 @anchor{qXfer threads read}
31402 Access the list of threads on target. @xref{Thread List Format}. The
31403 annex part of the generic @samp{qXfer} packet must be empty
31404 (@pxref{qXfer read}).
31406 This packet is not probed by default; the remote stub must request it,
31407 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
31409 @item qXfer:osdata:read::@var{offset},@var{length}
31410 @anchor{qXfer osdata read}
31411 Access the target's @dfn{operating system information}.
31412 @xref{Operating System Information}.
31419 Data @var{data} (@pxref{Binary Data}) has been read from the
31420 target. There may be more data at a higher address (although
31421 it is permitted to return @samp{m} even for the last valid
31422 block of data, as long as at least one byte of data was read).
31423 @var{data} may have fewer bytes than the @var{length} in the
31427 Data @var{data} (@pxref{Binary Data}) has been read from the target.
31428 There is no more data to be read. @var{data} may have fewer bytes
31429 than the @var{length} in the request.
31432 The @var{offset} in the request is at the end of the data.
31433 There is no more data to be read.
31436 The request was malformed, or @var{annex} was invalid.
31439 The offset was invalid, or there was an error encountered reading the data.
31440 @var{nn} is a hex-encoded @code{errno} value.
31443 An empty reply indicates the @var{object} string was not recognized by
31444 the stub, or that the object does not support reading.
31447 @item qXfer:@var{object}:write:@var{annex}:@var{offset}:@var{data}@dots{}
31448 @cindex write data into object, remote request
31449 @anchor{qXfer write}
31450 Write uninterpreted bytes into the target's special data area
31451 identified by the keyword @var{object}, starting at @var{offset} bytes
31452 into the data. @var{data}@dots{} is the binary-encoded data
31453 (@pxref{Binary Data}) to be written. The content and encoding of @var{annex}
31454 is specific to @var{object}; it can supply additional details about what data
31457 Here are the specific requests of this form defined so far. All
31458 @samp{qXfer:@var{object}:write:@dots{}} requests use the same reply
31459 formats, listed below.
31462 @item qXfer:siginfo:write::@var{offset}:@var{data}@dots{}
31463 @anchor{qXfer siginfo write}
31464 Write @var{data} to the extra signal information on the target system.
31465 The annex part of the generic @samp{qXfer} packet must be
31466 empty (@pxref{qXfer write}).
31468 This packet is not probed by default; the remote stub must request it,
31469 by supplying an appropriate @samp{qSupported} response
31470 (@pxref{qSupported}).
31472 @item qXfer:spu:write:@var{annex}:@var{offset}:@var{data}@dots{}
31473 @anchor{qXfer spu write}
31474 Write @var{data} to an @code{spufs} file on the target system. The
31475 annex specifies which file to write; it must be of the form
31476 @file{@var{id}/@var{name}}, where @var{id} specifies an SPU context ID
31477 in the target process, and @var{name} identifes the @code{spufs} file
31478 in that context to be accessed.
31480 This packet is not probed by default; the remote stub must request it,
31481 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
31487 @var{nn} (hex encoded) is the number of bytes written.
31488 This may be fewer bytes than supplied in the request.
31491 The request was malformed, or @var{annex} was invalid.
31494 The offset was invalid, or there was an error encountered writing the data.
31495 @var{nn} is a hex-encoded @code{errno} value.
31498 An empty reply indicates the @var{object} string was not
31499 recognized by the stub, or that the object does not support writing.
31502 @item qXfer:@var{object}:@var{operation}:@dots{}
31503 Requests of this form may be added in the future. When a stub does
31504 not recognize the @var{object} keyword, or its support for
31505 @var{object} does not recognize the @var{operation} keyword, the stub
31506 must respond with an empty packet.
31508 @item qAttached:@var{pid}
31509 @cindex query attached, remote request
31510 @cindex @samp{qAttached} packet
31511 Return an indication of whether the remote server attached to an
31512 existing process or created a new process. When the multiprocess
31513 protocol extensions are supported (@pxref{multiprocess extensions}),
31514 @var{pid} is an integer in hexadecimal format identifying the target
31515 process. Otherwise, @value{GDBN} will omit the @var{pid} field and
31516 the query packet will be simplified as @samp{qAttached}.
31518 This query is used, for example, to know whether the remote process
31519 should be detached or killed when a @value{GDBN} session is ended with
31520 the @code{quit} command.
31525 The remote server attached to an existing process.
31527 The remote server created a new process.
31529 A badly formed request or an error was encountered.
31534 @node Architecture-Specific Protocol Details
31535 @section Architecture-Specific Protocol Details
31537 This section describes how the remote protocol is applied to specific
31538 target architectures. Also see @ref{Standard Target Features}, for
31539 details of XML target descriptions for each architecture.
31543 @subsubsection Breakpoint Kinds
31545 These breakpoint kinds are defined for the @samp{Z0} and @samp{Z1} packets.
31550 16-bit Thumb mode breakpoint.
31553 32-bit Thumb mode (Thumb-2) breakpoint.
31556 32-bit ARM mode breakpoint.
31562 @subsubsection Register Packet Format
31564 The following @code{g}/@code{G} packets have previously been defined.
31565 In the below, some thirty-two bit registers are transferred as
31566 sixty-four bits. Those registers should be zero/sign extended (which?)
31567 to fill the space allocated. Register bytes are transferred in target
31568 byte order. The two nibbles within a register byte are transferred
31569 most-significant - least-significant.
31575 All registers are transferred as thirty-two bit quantities in the order:
31576 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
31577 registers; fsr; fir; fp.
31581 All registers are transferred as sixty-four bit quantities (including
31582 thirty-two bit registers such as @code{sr}). The ordering is the same
31587 @node Tracepoint Packets
31588 @section Tracepoint Packets
31589 @cindex tracepoint packets
31590 @cindex packets, tracepoint
31592 Here we describe the packets @value{GDBN} uses to implement
31593 tracepoints (@pxref{Tracepoints}).
31597 @item QTDP:@var{n}:@var{addr}:@var{ena}:@var{step}:@var{pass}[:F@var{flen}][:X@var{len},@var{bytes}]@r{[}-@r{]}
31598 Create a new tracepoint, number @var{n}, at @var{addr}. If @var{ena}
31599 is @samp{E}, then the tracepoint is enabled; if it is @samp{D}, then
31600 the tracepoint is disabled. @var{step} is the tracepoint's step
31601 count, and @var{pass} is its pass count. If an @samp{F} is present,
31602 then the tracepoint is to be a fast tracepoint, and the @var{flen} is
31603 the number of bytes that the target should copy elsewhere to make room
31604 for the tracepoint. If an @samp{X} is present, it introduces a
31605 tracepoint condition, which consists of a hexadecimal length, followed
31606 by a comma and hex-encoded bytes, in a manner similar to action
31607 encodings as described below. If the trailing @samp{-} is present,
31608 further @samp{QTDP} packets will follow to specify this tracepoint's
31614 The packet was understood and carried out.
31616 The packet was not recognized.
31619 @item QTDP:-@var{n}:@var{addr}:@r{[}S@r{]}@var{action}@dots{}@r{[}-@r{]}
31620 Define actions to be taken when a tracepoint is hit. @var{n} and
31621 @var{addr} must be the same as in the initial @samp{QTDP} packet for
31622 this tracepoint. This packet may only be sent immediately after
31623 another @samp{QTDP} packet that ended with a @samp{-}. If the
31624 trailing @samp{-} is present, further @samp{QTDP} packets will follow,
31625 specifying more actions for this tracepoint.
31627 In the series of action packets for a given tracepoint, at most one
31628 can have an @samp{S} before its first @var{action}. If such a packet
31629 is sent, it and the following packets define ``while-stepping''
31630 actions. Any prior packets define ordinary actions --- that is, those
31631 taken when the tracepoint is first hit. If no action packet has an
31632 @samp{S}, then all the packets in the series specify ordinary
31633 tracepoint actions.
31635 The @samp{@var{action}@dots{}} portion of the packet is a series of
31636 actions, concatenated without separators. Each action has one of the
31642 Collect the registers whose bits are set in @var{mask}. @var{mask} is
31643 a hexadecimal number whose @var{i}'th bit is set if register number
31644 @var{i} should be collected. (The least significant bit is numbered
31645 zero.) Note that @var{mask} may be any number of digits long; it may
31646 not fit in a 32-bit word.
31648 @item M @var{basereg},@var{offset},@var{len}
31649 Collect @var{len} bytes of memory starting at the address in register
31650 number @var{basereg}, plus @var{offset}. If @var{basereg} is
31651 @samp{-1}, then the range has a fixed address: @var{offset} is the
31652 address of the lowest byte to collect. The @var{basereg},
31653 @var{offset}, and @var{len} parameters are all unsigned hexadecimal
31654 values (the @samp{-1} value for @var{basereg} is a special case).
31656 @item X @var{len},@var{expr}
31657 Evaluate @var{expr}, whose length is @var{len}, and collect memory as
31658 it directs. @var{expr} is an agent expression, as described in
31659 @ref{Agent Expressions}. Each byte of the expression is encoded as a
31660 two-digit hex number in the packet; @var{len} is the number of bytes
31661 in the expression (and thus one-half the number of hex digits in the
31666 Any number of actions may be packed together in a single @samp{QTDP}
31667 packet, as long as the packet does not exceed the maximum packet
31668 length (400 bytes, for many stubs). There may be only one @samp{R}
31669 action per tracepoint, and it must precede any @samp{M} or @samp{X}
31670 actions. Any registers referred to by @samp{M} and @samp{X} actions
31671 must be collected by a preceding @samp{R} action. (The
31672 ``while-stepping'' actions are treated as if they were attached to a
31673 separate tracepoint, as far as these restrictions are concerned.)
31678 The packet was understood and carried out.
31680 The packet was not recognized.
31683 @item QTDPsrc:@var{n}:@var{addr}:@var{type}:@var{start}:@var{slen}:@var{bytes}
31684 @cindex @samp{QTDPsrc} packet
31685 Specify a source string of tracepoint @var{n} at address @var{addr}.
31686 This is useful to get accurate reproduction of the tracepoints
31687 originally downloaded at the beginning of the trace run. @var{type}
31688 is the name of the tracepoint part, such as @samp{cond} for the
31689 tracepoint's conditional expression (see below for a list of types), while
31690 @var{bytes} is the string, encoded in hexadecimal.
31692 @var{start} is the offset of the @var{bytes} within the overall source
31693 string, while @var{slen} is the total length of the source string.
31694 This is intended for handling source strings that are longer than will
31695 fit in a single packet.
31696 @c Add detailed example when this info is moved into a dedicated
31697 @c tracepoint descriptions section.
31699 The available string types are @samp{at} for the location,
31700 @samp{cond} for the conditional, and @samp{cmd} for an action command.
31701 @value{GDBN} sends a separate packet for each command in the action
31702 list, in the same order in which the commands are stored in the list.
31704 The target does not need to do anything with source strings except
31705 report them back as part of the replies to the @samp{qTfP}/@samp{qTsP}
31708 Although this packet is optional, and @value{GDBN} will only send it
31709 if the target replies with @samp{TracepointSource} @xref{General
31710 Query Packets}, it makes both disconnected tracing and trace files
31711 much easier to use. Otherwise the user must be careful that the
31712 tracepoints in effect while looking at trace frames are identical to
31713 the ones in effect during the trace run; even a small discrepancy
31714 could cause @samp{tdump} not to work, or a particular trace frame not
31717 @item QTDV:@var{n}:@var{value}
31718 @cindex define trace state variable, remote request
31719 @cindex @samp{QTDV} packet
31720 Create a new trace state variable, number @var{n}, with an initial
31721 value of @var{value}, which is a 64-bit signed integer. Both @var{n}
31722 and @var{value} are encoded as hexadecimal values. @value{GDBN} has
31723 the option of not using this packet for initial values of zero; the
31724 target should simply create the trace state variables as they are
31725 mentioned in expressions.
31727 @item QTFrame:@var{n}
31728 Select the @var{n}'th tracepoint frame from the buffer, and use the
31729 register and memory contents recorded there to answer subsequent
31730 request packets from @value{GDBN}.
31732 A successful reply from the stub indicates that the stub has found the
31733 requested frame. The response is a series of parts, concatenated
31734 without separators, describing the frame we selected. Each part has
31735 one of the following forms:
31739 The selected frame is number @var{n} in the trace frame buffer;
31740 @var{f} is a hexadecimal number. If @var{f} is @samp{-1}, then there
31741 was no frame matching the criteria in the request packet.
31744 The selected trace frame records a hit of tracepoint number @var{t};
31745 @var{t} is a hexadecimal number.
31749 @item QTFrame:pc:@var{addr}
31750 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
31751 currently selected frame whose PC is @var{addr};
31752 @var{addr} is a hexadecimal number.
31754 @item QTFrame:tdp:@var{t}
31755 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
31756 currently selected frame that is a hit of tracepoint @var{t}; @var{t}
31757 is a hexadecimal number.
31759 @item QTFrame:range:@var{start}:@var{end}
31760 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
31761 currently selected frame whose PC is between @var{start} (inclusive)
31762 and @var{end} (inclusive); @var{start} and @var{end} are hexadecimal
31765 @item QTFrame:outside:@var{start}:@var{end}
31766 Like @samp{QTFrame:range:@var{start}:@var{end}}, but select the first
31767 frame @emph{outside} the given range of addresses (exclusive).
31770 Begin the tracepoint experiment. Begin collecting data from tracepoint
31771 hits in the trace frame buffer.
31774 End the tracepoint experiment. Stop collecting trace frames.
31777 Clear the table of tracepoints, and empty the trace frame buffer.
31779 @item QTro:@var{start1},@var{end1}:@var{start2},@var{end2}:@dots{}
31780 Establish the given ranges of memory as ``transparent''. The stub
31781 will answer requests for these ranges from memory's current contents,
31782 if they were not collected as part of the tracepoint hit.
31784 @value{GDBN} uses this to mark read-only regions of memory, like those
31785 containing program code. Since these areas never change, they should
31786 still have the same contents they did when the tracepoint was hit, so
31787 there's no reason for the stub to refuse to provide their contents.
31789 @item QTDisconnected:@var{value}
31790 Set the choice to what to do with the tracing run when @value{GDBN}
31791 disconnects from the target. A @var{value} of 1 directs the target to
31792 continue the tracing run, while 0 tells the target to stop tracing if
31793 @value{GDBN} is no longer in the picture.
31796 Ask the stub if there is a trace experiment running right now.
31798 The reply has the form:
31802 @item T@var{running}@r{[};@var{field}@r{]}@dots{}
31803 @var{running} is a single digit @code{1} if the trace is presently
31804 running, or @code{0} if not. It is followed by semicolon-separated
31805 optional fields that an agent may use to report additional status.
31809 If the trace is not running, the agent may report any of several
31810 explanations as one of the optional fields:
31815 No trace has been run yet.
31818 The trace was stopped by a user-originated stop command.
31821 The trace stopped because the trace buffer filled up.
31823 @item tdisconnected:0
31824 The trace stopped because @value{GDBN} disconnected from the target.
31826 @item tpasscount:@var{tpnum}
31827 The trace stopped because tracepoint @var{tpnum} exceeded its pass count.
31829 @item terror:@var{text}:@var{tpnum}
31830 The trace stopped because tracepoint @var{tpnum} had an error. The
31831 string @var{text} is available to describe the nature of the error
31832 (for instance, a divide by zero in the condition expression).
31833 @var{text} is hex encoded.
31836 The trace stopped for some other reason.
31840 Additional optional fields supply statistical and other information.
31841 Although not required, they are extremely useful for users monitoring
31842 the progress of a trace run. If a trace has stopped, and these
31843 numbers are reported, they must reflect the state of the just-stopped
31848 @item tframes:@var{n}
31849 The number of trace frames in the buffer.
31851 @item tcreated:@var{n}
31852 The total number of trace frames created during the run. This may
31853 be larger than the trace frame count, if the buffer is circular.
31855 @item tsize:@var{n}
31856 The total size of the trace buffer, in bytes.
31858 @item tfree:@var{n}
31859 The number of bytes still unused in the buffer.
31861 @item circular:@var{n}
31862 The value of the circular trace buffer flag. @code{1} means that the
31863 trace buffer is circular and old trace frames will be discarded if
31864 necessary to make room, @code{0} means that the trace buffer is linear
31867 @item disconn:@var{n}
31868 The value of the disconnected tracing flag. @code{1} means that
31869 tracing will continue after @value{GDBN} disconnects, @code{0} means
31870 that the trace run will stop.
31874 @item qTV:@var{var}
31875 @cindex trace state variable value, remote request
31876 @cindex @samp{qTV} packet
31877 Ask the stub for the value of the trace state variable number @var{var}.
31882 The value of the variable is @var{value}. This will be the current
31883 value of the variable if the user is examining a running target, or a
31884 saved value if the variable was collected in the trace frame that the
31885 user is looking at. Note that multiple requests may result in
31886 different reply values, such as when requesting values while the
31887 program is running.
31890 The value of the variable is unknown. This would occur, for example,
31891 if the user is examining a trace frame in which the requested variable
31897 These packets request data about tracepoints that are being used by
31898 the target. @value{GDBN} sends @code{qTfP} to get the first piece
31899 of data, and multiple @code{qTsP} to get additional pieces. Replies
31900 to these packets generally take the form of the @code{QTDP} packets
31901 that define tracepoints. (FIXME add detailed syntax)
31905 These packets request data about trace state variables that are on the
31906 target. @value{GDBN} sends @code{qTfV} to get the first vari of data,
31907 and multiple @code{qTsV} to get additional variables. Replies to
31908 these packets follow the syntax of the @code{QTDV} packets that define
31909 trace state variables.
31911 @item QTSave:@var{filename}
31912 This packet directs the target to save trace data to the file name
31913 @var{filename} in the target's filesystem. @var{filename} is encoded
31914 as a hex string; the interpretation of the file name (relative vs
31915 absolute, wild cards, etc) is up to the target.
31917 @item qTBuffer:@var{offset},@var{len}
31918 Return up to @var{len} bytes of the current contents of trace buffer,
31919 starting at @var{offset}. The trace buffer is treated as if it were
31920 a contiguous collection of traceframes, as per the trace file format.
31921 The reply consists as many hex-encoded bytes as the target can deliver
31922 in a packet; it is not an error to return fewer than were asked for.
31923 A reply consisting of just @code{l} indicates that no bytes are
31926 @item QTBuffer:circular:@var{value}
31927 This packet directs the target to use a circular trace buffer if
31928 @var{value} is 1, or a linear buffer if the value is 0.
31932 @node Host I/O Packets
31933 @section Host I/O Packets
31934 @cindex Host I/O, remote protocol
31935 @cindex file transfer, remote protocol
31937 The @dfn{Host I/O} packets allow @value{GDBN} to perform I/O
31938 operations on the far side of a remote link. For example, Host I/O is
31939 used to upload and download files to a remote target with its own
31940 filesystem. Host I/O uses the same constant values and data structure
31941 layout as the target-initiated File-I/O protocol. However, the
31942 Host I/O packets are structured differently. The target-initiated
31943 protocol relies on target memory to store parameters and buffers.
31944 Host I/O requests are initiated by @value{GDBN}, and the
31945 target's memory is not involved. @xref{File-I/O Remote Protocol
31946 Extension}, for more details on the target-initiated protocol.
31948 The Host I/O request packets all encode a single operation along with
31949 its arguments. They have this format:
31953 @item vFile:@var{operation}: @var{parameter}@dots{}
31954 @var{operation} is the name of the particular request; the target
31955 should compare the entire packet name up to the second colon when checking
31956 for a supported operation. The format of @var{parameter} depends on
31957 the operation. Numbers are always passed in hexadecimal. Negative
31958 numbers have an explicit minus sign (i.e.@: two's complement is not
31959 used). Strings (e.g.@: filenames) are encoded as a series of
31960 hexadecimal bytes. The last argument to a system call may be a
31961 buffer of escaped binary data (@pxref{Binary Data}).
31965 The valid responses to Host I/O packets are:
31969 @item F @var{result} [, @var{errno}] [; @var{attachment}]
31970 @var{result} is the integer value returned by this operation, usually
31971 non-negative for success and -1 for errors. If an error has occured,
31972 @var{errno} will be included in the result. @var{errno} will have a
31973 value defined by the File-I/O protocol (@pxref{Errno Values}). For
31974 operations which return data, @var{attachment} supplies the data as a
31975 binary buffer. Binary buffers in response packets are escaped in the
31976 normal way (@pxref{Binary Data}). See the individual packet
31977 documentation for the interpretation of @var{result} and
31981 An empty response indicates that this operation is not recognized.
31985 These are the supported Host I/O operations:
31988 @item vFile:open: @var{pathname}, @var{flags}, @var{mode}
31989 Open a file at @var{pathname} and return a file descriptor for it, or
31990 return -1 if an error occurs. @var{pathname} is a string,
31991 @var{flags} is an integer indicating a mask of open flags
31992 (@pxref{Open Flags}), and @var{mode} is an integer indicating a mask
31993 of mode bits to use if the file is created (@pxref{mode_t Values}).
31994 @xref{open}, for details of the open flags and mode values.
31996 @item vFile:close: @var{fd}
31997 Close the open file corresponding to @var{fd} and return 0, or
31998 -1 if an error occurs.
32000 @item vFile:pread: @var{fd}, @var{count}, @var{offset}
32001 Read data from the open file corresponding to @var{fd}. Up to
32002 @var{count} bytes will be read from the file, starting at @var{offset}
32003 relative to the start of the file. The target may read fewer bytes;
32004 common reasons include packet size limits and an end-of-file
32005 condition. The number of bytes read is returned. Zero should only be
32006 returned for a successful read at the end of the file, or if
32007 @var{count} was zero.
32009 The data read should be returned as a binary attachment on success.
32010 If zero bytes were read, the response should include an empty binary
32011 attachment (i.e.@: a trailing semicolon). The return value is the
32012 number of target bytes read; the binary attachment may be longer if
32013 some characters were escaped.
32015 @item vFile:pwrite: @var{fd}, @var{offset}, @var{data}
32016 Write @var{data} (a binary buffer) to the open file corresponding
32017 to @var{fd}. Start the write at @var{offset} from the start of the
32018 file. Unlike many @code{write} system calls, there is no
32019 separate @var{count} argument; the length of @var{data} in the
32020 packet is used. @samp{vFile:write} returns the number of bytes written,
32021 which may be shorter than the length of @var{data}, or -1 if an
32024 @item vFile:unlink: @var{pathname}
32025 Delete the file at @var{pathname} on the target. Return 0,
32026 or -1 if an error occurs. @var{pathname} is a string.
32031 @section Interrupts
32032 @cindex interrupts (remote protocol)
32034 When a program on the remote target is running, @value{GDBN} may
32035 attempt to interrupt it by sending a @samp{Ctrl-C}, @code{BREAK} or
32036 a @code{BREAK} followed by @code{g},
32037 control of which is specified via @value{GDBN}'s @samp{interrupt-sequence}.
32039 The precise meaning of @code{BREAK} is defined by the transport
32040 mechanism and may, in fact, be undefined. @value{GDBN} does not
32041 currently define a @code{BREAK} mechanism for any of the network
32042 interfaces except for TCP, in which case @value{GDBN} sends the
32043 @code{telnet} BREAK sequence.
32045 @samp{Ctrl-C}, on the other hand, is defined and implemented for all
32046 transport mechanisms. It is represented by sending the single byte
32047 @code{0x03} without any of the usual packet overhead described in
32048 the Overview section (@pxref{Overview}). When a @code{0x03} byte is
32049 transmitted as part of a packet, it is considered to be packet data
32050 and does @emph{not} represent an interrupt. E.g., an @samp{X} packet
32051 (@pxref{X packet}), used for binary downloads, may include an unescaped
32052 @code{0x03} as part of its packet.
32054 @code{BREAK} followed by @code{g} is also known as Magic SysRq g.
32055 When Linux kernel receives this sequence from serial port,
32056 it stops execution and connects to gdb.
32058 Stubs are not required to recognize these interrupt mechanisms and the
32059 precise meaning associated with receipt of the interrupt is
32060 implementation defined. If the target supports debugging of multiple
32061 threads and/or processes, it should attempt to interrupt all
32062 currently-executing threads and processes.
32063 If the stub is successful at interrupting the
32064 running program, it should send one of the stop
32065 reply packets (@pxref{Stop Reply Packets}) to @value{GDBN} as a result
32066 of successfully stopping the program in all-stop mode, and a stop reply
32067 for each stopped thread in non-stop mode.
32068 Interrupts received while the
32069 program is stopped are discarded.
32071 @node Notification Packets
32072 @section Notification Packets
32073 @cindex notification packets
32074 @cindex packets, notification
32076 The @value{GDBN} remote serial protocol includes @dfn{notifications},
32077 packets that require no acknowledgment. Both the GDB and the stub
32078 may send notifications (although the only notifications defined at
32079 present are sent by the stub). Notifications carry information
32080 without incurring the round-trip latency of an acknowledgment, and so
32081 are useful for low-impact communications where occasional packet loss
32084 A notification packet has the form @samp{% @var{data} #
32085 @var{checksum}}, where @var{data} is the content of the notification,
32086 and @var{checksum} is a checksum of @var{data}, computed and formatted
32087 as for ordinary @value{GDBN} packets. A notification's @var{data}
32088 never contains @samp{$}, @samp{%} or @samp{#} characters. Upon
32089 receiving a notification, the recipient sends no @samp{+} or @samp{-}
32090 to acknowledge the notification's receipt or to report its corruption.
32092 Every notification's @var{data} begins with a name, which contains no
32093 colon characters, followed by a colon character.
32095 Recipients should silently ignore corrupted notifications and
32096 notifications they do not understand. Recipients should restart
32097 timeout periods on receipt of a well-formed notification, whether or
32098 not they understand it.
32100 Senders should only send the notifications described here when this
32101 protocol description specifies that they are permitted. In the
32102 future, we may extend the protocol to permit existing notifications in
32103 new contexts; this rule helps older senders avoid confusing newer
32106 (Older versions of @value{GDBN} ignore bytes received until they see
32107 the @samp{$} byte that begins an ordinary packet, so new stubs may
32108 transmit notifications without fear of confusing older clients. There
32109 are no notifications defined for @value{GDBN} to send at the moment, but we
32110 assume that most older stubs would ignore them, as well.)
32112 The following notification packets from the stub to @value{GDBN} are
32116 @item Stop: @var{reply}
32117 Report an asynchronous stop event in non-stop mode.
32118 The @var{reply} has the form of a stop reply, as
32119 described in @ref{Stop Reply Packets}. Refer to @ref{Remote Non-Stop},
32120 for information on how these notifications are acknowledged by
32124 @node Remote Non-Stop
32125 @section Remote Protocol Support for Non-Stop Mode
32127 @value{GDBN}'s remote protocol supports non-stop debugging of
32128 multi-threaded programs, as described in @ref{Non-Stop Mode}. If the stub
32129 supports non-stop mode, it should report that to @value{GDBN} by including
32130 @samp{QNonStop+} in its @samp{qSupported} response (@pxref{qSupported}).
32132 @value{GDBN} typically sends a @samp{QNonStop} packet only when
32133 establishing a new connection with the stub. Entering non-stop mode
32134 does not alter the state of any currently-running threads, but targets
32135 must stop all threads in any already-attached processes when entering
32136 all-stop mode. @value{GDBN} uses the @samp{?} packet as necessary to
32137 probe the target state after a mode change.
32139 In non-stop mode, when an attached process encounters an event that
32140 would otherwise be reported with a stop reply, it uses the
32141 asynchronous notification mechanism (@pxref{Notification Packets}) to
32142 inform @value{GDBN}. In contrast to all-stop mode, where all threads
32143 in all processes are stopped when a stop reply is sent, in non-stop
32144 mode only the thread reporting the stop event is stopped. That is,
32145 when reporting a @samp{S} or @samp{T} response to indicate completion
32146 of a step operation, hitting a breakpoint, or a fault, only the
32147 affected thread is stopped; any other still-running threads continue
32148 to run. When reporting a @samp{W} or @samp{X} response, all running
32149 threads belonging to other attached processes continue to run.
32151 Only one stop reply notification at a time may be pending; if
32152 additional stop events occur before @value{GDBN} has acknowledged the
32153 previous notification, they must be queued by the stub for later
32154 synchronous transmission in response to @samp{vStopped} packets from
32155 @value{GDBN}. Because the notification mechanism is unreliable,
32156 the stub is permitted to resend a stop reply notification
32157 if it believes @value{GDBN} may not have received it. @value{GDBN}
32158 ignores additional stop reply notifications received before it has
32159 finished processing a previous notification and the stub has completed
32160 sending any queued stop events.
32162 Otherwise, @value{GDBN} must be prepared to receive a stop reply
32163 notification at any time. Specifically, they may appear when
32164 @value{GDBN} is not otherwise reading input from the stub, or when
32165 @value{GDBN} is expecting to read a normal synchronous response or a
32166 @samp{+}/@samp{-} acknowledgment to a packet it has sent.
32167 Notification packets are distinct from any other communication from
32168 the stub so there is no ambiguity.
32170 After receiving a stop reply notification, @value{GDBN} shall
32171 acknowledge it by sending a @samp{vStopped} packet (@pxref{vStopped packet})
32172 as a regular, synchronous request to the stub. Such acknowledgment
32173 is not required to happen immediately, as @value{GDBN} is permitted to
32174 send other, unrelated packets to the stub first, which the stub should
32177 Upon receiving a @samp{vStopped} packet, if the stub has other queued
32178 stop events to report to @value{GDBN}, it shall respond by sending a
32179 normal stop reply response. @value{GDBN} shall then send another
32180 @samp{vStopped} packet to solicit further responses; again, it is
32181 permitted to send other, unrelated packets as well which the stub
32182 should process normally.
32184 If the stub receives a @samp{vStopped} packet and there are no
32185 additional stop events to report, the stub shall return an @samp{OK}
32186 response. At this point, if further stop events occur, the stub shall
32187 send a new stop reply notification, @value{GDBN} shall accept the
32188 notification, and the process shall be repeated.
32190 In non-stop mode, the target shall respond to the @samp{?} packet as
32191 follows. First, any incomplete stop reply notification/@samp{vStopped}
32192 sequence in progress is abandoned. The target must begin a new
32193 sequence reporting stop events for all stopped threads, whether or not
32194 it has previously reported those events to @value{GDBN}. The first
32195 stop reply is sent as a synchronous reply to the @samp{?} packet, and
32196 subsequent stop replies are sent as responses to @samp{vStopped} packets
32197 using the mechanism described above. The target must not send
32198 asynchronous stop reply notifications until the sequence is complete.
32199 If all threads are running when the target receives the @samp{?} packet,
32200 or if the target is not attached to any process, it shall respond
32203 @node Packet Acknowledgment
32204 @section Packet Acknowledgment
32206 @cindex acknowledgment, for @value{GDBN} remote
32207 @cindex packet acknowledgment, for @value{GDBN} remote
32208 By default, when either the host or the target machine receives a packet,
32209 the first response expected is an acknowledgment: either @samp{+} (to indicate
32210 the package was received correctly) or @samp{-} (to request retransmission).
32211 This mechanism allows the @value{GDBN} remote protocol to operate over
32212 unreliable transport mechanisms, such as a serial line.
32214 In cases where the transport mechanism is itself reliable (such as a pipe or
32215 TCP connection), the @samp{+}/@samp{-} acknowledgments are redundant.
32216 It may be desirable to disable them in that case to reduce communication
32217 overhead, or for other reasons. This can be accomplished by means of the
32218 @samp{QStartNoAckMode} packet; @pxref{QStartNoAckMode}.
32220 When in no-acknowledgment mode, neither the stub nor @value{GDBN} shall send or
32221 expect @samp{+}/@samp{-} protocol acknowledgments. The packet
32222 and response format still includes the normal checksum, as described in
32223 @ref{Overview}, but the checksum may be ignored by the receiver.
32225 If the stub supports @samp{QStartNoAckMode} and prefers to operate in
32226 no-acknowledgment mode, it should report that to @value{GDBN}
32227 by including @samp{QStartNoAckMode+} in its response to @samp{qSupported};
32228 @pxref{qSupported}.
32229 If @value{GDBN} also supports @samp{QStartNoAckMode} and it has not been
32230 disabled via the @code{set remote noack-packet off} command
32231 (@pxref{Remote Configuration}),
32232 @value{GDBN} may then send a @samp{QStartNoAckMode} packet to the stub.
32233 Only then may the stub actually turn off packet acknowledgments.
32234 @value{GDBN} sends a final @samp{+} acknowledgment of the stub's @samp{OK}
32235 response, which can be safely ignored by the stub.
32237 Note that @code{set remote noack-packet} command only affects negotiation
32238 between @value{GDBN} and the stub when subsequent connections are made;
32239 it does not affect the protocol acknowledgment state for any current
32241 Since @samp{+}/@samp{-} acknowledgments are enabled by default when a
32242 new connection is established,
32243 there is also no protocol request to re-enable the acknowledgments
32244 for the current connection, once disabled.
32249 Example sequence of a target being re-started. Notice how the restart
32250 does not get any direct output:
32255 @emph{target restarts}
32258 <- @code{T001:1234123412341234}
32262 Example sequence of a target being stepped by a single instruction:
32265 -> @code{G1445@dots{}}
32270 <- @code{T001:1234123412341234}
32274 <- @code{1455@dots{}}
32278 @node File-I/O Remote Protocol Extension
32279 @section File-I/O Remote Protocol Extension
32280 @cindex File-I/O remote protocol extension
32283 * File-I/O Overview::
32284 * Protocol Basics::
32285 * The F Request Packet::
32286 * The F Reply Packet::
32287 * The Ctrl-C Message::
32289 * List of Supported Calls::
32290 * Protocol-specific Representation of Datatypes::
32292 * File-I/O Examples::
32295 @node File-I/O Overview
32296 @subsection File-I/O Overview
32297 @cindex file-i/o overview
32299 The @dfn{File I/O remote protocol extension} (short: File-I/O) allows the
32300 target to use the host's file system and console I/O to perform various
32301 system calls. System calls on the target system are translated into a
32302 remote protocol packet to the host system, which then performs the needed
32303 actions and returns a response packet to the target system.
32304 This simulates file system operations even on targets that lack file systems.
32306 The protocol is defined to be independent of both the host and target systems.
32307 It uses its own internal representation of datatypes and values. Both
32308 @value{GDBN} and the target's @value{GDBN} stub are responsible for
32309 translating the system-dependent value representations into the internal
32310 protocol representations when data is transmitted.
32312 The communication is synchronous. A system call is possible only when
32313 @value{GDBN} is waiting for a response from the @samp{C}, @samp{c}, @samp{S}
32314 or @samp{s} packets. While @value{GDBN} handles the request for a system call,
32315 the target is stopped to allow deterministic access to the target's
32316 memory. Therefore File-I/O is not interruptible by target signals. On
32317 the other hand, it is possible to interrupt File-I/O by a user interrupt
32318 (@samp{Ctrl-C}) within @value{GDBN}.
32320 The target's request to perform a host system call does not finish
32321 the latest @samp{C}, @samp{c}, @samp{S} or @samp{s} action. That means,
32322 after finishing the system call, the target returns to continuing the
32323 previous activity (continue, step). No additional continue or step
32324 request from @value{GDBN} is required.
32327 (@value{GDBP}) continue
32328 <- target requests 'system call X'
32329 target is stopped, @value{GDBN} executes system call
32330 -> @value{GDBN} returns result
32331 ... target continues, @value{GDBN} returns to wait for the target
32332 <- target hits breakpoint and sends a Txx packet
32335 The protocol only supports I/O on the console and to regular files on
32336 the host file system. Character or block special devices, pipes,
32337 named pipes, sockets or any other communication method on the host
32338 system are not supported by this protocol.
32340 File I/O is not supported in non-stop mode.
32342 @node Protocol Basics
32343 @subsection Protocol Basics
32344 @cindex protocol basics, file-i/o
32346 The File-I/O protocol uses the @code{F} packet as the request as well
32347 as reply packet. Since a File-I/O system call can only occur when
32348 @value{GDBN} is waiting for a response from the continuing or stepping target,
32349 the File-I/O request is a reply that @value{GDBN} has to expect as a result
32350 of a previous @samp{C}, @samp{c}, @samp{S} or @samp{s} packet.
32351 This @code{F} packet contains all information needed to allow @value{GDBN}
32352 to call the appropriate host system call:
32356 A unique identifier for the requested system call.
32359 All parameters to the system call. Pointers are given as addresses
32360 in the target memory address space. Pointers to strings are given as
32361 pointer/length pair. Numerical values are given as they are.
32362 Numerical control flags are given in a protocol-specific representation.
32366 At this point, @value{GDBN} has to perform the following actions.
32370 If the parameters include pointer values to data needed as input to a
32371 system call, @value{GDBN} requests this data from the target with a
32372 standard @code{m} packet request. This additional communication has to be
32373 expected by the target implementation and is handled as any other @code{m}
32377 @value{GDBN} translates all value from protocol representation to host
32378 representation as needed. Datatypes are coerced into the host types.
32381 @value{GDBN} calls the system call.
32384 It then coerces datatypes back to protocol representation.
32387 If the system call is expected to return data in buffer space specified
32388 by pointer parameters to the call, the data is transmitted to the
32389 target using a @code{M} or @code{X} packet. This packet has to be expected
32390 by the target implementation and is handled as any other @code{M} or @code{X}
32395 Eventually @value{GDBN} replies with another @code{F} packet which contains all
32396 necessary information for the target to continue. This at least contains
32403 @code{errno}, if has been changed by the system call.
32410 After having done the needed type and value coercion, the target continues
32411 the latest continue or step action.
32413 @node The F Request Packet
32414 @subsection The @code{F} Request Packet
32415 @cindex file-i/o request packet
32416 @cindex @code{F} request packet
32418 The @code{F} request packet has the following format:
32421 @item F@var{call-id},@var{parameter@dots{}}
32423 @var{call-id} is the identifier to indicate the host system call to be called.
32424 This is just the name of the function.
32426 @var{parameter@dots{}} are the parameters to the system call.
32427 Parameters are hexadecimal integer values, either the actual values in case
32428 of scalar datatypes, pointers to target buffer space in case of compound
32429 datatypes and unspecified memory areas, or pointer/length pairs in case
32430 of string parameters. These are appended to the @var{call-id} as a
32431 comma-delimited list. All values are transmitted in ASCII
32432 string representation, pointer/length pairs separated by a slash.
32438 @node The F Reply Packet
32439 @subsection The @code{F} Reply Packet
32440 @cindex file-i/o reply packet
32441 @cindex @code{F} reply packet
32443 The @code{F} reply packet has the following format:
32447 @item F@var{retcode},@var{errno},@var{Ctrl-C flag};@var{call-specific attachment}
32449 @var{retcode} is the return code of the system call as hexadecimal value.
32451 @var{errno} is the @code{errno} set by the call, in protocol-specific
32453 This parameter can be omitted if the call was successful.
32455 @var{Ctrl-C flag} is only sent if the user requested a break. In this
32456 case, @var{errno} must be sent as well, even if the call was successful.
32457 The @var{Ctrl-C flag} itself consists of the character @samp{C}:
32464 or, if the call was interrupted before the host call has been performed:
32471 assuming 4 is the protocol-specific representation of @code{EINTR}.
32476 @node The Ctrl-C Message
32477 @subsection The @samp{Ctrl-C} Message
32478 @cindex ctrl-c message, in file-i/o protocol
32480 If the @samp{Ctrl-C} flag is set in the @value{GDBN}
32481 reply packet (@pxref{The F Reply Packet}),
32482 the target should behave as if it had
32483 gotten a break message. The meaning for the target is ``system call
32484 interrupted by @code{SIGINT}''. Consequentially, the target should actually stop
32485 (as with a break message) and return to @value{GDBN} with a @code{T02}
32488 It's important for the target to know in which
32489 state the system call was interrupted. There are two possible cases:
32493 The system call hasn't been performed on the host yet.
32496 The system call on the host has been finished.
32500 These two states can be distinguished by the target by the value of the
32501 returned @code{errno}. If it's the protocol representation of @code{EINTR}, the system
32502 call hasn't been performed. This is equivalent to the @code{EINTR} handling
32503 on POSIX systems. In any other case, the target may presume that the
32504 system call has been finished --- successfully or not --- and should behave
32505 as if the break message arrived right after the system call.
32507 @value{GDBN} must behave reliably. If the system call has not been called
32508 yet, @value{GDBN} may send the @code{F} reply immediately, setting @code{EINTR} as
32509 @code{errno} in the packet. If the system call on the host has been finished
32510 before the user requests a break, the full action must be finished by
32511 @value{GDBN}. This requires sending @code{M} or @code{X} packets as necessary.
32512 The @code{F} packet may only be sent when either nothing has happened
32513 or the full action has been completed.
32516 @subsection Console I/O
32517 @cindex console i/o as part of file-i/o
32519 By default and if not explicitly closed by the target system, the file
32520 descriptors 0, 1 and 2 are connected to the @value{GDBN} console. Output
32521 on the @value{GDBN} console is handled as any other file output operation
32522 (@code{write(1, @dots{})} or @code{write(2, @dots{})}). Console input is handled
32523 by @value{GDBN} so that after the target read request from file descriptor
32524 0 all following typing is buffered until either one of the following
32529 The user types @kbd{Ctrl-c}. The behaviour is as explained above, and the
32531 system call is treated as finished.
32534 The user presses @key{RET}. This is treated as end of input with a trailing
32538 The user types @kbd{Ctrl-d}. This is treated as end of input. No trailing
32539 character (neither newline nor @samp{Ctrl-D}) is appended to the input.
32543 If the user has typed more characters than fit in the buffer given to
32544 the @code{read} call, the trailing characters are buffered in @value{GDBN} until
32545 either another @code{read(0, @dots{})} is requested by the target, or debugging
32546 is stopped at the user's request.
32549 @node List of Supported Calls
32550 @subsection List of Supported Calls
32551 @cindex list of supported file-i/o calls
32568 @unnumberedsubsubsec open
32569 @cindex open, file-i/o system call
32574 int open(const char *pathname, int flags);
32575 int open(const char *pathname, int flags, mode_t mode);
32579 @samp{Fopen,@var{pathptr}/@var{len},@var{flags},@var{mode}}
32582 @var{flags} is the bitwise @code{OR} of the following values:
32586 If the file does not exist it will be created. The host
32587 rules apply as far as file ownership and time stamps
32591 When used with @code{O_CREAT}, if the file already exists it is
32592 an error and open() fails.
32595 If the file already exists and the open mode allows
32596 writing (@code{O_RDWR} or @code{O_WRONLY} is given) it will be
32597 truncated to zero length.
32600 The file is opened in append mode.
32603 The file is opened for reading only.
32606 The file is opened for writing only.
32609 The file is opened for reading and writing.
32613 Other bits are silently ignored.
32617 @var{mode} is the bitwise @code{OR} of the following values:
32621 User has read permission.
32624 User has write permission.
32627 Group has read permission.
32630 Group has write permission.
32633 Others have read permission.
32636 Others have write permission.
32640 Other bits are silently ignored.
32643 @item Return value:
32644 @code{open} returns the new file descriptor or -1 if an error
32651 @var{pathname} already exists and @code{O_CREAT} and @code{O_EXCL} were used.
32654 @var{pathname} refers to a directory.
32657 The requested access is not allowed.
32660 @var{pathname} was too long.
32663 A directory component in @var{pathname} does not exist.
32666 @var{pathname} refers to a device, pipe, named pipe or socket.
32669 @var{pathname} refers to a file on a read-only filesystem and
32670 write access was requested.
32673 @var{pathname} is an invalid pointer value.
32676 No space on device to create the file.
32679 The process already has the maximum number of files open.
32682 The limit on the total number of files open on the system
32686 The call was interrupted by the user.
32692 @unnumberedsubsubsec close
32693 @cindex close, file-i/o system call
32702 @samp{Fclose,@var{fd}}
32704 @item Return value:
32705 @code{close} returns zero on success, or -1 if an error occurred.
32711 @var{fd} isn't a valid open file descriptor.
32714 The call was interrupted by the user.
32720 @unnumberedsubsubsec read
32721 @cindex read, file-i/o system call
32726 int read(int fd, void *buf, unsigned int count);
32730 @samp{Fread,@var{fd},@var{bufptr},@var{count}}
32732 @item Return value:
32733 On success, the number of bytes read is returned.
32734 Zero indicates end of file. If count is zero, read
32735 returns zero as well. On error, -1 is returned.
32741 @var{fd} is not a valid file descriptor or is not open for
32745 @var{bufptr} is an invalid pointer value.
32748 The call was interrupted by the user.
32754 @unnumberedsubsubsec write
32755 @cindex write, file-i/o system call
32760 int write(int fd, const void *buf, unsigned int count);
32764 @samp{Fwrite,@var{fd},@var{bufptr},@var{count}}
32766 @item Return value:
32767 On success, the number of bytes written are returned.
32768 Zero indicates nothing was written. On error, -1
32775 @var{fd} is not a valid file descriptor or is not open for
32779 @var{bufptr} is an invalid pointer value.
32782 An attempt was made to write a file that exceeds the
32783 host-specific maximum file size allowed.
32786 No space on device to write the data.
32789 The call was interrupted by the user.
32795 @unnumberedsubsubsec lseek
32796 @cindex lseek, file-i/o system call
32801 long lseek (int fd, long offset, int flag);
32805 @samp{Flseek,@var{fd},@var{offset},@var{flag}}
32807 @var{flag} is one of:
32811 The offset is set to @var{offset} bytes.
32814 The offset is set to its current location plus @var{offset}
32818 The offset is set to the size of the file plus @var{offset}
32822 @item Return value:
32823 On success, the resulting unsigned offset in bytes from
32824 the beginning of the file is returned. Otherwise, a
32825 value of -1 is returned.
32831 @var{fd} is not a valid open file descriptor.
32834 @var{fd} is associated with the @value{GDBN} console.
32837 @var{flag} is not a proper value.
32840 The call was interrupted by the user.
32846 @unnumberedsubsubsec rename
32847 @cindex rename, file-i/o system call
32852 int rename(const char *oldpath, const char *newpath);
32856 @samp{Frename,@var{oldpathptr}/@var{len},@var{newpathptr}/@var{len}}
32858 @item Return value:
32859 On success, zero is returned. On error, -1 is returned.
32865 @var{newpath} is an existing directory, but @var{oldpath} is not a
32869 @var{newpath} is a non-empty directory.
32872 @var{oldpath} or @var{newpath} is a directory that is in use by some
32876 An attempt was made to make a directory a subdirectory
32880 A component used as a directory in @var{oldpath} or new
32881 path is not a directory. Or @var{oldpath} is a directory
32882 and @var{newpath} exists but is not a directory.
32885 @var{oldpathptr} or @var{newpathptr} are invalid pointer values.
32888 No access to the file or the path of the file.
32892 @var{oldpath} or @var{newpath} was too long.
32895 A directory component in @var{oldpath} or @var{newpath} does not exist.
32898 The file is on a read-only filesystem.
32901 The device containing the file has no room for the new
32905 The call was interrupted by the user.
32911 @unnumberedsubsubsec unlink
32912 @cindex unlink, file-i/o system call
32917 int unlink(const char *pathname);
32921 @samp{Funlink,@var{pathnameptr}/@var{len}}
32923 @item Return value:
32924 On success, zero is returned. On error, -1 is returned.
32930 No access to the file or the path of the file.
32933 The system does not allow unlinking of directories.
32936 The file @var{pathname} cannot be unlinked because it's
32937 being used by another process.
32940 @var{pathnameptr} is an invalid pointer value.
32943 @var{pathname} was too long.
32946 A directory component in @var{pathname} does not exist.
32949 A component of the path is not a directory.
32952 The file is on a read-only filesystem.
32955 The call was interrupted by the user.
32961 @unnumberedsubsubsec stat/fstat
32962 @cindex fstat, file-i/o system call
32963 @cindex stat, file-i/o system call
32968 int stat(const char *pathname, struct stat *buf);
32969 int fstat(int fd, struct stat *buf);
32973 @samp{Fstat,@var{pathnameptr}/@var{len},@var{bufptr}}@*
32974 @samp{Ffstat,@var{fd},@var{bufptr}}
32976 @item Return value:
32977 On success, zero is returned. On error, -1 is returned.
32983 @var{fd} is not a valid open file.
32986 A directory component in @var{pathname} does not exist or the
32987 path is an empty string.
32990 A component of the path is not a directory.
32993 @var{pathnameptr} is an invalid pointer value.
32996 No access to the file or the path of the file.
32999 @var{pathname} was too long.
33002 The call was interrupted by the user.
33008 @unnumberedsubsubsec gettimeofday
33009 @cindex gettimeofday, file-i/o system call
33014 int gettimeofday(struct timeval *tv, void *tz);
33018 @samp{Fgettimeofday,@var{tvptr},@var{tzptr}}
33020 @item Return value:
33021 On success, 0 is returned, -1 otherwise.
33027 @var{tz} is a non-NULL pointer.
33030 @var{tvptr} and/or @var{tzptr} is an invalid pointer value.
33036 @unnumberedsubsubsec isatty
33037 @cindex isatty, file-i/o system call
33042 int isatty(int fd);
33046 @samp{Fisatty,@var{fd}}
33048 @item Return value:
33049 Returns 1 if @var{fd} refers to the @value{GDBN} console, 0 otherwise.
33055 The call was interrupted by the user.
33060 Note that the @code{isatty} call is treated as a special case: it returns
33061 1 to the target if the file descriptor is attached
33062 to the @value{GDBN} console, 0 otherwise. Implementing through system calls
33063 would require implementing @code{ioctl} and would be more complex than
33068 @unnumberedsubsubsec system
33069 @cindex system, file-i/o system call
33074 int system(const char *command);
33078 @samp{Fsystem,@var{commandptr}/@var{len}}
33080 @item Return value:
33081 If @var{len} is zero, the return value indicates whether a shell is
33082 available. A zero return value indicates a shell is not available.
33083 For non-zero @var{len}, the value returned is -1 on error and the
33084 return status of the command otherwise. Only the exit status of the
33085 command is returned, which is extracted from the host's @code{system}
33086 return value by calling @code{WEXITSTATUS(retval)}. In case
33087 @file{/bin/sh} could not be executed, 127 is returned.
33093 The call was interrupted by the user.
33098 @value{GDBN} takes over the full task of calling the necessary host calls
33099 to perform the @code{system} call. The return value of @code{system} on
33100 the host is simplified before it's returned
33101 to the target. Any termination signal information from the child process
33102 is discarded, and the return value consists
33103 entirely of the exit status of the called command.
33105 Due to security concerns, the @code{system} call is by default refused
33106 by @value{GDBN}. The user has to allow this call explicitly with the
33107 @code{set remote system-call-allowed 1} command.
33110 @item set remote system-call-allowed
33111 @kindex set remote system-call-allowed
33112 Control whether to allow the @code{system} calls in the File I/O
33113 protocol for the remote target. The default is zero (disabled).
33115 @item show remote system-call-allowed
33116 @kindex show remote system-call-allowed
33117 Show whether the @code{system} calls are allowed in the File I/O
33121 @node Protocol-specific Representation of Datatypes
33122 @subsection Protocol-specific Representation of Datatypes
33123 @cindex protocol-specific representation of datatypes, in file-i/o protocol
33126 * Integral Datatypes::
33128 * Memory Transfer::
33133 @node Integral Datatypes
33134 @unnumberedsubsubsec Integral Datatypes
33135 @cindex integral datatypes, in file-i/o protocol
33137 The integral datatypes used in the system calls are @code{int},
33138 @code{unsigned int}, @code{long}, @code{unsigned long},
33139 @code{mode_t}, and @code{time_t}.
33141 @code{int}, @code{unsigned int}, @code{mode_t} and @code{time_t} are
33142 implemented as 32 bit values in this protocol.
33144 @code{long} and @code{unsigned long} are implemented as 64 bit types.
33146 @xref{Limits}, for corresponding MIN and MAX values (similar to those
33147 in @file{limits.h}) to allow range checking on host and target.
33149 @code{time_t} datatypes are defined as seconds since the Epoch.
33151 All integral datatypes transferred as part of a memory read or write of a
33152 structured datatype e.g.@: a @code{struct stat} have to be given in big endian
33155 @node Pointer Values
33156 @unnumberedsubsubsec Pointer Values
33157 @cindex pointer values, in file-i/o protocol
33159 Pointers to target data are transmitted as they are. An exception
33160 is made for pointers to buffers for which the length isn't
33161 transmitted as part of the function call, namely strings. Strings
33162 are transmitted as a pointer/length pair, both as hex values, e.g.@:
33169 which is a pointer to data of length 18 bytes at position 0x1aaf.
33170 The length is defined as the full string length in bytes, including
33171 the trailing null byte. For example, the string @code{"hello world"}
33172 at address 0x123456 is transmitted as
33178 @node Memory Transfer
33179 @unnumberedsubsubsec Memory Transfer
33180 @cindex memory transfer, in file-i/o protocol
33182 Structured data which is transferred using a memory read or write (for
33183 example, a @code{struct stat}) is expected to be in a protocol-specific format
33184 with all scalar multibyte datatypes being big endian. Translation to
33185 this representation needs to be done both by the target before the @code{F}
33186 packet is sent, and by @value{GDBN} before
33187 it transfers memory to the target. Transferred pointers to structured
33188 data should point to the already-coerced data at any time.
33192 @unnumberedsubsubsec struct stat
33193 @cindex struct stat, in file-i/o protocol
33195 The buffer of type @code{struct stat} used by the target and @value{GDBN}
33196 is defined as follows:
33200 unsigned int st_dev; /* device */
33201 unsigned int st_ino; /* inode */
33202 mode_t st_mode; /* protection */
33203 unsigned int st_nlink; /* number of hard links */
33204 unsigned int st_uid; /* user ID of owner */
33205 unsigned int st_gid; /* group ID of owner */
33206 unsigned int st_rdev; /* device type (if inode device) */
33207 unsigned long st_size; /* total size, in bytes */
33208 unsigned long st_blksize; /* blocksize for filesystem I/O */
33209 unsigned long st_blocks; /* number of blocks allocated */
33210 time_t st_atime; /* time of last access */
33211 time_t st_mtime; /* time of last modification */
33212 time_t st_ctime; /* time of last change */
33216 The integral datatypes conform to the definitions given in the
33217 appropriate section (see @ref{Integral Datatypes}, for details) so this
33218 structure is of size 64 bytes.
33220 The values of several fields have a restricted meaning and/or
33226 A value of 0 represents a file, 1 the console.
33229 No valid meaning for the target. Transmitted unchanged.
33232 Valid mode bits are described in @ref{Constants}. Any other
33233 bits have currently no meaning for the target.
33238 No valid meaning for the target. Transmitted unchanged.
33243 These values have a host and file system dependent
33244 accuracy. Especially on Windows hosts, the file system may not
33245 support exact timing values.
33248 The target gets a @code{struct stat} of the above representation and is
33249 responsible for coercing it to the target representation before
33252 Note that due to size differences between the host, target, and protocol
33253 representations of @code{struct stat} members, these members could eventually
33254 get truncated on the target.
33256 @node struct timeval
33257 @unnumberedsubsubsec struct timeval
33258 @cindex struct timeval, in file-i/o protocol
33260 The buffer of type @code{struct timeval} used by the File-I/O protocol
33261 is defined as follows:
33265 time_t tv_sec; /* second */
33266 long tv_usec; /* microsecond */
33270 The integral datatypes conform to the definitions given in the
33271 appropriate section (see @ref{Integral Datatypes}, for details) so this
33272 structure is of size 8 bytes.
33275 @subsection Constants
33276 @cindex constants, in file-i/o protocol
33278 The following values are used for the constants inside of the
33279 protocol. @value{GDBN} and target are responsible for translating these
33280 values before and after the call as needed.
33291 @unnumberedsubsubsec Open Flags
33292 @cindex open flags, in file-i/o protocol
33294 All values are given in hexadecimal representation.
33306 @node mode_t Values
33307 @unnumberedsubsubsec mode_t Values
33308 @cindex mode_t values, in file-i/o protocol
33310 All values are given in octal representation.
33327 @unnumberedsubsubsec Errno Values
33328 @cindex errno values, in file-i/o protocol
33330 All values are given in decimal representation.
33355 @code{EUNKNOWN} is used as a fallback error value if a host system returns
33356 any error value not in the list of supported error numbers.
33359 @unnumberedsubsubsec Lseek Flags
33360 @cindex lseek flags, in file-i/o protocol
33369 @unnumberedsubsubsec Limits
33370 @cindex limits, in file-i/o protocol
33372 All values are given in decimal representation.
33375 INT_MIN -2147483648
33377 UINT_MAX 4294967295
33378 LONG_MIN -9223372036854775808
33379 LONG_MAX 9223372036854775807
33380 ULONG_MAX 18446744073709551615
33383 @node File-I/O Examples
33384 @subsection File-I/O Examples
33385 @cindex file-i/o examples
33387 Example sequence of a write call, file descriptor 3, buffer is at target
33388 address 0x1234, 6 bytes should be written:
33391 <- @code{Fwrite,3,1234,6}
33392 @emph{request memory read from target}
33395 @emph{return "6 bytes written"}
33399 Example sequence of a read call, file descriptor 3, buffer is at target
33400 address 0x1234, 6 bytes should be read:
33403 <- @code{Fread,3,1234,6}
33404 @emph{request memory write to target}
33405 -> @code{X1234,6:XXXXXX}
33406 @emph{return "6 bytes read"}
33410 Example sequence of a read call, call fails on the host due to invalid
33411 file descriptor (@code{EBADF}):
33414 <- @code{Fread,3,1234,6}
33418 Example sequence of a read call, user presses @kbd{Ctrl-c} before syscall on
33422 <- @code{Fread,3,1234,6}
33427 Example sequence of a read call, user presses @kbd{Ctrl-c} after syscall on
33431 <- @code{Fread,3,1234,6}
33432 -> @code{X1234,6:XXXXXX}
33436 @node Library List Format
33437 @section Library List Format
33438 @cindex library list format, remote protocol
33440 On some platforms, a dynamic loader (e.g.@: @file{ld.so}) runs in the
33441 same process as your application to manage libraries. In this case,
33442 @value{GDBN} can use the loader's symbol table and normal memory
33443 operations to maintain a list of shared libraries. On other
33444 platforms, the operating system manages loaded libraries.
33445 @value{GDBN} can not retrieve the list of currently loaded libraries
33446 through memory operations, so it uses the @samp{qXfer:libraries:read}
33447 packet (@pxref{qXfer library list read}) instead. The remote stub
33448 queries the target's operating system and reports which libraries
33451 The @samp{qXfer:libraries:read} packet returns an XML document which
33452 lists loaded libraries and their offsets. Each library has an
33453 associated name and one or more segment or section base addresses,
33454 which report where the library was loaded in memory.
33456 For the common case of libraries that are fully linked binaries, the
33457 library should have a list of segments. If the target supports
33458 dynamic linking of a relocatable object file, its library XML element
33459 should instead include a list of allocated sections. The segment or
33460 section bases are start addresses, not relocation offsets; they do not
33461 depend on the library's link-time base addresses.
33463 @value{GDBN} must be linked with the Expat library to support XML
33464 library lists. @xref{Expat}.
33466 A simple memory map, with one loaded library relocated by a single
33467 offset, looks like this:
33471 <library name="/lib/libc.so.6">
33472 <segment address="0x10000000"/>
33477 Another simple memory map, with one loaded library with three
33478 allocated sections (.text, .data, .bss), looks like this:
33482 <library name="sharedlib.o">
33483 <section address="0x10000000"/>
33484 <section address="0x20000000"/>
33485 <section address="0x30000000"/>
33490 The format of a library list is described by this DTD:
33493 <!-- library-list: Root element with versioning -->
33494 <!ELEMENT library-list (library)*>
33495 <!ATTLIST library-list version CDATA #FIXED "1.0">
33496 <!ELEMENT library (segment*, section*)>
33497 <!ATTLIST library name CDATA #REQUIRED>
33498 <!ELEMENT segment EMPTY>
33499 <!ATTLIST segment address CDATA #REQUIRED>
33500 <!ELEMENT section EMPTY>
33501 <!ATTLIST section address CDATA #REQUIRED>
33504 In addition, segments and section descriptors cannot be mixed within a
33505 single library element, and you must supply at least one segment or
33506 section for each library.
33508 @node Memory Map Format
33509 @section Memory Map Format
33510 @cindex memory map format
33512 To be able to write into flash memory, @value{GDBN} needs to obtain a
33513 memory map from the target. This section describes the format of the
33516 The memory map is obtained using the @samp{qXfer:memory-map:read}
33517 (@pxref{qXfer memory map read}) packet and is an XML document that
33518 lists memory regions.
33520 @value{GDBN} must be linked with the Expat library to support XML
33521 memory maps. @xref{Expat}.
33523 The top-level structure of the document is shown below:
33526 <?xml version="1.0"?>
33527 <!DOCTYPE memory-map
33528 PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN"
33529 "http://sourceware.org/gdb/gdb-memory-map.dtd">
33535 Each region can be either:
33540 A region of RAM starting at @var{addr} and extending for @var{length}
33544 <memory type="ram" start="@var{addr}" length="@var{length}"/>
33549 A region of read-only memory:
33552 <memory type="rom" start="@var{addr}" length="@var{length}"/>
33557 A region of flash memory, with erasure blocks @var{blocksize}
33561 <memory type="flash" start="@var{addr}" length="@var{length}">
33562 <property name="blocksize">@var{blocksize}</property>
33568 Regions must not overlap. @value{GDBN} assumes that areas of memory not covered
33569 by the memory map are RAM, and uses the ordinary @samp{M} and @samp{X}
33570 packets to write to addresses in such ranges.
33572 The formal DTD for memory map format is given below:
33575 <!-- ................................................... -->
33576 <!-- Memory Map XML DTD ................................ -->
33577 <!-- File: memory-map.dtd .............................. -->
33578 <!-- .................................... .............. -->
33579 <!-- memory-map.dtd -->
33580 <!-- memory-map: Root element with versioning -->
33581 <!ELEMENT memory-map (memory | property)>
33582 <!ATTLIST memory-map version CDATA #FIXED "1.0.0">
33583 <!ELEMENT memory (property)>
33584 <!-- memory: Specifies a memory region,
33585 and its type, or device. -->
33586 <!ATTLIST memory type CDATA #REQUIRED
33587 start CDATA #REQUIRED
33588 length CDATA #REQUIRED
33589 device CDATA #IMPLIED>
33590 <!-- property: Generic attribute tag -->
33591 <!ELEMENT property (#PCDATA | property)*>
33592 <!ATTLIST property name CDATA #REQUIRED>
33595 @node Thread List Format
33596 @section Thread List Format
33597 @cindex thread list format
33599 To efficiently update the list of threads and their attributes,
33600 @value{GDBN} issues the @samp{qXfer:threads:read} packet
33601 (@pxref{qXfer threads read}) and obtains the XML document with
33602 the following structure:
33605 <?xml version="1.0"?>
33607 <thread id="id" core="0">
33608 ... description ...
33613 Each @samp{thread} element must have the @samp{id} attribute that
33614 identifies the thread (@pxref{thread-id syntax}). The
33615 @samp{core} attribute, if present, specifies which processor core
33616 the thread was last executing on. The content of the of @samp{thread}
33617 element is interpreted as human-readable auxilliary information.
33619 @include agentexpr.texi
33621 @node Trace File Format
33622 @appendix Trace File Format
33623 @cindex trace file format
33625 The trace file comes in three parts: a header, a textual description
33626 section, and a trace frame section with binary data.
33628 The header has the form @code{\x7fTRACE0\n}. The first byte is
33629 @code{0x7f} so as to indicate that the file contains binary data,
33630 while the @code{0} is a version number that may have different values
33633 The description section consists of multiple lines of @sc{ascii} text
33634 separated by newline characters (@code{0xa}). The lines may include a
33635 variety of optional descriptive or context-setting information, such
33636 as tracepoint definitions or register set size. @value{GDBN} will
33637 ignore any line that it does not recognize. An empty line marks the end
33640 @c FIXME add some specific types of data
33642 The trace frame section consists of a number of consecutive frames.
33643 Each frame begins with a two-byte tracepoint number, followed by a
33644 four-byte size giving the amount of data in the frame. The data in
33645 the frame consists of a number of blocks, each introduced by a
33646 character indicating its type (at least register, memory, and trace
33647 state variable). The data in this section is raw binary, not a
33648 hexadecimal or other encoding; its endianness matches the target's
33651 @c FIXME bi-arch may require endianness/arch info in description section
33654 @item R @var{bytes}
33655 Register block. The number and ordering of bytes matches that of a
33656 @code{g} packet in the remote protocol. Note that these are the
33657 actual bytes, in target order and @value{GDBN} register order, not a
33658 hexadecimal encoding.
33660 @item M @var{address} @var{length} @var{bytes}...
33661 Memory block. This is a contiguous block of memory, at the 8-byte
33662 address @var{address}, with a 2-byte length @var{length}, followed by
33663 @var{length} bytes.
33665 @item V @var{number} @var{value}
33666 Trace state variable block. This records the 8-byte signed value
33667 @var{value} of trace state variable numbered @var{number}.
33671 Future enhancements of the trace file format may include additional types
33674 @node Target Descriptions
33675 @appendix Target Descriptions
33676 @cindex target descriptions
33678 @strong{Warning:} target descriptions are still under active development,
33679 and the contents and format may change between @value{GDBN} releases.
33680 The format is expected to stabilize in the future.
33682 One of the challenges of using @value{GDBN} to debug embedded systems
33683 is that there are so many minor variants of each processor
33684 architecture in use. It is common practice for vendors to start with
33685 a standard processor core --- ARM, PowerPC, or MIPS, for example ---
33686 and then make changes to adapt it to a particular market niche. Some
33687 architectures have hundreds of variants, available from dozens of
33688 vendors. This leads to a number of problems:
33692 With so many different customized processors, it is difficult for
33693 the @value{GDBN} maintainers to keep up with the changes.
33695 Since individual variants may have short lifetimes or limited
33696 audiences, it may not be worthwhile to carry information about every
33697 variant in the @value{GDBN} source tree.
33699 When @value{GDBN} does support the architecture of the embedded system
33700 at hand, the task of finding the correct architecture name to give the
33701 @command{set architecture} command can be error-prone.
33704 To address these problems, the @value{GDBN} remote protocol allows a
33705 target system to not only identify itself to @value{GDBN}, but to
33706 actually describe its own features. This lets @value{GDBN} support
33707 processor variants it has never seen before --- to the extent that the
33708 descriptions are accurate, and that @value{GDBN} understands them.
33710 @value{GDBN} must be linked with the Expat library to support XML
33711 target descriptions. @xref{Expat}.
33714 * Retrieving Descriptions:: How descriptions are fetched from a target.
33715 * Target Description Format:: The contents of a target description.
33716 * Predefined Target Types:: Standard types available for target
33718 * Standard Target Features:: Features @value{GDBN} knows about.
33721 @node Retrieving Descriptions
33722 @section Retrieving Descriptions
33724 Target descriptions can be read from the target automatically, or
33725 specified by the user manually. The default behavior is to read the
33726 description from the target. @value{GDBN} retrieves it via the remote
33727 protocol using @samp{qXfer} requests (@pxref{General Query Packets,
33728 qXfer}). The @var{annex} in the @samp{qXfer} packet will be
33729 @samp{target.xml}. The contents of the @samp{target.xml} annex are an
33730 XML document, of the form described in @ref{Target Description
33733 Alternatively, you can specify a file to read for the target description.
33734 If a file is set, the target will not be queried. The commands to
33735 specify a file are:
33738 @cindex set tdesc filename
33739 @item set tdesc filename @var{path}
33740 Read the target description from @var{path}.
33742 @cindex unset tdesc filename
33743 @item unset tdesc filename
33744 Do not read the XML target description from a file. @value{GDBN}
33745 will use the description supplied by the current target.
33747 @cindex show tdesc filename
33748 @item show tdesc filename
33749 Show the filename to read for a target description, if any.
33753 @node Target Description Format
33754 @section Target Description Format
33755 @cindex target descriptions, XML format
33757 A target description annex is an @uref{http://www.w3.org/XML/, XML}
33758 document which complies with the Document Type Definition provided in
33759 the @value{GDBN} sources in @file{gdb/features/gdb-target.dtd}. This
33760 means you can use generally available tools like @command{xmllint} to
33761 check that your feature descriptions are well-formed and valid.
33762 However, to help people unfamiliar with XML write descriptions for
33763 their targets, we also describe the grammar here.
33765 Target descriptions can identify the architecture of the remote target
33766 and (for some architectures) provide information about custom register
33767 sets. They can also identify the OS ABI of the remote target.
33768 @value{GDBN} can use this information to autoconfigure for your
33769 target, or to warn you if you connect to an unsupported target.
33771 Here is a simple target description:
33774 <target version="1.0">
33775 <architecture>i386:x86-64</architecture>
33780 This minimal description only says that the target uses
33781 the x86-64 architecture.
33783 A target description has the following overall form, with [ ] marking
33784 optional elements and @dots{} marking repeatable elements. The elements
33785 are explained further below.
33788 <?xml version="1.0"?>
33789 <!DOCTYPE target SYSTEM "gdb-target.dtd">
33790 <target version="1.0">
33791 @r{[}@var{architecture}@r{]}
33792 @r{[}@var{osabi}@r{]}
33793 @r{[}@var{compatible}@r{]}
33794 @r{[}@var{feature}@dots{}@r{]}
33799 The description is generally insensitive to whitespace and line
33800 breaks, under the usual common-sense rules. The XML version
33801 declaration and document type declaration can generally be omitted
33802 (@value{GDBN} does not require them), but specifying them may be
33803 useful for XML validation tools. The @samp{version} attribute for
33804 @samp{<target>} may also be omitted, but we recommend
33805 including it; if future versions of @value{GDBN} use an incompatible
33806 revision of @file{gdb-target.dtd}, they will detect and report
33807 the version mismatch.
33809 @subsection Inclusion
33810 @cindex target descriptions, inclusion
33813 @cindex <xi:include>
33816 It can sometimes be valuable to split a target description up into
33817 several different annexes, either for organizational purposes, or to
33818 share files between different possible target descriptions. You can
33819 divide a description into multiple files by replacing any element of
33820 the target description with an inclusion directive of the form:
33823 <xi:include href="@var{document}"/>
33827 When @value{GDBN} encounters an element of this form, it will retrieve
33828 the named XML @var{document}, and replace the inclusion directive with
33829 the contents of that document. If the current description was read
33830 using @samp{qXfer}, then so will be the included document;
33831 @var{document} will be interpreted as the name of an annex. If the
33832 current description was read from a file, @value{GDBN} will look for
33833 @var{document} as a file in the same directory where it found the
33834 original description.
33836 @subsection Architecture
33837 @cindex <architecture>
33839 An @samp{<architecture>} element has this form:
33842 <architecture>@var{arch}</architecture>
33845 @var{arch} is one of the architectures from the set accepted by
33846 @code{set architecture} (@pxref{Targets, ,Specifying a Debugging Target}).
33849 @cindex @code{<osabi>}
33851 This optional field was introduced in @value{GDBN} version 7.0.
33852 Previous versions of @value{GDBN} ignore it.
33854 An @samp{<osabi>} element has this form:
33857 <osabi>@var{abi-name}</osabi>
33860 @var{abi-name} is an OS ABI name from the same selection accepted by
33861 @w{@code{set osabi}} (@pxref{ABI, ,Configuring the Current ABI}).
33863 @subsection Compatible Architecture
33864 @cindex @code{<compatible>}
33866 This optional field was introduced in @value{GDBN} version 7.0.
33867 Previous versions of @value{GDBN} ignore it.
33869 A @samp{<compatible>} element has this form:
33872 <compatible>@var{arch}</compatible>
33875 @var{arch} is one of the architectures from the set accepted by
33876 @code{set architecture} (@pxref{Targets, ,Specifying a Debugging Target}).
33878 A @samp{<compatible>} element is used to specify that the target
33879 is able to run binaries in some other than the main target architecture
33880 given by the @samp{<architecture>} element. For example, on the
33881 Cell Broadband Engine, the main architecture is @code{powerpc:common}
33882 or @code{powerpc:common64}, but the system is able to run binaries
33883 in the @code{spu} architecture as well. The way to describe this
33884 capability with @samp{<compatible>} is as follows:
33887 <architecture>powerpc:common</architecture>
33888 <compatible>spu</compatible>
33891 @subsection Features
33894 Each @samp{<feature>} describes some logical portion of the target
33895 system. Features are currently used to describe available CPU
33896 registers and the types of their contents. A @samp{<feature>} element
33900 <feature name="@var{name}">
33901 @r{[}@var{type}@dots{}@r{]}
33907 Each feature's name should be unique within the description. The name
33908 of a feature does not matter unless @value{GDBN} has some special
33909 knowledge of the contents of that feature; if it does, the feature
33910 should have its standard name. @xref{Standard Target Features}.
33914 Any register's value is a collection of bits which @value{GDBN} must
33915 interpret. The default interpretation is a two's complement integer,
33916 but other types can be requested by name in the register description.
33917 Some predefined types are provided by @value{GDBN} (@pxref{Predefined
33918 Target Types}), and the description can define additional composite types.
33920 Each type element must have an @samp{id} attribute, which gives
33921 a unique (within the containing @samp{<feature>}) name to the type.
33922 Types must be defined before they are used.
33925 Some targets offer vector registers, which can be treated as arrays
33926 of scalar elements. These types are written as @samp{<vector>} elements,
33927 specifying the array element type, @var{type}, and the number of elements,
33931 <vector id="@var{id}" type="@var{type}" count="@var{count}"/>
33935 If a register's value is usefully viewed in multiple ways, define it
33936 with a union type containing the useful representations. The
33937 @samp{<union>} element contains one or more @samp{<field>} elements,
33938 each of which has a @var{name} and a @var{type}:
33941 <union id="@var{id}">
33942 <field name="@var{name}" type="@var{type}"/>
33948 If a register's value is composed from several separate values, define
33949 it with a structure type. There are two forms of the @samp{<struct>}
33950 element; a @samp{<struct>} element must either contain only bitfields
33951 or contain no bitfields. If the structure contains only bitfields,
33952 its total size in bytes must be specified, each bitfield must have an
33953 explicit start and end, and bitfields are automatically assigned an
33954 integer type. The field's @var{start} should be less than or
33955 equal to its @var{end}, and zero represents the least significant bit.
33958 <struct id="@var{id}" size="@var{size}">
33959 <field name="@var{name}" start="@var{start}" end="@var{end}"/>
33964 If the structure contains no bitfields, then each field has an
33965 explicit type, and no implicit padding is added.
33968 <struct id="@var{id}">
33969 <field name="@var{name}" type="@var{type}"/>
33975 If a register's value is a series of single-bit flags, define it with
33976 a flags type. The @samp{<flags>} element has an explicit @var{size}
33977 and contains one or more @samp{<field>} elements. Each field has a
33978 @var{name}, a @var{start}, and an @var{end}. Only single-bit flags
33982 <flags id="@var{id}" size="@var{size}">
33983 <field name="@var{name}" start="@var{start}" end="@var{end}"/>
33988 @subsection Registers
33991 Each register is represented as an element with this form:
33994 <reg name="@var{name}"
33995 bitsize="@var{size}"
33996 @r{[}regnum="@var{num}"@r{]}
33997 @r{[}save-restore="@var{save-restore}"@r{]}
33998 @r{[}type="@var{type}"@r{]}
33999 @r{[}group="@var{group}"@r{]}/>
34003 The components are as follows:
34008 The register's name; it must be unique within the target description.
34011 The register's size, in bits.
34014 The register's number. If omitted, a register's number is one greater
34015 than that of the previous register (either in the current feature or in
34016 a preceeding feature); the first register in the target description
34017 defaults to zero. This register number is used to read or write
34018 the register; e.g.@: it is used in the remote @code{p} and @code{P}
34019 packets, and registers appear in the @code{g} and @code{G} packets
34020 in order of increasing register number.
34023 Whether the register should be preserved across inferior function
34024 calls; this must be either @code{yes} or @code{no}. The default is
34025 @code{yes}, which is appropriate for most registers except for
34026 some system control registers; this is not related to the target's
34030 The type of the register. @var{type} may be a predefined type, a type
34031 defined in the current feature, or one of the special types @code{int}
34032 and @code{float}. @code{int} is an integer type of the correct size
34033 for @var{bitsize}, and @code{float} is a floating point type (in the
34034 architecture's normal floating point format) of the correct size for
34035 @var{bitsize}. The default is @code{int}.
34038 The register group to which this register belongs. @var{group} must
34039 be either @code{general}, @code{float}, or @code{vector}. If no
34040 @var{group} is specified, @value{GDBN} will not display the register
34041 in @code{info registers}.
34045 @node Predefined Target Types
34046 @section Predefined Target Types
34047 @cindex target descriptions, predefined types
34049 Type definitions in the self-description can build up composite types
34050 from basic building blocks, but can not define fundamental types. Instead,
34051 standard identifiers are provided by @value{GDBN} for the fundamental
34052 types. The currently supported types are:
34061 Signed integer types holding the specified number of bits.
34068 Unsigned integer types holding the specified number of bits.
34072 Pointers to unspecified code and data. The program counter and
34073 any dedicated return address register may be marked as code
34074 pointers; printing a code pointer converts it into a symbolic
34075 address. The stack pointer and any dedicated address registers
34076 may be marked as data pointers.
34079 Single precision IEEE floating point.
34082 Double precision IEEE floating point.
34085 The 12-byte extended precision format used by ARM FPA registers.
34088 The 10-byte extended precision format used by x87 registers.
34091 32bit @sc{eflags} register used by x86.
34094 32bit @sc{mxcsr} register used by x86.
34098 @node Standard Target Features
34099 @section Standard Target Features
34100 @cindex target descriptions, standard features
34102 A target description must contain either no registers or all the
34103 target's registers. If the description contains no registers, then
34104 @value{GDBN} will assume a default register layout, selected based on
34105 the architecture. If the description contains any registers, the
34106 default layout will not be used; the standard registers must be
34107 described in the target description, in such a way that @value{GDBN}
34108 can recognize them.
34110 This is accomplished by giving specific names to feature elements
34111 which contain standard registers. @value{GDBN} will look for features
34112 with those names and verify that they contain the expected registers;
34113 if any known feature is missing required registers, or if any required
34114 feature is missing, @value{GDBN} will reject the target
34115 description. You can add additional registers to any of the
34116 standard features --- @value{GDBN} will display them just as if
34117 they were added to an unrecognized feature.
34119 This section lists the known features and their expected contents.
34120 Sample XML documents for these features are included in the
34121 @value{GDBN} source tree, in the directory @file{gdb/features}.
34123 Names recognized by @value{GDBN} should include the name of the
34124 company or organization which selected the name, and the overall
34125 architecture to which the feature applies; so e.g.@: the feature
34126 containing ARM core registers is named @samp{org.gnu.gdb.arm.core}.
34128 The names of registers are not case sensitive for the purpose
34129 of recognizing standard features, but @value{GDBN} will only display
34130 registers using the capitalization used in the description.
34137 * PowerPC Features::
34142 @subsection ARM Features
34143 @cindex target descriptions, ARM features
34145 The @samp{org.gnu.gdb.arm.core} feature is required for ARM targets.
34146 It should contain registers @samp{r0} through @samp{r13}, @samp{sp},
34147 @samp{lr}, @samp{pc}, and @samp{cpsr}.
34149 The @samp{org.gnu.gdb.arm.fpa} feature is optional. If present, it
34150 should contain registers @samp{f0} through @samp{f7} and @samp{fps}.
34152 The @samp{org.gnu.gdb.xscale.iwmmxt} feature is optional. If present,
34153 it should contain at least registers @samp{wR0} through @samp{wR15} and
34154 @samp{wCGR0} through @samp{wCGR3}. The @samp{wCID}, @samp{wCon},
34155 @samp{wCSSF}, and @samp{wCASF} registers are optional.
34157 The @samp{org.gnu.gdb.arm.vfp} feature is optional. If present, it
34158 should contain at least registers @samp{d0} through @samp{d15}. If
34159 they are present, @samp{d16} through @samp{d31} should also be included.
34160 @value{GDBN} will synthesize the single-precision registers from
34161 halves of the double-precision registers.
34163 The @samp{org.gnu.gdb.arm.neon} feature is optional. It does not
34164 need to contain registers; it instructs @value{GDBN} to display the
34165 VFP double-precision registers as vectors and to synthesize the
34166 quad-precision registers from pairs of double-precision registers.
34167 If this feature is present, @samp{org.gnu.gdb.arm.vfp} must also
34168 be present and include 32 double-precision registers.
34170 @node i386 Features
34171 @subsection i386 Features
34172 @cindex target descriptions, i386 features
34174 The @samp{org.gnu.gdb.i386.core} feature is required for i386/amd64
34175 targets. It should describe the following registers:
34179 @samp{eax} through @samp{edi} plus @samp{eip} for i386
34181 @samp{rax} through @samp{r15} plus @samp{rip} for amd64
34183 @samp{eflags}, @samp{cs}, @samp{ss}, @samp{ds}, @samp{es},
34184 @samp{fs}, @samp{gs}
34186 @samp{st0} through @samp{st7}
34188 @samp{fctrl}, @samp{fstat}, @samp{ftag}, @samp{fiseg}, @samp{fioff},
34189 @samp{foseg}, @samp{fooff} and @samp{fop}
34192 The register sets may be different, depending on the target.
34194 The @samp{org.gnu.gdb.i386.sse} feature is optional. It should
34195 describe registers:
34199 @samp{xmm0} through @samp{xmm7} for i386
34201 @samp{xmm0} through @samp{xmm15} for amd64
34206 The @samp{org.gnu.gdb.i386.avx} feature is optional and requires the
34207 @samp{org.gnu.gdb.i386.sse} feature. It should
34208 describe the upper 128 bits of @sc{ymm} registers:
34212 @samp{ymm0h} through @samp{ymm7h} for i386
34214 @samp{ymm0h} through @samp{ymm15h} for amd64
34218 The @samp{org.gnu.gdb.i386.linux} feature is optional. It should
34219 describe a single register, @samp{orig_eax}.
34221 @node MIPS Features
34222 @subsection MIPS Features
34223 @cindex target descriptions, MIPS features
34225 The @samp{org.gnu.gdb.mips.cpu} feature is required for MIPS targets.
34226 It should contain registers @samp{r0} through @samp{r31}, @samp{lo},
34227 @samp{hi}, and @samp{pc}. They may be 32-bit or 64-bit depending
34230 The @samp{org.gnu.gdb.mips.cp0} feature is also required. It should
34231 contain at least the @samp{status}, @samp{badvaddr}, and @samp{cause}
34232 registers. They may be 32-bit or 64-bit depending on the target.
34234 The @samp{org.gnu.gdb.mips.fpu} feature is currently required, though
34235 it may be optional in a future version of @value{GDBN}. It should
34236 contain registers @samp{f0} through @samp{f31}, @samp{fcsr}, and
34237 @samp{fir}. They may be 32-bit or 64-bit depending on the target.
34239 The @samp{org.gnu.gdb.mips.linux} feature is optional. It should
34240 contain a single register, @samp{restart}, which is used by the
34241 Linux kernel to control restartable syscalls.
34243 @node M68K Features
34244 @subsection M68K Features
34245 @cindex target descriptions, M68K features
34248 @item @samp{org.gnu.gdb.m68k.core}
34249 @itemx @samp{org.gnu.gdb.coldfire.core}
34250 @itemx @samp{org.gnu.gdb.fido.core}
34251 One of those features must be always present.
34252 The feature that is present determines which flavor of m68k is
34253 used. The feature that is present should contain registers
34254 @samp{d0} through @samp{d7}, @samp{a0} through @samp{a5}, @samp{fp},
34255 @samp{sp}, @samp{ps} and @samp{pc}.
34257 @item @samp{org.gnu.gdb.coldfire.fp}
34258 This feature is optional. If present, it should contain registers
34259 @samp{fp0} through @samp{fp7}, @samp{fpcontrol}, @samp{fpstatus} and
34263 @node PowerPC Features
34264 @subsection PowerPC Features
34265 @cindex target descriptions, PowerPC features
34267 The @samp{org.gnu.gdb.power.core} feature is required for PowerPC
34268 targets. It should contain registers @samp{r0} through @samp{r31},
34269 @samp{pc}, @samp{msr}, @samp{cr}, @samp{lr}, @samp{ctr}, and
34270 @samp{xer}. They may be 32-bit or 64-bit depending on the target.
34272 The @samp{org.gnu.gdb.power.fpu} feature is optional. It should
34273 contain registers @samp{f0} through @samp{f31} and @samp{fpscr}.
34275 The @samp{org.gnu.gdb.power.altivec} feature is optional. It should
34276 contain registers @samp{vr0} through @samp{vr31}, @samp{vscr},
34279 The @samp{org.gnu.gdb.power.vsx} feature is optional. It should
34280 contain registers @samp{vs0h} through @samp{vs31h}. @value{GDBN}
34281 will combine these registers with the floating point registers
34282 (@samp{f0} through @samp{f31}) and the altivec registers (@samp{vr0}
34283 through @samp{vr31}) to present the 128-bit wide registers @samp{vs0}
34284 through @samp{vs63}, the set of vector registers for POWER7.
34286 The @samp{org.gnu.gdb.power.spe} feature is optional. It should
34287 contain registers @samp{ev0h} through @samp{ev31h}, @samp{acc}, and
34288 @samp{spefscr}. SPE targets should provide 32-bit registers in
34289 @samp{org.gnu.gdb.power.core} and provide the upper halves in
34290 @samp{ev0h} through @samp{ev31h}. @value{GDBN} will combine
34291 these to present registers @samp{ev0} through @samp{ev31} to the
34294 @node Operating System Information
34295 @appendix Operating System Information
34296 @cindex operating system information
34302 Users of @value{GDBN} often wish to obtain information about the state of
34303 the operating system running on the target---for example the list of
34304 processes, or the list of open files. This section describes the
34305 mechanism that makes it possible. This mechanism is similar to the
34306 target features mechanism (@pxref{Target Descriptions}), but focuses
34307 on a different aspect of target.
34309 Operating system information is retrived from the target via the
34310 remote protocol, using @samp{qXfer} requests (@pxref{qXfer osdata
34311 read}). The object name in the request should be @samp{osdata}, and
34312 the @var{annex} identifies the data to be fetched.
34315 @appendixsection Process list
34316 @cindex operating system information, process list
34318 When requesting the process list, the @var{annex} field in the
34319 @samp{qXfer} request should be @samp{processes}. The returned data is
34320 an XML document. The formal syntax of this document is defined in
34321 @file{gdb/features/osdata.dtd}.
34323 An example document is:
34326 <?xml version="1.0"?>
34327 <!DOCTYPE target SYSTEM "osdata.dtd">
34328 <osdata type="processes">
34330 <column name="pid">1</column>
34331 <column name="user">root</column>
34332 <column name="command">/sbin/init</column>
34333 <column name="cores">1,2,3</column>
34338 Each item should include a column whose name is @samp{pid}. The value
34339 of that column should identify the process on the target. The
34340 @samp{user} and @samp{command} columns are optional, and will be
34341 displayed by @value{GDBN}. The @samp{cores} column, if present,
34342 should contain a comma-separated list of cores that this process
34343 is running on. Target may provide additional columns,
34344 which @value{GDBN} currently ignores.
34358 % I think something like @colophon should be in texinfo. In the
34360 \long\def\colophon{\hbox to0pt{}\vfill
34361 \centerline{The body of this manual is set in}
34362 \centerline{\fontname\tenrm,}
34363 \centerline{with headings in {\bf\fontname\tenbf}}
34364 \centerline{and examples in {\tt\fontname\tentt}.}
34365 \centerline{{\it\fontname\tenit\/},}
34366 \centerline{{\bf\fontname\tenbf}, and}
34367 \centerline{{\sl\fontname\tensl\/}}
34368 \centerline{are used for emphasis.}\vfill}
34370 % Blame: doc@cygnus.com, 1991.