1 \input texinfo @c -*-texinfo-*-
2 @c Copyright 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,
3 @c 1999, 2000, 2001, 2002
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
25 @c readline appendices use @vindex, @findex and @ftable,
26 @c annotate.texi and gdbmi use @findex.
30 @c !!set GDB manual's edition---not the same as GDB version!
33 @c !!set GDB manual's revision date
34 @set DATE December 2001
36 @c THIS MANUAL REQUIRES TEXINFO 4.0 OR LATER.
38 @c This is a dir.info fragment to support semi-automated addition of
39 @c manuals to an info tree.
40 @dircategory Programming & development tools.
42 * Gdb: (gdb). The @sc{gnu} debugger.
46 This file documents the @sc{gnu} debugger @value{GDBN}.
49 This is the @value{EDITION} Edition, @value{DATE},
50 of @cite{Debugging with @value{GDBN}: the @sc{gnu} Source-Level Debugger}
51 for @value{GDBN} Version @value{GDBVN}.
53 Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,@*
54 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
56 Permission is granted to copy, distribute and/or modify this document
57 under the terms of the GNU Free Documentation License, Version 1.1 or
58 any later version published by the Free Software Foundation; with the
59 Invariant Sections being ``Free Software'' and ``Free Software Needs
60 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
61 and with the Back-Cover Texts as in (a) below.
63 (a) The Free Software Foundation's Back-Cover Text is: ``You have
64 freedom to copy and modify this GNU Manual, like GNU software. Copies
65 published by the Free Software Foundation raise funds for GNU
70 @title Debugging with @value{GDBN}
71 @subtitle The @sc{gnu} Source-Level Debugger
73 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
74 @subtitle @value{DATE}
75 @author Richard Stallman, Roland Pesch, Stan Shebs, et al.
79 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@gnu.org.)\par
80 \hfill {\it Debugging with @value{GDBN}}\par
81 \hfill \TeX{}info \texinfoversion\par
85 @vskip 0pt plus 1filll
86 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995,
87 1996, 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
89 Published by the Free Software Foundation @*
90 59 Temple Place - Suite 330, @*
91 Boston, MA 02111-1307 USA @*
94 Permission is granted to copy, distribute and/or modify this document
95 under the terms of the GNU Free Documentation License, Version 1.1 or
96 any later version published by the Free Software Foundation; with the
97 Invariant Sections being ``Free Software'' and ``Free Software Needs
98 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
99 and with the Back-Cover Texts as in (a) below.
101 (a) The Free Software Foundation's Back-Cover Text is: ``You have
102 freedom to copy and modify this GNU Manual, like GNU software. Copies
103 published by the Free Software Foundation raise funds for GNU
109 @node Top, Summary, (dir), (dir)
111 @top Debugging with @value{GDBN}
113 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
115 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
118 Copyright (C) 1988-2002 Free Software Foundation, Inc.
121 * Summary:: Summary of @value{GDBN}
122 * Sample Session:: A sample @value{GDBN} session
124 * Invocation:: Getting in and out of @value{GDBN}
125 * Commands:: @value{GDBN} commands
126 * Running:: Running programs under @value{GDBN}
127 * Stopping:: Stopping and continuing
128 * Stack:: Examining the stack
129 * Source:: Examining source files
130 * Data:: Examining data
131 * Tracepoints:: Debugging remote targets non-intrusively
132 * Overlays:: Debugging programs that use overlays
134 * Languages:: Using @value{GDBN} with different languages
136 * Symbols:: Examining the symbol table
137 * Altering:: Altering execution
138 * GDB Files:: @value{GDBN} files
139 * Targets:: Specifying a debugging target
140 * Remote Debugging:: Debugging remote programs
141 * Configurations:: Configuration-specific information
142 * Controlling GDB:: Controlling @value{GDBN}
143 * Sequences:: Canned sequences of commands
144 * TUI:: @value{GDBN} Text User Interface
145 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
146 * Annotations:: @value{GDBN}'s annotation interface.
147 * GDB/MI:: @value{GDBN}'s Machine Interface.
149 * GDB Bugs:: Reporting bugs in @value{GDBN}
150 * Formatting Documentation:: How to format and print @value{GDBN} documentation
152 * Command Line Editing:: Command Line Editing
153 * Using History Interactively:: Using History Interactively
154 * Installing GDB:: Installing GDB
155 * Maintenance Commands:: Maintenance Commands
156 * Remote Protocol:: GDB Remote Serial Protocol
157 * Copying:: GNU General Public License says
158 how you can copy and share GDB
159 * GNU Free Documentation License:: The license for this documentation
168 @unnumbered Summary of @value{GDBN}
170 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
171 going on ``inside'' another program while it executes---or what another
172 program was doing at the moment it crashed.
174 @value{GDBN} can do four main kinds of things (plus other things in support of
175 these) to help you catch bugs in the act:
179 Start your program, specifying anything that might affect its behavior.
182 Make your program stop on specified conditions.
185 Examine what has happened, when your program has stopped.
188 Change things in your program, so you can experiment with correcting the
189 effects of one bug and go on to learn about another.
192 You can use @value{GDBN} to debug programs written in C and C++.
193 For more information, see @ref{Support,,Supported languages}.
194 For more information, see @ref{C,,C and C++}.
198 Support for Modula-2 and Chill is partial. For information on Modula-2,
199 see @ref{Modula-2,,Modula-2}. For information on Chill, see @ref{Chill}.
202 Debugging Pascal programs which use sets, subranges, file variables, or
203 nested functions does not currently work. @value{GDBN} does not support
204 entering expressions, printing values, or similar features using Pascal
208 @value{GDBN} can be used to debug programs written in Fortran, although
209 it may be necessary to refer to some variables with a trailing
213 * Free Software:: Freely redistributable software
214 * Contributors:: Contributors to GDB
218 @unnumberedsec Free software
220 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
221 General Public License
222 (GPL). The GPL gives you the freedom to copy or adapt a licensed
223 program---but every person getting a copy also gets with it the
224 freedom to modify that copy (which means that they must get access to
225 the source code), and the freedom to distribute further copies.
226 Typical software companies use copyrights to limit your freedoms; the
227 Free Software Foundation uses the GPL to preserve these freedoms.
229 Fundamentally, the General Public License is a license which says that
230 you have these freedoms and that you cannot take these freedoms away
233 @unnumberedsec Free Software Needs Free Documentation
235 The biggest deficiency in the free software community today is not in
236 the software---it is the lack of good free documentation that we can
237 include with the free software. Many of our most important
238 programs do not come with free reference manuals and free introductory
239 texts. Documentation is an essential part of any software package;
240 when an important free software package does not come with a free
241 manual and a free tutorial, that is a major gap. We have many such
244 Consider Perl, for instance. The tutorial manuals that people
245 normally use are non-free. How did this come about? Because the
246 authors of those manuals published them with restrictive terms---no
247 copying, no modification, source files not available---which exclude
248 them from the free software world.
250 That wasn't the first time this sort of thing happened, and it was far
251 from the last. Many times we have heard a GNU user eagerly describe a
252 manual that he is writing, his intended contribution to the community,
253 only to learn that he had ruined everything by signing a publication
254 contract to make it non-free.
256 Free documentation, like free software, is a matter of freedom, not
257 price. The problem with the non-free manual is not that publishers
258 charge a price for printed copies---that in itself is fine. (The Free
259 Software Foundation sells printed copies of manuals, too.) The
260 problem is the restrictions on the use of the manual. Free manuals
261 are available in source code form, and give you permission to copy and
262 modify. Non-free manuals do not allow this.
264 The criteria of freedom for a free manual are roughly the same as for
265 free software. Redistribution (including the normal kinds of
266 commercial redistribution) must be permitted, so that the manual can
267 accompany every copy of the program, both on-line and on paper.
269 Permission for modification of the technical content is crucial too.
270 When people modify the software, adding or changing features, if they
271 are conscientious they will change the manual too---so they can
272 provide accurate and clear documentation for the modified program. A
273 manual that leaves you no choice but to write a new manual to document
274 a changed version of the program is not really available to our
277 Some kinds of limits on the way modification is handled are
278 acceptable. For example, requirements to preserve the original
279 author's copyright notice, the distribution terms, or the list of
280 authors, are ok. It is also no problem to require modified versions
281 to include notice that they were modified. Even entire sections that
282 may not be deleted or changed are acceptable, as long as they deal
283 with nontechnical topics (like this one). These kinds of restrictions
284 are acceptable because they don't obstruct the community's normal use
287 However, it must be possible to modify all the @emph{technical}
288 content of the manual, and then distribute the result in all the usual
289 media, through all the usual channels. Otherwise, the restrictions
290 obstruct the use of the manual, it is not free, and we need another
291 manual to replace it.
293 Please spread the word about this issue. Our community continues to
294 lose manuals to proprietary publishing. If we spread the word that
295 free software needs free reference manuals and free tutorials, perhaps
296 the next person who wants to contribute by writing documentation will
297 realize, before it is too late, that only free manuals contribute to
298 the free software community.
300 If you are writing documentation, please insist on publishing it under
301 the GNU Free Documentation License or another free documentation
302 license. Remember that this decision requires your approval---you
303 don't have to let the publisher decide. Some commercial publishers
304 will use a free license if you insist, but they will not propose the
305 option; it is up to you to raise the issue and say firmly that this is
306 what you want. If the publisher you are dealing with refuses, please
307 try other publishers. If you're not sure whether a proposed license
308 is free, write to @email{licensing@@gnu.org}.
310 You can encourage commercial publishers to sell more free, copylefted
311 manuals and tutorials by buying them, and particularly by buying
312 copies from the publishers that paid for their writing or for major
313 improvements. Meanwhile, try to avoid buying non-free documentation
314 at all. Check the distribution terms of a manual before you buy it,
315 and insist that whoever seeks your business must respect your freedom.
316 Check the history of the book, and try to reward the publishers that
317 have paid or pay the authors to work on it.
319 The Free Software Foundation maintains a list of free documentation
320 published by other publishers, at
321 @url{http://www.fsf.org/doc/other-free-books.html}.
324 @unnumberedsec Contributors to @value{GDBN}
326 Richard Stallman was the original author of @value{GDBN}, and of many
327 other @sc{gnu} programs. Many others have contributed to its
328 development. This section attempts to credit major contributors. One
329 of the virtues of free software is that everyone is free to contribute
330 to it; with regret, we cannot actually acknowledge everyone here. The
331 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
332 blow-by-blow account.
334 Changes much prior to version 2.0 are lost in the mists of time.
337 @emph{Plea:} Additions to this section are particularly welcome. If you
338 or your friends (or enemies, to be evenhanded) have been unfairly
339 omitted from this list, we would like to add your names!
342 So that they may not regard their many labors as thankless, we
343 particularly thank those who shepherded @value{GDBN} through major
345 Andrew Cagney (releases 5.0 and 5.1);
346 Jim Blandy (release 4.18);
347 Jason Molenda (release 4.17);
348 Stan Shebs (release 4.14);
349 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
350 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
351 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
352 Jim Kingdon (releases 3.5, 3.4, and 3.3);
353 and Randy Smith (releases 3.2, 3.1, and 3.0).
355 Richard Stallman, assisted at various times by Peter TerMaat, Chris
356 Hanson, and Richard Mlynarik, handled releases through 2.8.
358 Michael Tiemann is the author of most of the @sc{gnu} C@t{++} support
359 in @value{GDBN}, with significant additional contributions from Per
360 Bothner and Daniel Berlin. James Clark wrote the @sc{gnu} C@t{++}
361 demangler. Early work on C@t{++} was by Peter TerMaat (who also did
362 much general update work leading to release 3.0).
364 @value{GDBN} uses the BFD subroutine library to examine multiple
365 object-file formats; BFD was a joint project of David V.
366 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
368 David Johnson wrote the original COFF support; Pace Willison did
369 the original support for encapsulated COFF.
371 Brent Benson of Harris Computer Systems contributed DWARF2 support.
373 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
374 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
376 Jean-Daniel Fekete contributed Sun 386i support.
377 Chris Hanson improved the HP9000 support.
378 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
379 David Johnson contributed Encore Umax support.
380 Jyrki Kuoppala contributed Altos 3068 support.
381 Jeff Law contributed HP PA and SOM support.
382 Keith Packard contributed NS32K support.
383 Doug Rabson contributed Acorn Risc Machine support.
384 Bob Rusk contributed Harris Nighthawk CX-UX support.
385 Chris Smith contributed Convex support (and Fortran debugging).
386 Jonathan Stone contributed Pyramid support.
387 Michael Tiemann contributed SPARC support.
388 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
389 Pace Willison contributed Intel 386 support.
390 Jay Vosburgh contributed Symmetry support.
392 Andreas Schwab contributed M68K Linux support.
394 Rich Schaefer and Peter Schauer helped with support of SunOS shared
397 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
398 about several machine instruction sets.
400 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
401 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
402 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
403 and RDI targets, respectively.
405 Brian Fox is the author of the readline libraries providing
406 command-line editing and command history.
408 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
409 Modula-2 support, and contributed the Languages chapter of this manual.
411 Fred Fish wrote most of the support for Unix System Vr4.
412 He also enhanced the command-completion support to cover C@t{++} overloaded
415 Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and
418 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
420 Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors.
422 Toshiba sponsored the support for the TX39 Mips processor.
424 Matsushita sponsored the support for the MN10200 and MN10300 processors.
426 Fujitsu sponsored the support for SPARClite and FR30 processors.
428 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
431 Michael Snyder added support for tracepoints.
433 Stu Grossman wrote gdbserver.
435 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
436 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
438 The following people at the Hewlett-Packard Company contributed
439 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
440 (narrow mode), HP's implementation of kernel threads, HP's aC@t{++}
441 compiler, and the terminal user interface: Ben Krepp, Richard Title,
442 John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve
443 Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific
444 information in this manual.
446 DJ Delorie ported @value{GDBN} to MS-DOS, for the DJGPP project.
447 Robert Hoehne made significant contributions to the DJGPP port.
449 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
450 development since 1991. Cygnus engineers who have worked on @value{GDBN}
451 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
452 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
453 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
454 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
455 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
456 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
457 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
458 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
459 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
460 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
461 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
462 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
463 Zuhn have made contributions both large and small.
467 @chapter A Sample @value{GDBN} Session
469 You can use this manual at your leisure to read all about @value{GDBN}.
470 However, a handful of commands are enough to get started using the
471 debugger. This chapter illustrates those commands.
474 In this sample session, we emphasize user input like this: @b{input},
475 to make it easier to pick out from the surrounding output.
478 @c FIXME: this example may not be appropriate for some configs, where
479 @c FIXME...primary interest is in remote use.
481 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
482 processor) exhibits the following bug: sometimes, when we change its
483 quote strings from the default, the commands used to capture one macro
484 definition within another stop working. In the following short @code{m4}
485 session, we define a macro @code{foo} which expands to @code{0000}; we
486 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
487 same thing. However, when we change the open quote string to
488 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
489 procedure fails to define a new synonym @code{baz}:
498 @b{define(bar,defn(`foo'))}
502 @b{changequote(<QUOTE>,<UNQUOTE>)}
504 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
507 m4: End of input: 0: fatal error: EOF in string
511 Let us use @value{GDBN} to try to see what is going on.
514 $ @b{@value{GDBP} m4}
515 @c FIXME: this falsifies the exact text played out, to permit smallbook
516 @c FIXME... format to come out better.
517 @value{GDBN} is free software and you are welcome to distribute copies
518 of it under certain conditions; type "show copying" to see
520 There is absolutely no warranty for @value{GDBN}; type "show warranty"
523 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
528 @value{GDBN} reads only enough symbol data to know where to find the
529 rest when needed; as a result, the first prompt comes up very quickly.
530 We now tell @value{GDBN} to use a narrower display width than usual, so
531 that examples fit in this manual.
534 (@value{GDBP}) @b{set width 70}
538 We need to see how the @code{m4} built-in @code{changequote} works.
539 Having looked at the source, we know the relevant subroutine is
540 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
541 @code{break} command.
544 (@value{GDBP}) @b{break m4_changequote}
545 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
549 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
550 control; as long as control does not reach the @code{m4_changequote}
551 subroutine, the program runs as usual:
554 (@value{GDBP}) @b{run}
555 Starting program: /work/Editorial/gdb/gnu/m4/m4
563 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
564 suspends execution of @code{m4}, displaying information about the
565 context where it stops.
568 @b{changequote(<QUOTE>,<UNQUOTE>)}
570 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
572 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
576 Now we use the command @code{n} (@code{next}) to advance execution to
577 the next line of the current function.
581 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
586 @code{set_quotes} looks like a promising subroutine. We can go into it
587 by using the command @code{s} (@code{step}) instead of @code{next}.
588 @code{step} goes to the next line to be executed in @emph{any}
589 subroutine, so it steps into @code{set_quotes}.
593 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
595 530 if (lquote != def_lquote)
599 The display that shows the subroutine where @code{m4} is now
600 suspended (and its arguments) is called a stack frame display. It
601 shows a summary of the stack. We can use the @code{backtrace}
602 command (which can also be spelled @code{bt}), to see where we are
603 in the stack as a whole: the @code{backtrace} command displays a
604 stack frame for each active subroutine.
607 (@value{GDBP}) @b{bt}
608 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
610 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
612 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
613 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
615 #4 0x79dc in expand_input () at macro.c:40
616 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
620 We step through a few more lines to see what happens. The first two
621 times, we can use @samp{s}; the next two times we use @code{n} to avoid
622 falling into the @code{xstrdup} subroutine.
626 0x3b5c 532 if (rquote != def_rquote)
628 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
629 def_lquote : xstrdup(lq);
631 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
634 538 len_lquote = strlen(rquote);
638 The last line displayed looks a little odd; we can examine the variables
639 @code{lquote} and @code{rquote} to see if they are in fact the new left
640 and right quotes we specified. We use the command @code{p}
641 (@code{print}) to see their values.
644 (@value{GDBP}) @b{p lquote}
645 $1 = 0x35d40 "<QUOTE>"
646 (@value{GDBP}) @b{p rquote}
647 $2 = 0x35d50 "<UNQUOTE>"
651 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
652 To look at some context, we can display ten lines of source
653 surrounding the current line with the @code{l} (@code{list}) command.
659 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
661 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
664 538 len_lquote = strlen(rquote);
665 539 len_rquote = strlen(lquote);
672 Let us step past the two lines that set @code{len_lquote} and
673 @code{len_rquote}, and then examine the values of those variables.
677 539 len_rquote = strlen(lquote);
680 (@value{GDBP}) @b{p len_lquote}
682 (@value{GDBP}) @b{p len_rquote}
687 That certainly looks wrong, assuming @code{len_lquote} and
688 @code{len_rquote} are meant to be the lengths of @code{lquote} and
689 @code{rquote} respectively. We can set them to better values using
690 the @code{p} command, since it can print the value of
691 any expression---and that expression can include subroutine calls and
695 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
697 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
702 Is that enough to fix the problem of using the new quotes with the
703 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
704 executing with the @code{c} (@code{continue}) command, and then try the
705 example that caused trouble initially:
711 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
718 Success! The new quotes now work just as well as the default ones. The
719 problem seems to have been just the two typos defining the wrong
720 lengths. We allow @code{m4} exit by giving it an EOF as input:
724 Program exited normally.
728 The message @samp{Program exited normally.} is from @value{GDBN}; it
729 indicates @code{m4} has finished executing. We can end our @value{GDBN}
730 session with the @value{GDBN} @code{quit} command.
733 (@value{GDBP}) @b{quit}
737 @chapter Getting In and Out of @value{GDBN}
739 This chapter discusses how to start @value{GDBN}, and how to get out of it.
743 type @samp{@value{GDBP}} to start @value{GDBN}.
745 type @kbd{quit} or @kbd{C-d} to exit.
749 * Invoking GDB:: How to start @value{GDBN}
750 * Quitting GDB:: How to quit @value{GDBN}
751 * Shell Commands:: How to use shell commands inside @value{GDBN}
755 @section Invoking @value{GDBN}
757 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
758 @value{GDBN} reads commands from the terminal until you tell it to exit.
760 You can also run @code{@value{GDBP}} with a variety of arguments and options,
761 to specify more of your debugging environment at the outset.
763 The command-line options described here are designed
764 to cover a variety of situations; in some environments, some of these
765 options may effectively be unavailable.
767 The most usual way to start @value{GDBN} is with one argument,
768 specifying an executable program:
771 @value{GDBP} @var{program}
775 You can also start with both an executable program and a core file
779 @value{GDBP} @var{program} @var{core}
782 You can, instead, specify a process ID as a second argument, if you want
783 to debug a running process:
786 @value{GDBP} @var{program} 1234
790 would attach @value{GDBN} to process @code{1234} (unless you also have a file
791 named @file{1234}; @value{GDBN} does check for a core file first).
793 Taking advantage of the second command-line argument requires a fairly
794 complete operating system; when you use @value{GDBN} as a remote
795 debugger attached to a bare board, there may not be any notion of
796 ``process'', and there is often no way to get a core dump. @value{GDBN}
797 will warn you if it is unable to attach or to read core dumps.
799 You can optionally have @code{@value{GDBP}} pass any arguments after the
800 executable file to the inferior using @code{--args}. This option stops
803 gdb --args gcc -O2 -c foo.c
805 This will cause @code{@value{GDBP}} to debug @code{gcc}, and to set
806 @code{gcc}'s command-line arguments (@pxref{Arguments}) to @samp{-O2 -c foo.c}.
808 You can run @code{@value{GDBP}} without printing the front material, which describes
809 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
816 You can further control how @value{GDBN} starts up by using command-line
817 options. @value{GDBN} itself can remind you of the options available.
827 to display all available options and briefly describe their use
828 (@samp{@value{GDBP} -h} is a shorter equivalent).
830 All options and command line arguments you give are processed
831 in sequential order. The order makes a difference when the
832 @samp{-x} option is used.
836 * File Options:: Choosing files
837 * Mode Options:: Choosing modes
841 @subsection Choosing files
843 When @value{GDBN} starts, it reads any arguments other than options as
844 specifying an executable file and core file (or process ID). This is
845 the same as if the arguments were specified by the @samp{-se} and
846 @samp{-c} (or @samp{-p} options respectively. (@value{GDBN} reads the
847 first argument that does not have an associated option flag as
848 equivalent to the @samp{-se} option followed by that argument; and the
849 second argument that does not have an associated option flag, if any, as
850 equivalent to the @samp{-c}/@samp{-p} option followed by that argument.)
851 If the second argument begins with a decimal digit, @value{GDBN} will
852 first attempt to attach to it as a process, and if that fails, attempt
853 to open it as a corefile. If you have a corefile whose name begins with
854 a digit, you can prevent @value{GDBN} from treating it as a pid by
855 prefixing it with @file{./}, eg. @file{./12345}.
857 If @value{GDBN} has not been configured to included core file support,
858 such as for most embedded targets, then it will complain about a second
859 argument and ignore it.
861 Many options have both long and short forms; both are shown in the
862 following list. @value{GDBN} also recognizes the long forms if you truncate
863 them, so long as enough of the option is present to be unambiguous.
864 (If you prefer, you can flag option arguments with @samp{--} rather
865 than @samp{-}, though we illustrate the more usual convention.)
867 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
868 @c way, both those who look for -foo and --foo in the index, will find
872 @item -symbols @var{file}
874 @cindex @code{--symbols}
876 Read symbol table from file @var{file}.
878 @item -exec @var{file}
880 @cindex @code{--exec}
882 Use file @var{file} as the executable file to execute when appropriate,
883 and for examining pure data in conjunction with a core dump.
887 Read symbol table from file @var{file} and use it as the executable
890 @item -core @var{file}
892 @cindex @code{--core}
894 Use file @var{file} as a core dump to examine.
896 @item -c @var{number}
897 @item -pid @var{number}
898 @itemx -p @var{number}
901 Connect to process ID @var{number}, as with the @code{attach} command.
902 If there is no such process, @value{GDBN} will attempt to open a core
903 file named @var{number}.
905 @item -command @var{file}
907 @cindex @code{--command}
909 Execute @value{GDBN} commands from file @var{file}. @xref{Command
910 Files,, Command files}.
912 @item -directory @var{directory}
913 @itemx -d @var{directory}
914 @cindex @code{--directory}
916 Add @var{directory} to the path to search for source files.
920 @cindex @code{--mapped}
922 @emph{Warning: this option depends on operating system facilities that are not
923 supported on all systems.}@*
924 If memory-mapped files are available on your system through the @code{mmap}
925 system call, you can use this option
926 to have @value{GDBN} write the symbols from your
927 program into a reusable file in the current directory. If the program you are debugging is
928 called @file{/tmp/fred}, the mapped symbol file is @file{/tmp/fred.syms}.
929 Future @value{GDBN} debugging sessions notice the presence of this file,
930 and can quickly map in symbol information from it, rather than reading
931 the symbol table from the executable program.
933 The @file{.syms} file is specific to the host machine where @value{GDBN}
934 is run. It holds an exact image of the internal @value{GDBN} symbol
935 table. It cannot be shared across multiple host platforms.
939 @cindex @code{--readnow}
941 Read each symbol file's entire symbol table immediately, rather than
942 the default, which is to read it incrementally as it is needed.
943 This makes startup slower, but makes future operations faster.
947 You typically combine the @code{-mapped} and @code{-readnow} options in
948 order to build a @file{.syms} file that contains complete symbol
949 information. (@xref{Files,,Commands to specify files}, for information
950 on @file{.syms} files.) A simple @value{GDBN} invocation to do nothing
951 but build a @file{.syms} file for future use is:
954 gdb -batch -nx -mapped -readnow programname
958 @subsection Choosing modes
960 You can run @value{GDBN} in various alternative modes---for example, in
961 batch mode or quiet mode.
968 Do not execute commands found in any initialization files. Normally,
969 @value{GDBN} executes the commands in these files after all the command
970 options and arguments have been processed. @xref{Command Files,,Command
976 @cindex @code{--quiet}
977 @cindex @code{--silent}
979 ``Quiet''. Do not print the introductory and copyright messages. These
980 messages are also suppressed in batch mode.
983 @cindex @code{--batch}
984 Run in batch mode. Exit with status @code{0} after processing all the
985 command files specified with @samp{-x} (and all commands from
986 initialization files, if not inhibited with @samp{-n}). Exit with
987 nonzero status if an error occurs in executing the @value{GDBN} commands
988 in the command files.
990 Batch mode may be useful for running @value{GDBN} as a filter, for
991 example to download and run a program on another computer; in order to
992 make this more useful, the message
995 Program exited normally.
999 (which is ordinarily issued whenever a program running under
1000 @value{GDBN} control terminates) is not issued when running in batch
1005 @cindex @code{--nowindows}
1007 ``No windows''. If @value{GDBN} comes with a graphical user interface
1008 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
1009 interface. If no GUI is available, this option has no effect.
1013 @cindex @code{--windows}
1015 If @value{GDBN} includes a GUI, then this option requires it to be
1018 @item -cd @var{directory}
1020 Run @value{GDBN} using @var{directory} as its working directory,
1021 instead of the current directory.
1025 @cindex @code{--fullname}
1027 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
1028 subprocess. It tells @value{GDBN} to output the full file name and line
1029 number in a standard, recognizable fashion each time a stack frame is
1030 displayed (which includes each time your program stops). This
1031 recognizable format looks like two @samp{\032} characters, followed by
1032 the file name, line number and character position separated by colons,
1033 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
1034 @samp{\032} characters as a signal to display the source code for the
1038 @cindex @code{--epoch}
1039 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
1040 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
1041 routines so as to allow Epoch to display values of expressions in a
1044 @item -annotate @var{level}
1045 @cindex @code{--annotate}
1046 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
1047 effect is identical to using @samp{set annotate @var{level}}
1048 (@pxref{Annotations}).
1049 Annotation level controls how much information does @value{GDBN} print
1050 together with its prompt, values of expressions, source lines, and other
1051 types of output. Level 0 is the normal, level 1 is for use when
1052 @value{GDBN} is run as a subprocess of @sc{gnu} Emacs, level 2 is the
1053 maximum annotation suitable for programs that control @value{GDBN}.
1056 @cindex @code{--async}
1057 Use the asynchronous event loop for the command-line interface.
1058 @value{GDBN} processes all events, such as user keyboard input, via a
1059 special event loop. This allows @value{GDBN} to accept and process user
1060 commands in parallel with the debugged process being
1061 run@footnote{@value{GDBN} built with @sc{djgpp} tools for
1062 MS-DOS/MS-Windows supports this mode of operation, but the event loop is
1063 suspended when the debuggee runs.}, so you don't need to wait for
1064 control to return to @value{GDBN} before you type the next command.
1065 (@emph{Note:} as of version 5.1, the target side of the asynchronous
1066 operation is not yet in place, so @samp{-async} does not work fully
1068 @c FIXME: when the target side of the event loop is done, the above NOTE
1069 @c should be removed.
1071 When the standard input is connected to a terminal device, @value{GDBN}
1072 uses the asynchronous event loop by default, unless disabled by the
1073 @samp{-noasync} option.
1076 @cindex @code{--noasync}
1077 Disable the asynchronous event loop for the command-line interface.
1080 @cindex @code{--args}
1081 Change interpretation of command line so that arguments following the
1082 executable file are passed as command line arguments to the inferior.
1083 This option stops option processing.
1085 @item -baud @var{bps}
1087 @cindex @code{--baud}
1089 Set the line speed (baud rate or bits per second) of any serial
1090 interface used by @value{GDBN} for remote debugging.
1092 @item -tty @var{device}
1093 @itemx -t @var{device}
1094 @cindex @code{--tty}
1096 Run using @var{device} for your program's standard input and output.
1097 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1099 @c resolve the situation of these eventually
1101 @cindex @code{--tui}
1102 Activate the Terminal User Interface when starting.
1103 The Terminal User Interface manages several text windows on the terminal,
1104 showing source, assembly, registers and @value{GDBN} command outputs
1105 (@pxref{TUI, ,@value{GDBN} Text User Interface}).
1106 Do not use this option if you run @value{GDBN} from Emacs
1107 (@pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}).
1110 @c @cindex @code{--xdb}
1111 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1112 @c For information, see the file @file{xdb_trans.html}, which is usually
1113 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1116 @item -interpreter @var{interp}
1117 @cindex @code{--interpreter}
1118 Use the interpreter @var{interp} for interface with the controlling
1119 program or device. This option is meant to be set by programs which
1120 communicate with @value{GDBN} using it as a back end.
1122 @samp{--interpreter=mi} (or @samp{--interpreter=mi1}) causes
1123 @value{GDBN} to use the @dfn{gdb/mi interface} (@pxref{GDB/MI, , The
1124 @sc{gdb/mi} Interface}). The older @sc{gdb/mi} interface, included in
1125 @value{GDBN} version 5.0 can be selected with @samp{--interpreter=mi0}.
1128 @cindex @code{--write}
1129 Open the executable and core files for both reading and writing. This
1130 is equivalent to the @samp{set write on} command inside @value{GDBN}
1134 @cindex @code{--statistics}
1135 This option causes @value{GDBN} to print statistics about time and
1136 memory usage after it completes each command and returns to the prompt.
1139 @cindex @code{--version}
1140 This option causes @value{GDBN} to print its version number and
1141 no-warranty blurb, and exit.
1146 @section Quitting @value{GDBN}
1147 @cindex exiting @value{GDBN}
1148 @cindex leaving @value{GDBN}
1151 @kindex quit @r{[}@var{expression}@r{]}
1152 @kindex q @r{(@code{quit})}
1153 @item quit @r{[}@var{expression}@r{]}
1155 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1156 @code{q}), or type an end-of-file character (usually @kbd{C-d}). If you
1157 do not supply @var{expression}, @value{GDBN} will terminate normally;
1158 otherwise it will terminate using the result of @var{expression} as the
1163 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1164 terminates the action of any @value{GDBN} command that is in progress and
1165 returns to @value{GDBN} command level. It is safe to type the interrupt
1166 character at any time because @value{GDBN} does not allow it to take effect
1167 until a time when it is safe.
1169 If you have been using @value{GDBN} to control an attached process or
1170 device, you can release it with the @code{detach} command
1171 (@pxref{Attach, ,Debugging an already-running process}).
1173 @node Shell Commands
1174 @section Shell commands
1176 If you need to execute occasional shell commands during your
1177 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1178 just use the @code{shell} command.
1182 @cindex shell escape
1183 @item shell @var{command string}
1184 Invoke a standard shell to execute @var{command string}.
1185 If it exists, the environment variable @code{SHELL} determines which
1186 shell to run. Otherwise @value{GDBN} uses the default shell
1187 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1190 The utility @code{make} is often needed in development environments.
1191 You do not have to use the @code{shell} command for this purpose in
1196 @cindex calling make
1197 @item make @var{make-args}
1198 Execute the @code{make} program with the specified
1199 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1203 @chapter @value{GDBN} Commands
1205 You can abbreviate a @value{GDBN} command to the first few letters of the command
1206 name, if that abbreviation is unambiguous; and you can repeat certain
1207 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1208 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1209 show you the alternatives available, if there is more than one possibility).
1212 * Command Syntax:: How to give commands to @value{GDBN}
1213 * Completion:: Command completion
1214 * Help:: How to ask @value{GDBN} for help
1217 @node Command Syntax
1218 @section Command syntax
1220 A @value{GDBN} command is a single line of input. There is no limit on
1221 how long it can be. It starts with a command name, which is followed by
1222 arguments whose meaning depends on the command name. For example, the
1223 command @code{step} accepts an argument which is the number of times to
1224 step, as in @samp{step 5}. You can also use the @code{step} command
1225 with no arguments. Some commands do not allow any arguments.
1227 @cindex abbreviation
1228 @value{GDBN} command names may always be truncated if that abbreviation is
1229 unambiguous. Other possible command abbreviations are listed in the
1230 documentation for individual commands. In some cases, even ambiguous
1231 abbreviations are allowed; for example, @code{s} is specially defined as
1232 equivalent to @code{step} even though there are other commands whose
1233 names start with @code{s}. You can test abbreviations by using them as
1234 arguments to the @code{help} command.
1236 @cindex repeating commands
1237 @kindex RET @r{(repeat last command)}
1238 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1239 repeat the previous command. Certain commands (for example, @code{run})
1240 will not repeat this way; these are commands whose unintentional
1241 repetition might cause trouble and which you are unlikely to want to
1244 The @code{list} and @code{x} commands, when you repeat them with
1245 @key{RET}, construct new arguments rather than repeating
1246 exactly as typed. This permits easy scanning of source or memory.
1248 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1249 output, in a way similar to the common utility @code{more}
1250 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1251 @key{RET} too many in this situation, @value{GDBN} disables command
1252 repetition after any command that generates this sort of display.
1254 @kindex # @r{(a comment)}
1256 Any text from a @kbd{#} to the end of the line is a comment; it does
1257 nothing. This is useful mainly in command files (@pxref{Command
1258 Files,,Command files}).
1260 @cindex repeating command sequences
1261 @kindex C-o @r{(operate-and-get-next)}
1262 The @kbd{C-o} binding is useful for repeating a complex sequence of
1263 commands. This command accepts the current line, like @kbd{RET}, and
1264 then fetches the next line relative to the current line from the history
1268 @section Command completion
1271 @cindex word completion
1272 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1273 only one possibility; it can also show you what the valid possibilities
1274 are for the next word in a command, at any time. This works for @value{GDBN}
1275 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1277 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1278 of a word. If there is only one possibility, @value{GDBN} fills in the
1279 word, and waits for you to finish the command (or press @key{RET} to
1280 enter it). For example, if you type
1282 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1283 @c complete accuracy in these examples; space introduced for clarity.
1284 @c If texinfo enhancements make it unnecessary, it would be nice to
1285 @c replace " @key" by "@key" in the following...
1287 (@value{GDBP}) info bre @key{TAB}
1291 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1292 the only @code{info} subcommand beginning with @samp{bre}:
1295 (@value{GDBP}) info breakpoints
1299 You can either press @key{RET} at this point, to run the @code{info
1300 breakpoints} command, or backspace and enter something else, if
1301 @samp{breakpoints} does not look like the command you expected. (If you
1302 were sure you wanted @code{info breakpoints} in the first place, you
1303 might as well just type @key{RET} immediately after @samp{info bre},
1304 to exploit command abbreviations rather than command completion).
1306 If there is more than one possibility for the next word when you press
1307 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1308 characters and try again, or just press @key{TAB} a second time;
1309 @value{GDBN} displays all the possible completions for that word. For
1310 example, you might want to set a breakpoint on a subroutine whose name
1311 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1312 just sounds the bell. Typing @key{TAB} again displays all the
1313 function names in your program that begin with those characters, for
1317 (@value{GDBP}) b make_ @key{TAB}
1318 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1319 make_a_section_from_file make_environ
1320 make_abs_section make_function_type
1321 make_blockvector make_pointer_type
1322 make_cleanup make_reference_type
1323 make_command make_symbol_completion_list
1324 (@value{GDBP}) b make_
1328 After displaying the available possibilities, @value{GDBN} copies your
1329 partial input (@samp{b make_} in the example) so you can finish the
1332 If you just want to see the list of alternatives in the first place, you
1333 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1334 means @kbd{@key{META} ?}. You can type this either by holding down a
1335 key designated as the @key{META} shift on your keyboard (if there is
1336 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1338 @cindex quotes in commands
1339 @cindex completion of quoted strings
1340 Sometimes the string you need, while logically a ``word'', may contain
1341 parentheses or other characters that @value{GDBN} normally excludes from
1342 its notion of a word. To permit word completion to work in this
1343 situation, you may enclose words in @code{'} (single quote marks) in
1344 @value{GDBN} commands.
1346 The most likely situation where you might need this is in typing the
1347 name of a C@t{++} function. This is because C@t{++} allows function
1348 overloading (multiple definitions of the same function, distinguished
1349 by argument type). For example, when you want to set a breakpoint you
1350 may need to distinguish whether you mean the version of @code{name}
1351 that takes an @code{int} parameter, @code{name(int)}, or the version
1352 that takes a @code{float} parameter, @code{name(float)}. To use the
1353 word-completion facilities in this situation, type a single quote
1354 @code{'} at the beginning of the function name. This alerts
1355 @value{GDBN} that it may need to consider more information than usual
1356 when you press @key{TAB} or @kbd{M-?} to request word completion:
1359 (@value{GDBP}) b 'bubble( @kbd{M-?}
1360 bubble(double,double) bubble(int,int)
1361 (@value{GDBP}) b 'bubble(
1364 In some cases, @value{GDBN} can tell that completing a name requires using
1365 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1366 completing as much as it can) if you do not type the quote in the first
1370 (@value{GDBP}) b bub @key{TAB}
1371 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1372 (@value{GDBP}) b 'bubble(
1376 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1377 you have not yet started typing the argument list when you ask for
1378 completion on an overloaded symbol.
1380 For more information about overloaded functions, see @ref{C plus plus
1381 expressions, ,C@t{++} expressions}. You can use the command @code{set
1382 overload-resolution off} to disable overload resolution;
1383 see @ref{Debugging C plus plus, ,@value{GDBN} features for C@t{++}}.
1387 @section Getting help
1388 @cindex online documentation
1391 You can always ask @value{GDBN} itself for information on its commands,
1392 using the command @code{help}.
1395 @kindex h @r{(@code{help})}
1398 You can use @code{help} (abbreviated @code{h}) with no arguments to
1399 display a short list of named classes of commands:
1403 List of classes of commands:
1405 aliases -- Aliases of other commands
1406 breakpoints -- Making program stop at certain points
1407 data -- Examining data
1408 files -- Specifying and examining files
1409 internals -- Maintenance commands
1410 obscure -- Obscure features
1411 running -- Running the program
1412 stack -- Examining the stack
1413 status -- Status inquiries
1414 support -- Support facilities
1415 tracepoints -- Tracing of program execution without@*
1416 stopping the program
1417 user-defined -- User-defined commands
1419 Type "help" followed by a class name for a list of
1420 commands in that class.
1421 Type "help" followed by command name for full
1423 Command name abbreviations are allowed if unambiguous.
1426 @c the above line break eliminates huge line overfull...
1428 @item help @var{class}
1429 Using one of the general help classes as an argument, you can get a
1430 list of the individual commands in that class. For example, here is the
1431 help display for the class @code{status}:
1434 (@value{GDBP}) help status
1439 @c Line break in "show" line falsifies real output, but needed
1440 @c to fit in smallbook page size.
1441 info -- Generic command for showing things
1442 about the program being debugged
1443 show -- Generic command for showing things
1446 Type "help" followed by command name for full
1448 Command name abbreviations are allowed if unambiguous.
1452 @item help @var{command}
1453 With a command name as @code{help} argument, @value{GDBN} displays a
1454 short paragraph on how to use that command.
1457 @item apropos @var{args}
1458 The @code{apropos @var{args}} command searches through all of the @value{GDBN}
1459 commands, and their documentation, for the regular expression specified in
1460 @var{args}. It prints out all matches found. For example:
1471 set symbol-reloading -- Set dynamic symbol table reloading
1472 multiple times in one run
1473 show symbol-reloading -- Show dynamic symbol table reloading
1474 multiple times in one run
1479 @item complete @var{args}
1480 The @code{complete @var{args}} command lists all the possible completions
1481 for the beginning of a command. Use @var{args} to specify the beginning of the
1482 command you want completed. For example:
1488 @noindent results in:
1499 @noindent This is intended for use by @sc{gnu} Emacs.
1502 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1503 and @code{show} to inquire about the state of your program, or the state
1504 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1505 manual introduces each of them in the appropriate context. The listings
1506 under @code{info} and under @code{show} in the Index point to
1507 all the sub-commands. @xref{Index}.
1512 @kindex i @r{(@code{info})}
1514 This command (abbreviated @code{i}) is for describing the state of your
1515 program. For example, you can list the arguments given to your program
1516 with @code{info args}, list the registers currently in use with @code{info
1517 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1518 You can get a complete list of the @code{info} sub-commands with
1519 @w{@code{help info}}.
1523 You can assign the result of an expression to an environment variable with
1524 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1525 @code{set prompt $}.
1529 In contrast to @code{info}, @code{show} is for describing the state of
1530 @value{GDBN} itself.
1531 You can change most of the things you can @code{show}, by using the
1532 related command @code{set}; for example, you can control what number
1533 system is used for displays with @code{set radix}, or simply inquire
1534 which is currently in use with @code{show radix}.
1537 To display all the settable parameters and their current
1538 values, you can use @code{show} with no arguments; you may also use
1539 @code{info set}. Both commands produce the same display.
1540 @c FIXME: "info set" violates the rule that "info" is for state of
1541 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1542 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1546 Here are three miscellaneous @code{show} subcommands, all of which are
1547 exceptional in lacking corresponding @code{set} commands:
1550 @kindex show version
1551 @cindex version number
1553 Show what version of @value{GDBN} is running. You should include this
1554 information in @value{GDBN} bug-reports. If multiple versions of
1555 @value{GDBN} are in use at your site, you may need to determine which
1556 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1557 commands are introduced, and old ones may wither away. Also, many
1558 system vendors ship variant versions of @value{GDBN}, and there are
1559 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1560 The version number is the same as the one announced when you start
1563 @kindex show copying
1565 Display information about permission for copying @value{GDBN}.
1567 @kindex show warranty
1569 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1570 if your version of @value{GDBN} comes with one.
1575 @chapter Running Programs Under @value{GDBN}
1577 When you run a program under @value{GDBN}, you must first generate
1578 debugging information when you compile it.
1580 You may start @value{GDBN} with its arguments, if any, in an environment
1581 of your choice. If you are doing native debugging, you may redirect
1582 your program's input and output, debug an already running process, or
1583 kill a child process.
1586 * Compilation:: Compiling for debugging
1587 * Starting:: Starting your program
1588 * Arguments:: Your program's arguments
1589 * Environment:: Your program's environment
1591 * Working Directory:: Your program's working directory
1592 * Input/Output:: Your program's input and output
1593 * Attach:: Debugging an already-running process
1594 * Kill Process:: Killing the child process
1596 * Threads:: Debugging programs with multiple threads
1597 * Processes:: Debugging programs with multiple processes
1601 @section Compiling for debugging
1603 In order to debug a program effectively, you need to generate
1604 debugging information when you compile it. This debugging information
1605 is stored in the object file; it describes the data type of each
1606 variable or function and the correspondence between source line numbers
1607 and addresses in the executable code.
1609 To request debugging information, specify the @samp{-g} option when you run
1612 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1613 options together. Using those compilers, you cannot generate optimized
1614 executables containing debugging information.
1616 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or
1617 without @samp{-O}, making it possible to debug optimized code. We
1618 recommend that you @emph{always} use @samp{-g} whenever you compile a
1619 program. You may think your program is correct, but there is no sense
1620 in pushing your luck.
1622 @cindex optimized code, debugging
1623 @cindex debugging optimized code
1624 When you debug a program compiled with @samp{-g -O}, remember that the
1625 optimizer is rearranging your code; the debugger shows you what is
1626 really there. Do not be too surprised when the execution path does not
1627 exactly match your source file! An extreme example: if you define a
1628 variable, but never use it, @value{GDBN} never sees that
1629 variable---because the compiler optimizes it out of existence.
1631 Some things do not work as well with @samp{-g -O} as with just
1632 @samp{-g}, particularly on machines with instruction scheduling. If in
1633 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1634 please report it to us as a bug (including a test case!).
1636 Older versions of the @sc{gnu} C compiler permitted a variant option
1637 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1638 format; if your @sc{gnu} C compiler has this option, do not use it.
1642 @section Starting your program
1648 @kindex r @r{(@code{run})}
1651 Use the @code{run} command to start your program under @value{GDBN}.
1652 You must first specify the program name (except on VxWorks) with an
1653 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1654 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1655 (@pxref{Files, ,Commands to specify files}).
1659 If you are running your program in an execution environment that
1660 supports processes, @code{run} creates an inferior process and makes
1661 that process run your program. (In environments without processes,
1662 @code{run} jumps to the start of your program.)
1664 The execution of a program is affected by certain information it
1665 receives from its superior. @value{GDBN} provides ways to specify this
1666 information, which you must do @emph{before} starting your program. (You
1667 can change it after starting your program, but such changes only affect
1668 your program the next time you start it.) This information may be
1669 divided into four categories:
1672 @item The @emph{arguments.}
1673 Specify the arguments to give your program as the arguments of the
1674 @code{run} command. If a shell is available on your target, the shell
1675 is used to pass the arguments, so that you may use normal conventions
1676 (such as wildcard expansion or variable substitution) in describing
1678 In Unix systems, you can control which shell is used with the
1679 @code{SHELL} environment variable.
1680 @xref{Arguments, ,Your program's arguments}.
1682 @item The @emph{environment.}
1683 Your program normally inherits its environment from @value{GDBN}, but you can
1684 use the @value{GDBN} commands @code{set environment} and @code{unset
1685 environment} to change parts of the environment that affect
1686 your program. @xref{Environment, ,Your program's environment}.
1688 @item The @emph{working directory.}
1689 Your program inherits its working directory from @value{GDBN}. You can set
1690 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1691 @xref{Working Directory, ,Your program's working directory}.
1693 @item The @emph{standard input and output.}
1694 Your program normally uses the same device for standard input and
1695 standard output as @value{GDBN} is using. You can redirect input and output
1696 in the @code{run} command line, or you can use the @code{tty} command to
1697 set a different device for your program.
1698 @xref{Input/Output, ,Your program's input and output}.
1701 @emph{Warning:} While input and output redirection work, you cannot use
1702 pipes to pass the output of the program you are debugging to another
1703 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1707 When you issue the @code{run} command, your program begins to execute
1708 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1709 of how to arrange for your program to stop. Once your program has
1710 stopped, you may call functions in your program, using the @code{print}
1711 or @code{call} commands. @xref{Data, ,Examining Data}.
1713 If the modification time of your symbol file has changed since the last
1714 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1715 table, and reads it again. When it does this, @value{GDBN} tries to retain
1716 your current breakpoints.
1719 @section Your program's arguments
1721 @cindex arguments (to your program)
1722 The arguments to your program can be specified by the arguments of the
1724 They are passed to a shell, which expands wildcard characters and
1725 performs redirection of I/O, and thence to your program. Your
1726 @code{SHELL} environment variable (if it exists) specifies what shell
1727 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1728 the default shell (@file{/bin/sh} on Unix).
1730 On non-Unix systems, the program is usually invoked directly by
1731 @value{GDBN}, which emulates I/O redirection via the appropriate system
1732 calls, and the wildcard characters are expanded by the startup code of
1733 the program, not by the shell.
1735 @code{run} with no arguments uses the same arguments used by the previous
1736 @code{run}, or those set by the @code{set args} command.
1741 Specify the arguments to be used the next time your program is run. If
1742 @code{set args} has no arguments, @code{run} executes your program
1743 with no arguments. Once you have run your program with arguments,
1744 using @code{set args} before the next @code{run} is the only way to run
1745 it again without arguments.
1749 Show the arguments to give your program when it is started.
1753 @section Your program's environment
1755 @cindex environment (of your program)
1756 The @dfn{environment} consists of a set of environment variables and
1757 their values. Environment variables conventionally record such things as
1758 your user name, your home directory, your terminal type, and your search
1759 path for programs to run. Usually you set up environment variables with
1760 the shell and they are inherited by all the other programs you run. When
1761 debugging, it can be useful to try running your program with a modified
1762 environment without having to start @value{GDBN} over again.
1766 @item path @var{directory}
1767 Add @var{directory} to the front of the @code{PATH} environment variable
1768 (the search path for executables) that will be passed to your program.
1769 The value of @code{PATH} used by @value{GDBN} does not change.
1770 You may specify several directory names, separated by whitespace or by a
1771 system-dependent separator character (@samp{:} on Unix, @samp{;} on
1772 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
1773 is moved to the front, so it is searched sooner.
1775 You can use the string @samp{$cwd} to refer to whatever is the current
1776 working directory at the time @value{GDBN} searches the path. If you
1777 use @samp{.} instead, it refers to the directory where you executed the
1778 @code{path} command. @value{GDBN} replaces @samp{.} in the
1779 @var{directory} argument (with the current path) before adding
1780 @var{directory} to the search path.
1781 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1782 @c document that, since repeating it would be a no-op.
1786 Display the list of search paths for executables (the @code{PATH}
1787 environment variable).
1789 @kindex show environment
1790 @item show environment @r{[}@var{varname}@r{]}
1791 Print the value of environment variable @var{varname} to be given to
1792 your program when it starts. If you do not supply @var{varname},
1793 print the names and values of all environment variables to be given to
1794 your program. You can abbreviate @code{environment} as @code{env}.
1796 @kindex set environment
1797 @item set environment @var{varname} @r{[}=@var{value}@r{]}
1798 Set environment variable @var{varname} to @var{value}. The value
1799 changes for your program only, not for @value{GDBN} itself. @var{value} may
1800 be any string; the values of environment variables are just strings, and
1801 any interpretation is supplied by your program itself. The @var{value}
1802 parameter is optional; if it is eliminated, the variable is set to a
1804 @c "any string" here does not include leading, trailing
1805 @c blanks. Gnu asks: does anyone care?
1807 For example, this command:
1814 tells the debugged program, when subsequently run, that its user is named
1815 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1816 are not actually required.)
1818 @kindex unset environment
1819 @item unset environment @var{varname}
1820 Remove variable @var{varname} from the environment to be passed to your
1821 program. This is different from @samp{set env @var{varname} =};
1822 @code{unset environment} removes the variable from the environment,
1823 rather than assigning it an empty value.
1826 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
1828 by your @code{SHELL} environment variable if it exists (or
1829 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1830 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1831 @file{.bashrc} for BASH---any variables you set in that file affect
1832 your program. You may wish to move setting of environment variables to
1833 files that are only run when you sign on, such as @file{.login} or
1836 @node Working Directory
1837 @section Your program's working directory
1839 @cindex working directory (of your program)
1840 Each time you start your program with @code{run}, it inherits its
1841 working directory from the current working directory of @value{GDBN}.
1842 The @value{GDBN} working directory is initially whatever it inherited
1843 from its parent process (typically the shell), but you can specify a new
1844 working directory in @value{GDBN} with the @code{cd} command.
1846 The @value{GDBN} working directory also serves as a default for the commands
1847 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1852 @item cd @var{directory}
1853 Set the @value{GDBN} working directory to @var{directory}.
1857 Print the @value{GDBN} working directory.
1861 @section Your program's input and output
1866 By default, the program you run under @value{GDBN} does input and output to
1867 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1868 to its own terminal modes to interact with you, but it records the terminal
1869 modes your program was using and switches back to them when you continue
1870 running your program.
1873 @kindex info terminal
1875 Displays information recorded by @value{GDBN} about the terminal modes your
1879 You can redirect your program's input and/or output using shell
1880 redirection with the @code{run} command. For example,
1887 starts your program, diverting its output to the file @file{outfile}.
1890 @cindex controlling terminal
1891 Another way to specify where your program should do input and output is
1892 with the @code{tty} command. This command accepts a file name as
1893 argument, and causes this file to be the default for future @code{run}
1894 commands. It also resets the controlling terminal for the child
1895 process, for future @code{run} commands. For example,
1902 directs that processes started with subsequent @code{run} commands
1903 default to do input and output on the terminal @file{/dev/ttyb} and have
1904 that as their controlling terminal.
1906 An explicit redirection in @code{run} overrides the @code{tty} command's
1907 effect on the input/output device, but not its effect on the controlling
1910 When you use the @code{tty} command or redirect input in the @code{run}
1911 command, only the input @emph{for your program} is affected. The input
1912 for @value{GDBN} still comes from your terminal.
1915 @section Debugging an already-running process
1920 @item attach @var{process-id}
1921 This command attaches to a running process---one that was started
1922 outside @value{GDBN}. (@code{info files} shows your active
1923 targets.) The command takes as argument a process ID. The usual way to
1924 find out the process-id of a Unix process is with the @code{ps} utility,
1925 or with the @samp{jobs -l} shell command.
1927 @code{attach} does not repeat if you press @key{RET} a second time after
1928 executing the command.
1931 To use @code{attach}, your program must be running in an environment
1932 which supports processes; for example, @code{attach} does not work for
1933 programs on bare-board targets that lack an operating system. You must
1934 also have permission to send the process a signal.
1936 When you use @code{attach}, the debugger finds the program running in
1937 the process first by looking in the current working directory, then (if
1938 the program is not found) by using the source file search path
1939 (@pxref{Source Path, ,Specifying source directories}). You can also use
1940 the @code{file} command to load the program. @xref{Files, ,Commands to
1943 The first thing @value{GDBN} does after arranging to debug the specified
1944 process is to stop it. You can examine and modify an attached process
1945 with all the @value{GDBN} commands that are ordinarily available when
1946 you start processes with @code{run}. You can insert breakpoints; you
1947 can step and continue; you can modify storage. If you would rather the
1948 process continue running, you may use the @code{continue} command after
1949 attaching @value{GDBN} to the process.
1954 When you have finished debugging the attached process, you can use the
1955 @code{detach} command to release it from @value{GDBN} control. Detaching
1956 the process continues its execution. After the @code{detach} command,
1957 that process and @value{GDBN} become completely independent once more, and you
1958 are ready to @code{attach} another process or start one with @code{run}.
1959 @code{detach} does not repeat if you press @key{RET} again after
1960 executing the command.
1963 If you exit @value{GDBN} or use the @code{run} command while you have an
1964 attached process, you kill that process. By default, @value{GDBN} asks
1965 for confirmation if you try to do either of these things; you can
1966 control whether or not you need to confirm by using the @code{set
1967 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1971 @section Killing the child process
1976 Kill the child process in which your program is running under @value{GDBN}.
1979 This command is useful if you wish to debug a core dump instead of a
1980 running process. @value{GDBN} ignores any core dump file while your program
1983 On some operating systems, a program cannot be executed outside @value{GDBN}
1984 while you have breakpoints set on it inside @value{GDBN}. You can use the
1985 @code{kill} command in this situation to permit running your program
1986 outside the debugger.
1988 The @code{kill} command is also useful if you wish to recompile and
1989 relink your program, since on many systems it is impossible to modify an
1990 executable file while it is running in a process. In this case, when you
1991 next type @code{run}, @value{GDBN} notices that the file has changed, and
1992 reads the symbol table again (while trying to preserve your current
1993 breakpoint settings).
1996 @section Debugging programs with multiple threads
1998 @cindex threads of execution
1999 @cindex multiple threads
2000 @cindex switching threads
2001 In some operating systems, such as HP-UX and Solaris, a single program
2002 may have more than one @dfn{thread} of execution. The precise semantics
2003 of threads differ from one operating system to another, but in general
2004 the threads of a single program are akin to multiple processes---except
2005 that they share one address space (that is, they can all examine and
2006 modify the same variables). On the other hand, each thread has its own
2007 registers and execution stack, and perhaps private memory.
2009 @value{GDBN} provides these facilities for debugging multi-thread
2013 @item automatic notification of new threads
2014 @item @samp{thread @var{threadno}}, a command to switch among threads
2015 @item @samp{info threads}, a command to inquire about existing threads
2016 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
2017 a command to apply a command to a list of threads
2018 @item thread-specific breakpoints
2022 @emph{Warning:} These facilities are not yet available on every
2023 @value{GDBN} configuration where the operating system supports threads.
2024 If your @value{GDBN} does not support threads, these commands have no
2025 effect. For example, a system without thread support shows no output
2026 from @samp{info threads}, and always rejects the @code{thread} command,
2030 (@value{GDBP}) info threads
2031 (@value{GDBP}) thread 1
2032 Thread ID 1 not known. Use the "info threads" command to
2033 see the IDs of currently known threads.
2035 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
2036 @c doesn't support threads"?
2039 @cindex focus of debugging
2040 @cindex current thread
2041 The @value{GDBN} thread debugging facility allows you to observe all
2042 threads while your program runs---but whenever @value{GDBN} takes
2043 control, one thread in particular is always the focus of debugging.
2044 This thread is called the @dfn{current thread}. Debugging commands show
2045 program information from the perspective of the current thread.
2047 @cindex @code{New} @var{systag} message
2048 @cindex thread identifier (system)
2049 @c FIXME-implementors!! It would be more helpful if the [New...] message
2050 @c included GDB's numeric thread handle, so you could just go to that
2051 @c thread without first checking `info threads'.
2052 Whenever @value{GDBN} detects a new thread in your program, it displays
2053 the target system's identification for the thread with a message in the
2054 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2055 whose form varies depending on the particular system. For example, on
2056 LynxOS, you might see
2059 [New process 35 thread 27]
2063 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
2064 the @var{systag} is simply something like @samp{process 368}, with no
2067 @c FIXME!! (1) Does the [New...] message appear even for the very first
2068 @c thread of a program, or does it only appear for the
2069 @c second---i.e.@: when it becomes obvious we have a multithread
2071 @c (2) *Is* there necessarily a first thread always? Or do some
2072 @c multithread systems permit starting a program with multiple
2073 @c threads ab initio?
2075 @cindex thread number
2076 @cindex thread identifier (GDB)
2077 For debugging purposes, @value{GDBN} associates its own thread
2078 number---always a single integer---with each thread in your program.
2081 @kindex info threads
2083 Display a summary of all threads currently in your
2084 program. @value{GDBN} displays for each thread (in this order):
2087 @item the thread number assigned by @value{GDBN}
2089 @item the target system's thread identifier (@var{systag})
2091 @item the current stack frame summary for that thread
2095 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2096 indicates the current thread.
2100 @c end table here to get a little more width for example
2103 (@value{GDBP}) info threads
2104 3 process 35 thread 27 0x34e5 in sigpause ()
2105 2 process 35 thread 23 0x34e5 in sigpause ()
2106 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2112 @cindex thread number
2113 @cindex thread identifier (GDB)
2114 For debugging purposes, @value{GDBN} associates its own thread
2115 number---a small integer assigned in thread-creation order---with each
2116 thread in your program.
2118 @cindex @code{New} @var{systag} message, on HP-UX
2119 @cindex thread identifier (system), on HP-UX
2120 @c FIXME-implementors!! It would be more helpful if the [New...] message
2121 @c included GDB's numeric thread handle, so you could just go to that
2122 @c thread without first checking `info threads'.
2123 Whenever @value{GDBN} detects a new thread in your program, it displays
2124 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2125 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2126 whose form varies depending on the particular system. For example, on
2130 [New thread 2 (system thread 26594)]
2134 when @value{GDBN} notices a new thread.
2137 @kindex info threads
2139 Display a summary of all threads currently in your
2140 program. @value{GDBN} displays for each thread (in this order):
2143 @item the thread number assigned by @value{GDBN}
2145 @item the target system's thread identifier (@var{systag})
2147 @item the current stack frame summary for that thread
2151 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2152 indicates the current thread.
2156 @c end table here to get a little more width for example
2159 (@value{GDBP}) info threads
2160 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2162 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2163 from /usr/lib/libc.2
2164 1 system thread 27905 0x7b003498 in _brk () \@*
2165 from /usr/lib/libc.2
2169 @kindex thread @var{threadno}
2170 @item thread @var{threadno}
2171 Make thread number @var{threadno} the current thread. The command
2172 argument @var{threadno} is the internal @value{GDBN} thread number, as
2173 shown in the first field of the @samp{info threads} display.
2174 @value{GDBN} responds by displaying the system identifier of the thread
2175 you selected, and its current stack frame summary:
2178 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2179 (@value{GDBP}) thread 2
2180 [Switching to process 35 thread 23]
2181 0x34e5 in sigpause ()
2185 As with the @samp{[New @dots{}]} message, the form of the text after
2186 @samp{Switching to} depends on your system's conventions for identifying
2189 @kindex thread apply
2190 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2191 The @code{thread apply} command allows you to apply a command to one or
2192 more threads. Specify the numbers of the threads that you want affected
2193 with the command argument @var{threadno}. @var{threadno} is the internal
2194 @value{GDBN} thread number, as shown in the first field of the @samp{info
2195 threads} display. To apply a command to all threads, use
2196 @code{thread apply all} @var{args}.
2199 @cindex automatic thread selection
2200 @cindex switching threads automatically
2201 @cindex threads, automatic switching
2202 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2203 signal, it automatically selects the thread where that breakpoint or
2204 signal happened. @value{GDBN} alerts you to the context switch with a
2205 message of the form @samp{[Switching to @var{systag}]} to identify the
2208 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2209 more information about how @value{GDBN} behaves when you stop and start
2210 programs with multiple threads.
2212 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2213 watchpoints in programs with multiple threads.
2216 @section Debugging programs with multiple processes
2218 @cindex fork, debugging programs which call
2219 @cindex multiple processes
2220 @cindex processes, multiple
2221 On most systems, @value{GDBN} has no special support for debugging
2222 programs which create additional processes using the @code{fork}
2223 function. When a program forks, @value{GDBN} will continue to debug the
2224 parent process and the child process will run unimpeded. If you have
2225 set a breakpoint in any code which the child then executes, the child
2226 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2227 will cause it to terminate.
2229 However, if you want to debug the child process there is a workaround
2230 which isn't too painful. Put a call to @code{sleep} in the code which
2231 the child process executes after the fork. It may be useful to sleep
2232 only if a certain environment variable is set, or a certain file exists,
2233 so that the delay need not occur when you don't want to run @value{GDBN}
2234 on the child. While the child is sleeping, use the @code{ps} program to
2235 get its process ID. Then tell @value{GDBN} (a new invocation of
2236 @value{GDBN} if you are also debugging the parent process) to attach to
2237 the child process (@pxref{Attach}). From that point on you can debug
2238 the child process just like any other process which you attached to.
2240 On HP-UX (11.x and later only?), @value{GDBN} provides support for
2241 debugging programs that create additional processes using the
2242 @code{fork} or @code{vfork} function.
2244 By default, when a program forks, @value{GDBN} will continue to debug
2245 the parent process and the child process will run unimpeded.
2247 If you want to follow the child process instead of the parent process,
2248 use the command @w{@code{set follow-fork-mode}}.
2251 @kindex set follow-fork-mode
2252 @item set follow-fork-mode @var{mode}
2253 Set the debugger response to a program call of @code{fork} or
2254 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2255 process. The @var{mode} can be:
2259 The original process is debugged after a fork. The child process runs
2260 unimpeded. This is the default.
2263 The new process is debugged after a fork. The parent process runs
2267 The debugger will ask for one of the above choices.
2270 @item show follow-fork-mode
2271 Display the current debugger response to a @code{fork} or @code{vfork} call.
2274 If you ask to debug a child process and a @code{vfork} is followed by an
2275 @code{exec}, @value{GDBN} executes the new target up to the first
2276 breakpoint in the new target. If you have a breakpoint set on
2277 @code{main} in your original program, the breakpoint will also be set on
2278 the child process's @code{main}.
2280 When a child process is spawned by @code{vfork}, you cannot debug the
2281 child or parent until an @code{exec} call completes.
2283 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2284 call executes, the new target restarts. To restart the parent process,
2285 use the @code{file} command with the parent executable name as its
2288 You can use the @code{catch} command to make @value{GDBN} stop whenever
2289 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2290 Catchpoints, ,Setting catchpoints}.
2293 @chapter Stopping and Continuing
2295 The principal purposes of using a debugger are so that you can stop your
2296 program before it terminates; or so that, if your program runs into
2297 trouble, you can investigate and find out why.
2299 Inside @value{GDBN}, your program may stop for any of several reasons,
2300 such as a signal, a breakpoint, or reaching a new line after a
2301 @value{GDBN} command such as @code{step}. You may then examine and
2302 change variables, set new breakpoints or remove old ones, and then
2303 continue execution. Usually, the messages shown by @value{GDBN} provide
2304 ample explanation of the status of your program---but you can also
2305 explicitly request this information at any time.
2308 @kindex info program
2310 Display information about the status of your program: whether it is
2311 running or not, what process it is, and why it stopped.
2315 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2316 * Continuing and Stepping:: Resuming execution
2318 * Thread Stops:: Stopping and starting multi-thread programs
2322 @section Breakpoints, watchpoints, and catchpoints
2325 A @dfn{breakpoint} makes your program stop whenever a certain point in
2326 the program is reached. For each breakpoint, you can add conditions to
2327 control in finer detail whether your program stops. You can set
2328 breakpoints with the @code{break} command and its variants (@pxref{Set
2329 Breaks, ,Setting breakpoints}), to specify the place where your program
2330 should stop by line number, function name or exact address in the
2333 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2334 breakpoints in shared libraries before the executable is run. There is
2335 a minor limitation on HP-UX systems: you must wait until the executable
2336 is run in order to set breakpoints in shared library routines that are
2337 not called directly by the program (for example, routines that are
2338 arguments in a @code{pthread_create} call).
2341 @cindex memory tracing
2342 @cindex breakpoint on memory address
2343 @cindex breakpoint on variable modification
2344 A @dfn{watchpoint} is a special breakpoint that stops your program
2345 when the value of an expression changes. You must use a different
2346 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2347 watchpoints}), but aside from that, you can manage a watchpoint like
2348 any other breakpoint: you enable, disable, and delete both breakpoints
2349 and watchpoints using the same commands.
2351 You can arrange to have values from your program displayed automatically
2352 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2356 @cindex breakpoint on events
2357 A @dfn{catchpoint} is another special breakpoint that stops your program
2358 when a certain kind of event occurs, such as the throwing of a C@t{++}
2359 exception or the loading of a library. As with watchpoints, you use a
2360 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2361 catchpoints}), but aside from that, you can manage a catchpoint like any
2362 other breakpoint. (To stop when your program receives a signal, use the
2363 @code{handle} command; see @ref{Signals, ,Signals}.)
2365 @cindex breakpoint numbers
2366 @cindex numbers for breakpoints
2367 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2368 catchpoint when you create it; these numbers are successive integers
2369 starting with one. In many of the commands for controlling various
2370 features of breakpoints you use the breakpoint number to say which
2371 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2372 @dfn{disabled}; if disabled, it has no effect on your program until you
2375 @cindex breakpoint ranges
2376 @cindex ranges of breakpoints
2377 Some @value{GDBN} commands accept a range of breakpoints on which to
2378 operate. A breakpoint range is either a single breakpoint number, like
2379 @samp{5}, or two such numbers, in increasing order, separated by a
2380 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
2381 all breakpoint in that range are operated on.
2384 * Set Breaks:: Setting breakpoints
2385 * Set Watchpoints:: Setting watchpoints
2386 * Set Catchpoints:: Setting catchpoints
2387 * Delete Breaks:: Deleting breakpoints
2388 * Disabling:: Disabling breakpoints
2389 * Conditions:: Break conditions
2390 * Break Commands:: Breakpoint command lists
2391 * Breakpoint Menus:: Breakpoint menus
2392 * Error in Breakpoints:: ``Cannot insert breakpoints''
2396 @subsection Setting breakpoints
2398 @c FIXME LMB what does GDB do if no code on line of breakpt?
2399 @c consider in particular declaration with/without initialization.
2401 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2404 @kindex b @r{(@code{break})}
2405 @vindex $bpnum@r{, convenience variable}
2406 @cindex latest breakpoint
2407 Breakpoints are set with the @code{break} command (abbreviated
2408 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2409 number of the breakpoint you've set most recently; see @ref{Convenience
2410 Vars,, Convenience variables}, for a discussion of what you can do with
2411 convenience variables.
2413 You have several ways to say where the breakpoint should go.
2416 @item break @var{function}
2417 Set a breakpoint at entry to function @var{function}.
2418 When using source languages that permit overloading of symbols, such as
2419 C@t{++}, @var{function} may refer to more than one possible place to break.
2420 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2422 @item break +@var{offset}
2423 @itemx break -@var{offset}
2424 Set a breakpoint some number of lines forward or back from the position
2425 at which execution stopped in the currently selected @dfn{stack frame}.
2426 (@xref{Frames, ,Frames}, for a description of stack frames.)
2428 @item break @var{linenum}
2429 Set a breakpoint at line @var{linenum} in the current source file.
2430 The current source file is the last file whose source text was printed.
2431 The breakpoint will stop your program just before it executes any of the
2434 @item break @var{filename}:@var{linenum}
2435 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2437 @item break @var{filename}:@var{function}
2438 Set a breakpoint at entry to function @var{function} found in file
2439 @var{filename}. Specifying a file name as well as a function name is
2440 superfluous except when multiple files contain similarly named
2443 @item break *@var{address}
2444 Set a breakpoint at address @var{address}. You can use this to set
2445 breakpoints in parts of your program which do not have debugging
2446 information or source files.
2449 When called without any arguments, @code{break} sets a breakpoint at
2450 the next instruction to be executed in the selected stack frame
2451 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2452 innermost, this makes your program stop as soon as control
2453 returns to that frame. This is similar to the effect of a
2454 @code{finish} command in the frame inside the selected frame---except
2455 that @code{finish} does not leave an active breakpoint. If you use
2456 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2457 the next time it reaches the current location; this may be useful
2460 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2461 least one instruction has been executed. If it did not do this, you
2462 would be unable to proceed past a breakpoint without first disabling the
2463 breakpoint. This rule applies whether or not the breakpoint already
2464 existed when your program stopped.
2466 @item break @dots{} if @var{cond}
2467 Set a breakpoint with condition @var{cond}; evaluate the expression
2468 @var{cond} each time the breakpoint is reached, and stop only if the
2469 value is nonzero---that is, if @var{cond} evaluates as true.
2470 @samp{@dots{}} stands for one of the possible arguments described
2471 above (or no argument) specifying where to break. @xref{Conditions,
2472 ,Break conditions}, for more information on breakpoint conditions.
2475 @item tbreak @var{args}
2476 Set a breakpoint enabled only for one stop. @var{args} are the
2477 same as for the @code{break} command, and the breakpoint is set in the same
2478 way, but the breakpoint is automatically deleted after the first time your
2479 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2482 @item hbreak @var{args}
2483 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2484 @code{break} command and the breakpoint is set in the same way, but the
2485 breakpoint requires hardware support and some target hardware may not
2486 have this support. The main purpose of this is EPROM/ROM code
2487 debugging, so you can set a breakpoint at an instruction without
2488 changing the instruction. This can be used with the new trap-generation
2489 provided by SPARClite DSU and some x86-based targets. These targets
2490 will generate traps when a program accesses some data or instruction
2491 address that is assigned to the debug registers. However the hardware
2492 breakpoint registers can take a limited number of breakpoints. For
2493 example, on the DSU, only two data breakpoints can be set at a time, and
2494 @value{GDBN} will reject this command if more than two are used. Delete
2495 or disable unused hardware breakpoints before setting new ones
2496 (@pxref{Disabling, ,Disabling}). @xref{Conditions, ,Break conditions}.
2499 @item thbreak @var{args}
2500 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2501 are the same as for the @code{hbreak} command and the breakpoint is set in
2502 the same way. However, like the @code{tbreak} command,
2503 the breakpoint is automatically deleted after the
2504 first time your program stops there. Also, like the @code{hbreak}
2505 command, the breakpoint requires hardware support and some target hardware
2506 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2507 See also @ref{Conditions, ,Break conditions}.
2510 @cindex regular expression
2511 @item rbreak @var{regex}
2512 Set breakpoints on all functions matching the regular expression
2513 @var{regex}. This command sets an unconditional breakpoint on all
2514 matches, printing a list of all breakpoints it set. Once these
2515 breakpoints are set, they are treated just like the breakpoints set with
2516 the @code{break} command. You can delete them, disable them, or make
2517 them conditional the same way as any other breakpoint.
2519 The syntax of the regular expression is the standard one used with tools
2520 like @file{grep}. Note that this is different from the syntax used by
2521 shells, so for instance @code{foo*} matches all functions that include
2522 an @code{fo} followed by zero or more @code{o}s. There is an implicit
2523 @code{.*} leading and trailing the regular expression you supply, so to
2524 match only functions that begin with @code{foo}, use @code{^foo}.
2526 When debugging C@t{++} programs, @code{rbreak} is useful for setting
2527 breakpoints on overloaded functions that are not members of any special
2530 @kindex info breakpoints
2531 @cindex @code{$_} and @code{info breakpoints}
2532 @item info breakpoints @r{[}@var{n}@r{]}
2533 @itemx info break @r{[}@var{n}@r{]}
2534 @itemx info watchpoints @r{[}@var{n}@r{]}
2535 Print a table of all breakpoints, watchpoints, and catchpoints set and
2536 not deleted, with the following columns for each breakpoint:
2539 @item Breakpoint Numbers
2541 Breakpoint, watchpoint, or catchpoint.
2543 Whether the breakpoint is marked to be disabled or deleted when hit.
2544 @item Enabled or Disabled
2545 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2546 that are not enabled.
2548 Where the breakpoint is in your program, as a memory address.
2550 Where the breakpoint is in the source for your program, as a file and
2555 If a breakpoint is conditional, @code{info break} shows the condition on
2556 the line following the affected breakpoint; breakpoint commands, if any,
2557 are listed after that.
2560 @code{info break} with a breakpoint
2561 number @var{n} as argument lists only that breakpoint. The
2562 convenience variable @code{$_} and the default examining-address for
2563 the @code{x} command are set to the address of the last breakpoint
2564 listed (@pxref{Memory, ,Examining memory}).
2567 @code{info break} displays a count of the number of times the breakpoint
2568 has been hit. This is especially useful in conjunction with the
2569 @code{ignore} command. You can ignore a large number of breakpoint
2570 hits, look at the breakpoint info to see how many times the breakpoint
2571 was hit, and then run again, ignoring one less than that number. This
2572 will get you quickly to the last hit of that breakpoint.
2575 @value{GDBN} allows you to set any number of breakpoints at the same place in
2576 your program. There is nothing silly or meaningless about this. When
2577 the breakpoints are conditional, this is even useful
2578 (@pxref{Conditions, ,Break conditions}).
2580 @cindex negative breakpoint numbers
2581 @cindex internal @value{GDBN} breakpoints
2582 @value{GDBN} itself sometimes sets breakpoints in your program for
2583 special purposes, such as proper handling of @code{longjmp} (in C
2584 programs). These internal breakpoints are assigned negative numbers,
2585 starting with @code{-1}; @samp{info breakpoints} does not display them.
2586 You can see these breakpoints with the @value{GDBN} maintenance command
2587 @samp{maint info breakpoints} (@pxref{maint info breakpoints}).
2590 @node Set Watchpoints
2591 @subsection Setting watchpoints
2593 @cindex setting watchpoints
2594 @cindex software watchpoints
2595 @cindex hardware watchpoints
2596 You can use a watchpoint to stop execution whenever the value of an
2597 expression changes, without having to predict a particular place where
2600 Depending on your system, watchpoints may be implemented in software or
2601 hardware. @value{GDBN} does software watchpointing by single-stepping your
2602 program and testing the variable's value each time, which is hundreds of
2603 times slower than normal execution. (But this may still be worth it, to
2604 catch errors where you have no clue what part of your program is the
2607 On some systems, such as HP-UX, Linux and some other x86-based targets,
2608 @value{GDBN} includes support for
2609 hardware watchpoints, which do not slow down the running of your
2614 @item watch @var{expr}
2615 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2616 is written into by the program and its value changes.
2619 @item rwatch @var{expr}
2620 Set a watchpoint that will break when watch @var{expr} is read by the program.
2623 @item awatch @var{expr}
2624 Set a watchpoint that will break when @var{expr} is either read or written into
2627 @kindex info watchpoints
2628 @item info watchpoints
2629 This command prints a list of watchpoints, breakpoints, and catchpoints;
2630 it is the same as @code{info break}.
2633 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2634 watchpoints execute very quickly, and the debugger reports a change in
2635 value at the exact instruction where the change occurs. If @value{GDBN}
2636 cannot set a hardware watchpoint, it sets a software watchpoint, which
2637 executes more slowly and reports the change in value at the next
2638 statement, not the instruction, after the change occurs.
2640 When you issue the @code{watch} command, @value{GDBN} reports
2643 Hardware watchpoint @var{num}: @var{expr}
2647 if it was able to set a hardware watchpoint.
2649 Currently, the @code{awatch} and @code{rwatch} commands can only set
2650 hardware watchpoints, because accesses to data that don't change the
2651 value of the watched expression cannot be detected without examining
2652 every instruction as it is being executed, and @value{GDBN} does not do
2653 that currently. If @value{GDBN} finds that it is unable to set a
2654 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
2655 will print a message like this:
2658 Expression cannot be implemented with read/access watchpoint.
2661 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
2662 data type of the watched expression is wider than what a hardware
2663 watchpoint on the target machine can handle. For example, some systems
2664 can only watch regions that are up to 4 bytes wide; on such systems you
2665 cannot set hardware watchpoints for an expression that yields a
2666 double-precision floating-point number (which is typically 8 bytes
2667 wide). As a work-around, it might be possible to break the large region
2668 into a series of smaller ones and watch them with separate watchpoints.
2670 If you set too many hardware watchpoints, @value{GDBN} might be unable
2671 to insert all of them when you resume the execution of your program.
2672 Since the precise number of active watchpoints is unknown until such
2673 time as the program is about to be resumed, @value{GDBN} might not be
2674 able to warn you about this when you set the watchpoints, and the
2675 warning will be printed only when the program is resumed:
2678 Hardware watchpoint @var{num}: Could not insert watchpoint
2682 If this happens, delete or disable some of the watchpoints.
2684 The SPARClite DSU will generate traps when a program accesses some data
2685 or instruction address that is assigned to the debug registers. For the
2686 data addresses, DSU facilitates the @code{watch} command. However the
2687 hardware breakpoint registers can only take two data watchpoints, and
2688 both watchpoints must be the same kind. For example, you can set two
2689 watchpoints with @code{watch} commands, two with @code{rwatch} commands,
2690 @strong{or} two with @code{awatch} commands, but you cannot set one
2691 watchpoint with one command and the other with a different command.
2692 @value{GDBN} will reject the command if you try to mix watchpoints.
2693 Delete or disable unused watchpoint commands before setting new ones.
2695 If you call a function interactively using @code{print} or @code{call},
2696 any watchpoints you have set will be inactive until @value{GDBN} reaches another
2697 kind of breakpoint or the call completes.
2699 @value{GDBN} automatically deletes watchpoints that watch local
2700 (automatic) variables, or expressions that involve such variables, when
2701 they go out of scope, that is, when the execution leaves the block in
2702 which these variables were defined. In particular, when the program
2703 being debugged terminates, @emph{all} local variables go out of scope,
2704 and so only watchpoints that watch global variables remain set. If you
2705 rerun the program, you will need to set all such watchpoints again. One
2706 way of doing that would be to set a code breakpoint at the entry to the
2707 @code{main} function and when it breaks, set all the watchpoints.
2710 @cindex watchpoints and threads
2711 @cindex threads and watchpoints
2712 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2713 usefulness. With the current watchpoint implementation, @value{GDBN}
2714 can only watch the value of an expression @emph{in a single thread}. If
2715 you are confident that the expression can only change due to the current
2716 thread's activity (and if you are also confident that no other thread
2717 can become current), then you can use watchpoints as usual. However,
2718 @value{GDBN} may not notice when a non-current thread's activity changes
2721 @c FIXME: this is almost identical to the previous paragraph.
2722 @emph{HP-UX Warning:} In multi-thread programs, software watchpoints
2723 have only limited usefulness. If @value{GDBN} creates a software
2724 watchpoint, it can only watch the value of an expression @emph{in a
2725 single thread}. If you are confident that the expression can only
2726 change due to the current thread's activity (and if you are also
2727 confident that no other thread can become current), then you can use
2728 software watchpoints as usual. However, @value{GDBN} may not notice
2729 when a non-current thread's activity changes the expression. (Hardware
2730 watchpoints, in contrast, watch an expression in all threads.)
2733 @node Set Catchpoints
2734 @subsection Setting catchpoints
2735 @cindex catchpoints, setting
2736 @cindex exception handlers
2737 @cindex event handling
2739 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2740 kinds of program events, such as C@t{++} exceptions or the loading of a
2741 shared library. Use the @code{catch} command to set a catchpoint.
2745 @item catch @var{event}
2746 Stop when @var{event} occurs. @var{event} can be any of the following:
2750 The throwing of a C@t{++} exception.
2754 The catching of a C@t{++} exception.
2758 A call to @code{exec}. This is currently only available for HP-UX.
2762 A call to @code{fork}. This is currently only available for HP-UX.
2766 A call to @code{vfork}. This is currently only available for HP-UX.
2769 @itemx load @var{libname}
2771 The dynamic loading of any shared library, or the loading of the library
2772 @var{libname}. This is currently only available for HP-UX.
2775 @itemx unload @var{libname}
2776 @kindex catch unload
2777 The unloading of any dynamically loaded shared library, or the unloading
2778 of the library @var{libname}. This is currently only available for HP-UX.
2781 @item tcatch @var{event}
2782 Set a catchpoint that is enabled only for one stop. The catchpoint is
2783 automatically deleted after the first time the event is caught.
2787 Use the @code{info break} command to list the current catchpoints.
2789 There are currently some limitations to C@t{++} exception handling
2790 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
2794 If you call a function interactively, @value{GDBN} normally returns
2795 control to you when the function has finished executing. If the call
2796 raises an exception, however, the call may bypass the mechanism that
2797 returns control to you and cause your program either to abort or to
2798 simply continue running until it hits a breakpoint, catches a signal
2799 that @value{GDBN} is listening for, or exits. This is the case even if
2800 you set a catchpoint for the exception; catchpoints on exceptions are
2801 disabled within interactive calls.
2804 You cannot raise an exception interactively.
2807 You cannot install an exception handler interactively.
2810 @cindex raise exceptions
2811 Sometimes @code{catch} is not the best way to debug exception handling:
2812 if you need to know exactly where an exception is raised, it is better to
2813 stop @emph{before} the exception handler is called, since that way you
2814 can see the stack before any unwinding takes place. If you set a
2815 breakpoint in an exception handler instead, it may not be easy to find
2816 out where the exception was raised.
2818 To stop just before an exception handler is called, you need some
2819 knowledge of the implementation. In the case of @sc{gnu} C@t{++}, exceptions are
2820 raised by calling a library function named @code{__raise_exception}
2821 which has the following ANSI C interface:
2824 /* @var{addr} is where the exception identifier is stored.
2825 @var{id} is the exception identifier. */
2826 void __raise_exception (void **addr, void *id);
2830 To make the debugger catch all exceptions before any stack
2831 unwinding takes place, set a breakpoint on @code{__raise_exception}
2832 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2834 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2835 that depends on the value of @var{id}, you can stop your program when
2836 a specific exception is raised. You can use multiple conditional
2837 breakpoints to stop your program when any of a number of exceptions are
2842 @subsection Deleting breakpoints
2844 @cindex clearing breakpoints, watchpoints, catchpoints
2845 @cindex deleting breakpoints, watchpoints, catchpoints
2846 It is often necessary to eliminate a breakpoint, watchpoint, or
2847 catchpoint once it has done its job and you no longer want your program
2848 to stop there. This is called @dfn{deleting} the breakpoint. A
2849 breakpoint that has been deleted no longer exists; it is forgotten.
2851 With the @code{clear} command you can delete breakpoints according to
2852 where they are in your program. With the @code{delete} command you can
2853 delete individual breakpoints, watchpoints, or catchpoints by specifying
2854 their breakpoint numbers.
2856 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2857 automatically ignores breakpoints on the first instruction to be executed
2858 when you continue execution without changing the execution address.
2863 Delete any breakpoints at the next instruction to be executed in the
2864 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2865 the innermost frame is selected, this is a good way to delete a
2866 breakpoint where your program just stopped.
2868 @item clear @var{function}
2869 @itemx clear @var{filename}:@var{function}
2870 Delete any breakpoints set at entry to the function @var{function}.
2872 @item clear @var{linenum}
2873 @itemx clear @var{filename}:@var{linenum}
2874 Delete any breakpoints set at or within the code of the specified line.
2876 @cindex delete breakpoints
2878 @kindex d @r{(@code{delete})}
2879 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2880 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
2881 ranges specified as arguments. If no argument is specified, delete all
2882 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
2883 confirm off}). You can abbreviate this command as @code{d}.
2887 @subsection Disabling breakpoints
2889 @kindex disable breakpoints
2890 @kindex enable breakpoints
2891 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
2892 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
2893 it had been deleted, but remembers the information on the breakpoint so
2894 that you can @dfn{enable} it again later.
2896 You disable and enable breakpoints, watchpoints, and catchpoints with
2897 the @code{enable} and @code{disable} commands, optionally specifying one
2898 or more breakpoint numbers as arguments. Use @code{info break} or
2899 @code{info watch} to print a list of breakpoints, watchpoints, and
2900 catchpoints if you do not know which numbers to use.
2902 A breakpoint, watchpoint, or catchpoint can have any of four different
2903 states of enablement:
2907 Enabled. The breakpoint stops your program. A breakpoint set
2908 with the @code{break} command starts out in this state.
2910 Disabled. The breakpoint has no effect on your program.
2912 Enabled once. The breakpoint stops your program, but then becomes
2915 Enabled for deletion. The breakpoint stops your program, but
2916 immediately after it does so it is deleted permanently. A breakpoint
2917 set with the @code{tbreak} command starts out in this state.
2920 You can use the following commands to enable or disable breakpoints,
2921 watchpoints, and catchpoints:
2924 @kindex disable breakpoints
2926 @kindex dis @r{(@code{disable})}
2927 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2928 Disable the specified breakpoints---or all breakpoints, if none are
2929 listed. A disabled breakpoint has no effect but is not forgotten. All
2930 options such as ignore-counts, conditions and commands are remembered in
2931 case the breakpoint is enabled again later. You may abbreviate
2932 @code{disable} as @code{dis}.
2934 @kindex enable breakpoints
2936 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2937 Enable the specified breakpoints (or all defined breakpoints). They
2938 become effective once again in stopping your program.
2940 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
2941 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2942 of these breakpoints immediately after stopping your program.
2944 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
2945 Enable the specified breakpoints to work once, then die. @value{GDBN}
2946 deletes any of these breakpoints as soon as your program stops there.
2949 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
2950 @c confusing: tbreak is also initially enabled.
2951 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2952 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2953 subsequently, they become disabled or enabled only when you use one of
2954 the commands above. (The command @code{until} can set and delete a
2955 breakpoint of its own, but it does not change the state of your other
2956 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2960 @subsection Break conditions
2961 @cindex conditional breakpoints
2962 @cindex breakpoint conditions
2964 @c FIXME what is scope of break condition expr? Context where wanted?
2965 @c in particular for a watchpoint?
2966 The simplest sort of breakpoint breaks every time your program reaches a
2967 specified place. You can also specify a @dfn{condition} for a
2968 breakpoint. A condition is just a Boolean expression in your
2969 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2970 a condition evaluates the expression each time your program reaches it,
2971 and your program stops only if the condition is @emph{true}.
2973 This is the converse of using assertions for program validation; in that
2974 situation, you want to stop when the assertion is violated---that is,
2975 when the condition is false. In C, if you want to test an assertion expressed
2976 by the condition @var{assert}, you should set the condition
2977 @samp{! @var{assert}} on the appropriate breakpoint.
2979 Conditions are also accepted for watchpoints; you may not need them,
2980 since a watchpoint is inspecting the value of an expression anyhow---but
2981 it might be simpler, say, to just set a watchpoint on a variable name,
2982 and specify a condition that tests whether the new value is an interesting
2985 Break conditions can have side effects, and may even call functions in
2986 your program. This can be useful, for example, to activate functions
2987 that log program progress, or to use your own print functions to
2988 format special data structures. The effects are completely predictable
2989 unless there is another enabled breakpoint at the same address. (In
2990 that case, @value{GDBN} might see the other breakpoint first and stop your
2991 program without checking the condition of this one.) Note that
2992 breakpoint commands are usually more convenient and flexible than break
2994 purpose of performing side effects when a breakpoint is reached
2995 (@pxref{Break Commands, ,Breakpoint command lists}).
2997 Break conditions can be specified when a breakpoint is set, by using
2998 @samp{if} in the arguments to the @code{break} command. @xref{Set
2999 Breaks, ,Setting breakpoints}. They can also be changed at any time
3000 with the @code{condition} command.
3002 You can also use the @code{if} keyword with the @code{watch} command.
3003 The @code{catch} command does not recognize the @code{if} keyword;
3004 @code{condition} is the only way to impose a further condition on a
3009 @item condition @var{bnum} @var{expression}
3010 Specify @var{expression} as the break condition for breakpoint,
3011 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
3012 breakpoint @var{bnum} stops your program only if the value of
3013 @var{expression} is true (nonzero, in C). When you use
3014 @code{condition}, @value{GDBN} checks @var{expression} immediately for
3015 syntactic correctness, and to determine whether symbols in it have
3016 referents in the context of your breakpoint. If @var{expression} uses
3017 symbols not referenced in the context of the breakpoint, @value{GDBN}
3018 prints an error message:
3021 No symbol "foo" in current context.
3026 not actually evaluate @var{expression} at the time the @code{condition}
3027 command (or a command that sets a breakpoint with a condition, like
3028 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
3030 @item condition @var{bnum}
3031 Remove the condition from breakpoint number @var{bnum}. It becomes
3032 an ordinary unconditional breakpoint.
3035 @cindex ignore count (of breakpoint)
3036 A special case of a breakpoint condition is to stop only when the
3037 breakpoint has been reached a certain number of times. This is so
3038 useful that there is a special way to do it, using the @dfn{ignore
3039 count} of the breakpoint. Every breakpoint has an ignore count, which
3040 is an integer. Most of the time, the ignore count is zero, and
3041 therefore has no effect. But if your program reaches a breakpoint whose
3042 ignore count is positive, then instead of stopping, it just decrements
3043 the ignore count by one and continues. As a result, if the ignore count
3044 value is @var{n}, the breakpoint does not stop the next @var{n} times
3045 your program reaches it.
3049 @item ignore @var{bnum} @var{count}
3050 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3051 The next @var{count} times the breakpoint is reached, your program's
3052 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3055 To make the breakpoint stop the next time it is reached, specify
3058 When you use @code{continue} to resume execution of your program from a
3059 breakpoint, you can specify an ignore count directly as an argument to
3060 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3061 Stepping,,Continuing and stepping}.
3063 If a breakpoint has a positive ignore count and a condition, the
3064 condition is not checked. Once the ignore count reaches zero,
3065 @value{GDBN} resumes checking the condition.
3067 You could achieve the effect of the ignore count with a condition such
3068 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3069 is decremented each time. @xref{Convenience Vars, ,Convenience
3073 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3076 @node Break Commands
3077 @subsection Breakpoint command lists
3079 @cindex breakpoint commands
3080 You can give any breakpoint (or watchpoint or catchpoint) a series of
3081 commands to execute when your program stops due to that breakpoint. For
3082 example, you might want to print the values of certain expressions, or
3083 enable other breakpoints.
3088 @item commands @r{[}@var{bnum}@r{]}
3089 @itemx @dots{} @var{command-list} @dots{}
3091 Specify a list of commands for breakpoint number @var{bnum}. The commands
3092 themselves appear on the following lines. Type a line containing just
3093 @code{end} to terminate the commands.
3095 To remove all commands from a breakpoint, type @code{commands} and
3096 follow it immediately with @code{end}; that is, give no commands.
3098 With no @var{bnum} argument, @code{commands} refers to the last
3099 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
3100 recently encountered).
3103 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
3104 disabled within a @var{command-list}.
3106 You can use breakpoint commands to start your program up again. Simply
3107 use the @code{continue} command, or @code{step}, or any other command
3108 that resumes execution.
3110 Any other commands in the command list, after a command that resumes
3111 execution, are ignored. This is because any time you resume execution
3112 (even with a simple @code{next} or @code{step}), you may encounter
3113 another breakpoint---which could have its own command list, leading to
3114 ambiguities about which list to execute.
3117 If the first command you specify in a command list is @code{silent}, the
3118 usual message about stopping at a breakpoint is not printed. This may
3119 be desirable for breakpoints that are to print a specific message and
3120 then continue. If none of the remaining commands print anything, you
3121 see no sign that the breakpoint was reached. @code{silent} is
3122 meaningful only at the beginning of a breakpoint command list.
3124 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3125 print precisely controlled output, and are often useful in silent
3126 breakpoints. @xref{Output, ,Commands for controlled output}.
3128 For example, here is how you could use breakpoint commands to print the
3129 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3135 printf "x is %d\n",x
3140 One application for breakpoint commands is to compensate for one bug so
3141 you can test for another. Put a breakpoint just after the erroneous line
3142 of code, give it a condition to detect the case in which something
3143 erroneous has been done, and give it commands to assign correct values
3144 to any variables that need them. End with the @code{continue} command
3145 so that your program does not stop, and start with the @code{silent}
3146 command so that no output is produced. Here is an example:
3157 @node Breakpoint Menus
3158 @subsection Breakpoint menus
3160 @cindex symbol overloading
3162 Some programming languages (notably C@t{++}) permit a single function name
3163 to be defined several times, for application in different contexts.
3164 This is called @dfn{overloading}. When a function name is overloaded,
3165 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3166 a breakpoint. If you realize this is a problem, you can use
3167 something like @samp{break @var{function}(@var{types})} to specify which
3168 particular version of the function you want. Otherwise, @value{GDBN} offers
3169 you a menu of numbered choices for different possible breakpoints, and
3170 waits for your selection with the prompt @samp{>}. The first two
3171 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3172 sets a breakpoint at each definition of @var{function}, and typing
3173 @kbd{0} aborts the @code{break} command without setting any new
3176 For example, the following session excerpt shows an attempt to set a
3177 breakpoint at the overloaded symbol @code{String::after}.
3178 We choose three particular definitions of that function name:
3180 @c FIXME! This is likely to change to show arg type lists, at least
3183 (@value{GDBP}) b String::after
3186 [2] file:String.cc; line number:867
3187 [3] file:String.cc; line number:860
3188 [4] file:String.cc; line number:875
3189 [5] file:String.cc; line number:853
3190 [6] file:String.cc; line number:846
3191 [7] file:String.cc; line number:735
3193 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3194 Breakpoint 2 at 0xb344: file String.cc, line 875.
3195 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3196 Multiple breakpoints were set.
3197 Use the "delete" command to delete unwanted
3203 @c @ifclear BARETARGET
3204 @node Error in Breakpoints
3205 @subsection ``Cannot insert breakpoints''
3207 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3209 Under some operating systems, breakpoints cannot be used in a program if
3210 any other process is running that program. In this situation,
3211 attempting to run or continue a program with a breakpoint causes
3212 @value{GDBN} to print an error message:
3215 Cannot insert breakpoints.
3216 The same program may be running in another process.
3219 When this happens, you have three ways to proceed:
3223 Remove or disable the breakpoints, then continue.
3226 Suspend @value{GDBN}, and copy the file containing your program to a new
3227 name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3228 that @value{GDBN} should run your program under that name.
3229 Then start your program again.
3232 Relink your program so that the text segment is nonsharable, using the
3233 linker option @samp{-N}. The operating system limitation may not apply
3234 to nonsharable executables.
3238 A similar message can be printed if you request too many active
3239 hardware-assisted breakpoints and watchpoints:
3241 @c FIXME: the precise wording of this message may change; the relevant
3242 @c source change is not committed yet (Sep 3, 1999).
3244 Stopped; cannot insert breakpoints.
3245 You may have requested too many hardware breakpoints and watchpoints.
3249 This message is printed when you attempt to resume the program, since
3250 only then @value{GDBN} knows exactly how many hardware breakpoints and
3251 watchpoints it needs to insert.
3253 When this message is printed, you need to disable or remove some of the
3254 hardware-assisted breakpoints and watchpoints, and then continue.
3257 @node Continuing and Stepping
3258 @section Continuing and stepping
3262 @cindex resuming execution
3263 @dfn{Continuing} means resuming program execution until your program
3264 completes normally. In contrast, @dfn{stepping} means executing just
3265 one more ``step'' of your program, where ``step'' may mean either one
3266 line of source code, or one machine instruction (depending on what
3267 particular command you use). Either when continuing or when stepping,
3268 your program may stop even sooner, due to a breakpoint or a signal. (If
3269 it stops due to a signal, you may want to use @code{handle}, or use
3270 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
3274 @kindex c @r{(@code{continue})}
3275 @kindex fg @r{(resume foreground execution)}
3276 @item continue @r{[}@var{ignore-count}@r{]}
3277 @itemx c @r{[}@var{ignore-count}@r{]}
3278 @itemx fg @r{[}@var{ignore-count}@r{]}
3279 Resume program execution, at the address where your program last stopped;
3280 any breakpoints set at that address are bypassed. The optional argument
3281 @var{ignore-count} allows you to specify a further number of times to
3282 ignore a breakpoint at this location; its effect is like that of
3283 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3285 The argument @var{ignore-count} is meaningful only when your program
3286 stopped due to a breakpoint. At other times, the argument to
3287 @code{continue} is ignored.
3289 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
3290 debugged program is deemed to be the foreground program) are provided
3291 purely for convenience, and have exactly the same behavior as
3295 To resume execution at a different place, you can use @code{return}
3296 (@pxref{Returning, ,Returning from a function}) to go back to the
3297 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3298 different address}) to go to an arbitrary location in your program.
3300 A typical technique for using stepping is to set a breakpoint
3301 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3302 beginning of the function or the section of your program where a problem
3303 is believed to lie, run your program until it stops at that breakpoint,
3304 and then step through the suspect area, examining the variables that are
3305 interesting, until you see the problem happen.
3309 @kindex s @r{(@code{step})}
3311 Continue running your program until control reaches a different source
3312 line, then stop it and return control to @value{GDBN}. This command is
3313 abbreviated @code{s}.
3316 @c "without debugging information" is imprecise; actually "without line
3317 @c numbers in the debugging information". (gcc -g1 has debugging info but
3318 @c not line numbers). But it seems complex to try to make that
3319 @c distinction here.
3320 @emph{Warning:} If you use the @code{step} command while control is
3321 within a function that was compiled without debugging information,
3322 execution proceeds until control reaches a function that does have
3323 debugging information. Likewise, it will not step into a function which
3324 is compiled without debugging information. To step through functions
3325 without debugging information, use the @code{stepi} command, described
3329 The @code{step} command only stops at the first instruction of a source
3330 line. This prevents the multiple stops that could otherwise occur in
3331 @code{switch} statements, @code{for} loops, etc. @code{step} continues
3332 to stop if a function that has debugging information is called within
3333 the line. In other words, @code{step} @emph{steps inside} any functions
3334 called within the line.
3336 Also, the @code{step} command only enters a function if there is line
3337 number information for the function. Otherwise it acts like the
3338 @code{next} command. This avoids problems when using @code{cc -gl}
3339 on MIPS machines. Previously, @code{step} entered subroutines if there
3340 was any debugging information about the routine.
3342 @item step @var{count}
3343 Continue running as in @code{step}, but do so @var{count} times. If a
3344 breakpoint is reached, or a signal not related to stepping occurs before
3345 @var{count} steps, stepping stops right away.
3348 @kindex n @r{(@code{next})}
3349 @item next @r{[}@var{count}@r{]}
3350 Continue to the next source line in the current (innermost) stack frame.
3351 This is similar to @code{step}, but function calls that appear within
3352 the line of code are executed without stopping. Execution stops when
3353 control reaches a different line of code at the original stack level
3354 that was executing when you gave the @code{next} command. This command
3355 is abbreviated @code{n}.
3357 An argument @var{count} is a repeat count, as for @code{step}.
3360 @c FIX ME!! Do we delete this, or is there a way it fits in with
3361 @c the following paragraph? --- Vctoria
3363 @c @code{next} within a function that lacks debugging information acts like
3364 @c @code{step}, but any function calls appearing within the code of the
3365 @c function are executed without stopping.
3367 The @code{next} command only stops at the first instruction of a
3368 source line. This prevents multiple stops that could otherwise occur in
3369 @code{switch} statements, @code{for} loops, etc.
3371 @kindex set step-mode
3373 @cindex functions without line info, and stepping
3374 @cindex stepping into functions with no line info
3375 @itemx set step-mode on
3376 The @code{set step-mode on} command causes the @code{step} command to
3377 stop at the first instruction of a function which contains no debug line
3378 information rather than stepping over it.
3380 This is useful in cases where you may be interested in inspecting the
3381 machine instructions of a function which has no symbolic info and do not
3382 want @value{GDBN} to automatically skip over this function.
3384 @item set step-mode off
3385 Causes the @code{step} command to step over any functions which contains no
3386 debug information. This is the default.
3390 Continue running until just after function in the selected stack frame
3391 returns. Print the returned value (if any).
3393 Contrast this with the @code{return} command (@pxref{Returning,
3394 ,Returning from a function}).
3397 @kindex u @r{(@code{until})}
3400 Continue running until a source line past the current line, in the
3401 current stack frame, is reached. This command is used to avoid single
3402 stepping through a loop more than once. It is like the @code{next}
3403 command, except that when @code{until} encounters a jump, it
3404 automatically continues execution until the program counter is greater
3405 than the address of the jump.
3407 This means that when you reach the end of a loop after single stepping
3408 though it, @code{until} makes your program continue execution until it
3409 exits the loop. In contrast, a @code{next} command at the end of a loop
3410 simply steps back to the beginning of the loop, which forces you to step
3411 through the next iteration.
3413 @code{until} always stops your program if it attempts to exit the current
3416 @code{until} may produce somewhat counterintuitive results if the order
3417 of machine code does not match the order of the source lines. For
3418 example, in the following excerpt from a debugging session, the @code{f}
3419 (@code{frame}) command shows that execution is stopped at line
3420 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3424 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3426 (@value{GDBP}) until
3427 195 for ( ; argc > 0; NEXTARG) @{
3430 This happened because, for execution efficiency, the compiler had
3431 generated code for the loop closure test at the end, rather than the
3432 start, of the loop---even though the test in a C @code{for}-loop is
3433 written before the body of the loop. The @code{until} command appeared
3434 to step back to the beginning of the loop when it advanced to this
3435 expression; however, it has not really gone to an earlier
3436 statement---not in terms of the actual machine code.
3438 @code{until} with no argument works by means of single
3439 instruction stepping, and hence is slower than @code{until} with an
3442 @item until @var{location}
3443 @itemx u @var{location}
3444 Continue running your program until either the specified location is
3445 reached, or the current stack frame returns. @var{location} is any of
3446 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3447 ,Setting breakpoints}). This form of the command uses breakpoints,
3448 and hence is quicker than @code{until} without an argument.
3451 @kindex si @r{(@code{stepi})}
3453 @itemx stepi @var{arg}
3455 Execute one machine instruction, then stop and return to the debugger.
3457 It is often useful to do @samp{display/i $pc} when stepping by machine
3458 instructions. This makes @value{GDBN} automatically display the next
3459 instruction to be executed, each time your program stops. @xref{Auto
3460 Display,, Automatic display}.
3462 An argument is a repeat count, as in @code{step}.
3466 @kindex ni @r{(@code{nexti})}
3468 @itemx nexti @var{arg}
3470 Execute one machine instruction, but if it is a function call,
3471 proceed until the function returns.
3473 An argument is a repeat count, as in @code{next}.
3480 A signal is an asynchronous event that can happen in a program. The
3481 operating system defines the possible kinds of signals, and gives each
3482 kind a name and a number. For example, in Unix @code{SIGINT} is the
3483 signal a program gets when you type an interrupt character (often @kbd{C-c});
3484 @code{SIGSEGV} is the signal a program gets from referencing a place in
3485 memory far away from all the areas in use; @code{SIGALRM} occurs when
3486 the alarm clock timer goes off (which happens only if your program has
3487 requested an alarm).
3489 @cindex fatal signals
3490 Some signals, including @code{SIGALRM}, are a normal part of the
3491 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3492 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
3493 program has not specified in advance some other way to handle the signal.
3494 @code{SIGINT} does not indicate an error in your program, but it is normally
3495 fatal so it can carry out the purpose of the interrupt: to kill the program.
3497 @value{GDBN} has the ability to detect any occurrence of a signal in your
3498 program. You can tell @value{GDBN} in advance what to do for each kind of
3501 @cindex handling signals
3502 Normally, @value{GDBN} is set up to let the non-erroneous signals like
3503 @code{SIGALRM} be silently passed to your program
3504 (so as not to interfere with their role in the program's functioning)
3505 but to stop your program immediately whenever an error signal happens.
3506 You can change these settings with the @code{handle} command.
3509 @kindex info signals
3512 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3513 handle each one. You can use this to see the signal numbers of all
3514 the defined types of signals.
3516 @code{info handle} is an alias for @code{info signals}.
3519 @item handle @var{signal} @var{keywords}@dots{}
3520 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
3521 can be the number of a signal or its name (with or without the
3522 @samp{SIG} at the beginning); a list of signal numbers of the form
3523 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
3524 known signals. The @var{keywords} say what change to make.
3528 The keywords allowed by the @code{handle} command can be abbreviated.
3529 Their full names are:
3533 @value{GDBN} should not stop your program when this signal happens. It may
3534 still print a message telling you that the signal has come in.
3537 @value{GDBN} should stop your program when this signal happens. This implies
3538 the @code{print} keyword as well.
3541 @value{GDBN} should print a message when this signal happens.
3544 @value{GDBN} should not mention the occurrence of the signal at all. This
3545 implies the @code{nostop} keyword as well.
3549 @value{GDBN} should allow your program to see this signal; your program
3550 can handle the signal, or else it may terminate if the signal is fatal
3551 and not handled. @code{pass} and @code{noignore} are synonyms.
3555 @value{GDBN} should not allow your program to see this signal.
3556 @code{nopass} and @code{ignore} are synonyms.
3560 When a signal stops your program, the signal is not visible to the
3562 continue. Your program sees the signal then, if @code{pass} is in
3563 effect for the signal in question @emph{at that time}. In other words,
3564 after @value{GDBN} reports a signal, you can use the @code{handle}
3565 command with @code{pass} or @code{nopass} to control whether your
3566 program sees that signal when you continue.
3568 The default is set to @code{nostop}, @code{noprint}, @code{pass} for
3569 non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and
3570 @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the
3573 You can also use the @code{signal} command to prevent your program from
3574 seeing a signal, or cause it to see a signal it normally would not see,
3575 or to give it any signal at any time. For example, if your program stopped
3576 due to some sort of memory reference error, you might store correct
3577 values into the erroneous variables and continue, hoping to see more
3578 execution; but your program would probably terminate immediately as
3579 a result of the fatal signal once it saw the signal. To prevent this,
3580 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3584 @section Stopping and starting multi-thread programs
3586 When your program has multiple threads (@pxref{Threads,, Debugging
3587 programs with multiple threads}), you can choose whether to set
3588 breakpoints on all threads, or on a particular thread.
3591 @cindex breakpoints and threads
3592 @cindex thread breakpoints
3593 @kindex break @dots{} thread @var{threadno}
3594 @item break @var{linespec} thread @var{threadno}
3595 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3596 @var{linespec} specifies source lines; there are several ways of
3597 writing them, but the effect is always to specify some source line.
3599 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3600 to specify that you only want @value{GDBN} to stop the program when a
3601 particular thread reaches this breakpoint. @var{threadno} is one of the
3602 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3603 column of the @samp{info threads} display.
3605 If you do not specify @samp{thread @var{threadno}} when you set a
3606 breakpoint, the breakpoint applies to @emph{all} threads of your
3609 You can use the @code{thread} qualifier on conditional breakpoints as
3610 well; in this case, place @samp{thread @var{threadno}} before the
3611 breakpoint condition, like this:
3614 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
3619 @cindex stopped threads
3620 @cindex threads, stopped
3621 Whenever your program stops under @value{GDBN} for any reason,
3622 @emph{all} threads of execution stop, not just the current thread. This
3623 allows you to examine the overall state of the program, including
3624 switching between threads, without worrying that things may change
3627 @cindex continuing threads
3628 @cindex threads, continuing
3629 Conversely, whenever you restart the program, @emph{all} threads start
3630 executing. @emph{This is true even when single-stepping} with commands
3631 like @code{step} or @code{next}.
3633 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3634 Since thread scheduling is up to your debugging target's operating
3635 system (not controlled by @value{GDBN}), other threads may
3636 execute more than one statement while the current thread completes a
3637 single step. Moreover, in general other threads stop in the middle of a
3638 statement, rather than at a clean statement boundary, when the program
3641 You might even find your program stopped in another thread after
3642 continuing or even single-stepping. This happens whenever some other
3643 thread runs into a breakpoint, a signal, or an exception before the
3644 first thread completes whatever you requested.
3646 On some OSes, you can lock the OS scheduler and thus allow only a single
3650 @item set scheduler-locking @var{mode}
3651 Set the scheduler locking mode. If it is @code{off}, then there is no
3652 locking and any thread may run at any time. If @code{on}, then only the
3653 current thread may run when the inferior is resumed. The @code{step}
3654 mode optimizes for single-stepping. It stops other threads from
3655 ``seizing the prompt'' by preempting the current thread while you are
3656 stepping. Other threads will only rarely (or never) get a chance to run
3657 when you step. They are more likely to run when you @samp{next} over a
3658 function call, and they are completely free to run when you use commands
3659 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
3660 thread hits a breakpoint during its timeslice, they will never steal the
3661 @value{GDBN} prompt away from the thread that you are debugging.
3663 @item show scheduler-locking
3664 Display the current scheduler locking mode.
3669 @chapter Examining the Stack
3671 When your program has stopped, the first thing you need to know is where it
3672 stopped and how it got there.
3675 Each time your program performs a function call, information about the call
3677 That information includes the location of the call in your program,
3678 the arguments of the call,
3679 and the local variables of the function being called.
3680 The information is saved in a block of data called a @dfn{stack frame}.
3681 The stack frames are allocated in a region of memory called the @dfn{call
3684 When your program stops, the @value{GDBN} commands for examining the
3685 stack allow you to see all of this information.
3687 @cindex selected frame
3688 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3689 @value{GDBN} commands refer implicitly to the selected frame. In
3690 particular, whenever you ask @value{GDBN} for the value of a variable in
3691 your program, the value is found in the selected frame. There are
3692 special @value{GDBN} commands to select whichever frame you are
3693 interested in. @xref{Selection, ,Selecting a frame}.
3695 When your program stops, @value{GDBN} automatically selects the
3696 currently executing frame and describes it briefly, similar to the
3697 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3700 * Frames:: Stack frames
3701 * Backtrace:: Backtraces
3702 * Selection:: Selecting a frame
3703 * Frame Info:: Information on a frame
3708 @section Stack frames
3710 @cindex frame, definition
3712 The call stack is divided up into contiguous pieces called @dfn{stack
3713 frames}, or @dfn{frames} for short; each frame is the data associated
3714 with one call to one function. The frame contains the arguments given
3715 to the function, the function's local variables, and the address at
3716 which the function is executing.
3718 @cindex initial frame
3719 @cindex outermost frame
3720 @cindex innermost frame
3721 When your program is started, the stack has only one frame, that of the
3722 function @code{main}. This is called the @dfn{initial} frame or the
3723 @dfn{outermost} frame. Each time a function is called, a new frame is
3724 made. Each time a function returns, the frame for that function invocation
3725 is eliminated. If a function is recursive, there can be many frames for
3726 the same function. The frame for the function in which execution is
3727 actually occurring is called the @dfn{innermost} frame. This is the most
3728 recently created of all the stack frames that still exist.
3730 @cindex frame pointer
3731 Inside your program, stack frames are identified by their addresses. A
3732 stack frame consists of many bytes, each of which has its own address; each
3733 kind of computer has a convention for choosing one byte whose
3734 address serves as the address of the frame. Usually this address is kept
3735 in a register called the @dfn{frame pointer register} while execution is
3736 going on in that frame.
3738 @cindex frame number
3739 @value{GDBN} assigns numbers to all existing stack frames, starting with
3740 zero for the innermost frame, one for the frame that called it,
3741 and so on upward. These numbers do not really exist in your program;
3742 they are assigned by @value{GDBN} to give you a way of designating stack
3743 frames in @value{GDBN} commands.
3745 @c The -fomit-frame-pointer below perennially causes hbox overflow
3746 @c underflow problems.
3747 @cindex frameless execution
3748 Some compilers provide a way to compile functions so that they operate
3749 without stack frames. (For example, the @value{GCC} option
3751 @samp{-fomit-frame-pointer}
3753 generates functions without a frame.)
3754 This is occasionally done with heavily used library functions to save
3755 the frame setup time. @value{GDBN} has limited facilities for dealing
3756 with these function invocations. If the innermost function invocation
3757 has no stack frame, @value{GDBN} nevertheless regards it as though
3758 it had a separate frame, which is numbered zero as usual, allowing
3759 correct tracing of the function call chain. However, @value{GDBN} has
3760 no provision for frameless functions elsewhere in the stack.
3763 @kindex frame@r{, command}
3764 @cindex current stack frame
3765 @item frame @var{args}
3766 The @code{frame} command allows you to move from one stack frame to another,
3767 and to print the stack frame you select. @var{args} may be either the
3768 address of the frame or the stack frame number. Without an argument,
3769 @code{frame} prints the current stack frame.
3771 @kindex select-frame
3772 @cindex selecting frame silently
3774 The @code{select-frame} command allows you to move from one stack frame
3775 to another without printing the frame. This is the silent version of
3784 @cindex stack traces
3785 A backtrace is a summary of how your program got where it is. It shows one
3786 line per frame, for many frames, starting with the currently executing
3787 frame (frame zero), followed by its caller (frame one), and on up the
3792 @kindex bt @r{(@code{backtrace})}
3795 Print a backtrace of the entire stack: one line per frame for all
3796 frames in the stack.
3798 You can stop the backtrace at any time by typing the system interrupt
3799 character, normally @kbd{C-c}.
3801 @item backtrace @var{n}
3803 Similar, but print only the innermost @var{n} frames.
3805 @item backtrace -@var{n}
3807 Similar, but print only the outermost @var{n} frames.
3812 @kindex info s @r{(@code{info stack})}
3813 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3814 are additional aliases for @code{backtrace}.
3816 Each line in the backtrace shows the frame number and the function name.
3817 The program counter value is also shown---unless you use @code{set
3818 print address off}. The backtrace also shows the source file name and
3819 line number, as well as the arguments to the function. The program
3820 counter value is omitted if it is at the beginning of the code for that
3823 Here is an example of a backtrace. It was made with the command
3824 @samp{bt 3}, so it shows the innermost three frames.
3828 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3830 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3831 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3833 (More stack frames follow...)
3838 The display for frame zero does not begin with a program counter
3839 value, indicating that your program has stopped at the beginning of the
3840 code for line @code{993} of @code{builtin.c}.
3843 @section Selecting a frame
3845 Most commands for examining the stack and other data in your program work on
3846 whichever stack frame is selected at the moment. Here are the commands for
3847 selecting a stack frame; all of them finish by printing a brief description
3848 of the stack frame just selected.
3851 @kindex frame@r{, selecting}
3852 @kindex f @r{(@code{frame})}
3855 Select frame number @var{n}. Recall that frame zero is the innermost
3856 (currently executing) frame, frame one is the frame that called the
3857 innermost one, and so on. The highest-numbered frame is the one for
3860 @item frame @var{addr}
3862 Select the frame at address @var{addr}. This is useful mainly if the
3863 chaining of stack frames has been damaged by a bug, making it
3864 impossible for @value{GDBN} to assign numbers properly to all frames. In
3865 addition, this can be useful when your program has multiple stacks and
3866 switches between them.
3868 On the SPARC architecture, @code{frame} needs two addresses to
3869 select an arbitrary frame: a frame pointer and a stack pointer.
3871 On the MIPS and Alpha architecture, it needs two addresses: a stack
3872 pointer and a program counter.
3874 On the 29k architecture, it needs three addresses: a register stack
3875 pointer, a program counter, and a memory stack pointer.
3876 @c note to future updaters: this is conditioned on a flag
3877 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3878 @c as of 27 Jan 1994.
3882 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3883 advances toward the outermost frame, to higher frame numbers, to frames
3884 that have existed longer. @var{n} defaults to one.
3887 @kindex do @r{(@code{down})}
3889 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3890 advances toward the innermost frame, to lower frame numbers, to frames
3891 that were created more recently. @var{n} defaults to one. You may
3892 abbreviate @code{down} as @code{do}.
3895 All of these commands end by printing two lines of output describing the
3896 frame. The first line shows the frame number, the function name, the
3897 arguments, and the source file and line number of execution in that
3898 frame. The second line shows the text of that source line.
3906 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3908 10 read_input_file (argv[i]);
3912 After such a printout, the @code{list} command with no arguments
3913 prints ten lines centered on the point of execution in the frame.
3914 @xref{List, ,Printing source lines}.
3917 @kindex down-silently
3919 @item up-silently @var{n}
3920 @itemx down-silently @var{n}
3921 These two commands are variants of @code{up} and @code{down},
3922 respectively; they differ in that they do their work silently, without
3923 causing display of the new frame. They are intended primarily for use
3924 in @value{GDBN} command scripts, where the output might be unnecessary and
3929 @section Information about a frame
3931 There are several other commands to print information about the selected
3937 When used without any argument, this command does not change which
3938 frame is selected, but prints a brief description of the currently
3939 selected stack frame. It can be abbreviated @code{f}. With an
3940 argument, this command is used to select a stack frame.
3941 @xref{Selection, ,Selecting a frame}.
3944 @kindex info f @r{(@code{info frame})}
3947 This command prints a verbose description of the selected stack frame,
3952 the address of the frame
3954 the address of the next frame down (called by this frame)
3956 the address of the next frame up (caller of this frame)
3958 the language in which the source code corresponding to this frame is written
3960 the address of the frame's arguments
3962 the address of the frame's local variables
3964 the program counter saved in it (the address of execution in the caller frame)
3966 which registers were saved in the frame
3969 @noindent The verbose description is useful when
3970 something has gone wrong that has made the stack format fail to fit
3971 the usual conventions.
3973 @item info frame @var{addr}
3974 @itemx info f @var{addr}
3975 Print a verbose description of the frame at address @var{addr}, without
3976 selecting that frame. The selected frame remains unchanged by this
3977 command. This requires the same kind of address (more than one for some
3978 architectures) that you specify in the @code{frame} command.
3979 @xref{Selection, ,Selecting a frame}.
3983 Print the arguments of the selected frame, each on a separate line.
3987 Print the local variables of the selected frame, each on a separate
3988 line. These are all variables (declared either static or automatic)
3989 accessible at the point of execution of the selected frame.
3992 @cindex catch exceptions, list active handlers
3993 @cindex exception handlers, how to list
3995 Print a list of all the exception handlers that are active in the
3996 current stack frame at the current point of execution. To see other
3997 exception handlers, visit the associated frame (using the @code{up},
3998 @code{down}, or @code{frame} commands); then type @code{info catch}.
3999 @xref{Set Catchpoints, , Setting catchpoints}.
4005 @chapter Examining Source Files
4007 @value{GDBN} can print parts of your program's source, since the debugging
4008 information recorded in the program tells @value{GDBN} what source files were
4009 used to build it. When your program stops, @value{GDBN} spontaneously prints
4010 the line where it stopped. Likewise, when you select a stack frame
4011 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
4012 execution in that frame has stopped. You can print other portions of
4013 source files by explicit command.
4015 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
4016 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
4017 @value{GDBN} under @sc{gnu} Emacs}.
4020 * List:: Printing source lines
4021 * Search:: Searching source files
4022 * Source Path:: Specifying source directories
4023 * Machine Code:: Source and machine code
4027 @section Printing source lines
4030 @kindex l @r{(@code{list})}
4031 To print lines from a source file, use the @code{list} command
4032 (abbreviated @code{l}). By default, ten lines are printed.
4033 There are several ways to specify what part of the file you want to print.
4035 Here are the forms of the @code{list} command most commonly used:
4038 @item list @var{linenum}
4039 Print lines centered around line number @var{linenum} in the
4040 current source file.
4042 @item list @var{function}
4043 Print lines centered around the beginning of function
4047 Print more lines. If the last lines printed were printed with a
4048 @code{list} command, this prints lines following the last lines
4049 printed; however, if the last line printed was a solitary line printed
4050 as part of displaying a stack frame (@pxref{Stack, ,Examining the
4051 Stack}), this prints lines centered around that line.
4054 Print lines just before the lines last printed.
4057 By default, @value{GDBN} prints ten source lines with any of these forms of
4058 the @code{list} command. You can change this using @code{set listsize}:
4061 @kindex set listsize
4062 @item set listsize @var{count}
4063 Make the @code{list} command display @var{count} source lines (unless
4064 the @code{list} argument explicitly specifies some other number).
4066 @kindex show listsize
4068 Display the number of lines that @code{list} prints.
4071 Repeating a @code{list} command with @key{RET} discards the argument,
4072 so it is equivalent to typing just @code{list}. This is more useful
4073 than listing the same lines again. An exception is made for an
4074 argument of @samp{-}; that argument is preserved in repetition so that
4075 each repetition moves up in the source file.
4078 In general, the @code{list} command expects you to supply zero, one or two
4079 @dfn{linespecs}. Linespecs specify source lines; there are several ways
4080 of writing them, but the effect is always to specify some source line.
4081 Here is a complete description of the possible arguments for @code{list}:
4084 @item list @var{linespec}
4085 Print lines centered around the line specified by @var{linespec}.
4087 @item list @var{first},@var{last}
4088 Print lines from @var{first} to @var{last}. Both arguments are
4091 @item list ,@var{last}
4092 Print lines ending with @var{last}.
4094 @item list @var{first},
4095 Print lines starting with @var{first}.
4098 Print lines just after the lines last printed.
4101 Print lines just before the lines last printed.
4104 As described in the preceding table.
4107 Here are the ways of specifying a single source line---all the
4112 Specifies line @var{number} of the current source file.
4113 When a @code{list} command has two linespecs, this refers to
4114 the same source file as the first linespec.
4117 Specifies the line @var{offset} lines after the last line printed.
4118 When used as the second linespec in a @code{list} command that has
4119 two, this specifies the line @var{offset} lines down from the
4123 Specifies the line @var{offset} lines before the last line printed.
4125 @item @var{filename}:@var{number}
4126 Specifies line @var{number} in the source file @var{filename}.
4128 @item @var{function}
4129 Specifies the line that begins the body of the function @var{function}.
4130 For example: in C, this is the line with the open brace.
4132 @item @var{filename}:@var{function}
4133 Specifies the line of the open-brace that begins the body of the
4134 function @var{function} in the file @var{filename}. You only need the
4135 file name with a function name to avoid ambiguity when there are
4136 identically named functions in different source files.
4138 @item *@var{address}
4139 Specifies the line containing the program address @var{address}.
4140 @var{address} may be any expression.
4144 @section Searching source files
4146 @kindex reverse-search
4148 There are two commands for searching through the current source file for a
4153 @kindex forward-search
4154 @item forward-search @var{regexp}
4155 @itemx search @var{regexp}
4156 The command @samp{forward-search @var{regexp}} checks each line,
4157 starting with the one following the last line listed, for a match for
4158 @var{regexp}. It lists the line that is found. You can use the
4159 synonym @samp{search @var{regexp}} or abbreviate the command name as
4162 @item reverse-search @var{regexp}
4163 The command @samp{reverse-search @var{regexp}} checks each line, starting
4164 with the one before the last line listed and going backward, for a match
4165 for @var{regexp}. It lists the line that is found. You can abbreviate
4166 this command as @code{rev}.
4170 @section Specifying source directories
4173 @cindex directories for source files
4174 Executable programs sometimes do not record the directories of the source
4175 files from which they were compiled, just the names. Even when they do,
4176 the directories could be moved between the compilation and your debugging
4177 session. @value{GDBN} has a list of directories to search for source files;
4178 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4179 it tries all the directories in the list, in the order they are present
4180 in the list, until it finds a file with the desired name. Note that
4181 the executable search path is @emph{not} used for this purpose. Neither is
4182 the current working directory, unless it happens to be in the source
4185 If @value{GDBN} cannot find a source file in the source path, and the
4186 object program records a directory, @value{GDBN} tries that directory
4187 too. If the source path is empty, and there is no record of the
4188 compilation directory, @value{GDBN} looks in the current directory as a
4191 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4192 any information it has cached about where source files are found and where
4193 each line is in the file.
4197 When you start @value{GDBN}, its source path includes only @samp{cdir}
4198 and @samp{cwd}, in that order.
4199 To add other directories, use the @code{directory} command.
4202 @item directory @var{dirname} @dots{}
4203 @item dir @var{dirname} @dots{}
4204 Add directory @var{dirname} to the front of the source path. Several
4205 directory names may be given to this command, separated by @samp{:}
4206 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
4207 part of absolute file names) or
4208 whitespace. You may specify a directory that is already in the source
4209 path; this moves it forward, so @value{GDBN} searches it sooner.
4213 @vindex $cdir@r{, convenience variable}
4214 @vindex $cwdr@r{, convenience variable}
4215 @cindex compilation directory
4216 @cindex current directory
4217 @cindex working directory
4218 @cindex directory, current
4219 @cindex directory, compilation
4220 You can use the string @samp{$cdir} to refer to the compilation
4221 directory (if one is recorded), and @samp{$cwd} to refer to the current
4222 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4223 tracks the current working directory as it changes during your @value{GDBN}
4224 session, while the latter is immediately expanded to the current
4225 directory at the time you add an entry to the source path.
4228 Reset the source path to empty again. This requires confirmation.
4230 @c RET-repeat for @code{directory} is explicitly disabled, but since
4231 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4233 @item show directories
4234 @kindex show directories
4235 Print the source path: show which directories it contains.
4238 If your source path is cluttered with directories that are no longer of
4239 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4240 versions of source. You can correct the situation as follows:
4244 Use @code{directory} with no argument to reset the source path to empty.
4247 Use @code{directory} with suitable arguments to reinstall the
4248 directories you want in the source path. You can add all the
4249 directories in one command.
4253 @section Source and machine code
4255 You can use the command @code{info line} to map source lines to program
4256 addresses (and vice versa), and the command @code{disassemble} to display
4257 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4258 mode, the @code{info line} command causes the arrow to point to the
4259 line specified. Also, @code{info line} prints addresses in symbolic form as
4264 @item info line @var{linespec}
4265 Print the starting and ending addresses of the compiled code for
4266 source line @var{linespec}. You can specify source lines in any of
4267 the ways understood by the @code{list} command (@pxref{List, ,Printing
4271 For example, we can use @code{info line} to discover the location of
4272 the object code for the first line of function
4273 @code{m4_changequote}:
4275 @c FIXME: I think this example should also show the addresses in
4276 @c symbolic form, as they usually would be displayed.
4278 (@value{GDBP}) info line m4_changequote
4279 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4283 We can also inquire (using @code{*@var{addr}} as the form for
4284 @var{linespec}) what source line covers a particular address:
4286 (@value{GDBP}) info line *0x63ff
4287 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4290 @cindex @code{$_} and @code{info line}
4291 @kindex x@r{(examine), and} info line
4292 After @code{info line}, the default address for the @code{x} command
4293 is changed to the starting address of the line, so that @samp{x/i} is
4294 sufficient to begin examining the machine code (@pxref{Memory,
4295 ,Examining memory}). Also, this address is saved as the value of the
4296 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4301 @cindex assembly instructions
4302 @cindex instructions, assembly
4303 @cindex machine instructions
4304 @cindex listing machine instructions
4306 This specialized command dumps a range of memory as machine
4307 instructions. The default memory range is the function surrounding the
4308 program counter of the selected frame. A single argument to this
4309 command is a program counter value; @value{GDBN} dumps the function
4310 surrounding this value. Two arguments specify a range of addresses
4311 (first inclusive, second exclusive) to dump.
4314 The following example shows the disassembly of a range of addresses of
4315 HP PA-RISC 2.0 code:
4318 (@value{GDBP}) disas 0x32c4 0x32e4
4319 Dump of assembler code from 0x32c4 to 0x32e4:
4320 0x32c4 <main+204>: addil 0,dp
4321 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4322 0x32cc <main+212>: ldil 0x3000,r31
4323 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4324 0x32d4 <main+220>: ldo 0(r31),rp
4325 0x32d8 <main+224>: addil -0x800,dp
4326 0x32dc <main+228>: ldo 0x588(r1),r26
4327 0x32e0 <main+232>: ldil 0x3000,r31
4328 End of assembler dump.
4331 Some architectures have more than one commonly-used set of instruction
4332 mnemonics or other syntax.
4335 @kindex set disassembly-flavor
4336 @cindex assembly instructions
4337 @cindex instructions, assembly
4338 @cindex machine instructions
4339 @cindex listing machine instructions
4340 @cindex Intel disassembly flavor
4341 @cindex AT&T disassembly flavor
4342 @item set disassembly-flavor @var{instruction-set}
4343 Select the instruction set to use when disassembling the
4344 program via the @code{disassemble} or @code{x/i} commands.
4346 Currently this command is only defined for the Intel x86 family. You
4347 can set @var{instruction-set} to either @code{intel} or @code{att}.
4348 The default is @code{att}, the AT&T flavor used by default by Unix
4349 assemblers for x86-based targets.
4354 @chapter Examining Data
4356 @cindex printing data
4357 @cindex examining data
4360 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4361 @c document because it is nonstandard... Under Epoch it displays in a
4362 @c different window or something like that.
4363 The usual way to examine data in your program is with the @code{print}
4364 command (abbreviated @code{p}), or its synonym @code{inspect}. It
4365 evaluates and prints the value of an expression of the language your
4366 program is written in (@pxref{Languages, ,Using @value{GDBN} with
4367 Different Languages}).
4370 @item print @var{expr}
4371 @itemx print /@var{f} @var{expr}
4372 @var{expr} is an expression (in the source language). By default the
4373 value of @var{expr} is printed in a format appropriate to its data type;
4374 you can choose a different format by specifying @samp{/@var{f}}, where
4375 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
4379 @itemx print /@var{f}
4380 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
4381 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4382 conveniently inspect the same value in an alternative format.
4385 A more low-level way of examining data is with the @code{x} command.
4386 It examines data in memory at a specified address and prints it in a
4387 specified format. @xref{Memory, ,Examining memory}.
4389 If you are interested in information about types, or about how the
4390 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
4391 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
4395 * Expressions:: Expressions
4396 * Variables:: Program variables
4397 * Arrays:: Artificial arrays
4398 * Output Formats:: Output formats
4399 * Memory:: Examining memory
4400 * Auto Display:: Automatic display
4401 * Print Settings:: Print settings
4402 * Value History:: Value history
4403 * Convenience Vars:: Convenience variables
4404 * Registers:: Registers
4405 * Floating Point Hardware:: Floating point hardware
4406 * Memory Region Attributes:: Memory region attributes
4407 * Dump/Restore Files:: Copy between memory and a file
4411 @section Expressions
4414 @code{print} and many other @value{GDBN} commands accept an expression and
4415 compute its value. Any kind of constant, variable or operator defined
4416 by the programming language you are using is valid in an expression in
4417 @value{GDBN}. This includes conditional expressions, function calls, casts
4418 and string constants. It unfortunately does not include symbols defined
4419 by preprocessor @code{#define} commands.
4421 @value{GDBN} supports array constants in expressions input by
4422 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
4423 you can use the command @code{print @{1, 2, 3@}} to build up an array in
4424 memory that is @code{malloc}ed in the target program.
4426 Because C is so widespread, most of the expressions shown in examples in
4427 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4428 Languages}, for information on how to use expressions in other
4431 In this section, we discuss operators that you can use in @value{GDBN}
4432 expressions regardless of your programming language.
4434 Casts are supported in all languages, not just in C, because it is so
4435 useful to cast a number into a pointer in order to examine a structure
4436 at that address in memory.
4437 @c FIXME: casts supported---Mod2 true?
4439 @value{GDBN} supports these operators, in addition to those common
4440 to programming languages:
4444 @samp{@@} is a binary operator for treating parts of memory as arrays.
4445 @xref{Arrays, ,Artificial arrays}, for more information.
4448 @samp{::} allows you to specify a variable in terms of the file or
4449 function where it is defined. @xref{Variables, ,Program variables}.
4451 @cindex @{@var{type}@}
4452 @cindex type casting memory
4453 @cindex memory, viewing as typed object
4454 @cindex casts, to view memory
4455 @item @{@var{type}@} @var{addr}
4456 Refers to an object of type @var{type} stored at address @var{addr} in
4457 memory. @var{addr} may be any expression whose value is an integer or
4458 pointer (but parentheses are required around binary operators, just as in
4459 a cast). This construct is allowed regardless of what kind of data is
4460 normally supposed to reside at @var{addr}.
4464 @section Program variables
4466 The most common kind of expression to use is the name of a variable
4469 Variables in expressions are understood in the selected stack frame
4470 (@pxref{Selection, ,Selecting a frame}); they must be either:
4474 global (or file-static)
4481 visible according to the scope rules of the
4482 programming language from the point of execution in that frame
4485 @noindent This means that in the function
4500 you can examine and use the variable @code{a} whenever your program is
4501 executing within the function @code{foo}, but you can only use or
4502 examine the variable @code{b} while your program is executing inside
4503 the block where @code{b} is declared.
4505 @cindex variable name conflict
4506 There is an exception: you can refer to a variable or function whose
4507 scope is a single source file even if the current execution point is not
4508 in this file. But it is possible to have more than one such variable or
4509 function with the same name (in different source files). If that
4510 happens, referring to that name has unpredictable effects. If you wish,
4511 you can specify a static variable in a particular function or file,
4512 using the colon-colon notation:
4514 @cindex colon-colon, context for variables/functions
4516 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4517 @cindex @code{::}, context for variables/functions
4520 @var{file}::@var{variable}
4521 @var{function}::@var{variable}
4525 Here @var{file} or @var{function} is the name of the context for the
4526 static @var{variable}. In the case of file names, you can use quotes to
4527 make sure @value{GDBN} parses the file name as a single word---for example,
4528 to print a global value of @code{x} defined in @file{f2.c}:
4531 (@value{GDBP}) p 'f2.c'::x
4534 @cindex C@t{++} scope resolution
4535 This use of @samp{::} is very rarely in conflict with the very similar
4536 use of the same notation in C@t{++}. @value{GDBN} also supports use of the C@t{++}
4537 scope resolution operator in @value{GDBN} expressions.
4538 @c FIXME: Um, so what happens in one of those rare cases where it's in
4541 @cindex wrong values
4542 @cindex variable values, wrong
4544 @emph{Warning:} Occasionally, a local variable may appear to have the
4545 wrong value at certain points in a function---just after entry to a new
4546 scope, and just before exit.
4548 You may see this problem when you are stepping by machine instructions.
4549 This is because, on most machines, it takes more than one instruction to
4550 set up a stack frame (including local variable definitions); if you are
4551 stepping by machine instructions, variables may appear to have the wrong
4552 values until the stack frame is completely built. On exit, it usually
4553 also takes more than one machine instruction to destroy a stack frame;
4554 after you begin stepping through that group of instructions, local
4555 variable definitions may be gone.
4557 This may also happen when the compiler does significant optimizations.
4558 To be sure of always seeing accurate values, turn off all optimization
4561 @cindex ``No symbol "foo" in current context''
4562 Another possible effect of compiler optimizations is to optimize
4563 unused variables out of existence, or assign variables to registers (as
4564 opposed to memory addresses). Depending on the support for such cases
4565 offered by the debug info format used by the compiler, @value{GDBN}
4566 might not be able to display values for such local variables. If that
4567 happens, @value{GDBN} will print a message like this:
4570 No symbol "foo" in current context.
4573 To solve such problems, either recompile without optimizations, or use a
4574 different debug info format, if the compiler supports several such
4575 formats. For example, @value{NGCC}, the @sc{gnu} C/C@t{++} compiler usually
4576 supports the @samp{-gstabs} option. @samp{-gstabs} produces debug info
4577 in a format that is superior to formats such as COFF. You may be able
4578 to use DWARF2 (@samp{-gdwarf-2}), which is also an effective form for
4579 debug info. See @ref{Debugging Options,,Options for Debugging Your
4580 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
4585 @section Artificial arrays
4587 @cindex artificial array
4588 @kindex @@@r{, referencing memory as an array}
4589 It is often useful to print out several successive objects of the
4590 same type in memory; a section of an array, or an array of
4591 dynamically determined size for which only a pointer exists in the
4594 You can do this by referring to a contiguous span of memory as an
4595 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4596 operand of @samp{@@} should be the first element of the desired array
4597 and be an individual object. The right operand should be the desired length
4598 of the array. The result is an array value whose elements are all of
4599 the type of the left argument. The first element is actually the left
4600 argument; the second element comes from bytes of memory immediately
4601 following those that hold the first element, and so on. Here is an
4602 example. If a program says
4605 int *array = (int *) malloc (len * sizeof (int));
4609 you can print the contents of @code{array} with
4615 The left operand of @samp{@@} must reside in memory. Array values made
4616 with @samp{@@} in this way behave just like other arrays in terms of
4617 subscripting, and are coerced to pointers when used in expressions.
4618 Artificial arrays most often appear in expressions via the value history
4619 (@pxref{Value History, ,Value history}), after printing one out.
4621 Another way to create an artificial array is to use a cast.
4622 This re-interprets a value as if it were an array.
4623 The value need not be in memory:
4625 (@value{GDBP}) p/x (short[2])0x12345678
4626 $1 = @{0x1234, 0x5678@}
4629 As a convenience, if you leave the array length out (as in
4630 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
4631 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4633 (@value{GDBP}) p/x (short[])0x12345678
4634 $2 = @{0x1234, 0x5678@}
4637 Sometimes the artificial array mechanism is not quite enough; in
4638 moderately complex data structures, the elements of interest may not
4639 actually be adjacent---for example, if you are interested in the values
4640 of pointers in an array. One useful work-around in this situation is
4641 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4642 variables}) as a counter in an expression that prints the first
4643 interesting value, and then repeat that expression via @key{RET}. For
4644 instance, suppose you have an array @code{dtab} of pointers to
4645 structures, and you are interested in the values of a field @code{fv}
4646 in each structure. Here is an example of what you might type:
4656 @node Output Formats
4657 @section Output formats
4659 @cindex formatted output
4660 @cindex output formats
4661 By default, @value{GDBN} prints a value according to its data type. Sometimes
4662 this is not what you want. For example, you might want to print a number
4663 in hex, or a pointer in decimal. Or you might want to view data in memory
4664 at a certain address as a character string or as an instruction. To do
4665 these things, specify an @dfn{output format} when you print a value.
4667 The simplest use of output formats is to say how to print a value
4668 already computed. This is done by starting the arguments of the
4669 @code{print} command with a slash and a format letter. The format
4670 letters supported are:
4674 Regard the bits of the value as an integer, and print the integer in
4678 Print as integer in signed decimal.
4681 Print as integer in unsigned decimal.
4684 Print as integer in octal.
4687 Print as integer in binary. The letter @samp{t} stands for ``two''.
4688 @footnote{@samp{b} cannot be used because these format letters are also
4689 used with the @code{x} command, where @samp{b} stands for ``byte'';
4690 see @ref{Memory,,Examining memory}.}
4693 @cindex unknown address, locating
4694 @cindex locate address
4695 Print as an address, both absolute in hexadecimal and as an offset from
4696 the nearest preceding symbol. You can use this format used to discover
4697 where (in what function) an unknown address is located:
4700 (@value{GDBP}) p/a 0x54320
4701 $3 = 0x54320 <_initialize_vx+396>
4705 The command @code{info symbol 0x54320} yields similar results.
4706 @xref{Symbols, info symbol}.
4709 Regard as an integer and print it as a character constant.
4712 Regard the bits of the value as a floating point number and print
4713 using typical floating point syntax.
4716 For example, to print the program counter in hex (@pxref{Registers}), type
4723 Note that no space is required before the slash; this is because command
4724 names in @value{GDBN} cannot contain a slash.
4726 To reprint the last value in the value history with a different format,
4727 you can use the @code{print} command with just a format and no
4728 expression. For example, @samp{p/x} reprints the last value in hex.
4731 @section Examining memory
4733 You can use the command @code{x} (for ``examine'') to examine memory in
4734 any of several formats, independently of your program's data types.
4736 @cindex examining memory
4738 @kindex x @r{(examine memory)}
4739 @item x/@var{nfu} @var{addr}
4742 Use the @code{x} command to examine memory.
4745 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4746 much memory to display and how to format it; @var{addr} is an
4747 expression giving the address where you want to start displaying memory.
4748 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4749 Several commands set convenient defaults for @var{addr}.
4752 @item @var{n}, the repeat count
4753 The repeat count is a decimal integer; the default is 1. It specifies
4754 how much memory (counting by units @var{u}) to display.
4755 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4758 @item @var{f}, the display format
4759 The display format is one of the formats used by @code{print},
4760 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4761 The default is @samp{x} (hexadecimal) initially.
4762 The default changes each time you use either @code{x} or @code{print}.
4764 @item @var{u}, the unit size
4765 The unit size is any of
4771 Halfwords (two bytes).
4773 Words (four bytes). This is the initial default.
4775 Giant words (eight bytes).
4778 Each time you specify a unit size with @code{x}, that size becomes the
4779 default unit the next time you use @code{x}. (For the @samp{s} and
4780 @samp{i} formats, the unit size is ignored and is normally not written.)
4782 @item @var{addr}, starting display address
4783 @var{addr} is the address where you want @value{GDBN} to begin displaying
4784 memory. The expression need not have a pointer value (though it may);
4785 it is always interpreted as an integer address of a byte of memory.
4786 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4787 @var{addr} is usually just after the last address examined---but several
4788 other commands also set the default address: @code{info breakpoints} (to
4789 the address of the last breakpoint listed), @code{info line} (to the
4790 starting address of a line), and @code{print} (if you use it to display
4791 a value from memory).
4794 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4795 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4796 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4797 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4798 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
4800 Since the letters indicating unit sizes are all distinct from the
4801 letters specifying output formats, you do not have to remember whether
4802 unit size or format comes first; either order works. The output
4803 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4804 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4806 Even though the unit size @var{u} is ignored for the formats @samp{s}
4807 and @samp{i}, you might still want to use a count @var{n}; for example,
4808 @samp{3i} specifies that you want to see three machine instructions,
4809 including any operands. The command @code{disassemble} gives an
4810 alternative way of inspecting machine instructions; see @ref{Machine
4811 Code,,Source and machine code}.
4813 All the defaults for the arguments to @code{x} are designed to make it
4814 easy to continue scanning memory with minimal specifications each time
4815 you use @code{x}. For example, after you have inspected three machine
4816 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4817 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4818 the repeat count @var{n} is used again; the other arguments default as
4819 for successive uses of @code{x}.
4821 @cindex @code{$_}, @code{$__}, and value history
4822 The addresses and contents printed by the @code{x} command are not saved
4823 in the value history because there is often too much of them and they
4824 would get in the way. Instead, @value{GDBN} makes these values available for
4825 subsequent use in expressions as values of the convenience variables
4826 @code{$_} and @code{$__}. After an @code{x} command, the last address
4827 examined is available for use in expressions in the convenience variable
4828 @code{$_}. The contents of that address, as examined, are available in
4829 the convenience variable @code{$__}.
4831 If the @code{x} command has a repeat count, the address and contents saved
4832 are from the last memory unit printed; this is not the same as the last
4833 address printed if several units were printed on the last line of output.
4836 @section Automatic display
4837 @cindex automatic display
4838 @cindex display of expressions
4840 If you find that you want to print the value of an expression frequently
4841 (to see how it changes), you might want to add it to the @dfn{automatic
4842 display list} so that @value{GDBN} prints its value each time your program stops.
4843 Each expression added to the list is given a number to identify it;
4844 to remove an expression from the list, you specify that number.
4845 The automatic display looks like this:
4849 3: bar[5] = (struct hack *) 0x3804
4853 This display shows item numbers, expressions and their current values. As with
4854 displays you request manually using @code{x} or @code{print}, you can
4855 specify the output format you prefer; in fact, @code{display} decides
4856 whether to use @code{print} or @code{x} depending on how elaborate your
4857 format specification is---it uses @code{x} if you specify a unit size,
4858 or one of the two formats (@samp{i} and @samp{s}) that are only
4859 supported by @code{x}; otherwise it uses @code{print}.
4863 @item display @var{expr}
4864 Add the expression @var{expr} to the list of expressions to display
4865 each time your program stops. @xref{Expressions, ,Expressions}.
4867 @code{display} does not repeat if you press @key{RET} again after using it.
4869 @item display/@var{fmt} @var{expr}
4870 For @var{fmt} specifying only a display format and not a size or
4871 count, add the expression @var{expr} to the auto-display list but
4872 arrange to display it each time in the specified format @var{fmt}.
4873 @xref{Output Formats,,Output formats}.
4875 @item display/@var{fmt} @var{addr}
4876 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4877 number of units, add the expression @var{addr} as a memory address to
4878 be examined each time your program stops. Examining means in effect
4879 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4882 For example, @samp{display/i $pc} can be helpful, to see the machine
4883 instruction about to be executed each time execution stops (@samp{$pc}
4884 is a common name for the program counter; @pxref{Registers, ,Registers}).
4887 @kindex delete display
4889 @item undisplay @var{dnums}@dots{}
4890 @itemx delete display @var{dnums}@dots{}
4891 Remove item numbers @var{dnums} from the list of expressions to display.
4893 @code{undisplay} does not repeat if you press @key{RET} after using it.
4894 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4896 @kindex disable display
4897 @item disable display @var{dnums}@dots{}
4898 Disable the display of item numbers @var{dnums}. A disabled display
4899 item is not printed automatically, but is not forgotten. It may be
4900 enabled again later.
4902 @kindex enable display
4903 @item enable display @var{dnums}@dots{}
4904 Enable display of item numbers @var{dnums}. It becomes effective once
4905 again in auto display of its expression, until you specify otherwise.
4908 Display the current values of the expressions on the list, just as is
4909 done when your program stops.
4911 @kindex info display
4913 Print the list of expressions previously set up to display
4914 automatically, each one with its item number, but without showing the
4915 values. This includes disabled expressions, which are marked as such.
4916 It also includes expressions which would not be displayed right now
4917 because they refer to automatic variables not currently available.
4920 If a display expression refers to local variables, then it does not make
4921 sense outside the lexical context for which it was set up. Such an
4922 expression is disabled when execution enters a context where one of its
4923 variables is not defined. For example, if you give the command
4924 @code{display last_char} while inside a function with an argument
4925 @code{last_char}, @value{GDBN} displays this argument while your program
4926 continues to stop inside that function. When it stops elsewhere---where
4927 there is no variable @code{last_char}---the display is disabled
4928 automatically. The next time your program stops where @code{last_char}
4929 is meaningful, you can enable the display expression once again.
4931 @node Print Settings
4932 @section Print settings
4934 @cindex format options
4935 @cindex print settings
4936 @value{GDBN} provides the following ways to control how arrays, structures,
4937 and symbols are printed.
4940 These settings are useful for debugging programs in any language:
4943 @kindex set print address
4944 @item set print address
4945 @itemx set print address on
4946 @value{GDBN} prints memory addresses showing the location of stack
4947 traces, structure values, pointer values, breakpoints, and so forth,
4948 even when it also displays the contents of those addresses. The default
4949 is @code{on}. For example, this is what a stack frame display looks like with
4950 @code{set print address on}:
4955 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4957 530 if (lquote != def_lquote)
4961 @item set print address off
4962 Do not print addresses when displaying their contents. For example,
4963 this is the same stack frame displayed with @code{set print address off}:
4967 (@value{GDBP}) set print addr off
4969 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4970 530 if (lquote != def_lquote)
4974 You can use @samp{set print address off} to eliminate all machine
4975 dependent displays from the @value{GDBN} interface. For example, with
4976 @code{print address off}, you should get the same text for backtraces on
4977 all machines---whether or not they involve pointer arguments.
4979 @kindex show print address
4980 @item show print address
4981 Show whether or not addresses are to be printed.
4984 When @value{GDBN} prints a symbolic address, it normally prints the
4985 closest earlier symbol plus an offset. If that symbol does not uniquely
4986 identify the address (for example, it is a name whose scope is a single
4987 source file), you may need to clarify. One way to do this is with
4988 @code{info line}, for example @samp{info line *0x4537}. Alternately,
4989 you can set @value{GDBN} to print the source file and line number when
4990 it prints a symbolic address:
4993 @kindex set print symbol-filename
4994 @item set print symbol-filename on
4995 Tell @value{GDBN} to print the source file name and line number of a
4996 symbol in the symbolic form of an address.
4998 @item set print symbol-filename off
4999 Do not print source file name and line number of a symbol. This is the
5002 @kindex show print symbol-filename
5003 @item show print symbol-filename
5004 Show whether or not @value{GDBN} will print the source file name and
5005 line number of a symbol in the symbolic form of an address.
5008 Another situation where it is helpful to show symbol filenames and line
5009 numbers is when disassembling code; @value{GDBN} shows you the line
5010 number and source file that corresponds to each instruction.
5012 Also, you may wish to see the symbolic form only if the address being
5013 printed is reasonably close to the closest earlier symbol:
5016 @kindex set print max-symbolic-offset
5017 @item set print max-symbolic-offset @var{max-offset}
5018 Tell @value{GDBN} to only display the symbolic form of an address if the
5019 offset between the closest earlier symbol and the address is less than
5020 @var{max-offset}. The default is 0, which tells @value{GDBN}
5021 to always print the symbolic form of an address if any symbol precedes it.
5023 @kindex show print max-symbolic-offset
5024 @item show print max-symbolic-offset
5025 Ask how large the maximum offset is that @value{GDBN} prints in a
5029 @cindex wild pointer, interpreting
5030 @cindex pointer, finding referent
5031 If you have a pointer and you are not sure where it points, try
5032 @samp{set print symbol-filename on}. Then you can determine the name
5033 and source file location of the variable where it points, using
5034 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
5035 For example, here @value{GDBN} shows that a variable @code{ptt} points
5036 at another variable @code{t}, defined in @file{hi2.c}:
5039 (@value{GDBP}) set print symbol-filename on
5040 (@value{GDBP}) p/a ptt
5041 $4 = 0xe008 <t in hi2.c>
5045 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
5046 does not show the symbol name and filename of the referent, even with
5047 the appropriate @code{set print} options turned on.
5050 Other settings control how different kinds of objects are printed:
5053 @kindex set print array
5054 @item set print array
5055 @itemx set print array on
5056 Pretty print arrays. This format is more convenient to read,
5057 but uses more space. The default is off.
5059 @item set print array off
5060 Return to compressed format for arrays.
5062 @kindex show print array
5063 @item show print array
5064 Show whether compressed or pretty format is selected for displaying
5067 @kindex set print elements
5068 @item set print elements @var{number-of-elements}
5069 Set a limit on how many elements of an array @value{GDBN} will print.
5070 If @value{GDBN} is printing a large array, it stops printing after it has
5071 printed the number of elements set by the @code{set print elements} command.
5072 This limit also applies to the display of strings.
5073 When @value{GDBN} starts, this limit is set to 200.
5074 Setting @var{number-of-elements} to zero means that the printing is unlimited.
5076 @kindex show print elements
5077 @item show print elements
5078 Display the number of elements of a large array that @value{GDBN} will print.
5079 If the number is 0, then the printing is unlimited.
5081 @kindex set print null-stop
5082 @item set print null-stop
5083 Cause @value{GDBN} to stop printing the characters of an array when the first
5084 @sc{null} is encountered. This is useful when large arrays actually
5085 contain only short strings.
5088 @kindex set print pretty
5089 @item set print pretty on
5090 Cause @value{GDBN} to print structures in an indented format with one member
5091 per line, like this:
5106 @item set print pretty off
5107 Cause @value{GDBN} to print structures in a compact format, like this:
5111 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
5112 meat = 0x54 "Pork"@}
5117 This is the default format.
5119 @kindex show print pretty
5120 @item show print pretty
5121 Show which format @value{GDBN} is using to print structures.
5123 @kindex set print sevenbit-strings
5124 @item set print sevenbit-strings on
5125 Print using only seven-bit characters; if this option is set,
5126 @value{GDBN} displays any eight-bit characters (in strings or
5127 character values) using the notation @code{\}@var{nnn}. This setting is
5128 best if you are working in English (@sc{ascii}) and you use the
5129 high-order bit of characters as a marker or ``meta'' bit.
5131 @item set print sevenbit-strings off
5132 Print full eight-bit characters. This allows the use of more
5133 international character sets, and is the default.
5135 @kindex show print sevenbit-strings
5136 @item show print sevenbit-strings
5137 Show whether or not @value{GDBN} is printing only seven-bit characters.
5139 @kindex set print union
5140 @item set print union on
5141 Tell @value{GDBN} to print unions which are contained in structures. This
5142 is the default setting.
5144 @item set print union off
5145 Tell @value{GDBN} not to print unions which are contained in structures.
5147 @kindex show print union
5148 @item show print union
5149 Ask @value{GDBN} whether or not it will print unions which are contained in
5152 For example, given the declarations
5155 typedef enum @{Tree, Bug@} Species;
5156 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5157 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5168 struct thing foo = @{Tree, @{Acorn@}@};
5172 with @code{set print union on} in effect @samp{p foo} would print
5175 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5179 and with @code{set print union off} in effect it would print
5182 $1 = @{it = Tree, form = @{...@}@}
5188 These settings are of interest when debugging C@t{++} programs:
5192 @kindex set print demangle
5193 @item set print demangle
5194 @itemx set print demangle on
5195 Print C@t{++} names in their source form rather than in the encoded
5196 (``mangled'') form passed to the assembler and linker for type-safe
5197 linkage. The default is on.
5199 @kindex show print demangle
5200 @item show print demangle
5201 Show whether C@t{++} names are printed in mangled or demangled form.
5203 @kindex set print asm-demangle
5204 @item set print asm-demangle
5205 @itemx set print asm-demangle on
5206 Print C@t{++} names in their source form rather than their mangled form, even
5207 in assembler code printouts such as instruction disassemblies.
5210 @kindex show print asm-demangle
5211 @item show print asm-demangle
5212 Show whether C@t{++} names in assembly listings are printed in mangled
5215 @kindex set demangle-style
5216 @cindex C@t{++} symbol decoding style
5217 @cindex symbol decoding style, C@t{++}
5218 @item set demangle-style @var{style}
5219 Choose among several encoding schemes used by different compilers to
5220 represent C@t{++} names. The choices for @var{style} are currently:
5224 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5227 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
5228 This is the default.
5231 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
5234 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
5237 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
5238 @strong{Warning:} this setting alone is not sufficient to allow
5239 debugging @code{cfront}-generated executables. @value{GDBN} would
5240 require further enhancement to permit that.
5243 If you omit @var{style}, you will see a list of possible formats.
5245 @kindex show demangle-style
5246 @item show demangle-style
5247 Display the encoding style currently in use for decoding C@t{++} symbols.
5249 @kindex set print object
5250 @item set print object
5251 @itemx set print object on
5252 When displaying a pointer to an object, identify the @emph{actual}
5253 (derived) type of the object rather than the @emph{declared} type, using
5254 the virtual function table.
5256 @item set print object off
5257 Display only the declared type of objects, without reference to the
5258 virtual function table. This is the default setting.
5260 @kindex show print object
5261 @item show print object
5262 Show whether actual, or declared, object types are displayed.
5264 @kindex set print static-members
5265 @item set print static-members
5266 @itemx set print static-members on
5267 Print static members when displaying a C@t{++} object. The default is on.
5269 @item set print static-members off
5270 Do not print static members when displaying a C@t{++} object.
5272 @kindex show print static-members
5273 @item show print static-members
5274 Show whether C@t{++} static members are printed, or not.
5276 @c These don't work with HP ANSI C++ yet.
5277 @kindex set print vtbl
5278 @item set print vtbl
5279 @itemx set print vtbl on
5280 Pretty print C@t{++} virtual function tables. The default is off.
5281 (The @code{vtbl} commands do not work on programs compiled with the HP
5282 ANSI C@t{++} compiler (@code{aCC}).)
5284 @item set print vtbl off
5285 Do not pretty print C@t{++} virtual function tables.
5287 @kindex show print vtbl
5288 @item show print vtbl
5289 Show whether C@t{++} virtual function tables are pretty printed, or not.
5293 @section Value history
5295 @cindex value history
5296 Values printed by the @code{print} command are saved in the @value{GDBN}
5297 @dfn{value history}. This allows you to refer to them in other expressions.
5298 Values are kept until the symbol table is re-read or discarded
5299 (for example with the @code{file} or @code{symbol-file} commands).
5300 When the symbol table changes, the value history is discarded,
5301 since the values may contain pointers back to the types defined in the
5306 @cindex history number
5307 The values printed are given @dfn{history numbers} by which you can
5308 refer to them. These are successive integers starting with one.
5309 @code{print} shows you the history number assigned to a value by
5310 printing @samp{$@var{num} = } before the value; here @var{num} is the
5313 To refer to any previous value, use @samp{$} followed by the value's
5314 history number. The way @code{print} labels its output is designed to
5315 remind you of this. Just @code{$} refers to the most recent value in
5316 the history, and @code{$$} refers to the value before that.
5317 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5318 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5319 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5321 For example, suppose you have just printed a pointer to a structure and
5322 want to see the contents of the structure. It suffices to type
5328 If you have a chain of structures where the component @code{next} points
5329 to the next one, you can print the contents of the next one with this:
5336 You can print successive links in the chain by repeating this
5337 command---which you can do by just typing @key{RET}.
5339 Note that the history records values, not expressions. If the value of
5340 @code{x} is 4 and you type these commands:
5348 then the value recorded in the value history by the @code{print} command
5349 remains 4 even though the value of @code{x} has changed.
5354 Print the last ten values in the value history, with their item numbers.
5355 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5356 values} does not change the history.
5358 @item show values @var{n}
5359 Print ten history values centered on history item number @var{n}.
5362 Print ten history values just after the values last printed. If no more
5363 values are available, @code{show values +} produces no display.
5366 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5367 same effect as @samp{show values +}.
5369 @node Convenience Vars
5370 @section Convenience variables
5372 @cindex convenience variables
5373 @value{GDBN} provides @dfn{convenience variables} that you can use within
5374 @value{GDBN} to hold on to a value and refer to it later. These variables
5375 exist entirely within @value{GDBN}; they are not part of your program, and
5376 setting a convenience variable has no direct effect on further execution
5377 of your program. That is why you can use them freely.
5379 Convenience variables are prefixed with @samp{$}. Any name preceded by
5380 @samp{$} can be used for a convenience variable, unless it is one of
5381 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
5382 (Value history references, in contrast, are @emph{numbers} preceded
5383 by @samp{$}. @xref{Value History, ,Value history}.)
5385 You can save a value in a convenience variable with an assignment
5386 expression, just as you would set a variable in your program.
5390 set $foo = *object_ptr
5394 would save in @code{$foo} the value contained in the object pointed to by
5397 Using a convenience variable for the first time creates it, but its
5398 value is @code{void} until you assign a new value. You can alter the
5399 value with another assignment at any time.
5401 Convenience variables have no fixed types. You can assign a convenience
5402 variable any type of value, including structures and arrays, even if
5403 that variable already has a value of a different type. The convenience
5404 variable, when used as an expression, has the type of its current value.
5407 @kindex show convenience
5408 @item show convenience
5409 Print a list of convenience variables used so far, and their values.
5410 Abbreviated @code{show conv}.
5413 One of the ways to use a convenience variable is as a counter to be
5414 incremented or a pointer to be advanced. For example, to print
5415 a field from successive elements of an array of structures:
5419 print bar[$i++]->contents
5423 Repeat that command by typing @key{RET}.
5425 Some convenience variables are created automatically by @value{GDBN} and given
5426 values likely to be useful.
5429 @vindex $_@r{, convenience variable}
5431 The variable @code{$_} is automatically set by the @code{x} command to
5432 the last address examined (@pxref{Memory, ,Examining memory}). Other
5433 commands which provide a default address for @code{x} to examine also
5434 set @code{$_} to that address; these commands include @code{info line}
5435 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5436 except when set by the @code{x} command, in which case it is a pointer
5437 to the type of @code{$__}.
5439 @vindex $__@r{, convenience variable}
5441 The variable @code{$__} is automatically set by the @code{x} command
5442 to the value found in the last address examined. Its type is chosen
5443 to match the format in which the data was printed.
5446 @vindex $_exitcode@r{, convenience variable}
5447 The variable @code{$_exitcode} is automatically set to the exit code when
5448 the program being debugged terminates.
5451 On HP-UX systems, if you refer to a function or variable name that
5452 begins with a dollar sign, @value{GDBN} searches for a user or system
5453 name first, before it searches for a convenience variable.
5459 You can refer to machine register contents, in expressions, as variables
5460 with names starting with @samp{$}. The names of registers are different
5461 for each machine; use @code{info registers} to see the names used on
5465 @kindex info registers
5466 @item info registers
5467 Print the names and values of all registers except floating-point
5468 registers (in the selected stack frame).
5470 @kindex info all-registers
5471 @cindex floating point registers
5472 @item info all-registers
5473 Print the names and values of all registers, including floating-point
5476 @item info registers @var{regname} @dots{}
5477 Print the @dfn{relativized} value of each specified register @var{regname}.
5478 As discussed in detail below, register values are normally relative to
5479 the selected stack frame. @var{regname} may be any register name valid on
5480 the machine you are using, with or without the initial @samp{$}.
5483 @value{GDBN} has four ``standard'' register names that are available (in
5484 expressions) on most machines---whenever they do not conflict with an
5485 architecture's canonical mnemonics for registers. The register names
5486 @code{$pc} and @code{$sp} are used for the program counter register and
5487 the stack pointer. @code{$fp} is used for a register that contains a
5488 pointer to the current stack frame, and @code{$ps} is used for a
5489 register that contains the processor status. For example,
5490 you could print the program counter in hex with
5497 or print the instruction to be executed next with
5504 or add four to the stack pointer@footnote{This is a way of removing
5505 one word from the stack, on machines where stacks grow downward in
5506 memory (most machines, nowadays). This assumes that the innermost
5507 stack frame is selected; setting @code{$sp} is not allowed when other
5508 stack frames are selected. To pop entire frames off the stack,
5509 regardless of machine architecture, use @code{return};
5510 see @ref{Returning, ,Returning from a function}.} with
5516 Whenever possible, these four standard register names are available on
5517 your machine even though the machine has different canonical mnemonics,
5518 so long as there is no conflict. The @code{info registers} command
5519 shows the canonical names. For example, on the SPARC, @code{info
5520 registers} displays the processor status register as @code{$psr} but you
5521 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
5522 is an alias for the @sc{eflags} register.
5524 @value{GDBN} always considers the contents of an ordinary register as an
5525 integer when the register is examined in this way. Some machines have
5526 special registers which can hold nothing but floating point; these
5527 registers are considered to have floating point values. There is no way
5528 to refer to the contents of an ordinary register as floating point value
5529 (although you can @emph{print} it as a floating point value with
5530 @samp{print/f $@var{regname}}).
5532 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5533 means that the data format in which the register contents are saved by
5534 the operating system is not the same one that your program normally
5535 sees. For example, the registers of the 68881 floating point
5536 coprocessor are always saved in ``extended'' (raw) format, but all C
5537 programs expect to work with ``double'' (virtual) format. In such
5538 cases, @value{GDBN} normally works with the virtual format only (the format
5539 that makes sense for your program), but the @code{info registers} command
5540 prints the data in both formats.
5542 Normally, register values are relative to the selected stack frame
5543 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5544 value that the register would contain if all stack frames farther in
5545 were exited and their saved registers restored. In order to see the
5546 true contents of hardware registers, you must select the innermost
5547 frame (with @samp{frame 0}).
5549 However, @value{GDBN} must deduce where registers are saved, from the machine
5550 code generated by your compiler. If some registers are not saved, or if
5551 @value{GDBN} is unable to locate the saved registers, the selected stack
5552 frame makes no difference.
5554 @node Floating Point Hardware
5555 @section Floating point hardware
5556 @cindex floating point
5558 Depending on the configuration, @value{GDBN} may be able to give
5559 you more information about the status of the floating point hardware.
5564 Display hardware-dependent information about the floating
5565 point unit. The exact contents and layout vary depending on the
5566 floating point chip. Currently, @samp{info float} is supported on
5567 the ARM and x86 machines.
5570 @node Memory Region Attributes
5571 @section Memory region attributes
5572 @cindex memory region attributes
5574 @dfn{Memory region attributes} allow you to describe special handling
5575 required by regions of your target's memory. @value{GDBN} uses attributes
5576 to determine whether to allow certain types of memory accesses; whether to
5577 use specific width accesses; and whether to cache target memory.
5579 Defined memory regions can be individually enabled and disabled. When a
5580 memory region is disabled, @value{GDBN} uses the default attributes when
5581 accessing memory in that region. Similarly, if no memory regions have
5582 been defined, @value{GDBN} uses the default attributes when accessing
5585 When a memory region is defined, it is given a number to identify it;
5586 to enable, disable, or remove a memory region, you specify that number.
5590 @item mem @var{address1} @var{address2} @var{attributes}@dots{}
5591 Define memory region bounded by @var{address1} and @var{address2}
5592 with attributes @var{attributes}@dots{}.
5595 @item delete mem @var{nums}@dots{}
5596 Remove memory regions @var{nums}@dots{}.
5599 @item disable mem @var{nums}@dots{}
5600 Disable memory regions @var{nums}@dots{}.
5601 A disabled memory region is not forgotten.
5602 It may be enabled again later.
5605 @item enable mem @var{nums}@dots{}
5606 Enable memory regions @var{nums}@dots{}.
5610 Print a table of all defined memory regions, with the following columns
5614 @item Memory Region Number
5615 @item Enabled or Disabled.
5616 Enabled memory regions are marked with @samp{y}.
5617 Disabled memory regions are marked with @samp{n}.
5620 The address defining the inclusive lower bound of the memory region.
5623 The address defining the exclusive upper bound of the memory region.
5626 The list of attributes set for this memory region.
5631 @subsection Attributes
5633 @subsubsection Memory Access Mode
5634 The access mode attributes set whether @value{GDBN} may make read or
5635 write accesses to a memory region.
5637 While these attributes prevent @value{GDBN} from performing invalid
5638 memory accesses, they do nothing to prevent the target system, I/O DMA,
5639 etc. from accessing memory.
5643 Memory is read only.
5645 Memory is write only.
5647 Memory is read/write. This is the default.
5650 @subsubsection Memory Access Size
5651 The acccess size attributes tells @value{GDBN} to use specific sized
5652 accesses in the memory region. Often memory mapped device registers
5653 require specific sized accesses. If no access size attribute is
5654 specified, @value{GDBN} may use accesses of any size.
5658 Use 8 bit memory accesses.
5660 Use 16 bit memory accesses.
5662 Use 32 bit memory accesses.
5664 Use 64 bit memory accesses.
5667 @c @subsubsection Hardware/Software Breakpoints
5668 @c The hardware/software breakpoint attributes set whether @value{GDBN}
5669 @c will use hardware or software breakpoints for the internal breakpoints
5670 @c used by the step, next, finish, until, etc. commands.
5674 @c Always use hardware breakpoints
5675 @c @item swbreak (default)
5678 @subsubsection Data Cache
5679 The data cache attributes set whether @value{GDBN} will cache target
5680 memory. While this generally improves performance by reducing debug
5681 protocol overhead, it can lead to incorrect results because @value{GDBN}
5682 does not know about volatile variables or memory mapped device
5687 Enable @value{GDBN} to cache target memory.
5689 Disable @value{GDBN} from caching target memory. This is the default.
5692 @c @subsubsection Memory Write Verification
5693 @c The memory write verification attributes set whether @value{GDBN}
5694 @c will re-reads data after each write to verify the write was successful.
5698 @c @item noverify (default)
5701 @node Dump/Restore Files
5702 @section Copy between memory and a file
5703 @cindex dump/restore files
5704 @cindex append data to a file
5705 @cindex dump data to a file
5706 @cindex restore data from a file
5711 The commands @code{dump}, @code{append}, and @code{restore} are used
5712 for copying data between target memory and a file. Data is written
5713 into a file using @code{dump} or @code{append}, and restored from a
5714 file into memory by using @code{restore}. Files may be binary, srec,
5715 intel hex, or tekhex (but only binary files can be appended).
5719 @kindex append binary
5720 @item dump binary memory @var{filename} @var{start_addr} @var{end_addr}
5721 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5722 raw binary format file @var{filename}.
5724 @item append binary memory @var{filename} @var{start_addr} @var{end_addr}
5725 Append contents of memory from @var{start_addr} to @var{end_addr} to
5726 raw binary format file @var{filename}.
5728 @item dump binary value @var{filename} @var{expression}
5729 Dump value of @var{expression} into raw binary format file @var{filename}.
5731 @item append binary memory @var{filename} @var{expression}
5732 Append value of @var{expression} to raw binary format file @var{filename}.
5735 @item dump ihex memory @var{filename} @var{start_addr} @var{end_addr}
5736 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5737 intel hex format file @var{filename}.
5739 @item dump ihex value @var{filename} @var{expression}
5740 Dump value of @var{expression} into intel hex format file @var{filename}.
5743 @item dump srec memory @var{filename} @var{start_addr} @var{end_addr}
5744 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5745 srec format file @var{filename}.
5747 @item dump srec value @var{filename} @var{expression}
5748 Dump value of @var{expression} into srec format file @var{filename}.
5751 @item dump tekhex memory @var{filename} @var{start_addr} @var{end_addr}
5752 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5753 tekhex format file @var{filename}.
5755 @item dump tekhex value @var{filename} @var{expression}
5756 Dump value of @var{expression} into tekhex format file @var{filename}.
5758 @item restore @var{filename} @var{[binary]} @var{bias} @var{start} @var{end}
5759 Restore the contents of file @var{filename} into memory. The @code{restore}
5760 command can automatically recognize any known bfd file format, except for
5761 raw binary. To restore a raw binary file you must use the optional argument
5762 @var{binary} after the filename.
5764 If @var{bias} is non-zero, its value will be added to the addresses
5765 contained in the file. Binary files always start at address zero, so
5766 they will be restored at address @var{bias}. Other bfd files have
5767 a built-in location; they will be restored at offset @var{bias}
5770 If @var{start} and/or @var{end} are non-zero, then only data between
5771 file offset @var{start} and file offset @var{end} will be restored.
5772 These offsets are relative to the addresses in the file, before
5773 the @var{bias} argument is applied.
5778 @chapter Tracepoints
5779 @c This chapter is based on the documentation written by Michael
5780 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
5783 In some applications, it is not feasible for the debugger to interrupt
5784 the program's execution long enough for the developer to learn
5785 anything helpful about its behavior. If the program's correctness
5786 depends on its real-time behavior, delays introduced by a debugger
5787 might cause the program to change its behavior drastically, or perhaps
5788 fail, even when the code itself is correct. It is useful to be able
5789 to observe the program's behavior without interrupting it.
5791 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
5792 specify locations in the program, called @dfn{tracepoints}, and
5793 arbitrary expressions to evaluate when those tracepoints are reached.
5794 Later, using the @code{tfind} command, you can examine the values
5795 those expressions had when the program hit the tracepoints. The
5796 expressions may also denote objects in memory---structures or arrays,
5797 for example---whose values @value{GDBN} should record; while visiting
5798 a particular tracepoint, you may inspect those objects as if they were
5799 in memory at that moment. However, because @value{GDBN} records these
5800 values without interacting with you, it can do so quickly and
5801 unobtrusively, hopefully not disturbing the program's behavior.
5803 The tracepoint facility is currently available only for remote
5804 targets. @xref{Targets}. In addition, your remote target must know how
5805 to collect trace data. This functionality is implemented in the remote
5806 stub; however, none of the stubs distributed with @value{GDBN} support
5807 tracepoints as of this writing.
5809 This chapter describes the tracepoint commands and features.
5813 * Analyze Collected Data::
5814 * Tracepoint Variables::
5817 @node Set Tracepoints
5818 @section Commands to Set Tracepoints
5820 Before running such a @dfn{trace experiment}, an arbitrary number of
5821 tracepoints can be set. Like a breakpoint (@pxref{Set Breaks}), a
5822 tracepoint has a number assigned to it by @value{GDBN}. Like with
5823 breakpoints, tracepoint numbers are successive integers starting from
5824 one. Many of the commands associated with tracepoints take the
5825 tracepoint number as their argument, to identify which tracepoint to
5828 For each tracepoint, you can specify, in advance, some arbitrary set
5829 of data that you want the target to collect in the trace buffer when
5830 it hits that tracepoint. The collected data can include registers,
5831 local variables, or global data. Later, you can use @value{GDBN}
5832 commands to examine the values these data had at the time the
5835 This section describes commands to set tracepoints and associated
5836 conditions and actions.
5839 * Create and Delete Tracepoints::
5840 * Enable and Disable Tracepoints::
5841 * Tracepoint Passcounts::
5842 * Tracepoint Actions::
5843 * Listing Tracepoints::
5844 * Starting and Stopping Trace Experiment::
5847 @node Create and Delete Tracepoints
5848 @subsection Create and Delete Tracepoints
5851 @cindex set tracepoint
5854 The @code{trace} command is very similar to the @code{break} command.
5855 Its argument can be a source line, a function name, or an address in
5856 the target program. @xref{Set Breaks}. The @code{trace} command
5857 defines a tracepoint, which is a point in the target program where the
5858 debugger will briefly stop, collect some data, and then allow the
5859 program to continue. Setting a tracepoint or changing its commands
5860 doesn't take effect until the next @code{tstart} command; thus, you
5861 cannot change the tracepoint attributes once a trace experiment is
5864 Here are some examples of using the @code{trace} command:
5867 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
5869 (@value{GDBP}) @b{trace +2} // 2 lines forward
5871 (@value{GDBP}) @b{trace my_function} // first source line of function
5873 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
5875 (@value{GDBP}) @b{trace *0x2117c4} // an address
5879 You can abbreviate @code{trace} as @code{tr}.
5882 @cindex last tracepoint number
5883 @cindex recent tracepoint number
5884 @cindex tracepoint number
5885 The convenience variable @code{$tpnum} records the tracepoint number
5886 of the most recently set tracepoint.
5888 @kindex delete tracepoint
5889 @cindex tracepoint deletion
5890 @item delete tracepoint @r{[}@var{num}@r{]}
5891 Permanently delete one or more tracepoints. With no argument, the
5892 default is to delete all tracepoints.
5897 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
5899 (@value{GDBP}) @b{delete trace} // remove all tracepoints
5903 You can abbreviate this command as @code{del tr}.
5906 @node Enable and Disable Tracepoints
5907 @subsection Enable and Disable Tracepoints
5910 @kindex disable tracepoint
5911 @item disable tracepoint @r{[}@var{num}@r{]}
5912 Disable tracepoint @var{num}, or all tracepoints if no argument
5913 @var{num} is given. A disabled tracepoint will have no effect during
5914 the next trace experiment, but it is not forgotten. You can re-enable
5915 a disabled tracepoint using the @code{enable tracepoint} command.
5917 @kindex enable tracepoint
5918 @item enable tracepoint @r{[}@var{num}@r{]}
5919 Enable tracepoint @var{num}, or all tracepoints. The enabled
5920 tracepoints will become effective the next time a trace experiment is
5924 @node Tracepoint Passcounts
5925 @subsection Tracepoint Passcounts
5929 @cindex tracepoint pass count
5930 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
5931 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
5932 automatically stop a trace experiment. If a tracepoint's passcount is
5933 @var{n}, then the trace experiment will be automatically stopped on
5934 the @var{n}'th time that tracepoint is hit. If the tracepoint number
5935 @var{num} is not specified, the @code{passcount} command sets the
5936 passcount of the most recently defined tracepoint. If no passcount is
5937 given, the trace experiment will run until stopped explicitly by the
5943 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of
5944 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// tracepoint 2}
5946 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
5947 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// most recently defined tracepoint.}
5948 (@value{GDBP}) @b{trace foo}
5949 (@value{GDBP}) @b{pass 3}
5950 (@value{GDBP}) @b{trace bar}
5951 (@value{GDBP}) @b{pass 2}
5952 (@value{GDBP}) @b{trace baz}
5953 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
5954 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// executed 3 times OR when bar has}
5955 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// been executed 2 times}
5956 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// OR when baz has been executed 1 time.}
5960 @node Tracepoint Actions
5961 @subsection Tracepoint Action Lists
5965 @cindex tracepoint actions
5966 @item actions @r{[}@var{num}@r{]}
5967 This command will prompt for a list of actions to be taken when the
5968 tracepoint is hit. If the tracepoint number @var{num} is not
5969 specified, this command sets the actions for the one that was most
5970 recently defined (so that you can define a tracepoint and then say
5971 @code{actions} without bothering about its number). You specify the
5972 actions themselves on the following lines, one action at a time, and
5973 terminate the actions list with a line containing just @code{end}. So
5974 far, the only defined actions are @code{collect} and
5975 @code{while-stepping}.
5977 @cindex remove actions from a tracepoint
5978 To remove all actions from a tracepoint, type @samp{actions @var{num}}
5979 and follow it immediately with @samp{end}.
5982 (@value{GDBP}) @b{collect @var{data}} // collect some data
5984 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times, collect data
5986 (@value{GDBP}) @b{end} // signals the end of actions.
5989 In the following example, the action list begins with @code{collect}
5990 commands indicating the things to be collected when the tracepoint is
5991 hit. Then, in order to single-step and collect additional data
5992 following the tracepoint, a @code{while-stepping} command is used,
5993 followed by the list of things to be collected while stepping. The
5994 @code{while-stepping} command is terminated by its own separate
5995 @code{end} command. Lastly, the action list is terminated by an
5999 (@value{GDBP}) @b{trace foo}
6000 (@value{GDBP}) @b{actions}
6001 Enter actions for tracepoint 1, one per line:
6010 @kindex collect @r{(tracepoints)}
6011 @item collect @var{expr1}, @var{expr2}, @dots{}
6012 Collect values of the given expressions when the tracepoint is hit.
6013 This command accepts a comma-separated list of any valid expressions.
6014 In addition to global, static, or local variables, the following
6015 special arguments are supported:
6019 collect all registers
6022 collect all function arguments
6025 collect all local variables.
6028 You can give several consecutive @code{collect} commands, each one
6029 with a single argument, or one @code{collect} command with several
6030 arguments separated by commas: the effect is the same.
6032 The command @code{info scope} (@pxref{Symbols, info scope}) is
6033 particularly useful for figuring out what data to collect.
6035 @kindex while-stepping @r{(tracepoints)}
6036 @item while-stepping @var{n}
6037 Perform @var{n} single-step traces after the tracepoint, collecting
6038 new data at each step. The @code{while-stepping} command is
6039 followed by the list of what to collect while stepping (followed by
6040 its own @code{end} command):
6044 > collect $regs, myglobal
6050 You may abbreviate @code{while-stepping} as @code{ws} or
6054 @node Listing Tracepoints
6055 @subsection Listing Tracepoints
6058 @kindex info tracepoints
6059 @cindex information about tracepoints
6060 @item info tracepoints @r{[}@var{num}@r{]}
6061 Display information about the tracepoint @var{num}. If you don't specify
6062 a tracepoint number, displays information about all the tracepoints
6063 defined so far. For each tracepoint, the following information is
6070 whether it is enabled or disabled
6074 its passcount as given by the @code{passcount @var{n}} command
6076 its step count as given by the @code{while-stepping @var{n}} command
6078 where in the source files is the tracepoint set
6080 its action list as given by the @code{actions} command
6084 (@value{GDBP}) @b{info trace}
6085 Num Enb Address PassC StepC What
6086 1 y 0x002117c4 0 0 <gdb_asm>
6087 2 y 0x0020dc64 0 0 in g_test at g_test.c:1375
6088 3 y 0x0020b1f4 0 0 in get_data at ../foo.c:41
6093 This command can be abbreviated @code{info tp}.
6096 @node Starting and Stopping Trace Experiment
6097 @subsection Starting and Stopping Trace Experiment
6101 @cindex start a new trace experiment
6102 @cindex collected data discarded
6104 This command takes no arguments. It starts the trace experiment, and
6105 begins collecting data. This has the side effect of discarding all
6106 the data collected in the trace buffer during the previous trace
6110 @cindex stop a running trace experiment
6112 This command takes no arguments. It ends the trace experiment, and
6113 stops collecting data.
6115 @strong{Note:} a trace experiment and data collection may stop
6116 automatically if any tracepoint's passcount is reached
6117 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
6120 @cindex status of trace data collection
6121 @cindex trace experiment, status of
6123 This command displays the status of the current trace data
6127 Here is an example of the commands we described so far:
6130 (@value{GDBP}) @b{trace gdb_c_test}
6131 (@value{GDBP}) @b{actions}
6132 Enter actions for tracepoint #1, one per line.
6133 > collect $regs,$locals,$args
6138 (@value{GDBP}) @b{tstart}
6139 [time passes @dots{}]
6140 (@value{GDBP}) @b{tstop}
6144 @node Analyze Collected Data
6145 @section Using the collected data
6147 After the tracepoint experiment ends, you use @value{GDBN} commands
6148 for examining the trace data. The basic idea is that each tracepoint
6149 collects a trace @dfn{snapshot} every time it is hit and another
6150 snapshot every time it single-steps. All these snapshots are
6151 consecutively numbered from zero and go into a buffer, and you can
6152 examine them later. The way you examine them is to @dfn{focus} on a
6153 specific trace snapshot. When the remote stub is focused on a trace
6154 snapshot, it will respond to all @value{GDBN} requests for memory and
6155 registers by reading from the buffer which belongs to that snapshot,
6156 rather than from @emph{real} memory or registers of the program being
6157 debugged. This means that @strong{all} @value{GDBN} commands
6158 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
6159 behave as if we were currently debugging the program state as it was
6160 when the tracepoint occurred. Any requests for data that are not in
6161 the buffer will fail.
6164 * tfind:: How to select a trace snapshot
6165 * tdump:: How to display all data for a snapshot
6166 * save-tracepoints:: How to save tracepoints for a future run
6170 @subsection @code{tfind @var{n}}
6173 @cindex select trace snapshot
6174 @cindex find trace snapshot
6175 The basic command for selecting a trace snapshot from the buffer is
6176 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
6177 counting from zero. If no argument @var{n} is given, the next
6178 snapshot is selected.
6180 Here are the various forms of using the @code{tfind} command.
6184 Find the first snapshot in the buffer. This is a synonym for
6185 @code{tfind 0} (since 0 is the number of the first snapshot).
6188 Stop debugging trace snapshots, resume @emph{live} debugging.
6191 Same as @samp{tfind none}.
6194 No argument means find the next trace snapshot.
6197 Find the previous trace snapshot before the current one. This permits
6198 retracing earlier steps.
6200 @item tfind tracepoint @var{num}
6201 Find the next snapshot associated with tracepoint @var{num}. Search
6202 proceeds forward from the last examined trace snapshot. If no
6203 argument @var{num} is given, it means find the next snapshot collected
6204 for the same tracepoint as the current snapshot.
6206 @item tfind pc @var{addr}
6207 Find the next snapshot associated with the value @var{addr} of the
6208 program counter. Search proceeds forward from the last examined trace
6209 snapshot. If no argument @var{addr} is given, it means find the next
6210 snapshot with the same value of PC as the current snapshot.
6212 @item tfind outside @var{addr1}, @var{addr2}
6213 Find the next snapshot whose PC is outside the given range of
6216 @item tfind range @var{addr1}, @var{addr2}
6217 Find the next snapshot whose PC is between @var{addr1} and
6218 @var{addr2}. @c FIXME: Is the range inclusive or exclusive?
6220 @item tfind line @r{[}@var{file}:@r{]}@var{n}
6221 Find the next snapshot associated with the source line @var{n}. If
6222 the optional argument @var{file} is given, refer to line @var{n} in
6223 that source file. Search proceeds forward from the last examined
6224 trace snapshot. If no argument @var{n} is given, it means find the
6225 next line other than the one currently being examined; thus saying
6226 @code{tfind line} repeatedly can appear to have the same effect as
6227 stepping from line to line in a @emph{live} debugging session.
6230 The default arguments for the @code{tfind} commands are specifically
6231 designed to make it easy to scan through the trace buffer. For
6232 instance, @code{tfind} with no argument selects the next trace
6233 snapshot, and @code{tfind -} with no argument selects the previous
6234 trace snapshot. So, by giving one @code{tfind} command, and then
6235 simply hitting @key{RET} repeatedly you can examine all the trace
6236 snapshots in order. Or, by saying @code{tfind -} and then hitting
6237 @key{RET} repeatedly you can examine the snapshots in reverse order.
6238 The @code{tfind line} command with no argument selects the snapshot
6239 for the next source line executed. The @code{tfind pc} command with
6240 no argument selects the next snapshot with the same program counter
6241 (PC) as the current frame. The @code{tfind tracepoint} command with
6242 no argument selects the next trace snapshot collected by the same
6243 tracepoint as the current one.
6245 In addition to letting you scan through the trace buffer manually,
6246 these commands make it easy to construct @value{GDBN} scripts that
6247 scan through the trace buffer and print out whatever collected data
6248 you are interested in. Thus, if we want to examine the PC, FP, and SP
6249 registers from each trace frame in the buffer, we can say this:
6252 (@value{GDBP}) @b{tfind start}
6253 (@value{GDBP}) @b{while ($trace_frame != -1)}
6254 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
6255 $trace_frame, $pc, $sp, $fp
6259 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
6260 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
6261 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
6262 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
6263 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
6264 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
6265 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
6266 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
6267 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
6268 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
6269 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
6272 Or, if we want to examine the variable @code{X} at each source line in
6276 (@value{GDBP}) @b{tfind start}
6277 (@value{GDBP}) @b{while ($trace_frame != -1)}
6278 > printf "Frame %d, X == %d\n", $trace_frame, X
6288 @subsection @code{tdump}
6290 @cindex dump all data collected at tracepoint
6291 @cindex tracepoint data, display
6293 This command takes no arguments. It prints all the data collected at
6294 the current trace snapshot.
6297 (@value{GDBP}) @b{trace 444}
6298 (@value{GDBP}) @b{actions}
6299 Enter actions for tracepoint #2, one per line:
6300 > collect $regs, $locals, $args, gdb_long_test
6303 (@value{GDBP}) @b{tstart}
6305 (@value{GDBP}) @b{tfind line 444}
6306 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
6308 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
6310 (@value{GDBP}) @b{tdump}
6311 Data collected at tracepoint 2, trace frame 1:
6312 d0 0xc4aa0085 -995491707
6316 d4 0x71aea3d 119204413
6321 a1 0x3000668 50333288
6324 a4 0x3000698 50333336
6326 fp 0x30bf3c 0x30bf3c
6327 sp 0x30bf34 0x30bf34
6329 pc 0x20b2c8 0x20b2c8
6333 p = 0x20e5b4 "gdb-test"
6340 gdb_long_test = 17 '\021'
6345 @node save-tracepoints
6346 @subsection @code{save-tracepoints @var{filename}}
6347 @kindex save-tracepoints
6348 @cindex save tracepoints for future sessions
6350 This command saves all current tracepoint definitions together with
6351 their actions and passcounts, into a file @file{@var{filename}}
6352 suitable for use in a later debugging session. To read the saved
6353 tracepoint definitions, use the @code{source} command (@pxref{Command
6356 @node Tracepoint Variables
6357 @section Convenience Variables for Tracepoints
6358 @cindex tracepoint variables
6359 @cindex convenience variables for tracepoints
6362 @vindex $trace_frame
6363 @item (int) $trace_frame
6364 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
6365 snapshot is selected.
6368 @item (int) $tracepoint
6369 The tracepoint for the current trace snapshot.
6372 @item (int) $trace_line
6373 The line number for the current trace snapshot.
6376 @item (char []) $trace_file
6377 The source file for the current trace snapshot.
6380 @item (char []) $trace_func
6381 The name of the function containing @code{$tracepoint}.
6384 Note: @code{$trace_file} is not suitable for use in @code{printf},
6385 use @code{output} instead.
6387 Here's a simple example of using these convenience variables for
6388 stepping through all the trace snapshots and printing some of their
6392 (@value{GDBP}) @b{tfind start}
6394 (@value{GDBP}) @b{while $trace_frame != -1}
6395 > output $trace_file
6396 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
6402 @chapter Debugging Programs That Use Overlays
6405 If your program is too large to fit completely in your target system's
6406 memory, you can sometimes use @dfn{overlays} to work around this
6407 problem. @value{GDBN} provides some support for debugging programs that
6411 * How Overlays Work:: A general explanation of overlays.
6412 * Overlay Commands:: Managing overlays in @value{GDBN}.
6413 * Automatic Overlay Debugging:: @value{GDBN} can find out which overlays are
6414 mapped by asking the inferior.
6415 * Overlay Sample Program:: A sample program using overlays.
6418 @node How Overlays Work
6419 @section How Overlays Work
6420 @cindex mapped overlays
6421 @cindex unmapped overlays
6422 @cindex load address, overlay's
6423 @cindex mapped address
6424 @cindex overlay area
6426 Suppose you have a computer whose instruction address space is only 64
6427 kilobytes long, but which has much more memory which can be accessed by
6428 other means: special instructions, segment registers, or memory
6429 management hardware, for example. Suppose further that you want to
6430 adapt a program which is larger than 64 kilobytes to run on this system.
6432 One solution is to identify modules of your program which are relatively
6433 independent, and need not call each other directly; call these modules
6434 @dfn{overlays}. Separate the overlays from the main program, and place
6435 their machine code in the larger memory. Place your main program in
6436 instruction memory, but leave at least enough space there to hold the
6437 largest overlay as well.
6439 Now, to call a function located in an overlay, you must first copy that
6440 overlay's machine code from the large memory into the space set aside
6441 for it in the instruction memory, and then jump to its entry point
6444 @c NB: In the below the mapped area's size is greater or equal to the
6445 @c size of all overlays. This is intentional to remind the developer
6446 @c that overlays don't necessarily need to be the same size.
6450 Data Instruction Larger
6451 Address Space Address Space Address Space
6452 +-----------+ +-----------+ +-----------+
6454 +-----------+ +-----------+ +-----------+<-- overlay 1
6455 | program | | main | .----| overlay 1 | load address
6456 | variables | | program | | +-----------+
6457 | and heap | | | | | |
6458 +-----------+ | | | +-----------+<-- overlay 2
6459 | | +-----------+ | | | load address
6460 +-----------+ | | | .-| overlay 2 |
6462 mapped --->+-----------+ | | +-----------+
6464 | overlay | <-' | | |
6465 | area | <---' +-----------+<-- overlay 3
6466 | | <---. | | load address
6467 +-----------+ `--| overlay 3 |
6474 @anchor{A code overlay}A code overlay
6478 The diagram (@pxref{A code overlay}) shows a system with separate data
6479 and instruction address spaces. To map an overlay, the program copies
6480 its code from the larger address space to the instruction address space.
6481 Since the overlays shown here all use the same mapped address, only one
6482 may be mapped at a time. For a system with a single address space for
6483 data and instructions, the diagram would be similar, except that the
6484 program variables and heap would share an address space with the main
6485 program and the overlay area.
6487 An overlay loaded into instruction memory and ready for use is called a
6488 @dfn{mapped} overlay; its @dfn{mapped address} is its address in the
6489 instruction memory. An overlay not present (or only partially present)
6490 in instruction memory is called @dfn{unmapped}; its @dfn{load address}
6491 is its address in the larger memory. The mapped address is also called
6492 the @dfn{virtual memory address}, or @dfn{VMA}; the load address is also
6493 called the @dfn{load memory address}, or @dfn{LMA}.
6495 Unfortunately, overlays are not a completely transparent way to adapt a
6496 program to limited instruction memory. They introduce a new set of
6497 global constraints you must keep in mind as you design your program:
6502 Before calling or returning to a function in an overlay, your program
6503 must make sure that overlay is actually mapped. Otherwise, the call or
6504 return will transfer control to the right address, but in the wrong
6505 overlay, and your program will probably crash.
6508 If the process of mapping an overlay is expensive on your system, you
6509 will need to choose your overlays carefully to minimize their effect on
6510 your program's performance.
6513 The executable file you load onto your system must contain each
6514 overlay's instructions, appearing at the overlay's load address, not its
6515 mapped address. However, each overlay's instructions must be relocated
6516 and its symbols defined as if the overlay were at its mapped address.
6517 You can use GNU linker scripts to specify different load and relocation
6518 addresses for pieces of your program; see @ref{Overlay Description,,,
6519 ld.info, Using ld: the GNU linker}.
6522 The procedure for loading executable files onto your system must be able
6523 to load their contents into the larger address space as well as the
6524 instruction and data spaces.
6528 The overlay system described above is rather simple, and could be
6529 improved in many ways:
6534 If your system has suitable bank switch registers or memory management
6535 hardware, you could use those facilities to make an overlay's load area
6536 contents simply appear at their mapped address in instruction space.
6537 This would probably be faster than copying the overlay to its mapped
6538 area in the usual way.
6541 If your overlays are small enough, you could set aside more than one
6542 overlay area, and have more than one overlay mapped at a time.
6545 You can use overlays to manage data, as well as instructions. In
6546 general, data overlays are even less transparent to your design than
6547 code overlays: whereas code overlays only require care when you call or
6548 return to functions, data overlays require care every time you access
6549 the data. Also, if you change the contents of a data overlay, you
6550 must copy its contents back out to its load address before you can copy a
6551 different data overlay into the same mapped area.
6556 @node Overlay Commands
6557 @section Overlay Commands
6559 To use @value{GDBN}'s overlay support, each overlay in your program must
6560 correspond to a separate section of the executable file. The section's
6561 virtual memory address and load memory address must be the overlay's
6562 mapped and load addresses. Identifying overlays with sections allows
6563 @value{GDBN} to determine the appropriate address of a function or
6564 variable, depending on whether the overlay is mapped or not.
6566 @value{GDBN}'s overlay commands all start with the word @code{overlay};
6567 you can abbreviate this as @code{ov} or @code{ovly}. The commands are:
6572 Disable @value{GDBN}'s overlay support. When overlay support is
6573 disabled, @value{GDBN} assumes that all functions and variables are
6574 always present at their mapped addresses. By default, @value{GDBN}'s
6575 overlay support is disabled.
6577 @item overlay manual
6578 @kindex overlay manual
6579 @cindex manual overlay debugging
6580 Enable @dfn{manual} overlay debugging. In this mode, @value{GDBN}
6581 relies on you to tell it which overlays are mapped, and which are not,
6582 using the @code{overlay map-overlay} and @code{overlay unmap-overlay}
6583 commands described below.
6585 @item overlay map-overlay @var{overlay}
6586 @itemx overlay map @var{overlay}
6587 @kindex overlay map-overlay
6588 @cindex map an overlay
6589 Tell @value{GDBN} that @var{overlay} is now mapped; @var{overlay} must
6590 be the name of the object file section containing the overlay. When an
6591 overlay is mapped, @value{GDBN} assumes it can find the overlay's
6592 functions and variables at their mapped addresses. @value{GDBN} assumes
6593 that any other overlays whose mapped ranges overlap that of
6594 @var{overlay} are now unmapped.
6596 @item overlay unmap-overlay @var{overlay}
6597 @itemx overlay unmap @var{overlay}
6598 @kindex overlay unmap-overlay
6599 @cindex unmap an overlay
6600 Tell @value{GDBN} that @var{overlay} is no longer mapped; @var{overlay}
6601 must be the name of the object file section containing the overlay.
6602 When an overlay is unmapped, @value{GDBN} assumes it can find the
6603 overlay's functions and variables at their load addresses.
6606 @kindex overlay auto
6607 Enable @dfn{automatic} overlay debugging. In this mode, @value{GDBN}
6608 consults a data structure the overlay manager maintains in the inferior
6609 to see which overlays are mapped. For details, see @ref{Automatic
6612 @item overlay load-target
6614 @kindex overlay load-target
6615 @cindex reloading the overlay table
6616 Re-read the overlay table from the inferior. Normally, @value{GDBN}
6617 re-reads the table @value{GDBN} automatically each time the inferior
6618 stops, so this command should only be necessary if you have changed the
6619 overlay mapping yourself using @value{GDBN}. This command is only
6620 useful when using automatic overlay debugging.
6622 @item overlay list-overlays
6624 @cindex listing mapped overlays
6625 Display a list of the overlays currently mapped, along with their mapped
6626 addresses, load addresses, and sizes.
6630 Normally, when @value{GDBN} prints a code address, it includes the name
6631 of the function the address falls in:
6635 $3 = @{int ()@} 0x11a0 <main>
6638 When overlay debugging is enabled, @value{GDBN} recognizes code in
6639 unmapped overlays, and prints the names of unmapped functions with
6640 asterisks around them. For example, if @code{foo} is a function in an
6641 unmapped overlay, @value{GDBN} prints it this way:
6645 No sections are mapped.
6647 $5 = @{int (int)@} 0x100000 <*foo*>
6650 When @code{foo}'s overlay is mapped, @value{GDBN} prints the function's
6655 Section .ov.foo.text, loaded at 0x100000 - 0x100034,
6656 mapped at 0x1016 - 0x104a
6658 $6 = @{int (int)@} 0x1016 <foo>
6661 When overlay debugging is enabled, @value{GDBN} can find the correct
6662 address for functions and variables in an overlay, whether or not the
6663 overlay is mapped. This allows most @value{GDBN} commands, like
6664 @code{break} and @code{disassemble}, to work normally, even on unmapped
6665 code. However, @value{GDBN}'s breakpoint support has some limitations:
6669 @cindex breakpoints in overlays
6670 @cindex overlays, setting breakpoints in
6671 You can set breakpoints in functions in unmapped overlays, as long as
6672 @value{GDBN} can write to the overlay at its load address.
6674 @value{GDBN} can not set hardware or simulator-based breakpoints in
6675 unmapped overlays. However, if you set a breakpoint at the end of your
6676 overlay manager (and tell @value{GDBN} which overlays are now mapped, if
6677 you are using manual overlay management), @value{GDBN} will re-set its
6678 breakpoints properly.
6682 @node Automatic Overlay Debugging
6683 @section Automatic Overlay Debugging
6684 @cindex automatic overlay debugging
6686 @value{GDBN} can automatically track which overlays are mapped and which
6687 are not, given some simple co-operation from the overlay manager in the
6688 inferior. If you enable automatic overlay debugging with the
6689 @code{overlay auto} command (@pxref{Overlay Commands}), @value{GDBN}
6690 looks in the inferior's memory for certain variables describing the
6691 current state of the overlays.
6693 Here are the variables your overlay manager must define to support
6694 @value{GDBN}'s automatic overlay debugging:
6698 @item @code{_ovly_table}:
6699 This variable must be an array of the following structures:
6704 /* The overlay's mapped address. */
6707 /* The size of the overlay, in bytes. */
6710 /* The overlay's load address. */
6713 /* Non-zero if the overlay is currently mapped;
6715 unsigned long mapped;
6719 @item @code{_novlys}:
6720 This variable must be a four-byte signed integer, holding the total
6721 number of elements in @code{_ovly_table}.
6725 To decide whether a particular overlay is mapped or not, @value{GDBN}
6726 looks for an entry in @w{@code{_ovly_table}} whose @code{vma} and
6727 @code{lma} members equal the VMA and LMA of the overlay's section in the
6728 executable file. When @value{GDBN} finds a matching entry, it consults
6729 the entry's @code{mapped} member to determine whether the overlay is
6732 In addition, your overlay manager may define a function called
6733 @code{_ovly_debug_event}. If this function is defined, @value{GDBN}
6734 will silently set a breakpoint there. If the overlay manager then
6735 calls this function whenever it has changed the overlay table, this
6736 will enable @value{GDBN} to accurately keep track of which overlays
6737 are in program memory, and update any breakpoints that may be set
6738 in overlays. This will allow breakpoints to work even if the
6739 overlays are kept in ROM or other non-writable memory while they
6740 are not being executed.
6742 @node Overlay Sample Program
6743 @section Overlay Sample Program
6744 @cindex overlay example program
6746 When linking a program which uses overlays, you must place the overlays
6747 at their load addresses, while relocating them to run at their mapped
6748 addresses. To do this, you must write a linker script (@pxref{Overlay
6749 Description,,, ld.info, Using ld: the GNU linker}). Unfortunately,
6750 since linker scripts are specific to a particular host system, target
6751 architecture, and target memory layout, this manual cannot provide
6752 portable sample code demonstrating @value{GDBN}'s overlay support.
6754 However, the @value{GDBN} source distribution does contain an overlaid
6755 program, with linker scripts for a few systems, as part of its test
6756 suite. The program consists of the following files from
6757 @file{gdb/testsuite/gdb.base}:
6761 The main program file.
6763 A simple overlay manager, used by @file{overlays.c}.
6768 Overlay modules, loaded and used by @file{overlays.c}.
6771 Linker scripts for linking the test program on the @code{d10v-elf}
6772 and @code{m32r-elf} targets.
6775 You can build the test program using the @code{d10v-elf} GCC
6776 cross-compiler like this:
6779 $ d10v-elf-gcc -g -c overlays.c
6780 $ d10v-elf-gcc -g -c ovlymgr.c
6781 $ d10v-elf-gcc -g -c foo.c
6782 $ d10v-elf-gcc -g -c bar.c
6783 $ d10v-elf-gcc -g -c baz.c
6784 $ d10v-elf-gcc -g -c grbx.c
6785 $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
6786 baz.o grbx.o -Wl,-Td10v.ld -o overlays
6789 The build process is identical for any other architecture, except that
6790 you must substitute the appropriate compiler and linker script for the
6791 target system for @code{d10v-elf-gcc} and @code{d10v.ld}.
6795 @chapter Using @value{GDBN} with Different Languages
6798 Although programming languages generally have common aspects, they are
6799 rarely expressed in the same manner. For instance, in ANSI C,
6800 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
6801 Modula-2, it is accomplished by @code{p^}. Values can also be
6802 represented (and displayed) differently. Hex numbers in C appear as
6803 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
6805 @cindex working language
6806 Language-specific information is built into @value{GDBN} for some languages,
6807 allowing you to express operations like the above in your program's
6808 native language, and allowing @value{GDBN} to output values in a manner
6809 consistent with the syntax of your program's native language. The
6810 language you use to build expressions is called the @dfn{working
6814 * Setting:: Switching between source languages
6815 * Show:: Displaying the language
6816 * Checks:: Type and range checks
6817 * Support:: Supported languages
6821 @section Switching between source languages
6823 There are two ways to control the working language---either have @value{GDBN}
6824 set it automatically, or select it manually yourself. You can use the
6825 @code{set language} command for either purpose. On startup, @value{GDBN}
6826 defaults to setting the language automatically. The working language is
6827 used to determine how expressions you type are interpreted, how values
6830 In addition to the working language, every source file that
6831 @value{GDBN} knows about has its own working language. For some object
6832 file formats, the compiler might indicate which language a particular
6833 source file is in. However, most of the time @value{GDBN} infers the
6834 language from the name of the file. The language of a source file
6835 controls whether C@t{++} names are demangled---this way @code{backtrace} can
6836 show each frame appropriately for its own language. There is no way to
6837 set the language of a source file from within @value{GDBN}, but you can
6838 set the language associated with a filename extension. @xref{Show, ,
6839 Displaying the language}.
6841 This is most commonly a problem when you use a program, such
6842 as @code{cfront} or @code{f2c}, that generates C but is written in
6843 another language. In that case, make the
6844 program use @code{#line} directives in its C output; that way
6845 @value{GDBN} will know the correct language of the source code of the original
6846 program, and will display that source code, not the generated C code.
6849 * Filenames:: Filename extensions and languages.
6850 * Manually:: Setting the working language manually
6851 * Automatically:: Having @value{GDBN} infer the source language
6855 @subsection List of filename extensions and languages
6857 If a source file name ends in one of the following extensions, then
6858 @value{GDBN} infers that its language is the one indicated.
6883 Modula-2 source file
6887 Assembler source file. This actually behaves almost like C, but
6888 @value{GDBN} does not skip over function prologues when stepping.
6891 In addition, you may set the language associated with a filename
6892 extension. @xref{Show, , Displaying the language}.
6895 @subsection Setting the working language
6897 If you allow @value{GDBN} to set the language automatically,
6898 expressions are interpreted the same way in your debugging session and
6901 @kindex set language
6902 If you wish, you may set the language manually. To do this, issue the
6903 command @samp{set language @var{lang}}, where @var{lang} is the name of
6905 @code{c} or @code{modula-2}.
6906 For a list of the supported languages, type @samp{set language}.
6908 Setting the language manually prevents @value{GDBN} from updating the working
6909 language automatically. This can lead to confusion if you try
6910 to debug a program when the working language is not the same as the
6911 source language, when an expression is acceptable to both
6912 languages---but means different things. For instance, if the current
6913 source file were written in C, and @value{GDBN} was parsing Modula-2, a
6921 might not have the effect you intended. In C, this means to add
6922 @code{b} and @code{c} and place the result in @code{a}. The result
6923 printed would be the value of @code{a}. In Modula-2, this means to compare
6924 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
6927 @subsection Having @value{GDBN} infer the source language
6929 To have @value{GDBN} set the working language automatically, use
6930 @samp{set language local} or @samp{set language auto}. @value{GDBN}
6931 then infers the working language. That is, when your program stops in a
6932 frame (usually by encountering a breakpoint), @value{GDBN} sets the
6933 working language to the language recorded for the function in that
6934 frame. If the language for a frame is unknown (that is, if the function
6935 or block corresponding to the frame was defined in a source file that
6936 does not have a recognized extension), the current working language is
6937 not changed, and @value{GDBN} issues a warning.
6939 This may not seem necessary for most programs, which are written
6940 entirely in one source language. However, program modules and libraries
6941 written in one source language can be used by a main program written in
6942 a different source language. Using @samp{set language auto} in this
6943 case frees you from having to set the working language manually.
6946 @section Displaying the language
6948 The following commands help you find out which language is the
6949 working language, and also what language source files were written in.
6951 @kindex show language
6952 @kindex info frame@r{, show the source language}
6953 @kindex info source@r{, show the source language}
6956 Display the current working language. This is the
6957 language you can use with commands such as @code{print} to
6958 build and compute expressions that may involve variables in your program.
6961 Display the source language for this frame. This language becomes the
6962 working language if you use an identifier from this frame.
6963 @xref{Frame Info, ,Information about a frame}, to identify the other
6964 information listed here.
6967 Display the source language of this source file.
6968 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
6969 information listed here.
6972 In unusual circumstances, you may have source files with extensions
6973 not in the standard list. You can then set the extension associated
6974 with a language explicitly:
6976 @kindex set extension-language
6977 @kindex info extensions
6979 @item set extension-language @var{.ext} @var{language}
6980 Set source files with extension @var{.ext} to be assumed to be in
6981 the source language @var{language}.
6983 @item info extensions
6984 List all the filename extensions and the associated languages.
6988 @section Type and range checking
6991 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
6992 checking are included, but they do not yet have any effect. This
6993 section documents the intended facilities.
6995 @c FIXME remove warning when type/range code added
6997 Some languages are designed to guard you against making seemingly common
6998 errors through a series of compile- and run-time checks. These include
6999 checking the type of arguments to functions and operators, and making
7000 sure mathematical overflows are caught at run time. Checks such as
7001 these help to ensure a program's correctness once it has been compiled
7002 by eliminating type mismatches, and providing active checks for range
7003 errors when your program is running.
7005 @value{GDBN} can check for conditions like the above if you wish.
7006 Although @value{GDBN} does not check the statements in your program, it
7007 can check expressions entered directly into @value{GDBN} for evaluation via
7008 the @code{print} command, for example. As with the working language,
7009 @value{GDBN} can also decide whether or not to check automatically based on
7010 your program's source language. @xref{Support, ,Supported languages},
7011 for the default settings of supported languages.
7014 * Type Checking:: An overview of type checking
7015 * Range Checking:: An overview of range checking
7018 @cindex type checking
7019 @cindex checks, type
7021 @subsection An overview of type checking
7023 Some languages, such as Modula-2, are strongly typed, meaning that the
7024 arguments to operators and functions have to be of the correct type,
7025 otherwise an error occurs. These checks prevent type mismatch
7026 errors from ever causing any run-time problems. For example,
7034 The second example fails because the @code{CARDINAL} 1 is not
7035 type-compatible with the @code{REAL} 2.3.
7037 For the expressions you use in @value{GDBN} commands, you can tell the
7038 @value{GDBN} type checker to skip checking;
7039 to treat any mismatches as errors and abandon the expression;
7040 or to only issue warnings when type mismatches occur,
7041 but evaluate the expression anyway. When you choose the last of
7042 these, @value{GDBN} evaluates expressions like the second example above, but
7043 also issues a warning.
7045 Even if you turn type checking off, there may be other reasons
7046 related to type that prevent @value{GDBN} from evaluating an expression.
7047 For instance, @value{GDBN} does not know how to add an @code{int} and
7048 a @code{struct foo}. These particular type errors have nothing to do
7049 with the language in use, and usually arise from expressions, such as
7050 the one described above, which make little sense to evaluate anyway.
7052 Each language defines to what degree it is strict about type. For
7053 instance, both Modula-2 and C require the arguments to arithmetical
7054 operators to be numbers. In C, enumerated types and pointers can be
7055 represented as numbers, so that they are valid arguments to mathematical
7056 operators. @xref{Support, ,Supported languages}, for further
7057 details on specific languages.
7059 @value{GDBN} provides some additional commands for controlling the type checker:
7061 @kindex set check@r{, type}
7062 @kindex set check type
7063 @kindex show check type
7065 @item set check type auto
7066 Set type checking on or off based on the current working language.
7067 @xref{Support, ,Supported languages}, for the default settings for
7070 @item set check type on
7071 @itemx set check type off
7072 Set type checking on or off, overriding the default setting for the
7073 current working language. Issue a warning if the setting does not
7074 match the language default. If any type mismatches occur in
7075 evaluating an expression while type checking is on, @value{GDBN} prints a
7076 message and aborts evaluation of the expression.
7078 @item set check type warn
7079 Cause the type checker to issue warnings, but to always attempt to
7080 evaluate the expression. Evaluating the expression may still
7081 be impossible for other reasons. For example, @value{GDBN} cannot add
7082 numbers and structures.
7085 Show the current setting of the type checker, and whether or not @value{GDBN}
7086 is setting it automatically.
7089 @cindex range checking
7090 @cindex checks, range
7091 @node Range Checking
7092 @subsection An overview of range checking
7094 In some languages (such as Modula-2), it is an error to exceed the
7095 bounds of a type; this is enforced with run-time checks. Such range
7096 checking is meant to ensure program correctness by making sure
7097 computations do not overflow, or indices on an array element access do
7098 not exceed the bounds of the array.
7100 For expressions you use in @value{GDBN} commands, you can tell
7101 @value{GDBN} to treat range errors in one of three ways: ignore them,
7102 always treat them as errors and abandon the expression, or issue
7103 warnings but evaluate the expression anyway.
7105 A range error can result from numerical overflow, from exceeding an
7106 array index bound, or when you type a constant that is not a member
7107 of any type. Some languages, however, do not treat overflows as an
7108 error. In many implementations of C, mathematical overflow causes the
7109 result to ``wrap around'' to lower values---for example, if @var{m} is
7110 the largest integer value, and @var{s} is the smallest, then
7113 @var{m} + 1 @result{} @var{s}
7116 This, too, is specific to individual languages, and in some cases
7117 specific to individual compilers or machines. @xref{Support, ,
7118 Supported languages}, for further details on specific languages.
7120 @value{GDBN} provides some additional commands for controlling the range checker:
7122 @kindex set check@r{, range}
7123 @kindex set check range
7124 @kindex show check range
7126 @item set check range auto
7127 Set range checking on or off based on the current working language.
7128 @xref{Support, ,Supported languages}, for the default settings for
7131 @item set check range on
7132 @itemx set check range off
7133 Set range checking on or off, overriding the default setting for the
7134 current working language. A warning is issued if the setting does not
7135 match the language default. If a range error occurs and range checking is on,
7136 then a message is printed and evaluation of the expression is aborted.
7138 @item set check range warn
7139 Output messages when the @value{GDBN} range checker detects a range error,
7140 but attempt to evaluate the expression anyway. Evaluating the
7141 expression may still be impossible for other reasons, such as accessing
7142 memory that the process does not own (a typical example from many Unix
7146 Show the current setting of the range checker, and whether or not it is
7147 being set automatically by @value{GDBN}.
7151 @section Supported languages
7153 @value{GDBN} supports C, C@t{++}, Fortran, Java, Chill, assembly, and Modula-2.
7154 @c This is false ...
7155 Some @value{GDBN} features may be used in expressions regardless of the
7156 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
7157 and the @samp{@{type@}addr} construct (@pxref{Expressions,
7158 ,Expressions}) can be used with the constructs of any supported
7161 The following sections detail to what degree each source language is
7162 supported by @value{GDBN}. These sections are not meant to be language
7163 tutorials or references, but serve only as a reference guide to what the
7164 @value{GDBN} expression parser accepts, and what input and output
7165 formats should look like for different languages. There are many good
7166 books written on each of these languages; please look to these for a
7167 language reference or tutorial.
7171 * Modula-2:: Modula-2
7176 @subsection C and C@t{++}
7178 @cindex C and C@t{++}
7179 @cindex expressions in C or C@t{++}
7181 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
7182 to both languages. Whenever this is the case, we discuss those languages
7186 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
7187 @cindex @sc{gnu} C@t{++}
7188 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
7189 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
7190 effectively, you must compile your C@t{++} programs with a supported
7191 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
7192 compiler (@code{aCC}).
7194 For best results when using @sc{gnu} C@t{++}, use the stabs debugging
7195 format. You can select that format explicitly with the @code{g++}
7196 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
7197 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
7198 CC, gcc.info, Using @sc{gnu} CC}, for more information.
7201 * C Operators:: C and C@t{++} operators
7202 * C Constants:: C and C@t{++} constants
7203 * C plus plus expressions:: C@t{++} expressions
7204 * C Defaults:: Default settings for C and C@t{++}
7205 * C Checks:: C and C@t{++} type and range checks
7206 * Debugging C:: @value{GDBN} and C
7207 * Debugging C plus plus:: @value{GDBN} features for C@t{++}
7211 @subsubsection C and C@t{++} operators
7213 @cindex C and C@t{++} operators
7215 Operators must be defined on values of specific types. For instance,
7216 @code{+} is defined on numbers, but not on structures. Operators are
7217 often defined on groups of types.
7219 For the purposes of C and C@t{++}, the following definitions hold:
7224 @emph{Integral types} include @code{int} with any of its storage-class
7225 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
7228 @emph{Floating-point types} include @code{float}, @code{double}, and
7229 @code{long double} (if supported by the target platform).
7232 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
7235 @emph{Scalar types} include all of the above.
7240 The following operators are supported. They are listed here
7241 in order of increasing precedence:
7245 The comma or sequencing operator. Expressions in a comma-separated list
7246 are evaluated from left to right, with the result of the entire
7247 expression being the last expression evaluated.
7250 Assignment. The value of an assignment expression is the value
7251 assigned. Defined on scalar types.
7254 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
7255 and translated to @w{@code{@var{a} = @var{a op b}}}.
7256 @w{@code{@var{op}=}} and @code{=} have the same precedence.
7257 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
7258 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
7261 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
7262 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
7266 Logical @sc{or}. Defined on integral types.
7269 Logical @sc{and}. Defined on integral types.
7272 Bitwise @sc{or}. Defined on integral types.
7275 Bitwise exclusive-@sc{or}. Defined on integral types.
7278 Bitwise @sc{and}. Defined on integral types.
7281 Equality and inequality. Defined on scalar types. The value of these
7282 expressions is 0 for false and non-zero for true.
7284 @item <@r{, }>@r{, }<=@r{, }>=
7285 Less than, greater than, less than or equal, greater than or equal.
7286 Defined on scalar types. The value of these expressions is 0 for false
7287 and non-zero for true.
7290 left shift, and right shift. Defined on integral types.
7293 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
7296 Addition and subtraction. Defined on integral types, floating-point types and
7299 @item *@r{, }/@r{, }%
7300 Multiplication, division, and modulus. Multiplication and division are
7301 defined on integral and floating-point types. Modulus is defined on
7305 Increment and decrement. When appearing before a variable, the
7306 operation is performed before the variable is used in an expression;
7307 when appearing after it, the variable's value is used before the
7308 operation takes place.
7311 Pointer dereferencing. Defined on pointer types. Same precedence as
7315 Address operator. Defined on variables. Same precedence as @code{++}.
7317 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
7318 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
7319 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
7320 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
7324 Negative. Defined on integral and floating-point types. Same
7325 precedence as @code{++}.
7328 Logical negation. Defined on integral types. Same precedence as
7332 Bitwise complement operator. Defined on integral types. Same precedence as
7337 Structure member, and pointer-to-structure member. For convenience,
7338 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
7339 pointer based on the stored type information.
7340 Defined on @code{struct} and @code{union} data.
7343 Dereferences of pointers to members.
7346 Array indexing. @code{@var{a}[@var{i}]} is defined as
7347 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
7350 Function parameter list. Same precedence as @code{->}.
7353 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
7354 and @code{class} types.
7357 Doubled colons also represent the @value{GDBN} scope operator
7358 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
7362 If an operator is redefined in the user code, @value{GDBN} usually
7363 attempts to invoke the redefined version instead of using the operator's
7371 @subsubsection C and C@t{++} constants
7373 @cindex C and C@t{++} constants
7375 @value{GDBN} allows you to express the constants of C and C@t{++} in the
7380 Integer constants are a sequence of digits. Octal constants are
7381 specified by a leading @samp{0} (i.e.@: zero), and hexadecimal constants
7382 by a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
7383 @samp{l}, specifying that the constant should be treated as a
7387 Floating point constants are a sequence of digits, followed by a decimal
7388 point, followed by a sequence of digits, and optionally followed by an
7389 exponent. An exponent is of the form:
7390 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
7391 sequence of digits. The @samp{+} is optional for positive exponents.
7392 A floating-point constant may also end with a letter @samp{f} or
7393 @samp{F}, specifying that the constant should be treated as being of
7394 the @code{float} (as opposed to the default @code{double}) type; or with
7395 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
7399 Enumerated constants consist of enumerated identifiers, or their
7400 integral equivalents.
7403 Character constants are a single character surrounded by single quotes
7404 (@code{'}), or a number---the ordinal value of the corresponding character
7405 (usually its @sc{ascii} value). Within quotes, the single character may
7406 be represented by a letter or by @dfn{escape sequences}, which are of
7407 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
7408 of the character's ordinal value; or of the form @samp{\@var{x}}, where
7409 @samp{@var{x}} is a predefined special character---for example,
7410 @samp{\n} for newline.
7413 String constants are a sequence of character constants surrounded by
7414 double quotes (@code{"}). Any valid character constant (as described
7415 above) may appear. Double quotes within the string must be preceded by
7416 a backslash, so for instance @samp{"a\"b'c"} is a string of five
7420 Pointer constants are an integral value. You can also write pointers
7421 to constants using the C operator @samp{&}.
7424 Array constants are comma-separated lists surrounded by braces @samp{@{}
7425 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
7426 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
7427 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
7431 * C plus plus expressions::
7438 @node C plus plus expressions
7439 @subsubsection C@t{++} expressions
7441 @cindex expressions in C@t{++}
7442 @value{GDBN} expression handling can interpret most C@t{++} expressions.
7444 @cindex C@t{++} support, not in @sc{coff}
7445 @cindex @sc{coff} versus C@t{++}
7446 @cindex C@t{++} and object formats
7447 @cindex object formats and C@t{++}
7448 @cindex a.out and C@t{++}
7449 @cindex @sc{ecoff} and C@t{++}
7450 @cindex @sc{xcoff} and C@t{++}
7451 @cindex @sc{elf}/stabs and C@t{++}
7452 @cindex @sc{elf}/@sc{dwarf} and C@t{++}
7453 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
7454 @c periodically whether this has happened...
7456 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the
7457 proper compiler. Typically, C@t{++} debugging depends on the use of
7458 additional debugging information in the symbol table, and thus requires
7459 special support. In particular, if your compiler generates a.out, MIPS
7460 @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the
7461 symbol table, these facilities are all available. (With @sc{gnu} CC,
7462 you can use the @samp{-gstabs} option to request stabs debugging
7463 extensions explicitly.) Where the object code format is standard
7464 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C@t{++}
7465 support in @value{GDBN} does @emph{not} work.
7470 @cindex member functions
7472 Member function calls are allowed; you can use expressions like
7475 count = aml->GetOriginal(x, y)
7478 @vindex this@r{, inside C@t{++} member functions}
7479 @cindex namespace in C@t{++}
7481 While a member function is active (in the selected stack frame), your
7482 expressions have the same namespace available as the member function;
7483 that is, @value{GDBN} allows implicit references to the class instance
7484 pointer @code{this} following the same rules as C@t{++}.
7486 @cindex call overloaded functions
7487 @cindex overloaded functions, calling
7488 @cindex type conversions in C@t{++}
7490 You can call overloaded functions; @value{GDBN} resolves the function
7491 call to the right definition, with some restrictions. @value{GDBN} does not
7492 perform overload resolution involving user-defined type conversions,
7493 calls to constructors, or instantiations of templates that do not exist
7494 in the program. It also cannot handle ellipsis argument lists or
7497 It does perform integral conversions and promotions, floating-point
7498 promotions, arithmetic conversions, pointer conversions, conversions of
7499 class objects to base classes, and standard conversions such as those of
7500 functions or arrays to pointers; it requires an exact match on the
7501 number of function arguments.
7503 Overload resolution is always performed, unless you have specified
7504 @code{set overload-resolution off}. @xref{Debugging C plus plus,
7505 ,@value{GDBN} features for C@t{++}}.
7507 You must specify @code{set overload-resolution off} in order to use an
7508 explicit function signature to call an overloaded function, as in
7510 p 'foo(char,int)'('x', 13)
7513 The @value{GDBN} command-completion facility can simplify this;
7514 see @ref{Completion, ,Command completion}.
7516 @cindex reference declarations
7518 @value{GDBN} understands variables declared as C@t{++} references; you can use
7519 them in expressions just as you do in C@t{++} source---they are automatically
7522 In the parameter list shown when @value{GDBN} displays a frame, the values of
7523 reference variables are not displayed (unlike other variables); this
7524 avoids clutter, since references are often used for large structures.
7525 The @emph{address} of a reference variable is always shown, unless
7526 you have specified @samp{set print address off}.
7529 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
7530 expressions can use it just as expressions in your program do. Since
7531 one scope may be defined in another, you can use @code{::} repeatedly if
7532 necessary, for example in an expression like
7533 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
7534 resolving name scope by reference to source files, in both C and C@t{++}
7535 debugging (@pxref{Variables, ,Program variables}).
7538 In addition, when used with HP's C@t{++} compiler, @value{GDBN} supports
7539 calling virtual functions correctly, printing out virtual bases of
7540 objects, calling functions in a base subobject, casting objects, and
7541 invoking user-defined operators.
7544 @subsubsection C and C@t{++} defaults
7546 @cindex C and C@t{++} defaults
7548 If you allow @value{GDBN} to set type and range checking automatically, they
7549 both default to @code{off} whenever the working language changes to
7550 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
7551 selects the working language.
7553 If you allow @value{GDBN} to set the language automatically, it
7554 recognizes source files whose names end with @file{.c}, @file{.C}, or
7555 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
7556 these files, it sets the working language to C or C@t{++}.
7557 @xref{Automatically, ,Having @value{GDBN} infer the source language},
7558 for further details.
7560 @c Type checking is (a) primarily motivated by Modula-2, and (b)
7561 @c unimplemented. If (b) changes, it might make sense to let this node
7562 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
7565 @subsubsection C and C@t{++} type and range checks
7567 @cindex C and C@t{++} checks
7569 By default, when @value{GDBN} parses C or C@t{++} expressions, type checking
7570 is not used. However, if you turn type checking on, @value{GDBN}
7571 considers two variables type equivalent if:
7575 The two variables are structured and have the same structure, union, or
7579 The two variables have the same type name, or types that have been
7580 declared equivalent through @code{typedef}.
7583 @c leaving this out because neither J Gilmore nor R Pesch understand it.
7586 The two @code{struct}, @code{union}, or @code{enum} variables are
7587 declared in the same declaration. (Note: this may not be true for all C
7592 Range checking, if turned on, is done on mathematical operations. Array
7593 indices are not checked, since they are often used to index a pointer
7594 that is not itself an array.
7597 @subsubsection @value{GDBN} and C
7599 The @code{set print union} and @code{show print union} commands apply to
7600 the @code{union} type. When set to @samp{on}, any @code{union} that is
7601 inside a @code{struct} or @code{class} is also printed. Otherwise, it
7602 appears as @samp{@{...@}}.
7604 The @code{@@} operator aids in the debugging of dynamic arrays, formed
7605 with pointers and a memory allocation function. @xref{Expressions,
7609 * Debugging C plus plus::
7612 @node Debugging C plus plus
7613 @subsubsection @value{GDBN} features for C@t{++}
7615 @cindex commands for C@t{++}
7617 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
7618 designed specifically for use with C@t{++}. Here is a summary:
7621 @cindex break in overloaded functions
7622 @item @r{breakpoint menus}
7623 When you want a breakpoint in a function whose name is overloaded,
7624 @value{GDBN} breakpoint menus help you specify which function definition
7625 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
7627 @cindex overloading in C@t{++}
7628 @item rbreak @var{regex}
7629 Setting breakpoints using regular expressions is helpful for setting
7630 breakpoints on overloaded functions that are not members of any special
7632 @xref{Set Breaks, ,Setting breakpoints}.
7634 @cindex C@t{++} exception handling
7637 Debug C@t{++} exception handling using these commands. @xref{Set
7638 Catchpoints, , Setting catchpoints}.
7641 @item ptype @var{typename}
7642 Print inheritance relationships as well as other information for type
7644 @xref{Symbols, ,Examining the Symbol Table}.
7646 @cindex C@t{++} symbol display
7647 @item set print demangle
7648 @itemx show print demangle
7649 @itemx set print asm-demangle
7650 @itemx show print asm-demangle
7651 Control whether C@t{++} symbols display in their source form, both when
7652 displaying code as C@t{++} source and when displaying disassemblies.
7653 @xref{Print Settings, ,Print settings}.
7655 @item set print object
7656 @itemx show print object
7657 Choose whether to print derived (actual) or declared types of objects.
7658 @xref{Print Settings, ,Print settings}.
7660 @item set print vtbl
7661 @itemx show print vtbl
7662 Control the format for printing virtual function tables.
7663 @xref{Print Settings, ,Print settings}.
7664 (The @code{vtbl} commands do not work on programs compiled with the HP
7665 ANSI C@t{++} compiler (@code{aCC}).)
7667 @kindex set overload-resolution
7668 @cindex overloaded functions, overload resolution
7669 @item set overload-resolution on
7670 Enable overload resolution for C@t{++} expression evaluation. The default
7671 is on. For overloaded functions, @value{GDBN} evaluates the arguments
7672 and searches for a function whose signature matches the argument types,
7673 using the standard C@t{++} conversion rules (see @ref{C plus plus expressions, ,C@t{++}
7674 expressions}, for details). If it cannot find a match, it emits a
7677 @item set overload-resolution off
7678 Disable overload resolution for C@t{++} expression evaluation. For
7679 overloaded functions that are not class member functions, @value{GDBN}
7680 chooses the first function of the specified name that it finds in the
7681 symbol table, whether or not its arguments are of the correct type. For
7682 overloaded functions that are class member functions, @value{GDBN}
7683 searches for a function whose signature @emph{exactly} matches the
7686 @item @r{Overloaded symbol names}
7687 You can specify a particular definition of an overloaded symbol, using
7688 the same notation that is used to declare such symbols in C@t{++}: type
7689 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
7690 also use the @value{GDBN} command-line word completion facilities to list the
7691 available choices, or to finish the type list for you.
7692 @xref{Completion,, Command completion}, for details on how to do this.
7696 @subsection Modula-2
7698 @cindex Modula-2, @value{GDBN} support
7700 The extensions made to @value{GDBN} to support Modula-2 only support
7701 output from the @sc{gnu} Modula-2 compiler (which is currently being
7702 developed). Other Modula-2 compilers are not currently supported, and
7703 attempting to debug executables produced by them is most likely
7704 to give an error as @value{GDBN} reads in the executable's symbol
7707 @cindex expressions in Modula-2
7709 * M2 Operators:: Built-in operators
7710 * Built-In Func/Proc:: Built-in functions and procedures
7711 * M2 Constants:: Modula-2 constants
7712 * M2 Defaults:: Default settings for Modula-2
7713 * Deviations:: Deviations from standard Modula-2
7714 * M2 Checks:: Modula-2 type and range checks
7715 * M2 Scope:: The scope operators @code{::} and @code{.}
7716 * GDB/M2:: @value{GDBN} and Modula-2
7720 @subsubsection Operators
7721 @cindex Modula-2 operators
7723 Operators must be defined on values of specific types. For instance,
7724 @code{+} is defined on numbers, but not on structures. Operators are
7725 often defined on groups of types. For the purposes of Modula-2, the
7726 following definitions hold:
7731 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
7735 @emph{Character types} consist of @code{CHAR} and its subranges.
7738 @emph{Floating-point types} consist of @code{REAL}.
7741 @emph{Pointer types} consist of anything declared as @code{POINTER TO
7745 @emph{Scalar types} consist of all of the above.
7748 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
7751 @emph{Boolean types} consist of @code{BOOLEAN}.
7755 The following operators are supported, and appear in order of
7756 increasing precedence:
7760 Function argument or array index separator.
7763 Assignment. The value of @var{var} @code{:=} @var{value} is
7767 Less than, greater than on integral, floating-point, or enumerated
7771 Less than or equal to, greater than or equal to
7772 on integral, floating-point and enumerated types, or set inclusion on
7773 set types. Same precedence as @code{<}.
7775 @item =@r{, }<>@r{, }#
7776 Equality and two ways of expressing inequality, valid on scalar types.
7777 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
7778 available for inequality, since @code{#} conflicts with the script
7782 Set membership. Defined on set types and the types of their members.
7783 Same precedence as @code{<}.
7786 Boolean disjunction. Defined on boolean types.
7789 Boolean conjunction. Defined on boolean types.
7792 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
7795 Addition and subtraction on integral and floating-point types, or union
7796 and difference on set types.
7799 Multiplication on integral and floating-point types, or set intersection
7803 Division on floating-point types, or symmetric set difference on set
7804 types. Same precedence as @code{*}.
7807 Integer division and remainder. Defined on integral types. Same
7808 precedence as @code{*}.
7811 Negative. Defined on @code{INTEGER} and @code{REAL} data.
7814 Pointer dereferencing. Defined on pointer types.
7817 Boolean negation. Defined on boolean types. Same precedence as
7821 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
7822 precedence as @code{^}.
7825 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
7828 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
7832 @value{GDBN} and Modula-2 scope operators.
7836 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
7837 treats the use of the operator @code{IN}, or the use of operators
7838 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
7839 @code{<=}, and @code{>=} on sets as an error.
7843 @node Built-In Func/Proc
7844 @subsubsection Built-in functions and procedures
7845 @cindex Modula-2 built-ins
7847 Modula-2 also makes available several built-in procedures and functions.
7848 In describing these, the following metavariables are used:
7853 represents an @code{ARRAY} variable.
7856 represents a @code{CHAR} constant or variable.
7859 represents a variable or constant of integral type.
7862 represents an identifier that belongs to a set. Generally used in the
7863 same function with the metavariable @var{s}. The type of @var{s} should
7864 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
7867 represents a variable or constant of integral or floating-point type.
7870 represents a variable or constant of floating-point type.
7876 represents a variable.
7879 represents a variable or constant of one of many types. See the
7880 explanation of the function for details.
7883 All Modula-2 built-in procedures also return a result, described below.
7887 Returns the absolute value of @var{n}.
7890 If @var{c} is a lower case letter, it returns its upper case
7891 equivalent, otherwise it returns its argument.
7894 Returns the character whose ordinal value is @var{i}.
7897 Decrements the value in the variable @var{v} by one. Returns the new value.
7899 @item DEC(@var{v},@var{i})
7900 Decrements the value in the variable @var{v} by @var{i}. Returns the
7903 @item EXCL(@var{m},@var{s})
7904 Removes the element @var{m} from the set @var{s}. Returns the new
7907 @item FLOAT(@var{i})
7908 Returns the floating point equivalent of the integer @var{i}.
7911 Returns the index of the last member of @var{a}.
7914 Increments the value in the variable @var{v} by one. Returns the new value.
7916 @item INC(@var{v},@var{i})
7917 Increments the value in the variable @var{v} by @var{i}. Returns the
7920 @item INCL(@var{m},@var{s})
7921 Adds the element @var{m} to the set @var{s} if it is not already
7922 there. Returns the new set.
7925 Returns the maximum value of the type @var{t}.
7928 Returns the minimum value of the type @var{t}.
7931 Returns boolean TRUE if @var{i} is an odd number.
7934 Returns the ordinal value of its argument. For example, the ordinal
7935 value of a character is its @sc{ascii} value (on machines supporting the
7936 @sc{ascii} character set). @var{x} must be of an ordered type, which include
7937 integral, character and enumerated types.
7940 Returns the size of its argument. @var{x} can be a variable or a type.
7942 @item TRUNC(@var{r})
7943 Returns the integral part of @var{r}.
7945 @item VAL(@var{t},@var{i})
7946 Returns the member of the type @var{t} whose ordinal value is @var{i}.
7950 @emph{Warning:} Sets and their operations are not yet supported, so
7951 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
7955 @cindex Modula-2 constants
7957 @subsubsection Constants
7959 @value{GDBN} allows you to express the constants of Modula-2 in the following
7965 Integer constants are simply a sequence of digits. When used in an
7966 expression, a constant is interpreted to be type-compatible with the
7967 rest of the expression. Hexadecimal integers are specified by a
7968 trailing @samp{H}, and octal integers by a trailing @samp{B}.
7971 Floating point constants appear as a sequence of digits, followed by a
7972 decimal point and another sequence of digits. An optional exponent can
7973 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
7974 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
7975 digits of the floating point constant must be valid decimal (base 10)
7979 Character constants consist of a single character enclosed by a pair of
7980 like quotes, either single (@code{'}) or double (@code{"}). They may
7981 also be expressed by their ordinal value (their @sc{ascii} value, usually)
7982 followed by a @samp{C}.
7985 String constants consist of a sequence of characters enclosed by a
7986 pair of like quotes, either single (@code{'}) or double (@code{"}).
7987 Escape sequences in the style of C are also allowed. @xref{C
7988 Constants, ,C and C@t{++} constants}, for a brief explanation of escape
7992 Enumerated constants consist of an enumerated identifier.
7995 Boolean constants consist of the identifiers @code{TRUE} and
7999 Pointer constants consist of integral values only.
8002 Set constants are not yet supported.
8006 @subsubsection Modula-2 defaults
8007 @cindex Modula-2 defaults
8009 If type and range checking are set automatically by @value{GDBN}, they
8010 both default to @code{on} whenever the working language changes to
8011 Modula-2. This happens regardless of whether you or @value{GDBN}
8012 selected the working language.
8014 If you allow @value{GDBN} to set the language automatically, then entering
8015 code compiled from a file whose name ends with @file{.mod} sets the
8016 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
8017 the language automatically}, for further details.
8020 @subsubsection Deviations from standard Modula-2
8021 @cindex Modula-2, deviations from
8023 A few changes have been made to make Modula-2 programs easier to debug.
8024 This is done primarily via loosening its type strictness:
8028 Unlike in standard Modula-2, pointer constants can be formed by
8029 integers. This allows you to modify pointer variables during
8030 debugging. (In standard Modula-2, the actual address contained in a
8031 pointer variable is hidden from you; it can only be modified
8032 through direct assignment to another pointer variable or expression that
8033 returned a pointer.)
8036 C escape sequences can be used in strings and characters to represent
8037 non-printable characters. @value{GDBN} prints out strings with these
8038 escape sequences embedded. Single non-printable characters are
8039 printed using the @samp{CHR(@var{nnn})} format.
8042 The assignment operator (@code{:=}) returns the value of its right-hand
8046 All built-in procedures both modify @emph{and} return their argument.
8050 @subsubsection Modula-2 type and range checks
8051 @cindex Modula-2 checks
8054 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
8057 @c FIXME remove warning when type/range checks added
8059 @value{GDBN} considers two Modula-2 variables type equivalent if:
8063 They are of types that have been declared equivalent via a @code{TYPE
8064 @var{t1} = @var{t2}} statement
8067 They have been declared on the same line. (Note: This is true of the
8068 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
8071 As long as type checking is enabled, any attempt to combine variables
8072 whose types are not equivalent is an error.
8074 Range checking is done on all mathematical operations, assignment, array
8075 index bounds, and all built-in functions and procedures.
8078 @subsubsection The scope operators @code{::} and @code{.}
8080 @cindex @code{.}, Modula-2 scope operator
8081 @cindex colon, doubled as scope operator
8083 @vindex colon-colon@r{, in Modula-2}
8084 @c Info cannot handle :: but TeX can.
8087 @vindex ::@r{, in Modula-2}
8090 There are a few subtle differences between the Modula-2 scope operator
8091 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
8096 @var{module} . @var{id}
8097 @var{scope} :: @var{id}
8101 where @var{scope} is the name of a module or a procedure,
8102 @var{module} the name of a module, and @var{id} is any declared
8103 identifier within your program, except another module.
8105 Using the @code{::} operator makes @value{GDBN} search the scope
8106 specified by @var{scope} for the identifier @var{id}. If it is not
8107 found in the specified scope, then @value{GDBN} searches all scopes
8108 enclosing the one specified by @var{scope}.
8110 Using the @code{.} operator makes @value{GDBN} search the current scope for
8111 the identifier specified by @var{id} that was imported from the
8112 definition module specified by @var{module}. With this operator, it is
8113 an error if the identifier @var{id} was not imported from definition
8114 module @var{module}, or if @var{id} is not an identifier in
8118 @subsubsection @value{GDBN} and Modula-2
8120 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
8121 Five subcommands of @code{set print} and @code{show print} apply
8122 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
8123 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
8124 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
8125 analogue in Modula-2.
8127 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
8128 with any language, is not useful with Modula-2. Its
8129 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
8130 created in Modula-2 as they can in C or C@t{++}. However, because an
8131 address can be specified by an integral constant, the construct
8132 @samp{@{@var{type}@}@var{adrexp}} is still useful.
8134 @cindex @code{#} in Modula-2
8135 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
8136 interpreted as the beginning of a comment. Use @code{<>} instead.
8141 The extensions made to @value{GDBN} to support Chill only support output
8142 from the @sc{gnu} Chill compiler. Other Chill compilers are not currently
8143 supported, and attempting to debug executables produced by them is most
8144 likely to give an error as @value{GDBN} reads in the executable's symbol
8147 @c This used to say "... following Chill related topics ...", but since
8148 @c menus are not shown in the printed manual, it would look awkward.
8149 This section covers the Chill related topics and the features
8150 of @value{GDBN} which support these topics.
8153 * How modes are displayed:: How modes are displayed
8154 * Locations:: Locations and their accesses
8155 * Values and their Operations:: Values and their Operations
8156 * Chill type and range checks::
8160 @node How modes are displayed
8161 @subsubsection How modes are displayed
8163 The Chill Datatype- (Mode) support of @value{GDBN} is directly related
8164 with the functionality of the @sc{gnu} Chill compiler, and therefore deviates
8165 slightly from the standard specification of the Chill language. The
8168 @c FIXME: this @table's contents effectively disable @code by using @r
8169 @c on every @item. So why does it need @code?
8171 @item @r{@emph{Discrete modes:}}
8174 @emph{Integer Modes} which are predefined by @code{BYTE, UBYTE, INT,
8177 @emph{Boolean Mode} which is predefined by @code{BOOL},
8179 @emph{Character Mode} which is predefined by @code{CHAR},
8181 @emph{Set Mode} which is displayed by the keyword @code{SET}.
8183 (@value{GDBP}) ptype x
8184 type = SET (karli = 10, susi = 20, fritzi = 100)
8186 If the type is an unnumbered set the set element values are omitted.
8188 @emph{Range Mode} which is displayed by
8190 @code{type = <basemode>(<lower bound> : <upper bound>)}
8192 where @code{<lower bound>, <upper bound>} can be of any discrete literal
8193 expression (e.g. set element names).
8196 @item @r{@emph{Powerset Mode:}}
8197 A Powerset Mode is displayed by the keyword @code{POWERSET} followed by
8198 the member mode of the powerset. The member mode can be any discrete mode.
8200 (@value{GDBP}) ptype x
8201 type = POWERSET SET (egon, hugo, otto)
8204 @item @r{@emph{Reference Modes:}}
8207 @emph{Bound Reference Mode} which is displayed by the keyword @code{REF}
8208 followed by the mode name to which the reference is bound.
8210 @emph{Free Reference Mode} which is displayed by the keyword @code{PTR}.
8213 @item @r{@emph{Procedure mode}}
8214 The procedure mode is displayed by @code{type = PROC(<parameter list>)
8215 <return mode> EXCEPTIONS (<exception list>)}. The @code{<parameter
8216 list>} is a list of the parameter modes. @code{<return mode>} indicates
8217 the mode of the result of the procedure if any. The exceptionlist lists
8218 all possible exceptions which can be raised by the procedure.
8221 @item @r{@emph{Instance mode}}
8222 The instance mode is represented by a structure, which has a static
8223 type, and is therefore not really of interest.
8226 @item @r{@emph{Synchronization Modes:}}
8229 @emph{Event Mode} which is displayed by
8231 @code{EVENT (<event length>)}
8233 where @code{(<event length>)} is optional.
8235 @emph{Buffer Mode} which is displayed by
8237 @code{BUFFER (<buffer length>)<buffer element mode>}
8239 where @code{(<buffer length>)} is optional.
8242 @item @r{@emph{Timing Modes:}}
8245 @emph{Duration Mode} which is predefined by @code{DURATION}
8247 @emph{Absolute Time Mode} which is predefined by @code{TIME}
8250 @item @r{@emph{Real Modes:}}
8251 Real Modes are predefined with @code{REAL} and @code{LONG_REAL}.
8253 @item @r{@emph{String Modes:}}
8256 @emph{Character String Mode} which is displayed by
8258 @code{CHARS(<string length>)}
8260 followed by the keyword @code{VARYING} if the String Mode is a varying
8263 @emph{Bit String Mode} which is displayed by
8270 @item @r{@emph{Array Mode:}}
8271 The Array Mode is displayed by the keyword @code{ARRAY(<range>)}
8272 followed by the element mode (which may in turn be an array mode).
8274 (@value{GDBP}) ptype x
8277 SET (karli = 10, susi = 20, fritzi = 100)
8280 @item @r{@emph{Structure Mode}}
8281 The Structure mode is displayed by the keyword @code{STRUCT(<field
8282 list>)}. The @code{<field list>} consists of names and modes of fields
8283 of the structure. Variant structures have the keyword @code{CASE <field>
8284 OF <variant fields> ESAC} in their field list. Since the current version
8285 of the GNU Chill compiler doesn't implement tag processing (no runtime
8286 checks of variant fields, and therefore no debugging info), the output
8287 always displays all variant fields.
8289 (@value{GDBP}) ptype str
8304 @subsubsection Locations and their accesses
8306 A location in Chill is an object which can contain values.
8308 A value of a location is generally accessed by the (declared) name of
8309 the location. The output conforms to the specification of values in
8310 Chill programs. How values are specified
8311 is the topic of the next section, @ref{Values and their Operations}.
8313 The pseudo-location @code{RESULT} (or @code{result}) can be used to
8314 display or change the result of a currently-active procedure:
8321 This does the same as the Chill action @code{RESULT EXPR} (which
8322 is not available in @value{GDBN}).
8324 Values of reference mode locations are printed by @code{PTR(<hex
8325 value>)} in case of a free reference mode, and by @code{(REF <reference
8326 mode>) (<hex-value>)} in case of a bound reference. @code{<hex value>}
8327 represents the address where the reference points to. To access the
8328 value of the location referenced by the pointer, use the dereference
8331 Values of procedure mode locations are displayed by
8334 (<argument modes> ) <return mode> @} <address> <name of procedure
8337 @code{<argument modes>} is a list of modes according to the parameter
8338 specification of the procedure and @code{<address>} shows the address of
8342 Locations of instance modes are displayed just like a structure with two
8343 fields specifying the @emph{process type} and the @emph{copy number} of
8344 the investigated instance location@footnote{This comes from the current
8345 implementation of instances. They are implemented as a structure (no
8346 na). The output should be something like @code{[<name of the process>;
8347 <instance number>]}.}. The field names are @code{__proc_type} and
8350 Locations of synchronization modes are displayed like a structure with
8351 the field name @code{__event_data} in case of a event mode location, and
8352 like a structure with the field @code{__buffer_data} in case of a buffer
8353 mode location (refer to previous paragraph).
8355 Structure Mode locations are printed by @code{[.<field name>: <value>,
8356 ...]}. The @code{<field name>} corresponds to the structure mode
8357 definition and the layout of @code{<value>} varies depending of the mode
8358 of the field. If the investigated structure mode location is of variant
8359 structure mode, the variant parts of the structure are enclosed in curled
8360 braces (@samp{@{@}}). Fields enclosed by @samp{@{,@}} are residing
8361 on the same memory location and represent the current values of the
8362 memory location in their specific modes. Since no tag processing is done
8363 all variants are displayed. A variant field is printed by
8364 @code{(<variant name>) = .<field name>: <value>}. (who implements the
8367 (@value{GDBP}) print str1 $4 = [.as: 0, .bs: karli, .<TAG>: { (karli) =
8368 [.cs: []], (susi) = [.ds: susi]}]
8372 Substructures of string mode-, array mode- or structure mode-values
8373 (e.g. array slices, fields of structure locations) are accessed using
8374 certain operations which are described in the next section, @ref{Values
8375 and their Operations}.
8377 A location value may be interpreted as having a different mode using the
8378 location conversion. This mode conversion is written as @code{<mode
8379 name>(<location>)}. The user has to consider that the sizes of the modes
8380 have to be equal otherwise an error occurs. Furthermore, no range
8381 checking of the location against the destination mode is performed, and
8382 therefore the result can be quite confusing.
8385 (@value{GDBP}) print int (s(3 up 4)) XXX TO be filled in !! XXX
8388 @node Values and their Operations
8389 @subsubsection Values and their Operations
8391 Values are used to alter locations, to investigate complex structures in
8392 more detail or to filter relevant information out of a large amount of
8393 data. There are several (mode dependent) operations defined which enable
8394 such investigations. These operations are not only applicable to
8395 constant values but also to locations, which can become quite useful
8396 when debugging complex structures. During parsing the command line
8397 (e.g. evaluating an expression) @value{GDBN} treats location names as
8398 the values behind these locations.
8400 This section describes how values have to be specified and which
8401 operations are legal to be used with such values.
8404 @item Literal Values
8405 Literal values are specified in the same manner as in @sc{gnu} Chill programs.
8406 For detailed specification refer to the @sc{gnu} Chill implementation Manual
8408 @c FIXME: if the Chill Manual is a Texinfo documents, the above should
8409 @c be converted to a @ref.
8414 @emph{Integer Literals} are specified in the same manner as in Chill
8415 programs (refer to the Chill Standard z200/88 chpt 5.2.4.2)
8417 @emph{Boolean Literals} are defined by @code{TRUE} and @code{FALSE}.
8419 @emph{Character Literals} are defined by @code{'<character>'}. (e.g.
8422 @emph{Set Literals} are defined by a name which was specified in a set
8423 mode. The value delivered by a Set Literal is the set value. This is
8424 comparable to an enumeration in C/C@t{++} language.
8426 @emph{Emptiness Literal} is predefined by @code{NULL}. The value of the
8427 emptiness literal delivers either the empty reference value, the empty
8428 procedure value or the empty instance value.
8431 @emph{Character String Literals} are defined by a sequence of characters
8432 enclosed in single- or double quotes. If a single- or double quote has
8433 to be part of the string literal it has to be stuffed (specified twice).
8435 @emph{Bitstring Literals} are specified in the same manner as in Chill
8436 programs (refer z200/88 chpt 5.2.4.8).
8438 @emph{Floating point literals} are specified in the same manner as in
8439 (gnu-)Chill programs (refer @sc{gnu} Chill implementation Manual chapter 1.5).
8444 A tuple is specified by @code{<mode name>[<tuple>]}, where @code{<mode
8445 name>} can be omitted if the mode of the tuple is unambiguous. This
8446 unambiguity is derived from the context of a evaluated expression.
8447 @code{<tuple>} can be one of the following:
8450 @item @emph{Powerset Tuple}
8451 @item @emph{Array Tuple}
8452 @item @emph{Structure Tuple}
8453 Powerset tuples, array tuples and structure tuples are specified in the
8454 same manner as in Chill programs refer to z200/88 chpt 5.2.5.
8457 @item String Element Value
8458 A string element value is specified by
8460 @code{<string value>(<index>)}
8462 where @code{<index>} is a integer expression. It delivers a character
8463 value which is equivalent to the character indexed by @code{<index>} in
8466 @item String Slice Value
8467 A string slice value is specified by @code{<string value>(<slice
8468 spec>)}, where @code{<slice spec>} can be either a range of integer
8469 expressions or specified by @code{<start expr> up <size>}.
8470 @code{<size>} denotes the number of elements which the slice contains.
8471 The delivered value is a string value, which is part of the specified
8474 @item Array Element Values
8475 An array element value is specified by @code{<array value>(<expr>)} and
8476 delivers a array element value of the mode of the specified array.
8478 @item Array Slice Values
8479 An array slice is specified by @code{<array value>(<slice spec>)}, where
8480 @code{<slice spec>} can be either a range specified by expressions or by
8481 @code{<start expr> up <size>}. @code{<size>} denotes the number of
8482 arrayelements the slice contains. The delivered value is an array value
8483 which is part of the specified array.
8485 @item Structure Field Values
8486 A structure field value is derived by @code{<structure value>.<field
8487 name>}, where @code{<field name>} indicates the name of a field specified
8488 in the mode definition of the structure. The mode of the delivered value
8489 corresponds to this mode definition in the structure definition.
8491 @item Procedure Call Value
8492 The procedure call value is derived from the return value of the
8493 procedure@footnote{If a procedure call is used for instance in an
8494 expression, then this procedure is called with all its side
8495 effects. This can lead to confusing results if used carelessly.}.
8497 Values of duration mode locations are represented by @code{ULONG} literals.
8499 Values of time mode locations appear as
8501 @code{TIME(<secs>:<nsecs>)}
8506 This is not implemented yet:
8507 @item Built-in Value
8509 The following built in functions are provided:
8521 @item @code{UPPER()}
8522 @item @code{LOWER()}
8523 @item @code{LENGTH()}
8527 @item @code{ARCSIN()}
8528 @item @code{ARCCOS()}
8529 @item @code{ARCTAN()}
8536 For a detailed description refer to the GNU Chill implementation manual
8540 @item Zero-adic Operator Value
8541 The zero-adic operator value is derived from the instance value for the
8542 current active process.
8544 @item Expression Values
8545 The value delivered by an expression is the result of the evaluation of
8546 the specified expression. If there are error conditions (mode
8547 incompatibility, etc.) the evaluation of expressions is aborted with a
8548 corresponding error message. Expressions may be parenthesised which
8549 causes the evaluation of this expression before any other expression
8550 which uses the result of the parenthesised expression. The following
8551 operators are supported by @value{GDBN}:
8554 @item @code{OR, ORIF, XOR}
8555 @itemx @code{AND, ANDIF}
8557 Logical operators defined over operands of boolean mode.
8560 Equality and inequality operators defined over all modes.
8564 Relational operators defined over predefined modes.
8567 @itemx @code{*, /, MOD, REM}
8568 Arithmetic operators defined over predefined modes.
8571 Change sign operator.
8574 String concatenation operator.
8577 String repetition operator.
8580 Referenced location operator which can be used either to take the
8581 address of a location (@code{->loc}), or to dereference a reference
8582 location (@code{loc->}).
8584 @item @code{OR, XOR}
8587 Powerset and bitstring operators.
8591 Powerset inclusion operators.
8594 Membership operator.
8598 @node Chill type and range checks
8599 @subsubsection Chill type and range checks
8601 @value{GDBN} considers two Chill variables mode equivalent if the sizes
8602 of the two modes are equal. This rule applies recursively to more
8603 complex datatypes which means that complex modes are treated
8604 equivalent if all element modes (which also can be complex modes like
8605 structures, arrays, etc.) have the same size.
8607 Range checking is done on all mathematical operations, assignment, array
8608 index bounds and all built in procedures.
8610 Strong type checks are forced using the @value{GDBN} command @code{set
8611 check strong}. This enforces strong type and range checks on all
8612 operations where Chill constructs are used (expressions, built in
8613 functions, etc.) in respect to the semantics as defined in the z.200
8614 language specification.
8616 All checks can be disabled by the @value{GDBN} command @code{set check
8620 @c Deviations from the Chill Standard Z200/88
8621 see last paragraph ?
8624 @node Chill defaults
8625 @subsubsection Chill defaults
8627 If type and range checking are set automatically by @value{GDBN}, they
8628 both default to @code{on} whenever the working language changes to
8629 Chill. This happens regardless of whether you or @value{GDBN}
8630 selected the working language.
8632 If you allow @value{GDBN} to set the language automatically, then entering
8633 code compiled from a file whose name ends with @file{.ch} sets the
8634 working language to Chill. @xref{Automatically, ,Having @value{GDBN} set
8635 the language automatically}, for further details.
8638 @chapter Examining the Symbol Table
8640 The commands described in this chapter allow you to inquire about the
8641 symbols (names of variables, functions and types) defined in your
8642 program. This information is inherent in the text of your program and
8643 does not change as your program executes. @value{GDBN} finds it in your
8644 program's symbol table, in the file indicated when you started @value{GDBN}
8645 (@pxref{File Options, ,Choosing files}), or by one of the
8646 file-management commands (@pxref{Files, ,Commands to specify files}).
8648 @cindex symbol names
8649 @cindex names of symbols
8650 @cindex quoting names
8651 Occasionally, you may need to refer to symbols that contain unusual
8652 characters, which @value{GDBN} ordinarily treats as word delimiters. The
8653 most frequent case is in referring to static variables in other
8654 source files (@pxref{Variables,,Program variables}). File names
8655 are recorded in object files as debugging symbols, but @value{GDBN} would
8656 ordinarily parse a typical file name, like @file{foo.c}, as the three words
8657 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
8658 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
8665 looks up the value of @code{x} in the scope of the file @file{foo.c}.
8668 @kindex info address
8669 @cindex address of a symbol
8670 @item info address @var{symbol}
8671 Describe where the data for @var{symbol} is stored. For a register
8672 variable, this says which register it is kept in. For a non-register
8673 local variable, this prints the stack-frame offset at which the variable
8676 Note the contrast with @samp{print &@var{symbol}}, which does not work
8677 at all for a register variable, and for a stack local variable prints
8678 the exact address of the current instantiation of the variable.
8681 @cindex symbol from address
8682 @item info symbol @var{addr}
8683 Print the name of a symbol which is stored at the address @var{addr}.
8684 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
8685 nearest symbol and an offset from it:
8688 (@value{GDBP}) info symbol 0x54320
8689 _initialize_vx + 396 in section .text
8693 This is the opposite of the @code{info address} command. You can use
8694 it to find out the name of a variable or a function given its address.
8697 @item whatis @var{expr}
8698 Print the data type of expression @var{expr}. @var{expr} is not
8699 actually evaluated, and any side-effecting operations (such as
8700 assignments or function calls) inside it do not take place.
8701 @xref{Expressions, ,Expressions}.
8704 Print the data type of @code{$}, the last value in the value history.
8707 @item ptype @var{typename}
8708 Print a description of data type @var{typename}. @var{typename} may be
8709 the name of a type, or for C code it may have the form @samp{class
8710 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
8711 @var{union-tag}} or @samp{enum @var{enum-tag}}.
8713 @item ptype @var{expr}
8715 Print a description of the type of expression @var{expr}. @code{ptype}
8716 differs from @code{whatis} by printing a detailed description, instead
8717 of just the name of the type.
8719 For example, for this variable declaration:
8722 struct complex @{double real; double imag;@} v;
8726 the two commands give this output:
8730 (@value{GDBP}) whatis v
8731 type = struct complex
8732 (@value{GDBP}) ptype v
8733 type = struct complex @{
8741 As with @code{whatis}, using @code{ptype} without an argument refers to
8742 the type of @code{$}, the last value in the value history.
8745 @item info types @var{regexp}
8747 Print a brief description of all types whose names match @var{regexp}
8748 (or all types in your program, if you supply no argument). Each
8749 complete typename is matched as though it were a complete line; thus,
8750 @samp{i type value} gives information on all types in your program whose
8751 names include the string @code{value}, but @samp{i type ^value$} gives
8752 information only on types whose complete name is @code{value}.
8754 This command differs from @code{ptype} in two ways: first, like
8755 @code{whatis}, it does not print a detailed description; second, it
8756 lists all source files where a type is defined.
8759 @cindex local variables
8760 @item info scope @var{addr}
8761 List all the variables local to a particular scope. This command
8762 accepts a location---a function name, a source line, or an address
8763 preceded by a @samp{*}, and prints all the variables local to the
8764 scope defined by that location. For example:
8767 (@value{GDBP}) @b{info scope command_line_handler}
8768 Scope for command_line_handler:
8769 Symbol rl is an argument at stack/frame offset 8, length 4.
8770 Symbol linebuffer is in static storage at address 0x150a18, length 4.
8771 Symbol linelength is in static storage at address 0x150a1c, length 4.
8772 Symbol p is a local variable in register $esi, length 4.
8773 Symbol p1 is a local variable in register $ebx, length 4.
8774 Symbol nline is a local variable in register $edx, length 4.
8775 Symbol repeat is a local variable at frame offset -8, length 4.
8779 This command is especially useful for determining what data to collect
8780 during a @dfn{trace experiment}, see @ref{Tracepoint Actions,
8785 Show the name of the current source file---that is, the source file for
8786 the function containing the current point of execution---and the language
8789 @kindex info sources
8791 Print the names of all source files in your program for which there is
8792 debugging information, organized into two lists: files whose symbols
8793 have already been read, and files whose symbols will be read when needed.
8795 @kindex info functions
8796 @item info functions
8797 Print the names and data types of all defined functions.
8799 @item info functions @var{regexp}
8800 Print the names and data types of all defined functions
8801 whose names contain a match for regular expression @var{regexp}.
8802 Thus, @samp{info fun step} finds all functions whose names
8803 include @code{step}; @samp{info fun ^step} finds those whose names
8804 start with @code{step}. If a function name contains characters
8805 that conflict with the regular expression language (eg.
8806 @samp{operator*()}), they may be quoted with a backslash.
8808 @kindex info variables
8809 @item info variables
8810 Print the names and data types of all variables that are declared
8811 outside of functions (i.e.@: excluding local variables).
8813 @item info variables @var{regexp}
8814 Print the names and data types of all variables (except for local
8815 variables) whose names contain a match for regular expression
8819 This was never implemented.
8820 @kindex info methods
8822 @itemx info methods @var{regexp}
8823 The @code{info methods} command permits the user to examine all defined
8824 methods within C@t{++} program, or (with the @var{regexp} argument) a
8825 specific set of methods found in the various C@t{++} classes. Many
8826 C@t{++} classes provide a large number of methods. Thus, the output
8827 from the @code{ptype} command can be overwhelming and hard to use. The
8828 @code{info-methods} command filters the methods, printing only those
8829 which match the regular-expression @var{regexp}.
8832 @cindex reloading symbols
8833 Some systems allow individual object files that make up your program to
8834 be replaced without stopping and restarting your program. For example,
8835 in VxWorks you can simply recompile a defective object file and keep on
8836 running. If you are running on one of these systems, you can allow
8837 @value{GDBN} to reload the symbols for automatically relinked modules:
8840 @kindex set symbol-reloading
8841 @item set symbol-reloading on
8842 Replace symbol definitions for the corresponding source file when an
8843 object file with a particular name is seen again.
8845 @item set symbol-reloading off
8846 Do not replace symbol definitions when encountering object files of the
8847 same name more than once. This is the default state; if you are not
8848 running on a system that permits automatic relinking of modules, you
8849 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
8850 may discard symbols when linking large programs, that may contain
8851 several modules (from different directories or libraries) with the same
8854 @kindex show symbol-reloading
8855 @item show symbol-reloading
8856 Show the current @code{on} or @code{off} setting.
8859 @kindex set opaque-type-resolution
8860 @item set opaque-type-resolution on
8861 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
8862 declared as a pointer to a @code{struct}, @code{class}, or
8863 @code{union}---for example, @code{struct MyType *}---that is used in one
8864 source file although the full declaration of @code{struct MyType} is in
8865 another source file. The default is on.
8867 A change in the setting of this subcommand will not take effect until
8868 the next time symbols for a file are loaded.
8870 @item set opaque-type-resolution off
8871 Tell @value{GDBN} not to resolve opaque types. In this case, the type
8872 is printed as follows:
8874 @{<no data fields>@}
8877 @kindex show opaque-type-resolution
8878 @item show opaque-type-resolution
8879 Show whether opaque types are resolved or not.
8881 @kindex maint print symbols
8883 @kindex maint print psymbols
8884 @cindex partial symbol dump
8885 @item maint print symbols @var{filename}
8886 @itemx maint print psymbols @var{filename}
8887 @itemx maint print msymbols @var{filename}
8888 Write a dump of debugging symbol data into the file @var{filename}.
8889 These commands are used to debug the @value{GDBN} symbol-reading code. Only
8890 symbols with debugging data are included. If you use @samp{maint print
8891 symbols}, @value{GDBN} includes all the symbols for which it has already
8892 collected full details: that is, @var{filename} reflects symbols for
8893 only those files whose symbols @value{GDBN} has read. You can use the
8894 command @code{info sources} to find out which files these are. If you
8895 use @samp{maint print psymbols} instead, the dump shows information about
8896 symbols that @value{GDBN} only knows partially---that is, symbols defined in
8897 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
8898 @samp{maint print msymbols} dumps just the minimal symbol information
8899 required for each object file from which @value{GDBN} has read some symbols.
8900 @xref{Files, ,Commands to specify files}, for a discussion of how
8901 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
8905 @chapter Altering Execution
8907 Once you think you have found an error in your program, you might want to
8908 find out for certain whether correcting the apparent error would lead to
8909 correct results in the rest of the run. You can find the answer by
8910 experiment, using the @value{GDBN} features for altering execution of the
8913 For example, you can store new values into variables or memory
8914 locations, give your program a signal, restart it at a different
8915 address, or even return prematurely from a function.
8918 * Assignment:: Assignment to variables
8919 * Jumping:: Continuing at a different address
8920 * Signaling:: Giving your program a signal
8921 * Returning:: Returning from a function
8922 * Calling:: Calling your program's functions
8923 * Patching:: Patching your program
8927 @section Assignment to variables
8930 @cindex setting variables
8931 To alter the value of a variable, evaluate an assignment expression.
8932 @xref{Expressions, ,Expressions}. For example,
8939 stores the value 4 into the variable @code{x}, and then prints the
8940 value of the assignment expression (which is 4).
8941 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
8942 information on operators in supported languages.
8944 @kindex set variable
8945 @cindex variables, setting
8946 If you are not interested in seeing the value of the assignment, use the
8947 @code{set} command instead of the @code{print} command. @code{set} is
8948 really the same as @code{print} except that the expression's value is
8949 not printed and is not put in the value history (@pxref{Value History,
8950 ,Value history}). The expression is evaluated only for its effects.
8952 If the beginning of the argument string of the @code{set} command
8953 appears identical to a @code{set} subcommand, use the @code{set
8954 variable} command instead of just @code{set}. This command is identical
8955 to @code{set} except for its lack of subcommands. For example, if your
8956 program has a variable @code{width}, you get an error if you try to set
8957 a new value with just @samp{set width=13}, because @value{GDBN} has the
8958 command @code{set width}:
8961 (@value{GDBP}) whatis width
8963 (@value{GDBP}) p width
8965 (@value{GDBP}) set width=47
8966 Invalid syntax in expression.
8970 The invalid expression, of course, is @samp{=47}. In
8971 order to actually set the program's variable @code{width}, use
8974 (@value{GDBP}) set var width=47
8977 Because the @code{set} command has many subcommands that can conflict
8978 with the names of program variables, it is a good idea to use the
8979 @code{set variable} command instead of just @code{set}. For example, if
8980 your program has a variable @code{g}, you run into problems if you try
8981 to set a new value with just @samp{set g=4}, because @value{GDBN} has
8982 the command @code{set gnutarget}, abbreviated @code{set g}:
8986 (@value{GDBP}) whatis g
8990 (@value{GDBP}) set g=4
8994 The program being debugged has been started already.
8995 Start it from the beginning? (y or n) y
8996 Starting program: /home/smith/cc_progs/a.out
8997 "/home/smith/cc_progs/a.out": can't open to read symbols:
8999 (@value{GDBP}) show g
9000 The current BFD target is "=4".
9005 The program variable @code{g} did not change, and you silently set the
9006 @code{gnutarget} to an invalid value. In order to set the variable
9010 (@value{GDBP}) set var g=4
9013 @value{GDBN} allows more implicit conversions in assignments than C; you can
9014 freely store an integer value into a pointer variable or vice versa,
9015 and you can convert any structure to any other structure that is the
9016 same length or shorter.
9017 @comment FIXME: how do structs align/pad in these conversions?
9018 @comment /doc@cygnus.com 18dec1990
9020 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
9021 construct to generate a value of specified type at a specified address
9022 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
9023 to memory location @code{0x83040} as an integer (which implies a certain size
9024 and representation in memory), and
9027 set @{int@}0x83040 = 4
9031 stores the value 4 into that memory location.
9034 @section Continuing at a different address
9036 Ordinarily, when you continue your program, you do so at the place where
9037 it stopped, with the @code{continue} command. You can instead continue at
9038 an address of your own choosing, with the following commands:
9042 @item jump @var{linespec}
9043 Resume execution at line @var{linespec}. Execution stops again
9044 immediately if there is a breakpoint there. @xref{List, ,Printing
9045 source lines}, for a description of the different forms of
9046 @var{linespec}. It is common practice to use the @code{tbreak} command
9047 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
9050 The @code{jump} command does not change the current stack frame, or
9051 the stack pointer, or the contents of any memory location or any
9052 register other than the program counter. If line @var{linespec} is in
9053 a different function from the one currently executing, the results may
9054 be bizarre if the two functions expect different patterns of arguments or
9055 of local variables. For this reason, the @code{jump} command requests
9056 confirmation if the specified line is not in the function currently
9057 executing. However, even bizarre results are predictable if you are
9058 well acquainted with the machine-language code of your program.
9060 @item jump *@var{address}
9061 Resume execution at the instruction at address @var{address}.
9064 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
9065 On many systems, you can get much the same effect as the @code{jump}
9066 command by storing a new value into the register @code{$pc}. The
9067 difference is that this does not start your program running; it only
9068 changes the address of where it @emph{will} run when you continue. For
9076 makes the next @code{continue} command or stepping command execute at
9077 address @code{0x485}, rather than at the address where your program stopped.
9078 @xref{Continuing and Stepping, ,Continuing and stepping}.
9080 The most common occasion to use the @code{jump} command is to back
9081 up---perhaps with more breakpoints set---over a portion of a program
9082 that has already executed, in order to examine its execution in more
9087 @section Giving your program a signal
9091 @item signal @var{signal}
9092 Resume execution where your program stopped, but immediately give it the
9093 signal @var{signal}. @var{signal} can be the name or the number of a
9094 signal. For example, on many systems @code{signal 2} and @code{signal
9095 SIGINT} are both ways of sending an interrupt signal.
9097 Alternatively, if @var{signal} is zero, continue execution without
9098 giving a signal. This is useful when your program stopped on account of
9099 a signal and would ordinary see the signal when resumed with the
9100 @code{continue} command; @samp{signal 0} causes it to resume without a
9103 @code{signal} does not repeat when you press @key{RET} a second time
9104 after executing the command.
9108 Invoking the @code{signal} command is not the same as invoking the
9109 @code{kill} utility from the shell. Sending a signal with @code{kill}
9110 causes @value{GDBN} to decide what to do with the signal depending on
9111 the signal handling tables (@pxref{Signals}). The @code{signal} command
9112 passes the signal directly to your program.
9116 @section Returning from a function
9119 @cindex returning from a function
9122 @itemx return @var{expression}
9123 You can cancel execution of a function call with the @code{return}
9124 command. If you give an
9125 @var{expression} argument, its value is used as the function's return
9129 When you use @code{return}, @value{GDBN} discards the selected stack frame
9130 (and all frames within it). You can think of this as making the
9131 discarded frame return prematurely. If you wish to specify a value to
9132 be returned, give that value as the argument to @code{return}.
9134 This pops the selected stack frame (@pxref{Selection, ,Selecting a
9135 frame}), and any other frames inside of it, leaving its caller as the
9136 innermost remaining frame. That frame becomes selected. The
9137 specified value is stored in the registers used for returning values
9140 The @code{return} command does not resume execution; it leaves the
9141 program stopped in the state that would exist if the function had just
9142 returned. In contrast, the @code{finish} command (@pxref{Continuing
9143 and Stepping, ,Continuing and stepping}) resumes execution until the
9144 selected stack frame returns naturally.
9147 @section Calling program functions
9149 @cindex calling functions
9152 @item call @var{expr}
9153 Evaluate the expression @var{expr} without displaying @code{void}
9157 You can use this variant of the @code{print} command if you want to
9158 execute a function from your program, but without cluttering the output
9159 with @code{void} returned values. If the result is not void, it
9160 is printed and saved in the value history.
9163 @section Patching programs
9165 @cindex patching binaries
9166 @cindex writing into executables
9167 @cindex writing into corefiles
9169 By default, @value{GDBN} opens the file containing your program's
9170 executable code (or the corefile) read-only. This prevents accidental
9171 alterations to machine code; but it also prevents you from intentionally
9172 patching your program's binary.
9174 If you'd like to be able to patch the binary, you can specify that
9175 explicitly with the @code{set write} command. For example, you might
9176 want to turn on internal debugging flags, or even to make emergency
9182 @itemx set write off
9183 If you specify @samp{set write on}, @value{GDBN} opens executable and
9184 core files for both reading and writing; if you specify @samp{set write
9185 off} (the default), @value{GDBN} opens them read-only.
9187 If you have already loaded a file, you must load it again (using the
9188 @code{exec-file} or @code{core-file} command) after changing @code{set
9189 write}, for your new setting to take effect.
9193 Display whether executable files and core files are opened for writing
9198 @chapter @value{GDBN} Files
9200 @value{GDBN} needs to know the file name of the program to be debugged,
9201 both in order to read its symbol table and in order to start your
9202 program. To debug a core dump of a previous run, you must also tell
9203 @value{GDBN} the name of the core dump file.
9206 * Files:: Commands to specify files
9207 * Symbol Errors:: Errors reading symbol files
9211 @section Commands to specify files
9213 @cindex symbol table
9214 @cindex core dump file
9216 You may want to specify executable and core dump file names. The usual
9217 way to do this is at start-up time, using the arguments to
9218 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
9219 Out of @value{GDBN}}).
9221 Occasionally it is necessary to change to a different file during a
9222 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
9223 a file you want to use. In these situations the @value{GDBN} commands
9224 to specify new files are useful.
9227 @cindex executable file
9229 @item file @var{filename}
9230 Use @var{filename} as the program to be debugged. It is read for its
9231 symbols and for the contents of pure memory. It is also the program
9232 executed when you use the @code{run} command. If you do not specify a
9233 directory and the file is not found in the @value{GDBN} working directory,
9234 @value{GDBN} uses the environment variable @code{PATH} as a list of
9235 directories to search, just as the shell does when looking for a program
9236 to run. You can change the value of this variable, for both @value{GDBN}
9237 and your program, using the @code{path} command.
9239 On systems with memory-mapped files, an auxiliary file named
9240 @file{@var{filename}.syms} may hold symbol table information for
9241 @var{filename}. If so, @value{GDBN} maps in the symbol table from
9242 @file{@var{filename}.syms}, starting up more quickly. See the
9243 descriptions of the file options @samp{-mapped} and @samp{-readnow}
9244 (available on the command line, and with the commands @code{file},
9245 @code{symbol-file}, or @code{add-symbol-file}, described below),
9246 for more information.
9249 @code{file} with no argument makes @value{GDBN} discard any information it
9250 has on both executable file and the symbol table.
9253 @item exec-file @r{[} @var{filename} @r{]}
9254 Specify that the program to be run (but not the symbol table) is found
9255 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
9256 if necessary to locate your program. Omitting @var{filename} means to
9257 discard information on the executable file.
9260 @item symbol-file @r{[} @var{filename} @r{]}
9261 Read symbol table information from file @var{filename}. @code{PATH} is
9262 searched when necessary. Use the @code{file} command to get both symbol
9263 table and program to run from the same file.
9265 @code{symbol-file} with no argument clears out @value{GDBN} information on your
9266 program's symbol table.
9268 The @code{symbol-file} command causes @value{GDBN} to forget the contents
9269 of its convenience variables, the value history, and all breakpoints and
9270 auto-display expressions. This is because they may contain pointers to
9271 the internal data recording symbols and data types, which are part of
9272 the old symbol table data being discarded inside @value{GDBN}.
9274 @code{symbol-file} does not repeat if you press @key{RET} again after
9277 When @value{GDBN} is configured for a particular environment, it
9278 understands debugging information in whatever format is the standard
9279 generated for that environment; you may use either a @sc{gnu} compiler, or
9280 other compilers that adhere to the local conventions.
9281 Best results are usually obtained from @sc{gnu} compilers; for example,
9282 using @code{@value{GCC}} you can generate debugging information for
9285 For most kinds of object files, with the exception of old SVR3 systems
9286 using COFF, the @code{symbol-file} command does not normally read the
9287 symbol table in full right away. Instead, it scans the symbol table
9288 quickly to find which source files and which symbols are present. The
9289 details are read later, one source file at a time, as they are needed.
9291 The purpose of this two-stage reading strategy is to make @value{GDBN}
9292 start up faster. For the most part, it is invisible except for
9293 occasional pauses while the symbol table details for a particular source
9294 file are being read. (The @code{set verbose} command can turn these
9295 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
9296 warnings and messages}.)
9298 We have not implemented the two-stage strategy for COFF yet. When the
9299 symbol table is stored in COFF format, @code{symbol-file} reads the
9300 symbol table data in full right away. Note that ``stabs-in-COFF''
9301 still does the two-stage strategy, since the debug info is actually
9305 @cindex reading symbols immediately
9306 @cindex symbols, reading immediately
9308 @cindex memory-mapped symbol file
9309 @cindex saving symbol table
9310 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9311 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9312 You can override the @value{GDBN} two-stage strategy for reading symbol
9313 tables by using the @samp{-readnow} option with any of the commands that
9314 load symbol table information, if you want to be sure @value{GDBN} has the
9315 entire symbol table available.
9317 If memory-mapped files are available on your system through the
9318 @code{mmap} system call, you can use another option, @samp{-mapped}, to
9319 cause @value{GDBN} to write the symbols for your program into a reusable
9320 file. Future @value{GDBN} debugging sessions map in symbol information
9321 from this auxiliary symbol file (if the program has not changed), rather
9322 than spending time reading the symbol table from the executable
9323 program. Using the @samp{-mapped} option has the same effect as
9324 starting @value{GDBN} with the @samp{-mapped} command-line option.
9326 You can use both options together, to make sure the auxiliary symbol
9327 file has all the symbol information for your program.
9329 The auxiliary symbol file for a program called @var{myprog} is called
9330 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
9331 than the corresponding executable), @value{GDBN} always attempts to use
9332 it when you debug @var{myprog}; no special options or commands are
9335 The @file{.syms} file is specific to the host machine where you run
9336 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
9337 symbol table. It cannot be shared across multiple host platforms.
9339 @c FIXME: for now no mention of directories, since this seems to be in
9340 @c flux. 13mar1992 status is that in theory GDB would look either in
9341 @c current dir or in same dir as myprog; but issues like competing
9342 @c GDB's, or clutter in system dirs, mean that in practice right now
9343 @c only current dir is used. FFish says maybe a special GDB hierarchy
9344 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
9349 @item core-file @r{[} @var{filename} @r{]}
9350 Specify the whereabouts of a core dump file to be used as the ``contents
9351 of memory''. Traditionally, core files contain only some parts of the
9352 address space of the process that generated them; @value{GDBN} can access the
9353 executable file itself for other parts.
9355 @code{core-file} with no argument specifies that no core file is
9358 Note that the core file is ignored when your program is actually running
9359 under @value{GDBN}. So, if you have been running your program and you
9360 wish to debug a core file instead, you must kill the subprocess in which
9361 the program is running. To do this, use the @code{kill} command
9362 (@pxref{Kill Process, ,Killing the child process}).
9364 @kindex add-symbol-file
9365 @cindex dynamic linking
9366 @item add-symbol-file @var{filename} @var{address}
9367 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9368 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address} @dots{}
9369 The @code{add-symbol-file} command reads additional symbol table
9370 information from the file @var{filename}. You would use this command
9371 when @var{filename} has been dynamically loaded (by some other means)
9372 into the program that is running. @var{address} should be the memory
9373 address at which the file has been loaded; @value{GDBN} cannot figure
9374 this out for itself. You can additionally specify an arbitrary number
9375 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
9376 section name and base address for that section. You can specify any
9377 @var{address} as an expression.
9379 The symbol table of the file @var{filename} is added to the symbol table
9380 originally read with the @code{symbol-file} command. You can use the
9381 @code{add-symbol-file} command any number of times; the new symbol data
9382 thus read keeps adding to the old. To discard all old symbol data
9383 instead, use the @code{symbol-file} command without any arguments.
9385 @cindex relocatable object files, reading symbols from
9386 @cindex object files, relocatable, reading symbols from
9387 @cindex reading symbols from relocatable object files
9388 @cindex symbols, reading from relocatable object files
9389 @cindex @file{.o} files, reading symbols from
9390 Although @var{filename} is typically a shared library file, an
9391 executable file, or some other object file which has been fully
9392 relocated for loading into a process, you can also load symbolic
9393 information from relocatable @file{.o} files, as long as:
9397 the file's symbolic information refers only to linker symbols defined in
9398 that file, not to symbols defined by other object files,
9400 every section the file's symbolic information refers to has actually
9401 been loaded into the inferior, as it appears in the file, and
9403 you can determine the address at which every section was loaded, and
9404 provide these to the @code{add-symbol-file} command.
9408 Some embedded operating systems, like Sun Chorus and VxWorks, can load
9409 relocatable files into an already running program; such systems
9410 typically make the requirements above easy to meet. However, it's
9411 important to recognize that many native systems use complex link
9412 procedures (@code{.linkonce} section factoring and C++ constructor table
9413 assembly, for example) that make the requirements difficult to meet. In
9414 general, one cannot assume that using @code{add-symbol-file} to read a
9415 relocatable object file's symbolic information will have the same effect
9416 as linking the relocatable object file into the program in the normal
9419 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
9421 You can use the @samp{-mapped} and @samp{-readnow} options just as with
9422 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
9423 table information for @var{filename}.
9425 @kindex add-shared-symbol-file
9426 @item add-shared-symbol-file
9427 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
9428 operating system for the Motorola 88k. @value{GDBN} automatically looks for
9429 shared libraries, however if @value{GDBN} does not find yours, you can run
9430 @code{add-shared-symbol-file}. It takes no arguments.
9434 The @code{section} command changes the base address of section SECTION of
9435 the exec file to ADDR. This can be used if the exec file does not contain
9436 section addresses, (such as in the a.out format), or when the addresses
9437 specified in the file itself are wrong. Each section must be changed
9438 separately. The @code{info files} command, described below, lists all
9439 the sections and their addresses.
9445 @code{info files} and @code{info target} are synonymous; both print the
9446 current target (@pxref{Targets, ,Specifying a Debugging Target}),
9447 including the names of the executable and core dump files currently in
9448 use by @value{GDBN}, and the files from which symbols were loaded. The
9449 command @code{help target} lists all possible targets rather than
9452 @kindex maint info sections
9453 @item maint info sections
9454 Another command that can give you extra information about program sections
9455 is @code{maint info sections}. In addition to the section information
9456 displayed by @code{info files}, this command displays the flags and file
9457 offset of each section in the executable and core dump files. In addition,
9458 @code{maint info sections} provides the following command options (which
9459 may be arbitrarily combined):
9463 Display sections for all loaded object files, including shared libraries.
9464 @item @var{sections}
9465 Display info only for named @var{sections}.
9466 @item @var{section-flags}
9467 Display info only for sections for which @var{section-flags} are true.
9468 The section flags that @value{GDBN} currently knows about are:
9471 Section will have space allocated in the process when loaded.
9472 Set for all sections except those containing debug information.
9474 Section will be loaded from the file into the child process memory.
9475 Set for pre-initialized code and data, clear for @code{.bss} sections.
9477 Section needs to be relocated before loading.
9479 Section cannot be modified by the child process.
9481 Section contains executable code only.
9483 Section contains data only (no executable code).
9485 Section will reside in ROM.
9487 Section contains data for constructor/destructor lists.
9489 Section is not empty.
9491 An instruction to the linker to not output the section.
9492 @item COFF_SHARED_LIBRARY
9493 A notification to the linker that the section contains
9494 COFF shared library information.
9496 Section contains common symbols.
9499 @kindex set trust-readonly-sections
9500 @item set trust-readonly-sections on
9501 Tell @value{GDBN} that readonly sections in your object file
9502 really are read-only (i.e.@: that their contents will not change).
9503 In that case, @value{GDBN} can fetch values from these sections
9504 out of the object file, rather than from the target program.
9505 For some targets (notably embedded ones), this can be a significant
9506 enhancement to debugging performance.
9510 @item set trust-readonly-sections off
9511 Tell @value{GDBN} not to trust readonly sections. This means that
9512 the contents of the section might change while the program is running,
9513 and must therefore be fetched from the target when needed.
9516 All file-specifying commands allow both absolute and relative file names
9517 as arguments. @value{GDBN} always converts the file name to an absolute file
9518 name and remembers it that way.
9520 @cindex shared libraries
9521 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
9524 @value{GDBN} automatically loads symbol definitions from shared libraries
9525 when you use the @code{run} command, or when you examine a core file.
9526 (Before you issue the @code{run} command, @value{GDBN} does not understand
9527 references to a function in a shared library, however---unless you are
9528 debugging a core file).
9530 On HP-UX, if the program loads a library explicitly, @value{GDBN}
9531 automatically loads the symbols at the time of the @code{shl_load} call.
9533 @c FIXME: some @value{GDBN} release may permit some refs to undef
9534 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
9535 @c FIXME...lib; check this from time to time when updating manual
9537 There are times, however, when you may wish to not automatically load
9538 symbol definitions from shared libraries, such as when they are
9539 particularly large or there are many of them.
9541 To control the automatic loading of shared library symbols, use the
9545 @kindex set auto-solib-add
9546 @item set auto-solib-add @var{mode}
9547 If @var{mode} is @code{on}, symbols from all shared object libraries
9548 will be loaded automatically when the inferior begins execution, you
9549 attach to an independently started inferior, or when the dynamic linker
9550 informs @value{GDBN} that a new library has been loaded. If @var{mode}
9551 is @code{off}, symbols must be loaded manually, using the
9552 @code{sharedlibrary} command. The default value is @code{on}.
9554 @kindex show auto-solib-add
9555 @item show auto-solib-add
9556 Display the current autoloading mode.
9559 To explicitly load shared library symbols, use the @code{sharedlibrary}
9563 @kindex info sharedlibrary
9566 @itemx info sharedlibrary
9567 Print the names of the shared libraries which are currently loaded.
9569 @kindex sharedlibrary
9571 @item sharedlibrary @var{regex}
9572 @itemx share @var{regex}
9573 Load shared object library symbols for files matching a
9574 Unix regular expression.
9575 As with files loaded automatically, it only loads shared libraries
9576 required by your program for a core file or after typing @code{run}. If
9577 @var{regex} is omitted all shared libraries required by your program are
9581 On some systems, such as HP-UX systems, @value{GDBN} supports
9582 autoloading shared library symbols until a limiting threshold size is
9583 reached. This provides the benefit of allowing autoloading to remain on
9584 by default, but avoids autoloading excessively large shared libraries,
9585 up to a threshold that is initially set, but which you can modify if you
9588 Beyond that threshold, symbols from shared libraries must be explicitly
9589 loaded. To load these symbols, use the command @code{sharedlibrary
9590 @var{filename}}. The base address of the shared library is determined
9591 automatically by @value{GDBN} and need not be specified.
9593 To display or set the threshold, use the commands:
9596 @kindex set auto-solib-limit
9597 @item set auto-solib-limit @var{threshold}
9598 Set the autoloading size threshold, in an integral number of megabytes.
9599 If @var{threshold} is nonzero and shared library autoloading is enabled,
9600 symbols from all shared object libraries will be loaded until the total
9601 size of the loaded shared library symbols exceeds this threshold.
9602 Otherwise, symbols must be loaded manually, using the
9603 @code{sharedlibrary} command. The default threshold is 100 (i.e.@: 100
9606 @kindex show auto-solib-limit
9607 @item show auto-solib-limit
9608 Display the current autoloading size threshold, in megabytes.
9612 @section Errors reading symbol files
9614 While reading a symbol file, @value{GDBN} occasionally encounters problems,
9615 such as symbol types it does not recognize, or known bugs in compiler
9616 output. By default, @value{GDBN} does not notify you of such problems, since
9617 they are relatively common and primarily of interest to people
9618 debugging compilers. If you are interested in seeing information
9619 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
9620 only one message about each such type of problem, no matter how many
9621 times the problem occurs; or you can ask @value{GDBN} to print more messages,
9622 to see how many times the problems occur, with the @code{set
9623 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
9626 The messages currently printed, and their meanings, include:
9629 @item inner block not inside outer block in @var{symbol}
9631 The symbol information shows where symbol scopes begin and end
9632 (such as at the start of a function or a block of statements). This
9633 error indicates that an inner scope block is not fully contained
9634 in its outer scope blocks.
9636 @value{GDBN} circumvents the problem by treating the inner block as if it had
9637 the same scope as the outer block. In the error message, @var{symbol}
9638 may be shown as ``@code{(don't know)}'' if the outer block is not a
9641 @item block at @var{address} out of order
9643 The symbol information for symbol scope blocks should occur in
9644 order of increasing addresses. This error indicates that it does not
9647 @value{GDBN} does not circumvent this problem, and has trouble
9648 locating symbols in the source file whose symbols it is reading. (You
9649 can often determine what source file is affected by specifying
9650 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
9653 @item bad block start address patched
9655 The symbol information for a symbol scope block has a start address
9656 smaller than the address of the preceding source line. This is known
9657 to occur in the SunOS 4.1.1 (and earlier) C compiler.
9659 @value{GDBN} circumvents the problem by treating the symbol scope block as
9660 starting on the previous source line.
9662 @item bad string table offset in symbol @var{n}
9665 Symbol number @var{n} contains a pointer into the string table which is
9666 larger than the size of the string table.
9668 @value{GDBN} circumvents the problem by considering the symbol to have the
9669 name @code{foo}, which may cause other problems if many symbols end up
9672 @item unknown symbol type @code{0x@var{nn}}
9674 The symbol information contains new data types that @value{GDBN} does
9675 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
9676 uncomprehended information, in hexadecimal.
9678 @value{GDBN} circumvents the error by ignoring this symbol information.
9679 This usually allows you to debug your program, though certain symbols
9680 are not accessible. If you encounter such a problem and feel like
9681 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
9682 on @code{complain}, then go up to the function @code{read_dbx_symtab}
9683 and examine @code{*bufp} to see the symbol.
9685 @item stub type has NULL name
9687 @value{GDBN} could not find the full definition for a struct or class.
9689 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
9690 The symbol information for a C@t{++} member function is missing some
9691 information that recent versions of the compiler should have output for
9694 @item info mismatch between compiler and debugger
9696 @value{GDBN} could not parse a type specification output by the compiler.
9701 @chapter Specifying a Debugging Target
9703 @cindex debugging target
9706 A @dfn{target} is the execution environment occupied by your program.
9708 Often, @value{GDBN} runs in the same host environment as your program;
9709 in that case, the debugging target is specified as a side effect when
9710 you use the @code{file} or @code{core} commands. When you need more
9711 flexibility---for example, running @value{GDBN} on a physically separate
9712 host, or controlling a standalone system over a serial port or a
9713 realtime system over a TCP/IP connection---you can use the @code{target}
9714 command to specify one of the target types configured for @value{GDBN}
9715 (@pxref{Target Commands, ,Commands for managing targets}).
9718 * Active Targets:: Active targets
9719 * Target Commands:: Commands for managing targets
9720 * Byte Order:: Choosing target byte order
9721 * Remote:: Remote debugging
9722 * KOD:: Kernel Object Display
9726 @node Active Targets
9727 @section Active targets
9729 @cindex stacking targets
9730 @cindex active targets
9731 @cindex multiple targets
9733 There are three classes of targets: processes, core files, and
9734 executable files. @value{GDBN} can work concurrently on up to three
9735 active targets, one in each class. This allows you to (for example)
9736 start a process and inspect its activity without abandoning your work on
9739 For example, if you execute @samp{gdb a.out}, then the executable file
9740 @code{a.out} is the only active target. If you designate a core file as
9741 well---presumably from a prior run that crashed and coredumped---then
9742 @value{GDBN} has two active targets and uses them in tandem, looking
9743 first in the corefile target, then in the executable file, to satisfy
9744 requests for memory addresses. (Typically, these two classes of target
9745 are complementary, since core files contain only a program's
9746 read-write memory---variables and so on---plus machine status, while
9747 executable files contain only the program text and initialized data.)
9749 When you type @code{run}, your executable file becomes an active process
9750 target as well. When a process target is active, all @value{GDBN}
9751 commands requesting memory addresses refer to that target; addresses in
9752 an active core file or executable file target are obscured while the
9753 process target is active.
9755 Use the @code{core-file} and @code{exec-file} commands to select a new
9756 core file or executable target (@pxref{Files, ,Commands to specify
9757 files}). To specify as a target a process that is already running, use
9758 the @code{attach} command (@pxref{Attach, ,Debugging an already-running
9761 @node Target Commands
9762 @section Commands for managing targets
9765 @item target @var{type} @var{parameters}
9766 Connects the @value{GDBN} host environment to a target machine or
9767 process. A target is typically a protocol for talking to debugging
9768 facilities. You use the argument @var{type} to specify the type or
9769 protocol of the target machine.
9771 Further @var{parameters} are interpreted by the target protocol, but
9772 typically include things like device names or host names to connect
9773 with, process numbers, and baud rates.
9775 The @code{target} command does not repeat if you press @key{RET} again
9776 after executing the command.
9780 Displays the names of all targets available. To display targets
9781 currently selected, use either @code{info target} or @code{info files}
9782 (@pxref{Files, ,Commands to specify files}).
9784 @item help target @var{name}
9785 Describe a particular target, including any parameters necessary to
9788 @kindex set gnutarget
9789 @item set gnutarget @var{args}
9790 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
9791 knows whether it is reading an @dfn{executable},
9792 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
9793 with the @code{set gnutarget} command. Unlike most @code{target} commands,
9794 with @code{gnutarget} the @code{target} refers to a program, not a machine.
9797 @emph{Warning:} To specify a file format with @code{set gnutarget},
9798 you must know the actual BFD name.
9802 @xref{Files, , Commands to specify files}.
9804 @kindex show gnutarget
9805 @item show gnutarget
9806 Use the @code{show gnutarget} command to display what file format
9807 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
9808 @value{GDBN} will determine the file format for each file automatically,
9809 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
9812 Here are some common targets (available, or not, depending on the GDB
9817 @item target exec @var{program}
9818 An executable file. @samp{target exec @var{program}} is the same as
9819 @samp{exec-file @var{program}}.
9822 @item target core @var{filename}
9823 A core dump file. @samp{target core @var{filename}} is the same as
9824 @samp{core-file @var{filename}}.
9826 @kindex target remote
9827 @item target remote @var{dev}
9828 Remote serial target in GDB-specific protocol. The argument @var{dev}
9829 specifies what serial device to use for the connection (e.g.
9830 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
9831 supports the @code{load} command. This is only useful if you have
9832 some other way of getting the stub to the target system, and you can put
9833 it somewhere in memory where it won't get clobbered by the download.
9837 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
9845 works; however, you cannot assume that a specific memory map, device
9846 drivers, or even basic I/O is available, although some simulators do
9847 provide these. For info about any processor-specific simulator details,
9848 see the appropriate section in @ref{Embedded Processors, ,Embedded
9853 Some configurations may include these targets as well:
9858 @item target nrom @var{dev}
9859 NetROM ROM emulator. This target only supports downloading.
9863 Different targets are available on different configurations of @value{GDBN};
9864 your configuration may have more or fewer targets.
9866 Many remote targets require you to download the executable's code
9867 once you've successfully established a connection.
9871 @kindex load @var{filename}
9872 @item load @var{filename}
9873 Depending on what remote debugging facilities are configured into
9874 @value{GDBN}, the @code{load} command may be available. Where it exists, it
9875 is meant to make @var{filename} (an executable) available for debugging
9876 on the remote system---by downloading, or dynamic linking, for example.
9877 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
9878 the @code{add-symbol-file} command.
9880 If your @value{GDBN} does not have a @code{load} command, attempting to
9881 execute it gets the error message ``@code{You can't do that when your
9882 target is @dots{}}''
9884 The file is loaded at whatever address is specified in the executable.
9885 For some object file formats, you can specify the load address when you
9886 link the program; for other formats, like a.out, the object file format
9887 specifies a fixed address.
9888 @c FIXME! This would be a good place for an xref to the GNU linker doc.
9890 @code{load} does not repeat if you press @key{RET} again after using it.
9894 @section Choosing target byte order
9896 @cindex choosing target byte order
9897 @cindex target byte order
9899 Some types of processors, such as the MIPS, PowerPC, and Hitachi SH,
9900 offer the ability to run either big-endian or little-endian byte
9901 orders. Usually the executable or symbol will include a bit to
9902 designate the endian-ness, and you will not need to worry about
9903 which to use. However, you may still find it useful to adjust
9904 @value{GDBN}'s idea of processor endian-ness manually.
9907 @kindex set endian big
9908 @item set endian big
9909 Instruct @value{GDBN} to assume the target is big-endian.
9911 @kindex set endian little
9912 @item set endian little
9913 Instruct @value{GDBN} to assume the target is little-endian.
9915 @kindex set endian auto
9916 @item set endian auto
9917 Instruct @value{GDBN} to use the byte order associated with the
9921 Display @value{GDBN}'s current idea of the target byte order.
9925 Note that these commands merely adjust interpretation of symbolic
9926 data on the host, and that they have absolutely no effect on the
9930 @section Remote debugging
9931 @cindex remote debugging
9933 If you are trying to debug a program running on a machine that cannot run
9934 @value{GDBN} in the usual way, it is often useful to use remote debugging.
9935 For example, you might use remote debugging on an operating system kernel,
9936 or on a small system which does not have a general purpose operating system
9937 powerful enough to run a full-featured debugger.
9939 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
9940 to make this work with particular debugging targets. In addition,
9941 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
9942 but not specific to any particular target system) which you can use if you
9943 write the remote stubs---the code that runs on the remote system to
9944 communicate with @value{GDBN}.
9946 Other remote targets may be available in your
9947 configuration of @value{GDBN}; use @code{help target} to list them.
9950 @section Kernel Object Display
9952 @cindex kernel object display
9953 @cindex kernel object
9956 Some targets support kernel object display. Using this facility,
9957 @value{GDBN} communicates specially with the underlying operating system
9958 and can display information about operating system-level objects such as
9959 mutexes and other synchronization objects. Exactly which objects can be
9960 displayed is determined on a per-OS basis.
9962 Use the @code{set os} command to set the operating system. This tells
9963 @value{GDBN} which kernel object display module to initialize:
9966 (@value{GDBP}) set os cisco
9969 If @code{set os} succeeds, @value{GDBN} will display some information
9970 about the operating system, and will create a new @code{info} command
9971 which can be used to query the target. The @code{info} command is named
9972 after the operating system:
9975 (@value{GDBP}) info cisco
9976 List of Cisco Kernel Objects
9978 any Any and all objects
9981 Further subcommands can be used to query about particular objects known
9984 There is currently no way to determine whether a given operating system
9985 is supported other than to try it.
9988 @node Remote Debugging
9989 @chapter Debugging remote programs
9992 * Server:: Using the gdbserver program
9993 * NetWare:: Using the gdbserve.nlm program
9994 * remote stub:: Implementing a remote stub
9998 @section Using the @code{gdbserver} program
10001 @cindex remote connection without stubs
10002 @code{gdbserver} is a control program for Unix-like systems, which
10003 allows you to connect your program with a remote @value{GDBN} via
10004 @code{target remote}---but without linking in the usual debugging stub.
10006 @code{gdbserver} is not a complete replacement for the debugging stubs,
10007 because it requires essentially the same operating-system facilities
10008 that @value{GDBN} itself does. In fact, a system that can run
10009 @code{gdbserver} to connect to a remote @value{GDBN} could also run
10010 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
10011 because it is a much smaller program than @value{GDBN} itself. It is
10012 also easier to port than all of @value{GDBN}, so you may be able to get
10013 started more quickly on a new system by using @code{gdbserver}.
10014 Finally, if you develop code for real-time systems, you may find that
10015 the tradeoffs involved in real-time operation make it more convenient to
10016 do as much development work as possible on another system, for example
10017 by cross-compiling. You can use @code{gdbserver} to make a similar
10018 choice for debugging.
10020 @value{GDBN} and @code{gdbserver} communicate via either a serial line
10021 or a TCP connection, using the standard @value{GDBN} remote serial
10025 @item On the target machine,
10026 you need to have a copy of the program you want to debug.
10027 @code{gdbserver} does not need your program's symbol table, so you can
10028 strip the program if necessary to save space. @value{GDBN} on the host
10029 system does all the symbol handling.
10031 To use the server, you must tell it how to communicate with @value{GDBN};
10032 the name of your program; and the arguments for your program. The usual
10036 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
10039 @var{comm} is either a device name (to use a serial line) or a TCP
10040 hostname and portnumber. For example, to debug Emacs with the argument
10041 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
10045 target> gdbserver /dev/com1 emacs foo.txt
10048 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
10051 To use a TCP connection instead of a serial line:
10054 target> gdbserver host:2345 emacs foo.txt
10057 The only difference from the previous example is the first argument,
10058 specifying that you are communicating with the host @value{GDBN} via
10059 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
10060 expect a TCP connection from machine @samp{host} to local TCP port 2345.
10061 (Currently, the @samp{host} part is ignored.) You can choose any number
10062 you want for the port number as long as it does not conflict with any
10063 TCP ports already in use on the target system (for example, @code{23} is
10064 reserved for @code{telnet}).@footnote{If you choose a port number that
10065 conflicts with another service, @code{gdbserver} prints an error message
10066 and exits.} You must use the same port number with the host @value{GDBN}
10067 @code{target remote} command.
10069 On some targets, @code{gdbserver} can also attach to running programs.
10070 This is accomplished via the @code{--attach} argument. The syntax is:
10073 target> gdbserver @var{comm} --attach @var{pid}
10076 @var{pid} is the process ID of a currently running process. It isn't necessary
10077 to point @code{gdbserver} at a binary for the running process.
10079 @item On the @value{GDBN} host machine,
10080 you need an unstripped copy of your program, since @value{GDBN} needs
10081 symbols and debugging information. Start up @value{GDBN} as usual,
10082 using the name of the local copy of your program as the first argument.
10083 (You may also need the @w{@samp{--baud}} option if the serial line is
10084 running at anything other than 9600@dmn{bps}.) After that, use @code{target
10085 remote} to establish communications with @code{gdbserver}. Its argument
10086 is either a device name (usually a serial device, like
10087 @file{/dev/ttyb}), or a TCP port descriptor in the form
10088 @code{@var{host}:@var{PORT}}. For example:
10091 (@value{GDBP}) target remote /dev/ttyb
10095 communicates with the server via serial line @file{/dev/ttyb}, and
10098 (@value{GDBP}) target remote the-target:2345
10102 communicates via a TCP connection to port 2345 on host @w{@file{the-target}}.
10103 For TCP connections, you must start up @code{gdbserver} prior to using
10104 the @code{target remote} command. Otherwise you may get an error whose
10105 text depends on the host system, but which usually looks something like
10106 @samp{Connection refused}.
10110 @section Using the @code{gdbserve.nlm} program
10112 @kindex gdbserve.nlm
10113 @code{gdbserve.nlm} is a control program for NetWare systems, which
10114 allows you to connect your program with a remote @value{GDBN} via
10115 @code{target remote}.
10117 @value{GDBN} and @code{gdbserve.nlm} communicate via a serial line,
10118 using the standard @value{GDBN} remote serial protocol.
10121 @item On the target machine,
10122 you need to have a copy of the program you want to debug.
10123 @code{gdbserve.nlm} does not need your program's symbol table, so you
10124 can strip the program if necessary to save space. @value{GDBN} on the
10125 host system does all the symbol handling.
10127 To use the server, you must tell it how to communicate with
10128 @value{GDBN}; the name of your program; and the arguments for your
10129 program. The syntax is:
10132 load gdbserve [ BOARD=@var{board} ] [ PORT=@var{port} ]
10133 [ BAUD=@var{baud} ] @var{program} [ @var{args} @dots{} ]
10136 @var{board} and @var{port} specify the serial line; @var{baud} specifies
10137 the baud rate used by the connection. @var{port} and @var{node} default
10138 to 0, @var{baud} defaults to 9600@dmn{bps}.
10140 For example, to debug Emacs with the argument @samp{foo.txt}and
10141 communicate with @value{GDBN} over serial port number 2 or board 1
10142 using a 19200@dmn{bps} connection:
10145 load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
10148 @item On the @value{GDBN} host machine,
10149 you need an unstripped copy of your program, since @value{GDBN} needs
10150 symbols and debugging information. Start up @value{GDBN} as usual,
10151 using the name of the local copy of your program as the first argument.
10152 (You may also need the @w{@samp{--baud}} option if the serial line is
10153 running at anything other than 9600@dmn{bps}. After that, use @code{target
10154 remote} to establish communications with @code{gdbserve.nlm}. Its
10155 argument is a device name (usually a serial device, like
10156 @file{/dev/ttyb}). For example:
10159 (@value{GDBP}) target remote /dev/ttyb
10163 communications with the server via serial line @file{/dev/ttyb}.
10167 @section Implementing a remote stub
10169 @cindex debugging stub, example
10170 @cindex remote stub, example
10171 @cindex stub example, remote debugging
10172 The stub files provided with @value{GDBN} implement the target side of the
10173 communication protocol, and the @value{GDBN} side is implemented in the
10174 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
10175 these subroutines to communicate, and ignore the details. (If you're
10176 implementing your own stub file, you can still ignore the details: start
10177 with one of the existing stub files. @file{sparc-stub.c} is the best
10178 organized, and therefore the easiest to read.)
10180 @cindex remote serial debugging, overview
10181 To debug a program running on another machine (the debugging
10182 @dfn{target} machine), you must first arrange for all the usual
10183 prerequisites for the program to run by itself. For example, for a C
10188 A startup routine to set up the C runtime environment; these usually
10189 have a name like @file{crt0}. The startup routine may be supplied by
10190 your hardware supplier, or you may have to write your own.
10193 A C subroutine library to support your program's
10194 subroutine calls, notably managing input and output.
10197 A way of getting your program to the other machine---for example, a
10198 download program. These are often supplied by the hardware
10199 manufacturer, but you may have to write your own from hardware
10203 The next step is to arrange for your program to use a serial port to
10204 communicate with the machine where @value{GDBN} is running (the @dfn{host}
10205 machine). In general terms, the scheme looks like this:
10209 @value{GDBN} already understands how to use this protocol; when everything
10210 else is set up, you can simply use the @samp{target remote} command
10211 (@pxref{Targets,,Specifying a Debugging Target}).
10213 @item On the target,
10214 you must link with your program a few special-purpose subroutines that
10215 implement the @value{GDBN} remote serial protocol. The file containing these
10216 subroutines is called a @dfn{debugging stub}.
10218 On certain remote targets, you can use an auxiliary program
10219 @code{gdbserver} instead of linking a stub into your program.
10220 @xref{Server,,Using the @code{gdbserver} program}, for details.
10223 The debugging stub is specific to the architecture of the remote
10224 machine; for example, use @file{sparc-stub.c} to debug programs on
10227 @cindex remote serial stub list
10228 These working remote stubs are distributed with @value{GDBN}:
10233 @cindex @file{i386-stub.c}
10236 For Intel 386 and compatible architectures.
10239 @cindex @file{m68k-stub.c}
10240 @cindex Motorola 680x0
10242 For Motorola 680x0 architectures.
10245 @cindex @file{sh-stub.c}
10248 For Hitachi SH architectures.
10251 @cindex @file{sparc-stub.c}
10253 For @sc{sparc} architectures.
10255 @item sparcl-stub.c
10256 @cindex @file{sparcl-stub.c}
10259 For Fujitsu @sc{sparclite} architectures.
10263 The @file{README} file in the @value{GDBN} distribution may list other
10264 recently added stubs.
10267 * Stub Contents:: What the stub can do for you
10268 * Bootstrapping:: What you must do for the stub
10269 * Debug Session:: Putting it all together
10272 @node Stub Contents
10273 @subsection What the stub can do for you
10275 @cindex remote serial stub
10276 The debugging stub for your architecture supplies these three
10280 @item set_debug_traps
10281 @kindex set_debug_traps
10282 @cindex remote serial stub, initialization
10283 This routine arranges for @code{handle_exception} to run when your
10284 program stops. You must call this subroutine explicitly near the
10285 beginning of your program.
10287 @item handle_exception
10288 @kindex handle_exception
10289 @cindex remote serial stub, main routine
10290 This is the central workhorse, but your program never calls it
10291 explicitly---the setup code arranges for @code{handle_exception} to
10292 run when a trap is triggered.
10294 @code{handle_exception} takes control when your program stops during
10295 execution (for example, on a breakpoint), and mediates communications
10296 with @value{GDBN} on the host machine. This is where the communications
10297 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
10298 representative on the target machine. It begins by sending summary
10299 information on the state of your program, then continues to execute,
10300 retrieving and transmitting any information @value{GDBN} needs, until you
10301 execute a @value{GDBN} command that makes your program resume; at that point,
10302 @code{handle_exception} returns control to your own code on the target
10306 @cindex @code{breakpoint} subroutine, remote
10307 Use this auxiliary subroutine to make your program contain a
10308 breakpoint. Depending on the particular situation, this may be the only
10309 way for @value{GDBN} to get control. For instance, if your target
10310 machine has some sort of interrupt button, you won't need to call this;
10311 pressing the interrupt button transfers control to
10312 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
10313 simply receiving characters on the serial port may also trigger a trap;
10314 again, in that situation, you don't need to call @code{breakpoint} from
10315 your own program---simply running @samp{target remote} from the host
10316 @value{GDBN} session gets control.
10318 Call @code{breakpoint} if none of these is true, or if you simply want
10319 to make certain your program stops at a predetermined point for the
10320 start of your debugging session.
10323 @node Bootstrapping
10324 @subsection What you must do for the stub
10326 @cindex remote stub, support routines
10327 The debugging stubs that come with @value{GDBN} are set up for a particular
10328 chip architecture, but they have no information about the rest of your
10329 debugging target machine.
10331 First of all you need to tell the stub how to communicate with the
10335 @item int getDebugChar()
10336 @kindex getDebugChar
10337 Write this subroutine to read a single character from the serial port.
10338 It may be identical to @code{getchar} for your target system; a
10339 different name is used to allow you to distinguish the two if you wish.
10341 @item void putDebugChar(int)
10342 @kindex putDebugChar
10343 Write this subroutine to write a single character to the serial port.
10344 It may be identical to @code{putchar} for your target system; a
10345 different name is used to allow you to distinguish the two if you wish.
10348 @cindex control C, and remote debugging
10349 @cindex interrupting remote targets
10350 If you want @value{GDBN} to be able to stop your program while it is
10351 running, you need to use an interrupt-driven serial driver, and arrange
10352 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
10353 character). That is the character which @value{GDBN} uses to tell the
10354 remote system to stop.
10356 Getting the debugging target to return the proper status to @value{GDBN}
10357 probably requires changes to the standard stub; one quick and dirty way
10358 is to just execute a breakpoint instruction (the ``dirty'' part is that
10359 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
10361 Other routines you need to supply are:
10364 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
10365 @kindex exceptionHandler
10366 Write this function to install @var{exception_address} in the exception
10367 handling tables. You need to do this because the stub does not have any
10368 way of knowing what the exception handling tables on your target system
10369 are like (for example, the processor's table might be in @sc{rom},
10370 containing entries which point to a table in @sc{ram}).
10371 @var{exception_number} is the exception number which should be changed;
10372 its meaning is architecture-dependent (for example, different numbers
10373 might represent divide by zero, misaligned access, etc). When this
10374 exception occurs, control should be transferred directly to
10375 @var{exception_address}, and the processor state (stack, registers,
10376 and so on) should be just as it is when a processor exception occurs. So if
10377 you want to use a jump instruction to reach @var{exception_address}, it
10378 should be a simple jump, not a jump to subroutine.
10380 For the 386, @var{exception_address} should be installed as an interrupt
10381 gate so that interrupts are masked while the handler runs. The gate
10382 should be at privilege level 0 (the most privileged level). The
10383 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
10384 help from @code{exceptionHandler}.
10386 @item void flush_i_cache()
10387 @kindex flush_i_cache
10388 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
10389 instruction cache, if any, on your target machine. If there is no
10390 instruction cache, this subroutine may be a no-op.
10392 On target machines that have instruction caches, @value{GDBN} requires this
10393 function to make certain that the state of your program is stable.
10397 You must also make sure this library routine is available:
10400 @item void *memset(void *, int, int)
10402 This is the standard library function @code{memset} that sets an area of
10403 memory to a known value. If you have one of the free versions of
10404 @code{libc.a}, @code{memset} can be found there; otherwise, you must
10405 either obtain it from your hardware manufacturer, or write your own.
10408 If you do not use the GNU C compiler, you may need other standard
10409 library subroutines as well; this varies from one stub to another,
10410 but in general the stubs are likely to use any of the common library
10411 subroutines which @code{@value{GCC}} generates as inline code.
10414 @node Debug Session
10415 @subsection Putting it all together
10417 @cindex remote serial debugging summary
10418 In summary, when your program is ready to debug, you must follow these
10423 Make sure you have defined the supporting low-level routines
10424 (@pxref{Bootstrapping,,What you must do for the stub}):
10426 @code{getDebugChar}, @code{putDebugChar},
10427 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
10431 Insert these lines near the top of your program:
10439 For the 680x0 stub only, you need to provide a variable called
10440 @code{exceptionHook}. Normally you just use:
10443 void (*exceptionHook)() = 0;
10447 but if before calling @code{set_debug_traps}, you set it to point to a
10448 function in your program, that function is called when
10449 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
10450 error). The function indicated by @code{exceptionHook} is called with
10451 one parameter: an @code{int} which is the exception number.
10454 Compile and link together: your program, the @value{GDBN} debugging stub for
10455 your target architecture, and the supporting subroutines.
10458 Make sure you have a serial connection between your target machine and
10459 the @value{GDBN} host, and identify the serial port on the host.
10462 @c The "remote" target now provides a `load' command, so we should
10463 @c document that. FIXME.
10464 Download your program to your target machine (or get it there by
10465 whatever means the manufacturer provides), and start it.
10468 To start remote debugging, run @value{GDBN} on the host machine, and specify
10469 as an executable file the program that is running in the remote machine.
10470 This tells @value{GDBN} how to find your program's symbols and the contents
10474 @cindex serial line, @code{target remote}
10475 Establish communication using the @code{target remote} command.
10476 Its argument specifies how to communicate with the target
10477 machine---either via a devicename attached to a direct serial line, or a
10478 TCP port (usually to a terminal server which in turn has a serial line
10479 to the target). For example, to use a serial line connected to the
10480 device named @file{/dev/ttyb}:
10483 target remote /dev/ttyb
10486 @cindex TCP port, @code{target remote}
10487 To use a TCP connection, use an argument of the form
10488 @code{@var{host}:port}. For example, to connect to port 2828 on a
10489 terminal server named @code{manyfarms}:
10492 target remote manyfarms:2828
10495 If your remote target is actually running on the same machine as
10496 your debugger session (e.g.@: a simulator of your target running on
10497 the same host), you can omit the hostname. For example, to connect
10498 to port 1234 on your local machine:
10501 target remote :1234
10505 Note that the colon is still required here.
10508 Now you can use all the usual commands to examine and change data and to
10509 step and continue the remote program.
10511 To resume the remote program and stop debugging it, use the @code{detach}
10514 @cindex interrupting remote programs
10515 @cindex remote programs, interrupting
10516 Whenever @value{GDBN} is waiting for the remote program, if you type the
10517 interrupt character (often @key{C-C}), @value{GDBN} attempts to stop the
10518 program. This may or may not succeed, depending in part on the hardware
10519 and the serial drivers the remote system uses. If you type the
10520 interrupt character once again, @value{GDBN} displays this prompt:
10523 Interrupted while waiting for the program.
10524 Give up (and stop debugging it)? (y or n)
10527 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
10528 (If you decide you want to try again later, you can use @samp{target
10529 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
10530 goes back to waiting.
10533 @node Configurations
10534 @chapter Configuration-Specific Information
10536 While nearly all @value{GDBN} commands are available for all native and
10537 cross versions of the debugger, there are some exceptions. This chapter
10538 describes things that are only available in certain configurations.
10540 There are three major categories of configurations: native
10541 configurations, where the host and target are the same, embedded
10542 operating system configurations, which are usually the same for several
10543 different processor architectures, and bare embedded processors, which
10544 are quite different from each other.
10549 * Embedded Processors::
10556 This section describes details specific to particular native
10561 * SVR4 Process Information:: SVR4 process information
10562 * DJGPP Native:: Features specific to the DJGPP port
10563 * Cygwin Native:: Features specific to the Cygwin port
10569 On HP-UX systems, if you refer to a function or variable name that
10570 begins with a dollar sign, @value{GDBN} searches for a user or system
10571 name first, before it searches for a convenience variable.
10573 @node SVR4 Process Information
10574 @subsection SVR4 process information
10577 @cindex process image
10579 Many versions of SVR4 provide a facility called @samp{/proc} that can be
10580 used to examine the image of a running process using file-system
10581 subroutines. If @value{GDBN} is configured for an operating system with
10582 this facility, the command @code{info proc} is available to report on
10583 several kinds of information about the process running your program.
10584 @code{info proc} works only on SVR4 systems that include the
10585 @code{procfs} code. This includes OSF/1 (Digital Unix), Solaris, Irix,
10586 and Unixware, but not HP-UX or Linux, for example.
10591 Summarize available information about the process.
10593 @kindex info proc mappings
10594 @item info proc mappings
10595 Report on the address ranges accessible in the program, with information
10596 on whether your program may read, write, or execute each range.
10598 @comment These sub-options of 'info proc' were not included when
10599 @comment procfs.c was re-written. Keep their descriptions around
10600 @comment against the day when someone finds the time to put them back in.
10601 @kindex info proc times
10602 @item info proc times
10603 Starting time, user CPU time, and system CPU time for your program and
10606 @kindex info proc id
10608 Report on the process IDs related to your program: its own process ID,
10609 the ID of its parent, the process group ID, and the session ID.
10611 @kindex info proc status
10612 @item info proc status
10613 General information on the state of the process. If the process is
10614 stopped, this report includes the reason for stopping, and any signal
10617 @item info proc all
10618 Show all the above information about the process.
10623 @subsection Features for Debugging @sc{djgpp} Programs
10624 @cindex @sc{djgpp} debugging
10625 @cindex native @sc{djgpp} debugging
10626 @cindex MS-DOS-specific commands
10628 @sc{djgpp} is the port of @sc{gnu} development tools to MS-DOS and
10629 MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs
10630 that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on
10631 top of real-mode DOS systems and their emulations.
10633 @value{GDBN} supports native debugging of @sc{djgpp} programs, and
10634 defines a few commands specific to the @sc{djgpp} port. This
10635 subsection describes those commands.
10640 This is a prefix of @sc{djgpp}-specific commands which print
10641 information about the target system and important OS structures.
10644 @cindex MS-DOS system info
10645 @cindex free memory information (MS-DOS)
10646 @item info dos sysinfo
10647 This command displays assorted information about the underlying
10648 platform: the CPU type and features, the OS version and flavor, the
10649 DPMI version, and the available conventional and DPMI memory.
10654 @cindex segment descriptor tables
10655 @cindex descriptor tables display
10657 @itemx info dos ldt
10658 @itemx info dos idt
10659 These 3 commands display entries from, respectively, Global, Local,
10660 and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor
10661 tables are data structures which store a descriptor for each segment
10662 that is currently in use. The segment's selector is an index into a
10663 descriptor table; the table entry for that index holds the
10664 descriptor's base address and limit, and its attributes and access
10667 A typical @sc{djgpp} program uses 3 segments: a code segment, a data
10668 segment (used for both data and the stack), and a DOS segment (which
10669 allows access to DOS/BIOS data structures and absolute addresses in
10670 conventional memory). However, the DPMI host will usually define
10671 additional segments in order to support the DPMI environment.
10673 @cindex garbled pointers
10674 These commands allow to display entries from the descriptor tables.
10675 Without an argument, all entries from the specified table are
10676 displayed. An argument, which should be an integer expression, means
10677 display a single entry whose index is given by the argument. For
10678 example, here's a convenient way to display information about the
10679 debugged program's data segment:
10682 @exdent @code{(@value{GDBP}) info dos ldt $ds}
10683 @exdent @code{0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)}
10687 This comes in handy when you want to see whether a pointer is outside
10688 the data segment's limit (i.e.@: @dfn{garbled}).
10690 @cindex page tables display (MS-DOS)
10692 @itemx info dos pte
10693 These two commands display entries from, respectively, the Page
10694 Directory and the Page Tables. Page Directories and Page Tables are
10695 data structures which control how virtual memory addresses are mapped
10696 into physical addresses. A Page Table includes an entry for every
10697 page of memory that is mapped into the program's address space; there
10698 may be several Page Tables, each one holding up to 4096 entries. A
10699 Page Directory has up to 4096 entries, one each for every Page Table
10700 that is currently in use.
10702 Without an argument, @kbd{info dos pde} displays the entire Page
10703 Directory, and @kbd{info dos pte} displays all the entries in all of
10704 the Page Tables. An argument, an integer expression, given to the
10705 @kbd{info dos pde} command means display only that entry from the Page
10706 Directory table. An argument given to the @kbd{info dos pte} command
10707 means display entries from a single Page Table, the one pointed to by
10708 the specified entry in the Page Directory.
10710 @cindex direct memory access (DMA) on MS-DOS
10711 These commands are useful when your program uses @dfn{DMA} (Direct
10712 Memory Access), which needs physical addresses to program the DMA
10715 These commands are supported only with some DPMI servers.
10717 @cindex physical address from linear address
10718 @item info dos address-pte @var{addr}
10719 This command displays the Page Table entry for a specified linear
10720 address. The argument linear address @var{addr} should already have the
10721 appropriate segment's base address added to it, because this command
10722 accepts addresses which may belong to @emph{any} segment. For
10723 example, here's how to display the Page Table entry for the page where
10724 the variable @code{i} is stored:
10727 @exdent @code{(@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i}
10728 @exdent @code{Page Table entry for address 0x11a00d30:}
10729 @exdent @code{Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30}
10733 This says that @code{i} is stored at offset @code{0xd30} from the page
10734 whose physical base address is @code{0x02698000}, and prints all the
10735 attributes of that page.
10737 Note that you must cast the addresses of variables to a @code{char *},
10738 since otherwise the value of @code{__djgpp_base_address}, the base
10739 address of all variables and functions in a @sc{djgpp} program, will
10740 be added using the rules of C pointer arithmetics: if @code{i} is
10741 declared an @code{int}, @value{GDBN} will add 4 times the value of
10742 @code{__djgpp_base_address} to the address of @code{i}.
10744 Here's another example, it displays the Page Table entry for the
10748 @exdent @code{(@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)}
10749 @exdent @code{Page Table entry for address 0x29110:}
10750 @exdent @code{Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110}
10754 (The @code{+ 3} offset is because the transfer buffer's address is the
10755 3rd member of the @code{_go32_info_block} structure.) The output of
10756 this command clearly shows that addresses in conventional memory are
10757 mapped 1:1, i.e.@: the physical and linear addresses are identical.
10759 This command is supported only with some DPMI servers.
10762 @node Cygwin Native
10763 @subsection Features for Debugging MS Windows PE executables
10764 @cindex MS Windows debugging
10765 @cindex native Cygwin debugging
10766 @cindex Cygwin-specific commands
10768 @value{GDBN} supports native debugging of MS Windows programs, and
10769 defines a few commands specific to the Cygwin port. This
10770 subsection describes those commands.
10775 This is a prefix of MS Windows specific commands which print
10776 information about the target system and important OS structures.
10778 @item info w32 selector
10779 This command displays information returned by
10780 the Win32 API @code{GetThreadSelectorEntry} function.
10781 It takes an optional argument that is evaluated to
10782 a long value to give the information about this given selector.
10783 Without argument, this command displays information
10784 about the the six segment registers.
10788 This is a Cygwin specific alias of info shared.
10790 @kindex dll-symbols
10792 This command loads symbols from a dll similarly to
10793 add-sym command but without the need to specify a base address.
10795 @kindex set new-console
10796 @item set new-console @var{mode}
10797 If @var{mode} is @code{on} the debuggee will
10798 be started in a new console on next start.
10799 If @var{mode} is @code{off}i, the debuggee will
10800 be started in the same console as the debugger.
10802 @kindex show new-console
10803 @item show new-console
10804 Displays whether a new console is used
10805 when the debuggee is started.
10807 @kindex set new-group
10808 @item set new-group @var{mode}
10809 This boolean value controls whether the debuggee should
10810 start a new group or stay in the same group as the debugger.
10811 This affects the way the Windows OS handles
10814 @kindex show new-group
10815 @item show new-group
10816 Displays current value of new-group boolean.
10818 @kindex set debugevents
10819 @item set debugevents
10820 This boolean value adds debug output concerning events seen by the debugger.
10822 @kindex set debugexec
10823 @item set debugexec
10824 This boolean value adds debug output concerning execute events
10825 seen by the debugger.
10827 @kindex set debugexceptions
10828 @item set debugexceptions
10829 This boolean value adds debug ouptut concerning exception events
10830 seen by the debugger.
10832 @kindex set debugmemory
10833 @item set debugmemory
10834 This boolean value adds debug ouptut concerning memory events
10835 seen by the debugger.
10839 This boolean values specifies whether the debuggee is called
10840 via a shell or directly (default value is on).
10844 Displays if the debuggee will be started with a shell.
10849 @section Embedded Operating Systems
10851 This section describes configurations involving the debugging of
10852 embedded operating systems that are available for several different
10856 * VxWorks:: Using @value{GDBN} with VxWorks
10859 @value{GDBN} includes the ability to debug programs running on
10860 various real-time operating systems.
10863 @subsection Using @value{GDBN} with VxWorks
10869 @kindex target vxworks
10870 @item target vxworks @var{machinename}
10871 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
10872 is the target system's machine name or IP address.
10876 On VxWorks, @code{load} links @var{filename} dynamically on the
10877 current target system as well as adding its symbols in @value{GDBN}.
10879 @value{GDBN} enables developers to spawn and debug tasks running on networked
10880 VxWorks targets from a Unix host. Already-running tasks spawned from
10881 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
10882 both the Unix host and on the VxWorks target. The program
10883 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
10884 installed with the name @code{vxgdb}, to distinguish it from a
10885 @value{GDBN} for debugging programs on the host itself.)
10888 @item VxWorks-timeout @var{args}
10889 @kindex vxworks-timeout
10890 All VxWorks-based targets now support the option @code{vxworks-timeout}.
10891 This option is set by the user, and @var{args} represents the number of
10892 seconds @value{GDBN} waits for responses to rpc's. You might use this if
10893 your VxWorks target is a slow software simulator or is on the far side
10894 of a thin network line.
10897 The following information on connecting to VxWorks was current when
10898 this manual was produced; newer releases of VxWorks may use revised
10901 @kindex INCLUDE_RDB
10902 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
10903 to include the remote debugging interface routines in the VxWorks
10904 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
10905 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
10906 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
10907 source debugging task @code{tRdbTask} when VxWorks is booted. For more
10908 information on configuring and remaking VxWorks, see the manufacturer's
10910 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
10912 Once you have included @file{rdb.a} in your VxWorks system image and set
10913 your Unix execution search path to find @value{GDBN}, you are ready to
10914 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
10915 @code{vxgdb}, depending on your installation).
10917 @value{GDBN} comes up showing the prompt:
10924 * VxWorks Connection:: Connecting to VxWorks
10925 * VxWorks Download:: VxWorks download
10926 * VxWorks Attach:: Running tasks
10929 @node VxWorks Connection
10930 @subsubsection Connecting to VxWorks
10932 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
10933 network. To connect to a target whose host name is ``@code{tt}'', type:
10936 (vxgdb) target vxworks tt
10940 @value{GDBN} displays messages like these:
10943 Attaching remote machine across net...
10948 @value{GDBN} then attempts to read the symbol tables of any object modules
10949 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
10950 these files by searching the directories listed in the command search
10951 path (@pxref{Environment, ,Your program's environment}); if it fails
10952 to find an object file, it displays a message such as:
10955 prog.o: No such file or directory.
10958 When this happens, add the appropriate directory to the search path with
10959 the @value{GDBN} command @code{path}, and execute the @code{target}
10962 @node VxWorks Download
10963 @subsubsection VxWorks download
10965 @cindex download to VxWorks
10966 If you have connected to the VxWorks target and you want to debug an
10967 object that has not yet been loaded, you can use the @value{GDBN}
10968 @code{load} command to download a file from Unix to VxWorks
10969 incrementally. The object file given as an argument to the @code{load}
10970 command is actually opened twice: first by the VxWorks target in order
10971 to download the code, then by @value{GDBN} in order to read the symbol
10972 table. This can lead to problems if the current working directories on
10973 the two systems differ. If both systems have NFS mounted the same
10974 filesystems, you can avoid these problems by using absolute paths.
10975 Otherwise, it is simplest to set the working directory on both systems
10976 to the directory in which the object file resides, and then to reference
10977 the file by its name, without any path. For instance, a program
10978 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
10979 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
10980 program, type this on VxWorks:
10983 -> cd "@var{vxpath}/vw/demo/rdb"
10987 Then, in @value{GDBN}, type:
10990 (vxgdb) cd @var{hostpath}/vw/demo/rdb
10991 (vxgdb) load prog.o
10994 @value{GDBN} displays a response similar to this:
10997 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
11000 You can also use the @code{load} command to reload an object module
11001 after editing and recompiling the corresponding source file. Note that
11002 this makes @value{GDBN} delete all currently-defined breakpoints,
11003 auto-displays, and convenience variables, and to clear the value
11004 history. (This is necessary in order to preserve the integrity of
11005 debugger's data structures that reference the target system's symbol
11008 @node VxWorks Attach
11009 @subsubsection Running tasks
11011 @cindex running VxWorks tasks
11012 You can also attach to an existing task using the @code{attach} command as
11016 (vxgdb) attach @var{task}
11020 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
11021 or suspended when you attach to it. Running tasks are suspended at
11022 the time of attachment.
11024 @node Embedded Processors
11025 @section Embedded Processors
11027 This section goes into details specific to particular embedded
11033 * H8/300:: Hitachi H8/300
11034 * H8/500:: Hitachi H8/500
11035 * i960:: Intel i960
11036 * M32R/D:: Mitsubishi M32R/D
11037 * M68K:: Motorola M68K
11038 * M88K:: Motorola M88K
11039 * MIPS Embedded:: MIPS Embedded
11040 * PA:: HP PA Embedded
11043 * Sparclet:: Tsqware Sparclet
11044 * Sparclite:: Fujitsu Sparclite
11045 * ST2000:: Tandem ST2000
11046 * Z8000:: Zilog Z8000
11055 @item target rdi @var{dev}
11056 ARM Angel monitor, via RDI library interface to ADP protocol. You may
11057 use this target to communicate with both boards running the Angel
11058 monitor, or with the EmbeddedICE JTAG debug device.
11061 @item target rdp @var{dev}
11067 @subsection Hitachi H8/300
11071 @kindex target hms@r{, with H8/300}
11072 @item target hms @var{dev}
11073 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
11074 Use special commands @code{device} and @code{speed} to control the serial
11075 line and the communications speed used.
11077 @kindex target e7000@r{, with H8/300}
11078 @item target e7000 @var{dev}
11079 E7000 emulator for Hitachi H8 and SH.
11081 @kindex target sh3@r{, with H8/300}
11082 @kindex target sh3e@r{, with H8/300}
11083 @item target sh3 @var{dev}
11084 @itemx target sh3e @var{dev}
11085 Hitachi SH-3 and SH-3E target systems.
11089 @cindex download to H8/300 or H8/500
11090 @cindex H8/300 or H8/500 download
11091 @cindex download to Hitachi SH
11092 @cindex Hitachi SH download
11093 When you select remote debugging to a Hitachi SH, H8/300, or H8/500
11094 board, the @code{load} command downloads your program to the Hitachi
11095 board and also opens it as the current executable target for
11096 @value{GDBN} on your host (like the @code{file} command).
11098 @value{GDBN} needs to know these things to talk to your
11099 Hitachi SH, H8/300, or H8/500:
11103 that you want to use @samp{target hms}, the remote debugging interface
11104 for Hitachi microprocessors, or @samp{target e7000}, the in-circuit
11105 emulator for the Hitachi SH and the Hitachi 300H. (@samp{target hms} is
11106 the default when @value{GDBN} is configured specifically for the Hitachi SH,
11107 H8/300, or H8/500.)
11110 what serial device connects your host to your Hitachi board (the first
11111 serial device available on your host is the default).
11114 what speed to use over the serial device.
11118 * Hitachi Boards:: Connecting to Hitachi boards.
11119 * Hitachi ICE:: Using the E7000 In-Circuit Emulator.
11120 * Hitachi Special:: Special @value{GDBN} commands for Hitachi micros.
11123 @node Hitachi Boards
11124 @subsubsection Connecting to Hitachi boards
11126 @c only for Unix hosts
11128 @cindex serial device, Hitachi micros
11129 Use the special @code{@value{GDBN}} command @samp{device @var{port}} if you
11130 need to explicitly set the serial device. The default @var{port} is the
11131 first available port on your host. This is only necessary on Unix
11132 hosts, where it is typically something like @file{/dev/ttya}.
11135 @cindex serial line speed, Hitachi micros
11136 @code{@value{GDBN}} has another special command to set the communications
11137 speed: @samp{speed @var{bps}}. This command also is only used from Unix
11138 hosts; on DOS hosts, set the line speed as usual from outside @value{GDBN} with
11139 the DOS @code{mode} command (for instance,
11140 @w{@kbd{mode com2:9600,n,8,1,p}} for a 9600@dmn{bps} connection).
11142 The @samp{device} and @samp{speed} commands are available only when you
11143 use a Unix host to debug your Hitachi microprocessor programs. If you
11145 @value{GDBN} depends on an auxiliary terminate-and-stay-resident program
11146 called @code{asynctsr} to communicate with the development board
11147 through a PC serial port. You must also use the DOS @code{mode} command
11148 to set up the serial port on the DOS side.
11150 The following sample session illustrates the steps needed to start a
11151 program under @value{GDBN} control on an H8/300. The example uses a
11152 sample H8/300 program called @file{t.x}. The procedure is the same for
11153 the Hitachi SH and the H8/500.
11155 First hook up your development board. In this example, we use a
11156 board attached to serial port @code{COM2}; if you use a different serial
11157 port, substitute its name in the argument of the @code{mode} command.
11158 When you call @code{asynctsr}, the auxiliary comms program used by the
11159 debugger, you give it just the numeric part of the serial port's name;
11160 for example, @samp{asyncstr 2} below runs @code{asyncstr} on
11164 C:\H8300\TEST> asynctsr 2
11165 C:\H8300\TEST> mode com2:9600,n,8,1,p
11167 Resident portion of MODE loaded
11169 COM2: 9600, n, 8, 1, p
11174 @emph{Warning:} We have noticed a bug in PC-NFS that conflicts with
11175 @code{asynctsr}. If you also run PC-NFS on your DOS host, you may need to
11176 disable it, or even boot without it, to use @code{asynctsr} to control
11177 your development board.
11180 @kindex target hms@r{, and serial protocol}
11181 Now that serial communications are set up, and the development board is
11182 connected, you can start up @value{GDBN}. Call @code{@value{GDBP}} with
11183 the name of your program as the argument. @code{@value{GDBN}} prompts
11184 you, as usual, with the prompt @samp{(@value{GDBP})}. Use two special
11185 commands to begin your debugging session: @samp{target hms} to specify
11186 cross-debugging to the Hitachi board, and the @code{load} command to
11187 download your program to the board. @code{load} displays the names of
11188 the program's sections, and a @samp{*} for each 2K of data downloaded.
11189 (If you want to refresh @value{GDBN} data on symbols or on the
11190 executable file without downloading, use the @value{GDBN} commands
11191 @code{file} or @code{symbol-file}. These commands, and @code{load}
11192 itself, are described in @ref{Files,,Commands to specify files}.)
11195 (eg-C:\H8300\TEST) @value{GDBP} t.x
11196 @value{GDBN} is free software and you are welcome to distribute copies
11197 of it under certain conditions; type "show copying" to see
11199 There is absolutely no warranty for @value{GDBN}; type "show warranty"
11201 @value{GDBN} @value{GDBVN}, Copyright 1992 Free Software Foundation, Inc...
11202 (@value{GDBP}) target hms
11203 Connected to remote H8/300 HMS system.
11204 (@value{GDBP}) load t.x
11205 .text : 0x8000 .. 0xabde ***********
11206 .data : 0xabde .. 0xad30 *
11207 .stack : 0xf000 .. 0xf014 *
11210 At this point, you're ready to run or debug your program. From here on,
11211 you can use all the usual @value{GDBN} commands. The @code{break} command
11212 sets breakpoints; the @code{run} command starts your program;
11213 @code{print} or @code{x} display data; the @code{continue} command
11214 resumes execution after stopping at a breakpoint. You can use the
11215 @code{help} command at any time to find out more about @value{GDBN} commands.
11217 Remember, however, that @emph{operating system} facilities aren't
11218 available on your development board; for example, if your program hangs,
11219 you can't send an interrupt---but you can press the @sc{reset} switch!
11221 Use the @sc{reset} button on the development board
11224 to interrupt your program (don't use @kbd{ctl-C} on the DOS host---it has
11225 no way to pass an interrupt signal to the development board); and
11228 to return to the @value{GDBN} command prompt after your program finishes
11229 normally. The communications protocol provides no other way for @value{GDBN}
11230 to detect program completion.
11233 In either case, @value{GDBN} sees the effect of a @sc{reset} on the
11234 development board as a ``normal exit'' of your program.
11237 @subsubsection Using the E7000 in-circuit emulator
11239 @kindex target e7000@r{, with Hitachi ICE}
11240 You can use the E7000 in-circuit emulator to develop code for either the
11241 Hitachi SH or the H8/300H. Use one of these forms of the @samp{target
11242 e7000} command to connect @value{GDBN} to your E7000:
11245 @item target e7000 @var{port} @var{speed}
11246 Use this form if your E7000 is connected to a serial port. The
11247 @var{port} argument identifies what serial port to use (for example,
11248 @samp{com2}). The third argument is the line speed in bits per second
11249 (for example, @samp{9600}).
11251 @item target e7000 @var{hostname}
11252 If your E7000 is installed as a host on a TCP/IP network, you can just
11253 specify its hostname; @value{GDBN} uses @code{telnet} to connect.
11256 @node Hitachi Special
11257 @subsubsection Special @value{GDBN} commands for Hitachi micros
11259 Some @value{GDBN} commands are available only for the H8/300:
11263 @kindex set machine
11264 @kindex show machine
11265 @item set machine h8300
11266 @itemx set machine h8300h
11267 Condition @value{GDBN} for one of the two variants of the H8/300
11268 architecture with @samp{set machine}. You can use @samp{show machine}
11269 to check which variant is currently in effect.
11278 @kindex set memory @var{mod}
11279 @cindex memory models, H8/500
11280 @item set memory @var{mod}
11282 Specify which H8/500 memory model (@var{mod}) you are using with
11283 @samp{set memory}; check which memory model is in effect with @samp{show
11284 memory}. The accepted values for @var{mod} are @code{small},
11285 @code{big}, @code{medium}, and @code{compact}.
11290 @subsection Intel i960
11294 @kindex target mon960
11295 @item target mon960 @var{dev}
11296 MON960 monitor for Intel i960.
11298 @kindex target nindy
11299 @item target nindy @var{devicename}
11300 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
11301 the name of the serial device to use for the connection, e.g.
11308 @dfn{Nindy} is a ROM Monitor program for Intel 960 target systems. When
11309 @value{GDBN} is configured to control a remote Intel 960 using Nindy, you can
11310 tell @value{GDBN} how to connect to the 960 in several ways:
11314 Through command line options specifying serial port, version of the
11315 Nindy protocol, and communications speed;
11318 By responding to a prompt on startup;
11321 By using the @code{target} command at any point during your @value{GDBN}
11322 session. @xref{Target Commands, ,Commands for managing targets}.
11326 @cindex download to Nindy-960
11327 With the Nindy interface to an Intel 960 board, @code{load}
11328 downloads @var{filename} to the 960 as well as adding its symbols in
11332 * Nindy Startup:: Startup with Nindy
11333 * Nindy Options:: Options for Nindy
11334 * Nindy Reset:: Nindy reset command
11337 @node Nindy Startup
11338 @subsubsection Startup with Nindy
11340 If you simply start @code{@value{GDBP}} without using any command-line
11341 options, you are prompted for what serial port to use, @emph{before} you
11342 reach the ordinary @value{GDBN} prompt:
11345 Attach /dev/ttyNN -- specify NN, or "quit" to quit:
11349 Respond to the prompt with whatever suffix (after @samp{/dev/tty})
11350 identifies the serial port you want to use. You can, if you choose,
11351 simply start up with no Nindy connection by responding to the prompt
11352 with an empty line. If you do this and later wish to attach to Nindy,
11353 use @code{target} (@pxref{Target Commands, ,Commands for managing targets}).
11355 @node Nindy Options
11356 @subsubsection Options for Nindy
11358 These are the startup options for beginning your @value{GDBN} session with a
11359 Nindy-960 board attached:
11362 @item -r @var{port}
11363 Specify the serial port name of a serial interface to be used to connect
11364 to the target system. This option is only available when @value{GDBN} is
11365 configured for the Intel 960 target architecture. You may specify
11366 @var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a
11367 device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique
11368 suffix for a specific @code{tty} (e.g. @samp{-r a}).
11371 (An uppercase letter ``O'', not a zero.) Specify that @value{GDBN} should use
11372 the ``old'' Nindy monitor protocol to connect to the target system.
11373 This option is only available when @value{GDBN} is configured for the Intel 960
11374 target architecture.
11377 @emph{Warning:} if you specify @samp{-O}, but are actually trying to
11378 connect to a target system that expects the newer protocol, the connection
11379 fails, appearing to be a speed mismatch. @value{GDBN} repeatedly
11380 attempts to reconnect at several different line speeds. You can abort
11381 this process with an interrupt.
11385 Specify that @value{GDBN} should first send a @code{BREAK} signal to the target
11386 system, in an attempt to reset it, before connecting to a Nindy target.
11389 @emph{Warning:} Many target systems do not have the hardware that this
11390 requires; it only works with a few boards.
11394 The standard @samp{-b} option controls the line speed used on the serial
11399 @subsubsection Nindy reset command
11404 For a Nindy target, this command sends a ``break'' to the remote target
11405 system; this is only useful if the target has been equipped with a
11406 circuit to perform a hard reset (or some other interesting action) when
11407 a break is detected.
11412 @subsection Mitsubishi M32R/D
11416 @kindex target m32r
11417 @item target m32r @var{dev}
11418 Mitsubishi M32R/D ROM monitor.
11425 The Motorola m68k configuration includes ColdFire support, and
11426 target command for the following ROM monitors.
11430 @kindex target abug
11431 @item target abug @var{dev}
11432 ABug ROM monitor for M68K.
11434 @kindex target cpu32bug
11435 @item target cpu32bug @var{dev}
11436 CPU32BUG monitor, running on a CPU32 (M68K) board.
11438 @kindex target dbug
11439 @item target dbug @var{dev}
11440 dBUG ROM monitor for Motorola ColdFire.
11443 @item target est @var{dev}
11444 EST-300 ICE monitor, running on a CPU32 (M68K) board.
11446 @kindex target rom68k
11447 @item target rom68k @var{dev}
11448 ROM 68K monitor, running on an M68K IDP board.
11452 If @value{GDBN} is configured with @code{m68*-ericsson-*}, it will
11453 instead have only a single special target command:
11457 @kindex target es1800
11458 @item target es1800 @var{dev}
11459 ES-1800 emulator for M68K.
11467 @kindex target rombug
11468 @item target rombug @var{dev}
11469 ROMBUG ROM monitor for OS/9000.
11479 @item target bug @var{dev}
11480 BUG monitor, running on a MVME187 (m88k) board.
11484 @node MIPS Embedded
11485 @subsection MIPS Embedded
11487 @cindex MIPS boards
11488 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
11489 MIPS board attached to a serial line. This is available when
11490 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
11493 Use these @value{GDBN} commands to specify the connection to your target board:
11496 @item target mips @var{port}
11497 @kindex target mips @var{port}
11498 To run a program on the board, start up @code{@value{GDBP}} with the
11499 name of your program as the argument. To connect to the board, use the
11500 command @samp{target mips @var{port}}, where @var{port} is the name of
11501 the serial port connected to the board. If the program has not already
11502 been downloaded to the board, you may use the @code{load} command to
11503 download it. You can then use all the usual @value{GDBN} commands.
11505 For example, this sequence connects to the target board through a serial
11506 port, and loads and runs a program called @var{prog} through the
11510 host$ @value{GDBP} @var{prog}
11511 @value{GDBN} is free software and @dots{}
11512 (@value{GDBP}) target mips /dev/ttyb
11513 (@value{GDBP}) load @var{prog}
11517 @item target mips @var{hostname}:@var{portnumber}
11518 On some @value{GDBN} host configurations, you can specify a TCP
11519 connection (for instance, to a serial line managed by a terminal
11520 concentrator) instead of a serial port, using the syntax
11521 @samp{@var{hostname}:@var{portnumber}}.
11523 @item target pmon @var{port}
11524 @kindex target pmon @var{port}
11527 @item target ddb @var{port}
11528 @kindex target ddb @var{port}
11529 NEC's DDB variant of PMON for Vr4300.
11531 @item target lsi @var{port}
11532 @kindex target lsi @var{port}
11533 LSI variant of PMON.
11535 @kindex target r3900
11536 @item target r3900 @var{dev}
11537 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
11539 @kindex target array
11540 @item target array @var{dev}
11541 Array Tech LSI33K RAID controller board.
11547 @value{GDBN} also supports these special commands for MIPS targets:
11550 @item set processor @var{args}
11551 @itemx show processor
11552 @kindex set processor @var{args}
11553 @kindex show processor
11554 Use the @code{set processor} command to set the type of MIPS
11555 processor when you want to access processor-type-specific registers.
11556 For example, @code{set processor @var{r3041}} tells @value{GDBN}
11557 to use the CPU registers appropriate for the 3041 chip.
11558 Use the @code{show processor} command to see what MIPS processor @value{GDBN}
11559 is using. Use the @code{info reg} command to see what registers
11560 @value{GDBN} is using.
11562 @item set mipsfpu double
11563 @itemx set mipsfpu single
11564 @itemx set mipsfpu none
11565 @itemx show mipsfpu
11566 @kindex set mipsfpu
11567 @kindex show mipsfpu
11568 @cindex MIPS remote floating point
11569 @cindex floating point, MIPS remote
11570 If your target board does not support the MIPS floating point
11571 coprocessor, you should use the command @samp{set mipsfpu none} (if you
11572 need this, you may wish to put the command in your @value{GDBN} init
11573 file). This tells @value{GDBN} how to find the return value of
11574 functions which return floating point values. It also allows
11575 @value{GDBN} to avoid saving the floating point registers when calling
11576 functions on the board. If you are using a floating point coprocessor
11577 with only single precision floating point support, as on the @sc{r4650}
11578 processor, use the command @samp{set mipsfpu single}. The default
11579 double precision floating point coprocessor may be selected using
11580 @samp{set mipsfpu double}.
11582 In previous versions the only choices were double precision or no
11583 floating point, so @samp{set mipsfpu on} will select double precision
11584 and @samp{set mipsfpu off} will select no floating point.
11586 As usual, you can inquire about the @code{mipsfpu} variable with
11587 @samp{show mipsfpu}.
11589 @item set remotedebug @var{n}
11590 @itemx show remotedebug
11591 @kindex set remotedebug@r{, MIPS protocol}
11592 @kindex show remotedebug@r{, MIPS protocol}
11593 @cindex @code{remotedebug}, MIPS protocol
11594 @cindex MIPS @code{remotedebug} protocol
11595 @c FIXME! For this to be useful, you must know something about the MIPS
11596 @c FIXME...protocol. Where is it described?
11597 You can see some debugging information about communications with the board
11598 by setting the @code{remotedebug} variable. If you set it to @code{1} using
11599 @samp{set remotedebug 1}, every packet is displayed. If you set it
11600 to @code{2}, every character is displayed. You can check the current value
11601 at any time with the command @samp{show remotedebug}.
11603 @item set timeout @var{seconds}
11604 @itemx set retransmit-timeout @var{seconds}
11605 @itemx show timeout
11606 @itemx show retransmit-timeout
11607 @cindex @code{timeout}, MIPS protocol
11608 @cindex @code{retransmit-timeout}, MIPS protocol
11609 @kindex set timeout
11610 @kindex show timeout
11611 @kindex set retransmit-timeout
11612 @kindex show retransmit-timeout
11613 You can control the timeout used while waiting for a packet, in the MIPS
11614 remote protocol, with the @code{set timeout @var{seconds}} command. The
11615 default is 5 seconds. Similarly, you can control the timeout used while
11616 waiting for an acknowledgement of a packet with the @code{set
11617 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
11618 You can inspect both values with @code{show timeout} and @code{show
11619 retransmit-timeout}. (These commands are @emph{only} available when
11620 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
11622 The timeout set by @code{set timeout} does not apply when @value{GDBN}
11623 is waiting for your program to stop. In that case, @value{GDBN} waits
11624 forever because it has no way of knowing how long the program is going
11625 to run before stopping.
11629 @subsection PowerPC
11633 @kindex target dink32
11634 @item target dink32 @var{dev}
11635 DINK32 ROM monitor.
11637 @kindex target ppcbug
11638 @item target ppcbug @var{dev}
11639 @kindex target ppcbug1
11640 @item target ppcbug1 @var{dev}
11641 PPCBUG ROM monitor for PowerPC.
11644 @item target sds @var{dev}
11645 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
11650 @subsection HP PA Embedded
11654 @kindex target op50n
11655 @item target op50n @var{dev}
11656 OP50N monitor, running on an OKI HPPA board.
11658 @kindex target w89k
11659 @item target w89k @var{dev}
11660 W89K monitor, running on a Winbond HPPA board.
11665 @subsection Hitachi SH
11669 @kindex target hms@r{, with Hitachi SH}
11670 @item target hms @var{dev}
11671 A Hitachi SH board attached via serial line to your host. Use special
11672 commands @code{device} and @code{speed} to control the serial line and
11673 the communications speed used.
11675 @kindex target e7000@r{, with Hitachi SH}
11676 @item target e7000 @var{dev}
11677 E7000 emulator for Hitachi SH.
11679 @kindex target sh3@r{, with SH}
11680 @kindex target sh3e@r{, with SH}
11681 @item target sh3 @var{dev}
11682 @item target sh3e @var{dev}
11683 Hitachi SH-3 and SH-3E target systems.
11688 @subsection Tsqware Sparclet
11692 @value{GDBN} enables developers to debug tasks running on
11693 Sparclet targets from a Unix host.
11694 @value{GDBN} uses code that runs on
11695 both the Unix host and on the Sparclet target. The program
11696 @code{@value{GDBP}} is installed and executed on the Unix host.
11699 @item remotetimeout @var{args}
11700 @kindex remotetimeout
11701 @value{GDBN} supports the option @code{remotetimeout}.
11702 This option is set by the user, and @var{args} represents the number of
11703 seconds @value{GDBN} waits for responses.
11706 @cindex compiling, on Sparclet
11707 When compiling for debugging, include the options @samp{-g} to get debug
11708 information and @samp{-Ttext} to relocate the program to where you wish to
11709 load it on the target. You may also want to add the options @samp{-n} or
11710 @samp{-N} in order to reduce the size of the sections. Example:
11713 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
11716 You can use @code{objdump} to verify that the addresses are what you intended:
11719 sparclet-aout-objdump --headers --syms prog
11722 @cindex running, on Sparclet
11724 your Unix execution search path to find @value{GDBN}, you are ready to
11725 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
11726 (or @code{sparclet-aout-gdb}, depending on your installation).
11728 @value{GDBN} comes up showing the prompt:
11735 * Sparclet File:: Setting the file to debug
11736 * Sparclet Connection:: Connecting to Sparclet
11737 * Sparclet Download:: Sparclet download
11738 * Sparclet Execution:: Running and debugging
11741 @node Sparclet File
11742 @subsubsection Setting file to debug
11744 The @value{GDBN} command @code{file} lets you choose with program to debug.
11747 (gdbslet) file prog
11751 @value{GDBN} then attempts to read the symbol table of @file{prog}.
11752 @value{GDBN} locates
11753 the file by searching the directories listed in the command search
11755 If the file was compiled with debug information (option "-g"), source
11756 files will be searched as well.
11757 @value{GDBN} locates
11758 the source files by searching the directories listed in the directory search
11759 path (@pxref{Environment, ,Your program's environment}).
11761 to find a file, it displays a message such as:
11764 prog: No such file or directory.
11767 When this happens, add the appropriate directories to the search paths with
11768 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
11769 @code{target} command again.
11771 @node Sparclet Connection
11772 @subsubsection Connecting to Sparclet
11774 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
11775 To connect to a target on serial port ``@code{ttya}'', type:
11778 (gdbslet) target sparclet /dev/ttya
11779 Remote target sparclet connected to /dev/ttya
11780 main () at ../prog.c:3
11784 @value{GDBN} displays messages like these:
11790 @node Sparclet Download
11791 @subsubsection Sparclet download
11793 @cindex download to Sparclet
11794 Once connected to the Sparclet target,
11795 you can use the @value{GDBN}
11796 @code{load} command to download the file from the host to the target.
11797 The file name and load offset should be given as arguments to the @code{load}
11799 Since the file format is aout, the program must be loaded to the starting
11800 address. You can use @code{objdump} to find out what this value is. The load
11801 offset is an offset which is added to the VMA (virtual memory address)
11802 of each of the file's sections.
11803 For instance, if the program
11804 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
11805 and bss at 0x12010170, in @value{GDBN}, type:
11808 (gdbslet) load prog 0x12010000
11809 Loading section .text, size 0xdb0 vma 0x12010000
11812 If the code is loaded at a different address then what the program was linked
11813 to, you may need to use the @code{section} and @code{add-symbol-file} commands
11814 to tell @value{GDBN} where to map the symbol table.
11816 @node Sparclet Execution
11817 @subsubsection Running and debugging
11819 @cindex running and debugging Sparclet programs
11820 You can now begin debugging the task using @value{GDBN}'s execution control
11821 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
11822 manual for the list of commands.
11826 Breakpoint 1 at 0x12010000: file prog.c, line 3.
11828 Starting program: prog
11829 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
11830 3 char *symarg = 0;
11832 4 char *execarg = "hello!";
11837 @subsection Fujitsu Sparclite
11841 @kindex target sparclite
11842 @item target sparclite @var{dev}
11843 Fujitsu sparclite boards, used only for the purpose of loading.
11844 You must use an additional command to debug the program.
11845 For example: target remote @var{dev} using @value{GDBN} standard
11851 @subsection Tandem ST2000
11853 @value{GDBN} may be used with a Tandem ST2000 phone switch, running Tandem's
11856 To connect your ST2000 to the host system, see the manufacturer's
11857 manual. Once the ST2000 is physically attached, you can run:
11860 target st2000 @var{dev} @var{speed}
11864 to establish it as your debugging environment. @var{dev} is normally
11865 the name of a serial device, such as @file{/dev/ttya}, connected to the
11866 ST2000 via a serial line. You can instead specify @var{dev} as a TCP
11867 connection (for example, to a serial line attached via a terminal
11868 concentrator) using the syntax @code{@var{hostname}:@var{portnumber}}.
11870 The @code{load} and @code{attach} commands are @emph{not} defined for
11871 this target; you must load your program into the ST2000 as you normally
11872 would for standalone operation. @value{GDBN} reads debugging information
11873 (such as symbols) from a separate, debugging version of the program
11874 available on your host computer.
11875 @c FIXME!! This is terribly vague; what little content is here is
11876 @c basically hearsay.
11878 @cindex ST2000 auxiliary commands
11879 These auxiliary @value{GDBN} commands are available to help you with the ST2000
11883 @item st2000 @var{command}
11884 @kindex st2000 @var{cmd}
11885 @cindex STDBUG commands (ST2000)
11886 @cindex commands to STDBUG (ST2000)
11887 Send a @var{command} to the STDBUG monitor. See the manufacturer's
11888 manual for available commands.
11891 @cindex connect (to STDBUG)
11892 Connect the controlling terminal to the STDBUG command monitor. When
11893 you are done interacting with STDBUG, typing either of two character
11894 sequences gets you back to the @value{GDBN} command prompt:
11895 @kbd{@key{RET}~.} (Return, followed by tilde and period) or
11896 @kbd{@key{RET}~@key{C-d}} (Return, followed by tilde and control-D).
11900 @subsection Zilog Z8000
11903 @cindex simulator, Z8000
11904 @cindex Zilog Z8000 simulator
11906 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
11909 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
11910 unsegmented variant of the Z8000 architecture) or the Z8001 (the
11911 segmented variant). The simulator recognizes which architecture is
11912 appropriate by inspecting the object code.
11915 @item target sim @var{args}
11917 @kindex target sim@r{, with Z8000}
11918 Debug programs on a simulated CPU. If the simulator supports setup
11919 options, specify them via @var{args}.
11923 After specifying this target, you can debug programs for the simulated
11924 CPU in the same style as programs for your host computer; use the
11925 @code{file} command to load a new program image, the @code{run} command
11926 to run your program, and so on.
11928 As well as making available all the usual machine registers
11929 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
11930 additional items of information as specially named registers:
11935 Counts clock-ticks in the simulator.
11938 Counts instructions run in the simulator.
11941 Execution time in 60ths of a second.
11945 You can refer to these values in @value{GDBN} expressions with the usual
11946 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
11947 conditional breakpoint that suspends only after at least 5000
11948 simulated clock ticks.
11950 @node Architectures
11951 @section Architectures
11953 This section describes characteristics of architectures that affect
11954 all uses of @value{GDBN} with the architecture, both native and cross.
11967 @kindex set rstack_high_address
11968 @cindex AMD 29K register stack
11969 @cindex register stack, AMD29K
11970 @item set rstack_high_address @var{address}
11971 On AMD 29000 family processors, registers are saved in a separate
11972 @dfn{register stack}. There is no way for @value{GDBN} to determine the
11973 extent of this stack. Normally, @value{GDBN} just assumes that the
11974 stack is ``large enough''. This may result in @value{GDBN} referencing
11975 memory locations that do not exist. If necessary, you can get around
11976 this problem by specifying the ending address of the register stack with
11977 the @code{set rstack_high_address} command. The argument should be an
11978 address, which you probably want to precede with @samp{0x} to specify in
11981 @kindex show rstack_high_address
11982 @item show rstack_high_address
11983 Display the current limit of the register stack, on AMD 29000 family
11991 See the following section.
11996 @cindex stack on Alpha
11997 @cindex stack on MIPS
11998 @cindex Alpha stack
12000 Alpha- and MIPS-based computers use an unusual stack frame, which
12001 sometimes requires @value{GDBN} to search backward in the object code to
12002 find the beginning of a function.
12004 @cindex response time, MIPS debugging
12005 To improve response time (especially for embedded applications, where
12006 @value{GDBN} may be restricted to a slow serial line for this search)
12007 you may want to limit the size of this search, using one of these
12011 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
12012 @item set heuristic-fence-post @var{limit}
12013 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
12014 search for the beginning of a function. A value of @var{0} (the
12015 default) means there is no limit. However, except for @var{0}, the
12016 larger the limit the more bytes @code{heuristic-fence-post} must search
12017 and therefore the longer it takes to run.
12019 @item show heuristic-fence-post
12020 Display the current limit.
12024 These commands are available @emph{only} when @value{GDBN} is configured
12025 for debugging programs on Alpha or MIPS processors.
12028 @node Controlling GDB
12029 @chapter Controlling @value{GDBN}
12031 You can alter the way @value{GDBN} interacts with you by using the
12032 @code{set} command. For commands controlling how @value{GDBN} displays
12033 data, see @ref{Print Settings, ,Print settings}. Other settings are
12038 * Editing:: Command editing
12039 * History:: Command history
12040 * Screen Size:: Screen size
12041 * Numbers:: Numbers
12042 * Messages/Warnings:: Optional warnings and messages
12043 * Debugging Output:: Optional messages about internal happenings
12051 @value{GDBN} indicates its readiness to read a command by printing a string
12052 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
12053 can change the prompt string with the @code{set prompt} command. For
12054 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
12055 the prompt in one of the @value{GDBN} sessions so that you can always tell
12056 which one you are talking to.
12058 @emph{Note:} @code{set prompt} does not add a space for you after the
12059 prompt you set. This allows you to set a prompt which ends in a space
12060 or a prompt that does not.
12064 @item set prompt @var{newprompt}
12065 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
12067 @kindex show prompt
12069 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
12073 @section Command editing
12075 @cindex command line editing
12077 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
12078 @sc{gnu} library provides consistent behavior for programs which provide a
12079 command line interface to the user. Advantages are @sc{gnu} Emacs-style
12080 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
12081 substitution, and a storage and recall of command history across
12082 debugging sessions.
12084 You may control the behavior of command line editing in @value{GDBN} with the
12085 command @code{set}.
12088 @kindex set editing
12091 @itemx set editing on
12092 Enable command line editing (enabled by default).
12094 @item set editing off
12095 Disable command line editing.
12097 @kindex show editing
12099 Show whether command line editing is enabled.
12103 @section Command history
12105 @value{GDBN} can keep track of the commands you type during your
12106 debugging sessions, so that you can be certain of precisely what
12107 happened. Use these commands to manage the @value{GDBN} command
12111 @cindex history substitution
12112 @cindex history file
12113 @kindex set history filename
12114 @kindex GDBHISTFILE
12115 @item set history filename @var{fname}
12116 Set the name of the @value{GDBN} command history file to @var{fname}.
12117 This is the file where @value{GDBN} reads an initial command history
12118 list, and where it writes the command history from this session when it
12119 exits. You can access this list through history expansion or through
12120 the history command editing characters listed below. This file defaults
12121 to the value of the environment variable @code{GDBHISTFILE}, or to
12122 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
12125 @cindex history save
12126 @kindex set history save
12127 @item set history save
12128 @itemx set history save on
12129 Record command history in a file, whose name may be specified with the
12130 @code{set history filename} command. By default, this option is disabled.
12132 @item set history save off
12133 Stop recording command history in a file.
12135 @cindex history size
12136 @kindex set history size
12137 @item set history size @var{size}
12138 Set the number of commands which @value{GDBN} keeps in its history list.
12139 This defaults to the value of the environment variable
12140 @code{HISTSIZE}, or to 256 if this variable is not set.
12143 @cindex history expansion
12144 History expansion assigns special meaning to the character @kbd{!}.
12145 @ifset have-readline-appendices
12146 @xref{Event Designators}.
12149 Since @kbd{!} is also the logical not operator in C, history expansion
12150 is off by default. If you decide to enable history expansion with the
12151 @code{set history expansion on} command, you may sometimes need to
12152 follow @kbd{!} (when it is used as logical not, in an expression) with
12153 a space or a tab to prevent it from being expanded. The readline
12154 history facilities do not attempt substitution on the strings
12155 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
12157 The commands to control history expansion are:
12160 @kindex set history expansion
12161 @item set history expansion on
12162 @itemx set history expansion
12163 Enable history expansion. History expansion is off by default.
12165 @item set history expansion off
12166 Disable history expansion.
12168 The readline code comes with more complete documentation of
12169 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
12170 or @code{vi} may wish to read it.
12171 @ifset have-readline-appendices
12172 @xref{Command Line Editing}.
12176 @kindex show history
12178 @itemx show history filename
12179 @itemx show history save
12180 @itemx show history size
12181 @itemx show history expansion
12182 These commands display the state of the @value{GDBN} history parameters.
12183 @code{show history} by itself displays all four states.
12189 @item show commands
12190 Display the last ten commands in the command history.
12192 @item show commands @var{n}
12193 Print ten commands centered on command number @var{n}.
12195 @item show commands +
12196 Print ten commands just after the commands last printed.
12200 @section Screen size
12201 @cindex size of screen
12202 @cindex pauses in output
12204 Certain commands to @value{GDBN} may produce large amounts of
12205 information output to the screen. To help you read all of it,
12206 @value{GDBN} pauses and asks you for input at the end of each page of
12207 output. Type @key{RET} when you want to continue the output, or @kbd{q}
12208 to discard the remaining output. Also, the screen width setting
12209 determines when to wrap lines of output. Depending on what is being
12210 printed, @value{GDBN} tries to break the line at a readable place,
12211 rather than simply letting it overflow onto the following line.
12213 Normally @value{GDBN} knows the size of the screen from the terminal
12214 driver software. For example, on Unix @value{GDBN} uses the termcap data base
12215 together with the value of the @code{TERM} environment variable and the
12216 @code{stty rows} and @code{stty cols} settings. If this is not correct,
12217 you can override it with the @code{set height} and @code{set
12224 @kindex show height
12225 @item set height @var{lpp}
12227 @itemx set width @var{cpl}
12229 These @code{set} commands specify a screen height of @var{lpp} lines and
12230 a screen width of @var{cpl} characters. The associated @code{show}
12231 commands display the current settings.
12233 If you specify a height of zero lines, @value{GDBN} does not pause during
12234 output no matter how long the output is. This is useful if output is to a
12235 file or to an editor buffer.
12237 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
12238 from wrapping its output.
12243 @cindex number representation
12244 @cindex entering numbers
12246 You can always enter numbers in octal, decimal, or hexadecimal in
12247 @value{GDBN} by the usual conventions: octal numbers begin with
12248 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
12249 begin with @samp{0x}. Numbers that begin with none of these are, by
12250 default, entered in base 10; likewise, the default display for
12251 numbers---when no particular format is specified---is base 10. You can
12252 change the default base for both input and output with the @code{set
12256 @kindex set input-radix
12257 @item set input-radix @var{base}
12258 Set the default base for numeric input. Supported choices
12259 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12260 specified either unambiguously or using the current default radix; for
12270 sets the base to decimal. On the other hand, @samp{set radix 10}
12271 leaves the radix unchanged no matter what it was.
12273 @kindex set output-radix
12274 @item set output-radix @var{base}
12275 Set the default base for numeric display. Supported choices
12276 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12277 specified either unambiguously or using the current default radix.
12279 @kindex show input-radix
12280 @item show input-radix
12281 Display the current default base for numeric input.
12283 @kindex show output-radix
12284 @item show output-radix
12285 Display the current default base for numeric display.
12288 @node Messages/Warnings
12289 @section Optional warnings and messages
12291 By default, @value{GDBN} is silent about its inner workings. If you are
12292 running on a slow machine, you may want to use the @code{set verbose}
12293 command. This makes @value{GDBN} tell you when it does a lengthy
12294 internal operation, so you will not think it has crashed.
12296 Currently, the messages controlled by @code{set verbose} are those
12297 which announce that the symbol table for a source file is being read;
12298 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
12301 @kindex set verbose
12302 @item set verbose on
12303 Enables @value{GDBN} output of certain informational messages.
12305 @item set verbose off
12306 Disables @value{GDBN} output of certain informational messages.
12308 @kindex show verbose
12310 Displays whether @code{set verbose} is on or off.
12313 By default, if @value{GDBN} encounters bugs in the symbol table of an
12314 object file, it is silent; but if you are debugging a compiler, you may
12315 find this information useful (@pxref{Symbol Errors, ,Errors reading
12320 @kindex set complaints
12321 @item set complaints @var{limit}
12322 Permits @value{GDBN} to output @var{limit} complaints about each type of
12323 unusual symbols before becoming silent about the problem. Set
12324 @var{limit} to zero to suppress all complaints; set it to a large number
12325 to prevent complaints from being suppressed.
12327 @kindex show complaints
12328 @item show complaints
12329 Displays how many symbol complaints @value{GDBN} is permitted to produce.
12333 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
12334 lot of stupid questions to confirm certain commands. For example, if
12335 you try to run a program which is already running:
12339 The program being debugged has been started already.
12340 Start it from the beginning? (y or n)
12343 If you are willing to unflinchingly face the consequences of your own
12344 commands, you can disable this ``feature'':
12348 @kindex set confirm
12350 @cindex confirmation
12351 @cindex stupid questions
12352 @item set confirm off
12353 Disables confirmation requests.
12355 @item set confirm on
12356 Enables confirmation requests (the default).
12358 @kindex show confirm
12360 Displays state of confirmation requests.
12364 @node Debugging Output
12365 @section Optional messages about internal happenings
12367 @kindex set debug arch
12368 @item set debug arch
12369 Turns on or off display of gdbarch debugging info. The default is off
12370 @kindex show debug arch
12371 @item show debug arch
12372 Displays the current state of displaying gdbarch debugging info.
12373 @kindex set debug event
12374 @item set debug event
12375 Turns on or off display of @value{GDBN} event debugging info. The
12377 @kindex show debug event
12378 @item show debug event
12379 Displays the current state of displaying @value{GDBN} event debugging
12381 @kindex set debug expression
12382 @item set debug expression
12383 Turns on or off display of @value{GDBN} expression debugging info. The
12385 @kindex show debug expression
12386 @item show debug expression
12387 Displays the current state of displaying @value{GDBN} expression
12389 @kindex set debug overload
12390 @item set debug overload
12391 Turns on or off display of @value{GDBN} C@t{++} overload debugging
12392 info. This includes info such as ranking of functions, etc. The default
12394 @kindex show debug overload
12395 @item show debug overload
12396 Displays the current state of displaying @value{GDBN} C@t{++} overload
12398 @kindex set debug remote
12399 @cindex packets, reporting on stdout
12400 @cindex serial connections, debugging
12401 @item set debug remote
12402 Turns on or off display of reports on all packets sent back and forth across
12403 the serial line to the remote machine. The info is printed on the
12404 @value{GDBN} standard output stream. The default is off.
12405 @kindex show debug remote
12406 @item show debug remote
12407 Displays the state of display of remote packets.
12408 @kindex set debug serial
12409 @item set debug serial
12410 Turns on or off display of @value{GDBN} serial debugging info. The
12412 @kindex show debug serial
12413 @item show debug serial
12414 Displays the current state of displaying @value{GDBN} serial debugging
12416 @kindex set debug target
12417 @item set debug target
12418 Turns on or off display of @value{GDBN} target debugging info. This info
12419 includes what is going on at the target level of GDB, as it happens. The
12421 @kindex show debug target
12422 @item show debug target
12423 Displays the current state of displaying @value{GDBN} target debugging
12425 @kindex set debug varobj
12426 @item set debug varobj
12427 Turns on or off display of @value{GDBN} variable object debugging
12428 info. The default is off.
12429 @kindex show debug varobj
12430 @item show debug varobj
12431 Displays the current state of displaying @value{GDBN} variable object
12436 @chapter Canned Sequences of Commands
12438 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
12439 command lists}), @value{GDBN} provides two ways to store sequences of
12440 commands for execution as a unit: user-defined commands and command
12444 * Define:: User-defined commands
12445 * Hooks:: User-defined command hooks
12446 * Command Files:: Command files
12447 * Output:: Commands for controlled output
12451 @section User-defined commands
12453 @cindex user-defined command
12454 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
12455 which you assign a new name as a command. This is done with the
12456 @code{define} command. User commands may accept up to 10 arguments
12457 separated by whitespace. Arguments are accessed within the user command
12458 via @var{$arg0@dots{}$arg9}. A trivial example:
12462 print $arg0 + $arg1 + $arg2
12466 To execute the command use:
12473 This defines the command @code{adder}, which prints the sum of
12474 its three arguments. Note the arguments are text substitutions, so they may
12475 reference variables, use complex expressions, or even perform inferior
12481 @item define @var{commandname}
12482 Define a command named @var{commandname}. If there is already a command
12483 by that name, you are asked to confirm that you want to redefine it.
12485 The definition of the command is made up of other @value{GDBN} command lines,
12486 which are given following the @code{define} command. The end of these
12487 commands is marked by a line containing @code{end}.
12492 Takes a single argument, which is an expression to evaluate.
12493 It is followed by a series of commands that are executed
12494 only if the expression is true (nonzero).
12495 There can then optionally be a line @code{else}, followed
12496 by a series of commands that are only executed if the expression
12497 was false. The end of the list is marked by a line containing @code{end}.
12501 The syntax is similar to @code{if}: the command takes a single argument,
12502 which is an expression to evaluate, and must be followed by the commands to
12503 execute, one per line, terminated by an @code{end}.
12504 The commands are executed repeatedly as long as the expression
12508 @item document @var{commandname}
12509 Document the user-defined command @var{commandname}, so that it can be
12510 accessed by @code{help}. The command @var{commandname} must already be
12511 defined. This command reads lines of documentation just as @code{define}
12512 reads the lines of the command definition, ending with @code{end}.
12513 After the @code{document} command is finished, @code{help} on command
12514 @var{commandname} displays the documentation you have written.
12516 You may use the @code{document} command again to change the
12517 documentation of a command. Redefining the command with @code{define}
12518 does not change the documentation.
12520 @kindex help user-defined
12521 @item help user-defined
12522 List all user-defined commands, with the first line of the documentation
12527 @itemx show user @var{commandname}
12528 Display the @value{GDBN} commands used to define @var{commandname} (but
12529 not its documentation). If no @var{commandname} is given, display the
12530 definitions for all user-defined commands.
12532 @kindex show max-user-call-depth
12533 @kindex set max-user-call-depth
12534 @item show max-user-call-depth
12535 @itemx set max-user-call-depth
12536 The value of @code{max-user-call-depth} controls how many recursion
12537 levels are allowed in user-defined commands before GDB suspects an
12538 infinite recursion and aborts the command.
12542 When user-defined commands are executed, the
12543 commands of the definition are not printed. An error in any command
12544 stops execution of the user-defined command.
12546 If used interactively, commands that would ask for confirmation proceed
12547 without asking when used inside a user-defined command. Many @value{GDBN}
12548 commands that normally print messages to say what they are doing omit the
12549 messages when used in a user-defined command.
12552 @section User-defined command hooks
12553 @cindex command hooks
12554 @cindex hooks, for commands
12555 @cindex hooks, pre-command
12559 You may define @dfn{hooks}, which are a special kind of user-defined
12560 command. Whenever you run the command @samp{foo}, if the user-defined
12561 command @samp{hook-foo} exists, it is executed (with no arguments)
12562 before that command.
12564 @cindex hooks, post-command
12567 A hook may also be defined which is run after the command you executed.
12568 Whenever you run the command @samp{foo}, if the user-defined command
12569 @samp{hookpost-foo} exists, it is executed (with no arguments) after
12570 that command. Post-execution hooks may exist simultaneously with
12571 pre-execution hooks, for the same command.
12573 It is valid for a hook to call the command which it hooks. If this
12574 occurs, the hook is not re-executed, thereby avoiding infinte recursion.
12576 @c It would be nice if hookpost could be passed a parameter indicating
12577 @c if the command it hooks executed properly or not. FIXME!
12579 @kindex stop@r{, a pseudo-command}
12580 In addition, a pseudo-command, @samp{stop} exists. Defining
12581 (@samp{hook-stop}) makes the associated commands execute every time
12582 execution stops in your program: before breakpoint commands are run,
12583 displays are printed, or the stack frame is printed.
12585 For example, to ignore @code{SIGALRM} signals while
12586 single-stepping, but treat them normally during normal execution,
12591 handle SIGALRM nopass
12595 handle SIGALRM pass
12598 define hook-continue
12599 handle SIGLARM pass
12603 As a further example, to hook at the begining and end of the @code{echo}
12604 command, and to add extra text to the beginning and end of the message,
12612 define hookpost-echo
12616 (@value{GDBP}) echo Hello World
12617 <<<---Hello World--->>>
12622 You can define a hook for any single-word command in @value{GDBN}, but
12623 not for command aliases; you should define a hook for the basic command
12624 name, e.g. @code{backtrace} rather than @code{bt}.
12625 @c FIXME! So how does Joe User discover whether a command is an alias
12627 If an error occurs during the execution of your hook, execution of
12628 @value{GDBN} commands stops and @value{GDBN} issues a prompt
12629 (before the command that you actually typed had a chance to run).
12631 If you try to define a hook which does not match any known command, you
12632 get a warning from the @code{define} command.
12634 @node Command Files
12635 @section Command files
12637 @cindex command files
12638 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
12639 commands. Comments (lines starting with @kbd{#}) may also be included.
12640 An empty line in a command file does nothing; it does not mean to repeat
12641 the last command, as it would from the terminal.
12644 @cindex @file{.gdbinit}
12645 @cindex @file{gdb.ini}
12646 When you start @value{GDBN}, it automatically executes commands from its
12647 @dfn{init files}, normally called @file{.gdbinit}@footnote{The DJGPP
12648 port of @value{GDBN} uses the name @file{gdb.ini} instead, due to the
12649 limitations of file names imposed by DOS filesystems.}.
12650 During startup, @value{GDBN} does the following:
12654 Reads the init file (if any) in your home directory@footnote{On
12655 DOS/Windows systems, the home directory is the one pointed to by the
12656 @code{HOME} environment variable.}.
12659 Processes command line options and operands.
12662 Reads the init file (if any) in the current working directory.
12665 Reads command files specified by the @samp{-x} option.
12668 The init file in your home directory can set options (such as @samp{set
12669 complaints}) that affect subsequent processing of command line options
12670 and operands. Init files are not executed if you use the @samp{-nx}
12671 option (@pxref{Mode Options, ,Choosing modes}).
12673 @cindex init file name
12674 On some configurations of @value{GDBN}, the init file is known by a
12675 different name (these are typically environments where a specialized
12676 form of @value{GDBN} may need to coexist with other forms, hence a
12677 different name for the specialized version's init file). These are the
12678 environments with special init file names:
12680 @cindex @file{.vxgdbinit}
12683 VxWorks (Wind River Systems real-time OS): @file{.vxgdbinit}
12685 @cindex @file{.os68gdbinit}
12687 OS68K (Enea Data Systems real-time OS): @file{.os68gdbinit}
12689 @cindex @file{.esgdbinit}
12691 ES-1800 (Ericsson Telecom AB M68000 emulator): @file{.esgdbinit}
12694 You can also request the execution of a command file with the
12695 @code{source} command:
12699 @item source @var{filename}
12700 Execute the command file @var{filename}.
12703 The lines in a command file are executed sequentially. They are not
12704 printed as they are executed. An error in any command terminates execution
12705 of the command file.
12707 Commands that would ask for confirmation if used interactively proceed
12708 without asking when used in a command file. Many @value{GDBN} commands that
12709 normally print messages to say what they are doing omit the messages
12710 when called from command files.
12712 @value{GDBN} also accepts command input from standard input. In this
12713 mode, normal output goes to standard output and error output goes to
12714 standard error. Errors in a command file supplied on standard input do
12715 not terminate execution of the command file --- execution continues with
12719 gdb < cmds > log 2>&1
12722 (The syntax above will vary depending on the shell used.) This example
12723 will execute commands from the file @file{cmds}. All output and errors
12724 would be directed to @file{log}.
12727 @section Commands for controlled output
12729 During the execution of a command file or a user-defined command, normal
12730 @value{GDBN} output is suppressed; the only output that appears is what is
12731 explicitly printed by the commands in the definition. This section
12732 describes three commands useful for generating exactly the output you
12737 @item echo @var{text}
12738 @c I do not consider backslash-space a standard C escape sequence
12739 @c because it is not in ANSI.
12740 Print @var{text}. Nonprinting characters can be included in
12741 @var{text} using C escape sequences, such as @samp{\n} to print a
12742 newline. @strong{No newline is printed unless you specify one.}
12743 In addition to the standard C escape sequences, a backslash followed
12744 by a space stands for a space. This is useful for displaying a
12745 string with spaces at the beginning or the end, since leading and
12746 trailing spaces are otherwise trimmed from all arguments.
12747 To print @samp{@w{ }and foo =@w{ }}, use the command
12748 @samp{echo \@w{ }and foo = \@w{ }}.
12750 A backslash at the end of @var{text} can be used, as in C, to continue
12751 the command onto subsequent lines. For example,
12754 echo This is some text\n\
12755 which is continued\n\
12756 onto several lines.\n
12759 produces the same output as
12762 echo This is some text\n
12763 echo which is continued\n
12764 echo onto several lines.\n
12768 @item output @var{expression}
12769 Print the value of @var{expression} and nothing but that value: no
12770 newlines, no @samp{$@var{nn} = }. The value is not entered in the
12771 value history either. @xref{Expressions, ,Expressions}, for more information
12774 @item output/@var{fmt} @var{expression}
12775 Print the value of @var{expression} in format @var{fmt}. You can use
12776 the same formats as for @code{print}. @xref{Output Formats,,Output
12777 formats}, for more information.
12780 @item printf @var{string}, @var{expressions}@dots{}
12781 Print the values of the @var{expressions} under the control of
12782 @var{string}. The @var{expressions} are separated by commas and may be
12783 either numbers or pointers. Their values are printed as specified by
12784 @var{string}, exactly as if your program were to execute the C
12786 @c FIXME: the above implies that at least all ANSI C formats are
12787 @c supported, but it isn't true: %E and %G don't work (or so it seems).
12788 @c Either this is a bug, or the manual should document what formats are
12792 printf (@var{string}, @var{expressions}@dots{});
12795 For example, you can print two values in hex like this:
12798 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
12801 The only backslash-escape sequences that you can use in the format
12802 string are the simple ones that consist of backslash followed by a
12807 @chapter @value{GDBN} Text User Interface
12811 * TUI Overview:: TUI overview
12812 * TUI Keys:: TUI key bindings
12813 * TUI Commands:: TUI specific commands
12814 * TUI Configuration:: TUI configuration variables
12817 The @value{GDBN} Text User Interface, TUI in short,
12818 is a terminal interface which uses the @code{curses} library
12819 to show the source file, the assembly output, the program registers
12820 and @value{GDBN} commands in separate text windows.
12821 The TUI is available only when @value{GDBN} is configured
12822 with the @code{--enable-tui} configure option (@pxref{Configure Options}).
12825 @section TUI overview
12827 The TUI has two display modes that can be switched while
12832 A curses (or TUI) mode in which it displays several text
12833 windows on the terminal.
12836 A standard mode which corresponds to the @value{GDBN} configured without
12840 In the TUI mode, @value{GDBN} can display several text window
12845 This window is the @value{GDBN} command window with the @value{GDBN}
12846 prompt and the @value{GDBN} outputs. The @value{GDBN} input is still
12847 managed using readline but through the TUI. The @emph{command}
12848 window is always visible.
12851 The source window shows the source file of the program. The current
12852 line as well as active breakpoints are displayed in this window.
12853 The current program position is shown with the @samp{>} marker and
12854 active breakpoints are shown with @samp{*} markers.
12857 The assembly window shows the disassembly output of the program.
12860 This window shows the processor registers. It detects when
12861 a register is changed and when this is the case, registers that have
12862 changed are highlighted.
12866 The source, assembly and register windows are attached to the thread
12867 and the frame position. They are updated when the current thread
12868 changes, when the frame changes or when the program counter changes.
12869 These three windows are arranged by the TUI according to several
12870 layouts. The layout defines which of these three windows are visible.
12871 The following layouts are available:
12881 source and assembly
12884 source and registers
12887 assembly and registers
12892 @section TUI Key Bindings
12893 @cindex TUI key bindings
12895 The TUI installs several key bindings in the readline keymaps
12896 (@pxref{Command Line Editing}).
12897 They allow to leave or enter in the TUI mode or they operate
12898 directly on the TUI layout and windows. The following key bindings
12899 are installed for both TUI mode and the @value{GDBN} standard mode.
12908 Enter or leave the TUI mode. When the TUI mode is left,
12909 the curses window management is left and @value{GDBN} operates using
12910 its standard mode writing on the terminal directly. When the TUI
12911 mode is entered, the control is given back to the curses windows.
12912 The screen is then refreshed.
12916 Use a TUI layout with only one window. The layout will
12917 either be @samp{source} or @samp{assembly}. When the TUI mode
12918 is not active, it will switch to the TUI mode.
12920 Think of this key binding as the Emacs @kbd{C-x 1} binding.
12924 Use a TUI layout with at least two windows. When the current
12925 layout shows already two windows, a next layout with two windows is used.
12926 When a new layout is chosen, one window will always be common to the
12927 previous layout and the new one.
12929 Think of it as the Emacs @kbd{C-x 2} binding.
12933 The following key bindings are handled only by the TUI mode:
12938 Scroll the active window one page up.
12942 Scroll the active window one page down.
12946 Scroll the active window one line up.
12950 Scroll the active window one line down.
12954 Scroll the active window one column left.
12958 Scroll the active window one column right.
12962 Refresh the screen.
12966 In the TUI mode, the arrow keys are used by the active window
12967 for scrolling. This means they are not available for readline. It is
12968 necessary to use other readline key bindings such as @key{C-p}, @key{C-n},
12969 @key{C-b} and @key{C-f}.
12972 @section TUI specific commands
12973 @cindex TUI commands
12975 The TUI has specific commands to control the text windows.
12976 These commands are always available, that is they do not depend on
12977 the current terminal mode in which @value{GDBN} runs. When @value{GDBN}
12978 is in the standard mode, using these commands will automatically switch
12983 @kindex layout next
12984 Display the next layout.
12987 @kindex layout prev
12988 Display the previous layout.
12992 Display the source window only.
12996 Display the assembly window only.
12999 @kindex layout split
13000 Display the source and assembly window.
13003 @kindex layout regs
13004 Display the register window together with the source or assembly window.
13006 @item focus next | prev | src | asm | regs | split
13008 Set the focus to the named window.
13009 This command allows to change the active window so that scrolling keys
13010 can be affected to another window.
13014 Refresh the screen. This is similar to using @key{C-L} key.
13018 Update the source window and the current execution point.
13020 @item winheight @var{name} +@var{count}
13021 @itemx winheight @var{name} -@var{count}
13023 Change the height of the window @var{name} by @var{count}
13024 lines. Positive counts increase the height, while negative counts
13029 @node TUI Configuration
13030 @section TUI configuration variables
13031 @cindex TUI configuration variables
13033 The TUI has several configuration variables that control the
13034 appearance of windows on the terminal.
13037 @item set tui border-kind @var{kind}
13038 @kindex set tui border-kind
13039 Select the border appearance for the source, assembly and register windows.
13040 The possible values are the following:
13043 Use a space character to draw the border.
13046 Use ascii characters + - and | to draw the border.
13049 Use the Alternate Character Set to draw the border. The border is
13050 drawn using character line graphics if the terminal supports them.
13054 @item set tui active-border-mode @var{mode}
13055 @kindex set tui active-border-mode
13056 Select the attributes to display the border of the active window.
13057 The possible values are @code{normal}, @code{standout}, @code{reverse},
13058 @code{half}, @code{half-standout}, @code{bold} and @code{bold-standout}.
13060 @item set tui border-mode @var{mode}
13061 @kindex set tui border-mode
13062 Select the attributes to display the border of other windows.
13063 The @var{mode} can be one of the following:
13066 Use normal attributes to display the border.
13072 Use reverse video mode.
13075 Use half bright mode.
13077 @item half-standout
13078 Use half bright and standout mode.
13081 Use extra bright or bold mode.
13083 @item bold-standout
13084 Use extra bright or bold and standout mode.
13091 @chapter Using @value{GDBN} under @sc{gnu} Emacs
13094 @cindex @sc{gnu} Emacs
13095 A special interface allows you to use @sc{gnu} Emacs to view (and
13096 edit) the source files for the program you are debugging with
13099 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
13100 executable file you want to debug as an argument. This command starts
13101 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
13102 created Emacs buffer.
13103 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
13105 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
13110 All ``terminal'' input and output goes through the Emacs buffer.
13113 This applies both to @value{GDBN} commands and their output, and to the input
13114 and output done by the program you are debugging.
13116 This is useful because it means that you can copy the text of previous
13117 commands and input them again; you can even use parts of the output
13120 All the facilities of Emacs' Shell mode are available for interacting
13121 with your program. In particular, you can send signals the usual
13122 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
13127 @value{GDBN} displays source code through Emacs.
13130 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
13131 source file for that frame and puts an arrow (@samp{=>}) at the
13132 left margin of the current line. Emacs uses a separate buffer for
13133 source display, and splits the screen to show both your @value{GDBN} session
13136 Explicit @value{GDBN} @code{list} or search commands still produce output as
13137 usual, but you probably have no reason to use them from Emacs.
13140 @emph{Warning:} If the directory where your program resides is not your
13141 current directory, it can be easy to confuse Emacs about the location of
13142 the source files, in which case the auxiliary display buffer does not
13143 appear to show your source. @value{GDBN} can find programs by searching your
13144 environment's @code{PATH} variable, so the @value{GDBN} input and output
13145 session proceeds normally; but Emacs does not get enough information
13146 back from @value{GDBN} to locate the source files in this situation. To
13147 avoid this problem, either start @value{GDBN} mode from the directory where
13148 your program resides, or specify an absolute file name when prompted for the
13149 @kbd{M-x gdb} argument.
13151 A similar confusion can result if you use the @value{GDBN} @code{file} command to
13152 switch to debugging a program in some other location, from an existing
13153 @value{GDBN} buffer in Emacs.
13156 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
13157 you need to call @value{GDBN} by a different name (for example, if you keep
13158 several configurations around, with different names) you can set the
13159 Emacs variable @code{gdb-command-name}; for example,
13162 (setq gdb-command-name "mygdb")
13166 (preceded by @kbd{M-:} or @kbd{ESC :}, or typed in the @code{*scratch*} buffer, or
13167 in your @file{.emacs} file) makes Emacs call the program named
13168 ``@code{mygdb}'' instead.
13170 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
13171 addition to the standard Shell mode commands:
13175 Describe the features of Emacs' @value{GDBN} Mode.
13178 Execute to another source line, like the @value{GDBN} @code{step} command; also
13179 update the display window to show the current file and location.
13182 Execute to next source line in this function, skipping all function
13183 calls, like the @value{GDBN} @code{next} command. Then update the display window
13184 to show the current file and location.
13187 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
13188 display window accordingly.
13190 @item M-x gdb-nexti
13191 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
13192 display window accordingly.
13195 Execute until exit from the selected stack frame, like the @value{GDBN}
13196 @code{finish} command.
13199 Continue execution of your program, like the @value{GDBN} @code{continue}
13202 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
13205 Go up the number of frames indicated by the numeric argument
13206 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
13207 like the @value{GDBN} @code{up} command.
13209 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
13212 Go down the number of frames indicated by the numeric argument, like the
13213 @value{GDBN} @code{down} command.
13215 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
13218 Read the number where the cursor is positioned, and insert it at the end
13219 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
13220 around an address that was displayed earlier, type @kbd{disassemble};
13221 then move the cursor to the address display, and pick up the
13222 argument for @code{disassemble} by typing @kbd{C-x &}.
13224 You can customize this further by defining elements of the list
13225 @code{gdb-print-command}; once it is defined, you can format or
13226 otherwise process numbers picked up by @kbd{C-x &} before they are
13227 inserted. A numeric argument to @kbd{C-x &} indicates that you
13228 wish special formatting, and also acts as an index to pick an element of the
13229 list. If the list element is a string, the number to be inserted is
13230 formatted using the Emacs function @code{format}; otherwise the number
13231 is passed as an argument to the corresponding list element.
13234 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
13235 tells @value{GDBN} to set a breakpoint on the source line point is on.
13237 If you accidentally delete the source-display buffer, an easy way to get
13238 it back is to type the command @code{f} in the @value{GDBN} buffer, to
13239 request a frame display; when you run under Emacs, this recreates
13240 the source buffer if necessary to show you the context of the current
13243 The source files displayed in Emacs are in ordinary Emacs buffers
13244 which are visiting the source files in the usual way. You can edit
13245 the files with these buffers if you wish; but keep in mind that @value{GDBN}
13246 communicates with Emacs in terms of line numbers. If you add or
13247 delete lines from the text, the line numbers that @value{GDBN} knows cease
13248 to correspond properly with the code.
13250 @c The following dropped because Epoch is nonstandard. Reactivate
13251 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
13253 @kindex Emacs Epoch environment
13257 Version 18 of @sc{gnu} Emacs has a built-in window system
13258 called the @code{epoch}
13259 environment. Users of this environment can use a new command,
13260 @code{inspect} which performs identically to @code{print} except that
13261 each value is printed in its own window.
13264 @include annotate.texi
13265 @include gdbmi.texinfo
13268 @chapter Reporting Bugs in @value{GDBN}
13269 @cindex bugs in @value{GDBN}
13270 @cindex reporting bugs in @value{GDBN}
13272 Your bug reports play an essential role in making @value{GDBN} reliable.
13274 Reporting a bug may help you by bringing a solution to your problem, or it
13275 may not. But in any case the principal function of a bug report is to help
13276 the entire community by making the next version of @value{GDBN} work better. Bug
13277 reports are your contribution to the maintenance of @value{GDBN}.
13279 In order for a bug report to serve its purpose, you must include the
13280 information that enables us to fix the bug.
13283 * Bug Criteria:: Have you found a bug?
13284 * Bug Reporting:: How to report bugs
13288 @section Have you found a bug?
13289 @cindex bug criteria
13291 If you are not sure whether you have found a bug, here are some guidelines:
13294 @cindex fatal signal
13295 @cindex debugger crash
13296 @cindex crash of debugger
13298 If the debugger gets a fatal signal, for any input whatever, that is a
13299 @value{GDBN} bug. Reliable debuggers never crash.
13301 @cindex error on valid input
13303 If @value{GDBN} produces an error message for valid input, that is a
13304 bug. (Note that if you're cross debugging, the problem may also be
13305 somewhere in the connection to the target.)
13307 @cindex invalid input
13309 If @value{GDBN} does not produce an error message for invalid input,
13310 that is a bug. However, you should note that your idea of
13311 ``invalid input'' might be our idea of ``an extension'' or ``support
13312 for traditional practice''.
13315 If you are an experienced user of debugging tools, your suggestions
13316 for improvement of @value{GDBN} are welcome in any case.
13319 @node Bug Reporting
13320 @section How to report bugs
13321 @cindex bug reports
13322 @cindex @value{GDBN} bugs, reporting
13324 A number of companies and individuals offer support for @sc{gnu} products.
13325 If you obtained @value{GDBN} from a support organization, we recommend you
13326 contact that organization first.
13328 You can find contact information for many support companies and
13329 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
13331 @c should add a web page ref...
13333 In any event, we also recommend that you submit bug reports for
13334 @value{GDBN}. The prefered method is to submit them directly using
13335 @uref{http://www.gnu.org/software/gdb/bugs/, @value{GDBN}'s Bugs web
13336 page}. Alternatively, the @email{bug-gdb@@gnu.org, e-mail gateway} can
13339 @strong{Do not send bug reports to @samp{info-gdb}, or to
13340 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
13341 not want to receive bug reports. Those that do have arranged to receive
13344 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
13345 serves as a repeater. The mailing list and the newsgroup carry exactly
13346 the same messages. Often people think of posting bug reports to the
13347 newsgroup instead of mailing them. This appears to work, but it has one
13348 problem which can be crucial: a newsgroup posting often lacks a mail
13349 path back to the sender. Thus, if we need to ask for more information,
13350 we may be unable to reach you. For this reason, it is better to send
13351 bug reports to the mailing list.
13353 The fundamental principle of reporting bugs usefully is this:
13354 @strong{report all the facts}. If you are not sure whether to state a
13355 fact or leave it out, state it!
13357 Often people omit facts because they think they know what causes the
13358 problem and assume that some details do not matter. Thus, you might
13359 assume that the name of the variable you use in an example does not matter.
13360 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
13361 stray memory reference which happens to fetch from the location where that
13362 name is stored in memory; perhaps, if the name were different, the contents
13363 of that location would fool the debugger into doing the right thing despite
13364 the bug. Play it safe and give a specific, complete example. That is the
13365 easiest thing for you to do, and the most helpful.
13367 Keep in mind that the purpose of a bug report is to enable us to fix the
13368 bug. It may be that the bug has been reported previously, but neither
13369 you nor we can know that unless your bug report is complete and
13372 Sometimes people give a few sketchy facts and ask, ``Does this ring a
13373 bell?'' Those bug reports are useless, and we urge everyone to
13374 @emph{refuse to respond to them} except to chide the sender to report
13377 To enable us to fix the bug, you should include all these things:
13381 The version of @value{GDBN}. @value{GDBN} announces it if you start
13382 with no arguments; you can also print it at any time using @code{show
13385 Without this, we will not know whether there is any point in looking for
13386 the bug in the current version of @value{GDBN}.
13389 The type of machine you are using, and the operating system name and
13393 What compiler (and its version) was used to compile @value{GDBN}---e.g.
13394 ``@value{GCC}--2.8.1''.
13397 What compiler (and its version) was used to compile the program you are
13398 debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
13399 C Compiler''. For GCC, you can say @code{gcc --version} to get this
13400 information; for other compilers, see the documentation for those
13404 The command arguments you gave the compiler to compile your example and
13405 observe the bug. For example, did you use @samp{-O}? To guarantee
13406 you will not omit something important, list them all. A copy of the
13407 Makefile (or the output from make) is sufficient.
13409 If we were to try to guess the arguments, we would probably guess wrong
13410 and then we might not encounter the bug.
13413 A complete input script, and all necessary source files, that will
13417 A description of what behavior you observe that you believe is
13418 incorrect. For example, ``It gets a fatal signal.''
13420 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
13421 will certainly notice it. But if the bug is incorrect output, we might
13422 not notice unless it is glaringly wrong. You might as well not give us
13423 a chance to make a mistake.
13425 Even if the problem you experience is a fatal signal, you should still
13426 say so explicitly. Suppose something strange is going on, such as, your
13427 copy of @value{GDBN} is out of synch, or you have encountered a bug in
13428 the C library on your system. (This has happened!) Your copy might
13429 crash and ours would not. If you told us to expect a crash, then when
13430 ours fails to crash, we would know that the bug was not happening for
13431 us. If you had not told us to expect a crash, then we would not be able
13432 to draw any conclusion from our observations.
13435 If you wish to suggest changes to the @value{GDBN} source, send us context
13436 diffs. If you even discuss something in the @value{GDBN} source, refer to
13437 it by context, not by line number.
13439 The line numbers in our development sources will not match those in your
13440 sources. Your line numbers would convey no useful information to us.
13444 Here are some things that are not necessary:
13448 A description of the envelope of the bug.
13450 Often people who encounter a bug spend a lot of time investigating
13451 which changes to the input file will make the bug go away and which
13452 changes will not affect it.
13454 This is often time consuming and not very useful, because the way we
13455 will find the bug is by running a single example under the debugger
13456 with breakpoints, not by pure deduction from a series of examples.
13457 We recommend that you save your time for something else.
13459 Of course, if you can find a simpler example to report @emph{instead}
13460 of the original one, that is a convenience for us. Errors in the
13461 output will be easier to spot, running under the debugger will take
13462 less time, and so on.
13464 However, simplification is not vital; if you do not want to do this,
13465 report the bug anyway and send us the entire test case you used.
13468 A patch for the bug.
13470 A patch for the bug does help us if it is a good one. But do not omit
13471 the necessary information, such as the test case, on the assumption that
13472 a patch is all we need. We might see problems with your patch and decide
13473 to fix the problem another way, or we might not understand it at all.
13475 Sometimes with a program as complicated as @value{GDBN} it is very hard to
13476 construct an example that will make the program follow a certain path
13477 through the code. If you do not send us the example, we will not be able
13478 to construct one, so we will not be able to verify that the bug is fixed.
13480 And if we cannot understand what bug you are trying to fix, or why your
13481 patch should be an improvement, we will not install it. A test case will
13482 help us to understand.
13485 A guess about what the bug is or what it depends on.
13487 Such guesses are usually wrong. Even we cannot guess right about such
13488 things without first using the debugger to find the facts.
13491 @c The readline documentation is distributed with the readline code
13492 @c and consists of the two following files:
13494 @c inc-hist.texinfo
13495 @c Use -I with makeinfo to point to the appropriate directory,
13496 @c environment var TEXINPUTS with TeX.
13497 @include rluser.texinfo
13498 @include inc-hist.texinfo
13501 @node Formatting Documentation
13502 @appendix Formatting Documentation
13504 @cindex @value{GDBN} reference card
13505 @cindex reference card
13506 The @value{GDBN} 4 release includes an already-formatted reference card, ready
13507 for printing with PostScript or Ghostscript, in the @file{gdb}
13508 subdirectory of the main source directory@footnote{In
13509 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
13510 release.}. If you can use PostScript or Ghostscript with your printer,
13511 you can print the reference card immediately with @file{refcard.ps}.
13513 The release also includes the source for the reference card. You
13514 can format it, using @TeX{}, by typing:
13520 The @value{GDBN} reference card is designed to print in @dfn{landscape}
13521 mode on US ``letter'' size paper;
13522 that is, on a sheet 11 inches wide by 8.5 inches
13523 high. You will need to specify this form of printing as an option to
13524 your @sc{dvi} output program.
13526 @cindex documentation
13528 All the documentation for @value{GDBN} comes as part of the machine-readable
13529 distribution. The documentation is written in Texinfo format, which is
13530 a documentation system that uses a single source file to produce both
13531 on-line information and a printed manual. You can use one of the Info
13532 formatting commands to create the on-line version of the documentation
13533 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
13535 @value{GDBN} includes an already formatted copy of the on-line Info
13536 version of this manual in the @file{gdb} subdirectory. The main Info
13537 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
13538 subordinate files matching @samp{gdb.info*} in the same directory. If
13539 necessary, you can print out these files, or read them with any editor;
13540 but they are easier to read using the @code{info} subsystem in @sc{gnu}
13541 Emacs or the standalone @code{info} program, available as part of the
13542 @sc{gnu} Texinfo distribution.
13544 If you want to format these Info files yourself, you need one of the
13545 Info formatting programs, such as @code{texinfo-format-buffer} or
13548 If you have @code{makeinfo} installed, and are in the top level
13549 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
13550 version @value{GDBVN}), you can make the Info file by typing:
13557 If you want to typeset and print copies of this manual, you need @TeX{},
13558 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
13559 Texinfo definitions file.
13561 @TeX{} is a typesetting program; it does not print files directly, but
13562 produces output files called @sc{dvi} files. To print a typeset
13563 document, you need a program to print @sc{dvi} files. If your system
13564 has @TeX{} installed, chances are it has such a program. The precise
13565 command to use depends on your system; @kbd{lpr -d} is common; another
13566 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
13567 require a file name without any extension or a @samp{.dvi} extension.
13569 @TeX{} also requires a macro definitions file called
13570 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
13571 written in Texinfo format. On its own, @TeX{} cannot either read or
13572 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
13573 and is located in the @file{gdb-@var{version-number}/texinfo}
13576 If you have @TeX{} and a @sc{dvi} printer program installed, you can
13577 typeset and print this manual. First switch to the the @file{gdb}
13578 subdirectory of the main source directory (for example, to
13579 @file{gdb-@value{GDBVN}/gdb}) and type:
13585 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
13587 @node Installing GDB
13588 @appendix Installing @value{GDBN}
13589 @cindex configuring @value{GDBN}
13590 @cindex installation
13592 @value{GDBN} comes with a @code{configure} script that automates the process
13593 of preparing @value{GDBN} for installation; you can then use @code{make} to
13594 build the @code{gdb} program.
13596 @c irrelevant in info file; it's as current as the code it lives with.
13597 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
13598 look at the @file{README} file in the sources; we may have improved the
13599 installation procedures since publishing this manual.}
13602 The @value{GDBN} distribution includes all the source code you need for
13603 @value{GDBN} in a single directory, whose name is usually composed by
13604 appending the version number to @samp{gdb}.
13606 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
13607 @file{gdb-@value{GDBVN}} directory. That directory contains:
13610 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
13611 script for configuring @value{GDBN} and all its supporting libraries
13613 @item gdb-@value{GDBVN}/gdb
13614 the source specific to @value{GDBN} itself
13616 @item gdb-@value{GDBVN}/bfd
13617 source for the Binary File Descriptor library
13619 @item gdb-@value{GDBVN}/include
13620 @sc{gnu} include files
13622 @item gdb-@value{GDBVN}/libiberty
13623 source for the @samp{-liberty} free software library
13625 @item gdb-@value{GDBVN}/opcodes
13626 source for the library of opcode tables and disassemblers
13628 @item gdb-@value{GDBVN}/readline
13629 source for the @sc{gnu} command-line interface
13631 @item gdb-@value{GDBVN}/glob
13632 source for the @sc{gnu} filename pattern-matching subroutine
13634 @item gdb-@value{GDBVN}/mmalloc
13635 source for the @sc{gnu} memory-mapped malloc package
13638 The simplest way to configure and build @value{GDBN} is to run @code{configure}
13639 from the @file{gdb-@var{version-number}} source directory, which in
13640 this example is the @file{gdb-@value{GDBVN}} directory.
13642 First switch to the @file{gdb-@var{version-number}} source directory
13643 if you are not already in it; then run @code{configure}. Pass the
13644 identifier for the platform on which @value{GDBN} will run as an
13650 cd gdb-@value{GDBVN}
13651 ./configure @var{host}
13656 where @var{host} is an identifier such as @samp{sun4} or
13657 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
13658 (You can often leave off @var{host}; @code{configure} tries to guess the
13659 correct value by examining your system.)
13661 Running @samp{configure @var{host}} and then running @code{make} builds the
13662 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
13663 libraries, then @code{gdb} itself. The configured source files, and the
13664 binaries, are left in the corresponding source directories.
13667 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
13668 system does not recognize this automatically when you run a different
13669 shell, you may need to run @code{sh} on it explicitly:
13672 sh configure @var{host}
13675 If you run @code{configure} from a directory that contains source
13676 directories for multiple libraries or programs, such as the
13677 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
13678 creates configuration files for every directory level underneath (unless
13679 you tell it not to, with the @samp{--norecursion} option).
13681 You can run the @code{configure} script from any of the
13682 subordinate directories in the @value{GDBN} distribution if you only want to
13683 configure that subdirectory, but be sure to specify a path to it.
13685 For example, with version @value{GDBVN}, type the following to configure only
13686 the @code{bfd} subdirectory:
13690 cd gdb-@value{GDBVN}/bfd
13691 ../configure @var{host}
13695 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
13696 However, you should make sure that the shell on your path (named by
13697 the @samp{SHELL} environment variable) is publicly readable. Remember
13698 that @value{GDBN} uses the shell to start your program---some systems refuse to
13699 let @value{GDBN} debug child processes whose programs are not readable.
13702 * Separate Objdir:: Compiling @value{GDBN} in another directory
13703 * Config Names:: Specifying names for hosts and targets
13704 * Configure Options:: Summary of options for configure
13707 @node Separate Objdir
13708 @section Compiling @value{GDBN} in another directory
13710 If you want to run @value{GDBN} versions for several host or target machines,
13711 you need a different @code{gdb} compiled for each combination of
13712 host and target. @code{configure} is designed to make this easy by
13713 allowing you to generate each configuration in a separate subdirectory,
13714 rather than in the source directory. If your @code{make} program
13715 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
13716 @code{make} in each of these directories builds the @code{gdb}
13717 program specified there.
13719 To build @code{gdb} in a separate directory, run @code{configure}
13720 with the @samp{--srcdir} option to specify where to find the source.
13721 (You also need to specify a path to find @code{configure}
13722 itself from your working directory. If the path to @code{configure}
13723 would be the same as the argument to @samp{--srcdir}, you can leave out
13724 the @samp{--srcdir} option; it is assumed.)
13726 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
13727 separate directory for a Sun 4 like this:
13731 cd gdb-@value{GDBVN}
13734 ../gdb-@value{GDBVN}/configure sun4
13739 When @code{configure} builds a configuration using a remote source
13740 directory, it creates a tree for the binaries with the same structure
13741 (and using the same names) as the tree under the source directory. In
13742 the example, you'd find the Sun 4 library @file{libiberty.a} in the
13743 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
13744 @file{gdb-sun4/gdb}.
13746 One popular reason to build several @value{GDBN} configurations in separate
13747 directories is to configure @value{GDBN} for cross-compiling (where
13748 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
13749 programs that run on another machine---the @dfn{target}).
13750 You specify a cross-debugging target by
13751 giving the @samp{--target=@var{target}} option to @code{configure}.
13753 When you run @code{make} to build a program or library, you must run
13754 it in a configured directory---whatever directory you were in when you
13755 called @code{configure} (or one of its subdirectories).
13757 The @code{Makefile} that @code{configure} generates in each source
13758 directory also runs recursively. If you type @code{make} in a source
13759 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
13760 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
13761 will build all the required libraries, and then build GDB.
13763 When you have multiple hosts or targets configured in separate
13764 directories, you can run @code{make} on them in parallel (for example,
13765 if they are NFS-mounted on each of the hosts); they will not interfere
13769 @section Specifying names for hosts and targets
13771 The specifications used for hosts and targets in the @code{configure}
13772 script are based on a three-part naming scheme, but some short predefined
13773 aliases are also supported. The full naming scheme encodes three pieces
13774 of information in the following pattern:
13777 @var{architecture}-@var{vendor}-@var{os}
13780 For example, you can use the alias @code{sun4} as a @var{host} argument,
13781 or as the value for @var{target} in a @code{--target=@var{target}}
13782 option. The equivalent full name is @samp{sparc-sun-sunos4}.
13784 The @code{configure} script accompanying @value{GDBN} does not provide
13785 any query facility to list all supported host and target names or
13786 aliases. @code{configure} calls the Bourne shell script
13787 @code{config.sub} to map abbreviations to full names; you can read the
13788 script, if you wish, or you can use it to test your guesses on
13789 abbreviations---for example:
13792 % sh config.sub i386-linux
13794 % sh config.sub alpha-linux
13795 alpha-unknown-linux-gnu
13796 % sh config.sub hp9k700
13798 % sh config.sub sun4
13799 sparc-sun-sunos4.1.1
13800 % sh config.sub sun3
13801 m68k-sun-sunos4.1.1
13802 % sh config.sub i986v
13803 Invalid configuration `i986v': machine `i986v' not recognized
13807 @code{config.sub} is also distributed in the @value{GDBN} source
13808 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
13810 @node Configure Options
13811 @section @code{configure} options
13813 Here is a summary of the @code{configure} options and arguments that
13814 are most often useful for building @value{GDBN}. @code{configure} also has
13815 several other options not listed here. @inforef{What Configure
13816 Does,,configure.info}, for a full explanation of @code{configure}.
13819 configure @r{[}--help@r{]}
13820 @r{[}--prefix=@var{dir}@r{]}
13821 @r{[}--exec-prefix=@var{dir}@r{]}
13822 @r{[}--srcdir=@var{dirname}@r{]}
13823 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
13824 @r{[}--target=@var{target}@r{]}
13829 You may introduce options with a single @samp{-} rather than
13830 @samp{--} if you prefer; but you may abbreviate option names if you use
13835 Display a quick summary of how to invoke @code{configure}.
13837 @item --prefix=@var{dir}
13838 Configure the source to install programs and files under directory
13841 @item --exec-prefix=@var{dir}
13842 Configure the source to install programs under directory
13845 @c avoid splitting the warning from the explanation:
13847 @item --srcdir=@var{dirname}
13848 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
13849 @code{make} that implements the @code{VPATH} feature.}@*
13850 Use this option to make configurations in directories separate from the
13851 @value{GDBN} source directories. Among other things, you can use this to
13852 build (or maintain) several configurations simultaneously, in separate
13853 directories. @code{configure} writes configuration specific files in
13854 the current directory, but arranges for them to use the source in the
13855 directory @var{dirname}. @code{configure} creates directories under
13856 the working directory in parallel to the source directories below
13859 @item --norecursion
13860 Configure only the directory level where @code{configure} is executed; do not
13861 propagate configuration to subdirectories.
13863 @item --target=@var{target}
13864 Configure @value{GDBN} for cross-debugging programs running on the specified
13865 @var{target}. Without this option, @value{GDBN} is configured to debug
13866 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
13868 There is no convenient way to generate a list of all available targets.
13870 @item @var{host} @dots{}
13871 Configure @value{GDBN} to run on the specified @var{host}.
13873 There is no convenient way to generate a list of all available hosts.
13876 There are many other options available as well, but they are generally
13877 needed for special purposes only.
13879 @node Maintenance Commands
13880 @appendix Maintenance Commands
13881 @cindex maintenance commands
13882 @cindex internal commands
13884 In addition to commands intended for @value{GDBN} users, @value{GDBN}
13885 includes a number of commands intended for @value{GDBN} developers.
13886 These commands are provided here for reference.
13889 @kindex maint info breakpoints
13890 @item @anchor{maint info breakpoints}maint info breakpoints
13891 Using the same format as @samp{info breakpoints}, display both the
13892 breakpoints you've set explicitly, and those @value{GDBN} is using for
13893 internal purposes. Internal breakpoints are shown with negative
13894 breakpoint numbers. The type column identifies what kind of breakpoint
13899 Normal, explicitly set breakpoint.
13902 Normal, explicitly set watchpoint.
13905 Internal breakpoint, used to handle correctly stepping through
13906 @code{longjmp} calls.
13908 @item longjmp resume
13909 Internal breakpoint at the target of a @code{longjmp}.
13912 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
13915 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
13918 Shared library events.
13925 @node Remote Protocol
13926 @appendix @value{GDBN} Remote Serial Protocol
13928 There may be occasions when you need to know something about the
13929 protocol---for example, if there is only one serial port to your target
13930 machine, you might want your program to do something special if it
13931 recognizes a packet meant for @value{GDBN}.
13933 In the examples below, @samp{<-} and @samp{->} are used to indicate
13934 transmitted and received data respectfully.
13936 @cindex protocol, @value{GDBN} remote serial
13937 @cindex serial protocol, @value{GDBN} remote
13938 @cindex remote serial protocol
13939 All @value{GDBN} commands and responses (other than acknowledgments) are
13940 sent as a @var{packet}. A @var{packet} is introduced with the character
13941 @samp{$}, the actual @var{packet-data}, and the terminating character
13942 @samp{#} followed by a two-digit @var{checksum}:
13945 @code{$}@var{packet-data}@code{#}@var{checksum}
13949 @cindex checksum, for @value{GDBN} remote
13951 The two-digit @var{checksum} is computed as the modulo 256 sum of all
13952 characters between the leading @samp{$} and the trailing @samp{#} (an
13953 eight bit unsigned checksum).
13955 Implementors should note that prior to @value{GDBN} 5.0 the protocol
13956 specification also included an optional two-digit @var{sequence-id}:
13959 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
13962 @cindex sequence-id, for @value{GDBN} remote
13964 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
13965 has never output @var{sequence-id}s. Stubs that handle packets added
13966 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
13968 @cindex acknowledgment, for @value{GDBN} remote
13969 When either the host or the target machine receives a packet, the first
13970 response expected is an acknowledgment: either @samp{+} (to indicate
13971 the package was received correctly) or @samp{-} (to request
13975 <- @code{$}@var{packet-data}@code{#}@var{checksum}
13980 The host (@value{GDBN}) sends @var{command}s, and the target (the
13981 debugging stub incorporated in your program) sends a @var{response}. In
13982 the case of step and continue @var{command}s, the response is only sent
13983 when the operation has completed (the target has again stopped).
13985 @var{packet-data} consists of a sequence of characters with the
13986 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
13989 Fields within the packet should be separated using @samp{,} @samp{;} or
13990 @samp{:}. Except where otherwise noted all numbers are represented in
13991 HEX with leading zeros suppressed.
13993 Implementors should note that prior to @value{GDBN} 5.0, the character
13994 @samp{:} could not appear as the third character in a packet (as it
13995 would potentially conflict with the @var{sequence-id}).
13997 Response @var{data} can be run-length encoded to save space. A @samp{*}
13998 means that the next character is an @sc{ascii} encoding giving a repeat count
13999 which stands for that many repetitions of the character preceding the
14000 @samp{*}. The encoding is @code{n+29}, yielding a printable character
14001 where @code{n >=3} (which is where rle starts to win). The printable
14002 characters @samp{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
14003 value greater than 126 should not be used.
14005 Some remote systems have used a different run-length encoding mechanism
14006 loosely refered to as the cisco encoding. Following the @samp{*}
14007 character are two hex digits that indicate the size of the packet.
14014 means the same as "0000".
14016 The error response returned for some packets includes a two character
14017 error number. That number is not well defined.
14019 For any @var{command} not supported by the stub, an empty response
14020 (@samp{$#00}) should be returned. That way it is possible to extend the
14021 protocol. A newer @value{GDBN} can tell if a packet is supported based
14024 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
14025 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
14028 Below is a complete list of all currently defined @var{command}s and
14029 their corresponding response @var{data}:
14031 @multitable @columnfractions .30 .30 .40
14036 @item extended mode
14039 Enable extended mode. In extended mode, the remote server is made
14040 persistent. The @samp{R} packet is used to restart the program being
14043 @tab reply @samp{OK}
14045 The remote target both supports and has enabled extended mode.
14050 Indicate the reason the target halted. The reply is the same as for step
14059 @tab Reserved for future use
14061 @item set program arguments @strong{(reserved)}
14062 @tab @code{A}@var{arglen}@code{,}@var{argnum}@code{,}@var{arg}@code{,...}
14067 Initialized @samp{argv[]} array passed into program. @var{arglen}
14068 specifies the number of bytes in the hex encoded byte stream @var{arg}.
14069 See @file{gdbserver} for more details.
14071 @tab reply @code{OK}
14073 @tab reply @code{E}@var{NN}
14075 @item set baud @strong{(deprecated)}
14076 @tab @code{b}@var{baud}
14078 Change the serial line speed to @var{baud}. JTC: @emph{When does the
14079 transport layer state change? When it's received, or after the ACK is
14080 transmitted. In either case, there are problems if the command or the
14081 acknowledgment packet is dropped.} Stan: @emph{If people really wanted
14082 to add something like this, and get it working for the first time, they
14083 ought to modify ser-unix.c to send some kind of out-of-band message to a
14084 specially-setup stub and have the switch happen "in between" packets, so
14085 that from remote protocol's point of view, nothing actually
14088 @item set breakpoint @strong{(deprecated)}
14089 @tab @code{B}@var{addr},@var{mode}
14091 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
14092 breakpoint at @var{addr}. @emph{This has been replaced by the @samp{Z} and
14096 @tab @code{c}@var{addr}
14098 @var{addr} is address to resume. If @var{addr} is omitted, resume at
14104 @item continue with signal
14105 @tab @code{C}@var{sig}@code{;}@var{addr}
14107 Continue with signal @var{sig} (hex signal number). If
14108 @code{;}@var{addr} is omitted, resume at same address.
14113 @item toggle debug @strong{(deprecated)}
14121 Detach @value{GDBN} from the remote system. Sent to the remote target before
14122 @value{GDBN} disconnects.
14124 @tab reply @emph{no response}
14126 @value{GDBN} does not check for any response after sending this packet.
14130 @tab Reserved for future use
14134 @tab Reserved for future use
14138 @tab Reserved for future use
14142 @tab Reserved for future use
14144 @item read registers
14146 @tab Read general registers.
14148 @tab reply @var{XX...}
14150 Each byte of register data is described by two hex digits. The bytes
14151 with the register are transmitted in target byte order. The size of
14152 each register and their position within the @samp{g} @var{packet} are
14153 determined by the @value{GDBN} internal macros @var{REGISTER_RAW_SIZE} and
14154 @var{REGISTER_NAME} macros. The specification of several standard
14155 @code{g} packets is specified below.
14157 @tab @code{E}@var{NN}
14161 @tab @code{G}@var{XX...}
14163 See @samp{g} for a description of the @var{XX...} data.
14165 @tab reply @code{OK}
14168 @tab reply @code{E}@var{NN}
14173 @tab Reserved for future use
14176 @tab @code{H}@var{c}@var{t...}
14178 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
14179 @samp{G}, et.al.). @var{c} = @samp{c} for thread used in step and
14180 continue; @var{t...} can be -1 for all threads. @var{c} = @samp{g} for
14181 thread used in other operations. If zero, pick a thread, any thread.
14183 @tab reply @code{OK}
14186 @tab reply @code{E}@var{NN}
14190 @c 'H': How restrictive (or permissive) is the thread model. If a
14191 @c thread is selected and stopped, are other threads allowed
14192 @c to continue to execute? As I mentioned above, I think the
14193 @c semantics of each command when a thread is selected must be
14194 @c described. For example:
14196 @c 'g': If the stub supports threads and a specific thread is
14197 @c selected, returns the register block from that thread;
14198 @c otherwise returns current registers.
14200 @c 'G' If the stub supports threads and a specific thread is
14201 @c selected, sets the registers of the register block of
14202 @c that thread; otherwise sets current registers.
14204 @item cycle step @strong{(draft)}
14205 @tab @code{i}@var{addr}@code{,}@var{nnn}
14207 Step the remote target by a single clock cycle. If @code{,}@var{nnn} is
14208 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
14209 step starting at that address.
14211 @item signal then cycle step @strong{(reserved)}
14214 See @samp{i} and @samp{S} for likely syntax and semantics.
14218 @tab Reserved for future use
14222 @tab Reserved for future use
14227 FIXME: @emph{There is no description of how to operate when a specific
14228 thread context has been selected (i.e.@: does 'k' kill only that thread?)}.
14232 @tab Reserved for future use
14236 @tab Reserved for future use
14239 @tab @code{m}@var{addr}@code{,}@var{length}
14241 Read @var{length} bytes of memory starting at address @var{addr}.
14242 Neither @value{GDBN} nor the stub assume that sized memory transfers are assumed
14243 using word alligned accesses. FIXME: @emph{A word aligned memory
14244 transfer mechanism is needed.}
14246 @tab reply @var{XX...}
14248 @var{XX...} is mem contents. Can be fewer bytes than requested if able
14249 to read only part of the data. Neither @value{GDBN} nor the stub assume that
14250 sized memory transfers are assumed using word alligned accesses. FIXME:
14251 @emph{A word aligned memory transfer mechanism is needed.}
14253 @tab reply @code{E}@var{NN}
14254 @tab @var{NN} is errno
14257 @tab @code{M}@var{addr},@var{length}@code{:}@var{XX...}
14259 Write @var{length} bytes of memory starting at address @var{addr}.
14260 @var{XX...} is the data.
14262 @tab reply @code{OK}
14265 @tab reply @code{E}@var{NN}
14267 for an error (this includes the case where only part of the data was
14272 @tab Reserved for future use
14276 @tab Reserved for future use
14280 @tab Reserved for future use
14284 @tab Reserved for future use
14286 @item read reg @strong{(reserved)}
14287 @tab @code{p}@var{n...}
14289 See write register.
14291 @tab return @var{r....}
14292 @tab The hex encoded value of the register in target byte order.
14295 @tab @code{P}@var{n...}@code{=}@var{r...}
14297 Write register @var{n...} with value @var{r...}, which contains two hex
14298 digits for each byte in the register (target byte order).
14300 @tab reply @code{OK}
14303 @tab reply @code{E}@var{NN}
14306 @item general query
14307 @tab @code{q}@var{query}
14309 Request info about @var{query}. In general @value{GDBN} queries
14310 have a leading upper case letter. Custom vendor queries should use a
14311 company prefix (in lower case) ex: @samp{qfsf.var}. @var{query} may
14312 optionally be followed by a @samp{,} or @samp{;} separated list. Stubs
14313 must ensure that they match the full @var{query} name.
14315 @tab reply @code{XX...}
14316 @tab Hex encoded data from query. The reply can not be empty.
14318 @tab reply @code{E}@var{NN}
14322 @tab Indicating an unrecognized @var{query}.
14325 @tab @code{Q}@var{var}@code{=}@var{val}
14327 Set value of @var{var} to @var{val}. See @samp{q} for a discussing of
14328 naming conventions.
14330 @item reset @strong{(deprecated)}
14333 Reset the entire system.
14335 @item remote restart
14336 @tab @code{R}@var{XX}
14338 Restart the program being debugged. @var{XX}, while needed, is ignored.
14339 This packet is only available in extended mode.
14344 The @samp{R} packet has no reply.
14347 @tab @code{s}@var{addr}
14349 @var{addr} is address to resume. If @var{addr} is omitted, resume at
14355 @item step with signal
14356 @tab @code{S}@var{sig}@code{;}@var{addr}
14358 Like @samp{C} but step not continue.
14364 @tab @code{t}@var{addr}@code{:}@var{PP}@code{,}@var{MM}
14366 Search backwards starting at address @var{addr} for a match with pattern
14367 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4
14368 bytes. @var{addr} must be at least 3 digits.
14371 @tab @code{T}@var{XX}
14372 @tab Find out if the thread XX is alive.
14374 @tab reply @code{OK}
14375 @tab thread is still alive
14377 @tab reply @code{E}@var{NN}
14378 @tab thread is dead
14382 @tab Reserved for future use
14386 @tab Reserved for future use
14390 @tab Reserved for future use
14394 @tab Reserved for future use
14398 @tab Reserved for future use
14402 @tab Reserved for future use
14406 @tab Reserved for future use
14408 @item write mem (binary)
14409 @tab @code{X}@var{addr}@code{,}@var{length}@var{:}@var{XX...}
14411 @var{addr} is address, @var{length} is number of bytes, @var{XX...} is
14412 binary data. The characters @code{$}, @code{#}, and @code{0x7d} are
14413 escaped using @code{0x7d}.
14415 @tab reply @code{OK}
14418 @tab reply @code{E}@var{NN}
14423 @tab Reserved for future use
14427 @tab Reserved for future use
14429 @item remove break or watchpoint @strong{(draft)}
14430 @tab @code{z}@var{t}@code{,}@var{addr}@code{,}@var{length}
14434 @item insert break or watchpoint @strong{(draft)}
14435 @tab @code{Z}@var{t}@code{,}@var{addr}@code{,}@var{length}
14437 @var{t} is type: @samp{0} - software breakpoint, @samp{1} - hardware
14438 breakpoint, @samp{2} - write watchpoint, @samp{3} - read watchpoint,
14439 @samp{4} - access watchpoint; @var{addr} is address; @var{length} is in
14440 bytes. For a software breakpoint, @var{length} specifies the size of
14441 the instruction to be patched. For hardware breakpoints and watchpoints
14442 @var{length} specifies the memory region to be monitored. To avoid
14443 potential problems with duplicate packets, the operations should be
14444 implemented in an idempotent way.
14446 @tab reply @code{E}@var{NN}
14449 @tab reply @code{OK}
14453 @tab If not supported.
14457 @tab Reserved for future use
14461 The @samp{C}, @samp{c}, @samp{S}, @samp{s} and @samp{?} packets can
14462 receive any of the below as a reply. In the case of the @samp{C},
14463 @samp{c}, @samp{S} and @samp{s} packets, that reply is only returned
14464 when the target halts. In the below the exact meaning of @samp{signal
14465 number} is poorly defined. In general one of the UNIX signal numbering
14466 conventions is used.
14468 @multitable @columnfractions .4 .6
14470 @item @code{S}@var{AA}
14471 @tab @var{AA} is the signal number
14473 @item @code{T}@var{AA}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}
14475 @var{AA} = two hex digit signal number; @var{n...} = register number
14476 (hex), @var{r...} = target byte ordered register contents, size defined
14477 by @code{REGISTER_RAW_SIZE}; @var{n...} = @samp{thread}, @var{r...} =
14478 thread process ID, this is a hex integer; @var{n...} = other string not
14479 starting with valid hex digit. @value{GDBN} should ignore this
14480 @var{n...}, @var{r...} pair and go on to the next. This way we can
14481 extend the protocol.
14483 @item @code{W}@var{AA}
14485 The process exited, and @var{AA} is the exit status. This is only
14486 applicable for certains sorts of targets.
14488 @item @code{X}@var{AA}
14490 The process terminated with signal @var{AA}.
14492 @item @code{N}@var{AA}@code{;}@var{t...}@code{;}@var{d...}@code{;}@var{b...} @strong{(obsolete)}
14494 @var{AA} = signal number; @var{t...} = address of symbol "_start";
14495 @var{d...} = base of data section; @var{b...} = base of bss section.
14496 @emph{Note: only used by Cisco Systems targets. The difference between
14497 this reply and the "qOffsets" query is that the 'N' packet may arrive
14498 spontaneously whereas the 'qOffsets' is a query initiated by the host
14501 @item @code{O}@var{XX...}
14503 @var{XX...} is hex encoding of @sc{ascii} data. This can happen at any time
14504 while the program is running and the debugger should continue to wait
14509 The following set and query packets have already been defined.
14511 @multitable @columnfractions .2 .2 .6
14513 @item current thread
14514 @tab @code{q}@code{C}
14515 @tab Return the current thread id.
14517 @tab reply @code{QC}@var{pid}
14519 Where @var{pid} is a HEX encoded 16 bit process id.
14522 @tab Any other reply implies the old pid.
14524 @item all thread ids
14525 @tab @code{q}@code{fThreadInfo}
14527 @tab @code{q}@code{sThreadInfo}
14529 Obtain a list of active thread ids from the target (OS). Since there
14530 may be too many active threads to fit into one reply packet, this query
14531 works iteratively: it may require more than one query/reply sequence to
14532 obtain the entire list of threads. The first query of the sequence will
14533 be the @code{qf}@code{ThreadInfo} query; subsequent queries in the
14534 sequence will be the @code{qs}@code{ThreadInfo} query.
14537 @tab NOTE: replaces the @code{qL} query (see below).
14539 @tab reply @code{m}@var{<id>}
14540 @tab A single thread id
14542 @tab reply @code{m}@var{<id>},@var{<id>...}
14543 @tab a comma-separated list of thread ids
14545 @tab reply @code{l}
14546 @tab (lower case 'el') denotes end of list.
14550 In response to each query, the target will reply with a list of one
14551 or more thread ids, in big-endian hex, separated by commas. GDB will
14552 respond to each reply with a request for more thread ids (using the
14553 @code{qs} form of the query), until the target responds with @code{l}
14554 (lower-case el, for @code{'last'}).
14556 @item extra thread info
14557 @tab @code{q}@code{ThreadExtraInfo}@code{,}@var{id}
14562 Where @var{<id>} is a thread-id in big-endian hex.
14563 Obtain a printable string description of a thread's attributes from
14564 the target OS. This string may contain anything that the target OS
14565 thinks is interesting for @value{GDBN} to tell the user about the thread.
14566 The string is displayed in @value{GDBN}'s @samp{info threads} display.
14567 Some examples of possible thread extra info strings are "Runnable", or
14568 "Blocked on Mutex".
14570 @tab reply @var{XX...}
14572 Where @var{XX...} is a hex encoding of @sc{ascii} data, comprising the
14573 printable string containing the extra information about the thread's
14576 @item query @var{LIST} or @var{threadLIST} @strong{(deprecated)}
14577 @tab @code{q}@code{L}@var{startflag}@var{threadcount}@var{nextthread}
14582 Obtain thread information from RTOS. Where: @var{startflag} (one hex
14583 digit) is one to indicate the first query and zero to indicate a
14584 subsequent query; @var{threadcount} (two hex digits) is the maximum
14585 number of threads the response packet can contain; and @var{nextthread}
14586 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
14587 returned in the response as @var{argthread}.
14590 @tab NOTE: this query is replaced by the @code{q}@code{fThreadInfo}
14593 @tab reply @code{q}@code{M}@var{count}@var{done}@var{argthread}@var{thread...}
14598 Where: @var{count} (two hex digits) is the number of threads being
14599 returned; @var{done} (one hex digit) is zero to indicate more threads
14600 and one indicates no further threads; @var{argthreadid} (eight hex
14601 digits) is @var{nextthread} from the request packet; @var{thread...} is
14602 a sequence of thread IDs from the target. @var{threadid} (eight hex
14603 digits). See @code{remote.c:parse_threadlist_response()}.
14605 @item compute CRC of memory block
14606 @tab @code{q}@code{CRC:}@var{addr}@code{,}@var{length}
14609 @tab reply @code{E}@var{NN}
14610 @tab An error (such as memory fault)
14612 @tab reply @code{C}@var{CRC32}
14613 @tab A 32 bit cyclic redundancy check of the specified memory region.
14615 @item query sect offs
14616 @tab @code{q}@code{Offsets}
14618 Get section offsets that the target used when re-locating the downloaded
14619 image. @emph{Note: while a @code{Bss} offset is included in the
14620 response, @value{GDBN} ignores this and instead applies the @code{Data}
14621 offset to the @code{Bss} section.}
14623 @tab reply @code{Text=}@var{xxx}@code{;Data=}@var{yyy}@code{;Bss=}@var{zzz}
14625 @item thread info request
14626 @tab @code{q}@code{P}@var{mode}@var{threadid}
14631 Returns information on @var{threadid}. Where: @var{mode} is a hex
14632 encoded 32 bit mode; @var{threadid} is a hex encoded 64 bit thread ID.
14636 See @code{remote.c:remote_unpack_thread_info_response()}.
14638 @item remote command
14639 @tab @code{q}@code{Rcmd,}@var{COMMAND}
14644 @var{COMMAND} (hex encoded) is passed to the local interpreter for
14645 execution. Invalid commands should be reported using the output string.
14646 Before the final result packet, the target may also respond with a
14647 number of intermediate @code{O}@var{OUTPUT} console output
14648 packets. @emph{Implementors should note that providing access to a
14649 stubs's interpreter may have security implications}.
14651 @tab reply @code{OK}
14653 A command response with no output.
14655 @tab reply @var{OUTPUT}
14657 A command response with the hex encoded output string @var{OUTPUT}.
14659 @tab reply @code{E}@var{NN}
14661 Indicate a badly formed request.
14666 When @samp{q}@samp{Rcmd} is not recognized.
14668 @item symbol lookup
14669 @tab @code{qSymbol::}
14671 Notify the target that @value{GDBN} is prepared to serve symbol lookup
14672 requests. Accept requests from the target for the values of symbols.
14677 @tab reply @code{OK}
14679 The target does not need to look up any (more) symbols.
14681 @tab reply @code{qSymbol:}@var{sym_name}
14685 The target requests the value of symbol @var{sym_name} (hex encoded).
14686 @value{GDBN} may provide the value by using the
14687 @code{qSymbol:}@var{sym_value}:@var{sym_name}
14688 message, described below.
14691 @tab @code{qSymbol:}@var{sym_value}:@var{sym_name}
14695 Set the value of SYM_NAME to SYM_VALUE.
14699 @var{sym_name} (hex encoded) is the name of a symbol whose value
14700 the target has previously requested.
14704 @var{sym_value} (hex) is the value for symbol @var{sym_name}.
14705 If @value{GDBN} cannot supply a value for @var{sym_name}, then this
14706 field will be empty.
14708 @tab reply @code{OK}
14710 The target does not need to look up any (more) symbols.
14712 @tab reply @code{qSymbol:}@var{sym_name}
14716 The target requests the value of a new symbol @var{sym_name} (hex encoded).
14717 @value{GDBN} will continue to supply the values of symbols (if available),
14718 until the target ceases to request them.
14722 The following @samp{g}/@samp{G} packets have previously been defined.
14723 In the below, some thirty-two bit registers are transferred as sixty-four
14724 bits. Those registers should be zero/sign extended (which?) to fill the
14725 space allocated. Register bytes are transfered in target byte order.
14726 The two nibbles within a register byte are transfered most-significant -
14729 @multitable @columnfractions .5 .5
14733 All registers are transfered as thirty-two bit quantities in the order:
14734 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
14735 registers; fsr; fir; fp.
14739 All registers are transfered as sixty-four bit quantities (including
14740 thirty-two bit registers such as @code{sr}). The ordering is the same
14745 Example sequence of a target being re-started. Notice how the restart
14746 does not get any direct output:
14751 @emph{target restarts}
14754 -> @code{T001:1234123412341234}
14758 Example sequence of a target being stepped by a single instruction:
14766 -> @code{T001:1234123412341234}
14784 % I think something like @colophon should be in texinfo. In the
14786 \long\def\colophon{\hbox to0pt{}\vfill
14787 \centerline{The body of this manual is set in}
14788 \centerline{\fontname\tenrm,}
14789 \centerline{with headings in {\bf\fontname\tenbf}}
14790 \centerline{and examples in {\tt\fontname\tentt}.}
14791 \centerline{{\it\fontname\tenit\/},}
14792 \centerline{{\bf\fontname\tenbf}, and}
14793 \centerline{{\sl\fontname\tensl\/}}
14794 \centerline{are used for emphasis.}\vfill}
14796 % Blame: doc@cygnus.com, 1991.