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
36 @c !!set GDB edit command default editor
39 @c THIS MANUAL REQUIRES TEXINFO 4.0 OR LATER.
41 @c This is a dir.info fragment to support semi-automated addition of
42 @c manuals to an info tree.
43 @dircategory Programming & development tools.
45 * Gdb: (gdb). The @sc{gnu} debugger.
49 This file documents the @sc{gnu} debugger @value{GDBN}.
52 This is the @value{EDITION} Edition, @value{DATE},
53 of @cite{Debugging with @value{GDBN}: the @sc{gnu} Source-Level Debugger}
54 for @value{GDBN} Version @value{GDBVN}.
56 Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,@*
57 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
59 Permission is granted to copy, distribute and/or modify this document
60 under the terms of the GNU Free Documentation License, Version 1.1 or
61 any later version published by the Free Software Foundation; with the
62 Invariant Sections being ``Free Software'' and ``Free Software Needs
63 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
64 and with the Back-Cover Texts as in (a) below.
66 (a) The Free Software Foundation's Back-Cover Text is: ``You have
67 freedom to copy and modify this GNU Manual, like GNU software. Copies
68 published by the Free Software Foundation raise funds for GNU
73 @title Debugging with @value{GDBN}
74 @subtitle The @sc{gnu} Source-Level Debugger
76 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
77 @subtitle @value{DATE}
78 @author Richard Stallman, Roland Pesch, Stan Shebs, et al.
82 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@gnu.org.)\par
83 \hfill {\it Debugging with @value{GDBN}}\par
84 \hfill \TeX{}info \texinfoversion\par
88 @vskip 0pt plus 1filll
89 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995,
90 1996, 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
92 Published by the Free Software Foundation @*
93 59 Temple Place - Suite 330, @*
94 Boston, MA 02111-1307 USA @*
97 Permission is granted to copy, distribute and/or modify this document
98 under the terms of the GNU Free Documentation License, Version 1.1 or
99 any later version published by the Free Software Foundation; with the
100 Invariant Sections being ``Free Software'' and ``Free Software Needs
101 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
102 and with the Back-Cover Texts as in (a) below.
104 (a) The Free Software Foundation's Back-Cover Text is: ``You have
105 freedom to copy and modify this GNU Manual, like GNU software. Copies
106 published by the Free Software Foundation raise funds for GNU
112 @node Top, Summary, (dir), (dir)
114 @top Debugging with @value{GDBN}
116 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
118 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
121 Copyright (C) 1988-2002 Free Software Foundation, Inc.
124 * Summary:: Summary of @value{GDBN}
125 * Sample Session:: A sample @value{GDBN} session
127 * Invocation:: Getting in and out of @value{GDBN}
128 * Commands:: @value{GDBN} commands
129 * Running:: Running programs under @value{GDBN}
130 * Stopping:: Stopping and continuing
131 * Stack:: Examining the stack
132 * Source:: Examining source files
133 * Data:: Examining data
134 * Macros:: Preprocessor Macros
135 * Tracepoints:: Debugging remote targets non-intrusively
136 * Overlays:: Debugging programs that use overlays
138 * Languages:: Using @value{GDBN} with different languages
140 * Symbols:: Examining the symbol table
141 * Altering:: Altering execution
142 * GDB Files:: @value{GDBN} files
143 * Targets:: Specifying a debugging target
144 * Remote Debugging:: Debugging remote programs
145 * Configurations:: Configuration-specific information
146 * Controlling GDB:: Controlling @value{GDBN}
147 * Sequences:: Canned sequences of commands
148 * TUI:: @value{GDBN} Text User Interface
149 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
150 * Annotations:: @value{GDBN}'s annotation interface.
151 * GDB/MI:: @value{GDBN}'s Machine Interface.
153 * GDB Bugs:: Reporting bugs in @value{GDBN}
154 * Formatting Documentation:: How to format and print @value{GDBN} documentation
156 * Command Line Editing:: Command Line Editing
157 * Using History Interactively:: Using History Interactively
158 * Installing GDB:: Installing GDB
159 * Maintenance Commands:: Maintenance Commands
160 * Remote Protocol:: GDB Remote Serial Protocol
161 * Copying:: GNU General Public License says
162 how you can copy and share GDB
163 * GNU Free Documentation License:: The license for this documentation
172 @unnumbered Summary of @value{GDBN}
174 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
175 going on ``inside'' another program while it executes---or what another
176 program was doing at the moment it crashed.
178 @value{GDBN} can do four main kinds of things (plus other things in support of
179 these) to help you catch bugs in the act:
183 Start your program, specifying anything that might affect its behavior.
186 Make your program stop on specified conditions.
189 Examine what has happened, when your program has stopped.
192 Change things in your program, so you can experiment with correcting the
193 effects of one bug and go on to learn about another.
196 You can use @value{GDBN} to debug programs written in C and C++.
197 For more information, see @ref{Support,,Supported languages}.
198 For more information, see @ref{C,,C and C++}.
200 @c OBSOLETE @cindex Chill
203 @c OBSOLETE and Chill
204 is partial. For information on Modula-2, see @ref{Modula-2,,Modula-2}.
205 @c OBSOLETE For information on Chill, see @ref{Chill}.
208 Debugging Pascal programs which use sets, subranges, file variables, or
209 nested functions does not currently work. @value{GDBN} does not support
210 entering expressions, printing values, or similar features using Pascal
214 @value{GDBN} can be used to debug programs written in Fortran, although
215 it may be necessary to refer to some variables with a trailing
219 * Free Software:: Freely redistributable software
220 * Contributors:: Contributors to GDB
224 @unnumberedsec Free software
226 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
227 General Public License
228 (GPL). The GPL gives you the freedom to copy or adapt a licensed
229 program---but every person getting a copy also gets with it the
230 freedom to modify that copy (which means that they must get access to
231 the source code), and the freedom to distribute further copies.
232 Typical software companies use copyrights to limit your freedoms; the
233 Free Software Foundation uses the GPL to preserve these freedoms.
235 Fundamentally, the General Public License is a license which says that
236 you have these freedoms and that you cannot take these freedoms away
239 @unnumberedsec Free Software Needs Free Documentation
241 The biggest deficiency in the free software community today is not in
242 the software---it is the lack of good free documentation that we can
243 include with the free software. Many of our most important
244 programs do not come with free reference manuals and free introductory
245 texts. Documentation is an essential part of any software package;
246 when an important free software package does not come with a free
247 manual and a free tutorial, that is a major gap. We have many such
250 Consider Perl, for instance. The tutorial manuals that people
251 normally use are non-free. How did this come about? Because the
252 authors of those manuals published them with restrictive terms---no
253 copying, no modification, source files not available---which exclude
254 them from the free software world.
256 That wasn't the first time this sort of thing happened, and it was far
257 from the last. Many times we have heard a GNU user eagerly describe a
258 manual that he is writing, his intended contribution to the community,
259 only to learn that he had ruined everything by signing a publication
260 contract to make it non-free.
262 Free documentation, like free software, is a matter of freedom, not
263 price. The problem with the non-free manual is not that publishers
264 charge a price for printed copies---that in itself is fine. (The Free
265 Software Foundation sells printed copies of manuals, too.) The
266 problem is the restrictions on the use of the manual. Free manuals
267 are available in source code form, and give you permission to copy and
268 modify. Non-free manuals do not allow this.
270 The criteria of freedom for a free manual are roughly the same as for
271 free software. Redistribution (including the normal kinds of
272 commercial redistribution) must be permitted, so that the manual can
273 accompany every copy of the program, both on-line and on paper.
275 Permission for modification of the technical content is crucial too.
276 When people modify the software, adding or changing features, if they
277 are conscientious they will change the manual too---so they can
278 provide accurate and clear documentation for the modified program. A
279 manual that leaves you no choice but to write a new manual to document
280 a changed version of the program is not really available to our
283 Some kinds of limits on the way modification is handled are
284 acceptable. For example, requirements to preserve the original
285 author's copyright notice, the distribution terms, or the list of
286 authors, are ok. It is also no problem to require modified versions
287 to include notice that they were modified. Even entire sections that
288 may not be deleted or changed are acceptable, as long as they deal
289 with nontechnical topics (like this one). These kinds of restrictions
290 are acceptable because they don't obstruct the community's normal use
293 However, it must be possible to modify all the @emph{technical}
294 content of the manual, and then distribute the result in all the usual
295 media, through all the usual channels. Otherwise, the restrictions
296 obstruct the use of the manual, it is not free, and we need another
297 manual to replace it.
299 Please spread the word about this issue. Our community continues to
300 lose manuals to proprietary publishing. If we spread the word that
301 free software needs free reference manuals and free tutorials, perhaps
302 the next person who wants to contribute by writing documentation will
303 realize, before it is too late, that only free manuals contribute to
304 the free software community.
306 If you are writing documentation, please insist on publishing it under
307 the GNU Free Documentation License or another free documentation
308 license. Remember that this decision requires your approval---you
309 don't have to let the publisher decide. Some commercial publishers
310 will use a free license if you insist, but they will not propose the
311 option; it is up to you to raise the issue and say firmly that this is
312 what you want. If the publisher you are dealing with refuses, please
313 try other publishers. If you're not sure whether a proposed license
314 is free, write to @email{licensing@@gnu.org}.
316 You can encourage commercial publishers to sell more free, copylefted
317 manuals and tutorials by buying them, and particularly by buying
318 copies from the publishers that paid for their writing or for major
319 improvements. Meanwhile, try to avoid buying non-free documentation
320 at all. Check the distribution terms of a manual before you buy it,
321 and insist that whoever seeks your business must respect your freedom.
322 Check the history of the book, and try to reward the publishers that
323 have paid or pay the authors to work on it.
325 The Free Software Foundation maintains a list of free documentation
326 published by other publishers, at
327 @url{http://www.fsf.org/doc/other-free-books.html}.
330 @unnumberedsec Contributors to @value{GDBN}
332 Richard Stallman was the original author of @value{GDBN}, and of many
333 other @sc{gnu} programs. Many others have contributed to its
334 development. This section attempts to credit major contributors. One
335 of the virtues of free software is that everyone is free to contribute
336 to it; with regret, we cannot actually acknowledge everyone here. The
337 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
338 blow-by-blow account.
340 Changes much prior to version 2.0 are lost in the mists of time.
343 @emph{Plea:} Additions to this section are particularly welcome. If you
344 or your friends (or enemies, to be evenhanded) have been unfairly
345 omitted from this list, we would like to add your names!
348 So that they may not regard their many labors as thankless, we
349 particularly thank those who shepherded @value{GDBN} through major
351 Andrew Cagney (releases 5.3, 5.2, 5.1 and 5.0);
352 Jim Blandy (release 4.18);
353 Jason Molenda (release 4.17);
354 Stan Shebs (release 4.14);
355 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
356 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
357 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
358 Jim Kingdon (releases 3.5, 3.4, and 3.3);
359 and Randy Smith (releases 3.2, 3.1, and 3.0).
361 Richard Stallman, assisted at various times by Peter TerMaat, Chris
362 Hanson, and Richard Mlynarik, handled releases through 2.8.
364 Michael Tiemann is the author of most of the @sc{gnu} C@t{++} support
365 in @value{GDBN}, with significant additional contributions from Per
366 Bothner and Daniel Berlin. James Clark wrote the @sc{gnu} C@t{++}
367 demangler. Early work on C@t{++} was by Peter TerMaat (who also did
368 much general update work leading to release 3.0).
370 @value{GDBN} uses the BFD subroutine library to examine multiple
371 object-file formats; BFD was a joint project of David V.
372 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
374 David Johnson wrote the original COFF support; Pace Willison did
375 the original support for encapsulated COFF.
377 Brent Benson of Harris Computer Systems contributed DWARF2 support.
379 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
380 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
382 Jean-Daniel Fekete contributed Sun 386i support.
383 Chris Hanson improved the HP9000 support.
384 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
385 David Johnson contributed Encore Umax support.
386 Jyrki Kuoppala contributed Altos 3068 support.
387 Jeff Law contributed HP PA and SOM support.
388 Keith Packard contributed NS32K support.
389 Doug Rabson contributed Acorn Risc Machine support.
390 Bob Rusk contributed Harris Nighthawk CX-UX support.
391 Chris Smith contributed Convex support (and Fortran debugging).
392 Jonathan Stone contributed Pyramid support.
393 Michael Tiemann contributed SPARC support.
394 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
395 Pace Willison contributed Intel 386 support.
396 Jay Vosburgh contributed Symmetry support.
398 Andreas Schwab contributed M68K Linux support.
400 Rich Schaefer and Peter Schauer helped with support of SunOS shared
403 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
404 about several machine instruction sets.
406 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
407 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
408 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
409 and RDI targets, respectively.
411 Brian Fox is the author of the readline libraries providing
412 command-line editing and command history.
414 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
415 Modula-2 support, and contributed the Languages chapter of this manual.
417 Fred Fish wrote most of the support for Unix System Vr4.
418 He also enhanced the command-completion support to cover C@t{++} overloaded
421 Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and
424 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
426 Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors.
428 Toshiba sponsored the support for the TX39 Mips processor.
430 Matsushita sponsored the support for the MN10200 and MN10300 processors.
432 Fujitsu sponsored the support for SPARClite and FR30 processors.
434 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
437 Michael Snyder added support for tracepoints.
439 Stu Grossman wrote gdbserver.
441 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
442 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
444 The following people at the Hewlett-Packard Company contributed
445 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
446 (narrow mode), HP's implementation of kernel threads, HP's aC@t{++}
447 compiler, and the terminal user interface: Ben Krepp, Richard Title,
448 John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve
449 Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific
450 information in this manual.
452 DJ Delorie ported @value{GDBN} to MS-DOS, for the DJGPP project.
453 Robert Hoehne made significant contributions to the DJGPP port.
455 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
456 development since 1991. Cygnus engineers who have worked on @value{GDBN}
457 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
458 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
459 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
460 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
461 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
462 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
463 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
464 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
465 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
466 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
467 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
468 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
469 Zuhn have made contributions both large and small.
471 Jim Blandy added support for preprocessor macros, while working for Red
475 @chapter A Sample @value{GDBN} Session
477 You can use this manual at your leisure to read all about @value{GDBN}.
478 However, a handful of commands are enough to get started using the
479 debugger. This chapter illustrates those commands.
482 In this sample session, we emphasize user input like this: @b{input},
483 to make it easier to pick out from the surrounding output.
486 @c FIXME: this example may not be appropriate for some configs, where
487 @c FIXME...primary interest is in remote use.
489 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
490 processor) exhibits the following bug: sometimes, when we change its
491 quote strings from the default, the commands used to capture one macro
492 definition within another stop working. In the following short @code{m4}
493 session, we define a macro @code{foo} which expands to @code{0000}; we
494 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
495 same thing. However, when we change the open quote string to
496 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
497 procedure fails to define a new synonym @code{baz}:
506 @b{define(bar,defn(`foo'))}
510 @b{changequote(<QUOTE>,<UNQUOTE>)}
512 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
515 m4: End of input: 0: fatal error: EOF in string
519 Let us use @value{GDBN} to try to see what is going on.
522 $ @b{@value{GDBP} m4}
523 @c FIXME: this falsifies the exact text played out, to permit smallbook
524 @c FIXME... format to come out better.
525 @value{GDBN} is free software and you are welcome to distribute copies
526 of it under certain conditions; type "show copying" to see
528 There is absolutely no warranty for @value{GDBN}; type "show warranty"
531 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
536 @value{GDBN} reads only enough symbol data to know where to find the
537 rest when needed; as a result, the first prompt comes up very quickly.
538 We now tell @value{GDBN} to use a narrower display width than usual, so
539 that examples fit in this manual.
542 (@value{GDBP}) @b{set width 70}
546 We need to see how the @code{m4} built-in @code{changequote} works.
547 Having looked at the source, we know the relevant subroutine is
548 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
549 @code{break} command.
552 (@value{GDBP}) @b{break m4_changequote}
553 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
557 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
558 control; as long as control does not reach the @code{m4_changequote}
559 subroutine, the program runs as usual:
562 (@value{GDBP}) @b{run}
563 Starting program: /work/Editorial/gdb/gnu/m4/m4
571 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
572 suspends execution of @code{m4}, displaying information about the
573 context where it stops.
576 @b{changequote(<QUOTE>,<UNQUOTE>)}
578 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
580 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
584 Now we use the command @code{n} (@code{next}) to advance execution to
585 the next line of the current function.
589 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
594 @code{set_quotes} looks like a promising subroutine. We can go into it
595 by using the command @code{s} (@code{step}) instead of @code{next}.
596 @code{step} goes to the next line to be executed in @emph{any}
597 subroutine, so it steps into @code{set_quotes}.
601 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
603 530 if (lquote != def_lquote)
607 The display that shows the subroutine where @code{m4} is now
608 suspended (and its arguments) is called a stack frame display. It
609 shows a summary of the stack. We can use the @code{backtrace}
610 command (which can also be spelled @code{bt}), to see where we are
611 in the stack as a whole: the @code{backtrace} command displays a
612 stack frame for each active subroutine.
615 (@value{GDBP}) @b{bt}
616 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
618 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
620 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
621 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
623 #4 0x79dc in expand_input () at macro.c:40
624 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
628 We step through a few more lines to see what happens. The first two
629 times, we can use @samp{s}; the next two times we use @code{n} to avoid
630 falling into the @code{xstrdup} subroutine.
634 0x3b5c 532 if (rquote != def_rquote)
636 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
637 def_lquote : xstrdup(lq);
639 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
642 538 len_lquote = strlen(rquote);
646 The last line displayed looks a little odd; we can examine the variables
647 @code{lquote} and @code{rquote} to see if they are in fact the new left
648 and right quotes we specified. We use the command @code{p}
649 (@code{print}) to see their values.
652 (@value{GDBP}) @b{p lquote}
653 $1 = 0x35d40 "<QUOTE>"
654 (@value{GDBP}) @b{p rquote}
655 $2 = 0x35d50 "<UNQUOTE>"
659 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
660 To look at some context, we can display ten lines of source
661 surrounding the current line with the @code{l} (@code{list}) command.
667 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
669 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
672 538 len_lquote = strlen(rquote);
673 539 len_rquote = strlen(lquote);
680 Let us step past the two lines that set @code{len_lquote} and
681 @code{len_rquote}, and then examine the values of those variables.
685 539 len_rquote = strlen(lquote);
688 (@value{GDBP}) @b{p len_lquote}
690 (@value{GDBP}) @b{p len_rquote}
695 That certainly looks wrong, assuming @code{len_lquote} and
696 @code{len_rquote} are meant to be the lengths of @code{lquote} and
697 @code{rquote} respectively. We can set them to better values using
698 the @code{p} command, since it can print the value of
699 any expression---and that expression can include subroutine calls and
703 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
705 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
710 Is that enough to fix the problem of using the new quotes with the
711 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
712 executing with the @code{c} (@code{continue}) command, and then try the
713 example that caused trouble initially:
719 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
726 Success! The new quotes now work just as well as the default ones. The
727 problem seems to have been just the two typos defining the wrong
728 lengths. We allow @code{m4} exit by giving it an EOF as input:
732 Program exited normally.
736 The message @samp{Program exited normally.} is from @value{GDBN}; it
737 indicates @code{m4} has finished executing. We can end our @value{GDBN}
738 session with the @value{GDBN} @code{quit} command.
741 (@value{GDBP}) @b{quit}
745 @chapter Getting In and Out of @value{GDBN}
747 This chapter discusses how to start @value{GDBN}, and how to get out of it.
751 type @samp{@value{GDBP}} to start @value{GDBN}.
753 type @kbd{quit} or @kbd{C-d} to exit.
757 * Invoking GDB:: How to start @value{GDBN}
758 * Quitting GDB:: How to quit @value{GDBN}
759 * Shell Commands:: How to use shell commands inside @value{GDBN}
763 @section Invoking @value{GDBN}
765 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
766 @value{GDBN} reads commands from the terminal until you tell it to exit.
768 You can also run @code{@value{GDBP}} with a variety of arguments and options,
769 to specify more of your debugging environment at the outset.
771 The command-line options described here are designed
772 to cover a variety of situations; in some environments, some of these
773 options may effectively be unavailable.
775 The most usual way to start @value{GDBN} is with one argument,
776 specifying an executable program:
779 @value{GDBP} @var{program}
783 You can also start with both an executable program and a core file
787 @value{GDBP} @var{program} @var{core}
790 You can, instead, specify a process ID as a second argument, if you want
791 to debug a running process:
794 @value{GDBP} @var{program} 1234
798 would attach @value{GDBN} to process @code{1234} (unless you also have a file
799 named @file{1234}; @value{GDBN} does check for a core file first).
801 Taking advantage of the second command-line argument requires a fairly
802 complete operating system; when you use @value{GDBN} as a remote
803 debugger attached to a bare board, there may not be any notion of
804 ``process'', and there is often no way to get a core dump. @value{GDBN}
805 will warn you if it is unable to attach or to read core dumps.
807 You can optionally have @code{@value{GDBP}} pass any arguments after the
808 executable file to the inferior using @code{--args}. This option stops
811 gdb --args gcc -O2 -c foo.c
813 This will cause @code{@value{GDBP}} to debug @code{gcc}, and to set
814 @code{gcc}'s command-line arguments (@pxref{Arguments}) to @samp{-O2 -c foo.c}.
816 You can run @code{@value{GDBP}} without printing the front material, which describes
817 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
824 You can further control how @value{GDBN} starts up by using command-line
825 options. @value{GDBN} itself can remind you of the options available.
835 to display all available options and briefly describe their use
836 (@samp{@value{GDBP} -h} is a shorter equivalent).
838 All options and command line arguments you give are processed
839 in sequential order. The order makes a difference when the
840 @samp{-x} option is used.
844 * File Options:: Choosing files
845 * Mode Options:: Choosing modes
849 @subsection Choosing files
851 When @value{GDBN} starts, it reads any arguments other than options as
852 specifying an executable file and core file (or process ID). This is
853 the same as if the arguments were specified by the @samp{-se} and
854 @samp{-c} (or @samp{-p} options respectively. (@value{GDBN} reads the
855 first argument that does not have an associated option flag as
856 equivalent to the @samp{-se} option followed by that argument; and the
857 second argument that does not have an associated option flag, if any, as
858 equivalent to the @samp{-c}/@samp{-p} option followed by that argument.)
859 If the second argument begins with a decimal digit, @value{GDBN} will
860 first attempt to attach to it as a process, and if that fails, attempt
861 to open it as a corefile. If you have a corefile whose name begins with
862 a digit, you can prevent @value{GDBN} from treating it as a pid by
863 prefixing it with @file{./}, eg. @file{./12345}.
865 If @value{GDBN} has not been configured to included core file support,
866 such as for most embedded targets, then it will complain about a second
867 argument and ignore it.
869 Many options have both long and short forms; both are shown in the
870 following list. @value{GDBN} also recognizes the long forms if you truncate
871 them, so long as enough of the option is present to be unambiguous.
872 (If you prefer, you can flag option arguments with @samp{--} rather
873 than @samp{-}, though we illustrate the more usual convention.)
875 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
876 @c way, both those who look for -foo and --foo in the index, will find
880 @item -symbols @var{file}
882 @cindex @code{--symbols}
884 Read symbol table from file @var{file}.
886 @item -exec @var{file}
888 @cindex @code{--exec}
890 Use file @var{file} as the executable file to execute when appropriate,
891 and for examining pure data in conjunction with a core dump.
895 Read symbol table from file @var{file} and use it as the executable
898 @item -core @var{file}
900 @cindex @code{--core}
902 Use file @var{file} as a core dump to examine.
904 @item -c @var{number}
905 @item -pid @var{number}
906 @itemx -p @var{number}
909 Connect to process ID @var{number}, as with the @code{attach} command.
910 If there is no such process, @value{GDBN} will attempt to open a core
911 file named @var{number}.
913 @item -command @var{file}
915 @cindex @code{--command}
917 Execute @value{GDBN} commands from file @var{file}. @xref{Command
918 Files,, Command files}.
920 @item -directory @var{directory}
921 @itemx -d @var{directory}
922 @cindex @code{--directory}
924 Add @var{directory} to the path to search for source files.
928 @cindex @code{--mapped}
930 @emph{Warning: this option depends on operating system facilities that are not
931 supported on all systems.}@*
932 If memory-mapped files are available on your system through the @code{mmap}
933 system call, you can use this option
934 to have @value{GDBN} write the symbols from your
935 program into a reusable file in the current directory. If the program you are debugging is
936 called @file{/tmp/fred}, the mapped symbol file is @file{/tmp/fred.syms}.
937 Future @value{GDBN} debugging sessions notice the presence of this file,
938 and can quickly map in symbol information from it, rather than reading
939 the symbol table from the executable program.
941 The @file{.syms} file is specific to the host machine where @value{GDBN}
942 is run. It holds an exact image of the internal @value{GDBN} symbol
943 table. It cannot be shared across multiple host platforms.
947 @cindex @code{--readnow}
949 Read each symbol file's entire symbol table immediately, rather than
950 the default, which is to read it incrementally as it is needed.
951 This makes startup slower, but makes future operations faster.
955 You typically combine the @code{-mapped} and @code{-readnow} options in
956 order to build a @file{.syms} file that contains complete symbol
957 information. (@xref{Files,,Commands to specify files}, for information
958 on @file{.syms} files.) A simple @value{GDBN} invocation to do nothing
959 but build a @file{.syms} file for future use is:
962 gdb -batch -nx -mapped -readnow programname
966 @subsection Choosing modes
968 You can run @value{GDBN} in various alternative modes---for example, in
969 batch mode or quiet mode.
976 Do not execute commands found in any initialization files. Normally,
977 @value{GDBN} executes the commands in these files after all the command
978 options and arguments have been processed. @xref{Command Files,,Command
984 @cindex @code{--quiet}
985 @cindex @code{--silent}
987 ``Quiet''. Do not print the introductory and copyright messages. These
988 messages are also suppressed in batch mode.
991 @cindex @code{--batch}
992 Run in batch mode. Exit with status @code{0} after processing all the
993 command files specified with @samp{-x} (and all commands from
994 initialization files, if not inhibited with @samp{-n}). Exit with
995 nonzero status if an error occurs in executing the @value{GDBN} commands
996 in the command files.
998 Batch mode may be useful for running @value{GDBN} as a filter, for
999 example to download and run a program on another computer; in order to
1000 make this more useful, the message
1003 Program exited normally.
1007 (which is ordinarily issued whenever a program running under
1008 @value{GDBN} control terminates) is not issued when running in batch
1013 @cindex @code{--nowindows}
1015 ``No windows''. If @value{GDBN} comes with a graphical user interface
1016 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
1017 interface. If no GUI is available, this option has no effect.
1021 @cindex @code{--windows}
1023 If @value{GDBN} includes a GUI, then this option requires it to be
1026 @item -cd @var{directory}
1028 Run @value{GDBN} using @var{directory} as its working directory,
1029 instead of the current directory.
1033 @cindex @code{--fullname}
1035 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
1036 subprocess. It tells @value{GDBN} to output the full file name and line
1037 number in a standard, recognizable fashion each time a stack frame is
1038 displayed (which includes each time your program stops). This
1039 recognizable format looks like two @samp{\032} characters, followed by
1040 the file name, line number and character position separated by colons,
1041 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
1042 @samp{\032} characters as a signal to display the source code for the
1046 @cindex @code{--epoch}
1047 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
1048 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
1049 routines so as to allow Epoch to display values of expressions in a
1052 @item -annotate @var{level}
1053 @cindex @code{--annotate}
1054 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
1055 effect is identical to using @samp{set annotate @var{level}}
1056 (@pxref{Annotations}).
1057 Annotation level controls how much information does @value{GDBN} print
1058 together with its prompt, values of expressions, source lines, and other
1059 types of output. Level 0 is the normal, level 1 is for use when
1060 @value{GDBN} is run as a subprocess of @sc{gnu} Emacs, level 2 is the
1061 maximum annotation suitable for programs that control @value{GDBN}.
1064 @cindex @code{--async}
1065 Use the asynchronous event loop for the command-line interface.
1066 @value{GDBN} processes all events, such as user keyboard input, via a
1067 special event loop. This allows @value{GDBN} to accept and process user
1068 commands in parallel with the debugged process being
1069 run@footnote{@value{GDBN} built with @sc{djgpp} tools for
1070 MS-DOS/MS-Windows supports this mode of operation, but the event loop is
1071 suspended when the debuggee runs.}, so you don't need to wait for
1072 control to return to @value{GDBN} before you type the next command.
1073 (@emph{Note:} as of version 5.1, the target side of the asynchronous
1074 operation is not yet in place, so @samp{-async} does not work fully
1076 @c FIXME: when the target side of the event loop is done, the above NOTE
1077 @c should be removed.
1079 When the standard input is connected to a terminal device, @value{GDBN}
1080 uses the asynchronous event loop by default, unless disabled by the
1081 @samp{-noasync} option.
1084 @cindex @code{--noasync}
1085 Disable the asynchronous event loop for the command-line interface.
1088 @cindex @code{--args}
1089 Change interpretation of command line so that arguments following the
1090 executable file are passed as command line arguments to the inferior.
1091 This option stops option processing.
1093 @item -baud @var{bps}
1095 @cindex @code{--baud}
1097 Set the line speed (baud rate or bits per second) of any serial
1098 interface used by @value{GDBN} for remote debugging.
1100 @item -tty @var{device}
1101 @itemx -t @var{device}
1102 @cindex @code{--tty}
1104 Run using @var{device} for your program's standard input and output.
1105 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1107 @c resolve the situation of these eventually
1109 @cindex @code{--tui}
1110 Activate the Terminal User Interface when starting.
1111 The Terminal User Interface manages several text windows on the terminal,
1112 showing source, assembly, registers and @value{GDBN} command outputs
1113 (@pxref{TUI, ,@value{GDBN} Text User Interface}).
1114 Do not use this option if you run @value{GDBN} from Emacs
1115 (@pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}).
1118 @c @cindex @code{--xdb}
1119 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1120 @c For information, see the file @file{xdb_trans.html}, which is usually
1121 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1124 @item -interpreter @var{interp}
1125 @cindex @code{--interpreter}
1126 Use the interpreter @var{interp} for interface with the controlling
1127 program or device. This option is meant to be set by programs which
1128 communicate with @value{GDBN} using it as a back end.
1130 @samp{--interpreter=mi} (or @samp{--interpreter=mi1}) causes
1131 @value{GDBN} to use the @dfn{gdb/mi interface} (@pxref{GDB/MI, , The
1132 @sc{gdb/mi} Interface}). The older @sc{gdb/mi} interface, included in
1133 @value{GDBN} version 5.0 can be selected with @samp{--interpreter=mi0}.
1136 @cindex @code{--write}
1137 Open the executable and core files for both reading and writing. This
1138 is equivalent to the @samp{set write on} command inside @value{GDBN}
1142 @cindex @code{--statistics}
1143 This option causes @value{GDBN} to print statistics about time and
1144 memory usage after it completes each command and returns to the prompt.
1147 @cindex @code{--version}
1148 This option causes @value{GDBN} to print its version number and
1149 no-warranty blurb, and exit.
1154 @section Quitting @value{GDBN}
1155 @cindex exiting @value{GDBN}
1156 @cindex leaving @value{GDBN}
1159 @kindex quit @r{[}@var{expression}@r{]}
1160 @kindex q @r{(@code{quit})}
1161 @item quit @r{[}@var{expression}@r{]}
1163 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1164 @code{q}), or type an end-of-file character (usually @kbd{C-d}). If you
1165 do not supply @var{expression}, @value{GDBN} will terminate normally;
1166 otherwise it will terminate using the result of @var{expression} as the
1171 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1172 terminates the action of any @value{GDBN} command that is in progress and
1173 returns to @value{GDBN} command level. It is safe to type the interrupt
1174 character at any time because @value{GDBN} does not allow it to take effect
1175 until a time when it is safe.
1177 If you have been using @value{GDBN} to control an attached process or
1178 device, you can release it with the @code{detach} command
1179 (@pxref{Attach, ,Debugging an already-running process}).
1181 @node Shell Commands
1182 @section Shell commands
1184 If you need to execute occasional shell commands during your
1185 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1186 just use the @code{shell} command.
1190 @cindex shell escape
1191 @item shell @var{command string}
1192 Invoke a standard shell to execute @var{command string}.
1193 If it exists, the environment variable @code{SHELL} determines which
1194 shell to run. Otherwise @value{GDBN} uses the default shell
1195 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1198 The utility @code{make} is often needed in development environments.
1199 You do not have to use the @code{shell} command for this purpose in
1204 @cindex calling make
1205 @item make @var{make-args}
1206 Execute the @code{make} program with the specified
1207 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1211 @chapter @value{GDBN} Commands
1213 You can abbreviate a @value{GDBN} command to the first few letters of the command
1214 name, if that abbreviation is unambiguous; and you can repeat certain
1215 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1216 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1217 show you the alternatives available, if there is more than one possibility).
1220 * Command Syntax:: How to give commands to @value{GDBN}
1221 * Completion:: Command completion
1222 * Help:: How to ask @value{GDBN} for help
1225 @node Command Syntax
1226 @section Command syntax
1228 A @value{GDBN} command is a single line of input. There is no limit on
1229 how long it can be. It starts with a command name, which is followed by
1230 arguments whose meaning depends on the command name. For example, the
1231 command @code{step} accepts an argument which is the number of times to
1232 step, as in @samp{step 5}. You can also use the @code{step} command
1233 with no arguments. Some commands do not allow any arguments.
1235 @cindex abbreviation
1236 @value{GDBN} command names may always be truncated if that abbreviation is
1237 unambiguous. Other possible command abbreviations are listed in the
1238 documentation for individual commands. In some cases, even ambiguous
1239 abbreviations are allowed; for example, @code{s} is specially defined as
1240 equivalent to @code{step} even though there are other commands whose
1241 names start with @code{s}. You can test abbreviations by using them as
1242 arguments to the @code{help} command.
1244 @cindex repeating commands
1245 @kindex RET @r{(repeat last command)}
1246 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1247 repeat the previous command. Certain commands (for example, @code{run})
1248 will not repeat this way; these are commands whose unintentional
1249 repetition might cause trouble and which you are unlikely to want to
1252 The @code{list} and @code{x} commands, when you repeat them with
1253 @key{RET}, construct new arguments rather than repeating
1254 exactly as typed. This permits easy scanning of source or memory.
1256 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1257 output, in a way similar to the common utility @code{more}
1258 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1259 @key{RET} too many in this situation, @value{GDBN} disables command
1260 repetition after any command that generates this sort of display.
1262 @kindex # @r{(a comment)}
1264 Any text from a @kbd{#} to the end of the line is a comment; it does
1265 nothing. This is useful mainly in command files (@pxref{Command
1266 Files,,Command files}).
1268 @cindex repeating command sequences
1269 @kindex C-o @r{(operate-and-get-next)}
1270 The @kbd{C-o} binding is useful for repeating a complex sequence of
1271 commands. This command accepts the current line, like @kbd{RET}, and
1272 then fetches the next line relative to the current line from the history
1276 @section Command completion
1279 @cindex word completion
1280 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1281 only one possibility; it can also show you what the valid possibilities
1282 are for the next word in a command, at any time. This works for @value{GDBN}
1283 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1285 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1286 of a word. If there is only one possibility, @value{GDBN} fills in the
1287 word, and waits for you to finish the command (or press @key{RET} to
1288 enter it). For example, if you type
1290 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1291 @c complete accuracy in these examples; space introduced for clarity.
1292 @c If texinfo enhancements make it unnecessary, it would be nice to
1293 @c replace " @key" by "@key" in the following...
1295 (@value{GDBP}) info bre @key{TAB}
1299 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1300 the only @code{info} subcommand beginning with @samp{bre}:
1303 (@value{GDBP}) info breakpoints
1307 You can either press @key{RET} at this point, to run the @code{info
1308 breakpoints} command, or backspace and enter something else, if
1309 @samp{breakpoints} does not look like the command you expected. (If you
1310 were sure you wanted @code{info breakpoints} in the first place, you
1311 might as well just type @key{RET} immediately after @samp{info bre},
1312 to exploit command abbreviations rather than command completion).
1314 If there is more than one possibility for the next word when you press
1315 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1316 characters and try again, or just press @key{TAB} a second time;
1317 @value{GDBN} displays all the possible completions for that word. For
1318 example, you might want to set a breakpoint on a subroutine whose name
1319 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1320 just sounds the bell. Typing @key{TAB} again displays all the
1321 function names in your program that begin with those characters, for
1325 (@value{GDBP}) b make_ @key{TAB}
1326 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1327 make_a_section_from_file make_environ
1328 make_abs_section make_function_type
1329 make_blockvector make_pointer_type
1330 make_cleanup make_reference_type
1331 make_command make_symbol_completion_list
1332 (@value{GDBP}) b make_
1336 After displaying the available possibilities, @value{GDBN} copies your
1337 partial input (@samp{b make_} in the example) so you can finish the
1340 If you just want to see the list of alternatives in the first place, you
1341 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1342 means @kbd{@key{META} ?}. You can type this either by holding down a
1343 key designated as the @key{META} shift on your keyboard (if there is
1344 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1346 @cindex quotes in commands
1347 @cindex completion of quoted strings
1348 Sometimes the string you need, while logically a ``word'', may contain
1349 parentheses or other characters that @value{GDBN} normally excludes from
1350 its notion of a word. To permit word completion to work in this
1351 situation, you may enclose words in @code{'} (single quote marks) in
1352 @value{GDBN} commands.
1354 The most likely situation where you might need this is in typing the
1355 name of a C@t{++} function. This is because C@t{++} allows function
1356 overloading (multiple definitions of the same function, distinguished
1357 by argument type). For example, when you want to set a breakpoint you
1358 may need to distinguish whether you mean the version of @code{name}
1359 that takes an @code{int} parameter, @code{name(int)}, or the version
1360 that takes a @code{float} parameter, @code{name(float)}. To use the
1361 word-completion facilities in this situation, type a single quote
1362 @code{'} at the beginning of the function name. This alerts
1363 @value{GDBN} that it may need to consider more information than usual
1364 when you press @key{TAB} or @kbd{M-?} to request word completion:
1367 (@value{GDBP}) b 'bubble( @kbd{M-?}
1368 bubble(double,double) bubble(int,int)
1369 (@value{GDBP}) b 'bubble(
1372 In some cases, @value{GDBN} can tell that completing a name requires using
1373 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1374 completing as much as it can) if you do not type the quote in the first
1378 (@value{GDBP}) b bub @key{TAB}
1379 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1380 (@value{GDBP}) b 'bubble(
1384 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1385 you have not yet started typing the argument list when you ask for
1386 completion on an overloaded symbol.
1388 For more information about overloaded functions, see @ref{C plus plus
1389 expressions, ,C@t{++} expressions}. You can use the command @code{set
1390 overload-resolution off} to disable overload resolution;
1391 see @ref{Debugging C plus plus, ,@value{GDBN} features for C@t{++}}.
1395 @section Getting help
1396 @cindex online documentation
1399 You can always ask @value{GDBN} itself for information on its commands,
1400 using the command @code{help}.
1403 @kindex h @r{(@code{help})}
1406 You can use @code{help} (abbreviated @code{h}) with no arguments to
1407 display a short list of named classes of commands:
1411 List of classes of commands:
1413 aliases -- Aliases of other commands
1414 breakpoints -- Making program stop at certain points
1415 data -- Examining data
1416 files -- Specifying and examining files
1417 internals -- Maintenance commands
1418 obscure -- Obscure features
1419 running -- Running the program
1420 stack -- Examining the stack
1421 status -- Status inquiries
1422 support -- Support facilities
1423 tracepoints -- Tracing of program execution without@*
1424 stopping the program
1425 user-defined -- User-defined commands
1427 Type "help" followed by a class name for a list of
1428 commands in that class.
1429 Type "help" followed by command name for full
1431 Command name abbreviations are allowed if unambiguous.
1434 @c the above line break eliminates huge line overfull...
1436 @item help @var{class}
1437 Using one of the general help classes as an argument, you can get a
1438 list of the individual commands in that class. For example, here is the
1439 help display for the class @code{status}:
1442 (@value{GDBP}) help status
1447 @c Line break in "show" line falsifies real output, but needed
1448 @c to fit in smallbook page size.
1449 info -- Generic command for showing things
1450 about the program being debugged
1451 show -- Generic command for showing things
1454 Type "help" followed by command name for full
1456 Command name abbreviations are allowed if unambiguous.
1460 @item help @var{command}
1461 With a command name as @code{help} argument, @value{GDBN} displays a
1462 short paragraph on how to use that command.
1465 @item apropos @var{args}
1466 The @code{apropos @var{args}} command searches through all of the @value{GDBN}
1467 commands, and their documentation, for the regular expression specified in
1468 @var{args}. It prints out all matches found. For example:
1479 set symbol-reloading -- Set dynamic symbol table reloading
1480 multiple times in one run
1481 show symbol-reloading -- Show dynamic symbol table reloading
1482 multiple times in one run
1487 @item complete @var{args}
1488 The @code{complete @var{args}} command lists all the possible completions
1489 for the beginning of a command. Use @var{args} to specify the beginning of the
1490 command you want completed. For example:
1496 @noindent results in:
1507 @noindent This is intended for use by @sc{gnu} Emacs.
1510 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1511 and @code{show} to inquire about the state of your program, or the state
1512 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1513 manual introduces each of them in the appropriate context. The listings
1514 under @code{info} and under @code{show} in the Index point to
1515 all the sub-commands. @xref{Index}.
1520 @kindex i @r{(@code{info})}
1522 This command (abbreviated @code{i}) is for describing the state of your
1523 program. For example, you can list the arguments given to your program
1524 with @code{info args}, list the registers currently in use with @code{info
1525 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1526 You can get a complete list of the @code{info} sub-commands with
1527 @w{@code{help info}}.
1531 You can assign the result of an expression to an environment variable with
1532 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1533 @code{set prompt $}.
1537 In contrast to @code{info}, @code{show} is for describing the state of
1538 @value{GDBN} itself.
1539 You can change most of the things you can @code{show}, by using the
1540 related command @code{set}; for example, you can control what number
1541 system is used for displays with @code{set radix}, or simply inquire
1542 which is currently in use with @code{show radix}.
1545 To display all the settable parameters and their current
1546 values, you can use @code{show} with no arguments; you may also use
1547 @code{info set}. Both commands produce the same display.
1548 @c FIXME: "info set" violates the rule that "info" is for state of
1549 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1550 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1554 Here are three miscellaneous @code{show} subcommands, all of which are
1555 exceptional in lacking corresponding @code{set} commands:
1558 @kindex show version
1559 @cindex version number
1561 Show what version of @value{GDBN} is running. You should include this
1562 information in @value{GDBN} bug-reports. If multiple versions of
1563 @value{GDBN} are in use at your site, you may need to determine which
1564 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1565 commands are introduced, and old ones may wither away. Also, many
1566 system vendors ship variant versions of @value{GDBN}, and there are
1567 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1568 The version number is the same as the one announced when you start
1571 @kindex show copying
1573 Display information about permission for copying @value{GDBN}.
1575 @kindex show warranty
1577 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1578 if your version of @value{GDBN} comes with one.
1583 @chapter Running Programs Under @value{GDBN}
1585 When you run a program under @value{GDBN}, you must first generate
1586 debugging information when you compile it.
1588 You may start @value{GDBN} with its arguments, if any, in an environment
1589 of your choice. If you are doing native debugging, you may redirect
1590 your program's input and output, debug an already running process, or
1591 kill a child process.
1594 * Compilation:: Compiling for debugging
1595 * Starting:: Starting your program
1596 * Arguments:: Your program's arguments
1597 * Environment:: Your program's environment
1599 * Working Directory:: Your program's working directory
1600 * Input/Output:: Your program's input and output
1601 * Attach:: Debugging an already-running process
1602 * Kill Process:: Killing the child process
1604 * Threads:: Debugging programs with multiple threads
1605 * Processes:: Debugging programs with multiple processes
1609 @section Compiling for debugging
1611 In order to debug a program effectively, you need to generate
1612 debugging information when you compile it. This debugging information
1613 is stored in the object file; it describes the data type of each
1614 variable or function and the correspondence between source line numbers
1615 and addresses in the executable code.
1617 To request debugging information, specify the @samp{-g} option when you run
1620 Most compilers do not include information about preprocessor macros in
1621 the debugging information if you specify the @option{-g} flag alone,
1622 because this information is rather large. Version 3.1 of @value{NGCC},
1623 the @sc{gnu} C compiler, provides macro information if you specify the
1624 options @option{-gdwarf-2} and @option{-g3}; the former option requests
1625 debugging information in the Dwarf 2 format, and the latter requests
1626 ``extra information''. In the future, we hope to find more compact ways
1627 to represent macro information, so that it can be included with
1630 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1631 options together. Using those compilers, you cannot generate optimized
1632 executables containing debugging information.
1634 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or
1635 without @samp{-O}, making it possible to debug optimized code. We
1636 recommend that you @emph{always} use @samp{-g} whenever you compile a
1637 program. You may think your program is correct, but there is no sense
1638 in pushing your luck.
1640 @cindex optimized code, debugging
1641 @cindex debugging optimized code
1642 When you debug a program compiled with @samp{-g -O}, remember that the
1643 optimizer is rearranging your code; the debugger shows you what is
1644 really there. Do not be too surprised when the execution path does not
1645 exactly match your source file! An extreme example: if you define a
1646 variable, but never use it, @value{GDBN} never sees that
1647 variable---because the compiler optimizes it out of existence.
1649 Some things do not work as well with @samp{-g -O} as with just
1650 @samp{-g}, particularly on machines with instruction scheduling. If in
1651 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1652 please report it to us as a bug (including a test case!).
1654 Older versions of the @sc{gnu} C compiler permitted a variant option
1655 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1656 format; if your @sc{gnu} C compiler has this option, do not use it.
1660 @section Starting your program
1666 @kindex r @r{(@code{run})}
1669 Use the @code{run} command to start your program under @value{GDBN}.
1670 You must first specify the program name (except on VxWorks) with an
1671 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1672 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1673 (@pxref{Files, ,Commands to specify files}).
1677 If you are running your program in an execution environment that
1678 supports processes, @code{run} creates an inferior process and makes
1679 that process run your program. (In environments without processes,
1680 @code{run} jumps to the start of your program.)
1682 The execution of a program is affected by certain information it
1683 receives from its superior. @value{GDBN} provides ways to specify this
1684 information, which you must do @emph{before} starting your program. (You
1685 can change it after starting your program, but such changes only affect
1686 your program the next time you start it.) This information may be
1687 divided into four categories:
1690 @item The @emph{arguments.}
1691 Specify the arguments to give your program as the arguments of the
1692 @code{run} command. If a shell is available on your target, the shell
1693 is used to pass the arguments, so that you may use normal conventions
1694 (such as wildcard expansion or variable substitution) in describing
1696 In Unix systems, you can control which shell is used with the
1697 @code{SHELL} environment variable.
1698 @xref{Arguments, ,Your program's arguments}.
1700 @item The @emph{environment.}
1701 Your program normally inherits its environment from @value{GDBN}, but you can
1702 use the @value{GDBN} commands @code{set environment} and @code{unset
1703 environment} to change parts of the environment that affect
1704 your program. @xref{Environment, ,Your program's environment}.
1706 @item The @emph{working directory.}
1707 Your program inherits its working directory from @value{GDBN}. You can set
1708 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1709 @xref{Working Directory, ,Your program's working directory}.
1711 @item The @emph{standard input and output.}
1712 Your program normally uses the same device for standard input and
1713 standard output as @value{GDBN} is using. You can redirect input and output
1714 in the @code{run} command line, or you can use the @code{tty} command to
1715 set a different device for your program.
1716 @xref{Input/Output, ,Your program's input and output}.
1719 @emph{Warning:} While input and output redirection work, you cannot use
1720 pipes to pass the output of the program you are debugging to another
1721 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1725 When you issue the @code{run} command, your program begins to execute
1726 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1727 of how to arrange for your program to stop. Once your program has
1728 stopped, you may call functions in your program, using the @code{print}
1729 or @code{call} commands. @xref{Data, ,Examining Data}.
1731 If the modification time of your symbol file has changed since the last
1732 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1733 table, and reads it again. When it does this, @value{GDBN} tries to retain
1734 your current breakpoints.
1737 @section Your program's arguments
1739 @cindex arguments (to your program)
1740 The arguments to your program can be specified by the arguments of the
1742 They are passed to a shell, which expands wildcard characters and
1743 performs redirection of I/O, and thence to your program. Your
1744 @code{SHELL} environment variable (if it exists) specifies what shell
1745 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1746 the default shell (@file{/bin/sh} on Unix).
1748 On non-Unix systems, the program is usually invoked directly by
1749 @value{GDBN}, which emulates I/O redirection via the appropriate system
1750 calls, and the wildcard characters are expanded by the startup code of
1751 the program, not by the shell.
1753 @code{run} with no arguments uses the same arguments used by the previous
1754 @code{run}, or those set by the @code{set args} command.
1759 Specify the arguments to be used the next time your program is run. If
1760 @code{set args} has no arguments, @code{run} executes your program
1761 with no arguments. Once you have run your program with arguments,
1762 using @code{set args} before the next @code{run} is the only way to run
1763 it again without arguments.
1767 Show the arguments to give your program when it is started.
1771 @section Your program's environment
1773 @cindex environment (of your program)
1774 The @dfn{environment} consists of a set of environment variables and
1775 their values. Environment variables conventionally record such things as
1776 your user name, your home directory, your terminal type, and your search
1777 path for programs to run. Usually you set up environment variables with
1778 the shell and they are inherited by all the other programs you run. When
1779 debugging, it can be useful to try running your program with a modified
1780 environment without having to start @value{GDBN} over again.
1784 @item path @var{directory}
1785 Add @var{directory} to the front of the @code{PATH} environment variable
1786 (the search path for executables) that will be passed to your program.
1787 The value of @code{PATH} used by @value{GDBN} does not change.
1788 You may specify several directory names, separated by whitespace or by a
1789 system-dependent separator character (@samp{:} on Unix, @samp{;} on
1790 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
1791 is moved to the front, so it is searched sooner.
1793 You can use the string @samp{$cwd} to refer to whatever is the current
1794 working directory at the time @value{GDBN} searches the path. If you
1795 use @samp{.} instead, it refers to the directory where you executed the
1796 @code{path} command. @value{GDBN} replaces @samp{.} in the
1797 @var{directory} argument (with the current path) before adding
1798 @var{directory} to the search path.
1799 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1800 @c document that, since repeating it would be a no-op.
1804 Display the list of search paths for executables (the @code{PATH}
1805 environment variable).
1807 @kindex show environment
1808 @item show environment @r{[}@var{varname}@r{]}
1809 Print the value of environment variable @var{varname} to be given to
1810 your program when it starts. If you do not supply @var{varname},
1811 print the names and values of all environment variables to be given to
1812 your program. You can abbreviate @code{environment} as @code{env}.
1814 @kindex set environment
1815 @item set environment @var{varname} @r{[}=@var{value}@r{]}
1816 Set environment variable @var{varname} to @var{value}. The value
1817 changes for your program only, not for @value{GDBN} itself. @var{value} may
1818 be any string; the values of environment variables are just strings, and
1819 any interpretation is supplied by your program itself. The @var{value}
1820 parameter is optional; if it is eliminated, the variable is set to a
1822 @c "any string" here does not include leading, trailing
1823 @c blanks. Gnu asks: does anyone care?
1825 For example, this command:
1832 tells the debugged program, when subsequently run, that its user is named
1833 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1834 are not actually required.)
1836 @kindex unset environment
1837 @item unset environment @var{varname}
1838 Remove variable @var{varname} from the environment to be passed to your
1839 program. This is different from @samp{set env @var{varname} =};
1840 @code{unset environment} removes the variable from the environment,
1841 rather than assigning it an empty value.
1844 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
1846 by your @code{SHELL} environment variable if it exists (or
1847 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1848 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1849 @file{.bashrc} for BASH---any variables you set in that file affect
1850 your program. You may wish to move setting of environment variables to
1851 files that are only run when you sign on, such as @file{.login} or
1854 @node Working Directory
1855 @section Your program's working directory
1857 @cindex working directory (of your program)
1858 Each time you start your program with @code{run}, it inherits its
1859 working directory from the current working directory of @value{GDBN}.
1860 The @value{GDBN} working directory is initially whatever it inherited
1861 from its parent process (typically the shell), but you can specify a new
1862 working directory in @value{GDBN} with the @code{cd} command.
1864 The @value{GDBN} working directory also serves as a default for the commands
1865 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1870 @item cd @var{directory}
1871 Set the @value{GDBN} working directory to @var{directory}.
1875 Print the @value{GDBN} working directory.
1879 @section Your program's input and output
1884 By default, the program you run under @value{GDBN} does input and output to
1885 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1886 to its own terminal modes to interact with you, but it records the terminal
1887 modes your program was using and switches back to them when you continue
1888 running your program.
1891 @kindex info terminal
1893 Displays information recorded by @value{GDBN} about the terminal modes your
1897 You can redirect your program's input and/or output using shell
1898 redirection with the @code{run} command. For example,
1905 starts your program, diverting its output to the file @file{outfile}.
1908 @cindex controlling terminal
1909 Another way to specify where your program should do input and output is
1910 with the @code{tty} command. This command accepts a file name as
1911 argument, and causes this file to be the default for future @code{run}
1912 commands. It also resets the controlling terminal for the child
1913 process, for future @code{run} commands. For example,
1920 directs that processes started with subsequent @code{run} commands
1921 default to do input and output on the terminal @file{/dev/ttyb} and have
1922 that as their controlling terminal.
1924 An explicit redirection in @code{run} overrides the @code{tty} command's
1925 effect on the input/output device, but not its effect on the controlling
1928 When you use the @code{tty} command or redirect input in the @code{run}
1929 command, only the input @emph{for your program} is affected. The input
1930 for @value{GDBN} still comes from your terminal.
1933 @section Debugging an already-running process
1938 @item attach @var{process-id}
1939 This command attaches to a running process---one that was started
1940 outside @value{GDBN}. (@code{info files} shows your active
1941 targets.) The command takes as argument a process ID. The usual way to
1942 find out the process-id of a Unix process is with the @code{ps} utility,
1943 or with the @samp{jobs -l} shell command.
1945 @code{attach} does not repeat if you press @key{RET} a second time after
1946 executing the command.
1949 To use @code{attach}, your program must be running in an environment
1950 which supports processes; for example, @code{attach} does not work for
1951 programs on bare-board targets that lack an operating system. You must
1952 also have permission to send the process a signal.
1954 When you use @code{attach}, the debugger finds the program running in
1955 the process first by looking in the current working directory, then (if
1956 the program is not found) by using the source file search path
1957 (@pxref{Source Path, ,Specifying source directories}). You can also use
1958 the @code{file} command to load the program. @xref{Files, ,Commands to
1961 The first thing @value{GDBN} does after arranging to debug the specified
1962 process is to stop it. You can examine and modify an attached process
1963 with all the @value{GDBN} commands that are ordinarily available when
1964 you start processes with @code{run}. You can insert breakpoints; you
1965 can step and continue; you can modify storage. If you would rather the
1966 process continue running, you may use the @code{continue} command after
1967 attaching @value{GDBN} to the process.
1972 When you have finished debugging the attached process, you can use the
1973 @code{detach} command to release it from @value{GDBN} control. Detaching
1974 the process continues its execution. After the @code{detach} command,
1975 that process and @value{GDBN} become completely independent once more, and you
1976 are ready to @code{attach} another process or start one with @code{run}.
1977 @code{detach} does not repeat if you press @key{RET} again after
1978 executing the command.
1981 If you exit @value{GDBN} or use the @code{run} command while you have an
1982 attached process, you kill that process. By default, @value{GDBN} asks
1983 for confirmation if you try to do either of these things; you can
1984 control whether or not you need to confirm by using the @code{set
1985 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1989 @section Killing the child process
1994 Kill the child process in which your program is running under @value{GDBN}.
1997 This command is useful if you wish to debug a core dump instead of a
1998 running process. @value{GDBN} ignores any core dump file while your program
2001 On some operating systems, a program cannot be executed outside @value{GDBN}
2002 while you have breakpoints set on it inside @value{GDBN}. You can use the
2003 @code{kill} command in this situation to permit running your program
2004 outside the debugger.
2006 The @code{kill} command is also useful if you wish to recompile and
2007 relink your program, since on many systems it is impossible to modify an
2008 executable file while it is running in a process. In this case, when you
2009 next type @code{run}, @value{GDBN} notices that the file has changed, and
2010 reads the symbol table again (while trying to preserve your current
2011 breakpoint settings).
2014 @section Debugging programs with multiple threads
2016 @cindex threads of execution
2017 @cindex multiple threads
2018 @cindex switching threads
2019 In some operating systems, such as HP-UX and Solaris, a single program
2020 may have more than one @dfn{thread} of execution. The precise semantics
2021 of threads differ from one operating system to another, but in general
2022 the threads of a single program are akin to multiple processes---except
2023 that they share one address space (that is, they can all examine and
2024 modify the same variables). On the other hand, each thread has its own
2025 registers and execution stack, and perhaps private memory.
2027 @value{GDBN} provides these facilities for debugging multi-thread
2031 @item automatic notification of new threads
2032 @item @samp{thread @var{threadno}}, a command to switch among threads
2033 @item @samp{info threads}, a command to inquire about existing threads
2034 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
2035 a command to apply a command to a list of threads
2036 @item thread-specific breakpoints
2040 @emph{Warning:} These facilities are not yet available on every
2041 @value{GDBN} configuration where the operating system supports threads.
2042 If your @value{GDBN} does not support threads, these commands have no
2043 effect. For example, a system without thread support shows no output
2044 from @samp{info threads}, and always rejects the @code{thread} command,
2048 (@value{GDBP}) info threads
2049 (@value{GDBP}) thread 1
2050 Thread ID 1 not known. Use the "info threads" command to
2051 see the IDs of currently known threads.
2053 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
2054 @c doesn't support threads"?
2057 @cindex focus of debugging
2058 @cindex current thread
2059 The @value{GDBN} thread debugging facility allows you to observe all
2060 threads while your program runs---but whenever @value{GDBN} takes
2061 control, one thread in particular is always the focus of debugging.
2062 This thread is called the @dfn{current thread}. Debugging commands show
2063 program information from the perspective of the current thread.
2065 @cindex @code{New} @var{systag} message
2066 @cindex thread identifier (system)
2067 @c FIXME-implementors!! It would be more helpful if the [New...] message
2068 @c included GDB's numeric thread handle, so you could just go to that
2069 @c thread without first checking `info threads'.
2070 Whenever @value{GDBN} detects a new thread in your program, it displays
2071 the target system's identification for the thread with a message in the
2072 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2073 whose form varies depending on the particular system. For example, on
2074 LynxOS, you might see
2077 [New process 35 thread 27]
2081 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
2082 the @var{systag} is simply something like @samp{process 368}, with no
2085 @c FIXME!! (1) Does the [New...] message appear even for the very first
2086 @c thread of a program, or does it only appear for the
2087 @c second---i.e.@: when it becomes obvious we have a multithread
2089 @c (2) *Is* there necessarily a first thread always? Or do some
2090 @c multithread systems permit starting a program with multiple
2091 @c threads ab initio?
2093 @cindex thread number
2094 @cindex thread identifier (GDB)
2095 For debugging purposes, @value{GDBN} associates its own thread
2096 number---always a single integer---with each thread in your program.
2099 @kindex info threads
2101 Display a summary of all threads currently in your
2102 program. @value{GDBN} displays for each thread (in this order):
2105 @item the thread number assigned by @value{GDBN}
2107 @item the target system's thread identifier (@var{systag})
2109 @item the current stack frame summary for that thread
2113 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2114 indicates the current thread.
2118 @c end table here to get a little more width for example
2121 (@value{GDBP}) info threads
2122 3 process 35 thread 27 0x34e5 in sigpause ()
2123 2 process 35 thread 23 0x34e5 in sigpause ()
2124 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2130 @cindex thread number
2131 @cindex thread identifier (GDB)
2132 For debugging purposes, @value{GDBN} associates its own thread
2133 number---a small integer assigned in thread-creation order---with each
2134 thread in your program.
2136 @cindex @code{New} @var{systag} message, on HP-UX
2137 @cindex thread identifier (system), on HP-UX
2138 @c FIXME-implementors!! It would be more helpful if the [New...] message
2139 @c included GDB's numeric thread handle, so you could just go to that
2140 @c thread without first checking `info threads'.
2141 Whenever @value{GDBN} detects a new thread in your program, it displays
2142 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2143 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2144 whose form varies depending on the particular system. For example, on
2148 [New thread 2 (system thread 26594)]
2152 when @value{GDBN} notices a new thread.
2155 @kindex info threads
2157 Display a summary of all threads currently in your
2158 program. @value{GDBN} displays for each thread (in this order):
2161 @item the thread number assigned by @value{GDBN}
2163 @item the target system's thread identifier (@var{systag})
2165 @item the current stack frame summary for that thread
2169 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2170 indicates the current thread.
2174 @c end table here to get a little more width for example
2177 (@value{GDBP}) info threads
2178 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2180 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2181 from /usr/lib/libc.2
2182 1 system thread 27905 0x7b003498 in _brk () \@*
2183 from /usr/lib/libc.2
2187 @kindex thread @var{threadno}
2188 @item thread @var{threadno}
2189 Make thread number @var{threadno} the current thread. The command
2190 argument @var{threadno} is the internal @value{GDBN} thread number, as
2191 shown in the first field of the @samp{info threads} display.
2192 @value{GDBN} responds by displaying the system identifier of the thread
2193 you selected, and its current stack frame summary:
2196 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2197 (@value{GDBP}) thread 2
2198 [Switching to process 35 thread 23]
2199 0x34e5 in sigpause ()
2203 As with the @samp{[New @dots{}]} message, the form of the text after
2204 @samp{Switching to} depends on your system's conventions for identifying
2207 @kindex thread apply
2208 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2209 The @code{thread apply} command allows you to apply a command to one or
2210 more threads. Specify the numbers of the threads that you want affected
2211 with the command argument @var{threadno}. @var{threadno} is the internal
2212 @value{GDBN} thread number, as shown in the first field of the @samp{info
2213 threads} display. To apply a command to all threads, use
2214 @code{thread apply all} @var{args}.
2217 @cindex automatic thread selection
2218 @cindex switching threads automatically
2219 @cindex threads, automatic switching
2220 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2221 signal, it automatically selects the thread where that breakpoint or
2222 signal happened. @value{GDBN} alerts you to the context switch with a
2223 message of the form @samp{[Switching to @var{systag}]} to identify the
2226 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2227 more information about how @value{GDBN} behaves when you stop and start
2228 programs with multiple threads.
2230 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2231 watchpoints in programs with multiple threads.
2234 @section Debugging programs with multiple processes
2236 @cindex fork, debugging programs which call
2237 @cindex multiple processes
2238 @cindex processes, multiple
2239 On most systems, @value{GDBN} has no special support for debugging
2240 programs which create additional processes using the @code{fork}
2241 function. When a program forks, @value{GDBN} will continue to debug the
2242 parent process and the child process will run unimpeded. If you have
2243 set a breakpoint in any code which the child then executes, the child
2244 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2245 will cause it to terminate.
2247 However, if you want to debug the child process there is a workaround
2248 which isn't too painful. Put a call to @code{sleep} in the code which
2249 the child process executes after the fork. It may be useful to sleep
2250 only if a certain environment variable is set, or a certain file exists,
2251 so that the delay need not occur when you don't want to run @value{GDBN}
2252 on the child. While the child is sleeping, use the @code{ps} program to
2253 get its process ID. Then tell @value{GDBN} (a new invocation of
2254 @value{GDBN} if you are also debugging the parent process) to attach to
2255 the child process (@pxref{Attach}). From that point on you can debug
2256 the child process just like any other process which you attached to.
2258 On HP-UX (11.x and later only?), @value{GDBN} provides support for
2259 debugging programs that create additional processes using the
2260 @code{fork} or @code{vfork} function.
2262 By default, when a program forks, @value{GDBN} will continue to debug
2263 the parent process and the child process will run unimpeded.
2265 If you want to follow the child process instead of the parent process,
2266 use the command @w{@code{set follow-fork-mode}}.
2269 @kindex set follow-fork-mode
2270 @item set follow-fork-mode @var{mode}
2271 Set the debugger response to a program call of @code{fork} or
2272 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2273 process. The @var{mode} can be:
2277 The original process is debugged after a fork. The child process runs
2278 unimpeded. This is the default.
2281 The new process is debugged after a fork. The parent process runs
2285 The debugger will ask for one of the above choices.
2288 @item show follow-fork-mode
2289 Display the current debugger response to a @code{fork} or @code{vfork} call.
2292 If you ask to debug a child process and a @code{vfork} is followed by an
2293 @code{exec}, @value{GDBN} executes the new target up to the first
2294 breakpoint in the new target. If you have a breakpoint set on
2295 @code{main} in your original program, the breakpoint will also be set on
2296 the child process's @code{main}.
2298 When a child process is spawned by @code{vfork}, you cannot debug the
2299 child or parent until an @code{exec} call completes.
2301 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2302 call executes, the new target restarts. To restart the parent process,
2303 use the @code{file} command with the parent executable name as its
2306 You can use the @code{catch} command to make @value{GDBN} stop whenever
2307 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2308 Catchpoints, ,Setting catchpoints}.
2311 @chapter Stopping and Continuing
2313 The principal purposes of using a debugger are so that you can stop your
2314 program before it terminates; or so that, if your program runs into
2315 trouble, you can investigate and find out why.
2317 Inside @value{GDBN}, your program may stop for any of several reasons,
2318 such as a signal, a breakpoint, or reaching a new line after a
2319 @value{GDBN} command such as @code{step}. You may then examine and
2320 change variables, set new breakpoints or remove old ones, and then
2321 continue execution. Usually, the messages shown by @value{GDBN} provide
2322 ample explanation of the status of your program---but you can also
2323 explicitly request this information at any time.
2326 @kindex info program
2328 Display information about the status of your program: whether it is
2329 running or not, what process it is, and why it stopped.
2333 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2334 * Continuing and Stepping:: Resuming execution
2336 * Thread Stops:: Stopping and starting multi-thread programs
2340 @section Breakpoints, watchpoints, and catchpoints
2343 A @dfn{breakpoint} makes your program stop whenever a certain point in
2344 the program is reached. For each breakpoint, you can add conditions to
2345 control in finer detail whether your program stops. You can set
2346 breakpoints with the @code{break} command and its variants (@pxref{Set
2347 Breaks, ,Setting breakpoints}), to specify the place where your program
2348 should stop by line number, function name or exact address in the
2351 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2352 breakpoints in shared libraries before the executable is run. There is
2353 a minor limitation on HP-UX systems: you must wait until the executable
2354 is run in order to set breakpoints in shared library routines that are
2355 not called directly by the program (for example, routines that are
2356 arguments in a @code{pthread_create} call).
2359 @cindex memory tracing
2360 @cindex breakpoint on memory address
2361 @cindex breakpoint on variable modification
2362 A @dfn{watchpoint} is a special breakpoint that stops your program
2363 when the value of an expression changes. You must use a different
2364 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2365 watchpoints}), but aside from that, you can manage a watchpoint like
2366 any other breakpoint: you enable, disable, and delete both breakpoints
2367 and watchpoints using the same commands.
2369 You can arrange to have values from your program displayed automatically
2370 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2374 @cindex breakpoint on events
2375 A @dfn{catchpoint} is another special breakpoint that stops your program
2376 when a certain kind of event occurs, such as the throwing of a C@t{++}
2377 exception or the loading of a library. As with watchpoints, you use a
2378 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2379 catchpoints}), but aside from that, you can manage a catchpoint like any
2380 other breakpoint. (To stop when your program receives a signal, use the
2381 @code{handle} command; see @ref{Signals, ,Signals}.)
2383 @cindex breakpoint numbers
2384 @cindex numbers for breakpoints
2385 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2386 catchpoint when you create it; these numbers are successive integers
2387 starting with one. In many of the commands for controlling various
2388 features of breakpoints you use the breakpoint number to say which
2389 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2390 @dfn{disabled}; if disabled, it has no effect on your program until you
2393 @cindex breakpoint ranges
2394 @cindex ranges of breakpoints
2395 Some @value{GDBN} commands accept a range of breakpoints on which to
2396 operate. A breakpoint range is either a single breakpoint number, like
2397 @samp{5}, or two such numbers, in increasing order, separated by a
2398 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
2399 all breakpoint in that range are operated on.
2402 * Set Breaks:: Setting breakpoints
2403 * Set Watchpoints:: Setting watchpoints
2404 * Set Catchpoints:: Setting catchpoints
2405 * Delete Breaks:: Deleting breakpoints
2406 * Disabling:: Disabling breakpoints
2407 * Conditions:: Break conditions
2408 * Break Commands:: Breakpoint command lists
2409 * Breakpoint Menus:: Breakpoint menus
2410 * Error in Breakpoints:: ``Cannot insert breakpoints''
2414 @subsection Setting breakpoints
2416 @c FIXME LMB what does GDB do if no code on line of breakpt?
2417 @c consider in particular declaration with/without initialization.
2419 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2422 @kindex b @r{(@code{break})}
2423 @vindex $bpnum@r{, convenience variable}
2424 @cindex latest breakpoint
2425 Breakpoints are set with the @code{break} command (abbreviated
2426 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2427 number of the breakpoint you've set most recently; see @ref{Convenience
2428 Vars,, Convenience variables}, for a discussion of what you can do with
2429 convenience variables.
2431 You have several ways to say where the breakpoint should go.
2434 @item break @var{function}
2435 Set a breakpoint at entry to function @var{function}.
2436 When using source languages that permit overloading of symbols, such as
2437 C@t{++}, @var{function} may refer to more than one possible place to break.
2438 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2440 @item break +@var{offset}
2441 @itemx break -@var{offset}
2442 Set a breakpoint some number of lines forward or back from the position
2443 at which execution stopped in the currently selected @dfn{stack frame}.
2444 (@xref{Frames, ,Frames}, for a description of stack frames.)
2446 @item break @var{linenum}
2447 Set a breakpoint at line @var{linenum} in the current source file.
2448 The current source file is the last file whose source text was printed.
2449 The breakpoint will stop your program just before it executes any of the
2452 @item break @var{filename}:@var{linenum}
2453 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2455 @item break @var{filename}:@var{function}
2456 Set a breakpoint at entry to function @var{function} found in file
2457 @var{filename}. Specifying a file name as well as a function name is
2458 superfluous except when multiple files contain similarly named
2461 @item break *@var{address}
2462 Set a breakpoint at address @var{address}. You can use this to set
2463 breakpoints in parts of your program which do not have debugging
2464 information or source files.
2467 When called without any arguments, @code{break} sets a breakpoint at
2468 the next instruction to be executed in the selected stack frame
2469 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2470 innermost, this makes your program stop as soon as control
2471 returns to that frame. This is similar to the effect of a
2472 @code{finish} command in the frame inside the selected frame---except
2473 that @code{finish} does not leave an active breakpoint. If you use
2474 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2475 the next time it reaches the current location; this may be useful
2478 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2479 least one instruction has been executed. If it did not do this, you
2480 would be unable to proceed past a breakpoint without first disabling the
2481 breakpoint. This rule applies whether or not the breakpoint already
2482 existed when your program stopped.
2484 @item break @dots{} if @var{cond}
2485 Set a breakpoint with condition @var{cond}; evaluate the expression
2486 @var{cond} each time the breakpoint is reached, and stop only if the
2487 value is nonzero---that is, if @var{cond} evaluates as true.
2488 @samp{@dots{}} stands for one of the possible arguments described
2489 above (or no argument) specifying where to break. @xref{Conditions,
2490 ,Break conditions}, for more information on breakpoint conditions.
2493 @item tbreak @var{args}
2494 Set a breakpoint enabled only for one stop. @var{args} are the
2495 same as for the @code{break} command, and the breakpoint is set in the same
2496 way, but the breakpoint is automatically deleted after the first time your
2497 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2500 @item hbreak @var{args}
2501 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2502 @code{break} command and the breakpoint is set in the same way, but the
2503 breakpoint requires hardware support and some target hardware may not
2504 have this support. The main purpose of this is EPROM/ROM code
2505 debugging, so you can set a breakpoint at an instruction without
2506 changing the instruction. This can be used with the new trap-generation
2507 provided by SPARClite DSU and some x86-based targets. These targets
2508 will generate traps when a program accesses some data or instruction
2509 address that is assigned to the debug registers. However the hardware
2510 breakpoint registers can take a limited number of breakpoints. For
2511 example, on the DSU, only two data breakpoints can be set at a time, and
2512 @value{GDBN} will reject this command if more than two are used. Delete
2513 or disable unused hardware breakpoints before setting new ones
2514 (@pxref{Disabling, ,Disabling}). @xref{Conditions, ,Break conditions}.
2517 @item thbreak @var{args}
2518 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2519 are the same as for the @code{hbreak} command and the breakpoint is set in
2520 the same way. However, like the @code{tbreak} command,
2521 the breakpoint is automatically deleted after the
2522 first time your program stops there. Also, like the @code{hbreak}
2523 command, the breakpoint requires hardware support and some target hardware
2524 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2525 See also @ref{Conditions, ,Break conditions}.
2528 @cindex regular expression
2529 @item rbreak @var{regex}
2530 Set breakpoints on all functions matching the regular expression
2531 @var{regex}. This command sets an unconditional breakpoint on all
2532 matches, printing a list of all breakpoints it set. Once these
2533 breakpoints are set, they are treated just like the breakpoints set with
2534 the @code{break} command. You can delete them, disable them, or make
2535 them conditional the same way as any other breakpoint.
2537 The syntax of the regular expression is the standard one used with tools
2538 like @file{grep}. Note that this is different from the syntax used by
2539 shells, so for instance @code{foo*} matches all functions that include
2540 an @code{fo} followed by zero or more @code{o}s. There is an implicit
2541 @code{.*} leading and trailing the regular expression you supply, so to
2542 match only functions that begin with @code{foo}, use @code{^foo}.
2544 When debugging C@t{++} programs, @code{rbreak} is useful for setting
2545 breakpoints on overloaded functions that are not members of any special
2548 @kindex info breakpoints
2549 @cindex @code{$_} and @code{info breakpoints}
2550 @item info breakpoints @r{[}@var{n}@r{]}
2551 @itemx info break @r{[}@var{n}@r{]}
2552 @itemx info watchpoints @r{[}@var{n}@r{]}
2553 Print a table of all breakpoints, watchpoints, and catchpoints set and
2554 not deleted, with the following columns for each breakpoint:
2557 @item Breakpoint Numbers
2559 Breakpoint, watchpoint, or catchpoint.
2561 Whether the breakpoint is marked to be disabled or deleted when hit.
2562 @item Enabled or Disabled
2563 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2564 that are not enabled.
2566 Where the breakpoint is in your program, as a memory address.
2568 Where the breakpoint is in the source for your program, as a file and
2573 If a breakpoint is conditional, @code{info break} shows the condition on
2574 the line following the affected breakpoint; breakpoint commands, if any,
2575 are listed after that.
2578 @code{info break} with a breakpoint
2579 number @var{n} as argument lists only that breakpoint. The
2580 convenience variable @code{$_} and the default examining-address for
2581 the @code{x} command are set to the address of the last breakpoint
2582 listed (@pxref{Memory, ,Examining memory}).
2585 @code{info break} displays a count of the number of times the breakpoint
2586 has been hit. This is especially useful in conjunction with the
2587 @code{ignore} command. You can ignore a large number of breakpoint
2588 hits, look at the breakpoint info to see how many times the breakpoint
2589 was hit, and then run again, ignoring one less than that number. This
2590 will get you quickly to the last hit of that breakpoint.
2593 @value{GDBN} allows you to set any number of breakpoints at the same place in
2594 your program. There is nothing silly or meaningless about this. When
2595 the breakpoints are conditional, this is even useful
2596 (@pxref{Conditions, ,Break conditions}).
2598 @cindex negative breakpoint numbers
2599 @cindex internal @value{GDBN} breakpoints
2600 @value{GDBN} itself sometimes sets breakpoints in your program for
2601 special purposes, such as proper handling of @code{longjmp} (in C
2602 programs). These internal breakpoints are assigned negative numbers,
2603 starting with @code{-1}; @samp{info breakpoints} does not display them.
2604 You can see these breakpoints with the @value{GDBN} maintenance command
2605 @samp{maint info breakpoints} (@pxref{maint info breakpoints}).
2608 @node Set Watchpoints
2609 @subsection Setting watchpoints
2611 @cindex setting watchpoints
2612 @cindex software watchpoints
2613 @cindex hardware watchpoints
2614 You can use a watchpoint to stop execution whenever the value of an
2615 expression changes, without having to predict a particular place where
2618 Depending on your system, watchpoints may be implemented in software or
2619 hardware. @value{GDBN} does software watchpointing by single-stepping your
2620 program and testing the variable's value each time, which is hundreds of
2621 times slower than normal execution. (But this may still be worth it, to
2622 catch errors where you have no clue what part of your program is the
2625 On some systems, such as HP-UX, Linux and some other x86-based targets,
2626 @value{GDBN} includes support for
2627 hardware watchpoints, which do not slow down the running of your
2632 @item watch @var{expr}
2633 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2634 is written into by the program and its value changes.
2637 @item rwatch @var{expr}
2638 Set a watchpoint that will break when watch @var{expr} is read by the program.
2641 @item awatch @var{expr}
2642 Set a watchpoint that will break when @var{expr} is either read or written into
2645 @kindex info watchpoints
2646 @item info watchpoints
2647 This command prints a list of watchpoints, breakpoints, and catchpoints;
2648 it is the same as @code{info break}.
2651 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2652 watchpoints execute very quickly, and the debugger reports a change in
2653 value at the exact instruction where the change occurs. If @value{GDBN}
2654 cannot set a hardware watchpoint, it sets a software watchpoint, which
2655 executes more slowly and reports the change in value at the next
2656 statement, not the instruction, after the change occurs.
2658 When you issue the @code{watch} command, @value{GDBN} reports
2661 Hardware watchpoint @var{num}: @var{expr}
2665 if it was able to set a hardware watchpoint.
2667 Currently, the @code{awatch} and @code{rwatch} commands can only set
2668 hardware watchpoints, because accesses to data that don't change the
2669 value of the watched expression cannot be detected without examining
2670 every instruction as it is being executed, and @value{GDBN} does not do
2671 that currently. If @value{GDBN} finds that it is unable to set a
2672 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
2673 will print a message like this:
2676 Expression cannot be implemented with read/access watchpoint.
2679 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
2680 data type of the watched expression is wider than what a hardware
2681 watchpoint on the target machine can handle. For example, some systems
2682 can only watch regions that are up to 4 bytes wide; on such systems you
2683 cannot set hardware watchpoints for an expression that yields a
2684 double-precision floating-point number (which is typically 8 bytes
2685 wide). As a work-around, it might be possible to break the large region
2686 into a series of smaller ones and watch them with separate watchpoints.
2688 If you set too many hardware watchpoints, @value{GDBN} might be unable
2689 to insert all of them when you resume the execution of your program.
2690 Since the precise number of active watchpoints is unknown until such
2691 time as the program is about to be resumed, @value{GDBN} might not be
2692 able to warn you about this when you set the watchpoints, and the
2693 warning will be printed only when the program is resumed:
2696 Hardware watchpoint @var{num}: Could not insert watchpoint
2700 If this happens, delete or disable some of the watchpoints.
2702 The SPARClite DSU will generate traps when a program accesses some data
2703 or instruction address that is assigned to the debug registers. For the
2704 data addresses, DSU facilitates the @code{watch} command. However the
2705 hardware breakpoint registers can only take two data watchpoints, and
2706 both watchpoints must be the same kind. For example, you can set two
2707 watchpoints with @code{watch} commands, two with @code{rwatch} commands,
2708 @strong{or} two with @code{awatch} commands, but you cannot set one
2709 watchpoint with one command and the other with a different command.
2710 @value{GDBN} will reject the command if you try to mix watchpoints.
2711 Delete or disable unused watchpoint commands before setting new ones.
2713 If you call a function interactively using @code{print} or @code{call},
2714 any watchpoints you have set will be inactive until @value{GDBN} reaches another
2715 kind of breakpoint or the call completes.
2717 @value{GDBN} automatically deletes watchpoints that watch local
2718 (automatic) variables, or expressions that involve such variables, when
2719 they go out of scope, that is, when the execution leaves the block in
2720 which these variables were defined. In particular, when the program
2721 being debugged terminates, @emph{all} local variables go out of scope,
2722 and so only watchpoints that watch global variables remain set. If you
2723 rerun the program, you will need to set all such watchpoints again. One
2724 way of doing that would be to set a code breakpoint at the entry to the
2725 @code{main} function and when it breaks, set all the watchpoints.
2728 @cindex watchpoints and threads
2729 @cindex threads and watchpoints
2730 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2731 usefulness. With the current watchpoint implementation, @value{GDBN}
2732 can only watch the value of an expression @emph{in a single thread}. If
2733 you are confident that the expression can only change due to the current
2734 thread's activity (and if you are also confident that no other thread
2735 can become current), then you can use watchpoints as usual. However,
2736 @value{GDBN} may not notice when a non-current thread's activity changes
2739 @c FIXME: this is almost identical to the previous paragraph.
2740 @emph{HP-UX Warning:} In multi-thread programs, software watchpoints
2741 have only limited usefulness. If @value{GDBN} creates a software
2742 watchpoint, it can only watch the value of an expression @emph{in a
2743 single thread}. If you are confident that the expression can only
2744 change due to the current thread's activity (and if you are also
2745 confident that no other thread can become current), then you can use
2746 software watchpoints as usual. However, @value{GDBN} may not notice
2747 when a non-current thread's activity changes the expression. (Hardware
2748 watchpoints, in contrast, watch an expression in all threads.)
2751 @node Set Catchpoints
2752 @subsection Setting catchpoints
2753 @cindex catchpoints, setting
2754 @cindex exception handlers
2755 @cindex event handling
2757 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2758 kinds of program events, such as C@t{++} exceptions or the loading of a
2759 shared library. Use the @code{catch} command to set a catchpoint.
2763 @item catch @var{event}
2764 Stop when @var{event} occurs. @var{event} can be any of the following:
2768 The throwing of a C@t{++} exception.
2772 The catching of a C@t{++} exception.
2776 A call to @code{exec}. This is currently only available for HP-UX.
2780 A call to @code{fork}. This is currently only available for HP-UX.
2784 A call to @code{vfork}. This is currently only available for HP-UX.
2787 @itemx load @var{libname}
2789 The dynamic loading of any shared library, or the loading of the library
2790 @var{libname}. This is currently only available for HP-UX.
2793 @itemx unload @var{libname}
2794 @kindex catch unload
2795 The unloading of any dynamically loaded shared library, or the unloading
2796 of the library @var{libname}. This is currently only available for HP-UX.
2799 @item tcatch @var{event}
2800 Set a catchpoint that is enabled only for one stop. The catchpoint is
2801 automatically deleted after the first time the event is caught.
2805 Use the @code{info break} command to list the current catchpoints.
2807 There are currently some limitations to C@t{++} exception handling
2808 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
2812 If you call a function interactively, @value{GDBN} normally returns
2813 control to you when the function has finished executing. If the call
2814 raises an exception, however, the call may bypass the mechanism that
2815 returns control to you and cause your program either to abort or to
2816 simply continue running until it hits a breakpoint, catches a signal
2817 that @value{GDBN} is listening for, or exits. This is the case even if
2818 you set a catchpoint for the exception; catchpoints on exceptions are
2819 disabled within interactive calls.
2822 You cannot raise an exception interactively.
2825 You cannot install an exception handler interactively.
2828 @cindex raise exceptions
2829 Sometimes @code{catch} is not the best way to debug exception handling:
2830 if you need to know exactly where an exception is raised, it is better to
2831 stop @emph{before} the exception handler is called, since that way you
2832 can see the stack before any unwinding takes place. If you set a
2833 breakpoint in an exception handler instead, it may not be easy to find
2834 out where the exception was raised.
2836 To stop just before an exception handler is called, you need some
2837 knowledge of the implementation. In the case of @sc{gnu} C@t{++}, exceptions are
2838 raised by calling a library function named @code{__raise_exception}
2839 which has the following ANSI C interface:
2842 /* @var{addr} is where the exception identifier is stored.
2843 @var{id} is the exception identifier. */
2844 void __raise_exception (void **addr, void *id);
2848 To make the debugger catch all exceptions before any stack
2849 unwinding takes place, set a breakpoint on @code{__raise_exception}
2850 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2852 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2853 that depends on the value of @var{id}, you can stop your program when
2854 a specific exception is raised. You can use multiple conditional
2855 breakpoints to stop your program when any of a number of exceptions are
2860 @subsection Deleting breakpoints
2862 @cindex clearing breakpoints, watchpoints, catchpoints
2863 @cindex deleting breakpoints, watchpoints, catchpoints
2864 It is often necessary to eliminate a breakpoint, watchpoint, or
2865 catchpoint once it has done its job and you no longer want your program
2866 to stop there. This is called @dfn{deleting} the breakpoint. A
2867 breakpoint that has been deleted no longer exists; it is forgotten.
2869 With the @code{clear} command you can delete breakpoints according to
2870 where they are in your program. With the @code{delete} command you can
2871 delete individual breakpoints, watchpoints, or catchpoints by specifying
2872 their breakpoint numbers.
2874 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2875 automatically ignores breakpoints on the first instruction to be executed
2876 when you continue execution without changing the execution address.
2881 Delete any breakpoints at the next instruction to be executed in the
2882 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2883 the innermost frame is selected, this is a good way to delete a
2884 breakpoint where your program just stopped.
2886 @item clear @var{function}
2887 @itemx clear @var{filename}:@var{function}
2888 Delete any breakpoints set at entry to the function @var{function}.
2890 @item clear @var{linenum}
2891 @itemx clear @var{filename}:@var{linenum}
2892 Delete any breakpoints set at or within the code of the specified line.
2894 @cindex delete breakpoints
2896 @kindex d @r{(@code{delete})}
2897 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2898 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
2899 ranges specified as arguments. If no argument is specified, delete all
2900 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
2901 confirm off}). You can abbreviate this command as @code{d}.
2905 @subsection Disabling breakpoints
2907 @kindex disable breakpoints
2908 @kindex enable breakpoints
2909 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
2910 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
2911 it had been deleted, but remembers the information on the breakpoint so
2912 that you can @dfn{enable} it again later.
2914 You disable and enable breakpoints, watchpoints, and catchpoints with
2915 the @code{enable} and @code{disable} commands, optionally specifying one
2916 or more breakpoint numbers as arguments. Use @code{info break} or
2917 @code{info watch} to print a list of breakpoints, watchpoints, and
2918 catchpoints if you do not know which numbers to use.
2920 A breakpoint, watchpoint, or catchpoint can have any of four different
2921 states of enablement:
2925 Enabled. The breakpoint stops your program. A breakpoint set
2926 with the @code{break} command starts out in this state.
2928 Disabled. The breakpoint has no effect on your program.
2930 Enabled once. The breakpoint stops your program, but then becomes
2933 Enabled for deletion. The breakpoint stops your program, but
2934 immediately after it does so it is deleted permanently. A breakpoint
2935 set with the @code{tbreak} command starts out in this state.
2938 You can use the following commands to enable or disable breakpoints,
2939 watchpoints, and catchpoints:
2942 @kindex disable breakpoints
2944 @kindex dis @r{(@code{disable})}
2945 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2946 Disable the specified breakpoints---or all breakpoints, if none are
2947 listed. A disabled breakpoint has no effect but is not forgotten. All
2948 options such as ignore-counts, conditions and commands are remembered in
2949 case the breakpoint is enabled again later. You may abbreviate
2950 @code{disable} as @code{dis}.
2952 @kindex enable breakpoints
2954 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2955 Enable the specified breakpoints (or all defined breakpoints). They
2956 become effective once again in stopping your program.
2958 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
2959 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2960 of these breakpoints immediately after stopping your program.
2962 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
2963 Enable the specified breakpoints to work once, then die. @value{GDBN}
2964 deletes any of these breakpoints as soon as your program stops there.
2967 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
2968 @c confusing: tbreak is also initially enabled.
2969 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2970 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2971 subsequently, they become disabled or enabled only when you use one of
2972 the commands above. (The command @code{until} can set and delete a
2973 breakpoint of its own, but it does not change the state of your other
2974 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2978 @subsection Break conditions
2979 @cindex conditional breakpoints
2980 @cindex breakpoint conditions
2982 @c FIXME what is scope of break condition expr? Context where wanted?
2983 @c in particular for a watchpoint?
2984 The simplest sort of breakpoint breaks every time your program reaches a
2985 specified place. You can also specify a @dfn{condition} for a
2986 breakpoint. A condition is just a Boolean expression in your
2987 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2988 a condition evaluates the expression each time your program reaches it,
2989 and your program stops only if the condition is @emph{true}.
2991 This is the converse of using assertions for program validation; in that
2992 situation, you want to stop when the assertion is violated---that is,
2993 when the condition is false. In C, if you want to test an assertion expressed
2994 by the condition @var{assert}, you should set the condition
2995 @samp{! @var{assert}} on the appropriate breakpoint.
2997 Conditions are also accepted for watchpoints; you may not need them,
2998 since a watchpoint is inspecting the value of an expression anyhow---but
2999 it might be simpler, say, to just set a watchpoint on a variable name,
3000 and specify a condition that tests whether the new value is an interesting
3003 Break conditions can have side effects, and may even call functions in
3004 your program. This can be useful, for example, to activate functions
3005 that log program progress, or to use your own print functions to
3006 format special data structures. The effects are completely predictable
3007 unless there is another enabled breakpoint at the same address. (In
3008 that case, @value{GDBN} might see the other breakpoint first and stop your
3009 program without checking the condition of this one.) Note that
3010 breakpoint commands are usually more convenient and flexible than break
3012 purpose of performing side effects when a breakpoint is reached
3013 (@pxref{Break Commands, ,Breakpoint command lists}).
3015 Break conditions can be specified when a breakpoint is set, by using
3016 @samp{if} in the arguments to the @code{break} command. @xref{Set
3017 Breaks, ,Setting breakpoints}. They can also be changed at any time
3018 with the @code{condition} command.
3020 You can also use the @code{if} keyword with the @code{watch} command.
3021 The @code{catch} command does not recognize the @code{if} keyword;
3022 @code{condition} is the only way to impose a further condition on a
3027 @item condition @var{bnum} @var{expression}
3028 Specify @var{expression} as the break condition for breakpoint,
3029 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
3030 breakpoint @var{bnum} stops your program only if the value of
3031 @var{expression} is true (nonzero, in C). When you use
3032 @code{condition}, @value{GDBN} checks @var{expression} immediately for
3033 syntactic correctness, and to determine whether symbols in it have
3034 referents in the context of your breakpoint. If @var{expression} uses
3035 symbols not referenced in the context of the breakpoint, @value{GDBN}
3036 prints an error message:
3039 No symbol "foo" in current context.
3044 not actually evaluate @var{expression} at the time the @code{condition}
3045 command (or a command that sets a breakpoint with a condition, like
3046 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
3048 @item condition @var{bnum}
3049 Remove the condition from breakpoint number @var{bnum}. It becomes
3050 an ordinary unconditional breakpoint.
3053 @cindex ignore count (of breakpoint)
3054 A special case of a breakpoint condition is to stop only when the
3055 breakpoint has been reached a certain number of times. This is so
3056 useful that there is a special way to do it, using the @dfn{ignore
3057 count} of the breakpoint. Every breakpoint has an ignore count, which
3058 is an integer. Most of the time, the ignore count is zero, and
3059 therefore has no effect. But if your program reaches a breakpoint whose
3060 ignore count is positive, then instead of stopping, it just decrements
3061 the ignore count by one and continues. As a result, if the ignore count
3062 value is @var{n}, the breakpoint does not stop the next @var{n} times
3063 your program reaches it.
3067 @item ignore @var{bnum} @var{count}
3068 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3069 The next @var{count} times the breakpoint is reached, your program's
3070 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3073 To make the breakpoint stop the next time it is reached, specify
3076 When you use @code{continue} to resume execution of your program from a
3077 breakpoint, you can specify an ignore count directly as an argument to
3078 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3079 Stepping,,Continuing and stepping}.
3081 If a breakpoint has a positive ignore count and a condition, the
3082 condition is not checked. Once the ignore count reaches zero,
3083 @value{GDBN} resumes checking the condition.
3085 You could achieve the effect of the ignore count with a condition such
3086 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3087 is decremented each time. @xref{Convenience Vars, ,Convenience
3091 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3094 @node Break Commands
3095 @subsection Breakpoint command lists
3097 @cindex breakpoint commands
3098 You can give any breakpoint (or watchpoint or catchpoint) a series of
3099 commands to execute when your program stops due to that breakpoint. For
3100 example, you might want to print the values of certain expressions, or
3101 enable other breakpoints.
3106 @item commands @r{[}@var{bnum}@r{]}
3107 @itemx @dots{} @var{command-list} @dots{}
3109 Specify a list of commands for breakpoint number @var{bnum}. The commands
3110 themselves appear on the following lines. Type a line containing just
3111 @code{end} to terminate the commands.
3113 To remove all commands from a breakpoint, type @code{commands} and
3114 follow it immediately with @code{end}; that is, give no commands.
3116 With no @var{bnum} argument, @code{commands} refers to the last
3117 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
3118 recently encountered).
3121 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
3122 disabled within a @var{command-list}.
3124 You can use breakpoint commands to start your program up again. Simply
3125 use the @code{continue} command, or @code{step}, or any other command
3126 that resumes execution.
3128 Any other commands in the command list, after a command that resumes
3129 execution, are ignored. This is because any time you resume execution
3130 (even with a simple @code{next} or @code{step}), you may encounter
3131 another breakpoint---which could have its own command list, leading to
3132 ambiguities about which list to execute.
3135 If the first command you specify in a command list is @code{silent}, the
3136 usual message about stopping at a breakpoint is not printed. This may
3137 be desirable for breakpoints that are to print a specific message and
3138 then continue. If none of the remaining commands print anything, you
3139 see no sign that the breakpoint was reached. @code{silent} is
3140 meaningful only at the beginning of a breakpoint command list.
3142 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3143 print precisely controlled output, and are often useful in silent
3144 breakpoints. @xref{Output, ,Commands for controlled output}.
3146 For example, here is how you could use breakpoint commands to print the
3147 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3153 printf "x is %d\n",x
3158 One application for breakpoint commands is to compensate for one bug so
3159 you can test for another. Put a breakpoint just after the erroneous line
3160 of code, give it a condition to detect the case in which something
3161 erroneous has been done, and give it commands to assign correct values
3162 to any variables that need them. End with the @code{continue} command
3163 so that your program does not stop, and start with the @code{silent}
3164 command so that no output is produced. Here is an example:
3175 @node Breakpoint Menus
3176 @subsection Breakpoint menus
3178 @cindex symbol overloading
3180 Some programming languages (notably C@t{++}) permit a single function name
3181 to be defined several times, for application in different contexts.
3182 This is called @dfn{overloading}. When a function name is overloaded,
3183 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3184 a breakpoint. If you realize this is a problem, you can use
3185 something like @samp{break @var{function}(@var{types})} to specify which
3186 particular version of the function you want. Otherwise, @value{GDBN} offers
3187 you a menu of numbered choices for different possible breakpoints, and
3188 waits for your selection with the prompt @samp{>}. The first two
3189 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3190 sets a breakpoint at each definition of @var{function}, and typing
3191 @kbd{0} aborts the @code{break} command without setting any new
3194 For example, the following session excerpt shows an attempt to set a
3195 breakpoint at the overloaded symbol @code{String::after}.
3196 We choose three particular definitions of that function name:
3198 @c FIXME! This is likely to change to show arg type lists, at least
3201 (@value{GDBP}) b String::after
3204 [2] file:String.cc; line number:867
3205 [3] file:String.cc; line number:860
3206 [4] file:String.cc; line number:875
3207 [5] file:String.cc; line number:853
3208 [6] file:String.cc; line number:846
3209 [7] file:String.cc; line number:735
3211 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3212 Breakpoint 2 at 0xb344: file String.cc, line 875.
3213 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3214 Multiple breakpoints were set.
3215 Use the "delete" command to delete unwanted
3221 @c @ifclear BARETARGET
3222 @node Error in Breakpoints
3223 @subsection ``Cannot insert breakpoints''
3225 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3227 Under some operating systems, breakpoints cannot be used in a program if
3228 any other process is running that program. In this situation,
3229 attempting to run or continue a program with a breakpoint causes
3230 @value{GDBN} to print an error message:
3233 Cannot insert breakpoints.
3234 The same program may be running in another process.
3237 When this happens, you have three ways to proceed:
3241 Remove or disable the breakpoints, then continue.
3244 Suspend @value{GDBN}, and copy the file containing your program to a new
3245 name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3246 that @value{GDBN} should run your program under that name.
3247 Then start your program again.
3250 Relink your program so that the text segment is nonsharable, using the
3251 linker option @samp{-N}. The operating system limitation may not apply
3252 to nonsharable executables.
3256 A similar message can be printed if you request too many active
3257 hardware-assisted breakpoints and watchpoints:
3259 @c FIXME: the precise wording of this message may change; the relevant
3260 @c source change is not committed yet (Sep 3, 1999).
3262 Stopped; cannot insert breakpoints.
3263 You may have requested too many hardware breakpoints and watchpoints.
3267 This message is printed when you attempt to resume the program, since
3268 only then @value{GDBN} knows exactly how many hardware breakpoints and
3269 watchpoints it needs to insert.
3271 When this message is printed, you need to disable or remove some of the
3272 hardware-assisted breakpoints and watchpoints, and then continue.
3275 @node Continuing and Stepping
3276 @section Continuing and stepping
3280 @cindex resuming execution
3281 @dfn{Continuing} means resuming program execution until your program
3282 completes normally. In contrast, @dfn{stepping} means executing just
3283 one more ``step'' of your program, where ``step'' may mean either one
3284 line of source code, or one machine instruction (depending on what
3285 particular command you use). Either when continuing or when stepping,
3286 your program may stop even sooner, due to a breakpoint or a signal. (If
3287 it stops due to a signal, you may want to use @code{handle}, or use
3288 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
3292 @kindex c @r{(@code{continue})}
3293 @kindex fg @r{(resume foreground execution)}
3294 @item continue @r{[}@var{ignore-count}@r{]}
3295 @itemx c @r{[}@var{ignore-count}@r{]}
3296 @itemx fg @r{[}@var{ignore-count}@r{]}
3297 Resume program execution, at the address where your program last stopped;
3298 any breakpoints set at that address are bypassed. The optional argument
3299 @var{ignore-count} allows you to specify a further number of times to
3300 ignore a breakpoint at this location; its effect is like that of
3301 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3303 The argument @var{ignore-count} is meaningful only when your program
3304 stopped due to a breakpoint. At other times, the argument to
3305 @code{continue} is ignored.
3307 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
3308 debugged program is deemed to be the foreground program) are provided
3309 purely for convenience, and have exactly the same behavior as
3313 To resume execution at a different place, you can use @code{return}
3314 (@pxref{Returning, ,Returning from a function}) to go back to the
3315 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3316 different address}) to go to an arbitrary location in your program.
3318 A typical technique for using stepping is to set a breakpoint
3319 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3320 beginning of the function or the section of your program where a problem
3321 is believed to lie, run your program until it stops at that breakpoint,
3322 and then step through the suspect area, examining the variables that are
3323 interesting, until you see the problem happen.
3327 @kindex s @r{(@code{step})}
3329 Continue running your program until control reaches a different source
3330 line, then stop it and return control to @value{GDBN}. This command is
3331 abbreviated @code{s}.
3334 @c "without debugging information" is imprecise; actually "without line
3335 @c numbers in the debugging information". (gcc -g1 has debugging info but
3336 @c not line numbers). But it seems complex to try to make that
3337 @c distinction here.
3338 @emph{Warning:} If you use the @code{step} command while control is
3339 within a function that was compiled without debugging information,
3340 execution proceeds until control reaches a function that does have
3341 debugging information. Likewise, it will not step into a function which
3342 is compiled without debugging information. To step through functions
3343 without debugging information, use the @code{stepi} command, described
3347 The @code{step} command only stops at the first instruction of a source
3348 line. This prevents the multiple stops that could otherwise occur in
3349 @code{switch} statements, @code{for} loops, etc. @code{step} continues
3350 to stop if a function that has debugging information is called within
3351 the line. In other words, @code{step} @emph{steps inside} any functions
3352 called within the line.
3354 Also, the @code{step} command only enters a function if there is line
3355 number information for the function. Otherwise it acts like the
3356 @code{next} command. This avoids problems when using @code{cc -gl}
3357 on MIPS machines. Previously, @code{step} entered subroutines if there
3358 was any debugging information about the routine.
3360 @item step @var{count}
3361 Continue running as in @code{step}, but do so @var{count} times. If a
3362 breakpoint is reached, or a signal not related to stepping occurs before
3363 @var{count} steps, stepping stops right away.
3366 @kindex n @r{(@code{next})}
3367 @item next @r{[}@var{count}@r{]}
3368 Continue to the next source line in the current (innermost) stack frame.
3369 This is similar to @code{step}, but function calls that appear within
3370 the line of code are executed without stopping. Execution stops when
3371 control reaches a different line of code at the original stack level
3372 that was executing when you gave the @code{next} command. This command
3373 is abbreviated @code{n}.
3375 An argument @var{count} is a repeat count, as for @code{step}.
3378 @c FIX ME!! Do we delete this, or is there a way it fits in with
3379 @c the following paragraph? --- Vctoria
3381 @c @code{next} within a function that lacks debugging information acts like
3382 @c @code{step}, but any function calls appearing within the code of the
3383 @c function are executed without stopping.
3385 The @code{next} command only stops at the first instruction of a
3386 source line. This prevents multiple stops that could otherwise occur in
3387 @code{switch} statements, @code{for} loops, etc.
3389 @kindex set step-mode
3391 @cindex functions without line info, and stepping
3392 @cindex stepping into functions with no line info
3393 @itemx set step-mode on
3394 The @code{set step-mode on} command causes the @code{step} command to
3395 stop at the first instruction of a function which contains no debug line
3396 information rather than stepping over it.
3398 This is useful in cases where you may be interested in inspecting the
3399 machine instructions of a function which has no symbolic info and do not
3400 want @value{GDBN} to automatically skip over this function.
3402 @item set step-mode off
3403 Causes the @code{step} command to step over any functions which contains no
3404 debug information. This is the default.
3408 Continue running until just after function in the selected stack frame
3409 returns. Print the returned value (if any).
3411 Contrast this with the @code{return} command (@pxref{Returning,
3412 ,Returning from a function}).
3415 @kindex u @r{(@code{until})}
3418 Continue running until a source line past the current line, in the
3419 current stack frame, is reached. This command is used to avoid single
3420 stepping through a loop more than once. It is like the @code{next}
3421 command, except that when @code{until} encounters a jump, it
3422 automatically continues execution until the program counter is greater
3423 than the address of the jump.
3425 This means that when you reach the end of a loop after single stepping
3426 though it, @code{until} makes your program continue execution until it
3427 exits the loop. In contrast, a @code{next} command at the end of a loop
3428 simply steps back to the beginning of the loop, which forces you to step
3429 through the next iteration.
3431 @code{until} always stops your program if it attempts to exit the current
3434 @code{until} may produce somewhat counterintuitive results if the order
3435 of machine code does not match the order of the source lines. For
3436 example, in the following excerpt from a debugging session, the @code{f}
3437 (@code{frame}) command shows that execution is stopped at line
3438 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3442 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3444 (@value{GDBP}) until
3445 195 for ( ; argc > 0; NEXTARG) @{
3448 This happened because, for execution efficiency, the compiler had
3449 generated code for the loop closure test at the end, rather than the
3450 start, of the loop---even though the test in a C @code{for}-loop is
3451 written before the body of the loop. The @code{until} command appeared
3452 to step back to the beginning of the loop when it advanced to this
3453 expression; however, it has not really gone to an earlier
3454 statement---not in terms of the actual machine code.
3456 @code{until} with no argument works by means of single
3457 instruction stepping, and hence is slower than @code{until} with an
3460 @item until @var{location}
3461 @itemx u @var{location}
3462 Continue running your program until either the specified location is
3463 reached, or the current stack frame returns. @var{location} is any of
3464 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3465 ,Setting breakpoints}). This form of the command uses breakpoints,
3466 and hence is quicker than @code{until} without an argument.
3469 @kindex si @r{(@code{stepi})}
3471 @itemx stepi @var{arg}
3473 Execute one machine instruction, then stop and return to the debugger.
3475 It is often useful to do @samp{display/i $pc} when stepping by machine
3476 instructions. This makes @value{GDBN} automatically display the next
3477 instruction to be executed, each time your program stops. @xref{Auto
3478 Display,, Automatic display}.
3480 An argument is a repeat count, as in @code{step}.
3484 @kindex ni @r{(@code{nexti})}
3486 @itemx nexti @var{arg}
3488 Execute one machine instruction, but if it is a function call,
3489 proceed until the function returns.
3491 An argument is a repeat count, as in @code{next}.
3498 A signal is an asynchronous event that can happen in a program. The
3499 operating system defines the possible kinds of signals, and gives each
3500 kind a name and a number. For example, in Unix @code{SIGINT} is the
3501 signal a program gets when you type an interrupt character (often @kbd{C-c});
3502 @code{SIGSEGV} is the signal a program gets from referencing a place in
3503 memory far away from all the areas in use; @code{SIGALRM} occurs when
3504 the alarm clock timer goes off (which happens only if your program has
3505 requested an alarm).
3507 @cindex fatal signals
3508 Some signals, including @code{SIGALRM}, are a normal part of the
3509 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3510 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
3511 program has not specified in advance some other way to handle the signal.
3512 @code{SIGINT} does not indicate an error in your program, but it is normally
3513 fatal so it can carry out the purpose of the interrupt: to kill the program.
3515 @value{GDBN} has the ability to detect any occurrence of a signal in your
3516 program. You can tell @value{GDBN} in advance what to do for each kind of
3519 @cindex handling signals
3520 Normally, @value{GDBN} is set up to let the non-erroneous signals like
3521 @code{SIGALRM} be silently passed to your program
3522 (so as not to interfere with their role in the program's functioning)
3523 but to stop your program immediately whenever an error signal happens.
3524 You can change these settings with the @code{handle} command.
3527 @kindex info signals
3530 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3531 handle each one. You can use this to see the signal numbers of all
3532 the defined types of signals.
3534 @code{info handle} is an alias for @code{info signals}.
3537 @item handle @var{signal} @var{keywords}@dots{}
3538 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
3539 can be the number of a signal or its name (with or without the
3540 @samp{SIG} at the beginning); a list of signal numbers of the form
3541 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
3542 known signals. The @var{keywords} say what change to make.
3546 The keywords allowed by the @code{handle} command can be abbreviated.
3547 Their full names are:
3551 @value{GDBN} should not stop your program when this signal happens. It may
3552 still print a message telling you that the signal has come in.
3555 @value{GDBN} should stop your program when this signal happens. This implies
3556 the @code{print} keyword as well.
3559 @value{GDBN} should print a message when this signal happens.
3562 @value{GDBN} should not mention the occurrence of the signal at all. This
3563 implies the @code{nostop} keyword as well.
3567 @value{GDBN} should allow your program to see this signal; your program
3568 can handle the signal, or else it may terminate if the signal is fatal
3569 and not handled. @code{pass} and @code{noignore} are synonyms.
3573 @value{GDBN} should not allow your program to see this signal.
3574 @code{nopass} and @code{ignore} are synonyms.
3578 When a signal stops your program, the signal is not visible to the
3580 continue. Your program sees the signal then, if @code{pass} is in
3581 effect for the signal in question @emph{at that time}. In other words,
3582 after @value{GDBN} reports a signal, you can use the @code{handle}
3583 command with @code{pass} or @code{nopass} to control whether your
3584 program sees that signal when you continue.
3586 The default is set to @code{nostop}, @code{noprint}, @code{pass} for
3587 non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and
3588 @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the
3591 You can also use the @code{signal} command to prevent your program from
3592 seeing a signal, or cause it to see a signal it normally would not see,
3593 or to give it any signal at any time. For example, if your program stopped
3594 due to some sort of memory reference error, you might store correct
3595 values into the erroneous variables and continue, hoping to see more
3596 execution; but your program would probably terminate immediately as
3597 a result of the fatal signal once it saw the signal. To prevent this,
3598 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3602 @section Stopping and starting multi-thread programs
3604 When your program has multiple threads (@pxref{Threads,, Debugging
3605 programs with multiple threads}), you can choose whether to set
3606 breakpoints on all threads, or on a particular thread.
3609 @cindex breakpoints and threads
3610 @cindex thread breakpoints
3611 @kindex break @dots{} thread @var{threadno}
3612 @item break @var{linespec} thread @var{threadno}
3613 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3614 @var{linespec} specifies source lines; there are several ways of
3615 writing them, but the effect is always to specify some source line.
3617 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3618 to specify that you only want @value{GDBN} to stop the program when a
3619 particular thread reaches this breakpoint. @var{threadno} is one of the
3620 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3621 column of the @samp{info threads} display.
3623 If you do not specify @samp{thread @var{threadno}} when you set a
3624 breakpoint, the breakpoint applies to @emph{all} threads of your
3627 You can use the @code{thread} qualifier on conditional breakpoints as
3628 well; in this case, place @samp{thread @var{threadno}} before the
3629 breakpoint condition, like this:
3632 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
3637 @cindex stopped threads
3638 @cindex threads, stopped
3639 Whenever your program stops under @value{GDBN} for any reason,
3640 @emph{all} threads of execution stop, not just the current thread. This
3641 allows you to examine the overall state of the program, including
3642 switching between threads, without worrying that things may change
3645 @cindex continuing threads
3646 @cindex threads, continuing
3647 Conversely, whenever you restart the program, @emph{all} threads start
3648 executing. @emph{This is true even when single-stepping} with commands
3649 like @code{step} or @code{next}.
3651 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3652 Since thread scheduling is up to your debugging target's operating
3653 system (not controlled by @value{GDBN}), other threads may
3654 execute more than one statement while the current thread completes a
3655 single step. Moreover, in general other threads stop in the middle of a
3656 statement, rather than at a clean statement boundary, when the program
3659 You might even find your program stopped in another thread after
3660 continuing or even single-stepping. This happens whenever some other
3661 thread runs into a breakpoint, a signal, or an exception before the
3662 first thread completes whatever you requested.
3664 On some OSes, you can lock the OS scheduler and thus allow only a single
3668 @item set scheduler-locking @var{mode}
3669 Set the scheduler locking mode. If it is @code{off}, then there is no
3670 locking and any thread may run at any time. If @code{on}, then only the
3671 current thread may run when the inferior is resumed. The @code{step}
3672 mode optimizes for single-stepping. It stops other threads from
3673 ``seizing the prompt'' by preempting the current thread while you are
3674 stepping. Other threads will only rarely (or never) get a chance to run
3675 when you step. They are more likely to run when you @samp{next} over a
3676 function call, and they are completely free to run when you use commands
3677 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
3678 thread hits a breakpoint during its timeslice, they will never steal the
3679 @value{GDBN} prompt away from the thread that you are debugging.
3681 @item show scheduler-locking
3682 Display the current scheduler locking mode.
3687 @chapter Examining the Stack
3689 When your program has stopped, the first thing you need to know is where it
3690 stopped and how it got there.
3693 Each time your program performs a function call, information about the call
3695 That information includes the location of the call in your program,
3696 the arguments of the call,
3697 and the local variables of the function being called.
3698 The information is saved in a block of data called a @dfn{stack frame}.
3699 The stack frames are allocated in a region of memory called the @dfn{call
3702 When your program stops, the @value{GDBN} commands for examining the
3703 stack allow you to see all of this information.
3705 @cindex selected frame
3706 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3707 @value{GDBN} commands refer implicitly to the selected frame. In
3708 particular, whenever you ask @value{GDBN} for the value of a variable in
3709 your program, the value is found in the selected frame. There are
3710 special @value{GDBN} commands to select whichever frame you are
3711 interested in. @xref{Selection, ,Selecting a frame}.
3713 When your program stops, @value{GDBN} automatically selects the
3714 currently executing frame and describes it briefly, similar to the
3715 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3718 * Frames:: Stack frames
3719 * Backtrace:: Backtraces
3720 * Selection:: Selecting a frame
3721 * Frame Info:: Information on a frame
3726 @section Stack frames
3728 @cindex frame, definition
3730 The call stack is divided up into contiguous pieces called @dfn{stack
3731 frames}, or @dfn{frames} for short; each frame is the data associated
3732 with one call to one function. The frame contains the arguments given
3733 to the function, the function's local variables, and the address at
3734 which the function is executing.
3736 @cindex initial frame
3737 @cindex outermost frame
3738 @cindex innermost frame
3739 When your program is started, the stack has only one frame, that of the
3740 function @code{main}. This is called the @dfn{initial} frame or the
3741 @dfn{outermost} frame. Each time a function is called, a new frame is
3742 made. Each time a function returns, the frame for that function invocation
3743 is eliminated. If a function is recursive, there can be many frames for
3744 the same function. The frame for the function in which execution is
3745 actually occurring is called the @dfn{innermost} frame. This is the most
3746 recently created of all the stack frames that still exist.
3748 @cindex frame pointer
3749 Inside your program, stack frames are identified by their addresses. A
3750 stack frame consists of many bytes, each of which has its own address; each
3751 kind of computer has a convention for choosing one byte whose
3752 address serves as the address of the frame. Usually this address is kept
3753 in a register called the @dfn{frame pointer register} while execution is
3754 going on in that frame.
3756 @cindex frame number
3757 @value{GDBN} assigns numbers to all existing stack frames, starting with
3758 zero for the innermost frame, one for the frame that called it,
3759 and so on upward. These numbers do not really exist in your program;
3760 they are assigned by @value{GDBN} to give you a way of designating stack
3761 frames in @value{GDBN} commands.
3763 @c The -fomit-frame-pointer below perennially causes hbox overflow
3764 @c underflow problems.
3765 @cindex frameless execution
3766 Some compilers provide a way to compile functions so that they operate
3767 without stack frames. (For example, the @value{GCC} option
3769 @samp{-fomit-frame-pointer}
3771 generates functions without a frame.)
3772 This is occasionally done with heavily used library functions to save
3773 the frame setup time. @value{GDBN} has limited facilities for dealing
3774 with these function invocations. If the innermost function invocation
3775 has no stack frame, @value{GDBN} nevertheless regards it as though
3776 it had a separate frame, which is numbered zero as usual, allowing
3777 correct tracing of the function call chain. However, @value{GDBN} has
3778 no provision for frameless functions elsewhere in the stack.
3781 @kindex frame@r{, command}
3782 @cindex current stack frame
3783 @item frame @var{args}
3784 The @code{frame} command allows you to move from one stack frame to another,
3785 and to print the stack frame you select. @var{args} may be either the
3786 address of the frame or the stack frame number. Without an argument,
3787 @code{frame} prints the current stack frame.
3789 @kindex select-frame
3790 @cindex selecting frame silently
3792 The @code{select-frame} command allows you to move from one stack frame
3793 to another without printing the frame. This is the silent version of
3802 @cindex stack traces
3803 A backtrace is a summary of how your program got where it is. It shows one
3804 line per frame, for many frames, starting with the currently executing
3805 frame (frame zero), followed by its caller (frame one), and on up the
3810 @kindex bt @r{(@code{backtrace})}
3813 Print a backtrace of the entire stack: one line per frame for all
3814 frames in the stack.
3816 You can stop the backtrace at any time by typing the system interrupt
3817 character, normally @kbd{C-c}.
3819 @item backtrace @var{n}
3821 Similar, but print only the innermost @var{n} frames.
3823 @item backtrace -@var{n}
3825 Similar, but print only the outermost @var{n} frames.
3830 @kindex info s @r{(@code{info stack})}
3831 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3832 are additional aliases for @code{backtrace}.
3834 Each line in the backtrace shows the frame number and the function name.
3835 The program counter value is also shown---unless you use @code{set
3836 print address off}. The backtrace also shows the source file name and
3837 line number, as well as the arguments to the function. The program
3838 counter value is omitted if it is at the beginning of the code for that
3841 Here is an example of a backtrace. It was made with the command
3842 @samp{bt 3}, so it shows the innermost three frames.
3846 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3848 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3849 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3851 (More stack frames follow...)
3856 The display for frame zero does not begin with a program counter
3857 value, indicating that your program has stopped at the beginning of the
3858 code for line @code{993} of @code{builtin.c}.
3861 @section Selecting a frame
3863 Most commands for examining the stack and other data in your program work on
3864 whichever stack frame is selected at the moment. Here are the commands for
3865 selecting a stack frame; all of them finish by printing a brief description
3866 of the stack frame just selected.
3869 @kindex frame@r{, selecting}
3870 @kindex f @r{(@code{frame})}
3873 Select frame number @var{n}. Recall that frame zero is the innermost
3874 (currently executing) frame, frame one is the frame that called the
3875 innermost one, and so on. The highest-numbered frame is the one for
3878 @item frame @var{addr}
3880 Select the frame at address @var{addr}. This is useful mainly if the
3881 chaining of stack frames has been damaged by a bug, making it
3882 impossible for @value{GDBN} to assign numbers properly to all frames. In
3883 addition, this can be useful when your program has multiple stacks and
3884 switches between them.
3886 On the SPARC architecture, @code{frame} needs two addresses to
3887 select an arbitrary frame: a frame pointer and a stack pointer.
3889 On the MIPS and Alpha architecture, it needs two addresses: a stack
3890 pointer and a program counter.
3892 On the 29k architecture, it needs three addresses: a register stack
3893 pointer, a program counter, and a memory stack pointer.
3894 @c note to future updaters: this is conditioned on a flag
3895 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3896 @c as of 27 Jan 1994.
3900 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3901 advances toward the outermost frame, to higher frame numbers, to frames
3902 that have existed longer. @var{n} defaults to one.
3905 @kindex do @r{(@code{down})}
3907 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3908 advances toward the innermost frame, to lower frame numbers, to frames
3909 that were created more recently. @var{n} defaults to one. You may
3910 abbreviate @code{down} as @code{do}.
3913 All of these commands end by printing two lines of output describing the
3914 frame. The first line shows the frame number, the function name, the
3915 arguments, and the source file and line number of execution in that
3916 frame. The second line shows the text of that source line.
3924 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3926 10 read_input_file (argv[i]);
3930 After such a printout, the @code{list} command with no arguments
3931 prints ten lines centered on the point of execution in the frame.
3932 You can also edit the program at the point of execution with your favorite
3933 editing program by typing @code{edit}.
3934 @xref{List, ,Printing source lines},
3938 @kindex down-silently
3940 @item up-silently @var{n}
3941 @itemx down-silently @var{n}
3942 These two commands are variants of @code{up} and @code{down},
3943 respectively; they differ in that they do their work silently, without
3944 causing display of the new frame. They are intended primarily for use
3945 in @value{GDBN} command scripts, where the output might be unnecessary and
3950 @section Information about a frame
3952 There are several other commands to print information about the selected
3958 When used without any argument, this command does not change which
3959 frame is selected, but prints a brief description of the currently
3960 selected stack frame. It can be abbreviated @code{f}. With an
3961 argument, this command is used to select a stack frame.
3962 @xref{Selection, ,Selecting a frame}.
3965 @kindex info f @r{(@code{info frame})}
3968 This command prints a verbose description of the selected stack frame,
3973 the address of the frame
3975 the address of the next frame down (called by this frame)
3977 the address of the next frame up (caller of this frame)
3979 the language in which the source code corresponding to this frame is written
3981 the address of the frame's arguments
3983 the address of the frame's local variables
3985 the program counter saved in it (the address of execution in the caller frame)
3987 which registers were saved in the frame
3990 @noindent The verbose description is useful when
3991 something has gone wrong that has made the stack format fail to fit
3992 the usual conventions.
3994 @item info frame @var{addr}
3995 @itemx info f @var{addr}
3996 Print a verbose description of the frame at address @var{addr}, without
3997 selecting that frame. The selected frame remains unchanged by this
3998 command. This requires the same kind of address (more than one for some
3999 architectures) that you specify in the @code{frame} command.
4000 @xref{Selection, ,Selecting a frame}.
4004 Print the arguments of the selected frame, each on a separate line.
4008 Print the local variables of the selected frame, each on a separate
4009 line. These are all variables (declared either static or automatic)
4010 accessible at the point of execution of the selected frame.
4013 @cindex catch exceptions, list active handlers
4014 @cindex exception handlers, how to list
4016 Print a list of all the exception handlers that are active in the
4017 current stack frame at the current point of execution. To see other
4018 exception handlers, visit the associated frame (using the @code{up},
4019 @code{down}, or @code{frame} commands); then type @code{info catch}.
4020 @xref{Set Catchpoints, , Setting catchpoints}.
4026 @chapter Examining Source Files
4028 @value{GDBN} can print parts of your program's source, since the debugging
4029 information recorded in the program tells @value{GDBN} what source files were
4030 used to build it. When your program stops, @value{GDBN} spontaneously prints
4031 the line where it stopped. Likewise, when you select a stack frame
4032 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
4033 execution in that frame has stopped. You can print other portions of
4034 source files by explicit command.
4036 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
4037 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
4038 @value{GDBN} under @sc{gnu} Emacs}.
4041 * List:: Printing source lines
4042 * Edit:: Editing source files
4043 * Search:: Searching source files
4044 * Source Path:: Specifying source directories
4045 * Machine Code:: Source and machine code
4049 @section Printing source lines
4052 @kindex l @r{(@code{list})}
4053 To print lines from a source file, use the @code{list} command
4054 (abbreviated @code{l}). By default, ten lines are printed.
4055 There are several ways to specify what part of the file you want to print.
4057 Here are the forms of the @code{list} command most commonly used:
4060 @item list @var{linenum}
4061 Print lines centered around line number @var{linenum} in the
4062 current source file.
4064 @item list @var{function}
4065 Print lines centered around the beginning of function
4069 Print more lines. If the last lines printed were printed with a
4070 @code{list} command, this prints lines following the last lines
4071 printed; however, if the last line printed was a solitary line printed
4072 as part of displaying a stack frame (@pxref{Stack, ,Examining the
4073 Stack}), this prints lines centered around that line.
4076 Print lines just before the lines last printed.
4079 By default, @value{GDBN} prints ten source lines with any of these forms of
4080 the @code{list} command. You can change this using @code{set listsize}:
4083 @kindex set listsize
4084 @item set listsize @var{count}
4085 Make the @code{list} command display @var{count} source lines (unless
4086 the @code{list} argument explicitly specifies some other number).
4088 @kindex show listsize
4090 Display the number of lines that @code{list} prints.
4093 Repeating a @code{list} command with @key{RET} discards the argument,
4094 so it is equivalent to typing just @code{list}. This is more useful
4095 than listing the same lines again. An exception is made for an
4096 argument of @samp{-}; that argument is preserved in repetition so that
4097 each repetition moves up in the source file.
4100 In general, the @code{list} command expects you to supply zero, one or two
4101 @dfn{linespecs}. Linespecs specify source lines; there are several ways
4102 of writing them, but the effect is always to specify some source line.
4103 Here is a complete description of the possible arguments for @code{list}:
4106 @item list @var{linespec}
4107 Print lines centered around the line specified by @var{linespec}.
4109 @item list @var{first},@var{last}
4110 Print lines from @var{first} to @var{last}. Both arguments are
4113 @item list ,@var{last}
4114 Print lines ending with @var{last}.
4116 @item list @var{first},
4117 Print lines starting with @var{first}.
4120 Print lines just after the lines last printed.
4123 Print lines just before the lines last printed.
4126 As described in the preceding table.
4129 Here are the ways of specifying a single source line---all the
4134 Specifies line @var{number} of the current source file.
4135 When a @code{list} command has two linespecs, this refers to
4136 the same source file as the first linespec.
4139 Specifies the line @var{offset} lines after the last line printed.
4140 When used as the second linespec in a @code{list} command that has
4141 two, this specifies the line @var{offset} lines down from the
4145 Specifies the line @var{offset} lines before the last line printed.
4147 @item @var{filename}:@var{number}
4148 Specifies line @var{number} in the source file @var{filename}.
4150 @item @var{function}
4151 Specifies the line that begins the body of the function @var{function}.
4152 For example: in C, this is the line with the open brace.
4154 @item @var{filename}:@var{function}
4155 Specifies the line of the open-brace that begins the body of the
4156 function @var{function} in the file @var{filename}. You only need the
4157 file name with a function name to avoid ambiguity when there are
4158 identically named functions in different source files.
4160 @item *@var{address}
4161 Specifies the line containing the program address @var{address}.
4162 @var{address} may be any expression.
4166 @section Editing source files
4167 @cindex editing source files
4170 @kindex e @r{(@code{edit})}
4171 To edit the lines in a source file, use the @code{edit} command.
4172 The editing program of your choice
4173 is invoked with the current line set to
4174 the active line in the program.
4175 Alternatively, there are several ways to specify what part of the file you
4176 want to print if you want to see other parts of the program.
4178 Here are the forms of the @code{edit} command most commonly used:
4182 Edit the current source file at the active line number in the program.
4184 @item edit @var{number}
4185 Edit the current source file with @var{number} as the active line number.
4187 @item edit @var{function}
4188 Edit the file containing @var{function} at the beginning of its definition.
4190 @item edit @var{filename}:@var{number}
4191 Specifies line @var{number} in the source file @var{filename}.
4193 @item edit @var{filename}:@var{function}
4194 Specifies the line that begins the body of the
4195 function @var{function} in the file @var{filename}. You only need the
4196 file name with a function name to avoid ambiguity when there are
4197 identically named functions in different source files.
4199 @item edit *@var{address}
4200 Specifies the line containing the program address @var{address}.
4201 @var{address} may be any expression.
4204 @subsection Choosing your editor
4205 You can customize @value{GDBN} to use any editor you want
4207 The only restriction is that your editor (say @code{ex}), recognizes the
4208 following command-line syntax:
4210 ex +@var{number} file
4212 The optional numeric value +@var{number} designates the active line in the file.
4214 By default, it is @value{EDITOR}, but you can change this by setting the
4215 environment variable @code{EDITOR} before using
4217 For example, to configure @value{GDBN} to use the @code{vi} editor, you
4218 could use these commands with the @code{sh} shell:
4224 or in the @code{csh} shell,
4226 setenv EDITOR /usr/bin/vi
4231 @section Searching source files
4233 @kindex reverse-search
4235 There are two commands for searching through the current source file for a
4240 @kindex forward-search
4241 @item forward-search @var{regexp}
4242 @itemx search @var{regexp}
4243 The command @samp{forward-search @var{regexp}} checks each line,
4244 starting with the one following the last line listed, for a match for
4245 @var{regexp}. It lists the line that is found. You can use the
4246 synonym @samp{search @var{regexp}} or abbreviate the command name as
4249 @item reverse-search @var{regexp}
4250 The command @samp{reverse-search @var{regexp}} checks each line, starting
4251 with the one before the last line listed and going backward, for a match
4252 for @var{regexp}. It lists the line that is found. You can abbreviate
4253 this command as @code{rev}.
4257 @section Specifying source directories
4260 @cindex directories for source files
4261 Executable programs sometimes do not record the directories of the source
4262 files from which they were compiled, just the names. Even when they do,
4263 the directories could be moved between the compilation and your debugging
4264 session. @value{GDBN} has a list of directories to search for source files;
4265 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4266 it tries all the directories in the list, in the order they are present
4267 in the list, until it finds a file with the desired name. Note that
4268 the executable search path is @emph{not} used for this purpose. Neither is
4269 the current working directory, unless it happens to be in the source
4272 If @value{GDBN} cannot find a source file in the source path, and the
4273 object program records a directory, @value{GDBN} tries that directory
4274 too. If the source path is empty, and there is no record of the
4275 compilation directory, @value{GDBN} looks in the current directory as a
4278 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4279 any information it has cached about where source files are found and where
4280 each line is in the file.
4284 When you start @value{GDBN}, its source path includes only @samp{cdir}
4285 and @samp{cwd}, in that order.
4286 To add other directories, use the @code{directory} command.
4289 @item directory @var{dirname} @dots{}
4290 @item dir @var{dirname} @dots{}
4291 Add directory @var{dirname} to the front of the source path. Several
4292 directory names may be given to this command, separated by @samp{:}
4293 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
4294 part of absolute file names) or
4295 whitespace. You may specify a directory that is already in the source
4296 path; this moves it forward, so @value{GDBN} searches it sooner.
4300 @vindex $cdir@r{, convenience variable}
4301 @vindex $cwdr@r{, convenience variable}
4302 @cindex compilation directory
4303 @cindex current directory
4304 @cindex working directory
4305 @cindex directory, current
4306 @cindex directory, compilation
4307 You can use the string @samp{$cdir} to refer to the compilation
4308 directory (if one is recorded), and @samp{$cwd} to refer to the current
4309 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4310 tracks the current working directory as it changes during your @value{GDBN}
4311 session, while the latter is immediately expanded to the current
4312 directory at the time you add an entry to the source path.
4315 Reset the source path to empty again. This requires confirmation.
4317 @c RET-repeat for @code{directory} is explicitly disabled, but since
4318 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4320 @item show directories
4321 @kindex show directories
4322 Print the source path: show which directories it contains.
4325 If your source path is cluttered with directories that are no longer of
4326 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4327 versions of source. You can correct the situation as follows:
4331 Use @code{directory} with no argument to reset the source path to empty.
4334 Use @code{directory} with suitable arguments to reinstall the
4335 directories you want in the source path. You can add all the
4336 directories in one command.
4340 @section Source and machine code
4342 You can use the command @code{info line} to map source lines to program
4343 addresses (and vice versa), and the command @code{disassemble} to display
4344 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4345 mode, the @code{info line} command causes the arrow to point to the
4346 line specified. Also, @code{info line} prints addresses in symbolic form as
4351 @item info line @var{linespec}
4352 Print the starting and ending addresses of the compiled code for
4353 source line @var{linespec}. You can specify source lines in any of
4354 the ways understood by the @code{list} command (@pxref{List, ,Printing
4358 For example, we can use @code{info line} to discover the location of
4359 the object code for the first line of function
4360 @code{m4_changequote}:
4362 @c FIXME: I think this example should also show the addresses in
4363 @c symbolic form, as they usually would be displayed.
4365 (@value{GDBP}) info line m4_changequote
4366 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4370 We can also inquire (using @code{*@var{addr}} as the form for
4371 @var{linespec}) what source line covers a particular address:
4373 (@value{GDBP}) info line *0x63ff
4374 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4377 @cindex @code{$_} and @code{info line}
4378 @kindex x@r{(examine), and} info line
4379 After @code{info line}, the default address for the @code{x} command
4380 is changed to the starting address of the line, so that @samp{x/i} is
4381 sufficient to begin examining the machine code (@pxref{Memory,
4382 ,Examining memory}). Also, this address is saved as the value of the
4383 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4388 @cindex assembly instructions
4389 @cindex instructions, assembly
4390 @cindex machine instructions
4391 @cindex listing machine instructions
4393 This specialized command dumps a range of memory as machine
4394 instructions. The default memory range is the function surrounding the
4395 program counter of the selected frame. A single argument to this
4396 command is a program counter value; @value{GDBN} dumps the function
4397 surrounding this value. Two arguments specify a range of addresses
4398 (first inclusive, second exclusive) to dump.
4401 The following example shows the disassembly of a range of addresses of
4402 HP PA-RISC 2.0 code:
4405 (@value{GDBP}) disas 0x32c4 0x32e4
4406 Dump of assembler code from 0x32c4 to 0x32e4:
4407 0x32c4 <main+204>: addil 0,dp
4408 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4409 0x32cc <main+212>: ldil 0x3000,r31
4410 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4411 0x32d4 <main+220>: ldo 0(r31),rp
4412 0x32d8 <main+224>: addil -0x800,dp
4413 0x32dc <main+228>: ldo 0x588(r1),r26
4414 0x32e0 <main+232>: ldil 0x3000,r31
4415 End of assembler dump.
4418 Some architectures have more than one commonly-used set of instruction
4419 mnemonics or other syntax.
4422 @kindex set disassembly-flavor
4423 @cindex assembly instructions
4424 @cindex instructions, assembly
4425 @cindex machine instructions
4426 @cindex listing machine instructions
4427 @cindex Intel disassembly flavor
4428 @cindex AT&T disassembly flavor
4429 @item set disassembly-flavor @var{instruction-set}
4430 Select the instruction set to use when disassembling the
4431 program via the @code{disassemble} or @code{x/i} commands.
4433 Currently this command is only defined for the Intel x86 family. You
4434 can set @var{instruction-set} to either @code{intel} or @code{att}.
4435 The default is @code{att}, the AT&T flavor used by default by Unix
4436 assemblers for x86-based targets.
4441 @chapter Examining Data
4443 @cindex printing data
4444 @cindex examining data
4447 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4448 @c document because it is nonstandard... Under Epoch it displays in a
4449 @c different window or something like that.
4450 The usual way to examine data in your program is with the @code{print}
4451 command (abbreviated @code{p}), or its synonym @code{inspect}. It
4452 evaluates and prints the value of an expression of the language your
4453 program is written in (@pxref{Languages, ,Using @value{GDBN} with
4454 Different Languages}).
4457 @item print @var{expr}
4458 @itemx print /@var{f} @var{expr}
4459 @var{expr} is an expression (in the source language). By default the
4460 value of @var{expr} is printed in a format appropriate to its data type;
4461 you can choose a different format by specifying @samp{/@var{f}}, where
4462 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
4466 @itemx print /@var{f}
4467 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
4468 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4469 conveniently inspect the same value in an alternative format.
4472 A more low-level way of examining data is with the @code{x} command.
4473 It examines data in memory at a specified address and prints it in a
4474 specified format. @xref{Memory, ,Examining memory}.
4476 If you are interested in information about types, or about how the
4477 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
4478 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
4482 * Expressions:: Expressions
4483 * Variables:: Program variables
4484 * Arrays:: Artificial arrays
4485 * Output Formats:: Output formats
4486 * Memory:: Examining memory
4487 * Auto Display:: Automatic display
4488 * Print Settings:: Print settings
4489 * Value History:: Value history
4490 * Convenience Vars:: Convenience variables
4491 * Registers:: Registers
4492 * Floating Point Hardware:: Floating point hardware
4493 * Vector Unit:: Vector Unit
4494 * Memory Region Attributes:: Memory region attributes
4495 * Dump/Restore Files:: Copy between memory and a file
4499 @section Expressions
4502 @code{print} and many other @value{GDBN} commands accept an expression and
4503 compute its value. Any kind of constant, variable or operator defined
4504 by the programming language you are using is valid in an expression in
4505 @value{GDBN}. This includes conditional expressions, function calls,
4506 casts, and string constants. It also includes preprocessor macros, if
4507 you compiled your program to include this information; see
4510 @value{GDBN} supports array constants in expressions input by
4511 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
4512 you can use the command @code{print @{1, 2, 3@}} to build up an array in
4513 memory that is @code{malloc}ed in the target program.
4515 Because C is so widespread, most of the expressions shown in examples in
4516 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4517 Languages}, for information on how to use expressions in other
4520 In this section, we discuss operators that you can use in @value{GDBN}
4521 expressions regardless of your programming language.
4523 Casts are supported in all languages, not just in C, because it is so
4524 useful to cast a number into a pointer in order to examine a structure
4525 at that address in memory.
4526 @c FIXME: casts supported---Mod2 true?
4528 @value{GDBN} supports these operators, in addition to those common
4529 to programming languages:
4533 @samp{@@} is a binary operator for treating parts of memory as arrays.
4534 @xref{Arrays, ,Artificial arrays}, for more information.
4537 @samp{::} allows you to specify a variable in terms of the file or
4538 function where it is defined. @xref{Variables, ,Program variables}.
4540 @cindex @{@var{type}@}
4541 @cindex type casting memory
4542 @cindex memory, viewing as typed object
4543 @cindex casts, to view memory
4544 @item @{@var{type}@} @var{addr}
4545 Refers to an object of type @var{type} stored at address @var{addr} in
4546 memory. @var{addr} may be any expression whose value is an integer or
4547 pointer (but parentheses are required around binary operators, just as in
4548 a cast). This construct is allowed regardless of what kind of data is
4549 normally supposed to reside at @var{addr}.
4553 @section Program variables
4555 The most common kind of expression to use is the name of a variable
4558 Variables in expressions are understood in the selected stack frame
4559 (@pxref{Selection, ,Selecting a frame}); they must be either:
4563 global (or file-static)
4570 visible according to the scope rules of the
4571 programming language from the point of execution in that frame
4574 @noindent This means that in the function
4589 you can examine and use the variable @code{a} whenever your program is
4590 executing within the function @code{foo}, but you can only use or
4591 examine the variable @code{b} while your program is executing inside
4592 the block where @code{b} is declared.
4594 @cindex variable name conflict
4595 There is an exception: you can refer to a variable or function whose
4596 scope is a single source file even if the current execution point is not
4597 in this file. But it is possible to have more than one such variable or
4598 function with the same name (in different source files). If that
4599 happens, referring to that name has unpredictable effects. If you wish,
4600 you can specify a static variable in a particular function or file,
4601 using the colon-colon notation:
4603 @cindex colon-colon, context for variables/functions
4605 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4606 @cindex @code{::}, context for variables/functions
4609 @var{file}::@var{variable}
4610 @var{function}::@var{variable}
4614 Here @var{file} or @var{function} is the name of the context for the
4615 static @var{variable}. In the case of file names, you can use quotes to
4616 make sure @value{GDBN} parses the file name as a single word---for example,
4617 to print a global value of @code{x} defined in @file{f2.c}:
4620 (@value{GDBP}) p 'f2.c'::x
4623 @cindex C@t{++} scope resolution
4624 This use of @samp{::} is very rarely in conflict with the very similar
4625 use of the same notation in C@t{++}. @value{GDBN} also supports use of the C@t{++}
4626 scope resolution operator in @value{GDBN} expressions.
4627 @c FIXME: Um, so what happens in one of those rare cases where it's in
4630 @cindex wrong values
4631 @cindex variable values, wrong
4633 @emph{Warning:} Occasionally, a local variable may appear to have the
4634 wrong value at certain points in a function---just after entry to a new
4635 scope, and just before exit.
4637 You may see this problem when you are stepping by machine instructions.
4638 This is because, on most machines, it takes more than one instruction to
4639 set up a stack frame (including local variable definitions); if you are
4640 stepping by machine instructions, variables may appear to have the wrong
4641 values until the stack frame is completely built. On exit, it usually
4642 also takes more than one machine instruction to destroy a stack frame;
4643 after you begin stepping through that group of instructions, local
4644 variable definitions may be gone.
4646 This may also happen when the compiler does significant optimizations.
4647 To be sure of always seeing accurate values, turn off all optimization
4650 @cindex ``No symbol "foo" in current context''
4651 Another possible effect of compiler optimizations is to optimize
4652 unused variables out of existence, or assign variables to registers (as
4653 opposed to memory addresses). Depending on the support for such cases
4654 offered by the debug info format used by the compiler, @value{GDBN}
4655 might not be able to display values for such local variables. If that
4656 happens, @value{GDBN} will print a message like this:
4659 No symbol "foo" in current context.
4662 To solve such problems, either recompile without optimizations, or use a
4663 different debug info format, if the compiler supports several such
4664 formats. For example, @value{NGCC}, the @sc{gnu} C/C@t{++} compiler usually
4665 supports the @samp{-gstabs} option. @samp{-gstabs} produces debug info
4666 in a format that is superior to formats such as COFF. You may be able
4667 to use DWARF2 (@samp{-gdwarf-2}), which is also an effective form for
4668 debug info. See @ref{Debugging Options,,Options for Debugging Your
4669 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
4674 @section Artificial arrays
4676 @cindex artificial array
4677 @kindex @@@r{, referencing memory as an array}
4678 It is often useful to print out several successive objects of the
4679 same type in memory; a section of an array, or an array of
4680 dynamically determined size for which only a pointer exists in the
4683 You can do this by referring to a contiguous span of memory as an
4684 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4685 operand of @samp{@@} should be the first element of the desired array
4686 and be an individual object. The right operand should be the desired length
4687 of the array. The result is an array value whose elements are all of
4688 the type of the left argument. The first element is actually the left
4689 argument; the second element comes from bytes of memory immediately
4690 following those that hold the first element, and so on. Here is an
4691 example. If a program says
4694 int *array = (int *) malloc (len * sizeof (int));
4698 you can print the contents of @code{array} with
4704 The left operand of @samp{@@} must reside in memory. Array values made
4705 with @samp{@@} in this way behave just like other arrays in terms of
4706 subscripting, and are coerced to pointers when used in expressions.
4707 Artificial arrays most often appear in expressions via the value history
4708 (@pxref{Value History, ,Value history}), after printing one out.
4710 Another way to create an artificial array is to use a cast.
4711 This re-interprets a value as if it were an array.
4712 The value need not be in memory:
4714 (@value{GDBP}) p/x (short[2])0x12345678
4715 $1 = @{0x1234, 0x5678@}
4718 As a convenience, if you leave the array length out (as in
4719 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
4720 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4722 (@value{GDBP}) p/x (short[])0x12345678
4723 $2 = @{0x1234, 0x5678@}
4726 Sometimes the artificial array mechanism is not quite enough; in
4727 moderately complex data structures, the elements of interest may not
4728 actually be adjacent---for example, if you are interested in the values
4729 of pointers in an array. One useful work-around in this situation is
4730 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4731 variables}) as a counter in an expression that prints the first
4732 interesting value, and then repeat that expression via @key{RET}. For
4733 instance, suppose you have an array @code{dtab} of pointers to
4734 structures, and you are interested in the values of a field @code{fv}
4735 in each structure. Here is an example of what you might type:
4745 @node Output Formats
4746 @section Output formats
4748 @cindex formatted output
4749 @cindex output formats
4750 By default, @value{GDBN} prints a value according to its data type. Sometimes
4751 this is not what you want. For example, you might want to print a number
4752 in hex, or a pointer in decimal. Or you might want to view data in memory
4753 at a certain address as a character string or as an instruction. To do
4754 these things, specify an @dfn{output format} when you print a value.
4756 The simplest use of output formats is to say how to print a value
4757 already computed. This is done by starting the arguments of the
4758 @code{print} command with a slash and a format letter. The format
4759 letters supported are:
4763 Regard the bits of the value as an integer, and print the integer in
4767 Print as integer in signed decimal.
4770 Print as integer in unsigned decimal.
4773 Print as integer in octal.
4776 Print as integer in binary. The letter @samp{t} stands for ``two''.
4777 @footnote{@samp{b} cannot be used because these format letters are also
4778 used with the @code{x} command, where @samp{b} stands for ``byte'';
4779 see @ref{Memory,,Examining memory}.}
4782 @cindex unknown address, locating
4783 @cindex locate address
4784 Print as an address, both absolute in hexadecimal and as an offset from
4785 the nearest preceding symbol. You can use this format used to discover
4786 where (in what function) an unknown address is located:
4789 (@value{GDBP}) p/a 0x54320
4790 $3 = 0x54320 <_initialize_vx+396>
4794 The command @code{info symbol 0x54320} yields similar results.
4795 @xref{Symbols, info symbol}.
4798 Regard as an integer and print it as a character constant.
4801 Regard the bits of the value as a floating point number and print
4802 using typical floating point syntax.
4805 For example, to print the program counter in hex (@pxref{Registers}), type
4812 Note that no space is required before the slash; this is because command
4813 names in @value{GDBN} cannot contain a slash.
4815 To reprint the last value in the value history with a different format,
4816 you can use the @code{print} command with just a format and no
4817 expression. For example, @samp{p/x} reprints the last value in hex.
4820 @section Examining memory
4822 You can use the command @code{x} (for ``examine'') to examine memory in
4823 any of several formats, independently of your program's data types.
4825 @cindex examining memory
4827 @kindex x @r{(examine memory)}
4828 @item x/@var{nfu} @var{addr}
4831 Use the @code{x} command to examine memory.
4834 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4835 much memory to display and how to format it; @var{addr} is an
4836 expression giving the address where you want to start displaying memory.
4837 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4838 Several commands set convenient defaults for @var{addr}.
4841 @item @var{n}, the repeat count
4842 The repeat count is a decimal integer; the default is 1. It specifies
4843 how much memory (counting by units @var{u}) to display.
4844 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4847 @item @var{f}, the display format
4848 The display format is one of the formats used by @code{print},
4849 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4850 The default is @samp{x} (hexadecimal) initially.
4851 The default changes each time you use either @code{x} or @code{print}.
4853 @item @var{u}, the unit size
4854 The unit size is any of
4860 Halfwords (two bytes).
4862 Words (four bytes). This is the initial default.
4864 Giant words (eight bytes).
4867 Each time you specify a unit size with @code{x}, that size becomes the
4868 default unit the next time you use @code{x}. (For the @samp{s} and
4869 @samp{i} formats, the unit size is ignored and is normally not written.)
4871 @item @var{addr}, starting display address
4872 @var{addr} is the address where you want @value{GDBN} to begin displaying
4873 memory. The expression need not have a pointer value (though it may);
4874 it is always interpreted as an integer address of a byte of memory.
4875 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4876 @var{addr} is usually just after the last address examined---but several
4877 other commands also set the default address: @code{info breakpoints} (to
4878 the address of the last breakpoint listed), @code{info line} (to the
4879 starting address of a line), and @code{print} (if you use it to display
4880 a value from memory).
4883 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4884 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4885 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4886 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4887 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
4889 Since the letters indicating unit sizes are all distinct from the
4890 letters specifying output formats, you do not have to remember whether
4891 unit size or format comes first; either order works. The output
4892 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4893 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4895 Even though the unit size @var{u} is ignored for the formats @samp{s}
4896 and @samp{i}, you might still want to use a count @var{n}; for example,
4897 @samp{3i} specifies that you want to see three machine instructions,
4898 including any operands. The command @code{disassemble} gives an
4899 alternative way of inspecting machine instructions; see @ref{Machine
4900 Code,,Source and machine code}.
4902 All the defaults for the arguments to @code{x} are designed to make it
4903 easy to continue scanning memory with minimal specifications each time
4904 you use @code{x}. For example, after you have inspected three machine
4905 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4906 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4907 the repeat count @var{n} is used again; the other arguments default as
4908 for successive uses of @code{x}.
4910 @cindex @code{$_}, @code{$__}, and value history
4911 The addresses and contents printed by the @code{x} command are not saved
4912 in the value history because there is often too much of them and they
4913 would get in the way. Instead, @value{GDBN} makes these values available for
4914 subsequent use in expressions as values of the convenience variables
4915 @code{$_} and @code{$__}. After an @code{x} command, the last address
4916 examined is available for use in expressions in the convenience variable
4917 @code{$_}. The contents of that address, as examined, are available in
4918 the convenience variable @code{$__}.
4920 If the @code{x} command has a repeat count, the address and contents saved
4921 are from the last memory unit printed; this is not the same as the last
4922 address printed if several units were printed on the last line of output.
4925 @section Automatic display
4926 @cindex automatic display
4927 @cindex display of expressions
4929 If you find that you want to print the value of an expression frequently
4930 (to see how it changes), you might want to add it to the @dfn{automatic
4931 display list} so that @value{GDBN} prints its value each time your program stops.
4932 Each expression added to the list is given a number to identify it;
4933 to remove an expression from the list, you specify that number.
4934 The automatic display looks like this:
4938 3: bar[5] = (struct hack *) 0x3804
4942 This display shows item numbers, expressions and their current values. As with
4943 displays you request manually using @code{x} or @code{print}, you can
4944 specify the output format you prefer; in fact, @code{display} decides
4945 whether to use @code{print} or @code{x} depending on how elaborate your
4946 format specification is---it uses @code{x} if you specify a unit size,
4947 or one of the two formats (@samp{i} and @samp{s}) that are only
4948 supported by @code{x}; otherwise it uses @code{print}.
4952 @item display @var{expr}
4953 Add the expression @var{expr} to the list of expressions to display
4954 each time your program stops. @xref{Expressions, ,Expressions}.
4956 @code{display} does not repeat if you press @key{RET} again after using it.
4958 @item display/@var{fmt} @var{expr}
4959 For @var{fmt} specifying only a display format and not a size or
4960 count, add the expression @var{expr} to the auto-display list but
4961 arrange to display it each time in the specified format @var{fmt}.
4962 @xref{Output Formats,,Output formats}.
4964 @item display/@var{fmt} @var{addr}
4965 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4966 number of units, add the expression @var{addr} as a memory address to
4967 be examined each time your program stops. Examining means in effect
4968 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4971 For example, @samp{display/i $pc} can be helpful, to see the machine
4972 instruction about to be executed each time execution stops (@samp{$pc}
4973 is a common name for the program counter; @pxref{Registers, ,Registers}).
4976 @kindex delete display
4978 @item undisplay @var{dnums}@dots{}
4979 @itemx delete display @var{dnums}@dots{}
4980 Remove item numbers @var{dnums} from the list of expressions to display.
4982 @code{undisplay} does not repeat if you press @key{RET} after using it.
4983 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4985 @kindex disable display
4986 @item disable display @var{dnums}@dots{}
4987 Disable the display of item numbers @var{dnums}. A disabled display
4988 item is not printed automatically, but is not forgotten. It may be
4989 enabled again later.
4991 @kindex enable display
4992 @item enable display @var{dnums}@dots{}
4993 Enable display of item numbers @var{dnums}. It becomes effective once
4994 again in auto display of its expression, until you specify otherwise.
4997 Display the current values of the expressions on the list, just as is
4998 done when your program stops.
5000 @kindex info display
5002 Print the list of expressions previously set up to display
5003 automatically, each one with its item number, but without showing the
5004 values. This includes disabled expressions, which are marked as such.
5005 It also includes expressions which would not be displayed right now
5006 because they refer to automatic variables not currently available.
5009 If a display expression refers to local variables, then it does not make
5010 sense outside the lexical context for which it was set up. Such an
5011 expression is disabled when execution enters a context where one of its
5012 variables is not defined. For example, if you give the command
5013 @code{display last_char} while inside a function with an argument
5014 @code{last_char}, @value{GDBN} displays this argument while your program
5015 continues to stop inside that function. When it stops elsewhere---where
5016 there is no variable @code{last_char}---the display is disabled
5017 automatically. The next time your program stops where @code{last_char}
5018 is meaningful, you can enable the display expression once again.
5020 @node Print Settings
5021 @section Print settings
5023 @cindex format options
5024 @cindex print settings
5025 @value{GDBN} provides the following ways to control how arrays, structures,
5026 and symbols are printed.
5029 These settings are useful for debugging programs in any language:
5032 @kindex set print address
5033 @item set print address
5034 @itemx set print address on
5035 @value{GDBN} prints memory addresses showing the location of stack
5036 traces, structure values, pointer values, breakpoints, and so forth,
5037 even when it also displays the contents of those addresses. The default
5038 is @code{on}. For example, this is what a stack frame display looks like with
5039 @code{set print address on}:
5044 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
5046 530 if (lquote != def_lquote)
5050 @item set print address off
5051 Do not print addresses when displaying their contents. For example,
5052 this is the same stack frame displayed with @code{set print address off}:
5056 (@value{GDBP}) set print addr off
5058 #0 set_quotes (lq="<<", rq=">>") at input.c:530
5059 530 if (lquote != def_lquote)
5063 You can use @samp{set print address off} to eliminate all machine
5064 dependent displays from the @value{GDBN} interface. For example, with
5065 @code{print address off}, you should get the same text for backtraces on
5066 all machines---whether or not they involve pointer arguments.
5068 @kindex show print address
5069 @item show print address
5070 Show whether or not addresses are to be printed.
5073 When @value{GDBN} prints a symbolic address, it normally prints the
5074 closest earlier symbol plus an offset. If that symbol does not uniquely
5075 identify the address (for example, it is a name whose scope is a single
5076 source file), you may need to clarify. One way to do this is with
5077 @code{info line}, for example @samp{info line *0x4537}. Alternately,
5078 you can set @value{GDBN} to print the source file and line number when
5079 it prints a symbolic address:
5082 @kindex set print symbol-filename
5083 @item set print symbol-filename on
5084 Tell @value{GDBN} to print the source file name and line number of a
5085 symbol in the symbolic form of an address.
5087 @item set print symbol-filename off
5088 Do not print source file name and line number of a symbol. This is the
5091 @kindex show print symbol-filename
5092 @item show print symbol-filename
5093 Show whether or not @value{GDBN} will print the source file name and
5094 line number of a symbol in the symbolic form of an address.
5097 Another situation where it is helpful to show symbol filenames and line
5098 numbers is when disassembling code; @value{GDBN} shows you the line
5099 number and source file that corresponds to each instruction.
5101 Also, you may wish to see the symbolic form only if the address being
5102 printed is reasonably close to the closest earlier symbol:
5105 @kindex set print max-symbolic-offset
5106 @item set print max-symbolic-offset @var{max-offset}
5107 Tell @value{GDBN} to only display the symbolic form of an address if the
5108 offset between the closest earlier symbol and the address is less than
5109 @var{max-offset}. The default is 0, which tells @value{GDBN}
5110 to always print the symbolic form of an address if any symbol precedes it.
5112 @kindex show print max-symbolic-offset
5113 @item show print max-symbolic-offset
5114 Ask how large the maximum offset is that @value{GDBN} prints in a
5118 @cindex wild pointer, interpreting
5119 @cindex pointer, finding referent
5120 If you have a pointer and you are not sure where it points, try
5121 @samp{set print symbol-filename on}. Then you can determine the name
5122 and source file location of the variable where it points, using
5123 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
5124 For example, here @value{GDBN} shows that a variable @code{ptt} points
5125 at another variable @code{t}, defined in @file{hi2.c}:
5128 (@value{GDBP}) set print symbol-filename on
5129 (@value{GDBP}) p/a ptt
5130 $4 = 0xe008 <t in hi2.c>
5134 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
5135 does not show the symbol name and filename of the referent, even with
5136 the appropriate @code{set print} options turned on.
5139 Other settings control how different kinds of objects are printed:
5142 @kindex set print array
5143 @item set print array
5144 @itemx set print array on
5145 Pretty print arrays. This format is more convenient to read,
5146 but uses more space. The default is off.
5148 @item set print array off
5149 Return to compressed format for arrays.
5151 @kindex show print array
5152 @item show print array
5153 Show whether compressed or pretty format is selected for displaying
5156 @kindex set print elements
5157 @item set print elements @var{number-of-elements}
5158 Set a limit on how many elements of an array @value{GDBN} will print.
5159 If @value{GDBN} is printing a large array, it stops printing after it has
5160 printed the number of elements set by the @code{set print elements} command.
5161 This limit also applies to the display of strings.
5162 When @value{GDBN} starts, this limit is set to 200.
5163 Setting @var{number-of-elements} to zero means that the printing is unlimited.
5165 @kindex show print elements
5166 @item show print elements
5167 Display the number of elements of a large array that @value{GDBN} will print.
5168 If the number is 0, then the printing is unlimited.
5170 @kindex set print null-stop
5171 @item set print null-stop
5172 Cause @value{GDBN} to stop printing the characters of an array when the first
5173 @sc{null} is encountered. This is useful when large arrays actually
5174 contain only short strings.
5177 @kindex set print pretty
5178 @item set print pretty on
5179 Cause @value{GDBN} to print structures in an indented format with one member
5180 per line, like this:
5195 @item set print pretty off
5196 Cause @value{GDBN} to print structures in a compact format, like this:
5200 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
5201 meat = 0x54 "Pork"@}
5206 This is the default format.
5208 @kindex show print pretty
5209 @item show print pretty
5210 Show which format @value{GDBN} is using to print structures.
5212 @kindex set print sevenbit-strings
5213 @item set print sevenbit-strings on
5214 Print using only seven-bit characters; if this option is set,
5215 @value{GDBN} displays any eight-bit characters (in strings or
5216 character values) using the notation @code{\}@var{nnn}. This setting is
5217 best if you are working in English (@sc{ascii}) and you use the
5218 high-order bit of characters as a marker or ``meta'' bit.
5220 @item set print sevenbit-strings off
5221 Print full eight-bit characters. This allows the use of more
5222 international character sets, and is the default.
5224 @kindex show print sevenbit-strings
5225 @item show print sevenbit-strings
5226 Show whether or not @value{GDBN} is printing only seven-bit characters.
5228 @kindex set print union
5229 @item set print union on
5230 Tell @value{GDBN} to print unions which are contained in structures. This
5231 is the default setting.
5233 @item set print union off
5234 Tell @value{GDBN} not to print unions which are contained in structures.
5236 @kindex show print union
5237 @item show print union
5238 Ask @value{GDBN} whether or not it will print unions which are contained in
5241 For example, given the declarations
5244 typedef enum @{Tree, Bug@} Species;
5245 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5246 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5257 struct thing foo = @{Tree, @{Acorn@}@};
5261 with @code{set print union on} in effect @samp{p foo} would print
5264 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5268 and with @code{set print union off} in effect it would print
5271 $1 = @{it = Tree, form = @{...@}@}
5277 These settings are of interest when debugging C@t{++} programs:
5281 @kindex set print demangle
5282 @item set print demangle
5283 @itemx set print demangle on
5284 Print C@t{++} names in their source form rather than in the encoded
5285 (``mangled'') form passed to the assembler and linker for type-safe
5286 linkage. The default is on.
5288 @kindex show print demangle
5289 @item show print demangle
5290 Show whether C@t{++} names are printed in mangled or demangled form.
5292 @kindex set print asm-demangle
5293 @item set print asm-demangle
5294 @itemx set print asm-demangle on
5295 Print C@t{++} names in their source form rather than their mangled form, even
5296 in assembler code printouts such as instruction disassemblies.
5299 @kindex show print asm-demangle
5300 @item show print asm-demangle
5301 Show whether C@t{++} names in assembly listings are printed in mangled
5304 @kindex set demangle-style
5305 @cindex C@t{++} symbol decoding style
5306 @cindex symbol decoding style, C@t{++}
5307 @item set demangle-style @var{style}
5308 Choose among several encoding schemes used by different compilers to
5309 represent C@t{++} names. The choices for @var{style} are currently:
5313 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5316 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
5317 This is the default.
5320 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
5323 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
5326 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
5327 @strong{Warning:} this setting alone is not sufficient to allow
5328 debugging @code{cfront}-generated executables. @value{GDBN} would
5329 require further enhancement to permit that.
5332 If you omit @var{style}, you will see a list of possible formats.
5334 @kindex show demangle-style
5335 @item show demangle-style
5336 Display the encoding style currently in use for decoding C@t{++} symbols.
5338 @kindex set print object
5339 @item set print object
5340 @itemx set print object on
5341 When displaying a pointer to an object, identify the @emph{actual}
5342 (derived) type of the object rather than the @emph{declared} type, using
5343 the virtual function table.
5345 @item set print object off
5346 Display only the declared type of objects, without reference to the
5347 virtual function table. This is the default setting.
5349 @kindex show print object
5350 @item show print object
5351 Show whether actual, or declared, object types are displayed.
5353 @kindex set print static-members
5354 @item set print static-members
5355 @itemx set print static-members on
5356 Print static members when displaying a C@t{++} object. The default is on.
5358 @item set print static-members off
5359 Do not print static members when displaying a C@t{++} object.
5361 @kindex show print static-members
5362 @item show print static-members
5363 Show whether C@t{++} static members are printed, or not.
5365 @c These don't work with HP ANSI C++ yet.
5366 @kindex set print vtbl
5367 @item set print vtbl
5368 @itemx set print vtbl on
5369 Pretty print C@t{++} virtual function tables. The default is off.
5370 (The @code{vtbl} commands do not work on programs compiled with the HP
5371 ANSI C@t{++} compiler (@code{aCC}).)
5373 @item set print vtbl off
5374 Do not pretty print C@t{++} virtual function tables.
5376 @kindex show print vtbl
5377 @item show print vtbl
5378 Show whether C@t{++} virtual function tables are pretty printed, or not.
5382 @section Value history
5384 @cindex value history
5385 Values printed by the @code{print} command are saved in the @value{GDBN}
5386 @dfn{value history}. This allows you to refer to them in other expressions.
5387 Values are kept until the symbol table is re-read or discarded
5388 (for example with the @code{file} or @code{symbol-file} commands).
5389 When the symbol table changes, the value history is discarded,
5390 since the values may contain pointers back to the types defined in the
5395 @cindex history number
5396 The values printed are given @dfn{history numbers} by which you can
5397 refer to them. These are successive integers starting with one.
5398 @code{print} shows you the history number assigned to a value by
5399 printing @samp{$@var{num} = } before the value; here @var{num} is the
5402 To refer to any previous value, use @samp{$} followed by the value's
5403 history number. The way @code{print} labels its output is designed to
5404 remind you of this. Just @code{$} refers to the most recent value in
5405 the history, and @code{$$} refers to the value before that.
5406 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5407 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5408 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5410 For example, suppose you have just printed a pointer to a structure and
5411 want to see the contents of the structure. It suffices to type
5417 If you have a chain of structures where the component @code{next} points
5418 to the next one, you can print the contents of the next one with this:
5425 You can print successive links in the chain by repeating this
5426 command---which you can do by just typing @key{RET}.
5428 Note that the history records values, not expressions. If the value of
5429 @code{x} is 4 and you type these commands:
5437 then the value recorded in the value history by the @code{print} command
5438 remains 4 even though the value of @code{x} has changed.
5443 Print the last ten values in the value history, with their item numbers.
5444 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5445 values} does not change the history.
5447 @item show values @var{n}
5448 Print ten history values centered on history item number @var{n}.
5451 Print ten history values just after the values last printed. If no more
5452 values are available, @code{show values +} produces no display.
5455 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5456 same effect as @samp{show values +}.
5458 @node Convenience Vars
5459 @section Convenience variables
5461 @cindex convenience variables
5462 @value{GDBN} provides @dfn{convenience variables} that you can use within
5463 @value{GDBN} to hold on to a value and refer to it later. These variables
5464 exist entirely within @value{GDBN}; they are not part of your program, and
5465 setting a convenience variable has no direct effect on further execution
5466 of your program. That is why you can use them freely.
5468 Convenience variables are prefixed with @samp{$}. Any name preceded by
5469 @samp{$} can be used for a convenience variable, unless it is one of
5470 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
5471 (Value history references, in contrast, are @emph{numbers} preceded
5472 by @samp{$}. @xref{Value History, ,Value history}.)
5474 You can save a value in a convenience variable with an assignment
5475 expression, just as you would set a variable in your program.
5479 set $foo = *object_ptr
5483 would save in @code{$foo} the value contained in the object pointed to by
5486 Using a convenience variable for the first time creates it, but its
5487 value is @code{void} until you assign a new value. You can alter the
5488 value with another assignment at any time.
5490 Convenience variables have no fixed types. You can assign a convenience
5491 variable any type of value, including structures and arrays, even if
5492 that variable already has a value of a different type. The convenience
5493 variable, when used as an expression, has the type of its current value.
5496 @kindex show convenience
5497 @item show convenience
5498 Print a list of convenience variables used so far, and their values.
5499 Abbreviated @code{show conv}.
5502 One of the ways to use a convenience variable is as a counter to be
5503 incremented or a pointer to be advanced. For example, to print
5504 a field from successive elements of an array of structures:
5508 print bar[$i++]->contents
5512 Repeat that command by typing @key{RET}.
5514 Some convenience variables are created automatically by @value{GDBN} and given
5515 values likely to be useful.
5518 @vindex $_@r{, convenience variable}
5520 The variable @code{$_} is automatically set by the @code{x} command to
5521 the last address examined (@pxref{Memory, ,Examining memory}). Other
5522 commands which provide a default address for @code{x} to examine also
5523 set @code{$_} to that address; these commands include @code{info line}
5524 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5525 except when set by the @code{x} command, in which case it is a pointer
5526 to the type of @code{$__}.
5528 @vindex $__@r{, convenience variable}
5530 The variable @code{$__} is automatically set by the @code{x} command
5531 to the value found in the last address examined. Its type is chosen
5532 to match the format in which the data was printed.
5535 @vindex $_exitcode@r{, convenience variable}
5536 The variable @code{$_exitcode} is automatically set to the exit code when
5537 the program being debugged terminates.
5540 On HP-UX systems, if you refer to a function or variable name that
5541 begins with a dollar sign, @value{GDBN} searches for a user or system
5542 name first, before it searches for a convenience variable.
5548 You can refer to machine register contents, in expressions, as variables
5549 with names starting with @samp{$}. The names of registers are different
5550 for each machine; use @code{info registers} to see the names used on
5554 @kindex info registers
5555 @item info registers
5556 Print the names and values of all registers except floating-point
5557 registers (in the selected stack frame).
5559 @kindex info all-registers
5560 @cindex floating point registers
5561 @item info all-registers
5562 Print the names and values of all registers, including floating-point
5565 @item info registers @var{regname} @dots{}
5566 Print the @dfn{relativized} value of each specified register @var{regname}.
5567 As discussed in detail below, register values are normally relative to
5568 the selected stack frame. @var{regname} may be any register name valid on
5569 the machine you are using, with or without the initial @samp{$}.
5572 @value{GDBN} has four ``standard'' register names that are available (in
5573 expressions) on most machines---whenever they do not conflict with an
5574 architecture's canonical mnemonics for registers. The register names
5575 @code{$pc} and @code{$sp} are used for the program counter register and
5576 the stack pointer. @code{$fp} is used for a register that contains a
5577 pointer to the current stack frame, and @code{$ps} is used for a
5578 register that contains the processor status. For example,
5579 you could print the program counter in hex with
5586 or print the instruction to be executed next with
5593 or add four to the stack pointer@footnote{This is a way of removing
5594 one word from the stack, on machines where stacks grow downward in
5595 memory (most machines, nowadays). This assumes that the innermost
5596 stack frame is selected; setting @code{$sp} is not allowed when other
5597 stack frames are selected. To pop entire frames off the stack,
5598 regardless of machine architecture, use @code{return};
5599 see @ref{Returning, ,Returning from a function}.} with
5605 Whenever possible, these four standard register names are available on
5606 your machine even though the machine has different canonical mnemonics,
5607 so long as there is no conflict. The @code{info registers} command
5608 shows the canonical names. For example, on the SPARC, @code{info
5609 registers} displays the processor status register as @code{$psr} but you
5610 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
5611 is an alias for the @sc{eflags} register.
5613 @value{GDBN} always considers the contents of an ordinary register as an
5614 integer when the register is examined in this way. Some machines have
5615 special registers which can hold nothing but floating point; these
5616 registers are considered to have floating point values. There is no way
5617 to refer to the contents of an ordinary register as floating point value
5618 (although you can @emph{print} it as a floating point value with
5619 @samp{print/f $@var{regname}}).
5621 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5622 means that the data format in which the register contents are saved by
5623 the operating system is not the same one that your program normally
5624 sees. For example, the registers of the 68881 floating point
5625 coprocessor are always saved in ``extended'' (raw) format, but all C
5626 programs expect to work with ``double'' (virtual) format. In such
5627 cases, @value{GDBN} normally works with the virtual format only (the format
5628 that makes sense for your program), but the @code{info registers} command
5629 prints the data in both formats.
5631 Normally, register values are relative to the selected stack frame
5632 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5633 value that the register would contain if all stack frames farther in
5634 were exited and their saved registers restored. In order to see the
5635 true contents of hardware registers, you must select the innermost
5636 frame (with @samp{frame 0}).
5638 However, @value{GDBN} must deduce where registers are saved, from the machine
5639 code generated by your compiler. If some registers are not saved, or if
5640 @value{GDBN} is unable to locate the saved registers, the selected stack
5641 frame makes no difference.
5643 @node Floating Point Hardware
5644 @section Floating point hardware
5645 @cindex floating point
5647 Depending on the configuration, @value{GDBN} may be able to give
5648 you more information about the status of the floating point hardware.
5653 Display hardware-dependent information about the floating
5654 point unit. The exact contents and layout vary depending on the
5655 floating point chip. Currently, @samp{info float} is supported on
5656 the ARM and x86 machines.
5660 @section Vector Unit
5663 Depending on the configuration, @value{GDBN} may be able to give you
5664 more information about the status of the vector unit.
5669 Display information about the vector unit. The exact contents and
5670 layout vary depending on the hardware.
5673 @node Memory Region Attributes
5674 @section Memory region attributes
5675 @cindex memory region attributes
5677 @dfn{Memory region attributes} allow you to describe special handling
5678 required by regions of your target's memory. @value{GDBN} uses attributes
5679 to determine whether to allow certain types of memory accesses; whether to
5680 use specific width accesses; and whether to cache target memory.
5682 Defined memory regions can be individually enabled and disabled. When a
5683 memory region is disabled, @value{GDBN} uses the default attributes when
5684 accessing memory in that region. Similarly, if no memory regions have
5685 been defined, @value{GDBN} uses the default attributes when accessing
5688 When a memory region is defined, it is given a number to identify it;
5689 to enable, disable, or remove a memory region, you specify that number.
5693 @item mem @var{lower} @var{upper} @var{attributes}@dots{}
5694 Define memory region bounded by @var{lower} and @var{upper} with
5695 attributes @var{attributes}@dots{}. Note that @var{upper} == 0 is a
5696 special case: it is treated as the the target's maximum memory address.
5697 (0xffff on 16 bit targets, 0xffffffff on 32 bit targets, etc.)
5700 @item delete mem @var{nums}@dots{}
5701 Remove memory regions @var{nums}@dots{}.
5704 @item disable mem @var{nums}@dots{}
5705 Disable memory regions @var{nums}@dots{}.
5706 A disabled memory region is not forgotten.
5707 It may be enabled again later.
5710 @item enable mem @var{nums}@dots{}
5711 Enable memory regions @var{nums}@dots{}.
5715 Print a table of all defined memory regions, with the following columns
5719 @item Memory Region Number
5720 @item Enabled or Disabled.
5721 Enabled memory regions are marked with @samp{y}.
5722 Disabled memory regions are marked with @samp{n}.
5725 The address defining the inclusive lower bound of the memory region.
5728 The address defining the exclusive upper bound of the memory region.
5731 The list of attributes set for this memory region.
5736 @subsection Attributes
5738 @subsubsection Memory Access Mode
5739 The access mode attributes set whether @value{GDBN} may make read or
5740 write accesses to a memory region.
5742 While these attributes prevent @value{GDBN} from performing invalid
5743 memory accesses, they do nothing to prevent the target system, I/O DMA,
5744 etc. from accessing memory.
5748 Memory is read only.
5750 Memory is write only.
5752 Memory is read/write. This is the default.
5755 @subsubsection Memory Access Size
5756 The acccess size attributes tells @value{GDBN} to use specific sized
5757 accesses in the memory region. Often memory mapped device registers
5758 require specific sized accesses. If no access size attribute is
5759 specified, @value{GDBN} may use accesses of any size.
5763 Use 8 bit memory accesses.
5765 Use 16 bit memory accesses.
5767 Use 32 bit memory accesses.
5769 Use 64 bit memory accesses.
5772 @c @subsubsection Hardware/Software Breakpoints
5773 @c The hardware/software breakpoint attributes set whether @value{GDBN}
5774 @c will use hardware or software breakpoints for the internal breakpoints
5775 @c used by the step, next, finish, until, etc. commands.
5779 @c Always use hardware breakpoints
5780 @c @item swbreak (default)
5783 @subsubsection Data Cache
5784 The data cache attributes set whether @value{GDBN} will cache target
5785 memory. While this generally improves performance by reducing debug
5786 protocol overhead, it can lead to incorrect results because @value{GDBN}
5787 does not know about volatile variables or memory mapped device
5792 Enable @value{GDBN} to cache target memory.
5794 Disable @value{GDBN} from caching target memory. This is the default.
5797 @c @subsubsection Memory Write Verification
5798 @c The memory write verification attributes set whether @value{GDBN}
5799 @c will re-reads data after each write to verify the write was successful.
5803 @c @item noverify (default)
5806 @node Dump/Restore Files
5807 @section Copy between memory and a file
5808 @cindex dump/restore files
5809 @cindex append data to a file
5810 @cindex dump data to a file
5811 @cindex restore data from a file
5816 The commands @code{dump}, @code{append}, and @code{restore} are used
5817 for copying data between target memory and a file. Data is written
5818 into a file using @code{dump} or @code{append}, and restored from a
5819 file into memory by using @code{restore}. Files may be binary, srec,
5820 intel hex, or tekhex (but only binary files can be appended).
5824 @kindex append binary
5825 @item dump binary memory @var{filename} @var{start_addr} @var{end_addr}
5826 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5827 raw binary format file @var{filename}.
5829 @item append binary memory @var{filename} @var{start_addr} @var{end_addr}
5830 Append contents of memory from @var{start_addr} to @var{end_addr} to
5831 raw binary format file @var{filename}.
5833 @item dump binary value @var{filename} @var{expression}
5834 Dump value of @var{expression} into raw binary format file @var{filename}.
5836 @item append binary memory @var{filename} @var{expression}
5837 Append value of @var{expression} to raw binary format file @var{filename}.
5840 @item dump ihex memory @var{filename} @var{start_addr} @var{end_addr}
5841 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5842 intel hex format file @var{filename}.
5844 @item dump ihex value @var{filename} @var{expression}
5845 Dump value of @var{expression} into intel hex format file @var{filename}.
5848 @item dump srec memory @var{filename} @var{start_addr} @var{end_addr}
5849 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5850 srec format file @var{filename}.
5852 @item dump srec value @var{filename} @var{expression}
5853 Dump value of @var{expression} into srec format file @var{filename}.
5856 @item dump tekhex memory @var{filename} @var{start_addr} @var{end_addr}
5857 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5858 tekhex format file @var{filename}.
5860 @item dump tekhex value @var{filename} @var{expression}
5861 Dump value of @var{expression} into tekhex format file @var{filename}.
5863 @item restore @var{filename} [@var{binary}] @var{bias} @var{start} @var{end}
5864 Restore the contents of file @var{filename} into memory. The @code{restore}
5865 command can automatically recognize any known bfd file format, except for
5866 raw binary. To restore a raw binary file you must use the optional argument
5867 @var{binary} after the filename.
5869 If @var{bias} is non-zero, its value will be added to the addresses
5870 contained in the file. Binary files always start at address zero, so
5871 they will be restored at address @var{bias}. Other bfd files have
5872 a built-in location; they will be restored at offset @var{bias}
5875 If @var{start} and/or @var{end} are non-zero, then only data between
5876 file offset @var{start} and file offset @var{end} will be restored.
5877 These offsets are relative to the addresses in the file, before
5878 the @var{bias} argument is applied.
5883 @chapter C Preprocessor Macros
5885 Some languages, such as C and C++, provide a way to define and invoke
5886 ``preprocessor macros'' which expand into strings of tokens.
5887 @value{GDBN} can evaluate expressions containing macro invocations, show
5888 the result of macro expansion, and show a macro's definition, including
5889 where it was defined.
5891 You may need to compile your program specially to provide @value{GDBN}
5892 with information about preprocessor macros. Most compilers do not
5893 include macros in their debugging information, even when you compile
5894 with the @option{-g} flag. @xref{Compilation}.
5896 A program may define a macro at one point, remove that definition later,
5897 and then provide a different definition after that. Thus, at different
5898 points in the program, a macro may have different definitions, or have
5899 no definition at all. If there is a current stack frame, @value{GDBN}
5900 uses the macros in scope at that frame's source code line. Otherwise,
5901 @value{GDBN} uses the macros in scope at the current listing location;
5904 At the moment, @value{GDBN} does not support the @code{##}
5905 token-splicing operator, the @code{#} stringification operator, or
5906 variable-arity macros.
5908 Whenever @value{GDBN} evaluates an expression, it always expands any
5909 macro invocations present in the expression. @value{GDBN} also provides
5910 the following commands for working with macros explicitly.
5914 @kindex macro expand
5915 @cindex macro expansion, showing the results of preprocessor
5916 @cindex preprocessor macro expansion, showing the results of
5917 @cindex expanding preprocessor macros
5918 @item macro expand @var{expression}
5919 @itemx macro exp @var{expression}
5920 Show the results of expanding all preprocessor macro invocations in
5921 @var{expression}. Since @value{GDBN} simply expands macros, but does
5922 not parse the result, @var{expression} need not be a valid expression;
5923 it can be any string of tokens.
5925 @kindex macro expand-once
5926 @item macro expand-once @var{expression}
5927 @itemx macro exp1 @var{expression}
5928 @i{(This command is not yet implemented.)} Show the results of
5929 expanding those preprocessor macro invocations that appear explicitly in
5930 @var{expression}. Macro invocations appearing in that expansion are
5931 left unchanged. This command allows you to see the effect of a
5932 particular macro more clearly, without being confused by further
5933 expansions. Since @value{GDBN} simply expands macros, but does not
5934 parse the result, @var{expression} need not be a valid expression; it
5935 can be any string of tokens.
5938 @cindex macro definition, showing
5939 @cindex definition, showing a macro's
5940 @item info macro @var{macro}
5941 Show the definition of the macro named @var{macro}, and describe the
5942 source location where that definition was established.
5944 @kindex macro define
5945 @cindex user-defined macros
5946 @cindex defining macros interactively
5947 @cindex macros, user-defined
5948 @item macro define @var{macro} @var{replacement-list}
5949 @itemx macro define @var{macro}(@var{arglist}) @var{replacement-list}
5950 @i{(This command is not yet implemented.)} Introduce a definition for a
5951 preprocessor macro named @var{macro}, invocations of which are replaced
5952 by the tokens given in @var{replacement-list}. The first form of this
5953 command defines an ``object-like'' macro, which takes no arguments; the
5954 second form defines a ``function-like'' macro, which takes the arguments
5955 given in @var{arglist}.
5957 A definition introduced by this command is in scope in every expression
5958 evaluated in @value{GDBN}, until it is removed with the @command{macro
5959 undef} command, described below. The definition overrides all
5960 definitions for @var{macro} present in the program being debugged, as
5961 well as any previous user-supplied definition.
5964 @item macro undef @var{macro}
5965 @i{(This command is not yet implemented.)} Remove any user-supplied
5966 definition for the macro named @var{macro}. This command only affects
5967 definitions provided with the @command{macro define} command, described
5968 above; it cannot remove definitions present in the program being
5973 @cindex macros, example of debugging with
5974 Here is a transcript showing the above commands in action. First, we
5975 show our source files:
5983 #define ADD(x) (M + x)
5988 printf ("Hello, world!\n");
5990 printf ("We're so creative.\n");
5992 printf ("Goodbye, world!\n");
5999 Now, we compile the program using the @sc{gnu} C compiler, @value{NGCC}.
6000 We pass the @option{-gdwarf-2} and @option{-g3} flags to ensure the
6001 compiler includes information about preprocessor macros in the debugging
6005 $ gcc -gdwarf-2 -g3 sample.c -o sample
6009 Now, we start @value{GDBN} on our sample program:
6013 GNU gdb 2002-05-06-cvs
6014 Copyright 2002 Free Software Foundation, Inc.
6015 GDB is free software, @dots{}
6019 We can expand macros and examine their definitions, even when the
6020 program is not running. @value{GDBN} uses the current listing position
6021 to decide which macro definitions are in scope:
6027 5 #define ADD(x) (M + x)
6032 10 printf ("Hello, world!\n");
6034 12 printf ("We're so creative.\n");
6035 (gdb) info macro ADD
6036 Defined at /home/jimb/gdb/macros/play/sample.c:5
6037 #define ADD(x) (M + x)
6039 Defined at /home/jimb/gdb/macros/play/sample.h:1
6040 included at /home/jimb/gdb/macros/play/sample.c:2
6042 (gdb) macro expand ADD(1)
6043 expands to: (42 + 1)
6044 (gdb) macro expand-once ADD(1)
6045 expands to: once (M + 1)
6049 In the example above, note that @command{macro expand-once} expands only
6050 the macro invocation explicit in the original text --- the invocation of
6051 @code{ADD} --- but does not expand the invocation of the macro @code{M},
6052 which was introduced by @code{ADD}.
6054 Once the program is running, GDB uses the macro definitions in force at
6055 the source line of the current stack frame:
6059 Breakpoint 1 at 0x8048370: file sample.c, line 10.
6061 Starting program: /home/jimb/gdb/macros/play/sample
6063 Breakpoint 1, main () at sample.c:10
6064 10 printf ("Hello, world!\n");
6068 At line 10, the definition of the macro @code{N} at line 9 is in force:
6072 Defined at /home/jimb/gdb/macros/play/sample.c:9
6074 (gdb) macro expand N Q M
6081 As we step over directives that remove @code{N}'s definition, and then
6082 give it a new definition, @value{GDBN} finds the definition (or lack
6083 thereof) in force at each point:
6088 12 printf ("We're so creative.\n");
6090 The symbol `N' has no definition as a C/C++ preprocessor macro
6091 at /home/jimb/gdb/macros/play/sample.c:12
6094 14 printf ("Goodbye, world!\n");
6096 Defined at /home/jimb/gdb/macros/play/sample.c:13
6098 (gdb) macro expand N Q M
6099 expands to: 1729 < 42
6107 @chapter Tracepoints
6108 @c This chapter is based on the documentation written by Michael
6109 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
6112 In some applications, it is not feasible for the debugger to interrupt
6113 the program's execution long enough for the developer to learn
6114 anything helpful about its behavior. If the program's correctness
6115 depends on its real-time behavior, delays introduced by a debugger
6116 might cause the program to change its behavior drastically, or perhaps
6117 fail, even when the code itself is correct. It is useful to be able
6118 to observe the program's behavior without interrupting it.
6120 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
6121 specify locations in the program, called @dfn{tracepoints}, and
6122 arbitrary expressions to evaluate when those tracepoints are reached.
6123 Later, using the @code{tfind} command, you can examine the values
6124 those expressions had when the program hit the tracepoints. The
6125 expressions may also denote objects in memory---structures or arrays,
6126 for example---whose values @value{GDBN} should record; while visiting
6127 a particular tracepoint, you may inspect those objects as if they were
6128 in memory at that moment. However, because @value{GDBN} records these
6129 values without interacting with you, it can do so quickly and
6130 unobtrusively, hopefully not disturbing the program's behavior.
6132 The tracepoint facility is currently available only for remote
6133 targets. @xref{Targets}. In addition, your remote target must know how
6134 to collect trace data. This functionality is implemented in the remote
6135 stub; however, none of the stubs distributed with @value{GDBN} support
6136 tracepoints as of this writing.
6138 This chapter describes the tracepoint commands and features.
6142 * Analyze Collected Data::
6143 * Tracepoint Variables::
6146 @node Set Tracepoints
6147 @section Commands to Set Tracepoints
6149 Before running such a @dfn{trace experiment}, an arbitrary number of
6150 tracepoints can be set. Like a breakpoint (@pxref{Set Breaks}), a
6151 tracepoint has a number assigned to it by @value{GDBN}. Like with
6152 breakpoints, tracepoint numbers are successive integers starting from
6153 one. Many of the commands associated with tracepoints take the
6154 tracepoint number as their argument, to identify which tracepoint to
6157 For each tracepoint, you can specify, in advance, some arbitrary set
6158 of data that you want the target to collect in the trace buffer when
6159 it hits that tracepoint. The collected data can include registers,
6160 local variables, or global data. Later, you can use @value{GDBN}
6161 commands to examine the values these data had at the time the
6164 This section describes commands to set tracepoints and associated
6165 conditions and actions.
6168 * Create and Delete Tracepoints::
6169 * Enable and Disable Tracepoints::
6170 * Tracepoint Passcounts::
6171 * Tracepoint Actions::
6172 * Listing Tracepoints::
6173 * Starting and Stopping Trace Experiment::
6176 @node Create and Delete Tracepoints
6177 @subsection Create and Delete Tracepoints
6180 @cindex set tracepoint
6183 The @code{trace} command is very similar to the @code{break} command.
6184 Its argument can be a source line, a function name, or an address in
6185 the target program. @xref{Set Breaks}. The @code{trace} command
6186 defines a tracepoint, which is a point in the target program where the
6187 debugger will briefly stop, collect some data, and then allow the
6188 program to continue. Setting a tracepoint or changing its commands
6189 doesn't take effect until the next @code{tstart} command; thus, you
6190 cannot change the tracepoint attributes once a trace experiment is
6193 Here are some examples of using the @code{trace} command:
6196 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
6198 (@value{GDBP}) @b{trace +2} // 2 lines forward
6200 (@value{GDBP}) @b{trace my_function} // first source line of function
6202 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
6204 (@value{GDBP}) @b{trace *0x2117c4} // an address
6208 You can abbreviate @code{trace} as @code{tr}.
6211 @cindex last tracepoint number
6212 @cindex recent tracepoint number
6213 @cindex tracepoint number
6214 The convenience variable @code{$tpnum} records the tracepoint number
6215 of the most recently set tracepoint.
6217 @kindex delete tracepoint
6218 @cindex tracepoint deletion
6219 @item delete tracepoint @r{[}@var{num}@r{]}
6220 Permanently delete one or more tracepoints. With no argument, the
6221 default is to delete all tracepoints.
6226 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
6228 (@value{GDBP}) @b{delete trace} // remove all tracepoints
6232 You can abbreviate this command as @code{del tr}.
6235 @node Enable and Disable Tracepoints
6236 @subsection Enable and Disable Tracepoints
6239 @kindex disable tracepoint
6240 @item disable tracepoint @r{[}@var{num}@r{]}
6241 Disable tracepoint @var{num}, or all tracepoints if no argument
6242 @var{num} is given. A disabled tracepoint will have no effect during
6243 the next trace experiment, but it is not forgotten. You can re-enable
6244 a disabled tracepoint using the @code{enable tracepoint} command.
6246 @kindex enable tracepoint
6247 @item enable tracepoint @r{[}@var{num}@r{]}
6248 Enable tracepoint @var{num}, or all tracepoints. The enabled
6249 tracepoints will become effective the next time a trace experiment is
6253 @node Tracepoint Passcounts
6254 @subsection Tracepoint Passcounts
6258 @cindex tracepoint pass count
6259 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
6260 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
6261 automatically stop a trace experiment. If a tracepoint's passcount is
6262 @var{n}, then the trace experiment will be automatically stopped on
6263 the @var{n}'th time that tracepoint is hit. If the tracepoint number
6264 @var{num} is not specified, the @code{passcount} command sets the
6265 passcount of the most recently defined tracepoint. If no passcount is
6266 given, the trace experiment will run until stopped explicitly by the
6272 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of
6273 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// tracepoint 2}
6275 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
6276 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// most recently defined tracepoint.}
6277 (@value{GDBP}) @b{trace foo}
6278 (@value{GDBP}) @b{pass 3}
6279 (@value{GDBP}) @b{trace bar}
6280 (@value{GDBP}) @b{pass 2}
6281 (@value{GDBP}) @b{trace baz}
6282 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
6283 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// executed 3 times OR when bar has}
6284 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// been executed 2 times}
6285 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// OR when baz has been executed 1 time.}
6289 @node Tracepoint Actions
6290 @subsection Tracepoint Action Lists
6294 @cindex tracepoint actions
6295 @item actions @r{[}@var{num}@r{]}
6296 This command will prompt for a list of actions to be taken when the
6297 tracepoint is hit. If the tracepoint number @var{num} is not
6298 specified, this command sets the actions for the one that was most
6299 recently defined (so that you can define a tracepoint and then say
6300 @code{actions} without bothering about its number). You specify the
6301 actions themselves on the following lines, one action at a time, and
6302 terminate the actions list with a line containing just @code{end}. So
6303 far, the only defined actions are @code{collect} and
6304 @code{while-stepping}.
6306 @cindex remove actions from a tracepoint
6307 To remove all actions from a tracepoint, type @samp{actions @var{num}}
6308 and follow it immediately with @samp{end}.
6311 (@value{GDBP}) @b{collect @var{data}} // collect some data
6313 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times, collect data
6315 (@value{GDBP}) @b{end} // signals the end of actions.
6318 In the following example, the action list begins with @code{collect}
6319 commands indicating the things to be collected when the tracepoint is
6320 hit. Then, in order to single-step and collect additional data
6321 following the tracepoint, a @code{while-stepping} command is used,
6322 followed by the list of things to be collected while stepping. The
6323 @code{while-stepping} command is terminated by its own separate
6324 @code{end} command. Lastly, the action list is terminated by an
6328 (@value{GDBP}) @b{trace foo}
6329 (@value{GDBP}) @b{actions}
6330 Enter actions for tracepoint 1, one per line:
6339 @kindex collect @r{(tracepoints)}
6340 @item collect @var{expr1}, @var{expr2}, @dots{}
6341 Collect values of the given expressions when the tracepoint is hit.
6342 This command accepts a comma-separated list of any valid expressions.
6343 In addition to global, static, or local variables, the following
6344 special arguments are supported:
6348 collect all registers
6351 collect all function arguments
6354 collect all local variables.
6357 You can give several consecutive @code{collect} commands, each one
6358 with a single argument, or one @code{collect} command with several
6359 arguments separated by commas: the effect is the same.
6361 The command @code{info scope} (@pxref{Symbols, info scope}) is
6362 particularly useful for figuring out what data to collect.
6364 @kindex while-stepping @r{(tracepoints)}
6365 @item while-stepping @var{n}
6366 Perform @var{n} single-step traces after the tracepoint, collecting
6367 new data at each step. The @code{while-stepping} command is
6368 followed by the list of what to collect while stepping (followed by
6369 its own @code{end} command):
6373 > collect $regs, myglobal
6379 You may abbreviate @code{while-stepping} as @code{ws} or
6383 @node Listing Tracepoints
6384 @subsection Listing Tracepoints
6387 @kindex info tracepoints
6388 @cindex information about tracepoints
6389 @item info tracepoints @r{[}@var{num}@r{]}
6390 Display information about the tracepoint @var{num}. If you don't specify
6391 a tracepoint number, displays information about all the tracepoints
6392 defined so far. For each tracepoint, the following information is
6399 whether it is enabled or disabled
6403 its passcount as given by the @code{passcount @var{n}} command
6405 its step count as given by the @code{while-stepping @var{n}} command
6407 where in the source files is the tracepoint set
6409 its action list as given by the @code{actions} command
6413 (@value{GDBP}) @b{info trace}
6414 Num Enb Address PassC StepC What
6415 1 y 0x002117c4 0 0 <gdb_asm>
6416 2 y 0x0020dc64 0 0 in g_test at g_test.c:1375
6417 3 y 0x0020b1f4 0 0 in get_data at ../foo.c:41
6422 This command can be abbreviated @code{info tp}.
6425 @node Starting and Stopping Trace Experiment
6426 @subsection Starting and Stopping Trace Experiment
6430 @cindex start a new trace experiment
6431 @cindex collected data discarded
6433 This command takes no arguments. It starts the trace experiment, and
6434 begins collecting data. This has the side effect of discarding all
6435 the data collected in the trace buffer during the previous trace
6439 @cindex stop a running trace experiment
6441 This command takes no arguments. It ends the trace experiment, and
6442 stops collecting data.
6444 @strong{Note:} a trace experiment and data collection may stop
6445 automatically if any tracepoint's passcount is reached
6446 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
6449 @cindex status of trace data collection
6450 @cindex trace experiment, status of
6452 This command displays the status of the current trace data
6456 Here is an example of the commands we described so far:
6459 (@value{GDBP}) @b{trace gdb_c_test}
6460 (@value{GDBP}) @b{actions}
6461 Enter actions for tracepoint #1, one per line.
6462 > collect $regs,$locals,$args
6467 (@value{GDBP}) @b{tstart}
6468 [time passes @dots{}]
6469 (@value{GDBP}) @b{tstop}
6473 @node Analyze Collected Data
6474 @section Using the collected data
6476 After the tracepoint experiment ends, you use @value{GDBN} commands
6477 for examining the trace data. The basic idea is that each tracepoint
6478 collects a trace @dfn{snapshot} every time it is hit and another
6479 snapshot every time it single-steps. All these snapshots are
6480 consecutively numbered from zero and go into a buffer, and you can
6481 examine them later. The way you examine them is to @dfn{focus} on a
6482 specific trace snapshot. When the remote stub is focused on a trace
6483 snapshot, it will respond to all @value{GDBN} requests for memory and
6484 registers by reading from the buffer which belongs to that snapshot,
6485 rather than from @emph{real} memory or registers of the program being
6486 debugged. This means that @strong{all} @value{GDBN} commands
6487 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
6488 behave as if we were currently debugging the program state as it was
6489 when the tracepoint occurred. Any requests for data that are not in
6490 the buffer will fail.
6493 * tfind:: How to select a trace snapshot
6494 * tdump:: How to display all data for a snapshot
6495 * save-tracepoints:: How to save tracepoints for a future run
6499 @subsection @code{tfind @var{n}}
6502 @cindex select trace snapshot
6503 @cindex find trace snapshot
6504 The basic command for selecting a trace snapshot from the buffer is
6505 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
6506 counting from zero. If no argument @var{n} is given, the next
6507 snapshot is selected.
6509 Here are the various forms of using the @code{tfind} command.
6513 Find the first snapshot in the buffer. This is a synonym for
6514 @code{tfind 0} (since 0 is the number of the first snapshot).
6517 Stop debugging trace snapshots, resume @emph{live} debugging.
6520 Same as @samp{tfind none}.
6523 No argument means find the next trace snapshot.
6526 Find the previous trace snapshot before the current one. This permits
6527 retracing earlier steps.
6529 @item tfind tracepoint @var{num}
6530 Find the next snapshot associated with tracepoint @var{num}. Search
6531 proceeds forward from the last examined trace snapshot. If no
6532 argument @var{num} is given, it means find the next snapshot collected
6533 for the same tracepoint as the current snapshot.
6535 @item tfind pc @var{addr}
6536 Find the next snapshot associated with the value @var{addr} of the
6537 program counter. Search proceeds forward from the last examined trace
6538 snapshot. If no argument @var{addr} is given, it means find the next
6539 snapshot with the same value of PC as the current snapshot.
6541 @item tfind outside @var{addr1}, @var{addr2}
6542 Find the next snapshot whose PC is outside the given range of
6545 @item tfind range @var{addr1}, @var{addr2}
6546 Find the next snapshot whose PC is between @var{addr1} and
6547 @var{addr2}. @c FIXME: Is the range inclusive or exclusive?
6549 @item tfind line @r{[}@var{file}:@r{]}@var{n}
6550 Find the next snapshot associated with the source line @var{n}. If
6551 the optional argument @var{file} is given, refer to line @var{n} in
6552 that source file. Search proceeds forward from the last examined
6553 trace snapshot. If no argument @var{n} is given, it means find the
6554 next line other than the one currently being examined; thus saying
6555 @code{tfind line} repeatedly can appear to have the same effect as
6556 stepping from line to line in a @emph{live} debugging session.
6559 The default arguments for the @code{tfind} commands are specifically
6560 designed to make it easy to scan through the trace buffer. For
6561 instance, @code{tfind} with no argument selects the next trace
6562 snapshot, and @code{tfind -} with no argument selects the previous
6563 trace snapshot. So, by giving one @code{tfind} command, and then
6564 simply hitting @key{RET} repeatedly you can examine all the trace
6565 snapshots in order. Or, by saying @code{tfind -} and then hitting
6566 @key{RET} repeatedly you can examine the snapshots in reverse order.
6567 The @code{tfind line} command with no argument selects the snapshot
6568 for the next source line executed. The @code{tfind pc} command with
6569 no argument selects the next snapshot with the same program counter
6570 (PC) as the current frame. The @code{tfind tracepoint} command with
6571 no argument selects the next trace snapshot collected by the same
6572 tracepoint as the current one.
6574 In addition to letting you scan through the trace buffer manually,
6575 these commands make it easy to construct @value{GDBN} scripts that
6576 scan through the trace buffer and print out whatever collected data
6577 you are interested in. Thus, if we want to examine the PC, FP, and SP
6578 registers from each trace frame in the buffer, we can say this:
6581 (@value{GDBP}) @b{tfind start}
6582 (@value{GDBP}) @b{while ($trace_frame != -1)}
6583 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
6584 $trace_frame, $pc, $sp, $fp
6588 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
6589 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
6590 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
6591 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
6592 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
6593 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
6594 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
6595 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
6596 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
6597 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
6598 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
6601 Or, if we want to examine the variable @code{X} at each source line in
6605 (@value{GDBP}) @b{tfind start}
6606 (@value{GDBP}) @b{while ($trace_frame != -1)}
6607 > printf "Frame %d, X == %d\n", $trace_frame, X
6617 @subsection @code{tdump}
6619 @cindex dump all data collected at tracepoint
6620 @cindex tracepoint data, display
6622 This command takes no arguments. It prints all the data collected at
6623 the current trace snapshot.
6626 (@value{GDBP}) @b{trace 444}
6627 (@value{GDBP}) @b{actions}
6628 Enter actions for tracepoint #2, one per line:
6629 > collect $regs, $locals, $args, gdb_long_test
6632 (@value{GDBP}) @b{tstart}
6634 (@value{GDBP}) @b{tfind line 444}
6635 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
6637 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
6639 (@value{GDBP}) @b{tdump}
6640 Data collected at tracepoint 2, trace frame 1:
6641 d0 0xc4aa0085 -995491707
6645 d4 0x71aea3d 119204413
6650 a1 0x3000668 50333288
6653 a4 0x3000698 50333336
6655 fp 0x30bf3c 0x30bf3c
6656 sp 0x30bf34 0x30bf34
6658 pc 0x20b2c8 0x20b2c8
6662 p = 0x20e5b4 "gdb-test"
6669 gdb_long_test = 17 '\021'
6674 @node save-tracepoints
6675 @subsection @code{save-tracepoints @var{filename}}
6676 @kindex save-tracepoints
6677 @cindex save tracepoints for future sessions
6679 This command saves all current tracepoint definitions together with
6680 their actions and passcounts, into a file @file{@var{filename}}
6681 suitable for use in a later debugging session. To read the saved
6682 tracepoint definitions, use the @code{source} command (@pxref{Command
6685 @node Tracepoint Variables
6686 @section Convenience Variables for Tracepoints
6687 @cindex tracepoint variables
6688 @cindex convenience variables for tracepoints
6691 @vindex $trace_frame
6692 @item (int) $trace_frame
6693 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
6694 snapshot is selected.
6697 @item (int) $tracepoint
6698 The tracepoint for the current trace snapshot.
6701 @item (int) $trace_line
6702 The line number for the current trace snapshot.
6705 @item (char []) $trace_file
6706 The source file for the current trace snapshot.
6709 @item (char []) $trace_func
6710 The name of the function containing @code{$tracepoint}.
6713 Note: @code{$trace_file} is not suitable for use in @code{printf},
6714 use @code{output} instead.
6716 Here's a simple example of using these convenience variables for
6717 stepping through all the trace snapshots and printing some of their
6721 (@value{GDBP}) @b{tfind start}
6723 (@value{GDBP}) @b{while $trace_frame != -1}
6724 > output $trace_file
6725 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
6731 @chapter Debugging Programs That Use Overlays
6734 If your program is too large to fit completely in your target system's
6735 memory, you can sometimes use @dfn{overlays} to work around this
6736 problem. @value{GDBN} provides some support for debugging programs that
6740 * How Overlays Work:: A general explanation of overlays.
6741 * Overlay Commands:: Managing overlays in @value{GDBN}.
6742 * Automatic Overlay Debugging:: @value{GDBN} can find out which overlays are
6743 mapped by asking the inferior.
6744 * Overlay Sample Program:: A sample program using overlays.
6747 @node How Overlays Work
6748 @section How Overlays Work
6749 @cindex mapped overlays
6750 @cindex unmapped overlays
6751 @cindex load address, overlay's
6752 @cindex mapped address
6753 @cindex overlay area
6755 Suppose you have a computer whose instruction address space is only 64
6756 kilobytes long, but which has much more memory which can be accessed by
6757 other means: special instructions, segment registers, or memory
6758 management hardware, for example. Suppose further that you want to
6759 adapt a program which is larger than 64 kilobytes to run on this system.
6761 One solution is to identify modules of your program which are relatively
6762 independent, and need not call each other directly; call these modules
6763 @dfn{overlays}. Separate the overlays from the main program, and place
6764 their machine code in the larger memory. Place your main program in
6765 instruction memory, but leave at least enough space there to hold the
6766 largest overlay as well.
6768 Now, to call a function located in an overlay, you must first copy that
6769 overlay's machine code from the large memory into the space set aside
6770 for it in the instruction memory, and then jump to its entry point
6773 @c NB: In the below the mapped area's size is greater or equal to the
6774 @c size of all overlays. This is intentional to remind the developer
6775 @c that overlays don't necessarily need to be the same size.
6779 Data Instruction Larger
6780 Address Space Address Space Address Space
6781 +-----------+ +-----------+ +-----------+
6783 +-----------+ +-----------+ +-----------+<-- overlay 1
6784 | program | | main | .----| overlay 1 | load address
6785 | variables | | program | | +-----------+
6786 | and heap | | | | | |
6787 +-----------+ | | | +-----------+<-- overlay 2
6788 | | +-----------+ | | | load address
6789 +-----------+ | | | .-| overlay 2 |
6791 mapped --->+-----------+ | | +-----------+
6793 | overlay | <-' | | |
6794 | area | <---' +-----------+<-- overlay 3
6795 | | <---. | | load address
6796 +-----------+ `--| overlay 3 |
6803 @anchor{A code overlay}A code overlay
6807 The diagram (@pxref{A code overlay}) shows a system with separate data
6808 and instruction address spaces. To map an overlay, the program copies
6809 its code from the larger address space to the instruction address space.
6810 Since the overlays shown here all use the same mapped address, only one
6811 may be mapped at a time. For a system with a single address space for
6812 data and instructions, the diagram would be similar, except that the
6813 program variables and heap would share an address space with the main
6814 program and the overlay area.
6816 An overlay loaded into instruction memory and ready for use is called a
6817 @dfn{mapped} overlay; its @dfn{mapped address} is its address in the
6818 instruction memory. An overlay not present (or only partially present)
6819 in instruction memory is called @dfn{unmapped}; its @dfn{load address}
6820 is its address in the larger memory. The mapped address is also called
6821 the @dfn{virtual memory address}, or @dfn{VMA}; the load address is also
6822 called the @dfn{load memory address}, or @dfn{LMA}.
6824 Unfortunately, overlays are not a completely transparent way to adapt a
6825 program to limited instruction memory. They introduce a new set of
6826 global constraints you must keep in mind as you design your program:
6831 Before calling or returning to a function in an overlay, your program
6832 must make sure that overlay is actually mapped. Otherwise, the call or
6833 return will transfer control to the right address, but in the wrong
6834 overlay, and your program will probably crash.
6837 If the process of mapping an overlay is expensive on your system, you
6838 will need to choose your overlays carefully to minimize their effect on
6839 your program's performance.
6842 The executable file you load onto your system must contain each
6843 overlay's instructions, appearing at the overlay's load address, not its
6844 mapped address. However, each overlay's instructions must be relocated
6845 and its symbols defined as if the overlay were at its mapped address.
6846 You can use GNU linker scripts to specify different load and relocation
6847 addresses for pieces of your program; see @ref{Overlay Description,,,
6848 ld.info, Using ld: the GNU linker}.
6851 The procedure for loading executable files onto your system must be able
6852 to load their contents into the larger address space as well as the
6853 instruction and data spaces.
6857 The overlay system described above is rather simple, and could be
6858 improved in many ways:
6863 If your system has suitable bank switch registers or memory management
6864 hardware, you could use those facilities to make an overlay's load area
6865 contents simply appear at their mapped address in instruction space.
6866 This would probably be faster than copying the overlay to its mapped
6867 area in the usual way.
6870 If your overlays are small enough, you could set aside more than one
6871 overlay area, and have more than one overlay mapped at a time.
6874 You can use overlays to manage data, as well as instructions. In
6875 general, data overlays are even less transparent to your design than
6876 code overlays: whereas code overlays only require care when you call or
6877 return to functions, data overlays require care every time you access
6878 the data. Also, if you change the contents of a data overlay, you
6879 must copy its contents back out to its load address before you can copy a
6880 different data overlay into the same mapped area.
6885 @node Overlay Commands
6886 @section Overlay Commands
6888 To use @value{GDBN}'s overlay support, each overlay in your program must
6889 correspond to a separate section of the executable file. The section's
6890 virtual memory address and load memory address must be the overlay's
6891 mapped and load addresses. Identifying overlays with sections allows
6892 @value{GDBN} to determine the appropriate address of a function or
6893 variable, depending on whether the overlay is mapped or not.
6895 @value{GDBN}'s overlay commands all start with the word @code{overlay};
6896 you can abbreviate this as @code{ov} or @code{ovly}. The commands are:
6901 Disable @value{GDBN}'s overlay support. When overlay support is
6902 disabled, @value{GDBN} assumes that all functions and variables are
6903 always present at their mapped addresses. By default, @value{GDBN}'s
6904 overlay support is disabled.
6906 @item overlay manual
6907 @kindex overlay manual
6908 @cindex manual overlay debugging
6909 Enable @dfn{manual} overlay debugging. In this mode, @value{GDBN}
6910 relies on you to tell it which overlays are mapped, and which are not,
6911 using the @code{overlay map-overlay} and @code{overlay unmap-overlay}
6912 commands described below.
6914 @item overlay map-overlay @var{overlay}
6915 @itemx overlay map @var{overlay}
6916 @kindex overlay map-overlay
6917 @cindex map an overlay
6918 Tell @value{GDBN} that @var{overlay} is now mapped; @var{overlay} must
6919 be the name of the object file section containing the overlay. When an
6920 overlay is mapped, @value{GDBN} assumes it can find the overlay's
6921 functions and variables at their mapped addresses. @value{GDBN} assumes
6922 that any other overlays whose mapped ranges overlap that of
6923 @var{overlay} are now unmapped.
6925 @item overlay unmap-overlay @var{overlay}
6926 @itemx overlay unmap @var{overlay}
6927 @kindex overlay unmap-overlay
6928 @cindex unmap an overlay
6929 Tell @value{GDBN} that @var{overlay} is no longer mapped; @var{overlay}
6930 must be the name of the object file section containing the overlay.
6931 When an overlay is unmapped, @value{GDBN} assumes it can find the
6932 overlay's functions and variables at their load addresses.
6935 @kindex overlay auto
6936 Enable @dfn{automatic} overlay debugging. In this mode, @value{GDBN}
6937 consults a data structure the overlay manager maintains in the inferior
6938 to see which overlays are mapped. For details, see @ref{Automatic
6941 @item overlay load-target
6943 @kindex overlay load-target
6944 @cindex reloading the overlay table
6945 Re-read the overlay table from the inferior. Normally, @value{GDBN}
6946 re-reads the table @value{GDBN} automatically each time the inferior
6947 stops, so this command should only be necessary if you have changed the
6948 overlay mapping yourself using @value{GDBN}. This command is only
6949 useful when using automatic overlay debugging.
6951 @item overlay list-overlays
6953 @cindex listing mapped overlays
6954 Display a list of the overlays currently mapped, along with their mapped
6955 addresses, load addresses, and sizes.
6959 Normally, when @value{GDBN} prints a code address, it includes the name
6960 of the function the address falls in:
6964 $3 = @{int ()@} 0x11a0 <main>
6967 When overlay debugging is enabled, @value{GDBN} recognizes code in
6968 unmapped overlays, and prints the names of unmapped functions with
6969 asterisks around them. For example, if @code{foo} is a function in an
6970 unmapped overlay, @value{GDBN} prints it this way:
6974 No sections are mapped.
6976 $5 = @{int (int)@} 0x100000 <*foo*>
6979 When @code{foo}'s overlay is mapped, @value{GDBN} prints the function's
6984 Section .ov.foo.text, loaded at 0x100000 - 0x100034,
6985 mapped at 0x1016 - 0x104a
6987 $6 = @{int (int)@} 0x1016 <foo>
6990 When overlay debugging is enabled, @value{GDBN} can find the correct
6991 address for functions and variables in an overlay, whether or not the
6992 overlay is mapped. This allows most @value{GDBN} commands, like
6993 @code{break} and @code{disassemble}, to work normally, even on unmapped
6994 code. However, @value{GDBN}'s breakpoint support has some limitations:
6998 @cindex breakpoints in overlays
6999 @cindex overlays, setting breakpoints in
7000 You can set breakpoints in functions in unmapped overlays, as long as
7001 @value{GDBN} can write to the overlay at its load address.
7003 @value{GDBN} can not set hardware or simulator-based breakpoints in
7004 unmapped overlays. However, if you set a breakpoint at the end of your
7005 overlay manager (and tell @value{GDBN} which overlays are now mapped, if
7006 you are using manual overlay management), @value{GDBN} will re-set its
7007 breakpoints properly.
7011 @node Automatic Overlay Debugging
7012 @section Automatic Overlay Debugging
7013 @cindex automatic overlay debugging
7015 @value{GDBN} can automatically track which overlays are mapped and which
7016 are not, given some simple co-operation from the overlay manager in the
7017 inferior. If you enable automatic overlay debugging with the
7018 @code{overlay auto} command (@pxref{Overlay Commands}), @value{GDBN}
7019 looks in the inferior's memory for certain variables describing the
7020 current state of the overlays.
7022 Here are the variables your overlay manager must define to support
7023 @value{GDBN}'s automatic overlay debugging:
7027 @item @code{_ovly_table}:
7028 This variable must be an array of the following structures:
7033 /* The overlay's mapped address. */
7036 /* The size of the overlay, in bytes. */
7039 /* The overlay's load address. */
7042 /* Non-zero if the overlay is currently mapped;
7044 unsigned long mapped;
7048 @item @code{_novlys}:
7049 This variable must be a four-byte signed integer, holding the total
7050 number of elements in @code{_ovly_table}.
7054 To decide whether a particular overlay is mapped or not, @value{GDBN}
7055 looks for an entry in @w{@code{_ovly_table}} whose @code{vma} and
7056 @code{lma} members equal the VMA and LMA of the overlay's section in the
7057 executable file. When @value{GDBN} finds a matching entry, it consults
7058 the entry's @code{mapped} member to determine whether the overlay is
7061 In addition, your overlay manager may define a function called
7062 @code{_ovly_debug_event}. If this function is defined, @value{GDBN}
7063 will silently set a breakpoint there. If the overlay manager then
7064 calls this function whenever it has changed the overlay table, this
7065 will enable @value{GDBN} to accurately keep track of which overlays
7066 are in program memory, and update any breakpoints that may be set
7067 in overlays. This will allow breakpoints to work even if the
7068 overlays are kept in ROM or other non-writable memory while they
7069 are not being executed.
7071 @node Overlay Sample Program
7072 @section Overlay Sample Program
7073 @cindex overlay example program
7075 When linking a program which uses overlays, you must place the overlays
7076 at their load addresses, while relocating them to run at their mapped
7077 addresses. To do this, you must write a linker script (@pxref{Overlay
7078 Description,,, ld.info, Using ld: the GNU linker}). Unfortunately,
7079 since linker scripts are specific to a particular host system, target
7080 architecture, and target memory layout, this manual cannot provide
7081 portable sample code demonstrating @value{GDBN}'s overlay support.
7083 However, the @value{GDBN} source distribution does contain an overlaid
7084 program, with linker scripts for a few systems, as part of its test
7085 suite. The program consists of the following files from
7086 @file{gdb/testsuite/gdb.base}:
7090 The main program file.
7092 A simple overlay manager, used by @file{overlays.c}.
7097 Overlay modules, loaded and used by @file{overlays.c}.
7100 Linker scripts for linking the test program on the @code{d10v-elf}
7101 and @code{m32r-elf} targets.
7104 You can build the test program using the @code{d10v-elf} GCC
7105 cross-compiler like this:
7108 $ d10v-elf-gcc -g -c overlays.c
7109 $ d10v-elf-gcc -g -c ovlymgr.c
7110 $ d10v-elf-gcc -g -c foo.c
7111 $ d10v-elf-gcc -g -c bar.c
7112 $ d10v-elf-gcc -g -c baz.c
7113 $ d10v-elf-gcc -g -c grbx.c
7114 $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
7115 baz.o grbx.o -Wl,-Td10v.ld -o overlays
7118 The build process is identical for any other architecture, except that
7119 you must substitute the appropriate compiler and linker script for the
7120 target system for @code{d10v-elf-gcc} and @code{d10v.ld}.
7124 @chapter Using @value{GDBN} with Different Languages
7127 Although programming languages generally have common aspects, they are
7128 rarely expressed in the same manner. For instance, in ANSI C,
7129 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
7130 Modula-2, it is accomplished by @code{p^}. Values can also be
7131 represented (and displayed) differently. Hex numbers in C appear as
7132 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
7134 @cindex working language
7135 Language-specific information is built into @value{GDBN} for some languages,
7136 allowing you to express operations like the above in your program's
7137 native language, and allowing @value{GDBN} to output values in a manner
7138 consistent with the syntax of your program's native language. The
7139 language you use to build expressions is called the @dfn{working
7143 * Setting:: Switching between source languages
7144 * Show:: Displaying the language
7145 * Checks:: Type and range checks
7146 * Support:: Supported languages
7150 @section Switching between source languages
7152 There are two ways to control the working language---either have @value{GDBN}
7153 set it automatically, or select it manually yourself. You can use the
7154 @code{set language} command for either purpose. On startup, @value{GDBN}
7155 defaults to setting the language automatically. The working language is
7156 used to determine how expressions you type are interpreted, how values
7159 In addition to the working language, every source file that
7160 @value{GDBN} knows about has its own working language. For some object
7161 file formats, the compiler might indicate which language a particular
7162 source file is in. However, most of the time @value{GDBN} infers the
7163 language from the name of the file. The language of a source file
7164 controls whether C@t{++} names are demangled---this way @code{backtrace} can
7165 show each frame appropriately for its own language. There is no way to
7166 set the language of a source file from within @value{GDBN}, but you can
7167 set the language associated with a filename extension. @xref{Show, ,
7168 Displaying the language}.
7170 This is most commonly a problem when you use a program, such
7171 as @code{cfront} or @code{f2c}, that generates C but is written in
7172 another language. In that case, make the
7173 program use @code{#line} directives in its C output; that way
7174 @value{GDBN} will know the correct language of the source code of the original
7175 program, and will display that source code, not the generated C code.
7178 * Filenames:: Filename extensions and languages.
7179 * Manually:: Setting the working language manually
7180 * Automatically:: Having @value{GDBN} infer the source language
7184 @subsection List of filename extensions and languages
7186 If a source file name ends in one of the following extensions, then
7187 @value{GDBN} infers that its language is the one indicated.
7206 @c OBSOLETE @item .ch
7207 @c OBSOLETE @itemx .c186
7208 @c OBSOLETE @itemx .c286
7209 @c OBSOLETE CHILL source file
7212 Modula-2 source file
7216 Assembler source file. This actually behaves almost like C, but
7217 @value{GDBN} does not skip over function prologues when stepping.
7220 In addition, you may set the language associated with a filename
7221 extension. @xref{Show, , Displaying the language}.
7224 @subsection Setting the working language
7226 If you allow @value{GDBN} to set the language automatically,
7227 expressions are interpreted the same way in your debugging session and
7230 @kindex set language
7231 If you wish, you may set the language manually. To do this, issue the
7232 command @samp{set language @var{lang}}, where @var{lang} is the name of
7234 @code{c} or @code{modula-2}.
7235 For a list of the supported languages, type @samp{set language}.
7237 Setting the language manually prevents @value{GDBN} from updating the working
7238 language automatically. This can lead to confusion if you try
7239 to debug a program when the working language is not the same as the
7240 source language, when an expression is acceptable to both
7241 languages---but means different things. For instance, if the current
7242 source file were written in C, and @value{GDBN} was parsing Modula-2, a
7250 might not have the effect you intended. In C, this means to add
7251 @code{b} and @code{c} and place the result in @code{a}. The result
7252 printed would be the value of @code{a}. In Modula-2, this means to compare
7253 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
7256 @subsection Having @value{GDBN} infer the source language
7258 To have @value{GDBN} set the working language automatically, use
7259 @samp{set language local} or @samp{set language auto}. @value{GDBN}
7260 then infers the working language. That is, when your program stops in a
7261 frame (usually by encountering a breakpoint), @value{GDBN} sets the
7262 working language to the language recorded for the function in that
7263 frame. If the language for a frame is unknown (that is, if the function
7264 or block corresponding to the frame was defined in a source file that
7265 does not have a recognized extension), the current working language is
7266 not changed, and @value{GDBN} issues a warning.
7268 This may not seem necessary for most programs, which are written
7269 entirely in one source language. However, program modules and libraries
7270 written in one source language can be used by a main program written in
7271 a different source language. Using @samp{set language auto} in this
7272 case frees you from having to set the working language manually.
7275 @section Displaying the language
7277 The following commands help you find out which language is the
7278 working language, and also what language source files were written in.
7280 @kindex show language
7281 @kindex info frame@r{, show the source language}
7282 @kindex info source@r{, show the source language}
7285 Display the current working language. This is the
7286 language you can use with commands such as @code{print} to
7287 build and compute expressions that may involve variables in your program.
7290 Display the source language for this frame. This language becomes the
7291 working language if you use an identifier from this frame.
7292 @xref{Frame Info, ,Information about a frame}, to identify the other
7293 information listed here.
7296 Display the source language of this source file.
7297 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
7298 information listed here.
7301 In unusual circumstances, you may have source files with extensions
7302 not in the standard list. You can then set the extension associated
7303 with a language explicitly:
7305 @kindex set extension-language
7306 @kindex info extensions
7308 @item set extension-language @var{.ext} @var{language}
7309 Set source files with extension @var{.ext} to be assumed to be in
7310 the source language @var{language}.
7312 @item info extensions
7313 List all the filename extensions and the associated languages.
7317 @section Type and range checking
7320 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
7321 checking are included, but they do not yet have any effect. This
7322 section documents the intended facilities.
7324 @c FIXME remove warning when type/range code added
7326 Some languages are designed to guard you against making seemingly common
7327 errors through a series of compile- and run-time checks. These include
7328 checking the type of arguments to functions and operators, and making
7329 sure mathematical overflows are caught at run time. Checks such as
7330 these help to ensure a program's correctness once it has been compiled
7331 by eliminating type mismatches, and providing active checks for range
7332 errors when your program is running.
7334 @value{GDBN} can check for conditions like the above if you wish.
7335 Although @value{GDBN} does not check the statements in your program, it
7336 can check expressions entered directly into @value{GDBN} for evaluation via
7337 the @code{print} command, for example. As with the working language,
7338 @value{GDBN} can also decide whether or not to check automatically based on
7339 your program's source language. @xref{Support, ,Supported languages},
7340 for the default settings of supported languages.
7343 * Type Checking:: An overview of type checking
7344 * Range Checking:: An overview of range checking
7347 @cindex type checking
7348 @cindex checks, type
7350 @subsection An overview of type checking
7352 Some languages, such as Modula-2, are strongly typed, meaning that the
7353 arguments to operators and functions have to be of the correct type,
7354 otherwise an error occurs. These checks prevent type mismatch
7355 errors from ever causing any run-time problems. For example,
7363 The second example fails because the @code{CARDINAL} 1 is not
7364 type-compatible with the @code{REAL} 2.3.
7366 For the expressions you use in @value{GDBN} commands, you can tell the
7367 @value{GDBN} type checker to skip checking;
7368 to treat any mismatches as errors and abandon the expression;
7369 or to only issue warnings when type mismatches occur,
7370 but evaluate the expression anyway. When you choose the last of
7371 these, @value{GDBN} evaluates expressions like the second example above, but
7372 also issues a warning.
7374 Even if you turn type checking off, there may be other reasons
7375 related to type that prevent @value{GDBN} from evaluating an expression.
7376 For instance, @value{GDBN} does not know how to add an @code{int} and
7377 a @code{struct foo}. These particular type errors have nothing to do
7378 with the language in use, and usually arise from expressions, such as
7379 the one described above, which make little sense to evaluate anyway.
7381 Each language defines to what degree it is strict about type. For
7382 instance, both Modula-2 and C require the arguments to arithmetical
7383 operators to be numbers. In C, enumerated types and pointers can be
7384 represented as numbers, so that they are valid arguments to mathematical
7385 operators. @xref{Support, ,Supported languages}, for further
7386 details on specific languages.
7388 @value{GDBN} provides some additional commands for controlling the type checker:
7390 @kindex set check@r{, type}
7391 @kindex set check type
7392 @kindex show check type
7394 @item set check type auto
7395 Set type checking on or off based on the current working language.
7396 @xref{Support, ,Supported languages}, for the default settings for
7399 @item set check type on
7400 @itemx set check type off
7401 Set type checking on or off, overriding the default setting for the
7402 current working language. Issue a warning if the setting does not
7403 match the language default. If any type mismatches occur in
7404 evaluating an expression while type checking is on, @value{GDBN} prints a
7405 message and aborts evaluation of the expression.
7407 @item set check type warn
7408 Cause the type checker to issue warnings, but to always attempt to
7409 evaluate the expression. Evaluating the expression may still
7410 be impossible for other reasons. For example, @value{GDBN} cannot add
7411 numbers and structures.
7414 Show the current setting of the type checker, and whether or not @value{GDBN}
7415 is setting it automatically.
7418 @cindex range checking
7419 @cindex checks, range
7420 @node Range Checking
7421 @subsection An overview of range checking
7423 In some languages (such as Modula-2), it is an error to exceed the
7424 bounds of a type; this is enforced with run-time checks. Such range
7425 checking is meant to ensure program correctness by making sure
7426 computations do not overflow, or indices on an array element access do
7427 not exceed the bounds of the array.
7429 For expressions you use in @value{GDBN} commands, you can tell
7430 @value{GDBN} to treat range errors in one of three ways: ignore them,
7431 always treat them as errors and abandon the expression, or issue
7432 warnings but evaluate the expression anyway.
7434 A range error can result from numerical overflow, from exceeding an
7435 array index bound, or when you type a constant that is not a member
7436 of any type. Some languages, however, do not treat overflows as an
7437 error. In many implementations of C, mathematical overflow causes the
7438 result to ``wrap around'' to lower values---for example, if @var{m} is
7439 the largest integer value, and @var{s} is the smallest, then
7442 @var{m} + 1 @result{} @var{s}
7445 This, too, is specific to individual languages, and in some cases
7446 specific to individual compilers or machines. @xref{Support, ,
7447 Supported languages}, for further details on specific languages.
7449 @value{GDBN} provides some additional commands for controlling the range checker:
7451 @kindex set check@r{, range}
7452 @kindex set check range
7453 @kindex show check range
7455 @item set check range auto
7456 Set range checking on or off based on the current working language.
7457 @xref{Support, ,Supported languages}, for the default settings for
7460 @item set check range on
7461 @itemx set check range off
7462 Set range checking on or off, overriding the default setting for the
7463 current working language. A warning is issued if the setting does not
7464 match the language default. If a range error occurs and range checking is on,
7465 then a message is printed and evaluation of the expression is aborted.
7467 @item set check range warn
7468 Output messages when the @value{GDBN} range checker detects a range error,
7469 but attempt to evaluate the expression anyway. Evaluating the
7470 expression may still be impossible for other reasons, such as accessing
7471 memory that the process does not own (a typical example from many Unix
7475 Show the current setting of the range checker, and whether or not it is
7476 being set automatically by @value{GDBN}.
7480 @section Supported languages
7482 @value{GDBN} supports C, C@t{++}, Fortran, Java,
7484 assembly, and Modula-2.
7485 @c This is false ...
7486 Some @value{GDBN} features may be used in expressions regardless of the
7487 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
7488 and the @samp{@{type@}addr} construct (@pxref{Expressions,
7489 ,Expressions}) can be used with the constructs of any supported
7492 The following sections detail to what degree each source language is
7493 supported by @value{GDBN}. These sections are not meant to be language
7494 tutorials or references, but serve only as a reference guide to what the
7495 @value{GDBN} expression parser accepts, and what input and output
7496 formats should look like for different languages. There are many good
7497 books written on each of these languages; please look to these for a
7498 language reference or tutorial.
7502 * Modula-2:: Modula-2
7503 @c OBSOLETE * Chill:: Chill
7507 @subsection C and C@t{++}
7509 @cindex C and C@t{++}
7510 @cindex expressions in C or C@t{++}
7512 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
7513 to both languages. Whenever this is the case, we discuss those languages
7517 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
7518 @cindex @sc{gnu} C@t{++}
7519 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
7520 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
7521 effectively, you must compile your C@t{++} programs with a supported
7522 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
7523 compiler (@code{aCC}).
7525 For best results when using @sc{gnu} C@t{++}, use the stabs debugging
7526 format. You can select that format explicitly with the @code{g++}
7527 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
7528 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
7529 CC, gcc.info, Using @sc{gnu} CC}, for more information.
7532 * C Operators:: C and C@t{++} operators
7533 * C Constants:: C and C@t{++} constants
7534 * C plus plus expressions:: C@t{++} expressions
7535 * C Defaults:: Default settings for C and C@t{++}
7536 * C Checks:: C and C@t{++} type and range checks
7537 * Debugging C:: @value{GDBN} and C
7538 * Debugging C plus plus:: @value{GDBN} features for C@t{++}
7542 @subsubsection C and C@t{++} operators
7544 @cindex C and C@t{++} operators
7546 Operators must be defined on values of specific types. For instance,
7547 @code{+} is defined on numbers, but not on structures. Operators are
7548 often defined on groups of types.
7550 For the purposes of C and C@t{++}, the following definitions hold:
7555 @emph{Integral types} include @code{int} with any of its storage-class
7556 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
7559 @emph{Floating-point types} include @code{float}, @code{double}, and
7560 @code{long double} (if supported by the target platform).
7563 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
7566 @emph{Scalar types} include all of the above.
7571 The following operators are supported. They are listed here
7572 in order of increasing precedence:
7576 The comma or sequencing operator. Expressions in a comma-separated list
7577 are evaluated from left to right, with the result of the entire
7578 expression being the last expression evaluated.
7581 Assignment. The value of an assignment expression is the value
7582 assigned. Defined on scalar types.
7585 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
7586 and translated to @w{@code{@var{a} = @var{a op b}}}.
7587 @w{@code{@var{op}=}} and @code{=} have the same precedence.
7588 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
7589 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
7592 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
7593 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
7597 Logical @sc{or}. Defined on integral types.
7600 Logical @sc{and}. Defined on integral types.
7603 Bitwise @sc{or}. Defined on integral types.
7606 Bitwise exclusive-@sc{or}. Defined on integral types.
7609 Bitwise @sc{and}. Defined on integral types.
7612 Equality and inequality. Defined on scalar types. The value of these
7613 expressions is 0 for false and non-zero for true.
7615 @item <@r{, }>@r{, }<=@r{, }>=
7616 Less than, greater than, less than or equal, greater than or equal.
7617 Defined on scalar types. The value of these expressions is 0 for false
7618 and non-zero for true.
7621 left shift, and right shift. Defined on integral types.
7624 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
7627 Addition and subtraction. Defined on integral types, floating-point types and
7630 @item *@r{, }/@r{, }%
7631 Multiplication, division, and modulus. Multiplication and division are
7632 defined on integral and floating-point types. Modulus is defined on
7636 Increment and decrement. When appearing before a variable, the
7637 operation is performed before the variable is used in an expression;
7638 when appearing after it, the variable's value is used before the
7639 operation takes place.
7642 Pointer dereferencing. Defined on pointer types. Same precedence as
7646 Address operator. Defined on variables. Same precedence as @code{++}.
7648 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
7649 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
7650 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
7651 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
7655 Negative. Defined on integral and floating-point types. Same
7656 precedence as @code{++}.
7659 Logical negation. Defined on integral types. Same precedence as
7663 Bitwise complement operator. Defined on integral types. Same precedence as
7668 Structure member, and pointer-to-structure member. For convenience,
7669 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
7670 pointer based on the stored type information.
7671 Defined on @code{struct} and @code{union} data.
7674 Dereferences of pointers to members.
7677 Array indexing. @code{@var{a}[@var{i}]} is defined as
7678 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
7681 Function parameter list. Same precedence as @code{->}.
7684 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
7685 and @code{class} types.
7688 Doubled colons also represent the @value{GDBN} scope operator
7689 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
7693 If an operator is redefined in the user code, @value{GDBN} usually
7694 attempts to invoke the redefined version instead of using the operator's
7702 @subsubsection C and C@t{++} constants
7704 @cindex C and C@t{++} constants
7706 @value{GDBN} allows you to express the constants of C and C@t{++} in the
7711 Integer constants are a sequence of digits. Octal constants are
7712 specified by a leading @samp{0} (i.e.@: zero), and hexadecimal constants
7713 by a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
7714 @samp{l}, specifying that the constant should be treated as a
7718 Floating point constants are a sequence of digits, followed by a decimal
7719 point, followed by a sequence of digits, and optionally followed by an
7720 exponent. An exponent is of the form:
7721 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
7722 sequence of digits. The @samp{+} is optional for positive exponents.
7723 A floating-point constant may also end with a letter @samp{f} or
7724 @samp{F}, specifying that the constant should be treated as being of
7725 the @code{float} (as opposed to the default @code{double}) type; or with
7726 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
7730 Enumerated constants consist of enumerated identifiers, or their
7731 integral equivalents.
7734 Character constants are a single character surrounded by single quotes
7735 (@code{'}), or a number---the ordinal value of the corresponding character
7736 (usually its @sc{ascii} value). Within quotes, the single character may
7737 be represented by a letter or by @dfn{escape sequences}, which are of
7738 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
7739 of the character's ordinal value; or of the form @samp{\@var{x}}, where
7740 @samp{@var{x}} is a predefined special character---for example,
7741 @samp{\n} for newline.
7744 String constants are a sequence of character constants surrounded by
7745 double quotes (@code{"}). Any valid character constant (as described
7746 above) may appear. Double quotes within the string must be preceded by
7747 a backslash, so for instance @samp{"a\"b'c"} is a string of five
7751 Pointer constants are an integral value. You can also write pointers
7752 to constants using the C operator @samp{&}.
7755 Array constants are comma-separated lists surrounded by braces @samp{@{}
7756 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
7757 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
7758 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
7762 * C plus plus expressions::
7769 @node C plus plus expressions
7770 @subsubsection C@t{++} expressions
7772 @cindex expressions in C@t{++}
7773 @value{GDBN} expression handling can interpret most C@t{++} expressions.
7775 @cindex C@t{++} support, not in @sc{coff}
7776 @cindex @sc{coff} versus C@t{++}
7777 @cindex C@t{++} and object formats
7778 @cindex object formats and C@t{++}
7779 @cindex a.out and C@t{++}
7780 @cindex @sc{ecoff} and C@t{++}
7781 @cindex @sc{xcoff} and C@t{++}
7782 @cindex @sc{elf}/stabs and C@t{++}
7783 @cindex @sc{elf}/@sc{dwarf} and C@t{++}
7784 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
7785 @c periodically whether this has happened...
7787 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the
7788 proper compiler. Typically, C@t{++} debugging depends on the use of
7789 additional debugging information in the symbol table, and thus requires
7790 special support. In particular, if your compiler generates a.out, MIPS
7791 @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the
7792 symbol table, these facilities are all available. (With @sc{gnu} CC,
7793 you can use the @samp{-gstabs} option to request stabs debugging
7794 extensions explicitly.) Where the object code format is standard
7795 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C@t{++}
7796 support in @value{GDBN} does @emph{not} work.
7801 @cindex member functions
7803 Member function calls are allowed; you can use expressions like
7806 count = aml->GetOriginal(x, y)
7809 @vindex this@r{, inside C@t{++} member functions}
7810 @cindex namespace in C@t{++}
7812 While a member function is active (in the selected stack frame), your
7813 expressions have the same namespace available as the member function;
7814 that is, @value{GDBN} allows implicit references to the class instance
7815 pointer @code{this} following the same rules as C@t{++}.
7817 @cindex call overloaded functions
7818 @cindex overloaded functions, calling
7819 @cindex type conversions in C@t{++}
7821 You can call overloaded functions; @value{GDBN} resolves the function
7822 call to the right definition, with some restrictions. @value{GDBN} does not
7823 perform overload resolution involving user-defined type conversions,
7824 calls to constructors, or instantiations of templates that do not exist
7825 in the program. It also cannot handle ellipsis argument lists or
7828 It does perform integral conversions and promotions, floating-point
7829 promotions, arithmetic conversions, pointer conversions, conversions of
7830 class objects to base classes, and standard conversions such as those of
7831 functions or arrays to pointers; it requires an exact match on the
7832 number of function arguments.
7834 Overload resolution is always performed, unless you have specified
7835 @code{set overload-resolution off}. @xref{Debugging C plus plus,
7836 ,@value{GDBN} features for C@t{++}}.
7838 You must specify @code{set overload-resolution off} in order to use an
7839 explicit function signature to call an overloaded function, as in
7841 p 'foo(char,int)'('x', 13)
7844 The @value{GDBN} command-completion facility can simplify this;
7845 see @ref{Completion, ,Command completion}.
7847 @cindex reference declarations
7849 @value{GDBN} understands variables declared as C@t{++} references; you can use
7850 them in expressions just as you do in C@t{++} source---they are automatically
7853 In the parameter list shown when @value{GDBN} displays a frame, the values of
7854 reference variables are not displayed (unlike other variables); this
7855 avoids clutter, since references are often used for large structures.
7856 The @emph{address} of a reference variable is always shown, unless
7857 you have specified @samp{set print address off}.
7860 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
7861 expressions can use it just as expressions in your program do. Since
7862 one scope may be defined in another, you can use @code{::} repeatedly if
7863 necessary, for example in an expression like
7864 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
7865 resolving name scope by reference to source files, in both C and C@t{++}
7866 debugging (@pxref{Variables, ,Program variables}).
7869 In addition, when used with HP's C@t{++} compiler, @value{GDBN} supports
7870 calling virtual functions correctly, printing out virtual bases of
7871 objects, calling functions in a base subobject, casting objects, and
7872 invoking user-defined operators.
7875 @subsubsection C and C@t{++} defaults
7877 @cindex C and C@t{++} defaults
7879 If you allow @value{GDBN} to set type and range checking automatically, they
7880 both default to @code{off} whenever the working language changes to
7881 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
7882 selects the working language.
7884 If you allow @value{GDBN} to set the language automatically, it
7885 recognizes source files whose names end with @file{.c}, @file{.C}, or
7886 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
7887 these files, it sets the working language to C or C@t{++}.
7888 @xref{Automatically, ,Having @value{GDBN} infer the source language},
7889 for further details.
7891 @c Type checking is (a) primarily motivated by Modula-2, and (b)
7892 @c unimplemented. If (b) changes, it might make sense to let this node
7893 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
7896 @subsubsection C and C@t{++} type and range checks
7898 @cindex C and C@t{++} checks
7900 By default, when @value{GDBN} parses C or C@t{++} expressions, type checking
7901 is not used. However, if you turn type checking on, @value{GDBN}
7902 considers two variables type equivalent if:
7906 The two variables are structured and have the same structure, union, or
7910 The two variables have the same type name, or types that have been
7911 declared equivalent through @code{typedef}.
7914 @c leaving this out because neither J Gilmore nor R Pesch understand it.
7917 The two @code{struct}, @code{union}, or @code{enum} variables are
7918 declared in the same declaration. (Note: this may not be true for all C
7923 Range checking, if turned on, is done on mathematical operations. Array
7924 indices are not checked, since they are often used to index a pointer
7925 that is not itself an array.
7928 @subsubsection @value{GDBN} and C
7930 The @code{set print union} and @code{show print union} commands apply to
7931 the @code{union} type. When set to @samp{on}, any @code{union} that is
7932 inside a @code{struct} or @code{class} is also printed. Otherwise, it
7933 appears as @samp{@{...@}}.
7935 The @code{@@} operator aids in the debugging of dynamic arrays, formed
7936 with pointers and a memory allocation function. @xref{Expressions,
7940 * Debugging C plus plus::
7943 @node Debugging C plus plus
7944 @subsubsection @value{GDBN} features for C@t{++}
7946 @cindex commands for C@t{++}
7948 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
7949 designed specifically for use with C@t{++}. Here is a summary:
7952 @cindex break in overloaded functions
7953 @item @r{breakpoint menus}
7954 When you want a breakpoint in a function whose name is overloaded,
7955 @value{GDBN} breakpoint menus help you specify which function definition
7956 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
7958 @cindex overloading in C@t{++}
7959 @item rbreak @var{regex}
7960 Setting breakpoints using regular expressions is helpful for setting
7961 breakpoints on overloaded functions that are not members of any special
7963 @xref{Set Breaks, ,Setting breakpoints}.
7965 @cindex C@t{++} exception handling
7968 Debug C@t{++} exception handling using these commands. @xref{Set
7969 Catchpoints, , Setting catchpoints}.
7972 @item ptype @var{typename}
7973 Print inheritance relationships as well as other information for type
7975 @xref{Symbols, ,Examining the Symbol Table}.
7977 @cindex C@t{++} symbol display
7978 @item set print demangle
7979 @itemx show print demangle
7980 @itemx set print asm-demangle
7981 @itemx show print asm-demangle
7982 Control whether C@t{++} symbols display in their source form, both when
7983 displaying code as C@t{++} source and when displaying disassemblies.
7984 @xref{Print Settings, ,Print settings}.
7986 @item set print object
7987 @itemx show print object
7988 Choose whether to print derived (actual) or declared types of objects.
7989 @xref{Print Settings, ,Print settings}.
7991 @item set print vtbl
7992 @itemx show print vtbl
7993 Control the format for printing virtual function tables.
7994 @xref{Print Settings, ,Print settings}.
7995 (The @code{vtbl} commands do not work on programs compiled with the HP
7996 ANSI C@t{++} compiler (@code{aCC}).)
7998 @kindex set overload-resolution
7999 @cindex overloaded functions, overload resolution
8000 @item set overload-resolution on
8001 Enable overload resolution for C@t{++} expression evaluation. The default
8002 is on. For overloaded functions, @value{GDBN} evaluates the arguments
8003 and searches for a function whose signature matches the argument types,
8004 using the standard C@t{++} conversion rules (see @ref{C plus plus expressions, ,C@t{++}
8005 expressions}, for details). If it cannot find a match, it emits a
8008 @item set overload-resolution off
8009 Disable overload resolution for C@t{++} expression evaluation. For
8010 overloaded functions that are not class member functions, @value{GDBN}
8011 chooses the first function of the specified name that it finds in the
8012 symbol table, whether or not its arguments are of the correct type. For
8013 overloaded functions that are class member functions, @value{GDBN}
8014 searches for a function whose signature @emph{exactly} matches the
8017 @item @r{Overloaded symbol names}
8018 You can specify a particular definition of an overloaded symbol, using
8019 the same notation that is used to declare such symbols in C@t{++}: type
8020 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
8021 also use the @value{GDBN} command-line word completion facilities to list the
8022 available choices, or to finish the type list for you.
8023 @xref{Completion,, Command completion}, for details on how to do this.
8027 @subsection Modula-2
8029 @cindex Modula-2, @value{GDBN} support
8031 The extensions made to @value{GDBN} to support Modula-2 only support
8032 output from the @sc{gnu} Modula-2 compiler (which is currently being
8033 developed). Other Modula-2 compilers are not currently supported, and
8034 attempting to debug executables produced by them is most likely
8035 to give an error as @value{GDBN} reads in the executable's symbol
8038 @cindex expressions in Modula-2
8040 * M2 Operators:: Built-in operators
8041 * Built-In Func/Proc:: Built-in functions and procedures
8042 * M2 Constants:: Modula-2 constants
8043 * M2 Defaults:: Default settings for Modula-2
8044 * Deviations:: Deviations from standard Modula-2
8045 * M2 Checks:: Modula-2 type and range checks
8046 * M2 Scope:: The scope operators @code{::} and @code{.}
8047 * GDB/M2:: @value{GDBN} and Modula-2
8051 @subsubsection Operators
8052 @cindex Modula-2 operators
8054 Operators must be defined on values of specific types. For instance,
8055 @code{+} is defined on numbers, but not on structures. Operators are
8056 often defined on groups of types. For the purposes of Modula-2, the
8057 following definitions hold:
8062 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
8066 @emph{Character types} consist of @code{CHAR} and its subranges.
8069 @emph{Floating-point types} consist of @code{REAL}.
8072 @emph{Pointer types} consist of anything declared as @code{POINTER TO
8076 @emph{Scalar types} consist of all of the above.
8079 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
8082 @emph{Boolean types} consist of @code{BOOLEAN}.
8086 The following operators are supported, and appear in order of
8087 increasing precedence:
8091 Function argument or array index separator.
8094 Assignment. The value of @var{var} @code{:=} @var{value} is
8098 Less than, greater than on integral, floating-point, or enumerated
8102 Less than or equal to, greater than or equal to
8103 on integral, floating-point and enumerated types, or set inclusion on
8104 set types. Same precedence as @code{<}.
8106 @item =@r{, }<>@r{, }#
8107 Equality and two ways of expressing inequality, valid on scalar types.
8108 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
8109 available for inequality, since @code{#} conflicts with the script
8113 Set membership. Defined on set types and the types of their members.
8114 Same precedence as @code{<}.
8117 Boolean disjunction. Defined on boolean types.
8120 Boolean conjunction. Defined on boolean types.
8123 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
8126 Addition and subtraction on integral and floating-point types, or union
8127 and difference on set types.
8130 Multiplication on integral and floating-point types, or set intersection
8134 Division on floating-point types, or symmetric set difference on set
8135 types. Same precedence as @code{*}.
8138 Integer division and remainder. Defined on integral types. Same
8139 precedence as @code{*}.
8142 Negative. Defined on @code{INTEGER} and @code{REAL} data.
8145 Pointer dereferencing. Defined on pointer types.
8148 Boolean negation. Defined on boolean types. Same precedence as
8152 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
8153 precedence as @code{^}.
8156 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
8159 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
8163 @value{GDBN} and Modula-2 scope operators.
8167 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
8168 treats the use of the operator @code{IN}, or the use of operators
8169 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
8170 @code{<=}, and @code{>=} on sets as an error.
8174 @node Built-In Func/Proc
8175 @subsubsection Built-in functions and procedures
8176 @cindex Modula-2 built-ins
8178 Modula-2 also makes available several built-in procedures and functions.
8179 In describing these, the following metavariables are used:
8184 represents an @code{ARRAY} variable.
8187 represents a @code{CHAR} constant or variable.
8190 represents a variable or constant of integral type.
8193 represents an identifier that belongs to a set. Generally used in the
8194 same function with the metavariable @var{s}. The type of @var{s} should
8195 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
8198 represents a variable or constant of integral or floating-point type.
8201 represents a variable or constant of floating-point type.
8207 represents a variable.
8210 represents a variable or constant of one of many types. See the
8211 explanation of the function for details.
8214 All Modula-2 built-in procedures also return a result, described below.
8218 Returns the absolute value of @var{n}.
8221 If @var{c} is a lower case letter, it returns its upper case
8222 equivalent, otherwise it returns its argument.
8225 Returns the character whose ordinal value is @var{i}.
8228 Decrements the value in the variable @var{v} by one. Returns the new value.
8230 @item DEC(@var{v},@var{i})
8231 Decrements the value in the variable @var{v} by @var{i}. Returns the
8234 @item EXCL(@var{m},@var{s})
8235 Removes the element @var{m} from the set @var{s}. Returns the new
8238 @item FLOAT(@var{i})
8239 Returns the floating point equivalent of the integer @var{i}.
8242 Returns the index of the last member of @var{a}.
8245 Increments the value in the variable @var{v} by one. Returns the new value.
8247 @item INC(@var{v},@var{i})
8248 Increments the value in the variable @var{v} by @var{i}. Returns the
8251 @item INCL(@var{m},@var{s})
8252 Adds the element @var{m} to the set @var{s} if it is not already
8253 there. Returns the new set.
8256 Returns the maximum value of the type @var{t}.
8259 Returns the minimum value of the type @var{t}.
8262 Returns boolean TRUE if @var{i} is an odd number.
8265 Returns the ordinal value of its argument. For example, the ordinal
8266 value of a character is its @sc{ascii} value (on machines supporting the
8267 @sc{ascii} character set). @var{x} must be of an ordered type, which include
8268 integral, character and enumerated types.
8271 Returns the size of its argument. @var{x} can be a variable or a type.
8273 @item TRUNC(@var{r})
8274 Returns the integral part of @var{r}.
8276 @item VAL(@var{t},@var{i})
8277 Returns the member of the type @var{t} whose ordinal value is @var{i}.
8281 @emph{Warning:} Sets and their operations are not yet supported, so
8282 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
8286 @cindex Modula-2 constants
8288 @subsubsection Constants
8290 @value{GDBN} allows you to express the constants of Modula-2 in the following
8296 Integer constants are simply a sequence of digits. When used in an
8297 expression, a constant is interpreted to be type-compatible with the
8298 rest of the expression. Hexadecimal integers are specified by a
8299 trailing @samp{H}, and octal integers by a trailing @samp{B}.
8302 Floating point constants appear as a sequence of digits, followed by a
8303 decimal point and another sequence of digits. An optional exponent can
8304 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
8305 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
8306 digits of the floating point constant must be valid decimal (base 10)
8310 Character constants consist of a single character enclosed by a pair of
8311 like quotes, either single (@code{'}) or double (@code{"}). They may
8312 also be expressed by their ordinal value (their @sc{ascii} value, usually)
8313 followed by a @samp{C}.
8316 String constants consist of a sequence of characters enclosed by a
8317 pair of like quotes, either single (@code{'}) or double (@code{"}).
8318 Escape sequences in the style of C are also allowed. @xref{C
8319 Constants, ,C and C@t{++} constants}, for a brief explanation of escape
8323 Enumerated constants consist of an enumerated identifier.
8326 Boolean constants consist of the identifiers @code{TRUE} and
8330 Pointer constants consist of integral values only.
8333 Set constants are not yet supported.
8337 @subsubsection Modula-2 defaults
8338 @cindex Modula-2 defaults
8340 If type and range checking are set automatically by @value{GDBN}, they
8341 both default to @code{on} whenever the working language changes to
8342 Modula-2. This happens regardless of whether you or @value{GDBN}
8343 selected the working language.
8345 If you allow @value{GDBN} to set the language automatically, then entering
8346 code compiled from a file whose name ends with @file{.mod} sets the
8347 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
8348 the language automatically}, for further details.
8351 @subsubsection Deviations from standard Modula-2
8352 @cindex Modula-2, deviations from
8354 A few changes have been made to make Modula-2 programs easier to debug.
8355 This is done primarily via loosening its type strictness:
8359 Unlike in standard Modula-2, pointer constants can be formed by
8360 integers. This allows you to modify pointer variables during
8361 debugging. (In standard Modula-2, the actual address contained in a
8362 pointer variable is hidden from you; it can only be modified
8363 through direct assignment to another pointer variable or expression that
8364 returned a pointer.)
8367 C escape sequences can be used in strings and characters to represent
8368 non-printable characters. @value{GDBN} prints out strings with these
8369 escape sequences embedded. Single non-printable characters are
8370 printed using the @samp{CHR(@var{nnn})} format.
8373 The assignment operator (@code{:=}) returns the value of its right-hand
8377 All built-in procedures both modify @emph{and} return their argument.
8381 @subsubsection Modula-2 type and range checks
8382 @cindex Modula-2 checks
8385 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
8388 @c FIXME remove warning when type/range checks added
8390 @value{GDBN} considers two Modula-2 variables type equivalent if:
8394 They are of types that have been declared equivalent via a @code{TYPE
8395 @var{t1} = @var{t2}} statement
8398 They have been declared on the same line. (Note: This is true of the
8399 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
8402 As long as type checking is enabled, any attempt to combine variables
8403 whose types are not equivalent is an error.
8405 Range checking is done on all mathematical operations, assignment, array
8406 index bounds, and all built-in functions and procedures.
8409 @subsubsection The scope operators @code{::} and @code{.}
8411 @cindex @code{.}, Modula-2 scope operator
8412 @cindex colon, doubled as scope operator
8414 @vindex colon-colon@r{, in Modula-2}
8415 @c Info cannot handle :: but TeX can.
8418 @vindex ::@r{, in Modula-2}
8421 There are a few subtle differences between the Modula-2 scope operator
8422 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
8427 @var{module} . @var{id}
8428 @var{scope} :: @var{id}
8432 where @var{scope} is the name of a module or a procedure,
8433 @var{module} the name of a module, and @var{id} is any declared
8434 identifier within your program, except another module.
8436 Using the @code{::} operator makes @value{GDBN} search the scope
8437 specified by @var{scope} for the identifier @var{id}. If it is not
8438 found in the specified scope, then @value{GDBN} searches all scopes
8439 enclosing the one specified by @var{scope}.
8441 Using the @code{.} operator makes @value{GDBN} search the current scope for
8442 the identifier specified by @var{id} that was imported from the
8443 definition module specified by @var{module}. With this operator, it is
8444 an error if the identifier @var{id} was not imported from definition
8445 module @var{module}, or if @var{id} is not an identifier in
8449 @subsubsection @value{GDBN} and Modula-2
8451 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
8452 Five subcommands of @code{set print} and @code{show print} apply
8453 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
8454 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
8455 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
8456 analogue in Modula-2.
8458 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
8459 with any language, is not useful with Modula-2. Its
8460 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
8461 created in Modula-2 as they can in C or C@t{++}. However, because an
8462 address can be specified by an integral constant, the construct
8463 @samp{@{@var{type}@}@var{adrexp}} is still useful.
8465 @cindex @code{#} in Modula-2
8466 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
8467 interpreted as the beginning of a comment. Use @code{<>} instead.
8469 @c OBSOLETE @node Chill
8470 @c OBSOLETE @subsection Chill
8472 @c OBSOLETE The extensions made to @value{GDBN} to support Chill only support output
8473 @c OBSOLETE from the @sc{gnu} Chill compiler. Other Chill compilers are not currently
8474 @c OBSOLETE supported, and attempting to debug executables produced by them is most
8475 @c OBSOLETE likely to give an error as @value{GDBN} reads in the executable's symbol
8478 @c OBSOLETE @c This used to say "... following Chill related topics ...", but since
8479 @c OBSOLETE @c menus are not shown in the printed manual, it would look awkward.
8480 @c OBSOLETE This section covers the Chill related topics and the features
8481 @c OBSOLETE of @value{GDBN} which support these topics.
8484 @c OBSOLETE * How modes are displayed:: How modes are displayed
8485 @c OBSOLETE * Locations:: Locations and their accesses
8486 @c OBSOLETE * Values and their Operations:: Values and their Operations
8487 @c OBSOLETE * Chill type and range checks::
8488 @c OBSOLETE * Chill defaults::
8489 @c OBSOLETE @end menu
8491 @c OBSOLETE @node How modes are displayed
8492 @c OBSOLETE @subsubsection How modes are displayed
8494 @c OBSOLETE The Chill Datatype- (Mode) support of @value{GDBN} is directly related
8495 @c OBSOLETE with the functionality of the @sc{gnu} Chill compiler, and therefore deviates
8496 @c OBSOLETE slightly from the standard specification of the Chill language. The
8497 @c OBSOLETE provided modes are:
8499 @c OBSOLETE @c FIXME: this @table's contents effectively disable @code by using @r
8500 @c OBSOLETE @c on every @item. So why does it need @code?
8501 @c OBSOLETE @table @code
8502 @c OBSOLETE @item @r{@emph{Discrete modes:}}
8503 @c OBSOLETE @itemize @bullet
8505 @c OBSOLETE @emph{Integer Modes} which are predefined by @code{BYTE, UBYTE, INT,
8506 @c OBSOLETE UINT, LONG, ULONG},
8508 @c OBSOLETE @emph{Boolean Mode} which is predefined by @code{BOOL},
8510 @c OBSOLETE @emph{Character Mode} which is predefined by @code{CHAR},
8512 @c OBSOLETE @emph{Set Mode} which is displayed by the keyword @code{SET}.
8513 @c OBSOLETE @smallexample
8514 @c OBSOLETE (@value{GDBP}) ptype x
8515 @c OBSOLETE type = SET (karli = 10, susi = 20, fritzi = 100)
8516 @c OBSOLETE @end smallexample
8517 @c OBSOLETE If the type is an unnumbered set the set element values are omitted.
8519 @c OBSOLETE @emph{Range Mode} which is displayed by
8520 @c OBSOLETE @smallexample
8521 @c OBSOLETE @code{type = <basemode>(<lower bound> : <upper bound>)}
8522 @c OBSOLETE @end smallexample
8523 @c OBSOLETE where @code{<lower bound>, <upper bound>} can be of any discrete literal
8524 @c OBSOLETE expression (e.g. set element names).
8525 @c OBSOLETE @end itemize
8527 @c OBSOLETE @item @r{@emph{Powerset Mode:}}
8528 @c OBSOLETE A Powerset Mode is displayed by the keyword @code{POWERSET} followed by
8529 @c OBSOLETE the member mode of the powerset. The member mode can be any discrete mode.
8530 @c OBSOLETE @smallexample
8531 @c OBSOLETE (@value{GDBP}) ptype x
8532 @c OBSOLETE type = POWERSET SET (egon, hugo, otto)
8533 @c OBSOLETE @end smallexample
8535 @c OBSOLETE @item @r{@emph{Reference Modes:}}
8536 @c OBSOLETE @itemize @bullet
8538 @c OBSOLETE @emph{Bound Reference Mode} which is displayed by the keyword @code{REF}
8539 @c OBSOLETE followed by the mode name to which the reference is bound.
8541 @c OBSOLETE @emph{Free Reference Mode} which is displayed by the keyword @code{PTR}.
8542 @c OBSOLETE @end itemize
8544 @c OBSOLETE @item @r{@emph{Procedure mode}}
8545 @c OBSOLETE The procedure mode is displayed by @code{type = PROC(<parameter list>)
8546 @c OBSOLETE <return mode> EXCEPTIONS (<exception list>)}. The @code{<parameter
8547 @c OBSOLETE list>} is a list of the parameter modes. @code{<return mode>} indicates
8548 @c OBSOLETE the mode of the result of the procedure if any. The exceptionlist lists
8549 @c OBSOLETE all possible exceptions which can be raised by the procedure.
8552 @c OBSOLETE @item @r{@emph{Instance mode}}
8553 @c OBSOLETE The instance mode is represented by a structure, which has a static
8554 @c OBSOLETE type, and is therefore not really of interest.
8555 @c OBSOLETE @end ignore
8557 @c OBSOLETE @item @r{@emph{Synchronization Modes:}}
8558 @c OBSOLETE @itemize @bullet
8560 @c OBSOLETE @emph{Event Mode} which is displayed by
8561 @c OBSOLETE @smallexample
8562 @c OBSOLETE @code{EVENT (<event length>)}
8563 @c OBSOLETE @end smallexample
8564 @c OBSOLETE where @code{(<event length>)} is optional.
8566 @c OBSOLETE @emph{Buffer Mode} which is displayed by
8567 @c OBSOLETE @smallexample
8568 @c OBSOLETE @code{BUFFER (<buffer length>)<buffer element mode>}
8569 @c OBSOLETE @end smallexample
8570 @c OBSOLETE where @code{(<buffer length>)} is optional.
8571 @c OBSOLETE @end itemize
8573 @c OBSOLETE @item @r{@emph{Timing Modes:}}
8574 @c OBSOLETE @itemize @bullet
8576 @c OBSOLETE @emph{Duration Mode} which is predefined by @code{DURATION}
8578 @c OBSOLETE @emph{Absolute Time Mode} which is predefined by @code{TIME}
8579 @c OBSOLETE @end itemize
8581 @c OBSOLETE @item @r{@emph{Real Modes:}}
8582 @c OBSOLETE Real Modes are predefined with @code{REAL} and @code{LONG_REAL}.
8584 @c OBSOLETE @item @r{@emph{String Modes:}}
8585 @c OBSOLETE @itemize @bullet
8587 @c OBSOLETE @emph{Character String Mode} which is displayed by
8588 @c OBSOLETE @smallexample
8589 @c OBSOLETE @code{CHARS(<string length>)}
8590 @c OBSOLETE @end smallexample
8591 @c OBSOLETE followed by the keyword @code{VARYING} if the String Mode is a varying
8594 @c OBSOLETE @emph{Bit String Mode} which is displayed by
8595 @c OBSOLETE @smallexample
8596 @c OBSOLETE @code{BOOLS(<string
8597 @c OBSOLETE length>)}
8598 @c OBSOLETE @end smallexample
8599 @c OBSOLETE @end itemize
8601 @c OBSOLETE @item @r{@emph{Array Mode:}}
8602 @c OBSOLETE The Array Mode is displayed by the keyword @code{ARRAY(<range>)}
8603 @c OBSOLETE followed by the element mode (which may in turn be an array mode).
8604 @c OBSOLETE @smallexample
8605 @c OBSOLETE (@value{GDBP}) ptype x
8606 @c OBSOLETE type = ARRAY (1:42)
8607 @c OBSOLETE ARRAY (1:20)
8608 @c OBSOLETE SET (karli = 10, susi = 20, fritzi = 100)
8609 @c OBSOLETE @end smallexample
8611 @c OBSOLETE @item @r{@emph{Structure Mode}}
8612 @c OBSOLETE The Structure mode is displayed by the keyword @code{STRUCT(<field
8613 @c OBSOLETE list>)}. The @code{<field list>} consists of names and modes of fields
8614 @c OBSOLETE of the structure. Variant structures have the keyword @code{CASE <field>
8615 @c OBSOLETE OF <variant fields> ESAC} in their field list. Since the current version
8616 @c OBSOLETE of the GNU Chill compiler doesn't implement tag processing (no runtime
8617 @c OBSOLETE checks of variant fields, and therefore no debugging info), the output
8618 @c OBSOLETE always displays all variant fields.
8619 @c OBSOLETE @smallexample
8620 @c OBSOLETE (@value{GDBP}) ptype str
8621 @c OBSOLETE type = STRUCT (
8624 @c OBSOLETE CASE bs OF
8625 @c OBSOLETE (karli):
8631 @c OBSOLETE @end smallexample
8632 @c OBSOLETE @end table
8634 @c OBSOLETE @node Locations
8635 @c OBSOLETE @subsubsection Locations and their accesses
8637 @c OBSOLETE A location in Chill is an object which can contain values.
8639 @c OBSOLETE A value of a location is generally accessed by the (declared) name of
8640 @c OBSOLETE the location. The output conforms to the specification of values in
8641 @c OBSOLETE Chill programs. How values are specified
8642 @c OBSOLETE is the topic of the next section, @ref{Values and their Operations}.
8644 @c OBSOLETE The pseudo-location @code{RESULT} (or @code{result}) can be used to
8645 @c OBSOLETE display or change the result of a currently-active procedure:
8647 @c OBSOLETE @smallexample
8648 @c OBSOLETE set result := EXPR
8649 @c OBSOLETE @end smallexample
8651 @c OBSOLETE @noindent
8652 @c OBSOLETE This does the same as the Chill action @code{RESULT EXPR} (which
8653 @c OBSOLETE is not available in @value{GDBN}).
8655 @c OBSOLETE Values of reference mode locations are printed by @code{PTR(<hex
8656 @c OBSOLETE value>)} in case of a free reference mode, and by @code{(REF <reference
8657 @c OBSOLETE mode>) (<hex-value>)} in case of a bound reference. @code{<hex value>}
8658 @c OBSOLETE represents the address where the reference points to. To access the
8659 @c OBSOLETE value of the location referenced by the pointer, use the dereference
8660 @c OBSOLETE operator @samp{->}.
8662 @c OBSOLETE Values of procedure mode locations are displayed by
8663 @c OBSOLETE @smallexample
8664 @c OBSOLETE @code{@{ PROC
8665 @c OBSOLETE (<argument modes> ) <return mode> @} <address> <name of procedure
8666 @c OBSOLETE location>}
8667 @c OBSOLETE @end smallexample
8668 @c OBSOLETE @code{<argument modes>} is a list of modes according to the parameter
8669 @c OBSOLETE specification of the procedure and @code{<address>} shows the address of
8670 @c OBSOLETE the entry point.
8673 @c OBSOLETE Locations of instance modes are displayed just like a structure with two
8674 @c OBSOLETE fields specifying the @emph{process type} and the @emph{copy number} of
8675 @c OBSOLETE the investigated instance location@footnote{This comes from the current
8676 @c OBSOLETE implementation of instances. They are implemented as a structure (no
8677 @c OBSOLETE na). The output should be something like @code{[<name of the process>;
8678 @c OBSOLETE <instance number>]}.}. The field names are @code{__proc_type} and
8679 @c OBSOLETE @code{__proc_copy}.
8681 @c OBSOLETE Locations of synchronization modes are displayed like a structure with
8682 @c OBSOLETE the field name @code{__event_data} in case of a event mode location, and
8683 @c OBSOLETE like a structure with the field @code{__buffer_data} in case of a buffer
8684 @c OBSOLETE mode location (refer to previous paragraph).
8686 @c OBSOLETE Structure Mode locations are printed by @code{[.<field name>: <value>,
8687 @c OBSOLETE ...]}. The @code{<field name>} corresponds to the structure mode
8688 @c OBSOLETE definition and the layout of @code{<value>} varies depending of the mode
8689 @c OBSOLETE of the field. If the investigated structure mode location is of variant
8690 @c OBSOLETE structure mode, the variant parts of the structure are enclosed in curled
8691 @c OBSOLETE braces (@samp{@{@}}). Fields enclosed by @samp{@{,@}} are residing
8692 @c OBSOLETE on the same memory location and represent the current values of the
8693 @c OBSOLETE memory location in their specific modes. Since no tag processing is done
8694 @c OBSOLETE all variants are displayed. A variant field is printed by
8695 @c OBSOLETE @code{(<variant name>) = .<field name>: <value>}. (who implements the
8696 @c OBSOLETE stuff ???)
8697 @c OBSOLETE @smallexample
8698 @c OBSOLETE (@value{GDBP}) print str1 $4 = [.as: 0, .bs: karli, .<TAG>: { (karli) =
8699 @c OBSOLETE [.cs: []], (susi) = [.ds: susi]}]
8700 @c OBSOLETE @end smallexample
8701 @c OBSOLETE @end ignore
8703 @c OBSOLETE Substructures of string mode-, array mode- or structure mode-values
8704 @c OBSOLETE (e.g. array slices, fields of structure locations) are accessed using
8705 @c OBSOLETE certain operations which are described in the next section, @ref{Values
8706 @c OBSOLETE and their Operations}.
8708 @c OBSOLETE A location value may be interpreted as having a different mode using the
8709 @c OBSOLETE location conversion. This mode conversion is written as @code{<mode
8710 @c OBSOLETE name>(<location>)}. The user has to consider that the sizes of the modes
8711 @c OBSOLETE have to be equal otherwise an error occurs. Furthermore, no range
8712 @c OBSOLETE checking of the location against the destination mode is performed, and
8713 @c OBSOLETE therefore the result can be quite confusing.
8715 @c OBSOLETE @smallexample
8716 @c OBSOLETE (@value{GDBP}) print int (s(3 up 4)) XXX TO be filled in !! XXX
8717 @c OBSOLETE @end smallexample
8719 @c OBSOLETE @node Values and their Operations
8720 @c OBSOLETE @subsubsection Values and their Operations
8722 @c OBSOLETE Values are used to alter locations, to investigate complex structures in
8723 @c OBSOLETE more detail or to filter relevant information out of a large amount of
8724 @c OBSOLETE data. There are several (mode dependent) operations defined which enable
8725 @c OBSOLETE such investigations. These operations are not only applicable to
8726 @c OBSOLETE constant values but also to locations, which can become quite useful
8727 @c OBSOLETE when debugging complex structures. During parsing the command line
8728 @c OBSOLETE (e.g. evaluating an expression) @value{GDBN} treats location names as
8729 @c OBSOLETE the values behind these locations.
8731 @c OBSOLETE This section describes how values have to be specified and which
8732 @c OBSOLETE operations are legal to be used with such values.
8734 @c OBSOLETE @table @code
8735 @c OBSOLETE @item Literal Values
8736 @c OBSOLETE Literal values are specified in the same manner as in @sc{gnu} Chill programs.
8737 @c OBSOLETE For detailed specification refer to the @sc{gnu} Chill implementation Manual
8738 @c OBSOLETE chapter 1.5.
8739 @c OBSOLETE @c FIXME: if the Chill Manual is a Texinfo documents, the above should
8740 @c OBSOLETE @c be converted to a @ref.
8743 @c OBSOLETE @itemize @bullet
8745 @c OBSOLETE @emph{Integer Literals} are specified in the same manner as in Chill
8746 @c OBSOLETE programs (refer to the Chill Standard z200/88 chpt 5.2.4.2)
8748 @c OBSOLETE @emph{Boolean Literals} are defined by @code{TRUE} and @code{FALSE}.
8750 @c OBSOLETE @emph{Character Literals} are defined by @code{'<character>'}. (e.g.
8751 @c OBSOLETE @code{'M'})
8753 @c OBSOLETE @emph{Set Literals} are defined by a name which was specified in a set
8754 @c OBSOLETE mode. The value delivered by a Set Literal is the set value. This is
8755 @c OBSOLETE comparable to an enumeration in C/C@t{++} language.
8757 @c OBSOLETE @emph{Emptiness Literal} is predefined by @code{NULL}. The value of the
8758 @c OBSOLETE emptiness literal delivers either the empty reference value, the empty
8759 @c OBSOLETE procedure value or the empty instance value.
8762 @c OBSOLETE @emph{Character String Literals} are defined by a sequence of characters
8763 @c OBSOLETE enclosed in single- or double quotes. If a single- or double quote has
8764 @c OBSOLETE to be part of the string literal it has to be stuffed (specified twice).
8766 @c OBSOLETE @emph{Bitstring Literals} are specified in the same manner as in Chill
8767 @c OBSOLETE programs (refer z200/88 chpt 5.2.4.8).
8769 @c OBSOLETE @emph{Floating point literals} are specified in the same manner as in
8770 @c OBSOLETE (gnu-)Chill programs (refer @sc{gnu} Chill implementation Manual chapter 1.5).
8771 @c OBSOLETE @end itemize
8772 @c OBSOLETE @end ignore
8774 @c OBSOLETE @item Tuple Values
8775 @c OBSOLETE A tuple is specified by @code{<mode name>[<tuple>]}, where @code{<mode
8776 @c OBSOLETE name>} can be omitted if the mode of the tuple is unambiguous. This
8777 @c OBSOLETE unambiguity is derived from the context of a evaluated expression.
8778 @c OBSOLETE @code{<tuple>} can be one of the following:
8780 @c OBSOLETE @itemize @bullet
8781 @c OBSOLETE @item @emph{Powerset Tuple}
8782 @c OBSOLETE @item @emph{Array Tuple}
8783 @c OBSOLETE @item @emph{Structure Tuple}
8784 @c OBSOLETE Powerset tuples, array tuples and structure tuples are specified in the
8785 @c OBSOLETE same manner as in Chill programs refer to z200/88 chpt 5.2.5.
8786 @c OBSOLETE @end itemize
8788 @c OBSOLETE @item String Element Value
8789 @c OBSOLETE A string element value is specified by
8790 @c OBSOLETE @smallexample
8791 @c OBSOLETE @code{<string value>(<index>)}
8792 @c OBSOLETE @end smallexample
8793 @c OBSOLETE where @code{<index>} is a integer expression. It delivers a character
8794 @c OBSOLETE value which is equivalent to the character indexed by @code{<index>} in
8795 @c OBSOLETE the string.
8797 @c OBSOLETE @item String Slice Value
8798 @c OBSOLETE A string slice value is specified by @code{<string value>(<slice
8799 @c OBSOLETE spec>)}, where @code{<slice spec>} can be either a range of integer
8800 @c OBSOLETE expressions or specified by @code{<start expr> up <size>}.
8801 @c OBSOLETE @code{<size>} denotes the number of elements which the slice contains.
8802 @c OBSOLETE The delivered value is a string value, which is part of the specified
8805 @c OBSOLETE @item Array Element Values
8806 @c OBSOLETE An array element value is specified by @code{<array value>(<expr>)} and
8807 @c OBSOLETE delivers a array element value of the mode of the specified array.
8809 @c OBSOLETE @item Array Slice Values
8810 @c OBSOLETE An array slice is specified by @code{<array value>(<slice spec>)}, where
8811 @c OBSOLETE @code{<slice spec>} can be either a range specified by expressions or by
8812 @c OBSOLETE @code{<start expr> up <size>}. @code{<size>} denotes the number of
8813 @c OBSOLETE arrayelements the slice contains. The delivered value is an array value
8814 @c OBSOLETE which is part of the specified array.
8816 @c OBSOLETE @item Structure Field Values
8817 @c OBSOLETE A structure field value is derived by @code{<structure value>.<field
8818 @c OBSOLETE name>}, where @code{<field name>} indicates the name of a field specified
8819 @c OBSOLETE in the mode definition of the structure. The mode of the delivered value
8820 @c OBSOLETE corresponds to this mode definition in the structure definition.
8822 @c OBSOLETE @item Procedure Call Value
8823 @c OBSOLETE The procedure call value is derived from the return value of the
8824 @c OBSOLETE procedure@footnote{If a procedure call is used for instance in an
8825 @c OBSOLETE expression, then this procedure is called with all its side
8826 @c OBSOLETE effects. This can lead to confusing results if used carelessly.}.
8828 @c OBSOLETE Values of duration mode locations are represented by @code{ULONG} literals.
8830 @c OBSOLETE Values of time mode locations appear as
8831 @c OBSOLETE @smallexample
8832 @c OBSOLETE @code{TIME(<secs>:<nsecs>)}
8833 @c OBSOLETE @end smallexample
8837 @c OBSOLETE This is not implemented yet:
8838 @c OBSOLETE @item Built-in Value
8839 @c OBSOLETE @noindent
8840 @c OBSOLETE The following built in functions are provided:
8842 @c OBSOLETE @table @code
8843 @c OBSOLETE @item @code{ADDR()}
8844 @c OBSOLETE @item @code{NUM()}
8845 @c OBSOLETE @item @code{PRED()}
8846 @c OBSOLETE @item @code{SUCC()}
8847 @c OBSOLETE @item @code{ABS()}
8848 @c OBSOLETE @item @code{CARD()}
8849 @c OBSOLETE @item @code{MAX()}
8850 @c OBSOLETE @item @code{MIN()}
8851 @c OBSOLETE @item @code{SIZE()}
8852 @c OBSOLETE @item @code{UPPER()}
8853 @c OBSOLETE @item @code{LOWER()}
8854 @c OBSOLETE @item @code{LENGTH()}
8855 @c OBSOLETE @item @code{SIN()}
8856 @c OBSOLETE @item @code{COS()}
8857 @c OBSOLETE @item @code{TAN()}
8858 @c OBSOLETE @item @code{ARCSIN()}
8859 @c OBSOLETE @item @code{ARCCOS()}
8860 @c OBSOLETE @item @code{ARCTAN()}
8861 @c OBSOLETE @item @code{EXP()}
8862 @c OBSOLETE @item @code{LN()}
8863 @c OBSOLETE @item @code{LOG()}
8864 @c OBSOLETE @item @code{SQRT()}
8865 @c OBSOLETE @end table
8867 @c OBSOLETE For a detailed description refer to the GNU Chill implementation manual
8868 @c OBSOLETE chapter 1.6.
8869 @c OBSOLETE @end ignore
8871 @c OBSOLETE @item Zero-adic Operator Value
8872 @c OBSOLETE The zero-adic operator value is derived from the instance value for the
8873 @c OBSOLETE current active process.
8875 @c OBSOLETE @item Expression Values
8876 @c OBSOLETE The value delivered by an expression is the result of the evaluation of
8877 @c OBSOLETE the specified expression. If there are error conditions (mode
8878 @c OBSOLETE incompatibility, etc.) the evaluation of expressions is aborted with a
8879 @c OBSOLETE corresponding error message. Expressions may be parenthesised which
8880 @c OBSOLETE causes the evaluation of this expression before any other expression
8881 @c OBSOLETE which uses the result of the parenthesised expression. The following
8882 @c OBSOLETE operators are supported by @value{GDBN}:
8884 @c OBSOLETE @table @code
8885 @c OBSOLETE @item @code{OR, ORIF, XOR}
8886 @c OBSOLETE @itemx @code{AND, ANDIF}
8887 @c OBSOLETE @itemx @code{NOT}
8888 @c OBSOLETE Logical operators defined over operands of boolean mode.
8890 @c OBSOLETE @item @code{=, /=}
8891 @c OBSOLETE Equality and inequality operators defined over all modes.
8893 @c OBSOLETE @item @code{>, >=}
8894 @c OBSOLETE @itemx @code{<, <=}
8895 @c OBSOLETE Relational operators defined over predefined modes.
8897 @c OBSOLETE @item @code{+, -}
8898 @c OBSOLETE @itemx @code{*, /, MOD, REM}
8899 @c OBSOLETE Arithmetic operators defined over predefined modes.
8901 @c OBSOLETE @item @code{-}
8902 @c OBSOLETE Change sign operator.
8904 @c OBSOLETE @item @code{//}
8905 @c OBSOLETE String concatenation operator.
8907 @c OBSOLETE @item @code{()}
8908 @c OBSOLETE String repetition operator.
8910 @c OBSOLETE @item @code{->}
8911 @c OBSOLETE Referenced location operator which can be used either to take the
8912 @c OBSOLETE address of a location (@code{->loc}), or to dereference a reference
8913 @c OBSOLETE location (@code{loc->}).
8915 @c OBSOLETE @item @code{OR, XOR}
8916 @c OBSOLETE @itemx @code{AND}
8917 @c OBSOLETE @itemx @code{NOT}
8918 @c OBSOLETE Powerset and bitstring operators.
8920 @c OBSOLETE @item @code{>, >=}
8921 @c OBSOLETE @itemx @code{<, <=}
8922 @c OBSOLETE Powerset inclusion operators.
8924 @c OBSOLETE @item @code{IN}
8925 @c OBSOLETE Membership operator.
8926 @c OBSOLETE @end table
8927 @c OBSOLETE @end table
8929 @c OBSOLETE @node Chill type and range checks
8930 @c OBSOLETE @subsubsection Chill type and range checks
8932 @c OBSOLETE @value{GDBN} considers two Chill variables mode equivalent if the sizes
8933 @c OBSOLETE of the two modes are equal. This rule applies recursively to more
8934 @c OBSOLETE complex datatypes which means that complex modes are treated
8935 @c OBSOLETE equivalent if all element modes (which also can be complex modes like
8936 @c OBSOLETE structures, arrays, etc.) have the same size.
8938 @c OBSOLETE Range checking is done on all mathematical operations, assignment, array
8939 @c OBSOLETE index bounds and all built in procedures.
8941 @c OBSOLETE Strong type checks are forced using the @value{GDBN} command @code{set
8942 @c OBSOLETE check strong}. This enforces strong type and range checks on all
8943 @c OBSOLETE operations where Chill constructs are used (expressions, built in
8944 @c OBSOLETE functions, etc.) in respect to the semantics as defined in the z.200
8945 @c OBSOLETE language specification.
8947 @c OBSOLETE All checks can be disabled by the @value{GDBN} command @code{set check
8951 @c OBSOLETE @c Deviations from the Chill Standard Z200/88
8952 @c OBSOLETE see last paragraph ?
8953 @c OBSOLETE @end ignore
8955 @c OBSOLETE @node Chill defaults
8956 @c OBSOLETE @subsubsection Chill defaults
8958 @c OBSOLETE If type and range checking are set automatically by @value{GDBN}, they
8959 @c OBSOLETE both default to @code{on} whenever the working language changes to
8960 @c OBSOLETE Chill. This happens regardless of whether you or @value{GDBN}
8961 @c OBSOLETE selected the working language.
8963 @c OBSOLETE If you allow @value{GDBN} to set the language automatically, then entering
8964 @c OBSOLETE code compiled from a file whose name ends with @file{.ch} sets the
8965 @c OBSOLETE working language to Chill. @xref{Automatically, ,Having @value{GDBN} set
8966 @c OBSOLETE the language automatically}, for further details.
8969 @chapter Examining the Symbol Table
8971 The commands described in this chapter allow you to inquire about the
8972 symbols (names of variables, functions and types) defined in your
8973 program. This information is inherent in the text of your program and
8974 does not change as your program executes. @value{GDBN} finds it in your
8975 program's symbol table, in the file indicated when you started @value{GDBN}
8976 (@pxref{File Options, ,Choosing files}), or by one of the
8977 file-management commands (@pxref{Files, ,Commands to specify files}).
8979 @cindex symbol names
8980 @cindex names of symbols
8981 @cindex quoting names
8982 Occasionally, you may need to refer to symbols that contain unusual
8983 characters, which @value{GDBN} ordinarily treats as word delimiters. The
8984 most frequent case is in referring to static variables in other
8985 source files (@pxref{Variables,,Program variables}). File names
8986 are recorded in object files as debugging symbols, but @value{GDBN} would
8987 ordinarily parse a typical file name, like @file{foo.c}, as the three words
8988 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
8989 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
8996 looks up the value of @code{x} in the scope of the file @file{foo.c}.
8999 @kindex info address
9000 @cindex address of a symbol
9001 @item info address @var{symbol}
9002 Describe where the data for @var{symbol} is stored. For a register
9003 variable, this says which register it is kept in. For a non-register
9004 local variable, this prints the stack-frame offset at which the variable
9007 Note the contrast with @samp{print &@var{symbol}}, which does not work
9008 at all for a register variable, and for a stack local variable prints
9009 the exact address of the current instantiation of the variable.
9012 @cindex symbol from address
9013 @item info symbol @var{addr}
9014 Print the name of a symbol which is stored at the address @var{addr}.
9015 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
9016 nearest symbol and an offset from it:
9019 (@value{GDBP}) info symbol 0x54320
9020 _initialize_vx + 396 in section .text
9024 This is the opposite of the @code{info address} command. You can use
9025 it to find out the name of a variable or a function given its address.
9028 @item whatis @var{expr}
9029 Print the data type of expression @var{expr}. @var{expr} is not
9030 actually evaluated, and any side-effecting operations (such as
9031 assignments or function calls) inside it do not take place.
9032 @xref{Expressions, ,Expressions}.
9035 Print the data type of @code{$}, the last value in the value history.
9038 @item ptype @var{typename}
9039 Print a description of data type @var{typename}. @var{typename} may be
9040 the name of a type, or for C code it may have the form @samp{class
9041 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
9042 @var{union-tag}} or @samp{enum @var{enum-tag}}.
9044 @item ptype @var{expr}
9046 Print a description of the type of expression @var{expr}. @code{ptype}
9047 differs from @code{whatis} by printing a detailed description, instead
9048 of just the name of the type.
9050 For example, for this variable declaration:
9053 struct complex @{double real; double imag;@} v;
9057 the two commands give this output:
9061 (@value{GDBP}) whatis v
9062 type = struct complex
9063 (@value{GDBP}) ptype v
9064 type = struct complex @{
9072 As with @code{whatis}, using @code{ptype} without an argument refers to
9073 the type of @code{$}, the last value in the value history.
9076 @item info types @var{regexp}
9078 Print a brief description of all types whose names match @var{regexp}
9079 (or all types in your program, if you supply no argument). Each
9080 complete typename is matched as though it were a complete line; thus,
9081 @samp{i type value} gives information on all types in your program whose
9082 names include the string @code{value}, but @samp{i type ^value$} gives
9083 information only on types whose complete name is @code{value}.
9085 This command differs from @code{ptype} in two ways: first, like
9086 @code{whatis}, it does not print a detailed description; second, it
9087 lists all source files where a type is defined.
9090 @cindex local variables
9091 @item info scope @var{addr}
9092 List all the variables local to a particular scope. This command
9093 accepts a location---a function name, a source line, or an address
9094 preceded by a @samp{*}, and prints all the variables local to the
9095 scope defined by that location. For example:
9098 (@value{GDBP}) @b{info scope command_line_handler}
9099 Scope for command_line_handler:
9100 Symbol rl is an argument at stack/frame offset 8, length 4.
9101 Symbol linebuffer is in static storage at address 0x150a18, length 4.
9102 Symbol linelength is in static storage at address 0x150a1c, length 4.
9103 Symbol p is a local variable in register $esi, length 4.
9104 Symbol p1 is a local variable in register $ebx, length 4.
9105 Symbol nline is a local variable in register $edx, length 4.
9106 Symbol repeat is a local variable at frame offset -8, length 4.
9110 This command is especially useful for determining what data to collect
9111 during a @dfn{trace experiment}, see @ref{Tracepoint Actions,
9116 Show information about the current source file---that is, the source file for
9117 the function containing the current point of execution:
9120 the name of the source file, and the directory containing it,
9122 the directory it was compiled in,
9124 its length, in lines,
9126 which programming language it is written in,
9128 whether the executable includes debugging information for that file, and
9129 if so, what format the information is in (e.g., STABS, Dwarf 2, etc.), and
9131 whether the debugging information includes information about
9132 preprocessor macros.
9136 @kindex info sources
9138 Print the names of all source files in your program for which there is
9139 debugging information, organized into two lists: files whose symbols
9140 have already been read, and files whose symbols will be read when needed.
9142 @kindex info functions
9143 @item info functions
9144 Print the names and data types of all defined functions.
9146 @item info functions @var{regexp}
9147 Print the names and data types of all defined functions
9148 whose names contain a match for regular expression @var{regexp}.
9149 Thus, @samp{info fun step} finds all functions whose names
9150 include @code{step}; @samp{info fun ^step} finds those whose names
9151 start with @code{step}. If a function name contains characters
9152 that conflict with the regular expression language (eg.
9153 @samp{operator*()}), they may be quoted with a backslash.
9155 @kindex info variables
9156 @item info variables
9157 Print the names and data types of all variables that are declared
9158 outside of functions (i.e.@: excluding local variables).
9160 @item info variables @var{regexp}
9161 Print the names and data types of all variables (except for local
9162 variables) whose names contain a match for regular expression
9166 This was never implemented.
9167 @kindex info methods
9169 @itemx info methods @var{regexp}
9170 The @code{info methods} command permits the user to examine all defined
9171 methods within C@t{++} program, or (with the @var{regexp} argument) a
9172 specific set of methods found in the various C@t{++} classes. Many
9173 C@t{++} classes provide a large number of methods. Thus, the output
9174 from the @code{ptype} command can be overwhelming and hard to use. The
9175 @code{info-methods} command filters the methods, printing only those
9176 which match the regular-expression @var{regexp}.
9179 @cindex reloading symbols
9180 Some systems allow individual object files that make up your program to
9181 be replaced without stopping and restarting your program. For example,
9182 in VxWorks you can simply recompile a defective object file and keep on
9183 running. If you are running on one of these systems, you can allow
9184 @value{GDBN} to reload the symbols for automatically relinked modules:
9187 @kindex set symbol-reloading
9188 @item set symbol-reloading on
9189 Replace symbol definitions for the corresponding source file when an
9190 object file with a particular name is seen again.
9192 @item set symbol-reloading off
9193 Do not replace symbol definitions when encountering object files of the
9194 same name more than once. This is the default state; if you are not
9195 running on a system that permits automatic relinking of modules, you
9196 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
9197 may discard symbols when linking large programs, that may contain
9198 several modules (from different directories or libraries) with the same
9201 @kindex show symbol-reloading
9202 @item show symbol-reloading
9203 Show the current @code{on} or @code{off} setting.
9206 @kindex set opaque-type-resolution
9207 @item set opaque-type-resolution on
9208 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
9209 declared as a pointer to a @code{struct}, @code{class}, or
9210 @code{union}---for example, @code{struct MyType *}---that is used in one
9211 source file although the full declaration of @code{struct MyType} is in
9212 another source file. The default is on.
9214 A change in the setting of this subcommand will not take effect until
9215 the next time symbols for a file are loaded.
9217 @item set opaque-type-resolution off
9218 Tell @value{GDBN} not to resolve opaque types. In this case, the type
9219 is printed as follows:
9221 @{<no data fields>@}
9224 @kindex show opaque-type-resolution
9225 @item show opaque-type-resolution
9226 Show whether opaque types are resolved or not.
9228 @kindex maint print symbols
9230 @kindex maint print psymbols
9231 @cindex partial symbol dump
9232 @item maint print symbols @var{filename}
9233 @itemx maint print psymbols @var{filename}
9234 @itemx maint print msymbols @var{filename}
9235 Write a dump of debugging symbol data into the file @var{filename}.
9236 These commands are used to debug the @value{GDBN} symbol-reading code. Only
9237 symbols with debugging data are included. If you use @samp{maint print
9238 symbols}, @value{GDBN} includes all the symbols for which it has already
9239 collected full details: that is, @var{filename} reflects symbols for
9240 only those files whose symbols @value{GDBN} has read. You can use the
9241 command @code{info sources} to find out which files these are. If you
9242 use @samp{maint print psymbols} instead, the dump shows information about
9243 symbols that @value{GDBN} only knows partially---that is, symbols defined in
9244 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
9245 @samp{maint print msymbols} dumps just the minimal symbol information
9246 required for each object file from which @value{GDBN} has read some symbols.
9247 @xref{Files, ,Commands to specify files}, for a discussion of how
9248 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
9252 @chapter Altering Execution
9254 Once you think you have found an error in your program, you might want to
9255 find out for certain whether correcting the apparent error would lead to
9256 correct results in the rest of the run. You can find the answer by
9257 experiment, using the @value{GDBN} features for altering execution of the
9260 For example, you can store new values into variables or memory
9261 locations, give your program a signal, restart it at a different
9262 address, or even return prematurely from a function.
9265 * Assignment:: Assignment to variables
9266 * Jumping:: Continuing at a different address
9267 * Signaling:: Giving your program a signal
9268 * Returning:: Returning from a function
9269 * Calling:: Calling your program's functions
9270 * Patching:: Patching your program
9274 @section Assignment to variables
9277 @cindex setting variables
9278 To alter the value of a variable, evaluate an assignment expression.
9279 @xref{Expressions, ,Expressions}. For example,
9286 stores the value 4 into the variable @code{x}, and then prints the
9287 value of the assignment expression (which is 4).
9288 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
9289 information on operators in supported languages.
9291 @kindex set variable
9292 @cindex variables, setting
9293 If you are not interested in seeing the value of the assignment, use the
9294 @code{set} command instead of the @code{print} command. @code{set} is
9295 really the same as @code{print} except that the expression's value is
9296 not printed and is not put in the value history (@pxref{Value History,
9297 ,Value history}). The expression is evaluated only for its effects.
9299 If the beginning of the argument string of the @code{set} command
9300 appears identical to a @code{set} subcommand, use the @code{set
9301 variable} command instead of just @code{set}. This command is identical
9302 to @code{set} except for its lack of subcommands. For example, if your
9303 program has a variable @code{width}, you get an error if you try to set
9304 a new value with just @samp{set width=13}, because @value{GDBN} has the
9305 command @code{set width}:
9308 (@value{GDBP}) whatis width
9310 (@value{GDBP}) p width
9312 (@value{GDBP}) set width=47
9313 Invalid syntax in expression.
9317 The invalid expression, of course, is @samp{=47}. In
9318 order to actually set the program's variable @code{width}, use
9321 (@value{GDBP}) set var width=47
9324 Because the @code{set} command has many subcommands that can conflict
9325 with the names of program variables, it is a good idea to use the
9326 @code{set variable} command instead of just @code{set}. For example, if
9327 your program has a variable @code{g}, you run into problems if you try
9328 to set a new value with just @samp{set g=4}, because @value{GDBN} has
9329 the command @code{set gnutarget}, abbreviated @code{set g}:
9333 (@value{GDBP}) whatis g
9337 (@value{GDBP}) set g=4
9341 The program being debugged has been started already.
9342 Start it from the beginning? (y or n) y
9343 Starting program: /home/smith/cc_progs/a.out
9344 "/home/smith/cc_progs/a.out": can't open to read symbols:
9346 (@value{GDBP}) show g
9347 The current BFD target is "=4".
9352 The program variable @code{g} did not change, and you silently set the
9353 @code{gnutarget} to an invalid value. In order to set the variable
9357 (@value{GDBP}) set var g=4
9360 @value{GDBN} allows more implicit conversions in assignments than C; you can
9361 freely store an integer value into a pointer variable or vice versa,
9362 and you can convert any structure to any other structure that is the
9363 same length or shorter.
9364 @comment FIXME: how do structs align/pad in these conversions?
9365 @comment /doc@cygnus.com 18dec1990
9367 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
9368 construct to generate a value of specified type at a specified address
9369 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
9370 to memory location @code{0x83040} as an integer (which implies a certain size
9371 and representation in memory), and
9374 set @{int@}0x83040 = 4
9378 stores the value 4 into that memory location.
9381 @section Continuing at a different address
9383 Ordinarily, when you continue your program, you do so at the place where
9384 it stopped, with the @code{continue} command. You can instead continue at
9385 an address of your own choosing, with the following commands:
9389 @item jump @var{linespec}
9390 Resume execution at line @var{linespec}. Execution stops again
9391 immediately if there is a breakpoint there. @xref{List, ,Printing
9392 source lines}, for a description of the different forms of
9393 @var{linespec}. It is common practice to use the @code{tbreak} command
9394 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
9397 The @code{jump} command does not change the current stack frame, or
9398 the stack pointer, or the contents of any memory location or any
9399 register other than the program counter. If line @var{linespec} is in
9400 a different function from the one currently executing, the results may
9401 be bizarre if the two functions expect different patterns of arguments or
9402 of local variables. For this reason, the @code{jump} command requests
9403 confirmation if the specified line is not in the function currently
9404 executing. However, even bizarre results are predictable if you are
9405 well acquainted with the machine-language code of your program.
9407 @item jump *@var{address}
9408 Resume execution at the instruction at address @var{address}.
9411 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
9412 On many systems, you can get much the same effect as the @code{jump}
9413 command by storing a new value into the register @code{$pc}. The
9414 difference is that this does not start your program running; it only
9415 changes the address of where it @emph{will} run when you continue. For
9423 makes the next @code{continue} command or stepping command execute at
9424 address @code{0x485}, rather than at the address where your program stopped.
9425 @xref{Continuing and Stepping, ,Continuing and stepping}.
9427 The most common occasion to use the @code{jump} command is to back
9428 up---perhaps with more breakpoints set---over a portion of a program
9429 that has already executed, in order to examine its execution in more
9434 @section Giving your program a signal
9438 @item signal @var{signal}
9439 Resume execution where your program stopped, but immediately give it the
9440 signal @var{signal}. @var{signal} can be the name or the number of a
9441 signal. For example, on many systems @code{signal 2} and @code{signal
9442 SIGINT} are both ways of sending an interrupt signal.
9444 Alternatively, if @var{signal} is zero, continue execution without
9445 giving a signal. This is useful when your program stopped on account of
9446 a signal and would ordinary see the signal when resumed with the
9447 @code{continue} command; @samp{signal 0} causes it to resume without a
9450 @code{signal} does not repeat when you press @key{RET} a second time
9451 after executing the command.
9455 Invoking the @code{signal} command is not the same as invoking the
9456 @code{kill} utility from the shell. Sending a signal with @code{kill}
9457 causes @value{GDBN} to decide what to do with the signal depending on
9458 the signal handling tables (@pxref{Signals}). The @code{signal} command
9459 passes the signal directly to your program.
9463 @section Returning from a function
9466 @cindex returning from a function
9469 @itemx return @var{expression}
9470 You can cancel execution of a function call with the @code{return}
9471 command. If you give an
9472 @var{expression} argument, its value is used as the function's return
9476 When you use @code{return}, @value{GDBN} discards the selected stack frame
9477 (and all frames within it). You can think of this as making the
9478 discarded frame return prematurely. If you wish to specify a value to
9479 be returned, give that value as the argument to @code{return}.
9481 This pops the selected stack frame (@pxref{Selection, ,Selecting a
9482 frame}), and any other frames inside of it, leaving its caller as the
9483 innermost remaining frame. That frame becomes selected. The
9484 specified value is stored in the registers used for returning values
9487 The @code{return} command does not resume execution; it leaves the
9488 program stopped in the state that would exist if the function had just
9489 returned. In contrast, the @code{finish} command (@pxref{Continuing
9490 and Stepping, ,Continuing and stepping}) resumes execution until the
9491 selected stack frame returns naturally.
9494 @section Calling program functions
9496 @cindex calling functions
9499 @item call @var{expr}
9500 Evaluate the expression @var{expr} without displaying @code{void}
9504 You can use this variant of the @code{print} command if you want to
9505 execute a function from your program, but without cluttering the output
9506 with @code{void} returned values. If the result is not void, it
9507 is printed and saved in the value history.
9510 @section Patching programs
9512 @cindex patching binaries
9513 @cindex writing into executables
9514 @cindex writing into corefiles
9516 By default, @value{GDBN} opens the file containing your program's
9517 executable code (or the corefile) read-only. This prevents accidental
9518 alterations to machine code; but it also prevents you from intentionally
9519 patching your program's binary.
9521 If you'd like to be able to patch the binary, you can specify that
9522 explicitly with the @code{set write} command. For example, you might
9523 want to turn on internal debugging flags, or even to make emergency
9529 @itemx set write off
9530 If you specify @samp{set write on}, @value{GDBN} opens executable and
9531 core files for both reading and writing; if you specify @samp{set write
9532 off} (the default), @value{GDBN} opens them read-only.
9534 If you have already loaded a file, you must load it again (using the
9535 @code{exec-file} or @code{core-file} command) after changing @code{set
9536 write}, for your new setting to take effect.
9540 Display whether executable files and core files are opened for writing
9545 @chapter @value{GDBN} Files
9547 @value{GDBN} needs to know the file name of the program to be debugged,
9548 both in order to read its symbol table and in order to start your
9549 program. To debug a core dump of a previous run, you must also tell
9550 @value{GDBN} the name of the core dump file.
9553 * Files:: Commands to specify files
9554 * Symbol Errors:: Errors reading symbol files
9558 @section Commands to specify files
9560 @cindex symbol table
9561 @cindex core dump file
9563 You may want to specify executable and core dump file names. The usual
9564 way to do this is at start-up time, using the arguments to
9565 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
9566 Out of @value{GDBN}}).
9568 Occasionally it is necessary to change to a different file during a
9569 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
9570 a file you want to use. In these situations the @value{GDBN} commands
9571 to specify new files are useful.
9574 @cindex executable file
9576 @item file @var{filename}
9577 Use @var{filename} as the program to be debugged. It is read for its
9578 symbols and for the contents of pure memory. It is also the program
9579 executed when you use the @code{run} command. If you do not specify a
9580 directory and the file is not found in the @value{GDBN} working directory,
9581 @value{GDBN} uses the environment variable @code{PATH} as a list of
9582 directories to search, just as the shell does when looking for a program
9583 to run. You can change the value of this variable, for both @value{GDBN}
9584 and your program, using the @code{path} command.
9586 On systems with memory-mapped files, an auxiliary file named
9587 @file{@var{filename}.syms} may hold symbol table information for
9588 @var{filename}. If so, @value{GDBN} maps in the symbol table from
9589 @file{@var{filename}.syms}, starting up more quickly. See the
9590 descriptions of the file options @samp{-mapped} and @samp{-readnow}
9591 (available on the command line, and with the commands @code{file},
9592 @code{symbol-file}, or @code{add-symbol-file}, described below),
9593 for more information.
9596 @code{file} with no argument makes @value{GDBN} discard any information it
9597 has on both executable file and the symbol table.
9600 @item exec-file @r{[} @var{filename} @r{]}
9601 Specify that the program to be run (but not the symbol table) is found
9602 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
9603 if necessary to locate your program. Omitting @var{filename} means to
9604 discard information on the executable file.
9607 @item symbol-file @r{[} @var{filename} @r{]}
9608 Read symbol table information from file @var{filename}. @code{PATH} is
9609 searched when necessary. Use the @code{file} command to get both symbol
9610 table and program to run from the same file.
9612 @code{symbol-file} with no argument clears out @value{GDBN} information on your
9613 program's symbol table.
9615 The @code{symbol-file} command causes @value{GDBN} to forget the contents
9616 of its convenience variables, the value history, and all breakpoints and
9617 auto-display expressions. This is because they may contain pointers to
9618 the internal data recording symbols and data types, which are part of
9619 the old symbol table data being discarded inside @value{GDBN}.
9621 @code{symbol-file} does not repeat if you press @key{RET} again after
9624 When @value{GDBN} is configured for a particular environment, it
9625 understands debugging information in whatever format is the standard
9626 generated for that environment; you may use either a @sc{gnu} compiler, or
9627 other compilers that adhere to the local conventions.
9628 Best results are usually obtained from @sc{gnu} compilers; for example,
9629 using @code{@value{GCC}} you can generate debugging information for
9632 For most kinds of object files, with the exception of old SVR3 systems
9633 using COFF, the @code{symbol-file} command does not normally read the
9634 symbol table in full right away. Instead, it scans the symbol table
9635 quickly to find which source files and which symbols are present. The
9636 details are read later, one source file at a time, as they are needed.
9638 The purpose of this two-stage reading strategy is to make @value{GDBN}
9639 start up faster. For the most part, it is invisible except for
9640 occasional pauses while the symbol table details for a particular source
9641 file are being read. (The @code{set verbose} command can turn these
9642 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
9643 warnings and messages}.)
9645 We have not implemented the two-stage strategy for COFF yet. When the
9646 symbol table is stored in COFF format, @code{symbol-file} reads the
9647 symbol table data in full right away. Note that ``stabs-in-COFF''
9648 still does the two-stage strategy, since the debug info is actually
9652 @cindex reading symbols immediately
9653 @cindex symbols, reading immediately
9655 @cindex memory-mapped symbol file
9656 @cindex saving symbol table
9657 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9658 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9659 You can override the @value{GDBN} two-stage strategy for reading symbol
9660 tables by using the @samp{-readnow} option with any of the commands that
9661 load symbol table information, if you want to be sure @value{GDBN} has the
9662 entire symbol table available.
9664 If memory-mapped files are available on your system through the
9665 @code{mmap} system call, you can use another option, @samp{-mapped}, to
9666 cause @value{GDBN} to write the symbols for your program into a reusable
9667 file. Future @value{GDBN} debugging sessions map in symbol information
9668 from this auxiliary symbol file (if the program has not changed), rather
9669 than spending time reading the symbol table from the executable
9670 program. Using the @samp{-mapped} option has the same effect as
9671 starting @value{GDBN} with the @samp{-mapped} command-line option.
9673 You can use both options together, to make sure the auxiliary symbol
9674 file has all the symbol information for your program.
9676 The auxiliary symbol file for a program called @var{myprog} is called
9677 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
9678 than the corresponding executable), @value{GDBN} always attempts to use
9679 it when you debug @var{myprog}; no special options or commands are
9682 The @file{.syms} file is specific to the host machine where you run
9683 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
9684 symbol table. It cannot be shared across multiple host platforms.
9686 @c FIXME: for now no mention of directories, since this seems to be in
9687 @c flux. 13mar1992 status is that in theory GDB would look either in
9688 @c current dir or in same dir as myprog; but issues like competing
9689 @c GDB's, or clutter in system dirs, mean that in practice right now
9690 @c only current dir is used. FFish says maybe a special GDB hierarchy
9691 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
9696 @item core-file @r{[} @var{filename} @r{]}
9697 Specify the whereabouts of a core dump file to be used as the ``contents
9698 of memory''. Traditionally, core files contain only some parts of the
9699 address space of the process that generated them; @value{GDBN} can access the
9700 executable file itself for other parts.
9702 @code{core-file} with no argument specifies that no core file is
9705 Note that the core file is ignored when your program is actually running
9706 under @value{GDBN}. So, if you have been running your program and you
9707 wish to debug a core file instead, you must kill the subprocess in which
9708 the program is running. To do this, use the @code{kill} command
9709 (@pxref{Kill Process, ,Killing the child process}).
9711 @kindex add-symbol-file
9712 @cindex dynamic linking
9713 @item add-symbol-file @var{filename} @var{address}
9714 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9715 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address} @dots{}
9716 The @code{add-symbol-file} command reads additional symbol table
9717 information from the file @var{filename}. You would use this command
9718 when @var{filename} has been dynamically loaded (by some other means)
9719 into the program that is running. @var{address} should be the memory
9720 address at which the file has been loaded; @value{GDBN} cannot figure
9721 this out for itself. You can additionally specify an arbitrary number
9722 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
9723 section name and base address for that section. You can specify any
9724 @var{address} as an expression.
9726 The symbol table of the file @var{filename} is added to the symbol table
9727 originally read with the @code{symbol-file} command. You can use the
9728 @code{add-symbol-file} command any number of times; the new symbol data
9729 thus read keeps adding to the old. To discard all old symbol data
9730 instead, use the @code{symbol-file} command without any arguments.
9732 @cindex relocatable object files, reading symbols from
9733 @cindex object files, relocatable, reading symbols from
9734 @cindex reading symbols from relocatable object files
9735 @cindex symbols, reading from relocatable object files
9736 @cindex @file{.o} files, reading symbols from
9737 Although @var{filename} is typically a shared library file, an
9738 executable file, or some other object file which has been fully
9739 relocated for loading into a process, you can also load symbolic
9740 information from relocatable @file{.o} files, as long as:
9744 the file's symbolic information refers only to linker symbols defined in
9745 that file, not to symbols defined by other object files,
9747 every section the file's symbolic information refers to has actually
9748 been loaded into the inferior, as it appears in the file, and
9750 you can determine the address at which every section was loaded, and
9751 provide these to the @code{add-symbol-file} command.
9755 Some embedded operating systems, like Sun Chorus and VxWorks, can load
9756 relocatable files into an already running program; such systems
9757 typically make the requirements above easy to meet. However, it's
9758 important to recognize that many native systems use complex link
9759 procedures (@code{.linkonce} section factoring and C++ constructor table
9760 assembly, for example) that make the requirements difficult to meet. In
9761 general, one cannot assume that using @code{add-symbol-file} to read a
9762 relocatable object file's symbolic information will have the same effect
9763 as linking the relocatable object file into the program in the normal
9766 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
9768 You can use the @samp{-mapped} and @samp{-readnow} options just as with
9769 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
9770 table information for @var{filename}.
9772 @kindex add-shared-symbol-file
9773 @item add-shared-symbol-file
9774 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
9775 operating system for the Motorola 88k. @value{GDBN} automatically looks for
9776 shared libraries, however if @value{GDBN} does not find yours, you can run
9777 @code{add-shared-symbol-file}. It takes no arguments.
9781 The @code{section} command changes the base address of section SECTION of
9782 the exec file to ADDR. This can be used if the exec file does not contain
9783 section addresses, (such as in the a.out format), or when the addresses
9784 specified in the file itself are wrong. Each section must be changed
9785 separately. The @code{info files} command, described below, lists all
9786 the sections and their addresses.
9792 @code{info files} and @code{info target} are synonymous; both print the
9793 current target (@pxref{Targets, ,Specifying a Debugging Target}),
9794 including the names of the executable and core dump files currently in
9795 use by @value{GDBN}, and the files from which symbols were loaded. The
9796 command @code{help target} lists all possible targets rather than
9799 @kindex maint info sections
9800 @item maint info sections
9801 Another command that can give you extra information about program sections
9802 is @code{maint info sections}. In addition to the section information
9803 displayed by @code{info files}, this command displays the flags and file
9804 offset of each section in the executable and core dump files. In addition,
9805 @code{maint info sections} provides the following command options (which
9806 may be arbitrarily combined):
9810 Display sections for all loaded object files, including shared libraries.
9811 @item @var{sections}
9812 Display info only for named @var{sections}.
9813 @item @var{section-flags}
9814 Display info only for sections for which @var{section-flags} are true.
9815 The section flags that @value{GDBN} currently knows about are:
9818 Section will have space allocated in the process when loaded.
9819 Set for all sections except those containing debug information.
9821 Section will be loaded from the file into the child process memory.
9822 Set for pre-initialized code and data, clear for @code{.bss} sections.
9824 Section needs to be relocated before loading.
9826 Section cannot be modified by the child process.
9828 Section contains executable code only.
9830 Section contains data only (no executable code).
9832 Section will reside in ROM.
9834 Section contains data for constructor/destructor lists.
9836 Section is not empty.
9838 An instruction to the linker to not output the section.
9839 @item COFF_SHARED_LIBRARY
9840 A notification to the linker that the section contains
9841 COFF shared library information.
9843 Section contains common symbols.
9846 @kindex set trust-readonly-sections
9847 @item set trust-readonly-sections on
9848 Tell @value{GDBN} that readonly sections in your object file
9849 really are read-only (i.e.@: that their contents will not change).
9850 In that case, @value{GDBN} can fetch values from these sections
9851 out of the object file, rather than from the target program.
9852 For some targets (notably embedded ones), this can be a significant
9853 enhancement to debugging performance.
9857 @item set trust-readonly-sections off
9858 Tell @value{GDBN} not to trust readonly sections. This means that
9859 the contents of the section might change while the program is running,
9860 and must therefore be fetched from the target when needed.
9863 All file-specifying commands allow both absolute and relative file names
9864 as arguments. @value{GDBN} always converts the file name to an absolute file
9865 name and remembers it that way.
9867 @cindex shared libraries
9868 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
9871 @value{GDBN} automatically loads symbol definitions from shared libraries
9872 when you use the @code{run} command, or when you examine a core file.
9873 (Before you issue the @code{run} command, @value{GDBN} does not understand
9874 references to a function in a shared library, however---unless you are
9875 debugging a core file).
9877 On HP-UX, if the program loads a library explicitly, @value{GDBN}
9878 automatically loads the symbols at the time of the @code{shl_load} call.
9880 @c FIXME: some @value{GDBN} release may permit some refs to undef
9881 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
9882 @c FIXME...lib; check this from time to time when updating manual
9884 There are times, however, when you may wish to not automatically load
9885 symbol definitions from shared libraries, such as when they are
9886 particularly large or there are many of them.
9888 To control the automatic loading of shared library symbols, use the
9892 @kindex set auto-solib-add
9893 @item set auto-solib-add @var{mode}
9894 If @var{mode} is @code{on}, symbols from all shared object libraries
9895 will be loaded automatically when the inferior begins execution, you
9896 attach to an independently started inferior, or when the dynamic linker
9897 informs @value{GDBN} that a new library has been loaded. If @var{mode}
9898 is @code{off}, symbols must be loaded manually, using the
9899 @code{sharedlibrary} command. The default value is @code{on}.
9901 @kindex show auto-solib-add
9902 @item show auto-solib-add
9903 Display the current autoloading mode.
9906 To explicitly load shared library symbols, use the @code{sharedlibrary}
9910 @kindex info sharedlibrary
9913 @itemx info sharedlibrary
9914 Print the names of the shared libraries which are currently loaded.
9916 @kindex sharedlibrary
9918 @item sharedlibrary @var{regex}
9919 @itemx share @var{regex}
9920 Load shared object library symbols for files matching a
9921 Unix regular expression.
9922 As with files loaded automatically, it only loads shared libraries
9923 required by your program for a core file or after typing @code{run}. If
9924 @var{regex} is omitted all shared libraries required by your program are
9928 On some systems, such as HP-UX systems, @value{GDBN} supports
9929 autoloading shared library symbols until a limiting threshold size is
9930 reached. This provides the benefit of allowing autoloading to remain on
9931 by default, but avoids autoloading excessively large shared libraries,
9932 up to a threshold that is initially set, but which you can modify if you
9935 Beyond that threshold, symbols from shared libraries must be explicitly
9936 loaded. To load these symbols, use the command @code{sharedlibrary
9937 @var{filename}}. The base address of the shared library is determined
9938 automatically by @value{GDBN} and need not be specified.
9940 To display or set the threshold, use the commands:
9943 @kindex set auto-solib-limit
9944 @item set auto-solib-limit @var{threshold}
9945 Set the autoloading size threshold, in an integral number of megabytes.
9946 If @var{threshold} is nonzero and shared library autoloading is enabled,
9947 symbols from all shared object libraries will be loaded until the total
9948 size of the loaded shared library symbols exceeds this threshold.
9949 Otherwise, symbols must be loaded manually, using the
9950 @code{sharedlibrary} command. The default threshold is 100 (i.e.@: 100
9953 @kindex show auto-solib-limit
9954 @item show auto-solib-limit
9955 Display the current autoloading size threshold, in megabytes.
9959 @section Errors reading symbol files
9961 While reading a symbol file, @value{GDBN} occasionally encounters problems,
9962 such as symbol types it does not recognize, or known bugs in compiler
9963 output. By default, @value{GDBN} does not notify you of such problems, since
9964 they are relatively common and primarily of interest to people
9965 debugging compilers. If you are interested in seeing information
9966 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
9967 only one message about each such type of problem, no matter how many
9968 times the problem occurs; or you can ask @value{GDBN} to print more messages,
9969 to see how many times the problems occur, with the @code{set
9970 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
9973 The messages currently printed, and their meanings, include:
9976 @item inner block not inside outer block in @var{symbol}
9978 The symbol information shows where symbol scopes begin and end
9979 (such as at the start of a function or a block of statements). This
9980 error indicates that an inner scope block is not fully contained
9981 in its outer scope blocks.
9983 @value{GDBN} circumvents the problem by treating the inner block as if it had
9984 the same scope as the outer block. In the error message, @var{symbol}
9985 may be shown as ``@code{(don't know)}'' if the outer block is not a
9988 @item block at @var{address} out of order
9990 The symbol information for symbol scope blocks should occur in
9991 order of increasing addresses. This error indicates that it does not
9994 @value{GDBN} does not circumvent this problem, and has trouble
9995 locating symbols in the source file whose symbols it is reading. (You
9996 can often determine what source file is affected by specifying
9997 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
10000 @item bad block start address patched
10002 The symbol information for a symbol scope block has a start address
10003 smaller than the address of the preceding source line. This is known
10004 to occur in the SunOS 4.1.1 (and earlier) C compiler.
10006 @value{GDBN} circumvents the problem by treating the symbol scope block as
10007 starting on the previous source line.
10009 @item bad string table offset in symbol @var{n}
10012 Symbol number @var{n} contains a pointer into the string table which is
10013 larger than the size of the string table.
10015 @value{GDBN} circumvents the problem by considering the symbol to have the
10016 name @code{foo}, which may cause other problems if many symbols end up
10019 @item unknown symbol type @code{0x@var{nn}}
10021 The symbol information contains new data types that @value{GDBN} does
10022 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
10023 uncomprehended information, in hexadecimal.
10025 @value{GDBN} circumvents the error by ignoring this symbol information.
10026 This usually allows you to debug your program, though certain symbols
10027 are not accessible. If you encounter such a problem and feel like
10028 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
10029 on @code{complain}, then go up to the function @code{read_dbx_symtab}
10030 and examine @code{*bufp} to see the symbol.
10032 @item stub type has NULL name
10034 @value{GDBN} could not find the full definition for a struct or class.
10036 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
10037 The symbol information for a C@t{++} member function is missing some
10038 information that recent versions of the compiler should have output for
10041 @item info mismatch between compiler and debugger
10043 @value{GDBN} could not parse a type specification output by the compiler.
10048 @chapter Specifying a Debugging Target
10050 @cindex debugging target
10053 A @dfn{target} is the execution environment occupied by your program.
10055 Often, @value{GDBN} runs in the same host environment as your program;
10056 in that case, the debugging target is specified as a side effect when
10057 you use the @code{file} or @code{core} commands. When you need more
10058 flexibility---for example, running @value{GDBN} on a physically separate
10059 host, or controlling a standalone system over a serial port or a
10060 realtime system over a TCP/IP connection---you can use the @code{target}
10061 command to specify one of the target types configured for @value{GDBN}
10062 (@pxref{Target Commands, ,Commands for managing targets}).
10065 * Active Targets:: Active targets
10066 * Target Commands:: Commands for managing targets
10067 * Byte Order:: Choosing target byte order
10068 * Remote:: Remote debugging
10069 * KOD:: Kernel Object Display
10073 @node Active Targets
10074 @section Active targets
10076 @cindex stacking targets
10077 @cindex active targets
10078 @cindex multiple targets
10080 There are three classes of targets: processes, core files, and
10081 executable files. @value{GDBN} can work concurrently on up to three
10082 active targets, one in each class. This allows you to (for example)
10083 start a process and inspect its activity without abandoning your work on
10086 For example, if you execute @samp{gdb a.out}, then the executable file
10087 @code{a.out} is the only active target. If you designate a core file as
10088 well---presumably from a prior run that crashed and coredumped---then
10089 @value{GDBN} has two active targets and uses them in tandem, looking
10090 first in the corefile target, then in the executable file, to satisfy
10091 requests for memory addresses. (Typically, these two classes of target
10092 are complementary, since core files contain only a program's
10093 read-write memory---variables and so on---plus machine status, while
10094 executable files contain only the program text and initialized data.)
10096 When you type @code{run}, your executable file becomes an active process
10097 target as well. When a process target is active, all @value{GDBN}
10098 commands requesting memory addresses refer to that target; addresses in
10099 an active core file or executable file target are obscured while the
10100 process target is active.
10102 Use the @code{core-file} and @code{exec-file} commands to select a new
10103 core file or executable target (@pxref{Files, ,Commands to specify
10104 files}). To specify as a target a process that is already running, use
10105 the @code{attach} command (@pxref{Attach, ,Debugging an already-running
10108 @node Target Commands
10109 @section Commands for managing targets
10112 @item target @var{type} @var{parameters}
10113 Connects the @value{GDBN} host environment to a target machine or
10114 process. A target is typically a protocol for talking to debugging
10115 facilities. You use the argument @var{type} to specify the type or
10116 protocol of the target machine.
10118 Further @var{parameters} are interpreted by the target protocol, but
10119 typically include things like device names or host names to connect
10120 with, process numbers, and baud rates.
10122 The @code{target} command does not repeat if you press @key{RET} again
10123 after executing the command.
10125 @kindex help target
10127 Displays the names of all targets available. To display targets
10128 currently selected, use either @code{info target} or @code{info files}
10129 (@pxref{Files, ,Commands to specify files}).
10131 @item help target @var{name}
10132 Describe a particular target, including any parameters necessary to
10135 @kindex set gnutarget
10136 @item set gnutarget @var{args}
10137 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
10138 knows whether it is reading an @dfn{executable},
10139 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
10140 with the @code{set gnutarget} command. Unlike most @code{target} commands,
10141 with @code{gnutarget} the @code{target} refers to a program, not a machine.
10144 @emph{Warning:} To specify a file format with @code{set gnutarget},
10145 you must know the actual BFD name.
10149 @xref{Files, , Commands to specify files}.
10151 @kindex show gnutarget
10152 @item show gnutarget
10153 Use the @code{show gnutarget} command to display what file format
10154 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
10155 @value{GDBN} will determine the file format for each file automatically,
10156 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
10159 Here are some common targets (available, or not, depending on the GDB
10163 @kindex target exec
10164 @item target exec @var{program}
10165 An executable file. @samp{target exec @var{program}} is the same as
10166 @samp{exec-file @var{program}}.
10168 @kindex target core
10169 @item target core @var{filename}
10170 A core dump file. @samp{target core @var{filename}} is the same as
10171 @samp{core-file @var{filename}}.
10173 @kindex target remote
10174 @item target remote @var{dev}
10175 Remote serial target in GDB-specific protocol. The argument @var{dev}
10176 specifies what serial device to use for the connection (e.g.
10177 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
10178 supports the @code{load} command. This is only useful if you have
10179 some other way of getting the stub to the target system, and you can put
10180 it somewhere in memory where it won't get clobbered by the download.
10184 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
10192 works; however, you cannot assume that a specific memory map, device
10193 drivers, or even basic I/O is available, although some simulators do
10194 provide these. For info about any processor-specific simulator details,
10195 see the appropriate section in @ref{Embedded Processors, ,Embedded
10200 Some configurations may include these targets as well:
10204 @kindex target nrom
10205 @item target nrom @var{dev}
10206 NetROM ROM emulator. This target only supports downloading.
10210 Different targets are available on different configurations of @value{GDBN};
10211 your configuration may have more or fewer targets.
10213 Many remote targets require you to download the executable's code
10214 once you've successfully established a connection.
10218 @kindex load @var{filename}
10219 @item load @var{filename}
10220 Depending on what remote debugging facilities are configured into
10221 @value{GDBN}, the @code{load} command may be available. Where it exists, it
10222 is meant to make @var{filename} (an executable) available for debugging
10223 on the remote system---by downloading, or dynamic linking, for example.
10224 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
10225 the @code{add-symbol-file} command.
10227 If your @value{GDBN} does not have a @code{load} command, attempting to
10228 execute it gets the error message ``@code{You can't do that when your
10229 target is @dots{}}''
10231 The file is loaded at whatever address is specified in the executable.
10232 For some object file formats, you can specify the load address when you
10233 link the program; for other formats, like a.out, the object file format
10234 specifies a fixed address.
10235 @c FIXME! This would be a good place for an xref to the GNU linker doc.
10237 @code{load} does not repeat if you press @key{RET} again after using it.
10241 @section Choosing target byte order
10243 @cindex choosing target byte order
10244 @cindex target byte order
10246 Some types of processors, such as the MIPS, PowerPC, and Hitachi SH,
10247 offer the ability to run either big-endian or little-endian byte
10248 orders. Usually the executable or symbol will include a bit to
10249 designate the endian-ness, and you will not need to worry about
10250 which to use. However, you may still find it useful to adjust
10251 @value{GDBN}'s idea of processor endian-ness manually.
10254 @kindex set endian big
10255 @item set endian big
10256 Instruct @value{GDBN} to assume the target is big-endian.
10258 @kindex set endian little
10259 @item set endian little
10260 Instruct @value{GDBN} to assume the target is little-endian.
10262 @kindex set endian auto
10263 @item set endian auto
10264 Instruct @value{GDBN} to use the byte order associated with the
10268 Display @value{GDBN}'s current idea of the target byte order.
10272 Note that these commands merely adjust interpretation of symbolic
10273 data on the host, and that they have absolutely no effect on the
10277 @section Remote debugging
10278 @cindex remote debugging
10280 If you are trying to debug a program running on a machine that cannot run
10281 @value{GDBN} in the usual way, it is often useful to use remote debugging.
10282 For example, you might use remote debugging on an operating system kernel,
10283 or on a small system which does not have a general purpose operating system
10284 powerful enough to run a full-featured debugger.
10286 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
10287 to make this work with particular debugging targets. In addition,
10288 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
10289 but not specific to any particular target system) which you can use if you
10290 write the remote stubs---the code that runs on the remote system to
10291 communicate with @value{GDBN}.
10293 Other remote targets may be available in your
10294 configuration of @value{GDBN}; use @code{help target} to list them.
10297 @section Kernel Object Display
10299 @cindex kernel object display
10300 @cindex kernel object
10303 Some targets support kernel object display. Using this facility,
10304 @value{GDBN} communicates specially with the underlying operating system
10305 and can display information about operating system-level objects such as
10306 mutexes and other synchronization objects. Exactly which objects can be
10307 displayed is determined on a per-OS basis.
10309 Use the @code{set os} command to set the operating system. This tells
10310 @value{GDBN} which kernel object display module to initialize:
10313 (@value{GDBP}) set os cisco
10316 If @code{set os} succeeds, @value{GDBN} will display some information
10317 about the operating system, and will create a new @code{info} command
10318 which can be used to query the target. The @code{info} command is named
10319 after the operating system:
10322 (@value{GDBP}) info cisco
10323 List of Cisco Kernel Objects
10325 any Any and all objects
10328 Further subcommands can be used to query about particular objects known
10331 There is currently no way to determine whether a given operating system
10332 is supported other than to try it.
10335 @node Remote Debugging
10336 @chapter Debugging remote programs
10339 * Server:: Using the gdbserver program
10340 * NetWare:: Using the gdbserve.nlm program
10341 * remote stub:: Implementing a remote stub
10345 @section Using the @code{gdbserver} program
10348 @cindex remote connection without stubs
10349 @code{gdbserver} is a control program for Unix-like systems, which
10350 allows you to connect your program with a remote @value{GDBN} via
10351 @code{target remote}---but without linking in the usual debugging stub.
10353 @code{gdbserver} is not a complete replacement for the debugging stubs,
10354 because it requires essentially the same operating-system facilities
10355 that @value{GDBN} itself does. In fact, a system that can run
10356 @code{gdbserver} to connect to a remote @value{GDBN} could also run
10357 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
10358 because it is a much smaller program than @value{GDBN} itself. It is
10359 also easier to port than all of @value{GDBN}, so you may be able to get
10360 started more quickly on a new system by using @code{gdbserver}.
10361 Finally, if you develop code for real-time systems, you may find that
10362 the tradeoffs involved in real-time operation make it more convenient to
10363 do as much development work as possible on another system, for example
10364 by cross-compiling. You can use @code{gdbserver} to make a similar
10365 choice for debugging.
10367 @value{GDBN} and @code{gdbserver} communicate via either a serial line
10368 or a TCP connection, using the standard @value{GDBN} remote serial
10372 @item On the target machine,
10373 you need to have a copy of the program you want to debug.
10374 @code{gdbserver} does not need your program's symbol table, so you can
10375 strip the program if necessary to save space. @value{GDBN} on the host
10376 system does all the symbol handling.
10378 To use the server, you must tell it how to communicate with @value{GDBN};
10379 the name of your program; and the arguments for your program. The usual
10383 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
10386 @var{comm} is either a device name (to use a serial line) or a TCP
10387 hostname and portnumber. For example, to debug Emacs with the argument
10388 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
10392 target> gdbserver /dev/com1 emacs foo.txt
10395 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
10398 To use a TCP connection instead of a serial line:
10401 target> gdbserver host:2345 emacs foo.txt
10404 The only difference from the previous example is the first argument,
10405 specifying that you are communicating with the host @value{GDBN} via
10406 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
10407 expect a TCP connection from machine @samp{host} to local TCP port 2345.
10408 (Currently, the @samp{host} part is ignored.) You can choose any number
10409 you want for the port number as long as it does not conflict with any
10410 TCP ports already in use on the target system (for example, @code{23} is
10411 reserved for @code{telnet}).@footnote{If you choose a port number that
10412 conflicts with another service, @code{gdbserver} prints an error message
10413 and exits.} You must use the same port number with the host @value{GDBN}
10414 @code{target remote} command.
10416 On some targets, @code{gdbserver} can also attach to running programs.
10417 This is accomplished via the @code{--attach} argument. The syntax is:
10420 target> gdbserver @var{comm} --attach @var{pid}
10423 @var{pid} is the process ID of a currently running process. It isn't necessary
10424 to point @code{gdbserver} at a binary for the running process.
10426 @item On the @value{GDBN} host machine,
10427 you need an unstripped copy of your program, since @value{GDBN} needs
10428 symbols and debugging information. Start up @value{GDBN} as usual,
10429 using the name of the local copy of your program as the first argument.
10430 (You may also need the @w{@samp{--baud}} option if the serial line is
10431 running at anything other than 9600@dmn{bps}.) After that, use @code{target
10432 remote} to establish communications with @code{gdbserver}. Its argument
10433 is either a device name (usually a serial device, like
10434 @file{/dev/ttyb}), or a TCP port descriptor in the form
10435 @code{@var{host}:@var{PORT}}. For example:
10438 (@value{GDBP}) target remote /dev/ttyb
10442 communicates with the server via serial line @file{/dev/ttyb}, and
10445 (@value{GDBP}) target remote the-target:2345
10449 communicates via a TCP connection to port 2345 on host @w{@file{the-target}}.
10450 For TCP connections, you must start up @code{gdbserver} prior to using
10451 the @code{target remote} command. Otherwise you may get an error whose
10452 text depends on the host system, but which usually looks something like
10453 @samp{Connection refused}.
10457 @section Using the @code{gdbserve.nlm} program
10459 @kindex gdbserve.nlm
10460 @code{gdbserve.nlm} is a control program for NetWare systems, which
10461 allows you to connect your program with a remote @value{GDBN} via
10462 @code{target remote}.
10464 @value{GDBN} and @code{gdbserve.nlm} communicate via a serial line,
10465 using the standard @value{GDBN} remote serial protocol.
10468 @item On the target machine,
10469 you need to have a copy of the program you want to debug.
10470 @code{gdbserve.nlm} does not need your program's symbol table, so you
10471 can strip the program if necessary to save space. @value{GDBN} on the
10472 host system does all the symbol handling.
10474 To use the server, you must tell it how to communicate with
10475 @value{GDBN}; the name of your program; and the arguments for your
10476 program. The syntax is:
10479 load gdbserve [ BOARD=@var{board} ] [ PORT=@var{port} ]
10480 [ BAUD=@var{baud} ] @var{program} [ @var{args} @dots{} ]
10483 @var{board} and @var{port} specify the serial line; @var{baud} specifies
10484 the baud rate used by the connection. @var{port} and @var{node} default
10485 to 0, @var{baud} defaults to 9600@dmn{bps}.
10487 For example, to debug Emacs with the argument @samp{foo.txt}and
10488 communicate with @value{GDBN} over serial port number 2 or board 1
10489 using a 19200@dmn{bps} connection:
10492 load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
10495 @item On the @value{GDBN} host machine,
10496 you need an unstripped copy of your program, since @value{GDBN} needs
10497 symbols and debugging information. Start up @value{GDBN} as usual,
10498 using the name of the local copy of your program as the first argument.
10499 (You may also need the @w{@samp{--baud}} option if the serial line is
10500 running at anything other than 9600@dmn{bps}. After that, use @code{target
10501 remote} to establish communications with @code{gdbserve.nlm}. Its
10502 argument is a device name (usually a serial device, like
10503 @file{/dev/ttyb}). For example:
10506 (@value{GDBP}) target remote /dev/ttyb
10510 communications with the server via serial line @file{/dev/ttyb}.
10514 @section Implementing a remote stub
10516 @cindex debugging stub, example
10517 @cindex remote stub, example
10518 @cindex stub example, remote debugging
10519 The stub files provided with @value{GDBN} implement the target side of the
10520 communication protocol, and the @value{GDBN} side is implemented in the
10521 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
10522 these subroutines to communicate, and ignore the details. (If you're
10523 implementing your own stub file, you can still ignore the details: start
10524 with one of the existing stub files. @file{sparc-stub.c} is the best
10525 organized, and therefore the easiest to read.)
10527 @cindex remote serial debugging, overview
10528 To debug a program running on another machine (the debugging
10529 @dfn{target} machine), you must first arrange for all the usual
10530 prerequisites for the program to run by itself. For example, for a C
10535 A startup routine to set up the C runtime environment; these usually
10536 have a name like @file{crt0}. The startup routine may be supplied by
10537 your hardware supplier, or you may have to write your own.
10540 A C subroutine library to support your program's
10541 subroutine calls, notably managing input and output.
10544 A way of getting your program to the other machine---for example, a
10545 download program. These are often supplied by the hardware
10546 manufacturer, but you may have to write your own from hardware
10550 The next step is to arrange for your program to use a serial port to
10551 communicate with the machine where @value{GDBN} is running (the @dfn{host}
10552 machine). In general terms, the scheme looks like this:
10556 @value{GDBN} already understands how to use this protocol; when everything
10557 else is set up, you can simply use the @samp{target remote} command
10558 (@pxref{Targets,,Specifying a Debugging Target}).
10560 @item On the target,
10561 you must link with your program a few special-purpose subroutines that
10562 implement the @value{GDBN} remote serial protocol. The file containing these
10563 subroutines is called a @dfn{debugging stub}.
10565 On certain remote targets, you can use an auxiliary program
10566 @code{gdbserver} instead of linking a stub into your program.
10567 @xref{Server,,Using the @code{gdbserver} program}, for details.
10570 The debugging stub is specific to the architecture of the remote
10571 machine; for example, use @file{sparc-stub.c} to debug programs on
10574 @cindex remote serial stub list
10575 These working remote stubs are distributed with @value{GDBN}:
10580 @cindex @file{i386-stub.c}
10583 For Intel 386 and compatible architectures.
10586 @cindex @file{m68k-stub.c}
10587 @cindex Motorola 680x0
10589 For Motorola 680x0 architectures.
10592 @cindex @file{sh-stub.c}
10595 For Hitachi SH architectures.
10598 @cindex @file{sparc-stub.c}
10600 For @sc{sparc} architectures.
10602 @item sparcl-stub.c
10603 @cindex @file{sparcl-stub.c}
10606 For Fujitsu @sc{sparclite} architectures.
10610 The @file{README} file in the @value{GDBN} distribution may list other
10611 recently added stubs.
10614 * Stub Contents:: What the stub can do for you
10615 * Bootstrapping:: What you must do for the stub
10616 * Debug Session:: Putting it all together
10619 @node Stub Contents
10620 @subsection What the stub can do for you
10622 @cindex remote serial stub
10623 The debugging stub for your architecture supplies these three
10627 @item set_debug_traps
10628 @kindex set_debug_traps
10629 @cindex remote serial stub, initialization
10630 This routine arranges for @code{handle_exception} to run when your
10631 program stops. You must call this subroutine explicitly near the
10632 beginning of your program.
10634 @item handle_exception
10635 @kindex handle_exception
10636 @cindex remote serial stub, main routine
10637 This is the central workhorse, but your program never calls it
10638 explicitly---the setup code arranges for @code{handle_exception} to
10639 run when a trap is triggered.
10641 @code{handle_exception} takes control when your program stops during
10642 execution (for example, on a breakpoint), and mediates communications
10643 with @value{GDBN} on the host machine. This is where the communications
10644 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
10645 representative on the target machine. It begins by sending summary
10646 information on the state of your program, then continues to execute,
10647 retrieving and transmitting any information @value{GDBN} needs, until you
10648 execute a @value{GDBN} command that makes your program resume; at that point,
10649 @code{handle_exception} returns control to your own code on the target
10653 @cindex @code{breakpoint} subroutine, remote
10654 Use this auxiliary subroutine to make your program contain a
10655 breakpoint. Depending on the particular situation, this may be the only
10656 way for @value{GDBN} to get control. For instance, if your target
10657 machine has some sort of interrupt button, you won't need to call this;
10658 pressing the interrupt button transfers control to
10659 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
10660 simply receiving characters on the serial port may also trigger a trap;
10661 again, in that situation, you don't need to call @code{breakpoint} from
10662 your own program---simply running @samp{target remote} from the host
10663 @value{GDBN} session gets control.
10665 Call @code{breakpoint} if none of these is true, or if you simply want
10666 to make certain your program stops at a predetermined point for the
10667 start of your debugging session.
10670 @node Bootstrapping
10671 @subsection What you must do for the stub
10673 @cindex remote stub, support routines
10674 The debugging stubs that come with @value{GDBN} are set up for a particular
10675 chip architecture, but they have no information about the rest of your
10676 debugging target machine.
10678 First of all you need to tell the stub how to communicate with the
10682 @item int getDebugChar()
10683 @kindex getDebugChar
10684 Write this subroutine to read a single character from the serial port.
10685 It may be identical to @code{getchar} for your target system; a
10686 different name is used to allow you to distinguish the two if you wish.
10688 @item void putDebugChar(int)
10689 @kindex putDebugChar
10690 Write this subroutine to write a single character to the serial port.
10691 It may be identical to @code{putchar} for your target system; a
10692 different name is used to allow you to distinguish the two if you wish.
10695 @cindex control C, and remote debugging
10696 @cindex interrupting remote targets
10697 If you want @value{GDBN} to be able to stop your program while it is
10698 running, you need to use an interrupt-driven serial driver, and arrange
10699 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
10700 character). That is the character which @value{GDBN} uses to tell the
10701 remote system to stop.
10703 Getting the debugging target to return the proper status to @value{GDBN}
10704 probably requires changes to the standard stub; one quick and dirty way
10705 is to just execute a breakpoint instruction (the ``dirty'' part is that
10706 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
10708 Other routines you need to supply are:
10711 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
10712 @kindex exceptionHandler
10713 Write this function to install @var{exception_address} in the exception
10714 handling tables. You need to do this because the stub does not have any
10715 way of knowing what the exception handling tables on your target system
10716 are like (for example, the processor's table might be in @sc{rom},
10717 containing entries which point to a table in @sc{ram}).
10718 @var{exception_number} is the exception number which should be changed;
10719 its meaning is architecture-dependent (for example, different numbers
10720 might represent divide by zero, misaligned access, etc). When this
10721 exception occurs, control should be transferred directly to
10722 @var{exception_address}, and the processor state (stack, registers,
10723 and so on) should be just as it is when a processor exception occurs. So if
10724 you want to use a jump instruction to reach @var{exception_address}, it
10725 should be a simple jump, not a jump to subroutine.
10727 For the 386, @var{exception_address} should be installed as an interrupt
10728 gate so that interrupts are masked while the handler runs. The gate
10729 should be at privilege level 0 (the most privileged level). The
10730 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
10731 help from @code{exceptionHandler}.
10733 @item void flush_i_cache()
10734 @kindex flush_i_cache
10735 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
10736 instruction cache, if any, on your target machine. If there is no
10737 instruction cache, this subroutine may be a no-op.
10739 On target machines that have instruction caches, @value{GDBN} requires this
10740 function to make certain that the state of your program is stable.
10744 You must also make sure this library routine is available:
10747 @item void *memset(void *, int, int)
10749 This is the standard library function @code{memset} that sets an area of
10750 memory to a known value. If you have one of the free versions of
10751 @code{libc.a}, @code{memset} can be found there; otherwise, you must
10752 either obtain it from your hardware manufacturer, or write your own.
10755 If you do not use the GNU C compiler, you may need other standard
10756 library subroutines as well; this varies from one stub to another,
10757 but in general the stubs are likely to use any of the common library
10758 subroutines which @code{@value{GCC}} generates as inline code.
10761 @node Debug Session
10762 @subsection Putting it all together
10764 @cindex remote serial debugging summary
10765 In summary, when your program is ready to debug, you must follow these
10770 Make sure you have defined the supporting low-level routines
10771 (@pxref{Bootstrapping,,What you must do for the stub}):
10773 @code{getDebugChar}, @code{putDebugChar},
10774 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
10778 Insert these lines near the top of your program:
10786 For the 680x0 stub only, you need to provide a variable called
10787 @code{exceptionHook}. Normally you just use:
10790 void (*exceptionHook)() = 0;
10794 but if before calling @code{set_debug_traps}, you set it to point to a
10795 function in your program, that function is called when
10796 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
10797 error). The function indicated by @code{exceptionHook} is called with
10798 one parameter: an @code{int} which is the exception number.
10801 Compile and link together: your program, the @value{GDBN} debugging stub for
10802 your target architecture, and the supporting subroutines.
10805 Make sure you have a serial connection between your target machine and
10806 the @value{GDBN} host, and identify the serial port on the host.
10809 @c The "remote" target now provides a `load' command, so we should
10810 @c document that. FIXME.
10811 Download your program to your target machine (or get it there by
10812 whatever means the manufacturer provides), and start it.
10815 To start remote debugging, run @value{GDBN} on the host machine, and specify
10816 as an executable file the program that is running in the remote machine.
10817 This tells @value{GDBN} how to find your program's symbols and the contents
10821 @cindex serial line, @code{target remote}
10822 Establish communication using the @code{target remote} command.
10823 Its argument specifies how to communicate with the target
10824 machine---either via a devicename attached to a direct serial line, or a
10825 TCP or UDP port (usually to a terminal server which in turn has a serial line
10826 to the target). For example, to use a serial line connected to the
10827 device named @file{/dev/ttyb}:
10830 target remote /dev/ttyb
10833 @cindex TCP port, @code{target remote}
10834 To use a TCP connection, use an argument of the form
10835 @code{@var{host}:@var{port}} or @code{tcp:@var{host}:@var{port}}.
10836 For example, to connect to port 2828 on a
10837 terminal server named @code{manyfarms}:
10840 target remote manyfarms:2828
10843 If your remote target is actually running on the same machine as
10844 your debugger session (e.g.@: a simulator of your target running on
10845 the same host), you can omit the hostname. For example, to connect
10846 to port 1234 on your local machine:
10849 target remote :1234
10853 Note that the colon is still required here.
10855 @cindex UDP port, @code{target remote}
10856 To use a UDP connection, use an argument of the form
10857 @code{udp:@var{host}:@var{port}}. For example, to connect to UDP port 2828
10858 on a terminal server named @code{manyfarms}:
10861 target remote udp:manyfarms:2828
10864 When using a UDP connection for remote debugging, you should keep in mind
10865 that the `U' stands for ``Unreliable''. UDP can silently drop packets on
10866 busy or unreliable networks, which will cause havoc with your debugging
10871 Now you can use all the usual commands to examine and change data and to
10872 step and continue the remote program.
10874 To resume the remote program and stop debugging it, use the @code{detach}
10877 @cindex interrupting remote programs
10878 @cindex remote programs, interrupting
10879 Whenever @value{GDBN} is waiting for the remote program, if you type the
10880 interrupt character (often @key{C-C}), @value{GDBN} attempts to stop the
10881 program. This may or may not succeed, depending in part on the hardware
10882 and the serial drivers the remote system uses. If you type the
10883 interrupt character once again, @value{GDBN} displays this prompt:
10886 Interrupted while waiting for the program.
10887 Give up (and stop debugging it)? (y or n)
10890 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
10891 (If you decide you want to try again later, you can use @samp{target
10892 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
10893 goes back to waiting.
10896 @node Configurations
10897 @chapter Configuration-Specific Information
10899 While nearly all @value{GDBN} commands are available for all native and
10900 cross versions of the debugger, there are some exceptions. This chapter
10901 describes things that are only available in certain configurations.
10903 There are three major categories of configurations: native
10904 configurations, where the host and target are the same, embedded
10905 operating system configurations, which are usually the same for several
10906 different processor architectures, and bare embedded processors, which
10907 are quite different from each other.
10912 * Embedded Processors::
10919 This section describes details specific to particular native
10924 * SVR4 Process Information:: SVR4 process information
10925 * DJGPP Native:: Features specific to the DJGPP port
10926 * Cygwin Native:: Features specific to the Cygwin port
10932 On HP-UX systems, if you refer to a function or variable name that
10933 begins with a dollar sign, @value{GDBN} searches for a user or system
10934 name first, before it searches for a convenience variable.
10936 @node SVR4 Process Information
10937 @subsection SVR4 process information
10940 @cindex process image
10942 Many versions of SVR4 provide a facility called @samp{/proc} that can be
10943 used to examine the image of a running process using file-system
10944 subroutines. If @value{GDBN} is configured for an operating system with
10945 this facility, the command @code{info proc} is available to report on
10946 several kinds of information about the process running your program.
10947 @code{info proc} works only on SVR4 systems that include the
10948 @code{procfs} code. This includes OSF/1 (Digital Unix), Solaris, Irix,
10949 and Unixware, but not HP-UX or Linux, for example.
10954 Summarize available information about the process.
10956 @kindex info proc mappings
10957 @item info proc mappings
10958 Report on the address ranges accessible in the program, with information
10959 on whether your program may read, write, or execute each range.
10961 @comment These sub-options of 'info proc' were not included when
10962 @comment procfs.c was re-written. Keep their descriptions around
10963 @comment against the day when someone finds the time to put them back in.
10964 @kindex info proc times
10965 @item info proc times
10966 Starting time, user CPU time, and system CPU time for your program and
10969 @kindex info proc id
10971 Report on the process IDs related to your program: its own process ID,
10972 the ID of its parent, the process group ID, and the session ID.
10974 @kindex info proc status
10975 @item info proc status
10976 General information on the state of the process. If the process is
10977 stopped, this report includes the reason for stopping, and any signal
10980 @item info proc all
10981 Show all the above information about the process.
10986 @subsection Features for Debugging @sc{djgpp} Programs
10987 @cindex @sc{djgpp} debugging
10988 @cindex native @sc{djgpp} debugging
10989 @cindex MS-DOS-specific commands
10991 @sc{djgpp} is the port of @sc{gnu} development tools to MS-DOS and
10992 MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs
10993 that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on
10994 top of real-mode DOS systems and their emulations.
10996 @value{GDBN} supports native debugging of @sc{djgpp} programs, and
10997 defines a few commands specific to the @sc{djgpp} port. This
10998 subsection describes those commands.
11003 This is a prefix of @sc{djgpp}-specific commands which print
11004 information about the target system and important OS structures.
11007 @cindex MS-DOS system info
11008 @cindex free memory information (MS-DOS)
11009 @item info dos sysinfo
11010 This command displays assorted information about the underlying
11011 platform: the CPU type and features, the OS version and flavor, the
11012 DPMI version, and the available conventional and DPMI memory.
11017 @cindex segment descriptor tables
11018 @cindex descriptor tables display
11020 @itemx info dos ldt
11021 @itemx info dos idt
11022 These 3 commands display entries from, respectively, Global, Local,
11023 and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor
11024 tables are data structures which store a descriptor for each segment
11025 that is currently in use. The segment's selector is an index into a
11026 descriptor table; the table entry for that index holds the
11027 descriptor's base address and limit, and its attributes and access
11030 A typical @sc{djgpp} program uses 3 segments: a code segment, a data
11031 segment (used for both data and the stack), and a DOS segment (which
11032 allows access to DOS/BIOS data structures and absolute addresses in
11033 conventional memory). However, the DPMI host will usually define
11034 additional segments in order to support the DPMI environment.
11036 @cindex garbled pointers
11037 These commands allow to display entries from the descriptor tables.
11038 Without an argument, all entries from the specified table are
11039 displayed. An argument, which should be an integer expression, means
11040 display a single entry whose index is given by the argument. For
11041 example, here's a convenient way to display information about the
11042 debugged program's data segment:
11045 @exdent @code{(@value{GDBP}) info dos ldt $ds}
11046 @exdent @code{0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)}
11050 This comes in handy when you want to see whether a pointer is outside
11051 the data segment's limit (i.e.@: @dfn{garbled}).
11053 @cindex page tables display (MS-DOS)
11055 @itemx info dos pte
11056 These two commands display entries from, respectively, the Page
11057 Directory and the Page Tables. Page Directories and Page Tables are
11058 data structures which control how virtual memory addresses are mapped
11059 into physical addresses. A Page Table includes an entry for every
11060 page of memory that is mapped into the program's address space; there
11061 may be several Page Tables, each one holding up to 4096 entries. A
11062 Page Directory has up to 4096 entries, one each for every Page Table
11063 that is currently in use.
11065 Without an argument, @kbd{info dos pde} displays the entire Page
11066 Directory, and @kbd{info dos pte} displays all the entries in all of
11067 the Page Tables. An argument, an integer expression, given to the
11068 @kbd{info dos pde} command means display only that entry from the Page
11069 Directory table. An argument given to the @kbd{info dos pte} command
11070 means display entries from a single Page Table, the one pointed to by
11071 the specified entry in the Page Directory.
11073 @cindex direct memory access (DMA) on MS-DOS
11074 These commands are useful when your program uses @dfn{DMA} (Direct
11075 Memory Access), which needs physical addresses to program the DMA
11078 These commands are supported only with some DPMI servers.
11080 @cindex physical address from linear address
11081 @item info dos address-pte @var{addr}
11082 This command displays the Page Table entry for a specified linear
11083 address. The argument linear address @var{addr} should already have the
11084 appropriate segment's base address added to it, because this command
11085 accepts addresses which may belong to @emph{any} segment. For
11086 example, here's how to display the Page Table entry for the page where
11087 the variable @code{i} is stored:
11090 @exdent @code{(@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i}
11091 @exdent @code{Page Table entry for address 0x11a00d30:}
11092 @exdent @code{Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30}
11096 This says that @code{i} is stored at offset @code{0xd30} from the page
11097 whose physical base address is @code{0x02698000}, and prints all the
11098 attributes of that page.
11100 Note that you must cast the addresses of variables to a @code{char *},
11101 since otherwise the value of @code{__djgpp_base_address}, the base
11102 address of all variables and functions in a @sc{djgpp} program, will
11103 be added using the rules of C pointer arithmetics: if @code{i} is
11104 declared an @code{int}, @value{GDBN} will add 4 times the value of
11105 @code{__djgpp_base_address} to the address of @code{i}.
11107 Here's another example, it displays the Page Table entry for the
11111 @exdent @code{(@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)}
11112 @exdent @code{Page Table entry for address 0x29110:}
11113 @exdent @code{Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110}
11117 (The @code{+ 3} offset is because the transfer buffer's address is the
11118 3rd member of the @code{_go32_info_block} structure.) The output of
11119 this command clearly shows that addresses in conventional memory are
11120 mapped 1:1, i.e.@: the physical and linear addresses are identical.
11122 This command is supported only with some DPMI servers.
11125 @node Cygwin Native
11126 @subsection Features for Debugging MS Windows PE executables
11127 @cindex MS Windows debugging
11128 @cindex native Cygwin debugging
11129 @cindex Cygwin-specific commands
11131 @value{GDBN} supports native debugging of MS Windows programs, and
11132 defines a few commands specific to the Cygwin port. This
11133 subsection describes those commands.
11138 This is a prefix of MS Windows specific commands which print
11139 information about the target system and important OS structures.
11141 @item info w32 selector
11142 This command displays information returned by
11143 the Win32 API @code{GetThreadSelectorEntry} function.
11144 It takes an optional argument that is evaluated to
11145 a long value to give the information about this given selector.
11146 Without argument, this command displays information
11147 about the the six segment registers.
11151 This is a Cygwin specific alias of info shared.
11153 @kindex dll-symbols
11155 This command loads symbols from a dll similarly to
11156 add-sym command but without the need to specify a base address.
11158 @kindex set new-console
11159 @item set new-console @var{mode}
11160 If @var{mode} is @code{on} the debuggee will
11161 be started in a new console on next start.
11162 If @var{mode} is @code{off}i, the debuggee will
11163 be started in the same console as the debugger.
11165 @kindex show new-console
11166 @item show new-console
11167 Displays whether a new console is used
11168 when the debuggee is started.
11170 @kindex set new-group
11171 @item set new-group @var{mode}
11172 This boolean value controls whether the debuggee should
11173 start a new group or stay in the same group as the debugger.
11174 This affects the way the Windows OS handles
11177 @kindex show new-group
11178 @item show new-group
11179 Displays current value of new-group boolean.
11181 @kindex set debugevents
11182 @item set debugevents
11183 This boolean value adds debug output concerning events seen by the debugger.
11185 @kindex set debugexec
11186 @item set debugexec
11187 This boolean value adds debug output concerning execute events
11188 seen by the debugger.
11190 @kindex set debugexceptions
11191 @item set debugexceptions
11192 This boolean value adds debug ouptut concerning exception events
11193 seen by the debugger.
11195 @kindex set debugmemory
11196 @item set debugmemory
11197 This boolean value adds debug ouptut concerning memory events
11198 seen by the debugger.
11202 This boolean values specifies whether the debuggee is called
11203 via a shell or directly (default value is on).
11207 Displays if the debuggee will be started with a shell.
11212 @section Embedded Operating Systems
11214 This section describes configurations involving the debugging of
11215 embedded operating systems that are available for several different
11219 * VxWorks:: Using @value{GDBN} with VxWorks
11222 @value{GDBN} includes the ability to debug programs running on
11223 various real-time operating systems.
11226 @subsection Using @value{GDBN} with VxWorks
11232 @kindex target vxworks
11233 @item target vxworks @var{machinename}
11234 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
11235 is the target system's machine name or IP address.
11239 On VxWorks, @code{load} links @var{filename} dynamically on the
11240 current target system as well as adding its symbols in @value{GDBN}.
11242 @value{GDBN} enables developers to spawn and debug tasks running on networked
11243 VxWorks targets from a Unix host. Already-running tasks spawned from
11244 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
11245 both the Unix host and on the VxWorks target. The program
11246 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
11247 installed with the name @code{vxgdb}, to distinguish it from a
11248 @value{GDBN} for debugging programs on the host itself.)
11251 @item VxWorks-timeout @var{args}
11252 @kindex vxworks-timeout
11253 All VxWorks-based targets now support the option @code{vxworks-timeout}.
11254 This option is set by the user, and @var{args} represents the number of
11255 seconds @value{GDBN} waits for responses to rpc's. You might use this if
11256 your VxWorks target is a slow software simulator or is on the far side
11257 of a thin network line.
11260 The following information on connecting to VxWorks was current when
11261 this manual was produced; newer releases of VxWorks may use revised
11264 @kindex INCLUDE_RDB
11265 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
11266 to include the remote debugging interface routines in the VxWorks
11267 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
11268 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
11269 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
11270 source debugging task @code{tRdbTask} when VxWorks is booted. For more
11271 information on configuring and remaking VxWorks, see the manufacturer's
11273 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
11275 Once you have included @file{rdb.a} in your VxWorks system image and set
11276 your Unix execution search path to find @value{GDBN}, you are ready to
11277 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
11278 @code{vxgdb}, depending on your installation).
11280 @value{GDBN} comes up showing the prompt:
11287 * VxWorks Connection:: Connecting to VxWorks
11288 * VxWorks Download:: VxWorks download
11289 * VxWorks Attach:: Running tasks
11292 @node VxWorks Connection
11293 @subsubsection Connecting to VxWorks
11295 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
11296 network. To connect to a target whose host name is ``@code{tt}'', type:
11299 (vxgdb) target vxworks tt
11303 @value{GDBN} displays messages like these:
11306 Attaching remote machine across net...
11311 @value{GDBN} then attempts to read the symbol tables of any object modules
11312 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
11313 these files by searching the directories listed in the command search
11314 path (@pxref{Environment, ,Your program's environment}); if it fails
11315 to find an object file, it displays a message such as:
11318 prog.o: No such file or directory.
11321 When this happens, add the appropriate directory to the search path with
11322 the @value{GDBN} command @code{path}, and execute the @code{target}
11325 @node VxWorks Download
11326 @subsubsection VxWorks download
11328 @cindex download to VxWorks
11329 If you have connected to the VxWorks target and you want to debug an
11330 object that has not yet been loaded, you can use the @value{GDBN}
11331 @code{load} command to download a file from Unix to VxWorks
11332 incrementally. The object file given as an argument to the @code{load}
11333 command is actually opened twice: first by the VxWorks target in order
11334 to download the code, then by @value{GDBN} in order to read the symbol
11335 table. This can lead to problems if the current working directories on
11336 the two systems differ. If both systems have NFS mounted the same
11337 filesystems, you can avoid these problems by using absolute paths.
11338 Otherwise, it is simplest to set the working directory on both systems
11339 to the directory in which the object file resides, and then to reference
11340 the file by its name, without any path. For instance, a program
11341 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
11342 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
11343 program, type this on VxWorks:
11346 -> cd "@var{vxpath}/vw/demo/rdb"
11350 Then, in @value{GDBN}, type:
11353 (vxgdb) cd @var{hostpath}/vw/demo/rdb
11354 (vxgdb) load prog.o
11357 @value{GDBN} displays a response similar to this:
11360 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
11363 You can also use the @code{load} command to reload an object module
11364 after editing and recompiling the corresponding source file. Note that
11365 this makes @value{GDBN} delete all currently-defined breakpoints,
11366 auto-displays, and convenience variables, and to clear the value
11367 history. (This is necessary in order to preserve the integrity of
11368 debugger's data structures that reference the target system's symbol
11371 @node VxWorks Attach
11372 @subsubsection Running tasks
11374 @cindex running VxWorks tasks
11375 You can also attach to an existing task using the @code{attach} command as
11379 (vxgdb) attach @var{task}
11383 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
11384 or suspended when you attach to it. Running tasks are suspended at
11385 the time of attachment.
11387 @node Embedded Processors
11388 @section Embedded Processors
11390 This section goes into details specific to particular embedded
11396 * H8/300:: Hitachi H8/300
11397 * H8/500:: Hitachi H8/500
11398 * i960:: Intel i960
11399 * M32R/D:: Mitsubishi M32R/D
11400 * M68K:: Motorola M68K
11401 @c OBSOLETE * M88K:: Motorola M88K
11402 * MIPS Embedded:: MIPS Embedded
11403 * PA:: HP PA Embedded
11406 * Sparclet:: Tsqware Sparclet
11407 * Sparclite:: Fujitsu Sparclite
11408 * ST2000:: Tandem ST2000
11409 * Z8000:: Zilog Z8000
11418 @item target rdi @var{dev}
11419 ARM Angel monitor, via RDI library interface to ADP protocol. You may
11420 use this target to communicate with both boards running the Angel
11421 monitor, or with the EmbeddedICE JTAG debug device.
11424 @item target rdp @var{dev}
11430 @subsection Hitachi H8/300
11434 @kindex target hms@r{, with H8/300}
11435 @item target hms @var{dev}
11436 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
11437 Use special commands @code{device} and @code{speed} to control the serial
11438 line and the communications speed used.
11440 @kindex target e7000@r{, with H8/300}
11441 @item target e7000 @var{dev}
11442 E7000 emulator for Hitachi H8 and SH.
11444 @kindex target sh3@r{, with H8/300}
11445 @kindex target sh3e@r{, with H8/300}
11446 @item target sh3 @var{dev}
11447 @itemx target sh3e @var{dev}
11448 Hitachi SH-3 and SH-3E target systems.
11452 @cindex download to H8/300 or H8/500
11453 @cindex H8/300 or H8/500 download
11454 @cindex download to Hitachi SH
11455 @cindex Hitachi SH download
11456 When you select remote debugging to a Hitachi SH, H8/300, or H8/500
11457 board, the @code{load} command downloads your program to the Hitachi
11458 board and also opens it as the current executable target for
11459 @value{GDBN} on your host (like the @code{file} command).
11461 @value{GDBN} needs to know these things to talk to your
11462 Hitachi SH, H8/300, or H8/500:
11466 that you want to use @samp{target hms}, the remote debugging interface
11467 for Hitachi microprocessors, or @samp{target e7000}, the in-circuit
11468 emulator for the Hitachi SH and the Hitachi 300H. (@samp{target hms} is
11469 the default when @value{GDBN} is configured specifically for the Hitachi SH,
11470 H8/300, or H8/500.)
11473 what serial device connects your host to your Hitachi board (the first
11474 serial device available on your host is the default).
11477 what speed to use over the serial device.
11481 * Hitachi Boards:: Connecting to Hitachi boards.
11482 * Hitachi ICE:: Using the E7000 In-Circuit Emulator.
11483 * Hitachi Special:: Special @value{GDBN} commands for Hitachi micros.
11486 @node Hitachi Boards
11487 @subsubsection Connecting to Hitachi boards
11489 @c only for Unix hosts
11491 @cindex serial device, Hitachi micros
11492 Use the special @code{@value{GDBN}} command @samp{device @var{port}} if you
11493 need to explicitly set the serial device. The default @var{port} is the
11494 first available port on your host. This is only necessary on Unix
11495 hosts, where it is typically something like @file{/dev/ttya}.
11498 @cindex serial line speed, Hitachi micros
11499 @code{@value{GDBN}} has another special command to set the communications
11500 speed: @samp{speed @var{bps}}. This command also is only used from Unix
11501 hosts; on DOS hosts, set the line speed as usual from outside @value{GDBN} with
11502 the DOS @code{mode} command (for instance,
11503 @w{@kbd{mode com2:9600,n,8,1,p}} for a 9600@dmn{bps} connection).
11505 The @samp{device} and @samp{speed} commands are available only when you
11506 use a Unix host to debug your Hitachi microprocessor programs. If you
11508 @value{GDBN} depends on an auxiliary terminate-and-stay-resident program
11509 called @code{asynctsr} to communicate with the development board
11510 through a PC serial port. You must also use the DOS @code{mode} command
11511 to set up the serial port on the DOS side.
11513 The following sample session illustrates the steps needed to start a
11514 program under @value{GDBN} control on an H8/300. The example uses a
11515 sample H8/300 program called @file{t.x}. The procedure is the same for
11516 the Hitachi SH and the H8/500.
11518 First hook up your development board. In this example, we use a
11519 board attached to serial port @code{COM2}; if you use a different serial
11520 port, substitute its name in the argument of the @code{mode} command.
11521 When you call @code{asynctsr}, the auxiliary comms program used by the
11522 debugger, you give it just the numeric part of the serial port's name;
11523 for example, @samp{asyncstr 2} below runs @code{asyncstr} on
11527 C:\H8300\TEST> asynctsr 2
11528 C:\H8300\TEST> mode com2:9600,n,8,1,p
11530 Resident portion of MODE loaded
11532 COM2: 9600, n, 8, 1, p
11537 @emph{Warning:} We have noticed a bug in PC-NFS that conflicts with
11538 @code{asynctsr}. If you also run PC-NFS on your DOS host, you may need to
11539 disable it, or even boot without it, to use @code{asynctsr} to control
11540 your development board.
11543 @kindex target hms@r{, and serial protocol}
11544 Now that serial communications are set up, and the development board is
11545 connected, you can start up @value{GDBN}. Call @code{@value{GDBP}} with
11546 the name of your program as the argument. @code{@value{GDBN}} prompts
11547 you, as usual, with the prompt @samp{(@value{GDBP})}. Use two special
11548 commands to begin your debugging session: @samp{target hms} to specify
11549 cross-debugging to the Hitachi board, and the @code{load} command to
11550 download your program to the board. @code{load} displays the names of
11551 the program's sections, and a @samp{*} for each 2K of data downloaded.
11552 (If you want to refresh @value{GDBN} data on symbols or on the
11553 executable file without downloading, use the @value{GDBN} commands
11554 @code{file} or @code{symbol-file}. These commands, and @code{load}
11555 itself, are described in @ref{Files,,Commands to specify files}.)
11558 (eg-C:\H8300\TEST) @value{GDBP} t.x
11559 @value{GDBN} is free software and you are welcome to distribute copies
11560 of it under certain conditions; type "show copying" to see
11562 There is absolutely no warranty for @value{GDBN}; type "show warranty"
11564 @value{GDBN} @value{GDBVN}, Copyright 1992 Free Software Foundation, Inc...
11565 (@value{GDBP}) target hms
11566 Connected to remote H8/300 HMS system.
11567 (@value{GDBP}) load t.x
11568 .text : 0x8000 .. 0xabde ***********
11569 .data : 0xabde .. 0xad30 *
11570 .stack : 0xf000 .. 0xf014 *
11573 At this point, you're ready to run or debug your program. From here on,
11574 you can use all the usual @value{GDBN} commands. The @code{break} command
11575 sets breakpoints; the @code{run} command starts your program;
11576 @code{print} or @code{x} display data; the @code{continue} command
11577 resumes execution after stopping at a breakpoint. You can use the
11578 @code{help} command at any time to find out more about @value{GDBN} commands.
11580 Remember, however, that @emph{operating system} facilities aren't
11581 available on your development board; for example, if your program hangs,
11582 you can't send an interrupt---but you can press the @sc{reset} switch!
11584 Use the @sc{reset} button on the development board
11587 to interrupt your program (don't use @kbd{ctl-C} on the DOS host---it has
11588 no way to pass an interrupt signal to the development board); and
11591 to return to the @value{GDBN} command prompt after your program finishes
11592 normally. The communications protocol provides no other way for @value{GDBN}
11593 to detect program completion.
11596 In either case, @value{GDBN} sees the effect of a @sc{reset} on the
11597 development board as a ``normal exit'' of your program.
11600 @subsubsection Using the E7000 in-circuit emulator
11602 @kindex target e7000@r{, with Hitachi ICE}
11603 You can use the E7000 in-circuit emulator to develop code for either the
11604 Hitachi SH or the H8/300H. Use one of these forms of the @samp{target
11605 e7000} command to connect @value{GDBN} to your E7000:
11608 @item target e7000 @var{port} @var{speed}
11609 Use this form if your E7000 is connected to a serial port. The
11610 @var{port} argument identifies what serial port to use (for example,
11611 @samp{com2}). The third argument is the line speed in bits per second
11612 (for example, @samp{9600}).
11614 @item target e7000 @var{hostname}
11615 If your E7000 is installed as a host on a TCP/IP network, you can just
11616 specify its hostname; @value{GDBN} uses @code{telnet} to connect.
11619 @node Hitachi Special
11620 @subsubsection Special @value{GDBN} commands for Hitachi micros
11622 Some @value{GDBN} commands are available only for the H8/300:
11626 @kindex set machine
11627 @kindex show machine
11628 @item set machine h8300
11629 @itemx set machine h8300h
11630 Condition @value{GDBN} for one of the two variants of the H8/300
11631 architecture with @samp{set machine}. You can use @samp{show machine}
11632 to check which variant is currently in effect.
11641 @kindex set memory @var{mod}
11642 @cindex memory models, H8/500
11643 @item set memory @var{mod}
11645 Specify which H8/500 memory model (@var{mod}) you are using with
11646 @samp{set memory}; check which memory model is in effect with @samp{show
11647 memory}. The accepted values for @var{mod} are @code{small},
11648 @code{big}, @code{medium}, and @code{compact}.
11653 @subsection Intel i960
11657 @kindex target mon960
11658 @item target mon960 @var{dev}
11659 MON960 monitor for Intel i960.
11661 @kindex target nindy
11662 @item target nindy @var{devicename}
11663 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
11664 the name of the serial device to use for the connection, e.g.
11671 @dfn{Nindy} is a ROM Monitor program for Intel 960 target systems. When
11672 @value{GDBN} is configured to control a remote Intel 960 using Nindy, you can
11673 tell @value{GDBN} how to connect to the 960 in several ways:
11677 Through command line options specifying serial port, version of the
11678 Nindy protocol, and communications speed;
11681 By responding to a prompt on startup;
11684 By using the @code{target} command at any point during your @value{GDBN}
11685 session. @xref{Target Commands, ,Commands for managing targets}.
11689 @cindex download to Nindy-960
11690 With the Nindy interface to an Intel 960 board, @code{load}
11691 downloads @var{filename} to the 960 as well as adding its symbols in
11695 * Nindy Startup:: Startup with Nindy
11696 * Nindy Options:: Options for Nindy
11697 * Nindy Reset:: Nindy reset command
11700 @node Nindy Startup
11701 @subsubsection Startup with Nindy
11703 If you simply start @code{@value{GDBP}} without using any command-line
11704 options, you are prompted for what serial port to use, @emph{before} you
11705 reach the ordinary @value{GDBN} prompt:
11708 Attach /dev/ttyNN -- specify NN, or "quit" to quit:
11712 Respond to the prompt with whatever suffix (after @samp{/dev/tty})
11713 identifies the serial port you want to use. You can, if you choose,
11714 simply start up with no Nindy connection by responding to the prompt
11715 with an empty line. If you do this and later wish to attach to Nindy,
11716 use @code{target} (@pxref{Target Commands, ,Commands for managing targets}).
11718 @node Nindy Options
11719 @subsubsection Options for Nindy
11721 These are the startup options for beginning your @value{GDBN} session with a
11722 Nindy-960 board attached:
11725 @item -r @var{port}
11726 Specify the serial port name of a serial interface to be used to connect
11727 to the target system. This option is only available when @value{GDBN} is
11728 configured for the Intel 960 target architecture. You may specify
11729 @var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a
11730 device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique
11731 suffix for a specific @code{tty} (e.g. @samp{-r a}).
11734 (An uppercase letter ``O'', not a zero.) Specify that @value{GDBN} should use
11735 the ``old'' Nindy monitor protocol to connect to the target system.
11736 This option is only available when @value{GDBN} is configured for the Intel 960
11737 target architecture.
11740 @emph{Warning:} if you specify @samp{-O}, but are actually trying to
11741 connect to a target system that expects the newer protocol, the connection
11742 fails, appearing to be a speed mismatch. @value{GDBN} repeatedly
11743 attempts to reconnect at several different line speeds. You can abort
11744 this process with an interrupt.
11748 Specify that @value{GDBN} should first send a @code{BREAK} signal to the target
11749 system, in an attempt to reset it, before connecting to a Nindy target.
11752 @emph{Warning:} Many target systems do not have the hardware that this
11753 requires; it only works with a few boards.
11757 The standard @samp{-b} option controls the line speed used on the serial
11762 @subsubsection Nindy reset command
11767 For a Nindy target, this command sends a ``break'' to the remote target
11768 system; this is only useful if the target has been equipped with a
11769 circuit to perform a hard reset (or some other interesting action) when
11770 a break is detected.
11775 @subsection Mitsubishi M32R/D
11779 @kindex target m32r
11780 @item target m32r @var{dev}
11781 Mitsubishi M32R/D ROM monitor.
11788 The Motorola m68k configuration includes ColdFire support, and
11789 target command for the following ROM monitors.
11793 @kindex target abug
11794 @item target abug @var{dev}
11795 ABug ROM monitor for M68K.
11797 @kindex target cpu32bug
11798 @item target cpu32bug @var{dev}
11799 CPU32BUG monitor, running on a CPU32 (M68K) board.
11801 @kindex target dbug
11802 @item target dbug @var{dev}
11803 dBUG ROM monitor for Motorola ColdFire.
11806 @item target est @var{dev}
11807 EST-300 ICE monitor, running on a CPU32 (M68K) board.
11809 @kindex target rom68k
11810 @item target rom68k @var{dev}
11811 ROM 68K monitor, running on an M68K IDP board.
11815 If @value{GDBN} is configured with @code{m68*-ericsson-*}, it will
11816 instead have only a single special target command:
11820 @kindex target es1800
11821 @item target es1800 @var{dev}
11822 ES-1800 emulator for M68K.
11830 @kindex target rombug
11831 @item target rombug @var{dev}
11832 ROMBUG ROM monitor for OS/9000.
11836 @c OBSOLETE @node M88K
11837 @c OBSOLETE @subsection M88K
11839 @c OBSOLETE @table @code
11841 @c OBSOLETE @kindex target bug
11842 @c OBSOLETE @item target bug @var{dev}
11843 @c OBSOLETE BUG monitor, running on a MVME187 (m88k) board.
11845 @c OBSOLETE @end table
11847 @node MIPS Embedded
11848 @subsection MIPS Embedded
11850 @cindex MIPS boards
11851 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
11852 MIPS board attached to a serial line. This is available when
11853 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
11856 Use these @value{GDBN} commands to specify the connection to your target board:
11859 @item target mips @var{port}
11860 @kindex target mips @var{port}
11861 To run a program on the board, start up @code{@value{GDBP}} with the
11862 name of your program as the argument. To connect to the board, use the
11863 command @samp{target mips @var{port}}, where @var{port} is the name of
11864 the serial port connected to the board. If the program has not already
11865 been downloaded to the board, you may use the @code{load} command to
11866 download it. You can then use all the usual @value{GDBN} commands.
11868 For example, this sequence connects to the target board through a serial
11869 port, and loads and runs a program called @var{prog} through the
11873 host$ @value{GDBP} @var{prog}
11874 @value{GDBN} is free software and @dots{}
11875 (@value{GDBP}) target mips /dev/ttyb
11876 (@value{GDBP}) load @var{prog}
11880 @item target mips @var{hostname}:@var{portnumber}
11881 On some @value{GDBN} host configurations, you can specify a TCP
11882 connection (for instance, to a serial line managed by a terminal
11883 concentrator) instead of a serial port, using the syntax
11884 @samp{@var{hostname}:@var{portnumber}}.
11886 @item target pmon @var{port}
11887 @kindex target pmon @var{port}
11890 @item target ddb @var{port}
11891 @kindex target ddb @var{port}
11892 NEC's DDB variant of PMON for Vr4300.
11894 @item target lsi @var{port}
11895 @kindex target lsi @var{port}
11896 LSI variant of PMON.
11898 @kindex target r3900
11899 @item target r3900 @var{dev}
11900 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
11902 @kindex target array
11903 @item target array @var{dev}
11904 Array Tech LSI33K RAID controller board.
11910 @value{GDBN} also supports these special commands for MIPS targets:
11913 @item set processor @var{args}
11914 @itemx show processor
11915 @kindex set processor @var{args}
11916 @kindex show processor
11917 Use the @code{set processor} command to set the type of MIPS
11918 processor when you want to access processor-type-specific registers.
11919 For example, @code{set processor @var{r3041}} tells @value{GDBN}
11920 to use the CPU registers appropriate for the 3041 chip.
11921 Use the @code{show processor} command to see what MIPS processor @value{GDBN}
11922 is using. Use the @code{info reg} command to see what registers
11923 @value{GDBN} is using.
11925 @item set mipsfpu double
11926 @itemx set mipsfpu single
11927 @itemx set mipsfpu none
11928 @itemx show mipsfpu
11929 @kindex set mipsfpu
11930 @kindex show mipsfpu
11931 @cindex MIPS remote floating point
11932 @cindex floating point, MIPS remote
11933 If your target board does not support the MIPS floating point
11934 coprocessor, you should use the command @samp{set mipsfpu none} (if you
11935 need this, you may wish to put the command in your @value{GDBN} init
11936 file). This tells @value{GDBN} how to find the return value of
11937 functions which return floating point values. It also allows
11938 @value{GDBN} to avoid saving the floating point registers when calling
11939 functions on the board. If you are using a floating point coprocessor
11940 with only single precision floating point support, as on the @sc{r4650}
11941 processor, use the command @samp{set mipsfpu single}. The default
11942 double precision floating point coprocessor may be selected using
11943 @samp{set mipsfpu double}.
11945 In previous versions the only choices were double precision or no
11946 floating point, so @samp{set mipsfpu on} will select double precision
11947 and @samp{set mipsfpu off} will select no floating point.
11949 As usual, you can inquire about the @code{mipsfpu} variable with
11950 @samp{show mipsfpu}.
11952 @item set remotedebug @var{n}
11953 @itemx show remotedebug
11954 @kindex set remotedebug@r{, MIPS protocol}
11955 @kindex show remotedebug@r{, MIPS protocol}
11956 @cindex @code{remotedebug}, MIPS protocol
11957 @cindex MIPS @code{remotedebug} protocol
11958 @c FIXME! For this to be useful, you must know something about the MIPS
11959 @c FIXME...protocol. Where is it described?
11960 You can see some debugging information about communications with the board
11961 by setting the @code{remotedebug} variable. If you set it to @code{1} using
11962 @samp{set remotedebug 1}, every packet is displayed. If you set it
11963 to @code{2}, every character is displayed. You can check the current value
11964 at any time with the command @samp{show remotedebug}.
11966 @item set timeout @var{seconds}
11967 @itemx set retransmit-timeout @var{seconds}
11968 @itemx show timeout
11969 @itemx show retransmit-timeout
11970 @cindex @code{timeout}, MIPS protocol
11971 @cindex @code{retransmit-timeout}, MIPS protocol
11972 @kindex set timeout
11973 @kindex show timeout
11974 @kindex set retransmit-timeout
11975 @kindex show retransmit-timeout
11976 You can control the timeout used while waiting for a packet, in the MIPS
11977 remote protocol, with the @code{set timeout @var{seconds}} command. The
11978 default is 5 seconds. Similarly, you can control the timeout used while
11979 waiting for an acknowledgement of a packet with the @code{set
11980 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
11981 You can inspect both values with @code{show timeout} and @code{show
11982 retransmit-timeout}. (These commands are @emph{only} available when
11983 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
11985 The timeout set by @code{set timeout} does not apply when @value{GDBN}
11986 is waiting for your program to stop. In that case, @value{GDBN} waits
11987 forever because it has no way of knowing how long the program is going
11988 to run before stopping.
11992 @subsection PowerPC
11996 @kindex target dink32
11997 @item target dink32 @var{dev}
11998 DINK32 ROM monitor.
12000 @kindex target ppcbug
12001 @item target ppcbug @var{dev}
12002 @kindex target ppcbug1
12003 @item target ppcbug1 @var{dev}
12004 PPCBUG ROM monitor for PowerPC.
12007 @item target sds @var{dev}
12008 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
12013 @subsection HP PA Embedded
12017 @kindex target op50n
12018 @item target op50n @var{dev}
12019 OP50N monitor, running on an OKI HPPA board.
12021 @kindex target w89k
12022 @item target w89k @var{dev}
12023 W89K monitor, running on a Winbond HPPA board.
12028 @subsection Hitachi SH
12032 @kindex target hms@r{, with Hitachi SH}
12033 @item target hms @var{dev}
12034 A Hitachi SH board attached via serial line to your host. Use special
12035 commands @code{device} and @code{speed} to control the serial line and
12036 the communications speed used.
12038 @kindex target e7000@r{, with Hitachi SH}
12039 @item target e7000 @var{dev}
12040 E7000 emulator for Hitachi SH.
12042 @kindex target sh3@r{, with SH}
12043 @kindex target sh3e@r{, with SH}
12044 @item target sh3 @var{dev}
12045 @item target sh3e @var{dev}
12046 Hitachi SH-3 and SH-3E target systems.
12051 @subsection Tsqware Sparclet
12055 @value{GDBN} enables developers to debug tasks running on
12056 Sparclet targets from a Unix host.
12057 @value{GDBN} uses code that runs on
12058 both the Unix host and on the Sparclet target. The program
12059 @code{@value{GDBP}} is installed and executed on the Unix host.
12062 @item remotetimeout @var{args}
12063 @kindex remotetimeout
12064 @value{GDBN} supports the option @code{remotetimeout}.
12065 This option is set by the user, and @var{args} represents the number of
12066 seconds @value{GDBN} waits for responses.
12069 @cindex compiling, on Sparclet
12070 When compiling for debugging, include the options @samp{-g} to get debug
12071 information and @samp{-Ttext} to relocate the program to where you wish to
12072 load it on the target. You may also want to add the options @samp{-n} or
12073 @samp{-N} in order to reduce the size of the sections. Example:
12076 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
12079 You can use @code{objdump} to verify that the addresses are what you intended:
12082 sparclet-aout-objdump --headers --syms prog
12085 @cindex running, on Sparclet
12087 your Unix execution search path to find @value{GDBN}, you are ready to
12088 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
12089 (or @code{sparclet-aout-gdb}, depending on your installation).
12091 @value{GDBN} comes up showing the prompt:
12098 * Sparclet File:: Setting the file to debug
12099 * Sparclet Connection:: Connecting to Sparclet
12100 * Sparclet Download:: Sparclet download
12101 * Sparclet Execution:: Running and debugging
12104 @node Sparclet File
12105 @subsubsection Setting file to debug
12107 The @value{GDBN} command @code{file} lets you choose with program to debug.
12110 (gdbslet) file prog
12114 @value{GDBN} then attempts to read the symbol table of @file{prog}.
12115 @value{GDBN} locates
12116 the file by searching the directories listed in the command search
12118 If the file was compiled with debug information (option "-g"), source
12119 files will be searched as well.
12120 @value{GDBN} locates
12121 the source files by searching the directories listed in the directory search
12122 path (@pxref{Environment, ,Your program's environment}).
12124 to find a file, it displays a message such as:
12127 prog: No such file or directory.
12130 When this happens, add the appropriate directories to the search paths with
12131 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
12132 @code{target} command again.
12134 @node Sparclet Connection
12135 @subsubsection Connecting to Sparclet
12137 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
12138 To connect to a target on serial port ``@code{ttya}'', type:
12141 (gdbslet) target sparclet /dev/ttya
12142 Remote target sparclet connected to /dev/ttya
12143 main () at ../prog.c:3
12147 @value{GDBN} displays messages like these:
12153 @node Sparclet Download
12154 @subsubsection Sparclet download
12156 @cindex download to Sparclet
12157 Once connected to the Sparclet target,
12158 you can use the @value{GDBN}
12159 @code{load} command to download the file from the host to the target.
12160 The file name and load offset should be given as arguments to the @code{load}
12162 Since the file format is aout, the program must be loaded to the starting
12163 address. You can use @code{objdump} to find out what this value is. The load
12164 offset is an offset which is added to the VMA (virtual memory address)
12165 of each of the file's sections.
12166 For instance, if the program
12167 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
12168 and bss at 0x12010170, in @value{GDBN}, type:
12171 (gdbslet) load prog 0x12010000
12172 Loading section .text, size 0xdb0 vma 0x12010000
12175 If the code is loaded at a different address then what the program was linked
12176 to, you may need to use the @code{section} and @code{add-symbol-file} commands
12177 to tell @value{GDBN} where to map the symbol table.
12179 @node Sparclet Execution
12180 @subsubsection Running and debugging
12182 @cindex running and debugging Sparclet programs
12183 You can now begin debugging the task using @value{GDBN}'s execution control
12184 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
12185 manual for the list of commands.
12189 Breakpoint 1 at 0x12010000: file prog.c, line 3.
12191 Starting program: prog
12192 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
12193 3 char *symarg = 0;
12195 4 char *execarg = "hello!";
12200 @subsection Fujitsu Sparclite
12204 @kindex target sparclite
12205 @item target sparclite @var{dev}
12206 Fujitsu sparclite boards, used only for the purpose of loading.
12207 You must use an additional command to debug the program.
12208 For example: target remote @var{dev} using @value{GDBN} standard
12214 @subsection Tandem ST2000
12216 @value{GDBN} may be used with a Tandem ST2000 phone switch, running Tandem's
12219 To connect your ST2000 to the host system, see the manufacturer's
12220 manual. Once the ST2000 is physically attached, you can run:
12223 target st2000 @var{dev} @var{speed}
12227 to establish it as your debugging environment. @var{dev} is normally
12228 the name of a serial device, such as @file{/dev/ttya}, connected to the
12229 ST2000 via a serial line. You can instead specify @var{dev} as a TCP
12230 connection (for example, to a serial line attached via a terminal
12231 concentrator) using the syntax @code{@var{hostname}:@var{portnumber}}.
12233 The @code{load} and @code{attach} commands are @emph{not} defined for
12234 this target; you must load your program into the ST2000 as you normally
12235 would for standalone operation. @value{GDBN} reads debugging information
12236 (such as symbols) from a separate, debugging version of the program
12237 available on your host computer.
12238 @c FIXME!! This is terribly vague; what little content is here is
12239 @c basically hearsay.
12241 @cindex ST2000 auxiliary commands
12242 These auxiliary @value{GDBN} commands are available to help you with the ST2000
12246 @item st2000 @var{command}
12247 @kindex st2000 @var{cmd}
12248 @cindex STDBUG commands (ST2000)
12249 @cindex commands to STDBUG (ST2000)
12250 Send a @var{command} to the STDBUG monitor. See the manufacturer's
12251 manual for available commands.
12254 @cindex connect (to STDBUG)
12255 Connect the controlling terminal to the STDBUG command monitor. When
12256 you are done interacting with STDBUG, typing either of two character
12257 sequences gets you back to the @value{GDBN} command prompt:
12258 @kbd{@key{RET}~.} (Return, followed by tilde and period) or
12259 @kbd{@key{RET}~@key{C-d}} (Return, followed by tilde and control-D).
12263 @subsection Zilog Z8000
12266 @cindex simulator, Z8000
12267 @cindex Zilog Z8000 simulator
12269 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
12272 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
12273 unsegmented variant of the Z8000 architecture) or the Z8001 (the
12274 segmented variant). The simulator recognizes which architecture is
12275 appropriate by inspecting the object code.
12278 @item target sim @var{args}
12280 @kindex target sim@r{, with Z8000}
12281 Debug programs on a simulated CPU. If the simulator supports setup
12282 options, specify them via @var{args}.
12286 After specifying this target, you can debug programs for the simulated
12287 CPU in the same style as programs for your host computer; use the
12288 @code{file} command to load a new program image, the @code{run} command
12289 to run your program, and so on.
12291 As well as making available all the usual machine registers
12292 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
12293 additional items of information as specially named registers:
12298 Counts clock-ticks in the simulator.
12301 Counts instructions run in the simulator.
12304 Execution time in 60ths of a second.
12308 You can refer to these values in @value{GDBN} expressions with the usual
12309 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
12310 conditional breakpoint that suspends only after at least 5000
12311 simulated clock ticks.
12313 @node Architectures
12314 @section Architectures
12316 This section describes characteristics of architectures that affect
12317 all uses of @value{GDBN} with the architecture, both native and cross.
12330 @kindex set rstack_high_address
12331 @cindex AMD 29K register stack
12332 @cindex register stack, AMD29K
12333 @item set rstack_high_address @var{address}
12334 On AMD 29000 family processors, registers are saved in a separate
12335 @dfn{register stack}. There is no way for @value{GDBN} to determine the
12336 extent of this stack. Normally, @value{GDBN} just assumes that the
12337 stack is ``large enough''. This may result in @value{GDBN} referencing
12338 memory locations that do not exist. If necessary, you can get around
12339 this problem by specifying the ending address of the register stack with
12340 the @code{set rstack_high_address} command. The argument should be an
12341 address, which you probably want to precede with @samp{0x} to specify in
12344 @kindex show rstack_high_address
12345 @item show rstack_high_address
12346 Display the current limit of the register stack, on AMD 29000 family
12354 See the following section.
12359 @cindex stack on Alpha
12360 @cindex stack on MIPS
12361 @cindex Alpha stack
12363 Alpha- and MIPS-based computers use an unusual stack frame, which
12364 sometimes requires @value{GDBN} to search backward in the object code to
12365 find the beginning of a function.
12367 @cindex response time, MIPS debugging
12368 To improve response time (especially for embedded applications, where
12369 @value{GDBN} may be restricted to a slow serial line for this search)
12370 you may want to limit the size of this search, using one of these
12374 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
12375 @item set heuristic-fence-post @var{limit}
12376 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
12377 search for the beginning of a function. A value of @var{0} (the
12378 default) means there is no limit. However, except for @var{0}, the
12379 larger the limit the more bytes @code{heuristic-fence-post} must search
12380 and therefore the longer it takes to run.
12382 @item show heuristic-fence-post
12383 Display the current limit.
12387 These commands are available @emph{only} when @value{GDBN} is configured
12388 for debugging programs on Alpha or MIPS processors.
12391 @node Controlling GDB
12392 @chapter Controlling @value{GDBN}
12394 You can alter the way @value{GDBN} interacts with you by using the
12395 @code{set} command. For commands controlling how @value{GDBN} displays
12396 data, see @ref{Print Settings, ,Print settings}. Other settings are
12401 * Editing:: Command editing
12402 * History:: Command history
12403 * Screen Size:: Screen size
12404 * Numbers:: Numbers
12405 * Messages/Warnings:: Optional warnings and messages
12406 * Debugging Output:: Optional messages about internal happenings
12414 @value{GDBN} indicates its readiness to read a command by printing a string
12415 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
12416 can change the prompt string with the @code{set prompt} command. For
12417 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
12418 the prompt in one of the @value{GDBN} sessions so that you can always tell
12419 which one you are talking to.
12421 @emph{Note:} @code{set prompt} does not add a space for you after the
12422 prompt you set. This allows you to set a prompt which ends in a space
12423 or a prompt that does not.
12427 @item set prompt @var{newprompt}
12428 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
12430 @kindex show prompt
12432 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
12436 @section Command editing
12438 @cindex command line editing
12440 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
12441 @sc{gnu} library provides consistent behavior for programs which provide a
12442 command line interface to the user. Advantages are @sc{gnu} Emacs-style
12443 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
12444 substitution, and a storage and recall of command history across
12445 debugging sessions.
12447 You may control the behavior of command line editing in @value{GDBN} with the
12448 command @code{set}.
12451 @kindex set editing
12454 @itemx set editing on
12455 Enable command line editing (enabled by default).
12457 @item set editing off
12458 Disable command line editing.
12460 @kindex show editing
12462 Show whether command line editing is enabled.
12466 @section Command history
12468 @value{GDBN} can keep track of the commands you type during your
12469 debugging sessions, so that you can be certain of precisely what
12470 happened. Use these commands to manage the @value{GDBN} command
12474 @cindex history substitution
12475 @cindex history file
12476 @kindex set history filename
12477 @kindex GDBHISTFILE
12478 @item set history filename @var{fname}
12479 Set the name of the @value{GDBN} command history file to @var{fname}.
12480 This is the file where @value{GDBN} reads an initial command history
12481 list, and where it writes the command history from this session when it
12482 exits. You can access this list through history expansion or through
12483 the history command editing characters listed below. This file defaults
12484 to the value of the environment variable @code{GDBHISTFILE}, or to
12485 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
12488 @cindex history save
12489 @kindex set history save
12490 @item set history save
12491 @itemx set history save on
12492 Record command history in a file, whose name may be specified with the
12493 @code{set history filename} command. By default, this option is disabled.
12495 @item set history save off
12496 Stop recording command history in a file.
12498 @cindex history size
12499 @kindex set history size
12500 @item set history size @var{size}
12501 Set the number of commands which @value{GDBN} keeps in its history list.
12502 This defaults to the value of the environment variable
12503 @code{HISTSIZE}, or to 256 if this variable is not set.
12506 @cindex history expansion
12507 History expansion assigns special meaning to the character @kbd{!}.
12508 @ifset have-readline-appendices
12509 @xref{Event Designators}.
12512 Since @kbd{!} is also the logical not operator in C, history expansion
12513 is off by default. If you decide to enable history expansion with the
12514 @code{set history expansion on} command, you may sometimes need to
12515 follow @kbd{!} (when it is used as logical not, in an expression) with
12516 a space or a tab to prevent it from being expanded. The readline
12517 history facilities do not attempt substitution on the strings
12518 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
12520 The commands to control history expansion are:
12523 @kindex set history expansion
12524 @item set history expansion on
12525 @itemx set history expansion
12526 Enable history expansion. History expansion is off by default.
12528 @item set history expansion off
12529 Disable history expansion.
12531 The readline code comes with more complete documentation of
12532 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
12533 or @code{vi} may wish to read it.
12534 @ifset have-readline-appendices
12535 @xref{Command Line Editing}.
12539 @kindex show history
12541 @itemx show history filename
12542 @itemx show history save
12543 @itemx show history size
12544 @itemx show history expansion
12545 These commands display the state of the @value{GDBN} history parameters.
12546 @code{show history} by itself displays all four states.
12552 @item show commands
12553 Display the last ten commands in the command history.
12555 @item show commands @var{n}
12556 Print ten commands centered on command number @var{n}.
12558 @item show commands +
12559 Print ten commands just after the commands last printed.
12563 @section Screen size
12564 @cindex size of screen
12565 @cindex pauses in output
12567 Certain commands to @value{GDBN} may produce large amounts of
12568 information output to the screen. To help you read all of it,
12569 @value{GDBN} pauses and asks you for input at the end of each page of
12570 output. Type @key{RET} when you want to continue the output, or @kbd{q}
12571 to discard the remaining output. Also, the screen width setting
12572 determines when to wrap lines of output. Depending on what is being
12573 printed, @value{GDBN} tries to break the line at a readable place,
12574 rather than simply letting it overflow onto the following line.
12576 Normally @value{GDBN} knows the size of the screen from the terminal
12577 driver software. For example, on Unix @value{GDBN} uses the termcap data base
12578 together with the value of the @code{TERM} environment variable and the
12579 @code{stty rows} and @code{stty cols} settings. If this is not correct,
12580 you can override it with the @code{set height} and @code{set
12587 @kindex show height
12588 @item set height @var{lpp}
12590 @itemx set width @var{cpl}
12592 These @code{set} commands specify a screen height of @var{lpp} lines and
12593 a screen width of @var{cpl} characters. The associated @code{show}
12594 commands display the current settings.
12596 If you specify a height of zero lines, @value{GDBN} does not pause during
12597 output no matter how long the output is. This is useful if output is to a
12598 file or to an editor buffer.
12600 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
12601 from wrapping its output.
12606 @cindex number representation
12607 @cindex entering numbers
12609 You can always enter numbers in octal, decimal, or hexadecimal in
12610 @value{GDBN} by the usual conventions: octal numbers begin with
12611 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
12612 begin with @samp{0x}. Numbers that begin with none of these are, by
12613 default, entered in base 10; likewise, the default display for
12614 numbers---when no particular format is specified---is base 10. You can
12615 change the default base for both input and output with the @code{set
12619 @kindex set input-radix
12620 @item set input-radix @var{base}
12621 Set the default base for numeric input. Supported choices
12622 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12623 specified either unambiguously or using the current default radix; for
12633 sets the base to decimal. On the other hand, @samp{set radix 10}
12634 leaves the radix unchanged no matter what it was.
12636 @kindex set output-radix
12637 @item set output-radix @var{base}
12638 Set the default base for numeric display. Supported choices
12639 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12640 specified either unambiguously or using the current default radix.
12642 @kindex show input-radix
12643 @item show input-radix
12644 Display the current default base for numeric input.
12646 @kindex show output-radix
12647 @item show output-radix
12648 Display the current default base for numeric display.
12651 @node Messages/Warnings
12652 @section Optional warnings and messages
12654 By default, @value{GDBN} is silent about its inner workings. If you are
12655 running on a slow machine, you may want to use the @code{set verbose}
12656 command. This makes @value{GDBN} tell you when it does a lengthy
12657 internal operation, so you will not think it has crashed.
12659 Currently, the messages controlled by @code{set verbose} are those
12660 which announce that the symbol table for a source file is being read;
12661 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
12664 @kindex set verbose
12665 @item set verbose on
12666 Enables @value{GDBN} output of certain informational messages.
12668 @item set verbose off
12669 Disables @value{GDBN} output of certain informational messages.
12671 @kindex show verbose
12673 Displays whether @code{set verbose} is on or off.
12676 By default, if @value{GDBN} encounters bugs in the symbol table of an
12677 object file, it is silent; but if you are debugging a compiler, you may
12678 find this information useful (@pxref{Symbol Errors, ,Errors reading
12683 @kindex set complaints
12684 @item set complaints @var{limit}
12685 Permits @value{GDBN} to output @var{limit} complaints about each type of
12686 unusual symbols before becoming silent about the problem. Set
12687 @var{limit} to zero to suppress all complaints; set it to a large number
12688 to prevent complaints from being suppressed.
12690 @kindex show complaints
12691 @item show complaints
12692 Displays how many symbol complaints @value{GDBN} is permitted to produce.
12696 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
12697 lot of stupid questions to confirm certain commands. For example, if
12698 you try to run a program which is already running:
12702 The program being debugged has been started already.
12703 Start it from the beginning? (y or n)
12706 If you are willing to unflinchingly face the consequences of your own
12707 commands, you can disable this ``feature'':
12711 @kindex set confirm
12713 @cindex confirmation
12714 @cindex stupid questions
12715 @item set confirm off
12716 Disables confirmation requests.
12718 @item set confirm on
12719 Enables confirmation requests (the default).
12721 @kindex show confirm
12723 Displays state of confirmation requests.
12727 @node Debugging Output
12728 @section Optional messages about internal happenings
12730 @kindex set debug arch
12731 @item set debug arch
12732 Turns on or off display of gdbarch debugging info. The default is off
12733 @kindex show debug arch
12734 @item show debug arch
12735 Displays the current state of displaying gdbarch debugging info.
12736 @kindex set debug event
12737 @item set debug event
12738 Turns on or off display of @value{GDBN} event debugging info. The
12740 @kindex show debug event
12741 @item show debug event
12742 Displays the current state of displaying @value{GDBN} event debugging
12744 @kindex set debug expression
12745 @item set debug expression
12746 Turns on or off display of @value{GDBN} expression debugging info. The
12748 @kindex show debug expression
12749 @item show debug expression
12750 Displays the current state of displaying @value{GDBN} expression
12752 @kindex set debug overload
12753 @item set debug overload
12754 Turns on or off display of @value{GDBN} C@t{++} overload debugging
12755 info. This includes info such as ranking of functions, etc. The default
12757 @kindex show debug overload
12758 @item show debug overload
12759 Displays the current state of displaying @value{GDBN} C@t{++} overload
12761 @kindex set debug remote
12762 @cindex packets, reporting on stdout
12763 @cindex serial connections, debugging
12764 @item set debug remote
12765 Turns on or off display of reports on all packets sent back and forth across
12766 the serial line to the remote machine. The info is printed on the
12767 @value{GDBN} standard output stream. The default is off.
12768 @kindex show debug remote
12769 @item show debug remote
12770 Displays the state of display of remote packets.
12771 @kindex set debug serial
12772 @item set debug serial
12773 Turns on or off display of @value{GDBN} serial debugging info. The
12775 @kindex show debug serial
12776 @item show debug serial
12777 Displays the current state of displaying @value{GDBN} serial debugging
12779 @kindex set debug target
12780 @item set debug target
12781 Turns on or off display of @value{GDBN} target debugging info. This info
12782 includes what is going on at the target level of GDB, as it happens. The
12784 @kindex show debug target
12785 @item show debug target
12786 Displays the current state of displaying @value{GDBN} target debugging
12788 @kindex set debug varobj
12789 @item set debug varobj
12790 Turns on or off display of @value{GDBN} variable object debugging
12791 info. The default is off.
12792 @kindex show debug varobj
12793 @item show debug varobj
12794 Displays the current state of displaying @value{GDBN} variable object
12799 @chapter Canned Sequences of Commands
12801 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
12802 command lists}), @value{GDBN} provides two ways to store sequences of
12803 commands for execution as a unit: user-defined commands and command
12807 * Define:: User-defined commands
12808 * Hooks:: User-defined command hooks
12809 * Command Files:: Command files
12810 * Output:: Commands for controlled output
12814 @section User-defined commands
12816 @cindex user-defined command
12817 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
12818 which you assign a new name as a command. This is done with the
12819 @code{define} command. User commands may accept up to 10 arguments
12820 separated by whitespace. Arguments are accessed within the user command
12821 via @var{$arg0@dots{}$arg9}. A trivial example:
12825 print $arg0 + $arg1 + $arg2
12829 To execute the command use:
12836 This defines the command @code{adder}, which prints the sum of
12837 its three arguments. Note the arguments are text substitutions, so they may
12838 reference variables, use complex expressions, or even perform inferior
12844 @item define @var{commandname}
12845 Define a command named @var{commandname}. If there is already a command
12846 by that name, you are asked to confirm that you want to redefine it.
12848 The definition of the command is made up of other @value{GDBN} command lines,
12849 which are given following the @code{define} command. The end of these
12850 commands is marked by a line containing @code{end}.
12855 Takes a single argument, which is an expression to evaluate.
12856 It is followed by a series of commands that are executed
12857 only if the expression is true (nonzero).
12858 There can then optionally be a line @code{else}, followed
12859 by a series of commands that are only executed if the expression
12860 was false. The end of the list is marked by a line containing @code{end}.
12864 The syntax is similar to @code{if}: the command takes a single argument,
12865 which is an expression to evaluate, and must be followed by the commands to
12866 execute, one per line, terminated by an @code{end}.
12867 The commands are executed repeatedly as long as the expression
12871 @item document @var{commandname}
12872 Document the user-defined command @var{commandname}, so that it can be
12873 accessed by @code{help}. The command @var{commandname} must already be
12874 defined. This command reads lines of documentation just as @code{define}
12875 reads the lines of the command definition, ending with @code{end}.
12876 After the @code{document} command is finished, @code{help} on command
12877 @var{commandname} displays the documentation you have written.
12879 You may use the @code{document} command again to change the
12880 documentation of a command. Redefining the command with @code{define}
12881 does not change the documentation.
12883 @kindex help user-defined
12884 @item help user-defined
12885 List all user-defined commands, with the first line of the documentation
12890 @itemx show user @var{commandname}
12891 Display the @value{GDBN} commands used to define @var{commandname} (but
12892 not its documentation). If no @var{commandname} is given, display the
12893 definitions for all user-defined commands.
12895 @kindex show max-user-call-depth
12896 @kindex set max-user-call-depth
12897 @item show max-user-call-depth
12898 @itemx set max-user-call-depth
12899 The value of @code{max-user-call-depth} controls how many recursion
12900 levels are allowed in user-defined commands before GDB suspects an
12901 infinite recursion and aborts the command.
12905 When user-defined commands are executed, the
12906 commands of the definition are not printed. An error in any command
12907 stops execution of the user-defined command.
12909 If used interactively, commands that would ask for confirmation proceed
12910 without asking when used inside a user-defined command. Many @value{GDBN}
12911 commands that normally print messages to say what they are doing omit the
12912 messages when used in a user-defined command.
12915 @section User-defined command hooks
12916 @cindex command hooks
12917 @cindex hooks, for commands
12918 @cindex hooks, pre-command
12922 You may define @dfn{hooks}, which are a special kind of user-defined
12923 command. Whenever you run the command @samp{foo}, if the user-defined
12924 command @samp{hook-foo} exists, it is executed (with no arguments)
12925 before that command.
12927 @cindex hooks, post-command
12930 A hook may also be defined which is run after the command you executed.
12931 Whenever you run the command @samp{foo}, if the user-defined command
12932 @samp{hookpost-foo} exists, it is executed (with no arguments) after
12933 that command. Post-execution hooks may exist simultaneously with
12934 pre-execution hooks, for the same command.
12936 It is valid for a hook to call the command which it hooks. If this
12937 occurs, the hook is not re-executed, thereby avoiding infinte recursion.
12939 @c It would be nice if hookpost could be passed a parameter indicating
12940 @c if the command it hooks executed properly or not. FIXME!
12942 @kindex stop@r{, a pseudo-command}
12943 In addition, a pseudo-command, @samp{stop} exists. Defining
12944 (@samp{hook-stop}) makes the associated commands execute every time
12945 execution stops in your program: before breakpoint commands are run,
12946 displays are printed, or the stack frame is printed.
12948 For example, to ignore @code{SIGALRM} signals while
12949 single-stepping, but treat them normally during normal execution,
12954 handle SIGALRM nopass
12958 handle SIGALRM pass
12961 define hook-continue
12962 handle SIGLARM pass
12966 As a further example, to hook at the begining and end of the @code{echo}
12967 command, and to add extra text to the beginning and end of the message,
12975 define hookpost-echo
12979 (@value{GDBP}) echo Hello World
12980 <<<---Hello World--->>>
12985 You can define a hook for any single-word command in @value{GDBN}, but
12986 not for command aliases; you should define a hook for the basic command
12987 name, e.g. @code{backtrace} rather than @code{bt}.
12988 @c FIXME! So how does Joe User discover whether a command is an alias
12990 If an error occurs during the execution of your hook, execution of
12991 @value{GDBN} commands stops and @value{GDBN} issues a prompt
12992 (before the command that you actually typed had a chance to run).
12994 If you try to define a hook which does not match any known command, you
12995 get a warning from the @code{define} command.
12997 @node Command Files
12998 @section Command files
13000 @cindex command files
13001 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
13002 commands. Comments (lines starting with @kbd{#}) may also be included.
13003 An empty line in a command file does nothing; it does not mean to repeat
13004 the last command, as it would from the terminal.
13007 @cindex @file{.gdbinit}
13008 @cindex @file{gdb.ini}
13009 When you start @value{GDBN}, it automatically executes commands from its
13010 @dfn{init files}, normally called @file{.gdbinit}@footnote{The DJGPP
13011 port of @value{GDBN} uses the name @file{gdb.ini} instead, due to the
13012 limitations of file names imposed by DOS filesystems.}.
13013 During startup, @value{GDBN} does the following:
13017 Reads the init file (if any) in your home directory@footnote{On
13018 DOS/Windows systems, the home directory is the one pointed to by the
13019 @code{HOME} environment variable.}.
13022 Processes command line options and operands.
13025 Reads the init file (if any) in the current working directory.
13028 Reads command files specified by the @samp{-x} option.
13031 The init file in your home directory can set options (such as @samp{set
13032 complaints}) that affect subsequent processing of command line options
13033 and operands. Init files are not executed if you use the @samp{-nx}
13034 option (@pxref{Mode Options, ,Choosing modes}).
13036 @cindex init file name
13037 On some configurations of @value{GDBN}, the init file is known by a
13038 different name (these are typically environments where a specialized
13039 form of @value{GDBN} may need to coexist with other forms, hence a
13040 different name for the specialized version's init file). These are the
13041 environments with special init file names:
13043 @cindex @file{.vxgdbinit}
13046 VxWorks (Wind River Systems real-time OS): @file{.vxgdbinit}
13048 @cindex @file{.os68gdbinit}
13050 OS68K (Enea Data Systems real-time OS): @file{.os68gdbinit}
13052 @cindex @file{.esgdbinit}
13054 ES-1800 (Ericsson Telecom AB M68000 emulator): @file{.esgdbinit}
13057 You can also request the execution of a command file with the
13058 @code{source} command:
13062 @item source @var{filename}
13063 Execute the command file @var{filename}.
13066 The lines in a command file are executed sequentially. They are not
13067 printed as they are executed. An error in any command terminates
13068 execution of the command file and control is returned to the console.
13070 Commands that would ask for confirmation if used interactively proceed
13071 without asking when used in a command file. Many @value{GDBN} commands that
13072 normally print messages to say what they are doing omit the messages
13073 when called from command files.
13075 @value{GDBN} also accepts command input from standard input. In this
13076 mode, normal output goes to standard output and error output goes to
13077 standard error. Errors in a command file supplied on standard input do
13078 not terminate execution of the command file --- execution continues with
13082 gdb < cmds > log 2>&1
13085 (The syntax above will vary depending on the shell used.) This example
13086 will execute commands from the file @file{cmds}. All output and errors
13087 would be directed to @file{log}.
13090 @section Commands for controlled output
13092 During the execution of a command file or a user-defined command, normal
13093 @value{GDBN} output is suppressed; the only output that appears is what is
13094 explicitly printed by the commands in the definition. This section
13095 describes three commands useful for generating exactly the output you
13100 @item echo @var{text}
13101 @c I do not consider backslash-space a standard C escape sequence
13102 @c because it is not in ANSI.
13103 Print @var{text}. Nonprinting characters can be included in
13104 @var{text} using C escape sequences, such as @samp{\n} to print a
13105 newline. @strong{No newline is printed unless you specify one.}
13106 In addition to the standard C escape sequences, a backslash followed
13107 by a space stands for a space. This is useful for displaying a
13108 string with spaces at the beginning or the end, since leading and
13109 trailing spaces are otherwise trimmed from all arguments.
13110 To print @samp{@w{ }and foo =@w{ }}, use the command
13111 @samp{echo \@w{ }and foo = \@w{ }}.
13113 A backslash at the end of @var{text} can be used, as in C, to continue
13114 the command onto subsequent lines. For example,
13117 echo This is some text\n\
13118 which is continued\n\
13119 onto several lines.\n
13122 produces the same output as
13125 echo This is some text\n
13126 echo which is continued\n
13127 echo onto several lines.\n
13131 @item output @var{expression}
13132 Print the value of @var{expression} and nothing but that value: no
13133 newlines, no @samp{$@var{nn} = }. The value is not entered in the
13134 value history either. @xref{Expressions, ,Expressions}, for more information
13137 @item output/@var{fmt} @var{expression}
13138 Print the value of @var{expression} in format @var{fmt}. You can use
13139 the same formats as for @code{print}. @xref{Output Formats,,Output
13140 formats}, for more information.
13143 @item printf @var{string}, @var{expressions}@dots{}
13144 Print the values of the @var{expressions} under the control of
13145 @var{string}. The @var{expressions} are separated by commas and may be
13146 either numbers or pointers. Their values are printed as specified by
13147 @var{string}, exactly as if your program were to execute the C
13149 @c FIXME: the above implies that at least all ANSI C formats are
13150 @c supported, but it isn't true: %E and %G don't work (or so it seems).
13151 @c Either this is a bug, or the manual should document what formats are
13155 printf (@var{string}, @var{expressions}@dots{});
13158 For example, you can print two values in hex like this:
13161 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
13164 The only backslash-escape sequences that you can use in the format
13165 string are the simple ones that consist of backslash followed by a
13170 @chapter @value{GDBN} Text User Interface
13174 * TUI Overview:: TUI overview
13175 * TUI Keys:: TUI key bindings
13176 * TUI Single Key Mode:: TUI single key mode
13177 * TUI Commands:: TUI specific commands
13178 * TUI Configuration:: TUI configuration variables
13181 The @value{GDBN} Text User Interface, TUI in short,
13182 is a terminal interface which uses the @code{curses} library
13183 to show the source file, the assembly output, the program registers
13184 and @value{GDBN} commands in separate text windows.
13185 The TUI is available only when @value{GDBN} is configured
13186 with the @code{--enable-tui} configure option (@pxref{Configure Options}).
13189 @section TUI overview
13191 The TUI has two display modes that can be switched while
13196 A curses (or TUI) mode in which it displays several text
13197 windows on the terminal.
13200 A standard mode which corresponds to the @value{GDBN} configured without
13204 In the TUI mode, @value{GDBN} can display several text window
13209 This window is the @value{GDBN} command window with the @value{GDBN}
13210 prompt and the @value{GDBN} outputs. The @value{GDBN} input is still
13211 managed using readline but through the TUI. The @emph{command}
13212 window is always visible.
13215 The source window shows the source file of the program. The current
13216 line as well as active breakpoints are displayed in this window.
13219 The assembly window shows the disassembly output of the program.
13222 This window shows the processor registers. It detects when
13223 a register is changed and when this is the case, registers that have
13224 changed are highlighted.
13228 The source and assembly windows show the current program position
13229 by highlighting the current line and marking them with the @samp{>} marker.
13230 Breakpoints are also indicated with two markers. A first one
13231 indicates the breakpoint type:
13235 Breakpoint which was hit at least once.
13238 Breakpoint which was never hit.
13241 Hardware breakpoint which was hit at least once.
13244 Hardware breakpoint which was never hit.
13248 The second marker indicates whether the breakpoint is enabled or not:
13252 Breakpoint is enabled.
13255 Breakpoint is disabled.
13259 The source, assembly and register windows are attached to the thread
13260 and the frame position. They are updated when the current thread
13261 changes, when the frame changes or when the program counter changes.
13262 These three windows are arranged by the TUI according to several
13263 layouts. The layout defines which of these three windows are visible.
13264 The following layouts are available:
13274 source and assembly
13277 source and registers
13280 assembly and registers
13284 On top of the command window a status line gives various information
13285 concerning the current process begin debugged. The status line is
13286 updated when the information it shows changes. The following fields
13291 Indicates the current gdb target
13292 (@pxref{Targets, ,Specifying a Debugging Target}).
13295 Gives information about the current process or thread number.
13296 When no process is being debugged, this field is set to @code{No process}.
13299 Gives the current function name for the selected frame.
13300 The name is demangled if demangling is turned on (@pxref{Print Settings}).
13301 When there is no symbol corresponding to the current program counter
13302 the string @code{??} is displayed.
13305 Indicates the current line number for the selected frame.
13306 When the current line number is not known the string @code{??} is displayed.
13309 Indicates the current program counter address.
13314 @section TUI Key Bindings
13315 @cindex TUI key bindings
13317 The TUI installs several key bindings in the readline keymaps
13318 (@pxref{Command Line Editing}).
13319 They allow to leave or enter in the TUI mode or they operate
13320 directly on the TUI layout and windows. The TUI also provides
13321 a @emph{SingleKey} keymap which binds several keys directly to
13322 @value{GDBN} commands. The following key bindings
13323 are installed for both TUI mode and the @value{GDBN} standard mode.
13332 Enter or leave the TUI mode. When the TUI mode is left,
13333 the curses window management is left and @value{GDBN} operates using
13334 its standard mode writing on the terminal directly. When the TUI
13335 mode is entered, the control is given back to the curses windows.
13336 The screen is then refreshed.
13340 Use a TUI layout with only one window. The layout will
13341 either be @samp{source} or @samp{assembly}. When the TUI mode
13342 is not active, it will switch to the TUI mode.
13344 Think of this key binding as the Emacs @kbd{C-x 1} binding.
13348 Use a TUI layout with at least two windows. When the current
13349 layout shows already two windows, a next layout with two windows is used.
13350 When a new layout is chosen, one window will always be common to the
13351 previous layout and the new one.
13353 Think of it as the Emacs @kbd{C-x 2} binding.
13357 Use the TUI @emph{SingleKey} keymap that binds single key to gdb commands
13358 (@pxref{TUI Single Key Mode}).
13362 The following key bindings are handled only by the TUI mode:
13367 Scroll the active window one page up.
13371 Scroll the active window one page down.
13375 Scroll the active window one line up.
13379 Scroll the active window one line down.
13383 Scroll the active window one column left.
13387 Scroll the active window one column right.
13391 Refresh the screen.
13395 In the TUI mode, the arrow keys are used by the active window
13396 for scrolling. This means they are not available for readline. It is
13397 necessary to use other readline key bindings such as @key{C-p}, @key{C-n},
13398 @key{C-b} and @key{C-f}.
13400 @node TUI Single Key Mode
13401 @section TUI Single Key Mode
13402 @cindex TUI single key mode
13404 The TUI provides a @emph{SingleKey} mode in which it installs a particular
13405 key binding in the readline keymaps to connect single keys to
13409 @kindex c @r{(SingleKey TUI key)}
13413 @kindex d @r{(SingleKey TUI key)}
13417 @kindex f @r{(SingleKey TUI key)}
13421 @kindex n @r{(SingleKey TUI key)}
13425 @kindex q @r{(SingleKey TUI key)}
13427 exit the @emph{SingleKey} mode.
13429 @kindex r @r{(SingleKey TUI key)}
13433 @kindex s @r{(SingleKey TUI key)}
13437 @kindex u @r{(SingleKey TUI key)}
13441 @kindex v @r{(SingleKey TUI key)}
13445 @kindex w @r{(SingleKey TUI key)}
13451 Other keys temporarily switch to the @value{GDBN} command prompt.
13452 The key that was pressed is inserted in the editing buffer so that
13453 it is possible to type most @value{GDBN} commands without interaction
13454 with the TUI @emph{SingleKey} mode. Once the command is entered the TUI
13455 @emph{SingleKey} mode is restored. The only way to permanently leave
13456 this mode is by hitting @key{q} or @samp{@key{C-x} @key{s}}.
13460 @section TUI specific commands
13461 @cindex TUI commands
13463 The TUI has specific commands to control the text windows.
13464 These commands are always available, that is they do not depend on
13465 the current terminal mode in which @value{GDBN} runs. When @value{GDBN}
13466 is in the standard mode, using these commands will automatically switch
13472 List and give the size of all displayed windows.
13475 @kindex layout next
13476 Display the next layout.
13479 @kindex layout prev
13480 Display the previous layout.
13484 Display the source window only.
13488 Display the assembly window only.
13491 @kindex layout split
13492 Display the source and assembly window.
13495 @kindex layout regs
13496 Display the register window together with the source or assembly window.
13498 @item focus next | prev | src | asm | regs | split
13500 Set the focus to the named window.
13501 This command allows to change the active window so that scrolling keys
13502 can be affected to another window.
13506 Refresh the screen. This is similar to using @key{C-L} key.
13510 Update the source window and the current execution point.
13512 @item winheight @var{name} +@var{count}
13513 @itemx winheight @var{name} -@var{count}
13515 Change the height of the window @var{name} by @var{count}
13516 lines. Positive counts increase the height, while negative counts
13521 @node TUI Configuration
13522 @section TUI configuration variables
13523 @cindex TUI configuration variables
13525 The TUI has several configuration variables that control the
13526 appearance of windows on the terminal.
13529 @item set tui border-kind @var{kind}
13530 @kindex set tui border-kind
13531 Select the border appearance for the source, assembly and register windows.
13532 The possible values are the following:
13535 Use a space character to draw the border.
13538 Use ascii characters + - and | to draw the border.
13541 Use the Alternate Character Set to draw the border. The border is
13542 drawn using character line graphics if the terminal supports them.
13546 @item set tui active-border-mode @var{mode}
13547 @kindex set tui active-border-mode
13548 Select the attributes to display the border of the active window.
13549 The possible values are @code{normal}, @code{standout}, @code{reverse},
13550 @code{half}, @code{half-standout}, @code{bold} and @code{bold-standout}.
13552 @item set tui border-mode @var{mode}
13553 @kindex set tui border-mode
13554 Select the attributes to display the border of other windows.
13555 The @var{mode} can be one of the following:
13558 Use normal attributes to display the border.
13564 Use reverse video mode.
13567 Use half bright mode.
13569 @item half-standout
13570 Use half bright and standout mode.
13573 Use extra bright or bold mode.
13575 @item bold-standout
13576 Use extra bright or bold and standout mode.
13583 @chapter Using @value{GDBN} under @sc{gnu} Emacs
13586 @cindex @sc{gnu} Emacs
13587 A special interface allows you to use @sc{gnu} Emacs to view (and
13588 edit) the source files for the program you are debugging with
13591 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
13592 executable file you want to debug as an argument. This command starts
13593 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
13594 created Emacs buffer.
13595 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
13597 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
13602 All ``terminal'' input and output goes through the Emacs buffer.
13605 This applies both to @value{GDBN} commands and their output, and to the input
13606 and output done by the program you are debugging.
13608 This is useful because it means that you can copy the text of previous
13609 commands and input them again; you can even use parts of the output
13612 All the facilities of Emacs' Shell mode are available for interacting
13613 with your program. In particular, you can send signals the usual
13614 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
13619 @value{GDBN} displays source code through Emacs.
13622 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
13623 source file for that frame and puts an arrow (@samp{=>}) at the
13624 left margin of the current line. Emacs uses a separate buffer for
13625 source display, and splits the screen to show both your @value{GDBN} session
13628 Explicit @value{GDBN} @code{list} or search commands still produce output as
13629 usual, but you probably have no reason to use them from Emacs.
13632 @emph{Warning:} If the directory where your program resides is not your
13633 current directory, it can be easy to confuse Emacs about the location of
13634 the source files, in which case the auxiliary display buffer does not
13635 appear to show your source. @value{GDBN} can find programs by searching your
13636 environment's @code{PATH} variable, so the @value{GDBN} input and output
13637 session proceeds normally; but Emacs does not get enough information
13638 back from @value{GDBN} to locate the source files in this situation. To
13639 avoid this problem, either start @value{GDBN} mode from the directory where
13640 your program resides, or specify an absolute file name when prompted for the
13641 @kbd{M-x gdb} argument.
13643 A similar confusion can result if you use the @value{GDBN} @code{file} command to
13644 switch to debugging a program in some other location, from an existing
13645 @value{GDBN} buffer in Emacs.
13648 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
13649 you need to call @value{GDBN} by a different name (for example, if you keep
13650 several configurations around, with different names) you can set the
13651 Emacs variable @code{gdb-command-name}; for example,
13654 (setq gdb-command-name "mygdb")
13658 (preceded by @kbd{M-:} or @kbd{ESC :}, or typed in the @code{*scratch*} buffer, or
13659 in your @file{.emacs} file) makes Emacs call the program named
13660 ``@code{mygdb}'' instead.
13662 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
13663 addition to the standard Shell mode commands:
13667 Describe the features of Emacs' @value{GDBN} Mode.
13670 Execute to another source line, like the @value{GDBN} @code{step} command; also
13671 update the display window to show the current file and location.
13674 Execute to next source line in this function, skipping all function
13675 calls, like the @value{GDBN} @code{next} command. Then update the display window
13676 to show the current file and location.
13679 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
13680 display window accordingly.
13682 @item M-x gdb-nexti
13683 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
13684 display window accordingly.
13687 Execute until exit from the selected stack frame, like the @value{GDBN}
13688 @code{finish} command.
13691 Continue execution of your program, like the @value{GDBN} @code{continue}
13694 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
13697 Go up the number of frames indicated by the numeric argument
13698 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
13699 like the @value{GDBN} @code{up} command.
13701 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
13704 Go down the number of frames indicated by the numeric argument, like the
13705 @value{GDBN} @code{down} command.
13707 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
13710 Read the number where the cursor is positioned, and insert it at the end
13711 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
13712 around an address that was displayed earlier, type @kbd{disassemble};
13713 then move the cursor to the address display, and pick up the
13714 argument for @code{disassemble} by typing @kbd{C-x &}.
13716 You can customize this further by defining elements of the list
13717 @code{gdb-print-command}; once it is defined, you can format or
13718 otherwise process numbers picked up by @kbd{C-x &} before they are
13719 inserted. A numeric argument to @kbd{C-x &} indicates that you
13720 wish special formatting, and also acts as an index to pick an element of the
13721 list. If the list element is a string, the number to be inserted is
13722 formatted using the Emacs function @code{format}; otherwise the number
13723 is passed as an argument to the corresponding list element.
13726 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
13727 tells @value{GDBN} to set a breakpoint on the source line point is on.
13729 If you accidentally delete the source-display buffer, an easy way to get
13730 it back is to type the command @code{f} in the @value{GDBN} buffer, to
13731 request a frame display; when you run under Emacs, this recreates
13732 the source buffer if necessary to show you the context of the current
13735 The source files displayed in Emacs are in ordinary Emacs buffers
13736 which are visiting the source files in the usual way. You can edit
13737 the files with these buffers if you wish; but keep in mind that @value{GDBN}
13738 communicates with Emacs in terms of line numbers. If you add or
13739 delete lines from the text, the line numbers that @value{GDBN} knows cease
13740 to correspond properly with the code.
13742 @c The following dropped because Epoch is nonstandard. Reactivate
13743 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
13745 @kindex Emacs Epoch environment
13749 Version 18 of @sc{gnu} Emacs has a built-in window system
13750 called the @code{epoch}
13751 environment. Users of this environment can use a new command,
13752 @code{inspect} which performs identically to @code{print} except that
13753 each value is printed in its own window.
13756 @include annotate.texi
13757 @include gdbmi.texinfo
13760 @chapter Reporting Bugs in @value{GDBN}
13761 @cindex bugs in @value{GDBN}
13762 @cindex reporting bugs in @value{GDBN}
13764 Your bug reports play an essential role in making @value{GDBN} reliable.
13766 Reporting a bug may help you by bringing a solution to your problem, or it
13767 may not. But in any case the principal function of a bug report is to help
13768 the entire community by making the next version of @value{GDBN} work better. Bug
13769 reports are your contribution to the maintenance of @value{GDBN}.
13771 In order for a bug report to serve its purpose, you must include the
13772 information that enables us to fix the bug.
13775 * Bug Criteria:: Have you found a bug?
13776 * Bug Reporting:: How to report bugs
13780 @section Have you found a bug?
13781 @cindex bug criteria
13783 If you are not sure whether you have found a bug, here are some guidelines:
13786 @cindex fatal signal
13787 @cindex debugger crash
13788 @cindex crash of debugger
13790 If the debugger gets a fatal signal, for any input whatever, that is a
13791 @value{GDBN} bug. Reliable debuggers never crash.
13793 @cindex error on valid input
13795 If @value{GDBN} produces an error message for valid input, that is a
13796 bug. (Note that if you're cross debugging, the problem may also be
13797 somewhere in the connection to the target.)
13799 @cindex invalid input
13801 If @value{GDBN} does not produce an error message for invalid input,
13802 that is a bug. However, you should note that your idea of
13803 ``invalid input'' might be our idea of ``an extension'' or ``support
13804 for traditional practice''.
13807 If you are an experienced user of debugging tools, your suggestions
13808 for improvement of @value{GDBN} are welcome in any case.
13811 @node Bug Reporting
13812 @section How to report bugs
13813 @cindex bug reports
13814 @cindex @value{GDBN} bugs, reporting
13816 A number of companies and individuals offer support for @sc{gnu} products.
13817 If you obtained @value{GDBN} from a support organization, we recommend you
13818 contact that organization first.
13820 You can find contact information for many support companies and
13821 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
13823 @c should add a web page ref...
13825 In any event, we also recommend that you submit bug reports for
13826 @value{GDBN}. The prefered method is to submit them directly using
13827 @uref{http://www.gnu.org/software/gdb/bugs/, @value{GDBN}'s Bugs web
13828 page}. Alternatively, the @email{bug-gdb@@gnu.org, e-mail gateway} can
13831 @strong{Do not send bug reports to @samp{info-gdb}, or to
13832 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
13833 not want to receive bug reports. Those that do have arranged to receive
13836 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
13837 serves as a repeater. The mailing list and the newsgroup carry exactly
13838 the same messages. Often people think of posting bug reports to the
13839 newsgroup instead of mailing them. This appears to work, but it has one
13840 problem which can be crucial: a newsgroup posting often lacks a mail
13841 path back to the sender. Thus, if we need to ask for more information,
13842 we may be unable to reach you. For this reason, it is better to send
13843 bug reports to the mailing list.
13845 The fundamental principle of reporting bugs usefully is this:
13846 @strong{report all the facts}. If you are not sure whether to state a
13847 fact or leave it out, state it!
13849 Often people omit facts because they think they know what causes the
13850 problem and assume that some details do not matter. Thus, you might
13851 assume that the name of the variable you use in an example does not matter.
13852 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
13853 stray memory reference which happens to fetch from the location where that
13854 name is stored in memory; perhaps, if the name were different, the contents
13855 of that location would fool the debugger into doing the right thing despite
13856 the bug. Play it safe and give a specific, complete example. That is the
13857 easiest thing for you to do, and the most helpful.
13859 Keep in mind that the purpose of a bug report is to enable us to fix the
13860 bug. It may be that the bug has been reported previously, but neither
13861 you nor we can know that unless your bug report is complete and
13864 Sometimes people give a few sketchy facts and ask, ``Does this ring a
13865 bell?'' Those bug reports are useless, and we urge everyone to
13866 @emph{refuse to respond to them} except to chide the sender to report
13869 To enable us to fix the bug, you should include all these things:
13873 The version of @value{GDBN}. @value{GDBN} announces it if you start
13874 with no arguments; you can also print it at any time using @code{show
13877 Without this, we will not know whether there is any point in looking for
13878 the bug in the current version of @value{GDBN}.
13881 The type of machine you are using, and the operating system name and
13885 What compiler (and its version) was used to compile @value{GDBN}---e.g.
13886 ``@value{GCC}--2.8.1''.
13889 What compiler (and its version) was used to compile the program you are
13890 debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
13891 C Compiler''. For GCC, you can say @code{gcc --version} to get this
13892 information; for other compilers, see the documentation for those
13896 The command arguments you gave the compiler to compile your example and
13897 observe the bug. For example, did you use @samp{-O}? To guarantee
13898 you will not omit something important, list them all. A copy of the
13899 Makefile (or the output from make) is sufficient.
13901 If we were to try to guess the arguments, we would probably guess wrong
13902 and then we might not encounter the bug.
13905 A complete input script, and all necessary source files, that will
13909 A description of what behavior you observe that you believe is
13910 incorrect. For example, ``It gets a fatal signal.''
13912 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
13913 will certainly notice it. But if the bug is incorrect output, we might
13914 not notice unless it is glaringly wrong. You might as well not give us
13915 a chance to make a mistake.
13917 Even if the problem you experience is a fatal signal, you should still
13918 say so explicitly. Suppose something strange is going on, such as, your
13919 copy of @value{GDBN} is out of synch, or you have encountered a bug in
13920 the C library on your system. (This has happened!) Your copy might
13921 crash and ours would not. If you told us to expect a crash, then when
13922 ours fails to crash, we would know that the bug was not happening for
13923 us. If you had not told us to expect a crash, then we would not be able
13924 to draw any conclusion from our observations.
13927 If you wish to suggest changes to the @value{GDBN} source, send us context
13928 diffs. If you even discuss something in the @value{GDBN} source, refer to
13929 it by context, not by line number.
13931 The line numbers in our development sources will not match those in your
13932 sources. Your line numbers would convey no useful information to us.
13936 Here are some things that are not necessary:
13940 A description of the envelope of the bug.
13942 Often people who encounter a bug spend a lot of time investigating
13943 which changes to the input file will make the bug go away and which
13944 changes will not affect it.
13946 This is often time consuming and not very useful, because the way we
13947 will find the bug is by running a single example under the debugger
13948 with breakpoints, not by pure deduction from a series of examples.
13949 We recommend that you save your time for something else.
13951 Of course, if you can find a simpler example to report @emph{instead}
13952 of the original one, that is a convenience for us. Errors in the
13953 output will be easier to spot, running under the debugger will take
13954 less time, and so on.
13956 However, simplification is not vital; if you do not want to do this,
13957 report the bug anyway and send us the entire test case you used.
13960 A patch for the bug.
13962 A patch for the bug does help us if it is a good one. But do not omit
13963 the necessary information, such as the test case, on the assumption that
13964 a patch is all we need. We might see problems with your patch and decide
13965 to fix the problem another way, or we might not understand it at all.
13967 Sometimes with a program as complicated as @value{GDBN} it is very hard to
13968 construct an example that will make the program follow a certain path
13969 through the code. If you do not send us the example, we will not be able
13970 to construct one, so we will not be able to verify that the bug is fixed.
13972 And if we cannot understand what bug you are trying to fix, or why your
13973 patch should be an improvement, we will not install it. A test case will
13974 help us to understand.
13977 A guess about what the bug is or what it depends on.
13979 Such guesses are usually wrong. Even we cannot guess right about such
13980 things without first using the debugger to find the facts.
13983 @c The readline documentation is distributed with the readline code
13984 @c and consists of the two following files:
13986 @c inc-hist.texinfo
13987 @c Use -I with makeinfo to point to the appropriate directory,
13988 @c environment var TEXINPUTS with TeX.
13989 @include rluser.texinfo
13990 @include inc-hist.texinfo
13993 @node Formatting Documentation
13994 @appendix Formatting Documentation
13996 @cindex @value{GDBN} reference card
13997 @cindex reference card
13998 The @value{GDBN} 4 release includes an already-formatted reference card, ready
13999 for printing with PostScript or Ghostscript, in the @file{gdb}
14000 subdirectory of the main source directory@footnote{In
14001 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
14002 release.}. If you can use PostScript or Ghostscript with your printer,
14003 you can print the reference card immediately with @file{refcard.ps}.
14005 The release also includes the source for the reference card. You
14006 can format it, using @TeX{}, by typing:
14012 The @value{GDBN} reference card is designed to print in @dfn{landscape}
14013 mode on US ``letter'' size paper;
14014 that is, on a sheet 11 inches wide by 8.5 inches
14015 high. You will need to specify this form of printing as an option to
14016 your @sc{dvi} output program.
14018 @cindex documentation
14020 All the documentation for @value{GDBN} comes as part of the machine-readable
14021 distribution. The documentation is written in Texinfo format, which is
14022 a documentation system that uses a single source file to produce both
14023 on-line information and a printed manual. You can use one of the Info
14024 formatting commands to create the on-line version of the documentation
14025 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
14027 @value{GDBN} includes an already formatted copy of the on-line Info
14028 version of this manual in the @file{gdb} subdirectory. The main Info
14029 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
14030 subordinate files matching @samp{gdb.info*} in the same directory. If
14031 necessary, you can print out these files, or read them with any editor;
14032 but they are easier to read using the @code{info} subsystem in @sc{gnu}
14033 Emacs or the standalone @code{info} program, available as part of the
14034 @sc{gnu} Texinfo distribution.
14036 If you want to format these Info files yourself, you need one of the
14037 Info formatting programs, such as @code{texinfo-format-buffer} or
14040 If you have @code{makeinfo} installed, and are in the top level
14041 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
14042 version @value{GDBVN}), you can make the Info file by typing:
14049 If you want to typeset and print copies of this manual, you need @TeX{},
14050 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
14051 Texinfo definitions file.
14053 @TeX{} is a typesetting program; it does not print files directly, but
14054 produces output files called @sc{dvi} files. To print a typeset
14055 document, you need a program to print @sc{dvi} files. If your system
14056 has @TeX{} installed, chances are it has such a program. The precise
14057 command to use depends on your system; @kbd{lpr -d} is common; another
14058 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
14059 require a file name without any extension or a @samp{.dvi} extension.
14061 @TeX{} also requires a macro definitions file called
14062 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
14063 written in Texinfo format. On its own, @TeX{} cannot either read or
14064 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
14065 and is located in the @file{gdb-@var{version-number}/texinfo}
14068 If you have @TeX{} and a @sc{dvi} printer program installed, you can
14069 typeset and print this manual. First switch to the the @file{gdb}
14070 subdirectory of the main source directory (for example, to
14071 @file{gdb-@value{GDBVN}/gdb}) and type:
14077 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
14079 @node Installing GDB
14080 @appendix Installing @value{GDBN}
14081 @cindex configuring @value{GDBN}
14082 @cindex installation
14084 @value{GDBN} comes with a @code{configure} script that automates the process
14085 of preparing @value{GDBN} for installation; you can then use @code{make} to
14086 build the @code{gdb} program.
14088 @c irrelevant in info file; it's as current as the code it lives with.
14089 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
14090 look at the @file{README} file in the sources; we may have improved the
14091 installation procedures since publishing this manual.}
14094 The @value{GDBN} distribution includes all the source code you need for
14095 @value{GDBN} in a single directory, whose name is usually composed by
14096 appending the version number to @samp{gdb}.
14098 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
14099 @file{gdb-@value{GDBVN}} directory. That directory contains:
14102 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
14103 script for configuring @value{GDBN} and all its supporting libraries
14105 @item gdb-@value{GDBVN}/gdb
14106 the source specific to @value{GDBN} itself
14108 @item gdb-@value{GDBVN}/bfd
14109 source for the Binary File Descriptor library
14111 @item gdb-@value{GDBVN}/include
14112 @sc{gnu} include files
14114 @item gdb-@value{GDBVN}/libiberty
14115 source for the @samp{-liberty} free software library
14117 @item gdb-@value{GDBVN}/opcodes
14118 source for the library of opcode tables and disassemblers
14120 @item gdb-@value{GDBVN}/readline
14121 source for the @sc{gnu} command-line interface
14123 @item gdb-@value{GDBVN}/glob
14124 source for the @sc{gnu} filename pattern-matching subroutine
14126 @item gdb-@value{GDBVN}/mmalloc
14127 source for the @sc{gnu} memory-mapped malloc package
14130 The simplest way to configure and build @value{GDBN} is to run @code{configure}
14131 from the @file{gdb-@var{version-number}} source directory, which in
14132 this example is the @file{gdb-@value{GDBVN}} directory.
14134 First switch to the @file{gdb-@var{version-number}} source directory
14135 if you are not already in it; then run @code{configure}. Pass the
14136 identifier for the platform on which @value{GDBN} will run as an
14142 cd gdb-@value{GDBVN}
14143 ./configure @var{host}
14148 where @var{host} is an identifier such as @samp{sun4} or
14149 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
14150 (You can often leave off @var{host}; @code{configure} tries to guess the
14151 correct value by examining your system.)
14153 Running @samp{configure @var{host}} and then running @code{make} builds the
14154 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
14155 libraries, then @code{gdb} itself. The configured source files, and the
14156 binaries, are left in the corresponding source directories.
14159 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
14160 system does not recognize this automatically when you run a different
14161 shell, you may need to run @code{sh} on it explicitly:
14164 sh configure @var{host}
14167 If you run @code{configure} from a directory that contains source
14168 directories for multiple libraries or programs, such as the
14169 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
14170 creates configuration files for every directory level underneath (unless
14171 you tell it not to, with the @samp{--norecursion} option).
14173 You can run the @code{configure} script from any of the
14174 subordinate directories in the @value{GDBN} distribution if you only want to
14175 configure that subdirectory, but be sure to specify a path to it.
14177 For example, with version @value{GDBVN}, type the following to configure only
14178 the @code{bfd} subdirectory:
14182 cd gdb-@value{GDBVN}/bfd
14183 ../configure @var{host}
14187 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
14188 However, you should make sure that the shell on your path (named by
14189 the @samp{SHELL} environment variable) is publicly readable. Remember
14190 that @value{GDBN} uses the shell to start your program---some systems refuse to
14191 let @value{GDBN} debug child processes whose programs are not readable.
14194 * Separate Objdir:: Compiling @value{GDBN} in another directory
14195 * Config Names:: Specifying names for hosts and targets
14196 * Configure Options:: Summary of options for configure
14199 @node Separate Objdir
14200 @section Compiling @value{GDBN} in another directory
14202 If you want to run @value{GDBN} versions for several host or target machines,
14203 you need a different @code{gdb} compiled for each combination of
14204 host and target. @code{configure} is designed to make this easy by
14205 allowing you to generate each configuration in a separate subdirectory,
14206 rather than in the source directory. If your @code{make} program
14207 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
14208 @code{make} in each of these directories builds the @code{gdb}
14209 program specified there.
14211 To build @code{gdb} in a separate directory, run @code{configure}
14212 with the @samp{--srcdir} option to specify where to find the source.
14213 (You also need to specify a path to find @code{configure}
14214 itself from your working directory. If the path to @code{configure}
14215 would be the same as the argument to @samp{--srcdir}, you can leave out
14216 the @samp{--srcdir} option; it is assumed.)
14218 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
14219 separate directory for a Sun 4 like this:
14223 cd gdb-@value{GDBVN}
14226 ../gdb-@value{GDBVN}/configure sun4
14231 When @code{configure} builds a configuration using a remote source
14232 directory, it creates a tree for the binaries with the same structure
14233 (and using the same names) as the tree under the source directory. In
14234 the example, you'd find the Sun 4 library @file{libiberty.a} in the
14235 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
14236 @file{gdb-sun4/gdb}.
14238 One popular reason to build several @value{GDBN} configurations in separate
14239 directories is to configure @value{GDBN} for cross-compiling (where
14240 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
14241 programs that run on another machine---the @dfn{target}).
14242 You specify a cross-debugging target by
14243 giving the @samp{--target=@var{target}} option to @code{configure}.
14245 When you run @code{make} to build a program or library, you must run
14246 it in a configured directory---whatever directory you were in when you
14247 called @code{configure} (or one of its subdirectories).
14249 The @code{Makefile} that @code{configure} generates in each source
14250 directory also runs recursively. If you type @code{make} in a source
14251 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
14252 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
14253 will build all the required libraries, and then build GDB.
14255 When you have multiple hosts or targets configured in separate
14256 directories, you can run @code{make} on them in parallel (for example,
14257 if they are NFS-mounted on each of the hosts); they will not interfere
14261 @section Specifying names for hosts and targets
14263 The specifications used for hosts and targets in the @code{configure}
14264 script are based on a three-part naming scheme, but some short predefined
14265 aliases are also supported. The full naming scheme encodes three pieces
14266 of information in the following pattern:
14269 @var{architecture}-@var{vendor}-@var{os}
14272 For example, you can use the alias @code{sun4} as a @var{host} argument,
14273 or as the value for @var{target} in a @code{--target=@var{target}}
14274 option. The equivalent full name is @samp{sparc-sun-sunos4}.
14276 The @code{configure} script accompanying @value{GDBN} does not provide
14277 any query facility to list all supported host and target names or
14278 aliases. @code{configure} calls the Bourne shell script
14279 @code{config.sub} to map abbreviations to full names; you can read the
14280 script, if you wish, or you can use it to test your guesses on
14281 abbreviations---for example:
14284 % sh config.sub i386-linux
14286 % sh config.sub alpha-linux
14287 alpha-unknown-linux-gnu
14288 % sh config.sub hp9k700
14290 % sh config.sub sun4
14291 sparc-sun-sunos4.1.1
14292 % sh config.sub sun3
14293 m68k-sun-sunos4.1.1
14294 % sh config.sub i986v
14295 Invalid configuration `i986v': machine `i986v' not recognized
14299 @code{config.sub} is also distributed in the @value{GDBN} source
14300 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
14302 @node Configure Options
14303 @section @code{configure} options
14305 Here is a summary of the @code{configure} options and arguments that
14306 are most often useful for building @value{GDBN}. @code{configure} also has
14307 several other options not listed here. @inforef{What Configure
14308 Does,,configure.info}, for a full explanation of @code{configure}.
14311 configure @r{[}--help@r{]}
14312 @r{[}--prefix=@var{dir}@r{]}
14313 @r{[}--exec-prefix=@var{dir}@r{]}
14314 @r{[}--srcdir=@var{dirname}@r{]}
14315 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
14316 @r{[}--target=@var{target}@r{]}
14321 You may introduce options with a single @samp{-} rather than
14322 @samp{--} if you prefer; but you may abbreviate option names if you use
14327 Display a quick summary of how to invoke @code{configure}.
14329 @item --prefix=@var{dir}
14330 Configure the source to install programs and files under directory
14333 @item --exec-prefix=@var{dir}
14334 Configure the source to install programs under directory
14337 @c avoid splitting the warning from the explanation:
14339 @item --srcdir=@var{dirname}
14340 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
14341 @code{make} that implements the @code{VPATH} feature.}@*
14342 Use this option to make configurations in directories separate from the
14343 @value{GDBN} source directories. Among other things, you can use this to
14344 build (or maintain) several configurations simultaneously, in separate
14345 directories. @code{configure} writes configuration specific files in
14346 the current directory, but arranges for them to use the source in the
14347 directory @var{dirname}. @code{configure} creates directories under
14348 the working directory in parallel to the source directories below
14351 @item --norecursion
14352 Configure only the directory level where @code{configure} is executed; do not
14353 propagate configuration to subdirectories.
14355 @item --target=@var{target}
14356 Configure @value{GDBN} for cross-debugging programs running on the specified
14357 @var{target}. Without this option, @value{GDBN} is configured to debug
14358 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
14360 There is no convenient way to generate a list of all available targets.
14362 @item @var{host} @dots{}
14363 Configure @value{GDBN} to run on the specified @var{host}.
14365 There is no convenient way to generate a list of all available hosts.
14368 There are many other options available as well, but they are generally
14369 needed for special purposes only.
14371 @node Maintenance Commands
14372 @appendix Maintenance Commands
14373 @cindex maintenance commands
14374 @cindex internal commands
14376 In addition to commands intended for @value{GDBN} users, @value{GDBN}
14377 includes a number of commands intended for @value{GDBN} developers.
14378 These commands are provided here for reference.
14381 @kindex maint info breakpoints
14382 @item @anchor{maint info breakpoints}maint info breakpoints
14383 Using the same format as @samp{info breakpoints}, display both the
14384 breakpoints you've set explicitly, and those @value{GDBN} is using for
14385 internal purposes. Internal breakpoints are shown with negative
14386 breakpoint numbers. The type column identifies what kind of breakpoint
14391 Normal, explicitly set breakpoint.
14394 Normal, explicitly set watchpoint.
14397 Internal breakpoint, used to handle correctly stepping through
14398 @code{longjmp} calls.
14400 @item longjmp resume
14401 Internal breakpoint at the target of a @code{longjmp}.
14404 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
14407 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
14410 Shared library events.
14414 @kindex maint internal-error
14415 @kindex maint internal-warning
14416 @item maint internal-error
14417 @itemx maint internal-warning
14418 Cause @value{GDBN} to call the internal function @code{internal_error}
14419 or @code{internal_warning} and hence behave as though an internal error
14420 or internal warning has been detected. In addition to reporting the
14421 internal problem, these functions give the user the opportunity to
14422 either quit @value{GDBN} or create a core file of the current
14423 @value{GDBN} session.
14426 (gdb) @kbd{maint internal-error testing, 1, 2}
14427 @dots{}/maint.c:121: internal-error: testing, 1, 2
14428 A problem internal to GDB has been detected. Further
14429 debugging may prove unreliable.
14430 Quit this debugging session? (y or n) @kbd{n}
14431 Create a core file? (y or n) @kbd{n}
14435 Takes an optional parameter that is used as the text of the error or
14438 @kindex maint print registers
14439 @kindex maint print raw-registers
14440 @kindex maint print cooked-registers
14441 @item maint print registers
14442 @itemx maint print raw-registers
14443 @itemx maint print cooked-registers
14444 Print @value{GDBN}'s internal register data structures.
14446 The command @samp{maint print raw-registers} includes the contents of
14447 the raw register cache; and the command @samp{maint print
14448 cooked-registers} includes the (cooked) value of all registers.
14449 @xref{Registers,, Registers, gdbint, @value{GDBN} Internals}.
14451 Takes an optional file parameter.
14456 @node Remote Protocol
14457 @appendix @value{GDBN} Remote Serial Protocol
14462 * Stop Reply Packets::
14463 * General Query Packets::
14464 * Register Packet Format::
14471 There may be occasions when you need to know something about the
14472 protocol---for example, if there is only one serial port to your target
14473 machine, you might want your program to do something special if it
14474 recognizes a packet meant for @value{GDBN}.
14476 In the examples below, @samp{->} and @samp{<-} are used to indicate
14477 transmitted and received data respectfully.
14479 @cindex protocol, @value{GDBN} remote serial
14480 @cindex serial protocol, @value{GDBN} remote
14481 @cindex remote serial protocol
14482 All @value{GDBN} commands and responses (other than acknowledgments) are
14483 sent as a @var{packet}. A @var{packet} is introduced with the character
14484 @samp{$}, the actual @var{packet-data}, and the terminating character
14485 @samp{#} followed by a two-digit @var{checksum}:
14488 @code{$}@var{packet-data}@code{#}@var{checksum}
14492 @cindex checksum, for @value{GDBN} remote
14494 The two-digit @var{checksum} is computed as the modulo 256 sum of all
14495 characters between the leading @samp{$} and the trailing @samp{#} (an
14496 eight bit unsigned checksum).
14498 Implementors should note that prior to @value{GDBN} 5.0 the protocol
14499 specification also included an optional two-digit @var{sequence-id}:
14502 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
14505 @cindex sequence-id, for @value{GDBN} remote
14507 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
14508 has never output @var{sequence-id}s. Stubs that handle packets added
14509 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
14511 @cindex acknowledgment, for @value{GDBN} remote
14512 When either the host or the target machine receives a packet, the first
14513 response expected is an acknowledgment: either @samp{+} (to indicate
14514 the package was received correctly) or @samp{-} (to request
14518 -> @code{$}@var{packet-data}@code{#}@var{checksum}
14523 The host (@value{GDBN}) sends @var{command}s, and the target (the
14524 debugging stub incorporated in your program) sends a @var{response}. In
14525 the case of step and continue @var{command}s, the response is only sent
14526 when the operation has completed (the target has again stopped).
14528 @var{packet-data} consists of a sequence of characters with the
14529 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
14532 Fields within the packet should be separated using @samp{,} @samp{;} or
14533 @cindex remote protocol, field separator
14534 @samp{:}. Except where otherwise noted all numbers are represented in
14535 @sc{hex} with leading zeros suppressed.
14537 Implementors should note that prior to @value{GDBN} 5.0, the character
14538 @samp{:} could not appear as the third character in a packet (as it
14539 would potentially conflict with the @var{sequence-id}).
14541 Response @var{data} can be run-length encoded to save space. A @samp{*}
14542 means that the next character is an @sc{ascii} encoding giving a repeat count
14543 which stands for that many repetitions of the character preceding the
14544 @samp{*}. The encoding is @code{n+29}, yielding a printable character
14545 where @code{n >=3} (which is where rle starts to win). The printable
14546 characters @samp{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
14547 value greater than 126 should not be used.
14549 Some remote systems have used a different run-length encoding mechanism
14550 loosely refered to as the cisco encoding. Following the @samp{*}
14551 character are two hex digits that indicate the size of the packet.
14558 means the same as "0000".
14560 The error response returned for some packets includes a two character
14561 error number. That number is not well defined.
14563 For any @var{command} not supported by the stub, an empty response
14564 (@samp{$#00}) should be returned. That way it is possible to extend the
14565 protocol. A newer @value{GDBN} can tell if a packet is supported based
14568 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
14569 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
14575 The following table provides a complete list of all currently defined
14576 @var{command}s and their corresponding response @var{data}.
14580 @item @code{!} --- extended mode
14581 @cindex @code{!} packet
14583 Enable extended mode. In extended mode, the remote server is made
14584 persistent. The @samp{R} packet is used to restart the program being
14590 The remote target both supports and has enabled extended mode.
14593 @item @code{?} --- last signal
14594 @cindex @code{?} packet
14596 Indicate the reason the target halted. The reply is the same as for
14600 @xref{Stop Reply Packets}, for the reply specifications.
14602 @item @code{a} --- reserved
14604 Reserved for future use.
14606 @item @code{A}@var{arglen}@code{,}@var{argnum}@code{,}@var{arg}@code{,@dots{}} --- set program arguments @strong{(reserved)}
14607 @cindex @code{A} packet
14609 Initialized @samp{argv[]} array passed into program. @var{arglen}
14610 specifies the number of bytes in the hex encoded byte stream @var{arg}.
14611 See @code{gdbserver} for more details.
14619 @item @code{b}@var{baud} --- set baud @strong{(deprecated)}
14620 @cindex @code{b} packet
14622 Change the serial line speed to @var{baud}.
14624 JTC: @emph{When does the transport layer state change? When it's
14625 received, or after the ACK is transmitted. In either case, there are
14626 problems if the command or the acknowledgment packet is dropped.}
14628 Stan: @emph{If people really wanted to add something like this, and get
14629 it working for the first time, they ought to modify ser-unix.c to send
14630 some kind of out-of-band message to a specially-setup stub and have the
14631 switch happen "in between" packets, so that from remote protocol's point
14632 of view, nothing actually happened.}
14634 @item @code{B}@var{addr},@var{mode} --- set breakpoint @strong{(deprecated)}
14635 @cindex @code{B} packet
14637 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
14638 breakpoint at @var{addr}.
14640 This packet has been replaced by the @samp{Z} and @samp{z} packets
14641 (@pxref{insert breakpoint or watchpoint packet}).
14643 @item @code{c}@var{addr} --- continue
14644 @cindex @code{c} packet
14646 @var{addr} is address to resume. If @var{addr} is omitted, resume at
14650 @xref{Stop Reply Packets}, for the reply specifications.
14652 @item @code{C}@var{sig}@code{;}@var{addr} --- continue with signal
14653 @cindex @code{C} packet
14655 Continue with signal @var{sig} (hex signal number). If
14656 @code{;}@var{addr} is omitted, resume at same address.
14659 @xref{Stop Reply Packets}, for the reply specifications.
14661 @item @code{d} --- toggle debug @strong{(deprecated)}
14662 @cindex @code{d} packet
14666 @item @code{D} --- detach
14667 @cindex @code{D} packet
14669 Detach @value{GDBN} from the remote system. Sent to the remote target
14670 before @value{GDBN} disconnects.
14674 @item @emph{no response}
14675 @value{GDBN} does not check for any response after sending this packet.
14678 @item @code{e} --- reserved
14680 Reserved for future use.
14682 @item @code{E} --- reserved
14684 Reserved for future use.
14686 @item @code{f} --- reserved
14688 Reserved for future use.
14690 @item @code{F} --- reserved
14692 Reserved for future use.
14694 @item @code{g} --- read registers
14695 @anchor{read registers packet}
14696 @cindex @code{g} packet
14698 Read general registers.
14702 @item @var{XX@dots{}}
14703 Each byte of register data is described by two hex digits. The bytes
14704 with the register are transmitted in target byte order. The size of
14705 each register and their position within the @samp{g} @var{packet} are
14706 determined by the @value{GDBN} internal macros @var{REGISTER_RAW_SIZE}
14707 and @var{REGISTER_NAME} macros. The specification of several standard
14708 @code{g} packets is specified below.
14713 @item @code{G}@var{XX@dots{}} --- write regs
14714 @cindex @code{G} packet
14716 @xref{read registers packet}, for a description of the @var{XX@dots{}}
14727 @item @code{h} --- reserved
14729 Reserved for future use.
14731 @item @code{H}@var{c}@var{t@dots{}} --- set thread
14732 @cindex @code{H} packet
14734 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
14735 @samp{G}, et.al.). @var{c} depends on the operation to be performed: it
14736 should be @samp{c} for step and continue operations, @samp{g} for other
14737 operations. The thread designator @var{t@dots{}} may be -1, meaning all
14738 the threads, a thread number, or zero which means pick any thread.
14749 @c 'H': How restrictive (or permissive) is the thread model. If a
14750 @c thread is selected and stopped, are other threads allowed
14751 @c to continue to execute? As I mentioned above, I think the
14752 @c semantics of each command when a thread is selected must be
14753 @c described. For example:
14755 @c 'g': If the stub supports threads and a specific thread is
14756 @c selected, returns the register block from that thread;
14757 @c otherwise returns current registers.
14759 @c 'G' If the stub supports threads and a specific thread is
14760 @c selected, sets the registers of the register block of
14761 @c that thread; otherwise sets current registers.
14763 @item @code{i}@var{addr}@code{,}@var{nnn} --- cycle step @strong{(draft)}
14764 @anchor{cycle step packet}
14765 @cindex @code{i} packet
14767 Step the remote target by a single clock cycle. If @code{,}@var{nnn} is
14768 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
14769 step starting at that address.
14771 @item @code{I} --- signal then cycle step @strong{(reserved)}
14772 @cindex @code{I} packet
14774 @xref{step with signal packet}. @xref{cycle step packet}.
14776 @item @code{j} --- reserved
14778 Reserved for future use.
14780 @item @code{J} --- reserved
14782 Reserved for future use.
14784 @item @code{k} --- kill request
14785 @cindex @code{k} packet
14787 FIXME: @emph{There is no description of how to operate when a specific
14788 thread context has been selected (i.e.@: does 'k' kill only that
14791 @item @code{K} --- reserved
14793 Reserved for future use.
14795 @item @code{l} --- reserved
14797 Reserved for future use.
14799 @item @code{L} --- reserved
14801 Reserved for future use.
14803 @item @code{m}@var{addr}@code{,}@var{length} --- read memory
14804 @cindex @code{m} packet
14806 Read @var{length} bytes of memory starting at address @var{addr}.
14807 Neither @value{GDBN} nor the stub assume that sized memory transfers are
14808 assumed using word alligned accesses. FIXME: @emph{A word aligned memory
14809 transfer mechanism is needed.}
14813 @item @var{XX@dots{}}
14814 @var{XX@dots{}} is mem contents. Can be fewer bytes than requested if able
14815 to read only part of the data. Neither @value{GDBN} nor the stub assume
14816 that sized memory transfers are assumed using word alligned
14817 accesses. FIXME: @emph{A word aligned memory transfer mechanism is
14823 @item @code{M}@var{addr},@var{length}@code{:}@var{XX@dots{}} --- write mem
14824 @cindex @code{M} packet
14826 Write @var{length} bytes of memory starting at address @var{addr}.
14827 @var{XX@dots{}} is the data.
14834 for an error (this includes the case where only part of the data was
14838 @item @code{n} --- reserved
14840 Reserved for future use.
14842 @item @code{N} --- reserved
14844 Reserved for future use.
14846 @item @code{o} --- reserved
14848 Reserved for future use.
14850 @item @code{O} --- reserved
14852 Reserved for future use.
14854 @item @code{p}@var{n@dots{}} --- read reg @strong{(reserved)}
14855 @cindex @code{p} packet
14857 @xref{write register packet}.
14861 @item @var{r@dots{}.}
14862 The hex encoded value of the register in target byte order.
14865 @item @code{P}@var{n@dots{}}@code{=}@var{r@dots{}} --- write register
14866 @anchor{write register packet}
14867 @cindex @code{P} packet
14869 Write register @var{n@dots{}} with value @var{r@dots{}}, which contains two hex
14870 digits for each byte in the register (target byte order).
14880 @item @code{q}@var{query} --- general query
14881 @anchor{general query packet}
14882 @cindex @code{q} packet
14884 Request info about @var{query}. In general @value{GDBN} queries have a
14885 leading upper case letter. Custom vendor queries should use a company
14886 prefix (in lower case) ex: @samp{qfsf.var}. @var{query} may optionally
14887 be followed by a @samp{,} or @samp{;} separated list. Stubs must ensure
14888 that they match the full @var{query} name.
14892 @item @var{XX@dots{}}
14893 Hex encoded data from query. The reply can not be empty.
14897 Indicating an unrecognized @var{query}.
14900 @item @code{Q}@var{var}@code{=}@var{val} --- general set
14901 @cindex @code{Q} packet
14903 Set value of @var{var} to @var{val}.
14905 @xref{general query packet}, for a discussion of naming conventions.
14907 @item @code{r} --- reset @strong{(deprecated)}
14908 @cindex @code{r} packet
14910 Reset the entire system.
14912 @item @code{R}@var{XX} --- remote restart
14913 @cindex @code{R} packet
14915 Restart the program being debugged. @var{XX}, while needed, is ignored.
14916 This packet is only available in extended mode.
14920 @item @emph{no reply}
14921 The @samp{R} packet has no reply.
14924 @item @code{s}@var{addr} --- step
14925 @cindex @code{s} packet
14927 @var{addr} is address to resume. If @var{addr} is omitted, resume at
14931 @xref{Stop Reply Packets}, for the reply specifications.
14933 @item @code{S}@var{sig}@code{;}@var{addr} --- step with signal
14934 @anchor{step with signal packet}
14935 @cindex @code{S} packet
14937 Like @samp{C} but step not continue.
14940 @xref{Stop Reply Packets}, for the reply specifications.
14942 @item @code{t}@var{addr}@code{:}@var{PP}@code{,}@var{MM} --- search
14943 @cindex @code{t} packet
14945 Search backwards starting at address @var{addr} for a match with pattern
14946 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4 bytes.
14947 @var{addr} must be at least 3 digits.
14949 @item @code{T}@var{XX} --- thread alive
14950 @cindex @code{T} packet
14952 Find out if the thread XX is alive.
14957 thread is still alive
14962 @item @code{u} --- reserved
14964 Reserved for future use.
14966 @item @code{U} --- reserved
14968 Reserved for future use.
14970 @item @code{v} --- reserved
14972 Reserved for future use.
14974 @item @code{V} --- reserved
14976 Reserved for future use.
14978 @item @code{w} --- reserved
14980 Reserved for future use.
14982 @item @code{W} --- reserved
14984 Reserved for future use.
14986 @item @code{x} --- reserved
14988 Reserved for future use.
14990 @item @code{X}@var{addr}@code{,}@var{length}@var{:}@var{XX@dots{}} --- write mem (binary)
14991 @cindex @code{X} packet
14993 @var{addr} is address, @var{length} is number of bytes, @var{XX@dots{}}
14994 is binary data. The characters @code{$}, @code{#}, and @code{0x7d} are
14995 escaped using @code{0x7d}.
15005 @item @code{y} --- reserved
15007 Reserved for future use.
15009 @item @code{Y} reserved
15011 Reserved for future use.
15013 @item @code{z}@var{type}@code{,}@var{addr}@code{,}@var{length} --- remove breakpoint or watchpoint @strong{(draft)}
15014 @itemx @code{Z}@var{type}@code{,}@var{addr}@code{,}@var{length} --- insert breakpoint or watchpoint @strong{(draft)}
15015 @anchor{insert breakpoint or watchpoint packet}
15016 @cindex @code{z} packet
15017 @cindex @code{Z} packets
15019 Insert (@code{Z}) or remove (@code{z}) a @var{type} breakpoint or
15020 watchpoint starting at address @var{address} and covering the next
15021 @var{length} bytes.
15023 Each breakpoint and watchpoint packet @var{type} is documented
15026 @emph{Implementation notes: A remote target shall return @samp{} for an
15027 unrecognized breakpoint or watchpoint packet @var{type}. A remote
15028 target shall support either both or neither of a given
15029 @code{Z}@var{type}@dots{} and @code{z}@var{type}@dots{} packet pair. To
15030 avoid potential problems with duplicate packets, the operations should
15031 be implemented in an idempotent way.}
15033 @item @code{z}@code{0}@code{,}@var{addr}@code{,}@var{length} --- remove memory breakpoint @strong{(draft)}
15034 @item @code{Z}@code{0}@code{,}@var{addr}@code{,}@var{length} --- insert memory breakpoint @strong{(draft)}
15035 @cindex @code{z0} packet
15036 @cindex @code{Z0} packet
15038 Insert (@code{Z0}) or remove (@code{z0}) a memory breakpoint at address
15039 @code{addr} of size @code{length}.
15041 A memory breakpoint is implemented by replacing the instruction at
15042 @var{addr} with a software breakpoint or trap instruction. The
15043 @code{length} is used by targets that indicates the size of the
15044 breakpoint (in bytes) that should be inserted (e.g., the @sc{arm} and
15045 @sc{mips} can insert either a 2 or 4 byte breakpoint).
15047 @emph{Implementation note: It is possible for a target to copy or move
15048 code that contains memory breakpoints (e.g., when implementing
15049 overlays). The behavior of this packet, in the presence of such a
15050 target, is not defined.}
15062 @item @code{z}@code{1}@code{,}@var{addr}@code{,}@var{length} --- remove hardware breakpoint @strong{(draft)}
15063 @item @code{Z}@code{1}@code{,}@var{addr}@code{,}@var{length} --- insert hardware breakpoint @strong{(draft)}
15064 @cindex @code{z1} packet
15065 @cindex @code{Z1} packet
15067 Insert (@code{Z1}) or remove (@code{z1}) a hardware breakpoint at
15068 address @code{addr} of size @code{length}.
15070 A hardware breakpoint is implemented using a mechanism that is not
15071 dependant on being able to modify the target's memory.
15073 @emph{Implementation note: A hardware breakpoint is not affected by code
15086 @item @code{z}@code{2}@code{,}@var{addr}@code{,}@var{length} --- remove write watchpoint @strong{(draft)}
15087 @item @code{Z}@code{2}@code{,}@var{addr}@code{,}@var{length} --- insert write watchpoint @strong{(draft)}
15088 @cindex @code{z2} packet
15089 @cindex @code{Z2} packet
15091 Insert (@code{Z2}) or remove (@code{z2}) a write watchpoint.
15103 @item @code{z}@code{3}@code{,}@var{addr}@code{,}@var{length} --- remove read watchpoint @strong{(draft)}
15104 @item @code{Z}@code{3}@code{,}@var{addr}@code{,}@var{length} --- insert read watchpoint @strong{(draft)}
15105 @cindex @code{z3} packet
15106 @cindex @code{Z3} packet
15108 Insert (@code{Z3}) or remove (@code{z3}) a write watchpoint.
15120 @item @code{z}@code{4}@code{,}@var{addr}@code{,}@var{length} --- remove read watchpoint @strong{(draft)}
15121 @item @code{Z}@code{4}@code{,}@var{addr}@code{,}@var{length} --- insert read watchpoint @strong{(draft)}
15122 @cindex @code{z4} packet
15123 @cindex @code{Z4} packet
15125 Insert (@code{Z4}) or remove (@code{z4}) an access watchpoint.
15139 @node Stop Reply Packets
15140 @section Stop Reply Packets
15141 @cindex stop reply packets
15143 The @samp{C}, @samp{c}, @samp{S}, @samp{s} and @samp{?} packets can
15144 receive any of the below as a reply. In the case of the @samp{C},
15145 @samp{c}, @samp{S} and @samp{s} packets, that reply is only returned
15146 when the target halts. In the below the exact meaning of @samp{signal
15147 number} is poorly defined. In general one of the UNIX signal numbering
15148 conventions is used.
15153 @var{AA} is the signal number
15155 @item @code{T}@var{AA}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}
15156 @cindex @code{T} packet reply
15158 @var{AA} = two hex digit signal number; @var{n...} = register number
15159 (hex), @var{r...} = target byte ordered register contents, size defined
15160 by @code{REGISTER_RAW_SIZE}; @var{n...} = @samp{thread}, @var{r...} =
15161 thread process ID, this is a hex integer; @var{n...} = (@samp{watch} |
15162 @samp{rwatch} | @samp{awatch}, @var{r...} = data address, this is a hex
15163 integer; @var{n...} = other string not starting with valid hex digit.
15164 @value{GDBN} should ignore this @var{n...}, @var{r...} pair and go on
15165 to the next. This way we can extend the protocol.
15169 The process exited, and @var{AA} is the exit status. This is only
15170 applicable to certain targets.
15174 The process terminated with signal @var{AA}.
15176 @item N@var{AA};@var{t@dots{}};@var{d@dots{}};@var{b@dots{}} @strong{(obsolete)}
15178 @var{AA} = signal number; @var{t@dots{}} = address of symbol
15179 @code{_start}; @var{d@dots{}} = base of data section; @var{b@dots{}} =
15180 base of bss section. @emph{Note: only used by Cisco Systems targets.
15181 The difference between this reply and the @samp{qOffsets} query is that
15182 the @samp{N} packet may arrive spontaneously whereas the @samp{qOffsets}
15183 is a query initiated by the host debugger.}
15185 @item O@var{XX@dots{}}
15187 @var{XX@dots{}} is hex encoding of @sc{ascii} data. This can happen at
15188 any time while the program is running and the debugger should continue
15189 to wait for @samp{W}, @samp{T}, etc.
15193 @node General Query Packets
15194 @section General Query Packets
15196 The following set and query packets have already been defined.
15200 @item @code{q}@code{C} --- current thread
15202 Return the current thread id.
15206 @item @code{QC}@var{pid}
15207 Where @var{pid} is a HEX encoded 16 bit process id.
15209 Any other reply implies the old pid.
15212 @item @code{q}@code{fThreadInfo} -- all thread ids
15214 @code{q}@code{sThreadInfo}
15216 Obtain a list of active thread ids from the target (OS). Since there
15217 may be too many active threads to fit into one reply packet, this query
15218 works iteratively: it may require more than one query/reply sequence to
15219 obtain the entire list of threads. The first query of the sequence will
15220 be the @code{qf}@code{ThreadInfo} query; subsequent queries in the
15221 sequence will be the @code{qs}@code{ThreadInfo} query.
15223 NOTE: replaces the @code{qL} query (see below).
15227 @item @code{m}@var{id}
15229 @item @code{m}@var{id},@var{id}@dots{}
15230 a comma-separated list of thread ids
15232 (lower case 'el') denotes end of list.
15235 In response to each query, the target will reply with a list of one or
15236 more thread ids, in big-endian hex, separated by commas. @value{GDBN}
15237 will respond to each reply with a request for more thread ids (using the
15238 @code{qs} form of the query), until the target responds with @code{l}
15239 (lower-case el, for @code{'last'}).
15241 @item @code{q}@code{ThreadExtraInfo}@code{,}@var{id} --- extra thread info
15243 Where @var{id} is a thread-id in big-endian hex. Obtain a printable
15244 string description of a thread's attributes from the target OS. This
15245 string may contain anything that the target OS thinks is interesting for
15246 @value{GDBN} to tell the user about the thread. The string is displayed
15247 in @value{GDBN}'s @samp{info threads} display. Some examples of
15248 possible thread extra info strings are ``Runnable'', or ``Blocked on
15253 @item @var{XX@dots{}}
15254 Where @var{XX@dots{}} is a hex encoding of @sc{ascii} data, comprising
15255 the printable string containing the extra information about the thread's
15259 @item @code{q}@code{L}@var{startflag}@var{threadcount}@var{nextthread} --- query @var{LIST} or @var{threadLIST} @strong{(deprecated)}
15261 Obtain thread information from RTOS. Where: @var{startflag} (one hex
15262 digit) is one to indicate the first query and zero to indicate a
15263 subsequent query; @var{threadcount} (two hex digits) is the maximum
15264 number of threads the response packet can contain; and @var{nextthread}
15265 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
15266 returned in the response as @var{argthread}.
15268 NOTE: this query is replaced by the @code{q}@code{fThreadInfo} query
15273 @item @code{q}@code{M}@var{count}@var{done}@var{argthread}@var{thread@dots{}}
15274 Where: @var{count} (two hex digits) is the number of threads being
15275 returned; @var{done} (one hex digit) is zero to indicate more threads
15276 and one indicates no further threads; @var{argthreadid} (eight hex
15277 digits) is @var{nextthread} from the request packet; @var{thread@dots{}}
15278 is a sequence of thread IDs from the target. @var{threadid} (eight hex
15279 digits). See @code{remote.c:parse_threadlist_response()}.
15282 @item @code{q}@code{CRC:}@var{addr}@code{,}@var{length} --- compute CRC of memory block
15286 @item @code{E}@var{NN}
15287 An error (such as memory fault)
15288 @item @code{C}@var{CRC32}
15289 A 32 bit cyclic redundancy check of the specified memory region.
15292 @item @code{q}@code{Offsets} --- query sect offs
15294 Get section offsets that the target used when re-locating the downloaded
15295 image. @emph{Note: while a @code{Bss} offset is included in the
15296 response, @value{GDBN} ignores this and instead applies the @code{Data}
15297 offset to the @code{Bss} section.}
15301 @item @code{Text=}@var{xxx}@code{;Data=}@var{yyy}@code{;Bss=}@var{zzz}
15304 @item @code{q}@code{P}@var{mode}@var{threadid} --- thread info request
15306 Returns information on @var{threadid}. Where: @var{mode} is a hex
15307 encoded 32 bit mode; @var{threadid} is a hex encoded 64 bit thread ID.
15314 See @code{remote.c:remote_unpack_thread_info_response()}.
15316 @item @code{q}@code{Rcmd,}@var{command} --- remote command
15318 @var{command} (hex encoded) is passed to the local interpreter for
15319 execution. Invalid commands should be reported using the output string.
15320 Before the final result packet, the target may also respond with a
15321 number of intermediate @code{O}@var{output} console output packets.
15322 @emph{Implementors should note that providing access to a stubs's
15323 interpreter may have security implications}.
15328 A command response with no output.
15330 A command response with the hex encoded output string @var{OUTPUT}.
15331 @item @code{E}@var{NN}
15332 Indicate a badly formed request.
15334 When @samp{q}@samp{Rcmd} is not recognized.
15337 @item @code{qSymbol::} --- symbol lookup
15339 Notify the target that @value{GDBN} is prepared to serve symbol lookup
15340 requests. Accept requests from the target for the values of symbols.
15345 The target does not need to look up any (more) symbols.
15346 @item @code{qSymbol:}@var{sym_name}
15347 The target requests the value of symbol @var{sym_name} (hex encoded).
15348 @value{GDBN} may provide the value by using the
15349 @code{qSymbol:}@var{sym_value}:@var{sym_name} message, described below.
15352 @item @code{qSymbol:}@var{sym_value}:@var{sym_name} --- symbol value
15354 Set the value of @var{sym_name} to @var{sym_value}.
15356 @var{sym_name} (hex encoded) is the name of a symbol whose value the
15357 target has previously requested.
15359 @var{sym_value} (hex) is the value for symbol @var{sym_name}. If
15360 @value{GDBN} cannot supply a value for @var{sym_name}, then this field
15366 The target does not need to look up any (more) symbols.
15367 @item @code{qSymbol:}@var{sym_name}
15368 The target requests the value of a new symbol @var{sym_name} (hex
15369 encoded). @value{GDBN} will continue to supply the values of symbols
15370 (if available), until the target ceases to request them.
15375 @node Register Packet Format
15376 @section Register Packet Format
15378 The following @samp{g}/@samp{G} packets have previously been defined.
15379 In the below, some thirty-two bit registers are transferred as
15380 sixty-four bits. Those registers should be zero/sign extended (which?)
15381 to fill the space allocated. Register bytes are transfered in target
15382 byte order. The two nibbles within a register byte are transfered
15383 most-significant - least-significant.
15389 All registers are transfered as thirty-two bit quantities in the order:
15390 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
15391 registers; fsr; fir; fp.
15395 All registers are transfered as sixty-four bit quantities (including
15396 thirty-two bit registers such as @code{sr}). The ordering is the same
15404 Example sequence of a target being re-started. Notice how the restart
15405 does not get any direct output:
15410 @emph{target restarts}
15413 <- @code{T001:1234123412341234}
15417 Example sequence of a target being stepped by a single instruction:
15420 -> @code{G1445@dots{}}
15425 <- @code{T001:1234123412341234}
15429 <- @code{1455@dots{}}
15443 % I think something like @colophon should be in texinfo. In the
15445 \long\def\colophon{\hbox to0pt{}\vfill
15446 \centerline{The body of this manual is set in}
15447 \centerline{\fontname\tenrm,}
15448 \centerline{with headings in {\bf\fontname\tenbf}}
15449 \centerline{and examples in {\tt\fontname\tentt}.}
15450 \centerline{{\it\fontname\tenit\/},}
15451 \centerline{{\bf\fontname\tenbf}, and}
15452 \centerline{{\sl\fontname\tensl\/}}
15453 \centerline{are used for emphasis.}\vfill}
15455 % Blame: doc@cygnus.com, 1991.