1 \input texinfo @c -*-texinfo-*-
3 @c Free Software Foundation, Inc.
6 @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use
7 @c of @set vars. However, you can override filename with makeinfo -o.
12 @settitle Debugging with @value{GDBN}
13 @setchapternewpage odd
24 @c readline appendices use @vindex, @findex and @ftable,
25 @c annotate.texi and gdbmi use @findex.
29 @c !!set GDB manual's edition---not the same as GDB version!
32 @c !!set GDB manual's revision date
35 @c THIS MANUAL REQUIRES TEXINFO 3.12 OR LATER.
37 @c This is a dir.info fragment to support semi-automated addition of
38 @c manuals to an info tree.
39 @dircategory Programming & development tools.
41 * Gdb: (gdb). The @sc{gnu} debugger.
45 This file documents the @sc{gnu} debugger @value{GDBN}.
48 This is the @value{EDITION} Edition, @value{DATE},
49 of @cite{Debugging with @value{GDBN}: the @sc{gnu} Source-Level Debugger}
50 for @value{GDBN} Version @value{GDBVN}.
52 Copyright (C) 1988-2000 Free Software Foundation, Inc.
54 Permission is granted to make and distribute verbatim copies of
55 this manual provided the copyright notice and this permission notice
56 are preserved on all copies.
59 Permission is granted to process this file through TeX and print the
60 results, provided the printed document carries copying permission
61 notice identical to this one except for the removal of this paragraph
62 (this paragraph not being relevant to the printed manual).
65 Permission is granted to copy and distribute modified versions of this
66 manual under the conditions for verbatim copying, provided also that the
67 entire resulting derived work is distributed under the terms of a
68 permission notice identical to this one.
70 Permission is granted to copy and distribute translations of this manual
71 into another language, under the above conditions for modified versions.
75 @title Debugging with @value{GDBN}
76 @subtitle The @sc{gnu} Source-Level Debugger
78 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
79 @subtitle @value{DATE}
80 @author Richard Stallman, Roland Pesch, Stan Shebs, et al.
84 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@gnu.org.)\par
85 \hfill {\it Debugging with @value{GDBN}}\par
86 \hfill \TeX{}info \texinfoversion\par
90 @vskip 0pt plus 1filll
91 Copyright @copyright{} 1988-2000 Free Software Foundation, Inc.
93 Published by the Free Software Foundation @*
94 59 Temple Place - Suite 330, @*
95 Boston, MA 02111-1307 USA @*
98 Permission is granted to make and distribute verbatim copies of
99 this manual provided the copyright notice and this permission notice
100 are preserved on all copies.
102 Permission is granted to copy and distribute modified versions of this
103 manual under the conditions for verbatim copying, provided also that the
104 entire resulting derived work is distributed under the terms of a
105 permission notice identical to this one.
107 Permission is granted to copy and distribute translations of this manual
108 into another language, under the above conditions for modified versions.
113 @node Top, Summary, (dir), (dir)
115 @top Debugging with @value{GDBN}
117 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
119 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
122 Copyright (C) 1988-2000 Free Software Foundation, Inc.
125 * Summary:: Summary of @value{GDBN}
126 * Sample Session:: A sample @value{GDBN} session
128 * Invocation:: Getting in and out of @value{GDBN}
129 * Commands:: @value{GDBN} commands
130 * Running:: Running programs under @value{GDBN}
131 * Stopping:: Stopping and continuing
132 * Stack:: Examining the stack
133 * Source:: Examining source files
134 * Data:: Examining data
136 * Languages:: Using @value{GDBN} with different languages
138 * Symbols:: Examining the symbol table
139 * Altering:: Altering execution
140 * GDB Files:: @value{GDBN} files
141 * Targets:: Specifying a debugging target
142 * Configurations:: Configuration-specific information
143 * Controlling GDB:: Controlling @value{GDBN}
144 * Sequences:: Canned sequences of commands
145 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
146 * Annotations:: @value{GDBN}'s annotation interface.
147 * GDB/MI:: @value{GDBN}'s Machine Interface.
149 * GDB Bugs:: Reporting bugs in @value{GDBN}
150 * Formatting Documentation:: How to format and print @value{GDBN} documentation
152 * Command Line Editing:: Command Line Editing
153 * Using History Interactively:: Using History Interactively
154 * Installing GDB:: Installing GDB
160 @c the replication sucks, but this avoids a texinfo 3.12 lameness
165 @top Debugging with @value{GDBN}
167 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
169 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
172 Copyright (C) 1988-2000 Free Software Foundation, Inc.
175 * Summary:: Summary of @value{GDBN}
176 * Sample Session:: A sample @value{GDBN} session
178 * Invocation:: Getting in and out of @value{GDBN}
179 * Commands:: @value{GDBN} commands
180 * Running:: Running programs under @value{GDBN}
181 * Stopping:: Stopping and continuing
182 * Stack:: Examining the stack
183 * Source:: Examining source files
184 * Data:: Examining data
186 * Languages:: Using @value{GDBN} with different languages
188 * Symbols:: Examining the symbol table
189 * Altering:: Altering execution
190 * GDB Files:: @value{GDBN} files
191 * Targets:: Specifying a debugging target
192 * Configurations:: Configuration-specific information
193 * Controlling GDB:: Controlling @value{GDBN}
194 * Sequences:: Canned sequences of commands
195 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
196 * Annotations:: @value{GDBN}'s annotation interface.
198 * GDB Bugs:: Reporting bugs in @value{GDBN}
199 * Formatting Documentation:: How to format and print @value{GDBN} documentation
201 * Command Line Editing:: Command Line Editing
202 * Using History Interactively:: Using History Interactively
203 * Installing GDB:: Installing GDB
209 @c TeX can handle the contents at the start but makeinfo 3.12 can not
215 @unnumbered Summary of @value{GDBN}
217 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
218 going on ``inside'' another program while it executes---or what another
219 program was doing at the moment it crashed.
221 @value{GDBN} can do four main kinds of things (plus other things in support of
222 these) to help you catch bugs in the act:
226 Start your program, specifying anything that might affect its behavior.
229 Make your program stop on specified conditions.
232 Examine what has happened, when your program has stopped.
235 Change things in your program, so you can experiment with correcting the
236 effects of one bug and go on to learn about another.
239 You can use @value{GDBN} to debug programs written in C and C++.
240 For more information, see @ref{Support,,Supported languages}.
241 For more information, see @ref{C,,C and C++}.
245 Support for Modula-2 and Chill is partial. For information on Modula-2,
246 see @ref{Modula-2,,Modula-2}. For information on Chill, see @ref{Chill}.
249 Debugging Pascal programs which use sets, subranges, file variables, or
250 nested functions does not currently work. @value{GDBN} does not support
251 entering expressions, printing values, or similar features using Pascal
255 @value{GDBN} can be used to debug programs written in Fortran, although
256 it may be necessary to refer to some variables with a trailing
260 * Free Software:: Freely redistributable software
261 * Contributors:: Contributors to GDB
265 @unnumberedsec Free software
267 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
268 General Public License
269 (GPL). The GPL gives you the freedom to copy or adapt a licensed
270 program---but every person getting a copy also gets with it the
271 freedom to modify that copy (which means that they must get access to
272 the source code), and the freedom to distribute further copies.
273 Typical software companies use copyrights to limit your freedoms; the
274 Free Software Foundation uses the GPL to preserve these freedoms.
276 Fundamentally, the General Public License is a license which says that
277 you have these freedoms and that you cannot take these freedoms away
281 @unnumberedsec Contributors to @value{GDBN}
283 Richard Stallman was the original author of @value{GDBN}, and of many
284 other @sc{gnu} programs. Many others have contributed to its
285 development. This section attempts to credit major contributors. One
286 of the virtues of free software is that everyone is free to contribute
287 to it; with regret, we cannot actually acknowledge everyone here. The
288 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
289 blow-by-blow account.
291 Changes much prior to version 2.0 are lost in the mists of time.
294 @emph{Plea:} Additions to this section are particularly welcome. If you
295 or your friends (or enemies, to be evenhanded) have been unfairly
296 omitted from this list, we would like to add your names!
299 So that they may not regard their many labors as thankless, we
300 particularly thank those who shepherded @value{GDBN} through major
302 Andrew Cagney (release 5.0);
303 Jim Blandy (release 4.18);
304 Jason Molenda (release 4.17);
305 Stan Shebs (release 4.14);
306 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
307 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
308 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
309 Jim Kingdon (releases 3.5, 3.4, and 3.3);
310 and Randy Smith (releases 3.2, 3.1, and 3.0).
312 Richard Stallman, assisted at various times by Peter TerMaat, Chris
313 Hanson, and Richard Mlynarik, handled releases through 2.8.
315 Michael Tiemann is the author of most of the @sc{gnu} C++ support in
316 @value{GDBN}, with significant additional contributions from Per
317 Bothner. James Clark wrote the @sc{gnu} C++ demangler. Early work on
318 C++ was by Peter TerMaat (who also did much general update work leading
321 @value{GDBN} 4 uses the BFD subroutine library to examine multiple
322 object-file formats; BFD was a joint project of David V.
323 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
325 David Johnson wrote the original COFF support; Pace Willison did
326 the original support for encapsulated COFF.
328 Brent Benson of Harris Computer Systems contributed DWARF2 support.
330 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
331 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
333 Jean-Daniel Fekete contributed Sun 386i support.
334 Chris Hanson improved the HP9000 support.
335 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
336 David Johnson contributed Encore Umax support.
337 Jyrki Kuoppala contributed Altos 3068 support.
338 Jeff Law contributed HP PA and SOM support.
339 Keith Packard contributed NS32K support.
340 Doug Rabson contributed Acorn Risc Machine support.
341 Bob Rusk contributed Harris Nighthawk CX-UX support.
342 Chris Smith contributed Convex support (and Fortran debugging).
343 Jonathan Stone contributed Pyramid support.
344 Michael Tiemann contributed SPARC support.
345 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
346 Pace Willison contributed Intel 386 support.
347 Jay Vosburgh contributed Symmetry support.
349 Andreas Schwab contributed M68K Linux support.
351 Rich Schaefer and Peter Schauer helped with support of SunOS shared
354 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
355 about several machine instruction sets.
357 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
358 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
359 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
360 and RDI targets, respectively.
362 Brian Fox is the author of the readline libraries providing
363 command-line editing and command history.
365 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
366 Modula-2 support, and contributed the Languages chapter of this manual.
368 Fred Fish wrote most of the support for Unix System Vr4.
369 He also enhanced the command-completion support to cover C++ overloaded
372 Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and
375 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
377 Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors.
379 Toshiba sponsored the support for the TX39 Mips processor.
381 Matsushita sponsored the support for the MN10200 and MN10300 processors.
383 Fujitsu sponsored the support for SPARClite and FR30 processors.
385 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
388 Michael Snyder added support for tracepoints.
390 Stu Grossman wrote gdbserver.
392 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
393 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
395 The following people at the Hewlett-Packard Company contributed
396 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
397 (narrow mode), HP's implementation of kernel threads, HP's aC++
398 compiler, and the terminal user interface: Ben Krepp, Richard Title,
399 John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve
400 Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific
401 information in this manual.
403 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
404 development since 1991. Cygnus engineers who have worked on @value{GDBN}
405 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
406 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
407 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
408 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
409 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
410 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
411 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
412 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
413 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
414 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
415 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
416 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
417 Zuhn have made contributions both large and small.
421 @chapter A Sample @value{GDBN} Session
423 You can use this manual at your leisure to read all about @value{GDBN}.
424 However, a handful of commands are enough to get started using the
425 debugger. This chapter illustrates those commands.
428 In this sample session, we emphasize user input like this: @b{input},
429 to make it easier to pick out from the surrounding output.
432 @c FIXME: this example may not be appropriate for some configs, where
433 @c FIXME...primary interest is in remote use.
435 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
436 processor) exhibits the following bug: sometimes, when we change its
437 quote strings from the default, the commands used to capture one macro
438 definition within another stop working. In the following short @code{m4}
439 session, we define a macro @code{foo} which expands to @code{0000}; we
440 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
441 same thing. However, when we change the open quote string to
442 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
443 procedure fails to define a new synonym @code{baz}:
452 @b{define(bar,defn(`foo'))}
456 @b{changequote(<QUOTE>,<UNQUOTE>)}
458 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
461 m4: End of input: 0: fatal error: EOF in string
465 Let us use @value{GDBN} to try to see what is going on.
468 $ @b{@value{GDBP} m4}
469 @c FIXME: this falsifies the exact text played out, to permit smallbook
470 @c FIXME... format to come out better.
471 @value{GDBN} is free software and you are welcome to distribute copies
472 of it under certain conditions; type "show copying" to see
474 There is absolutely no warranty for @value{GDBN}; type "show warranty"
477 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
482 @value{GDBN} reads only enough symbol data to know where to find the
483 rest when needed; as a result, the first prompt comes up very quickly.
484 We now tell @value{GDBN} to use a narrower display width than usual, so
485 that examples fit in this manual.
488 (@value{GDBP}) @b{set width 70}
492 We need to see how the @code{m4} built-in @code{changequote} works.
493 Having looked at the source, we know the relevant subroutine is
494 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
495 @code{break} command.
498 (@value{GDBP}) @b{break m4_changequote}
499 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
503 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
504 control; as long as control does not reach the @code{m4_changequote}
505 subroutine, the program runs as usual:
508 (@value{GDBP}) @b{run}
509 Starting program: /work/Editorial/gdb/gnu/m4/m4
517 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
518 suspends execution of @code{m4}, displaying information about the
519 context where it stops.
522 @b{changequote(<QUOTE>,<UNQUOTE>)}
524 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
526 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
530 Now we use the command @code{n} (@code{next}) to advance execution to
531 the next line of the current function.
535 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
540 @code{set_quotes} looks like a promising subroutine. We can go into it
541 by using the command @code{s} (@code{step}) instead of @code{next}.
542 @code{step} goes to the next line to be executed in @emph{any}
543 subroutine, so it steps into @code{set_quotes}.
547 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
549 530 if (lquote != def_lquote)
553 The display that shows the subroutine where @code{m4} is now
554 suspended (and its arguments) is called a stack frame display. It
555 shows a summary of the stack. We can use the @code{backtrace}
556 command (which can also be spelled @code{bt}), to see where we are
557 in the stack as a whole: the @code{backtrace} command displays a
558 stack frame for each active subroutine.
561 (@value{GDBP}) @b{bt}
562 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
564 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
566 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
567 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
569 #4 0x79dc in expand_input () at macro.c:40
570 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
574 We step through a few more lines to see what happens. The first two
575 times, we can use @samp{s}; the next two times we use @code{n} to avoid
576 falling into the @code{xstrdup} subroutine.
580 0x3b5c 532 if (rquote != def_rquote)
582 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
583 def_lquote : xstrdup(lq);
585 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
588 538 len_lquote = strlen(rquote);
592 The last line displayed looks a little odd; we can examine the variables
593 @code{lquote} and @code{rquote} to see if they are in fact the new left
594 and right quotes we specified. We use the command @code{p}
595 (@code{print}) to see their values.
598 (@value{GDBP}) @b{p lquote}
599 $1 = 0x35d40 "<QUOTE>"
600 (@value{GDBP}) @b{p rquote}
601 $2 = 0x35d50 "<UNQUOTE>"
605 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
606 To look at some context, we can display ten lines of source
607 surrounding the current line with the @code{l} (@code{list}) command.
613 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
615 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
618 538 len_lquote = strlen(rquote);
619 539 len_rquote = strlen(lquote);
626 Let us step past the two lines that set @code{len_lquote} and
627 @code{len_rquote}, and then examine the values of those variables.
631 539 len_rquote = strlen(lquote);
634 (@value{GDBP}) @b{p len_lquote}
636 (@value{GDBP}) @b{p len_rquote}
641 That certainly looks wrong, assuming @code{len_lquote} and
642 @code{len_rquote} are meant to be the lengths of @code{lquote} and
643 @code{rquote} respectively. We can set them to better values using
644 the @code{p} command, since it can print the value of
645 any expression---and that expression can include subroutine calls and
649 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
651 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
656 Is that enough to fix the problem of using the new quotes with the
657 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
658 executing with the @code{c} (@code{continue}) command, and then try the
659 example that caused trouble initially:
665 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
672 Success! The new quotes now work just as well as the default ones. The
673 problem seems to have been just the two typos defining the wrong
674 lengths. We allow @code{m4} exit by giving it an EOF as input:
678 Program exited normally.
682 The message @samp{Program exited normally.} is from @value{GDBN}; it
683 indicates @code{m4} has finished executing. We can end our @value{GDBN}
684 session with the @value{GDBN} @code{quit} command.
687 (@value{GDBP}) @b{quit}
691 @chapter Getting In and Out of @value{GDBN}
693 This chapter discusses how to start @value{GDBN}, and how to get out of it.
697 type @samp{@value{GDBP}} to start @value{GDBN}.
699 type @kbd{quit} or @kbd{C-d} to exit.
703 * Invoking GDB:: How to start @value{GDBN}
704 * Quitting GDB:: How to quit @value{GDBN}
705 * Shell Commands:: How to use shell commands inside @value{GDBN}
709 @section Invoking @value{GDBN}
711 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
712 @value{GDBN} reads commands from the terminal until you tell it to exit.
714 You can also run @code{@value{GDBP}} with a variety of arguments and options,
715 to specify more of your debugging environment at the outset.
717 The command-line options described here are designed
718 to cover a variety of situations; in some environments, some of these
719 options may effectively be unavailable.
721 The most usual way to start @value{GDBN} is with one argument,
722 specifying an executable program:
725 @value{GDBP} @var{program}
729 You can also start with both an executable program and a core file
733 @value{GDBP} @var{program} @var{core}
736 You can, instead, specify a process ID as a second argument, if you want
737 to debug a running process:
740 @value{GDBP} @var{program} 1234
744 would attach @value{GDBN} to process @code{1234} (unless you also have a file
745 named @file{1234}; @value{GDBN} does check for a core file first).
747 Taking advantage of the second command-line argument requires a fairly
748 complete operating system; when you use @value{GDBN} as a remote
749 debugger attached to a bare board, there may not be any notion of
750 ``process'', and there is often no way to get a core dump. @value{GDBN}
751 will warn you if it is unable to attach or to read core dumps.
753 You can run @code{@value{GDBP}} without printing the front material, which describes
754 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
761 You can further control how @value{GDBN} starts up by using command-line
762 options. @value{GDBN} itself can remind you of the options available.
772 to display all available options and briefly describe their use
773 (@samp{@value{GDBP} -h} is a shorter equivalent).
775 All options and command line arguments you give are processed
776 in sequential order. The order makes a difference when the
777 @samp{-x} option is used.
781 * File Options:: Choosing files
782 * Mode Options:: Choosing modes
786 @subsection Choosing files
788 When @value{GDBN} starts, it reads any arguments other than options as
789 specifying an executable file and core file (or process ID). This is
790 the same as if the arguments were specified by the @samp{-se} and
791 @samp{-c} options respectively. (@value{GDBN} reads the first argument
792 that does not have an associated option flag as equivalent to the
793 @samp{-se} option followed by that argument; and the second argument
794 that does not have an associated option flag, if any, as equivalent to
795 the @samp{-c} option followed by that argument.)
797 If @value{GDBN} has not been configured to included core file support,
798 such as for most embedded targets, then it will complain about a second
799 argument and ignore it.
801 Many options have both long and short forms; both are shown in the
802 following list. @value{GDBN} also recognizes the long forms if you truncate
803 them, so long as enough of the option is present to be unambiguous.
804 (If you prefer, you can flag option arguments with @samp{--} rather
805 than @samp{-}, though we illustrate the more usual convention.)
807 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
808 @c way, both those who look for -foo and --foo in the index, will find
812 @item -symbols @var{file}
814 @cindex @code{--symbols}
816 Read symbol table from file @var{file}.
818 @item -exec @var{file}
820 @cindex @code{--exec}
822 Use file @var{file} as the executable file to execute when appropriate,
823 and for examining pure data in conjunction with a core dump.
827 Read symbol table from file @var{file} and use it as the executable
830 @item -core @var{file}
832 @cindex @code{--core}
834 Use file @var{file} as a core dump to examine.
836 @item -c @var{number}
837 Connect to process ID @var{number}, as with the @code{attach} command
838 (unless there is a file in core-dump format named @var{number}, in which
839 case @samp{-c} specifies that file as a core dump to read).
841 @item -command @var{file}
843 @cindex @code{--command}
845 Execute @value{GDBN} commands from file @var{file}. @xref{Command
846 Files,, Command files}.
848 @item -directory @var{directory}
849 @itemx -d @var{directory}
850 @cindex @code{--directory}
852 Add @var{directory} to the path to search for source files.
856 @cindex @code{--mapped}
858 @emph{Warning: this option depends on operating system facilities that are not
859 supported on all systems.}@*
860 If memory-mapped files are available on your system through the @code{mmap}
861 system call, you can use this option
862 to have @value{GDBN} write the symbols from your
863 program into a reusable file in the current directory. If the program you are debugging is
864 called @file{/tmp/fred}, the mapped symbol file is @file{/tmp/fred.syms}.
865 Future @value{GDBN} debugging sessions notice the presence of this file,
866 and can quickly map in symbol information from it, rather than reading
867 the symbol table from the executable program.
869 The @file{.syms} file is specific to the host machine where @value{GDBN}
870 is run. It holds an exact image of the internal @value{GDBN} symbol
871 table. It cannot be shared across multiple host platforms.
875 @cindex @code{--readnow}
877 Read each symbol file's entire symbol table immediately, rather than
878 the default, which is to read it incrementally as it is needed.
879 This makes startup slower, but makes future operations faster.
883 You typically combine the @code{-mapped} and @code{-readnow} options in
884 order to build a @file{.syms} file that contains complete symbol
885 information. (@xref{Files,,Commands to specify files}, for information
886 on @file{.syms} files.) A simple @value{GDBN} invocation to do nothing
887 but build a @file{.syms} file for future use is:
890 gdb -batch -nx -mapped -readnow programname
894 @subsection Choosing modes
896 You can run @value{GDBN} in various alternative modes---for example, in
897 batch mode or quiet mode.
904 Do not execute commands found in any initialization files (normally
905 called @file{.gdbinit}, or @file{gdb.ini} on PCs). Normally,
906 @value{GDBN} executes the commands in these files after all the command
907 options and arguments have been processed. @xref{Command Files,,Command
913 @cindex @code{--quiet}
914 @cindex @code{--silent}
916 ``Quiet''. Do not print the introductory and copyright messages. These
917 messages are also suppressed in batch mode.
920 @cindex @code{--batch}
921 Run in batch mode. Exit with status @code{0} after processing all the
922 command files specified with @samp{-x} (and all commands from
923 initialization files, if not inhibited with @samp{-n}). Exit with
924 nonzero status if an error occurs in executing the @value{GDBN} commands
925 in the command files.
927 Batch mode may be useful for running @value{GDBN} as a filter, for
928 example to download and run a program on another computer; in order to
929 make this more useful, the message
932 Program exited normally.
936 (which is ordinarily issued whenever a program running under
937 @value{GDBN} control terminates) is not issued when running in batch
942 @cindex @code{--nowindows}
944 ``No windows''. If @value{GDBN} comes with a graphical user interface
945 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
946 interface. If no GUI is available, this option has no effect.
950 @cindex @code{--windows}
952 If @value{GDBN} includes a GUI, then this option requires it to be
955 @item -cd @var{directory}
957 Run @value{GDBN} using @var{directory} as its working directory,
958 instead of the current directory.
962 @cindex @code{--fullname}
964 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
965 subprocess. It tells @value{GDBN} to output the full file name and line
966 number in a standard, recognizable fashion each time a stack frame is
967 displayed (which includes each time your program stops). This
968 recognizable format looks like two @samp{\032} characters, followed by
969 the file name, line number and character position separated by colons,
970 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
971 @samp{\032} characters as a signal to display the source code for the
975 @cindex @code{--epoch}
976 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
977 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
978 routines so as to allow Epoch to display values of expressions in a
981 @item -annotate @var{level}
982 @cindex @code{--annotate}
983 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
984 effect is identical to using @samp{set annotate @var{level}}
985 (@pxref{Annotations}).
986 Annotation level controls how much information does @value{GDBN} print
987 together with its prompt, values of expressions, source lines, and other
988 types of output. Level 0 is the normal, level 1 is for use when
989 @value{GDBN} is run as a subprocess of @sc{gnu} Emacs, level 2 is the
990 maximum annotation suitable for programs that control @value{GDBN}.
993 @cindex @code{--async}
994 Use the asynchronous event loop for the command-line interface.
995 @value{GDBN} processes all events, such as user keyboard input, via a
996 special event loop. This allows @value{GDBN} to accept and process user
997 commands in parallel with the debugged process being
998 run@footnote{@value{GDBN} built with @sc{djgpp} tools for
999 MS-DOS/MS-Windows supports this mode of operation, but the event loop is
1000 suspended when the debuggee runs.}, so you don't need to wait for
1001 control to return to @value{GDBN} before you type the next command.
1002 (@emph{Note:} as of version 5.0, the target side of the asynchronous
1003 operation is not yet in place, so @samp{-async} does not work fully
1005 @c FIXME: when the target side of the event loop is done, the above NOTE
1006 @c should be removed.
1008 When the standard input is connected to a terminal device, @value{GDBN}
1009 uses the asynchronous event loop by default, unless disabled by the
1010 @samp{-noasync} option.
1013 @cindex @code{--noasync}
1014 Disable the asynchronous event loop for the command-line interface.
1016 @item -baud @var{bps}
1018 @cindex @code{--baud}
1020 Set the line speed (baud rate or bits per second) of any serial
1021 interface used by @value{GDBN} for remote debugging.
1023 @item -tty @var{device}
1024 @itemx -t @var{device}
1025 @cindex @code{--tty}
1027 Run using @var{device} for your program's standard input and output.
1028 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1030 @c resolve the situation of these eventually
1032 @c @cindex @code{--tui}
1033 @c Use a Terminal User Interface. For information, use your Web browser to
1034 @c read the file @file{TUI.html}, which is usually installed in the
1035 @c directory @code{/opt/langtools/wdb/doc} on HP-UX systems. Do not use
1036 @c this option if you run @value{GDBN} from Emacs (see @pxref{Emacs, ,Using
1037 @c @value{GDBN} under @sc{gnu} Emacs}).
1040 @c @cindex @code{--xdb}
1041 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1042 @c For information, see the file @file{xdb_trans.html}, which is usually
1043 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1046 @item -interpreter @var{interp}
1047 @cindex @code{--interpreter}
1048 Use the interpreter @var{interp} for interface with the controlling
1049 program or device. This option is meant to be set by programs which
1050 communicate with @value{GDBN} using it as a back end. For example,
1051 @samp{--interpreter=mi} causes @value{GDBN} to use the @dfn{gdbmi
1052 interface} (@pxref{GDB/MI, , The @sc{gdb/mi} Interface}).
1055 @cindex @code{--write}
1056 Open the executable and core files for both reading and writing. This
1057 is equivalent to the @samp{set write on} command inside @value{GDBN}
1061 @cindex @code{--statistics}
1062 This option causes @value{GDBN} to print statistics about time and
1063 memory usage after it completes each command and returns to the prompt.
1066 @cindex @code{--version}
1067 This option causes @value{GDBN} to print its version number and
1068 no-warranty blurb, and exit.
1073 @section Quitting @value{GDBN}
1074 @cindex exiting @value{GDBN}
1075 @cindex leaving @value{GDBN}
1078 @kindex quit @r{[}@var{expression}@r{]}
1079 @kindex q @r{(@code{quit})}
1080 @item quit @r{[}@var{expression}@r{]}
1082 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1083 @code{q}), or type an end-of-file character (usually @kbd{C-d}). If you
1084 do not supply @var{expression}, @value{GDBN} will terminate normally;
1085 otherwise it will terminate using the result of @var{expression} as the
1090 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1091 terminates the action of any @value{GDBN} command that is in progress and
1092 returns to @value{GDBN} command level. It is safe to type the interrupt
1093 character at any time because @value{GDBN} does not allow it to take effect
1094 until a time when it is safe.
1096 If you have been using @value{GDBN} to control an attached process or
1097 device, you can release it with the @code{detach} command
1098 (@pxref{Attach, ,Debugging an already-running process}).
1100 @node Shell Commands
1101 @section Shell commands
1103 If you need to execute occasional shell commands during your
1104 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1105 just use the @code{shell} command.
1109 @cindex shell escape
1110 @item shell @var{command string}
1111 Invoke a standard shell to execute @var{command string}.
1112 If it exists, the environment variable @code{SHELL} determines which
1113 shell to run. Otherwise @value{GDBN} uses the default shell
1114 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1117 The utility @code{make} is often needed in development environments.
1118 You do not have to use the @code{shell} command for this purpose in
1123 @cindex calling make
1124 @item make @var{make-args}
1125 Execute the @code{make} program with the specified
1126 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1130 @chapter @value{GDBN} Commands
1132 You can abbreviate a @value{GDBN} command to the first few letters of the command
1133 name, if that abbreviation is unambiguous; and you can repeat certain
1134 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1135 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1136 show you the alternatives available, if there is more than one possibility).
1139 * Command Syntax:: How to give commands to @value{GDBN}
1140 * Completion:: Command completion
1141 * Help:: How to ask @value{GDBN} for help
1144 @node Command Syntax
1145 @section Command syntax
1147 A @value{GDBN} command is a single line of input. There is no limit on
1148 how long it can be. It starts with a command name, which is followed by
1149 arguments whose meaning depends on the command name. For example, the
1150 command @code{step} accepts an argument which is the number of times to
1151 step, as in @samp{step 5}. You can also use the @code{step} command
1152 with no arguments. Some commands do not allow any arguments.
1154 @cindex abbreviation
1155 @value{GDBN} command names may always be truncated if that abbreviation is
1156 unambiguous. Other possible command abbreviations are listed in the
1157 documentation for individual commands. In some cases, even ambiguous
1158 abbreviations are allowed; for example, @code{s} is specially defined as
1159 equivalent to @code{step} even though there are other commands whose
1160 names start with @code{s}. You can test abbreviations by using them as
1161 arguments to the @code{help} command.
1163 @cindex repeating commands
1164 @kindex RET @r{(repeat last command)}
1165 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1166 repeat the previous command. Certain commands (for example, @code{run})
1167 will not repeat this way; these are commands whose unintentional
1168 repetition might cause trouble and which you are unlikely to want to
1171 The @code{list} and @code{x} commands, when you repeat them with
1172 @key{RET}, construct new arguments rather than repeating
1173 exactly as typed. This permits easy scanning of source or memory.
1175 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1176 output, in a way similar to the common utility @code{more}
1177 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1178 @key{RET} too many in this situation, @value{GDBN} disables command
1179 repetition after any command that generates this sort of display.
1181 @kindex # @r{(a comment)}
1183 Any text from a @kbd{#} to the end of the line is a comment; it does
1184 nothing. This is useful mainly in command files (@pxref{Command
1185 Files,,Command files}).
1188 @section Command completion
1191 @cindex word completion
1192 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1193 only one possibility; it can also show you what the valid possibilities
1194 are for the next word in a command, at any time. This works for @value{GDBN}
1195 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1197 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1198 of a word. If there is only one possibility, @value{GDBN} fills in the
1199 word, and waits for you to finish the command (or press @key{RET} to
1200 enter it). For example, if you type
1202 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1203 @c complete accuracy in these examples; space introduced for clarity.
1204 @c If texinfo enhancements make it unnecessary, it would be nice to
1205 @c replace " @key" by "@key" in the following...
1207 (@value{GDBP}) info bre @key{TAB}
1211 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1212 the only @code{info} subcommand beginning with @samp{bre}:
1215 (@value{GDBP}) info breakpoints
1219 You can either press @key{RET} at this point, to run the @code{info
1220 breakpoints} command, or backspace and enter something else, if
1221 @samp{breakpoints} does not look like the command you expected. (If you
1222 were sure you wanted @code{info breakpoints} in the first place, you
1223 might as well just type @key{RET} immediately after @samp{info bre},
1224 to exploit command abbreviations rather than command completion).
1226 If there is more than one possibility for the next word when you press
1227 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1228 characters and try again, or just press @key{TAB} a second time;
1229 @value{GDBN} displays all the possible completions for that word. For
1230 example, you might want to set a breakpoint on a subroutine whose name
1231 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1232 just sounds the bell. Typing @key{TAB} again displays all the
1233 function names in your program that begin with those characters, for
1237 (@value{GDBP}) b make_ @key{TAB}
1238 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1239 make_a_section_from_file make_environ
1240 make_abs_section make_function_type
1241 make_blockvector make_pointer_type
1242 make_cleanup make_reference_type
1243 make_command make_symbol_completion_list
1244 (@value{GDBP}) b make_
1248 After displaying the available possibilities, @value{GDBN} copies your
1249 partial input (@samp{b make_} in the example) so you can finish the
1252 If you just want to see the list of alternatives in the first place, you
1253 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1254 means @kbd{@key{META} ?}. You can type this either by holding down a
1255 key designated as the @key{META} shift on your keyboard (if there is
1256 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1258 @cindex quotes in commands
1259 @cindex completion of quoted strings
1260 Sometimes the string you need, while logically a ``word'', may contain
1261 parentheses or other characters that @value{GDBN} normally excludes from
1262 its notion of a word. To permit word completion to work in this
1263 situation, you may enclose words in @code{'} (single quote marks) in
1264 @value{GDBN} commands.
1266 The most likely situation where you might need this is in typing the
1267 name of a C++ function. This is because C++ allows function overloading
1268 (multiple definitions of the same function, distinguished by argument
1269 type). For example, when you want to set a breakpoint you may need to
1270 distinguish whether you mean the version of @code{name} that takes an
1271 @code{int} parameter, @code{name(int)}, or the version that takes a
1272 @code{float} parameter, @code{name(float)}. To use the word-completion
1273 facilities in this situation, type a single quote @code{'} at the
1274 beginning of the function name. This alerts @value{GDBN} that it may need to
1275 consider more information than usual when you press @key{TAB} or
1276 @kbd{M-?} to request word completion:
1279 (@value{GDBP}) b 'bubble( @kbd{M-?}
1280 bubble(double,double) bubble(int,int)
1281 (@value{GDBP}) b 'bubble(
1284 In some cases, @value{GDBN} can tell that completing a name requires using
1285 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1286 completing as much as it can) if you do not type the quote in the first
1290 (@value{GDBP}) b bub @key{TAB}
1291 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1292 (@value{GDBP}) b 'bubble(
1296 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1297 you have not yet started typing the argument list when you ask for
1298 completion on an overloaded symbol.
1300 For more information about overloaded functions, see @ref{C plus plus
1301 expressions, ,C++ expressions}. You can use the command @code{set
1302 overload-resolution off} to disable overload resolution;
1303 see @ref{Debugging C plus plus, ,@value{GDBN} features for C++}.
1307 @section Getting help
1308 @cindex online documentation
1311 You can always ask @value{GDBN} itself for information on its commands,
1312 using the command @code{help}.
1315 @kindex h @r{(@code{help})}
1318 You can use @code{help} (abbreviated @code{h}) with no arguments to
1319 display a short list of named classes of commands:
1323 List of classes of commands:
1325 aliases -- Aliases of other commands
1326 breakpoints -- Making program stop at certain points
1327 data -- Examining data
1328 files -- Specifying and examining files
1329 internals -- Maintenance commands
1330 obscure -- Obscure features
1331 running -- Running the program
1332 stack -- Examining the stack
1333 status -- Status inquiries
1334 support -- Support facilities
1335 tracepoints -- Tracing of program execution without@*
1336 stopping the program
1337 user-defined -- User-defined commands
1339 Type "help" followed by a class name for a list of
1340 commands in that class.
1341 Type "help" followed by command name for full
1343 Command name abbreviations are allowed if unambiguous.
1346 @c the above line break eliminates huge line overfull...
1348 @item help @var{class}
1349 Using one of the general help classes as an argument, you can get a
1350 list of the individual commands in that class. For example, here is the
1351 help display for the class @code{status}:
1354 (@value{GDBP}) help status
1359 @c Line break in "show" line falsifies real output, but needed
1360 @c to fit in smallbook page size.
1361 info -- Generic command for showing things
1362 about the program being debugged
1363 show -- Generic command for showing things
1366 Type "help" followed by command name for full
1368 Command name abbreviations are allowed if unambiguous.
1372 @item help @var{command}
1373 With a command name as @code{help} argument, @value{GDBN} displays a
1374 short paragraph on how to use that command.
1377 @item apropos @var{args}
1378 The @code{apropos @var{args}} command searches through all of the @value{GDBN}
1379 commands, and their documentation, for the regular expression specified in
1380 @var{args}. It prints out all matches found. For example:
1386 @noindent results in:
1390 set symbol-reloading -- Set dynamic symbol table reloading
1391 multiple times in one run
1392 show symbol-reloading -- Show dynamic symbol table reloading
1393 multiple times in one run
1398 @item complete @var{args}
1399 The @code{complete @var{args}} command lists all the possible completions
1400 for the beginning of a command. Use @var{args} to specify the beginning of the
1401 command you want completed. For example:
1407 @noindent results in:
1418 @noindent This is intended for use by @sc{gnu} Emacs.
1421 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1422 and @code{show} to inquire about the state of your program, or the state
1423 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1424 manual introduces each of them in the appropriate context. The listings
1425 under @code{info} and under @code{show} in the Index point to
1426 all the sub-commands. @xref{Index}.
1431 @kindex i @r{(@code{info})}
1433 This command (abbreviated @code{i}) is for describing the state of your
1434 program. For example, you can list the arguments given to your program
1435 with @code{info args}, list the registers currently in use with @code{info
1436 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1437 You can get a complete list of the @code{info} sub-commands with
1438 @w{@code{help info}}.
1442 You can assign the result of an expression to an environment variable with
1443 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1444 @code{set prompt $}.
1448 In contrast to @code{info}, @code{show} is for describing the state of
1449 @value{GDBN} itself.
1450 You can change most of the things you can @code{show}, by using the
1451 related command @code{set}; for example, you can control what number
1452 system is used for displays with @code{set radix}, or simply inquire
1453 which is currently in use with @code{show radix}.
1456 To display all the settable parameters and their current
1457 values, you can use @code{show} with no arguments; you may also use
1458 @code{info set}. Both commands produce the same display.
1459 @c FIXME: "info set" violates the rule that "info" is for state of
1460 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1461 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1465 Here are three miscellaneous @code{show} subcommands, all of which are
1466 exceptional in lacking corresponding @code{set} commands:
1469 @kindex show version
1470 @cindex version number
1472 Show what version of @value{GDBN} is running. You should include this
1473 information in @value{GDBN} bug-reports. If multiple versions of
1474 @value{GDBN} are in use at your site, you may need to determine which
1475 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1476 commands are introduced, and old ones may wither away. Also, many
1477 system vendors ship variant versions of @value{GDBN}, and there are
1478 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1479 The version number is the same as the one announced when you start
1482 @kindex show copying
1484 Display information about permission for copying @value{GDBN}.
1486 @kindex show warranty
1488 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1489 if your version of @value{GDBN} comes with one.
1494 @chapter Running Programs Under @value{GDBN}
1496 When you run a program under @value{GDBN}, you must first generate
1497 debugging information when you compile it.
1499 You may start @value{GDBN} with its arguments, if any, in an environment
1500 of your choice. If you are doing native debugging, you may redirect
1501 your program's input and output, debug an already running process, or
1502 kill a child process.
1505 * Compilation:: Compiling for debugging
1506 * Starting:: Starting your program
1507 * Arguments:: Your program's arguments
1508 * Environment:: Your program's environment
1510 * Working Directory:: Your program's working directory
1511 * Input/Output:: Your program's input and output
1512 * Attach:: Debugging an already-running process
1513 * Kill Process:: Killing the child process
1515 * Threads:: Debugging programs with multiple threads
1516 * Processes:: Debugging programs with multiple processes
1520 @section Compiling for debugging
1522 In order to debug a program effectively, you need to generate
1523 debugging information when you compile it. This debugging information
1524 is stored in the object file; it describes the data type of each
1525 variable or function and the correspondence between source line numbers
1526 and addresses in the executable code.
1528 To request debugging information, specify the @samp{-g} option when you run
1531 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1532 options together. Using those compilers, you cannot generate optimized
1533 executables containing debugging information.
1535 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or
1536 without @samp{-O}, making it possible to debug optimized code. We
1537 recommend that you @emph{always} use @samp{-g} whenever you compile a
1538 program. You may think your program is correct, but there is no sense
1539 in pushing your luck.
1541 @cindex optimized code, debugging
1542 @cindex debugging optimized code
1543 When you debug a program compiled with @samp{-g -O}, remember that the
1544 optimizer is rearranging your code; the debugger shows you what is
1545 really there. Do not be too surprised when the execution path does not
1546 exactly match your source file! An extreme example: if you define a
1547 variable, but never use it, @value{GDBN} never sees that
1548 variable---because the compiler optimizes it out of existence.
1550 Some things do not work as well with @samp{-g -O} as with just
1551 @samp{-g}, particularly on machines with instruction scheduling. If in
1552 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1553 please report it to us as a bug (including a test case!).
1555 Older versions of the @sc{gnu} C compiler permitted a variant option
1556 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1557 format; if your @sc{gnu} C compiler has this option, do not use it.
1561 @section Starting your program
1567 @kindex r @r{(@code{run})}
1570 Use the @code{run} command to start your program under @value{GDBN}.
1571 You must first specify the program name (except on VxWorks) with an
1572 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1573 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1574 (@pxref{Files, ,Commands to specify files}).
1578 If you are running your program in an execution environment that
1579 supports processes, @code{run} creates an inferior process and makes
1580 that process run your program. (In environments without processes,
1581 @code{run} jumps to the start of your program.)
1583 The execution of a program is affected by certain information it
1584 receives from its superior. @value{GDBN} provides ways to specify this
1585 information, which you must do @emph{before} starting your program. (You
1586 can change it after starting your program, but such changes only affect
1587 your program the next time you start it.) This information may be
1588 divided into four categories:
1591 @item The @emph{arguments.}
1592 Specify the arguments to give your program as the arguments of the
1593 @code{run} command. If a shell is available on your target, the shell
1594 is used to pass the arguments, so that you may use normal conventions
1595 (such as wildcard expansion or variable substitution) in describing
1597 In Unix systems, you can control which shell is used with the
1598 @code{SHELL} environment variable.
1599 @xref{Arguments, ,Your program's arguments}.
1601 @item The @emph{environment.}
1602 Your program normally inherits its environment from @value{GDBN}, but you can
1603 use the @value{GDBN} commands @code{set environment} and @code{unset
1604 environment} to change parts of the environment that affect
1605 your program. @xref{Environment, ,Your program's environment}.
1607 @item The @emph{working directory.}
1608 Your program inherits its working directory from @value{GDBN}. You can set
1609 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1610 @xref{Working Directory, ,Your program's working directory}.
1612 @item The @emph{standard input and output.}
1613 Your program normally uses the same device for standard input and
1614 standard output as @value{GDBN} is using. You can redirect input and output
1615 in the @code{run} command line, or you can use the @code{tty} command to
1616 set a different device for your program.
1617 @xref{Input/Output, ,Your program's input and output}.
1620 @emph{Warning:} While input and output redirection work, you cannot use
1621 pipes to pass the output of the program you are debugging to another
1622 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1626 When you issue the @code{run} command, your program begins to execute
1627 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1628 of how to arrange for your program to stop. Once your program has
1629 stopped, you may call functions in your program, using the @code{print}
1630 or @code{call} commands. @xref{Data, ,Examining Data}.
1632 If the modification time of your symbol file has changed since the last
1633 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1634 table, and reads it again. When it does this, @value{GDBN} tries to retain
1635 your current breakpoints.
1638 @section Your program's arguments
1640 @cindex arguments (to your program)
1641 The arguments to your program can be specified by the arguments of the
1643 They are passed to a shell, which expands wildcard characters and
1644 performs redirection of I/O, and thence to your program. Your
1645 @code{SHELL} environment variable (if it exists) specifies what shell
1646 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1647 the default shell (@file{/bin/sh} on Unix).
1649 On non-Unix systems, the program is usually invoked directly by
1650 @value{GDBN}, which emulates I/O redirection via the appropriate system
1651 calls, and the wildcard characters are expanded by the startup code of
1652 the program, not by the shell.
1654 @code{run} with no arguments uses the same arguments used by the previous
1655 @code{run}, or those set by the @code{set args} command.
1660 Specify the arguments to be used the next time your program is run. If
1661 @code{set args} has no arguments, @code{run} executes your program
1662 with no arguments. Once you have run your program with arguments,
1663 using @code{set args} before the next @code{run} is the only way to run
1664 it again without arguments.
1668 Show the arguments to give your program when it is started.
1672 @section Your program's environment
1674 @cindex environment (of your program)
1675 The @dfn{environment} consists of a set of environment variables and
1676 their values. Environment variables conventionally record such things as
1677 your user name, your home directory, your terminal type, and your search
1678 path for programs to run. Usually you set up environment variables with
1679 the shell and they are inherited by all the other programs you run. When
1680 debugging, it can be useful to try running your program with a modified
1681 environment without having to start @value{GDBN} over again.
1685 @item path @var{directory}
1686 Add @var{directory} to the front of the @code{PATH} environment variable
1687 (the search path for executables), for both @value{GDBN} and your program.
1688 You may specify several directory names, separated by whitespace or by a
1689 system-dependent separator character (@samp{:} on Unix, @samp{;} on
1690 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
1691 is moved to the front, so it is searched sooner.
1693 You can use the string @samp{$cwd} to refer to whatever is the current
1694 working directory at the time @value{GDBN} searches the path. If you
1695 use @samp{.} instead, it refers to the directory where you executed the
1696 @code{path} command. @value{GDBN} replaces @samp{.} in the
1697 @var{directory} argument (with the current path) before adding
1698 @var{directory} to the search path.
1699 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1700 @c document that, since repeating it would be a no-op.
1704 Display the list of search paths for executables (the @code{PATH}
1705 environment variable).
1707 @kindex show environment
1708 @item show environment @r{[}@var{varname}@r{]}
1709 Print the value of environment variable @var{varname} to be given to
1710 your program when it starts. If you do not supply @var{varname},
1711 print the names and values of all environment variables to be given to
1712 your program. You can abbreviate @code{environment} as @code{env}.
1714 @kindex set environment
1715 @item set environment @var{varname} @r{[}=@var{value}@r{]}
1716 Set environment variable @var{varname} to @var{value}. The value
1717 changes for your program only, not for @value{GDBN} itself. @var{value} may
1718 be any string; the values of environment variables are just strings, and
1719 any interpretation is supplied by your program itself. The @var{value}
1720 parameter is optional; if it is eliminated, the variable is set to a
1722 @c "any string" here does not include leading, trailing
1723 @c blanks. Gnu asks: does anyone care?
1725 For example, this command:
1732 tells the debugged program, when subsequently run, that its user is named
1733 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1734 are not actually required.)
1736 @kindex unset environment
1737 @item unset environment @var{varname}
1738 Remove variable @var{varname} from the environment to be passed to your
1739 program. This is different from @samp{set env @var{varname} =};
1740 @code{unset environment} removes the variable from the environment,
1741 rather than assigning it an empty value.
1744 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
1746 by your @code{SHELL} environment variable if it exists (or
1747 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1748 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1749 @file{.bashrc} for BASH---any variables you set in that file affect
1750 your program. You may wish to move setting of environment variables to
1751 files that are only run when you sign on, such as @file{.login} or
1754 @node Working Directory
1755 @section Your program's working directory
1757 @cindex working directory (of your program)
1758 Each time you start your program with @code{run}, it inherits its
1759 working directory from the current working directory of @value{GDBN}.
1760 The @value{GDBN} working directory is initially whatever it inherited
1761 from its parent process (typically the shell), but you can specify a new
1762 working directory in @value{GDBN} with the @code{cd} command.
1764 The @value{GDBN} working directory also serves as a default for the commands
1765 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1770 @item cd @var{directory}
1771 Set the @value{GDBN} working directory to @var{directory}.
1775 Print the @value{GDBN} working directory.
1779 @section Your program's input and output
1784 By default, the program you run under @value{GDBN} does input and output to
1785 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1786 to its own terminal modes to interact with you, but it records the terminal
1787 modes your program was using and switches back to them when you continue
1788 running your program.
1791 @kindex info terminal
1793 Displays information recorded by @value{GDBN} about the terminal modes your
1797 You can redirect your program's input and/or output using shell
1798 redirection with the @code{run} command. For example,
1805 starts your program, diverting its output to the file @file{outfile}.
1808 @cindex controlling terminal
1809 Another way to specify where your program should do input and output is
1810 with the @code{tty} command. This command accepts a file name as
1811 argument, and causes this file to be the default for future @code{run}
1812 commands. It also resets the controlling terminal for the child
1813 process, for future @code{run} commands. For example,
1820 directs that processes started with subsequent @code{run} commands
1821 default to do input and output on the terminal @file{/dev/ttyb} and have
1822 that as their controlling terminal.
1824 An explicit redirection in @code{run} overrides the @code{tty} command's
1825 effect on the input/output device, but not its effect on the controlling
1828 When you use the @code{tty} command or redirect input in the @code{run}
1829 command, only the input @emph{for your program} is affected. The input
1830 for @value{GDBN} still comes from your terminal.
1833 @section Debugging an already-running process
1838 @item attach @var{process-id}
1839 This command attaches to a running process---one that was started
1840 outside @value{GDBN}. (@code{info files} shows your active
1841 targets.) The command takes as argument a process ID. The usual way to
1842 find out the process-id of a Unix process is with the @code{ps} utility,
1843 or with the @samp{jobs -l} shell command.
1845 @code{attach} does not repeat if you press @key{RET} a second time after
1846 executing the command.
1849 To use @code{attach}, your program must be running in an environment
1850 which supports processes; for example, @code{attach} does not work for
1851 programs on bare-board targets that lack an operating system. You must
1852 also have permission to send the process a signal.
1854 When you use @code{attach}, the debugger finds the program running in
1855 the process first by looking in the current working directory, then (if
1856 the program is not found) by using the source file search path
1857 (@pxref{Source Path, ,Specifying source directories}). You can also use
1858 the @code{file} command to load the program. @xref{Files, ,Commands to
1861 The first thing @value{GDBN} does after arranging to debug the specified
1862 process is to stop it. You can examine and modify an attached process
1863 with all the @value{GDBN} commands that are ordinarily available when
1864 you start processes with @code{run}. You can insert breakpoints; you
1865 can step and continue; you can modify storage. If you would rather the
1866 process continue running, you may use the @code{continue} command after
1867 attaching @value{GDBN} to the process.
1872 When you have finished debugging the attached process, you can use the
1873 @code{detach} command to release it from @value{GDBN} control. Detaching
1874 the process continues its execution. After the @code{detach} command,
1875 that process and @value{GDBN} become completely independent once more, and you
1876 are ready to @code{attach} another process or start one with @code{run}.
1877 @code{detach} does not repeat if you press @key{RET} again after
1878 executing the command.
1881 If you exit @value{GDBN} or use the @code{run} command while you have an
1882 attached process, you kill that process. By default, @value{GDBN} asks
1883 for confirmation if you try to do either of these things; you can
1884 control whether or not you need to confirm by using the @code{set
1885 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1889 @section Killing the child process
1894 Kill the child process in which your program is running under @value{GDBN}.
1897 This command is useful if you wish to debug a core dump instead of a
1898 running process. @value{GDBN} ignores any core dump file while your program
1901 On some operating systems, a program cannot be executed outside @value{GDBN}
1902 while you have breakpoints set on it inside @value{GDBN}. You can use the
1903 @code{kill} command in this situation to permit running your program
1904 outside the debugger.
1906 The @code{kill} command is also useful if you wish to recompile and
1907 relink your program, since on many systems it is impossible to modify an
1908 executable file while it is running in a process. In this case, when you
1909 next type @code{run}, @value{GDBN} notices that the file has changed, and
1910 reads the symbol table again (while trying to preserve your current
1911 breakpoint settings).
1914 @section Debugging programs with multiple threads
1916 @cindex threads of execution
1917 @cindex multiple threads
1918 @cindex switching threads
1919 In some operating systems, such as HP-UX and Solaris, a single program
1920 may have more than one @dfn{thread} of execution. The precise semantics
1921 of threads differ from one operating system to another, but in general
1922 the threads of a single program are akin to multiple processes---except
1923 that they share one address space (that is, they can all examine and
1924 modify the same variables). On the other hand, each thread has its own
1925 registers and execution stack, and perhaps private memory.
1927 @value{GDBN} provides these facilities for debugging multi-thread
1931 @item automatic notification of new threads
1932 @item @samp{thread @var{threadno}}, a command to switch among threads
1933 @item @samp{info threads}, a command to inquire about existing threads
1934 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
1935 a command to apply a command to a list of threads
1936 @item thread-specific breakpoints
1940 @emph{Warning:} These facilities are not yet available on every
1941 @value{GDBN} configuration where the operating system supports threads.
1942 If your @value{GDBN} does not support threads, these commands have no
1943 effect. For example, a system without thread support shows no output
1944 from @samp{info threads}, and always rejects the @code{thread} command,
1948 (@value{GDBP}) info threads
1949 (@value{GDBP}) thread 1
1950 Thread ID 1 not known. Use the "info threads" command to
1951 see the IDs of currently known threads.
1953 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
1954 @c doesn't support threads"?
1957 @cindex focus of debugging
1958 @cindex current thread
1959 The @value{GDBN} thread debugging facility allows you to observe all
1960 threads while your program runs---but whenever @value{GDBN} takes
1961 control, one thread in particular is always the focus of debugging.
1962 This thread is called the @dfn{current thread}. Debugging commands show
1963 program information from the perspective of the current thread.
1965 @cindex @code{New} @var{systag} message
1966 @cindex thread identifier (system)
1967 @c FIXME-implementors!! It would be more helpful if the [New...] message
1968 @c included GDB's numeric thread handle, so you could just go to that
1969 @c thread without first checking `info threads'.
1970 Whenever @value{GDBN} detects a new thread in your program, it displays
1971 the target system's identification for the thread with a message in the
1972 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
1973 whose form varies depending on the particular system. For example, on
1974 LynxOS, you might see
1977 [New process 35 thread 27]
1981 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
1982 the @var{systag} is simply something like @samp{process 368}, with no
1985 @c FIXME!! (1) Does the [New...] message appear even for the very first
1986 @c thread of a program, or does it only appear for the
1987 @c second---i.e., when it becomes obvious we have a multithread
1989 @c (2) *Is* there necessarily a first thread always? Or do some
1990 @c multithread systems permit starting a program with multiple
1991 @c threads ab initio?
1993 @cindex thread number
1994 @cindex thread identifier (GDB)
1995 For debugging purposes, @value{GDBN} associates its own thread
1996 number---always a single integer---with each thread in your program.
1999 @kindex info threads
2001 Display a summary of all threads currently in your
2002 program. @value{GDBN} displays for each thread (in this order):
2005 @item the thread number assigned by @value{GDBN}
2007 @item the target system's thread identifier (@var{systag})
2009 @item the current stack frame summary for that thread
2013 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2014 indicates the current thread.
2018 @c end table here to get a little more width for example
2021 (@value{GDBP}) info threads
2022 3 process 35 thread 27 0x34e5 in sigpause ()
2023 2 process 35 thread 23 0x34e5 in sigpause ()
2024 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2030 @cindex thread number
2031 @cindex thread identifier (GDB)
2032 For debugging purposes, @value{GDBN} associates its own thread
2033 number---a small integer assigned in thread-creation order---with each
2034 thread in your program.
2036 @cindex @code{New} @var{systag} message, on HP-UX
2037 @cindex thread identifier (system), on HP-UX
2038 @c FIXME-implementors!! It would be more helpful if the [New...] message
2039 @c included GDB's numeric thread handle, so you could just go to that
2040 @c thread without first checking `info threads'.
2041 Whenever @value{GDBN} detects a new thread in your program, it displays
2042 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2043 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2044 whose form varies depending on the particular system. For example, on
2048 [New thread 2 (system thread 26594)]
2052 when @value{GDBN} notices a new thread.
2055 @kindex info threads
2057 Display a summary of all threads currently in your
2058 program. @value{GDBN} displays for each thread (in this order):
2061 @item the thread number assigned by @value{GDBN}
2063 @item the target system's thread identifier (@var{systag})
2065 @item the current stack frame summary for that thread
2069 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2070 indicates the current thread.
2074 @c end table here to get a little more width for example
2077 (@value{GDBP}) info threads
2078 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2080 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2081 from /usr/lib/libc.2
2082 1 system thread 27905 0x7b003498 in _brk () \@*
2083 from /usr/lib/libc.2
2087 @kindex thread @var{threadno}
2088 @item thread @var{threadno}
2089 Make thread number @var{threadno} the current thread. The command
2090 argument @var{threadno} is the internal @value{GDBN} thread number, as
2091 shown in the first field of the @samp{info threads} display.
2092 @value{GDBN} responds by displaying the system identifier of the thread
2093 you selected, and its current stack frame summary:
2096 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2097 (@value{GDBP}) thread 2
2098 [Switching to process 35 thread 23]
2099 0x34e5 in sigpause ()
2103 As with the @samp{[New @dots{}]} message, the form of the text after
2104 @samp{Switching to} depends on your system's conventions for identifying
2107 @kindex thread apply
2108 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2109 The @code{thread apply} command allows you to apply a command to one or
2110 more threads. Specify the numbers of the threads that you want affected
2111 with the command argument @var{threadno}. @var{threadno} is the internal
2112 @value{GDBN} thread number, as shown in the first field of the @samp{info
2113 threads} display. To apply a command to all threads, use
2114 @code{thread apply all} @var{args}.
2117 @cindex automatic thread selection
2118 @cindex switching threads automatically
2119 @cindex threads, automatic switching
2120 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2121 signal, it automatically selects the thread where that breakpoint or
2122 signal happened. @value{GDBN} alerts you to the context switch with a
2123 message of the form @samp{[Switching to @var{systag}]} to identify the
2126 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2127 more information about how @value{GDBN} behaves when you stop and start
2128 programs with multiple threads.
2130 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2131 watchpoints in programs with multiple threads.
2134 @section Debugging programs with multiple processes
2136 @cindex fork, debugging programs which call
2137 @cindex multiple processes
2138 @cindex processes, multiple
2139 On most systems, @value{GDBN} has no special support for debugging
2140 programs which create additional processes using the @code{fork}
2141 function. When a program forks, @value{GDBN} will continue to debug the
2142 parent process and the child process will run unimpeded. If you have
2143 set a breakpoint in any code which the child then executes, the child
2144 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2145 will cause it to terminate.
2147 However, if you want to debug the child process there is a workaround
2148 which isn't too painful. Put a call to @code{sleep} in the code which
2149 the child process executes after the fork. It may be useful to sleep
2150 only if a certain environment variable is set, or a certain file exists,
2151 so that the delay need not occur when you don't want to run @value{GDBN}
2152 on the child. While the child is sleeping, use the @code{ps} program to
2153 get its process ID. Then tell @value{GDBN} (a new invocation of
2154 @value{GDBN} if you are also debugging the parent process) to attach to
2155 the child process (@pxref{Attach}). From that point on you can debug
2156 the child process just like any other process which you attached to.
2158 On HP-UX (11.x and later only?), @value{GDBN} provides support for
2159 debugging programs that create additional processes using the
2160 @code{fork} or @code{vfork} function.
2162 By default, when a program forks, @value{GDBN} will continue to debug
2163 the parent process and the child process will run unimpeded.
2165 If you want to follow the child process instead of the parent process,
2166 use the command @w{@code{set follow-fork-mode}}.
2169 @kindex set follow-fork-mode
2170 @item set follow-fork-mode @var{mode}
2171 Set the debugger response to a program call of @code{fork} or
2172 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2173 process. The @var{mode} can be:
2177 The original process is debugged after a fork. The child process runs
2178 unimpeded. This is the default.
2181 The new process is debugged after a fork. The parent process runs
2185 The debugger will ask for one of the above choices.
2188 @item show follow-fork-mode
2189 Display the current debugger response to a @code{fork} or @code{vfork} call.
2192 If you ask to debug a child process and a @code{vfork} is followed by an
2193 @code{exec}, @value{GDBN} executes the new target up to the first
2194 breakpoint in the new target. If you have a breakpoint set on
2195 @code{main} in your original program, the breakpoint will also be set on
2196 the child process's @code{main}.
2198 When a child process is spawned by @code{vfork}, you cannot debug the
2199 child or parent until an @code{exec} call completes.
2201 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2202 call executes, the new target restarts. To restart the parent process,
2203 use the @code{file} command with the parent executable name as its
2206 You can use the @code{catch} command to make @value{GDBN} stop whenever
2207 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2208 Catchpoints, ,Setting catchpoints}.
2211 @chapter Stopping and Continuing
2213 The principal purposes of using a debugger are so that you can stop your
2214 program before it terminates; or so that, if your program runs into
2215 trouble, you can investigate and find out why.
2217 Inside @value{GDBN}, your program may stop for any of several reasons,
2218 such as a signal, a breakpoint, or reaching a new line after a
2219 @value{GDBN} command such as @code{step}. You may then examine and
2220 change variables, set new breakpoints or remove old ones, and then
2221 continue execution. Usually, the messages shown by @value{GDBN} provide
2222 ample explanation of the status of your program---but you can also
2223 explicitly request this information at any time.
2226 @kindex info program
2228 Display information about the status of your program: whether it is
2229 running or not, what process it is, and why it stopped.
2233 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2234 * Continuing and Stepping:: Resuming execution
2236 * Thread Stops:: Stopping and starting multi-thread programs
2240 @section Breakpoints, watchpoints, and catchpoints
2243 A @dfn{breakpoint} makes your program stop whenever a certain point in
2244 the program is reached. For each breakpoint, you can add conditions to
2245 control in finer detail whether your program stops. You can set
2246 breakpoints with the @code{break} command and its variants (@pxref{Set
2247 Breaks, ,Setting breakpoints}), to specify the place where your program
2248 should stop by line number, function name or exact address in the
2251 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2252 breakpoints in shared libraries before the executable is run. There is
2253 a minor limitation on HP-UX systems: you must wait until the executable
2254 is run in order to set breakpoints in shared library routines that are
2255 not called directly by the program (for example, routines that are
2256 arguments in a @code{pthread_create} call).
2259 @cindex memory tracing
2260 @cindex breakpoint on memory address
2261 @cindex breakpoint on variable modification
2262 A @dfn{watchpoint} is a special breakpoint that stops your program
2263 when the value of an expression changes. You must use a different
2264 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2265 watchpoints}), but aside from that, you can manage a watchpoint like
2266 any other breakpoint: you enable, disable, and delete both breakpoints
2267 and watchpoints using the same commands.
2269 You can arrange to have values from your program displayed automatically
2270 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2274 @cindex breakpoint on events
2275 A @dfn{catchpoint} is another special breakpoint that stops your program
2276 when a certain kind of event occurs, such as the throwing of a C++
2277 exception or the loading of a library. As with watchpoints, you use a
2278 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2279 catchpoints}), but aside from that, you can manage a catchpoint like any
2280 other breakpoint. (To stop when your program receives a signal, use the
2281 @code{handle} command; see @ref{Signals, ,Signals}.)
2283 @cindex breakpoint numbers
2284 @cindex numbers for breakpoints
2285 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2286 catchpoint when you create it; these numbers are successive integers
2287 starting with one. In many of the commands for controlling various
2288 features of breakpoints you use the breakpoint number to say which
2289 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2290 @dfn{disabled}; if disabled, it has no effect on your program until you
2293 @cindex breakpoint ranges
2294 @cindex ranges of breakpoints
2295 Some @value{GDBN} commands accept a range of breakpoints on which to
2296 operate. A breakpoint range is either a single breakpoint number, like
2297 @samp{5}, or two such numbers, in increasing order, separated by a
2298 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
2299 all breakpoint in that range are operated on.
2302 * Set Breaks:: Setting breakpoints
2303 * Set Watchpoints:: Setting watchpoints
2304 * Set Catchpoints:: Setting catchpoints
2305 * Delete Breaks:: Deleting breakpoints
2306 * Disabling:: Disabling breakpoints
2307 * Conditions:: Break conditions
2308 * Break Commands:: Breakpoint command lists
2309 * Breakpoint Menus:: Breakpoint menus
2310 * Error in Breakpoints:: ``Cannot insert breakpoints''
2314 @subsection Setting breakpoints
2316 @c FIXME LMB what does GDB do if no code on line of breakpt?
2317 @c consider in particular declaration with/without initialization.
2319 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2322 @kindex b @r{(@code{break})}
2323 @vindex $bpnum@r{, convenience variable}
2324 @cindex latest breakpoint
2325 Breakpoints are set with the @code{break} command (abbreviated
2326 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2327 number of the breakpoint you've set most recently; see @ref{Convenience
2328 Vars,, Convenience variables}, for a discussion of what you can do with
2329 convenience variables.
2331 You have several ways to say where the breakpoint should go.
2334 @item break @var{function}
2335 Set a breakpoint at entry to function @var{function}.
2336 When using source languages that permit overloading of symbols, such as
2337 C++, @var{function} may refer to more than one possible place to break.
2338 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2340 @item break +@var{offset}
2341 @itemx break -@var{offset}
2342 Set a breakpoint some number of lines forward or back from the position
2343 at which execution stopped in the currently selected @dfn{stack frame}.
2344 (@xref{Frames, ,Frames}, for a description of stack frames.)
2346 @item break @var{linenum}
2347 Set a breakpoint at line @var{linenum} in the current source file.
2348 The current source file is the last file whose source text was printed.
2349 The breakpoint will stop your program just before it executes any of the
2352 @item break @var{filename}:@var{linenum}
2353 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2355 @item break @var{filename}:@var{function}
2356 Set a breakpoint at entry to function @var{function} found in file
2357 @var{filename}. Specifying a file name as well as a function name is
2358 superfluous except when multiple files contain similarly named
2361 @item break *@var{address}
2362 Set a breakpoint at address @var{address}. You can use this to set
2363 breakpoints in parts of your program which do not have debugging
2364 information or source files.
2367 When called without any arguments, @code{break} sets a breakpoint at
2368 the next instruction to be executed in the selected stack frame
2369 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2370 innermost, this makes your program stop as soon as control
2371 returns to that frame. This is similar to the effect of a
2372 @code{finish} command in the frame inside the selected frame---except
2373 that @code{finish} does not leave an active breakpoint. If you use
2374 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2375 the next time it reaches the current location; this may be useful
2378 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2379 least one instruction has been executed. If it did not do this, you
2380 would be unable to proceed past a breakpoint without first disabling the
2381 breakpoint. This rule applies whether or not the breakpoint already
2382 existed when your program stopped.
2384 @item break @dots{} if @var{cond}
2385 Set a breakpoint with condition @var{cond}; evaluate the expression
2386 @var{cond} each time the breakpoint is reached, and stop only if the
2387 value is nonzero---that is, if @var{cond} evaluates as true.
2388 @samp{@dots{}} stands for one of the possible arguments described
2389 above (or no argument) specifying where to break. @xref{Conditions,
2390 ,Break conditions}, for more information on breakpoint conditions.
2393 @item tbreak @var{args}
2394 Set a breakpoint enabled only for one stop. @var{args} are the
2395 same as for the @code{break} command, and the breakpoint is set in the same
2396 way, but the breakpoint is automatically deleted after the first time your
2397 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2400 @item hbreak @var{args}
2401 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2402 @code{break} command and the breakpoint is set in the same way, but the
2403 breakpoint requires hardware support and some target hardware may not
2404 have this support. The main purpose of this is EPROM/ROM code
2405 debugging, so you can set a breakpoint at an instruction without
2406 changing the instruction. This can be used with the new trap-generation
2407 provided by SPARClite DSU and some x86-based targets. These targets
2408 will generate traps when a program accesses some data or instruction
2409 address that is assigned to the debug registers. However the hardware
2410 breakpoint registers can take a limited number of breakpoints. For
2411 example, on the DSU, only two data breakpoints can be set at a time, and
2412 @value{GDBN} will reject this command if more than two are used. Delete
2413 or disable unused hardware breakpoints before setting new ones
2414 (@pxref{Disabling, ,Disabling}). @xref{Conditions, ,Break conditions}.
2417 @item thbreak @var{args}
2418 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2419 are the same as for the @code{hbreak} command and the breakpoint is set in
2420 the same way. However, like the @code{tbreak} command,
2421 the breakpoint is automatically deleted after the
2422 first time your program stops there. Also, like the @code{hbreak}
2423 command, the breakpoint requires hardware support and some target hardware
2424 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2425 See also @ref{Conditions, ,Break conditions}.
2428 @cindex regular expression
2429 @item rbreak @var{regex}
2430 Set breakpoints on all functions matching the regular expression
2431 @var{regex}. This command sets an unconditional breakpoint on all
2432 matches, printing a list of all breakpoints it set. Once these
2433 breakpoints are set, they are treated just like the breakpoints set with
2434 the @code{break} command. You can delete them, disable them, or make
2435 them conditional the same way as any other breakpoint.
2437 The syntax of the regular expression is the standard one used with tools
2438 like @file{grep}. Note that this is different from the syntax used by
2439 shells, so for instance @code{foo*} matches all functions that include
2440 an @code{fo} followed by zero or more @code{o}s. There is an implicit
2441 @code{.*} leading and trailing the regular expression you supply, so to
2442 match only functions that begin with @code{foo}, use @code{^foo}.
2444 When debugging C++ programs, @code{rbreak} is useful for setting
2445 breakpoints on overloaded functions that are not members of any special
2448 @kindex info breakpoints
2449 @cindex @code{$_} and @code{info breakpoints}
2450 @item info breakpoints @r{[}@var{n}@r{]}
2451 @itemx info break @r{[}@var{n}@r{]}
2452 @itemx info watchpoints @r{[}@var{n}@r{]}
2453 Print a table of all breakpoints, watchpoints, and catchpoints set and
2454 not deleted, with the following columns for each breakpoint:
2457 @item Breakpoint Numbers
2459 Breakpoint, watchpoint, or catchpoint.
2461 Whether the breakpoint is marked to be disabled or deleted when hit.
2462 @item Enabled or Disabled
2463 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2464 that are not enabled.
2466 Where the breakpoint is in your program, as a memory address.
2468 Where the breakpoint is in the source for your program, as a file and
2473 If a breakpoint is conditional, @code{info break} shows the condition on
2474 the line following the affected breakpoint; breakpoint commands, if any,
2475 are listed after that.
2478 @code{info break} with a breakpoint
2479 number @var{n} as argument lists only that breakpoint. The
2480 convenience variable @code{$_} and the default examining-address for
2481 the @code{x} command are set to the address of the last breakpoint
2482 listed (@pxref{Memory, ,Examining memory}).
2485 @code{info break} displays a count of the number of times the breakpoint
2486 has been hit. This is especially useful in conjunction with the
2487 @code{ignore} command. You can ignore a large number of breakpoint
2488 hits, look at the breakpoint info to see how many times the breakpoint
2489 was hit, and then run again, ignoring one less than that number. This
2490 will get you quickly to the last hit of that breakpoint.
2493 @value{GDBN} allows you to set any number of breakpoints at the same place in
2494 your program. There is nothing silly or meaningless about this. When
2495 the breakpoints are conditional, this is even useful
2496 (@pxref{Conditions, ,Break conditions}).
2498 @cindex negative breakpoint numbers
2499 @cindex internal @value{GDBN} breakpoints
2500 @value{GDBN} itself sometimes sets breakpoints in your program for special
2501 purposes, such as proper handling of @code{longjmp} (in C programs).
2502 These internal breakpoints are assigned negative numbers, starting with
2503 @code{-1}; @samp{info breakpoints} does not display them.
2505 You can see these breakpoints with the @value{GDBN} maintenance command
2506 @samp{maint info breakpoints}.
2509 @kindex maint info breakpoints
2510 @item maint info breakpoints
2511 Using the same format as @samp{info breakpoints}, display both the
2512 breakpoints you've set explicitly, and those @value{GDBN} is using for
2513 internal purposes. Internal breakpoints are shown with negative
2514 breakpoint numbers. The type column identifies what kind of breakpoint
2519 Normal, explicitly set breakpoint.
2522 Normal, explicitly set watchpoint.
2525 Internal breakpoint, used to handle correctly stepping through
2526 @code{longjmp} calls.
2528 @item longjmp resume
2529 Internal breakpoint at the target of a @code{longjmp}.
2532 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2535 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2538 Shared library events.
2545 @node Set Watchpoints
2546 @subsection Setting watchpoints
2548 @cindex setting watchpoints
2549 @cindex software watchpoints
2550 @cindex hardware watchpoints
2551 You can use a watchpoint to stop execution whenever the value of an
2552 expression changes, without having to predict a particular place where
2555 Depending on your system, watchpoints may be implemented in software or
2556 hardware. @value{GDBN} does software watchpointing by single-stepping your
2557 program and testing the variable's value each time, which is hundreds of
2558 times slower than normal execution. (But this may still be worth it, to
2559 catch errors where you have no clue what part of your program is the
2562 On some systems, such as HP-UX, Linux and some other x86-based targets,
2563 @value{GDBN} includes support for
2564 hardware watchpoints, which do not slow down the running of your
2569 @item watch @var{expr}
2570 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2571 is written into by the program and its value changes.
2574 @item rwatch @var{expr}
2575 Set a watchpoint that will break when watch @var{expr} is read by the program.
2578 @item awatch @var{expr}
2579 Set a watchpoint that will break when @var{expr} is either read or written into
2582 @kindex info watchpoints
2583 @item info watchpoints
2584 This command prints a list of watchpoints, breakpoints, and catchpoints;
2585 it is the same as @code{info break}.
2588 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2589 watchpoints execute very quickly, and the debugger reports a change in
2590 value at the exact instruction where the change occurs. If @value{GDBN}
2591 cannot set a hardware watchpoint, it sets a software watchpoint, which
2592 executes more slowly and reports the change in value at the next
2593 statement, not the instruction, after the change occurs.
2595 When you issue the @code{watch} command, @value{GDBN} reports
2598 Hardware watchpoint @var{num}: @var{expr}
2602 if it was able to set a hardware watchpoint.
2604 Currently, the @code{awatch} and @code{rwatch} commands can only set
2605 hardware watchpoints, because accesses to data that don't change the
2606 value of the watched expression cannot be detected without examining
2607 every instruction as it is being executed, and @value{GDBN} does not do
2608 that currently. If @value{GDBN} finds that it is unable to set a
2609 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
2610 will print a message like this:
2613 Expression cannot be implemented with read/access watchpoint.
2616 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
2617 data type of the watched expression is wider than what a hardware
2618 watchpoint on the target machine can handle. For example, some systems
2619 can only watch regions that are up to 4 bytes wide; on such systems you
2620 cannot set hardware watchpoints for an expression that yields a
2621 double-precision floating-point number (which is typically 8 bytes
2622 wide). As a work-around, it might be possible to break the large region
2623 into a series of smaller ones and watch them with separate watchpoints.
2625 If you set too many hardware watchpoints, @value{GDBN} might be unable
2626 to insert all of them when you resume the execution of your program.
2627 Since the precise number of active watchpoints is unknown until such
2628 time as the program is about to be resumed, @value{GDBN} might not be
2629 able to warn you about this when you set the watchpoints, and the
2630 warning will be printed only when the program is resumed:
2633 Hardware watchpoint @var{num}: Could not insert watchpoint
2637 If this happens, delete or disable some of the watchpoints.
2639 The SPARClite DSU will generate traps when a program accesses some data
2640 or instruction address that is assigned to the debug registers. For the
2641 data addresses, DSU facilitates the @code{watch} command. However the
2642 hardware breakpoint registers can only take two data watchpoints, and
2643 both watchpoints must be the same kind. For example, you can set two
2644 watchpoints with @code{watch} commands, two with @code{rwatch} commands,
2645 @strong{or} two with @code{awatch} commands, but you cannot set one
2646 watchpoint with one command and the other with a different command.
2647 @value{GDBN} will reject the command if you try to mix watchpoints.
2648 Delete or disable unused watchpoint commands before setting new ones.
2650 If you call a function interactively using @code{print} or @code{call},
2651 any watchpoints you have set will be inactive until @value{GDBN} reaches another
2652 kind of breakpoint or the call completes.
2654 @value{GDBN} automatically deletes watchpoints that watch local
2655 (automatic) variables, or expressions that involve such variables, when
2656 they go out of scope, that is, when the execution leaves the block in
2657 which these variables were defined. In particular, when the program
2658 being debugged terminates, @emph{all} local variables go out of scope,
2659 and so only watchpoints that watch global variables remain set. If you
2660 rerun the program, you will need to set all such watchpoints again. One
2661 way of doing that would be to set a code breakpoint at the entry to the
2662 @code{main} function and when it breaks, set all the watchpoints.
2665 @cindex watchpoints and threads
2666 @cindex threads and watchpoints
2667 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2668 usefulness. With the current watchpoint implementation, @value{GDBN}
2669 can only watch the value of an expression @emph{in a single thread}. If
2670 you are confident that the expression can only change due to the current
2671 thread's activity (and if you are also confident that no other thread
2672 can become current), then you can use watchpoints as usual. However,
2673 @value{GDBN} may not notice when a non-current thread's activity changes
2676 @c FIXME: this is almost identical to the previous paragraph.
2677 @emph{HP-UX Warning:} In multi-thread programs, software watchpoints
2678 have only limited usefulness. If @value{GDBN} creates a software
2679 watchpoint, it can only watch the value of an expression @emph{in a
2680 single thread}. If you are confident that the expression can only
2681 change due to the current thread's activity (and if you are also
2682 confident that no other thread can become current), then you can use
2683 software watchpoints as usual. However, @value{GDBN} may not notice
2684 when a non-current thread's activity changes the expression. (Hardware
2685 watchpoints, in contrast, watch an expression in all threads.)
2688 @node Set Catchpoints
2689 @subsection Setting catchpoints
2690 @cindex catchpoints, setting
2691 @cindex exception handlers
2692 @cindex event handling
2694 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2695 kinds of program events, such as C++ exceptions or the loading of a
2696 shared library. Use the @code{catch} command to set a catchpoint.
2700 @item catch @var{event}
2701 Stop when @var{event} occurs. @var{event} can be any of the following:
2705 The throwing of a C++ exception.
2709 The catching of a C++ exception.
2713 A call to @code{exec}. This is currently only available for HP-UX.
2717 A call to @code{fork}. This is currently only available for HP-UX.
2721 A call to @code{vfork}. This is currently only available for HP-UX.
2724 @itemx load @var{libname}
2726 The dynamic loading of any shared library, or the loading of the library
2727 @var{libname}. This is currently only available for HP-UX.
2730 @itemx unload @var{libname}
2731 @kindex catch unload
2732 The unloading of any dynamically loaded shared library, or the unloading
2733 of the library @var{libname}. This is currently only available for HP-UX.
2736 @item tcatch @var{event}
2737 Set a catchpoint that is enabled only for one stop. The catchpoint is
2738 automatically deleted after the first time the event is caught.
2742 Use the @code{info break} command to list the current catchpoints.
2744 There are currently some limitations to C++ exception handling
2745 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
2749 If you call a function interactively, @value{GDBN} normally returns
2750 control to you when the function has finished executing. If the call
2751 raises an exception, however, the call may bypass the mechanism that
2752 returns control to you and cause your program either to abort or to
2753 simply continue running until it hits a breakpoint, catches a signal
2754 that @value{GDBN} is listening for, or exits. This is the case even if
2755 you set a catchpoint for the exception; catchpoints on exceptions are
2756 disabled within interactive calls.
2759 You cannot raise an exception interactively.
2762 You cannot install an exception handler interactively.
2765 @cindex raise exceptions
2766 Sometimes @code{catch} is not the best way to debug exception handling:
2767 if you need to know exactly where an exception is raised, it is better to
2768 stop @emph{before} the exception handler is called, since that way you
2769 can see the stack before any unwinding takes place. If you set a
2770 breakpoint in an exception handler instead, it may not be easy to find
2771 out where the exception was raised.
2773 To stop just before an exception handler is called, you need some
2774 knowledge of the implementation. In the case of @sc{gnu} C++, exceptions are
2775 raised by calling a library function named @code{__raise_exception}
2776 which has the following ANSI C interface:
2779 /* @var{addr} is where the exception identifier is stored.
2780 @var{id} is the exception identifier. */
2781 void __raise_exception (void **addr, void *id);
2785 To make the debugger catch all exceptions before any stack
2786 unwinding takes place, set a breakpoint on @code{__raise_exception}
2787 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2789 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2790 that depends on the value of @var{id}, you can stop your program when
2791 a specific exception is raised. You can use multiple conditional
2792 breakpoints to stop your program when any of a number of exceptions are
2797 @subsection Deleting breakpoints
2799 @cindex clearing breakpoints, watchpoints, catchpoints
2800 @cindex deleting breakpoints, watchpoints, catchpoints
2801 It is often necessary to eliminate a breakpoint, watchpoint, or
2802 catchpoint once it has done its job and you no longer want your program
2803 to stop there. This is called @dfn{deleting} the breakpoint. A
2804 breakpoint that has been deleted no longer exists; it is forgotten.
2806 With the @code{clear} command you can delete breakpoints according to
2807 where they are in your program. With the @code{delete} command you can
2808 delete individual breakpoints, watchpoints, or catchpoints by specifying
2809 their breakpoint numbers.
2811 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2812 automatically ignores breakpoints on the first instruction to be executed
2813 when you continue execution without changing the execution address.
2818 Delete any breakpoints at the next instruction to be executed in the
2819 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2820 the innermost frame is selected, this is a good way to delete a
2821 breakpoint where your program just stopped.
2823 @item clear @var{function}
2824 @itemx clear @var{filename}:@var{function}
2825 Delete any breakpoints set at entry to the function @var{function}.
2827 @item clear @var{linenum}
2828 @itemx clear @var{filename}:@var{linenum}
2829 Delete any breakpoints set at or within the code of the specified line.
2831 @cindex delete breakpoints
2833 @kindex d @r{(@code{delete})}
2834 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2835 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
2836 ranges specified as arguments. If no argument is specified, delete all
2837 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
2838 confirm off}). You can abbreviate this command as @code{d}.
2842 @subsection Disabling breakpoints
2844 @kindex disable breakpoints
2845 @kindex enable breakpoints
2846 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
2847 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
2848 it had been deleted, but remembers the information on the breakpoint so
2849 that you can @dfn{enable} it again later.
2851 You disable and enable breakpoints, watchpoints, and catchpoints with
2852 the @code{enable} and @code{disable} commands, optionally specifying one
2853 or more breakpoint numbers as arguments. Use @code{info break} or
2854 @code{info watch} to print a list of breakpoints, watchpoints, and
2855 catchpoints if you do not know which numbers to use.
2857 A breakpoint, watchpoint, or catchpoint can have any of four different
2858 states of enablement:
2862 Enabled. The breakpoint stops your program. A breakpoint set
2863 with the @code{break} command starts out in this state.
2865 Disabled. The breakpoint has no effect on your program.
2867 Enabled once. The breakpoint stops your program, but then becomes
2870 Enabled for deletion. The breakpoint stops your program, but
2871 immediately after it does so it is deleted permanently. A breakpoint
2872 set with the @code{tbreak} command starts out in this state.
2875 You can use the following commands to enable or disable breakpoints,
2876 watchpoints, and catchpoints:
2879 @kindex disable breakpoints
2881 @kindex dis @r{(@code{disable})}
2882 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2883 Disable the specified breakpoints---or all breakpoints, if none are
2884 listed. A disabled breakpoint has no effect but is not forgotten. All
2885 options such as ignore-counts, conditions and commands are remembered in
2886 case the breakpoint is enabled again later. You may abbreviate
2887 @code{disable} as @code{dis}.
2889 @kindex enable breakpoints
2891 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2892 Enable the specified breakpoints (or all defined breakpoints). They
2893 become effective once again in stopping your program.
2895 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
2896 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2897 of these breakpoints immediately after stopping your program.
2899 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
2900 Enable the specified breakpoints to work once, then die. @value{GDBN}
2901 deletes any of these breakpoints as soon as your program stops there.
2904 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
2905 @c confusing: tbreak is also initially enabled.
2906 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2907 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2908 subsequently, they become disabled or enabled only when you use one of
2909 the commands above. (The command @code{until} can set and delete a
2910 breakpoint of its own, but it does not change the state of your other
2911 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2915 @subsection Break conditions
2916 @cindex conditional breakpoints
2917 @cindex breakpoint conditions
2919 @c FIXME what is scope of break condition expr? Context where wanted?
2920 @c in particular for a watchpoint?
2921 The simplest sort of breakpoint breaks every time your program reaches a
2922 specified place. You can also specify a @dfn{condition} for a
2923 breakpoint. A condition is just a Boolean expression in your
2924 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2925 a condition evaluates the expression each time your program reaches it,
2926 and your program stops only if the condition is @emph{true}.
2928 This is the converse of using assertions for program validation; in that
2929 situation, you want to stop when the assertion is violated---that is,
2930 when the condition is false. In C, if you want to test an assertion expressed
2931 by the condition @var{assert}, you should set the condition
2932 @samp{! @var{assert}} on the appropriate breakpoint.
2934 Conditions are also accepted for watchpoints; you may not need them,
2935 since a watchpoint is inspecting the value of an expression anyhow---but
2936 it might be simpler, say, to just set a watchpoint on a variable name,
2937 and specify a condition that tests whether the new value is an interesting
2940 Break conditions can have side effects, and may even call functions in
2941 your program. This can be useful, for example, to activate functions
2942 that log program progress, or to use your own print functions to
2943 format special data structures. The effects are completely predictable
2944 unless there is another enabled breakpoint at the same address. (In
2945 that case, @value{GDBN} might see the other breakpoint first and stop your
2946 program without checking the condition of this one.) Note that
2947 breakpoint commands are usually more convenient and flexible than break
2949 purpose of performing side effects when a breakpoint is reached
2950 (@pxref{Break Commands, ,Breakpoint command lists}).
2952 Break conditions can be specified when a breakpoint is set, by using
2953 @samp{if} in the arguments to the @code{break} command. @xref{Set
2954 Breaks, ,Setting breakpoints}. They can also be changed at any time
2955 with the @code{condition} command.
2957 You can also use the @code{if} keyword with the @code{watch} command.
2958 The @code{catch} command does not recognize the @code{if} keyword;
2959 @code{condition} is the only way to impose a further condition on a
2964 @item condition @var{bnum} @var{expression}
2965 Specify @var{expression} as the break condition for breakpoint,
2966 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
2967 breakpoint @var{bnum} stops your program only if the value of
2968 @var{expression} is true (nonzero, in C). When you use
2969 @code{condition}, @value{GDBN} checks @var{expression} immediately for
2970 syntactic correctness, and to determine whether symbols in it have
2971 referents in the context of your breakpoint. If @var{expression} uses
2972 symbols not referenced in the context of the breakpoint, @value{GDBN}
2973 prints an error message:
2976 No symbol "foo" in current context.
2981 not actually evaluate @var{expression} at the time the @code{condition}
2982 command (or a command that sets a breakpoint with a condition, like
2983 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
2985 @item condition @var{bnum}
2986 Remove the condition from breakpoint number @var{bnum}. It becomes
2987 an ordinary unconditional breakpoint.
2990 @cindex ignore count (of breakpoint)
2991 A special case of a breakpoint condition is to stop only when the
2992 breakpoint has been reached a certain number of times. This is so
2993 useful that there is a special way to do it, using the @dfn{ignore
2994 count} of the breakpoint. Every breakpoint has an ignore count, which
2995 is an integer. Most of the time, the ignore count is zero, and
2996 therefore has no effect. But if your program reaches a breakpoint whose
2997 ignore count is positive, then instead of stopping, it just decrements
2998 the ignore count by one and continues. As a result, if the ignore count
2999 value is @var{n}, the breakpoint does not stop the next @var{n} times
3000 your program reaches it.
3004 @item ignore @var{bnum} @var{count}
3005 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3006 The next @var{count} times the breakpoint is reached, your program's
3007 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3010 To make the breakpoint stop the next time it is reached, specify
3013 When you use @code{continue} to resume execution of your program from a
3014 breakpoint, you can specify an ignore count directly as an argument to
3015 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3016 Stepping,,Continuing and stepping}.
3018 If a breakpoint has a positive ignore count and a condition, the
3019 condition is not checked. Once the ignore count reaches zero,
3020 @value{GDBN} resumes checking the condition.
3022 You could achieve the effect of the ignore count with a condition such
3023 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3024 is decremented each time. @xref{Convenience Vars, ,Convenience
3028 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3031 @node Break Commands
3032 @subsection Breakpoint command lists
3034 @cindex breakpoint commands
3035 You can give any breakpoint (or watchpoint or catchpoint) a series of
3036 commands to execute when your program stops due to that breakpoint. For
3037 example, you might want to print the values of certain expressions, or
3038 enable other breakpoints.
3043 @item commands @r{[}@var{bnum}@r{]}
3044 @itemx @dots{} @var{command-list} @dots{}
3046 Specify a list of commands for breakpoint number @var{bnum}. The commands
3047 themselves appear on the following lines. Type a line containing just
3048 @code{end} to terminate the commands.
3050 To remove all commands from a breakpoint, type @code{commands} and
3051 follow it immediately with @code{end}; that is, give no commands.
3053 With no @var{bnum} argument, @code{commands} refers to the last
3054 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
3055 recently encountered).
3058 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
3059 disabled within a @var{command-list}.
3061 You can use breakpoint commands to start your program up again. Simply
3062 use the @code{continue} command, or @code{step}, or any other command
3063 that resumes execution.
3065 Any other commands in the command list, after a command that resumes
3066 execution, are ignored. This is because any time you resume execution
3067 (even with a simple @code{next} or @code{step}), you may encounter
3068 another breakpoint---which could have its own command list, leading to
3069 ambiguities about which list to execute.
3072 If the first command you specify in a command list is @code{silent}, the
3073 usual message about stopping at a breakpoint is not printed. This may
3074 be desirable for breakpoints that are to print a specific message and
3075 then continue. If none of the remaining commands print anything, you
3076 see no sign that the breakpoint was reached. @code{silent} is
3077 meaningful only at the beginning of a breakpoint command list.
3079 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3080 print precisely controlled output, and are often useful in silent
3081 breakpoints. @xref{Output, ,Commands for controlled output}.
3083 For example, here is how you could use breakpoint commands to print the
3084 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3090 printf "x is %d\n",x
3095 One application for breakpoint commands is to compensate for one bug so
3096 you can test for another. Put a breakpoint just after the erroneous line
3097 of code, give it a condition to detect the case in which something
3098 erroneous has been done, and give it commands to assign correct values
3099 to any variables that need them. End with the @code{continue} command
3100 so that your program does not stop, and start with the @code{silent}
3101 command so that no output is produced. Here is an example:
3112 @node Breakpoint Menus
3113 @subsection Breakpoint menus
3115 @cindex symbol overloading
3117 Some programming languages (notably C++) permit a single function name
3118 to be defined several times, for application in different contexts.
3119 This is called @dfn{overloading}. When a function name is overloaded,
3120 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3121 a breakpoint. If you realize this is a problem, you can use
3122 something like @samp{break @var{function}(@var{types})} to specify which
3123 particular version of the function you want. Otherwise, @value{GDBN} offers
3124 you a menu of numbered choices for different possible breakpoints, and
3125 waits for your selection with the prompt @samp{>}. The first two
3126 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3127 sets a breakpoint at each definition of @var{function}, and typing
3128 @kbd{0} aborts the @code{break} command without setting any new
3131 For example, the following session excerpt shows an attempt to set a
3132 breakpoint at the overloaded symbol @code{String::after}.
3133 We choose three particular definitions of that function name:
3135 @c FIXME! This is likely to change to show arg type lists, at least
3138 (@value{GDBP}) b String::after
3141 [2] file:String.cc; line number:867
3142 [3] file:String.cc; line number:860
3143 [4] file:String.cc; line number:875
3144 [5] file:String.cc; line number:853
3145 [6] file:String.cc; line number:846
3146 [7] file:String.cc; line number:735
3148 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3149 Breakpoint 2 at 0xb344: file String.cc, line 875.
3150 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3151 Multiple breakpoints were set.
3152 Use the "delete" command to delete unwanted
3158 @c @ifclear BARETARGET
3159 @node Error in Breakpoints
3160 @subsection ``Cannot insert breakpoints''
3162 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3164 Under some operating systems, breakpoints cannot be used in a program if
3165 any other process is running that program. In this situation,
3166 attempting to run or continue a program with a breakpoint causes
3167 @value{GDBN} to print an error message:
3170 Cannot insert breakpoints.
3171 The same program may be running in another process.
3174 When this happens, you have three ways to proceed:
3178 Remove or disable the breakpoints, then continue.
3181 Suspend @value{GDBN}, and copy the file containing your program to a new
3182 name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3183 that @value{GDBN} should run your program under that name.
3184 Then start your program again.
3187 Relink your program so that the text segment is nonsharable, using the
3188 linker option @samp{-N}. The operating system limitation may not apply
3189 to nonsharable executables.
3193 A similar message can be printed if you request too many active
3194 hardware-assisted breakpoints and watchpoints:
3196 @c FIXME: the precise wording of this message may change; the relevant
3197 @c source change is not committed yet (Sep 3, 1999).
3199 Stopped; cannot insert breakpoints.
3200 You may have requested too many hardware breakpoints and watchpoints.
3204 This message is printed when you attempt to resume the program, since
3205 only then @value{GDBN} knows exactly how many hardware breakpoints and
3206 watchpoints it needs to insert.
3208 When this message is printed, you need to disable or remove some of the
3209 hardware-assisted breakpoints and watchpoints, and then continue.
3212 @node Continuing and Stepping
3213 @section Continuing and stepping
3217 @cindex resuming execution
3218 @dfn{Continuing} means resuming program execution until your program
3219 completes normally. In contrast, @dfn{stepping} means executing just
3220 one more ``step'' of your program, where ``step'' may mean either one
3221 line of source code, or one machine instruction (depending on what
3222 particular command you use). Either when continuing or when stepping,
3223 your program may stop even sooner, due to a breakpoint or a signal. (If
3224 it stops due to a signal, you may want to use @code{handle}, or use
3225 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
3229 @kindex c @r{(@code{continue})}
3230 @kindex fg @r{(resume foreground execution)}
3231 @item continue @r{[}@var{ignore-count}@r{]}
3232 @itemx c @r{[}@var{ignore-count}@r{]}
3233 @itemx fg @r{[}@var{ignore-count}@r{]}
3234 Resume program execution, at the address where your program last stopped;
3235 any breakpoints set at that address are bypassed. The optional argument
3236 @var{ignore-count} allows you to specify a further number of times to
3237 ignore a breakpoint at this location; its effect is like that of
3238 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3240 The argument @var{ignore-count} is meaningful only when your program
3241 stopped due to a breakpoint. At other times, the argument to
3242 @code{continue} is ignored.
3244 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
3245 debugged program is deemed to be the foreground program) are provided
3246 purely for convenience, and have exactly the same behavior as
3250 To resume execution at a different place, you can use @code{return}
3251 (@pxref{Returning, ,Returning from a function}) to go back to the
3252 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3253 different address}) to go to an arbitrary location in your program.
3255 A typical technique for using stepping is to set a breakpoint
3256 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3257 beginning of the function or the section of your program where a problem
3258 is believed to lie, run your program until it stops at that breakpoint,
3259 and then step through the suspect area, examining the variables that are
3260 interesting, until you see the problem happen.
3264 @kindex s @r{(@code{step})}
3266 Continue running your program until control reaches a different source
3267 line, then stop it and return control to @value{GDBN}. This command is
3268 abbreviated @code{s}.
3271 @c "without debugging information" is imprecise; actually "without line
3272 @c numbers in the debugging information". (gcc -g1 has debugging info but
3273 @c not line numbers). But it seems complex to try to make that
3274 @c distinction here.
3275 @emph{Warning:} If you use the @code{step} command while control is
3276 within a function that was compiled without debugging information,
3277 execution proceeds until control reaches a function that does have
3278 debugging information. Likewise, it will not step into a function which
3279 is compiled without debugging information. To step through functions
3280 without debugging information, use the @code{stepi} command, described
3284 The @code{step} command only stops at the first instruction of a source
3285 line. This prevents the multiple stops that could otherwise occur in
3286 @code{switch} statements, @code{for} loops, etc. @code{step} continues
3287 to stop if a function that has debugging information is called within
3288 the line. In other words, @code{step} @emph{steps inside} any functions
3289 called within the line.
3291 Also, the @code{step} command only enters a function if there is line
3292 number information for the function. Otherwise it acts like the
3293 @code{next} command. This avoids problems when using @code{cc -gl}
3294 on MIPS machines. Previously, @code{step} entered subroutines if there
3295 was any debugging information about the routine.
3297 @item step @var{count}
3298 Continue running as in @code{step}, but do so @var{count} times. If a
3299 breakpoint is reached, or a signal not related to stepping occurs before
3300 @var{count} steps, stepping stops right away.
3303 @kindex n @r{(@code{next})}
3304 @item next @r{[}@var{count}@r{]}
3305 Continue to the next source line in the current (innermost) stack frame.
3306 This is similar to @code{step}, but function calls that appear within
3307 the line of code are executed without stopping. Execution stops when
3308 control reaches a different line of code at the original stack level
3309 that was executing when you gave the @code{next} command. This command
3310 is abbreviated @code{n}.
3312 An argument @var{count} is a repeat count, as for @code{step}.
3315 @c FIX ME!! Do we delete this, or is there a way it fits in with
3316 @c the following paragraph? --- Vctoria
3318 @c @code{next} within a function that lacks debugging information acts like
3319 @c @code{step}, but any function calls appearing within the code of the
3320 @c function are executed without stopping.
3322 The @code{next} command only stops at the first instruction of a
3323 source line. This prevents multiple stops that could otherwise occur in
3324 @code{switch} statements, @code{for} loops, etc.
3326 @kindex set step-mode
3328 @cindex functions without line info, and stepping
3329 @cindex stepping into functions with no line info
3330 @itemx set step-mode on
3331 The @code{set step-mode on} command causes the @code{step} command to
3332 stop at the first instruction of a function which contains no debug line
3333 information rather than stepping over it.
3335 This is useful in cases where you may be interested in inspecting the
3336 machine instructions of a function which has no symbolic info and do not
3337 want @value{GDBN} to automatically skip over this function.
3339 @item set step-mode off
3340 Causes the @code{step} command to step over any functions which contains no
3341 debug information. This is the default.
3345 Continue running until just after function in the selected stack frame
3346 returns. Print the returned value (if any).
3348 Contrast this with the @code{return} command (@pxref{Returning,
3349 ,Returning from a function}).
3352 @kindex u @r{(@code{until})}
3355 Continue running until a source line past the current line, in the
3356 current stack frame, is reached. This command is used to avoid single
3357 stepping through a loop more than once. It is like the @code{next}
3358 command, except that when @code{until} encounters a jump, it
3359 automatically continues execution until the program counter is greater
3360 than the address of the jump.
3362 This means that when you reach the end of a loop after single stepping
3363 though it, @code{until} makes your program continue execution until it
3364 exits the loop. In contrast, a @code{next} command at the end of a loop
3365 simply steps back to the beginning of the loop, which forces you to step
3366 through the next iteration.
3368 @code{until} always stops your program if it attempts to exit the current
3371 @code{until} may produce somewhat counterintuitive results if the order
3372 of machine code does not match the order of the source lines. For
3373 example, in the following excerpt from a debugging session, the @code{f}
3374 (@code{frame}) command shows that execution is stopped at line
3375 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3379 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3381 (@value{GDBP}) until
3382 195 for ( ; argc > 0; NEXTARG) @{
3385 This happened because, for execution efficiency, the compiler had
3386 generated code for the loop closure test at the end, rather than the
3387 start, of the loop---even though the test in a C @code{for}-loop is
3388 written before the body of the loop. The @code{until} command appeared
3389 to step back to the beginning of the loop when it advanced to this
3390 expression; however, it has not really gone to an earlier
3391 statement---not in terms of the actual machine code.
3393 @code{until} with no argument works by means of single
3394 instruction stepping, and hence is slower than @code{until} with an
3397 @item until @var{location}
3398 @itemx u @var{location}
3399 Continue running your program until either the specified location is
3400 reached, or the current stack frame returns. @var{location} is any of
3401 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3402 ,Setting breakpoints}). This form of the command uses breakpoints,
3403 and hence is quicker than @code{until} without an argument.
3406 @kindex si @r{(@code{stepi})}
3408 @itemx stepi @var{arg}
3410 Execute one machine instruction, then stop and return to the debugger.
3412 It is often useful to do @samp{display/i $pc} when stepping by machine
3413 instructions. This makes @value{GDBN} automatically display the next
3414 instruction to be executed, each time your program stops. @xref{Auto
3415 Display,, Automatic display}.
3417 An argument is a repeat count, as in @code{step}.
3421 @kindex ni @r{(@code{nexti})}
3423 @itemx nexti @var{arg}
3425 Execute one machine instruction, but if it is a function call,
3426 proceed until the function returns.
3428 An argument is a repeat count, as in @code{next}.
3435 A signal is an asynchronous event that can happen in a program. The
3436 operating system defines the possible kinds of signals, and gives each
3437 kind a name and a number. For example, in Unix @code{SIGINT} is the
3438 signal a program gets when you type an interrupt character (often @kbd{C-c});
3439 @code{SIGSEGV} is the signal a program gets from referencing a place in
3440 memory far away from all the areas in use; @code{SIGALRM} occurs when
3441 the alarm clock timer goes off (which happens only if your program has
3442 requested an alarm).
3444 @cindex fatal signals
3445 Some signals, including @code{SIGALRM}, are a normal part of the
3446 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3447 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
3448 program has not specified in advance some other way to handle the signal.
3449 @code{SIGINT} does not indicate an error in your program, but it is normally
3450 fatal so it can carry out the purpose of the interrupt: to kill the program.
3452 @value{GDBN} has the ability to detect any occurrence of a signal in your
3453 program. You can tell @value{GDBN} in advance what to do for each kind of
3456 @cindex handling signals
3457 Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM}
3458 (so as not to interfere with their role in the functioning of your program)
3459 but to stop your program immediately whenever an error signal happens.
3460 You can change these settings with the @code{handle} command.
3463 @kindex info signals
3466 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3467 handle each one. You can use this to see the signal numbers of all
3468 the defined types of signals.
3470 @code{info handle} is an alias for @code{info signals}.
3473 @item handle @var{signal} @var{keywords}@dots{}
3474 Change the way @value{GDBN} handles signal @var{signal}. @var{signal} can
3475 be the number of a signal or its name (with or without the @samp{SIG} at the
3476 beginning). The @var{keywords} say what change to make.
3480 The keywords allowed by the @code{handle} command can be abbreviated.
3481 Their full names are:
3485 @value{GDBN} should not stop your program when this signal happens. It may
3486 still print a message telling you that the signal has come in.
3489 @value{GDBN} should stop your program when this signal happens. This implies
3490 the @code{print} keyword as well.
3493 @value{GDBN} should print a message when this signal happens.
3496 @value{GDBN} should not mention the occurrence of the signal at all. This
3497 implies the @code{nostop} keyword as well.
3500 @value{GDBN} should allow your program to see this signal; your program
3501 can handle the signal, or else it may terminate if the signal is fatal
3505 @value{GDBN} should not allow your program to see this signal.
3509 When a signal stops your program, the signal is not visible to the
3511 continue. Your program sees the signal then, if @code{pass} is in
3512 effect for the signal in question @emph{at that time}. In other words,
3513 after @value{GDBN} reports a signal, you can use the @code{handle}
3514 command with @code{pass} or @code{nopass} to control whether your
3515 program sees that signal when you continue.
3517 You can also use the @code{signal} command to prevent your program from
3518 seeing a signal, or cause it to see a signal it normally would not see,
3519 or to give it any signal at any time. For example, if your program stopped
3520 due to some sort of memory reference error, you might store correct
3521 values into the erroneous variables and continue, hoping to see more
3522 execution; but your program would probably terminate immediately as
3523 a result of the fatal signal once it saw the signal. To prevent this,
3524 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3528 @section Stopping and starting multi-thread programs
3530 When your program has multiple threads (@pxref{Threads,, Debugging
3531 programs with multiple threads}), you can choose whether to set
3532 breakpoints on all threads, or on a particular thread.
3535 @cindex breakpoints and threads
3536 @cindex thread breakpoints
3537 @kindex break @dots{} thread @var{threadno}
3538 @item break @var{linespec} thread @var{threadno}
3539 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3540 @var{linespec} specifies source lines; there are several ways of
3541 writing them, but the effect is always to specify some source line.
3543 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3544 to specify that you only want @value{GDBN} to stop the program when a
3545 particular thread reaches this breakpoint. @var{threadno} is one of the
3546 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3547 column of the @samp{info threads} display.
3549 If you do not specify @samp{thread @var{threadno}} when you set a
3550 breakpoint, the breakpoint applies to @emph{all} threads of your
3553 You can use the @code{thread} qualifier on conditional breakpoints as
3554 well; in this case, place @samp{thread @var{threadno}} before the
3555 breakpoint condition, like this:
3558 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
3563 @cindex stopped threads
3564 @cindex threads, stopped
3565 Whenever your program stops under @value{GDBN} for any reason,
3566 @emph{all} threads of execution stop, not just the current thread. This
3567 allows you to examine the overall state of the program, including
3568 switching between threads, without worrying that things may change
3571 @cindex continuing threads
3572 @cindex threads, continuing
3573 Conversely, whenever you restart the program, @emph{all} threads start
3574 executing. @emph{This is true even when single-stepping} with commands
3575 like @code{step} or @code{next}.
3577 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3578 Since thread scheduling is up to your debugging target's operating
3579 system (not controlled by @value{GDBN}), other threads may
3580 execute more than one statement while the current thread completes a
3581 single step. Moreover, in general other threads stop in the middle of a
3582 statement, rather than at a clean statement boundary, when the program
3585 You might even find your program stopped in another thread after
3586 continuing or even single-stepping. This happens whenever some other
3587 thread runs into a breakpoint, a signal, or an exception before the
3588 first thread completes whatever you requested.
3590 On some OSes, you can lock the OS scheduler and thus allow only a single
3594 @item set scheduler-locking @var{mode}
3595 Set the scheduler locking mode. If it is @code{off}, then there is no
3596 locking and any thread may run at any time. If @code{on}, then only the
3597 current thread may run when the inferior is resumed. The @code{step}
3598 mode optimizes for single-stepping. It stops other threads from
3599 ``seizing the prompt'' by preempting the current thread while you are
3600 stepping. Other threads will only rarely (or never) get a chance to run
3601 when you step. They are more likely to run when you @samp{next} over a
3602 function call, and they are completely free to run when you use commands
3603 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
3604 thread hits a breakpoint during its timeslice, they will never steal the
3605 @value{GDBN} prompt away from the thread that you are debugging.
3607 @item show scheduler-locking
3608 Display the current scheduler locking mode.
3613 @chapter Examining the Stack
3615 When your program has stopped, the first thing you need to know is where it
3616 stopped and how it got there.
3619 Each time your program performs a function call, information about the call
3621 That information includes the location of the call in your program,
3622 the arguments of the call,
3623 and the local variables of the function being called.
3624 The information is saved in a block of data called a @dfn{stack frame}.
3625 The stack frames are allocated in a region of memory called the @dfn{call
3628 When your program stops, the @value{GDBN} commands for examining the
3629 stack allow you to see all of this information.
3631 @cindex selected frame
3632 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3633 @value{GDBN} commands refer implicitly to the selected frame. In
3634 particular, whenever you ask @value{GDBN} for the value of a variable in
3635 your program, the value is found in the selected frame. There are
3636 special @value{GDBN} commands to select whichever frame you are
3637 interested in. @xref{Selection, ,Selecting a frame}.
3639 When your program stops, @value{GDBN} automatically selects the
3640 currently executing frame and describes it briefly, similar to the
3641 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3644 * Frames:: Stack frames
3645 * Backtrace:: Backtraces
3646 * Selection:: Selecting a frame
3647 * Frame Info:: Information on a frame
3652 @section Stack frames
3654 @cindex frame, definition
3656 The call stack is divided up into contiguous pieces called @dfn{stack
3657 frames}, or @dfn{frames} for short; each frame is the data associated
3658 with one call to one function. The frame contains the arguments given
3659 to the function, the function's local variables, and the address at
3660 which the function is executing.
3662 @cindex initial frame
3663 @cindex outermost frame
3664 @cindex innermost frame
3665 When your program is started, the stack has only one frame, that of the
3666 function @code{main}. This is called the @dfn{initial} frame or the
3667 @dfn{outermost} frame. Each time a function is called, a new frame is
3668 made. Each time a function returns, the frame for that function invocation
3669 is eliminated. If a function is recursive, there can be many frames for
3670 the same function. The frame for the function in which execution is
3671 actually occurring is called the @dfn{innermost} frame. This is the most
3672 recently created of all the stack frames that still exist.
3674 @cindex frame pointer
3675 Inside your program, stack frames are identified by their addresses. A
3676 stack frame consists of many bytes, each of which has its own address; each
3677 kind of computer has a convention for choosing one byte whose
3678 address serves as the address of the frame. Usually this address is kept
3679 in a register called the @dfn{frame pointer register} while execution is
3680 going on in that frame.
3682 @cindex frame number
3683 @value{GDBN} assigns numbers to all existing stack frames, starting with
3684 zero for the innermost frame, one for the frame that called it,
3685 and so on upward. These numbers do not really exist in your program;
3686 they are assigned by @value{GDBN} to give you a way of designating stack
3687 frames in @value{GDBN} commands.
3689 @c The -fomit-frame-pointer below perennially causes hbox overflow
3690 @c underflow problems.
3691 @cindex frameless execution
3692 Some compilers provide a way to compile functions so that they operate
3693 without stack frames. (For example, the @value{GCC} option
3695 @samp{-fomit-frame-pointer}
3697 generates functions without a frame.)
3698 This is occasionally done with heavily used library functions to save
3699 the frame setup time. @value{GDBN} has limited facilities for dealing
3700 with these function invocations. If the innermost function invocation
3701 has no stack frame, @value{GDBN} nevertheless regards it as though
3702 it had a separate frame, which is numbered zero as usual, allowing
3703 correct tracing of the function call chain. However, @value{GDBN} has
3704 no provision for frameless functions elsewhere in the stack.
3707 @kindex frame@r{, command}
3708 @cindex current stack frame
3709 @item frame @var{args}
3710 The @code{frame} command allows you to move from one stack frame to another,
3711 and to print the stack frame you select. @var{args} may be either the
3712 address of the frame or the stack frame number. Without an argument,
3713 @code{frame} prints the current stack frame.
3715 @kindex select-frame
3716 @cindex selecting frame silently
3718 The @code{select-frame} command allows you to move from one stack frame
3719 to another without printing the frame. This is the silent version of
3728 @cindex stack traces
3729 A backtrace is a summary of how your program got where it is. It shows one
3730 line per frame, for many frames, starting with the currently executing
3731 frame (frame zero), followed by its caller (frame one), and on up the
3736 @kindex bt @r{(@code{backtrace})}
3739 Print a backtrace of the entire stack: one line per frame for all
3740 frames in the stack.
3742 You can stop the backtrace at any time by typing the system interrupt
3743 character, normally @kbd{C-c}.
3745 @item backtrace @var{n}
3747 Similar, but print only the innermost @var{n} frames.
3749 @item backtrace -@var{n}
3751 Similar, but print only the outermost @var{n} frames.
3756 @kindex info s @r{(@code{info stack})}
3757 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3758 are additional aliases for @code{backtrace}.
3760 Each line in the backtrace shows the frame number and the function name.
3761 The program counter value is also shown---unless you use @code{set
3762 print address off}. The backtrace also shows the source file name and
3763 line number, as well as the arguments to the function. The program
3764 counter value is omitted if it is at the beginning of the code for that
3767 Here is an example of a backtrace. It was made with the command
3768 @samp{bt 3}, so it shows the innermost three frames.
3772 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3774 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3775 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3777 (More stack frames follow...)
3782 The display for frame zero does not begin with a program counter
3783 value, indicating that your program has stopped at the beginning of the
3784 code for line @code{993} of @code{builtin.c}.
3787 @section Selecting a frame
3789 Most commands for examining the stack and other data in your program work on
3790 whichever stack frame is selected at the moment. Here are the commands for
3791 selecting a stack frame; all of them finish by printing a brief description
3792 of the stack frame just selected.
3795 @kindex frame@r{, selecting}
3796 @kindex f @r{(@code{frame})}
3799 Select frame number @var{n}. Recall that frame zero is the innermost
3800 (currently executing) frame, frame one is the frame that called the
3801 innermost one, and so on. The highest-numbered frame is the one for
3804 @item frame @var{addr}
3806 Select the frame at address @var{addr}. This is useful mainly if the
3807 chaining of stack frames has been damaged by a bug, making it
3808 impossible for @value{GDBN} to assign numbers properly to all frames. In
3809 addition, this can be useful when your program has multiple stacks and
3810 switches between them.
3812 On the SPARC architecture, @code{frame} needs two addresses to
3813 select an arbitrary frame: a frame pointer and a stack pointer.
3815 On the MIPS and Alpha architecture, it needs two addresses: a stack
3816 pointer and a program counter.
3818 On the 29k architecture, it needs three addresses: a register stack
3819 pointer, a program counter, and a memory stack pointer.
3820 @c note to future updaters: this is conditioned on a flag
3821 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3822 @c as of 27 Jan 1994.
3826 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3827 advances toward the outermost frame, to higher frame numbers, to frames
3828 that have existed longer. @var{n} defaults to one.
3831 @kindex do @r{(@code{down})}
3833 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3834 advances toward the innermost frame, to lower frame numbers, to frames
3835 that were created more recently. @var{n} defaults to one. You may
3836 abbreviate @code{down} as @code{do}.
3839 All of these commands end by printing two lines of output describing the
3840 frame. The first line shows the frame number, the function name, the
3841 arguments, and the source file and line number of execution in that
3842 frame. The second line shows the text of that source line.
3850 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3852 10 read_input_file (argv[i]);
3856 After such a printout, the @code{list} command with no arguments
3857 prints ten lines centered on the point of execution in the frame.
3858 @xref{List, ,Printing source lines}.
3861 @kindex down-silently
3863 @item up-silently @var{n}
3864 @itemx down-silently @var{n}
3865 These two commands are variants of @code{up} and @code{down},
3866 respectively; they differ in that they do their work silently, without
3867 causing display of the new frame. They are intended primarily for use
3868 in @value{GDBN} command scripts, where the output might be unnecessary and
3873 @section Information about a frame
3875 There are several other commands to print information about the selected
3881 When used without any argument, this command does not change which
3882 frame is selected, but prints a brief description of the currently
3883 selected stack frame. It can be abbreviated @code{f}. With an
3884 argument, this command is used to select a stack frame.
3885 @xref{Selection, ,Selecting a frame}.
3888 @kindex info f @r{(@code{info frame})}
3891 This command prints a verbose description of the selected stack frame,
3896 the address of the frame
3898 the address of the next frame down (called by this frame)
3900 the address of the next frame up (caller of this frame)
3902 the language in which the source code corresponding to this frame is written
3904 the address of the frame's arguments
3906 the address of the frame's local variables
3908 the program counter saved in it (the address of execution in the caller frame)
3910 which registers were saved in the frame
3913 @noindent The verbose description is useful when
3914 something has gone wrong that has made the stack format fail to fit
3915 the usual conventions.
3917 @item info frame @var{addr}
3918 @itemx info f @var{addr}
3919 Print a verbose description of the frame at address @var{addr}, without
3920 selecting that frame. The selected frame remains unchanged by this
3921 command. This requires the same kind of address (more than one for some
3922 architectures) that you specify in the @code{frame} command.
3923 @xref{Selection, ,Selecting a frame}.
3927 Print the arguments of the selected frame, each on a separate line.
3931 Print the local variables of the selected frame, each on a separate
3932 line. These are all variables (declared either static or automatic)
3933 accessible at the point of execution of the selected frame.
3936 @cindex catch exceptions, list active handlers
3937 @cindex exception handlers, how to list
3939 Print a list of all the exception handlers that are active in the
3940 current stack frame at the current point of execution. To see other
3941 exception handlers, visit the associated frame (using the @code{up},
3942 @code{down}, or @code{frame} commands); then type @code{info catch}.
3943 @xref{Set Catchpoints, , Setting catchpoints}.
3949 @chapter Examining Source Files
3951 @value{GDBN} can print parts of your program's source, since the debugging
3952 information recorded in the program tells @value{GDBN} what source files were
3953 used to build it. When your program stops, @value{GDBN} spontaneously prints
3954 the line where it stopped. Likewise, when you select a stack frame
3955 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
3956 execution in that frame has stopped. You can print other portions of
3957 source files by explicit command.
3959 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
3960 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
3961 @value{GDBN} under @sc{gnu} Emacs}.
3964 * List:: Printing source lines
3965 * Search:: Searching source files
3966 * Source Path:: Specifying source directories
3967 * Machine Code:: Source and machine code
3971 @section Printing source lines
3974 @kindex l @r{(@code{list})}
3975 To print lines from a source file, use the @code{list} command
3976 (abbreviated @code{l}). By default, ten lines are printed.
3977 There are several ways to specify what part of the file you want to print.
3979 Here are the forms of the @code{list} command most commonly used:
3982 @item list @var{linenum}
3983 Print lines centered around line number @var{linenum} in the
3984 current source file.
3986 @item list @var{function}
3987 Print lines centered around the beginning of function
3991 Print more lines. If the last lines printed were printed with a
3992 @code{list} command, this prints lines following the last lines
3993 printed; however, if the last line printed was a solitary line printed
3994 as part of displaying a stack frame (@pxref{Stack, ,Examining the
3995 Stack}), this prints lines centered around that line.
3998 Print lines just before the lines last printed.
4001 By default, @value{GDBN} prints ten source lines with any of these forms of
4002 the @code{list} command. You can change this using @code{set listsize}:
4005 @kindex set listsize
4006 @item set listsize @var{count}
4007 Make the @code{list} command display @var{count} source lines (unless
4008 the @code{list} argument explicitly specifies some other number).
4010 @kindex show listsize
4012 Display the number of lines that @code{list} prints.
4015 Repeating a @code{list} command with @key{RET} discards the argument,
4016 so it is equivalent to typing just @code{list}. This is more useful
4017 than listing the same lines again. An exception is made for an
4018 argument of @samp{-}; that argument is preserved in repetition so that
4019 each repetition moves up in the source file.
4022 In general, the @code{list} command expects you to supply zero, one or two
4023 @dfn{linespecs}. Linespecs specify source lines; there are several ways
4024 of writing them, but the effect is always to specify some source line.
4025 Here is a complete description of the possible arguments for @code{list}:
4028 @item list @var{linespec}
4029 Print lines centered around the line specified by @var{linespec}.
4031 @item list @var{first},@var{last}
4032 Print lines from @var{first} to @var{last}. Both arguments are
4035 @item list ,@var{last}
4036 Print lines ending with @var{last}.
4038 @item list @var{first},
4039 Print lines starting with @var{first}.
4042 Print lines just after the lines last printed.
4045 Print lines just before the lines last printed.
4048 As described in the preceding table.
4051 Here are the ways of specifying a single source line---all the
4056 Specifies line @var{number} of the current source file.
4057 When a @code{list} command has two linespecs, this refers to
4058 the same source file as the first linespec.
4061 Specifies the line @var{offset} lines after the last line printed.
4062 When used as the second linespec in a @code{list} command that has
4063 two, this specifies the line @var{offset} lines down from the
4067 Specifies the line @var{offset} lines before the last line printed.
4069 @item @var{filename}:@var{number}
4070 Specifies line @var{number} in the source file @var{filename}.
4072 @item @var{function}
4073 Specifies the line that begins the body of the function @var{function}.
4074 For example: in C, this is the line with the open brace.
4076 @item @var{filename}:@var{function}
4077 Specifies the line of the open-brace that begins the body of the
4078 function @var{function} in the file @var{filename}. You only need the
4079 file name with a function name to avoid ambiguity when there are
4080 identically named functions in different source files.
4082 @item *@var{address}
4083 Specifies the line containing the program address @var{address}.
4084 @var{address} may be any expression.
4088 @section Searching source files
4090 @kindex reverse-search
4092 There are two commands for searching through the current source file for a
4097 @kindex forward-search
4098 @item forward-search @var{regexp}
4099 @itemx search @var{regexp}
4100 The command @samp{forward-search @var{regexp}} checks each line,
4101 starting with the one following the last line listed, for a match for
4102 @var{regexp}. It lists the line that is found. You can use the
4103 synonym @samp{search @var{regexp}} or abbreviate the command name as
4106 @item reverse-search @var{regexp}
4107 The command @samp{reverse-search @var{regexp}} checks each line, starting
4108 with the one before the last line listed and going backward, for a match
4109 for @var{regexp}. It lists the line that is found. You can abbreviate
4110 this command as @code{rev}.
4114 @section Specifying source directories
4117 @cindex directories for source files
4118 Executable programs sometimes do not record the directories of the source
4119 files from which they were compiled, just the names. Even when they do,
4120 the directories could be moved between the compilation and your debugging
4121 session. @value{GDBN} has a list of directories to search for source files;
4122 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4123 it tries all the directories in the list, in the order they are present
4124 in the list, until it finds a file with the desired name. Note that
4125 the executable search path is @emph{not} used for this purpose. Neither is
4126 the current working directory, unless it happens to be in the source
4129 If @value{GDBN} cannot find a source file in the source path, and the
4130 object program records a directory, @value{GDBN} tries that directory
4131 too. If the source path is empty, and there is no record of the
4132 compilation directory, @value{GDBN} looks in the current directory as a
4135 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4136 any information it has cached about where source files are found and where
4137 each line is in the file.
4141 When you start @value{GDBN}, its source path includes only @samp{cdir}
4142 and @samp{cwd}, in that order.
4143 To add other directories, use the @code{directory} command.
4146 @item directory @var{dirname} @dots{}
4147 @item dir @var{dirname} @dots{}
4148 Add directory @var{dirname} to the front of the source path. Several
4149 directory names may be given to this command, separated by @samp{:}
4150 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
4151 part of absolute file names) or
4152 whitespace. You may specify a directory that is already in the source
4153 path; this moves it forward, so @value{GDBN} searches it sooner.
4157 @vindex $cdir@r{, convenience variable}
4158 @vindex $cwdr@r{, convenience variable}
4159 @cindex compilation directory
4160 @cindex current directory
4161 @cindex working directory
4162 @cindex directory, current
4163 @cindex directory, compilation
4164 You can use the string @samp{$cdir} to refer to the compilation
4165 directory (if one is recorded), and @samp{$cwd} to refer to the current
4166 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4167 tracks the current working directory as it changes during your @value{GDBN}
4168 session, while the latter is immediately expanded to the current
4169 directory at the time you add an entry to the source path.
4172 Reset the source path to empty again. This requires confirmation.
4174 @c RET-repeat for @code{directory} is explicitly disabled, but since
4175 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4177 @item show directories
4178 @kindex show directories
4179 Print the source path: show which directories it contains.
4182 If your source path is cluttered with directories that are no longer of
4183 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4184 versions of source. You can correct the situation as follows:
4188 Use @code{directory} with no argument to reset the source path to empty.
4191 Use @code{directory} with suitable arguments to reinstall the
4192 directories you want in the source path. You can add all the
4193 directories in one command.
4197 @section Source and machine code
4199 You can use the command @code{info line} to map source lines to program
4200 addresses (and vice versa), and the command @code{disassemble} to display
4201 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4202 mode, the @code{info line} command causes the arrow to point to the
4203 line specified. Also, @code{info line} prints addresses in symbolic form as
4208 @item info line @var{linespec}
4209 Print the starting and ending addresses of the compiled code for
4210 source line @var{linespec}. You can specify source lines in any of
4211 the ways understood by the @code{list} command (@pxref{List, ,Printing
4215 For example, we can use @code{info line} to discover the location of
4216 the object code for the first line of function
4217 @code{m4_changequote}:
4219 @c FIXME: I think this example should also show the addresses in
4220 @c symbolic form, as they usually would be displayed.
4222 (@value{GDBP}) info line m4_changequote
4223 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4227 We can also inquire (using @code{*@var{addr}} as the form for
4228 @var{linespec}) what source line covers a particular address:
4230 (@value{GDBP}) info line *0x63ff
4231 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4234 @cindex @code{$_} and @code{info line}
4235 @kindex x@r{(examine), and} info line
4236 After @code{info line}, the default address for the @code{x} command
4237 is changed to the starting address of the line, so that @samp{x/i} is
4238 sufficient to begin examining the machine code (@pxref{Memory,
4239 ,Examining memory}). Also, this address is saved as the value of the
4240 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4245 @cindex assembly instructions
4246 @cindex instructions, assembly
4247 @cindex machine instructions
4248 @cindex listing machine instructions
4250 This specialized command dumps a range of memory as machine
4251 instructions. The default memory range is the function surrounding the
4252 program counter of the selected frame. A single argument to this
4253 command is a program counter value; @value{GDBN} dumps the function
4254 surrounding this value. Two arguments specify a range of addresses
4255 (first inclusive, second exclusive) to dump.
4258 The following example shows the disassembly of a range of addresses of
4259 HP PA-RISC 2.0 code:
4262 (@value{GDBP}) disas 0x32c4 0x32e4
4263 Dump of assembler code from 0x32c4 to 0x32e4:
4264 0x32c4 <main+204>: addil 0,dp
4265 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4266 0x32cc <main+212>: ldil 0x3000,r31
4267 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4268 0x32d4 <main+220>: ldo 0(r31),rp
4269 0x32d8 <main+224>: addil -0x800,dp
4270 0x32dc <main+228>: ldo 0x588(r1),r26
4271 0x32e0 <main+232>: ldil 0x3000,r31
4272 End of assembler dump.
4275 Some architectures have more than one commonly-used set of instruction
4276 mnemonics or other syntax.
4279 @kindex set disassembly-flavor
4280 @cindex assembly instructions
4281 @cindex instructions, assembly
4282 @cindex machine instructions
4283 @cindex listing machine instructions
4284 @cindex Intel disassembly flavor
4285 @cindex AT&T disassembly flavor
4286 @item set disassembly-flavor @var{instruction-set}
4287 Select the instruction set to use when disassembling the
4288 program via the @code{disassemble} or @code{x/i} commands.
4290 Currently this command is only defined for the Intel x86 family. You
4291 can set @var{instruction-set} to either @code{intel} or @code{att}.
4292 The default is @code{att}, the AT&T flavor used by default by Unix
4293 assemblers for x86-based targets.
4298 @chapter Examining Data
4300 @cindex printing data
4301 @cindex examining data
4304 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4305 @c document because it is nonstandard... Under Epoch it displays in a
4306 @c different window or something like that.
4307 The usual way to examine data in your program is with the @code{print}
4308 command (abbreviated @code{p}), or its synonym @code{inspect}. It
4309 evaluates and prints the value of an expression of the language your
4310 program is written in (@pxref{Languages, ,Using @value{GDBN} with
4311 Different Languages}).
4314 @item print @var{expr}
4315 @itemx print /@var{f} @var{expr}
4316 @var{expr} is an expression (in the source language). By default the
4317 value of @var{expr} is printed in a format appropriate to its data type;
4318 you can choose a different format by specifying @samp{/@var{f}}, where
4319 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
4323 @itemx print /@var{f}
4324 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
4325 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4326 conveniently inspect the same value in an alternative format.
4329 A more low-level way of examining data is with the @code{x} command.
4330 It examines data in memory at a specified address and prints it in a
4331 specified format. @xref{Memory, ,Examining memory}.
4333 If you are interested in information about types, or about how the
4334 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
4335 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
4339 * Expressions:: Expressions
4340 * Variables:: Program variables
4341 * Arrays:: Artificial arrays
4342 * Output Formats:: Output formats
4343 * Memory:: Examining memory
4344 * Auto Display:: Automatic display
4345 * Print Settings:: Print settings
4346 * Value History:: Value history
4347 * Convenience Vars:: Convenience variables
4348 * Registers:: Registers
4349 * Floating Point Hardware:: Floating point hardware
4350 * Memory Region Attributes:: Memory region attributes
4354 @section Expressions
4357 @code{print} and many other @value{GDBN} commands accept an expression and
4358 compute its value. Any kind of constant, variable or operator defined
4359 by the programming language you are using is valid in an expression in
4360 @value{GDBN}. This includes conditional expressions, function calls, casts
4361 and string constants. It unfortunately does not include symbols defined
4362 by preprocessor @code{#define} commands.
4364 @value{GDBN} supports array constants in expressions input by
4365 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
4366 you can use the command @code{print @{1, 2, 3@}} to build up an array in
4367 memory that is @code{malloc}ed in the target program.
4369 Because C is so widespread, most of the expressions shown in examples in
4370 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4371 Languages}, for information on how to use expressions in other
4374 In this section, we discuss operators that you can use in @value{GDBN}
4375 expressions regardless of your programming language.
4377 Casts are supported in all languages, not just in C, because it is so
4378 useful to cast a number into a pointer in order to examine a structure
4379 at that address in memory.
4380 @c FIXME: casts supported---Mod2 true?
4382 @value{GDBN} supports these operators, in addition to those common
4383 to programming languages:
4387 @samp{@@} is a binary operator for treating parts of memory as arrays.
4388 @xref{Arrays, ,Artificial arrays}, for more information.
4391 @samp{::} allows you to specify a variable in terms of the file or
4392 function where it is defined. @xref{Variables, ,Program variables}.
4394 @cindex @{@var{type}@}
4395 @cindex type casting memory
4396 @cindex memory, viewing as typed object
4397 @cindex casts, to view memory
4398 @item @{@var{type}@} @var{addr}
4399 Refers to an object of type @var{type} stored at address @var{addr} in
4400 memory. @var{addr} may be any expression whose value is an integer or
4401 pointer (but parentheses are required around binary operators, just as in
4402 a cast). This construct is allowed regardless of what kind of data is
4403 normally supposed to reside at @var{addr}.
4407 @section Program variables
4409 The most common kind of expression to use is the name of a variable
4412 Variables in expressions are understood in the selected stack frame
4413 (@pxref{Selection, ,Selecting a frame}); they must be either:
4417 global (or file-static)
4424 visible according to the scope rules of the
4425 programming language from the point of execution in that frame
4428 @noindent This means that in the function
4443 you can examine and use the variable @code{a} whenever your program is
4444 executing within the function @code{foo}, but you can only use or
4445 examine the variable @code{b} while your program is executing inside
4446 the block where @code{b} is declared.
4448 @cindex variable name conflict
4449 There is an exception: you can refer to a variable or function whose
4450 scope is a single source file even if the current execution point is not
4451 in this file. But it is possible to have more than one such variable or
4452 function with the same name (in different source files). If that
4453 happens, referring to that name has unpredictable effects. If you wish,
4454 you can specify a static variable in a particular function or file,
4455 using the colon-colon notation:
4457 @cindex colon-colon, context for variables/functions
4459 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4460 @cindex @code{::}, context for variables/functions
4463 @var{file}::@var{variable}
4464 @var{function}::@var{variable}
4468 Here @var{file} or @var{function} is the name of the context for the
4469 static @var{variable}. In the case of file names, you can use quotes to
4470 make sure @value{GDBN} parses the file name as a single word---for example,
4471 to print a global value of @code{x} defined in @file{f2.c}:
4474 (@value{GDBP}) p 'f2.c'::x
4477 @cindex C++ scope resolution
4478 This use of @samp{::} is very rarely in conflict with the very similar
4479 use of the same notation in C++. @value{GDBN} also supports use of the C++
4480 scope resolution operator in @value{GDBN} expressions.
4481 @c FIXME: Um, so what happens in one of those rare cases where it's in
4484 @cindex wrong values
4485 @cindex variable values, wrong
4487 @emph{Warning:} Occasionally, a local variable may appear to have the
4488 wrong value at certain points in a function---just after entry to a new
4489 scope, and just before exit.
4491 You may see this problem when you are stepping by machine instructions.
4492 This is because, on most machines, it takes more than one instruction to
4493 set up a stack frame (including local variable definitions); if you are
4494 stepping by machine instructions, variables may appear to have the wrong
4495 values until the stack frame is completely built. On exit, it usually
4496 also takes more than one machine instruction to destroy a stack frame;
4497 after you begin stepping through that group of instructions, local
4498 variable definitions may be gone.
4500 This may also happen when the compiler does significant optimizations.
4501 To be sure of always seeing accurate values, turn off all optimization
4504 @cindex ``No symbol "foo" in current context''
4505 Another possible effect of compiler optimizations is to optimize
4506 unused variables out of existence, or assign variables to registers (as
4507 opposed to memory addresses). Depending on the support for such cases
4508 offered by the debug info format used by the compiler, @value{GDBN}
4509 might not be able to display values for such local variables. If that
4510 happens, @value{GDBN} will print a message like this:
4513 No symbol "foo" in current context.
4516 To solve such problems, either recompile without optimizations, or use a
4517 different debug info format, if the compiler supports several such
4518 formats. For example, @value{NGCC}, the @sc{gnu} C/C++ compiler usually
4519 supports the @samp{-gstabs} option. @samp{-gstabs} produces debug info
4520 in a format that is superior to formats such as COFF. You may be able
4521 to use DWARF2 (@samp{-gdwarf-2}), which is also an effective form for
4522 debug info. See @ref{Debugging Options,,Options for Debugging Your
4523 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
4528 @section Artificial arrays
4530 @cindex artificial array
4531 @kindex @@@r{, referencing memory as an array}
4532 It is often useful to print out several successive objects of the
4533 same type in memory; a section of an array, or an array of
4534 dynamically determined size for which only a pointer exists in the
4537 You can do this by referring to a contiguous span of memory as an
4538 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4539 operand of @samp{@@} should be the first element of the desired array
4540 and be an individual object. The right operand should be the desired length
4541 of the array. The result is an array value whose elements are all of
4542 the type of the left argument. The first element is actually the left
4543 argument; the second element comes from bytes of memory immediately
4544 following those that hold the first element, and so on. Here is an
4545 example. If a program says
4548 int *array = (int *) malloc (len * sizeof (int));
4552 you can print the contents of @code{array} with
4558 The left operand of @samp{@@} must reside in memory. Array values made
4559 with @samp{@@} in this way behave just like other arrays in terms of
4560 subscripting, and are coerced to pointers when used in expressions.
4561 Artificial arrays most often appear in expressions via the value history
4562 (@pxref{Value History, ,Value history}), after printing one out.
4564 Another way to create an artificial array is to use a cast.
4565 This re-interprets a value as if it were an array.
4566 The value need not be in memory:
4568 (@value{GDBP}) p/x (short[2])0x12345678
4569 $1 = @{0x1234, 0x5678@}
4572 As a convenience, if you leave the array length out (as in
4573 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
4574 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4576 (@value{GDBP}) p/x (short[])0x12345678
4577 $2 = @{0x1234, 0x5678@}
4580 Sometimes the artificial array mechanism is not quite enough; in
4581 moderately complex data structures, the elements of interest may not
4582 actually be adjacent---for example, if you are interested in the values
4583 of pointers in an array. One useful work-around in this situation is
4584 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4585 variables}) as a counter in an expression that prints the first
4586 interesting value, and then repeat that expression via @key{RET}. For
4587 instance, suppose you have an array @code{dtab} of pointers to
4588 structures, and you are interested in the values of a field @code{fv}
4589 in each structure. Here is an example of what you might type:
4599 @node Output Formats
4600 @section Output formats
4602 @cindex formatted output
4603 @cindex output formats
4604 By default, @value{GDBN} prints a value according to its data type. Sometimes
4605 this is not what you want. For example, you might want to print a number
4606 in hex, or a pointer in decimal. Or you might want to view data in memory
4607 at a certain address as a character string or as an instruction. To do
4608 these things, specify an @dfn{output format} when you print a value.
4610 The simplest use of output formats is to say how to print a value
4611 already computed. This is done by starting the arguments of the
4612 @code{print} command with a slash and a format letter. The format
4613 letters supported are:
4617 Regard the bits of the value as an integer, and print the integer in
4621 Print as integer in signed decimal.
4624 Print as integer in unsigned decimal.
4627 Print as integer in octal.
4630 Print as integer in binary. The letter @samp{t} stands for ``two''.
4631 @footnote{@samp{b} cannot be used because these format letters are also
4632 used with the @code{x} command, where @samp{b} stands for ``byte'';
4633 see @ref{Memory,,Examining memory}.}
4636 @cindex unknown address, locating
4637 Print as an address, both absolute in hexadecimal and as an offset from
4638 the nearest preceding symbol. You can use this format used to discover
4639 where (in what function) an unknown address is located:
4642 (@value{GDBP}) p/a 0x54320
4643 $3 = 0x54320 <_initialize_vx+396>
4647 Regard as an integer and print it as a character constant.
4650 Regard the bits of the value as a floating point number and print
4651 using typical floating point syntax.
4654 For example, to print the program counter in hex (@pxref{Registers}), type
4661 Note that no space is required before the slash; this is because command
4662 names in @value{GDBN} cannot contain a slash.
4664 To reprint the last value in the value history with a different format,
4665 you can use the @code{print} command with just a format and no
4666 expression. For example, @samp{p/x} reprints the last value in hex.
4669 @section Examining memory
4671 You can use the command @code{x} (for ``examine'') to examine memory in
4672 any of several formats, independently of your program's data types.
4674 @cindex examining memory
4676 @kindex x @r{(examine memory)}
4677 @item x/@var{nfu} @var{addr}
4680 Use the @code{x} command to examine memory.
4683 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4684 much memory to display and how to format it; @var{addr} is an
4685 expression giving the address where you want to start displaying memory.
4686 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4687 Several commands set convenient defaults for @var{addr}.
4690 @item @var{n}, the repeat count
4691 The repeat count is a decimal integer; the default is 1. It specifies
4692 how much memory (counting by units @var{u}) to display.
4693 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4696 @item @var{f}, the display format
4697 The display format is one of the formats used by @code{print},
4698 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4699 The default is @samp{x} (hexadecimal) initially.
4700 The default changes each time you use either @code{x} or @code{print}.
4702 @item @var{u}, the unit size
4703 The unit size is any of
4709 Halfwords (two bytes).
4711 Words (four bytes). This is the initial default.
4713 Giant words (eight bytes).
4716 Each time you specify a unit size with @code{x}, that size becomes the
4717 default unit the next time you use @code{x}. (For the @samp{s} and
4718 @samp{i} formats, the unit size is ignored and is normally not written.)
4720 @item @var{addr}, starting display address
4721 @var{addr} is the address where you want @value{GDBN} to begin displaying
4722 memory. The expression need not have a pointer value (though it may);
4723 it is always interpreted as an integer address of a byte of memory.
4724 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4725 @var{addr} is usually just after the last address examined---but several
4726 other commands also set the default address: @code{info breakpoints} (to
4727 the address of the last breakpoint listed), @code{info line} (to the
4728 starting address of a line), and @code{print} (if you use it to display
4729 a value from memory).
4732 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4733 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4734 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4735 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4736 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
4738 Since the letters indicating unit sizes are all distinct from the
4739 letters specifying output formats, you do not have to remember whether
4740 unit size or format comes first; either order works. The output
4741 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4742 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4744 Even though the unit size @var{u} is ignored for the formats @samp{s}
4745 and @samp{i}, you might still want to use a count @var{n}; for example,
4746 @samp{3i} specifies that you want to see three machine instructions,
4747 including any operands. The command @code{disassemble} gives an
4748 alternative way of inspecting machine instructions; see @ref{Machine
4749 Code,,Source and machine code}.
4751 All the defaults for the arguments to @code{x} are designed to make it
4752 easy to continue scanning memory with minimal specifications each time
4753 you use @code{x}. For example, after you have inspected three machine
4754 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4755 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4756 the repeat count @var{n} is used again; the other arguments default as
4757 for successive uses of @code{x}.
4759 @cindex @code{$_}, @code{$__}, and value history
4760 The addresses and contents printed by the @code{x} command are not saved
4761 in the value history because there is often too much of them and they
4762 would get in the way. Instead, @value{GDBN} makes these values available for
4763 subsequent use in expressions as values of the convenience variables
4764 @code{$_} and @code{$__}. After an @code{x} command, the last address
4765 examined is available for use in expressions in the convenience variable
4766 @code{$_}. The contents of that address, as examined, are available in
4767 the convenience variable @code{$__}.
4769 If the @code{x} command has a repeat count, the address and contents saved
4770 are from the last memory unit printed; this is not the same as the last
4771 address printed if several units were printed on the last line of output.
4774 @section Automatic display
4775 @cindex automatic display
4776 @cindex display of expressions
4778 If you find that you want to print the value of an expression frequently
4779 (to see how it changes), you might want to add it to the @dfn{automatic
4780 display list} so that @value{GDBN} prints its value each time your program stops.
4781 Each expression added to the list is given a number to identify it;
4782 to remove an expression from the list, you specify that number.
4783 The automatic display looks like this:
4787 3: bar[5] = (struct hack *) 0x3804
4791 This display shows item numbers, expressions and their current values. As with
4792 displays you request manually using @code{x} or @code{print}, you can
4793 specify the output format you prefer; in fact, @code{display} decides
4794 whether to use @code{print} or @code{x} depending on how elaborate your
4795 format specification is---it uses @code{x} if you specify a unit size,
4796 or one of the two formats (@samp{i} and @samp{s}) that are only
4797 supported by @code{x}; otherwise it uses @code{print}.
4801 @item display @var{expr}
4802 Add the expression @var{expr} to the list of expressions to display
4803 each time your program stops. @xref{Expressions, ,Expressions}.
4805 @code{display} does not repeat if you press @key{RET} again after using it.
4807 @item display/@var{fmt} @var{expr}
4808 For @var{fmt} specifying only a display format and not a size or
4809 count, add the expression @var{expr} to the auto-display list but
4810 arrange to display it each time in the specified format @var{fmt}.
4811 @xref{Output Formats,,Output formats}.
4813 @item display/@var{fmt} @var{addr}
4814 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4815 number of units, add the expression @var{addr} as a memory address to
4816 be examined each time your program stops. Examining means in effect
4817 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4820 For example, @samp{display/i $pc} can be helpful, to see the machine
4821 instruction about to be executed each time execution stops (@samp{$pc}
4822 is a common name for the program counter; @pxref{Registers, ,Registers}).
4825 @kindex delete display
4827 @item undisplay @var{dnums}@dots{}
4828 @itemx delete display @var{dnums}@dots{}
4829 Remove item numbers @var{dnums} from the list of expressions to display.
4831 @code{undisplay} does not repeat if you press @key{RET} after using it.
4832 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4834 @kindex disable display
4835 @item disable display @var{dnums}@dots{}
4836 Disable the display of item numbers @var{dnums}. A disabled display
4837 item is not printed automatically, but is not forgotten. It may be
4838 enabled again later.
4840 @kindex enable display
4841 @item enable display @var{dnums}@dots{}
4842 Enable display of item numbers @var{dnums}. It becomes effective once
4843 again in auto display of its expression, until you specify otherwise.
4846 Display the current values of the expressions on the list, just as is
4847 done when your program stops.
4849 @kindex info display
4851 Print the list of expressions previously set up to display
4852 automatically, each one with its item number, but without showing the
4853 values. This includes disabled expressions, which are marked as such.
4854 It also includes expressions which would not be displayed right now
4855 because they refer to automatic variables not currently available.
4858 If a display expression refers to local variables, then it does not make
4859 sense outside the lexical context for which it was set up. Such an
4860 expression is disabled when execution enters a context where one of its
4861 variables is not defined. For example, if you give the command
4862 @code{display last_char} while inside a function with an argument
4863 @code{last_char}, @value{GDBN} displays this argument while your program
4864 continues to stop inside that function. When it stops elsewhere---where
4865 there is no variable @code{last_char}---the display is disabled
4866 automatically. The next time your program stops where @code{last_char}
4867 is meaningful, you can enable the display expression once again.
4869 @node Print Settings
4870 @section Print settings
4872 @cindex format options
4873 @cindex print settings
4874 @value{GDBN} provides the following ways to control how arrays, structures,
4875 and symbols are printed.
4878 These settings are useful for debugging programs in any language:
4881 @kindex set print address
4882 @item set print address
4883 @itemx set print address on
4884 @value{GDBN} prints memory addresses showing the location of stack
4885 traces, structure values, pointer values, breakpoints, and so forth,
4886 even when it also displays the contents of those addresses. The default
4887 is @code{on}. For example, this is what a stack frame display looks like with
4888 @code{set print address on}:
4893 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4895 530 if (lquote != def_lquote)
4899 @item set print address off
4900 Do not print addresses when displaying their contents. For example,
4901 this is the same stack frame displayed with @code{set print address off}:
4905 (@value{GDBP}) set print addr off
4907 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4908 530 if (lquote != def_lquote)
4912 You can use @samp{set print address off} to eliminate all machine
4913 dependent displays from the @value{GDBN} interface. For example, with
4914 @code{print address off}, you should get the same text for backtraces on
4915 all machines---whether or not they involve pointer arguments.
4917 @kindex show print address
4918 @item show print address
4919 Show whether or not addresses are to be printed.
4922 When @value{GDBN} prints a symbolic address, it normally prints the
4923 closest earlier symbol plus an offset. If that symbol does not uniquely
4924 identify the address (for example, it is a name whose scope is a single
4925 source file), you may need to clarify. One way to do this is with
4926 @code{info line}, for example @samp{info line *0x4537}. Alternately,
4927 you can set @value{GDBN} to print the source file and line number when
4928 it prints a symbolic address:
4931 @kindex set print symbol-filename
4932 @item set print symbol-filename on
4933 Tell @value{GDBN} to print the source file name and line number of a
4934 symbol in the symbolic form of an address.
4936 @item set print symbol-filename off
4937 Do not print source file name and line number of a symbol. This is the
4940 @kindex show print symbol-filename
4941 @item show print symbol-filename
4942 Show whether or not @value{GDBN} will print the source file name and
4943 line number of a symbol in the symbolic form of an address.
4946 Another situation where it is helpful to show symbol filenames and line
4947 numbers is when disassembling code; @value{GDBN} shows you the line
4948 number and source file that corresponds to each instruction.
4950 Also, you may wish to see the symbolic form only if the address being
4951 printed is reasonably close to the closest earlier symbol:
4954 @kindex set print max-symbolic-offset
4955 @item set print max-symbolic-offset @var{max-offset}
4956 Tell @value{GDBN} to only display the symbolic form of an address if the
4957 offset between the closest earlier symbol and the address is less than
4958 @var{max-offset}. The default is 0, which tells @value{GDBN}
4959 to always print the symbolic form of an address if any symbol precedes it.
4961 @kindex show print max-symbolic-offset
4962 @item show print max-symbolic-offset
4963 Ask how large the maximum offset is that @value{GDBN} prints in a
4967 @cindex wild pointer, interpreting
4968 @cindex pointer, finding referent
4969 If you have a pointer and you are not sure where it points, try
4970 @samp{set print symbol-filename on}. Then you can determine the name
4971 and source file location of the variable where it points, using
4972 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
4973 For example, here @value{GDBN} shows that a variable @code{ptt} points
4974 at another variable @code{t}, defined in @file{hi2.c}:
4977 (@value{GDBP}) set print symbol-filename on
4978 (@value{GDBP}) p/a ptt
4979 $4 = 0xe008 <t in hi2.c>
4983 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
4984 does not show the symbol name and filename of the referent, even with
4985 the appropriate @code{set print} options turned on.
4988 Other settings control how different kinds of objects are printed:
4991 @kindex set print array
4992 @item set print array
4993 @itemx set print array on
4994 Pretty print arrays. This format is more convenient to read,
4995 but uses more space. The default is off.
4997 @item set print array off
4998 Return to compressed format for arrays.
5000 @kindex show print array
5001 @item show print array
5002 Show whether compressed or pretty format is selected for displaying
5005 @kindex set print elements
5006 @item set print elements @var{number-of-elements}
5007 Set a limit on how many elements of an array @value{GDBN} will print.
5008 If @value{GDBN} is printing a large array, it stops printing after it has
5009 printed the number of elements set by the @code{set print elements} command.
5010 This limit also applies to the display of strings.
5011 When @value{GDBN} starts, this limit is set to 200.
5012 Setting @var{number-of-elements} to zero means that the printing is unlimited.
5014 @kindex show print elements
5015 @item show print elements
5016 Display the number of elements of a large array that @value{GDBN} will print.
5017 If the number is 0, then the printing is unlimited.
5019 @kindex set print null-stop
5020 @item set print null-stop
5021 Cause @value{GDBN} to stop printing the characters of an array when the first
5022 @sc{null} is encountered. This is useful when large arrays actually
5023 contain only short strings.
5026 @kindex set print pretty
5027 @item set print pretty on
5028 Cause @value{GDBN} to print structures in an indented format with one member
5029 per line, like this:
5044 @item set print pretty off
5045 Cause @value{GDBN} to print structures in a compact format, like this:
5049 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
5050 meat = 0x54 "Pork"@}
5055 This is the default format.
5057 @kindex show print pretty
5058 @item show print pretty
5059 Show which format @value{GDBN} is using to print structures.
5061 @kindex set print sevenbit-strings
5062 @item set print sevenbit-strings on
5063 Print using only seven-bit characters; if this option is set,
5064 @value{GDBN} displays any eight-bit characters (in strings or
5065 character values) using the notation @code{\}@var{nnn}. This setting is
5066 best if you are working in English (@sc{ascii}) and you use the
5067 high-order bit of characters as a marker or ``meta'' bit.
5069 @item set print sevenbit-strings off
5070 Print full eight-bit characters. This allows the use of more
5071 international character sets, and is the default.
5073 @kindex show print sevenbit-strings
5074 @item show print sevenbit-strings
5075 Show whether or not @value{GDBN} is printing only seven-bit characters.
5077 @kindex set print union
5078 @item set print union on
5079 Tell @value{GDBN} to print unions which are contained in structures. This
5080 is the default setting.
5082 @item set print union off
5083 Tell @value{GDBN} not to print unions which are contained in structures.
5085 @kindex show print union
5086 @item show print union
5087 Ask @value{GDBN} whether or not it will print unions which are contained in
5090 For example, given the declarations
5093 typedef enum @{Tree, Bug@} Species;
5094 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5095 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5106 struct thing foo = @{Tree, @{Acorn@}@};
5110 with @code{set print union on} in effect @samp{p foo} would print
5113 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5117 and with @code{set print union off} in effect it would print
5120 $1 = @{it = Tree, form = @{...@}@}
5126 These settings are of interest when debugging C++ programs:
5130 @kindex set print demangle
5131 @item set print demangle
5132 @itemx set print demangle on
5133 Print C++ names in their source form rather than in the encoded
5134 (``mangled'') form passed to the assembler and linker for type-safe
5135 linkage. The default is on.
5137 @kindex show print demangle
5138 @item show print demangle
5139 Show whether C++ names are printed in mangled or demangled form.
5141 @kindex set print asm-demangle
5142 @item set print asm-demangle
5143 @itemx set print asm-demangle on
5144 Print C++ names in their source form rather than their mangled form, even
5145 in assembler code printouts such as instruction disassemblies.
5148 @kindex show print asm-demangle
5149 @item show print asm-demangle
5150 Show whether C++ names in assembly listings are printed in mangled
5153 @kindex set demangle-style
5154 @cindex C++ symbol decoding style
5155 @cindex symbol decoding style, C++
5156 @item set demangle-style @var{style}
5157 Choose among several encoding schemes used by different compilers to
5158 represent C++ names. The choices for @var{style} are currently:
5162 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5165 Decode based on the @sc{gnu} C++ compiler (@code{g++}) encoding algorithm.
5166 This is the default.
5169 Decode based on the HP ANSI C++ (@code{aCC}) encoding algorithm.
5172 Decode based on the Lucid C++ compiler (@code{lcc}) encoding algorithm.
5175 Decode using the algorithm in the @cite{C++ Annotated Reference Manual}.
5176 @strong{Warning:} this setting alone is not sufficient to allow
5177 debugging @code{cfront}-generated executables. @value{GDBN} would
5178 require further enhancement to permit that.
5181 If you omit @var{style}, you will see a list of possible formats.
5183 @kindex show demangle-style
5184 @item show demangle-style
5185 Display the encoding style currently in use for decoding C++ symbols.
5187 @kindex set print object
5188 @item set print object
5189 @itemx set print object on
5190 When displaying a pointer to an object, identify the @emph{actual}
5191 (derived) type of the object rather than the @emph{declared} type, using
5192 the virtual function table.
5194 @item set print object off
5195 Display only the declared type of objects, without reference to the
5196 virtual function table. This is the default setting.
5198 @kindex show print object
5199 @item show print object
5200 Show whether actual, or declared, object types are displayed.
5202 @kindex set print static-members
5203 @item set print static-members
5204 @itemx set print static-members on
5205 Print static members when displaying a C++ object. The default is on.
5207 @item set print static-members off
5208 Do not print static members when displaying a C++ object.
5210 @kindex show print static-members
5211 @item show print static-members
5212 Show whether C++ static members are printed, or not.
5214 @c These don't work with HP ANSI C++ yet.
5215 @kindex set print vtbl
5216 @item set print vtbl
5217 @itemx set print vtbl on
5218 Pretty print C++ virtual function tables. The default is off.
5219 (The @code{vtbl} commands do not work on programs compiled with the HP
5220 ANSI C++ compiler (@code{aCC}).)
5222 @item set print vtbl off
5223 Do not pretty print C++ virtual function tables.
5225 @kindex show print vtbl
5226 @item show print vtbl
5227 Show whether C++ virtual function tables are pretty printed, or not.
5231 @section Value history
5233 @cindex value history
5234 Values printed by the @code{print} command are saved in the @value{GDBN}
5235 @dfn{value history}. This allows you to refer to them in other expressions.
5236 Values are kept until the symbol table is re-read or discarded
5237 (for example with the @code{file} or @code{symbol-file} commands).
5238 When the symbol table changes, the value history is discarded,
5239 since the values may contain pointers back to the types defined in the
5244 @cindex history number
5245 The values printed are given @dfn{history numbers} by which you can
5246 refer to them. These are successive integers starting with one.
5247 @code{print} shows you the history number assigned to a value by
5248 printing @samp{$@var{num} = } before the value; here @var{num} is the
5251 To refer to any previous value, use @samp{$} followed by the value's
5252 history number. The way @code{print} labels its output is designed to
5253 remind you of this. Just @code{$} refers to the most recent value in
5254 the history, and @code{$$} refers to the value before that.
5255 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5256 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5257 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5259 For example, suppose you have just printed a pointer to a structure and
5260 want to see the contents of the structure. It suffices to type
5266 If you have a chain of structures where the component @code{next} points
5267 to the next one, you can print the contents of the next one with this:
5274 You can print successive links in the chain by repeating this
5275 command---which you can do by just typing @key{RET}.
5277 Note that the history records values, not expressions. If the value of
5278 @code{x} is 4 and you type these commands:
5286 then the value recorded in the value history by the @code{print} command
5287 remains 4 even though the value of @code{x} has changed.
5292 Print the last ten values in the value history, with their item numbers.
5293 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5294 values} does not change the history.
5296 @item show values @var{n}
5297 Print ten history values centered on history item number @var{n}.
5300 Print ten history values just after the values last printed. If no more
5301 values are available, @code{show values +} produces no display.
5304 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5305 same effect as @samp{show values +}.
5307 @node Convenience Vars
5308 @section Convenience variables
5310 @cindex convenience variables
5311 @value{GDBN} provides @dfn{convenience variables} that you can use within
5312 @value{GDBN} to hold on to a value and refer to it later. These variables
5313 exist entirely within @value{GDBN}; they are not part of your program, and
5314 setting a convenience variable has no direct effect on further execution
5315 of your program. That is why you can use them freely.
5317 Convenience variables are prefixed with @samp{$}. Any name preceded by
5318 @samp{$} can be used for a convenience variable, unless it is one of
5319 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
5320 (Value history references, in contrast, are @emph{numbers} preceded
5321 by @samp{$}. @xref{Value History, ,Value history}.)
5323 You can save a value in a convenience variable with an assignment
5324 expression, just as you would set a variable in your program.
5328 set $foo = *object_ptr
5332 would save in @code{$foo} the value contained in the object pointed to by
5335 Using a convenience variable for the first time creates it, but its
5336 value is @code{void} until you assign a new value. You can alter the
5337 value with another assignment at any time.
5339 Convenience variables have no fixed types. You can assign a convenience
5340 variable any type of value, including structures and arrays, even if
5341 that variable already has a value of a different type. The convenience
5342 variable, when used as an expression, has the type of its current value.
5345 @kindex show convenience
5346 @item show convenience
5347 Print a list of convenience variables used so far, and their values.
5348 Abbreviated @code{show conv}.
5351 One of the ways to use a convenience variable is as a counter to be
5352 incremented or a pointer to be advanced. For example, to print
5353 a field from successive elements of an array of structures:
5357 print bar[$i++]->contents
5361 Repeat that command by typing @key{RET}.
5363 Some convenience variables are created automatically by @value{GDBN} and given
5364 values likely to be useful.
5367 @vindex $_@r{, convenience variable}
5369 The variable @code{$_} is automatically set by the @code{x} command to
5370 the last address examined (@pxref{Memory, ,Examining memory}). Other
5371 commands which provide a default address for @code{x} to examine also
5372 set @code{$_} to that address; these commands include @code{info line}
5373 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5374 except when set by the @code{x} command, in which case it is a pointer
5375 to the type of @code{$__}.
5377 @vindex $__@r{, convenience variable}
5379 The variable @code{$__} is automatically set by the @code{x} command
5380 to the value found in the last address examined. Its type is chosen
5381 to match the format in which the data was printed.
5384 @vindex $_exitcode@r{, convenience variable}
5385 The variable @code{$_exitcode} is automatically set to the exit code when
5386 the program being debugged terminates.
5389 On HP-UX systems, if you refer to a function or variable name that
5390 begins with a dollar sign, @value{GDBN} searches for a user or system
5391 name first, before it searches for a convenience variable.
5397 You can refer to machine register contents, in expressions, as variables
5398 with names starting with @samp{$}. The names of registers are different
5399 for each machine; use @code{info registers} to see the names used on
5403 @kindex info registers
5404 @item info registers
5405 Print the names and values of all registers except floating-point
5406 registers (in the selected stack frame).
5408 @kindex info all-registers
5409 @cindex floating point registers
5410 @item info all-registers
5411 Print the names and values of all registers, including floating-point
5414 @item info registers @var{regname} @dots{}
5415 Print the @dfn{relativized} value of each specified register @var{regname}.
5416 As discussed in detail below, register values are normally relative to
5417 the selected stack frame. @var{regname} may be any register name valid on
5418 the machine you are using, with or without the initial @samp{$}.
5421 @value{GDBN} has four ``standard'' register names that are available (in
5422 expressions) on most machines---whenever they do not conflict with an
5423 architecture's canonical mnemonics for registers. The register names
5424 @code{$pc} and @code{$sp} are used for the program counter register and
5425 the stack pointer. @code{$fp} is used for a register that contains a
5426 pointer to the current stack frame, and @code{$ps} is used for a
5427 register that contains the processor status. For example,
5428 you could print the program counter in hex with
5435 or print the instruction to be executed next with
5442 or add four to the stack pointer@footnote{This is a way of removing
5443 one word from the stack, on machines where stacks grow downward in
5444 memory (most machines, nowadays). This assumes that the innermost
5445 stack frame is selected; setting @code{$sp} is not allowed when other
5446 stack frames are selected. To pop entire frames off the stack,
5447 regardless of machine architecture, use @code{return};
5448 see @ref{Returning, ,Returning from a function}.} with
5454 Whenever possible, these four standard register names are available on
5455 your machine even though the machine has different canonical mnemonics,
5456 so long as there is no conflict. The @code{info registers} command
5457 shows the canonical names. For example, on the SPARC, @code{info
5458 registers} displays the processor status register as @code{$psr} but you
5459 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
5460 is an alias for the @sc{eflags} register.
5462 @value{GDBN} always considers the contents of an ordinary register as an
5463 integer when the register is examined in this way. Some machines have
5464 special registers which can hold nothing but floating point; these
5465 registers are considered to have floating point values. There is no way
5466 to refer to the contents of an ordinary register as floating point value
5467 (although you can @emph{print} it as a floating point value with
5468 @samp{print/f $@var{regname}}).
5470 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5471 means that the data format in which the register contents are saved by
5472 the operating system is not the same one that your program normally
5473 sees. For example, the registers of the 68881 floating point
5474 coprocessor are always saved in ``extended'' (raw) format, but all C
5475 programs expect to work with ``double'' (virtual) format. In such
5476 cases, @value{GDBN} normally works with the virtual format only (the format
5477 that makes sense for your program), but the @code{info registers} command
5478 prints the data in both formats.
5480 Normally, register values are relative to the selected stack frame
5481 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5482 value that the register would contain if all stack frames farther in
5483 were exited and their saved registers restored. In order to see the
5484 true contents of hardware registers, you must select the innermost
5485 frame (with @samp{frame 0}).
5487 However, @value{GDBN} must deduce where registers are saved, from the machine
5488 code generated by your compiler. If some registers are not saved, or if
5489 @value{GDBN} is unable to locate the saved registers, the selected stack
5490 frame makes no difference.
5492 @node Floating Point Hardware
5493 @section Floating point hardware
5494 @cindex floating point
5496 Depending on the configuration, @value{GDBN} may be able to give
5497 you more information about the status of the floating point hardware.
5502 Display hardware-dependent information about the floating
5503 point unit. The exact contents and layout vary depending on the
5504 floating point chip. Currently, @samp{info float} is supported on
5505 the ARM and x86 machines.
5508 @node Memory Region Attributes
5509 @section Memory Region Attributes
5510 @cindex memory region attributes
5512 @dfn{Memory region attributes} allow you to describe special handling
5513 required by regions of your target's memory. @value{GDBN} uses attributes
5514 to determine whether to allow certain types of memory accesses; whether to
5515 use specific width accesses; and whether to cache target memory.
5517 Defined memory regions can be individually enabled and disabled. When a
5518 memory region is disabled, @value{GDBN} uses the default attributes when
5519 accessing memory in that region. Similarly, if no memory regions have
5520 been defined, @value{GDBN} uses the default attributes when accessing
5523 When a memory region is defined, it is given a number to identify it;
5524 to enable, disable, or remove a memory region, you specify that number.
5528 @item mem @var{address1} @var{address1} @var{attributes}@dots{}
5529 Define memory region bounded by @var{address1} and @var{address2}
5530 with attributes @var{attributes}@dots{}.
5533 @item delete mem @var{nums}@dots{}
5534 Remove memory region numbers @var{nums}.
5537 @item disable mem @var{nums}@dots{}
5538 Disable memory region numbers @var{nums}.
5539 A disabled memory region is not forgotten.
5540 It may be enabled again later.
5543 @item enable mem @var{nums}@dots{}
5544 Enable memory region numbers @var{nums}.
5548 Print a table of all defined memory regions, with the following columns
5552 @item Memory Region Number
5553 @item Enabled or Disabled.
5554 Enabled memory regions are marked with @samp{y}.
5555 Disabled memory regions are marked with @samp{n}.
5558 The address defining the inclusive lower bound of the memory region.
5561 The address defining the exclusive upper bound of the memory region.
5564 The list of attributes set for this memory region.
5569 @subsection Attributes
5571 @subsubsection Memory Access Mode
5572 The access mode attributes set whether @value{GDBN} may make read or
5573 write accesses to a memory region.
5575 While these attributes prevent @value{GDBN} from performing invalid
5576 memory accesses, they do nothing to prevent the target system, I/O DMA,
5577 etc. from accessing memory.
5581 Memory is read only.
5583 Memory is write only.
5585 Memory is read/write (default).
5588 @subsubsection Memory Access Size
5589 The acccess size attributes tells @value{GDBN} to use specific sized
5590 accesses in the memory region. Often memory mapped device registers
5591 require specific sized accesses. If no access size attribute is
5592 specified, @value{GDBN} may use accesses of any size.
5596 Use 8 bit memory accesses.
5598 Use 16 bit memory accesses.
5600 Use 32 bit memory accesses.
5602 Use 64 bit memory accesses.
5605 @c @subsubsection Hardware/Software Breakpoints
5606 @c The hardware/software breakpoint attributes set whether @value{GDBN}
5607 @c will use hardware or software breakpoints for the internal breakpoints
5608 @c used by the step, next, finish, until, etc. commands.
5612 @c Always use hardware breakpoints
5613 @c @item swbreak (default)
5616 @subsubsection Data Cache
5617 The data cache attributes set whether @value{GDBN} will cache target
5618 memory. While this generally improves performance by reducing debug
5619 protocol overhead, it can lead to incorrect results because @value{GDBN}
5620 does not know about volatile variables or memory mapped device
5625 Enable @value{GDBN} to cache target memory.
5626 @item nocache (default)
5627 Disable @value{GDBN} from caching target memory.
5630 @c @subsubsection Memory Write Verification
5631 @c The memory write verification attributes set whether @value{GDBN}
5632 @c will re-reads data after each write to verify the write was successful.
5636 @c @item noverify (default)
5640 @chapter Using @value{GDBN} with Different Languages
5643 Although programming languages generally have common aspects, they are
5644 rarely expressed in the same manner. For instance, in ANSI C,
5645 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
5646 Modula-2, it is accomplished by @code{p^}. Values can also be
5647 represented (and displayed) differently. Hex numbers in C appear as
5648 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
5650 @cindex working language
5651 Language-specific information is built into @value{GDBN} for some languages,
5652 allowing you to express operations like the above in your program's
5653 native language, and allowing @value{GDBN} to output values in a manner
5654 consistent with the syntax of your program's native language. The
5655 language you use to build expressions is called the @dfn{working
5659 * Setting:: Switching between source languages
5660 * Show:: Displaying the language
5661 * Checks:: Type and range checks
5662 * Support:: Supported languages
5666 @section Switching between source languages
5668 There are two ways to control the working language---either have @value{GDBN}
5669 set it automatically, or select it manually yourself. You can use the
5670 @code{set language} command for either purpose. On startup, @value{GDBN}
5671 defaults to setting the language automatically. The working language is
5672 used to determine how expressions you type are interpreted, how values
5675 In addition to the working language, every source file that
5676 @value{GDBN} knows about has its own working language. For some object
5677 file formats, the compiler might indicate which language a particular
5678 source file is in. However, most of the time @value{GDBN} infers the
5679 language from the name of the file. The language of a source file
5680 controls whether C++ names are demangled---this way @code{backtrace} can
5681 show each frame appropriately for its own language. There is no way to
5682 set the language of a source file from within @value{GDBN}, but you can
5683 set the language associated with a filename extension. @xref{Show, ,
5684 Displaying the language}.
5686 This is most commonly a problem when you use a program, such
5687 as @code{cfront} or @code{f2c}, that generates C but is written in
5688 another language. In that case, make the
5689 program use @code{#line} directives in its C output; that way
5690 @value{GDBN} will know the correct language of the source code of the original
5691 program, and will display that source code, not the generated C code.
5694 * Filenames:: Filename extensions and languages.
5695 * Manually:: Setting the working language manually
5696 * Automatically:: Having @value{GDBN} infer the source language
5700 @subsection List of filename extensions and languages
5702 If a source file name ends in one of the following extensions, then
5703 @value{GDBN} infers that its language is the one indicated.
5728 Modula-2 source file
5732 Assembler source file. This actually behaves almost like C, but
5733 @value{GDBN} does not skip over function prologues when stepping.
5736 In addition, you may set the language associated with a filename
5737 extension. @xref{Show, , Displaying the language}.
5740 @subsection Setting the working language
5742 If you allow @value{GDBN} to set the language automatically,
5743 expressions are interpreted the same way in your debugging session and
5746 @kindex set language
5747 If you wish, you may set the language manually. To do this, issue the
5748 command @samp{set language @var{lang}}, where @var{lang} is the name of
5750 @code{c} or @code{modula-2}.
5751 For a list of the supported languages, type @samp{set language}.
5753 Setting the language manually prevents @value{GDBN} from updating the working
5754 language automatically. This can lead to confusion if you try
5755 to debug a program when the working language is not the same as the
5756 source language, when an expression is acceptable to both
5757 languages---but means different things. For instance, if the current
5758 source file were written in C, and @value{GDBN} was parsing Modula-2, a
5766 might not have the effect you intended. In C, this means to add
5767 @code{b} and @code{c} and place the result in @code{a}. The result
5768 printed would be the value of @code{a}. In Modula-2, this means to compare
5769 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
5772 @subsection Having @value{GDBN} infer the source language
5774 To have @value{GDBN} set the working language automatically, use
5775 @samp{set language local} or @samp{set language auto}. @value{GDBN}
5776 then infers the working language. That is, when your program stops in a
5777 frame (usually by encountering a breakpoint), @value{GDBN} sets the
5778 working language to the language recorded for the function in that
5779 frame. If the language for a frame is unknown (that is, if the function
5780 or block corresponding to the frame was defined in a source file that
5781 does not have a recognized extension), the current working language is
5782 not changed, and @value{GDBN} issues a warning.
5784 This may not seem necessary for most programs, which are written
5785 entirely in one source language. However, program modules and libraries
5786 written in one source language can be used by a main program written in
5787 a different source language. Using @samp{set language auto} in this
5788 case frees you from having to set the working language manually.
5791 @section Displaying the language
5793 The following commands help you find out which language is the
5794 working language, and also what language source files were written in.
5796 @kindex show language
5797 @kindex info frame@r{, show the source language}
5798 @kindex info source@r{, show the source language}
5801 Display the current working language. This is the
5802 language you can use with commands such as @code{print} to
5803 build and compute expressions that may involve variables in your program.
5806 Display the source language for this frame. This language becomes the
5807 working language if you use an identifier from this frame.
5808 @xref{Frame Info, ,Information about a frame}, to identify the other
5809 information listed here.
5812 Display the source language of this source file.
5813 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
5814 information listed here.
5817 In unusual circumstances, you may have source files with extensions
5818 not in the standard list. You can then set the extension associated
5819 with a language explicitly:
5821 @kindex set extension-language
5822 @kindex info extensions
5824 @item set extension-language @var{.ext} @var{language}
5825 Set source files with extension @var{.ext} to be assumed to be in
5826 the source language @var{language}.
5828 @item info extensions
5829 List all the filename extensions and the associated languages.
5833 @section Type and range checking
5836 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
5837 checking are included, but they do not yet have any effect. This
5838 section documents the intended facilities.
5840 @c FIXME remove warning when type/range code added
5842 Some languages are designed to guard you against making seemingly common
5843 errors through a series of compile- and run-time checks. These include
5844 checking the type of arguments to functions and operators, and making
5845 sure mathematical overflows are caught at run time. Checks such as
5846 these help to ensure a program's correctness once it has been compiled
5847 by eliminating type mismatches, and providing active checks for range
5848 errors when your program is running.
5850 @value{GDBN} can check for conditions like the above if you wish.
5851 Although @value{GDBN} does not check the statements in your program, it
5852 can check expressions entered directly into @value{GDBN} for evaluation via
5853 the @code{print} command, for example. As with the working language,
5854 @value{GDBN} can also decide whether or not to check automatically based on
5855 your program's source language. @xref{Support, ,Supported languages},
5856 for the default settings of supported languages.
5859 * Type Checking:: An overview of type checking
5860 * Range Checking:: An overview of range checking
5863 @cindex type checking
5864 @cindex checks, type
5866 @subsection An overview of type checking
5868 Some languages, such as Modula-2, are strongly typed, meaning that the
5869 arguments to operators and functions have to be of the correct type,
5870 otherwise an error occurs. These checks prevent type mismatch
5871 errors from ever causing any run-time problems. For example,
5879 The second example fails because the @code{CARDINAL} 1 is not
5880 type-compatible with the @code{REAL} 2.3.
5882 For the expressions you use in @value{GDBN} commands, you can tell the
5883 @value{GDBN} type checker to skip checking;
5884 to treat any mismatches as errors and abandon the expression;
5885 or to only issue warnings when type mismatches occur,
5886 but evaluate the expression anyway. When you choose the last of
5887 these, @value{GDBN} evaluates expressions like the second example above, but
5888 also issues a warning.
5890 Even if you turn type checking off, there may be other reasons
5891 related to type that prevent @value{GDBN} from evaluating an expression.
5892 For instance, @value{GDBN} does not know how to add an @code{int} and
5893 a @code{struct foo}. These particular type errors have nothing to do
5894 with the language in use, and usually arise from expressions, such as
5895 the one described above, which make little sense to evaluate anyway.
5897 Each language defines to what degree it is strict about type. For
5898 instance, both Modula-2 and C require the arguments to arithmetical
5899 operators to be numbers. In C, enumerated types and pointers can be
5900 represented as numbers, so that they are valid arguments to mathematical
5901 operators. @xref{Support, ,Supported languages}, for further
5902 details on specific languages.
5904 @value{GDBN} provides some additional commands for controlling the type checker:
5906 @kindex set check@r{, type}
5907 @kindex set check type
5908 @kindex show check type
5910 @item set check type auto
5911 Set type checking on or off based on the current working language.
5912 @xref{Support, ,Supported languages}, for the default settings for
5915 @item set check type on
5916 @itemx set check type off
5917 Set type checking on or off, overriding the default setting for the
5918 current working language. Issue a warning if the setting does not
5919 match the language default. If any type mismatches occur in
5920 evaluating an expression while type checking is on, @value{GDBN} prints a
5921 message and aborts evaluation of the expression.
5923 @item set check type warn
5924 Cause the type checker to issue warnings, but to always attempt to
5925 evaluate the expression. Evaluating the expression may still
5926 be impossible for other reasons. For example, @value{GDBN} cannot add
5927 numbers and structures.
5930 Show the current setting of the type checker, and whether or not @value{GDBN}
5931 is setting it automatically.
5934 @cindex range checking
5935 @cindex checks, range
5936 @node Range Checking
5937 @subsection An overview of range checking
5939 In some languages (such as Modula-2), it is an error to exceed the
5940 bounds of a type; this is enforced with run-time checks. Such range
5941 checking is meant to ensure program correctness by making sure
5942 computations do not overflow, or indices on an array element access do
5943 not exceed the bounds of the array.
5945 For expressions you use in @value{GDBN} commands, you can tell
5946 @value{GDBN} to treat range errors in one of three ways: ignore them,
5947 always treat them as errors and abandon the expression, or issue
5948 warnings but evaluate the expression anyway.
5950 A range error can result from numerical overflow, from exceeding an
5951 array index bound, or when you type a constant that is not a member
5952 of any type. Some languages, however, do not treat overflows as an
5953 error. In many implementations of C, mathematical overflow causes the
5954 result to ``wrap around'' to lower values---for example, if @var{m} is
5955 the largest integer value, and @var{s} is the smallest, then
5958 @var{m} + 1 @result{} @var{s}
5961 This, too, is specific to individual languages, and in some cases
5962 specific to individual compilers or machines. @xref{Support, ,
5963 Supported languages}, for further details on specific languages.
5965 @value{GDBN} provides some additional commands for controlling the range checker:
5967 @kindex set check@r{, range}
5968 @kindex set check range
5969 @kindex show check range
5971 @item set check range auto
5972 Set range checking on or off based on the current working language.
5973 @xref{Support, ,Supported languages}, for the default settings for
5976 @item set check range on
5977 @itemx set check range off
5978 Set range checking on or off, overriding the default setting for the
5979 current working language. A warning is issued if the setting does not
5980 match the language default. If a range error occurs and range checking is on,
5981 then a message is printed and evaluation of the expression is aborted.
5983 @item set check range warn
5984 Output messages when the @value{GDBN} range checker detects a range error,
5985 but attempt to evaluate the expression anyway. Evaluating the
5986 expression may still be impossible for other reasons, such as accessing
5987 memory that the process does not own (a typical example from many Unix
5991 Show the current setting of the range checker, and whether or not it is
5992 being set automatically by @value{GDBN}.
5996 @section Supported languages
5998 @value{GDBN} supports C, C++, Fortran, Java, Chill, assembly, and Modula-2.
5999 @c This is false ...
6000 Some @value{GDBN} features may be used in expressions regardless of the
6001 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
6002 and the @samp{@{type@}addr} construct (@pxref{Expressions,
6003 ,Expressions}) can be used with the constructs of any supported
6006 The following sections detail to what degree each source language is
6007 supported by @value{GDBN}. These sections are not meant to be language
6008 tutorials or references, but serve only as a reference guide to what the
6009 @value{GDBN} expression parser accepts, and what input and output
6010 formats should look like for different languages. There are many good
6011 books written on each of these languages; please look to these for a
6012 language reference or tutorial.
6016 * Modula-2:: Modula-2
6021 @subsection C and C++
6024 @cindex expressions in C or C++
6026 Since C and C++ are so closely related, many features of @value{GDBN} apply
6027 to both languages. Whenever this is the case, we discuss those languages
6031 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
6032 @cindex @sc{gnu} C++
6033 The C++ debugging facilities are jointly implemented by the C++
6034 compiler and @value{GDBN}. Therefore, to debug your C++ code
6035 effectively, you must compile your C++ programs with a supported
6036 C++ compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C++
6037 compiler (@code{aCC}).
6039 For best results when using @sc{gnu} C++, use the stabs debugging
6040 format. You can select that format explicitly with the @code{g++}
6041 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
6042 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
6043 CC, gcc.info, Using @sc{gnu} CC}, for more information.
6046 * C Operators:: C and C++ operators
6047 * C Constants:: C and C++ constants
6048 * C plus plus expressions:: C++ expressions
6049 * C Defaults:: Default settings for C and C++
6050 * C Checks:: C and C++ type and range checks
6051 * Debugging C:: @value{GDBN} and C
6052 * Debugging C plus plus:: @value{GDBN} features for C++
6056 @subsubsection C and C++ operators
6058 @cindex C and C++ operators
6060 Operators must be defined on values of specific types. For instance,
6061 @code{+} is defined on numbers, but not on structures. Operators are
6062 often defined on groups of types.
6064 For the purposes of C and C++, the following definitions hold:
6069 @emph{Integral types} include @code{int} with any of its storage-class
6070 specifiers; @code{char}; @code{enum}; and, for C++, @code{bool}.
6073 @emph{Floating-point types} include @code{float}, @code{double}, and
6074 @code{long double} (if supported by the target platform).
6077 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
6080 @emph{Scalar types} include all of the above.
6085 The following operators are supported. They are listed here
6086 in order of increasing precedence:
6090 The comma or sequencing operator. Expressions in a comma-separated list
6091 are evaluated from left to right, with the result of the entire
6092 expression being the last expression evaluated.
6095 Assignment. The value of an assignment expression is the value
6096 assigned. Defined on scalar types.
6099 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
6100 and translated to @w{@code{@var{a} = @var{a op b}}}.
6101 @w{@code{@var{op}=}} and @code{=} have the same precedence.
6102 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
6103 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
6106 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
6107 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
6111 Logical @sc{or}. Defined on integral types.
6114 Logical @sc{and}. Defined on integral types.
6117 Bitwise @sc{or}. Defined on integral types.
6120 Bitwise exclusive-@sc{or}. Defined on integral types.
6123 Bitwise @sc{and}. Defined on integral types.
6126 Equality and inequality. Defined on scalar types. The value of these
6127 expressions is 0 for false and non-zero for true.
6129 @item <@r{, }>@r{, }<=@r{, }>=
6130 Less than, greater than, less than or equal, greater than or equal.
6131 Defined on scalar types. The value of these expressions is 0 for false
6132 and non-zero for true.
6135 left shift, and right shift. Defined on integral types.
6138 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
6141 Addition and subtraction. Defined on integral types, floating-point types and
6144 @item *@r{, }/@r{, }%
6145 Multiplication, division, and modulus. Multiplication and division are
6146 defined on integral and floating-point types. Modulus is defined on
6150 Increment and decrement. When appearing before a variable, the
6151 operation is performed before the variable is used in an expression;
6152 when appearing after it, the variable's value is used before the
6153 operation takes place.
6156 Pointer dereferencing. Defined on pointer types. Same precedence as
6160 Address operator. Defined on variables. Same precedence as @code{++}.
6162 For debugging C++, @value{GDBN} implements a use of @samp{&} beyond what is
6163 allowed in the C++ language itself: you can use @samp{&(&@var{ref})}
6164 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
6165 where a C++ reference variable (declared with @samp{&@var{ref}}) is
6169 Negative. Defined on integral and floating-point types. Same
6170 precedence as @code{++}.
6173 Logical negation. Defined on integral types. Same precedence as
6177 Bitwise complement operator. Defined on integral types. Same precedence as
6182 Structure member, and pointer-to-structure member. For convenience,
6183 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
6184 pointer based on the stored type information.
6185 Defined on @code{struct} and @code{union} data.
6188 Dereferences of pointers to members.
6191 Array indexing. @code{@var{a}[@var{i}]} is defined as
6192 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
6195 Function parameter list. Same precedence as @code{->}.
6198 C++ scope resolution operator. Defined on @code{struct}, @code{union},
6199 and @code{class} types.
6202 Doubled colons also represent the @value{GDBN} scope operator
6203 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
6207 If an operator is redefined in the user code, @value{GDBN} usually
6208 attempts to invoke the redefined version instead of using the operator's
6216 @subsubsection C and C++ constants
6218 @cindex C and C++ constants
6220 @value{GDBN} allows you to express the constants of C and C++ in the
6225 Integer constants are a sequence of digits. Octal constants are
6226 specified by a leading @samp{0} (i.e. zero), and hexadecimal constants by
6227 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
6228 @samp{l}, specifying that the constant should be treated as a
6232 Floating point constants are a sequence of digits, followed by a decimal
6233 point, followed by a sequence of digits, and optionally followed by an
6234 exponent. An exponent is of the form:
6235 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
6236 sequence of digits. The @samp{+} is optional for positive exponents.
6237 A floating-point constant may also end with a letter @samp{f} or
6238 @samp{F}, specifying that the constant should be treated as being of
6239 the @code{float} (as opposed to the default @code{double}) type; or with
6240 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
6244 Enumerated constants consist of enumerated identifiers, or their
6245 integral equivalents.
6248 Character constants are a single character surrounded by single quotes
6249 (@code{'}), or a number---the ordinal value of the corresponding character
6250 (usually its @sc{ascii} value). Within quotes, the single character may
6251 be represented by a letter or by @dfn{escape sequences}, which are of
6252 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
6253 of the character's ordinal value; or of the form @samp{\@var{x}}, where
6254 @samp{@var{x}} is a predefined special character---for example,
6255 @samp{\n} for newline.
6258 String constants are a sequence of character constants surrounded by
6259 double quotes (@code{"}). Any valid character constant (as described
6260 above) may appear. Double quotes within the string must be preceded by
6261 a backslash, so for instance @samp{"a\"b'c"} is a string of five
6265 Pointer constants are an integral value. You can also write pointers
6266 to constants using the C operator @samp{&}.
6269 Array constants are comma-separated lists surrounded by braces @samp{@{}
6270 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
6271 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
6272 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
6276 * C plus plus expressions::
6283 @node C plus plus expressions
6284 @subsubsection C++ expressions
6286 @cindex expressions in C++
6287 @value{GDBN} expression handling can interpret most C++ expressions.
6289 @cindex C++ support, not in @sc{coff}
6290 @cindex @sc{coff} versus C++
6291 @cindex C++ and object formats
6292 @cindex object formats and C++
6293 @cindex a.out and C++
6294 @cindex @sc{ecoff} and C++
6295 @cindex @sc{xcoff} and C++
6296 @cindex @sc{elf}/stabs and C++
6297 @cindex @sc{elf}/@sc{dwarf} and C++
6298 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
6299 @c periodically whether this has happened...
6301 @emph{Warning:} @value{GDBN} can only debug C++ code if you use the
6302 proper compiler. Typically, C++ debugging depends on the use of
6303 additional debugging information in the symbol table, and thus requires
6304 special support. In particular, if your compiler generates a.out, MIPS
6305 @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the
6306 symbol table, these facilities are all available. (With @sc{gnu} CC,
6307 you can use the @samp{-gstabs} option to request stabs debugging
6308 extensions explicitly.) Where the object code format is standard
6309 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C++
6310 support in @value{GDBN} does @emph{not} work.
6315 @cindex member functions
6317 Member function calls are allowed; you can use expressions like
6320 count = aml->GetOriginal(x, y)
6323 @vindex this@r{, inside C@t{++} member functions}
6324 @cindex namespace in C++
6326 While a member function is active (in the selected stack frame), your
6327 expressions have the same namespace available as the member function;
6328 that is, @value{GDBN} allows implicit references to the class instance
6329 pointer @code{this} following the same rules as C++.
6331 @cindex call overloaded functions
6332 @cindex overloaded functions, calling
6333 @cindex type conversions in C++
6335 You can call overloaded functions; @value{GDBN} resolves the function
6336 call to the right definition, with some restrictions. @value{GDBN} does not
6337 perform overload resolution involving user-defined type conversions,
6338 calls to constructors, or instantiations of templates that do not exist
6339 in the program. It also cannot handle ellipsis argument lists or
6342 It does perform integral conversions and promotions, floating-point
6343 promotions, arithmetic conversions, pointer conversions, conversions of
6344 class objects to base classes, and standard conversions such as those of
6345 functions or arrays to pointers; it requires an exact match on the
6346 number of function arguments.
6348 Overload resolution is always performed, unless you have specified
6349 @code{set overload-resolution off}. @xref{Debugging C plus plus,
6350 ,@value{GDBN} features for C++}.
6352 You must specify @code{set overload-resolution off} in order to use an
6353 explicit function signature to call an overloaded function, as in
6355 p 'foo(char,int)'('x', 13)
6358 The @value{GDBN} command-completion facility can simplify this;
6359 see @ref{Completion, ,Command completion}.
6361 @cindex reference declarations
6363 @value{GDBN} understands variables declared as C++ references; you can use
6364 them in expressions just as you do in C++ source---they are automatically
6367 In the parameter list shown when @value{GDBN} displays a frame, the values of
6368 reference variables are not displayed (unlike other variables); this
6369 avoids clutter, since references are often used for large structures.
6370 The @emph{address} of a reference variable is always shown, unless
6371 you have specified @samp{set print address off}.
6374 @value{GDBN} supports the C++ name resolution operator @code{::}---your
6375 expressions can use it just as expressions in your program do. Since
6376 one scope may be defined in another, you can use @code{::} repeatedly if
6377 necessary, for example in an expression like
6378 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
6379 resolving name scope by reference to source files, in both C and C++
6380 debugging (@pxref{Variables, ,Program variables}).
6383 In addition, when used with HP's C++ compiler, @value{GDBN} supports
6384 calling virtual functions correctly, printing out virtual bases of
6385 objects, calling functions in a base subobject, casting objects, and
6386 invoking user-defined operators.
6389 @subsubsection C and C++ defaults
6391 @cindex C and C++ defaults
6393 If you allow @value{GDBN} to set type and range checking automatically, they
6394 both default to @code{off} whenever the working language changes to
6395 C or C++. This happens regardless of whether you or @value{GDBN}
6396 selects the working language.
6398 If you allow @value{GDBN} to set the language automatically, it
6399 recognizes source files whose names end with @file{.c}, @file{.C}, or
6400 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
6401 these files, it sets the working language to C or C++.
6402 @xref{Automatically, ,Having @value{GDBN} infer the source language},
6403 for further details.
6405 @c Type checking is (a) primarily motivated by Modula-2, and (b)
6406 @c unimplemented. If (b) changes, it might make sense to let this node
6407 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
6410 @subsubsection C and C++ type and range checks
6412 @cindex C and C++ checks
6414 By default, when @value{GDBN} parses C or C++ expressions, type checking
6415 is not used. However, if you turn type checking on, @value{GDBN}
6416 considers two variables type equivalent if:
6420 The two variables are structured and have the same structure, union, or
6424 The two variables have the same type name, or types that have been
6425 declared equivalent through @code{typedef}.
6428 @c leaving this out because neither J Gilmore nor R Pesch understand it.
6431 The two @code{struct}, @code{union}, or @code{enum} variables are
6432 declared in the same declaration. (Note: this may not be true for all C
6437 Range checking, if turned on, is done on mathematical operations. Array
6438 indices are not checked, since they are often used to index a pointer
6439 that is not itself an array.
6442 @subsubsection @value{GDBN} and C
6444 The @code{set print union} and @code{show print union} commands apply to
6445 the @code{union} type. When set to @samp{on}, any @code{union} that is
6446 inside a @code{struct} or @code{class} is also printed. Otherwise, it
6447 appears as @samp{@{...@}}.
6449 The @code{@@} operator aids in the debugging of dynamic arrays, formed
6450 with pointers and a memory allocation function. @xref{Expressions,
6454 * Debugging C plus plus::
6457 @node Debugging C plus plus
6458 @subsubsection @value{GDBN} features for C++
6460 @cindex commands for C++
6462 Some @value{GDBN} commands are particularly useful with C++, and some are
6463 designed specifically for use with C++. Here is a summary:
6466 @cindex break in overloaded functions
6467 @item @r{breakpoint menus}
6468 When you want a breakpoint in a function whose name is overloaded,
6469 @value{GDBN} breakpoint menus help you specify which function definition
6470 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
6472 @cindex overloading in C++
6473 @item rbreak @var{regex}
6474 Setting breakpoints using regular expressions is helpful for setting
6475 breakpoints on overloaded functions that are not members of any special
6477 @xref{Set Breaks, ,Setting breakpoints}.
6479 @cindex C++ exception handling
6482 Debug C++ exception handling using these commands. @xref{Set
6483 Catchpoints, , Setting catchpoints}.
6486 @item ptype @var{typename}
6487 Print inheritance relationships as well as other information for type
6489 @xref{Symbols, ,Examining the Symbol Table}.
6491 @cindex C++ symbol display
6492 @item set print demangle
6493 @itemx show print demangle
6494 @itemx set print asm-demangle
6495 @itemx show print asm-demangle
6496 Control whether C++ symbols display in their source form, both when
6497 displaying code as C++ source and when displaying disassemblies.
6498 @xref{Print Settings, ,Print settings}.
6500 @item set print object
6501 @itemx show print object
6502 Choose whether to print derived (actual) or declared types of objects.
6503 @xref{Print Settings, ,Print settings}.
6505 @item set print vtbl
6506 @itemx show print vtbl
6507 Control the format for printing virtual function tables.
6508 @xref{Print Settings, ,Print settings}.
6509 (The @code{vtbl} commands do not work on programs compiled with the HP
6510 ANSI C++ compiler (@code{aCC}).)
6512 @kindex set overload-resolution
6513 @cindex overloaded functions, overload resolution
6514 @item set overload-resolution on
6515 Enable overload resolution for C++ expression evaluation. The default
6516 is on. For overloaded functions, @value{GDBN} evaluates the arguments
6517 and searches for a function whose signature matches the argument types,
6518 using the standard C++ conversion rules (see @ref{C plus plus expressions, ,C++
6519 expressions}, for details). If it cannot find a match, it emits a
6522 @item set overload-resolution off
6523 Disable overload resolution for C++ expression evaluation. For
6524 overloaded functions that are not class member functions, @value{GDBN}
6525 chooses the first function of the specified name that it finds in the
6526 symbol table, whether or not its arguments are of the correct type. For
6527 overloaded functions that are class member functions, @value{GDBN}
6528 searches for a function whose signature @emph{exactly} matches the
6531 @item @r{Overloaded symbol names}
6532 You can specify a particular definition of an overloaded symbol, using
6533 the same notation that is used to declare such symbols in C++: type
6534 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
6535 also use the @value{GDBN} command-line word completion facilities to list the
6536 available choices, or to finish the type list for you.
6537 @xref{Completion,, Command completion}, for details on how to do this.
6541 @subsection Modula-2
6543 @cindex Modula-2, @value{GDBN} support
6545 The extensions made to @value{GDBN} to support Modula-2 only support
6546 output from the @sc{gnu} Modula-2 compiler (which is currently being
6547 developed). Other Modula-2 compilers are not currently supported, and
6548 attempting to debug executables produced by them is most likely
6549 to give an error as @value{GDBN} reads in the executable's symbol
6552 @cindex expressions in Modula-2
6554 * M2 Operators:: Built-in operators
6555 * Built-In Func/Proc:: Built-in functions and procedures
6556 * M2 Constants:: Modula-2 constants
6557 * M2 Defaults:: Default settings for Modula-2
6558 * Deviations:: Deviations from standard Modula-2
6559 * M2 Checks:: Modula-2 type and range checks
6560 * M2 Scope:: The scope operators @code{::} and @code{.}
6561 * GDB/M2:: @value{GDBN} and Modula-2
6565 @subsubsection Operators
6566 @cindex Modula-2 operators
6568 Operators must be defined on values of specific types. For instance,
6569 @code{+} is defined on numbers, but not on structures. Operators are
6570 often defined on groups of types. For the purposes of Modula-2, the
6571 following definitions hold:
6576 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
6580 @emph{Character types} consist of @code{CHAR} and its subranges.
6583 @emph{Floating-point types} consist of @code{REAL}.
6586 @emph{Pointer types} consist of anything declared as @code{POINTER TO
6590 @emph{Scalar types} consist of all of the above.
6593 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
6596 @emph{Boolean types} consist of @code{BOOLEAN}.
6600 The following operators are supported, and appear in order of
6601 increasing precedence:
6605 Function argument or array index separator.
6608 Assignment. The value of @var{var} @code{:=} @var{value} is
6612 Less than, greater than on integral, floating-point, or enumerated
6616 Less than or equal to, greater than or equal to
6617 on integral, floating-point and enumerated types, or set inclusion on
6618 set types. Same precedence as @code{<}.
6620 @item =@r{, }<>@r{, }#
6621 Equality and two ways of expressing inequality, valid on scalar types.
6622 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
6623 available for inequality, since @code{#} conflicts with the script
6627 Set membership. Defined on set types and the types of their members.
6628 Same precedence as @code{<}.
6631 Boolean disjunction. Defined on boolean types.
6634 Boolean conjunction. Defined on boolean types.
6637 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
6640 Addition and subtraction on integral and floating-point types, or union
6641 and difference on set types.
6644 Multiplication on integral and floating-point types, or set intersection
6648 Division on floating-point types, or symmetric set difference on set
6649 types. Same precedence as @code{*}.
6652 Integer division and remainder. Defined on integral types. Same
6653 precedence as @code{*}.
6656 Negative. Defined on @code{INTEGER} and @code{REAL} data.
6659 Pointer dereferencing. Defined on pointer types.
6662 Boolean negation. Defined on boolean types. Same precedence as
6666 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
6667 precedence as @code{^}.
6670 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
6673 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
6677 @value{GDBN} and Modula-2 scope operators.
6681 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
6682 treats the use of the operator @code{IN}, or the use of operators
6683 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
6684 @code{<=}, and @code{>=} on sets as an error.
6687 @cindex Modula-2 built-ins
6688 @node Built-In Func/Proc
6689 @subsubsection Built-in functions and procedures
6691 Modula-2 also makes available several built-in procedures and functions.
6692 In describing these, the following metavariables are used:
6697 represents an @code{ARRAY} variable.
6700 represents a @code{CHAR} constant or variable.
6703 represents a variable or constant of integral type.
6706 represents an identifier that belongs to a set. Generally used in the
6707 same function with the metavariable @var{s}. The type of @var{s} should
6708 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
6711 represents a variable or constant of integral or floating-point type.
6714 represents a variable or constant of floating-point type.
6720 represents a variable.
6723 represents a variable or constant of one of many types. See the
6724 explanation of the function for details.
6727 All Modula-2 built-in procedures also return a result, described below.
6731 Returns the absolute value of @var{n}.
6734 If @var{c} is a lower case letter, it returns its upper case
6735 equivalent, otherwise it returns its argument.
6738 Returns the character whose ordinal value is @var{i}.
6741 Decrements the value in the variable @var{v} by one. Returns the new value.
6743 @item DEC(@var{v},@var{i})
6744 Decrements the value in the variable @var{v} by @var{i}. Returns the
6747 @item EXCL(@var{m},@var{s})
6748 Removes the element @var{m} from the set @var{s}. Returns the new
6751 @item FLOAT(@var{i})
6752 Returns the floating point equivalent of the integer @var{i}.
6755 Returns the index of the last member of @var{a}.
6758 Increments the value in the variable @var{v} by one. Returns the new value.
6760 @item INC(@var{v},@var{i})
6761 Increments the value in the variable @var{v} by @var{i}. Returns the
6764 @item INCL(@var{m},@var{s})
6765 Adds the element @var{m} to the set @var{s} if it is not already
6766 there. Returns the new set.
6769 Returns the maximum value of the type @var{t}.
6772 Returns the minimum value of the type @var{t}.
6775 Returns boolean TRUE if @var{i} is an odd number.
6778 Returns the ordinal value of its argument. For example, the ordinal
6779 value of a character is its @sc{ascii} value (on machines supporting the
6780 @sc{ascii} character set). @var{x} must be of an ordered type, which include
6781 integral, character and enumerated types.
6784 Returns the size of its argument. @var{x} can be a variable or a type.
6786 @item TRUNC(@var{r})
6787 Returns the integral part of @var{r}.
6789 @item VAL(@var{t},@var{i})
6790 Returns the member of the type @var{t} whose ordinal value is @var{i}.
6794 @emph{Warning:} Sets and their operations are not yet supported, so
6795 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
6799 @cindex Modula-2 constants
6801 @subsubsection Constants
6803 @value{GDBN} allows you to express the constants of Modula-2 in the following
6809 Integer constants are simply a sequence of digits. When used in an
6810 expression, a constant is interpreted to be type-compatible with the
6811 rest of the expression. Hexadecimal integers are specified by a
6812 trailing @samp{H}, and octal integers by a trailing @samp{B}.
6815 Floating point constants appear as a sequence of digits, followed by a
6816 decimal point and another sequence of digits. An optional exponent can
6817 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
6818 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
6819 digits of the floating point constant must be valid decimal (base 10)
6823 Character constants consist of a single character enclosed by a pair of
6824 like quotes, either single (@code{'}) or double (@code{"}). They may
6825 also be expressed by their ordinal value (their @sc{ascii} value, usually)
6826 followed by a @samp{C}.
6829 String constants consist of a sequence of characters enclosed by a
6830 pair of like quotes, either single (@code{'}) or double (@code{"}).
6831 Escape sequences in the style of C are also allowed. @xref{C
6832 Constants, ,C and C++ constants}, for a brief explanation of escape
6836 Enumerated constants consist of an enumerated identifier.
6839 Boolean constants consist of the identifiers @code{TRUE} and
6843 Pointer constants consist of integral values only.
6846 Set constants are not yet supported.
6850 @subsubsection Modula-2 defaults
6851 @cindex Modula-2 defaults
6853 If type and range checking are set automatically by @value{GDBN}, they
6854 both default to @code{on} whenever the working language changes to
6855 Modula-2. This happens regardless of whether you or @value{GDBN}
6856 selected the working language.
6858 If you allow @value{GDBN} to set the language automatically, then entering
6859 code compiled from a file whose name ends with @file{.mod} sets the
6860 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
6861 the language automatically}, for further details.
6864 @subsubsection Deviations from standard Modula-2
6865 @cindex Modula-2, deviations from
6867 A few changes have been made to make Modula-2 programs easier to debug.
6868 This is done primarily via loosening its type strictness:
6872 Unlike in standard Modula-2, pointer constants can be formed by
6873 integers. This allows you to modify pointer variables during
6874 debugging. (In standard Modula-2, the actual address contained in a
6875 pointer variable is hidden from you; it can only be modified
6876 through direct assignment to another pointer variable or expression that
6877 returned a pointer.)
6880 C escape sequences can be used in strings and characters to represent
6881 non-printable characters. @value{GDBN} prints out strings with these
6882 escape sequences embedded. Single non-printable characters are
6883 printed using the @samp{CHR(@var{nnn})} format.
6886 The assignment operator (@code{:=}) returns the value of its right-hand
6890 All built-in procedures both modify @emph{and} return their argument.
6894 @subsubsection Modula-2 type and range checks
6895 @cindex Modula-2 checks
6898 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
6901 @c FIXME remove warning when type/range checks added
6903 @value{GDBN} considers two Modula-2 variables type equivalent if:
6907 They are of types that have been declared equivalent via a @code{TYPE
6908 @var{t1} = @var{t2}} statement
6911 They have been declared on the same line. (Note: This is true of the
6912 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
6915 As long as type checking is enabled, any attempt to combine variables
6916 whose types are not equivalent is an error.
6918 Range checking is done on all mathematical operations, assignment, array
6919 index bounds, and all built-in functions and procedures.
6922 @subsubsection The scope operators @code{::} and @code{.}
6924 @cindex @code{.}, Modula-2 scope operator
6925 @cindex colon, doubled as scope operator
6927 @vindex colon-colon@r{, in Modula-2}
6928 @c Info cannot handle :: but TeX can.
6931 @vindex ::@r{, in Modula-2}
6934 There are a few subtle differences between the Modula-2 scope operator
6935 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
6940 @var{module} . @var{id}
6941 @var{scope} :: @var{id}
6945 where @var{scope} is the name of a module or a procedure,
6946 @var{module} the name of a module, and @var{id} is any declared
6947 identifier within your program, except another module.
6949 Using the @code{::} operator makes @value{GDBN} search the scope
6950 specified by @var{scope} for the identifier @var{id}. If it is not
6951 found in the specified scope, then @value{GDBN} searches all scopes
6952 enclosing the one specified by @var{scope}.
6954 Using the @code{.} operator makes @value{GDBN} search the current scope for
6955 the identifier specified by @var{id} that was imported from the
6956 definition module specified by @var{module}. With this operator, it is
6957 an error if the identifier @var{id} was not imported from definition
6958 module @var{module}, or if @var{id} is not an identifier in
6962 @subsubsection @value{GDBN} and Modula-2
6964 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
6965 Five subcommands of @code{set print} and @code{show print} apply
6966 specifically to C and C++: @samp{vtbl}, @samp{demangle},
6967 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
6968 apply to C++, and the last to the C @code{union} type, which has no direct
6969 analogue in Modula-2.
6971 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
6972 with any language, is not useful with Modula-2. Its
6973 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
6974 created in Modula-2 as they can in C or C++. However, because an
6975 address can be specified by an integral constant, the construct
6976 @samp{@{@var{type}@}@var{adrexp}} is still useful.
6978 @cindex @code{#} in Modula-2
6979 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
6980 interpreted as the beginning of a comment. Use @code{<>} instead.
6985 The extensions made to @value{GDBN} to support Chill only support output
6986 from the @sc{gnu} Chill compiler. Other Chill compilers are not currently
6987 supported, and attempting to debug executables produced by them is most
6988 likely to give an error as @value{GDBN} reads in the executable's symbol
6991 @c This used to say "... following Chill related topics ...", but since
6992 @c menus are not shown in the printed manual, it would look awkward.
6993 This section covers the Chill related topics and the features
6994 of @value{GDBN} which support these topics.
6997 * How modes are displayed:: How modes are displayed
6998 * Locations:: Locations and their accesses
6999 * Values and their Operations:: Values and their Operations
7000 * Chill type and range checks::
7004 @node How modes are displayed
7005 @subsubsection How modes are displayed
7007 The Chill Datatype- (Mode) support of @value{GDBN} is directly related
7008 with the functionality of the @sc{gnu} Chill compiler, and therefore deviates
7009 slightly from the standard specification of the Chill language. The
7012 @c FIXME: this @table's contents effectively disable @code by using @r
7013 @c on every @item. So why does it need @code?
7015 @item @r{@emph{Discrete modes:}}
7018 @emph{Integer Modes} which are predefined by @code{BYTE, UBYTE, INT,
7021 @emph{Boolean Mode} which is predefined by @code{BOOL},
7023 @emph{Character Mode} which is predefined by @code{CHAR},
7025 @emph{Set Mode} which is displayed by the keyword @code{SET}.
7027 (@value{GDBP}) ptype x
7028 type = SET (karli = 10, susi = 20, fritzi = 100)
7030 If the type is an unnumbered set the set element values are omitted.
7032 @emph{Range Mode} which is displayed by
7034 @code{type = <basemode>(<lower bound> : <upper bound>)}
7036 where @code{<lower bound>, <upper bound>} can be of any discrete literal
7037 expression (e.g. set element names).
7040 @item @r{@emph{Powerset Mode:}}
7041 A Powerset Mode is displayed by the keyword @code{POWERSET} followed by
7042 the member mode of the powerset. The member mode can be any discrete mode.
7044 (@value{GDBP}) ptype x
7045 type = POWERSET SET (egon, hugo, otto)
7048 @item @r{@emph{Reference Modes:}}
7051 @emph{Bound Reference Mode} which is displayed by the keyword @code{REF}
7052 followed by the mode name to which the reference is bound.
7054 @emph{Free Reference Mode} which is displayed by the keyword @code{PTR}.
7057 @item @r{@emph{Procedure mode}}
7058 The procedure mode is displayed by @code{type = PROC(<parameter list>)
7059 <return mode> EXCEPTIONS (<exception list>)}. The @code{<parameter
7060 list>} is a list of the parameter modes. @code{<return mode>} indicates
7061 the mode of the result of the procedure if any. The exceptionlist lists
7062 all possible exceptions which can be raised by the procedure.
7065 @item @r{@emph{Instance mode}}
7066 The instance mode is represented by a structure, which has a static
7067 type, and is therefore not really of interest.
7070 @item @r{@emph{Synchronization Modes:}}
7073 @emph{Event Mode} which is displayed by
7075 @code{EVENT (<event length>)}
7077 where @code{(<event length>)} is optional.
7079 @emph{Buffer Mode} which is displayed by
7081 @code{BUFFER (<buffer length>)<buffer element mode>}
7083 where @code{(<buffer length>)} is optional.
7086 @item @r{@emph{Timing Modes:}}
7089 @emph{Duration Mode} which is predefined by @code{DURATION}
7091 @emph{Absolute Time Mode} which is predefined by @code{TIME}
7094 @item @r{@emph{Real Modes:}}
7095 Real Modes are predefined with @code{REAL} and @code{LONG_REAL}.
7097 @item @r{@emph{String Modes:}}
7100 @emph{Character String Mode} which is displayed by
7102 @code{CHARS(<string length>)}
7104 followed by the keyword @code{VARYING} if the String Mode is a varying
7107 @emph{Bit String Mode} which is displayed by
7114 @item @r{@emph{Array Mode:}}
7115 The Array Mode is displayed by the keyword @code{ARRAY(<range>)}
7116 followed by the element mode (which may in turn be an array mode).
7118 (@value{GDBP}) ptype x
7121 SET (karli = 10, susi = 20, fritzi = 100)
7124 @item @r{@emph{Structure Mode}}
7125 The Structure mode is displayed by the keyword @code{STRUCT(<field
7126 list>)}. The @code{<field list>} consists of names and modes of fields
7127 of the structure. Variant structures have the keyword @code{CASE <field>
7128 OF <variant fields> ESAC} in their field list. Since the current version
7129 of the GNU Chill compiler doesn't implement tag processing (no runtime
7130 checks of variant fields, and therefore no debugging info), the output
7131 always displays all variant fields.
7133 (@value{GDBP}) ptype str
7148 @subsubsection Locations and their accesses
7150 A location in Chill is an object which can contain values.
7152 A value of a location is generally accessed by the (declared) name of
7153 the location. The output conforms to the specification of values in
7154 Chill programs. How values are specified
7155 is the topic of the next section, @ref{Values and their Operations}.
7157 The pseudo-location @code{RESULT} (or @code{result}) can be used to
7158 display or change the result of a currently-active procedure:
7165 This does the same as the Chill action @code{RESULT EXPR} (which
7166 is not available in @value{GDBN}).
7168 Values of reference mode locations are printed by @code{PTR(<hex
7169 value>)} in case of a free reference mode, and by @code{(REF <reference
7170 mode>) (<hex-value>)} in case of a bound reference. @code{<hex value>}
7171 represents the address where the reference points to. To access the
7172 value of the location referenced by the pointer, use the dereference
7175 Values of procedure mode locations are displayed by
7178 (<argument modes> ) <return mode> @} <address> <name of procedure
7181 @code{<argument modes>} is a list of modes according to the parameter
7182 specification of the procedure and @code{<address>} shows the address of
7186 Locations of instance modes are displayed just like a structure with two
7187 fields specifying the @emph{process type} and the @emph{copy number} of
7188 the investigated instance location@footnote{This comes from the current
7189 implementation of instances. They are implemented as a structure (no
7190 na). The output should be something like @code{[<name of the process>;
7191 <instance number>]}.}. The field names are @code{__proc_type} and
7194 Locations of synchronization modes are displayed like a structure with
7195 the field name @code{__event_data} in case of a event mode location, and
7196 like a structure with the field @code{__buffer_data} in case of a buffer
7197 mode location (refer to previous paragraph).
7199 Structure Mode locations are printed by @code{[.<field name>: <value>,
7200 ...]}. The @code{<field name>} corresponds to the structure mode
7201 definition and the layout of @code{<value>} varies depending of the mode
7202 of the field. If the investigated structure mode location is of variant
7203 structure mode, the variant parts of the structure are enclosed in curled
7204 braces (@samp{@{@}}). Fields enclosed by @samp{@{,@}} are residing
7205 on the same memory location and represent the current values of the
7206 memory location in their specific modes. Since no tag processing is done
7207 all variants are displayed. A variant field is printed by
7208 @code{(<variant name>) = .<field name>: <value>}. (who implements the
7211 (@value{GDBP}) print str1 $4 = [.as: 0, .bs: karli, .<TAG>: { (karli) =
7212 [.cs: []], (susi) = [.ds: susi]}]
7216 Substructures of string mode-, array mode- or structure mode-values
7217 (e.g. array slices, fields of structure locations) are accessed using
7218 certain operations which are described in the next section, @ref{Values
7219 and their Operations}.
7221 A location value may be interpreted as having a different mode using the
7222 location conversion. This mode conversion is written as @code{<mode
7223 name>(<location>)}. The user has to consider that the sizes of the modes
7224 have to be equal otherwise an error occurs. Furthermore, no range
7225 checking of the location against the destination mode is performed, and
7226 therefore the result can be quite confusing.
7229 (@value{GDBP}) print int (s(3 up 4)) XXX TO be filled in !! XXX
7232 @node Values and their Operations
7233 @subsubsection Values and their Operations
7235 Values are used to alter locations, to investigate complex structures in
7236 more detail or to filter relevant information out of a large amount of
7237 data. There are several (mode dependent) operations defined which enable
7238 such investigations. These operations are not only applicable to
7239 constant values but also to locations, which can become quite useful
7240 when debugging complex structures. During parsing the command line
7241 (e.g. evaluating an expression) @value{GDBN} treats location names as
7242 the values behind these locations.
7244 This section describes how values have to be specified and which
7245 operations are legal to be used with such values.
7248 @item Literal Values
7249 Literal values are specified in the same manner as in @sc{gnu} Chill programs.
7250 For detailed specification refer to the @sc{gnu} Chill implementation Manual
7252 @c FIXME: if the Chill Manual is a Texinfo documents, the above should
7253 @c be converted to a @ref.
7258 @emph{Integer Literals} are specified in the same manner as in Chill
7259 programs (refer to the Chill Standard z200/88 chpt 5.2.4.2)
7261 @emph{Boolean Literals} are defined by @code{TRUE} and @code{FALSE}.
7263 @emph{Character Literals} are defined by @code{'<character>'}. (e.g.
7266 @emph{Set Literals} are defined by a name which was specified in a set
7267 mode. The value delivered by a Set Literal is the set value. This is
7268 comparable to an enumeration in C/C++ language.
7270 @emph{Emptiness Literal} is predefined by @code{NULL}. The value of the
7271 emptiness literal delivers either the empty reference value, the empty
7272 procedure value or the empty instance value.
7275 @emph{Character String Literals} are defined by a sequence of characters
7276 enclosed in single- or double quotes. If a single- or double quote has
7277 to be part of the string literal it has to be stuffed (specified twice).
7279 @emph{Bitstring Literals} are specified in the same manner as in Chill
7280 programs (refer z200/88 chpt 5.2.4.8).
7282 @emph{Floating point literals} are specified in the same manner as in
7283 (gnu-)Chill programs (refer @sc{gnu} Chill implementation Manual chapter 1.5).
7288 A tuple is specified by @code{<mode name>[<tuple>]}, where @code{<mode
7289 name>} can be omitted if the mode of the tuple is unambiguous. This
7290 unambiguity is derived from the context of a evaluated expression.
7291 @code{<tuple>} can be one of the following:
7294 @item @emph{Powerset Tuple}
7295 @item @emph{Array Tuple}
7296 @item @emph{Structure Tuple}
7297 Powerset tuples, array tuples and structure tuples are specified in the
7298 same manner as in Chill programs refer to z200/88 chpt 5.2.5.
7301 @item String Element Value
7302 A string element value is specified by
7304 @code{<string value>(<index>)}
7306 where @code{<index>} is a integer expression. It delivers a character
7307 value which is equivalent to the character indexed by @code{<index>} in
7310 @item String Slice Value
7311 A string slice value is specified by @code{<string value>(<slice
7312 spec>)}, where @code{<slice spec>} can be either a range of integer
7313 expressions or specified by @code{<start expr> up <size>}.
7314 @code{<size>} denotes the number of elements which the slice contains.
7315 The delivered value is a string value, which is part of the specified
7318 @item Array Element Values
7319 An array element value is specified by @code{<array value>(<expr>)} and
7320 delivers a array element value of the mode of the specified array.
7322 @item Array Slice Values
7323 An array slice is specified by @code{<array value>(<slice spec>)}, where
7324 @code{<slice spec>} can be either a range specified by expressions or by
7325 @code{<start expr> up <size>}. @code{<size>} denotes the number of
7326 arrayelements the slice contains. The delivered value is an array value
7327 which is part of the specified array.
7329 @item Structure Field Values
7330 A structure field value is derived by @code{<structure value>.<field
7331 name>}, where @code{<field name>} indicates the name of a field specified
7332 in the mode definition of the structure. The mode of the delivered value
7333 corresponds to this mode definition in the structure definition.
7335 @item Procedure Call Value
7336 The procedure call value is derived from the return value of the
7337 procedure@footnote{If a procedure call is used for instance in an
7338 expression, then this procedure is called with all its side
7339 effects. This can lead to confusing results if used carelessly.}.
7341 Values of duration mode locations are represented by @code{ULONG} literals.
7343 Values of time mode locations appear as
7345 @code{TIME(<secs>:<nsecs>)}
7350 This is not implemented yet:
7351 @item Built-in Value
7353 The following built in functions are provided:
7365 @item @code{UPPER()}
7366 @item @code{LOWER()}
7367 @item @code{LENGTH()}
7371 @item @code{ARCSIN()}
7372 @item @code{ARCCOS()}
7373 @item @code{ARCTAN()}
7380 For a detailed description refer to the GNU Chill implementation manual
7384 @item Zero-adic Operator Value
7385 The zero-adic operator value is derived from the instance value for the
7386 current active process.
7388 @item Expression Values
7389 The value delivered by an expression is the result of the evaluation of
7390 the specified expression. If there are error conditions (mode
7391 incompatibility, etc.) the evaluation of expressions is aborted with a
7392 corresponding error message. Expressions may be parenthesised which
7393 causes the evaluation of this expression before any other expression
7394 which uses the result of the parenthesised expression. The following
7395 operators are supported by @value{GDBN}:
7398 @item @code{OR, ORIF, XOR}
7399 @itemx @code{AND, ANDIF}
7401 Logical operators defined over operands of boolean mode.
7404 Equality and inequality operators defined over all modes.
7408 Relational operators defined over predefined modes.
7411 @itemx @code{*, /, MOD, REM}
7412 Arithmetic operators defined over predefined modes.
7415 Change sign operator.
7418 String concatenation operator.
7421 String repetition operator.
7424 Referenced location operator which can be used either to take the
7425 address of a location (@code{->loc}), or to dereference a reference
7426 location (@code{loc->}).
7428 @item @code{OR, XOR}
7431 Powerset and bitstring operators.
7435 Powerset inclusion operators.
7438 Membership operator.
7442 @node Chill type and range checks
7443 @subsubsection Chill type and range checks
7445 @value{GDBN} considers two Chill variables mode equivalent if the sizes
7446 of the two modes are equal. This rule applies recursively to more
7447 complex datatypes which means that complex modes are treated
7448 equivalent if all element modes (which also can be complex modes like
7449 structures, arrays, etc.) have the same size.
7451 Range checking is done on all mathematical operations, assignment, array
7452 index bounds and all built in procedures.
7454 Strong type checks are forced using the @value{GDBN} command @code{set
7455 check strong}. This enforces strong type and range checks on all
7456 operations where Chill constructs are used (expressions, built in
7457 functions, etc.) in respect to the semantics as defined in the z.200
7458 language specification.
7460 All checks can be disabled by the @value{GDBN} command @code{set check
7464 @c Deviations from the Chill Standard Z200/88
7465 see last paragraph ?
7468 @node Chill defaults
7469 @subsubsection Chill defaults
7471 If type and range checking are set automatically by @value{GDBN}, they
7472 both default to @code{on} whenever the working language changes to
7473 Chill. This happens regardless of whether you or @value{GDBN}
7474 selected the working language.
7476 If you allow @value{GDBN} to set the language automatically, then entering
7477 code compiled from a file whose name ends with @file{.ch} sets the
7478 working language to Chill. @xref{Automatically, ,Having @value{GDBN} set
7479 the language automatically}, for further details.
7482 @chapter Examining the Symbol Table
7484 The commands described in this chapter allow you to inquire about the
7485 symbols (names of variables, functions and types) defined in your
7486 program. This information is inherent in the text of your program and
7487 does not change as your program executes. @value{GDBN} finds it in your
7488 program's symbol table, in the file indicated when you started @value{GDBN}
7489 (@pxref{File Options, ,Choosing files}), or by one of the
7490 file-management commands (@pxref{Files, ,Commands to specify files}).
7492 @cindex symbol names
7493 @cindex names of symbols
7494 @cindex quoting names
7495 Occasionally, you may need to refer to symbols that contain unusual
7496 characters, which @value{GDBN} ordinarily treats as word delimiters. The
7497 most frequent case is in referring to static variables in other
7498 source files (@pxref{Variables,,Program variables}). File names
7499 are recorded in object files as debugging symbols, but @value{GDBN} would
7500 ordinarily parse a typical file name, like @file{foo.c}, as the three words
7501 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
7502 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
7509 looks up the value of @code{x} in the scope of the file @file{foo.c}.
7512 @kindex info address
7513 @item info address @var{symbol}
7514 Describe where the data for @var{symbol} is stored. For a register
7515 variable, this says which register it is kept in. For a non-register
7516 local variable, this prints the stack-frame offset at which the variable
7519 Note the contrast with @samp{print &@var{symbol}}, which does not work
7520 at all for a register variable, and for a stack local variable prints
7521 the exact address of the current instantiation of the variable.
7524 @item whatis @var{expr}
7525 Print the data type of expression @var{expr}. @var{expr} is not
7526 actually evaluated, and any side-effecting operations (such as
7527 assignments or function calls) inside it do not take place.
7528 @xref{Expressions, ,Expressions}.
7531 Print the data type of @code{$}, the last value in the value history.
7534 @item ptype @var{typename}
7535 Print a description of data type @var{typename}. @var{typename} may be
7536 the name of a type, or for C code it may have the form @samp{class
7537 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
7538 @var{union-tag}} or @samp{enum @var{enum-tag}}.
7540 @item ptype @var{expr}
7542 Print a description of the type of expression @var{expr}. @code{ptype}
7543 differs from @code{whatis} by printing a detailed description, instead
7544 of just the name of the type.
7546 For example, for this variable declaration:
7549 struct complex @{double real; double imag;@} v;
7553 the two commands give this output:
7557 (@value{GDBP}) whatis v
7558 type = struct complex
7559 (@value{GDBP}) ptype v
7560 type = struct complex @{
7568 As with @code{whatis}, using @code{ptype} without an argument refers to
7569 the type of @code{$}, the last value in the value history.
7572 @item info types @var{regexp}
7574 Print a brief description of all types whose names match @var{regexp}
7575 (or all types in your program, if you supply no argument). Each
7576 complete typename is matched as though it were a complete line; thus,
7577 @samp{i type value} gives information on all types in your program whose
7578 names include the string @code{value}, but @samp{i type ^value$} gives
7579 information only on types whose complete name is @code{value}.
7581 This command differs from @code{ptype} in two ways: first, like
7582 @code{whatis}, it does not print a detailed description; second, it
7583 lists all source files where a type is defined.
7587 Show the name of the current source file---that is, the source file for
7588 the function containing the current point of execution---and the language
7591 @kindex info sources
7593 Print the names of all source files in your program for which there is
7594 debugging information, organized into two lists: files whose symbols
7595 have already been read, and files whose symbols will be read when needed.
7597 @kindex info functions
7598 @item info functions
7599 Print the names and data types of all defined functions.
7601 @item info functions @var{regexp}
7602 Print the names and data types of all defined functions
7603 whose names contain a match for regular expression @var{regexp}.
7604 Thus, @samp{info fun step} finds all functions whose names
7605 include @code{step}; @samp{info fun ^step} finds those whose names
7606 start with @code{step}.
7608 @kindex info variables
7609 @item info variables
7610 Print the names and data types of all variables that are declared
7611 outside of functions (i.e., excluding local variables).
7613 @item info variables @var{regexp}
7614 Print the names and data types of all variables (except for local
7615 variables) whose names contain a match for regular expression
7619 This was never implemented.
7620 @kindex info methods
7622 @itemx info methods @var{regexp}
7623 The @code{info methods} command permits the user to examine all defined
7624 methods within C++ program, or (with the @var{regexp} argument) a
7625 specific set of methods found in the various C++ classes. Many
7626 C++ classes provide a large number of methods. Thus, the output
7627 from the @code{ptype} command can be overwhelming and hard to use. The
7628 @code{info-methods} command filters the methods, printing only those
7629 which match the regular-expression @var{regexp}.
7632 @cindex reloading symbols
7633 Some systems allow individual object files that make up your program to
7634 be replaced without stopping and restarting your program. For example,
7635 in VxWorks you can simply recompile a defective object file and keep on
7636 running. If you are running on one of these systems, you can allow
7637 @value{GDBN} to reload the symbols for automatically relinked modules:
7640 @kindex set symbol-reloading
7641 @item set symbol-reloading on
7642 Replace symbol definitions for the corresponding source file when an
7643 object file with a particular name is seen again.
7645 @item set symbol-reloading off
7646 Do not replace symbol definitions when encountering object files of the
7647 same name more than once. This is the default state; if you are not
7648 running on a system that permits automatic relinking of modules, you
7649 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
7650 may discard symbols when linking large programs, that may contain
7651 several modules (from different directories or libraries) with the same
7654 @kindex show symbol-reloading
7655 @item show symbol-reloading
7656 Show the current @code{on} or @code{off} setting.
7659 @kindex set opaque-type-resolution
7660 @item set opaque-type-resolution on
7661 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
7662 declared as a pointer to a @code{struct}, @code{class}, or
7663 @code{union}---for example, @code{struct MyType *}---that is used in one
7664 source file although the full declaration of @code{struct MyType} is in
7665 another source file. The default is on.
7667 A change in the setting of this subcommand will not take effect until
7668 the next time symbols for a file are loaded.
7670 @item set opaque-type-resolution off
7671 Tell @value{GDBN} not to resolve opaque types. In this case, the type
7672 is printed as follows:
7674 @{<no data fields>@}
7677 @kindex show opaque-type-resolution
7678 @item show opaque-type-resolution
7679 Show whether opaque types are resolved or not.
7681 @kindex maint print symbols
7683 @kindex maint print psymbols
7684 @cindex partial symbol dump
7685 @item maint print symbols @var{filename}
7686 @itemx maint print psymbols @var{filename}
7687 @itemx maint print msymbols @var{filename}
7688 Write a dump of debugging symbol data into the file @var{filename}.
7689 These commands are used to debug the @value{GDBN} symbol-reading code. Only
7690 symbols with debugging data are included. If you use @samp{maint print
7691 symbols}, @value{GDBN} includes all the symbols for which it has already
7692 collected full details: that is, @var{filename} reflects symbols for
7693 only those files whose symbols @value{GDBN} has read. You can use the
7694 command @code{info sources} to find out which files these are. If you
7695 use @samp{maint print psymbols} instead, the dump shows information about
7696 symbols that @value{GDBN} only knows partially---that is, symbols defined in
7697 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
7698 @samp{maint print msymbols} dumps just the minimal symbol information
7699 required for each object file from which @value{GDBN} has read some symbols.
7700 @xref{Files, ,Commands to specify files}, for a discussion of how
7701 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
7705 @chapter Altering Execution
7707 Once you think you have found an error in your program, you might want to
7708 find out for certain whether correcting the apparent error would lead to
7709 correct results in the rest of the run. You can find the answer by
7710 experiment, using the @value{GDBN} features for altering execution of the
7713 For example, you can store new values into variables or memory
7714 locations, give your program a signal, restart it at a different
7715 address, or even return prematurely from a function.
7718 * Assignment:: Assignment to variables
7719 * Jumping:: Continuing at a different address
7720 * Signaling:: Giving your program a signal
7721 * Returning:: Returning from a function
7722 * Calling:: Calling your program's functions
7723 * Patching:: Patching your program
7727 @section Assignment to variables
7730 @cindex setting variables
7731 To alter the value of a variable, evaluate an assignment expression.
7732 @xref{Expressions, ,Expressions}. For example,
7739 stores the value 4 into the variable @code{x}, and then prints the
7740 value of the assignment expression (which is 4).
7741 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
7742 information on operators in supported languages.
7744 @kindex set variable
7745 @cindex variables, setting
7746 If you are not interested in seeing the value of the assignment, use the
7747 @code{set} command instead of the @code{print} command. @code{set} is
7748 really the same as @code{print} except that the expression's value is
7749 not printed and is not put in the value history (@pxref{Value History,
7750 ,Value history}). The expression is evaluated only for its effects.
7752 If the beginning of the argument string of the @code{set} command
7753 appears identical to a @code{set} subcommand, use the @code{set
7754 variable} command instead of just @code{set}. This command is identical
7755 to @code{set} except for its lack of subcommands. For example, if your
7756 program has a variable @code{width}, you get an error if you try to set
7757 a new value with just @samp{set width=13}, because @value{GDBN} has the
7758 command @code{set width}:
7761 (@value{GDBP}) whatis width
7763 (@value{GDBP}) p width
7765 (@value{GDBP}) set width=47
7766 Invalid syntax in expression.
7770 The invalid expression, of course, is @samp{=47}. In
7771 order to actually set the program's variable @code{width}, use
7774 (@value{GDBP}) set var width=47
7777 Because the @code{set} command has many subcommands that can conflict
7778 with the names of program variables, it is a good idea to use the
7779 @code{set variable} command instead of just @code{set}. For example, if
7780 your program has a variable @code{g}, you run into problems if you try
7781 to set a new value with just @samp{set g=4}, because @value{GDBN} has
7782 the command @code{set gnutarget}, abbreviated @code{set g}:
7786 (@value{GDBP}) whatis g
7790 (@value{GDBP}) set g=4
7794 The program being debugged has been started already.
7795 Start it from the beginning? (y or n) y
7796 Starting program: /home/smith/cc_progs/a.out
7797 "/home/smith/cc_progs/a.out": can't open to read symbols:
7799 (@value{GDBP}) show g
7800 The current BFD target is "=4".
7805 The program variable @code{g} did not change, and you silently set the
7806 @code{gnutarget} to an invalid value. In order to set the variable
7810 (@value{GDBP}) set var g=4
7813 @value{GDBN} allows more implicit conversions in assignments than C; you can
7814 freely store an integer value into a pointer variable or vice versa,
7815 and you can convert any structure to any other structure that is the
7816 same length or shorter.
7817 @comment FIXME: how do structs align/pad in these conversions?
7818 @comment /doc@cygnus.com 18dec1990
7820 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
7821 construct to generate a value of specified type at a specified address
7822 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
7823 to memory location @code{0x83040} as an integer (which implies a certain size
7824 and representation in memory), and
7827 set @{int@}0x83040 = 4
7831 stores the value 4 into that memory location.
7834 @section Continuing at a different address
7836 Ordinarily, when you continue your program, you do so at the place where
7837 it stopped, with the @code{continue} command. You can instead continue at
7838 an address of your own choosing, with the following commands:
7842 @item jump @var{linespec}
7843 Resume execution at line @var{linespec}. Execution stops again
7844 immediately if there is a breakpoint there. @xref{List, ,Printing
7845 source lines}, for a description of the different forms of
7846 @var{linespec}. It is common practice to use the @code{tbreak} command
7847 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
7850 The @code{jump} command does not change the current stack frame, or
7851 the stack pointer, or the contents of any memory location or any
7852 register other than the program counter. If line @var{linespec} is in
7853 a different function from the one currently executing, the results may
7854 be bizarre if the two functions expect different patterns of arguments or
7855 of local variables. For this reason, the @code{jump} command requests
7856 confirmation if the specified line is not in the function currently
7857 executing. However, even bizarre results are predictable if you are
7858 well acquainted with the machine-language code of your program.
7860 @item jump *@var{address}
7861 Resume execution at the instruction at address @var{address}.
7864 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
7865 On many systems, you can get much the same effect as the @code{jump}
7866 command by storing a new value into the register @code{$pc}. The
7867 difference is that this does not start your program running; it only
7868 changes the address of where it @emph{will} run when you continue. For
7876 makes the next @code{continue} command or stepping command execute at
7877 address @code{0x485}, rather than at the address where your program stopped.
7878 @xref{Continuing and Stepping, ,Continuing and stepping}.
7880 The most common occasion to use the @code{jump} command is to back
7881 up---perhaps with more breakpoints set---over a portion of a program
7882 that has already executed, in order to examine its execution in more
7887 @section Giving your program a signal
7891 @item signal @var{signal}
7892 Resume execution where your program stopped, but immediately give it the
7893 signal @var{signal}. @var{signal} can be the name or the number of a
7894 signal. For example, on many systems @code{signal 2} and @code{signal
7895 SIGINT} are both ways of sending an interrupt signal.
7897 Alternatively, if @var{signal} is zero, continue execution without
7898 giving a signal. This is useful when your program stopped on account of
7899 a signal and would ordinary see the signal when resumed with the
7900 @code{continue} command; @samp{signal 0} causes it to resume without a
7903 @code{signal} does not repeat when you press @key{RET} a second time
7904 after executing the command.
7908 Invoking the @code{signal} command is not the same as invoking the
7909 @code{kill} utility from the shell. Sending a signal with @code{kill}
7910 causes @value{GDBN} to decide what to do with the signal depending on
7911 the signal handling tables (@pxref{Signals}). The @code{signal} command
7912 passes the signal directly to your program.
7916 @section Returning from a function
7919 @cindex returning from a function
7922 @itemx return @var{expression}
7923 You can cancel execution of a function call with the @code{return}
7924 command. If you give an
7925 @var{expression} argument, its value is used as the function's return
7929 When you use @code{return}, @value{GDBN} discards the selected stack frame
7930 (and all frames within it). You can think of this as making the
7931 discarded frame return prematurely. If you wish to specify a value to
7932 be returned, give that value as the argument to @code{return}.
7934 This pops the selected stack frame (@pxref{Selection, ,Selecting a
7935 frame}), and any other frames inside of it, leaving its caller as the
7936 innermost remaining frame. That frame becomes selected. The
7937 specified value is stored in the registers used for returning values
7940 The @code{return} command does not resume execution; it leaves the
7941 program stopped in the state that would exist if the function had just
7942 returned. In contrast, the @code{finish} command (@pxref{Continuing
7943 and Stepping, ,Continuing and stepping}) resumes execution until the
7944 selected stack frame returns naturally.
7947 @section Calling program functions
7949 @cindex calling functions
7952 @item call @var{expr}
7953 Evaluate the expression @var{expr} without displaying @code{void}
7957 You can use this variant of the @code{print} command if you want to
7958 execute a function from your program, but without cluttering the output
7959 with @code{void} returned values. If the result is not void, it
7960 is printed and saved in the value history.
7962 For the A29K, a user-controlled variable @code{call_scratch_address},
7963 specifies the location of a scratch area to be used when @value{GDBN}
7964 calls a function in the target. This is necessary because the usual
7965 method of putting the scratch area on the stack does not work in systems
7966 that have separate instruction and data spaces.
7969 @section Patching programs
7971 @cindex patching binaries
7972 @cindex writing into executables
7973 @cindex writing into corefiles
7975 By default, @value{GDBN} opens the file containing your program's
7976 executable code (or the corefile) read-only. This prevents accidental
7977 alterations to machine code; but it also prevents you from intentionally
7978 patching your program's binary.
7980 If you'd like to be able to patch the binary, you can specify that
7981 explicitly with the @code{set write} command. For example, you might
7982 want to turn on internal debugging flags, or even to make emergency
7988 @itemx set write off
7989 If you specify @samp{set write on}, @value{GDBN} opens executable and
7990 core files for both reading and writing; if you specify @samp{set write
7991 off} (the default), @value{GDBN} opens them read-only.
7993 If you have already loaded a file, you must load it again (using the
7994 @code{exec-file} or @code{core-file} command) after changing @code{set
7995 write}, for your new setting to take effect.
7999 Display whether executable files and core files are opened for writing
8004 @chapter @value{GDBN} Files
8006 @value{GDBN} needs to know the file name of the program to be debugged,
8007 both in order to read its symbol table and in order to start your
8008 program. To debug a core dump of a previous run, you must also tell
8009 @value{GDBN} the name of the core dump file.
8012 * Files:: Commands to specify files
8013 * Symbol Errors:: Errors reading symbol files
8017 @section Commands to specify files
8019 @cindex symbol table
8020 @cindex core dump file
8022 You may want to specify executable and core dump file names. The usual
8023 way to do this is at start-up time, using the arguments to
8024 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
8025 Out of @value{GDBN}}).
8027 Occasionally it is necessary to change to a different file during a
8028 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
8029 a file you want to use. In these situations the @value{GDBN} commands
8030 to specify new files are useful.
8033 @cindex executable file
8035 @item file @var{filename}
8036 Use @var{filename} as the program to be debugged. It is read for its
8037 symbols and for the contents of pure memory. It is also the program
8038 executed when you use the @code{run} command. If you do not specify a
8039 directory and the file is not found in the @value{GDBN} working directory,
8040 @value{GDBN} uses the environment variable @code{PATH} as a list of
8041 directories to search, just as the shell does when looking for a program
8042 to run. You can change the value of this variable, for both @value{GDBN}
8043 and your program, using the @code{path} command.
8045 On systems with memory-mapped files, an auxiliary file named
8046 @file{@var{filename}.syms} may hold symbol table information for
8047 @var{filename}. If so, @value{GDBN} maps in the symbol table from
8048 @file{@var{filename}.syms}, starting up more quickly. See the
8049 descriptions of the file options @samp{-mapped} and @samp{-readnow}
8050 (available on the command line, and with the commands @code{file},
8051 @code{symbol-file}, or @code{add-symbol-file}, described below),
8052 for more information.
8055 @code{file} with no argument makes @value{GDBN} discard any information it
8056 has on both executable file and the symbol table.
8059 @item exec-file @r{[} @var{filename} @r{]}
8060 Specify that the program to be run (but not the symbol table) is found
8061 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
8062 if necessary to locate your program. Omitting @var{filename} means to
8063 discard information on the executable file.
8066 @item symbol-file @r{[} @var{filename} @r{]}
8067 Read symbol table information from file @var{filename}. @code{PATH} is
8068 searched when necessary. Use the @code{file} command to get both symbol
8069 table and program to run from the same file.
8071 @code{symbol-file} with no argument clears out @value{GDBN} information on your
8072 program's symbol table.
8074 The @code{symbol-file} command causes @value{GDBN} to forget the contents
8075 of its convenience variables, the value history, and all breakpoints and
8076 auto-display expressions. This is because they may contain pointers to
8077 the internal data recording symbols and data types, which are part of
8078 the old symbol table data being discarded inside @value{GDBN}.
8080 @code{symbol-file} does not repeat if you press @key{RET} again after
8083 When @value{GDBN} is configured for a particular environment, it
8084 understands debugging information in whatever format is the standard
8085 generated for that environment; you may use either a @sc{gnu} compiler, or
8086 other compilers that adhere to the local conventions.
8087 Best results are usually obtained from @sc{gnu} compilers; for example,
8088 using @code{@value{GCC}} you can generate debugging information for
8091 For most kinds of object files, with the exception of old SVR3 systems
8092 using COFF, the @code{symbol-file} command does not normally read the
8093 symbol table in full right away. Instead, it scans the symbol table
8094 quickly to find which source files and which symbols are present. The
8095 details are read later, one source file at a time, as they are needed.
8097 The purpose of this two-stage reading strategy is to make @value{GDBN}
8098 start up faster. For the most part, it is invisible except for
8099 occasional pauses while the symbol table details for a particular source
8100 file are being read. (The @code{set verbose} command can turn these
8101 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
8102 warnings and messages}.)
8104 We have not implemented the two-stage strategy for COFF yet. When the
8105 symbol table is stored in COFF format, @code{symbol-file} reads the
8106 symbol table data in full right away. Note that ``stabs-in-COFF''
8107 still does the two-stage strategy, since the debug info is actually
8111 @cindex reading symbols immediately
8112 @cindex symbols, reading immediately
8114 @cindex memory-mapped symbol file
8115 @cindex saving symbol table
8116 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8117 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8118 You can override the @value{GDBN} two-stage strategy for reading symbol
8119 tables by using the @samp{-readnow} option with any of the commands that
8120 load symbol table information, if you want to be sure @value{GDBN} has the
8121 entire symbol table available.
8123 If memory-mapped files are available on your system through the
8124 @code{mmap} system call, you can use another option, @samp{-mapped}, to
8125 cause @value{GDBN} to write the symbols for your program into a reusable
8126 file. Future @value{GDBN} debugging sessions map in symbol information
8127 from this auxiliary symbol file (if the program has not changed), rather
8128 than spending time reading the symbol table from the executable
8129 program. Using the @samp{-mapped} option has the same effect as
8130 starting @value{GDBN} with the @samp{-mapped} command-line option.
8132 You can use both options together, to make sure the auxiliary symbol
8133 file has all the symbol information for your program.
8135 The auxiliary symbol file for a program called @var{myprog} is called
8136 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
8137 than the corresponding executable), @value{GDBN} always attempts to use
8138 it when you debug @var{myprog}; no special options or commands are
8141 The @file{.syms} file is specific to the host machine where you run
8142 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
8143 symbol table. It cannot be shared across multiple host platforms.
8145 @c FIXME: for now no mention of directories, since this seems to be in
8146 @c flux. 13mar1992 status is that in theory GDB would look either in
8147 @c current dir or in same dir as myprog; but issues like competing
8148 @c GDB's, or clutter in system dirs, mean that in practice right now
8149 @c only current dir is used. FFish says maybe a special GDB hierarchy
8150 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
8155 @item core-file @r{[} @var{filename} @r{]}
8156 Specify the whereabouts of a core dump file to be used as the ``contents
8157 of memory''. Traditionally, core files contain only some parts of the
8158 address space of the process that generated them; @value{GDBN} can access the
8159 executable file itself for other parts.
8161 @code{core-file} with no argument specifies that no core file is
8164 Note that the core file is ignored when your program is actually running
8165 under @value{GDBN}. So, if you have been running your program and you
8166 wish to debug a core file instead, you must kill the subprocess in which
8167 the program is running. To do this, use the @code{kill} command
8168 (@pxref{Kill Process, ,Killing the child process}).
8170 @kindex add-symbol-file
8171 @cindex dynamic linking
8172 @item add-symbol-file @var{filename} @var{address}
8173 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8174 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address}
8175 The @code{add-symbol-file} command reads additional symbol table
8176 information from the file @var{filename}. You would use this command
8177 when @var{filename} has been dynamically loaded (by some other means)
8178 into the program that is running. @var{address} should be the memory
8179 address at which the file has been loaded; @value{GDBN} cannot figure
8180 this out for itself. You can additionally specify an arbitrary number
8181 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
8182 section name and base address for that section. You can specify any
8183 @var{address} as an expression.
8185 The symbol table of the file @var{filename} is added to the symbol table
8186 originally read with the @code{symbol-file} command. You can use the
8187 @code{add-symbol-file} command any number of times; the new symbol data
8188 thus read keeps adding to the old. To discard all old symbol data
8189 instead, use the @code{symbol-file} command without any arguments.
8191 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
8193 You can use the @samp{-mapped} and @samp{-readnow} options just as with
8194 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
8195 table information for @var{filename}.
8197 @kindex add-shared-symbol-file
8198 @item add-shared-symbol-file
8199 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
8200 operating system for the Motorola 88k. @value{GDBN} automatically looks for
8201 shared libraries, however if @value{GDBN} does not find yours, you can run
8202 @code{add-shared-symbol-file}. It takes no arguments.
8206 The @code{section} command changes the base address of section SECTION of
8207 the exec file to ADDR. This can be used if the exec file does not contain
8208 section addresses, (such as in the a.out format), or when the addresses
8209 specified in the file itself are wrong. Each section must be changed
8210 separately. The @code{info files} command, described below, lists all
8211 the sections and their addresses.
8217 @code{info files} and @code{info target} are synonymous; both print the
8218 current target (@pxref{Targets, ,Specifying a Debugging Target}),
8219 including the names of the executable and core dump files currently in
8220 use by @value{GDBN}, and the files from which symbols were loaded. The
8221 command @code{help target} lists all possible targets rather than
8226 All file-specifying commands allow both absolute and relative file names
8227 as arguments. @value{GDBN} always converts the file name to an absolute file
8228 name and remembers it that way.
8230 @cindex shared libraries
8231 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
8234 @value{GDBN} automatically loads symbol definitions from shared libraries
8235 when you use the @code{run} command, or when you examine a core file.
8236 (Before you issue the @code{run} command, @value{GDBN} does not understand
8237 references to a function in a shared library, however---unless you are
8238 debugging a core file).
8240 On HP-UX, if the program loads a library explicitly, @value{GDBN}
8241 automatically loads the symbols at the time of the @code{shl_load} call.
8243 @c FIXME: some @value{GDBN} release may permit some refs to undef
8244 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
8245 @c FIXME...lib; check this from time to time when updating manual
8248 @kindex info sharedlibrary
8251 @itemx info sharedlibrary
8252 Print the names of the shared libraries which are currently loaded.
8254 @kindex sharedlibrary
8256 @item sharedlibrary @var{regex}
8257 @itemx share @var{regex}
8258 Load shared object library symbols for files matching a
8259 Unix regular expression.
8260 As with files loaded automatically, it only loads shared libraries
8261 required by your program for a core file or after typing @code{run}. If
8262 @var{regex} is omitted all shared libraries required by your program are
8266 On HP-UX systems, @value{GDBN} detects the loading of a shared library
8267 and automatically reads in symbols from the newly loaded library, up to
8268 a threshold that is initially set but that you can modify if you wish.
8270 Beyond that threshold, symbols from shared libraries must be explicitly
8271 loaded. To load these symbols, use the command @code{sharedlibrary
8272 @var{filename}}. The base address of the shared library is determined
8273 automatically by @value{GDBN} and need not be specified.
8275 To display or set the threshold, use the commands:
8278 @kindex set auto-solib-add
8279 @item set auto-solib-add @var{threshold}
8280 Set the autoloading size threshold, in megabytes. If @var{threshold} is
8281 nonzero, symbols from all shared object libraries will be loaded
8282 automatically when the inferior begins execution or when the dynamic
8283 linker informs @value{GDBN} that a new library has been loaded, until
8284 the symbol table of the program and libraries exceeds this threshold.
8285 Otherwise, symbols must be loaded manually, using the
8286 @code{sharedlibrary} command. The default threshold is 100 megabytes.
8288 @kindex show auto-solib-add
8289 @item show auto-solib-add
8290 Display the current autoloading size threshold, in megabytes.
8294 @section Errors reading symbol files
8296 While reading a symbol file, @value{GDBN} occasionally encounters problems,
8297 such as symbol types it does not recognize, or known bugs in compiler
8298 output. By default, @value{GDBN} does not notify you of such problems, since
8299 they are relatively common and primarily of interest to people
8300 debugging compilers. If you are interested in seeing information
8301 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
8302 only one message about each such type of problem, no matter how many
8303 times the problem occurs; or you can ask @value{GDBN} to print more messages,
8304 to see how many times the problems occur, with the @code{set
8305 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
8308 The messages currently printed, and their meanings, include:
8311 @item inner block not inside outer block in @var{symbol}
8313 The symbol information shows where symbol scopes begin and end
8314 (such as at the start of a function or a block of statements). This
8315 error indicates that an inner scope block is not fully contained
8316 in its outer scope blocks.
8318 @value{GDBN} circumvents the problem by treating the inner block as if it had
8319 the same scope as the outer block. In the error message, @var{symbol}
8320 may be shown as ``@code{(don't know)}'' if the outer block is not a
8323 @item block at @var{address} out of order
8325 The symbol information for symbol scope blocks should occur in
8326 order of increasing addresses. This error indicates that it does not
8329 @value{GDBN} does not circumvent this problem, and has trouble
8330 locating symbols in the source file whose symbols it is reading. (You
8331 can often determine what source file is affected by specifying
8332 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
8335 @item bad block start address patched
8337 The symbol information for a symbol scope block has a start address
8338 smaller than the address of the preceding source line. This is known
8339 to occur in the SunOS 4.1.1 (and earlier) C compiler.
8341 @value{GDBN} circumvents the problem by treating the symbol scope block as
8342 starting on the previous source line.
8344 @item bad string table offset in symbol @var{n}
8347 Symbol number @var{n} contains a pointer into the string table which is
8348 larger than the size of the string table.
8350 @value{GDBN} circumvents the problem by considering the symbol to have the
8351 name @code{foo}, which may cause other problems if many symbols end up
8354 @item unknown symbol type @code{0x@var{nn}}
8356 The symbol information contains new data types that @value{GDBN} does
8357 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
8358 uncomprehended information, in hexadecimal.
8360 @value{GDBN} circumvents the error by ignoring this symbol information.
8361 This usually allows you to debug your program, though certain symbols
8362 are not accessible. If you encounter such a problem and feel like
8363 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
8364 on @code{complain}, then go up to the function @code{read_dbx_symtab}
8365 and examine @code{*bufp} to see the symbol.
8367 @item stub type has NULL name
8369 @value{GDBN} could not find the full definition for a struct or class.
8371 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
8372 The symbol information for a C++ member function is missing some
8373 information that recent versions of the compiler should have output for
8376 @item info mismatch between compiler and debugger
8378 @value{GDBN} could not parse a type specification output by the compiler.
8383 @chapter Specifying a Debugging Target
8385 @cindex debugging target
8388 A @dfn{target} is the execution environment occupied by your program.
8390 Often, @value{GDBN} runs in the same host environment as your program;
8391 in that case, the debugging target is specified as a side effect when
8392 you use the @code{file} or @code{core} commands. When you need more
8393 flexibility---for example, running @value{GDBN} on a physically separate
8394 host, or controlling a standalone system over a serial port or a
8395 realtime system over a TCP/IP connection---you can use the @code{target}
8396 command to specify one of the target types configured for @value{GDBN}
8397 (@pxref{Target Commands, ,Commands for managing targets}).
8400 * Active Targets:: Active targets
8401 * Target Commands:: Commands for managing targets
8402 * Byte Order:: Choosing target byte order
8403 * Remote:: Remote debugging
8404 * KOD:: Kernel Object Display
8408 @node Active Targets
8409 @section Active targets
8411 @cindex stacking targets
8412 @cindex active targets
8413 @cindex multiple targets
8415 There are three classes of targets: processes, core files, and
8416 executable files. @value{GDBN} can work concurrently on up to three
8417 active targets, one in each class. This allows you to (for example)
8418 start a process and inspect its activity without abandoning your work on
8421 For example, if you execute @samp{gdb a.out}, then the executable file
8422 @code{a.out} is the only active target. If you designate a core file as
8423 well---presumably from a prior run that crashed and coredumped---then
8424 @value{GDBN} has two active targets and uses them in tandem, looking
8425 first in the corefile target, then in the executable file, to satisfy
8426 requests for memory addresses. (Typically, these two classes of target
8427 are complementary, since core files contain only a program's
8428 read-write memory---variables and so on---plus machine status, while
8429 executable files contain only the program text and initialized data.)
8431 When you type @code{run}, your executable file becomes an active process
8432 target as well. When a process target is active, all @value{GDBN}
8433 commands requesting memory addresses refer to that target; addresses in
8434 an active core file or executable file target are obscured while the
8435 process target is active.
8437 Use the @code{core-file} and @code{exec-file} commands to select a new
8438 core file or executable target (@pxref{Files, ,Commands to specify
8439 files}). To specify as a target a process that is already running, use
8440 the @code{attach} command (@pxref{Attach, ,Debugging an already-running
8443 @node Target Commands
8444 @section Commands for managing targets
8447 @item target @var{type} @var{parameters}
8448 Connects the @value{GDBN} host environment to a target machine or
8449 process. A target is typically a protocol for talking to debugging
8450 facilities. You use the argument @var{type} to specify the type or
8451 protocol of the target machine.
8453 Further @var{parameters} are interpreted by the target protocol, but
8454 typically include things like device names or host names to connect
8455 with, process numbers, and baud rates.
8457 The @code{target} command does not repeat if you press @key{RET} again
8458 after executing the command.
8462 Displays the names of all targets available. To display targets
8463 currently selected, use either @code{info target} or @code{info files}
8464 (@pxref{Files, ,Commands to specify files}).
8466 @item help target @var{name}
8467 Describe a particular target, including any parameters necessary to
8470 @kindex set gnutarget
8471 @item set gnutarget @var{args}
8472 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
8473 knows whether it is reading an @dfn{executable},
8474 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
8475 with the @code{set gnutarget} command. Unlike most @code{target} commands,
8476 with @code{gnutarget} the @code{target} refers to a program, not a machine.
8479 @emph{Warning:} To specify a file format with @code{set gnutarget},
8480 you must know the actual BFD name.
8484 @xref{Files, , Commands to specify files}.
8486 @kindex show gnutarget
8487 @item show gnutarget
8488 Use the @code{show gnutarget} command to display what file format
8489 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
8490 @value{GDBN} will determine the file format for each file automatically,
8491 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
8494 Here are some common targets (available, or not, depending on the GDB
8499 @item target exec @var{program}
8500 An executable file. @samp{target exec @var{program}} is the same as
8501 @samp{exec-file @var{program}}.
8504 @item target core @var{filename}
8505 A core dump file. @samp{target core @var{filename}} is the same as
8506 @samp{core-file @var{filename}}.
8508 @kindex target remote
8509 @item target remote @var{dev}
8510 Remote serial target in GDB-specific protocol. The argument @var{dev}
8511 specifies what serial device to use for the connection (e.g.
8512 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
8513 supports the @code{load} command. This is only useful if you have
8514 some other way of getting the stub to the target system, and you can put
8515 it somewhere in memory where it won't get clobbered by the download.
8519 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
8527 works; however, you cannot assume that a specific memory map, device
8528 drivers, or even basic I/O is available, although some simulators do
8529 provide these. For info about any processor-specific simulator details,
8530 see the appropriate section in @ref{Embedded Processors, ,Embedded
8535 Some configurations may include these targets as well:
8540 @item target nrom @var{dev}
8541 NetROM ROM emulator. This target only supports downloading.
8545 Different targets are available on different configurations of @value{GDBN};
8546 your configuration may have more or fewer targets.
8548 Many remote targets require you to download the executable's code
8549 once you've successfully established a connection.
8553 @kindex load @var{filename}
8554 @item load @var{filename}
8555 Depending on what remote debugging facilities are configured into
8556 @value{GDBN}, the @code{load} command may be available. Where it exists, it
8557 is meant to make @var{filename} (an executable) available for debugging
8558 on the remote system---by downloading, or dynamic linking, for example.
8559 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
8560 the @code{add-symbol-file} command.
8562 If your @value{GDBN} does not have a @code{load} command, attempting to
8563 execute it gets the error message ``@code{You can't do that when your
8564 target is @dots{}}''
8566 The file is loaded at whatever address is specified in the executable.
8567 For some object file formats, you can specify the load address when you
8568 link the program; for other formats, like a.out, the object file format
8569 specifies a fixed address.
8570 @c FIXME! This would be a good place for an xref to the GNU linker doc.
8572 @code{load} does not repeat if you press @key{RET} again after using it.
8576 @section Choosing target byte order
8578 @cindex choosing target byte order
8579 @cindex target byte order
8581 Some types of processors, such as the MIPS, PowerPC, and Hitachi SH,
8582 offer the ability to run either big-endian or little-endian byte
8583 orders. Usually the executable or symbol will include a bit to
8584 designate the endian-ness, and you will not need to worry about
8585 which to use. However, you may still find it useful to adjust
8586 @value{GDBN}'s idea of processor endian-ness manually.
8589 @kindex set endian big
8590 @item set endian big
8591 Instruct @value{GDBN} to assume the target is big-endian.
8593 @kindex set endian little
8594 @item set endian little
8595 Instruct @value{GDBN} to assume the target is little-endian.
8597 @kindex set endian auto
8598 @item set endian auto
8599 Instruct @value{GDBN} to use the byte order associated with the
8603 Display @value{GDBN}'s current idea of the target byte order.
8607 Note that these commands merely adjust interpretation of symbolic
8608 data on the host, and that they have absolutely no effect on the
8612 @section Remote debugging
8613 @cindex remote debugging
8615 If you are trying to debug a program running on a machine that cannot run
8616 @value{GDBN} in the usual way, it is often useful to use remote debugging.
8617 For example, you might use remote debugging on an operating system kernel,
8618 or on a small system which does not have a general purpose operating system
8619 powerful enough to run a full-featured debugger.
8621 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
8622 to make this work with particular debugging targets. In addition,
8623 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
8624 but not specific to any particular target system) which you can use if you
8625 write the remote stubs---the code that runs on the remote system to
8626 communicate with @value{GDBN}.
8628 Other remote targets may be available in your
8629 configuration of @value{GDBN}; use @code{help target} to list them.
8632 * Remote Serial:: @value{GDBN} remote serial protocol
8636 @subsection The @value{GDBN} remote serial protocol
8638 @cindex remote serial debugging, overview
8639 To debug a program running on another machine (the debugging
8640 @dfn{target} machine), you must first arrange for all the usual
8641 prerequisites for the program to run by itself. For example, for a C
8646 A startup routine to set up the C runtime environment; these usually
8647 have a name like @file{crt0}. The startup routine may be supplied by
8648 your hardware supplier, or you may have to write your own.
8651 A C subroutine library to support your program's
8652 subroutine calls, notably managing input and output.
8655 A way of getting your program to the other machine---for example, a
8656 download program. These are often supplied by the hardware
8657 manufacturer, but you may have to write your own from hardware
8661 The next step is to arrange for your program to use a serial port to
8662 communicate with the machine where @value{GDBN} is running (the @dfn{host}
8663 machine). In general terms, the scheme looks like this:
8667 @value{GDBN} already understands how to use this protocol; when everything
8668 else is set up, you can simply use the @samp{target remote} command
8669 (@pxref{Targets,,Specifying a Debugging Target}).
8671 @item On the target,
8672 you must link with your program a few special-purpose subroutines that
8673 implement the @value{GDBN} remote serial protocol. The file containing these
8674 subroutines is called a @dfn{debugging stub}.
8676 On certain remote targets, you can use an auxiliary program
8677 @code{gdbserver} instead of linking a stub into your program.
8678 @xref{Server,,Using the @code{gdbserver} program}, for details.
8681 The debugging stub is specific to the architecture of the remote
8682 machine; for example, use @file{sparc-stub.c} to debug programs on
8685 @cindex remote serial stub list
8686 These working remote stubs are distributed with @value{GDBN}:
8691 @cindex @file{i386-stub.c}
8694 For Intel 386 and compatible architectures.
8697 @cindex @file{m68k-stub.c}
8698 @cindex Motorola 680x0
8700 For Motorola 680x0 architectures.
8703 @cindex @file{sh-stub.c}
8706 For Hitachi SH architectures.
8709 @cindex @file{sparc-stub.c}
8711 For @sc{sparc} architectures.
8714 @cindex @file{sparcl-stub.c}
8717 For Fujitsu @sc{sparclite} architectures.
8721 The @file{README} file in the @value{GDBN} distribution may list other
8722 recently added stubs.
8725 * Stub Contents:: What the stub can do for you
8726 * Bootstrapping:: What you must do for the stub
8727 * Debug Session:: Putting it all together
8728 * Protocol:: Definition of the communication protocol
8729 * Server:: Using the `gdbserver' program
8730 * NetWare:: Using the `gdbserve.nlm' program
8734 @subsubsection What the stub can do for you
8736 @cindex remote serial stub
8737 The debugging stub for your architecture supplies these three
8741 @item set_debug_traps
8742 @kindex set_debug_traps
8743 @cindex remote serial stub, initialization
8744 This routine arranges for @code{handle_exception} to run when your
8745 program stops. You must call this subroutine explicitly near the
8746 beginning of your program.
8748 @item handle_exception
8749 @kindex handle_exception
8750 @cindex remote serial stub, main routine
8751 This is the central workhorse, but your program never calls it
8752 explicitly---the setup code arranges for @code{handle_exception} to
8753 run when a trap is triggered.
8755 @code{handle_exception} takes control when your program stops during
8756 execution (for example, on a breakpoint), and mediates communications
8757 with @value{GDBN} on the host machine. This is where the communications
8758 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
8759 representative on the target machine. It begins by sending summary
8760 information on the state of your program, then continues to execute,
8761 retrieving and transmitting any information @value{GDBN} needs, until you
8762 execute a @value{GDBN} command that makes your program resume; at that point,
8763 @code{handle_exception} returns control to your own code on the target
8767 @cindex @code{breakpoint} subroutine, remote
8768 Use this auxiliary subroutine to make your program contain a
8769 breakpoint. Depending on the particular situation, this may be the only
8770 way for @value{GDBN} to get control. For instance, if your target
8771 machine has some sort of interrupt button, you won't need to call this;
8772 pressing the interrupt button transfers control to
8773 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
8774 simply receiving characters on the serial port may also trigger a trap;
8775 again, in that situation, you don't need to call @code{breakpoint} from
8776 your own program---simply running @samp{target remote} from the host
8777 @value{GDBN} session gets control.
8779 Call @code{breakpoint} if none of these is true, or if you simply want
8780 to make certain your program stops at a predetermined point for the
8781 start of your debugging session.
8785 @subsubsection What you must do for the stub
8787 @cindex remote stub, support routines
8788 The debugging stubs that come with @value{GDBN} are set up for a particular
8789 chip architecture, but they have no information about the rest of your
8790 debugging target machine.
8792 First of all you need to tell the stub how to communicate with the
8796 @item int getDebugChar()
8797 @kindex getDebugChar
8798 Write this subroutine to read a single character from the serial port.
8799 It may be identical to @code{getchar} for your target system; a
8800 different name is used to allow you to distinguish the two if you wish.
8802 @item void putDebugChar(int)
8803 @kindex putDebugChar
8804 Write this subroutine to write a single character to the serial port.
8805 It may be identical to @code{putchar} for your target system; a
8806 different name is used to allow you to distinguish the two if you wish.
8809 @cindex control C, and remote debugging
8810 @cindex interrupting remote targets
8811 If you want @value{GDBN} to be able to stop your program while it is
8812 running, you need to use an interrupt-driven serial driver, and arrange
8813 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
8814 character). That is the character which @value{GDBN} uses to tell the
8815 remote system to stop.
8817 Getting the debugging target to return the proper status to @value{GDBN}
8818 probably requires changes to the standard stub; one quick and dirty way
8819 is to just execute a breakpoint instruction (the ``dirty'' part is that
8820 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
8822 Other routines you need to supply are:
8825 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
8826 @kindex exceptionHandler
8827 Write this function to install @var{exception_address} in the exception
8828 handling tables. You need to do this because the stub does not have any
8829 way of knowing what the exception handling tables on your target system
8830 are like (for example, the processor's table might be in @sc{rom},
8831 containing entries which point to a table in @sc{ram}).
8832 @var{exception_number} is the exception number which should be changed;
8833 its meaning is architecture-dependent (for example, different numbers
8834 might represent divide by zero, misaligned access, etc). When this
8835 exception occurs, control should be transferred directly to
8836 @var{exception_address}, and the processor state (stack, registers,
8837 and so on) should be just as it is when a processor exception occurs. So if
8838 you want to use a jump instruction to reach @var{exception_address}, it
8839 should be a simple jump, not a jump to subroutine.
8841 For the 386, @var{exception_address} should be installed as an interrupt
8842 gate so that interrupts are masked while the handler runs. The gate
8843 should be at privilege level 0 (the most privileged level). The
8844 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
8845 help from @code{exceptionHandler}.
8847 @item void flush_i_cache()
8848 @kindex flush_i_cache
8849 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
8850 instruction cache, if any, on your target machine. If there is no
8851 instruction cache, this subroutine may be a no-op.
8853 On target machines that have instruction caches, @value{GDBN} requires this
8854 function to make certain that the state of your program is stable.
8858 You must also make sure this library routine is available:
8861 @item void *memset(void *, int, int)
8863 This is the standard library function @code{memset} that sets an area of
8864 memory to a known value. If you have one of the free versions of
8865 @code{libc.a}, @code{memset} can be found there; otherwise, you must
8866 either obtain it from your hardware manufacturer, or write your own.
8869 If you do not use the GNU C compiler, you may need other standard
8870 library subroutines as well; this varies from one stub to another,
8871 but in general the stubs are likely to use any of the common library
8872 subroutines which @code{@value{GCC}} generates as inline code.
8876 @subsubsection Putting it all together
8878 @cindex remote serial debugging summary
8879 In summary, when your program is ready to debug, you must follow these
8884 Make sure you have defined the supporting low-level routines
8885 (@pxref{Bootstrapping,,What you must do for the stub}):
8887 @code{getDebugChar}, @code{putDebugChar},
8888 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
8892 Insert these lines near the top of your program:
8900 For the 680x0 stub only, you need to provide a variable called
8901 @code{exceptionHook}. Normally you just use:
8904 void (*exceptionHook)() = 0;
8908 but if before calling @code{set_debug_traps}, you set it to point to a
8909 function in your program, that function is called when
8910 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
8911 error). The function indicated by @code{exceptionHook} is called with
8912 one parameter: an @code{int} which is the exception number.
8915 Compile and link together: your program, the @value{GDBN} debugging stub for
8916 your target architecture, and the supporting subroutines.
8919 Make sure you have a serial connection between your target machine and
8920 the @value{GDBN} host, and identify the serial port on the host.
8923 @c The "remote" target now provides a `load' command, so we should
8924 @c document that. FIXME.
8925 Download your program to your target machine (or get it there by
8926 whatever means the manufacturer provides), and start it.
8929 To start remote debugging, run @value{GDBN} on the host machine, and specify
8930 as an executable file the program that is running in the remote machine.
8931 This tells @value{GDBN} how to find your program's symbols and the contents
8935 @cindex serial line, @code{target remote}
8936 Establish communication using the @code{target remote} command.
8937 Its argument specifies how to communicate with the target
8938 machine---either via a devicename attached to a direct serial line, or a
8939 TCP port (usually to a terminal server which in turn has a serial line
8940 to the target). For example, to use a serial line connected to the
8941 device named @file{/dev/ttyb}:
8944 target remote /dev/ttyb
8947 @cindex TCP port, @code{target remote}
8948 To use a TCP connection, use an argument of the form
8949 @code{@var{host}:port}. For example, to connect to port 2828 on a
8950 terminal server named @code{manyfarms}:
8953 target remote manyfarms:2828
8957 Now you can use all the usual commands to examine and change data and to
8958 step and continue the remote program.
8960 To resume the remote program and stop debugging it, use the @code{detach}
8963 @cindex interrupting remote programs
8964 @cindex remote programs, interrupting
8965 Whenever @value{GDBN} is waiting for the remote program, if you type the
8966 interrupt character (often @key{C-C}), @value{GDBN} attempts to stop the
8967 program. This may or may not succeed, depending in part on the hardware
8968 and the serial drivers the remote system uses. If you type the
8969 interrupt character once again, @value{GDBN} displays this prompt:
8972 Interrupted while waiting for the program.
8973 Give up (and stop debugging it)? (y or n)
8976 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
8977 (If you decide you want to try again later, you can use @samp{target
8978 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
8979 goes back to waiting.
8982 @subsubsection Communication protocol
8984 @cindex debugging stub, example
8985 @cindex remote stub, example
8986 @cindex stub example, remote debugging
8987 The stub files provided with @value{GDBN} implement the target side of the
8988 communication protocol, and the @value{GDBN} side is implemented in the
8989 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
8990 these subroutines to communicate, and ignore the details. (If you're
8991 implementing your own stub file, you can still ignore the details: start
8992 with one of the existing stub files. @file{sparc-stub.c} is the best
8993 organized, and therefore the easiest to read.)
8995 However, there may be occasions when you need to know something about
8996 the protocol---for example, if there is only one serial port to your
8997 target machine, you might want your program to do something special if
8998 it recognizes a packet meant for @value{GDBN}.
9000 In the examples below, @samp{<-} and @samp{->} are used to indicate
9001 transmitted and received data respectfully.
9003 @cindex protocol, @value{GDBN} remote serial
9004 @cindex serial protocol, @value{GDBN} remote
9005 @cindex remote serial protocol
9006 All @value{GDBN} commands and responses (other than acknowledgments) are
9007 sent as a @var{packet}. A @var{packet} is introduced with the character
9008 @samp{$}, the actual @var{packet-data}, and the terminating character
9009 @samp{#} followed by a two-digit @var{checksum}:
9012 @code{$}@var{packet-data}@code{#}@var{checksum}
9016 @cindex checksum, for @value{GDBN} remote
9018 The two-digit @var{checksum} is computed as the modulo 256 sum of all
9019 characters between the leading @samp{$} and the trailing @samp{#} (an
9020 eight bit unsigned checksum).
9022 Implementors should note that prior to @value{GDBN} 5.0 the protocol
9023 specification also included an optional two-digit @var{sequence-id}:
9026 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
9029 @cindex sequence-id, for @value{GDBN} remote
9031 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
9032 has never output @var{sequence-id}s. Stubs that handle packets added
9033 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
9035 @cindex acknowledgment, for @value{GDBN} remote
9036 When either the host or the target machine receives a packet, the first
9037 response expected is an acknowledgment: either @samp{+} (to indicate
9038 the package was received correctly) or @samp{-} (to request
9042 <- @code{$}@var{packet-data}@code{#}@var{checksum}
9047 The host (@value{GDBN}) sends @var{command}s, and the target (the
9048 debugging stub incorporated in your program) sends a @var{response}. In
9049 the case of step and continue @var{command}s, the response is only sent
9050 when the operation has completed (the target has again stopped).
9052 @var{packet-data} consists of a sequence of characters with the
9053 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
9056 Fields within the packet should be separated using @samp{,} @samp{;} or
9057 @samp{:}. Except where otherwise noted all numbers are represented in
9058 HEX with leading zeros suppressed.
9060 Implementors should note that prior to @value{GDBN} 5.0, the character
9061 @samp{:} could not appear as the third character in a packet (as it
9062 would potentially conflict with the @var{sequence-id}).
9064 Response @var{data} can be run-length encoded to save space. A @samp{*}
9065 means that the next character is an @sc{ascii} encoding giving a repeat count
9066 which stands for that many repetitions of the character preceding the
9067 @samp{*}. The encoding is @code{n+29}, yielding a printable character
9068 where @code{n >=3} (which is where rle starts to win). The printable
9069 characters @samp{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
9070 value greater than 126 should not be used.
9072 Some remote systems have used a different run-length encoding mechanism
9073 loosely refered to as the cisco encoding. Following the @samp{*}
9074 character are two hex digits that indicate the size of the packet.
9081 means the same as "0000".
9083 The error response returned for some packets includes a two character
9084 error number. That number is not well defined.
9086 For any @var{command} not supported by the stub, an empty response
9087 (@samp{$#00}) should be returned. That way it is possible to extend the
9088 protocol. A newer @value{GDBN} can tell if a packet is supported based
9091 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
9092 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
9095 Below is a complete list of all currently defined @var{command}s and
9096 their corresponding response @var{data}:
9098 @multitable @columnfractions .30 .30 .40
9106 Use the extended remote protocol. Sticky---only needs to be set once.
9107 The extended remote protocol supports the @samp{R} packet.
9111 Stubs that support the extended remote protocol return @samp{} which,
9112 unfortunately, is identical to the response returned by stubs that do not
9113 support protocol extensions.
9118 Indicate the reason the target halted. The reply is the same as for step
9127 @tab Reserved for future use
9129 @item set program arguments @strong{(reserved)}
9130 @tab @code{A}@var{arglen}@code{,}@var{argnum}@code{,}@var{arg}@code{,...}
9135 Initialized @samp{argv[]} array passed into program. @var{arglen}
9136 specifies the number of bytes in the hex encoded byte stream @var{arg}.
9137 See @file{gdbserver} for more details.
9139 @tab reply @code{OK}
9141 @tab reply @code{E}@var{NN}
9143 @item set baud @strong{(deprecated)}
9144 @tab @code{b}@var{baud}
9146 Change the serial line speed to @var{baud}. JTC: @emph{When does the
9147 transport layer state change? When it's received, or after the ACK is
9148 transmitted. In either case, there are problems if the command or the
9149 acknowledgment packet is dropped.} Stan: @emph{If people really wanted
9150 to add something like this, and get it working for the first time, they
9151 ought to modify ser-unix.c to send some kind of out-of-band message to a
9152 specially-setup stub and have the switch happen "in between" packets, so
9153 that from remote protocol's point of view, nothing actually
9156 @item set breakpoint @strong{(deprecated)}
9157 @tab @code{B}@var{addr},@var{mode}
9159 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
9160 breakpoint at @var{addr}. @emph{This has been replaced by the @samp{Z} and
9164 @tab @code{c}@var{addr}
9166 @var{addr} is address to resume. If @var{addr} is omitted, resume at
9172 @item continue with signal
9173 @tab @code{C}@var{sig}@code{;}@var{addr}
9175 Continue with signal @var{sig} (hex signal number). If
9176 @code{;}@var{addr} is omitted, resume at same address.
9181 @item toggle debug @strong{(deprecated)}
9189 Detach @value{GDBN} from the remote system. Sent to the remote target before
9190 @value{GDBN} disconnects.
9192 @tab reply @emph{no response}
9194 @value{GDBN} does not check for any response after sending this packet.
9198 @tab Reserved for future use
9202 @tab Reserved for future use
9206 @tab Reserved for future use
9210 @tab Reserved for future use
9212 @item read registers
9214 @tab Read general registers.
9216 @tab reply @var{XX...}
9218 Each byte of register data is described by two hex digits. The bytes
9219 with the register are transmitted in target byte order. The size of
9220 each register and their position within the @samp{g} @var{packet} are
9221 determined by the @value{GDBN} internal macros @var{REGISTER_RAW_SIZE} and
9222 @var{REGISTER_NAME} macros. The specification of several standard
9223 @code{g} packets is specified below.
9225 @tab @code{E}@var{NN}
9229 @tab @code{G}@var{XX...}
9231 See @samp{g} for a description of the @var{XX...} data.
9233 @tab reply @code{OK}
9236 @tab reply @code{E}@var{NN}
9241 @tab Reserved for future use
9244 @tab @code{H}@var{c}@var{t...}
9246 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
9247 @samp{G}, et.al.). @var{c} = @samp{c} for thread used in step and
9248 continue; @var{t...} can be -1 for all threads. @var{c} = @samp{g} for
9249 thread used in other operations. If zero, pick a thread, any thread.
9251 @tab reply @code{OK}
9254 @tab reply @code{E}@var{NN}
9258 @c 'H': How restrictive (or permissive) is the thread model. If a
9259 @c thread is selected and stopped, are other threads allowed
9260 @c to continue to execute? As I mentioned above, I think the
9261 @c semantics of each command when a thread is selected must be
9262 @c described. For example:
9264 @c 'g': If the stub supports threads and a specific thread is
9265 @c selected, returns the register block from that thread;
9266 @c otherwise returns current registers.
9268 @c 'G' If the stub supports threads and a specific thread is
9269 @c selected, sets the registers of the register block of
9270 @c that thread; otherwise sets current registers.
9272 @item cycle step @strong{(draft)}
9273 @tab @code{i}@var{addr}@code{,}@var{nnn}
9275 Step the remote target by a single clock cycle. If @code{,}@var{nnn} is
9276 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
9277 step starting at that address.
9279 @item signal then cycle step @strong{(reserved)}
9282 See @samp{i} and @samp{S} for likely syntax and semantics.
9286 @tab Reserved for future use
9290 @tab Reserved for future use
9295 FIXME: @emph{There is no description of how operate when a specific
9296 thread context has been selected (ie. does 'k' kill only that thread?)}.
9300 @tab Reserved for future use
9304 @tab Reserved for future use
9307 @tab @code{m}@var{addr}@code{,}@var{length}
9309 Read @var{length} bytes of memory starting at address @var{addr}.
9310 Neither @value{GDBN} nor the stub assume that sized memory transfers are assumed
9311 using word alligned accesses. FIXME: @emph{A word aligned memory
9312 transfer mechanism is needed.}
9314 @tab reply @var{XX...}
9316 @var{XX...} is mem contents. Can be fewer bytes than requested if able
9317 to read only part of the data. Neither @value{GDBN} nor the stub assume that
9318 sized memory transfers are assumed using word alligned accesses. FIXME:
9319 @emph{A word aligned memory transfer mechanism is needed.}
9321 @tab reply @code{E}@var{NN}
9322 @tab @var{NN} is errno
9325 @tab @code{M}@var{addr},@var{length}@code{:}@var{XX...}
9327 Write @var{length} bytes of memory starting at address @var{addr}.
9328 @var{XX...} is the data.
9330 @tab reply @code{OK}
9333 @tab reply @code{E}@var{NN}
9335 for an error (this includes the case where only part of the data was
9340 @tab Reserved for future use
9344 @tab Reserved for future use
9348 @tab Reserved for future use
9352 @tab Reserved for future use
9354 @item read reg @strong{(reserved)}
9355 @tab @code{p}@var{n...}
9359 @tab return @var{r....}
9360 @tab The hex encoded value of the register in target byte order.
9363 @tab @code{P}@var{n...}@code{=}@var{r...}
9365 Write register @var{n...} with value @var{r...}, which contains two hex
9366 digits for each byte in the register (target byte order).
9368 @tab reply @code{OK}
9371 @tab reply @code{E}@var{NN}
9375 @tab @code{q}@var{query}
9377 Request info about @var{query}. In general @value{GDBN} queries
9378 have a leading upper case letter. Custom vendor queries should use a
9379 company prefix (in lower case) ex: @samp{qfsf.var}. @var{query} may
9380 optionally be followed by a @samp{,} or @samp{;} separated list. Stubs
9381 must ensure that they match the full @var{query} name.
9383 @tab reply @code{XX...}
9384 @tab Hex encoded data from query. The reply can not be empty.
9386 @tab reply @code{E}@var{NN}
9390 @tab Indicating an unrecognized @var{query}.
9393 @tab @code{Q}@var{var}@code{=}@var{val}
9395 Set value of @var{var} to @var{val}. See @samp{q} for a discussing of
9398 @item reset @strong{(deprecated)}
9401 Reset the entire system.
9403 @item remote restart
9404 @tab @code{R}@var{XX}
9406 Restart the remote server. @var{XX} while needed has no clear
9407 definition. FIXME: @emph{An example interaction explaining how this
9408 packet is used in extended-remote mode is needed}.
9411 @tab @code{s}@var{addr}
9413 @var{addr} is address to resume. If @var{addr} is omitted, resume at
9419 @item step with signal
9420 @tab @code{S}@var{sig}@code{;}@var{addr}
9422 Like @samp{C} but step not continue.
9428 @tab @code{t}@var{addr}@code{:}@var{PP}@code{,}@var{MM}
9430 Search backwards starting at address @var{addr} for a match with pattern
9431 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4
9432 bytes. @var{addr} must be at least 3 digits.
9435 @tab @code{T}@var{XX}
9436 @tab Find out if the thread XX is alive.
9438 @tab reply @code{OK}
9439 @tab thread is still alive
9441 @tab reply @code{E}@var{NN}
9446 @tab Reserved for future use
9450 @tab Reserved for future use
9454 @tab Reserved for future use
9458 @tab Reserved for future use
9462 @tab Reserved for future use
9466 @tab Reserved for future use
9470 @tab Reserved for future use
9472 @item write mem (binary)
9473 @tab @code{X}@var{addr}@code{,}@var{length}@var{:}@var{XX...}
9475 @var{addr} is address, @var{length} is number of bytes, @var{XX...} is
9476 binary data. The characters @code{$}, @code{#}, and @code{0x7d} are
9477 escaped using @code{0x7d}.
9479 @tab reply @code{OK}
9482 @tab reply @code{E}@var{NN}
9487 @tab Reserved for future use
9491 @tab Reserved for future use
9493 @item remove break or watchpoint @strong{(draft)}
9494 @tab @code{z}@var{t}@code{,}@var{addr}@code{,}@var{length}
9498 @item insert break or watchpoint @strong{(draft)}
9499 @tab @code{Z}@var{t}@code{,}@var{addr}@code{,}@var{length}
9501 @var{t} is type: @samp{0} - software breakpoint, @samp{1} - hardware
9502 breakpoint, @samp{2} - write watchpoint, @samp{3} - read watchpoint,
9503 @samp{4} - access watchpoint; @var{addr} is address; @var{length} is in
9504 bytes. For a software breakpoint, @var{length} specifies the size of
9505 the instruction to be patched. For hardware breakpoints and watchpoints
9506 @var{length} specifies the memory region to be monitored. To avoid
9507 potential problems with duplicate packets, the operations should be
9508 implemented in an idempotent way.
9510 @tab reply @code{E}@var{NN}
9513 @tab reply @code{OK}
9517 @tab If not supported.
9521 @tab Reserved for future use
9525 The @samp{C}, @samp{c}, @samp{S}, @samp{s} and @samp{?} packets can
9526 receive any of the below as a reply. In the case of the @samp{C},
9527 @samp{c}, @samp{S} and @samp{s} packets, that reply is only returned
9528 when the target halts. In the below the exact meaning of @samp{signal
9529 number} is poorly defined. In general one of the UNIX signal numbering
9530 conventions is used.
9532 @multitable @columnfractions .4 .6
9534 @item @code{S}@var{AA}
9535 @tab @var{AA} is the signal number
9537 @item @code{T}@var{AA}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}
9539 @var{AA} = two hex digit signal number; @var{n...} = register number
9540 (hex), @var{r...} = target byte ordered register contents, size defined
9541 by @code{REGISTER_RAW_SIZE}; @var{n...} = @samp{thread}, @var{r...} =
9542 thread process ID, this is a hex integer; @var{n...} = other string not
9543 starting with valid hex digit. @value{GDBN} should ignore this
9544 @var{n...}, @var{r...} pair and go on to the next. This way we can
9545 extend the protocol.
9547 @item @code{W}@var{AA}
9549 The process exited, and @var{AA} is the exit status. This is only
9550 applicable for certains sorts of targets.
9552 @item @code{X}@var{AA}
9554 The process terminated with signal @var{AA}.
9556 @item @code{N}@var{AA}@code{;}@var{t...}@code{;}@var{d...}@code{;}@var{b...} @strong{(obsolete)}
9558 @var{AA} = signal number; @var{t...} = address of symbol "_start";
9559 @var{d...} = base of data section; @var{b...} = base of bss section.
9560 @emph{Note: only used by Cisco Systems targets. The difference between
9561 this reply and the "qOffsets" query is that the 'N' packet may arrive
9562 spontaneously whereas the 'qOffsets' is a query initiated by the host
9565 @item @code{O}@var{XX...}
9567 @var{XX...} is hex encoding of @sc{ascii} data. This can happen at any time
9568 while the program is running and the debugger should continue to wait
9573 The following set and query packets have already been defined.
9575 @multitable @columnfractions .2 .2 .6
9577 @item current thread
9578 @tab @code{q}@code{C}
9579 @tab Return the current thread id.
9581 @tab reply @code{QC}@var{pid}
9583 Where @var{pid} is a HEX encoded 16 bit process id.
9586 @tab Any other reply implies the old pid.
9588 @item all thread ids
9589 @tab @code{q}@code{fThreadInfo}
9591 @tab @code{q}@code{sThreadInfo}
9593 Obtain a list of active thread ids from the target (OS). Since there
9594 may be too many active threads to fit into one reply packet, this query
9595 works iteratively: it may require more than one query/reply sequence to
9596 obtain the entire list of threads. The first query of the sequence will
9597 be the @code{qf}@code{ThreadInfo} query; subsequent queries in the
9598 sequence will be the @code{qs}@code{ThreadInfo} query.
9601 @tab NOTE: replaces the @code{qL} query (see below).
9603 @tab reply @code{m}@var{<id>}
9604 @tab A single thread id
9606 @tab reply @code{m}@var{<id>},@var{<id>...}
9607 @tab a comma-separated list of thread ids
9610 @tab (lower case 'el') denotes end of list.
9614 In response to each query, the target will reply with a list of one
9615 or more thread ids, in big-endian hex, separated by commas. GDB will
9616 respond to each reply with a request for more thread ids (using the
9617 @code{qs} form of the query), until the target responds with @code{l}
9618 (lower-case el, for @code{'last'}).
9620 @item extra thread info
9621 @tab @code{q}@code{ThreadExtraInfo}@code{,}@var{id}
9626 Where @var{<id>} is a thread-id in big-endian hex.
9627 Obtain a printable string description of a thread's attributes from
9628 the target OS. This string may contain anything that the target OS
9629 thinks is interesting for @value{GDBN} to tell the user about the thread.
9630 The string is displayed in @value{GDBN}'s @samp{info threads} display.
9631 Some examples of possible thread extra info strings are "Runnable", or
9634 @tab reply @var{XX...}
9636 Where @var{XX...} is a hex encoding of @sc{ascii} data, comprising the
9637 printable string containing the extra information about the thread's
9640 @item query @var{LIST} or @var{threadLIST} @strong{(deprecated)}
9641 @tab @code{q}@code{L}@var{startflag}@var{threadcount}@var{nextthread}
9646 Obtain thread information from RTOS. Where: @var{startflag} (one hex
9647 digit) is one to indicate the first query and zero to indicate a
9648 subsequent query; @var{threadcount} (two hex digits) is the maximum
9649 number of threads the response packet can contain; and @var{nextthread}
9650 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
9651 returned in the response as @var{argthread}.
9654 @tab NOTE: this query is replaced by the @code{q}@code{fThreadInfo}
9657 @tab reply @code{q}@code{M}@var{count}@var{done}@var{argthread}@var{thread...}
9662 Where: @var{count} (two hex digits) is the number of threads being
9663 returned; @var{done} (one hex digit) is zero to indicate more threads
9664 and one indicates no further threads; @var{argthreadid} (eight hex
9665 digits) is @var{nextthread} from the request packet; @var{thread...} is
9666 a sequence of thread IDs from the target. @var{threadid} (eight hex
9667 digits). See @code{remote.c:parse_threadlist_response()}.
9669 @item compute CRC of memory block
9670 @tab @code{q}@code{CRC:}@var{addr}@code{,}@var{length}
9673 @tab reply @code{E}@var{NN}
9674 @tab An error (such as memory fault)
9676 @tab reply @code{C}@var{CRC32}
9677 @tab A 32 bit cyclic redundancy check of the specified memory region.
9679 @item query sect offs
9680 @tab @code{q}@code{Offsets}
9682 Get section offsets that the target used when re-locating the downloaded
9683 image. @emph{Note: while a @code{Bss} offset is included in the
9684 response, @value{GDBN} ignores this and instead applies the @code{Data}
9685 offset to the @code{Bss} section.}
9687 @tab reply @code{Text=}@var{xxx}@code{;Data=}@var{yyy}@code{;Bss=}@var{zzz}
9689 @item thread info request
9690 @tab @code{q}@code{P}@var{mode}@var{threadid}
9695 Returns information on @var{threadid}. Where: @var{mode} is a hex
9696 encoded 32 bit mode; @var{threadid} is a hex encoded 64 bit thread ID.
9700 See @code{remote.c:remote_unpack_thread_info_response()}.
9702 @item remote command
9703 @tab @code{q}@code{Rcmd,}@var{COMMAND}
9708 @var{COMMAND} (hex encoded) is passed to the local interpreter for
9709 execution. Invalid commands should be reported using the output string.
9710 Before the final result packet, the target may also respond with a
9711 number of intermediate @code{O}@var{OUTPUT} console output
9712 packets. @emph{Implementors should note that providing access to a
9713 stubs's interpreter may have security implications}.
9715 @tab reply @code{OK}
9717 A command response with no output.
9719 @tab reply @var{OUTPUT}
9721 A command response with the hex encoded output string @var{OUTPUT}.
9723 @tab reply @code{E}@var{NN}
9725 Indicate a badly formed request.
9730 When @samp{q}@samp{Rcmd} is not recognized.
9734 The following @samp{g}/@samp{G} packets have previously been defined.
9735 In the below, some thirty-two bit registers are transferred as sixty-four
9736 bits. Those registers should be zero/sign extended (which?) to fill the
9737 space allocated. Register bytes are transfered in target byte order.
9738 The two nibbles within a register byte are transfered most-significant -
9741 @multitable @columnfractions .5 .5
9745 All registers are transfered as thirty-two bit quantities in the order:
9746 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
9747 registers; fsr; fir; fp.
9751 All registers are transfered as sixty-four bit quantities (including
9752 thirty-two bit registers such as @code{sr}). The ordering is the same
9757 Example sequence of a target being re-started. Notice how the restart
9758 does not get any direct output:
9763 @emph{target restarts}
9766 -> @code{T001:1234123412341234}
9770 Example sequence of a target being stepped by a single instruction:
9778 -> @code{T001:1234123412341234}
9787 @subsubsection Using the @code{gdbserver} program
9790 @cindex remote connection without stubs
9791 @code{gdbserver} is a control program for Unix-like systems, which
9792 allows you to connect your program with a remote @value{GDBN} via
9793 @code{target remote}---but without linking in the usual debugging stub.
9795 @code{gdbserver} is not a complete replacement for the debugging stubs,
9796 because it requires essentially the same operating-system facilities
9797 that @value{GDBN} itself does. In fact, a system that can run
9798 @code{gdbserver} to connect to a remote @value{GDBN} could also run
9799 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
9800 because it is a much smaller program than @value{GDBN} itself. It is
9801 also easier to port than all of @value{GDBN}, so you may be able to get
9802 started more quickly on a new system by using @code{gdbserver}.
9803 Finally, if you develop code for real-time systems, you may find that
9804 the tradeoffs involved in real-time operation make it more convenient to
9805 do as much development work as possible on another system, for example
9806 by cross-compiling. You can use @code{gdbserver} to make a similar
9807 choice for debugging.
9809 @value{GDBN} and @code{gdbserver} communicate via either a serial line
9810 or a TCP connection, using the standard @value{GDBN} remote serial
9814 @item On the target machine,
9815 you need to have a copy of the program you want to debug.
9816 @code{gdbserver} does not need your program's symbol table, so you can
9817 strip the program if necessary to save space. @value{GDBN} on the host
9818 system does all the symbol handling.
9820 To use the server, you must tell it how to communicate with @value{GDBN};
9821 the name of your program; and the arguments for your program. The
9825 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
9828 @var{comm} is either a device name (to use a serial line) or a TCP
9829 hostname and portnumber. For example, to debug Emacs with the argument
9830 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
9834 target> gdbserver /dev/com1 emacs foo.txt
9837 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
9840 To use a TCP connection instead of a serial line:
9843 target> gdbserver host:2345 emacs foo.txt
9846 The only difference from the previous example is the first argument,
9847 specifying that you are communicating with the host @value{GDBN} via
9848 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
9849 expect a TCP connection from machine @samp{host} to local TCP port 2345.
9850 (Currently, the @samp{host} part is ignored.) You can choose any number
9851 you want for the port number as long as it does not conflict with any
9852 TCP ports already in use on the target system (for example, @code{23} is
9853 reserved for @code{telnet}).@footnote{If you choose a port number that
9854 conflicts with another service, @code{gdbserver} prints an error message
9855 and exits.} You must use the same port number with the host @value{GDBN}
9856 @code{target remote} command.
9858 @item On the @value{GDBN} host machine,
9859 you need an unstripped copy of your program, since @value{GDBN} needs
9860 symbols and debugging information. Start up @value{GDBN} as usual,
9861 using the name of the local copy of your program as the first argument.
9862 (You may also need the @w{@samp{--baud}} option if the serial line is
9863 running at anything other than 9600@dmn{bps}.) After that, use @code{target
9864 remote} to establish communications with @code{gdbserver}. Its argument
9865 is either a device name (usually a serial device, like
9866 @file{/dev/ttyb}), or a TCP port descriptor in the form
9867 @code{@var{host}:@var{PORT}}. For example:
9870 (@value{GDBP}) target remote /dev/ttyb
9874 communicates with the server via serial line @file{/dev/ttyb}, and
9877 (@value{GDBP}) target remote the-target:2345
9881 communicates via a TCP connection to port 2345 on host @w{@file{the-target}}.
9882 For TCP connections, you must start up @code{gdbserver} prior to using
9883 the @code{target remote} command. Otherwise you may get an error whose
9884 text depends on the host system, but which usually looks something like
9885 @samp{Connection refused}.
9889 @subsubsection Using the @code{gdbserve.nlm} program
9891 @kindex gdbserve.nlm
9892 @code{gdbserve.nlm} is a control program for NetWare systems, which
9893 allows you to connect your program with a remote @value{GDBN} via
9894 @code{target remote}.
9896 @value{GDBN} and @code{gdbserve.nlm} communicate via a serial line,
9897 using the standard @value{GDBN} remote serial protocol.
9900 @item On the target machine,
9901 you need to have a copy of the program you want to debug.
9902 @code{gdbserve.nlm} does not need your program's symbol table, so you
9903 can strip the program if necessary to save space. @value{GDBN} on the
9904 host system does all the symbol handling.
9906 To use the server, you must tell it how to communicate with
9907 @value{GDBN}; the name of your program; and the arguments for your
9908 program. The syntax is:
9911 load gdbserve [ BOARD=@var{board} ] [ PORT=@var{port} ]
9912 [ BAUD=@var{baud} ] @var{program} [ @var{args} @dots{} ]
9915 @var{board} and @var{port} specify the serial line; @var{baud} specifies
9916 the baud rate used by the connection. @var{port} and @var{node} default
9917 to 0, @var{baud} defaults to 9600@dmn{bps}.
9919 For example, to debug Emacs with the argument @samp{foo.txt}and
9920 communicate with @value{GDBN} over serial port number 2 or board 1
9921 using a 19200@dmn{bps} connection:
9924 load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
9927 @item On the @value{GDBN} host machine,
9928 you need an unstripped copy of your program, since @value{GDBN} needs
9929 symbols and debugging information. Start up @value{GDBN} as usual,
9930 using the name of the local copy of your program as the first argument.
9931 (You may also need the @w{@samp{--baud}} option if the serial line is
9932 running at anything other than 9600@dmn{bps}. After that, use @code{target
9933 remote} to establish communications with @code{gdbserve.nlm}. Its
9934 argument is a device name (usually a serial device, like
9935 @file{/dev/ttyb}). For example:
9938 (@value{GDBP}) target remote /dev/ttyb
9942 communications with the server via serial line @file{/dev/ttyb}.
9946 @section Kernel Object Display
9948 @cindex kernel object display
9949 @cindex kernel object
9952 Some targets support kernel object display. Using this facility,
9953 @value{GDBN} communicates specially with the underlying operating system
9954 and can display information about operating system-level objects such as
9955 mutexes and other synchronization objects. Exactly which objects can be
9956 displayed is determined on a per-OS basis.
9958 Use the @code{set os} command to set the operating system. This tells
9959 @value{GDBN} which kernel object display module to initialize:
9962 (@value{GDBP}) set os cisco
9965 If @code{set os} succeeds, @value{GDBN} will display some information
9966 about the operating system, and will create a new @code{info} command
9967 which can be used to query the target. The @code{info} command is named
9968 after the operating system:
9971 (@value{GDBP}) info cisco
9972 List of Cisco Kernel Objects
9974 any Any and all objects
9977 Further subcommands can be used to query about particular objects known
9980 There is currently no way to determine whether a given operating system
9981 is supported other than to try it.
9984 @node Configurations
9985 @chapter Configuration-Specific Information
9987 While nearly all @value{GDBN} commands are available for all native and
9988 cross versions of the debugger, there are some exceptions. This chapter
9989 describes things that are only available in certain configurations.
9991 There are three major categories of configurations: native
9992 configurations, where the host and target are the same, embedded
9993 operating system configurations, which are usually the same for several
9994 different processor architectures, and bare embedded processors, which
9995 are quite different from each other.
10000 * Embedded Processors::
10007 This section describes details specific to particular native
10012 * SVR4 Process Information:: SVR4 process information
10018 On HP-UX systems, if you refer to a function or variable name that
10019 begins with a dollar sign, @value{GDBN} searches for a user or system
10020 name first, before it searches for a convenience variable.
10022 @node SVR4 Process Information
10023 @subsection SVR4 process information
10026 @cindex process image
10028 Many versions of SVR4 provide a facility called @samp{/proc} that can be
10029 used to examine the image of a running process using file-system
10030 subroutines. If @value{GDBN} is configured for an operating system with
10031 this facility, the command @code{info proc} is available to report on
10032 several kinds of information about the process running your program.
10033 @code{info proc} works only on SVR4 systems that include the
10034 @code{procfs} code. This includes OSF/1 (Digital Unix), Solaris, Irix,
10035 and Unixware, but not HP-UX or Linux, for example.
10040 Summarize available information about the process.
10042 @kindex info proc mappings
10043 @item info proc mappings
10044 Report on the address ranges accessible in the program, with information
10045 on whether your program may read, write, or execute each range.
10047 @kindex info proc times
10048 @item info proc times
10049 Starting time, user CPU time, and system CPU time for your program and
10052 @kindex info proc id
10054 Report on the process IDs related to your program: its own process ID,
10055 the ID of its parent, the process group ID, and the session ID.
10057 @kindex info proc status
10058 @item info proc status
10059 General information on the state of the process. If the process is
10060 stopped, this report includes the reason for stopping, and any signal
10063 @item info proc all
10064 Show all the above information about the process.
10068 @section Embedded Operating Systems
10070 This section describes configurations involving the debugging of
10071 embedded operating systems that are available for several different
10075 * VxWorks:: Using @value{GDBN} with VxWorks
10078 @value{GDBN} includes the ability to debug programs running on
10079 various real-time operating systems.
10082 @subsection Using @value{GDBN} with VxWorks
10088 @kindex target vxworks
10089 @item target vxworks @var{machinename}
10090 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
10091 is the target system's machine name or IP address.
10095 On VxWorks, @code{load} links @var{filename} dynamically on the
10096 current target system as well as adding its symbols in @value{GDBN}.
10098 @value{GDBN} enables developers to spawn and debug tasks running on networked
10099 VxWorks targets from a Unix host. Already-running tasks spawned from
10100 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
10101 both the Unix host and on the VxWorks target. The program
10102 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
10103 installed with the name @code{vxgdb}, to distinguish it from a
10104 @value{GDBN} for debugging programs on the host itself.)
10107 @item VxWorks-timeout @var{args}
10108 @kindex vxworks-timeout
10109 All VxWorks-based targets now support the option @code{vxworks-timeout}.
10110 This option is set by the user, and @var{args} represents the number of
10111 seconds @value{GDBN} waits for responses to rpc's. You might use this if
10112 your VxWorks target is a slow software simulator or is on the far side
10113 of a thin network line.
10116 The following information on connecting to VxWorks was current when
10117 this manual was produced; newer releases of VxWorks may use revised
10120 @kindex INCLUDE_RDB
10121 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
10122 to include the remote debugging interface routines in the VxWorks
10123 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
10124 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
10125 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
10126 source debugging task @code{tRdbTask} when VxWorks is booted. For more
10127 information on configuring and remaking VxWorks, see the manufacturer's
10129 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
10131 Once you have included @file{rdb.a} in your VxWorks system image and set
10132 your Unix execution search path to find @value{GDBN}, you are ready to
10133 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
10134 @code{vxgdb}, depending on your installation).
10136 @value{GDBN} comes up showing the prompt:
10143 * VxWorks Connection:: Connecting to VxWorks
10144 * VxWorks Download:: VxWorks download
10145 * VxWorks Attach:: Running tasks
10148 @node VxWorks Connection
10149 @subsubsection Connecting to VxWorks
10151 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
10152 network. To connect to a target whose host name is ``@code{tt}'', type:
10155 (vxgdb) target vxworks tt
10159 @value{GDBN} displays messages like these:
10162 Attaching remote machine across net...
10167 @value{GDBN} then attempts to read the symbol tables of any object modules
10168 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
10169 these files by searching the directories listed in the command search
10170 path (@pxref{Environment, ,Your program's environment}); if it fails
10171 to find an object file, it displays a message such as:
10174 prog.o: No such file or directory.
10177 When this happens, add the appropriate directory to the search path with
10178 the @value{GDBN} command @code{path}, and execute the @code{target}
10181 @node VxWorks Download
10182 @subsubsection VxWorks download
10184 @cindex download to VxWorks
10185 If you have connected to the VxWorks target and you want to debug an
10186 object that has not yet been loaded, you can use the @value{GDBN}
10187 @code{load} command to download a file from Unix to VxWorks
10188 incrementally. The object file given as an argument to the @code{load}
10189 command is actually opened twice: first by the VxWorks target in order
10190 to download the code, then by @value{GDBN} in order to read the symbol
10191 table. This can lead to problems if the current working directories on
10192 the two systems differ. If both systems have NFS mounted the same
10193 filesystems, you can avoid these problems by using absolute paths.
10194 Otherwise, it is simplest to set the working directory on both systems
10195 to the directory in which the object file resides, and then to reference
10196 the file by its name, without any path. For instance, a program
10197 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
10198 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
10199 program, type this on VxWorks:
10202 -> cd "@var{vxpath}/vw/demo/rdb"
10206 Then, in @value{GDBN}, type:
10209 (vxgdb) cd @var{hostpath}/vw/demo/rdb
10210 (vxgdb) load prog.o
10213 @value{GDBN} displays a response similar to this:
10216 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
10219 You can also use the @code{load} command to reload an object module
10220 after editing and recompiling the corresponding source file. Note that
10221 this makes @value{GDBN} delete all currently-defined breakpoints,
10222 auto-displays, and convenience variables, and to clear the value
10223 history. (This is necessary in order to preserve the integrity of
10224 debugger's data structures that reference the target system's symbol
10227 @node VxWorks Attach
10228 @subsubsection Running tasks
10230 @cindex running VxWorks tasks
10231 You can also attach to an existing task using the @code{attach} command as
10235 (vxgdb) attach @var{task}
10239 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
10240 or suspended when you attach to it. Running tasks are suspended at
10241 the time of attachment.
10243 @node Embedded Processors
10244 @section Embedded Processors
10246 This section goes into details specific to particular embedded
10250 * A29K Embedded:: AMD A29K Embedded
10252 * H8/300:: Hitachi H8/300
10253 * H8/500:: Hitachi H8/500
10254 * i960:: Intel i960
10255 * M32R/D:: Mitsubishi M32R/D
10256 * M68K:: Motorola M68K
10257 * M88K:: Motorola M88K
10258 * MIPS Embedded:: MIPS Embedded
10259 * PA:: HP PA Embedded
10262 * Sparclet:: Tsqware Sparclet
10263 * Sparclite:: Fujitsu Sparclite
10264 * ST2000:: Tandem ST2000
10265 * Z8000:: Zilog Z8000
10268 @node A29K Embedded
10269 @subsection AMD A29K Embedded
10274 * Comms (EB29K):: Communications setup
10275 * gdb-EB29K:: EB29K cross-debugging
10276 * Remote Log:: Remote log
10281 @kindex target adapt
10282 @item target adapt @var{dev}
10283 Adapt monitor for A29K.
10285 @kindex target amd-eb
10286 @item target amd-eb @var{dev} @var{speed} @var{PROG}
10288 Remote PC-resident AMD EB29K board, attached over serial lines.
10289 @var{dev} is the serial device, as for @code{target remote};
10290 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
10291 name of the program to be debugged, as it appears to DOS on the PC.
10292 @xref{A29K EB29K, ,EBMON protocol for AMD29K}.
10297 @subsubsection A29K UDI
10300 @cindex AMD29K via UDI
10302 @value{GDBN} supports AMD's UDI (``Universal Debugger Interface'')
10303 protocol for debugging the a29k processor family. To use this
10304 configuration with AMD targets running the MiniMON monitor, you need the
10305 program @code{MONTIP}, available from AMD at no charge. You can also
10306 use @value{GDBN} with the UDI-conformant a29k simulator program
10307 @code{ISSTIP}, also available from AMD.
10310 @item target udi @var{keyword}
10312 Select the UDI interface to a remote a29k board or simulator, where
10313 @var{keyword} is an entry in the AMD configuration file @file{udi_soc}.
10314 This file contains keyword entries which specify parameters used to
10315 connect to a29k targets. If the @file{udi_soc} file is not in your
10316 working directory, you must set the environment variable @samp{UDICONF}
10321 @subsubsection EBMON protocol for AMD29K
10323 @cindex EB29K board
10324 @cindex running 29K programs
10326 AMD distributes a 29K development board meant to fit in a PC, together
10327 with a DOS-hosted monitor program called @code{EBMON}. As a shorthand
10328 term, this development system is called the ``EB29K''. To use
10329 @value{GDBN} from a Unix system to run programs on the EB29K board, you
10330 must first connect a serial cable between the PC (which hosts the EB29K
10331 board) and a serial port on the Unix system. In the following, we
10332 assume you've hooked the cable between the PC's @file{COM1} port and
10333 @file{/dev/ttya} on the Unix system.
10335 @node Comms (EB29K)
10336 @subsubsection Communications setup
10338 The next step is to set up the PC's port, by doing something like this
10342 C:\> MODE com1:9600,n,8,1,none
10346 This example---run on an MS DOS 4.0 system---sets the PC port to 9600
10347 bps, no parity, eight data bits, one stop bit, and no ``retry'' action;
10348 you must match the communications parameters when establishing the Unix
10349 end of the connection as well.
10350 @c FIXME: Who knows what this "no retry action" crud from the DOS manual may
10351 @c mean? It's optional; leave it out? ---doc@cygnus.com, 25feb91
10353 @c It's optional, but it's unwise to omit it: who knows what is the
10354 @c default value set when the DOS machines boots? "No retry" means that
10355 @c the DOS serial device driver won't retry the operation if it fails;
10356 @c I understand that this is needed because the GDB serial protocol
10357 @c handles any errors and retransmissions itself. ---Eli Zaretskii, 3sep99
10359 To give control of the PC to the Unix side of the serial line, type
10360 the following at the DOS console:
10367 (Later, if you wish to return control to the DOS console, you can use
10368 the command @code{CTTY con}---but you must send it over the device that
10369 had control, in our example over the @file{COM1} serial line.)
10371 From the Unix host, use a communications program such as @code{tip} or
10372 @code{cu} to communicate with the PC; for example,
10375 cu -s 9600 -l /dev/ttya
10379 The @code{cu} options shown specify, respectively, the linespeed and the
10380 serial port to use. If you use @code{tip} instead, your command line
10381 may look something like the following:
10384 tip -9600 /dev/ttya
10388 Your system may require a different name where we show
10389 @file{/dev/ttya} as the argument to @code{tip}. The communications
10390 parameters, including which port to use, are associated with the
10391 @code{tip} argument in the ``remote'' descriptions file---normally the
10392 system table @file{/etc/remote}.
10393 @c FIXME: What if anything needs doing to match the "n,8,1,none" part of
10394 @c the DOS side's comms setup? cu can support -o (odd
10395 @c parity), -e (even parity)---apparently no settings for no parity or
10396 @c for character size. Taken from stty maybe...? John points out tip
10397 @c can set these as internal variables, eg ~s parity=none; man stty
10398 @c suggests that it *might* work to stty these options with stdin or
10399 @c stdout redirected... ---doc@cygnus.com, 25feb91
10401 @c There's nothing to be done for the "none" part of the DOS MODE
10402 @c command. The rest of the parameters should be matched by the
10403 @c baudrate, bits, and parity used by the Unix side. ---Eli Zaretskii, 3Sep99
10406 Using the @code{tip} or @code{cu} connection, change the DOS working
10407 directory to the directory containing a copy of your 29K program, then
10408 start the PC program @code{EBMON} (an EB29K control program supplied
10409 with your board by AMD). You should see an initial display from
10410 @code{EBMON} similar to the one that follows, ending with the
10411 @code{EBMON} prompt @samp{#}---
10416 G:\> CD \usr\joe\work29k
10418 G:\USR\JOE\WORK29K> EBMON
10419 Am29000 PC Coprocessor Board Monitor, version 3.0-18
10420 Copyright 1990 Advanced Micro Devices, Inc.
10421 Written by Gibbons and Associates, Inc.
10423 Enter '?' or 'H' for help
10425 PC Coprocessor Type = EB29K
10427 Memory Base = 0xd0000
10429 Data Memory Size = 2048KB
10430 Available I-RAM Range = 0x8000 to 0x1fffff
10431 Available D-RAM Range = 0x80002000 to 0x801fffff
10434 Register Stack Size = 0x800
10435 Memory Stack Size = 0x1800
10438 Am29027 Available = No
10439 Byte Write Available = Yes
10444 Then exit the @code{cu} or @code{tip} program (done in the example by
10445 typing @code{~.} at the @code{EBMON} prompt). @code{EBMON} keeps
10446 running, ready for @value{GDBN} to take over.
10448 For this example, we've assumed what is probably the most convenient
10449 way to make sure the same 29K program is on both the PC and the Unix
10450 system: a PC/NFS connection that establishes ``drive @file{G:}'' on the
10451 PC as a file system on the Unix host. If you do not have PC/NFS or
10452 something similar connecting the two systems, you must arrange some
10453 other way---perhaps floppy-disk transfer---of getting the 29K program
10454 from the Unix system to the PC; @value{GDBN} does @emph{not} download it over the
10458 @subsubsection EB29K cross-debugging
10460 Finally, @code{cd} to the directory containing an image of your 29K
10461 program on the Unix system, and start @value{GDBN}---specifying as argument the
10462 name of your 29K program:
10465 cd /usr/joe/work29k
10470 Now you can use the @code{target} command:
10473 target amd-eb /dev/ttya 9600 MYFOO
10474 @c FIXME: test above 'target amd-eb' as spelled, with caps! caps are meant to
10475 @c emphasize that this is the name as seen by DOS (since I think DOS is
10476 @c single-minded about case of letters). ---doc@cygnus.com, 25feb91
10480 In this example, we've assumed your program is in a file called
10481 @file{myfoo}. Note that the filename given as the last argument to
10482 @code{target amd-eb} should be the name of the program as it appears to DOS.
10483 In our example this is simply @code{MYFOO}, but in general it can include
10484 a DOS path, and depending on your transfer mechanism may not resemble
10485 the name on the Unix side.
10487 At this point, you can set any breakpoints you wish; when you are ready
10488 to see your program run on the 29K board, use the @value{GDBN} command
10491 To stop debugging the remote program, use the @value{GDBN} @code{detach}
10494 To return control of the PC to its console, use @code{tip} or @code{cu}
10495 once again, after your @value{GDBN} session has concluded, to attach to
10496 @code{EBMON}. You can then type the command @code{q} to shut down
10497 @code{EBMON}, returning control to the DOS command-line interpreter.
10498 Type @kbd{CTTY con} to return command input to the main DOS console,
10499 and type @kbd{~.} to leave @code{tip} or @code{cu}.
10502 @subsubsection Remote log
10503 @cindex @file{eb.log}, a log file for EB29K
10504 @cindex log file for EB29K
10506 The @code{target amd-eb} command creates a file @file{eb.log} in the
10507 current working directory, to help debug problems with the connection.
10508 @file{eb.log} records all the output from @code{EBMON}, including echoes
10509 of the commands sent to it. Running @samp{tail -f} on this file in
10510 another window often helps to understand trouble with @code{EBMON}, or
10511 unexpected events on the PC side of the connection.
10519 @item target rdi @var{dev}
10520 ARM Angel monitor, via RDI library interface to ADP protocol. You may
10521 use this target to communicate with both boards running the Angel
10522 monitor, or with the EmbeddedICE JTAG debug device.
10525 @item target rdp @var{dev}
10531 @subsection Hitachi H8/300
10535 @kindex target hms@r{, with H8/300}
10536 @item target hms @var{dev}
10537 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
10538 Use special commands @code{device} and @code{speed} to control the serial
10539 line and the communications speed used.
10541 @kindex target e7000@r{, with H8/300}
10542 @item target e7000 @var{dev}
10543 E7000 emulator for Hitachi H8 and SH.
10545 @kindex target sh3@r{, with H8/300}
10546 @kindex target sh3e@r{, with H8/300}
10547 @item target sh3 @var{dev}
10548 @itemx target sh3e @var{dev}
10549 Hitachi SH-3 and SH-3E target systems.
10553 @cindex download to H8/300 or H8/500
10554 @cindex H8/300 or H8/500 download
10555 @cindex download to Hitachi SH
10556 @cindex Hitachi SH download
10557 When you select remote debugging to a Hitachi SH, H8/300, or H8/500
10558 board, the @code{load} command downloads your program to the Hitachi
10559 board and also opens it as the current executable target for
10560 @value{GDBN} on your host (like the @code{file} command).
10562 @value{GDBN} needs to know these things to talk to your
10563 Hitachi SH, H8/300, or H8/500:
10567 that you want to use @samp{target hms}, the remote debugging interface
10568 for Hitachi microprocessors, or @samp{target e7000}, the in-circuit
10569 emulator for the Hitachi SH and the Hitachi 300H. (@samp{target hms} is
10570 the default when @value{GDBN} is configured specifically for the Hitachi SH,
10571 H8/300, or H8/500.)
10574 what serial device connects your host to your Hitachi board (the first
10575 serial device available on your host is the default).
10578 what speed to use over the serial device.
10582 * Hitachi Boards:: Connecting to Hitachi boards.
10583 * Hitachi ICE:: Using the E7000 In-Circuit Emulator.
10584 * Hitachi Special:: Special @value{GDBN} commands for Hitachi micros.
10587 @node Hitachi Boards
10588 @subsubsection Connecting to Hitachi boards
10590 @c only for Unix hosts
10592 @cindex serial device, Hitachi micros
10593 Use the special @code{@value{GDBN}} command @samp{device @var{port}} if you
10594 need to explicitly set the serial device. The default @var{port} is the
10595 first available port on your host. This is only necessary on Unix
10596 hosts, where it is typically something like @file{/dev/ttya}.
10599 @cindex serial line speed, Hitachi micros
10600 @code{@value{GDBN}} has another special command to set the communications
10601 speed: @samp{speed @var{bps}}. This command also is only used from Unix
10602 hosts; on DOS hosts, set the line speed as usual from outside @value{GDBN} with
10603 the DOS @code{mode} command (for instance,
10604 @w{@kbd{mode com2:9600,n,8,1,p}} for a 9600@dmn{bps} connection).
10606 The @samp{device} and @samp{speed} commands are available only when you
10607 use a Unix host to debug your Hitachi microprocessor programs. If you
10609 @value{GDBN} depends on an auxiliary terminate-and-stay-resident program
10610 called @code{asynctsr} to communicate with the development board
10611 through a PC serial port. You must also use the DOS @code{mode} command
10612 to set up the serial port on the DOS side.
10614 The following sample session illustrates the steps needed to start a
10615 program under @value{GDBN} control on an H8/300. The example uses a
10616 sample H8/300 program called @file{t.x}. The procedure is the same for
10617 the Hitachi SH and the H8/500.
10619 First hook up your development board. In this example, we use a
10620 board attached to serial port @code{COM2}; if you use a different serial
10621 port, substitute its name in the argument of the @code{mode} command.
10622 When you call @code{asynctsr}, the auxiliary comms program used by the
10623 debugger, you give it just the numeric part of the serial port's name;
10624 for example, @samp{asyncstr 2} below runs @code{asyncstr} on
10628 C:\H8300\TEST> asynctsr 2
10629 C:\H8300\TEST> mode com2:9600,n,8,1,p
10631 Resident portion of MODE loaded
10633 COM2: 9600, n, 8, 1, p
10638 @emph{Warning:} We have noticed a bug in PC-NFS that conflicts with
10639 @code{asynctsr}. If you also run PC-NFS on your DOS host, you may need to
10640 disable it, or even boot without it, to use @code{asynctsr} to control
10641 your development board.
10644 @kindex target hms@r{, and serial protocol}
10645 Now that serial communications are set up, and the development board is
10646 connected, you can start up @value{GDBN}. Call @code{@value{GDBP}} with
10647 the name of your program as the argument. @code{@value{GDBN}} prompts
10648 you, as usual, with the prompt @samp{(@value{GDBP})}. Use two special
10649 commands to begin your debugging session: @samp{target hms} to specify
10650 cross-debugging to the Hitachi board, and the @code{load} command to
10651 download your program to the board. @code{load} displays the names of
10652 the program's sections, and a @samp{*} for each 2K of data downloaded.
10653 (If you want to refresh @value{GDBN} data on symbols or on the
10654 executable file without downloading, use the @value{GDBN} commands
10655 @code{file} or @code{symbol-file}. These commands, and @code{load}
10656 itself, are described in @ref{Files,,Commands to specify files}.)
10659 (eg-C:\H8300\TEST) @value{GDBP} t.x
10660 @value{GDBN} is free software and you are welcome to distribute copies
10661 of it under certain conditions; type "show copying" to see
10663 There is absolutely no warranty for @value{GDBN}; type "show warranty"
10665 @value{GDBN} @value{GDBVN}, Copyright 1992 Free Software Foundation, Inc...
10666 (@value{GDBP}) target hms
10667 Connected to remote H8/300 HMS system.
10668 (@value{GDBP}) load t.x
10669 .text : 0x8000 .. 0xabde ***********
10670 .data : 0xabde .. 0xad30 *
10671 .stack : 0xf000 .. 0xf014 *
10674 At this point, you're ready to run or debug your program. From here on,
10675 you can use all the usual @value{GDBN} commands. The @code{break} command
10676 sets breakpoints; the @code{run} command starts your program;
10677 @code{print} or @code{x} display data; the @code{continue} command
10678 resumes execution after stopping at a breakpoint. You can use the
10679 @code{help} command at any time to find out more about @value{GDBN} commands.
10681 Remember, however, that @emph{operating system} facilities aren't
10682 available on your development board; for example, if your program hangs,
10683 you can't send an interrupt---but you can press the @sc{reset} switch!
10685 Use the @sc{reset} button on the development board
10688 to interrupt your program (don't use @kbd{ctl-C} on the DOS host---it has
10689 no way to pass an interrupt signal to the development board); and
10692 to return to the @value{GDBN} command prompt after your program finishes
10693 normally. The communications protocol provides no other way for @value{GDBN}
10694 to detect program completion.
10697 In either case, @value{GDBN} sees the effect of a @sc{reset} on the
10698 development board as a ``normal exit'' of your program.
10701 @subsubsection Using the E7000 in-circuit emulator
10703 @kindex target e7000@r{, with Hitachi ICE}
10704 You can use the E7000 in-circuit emulator to develop code for either the
10705 Hitachi SH or the H8/300H. Use one of these forms of the @samp{target
10706 e7000} command to connect @value{GDBN} to your E7000:
10709 @item target e7000 @var{port} @var{speed}
10710 Use this form if your E7000 is connected to a serial port. The
10711 @var{port} argument identifies what serial port to use (for example,
10712 @samp{com2}). The third argument is the line speed in bits per second
10713 (for example, @samp{9600}).
10715 @item target e7000 @var{hostname}
10716 If your E7000 is installed as a host on a TCP/IP network, you can just
10717 specify its hostname; @value{GDBN} uses @code{telnet} to connect.
10720 @node Hitachi Special
10721 @subsubsection Special @value{GDBN} commands for Hitachi micros
10723 Some @value{GDBN} commands are available only for the H8/300:
10727 @kindex set machine
10728 @kindex show machine
10729 @item set machine h8300
10730 @itemx set machine h8300h
10731 Condition @value{GDBN} for one of the two variants of the H8/300
10732 architecture with @samp{set machine}. You can use @samp{show machine}
10733 to check which variant is currently in effect.
10742 @kindex set memory @var{mod}
10743 @cindex memory models, H8/500
10744 @item set memory @var{mod}
10746 Specify which H8/500 memory model (@var{mod}) you are using with
10747 @samp{set memory}; check which memory model is in effect with @samp{show
10748 memory}. The accepted values for @var{mod} are @code{small},
10749 @code{big}, @code{medium}, and @code{compact}.
10754 @subsection Intel i960
10758 @kindex target mon960
10759 @item target mon960 @var{dev}
10760 MON960 monitor for Intel i960.
10762 @kindex target nindy
10763 @item target nindy @var{devicename}
10764 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
10765 the name of the serial device to use for the connection, e.g.
10772 @dfn{Nindy} is a ROM Monitor program for Intel 960 target systems. When
10773 @value{GDBN} is configured to control a remote Intel 960 using Nindy, you can
10774 tell @value{GDBN} how to connect to the 960 in several ways:
10778 Through command line options specifying serial port, version of the
10779 Nindy protocol, and communications speed;
10782 By responding to a prompt on startup;
10785 By using the @code{target} command at any point during your @value{GDBN}
10786 session. @xref{Target Commands, ,Commands for managing targets}.
10790 @cindex download to Nindy-960
10791 With the Nindy interface to an Intel 960 board, @code{load}
10792 downloads @var{filename} to the 960 as well as adding its symbols in
10796 * Nindy Startup:: Startup with Nindy
10797 * Nindy Options:: Options for Nindy
10798 * Nindy Reset:: Nindy reset command
10801 @node Nindy Startup
10802 @subsubsection Startup with Nindy
10804 If you simply start @code{@value{GDBP}} without using any command-line
10805 options, you are prompted for what serial port to use, @emph{before} you
10806 reach the ordinary @value{GDBN} prompt:
10809 Attach /dev/ttyNN -- specify NN, or "quit" to quit:
10813 Respond to the prompt with whatever suffix (after @samp{/dev/tty})
10814 identifies the serial port you want to use. You can, if you choose,
10815 simply start up with no Nindy connection by responding to the prompt
10816 with an empty line. If you do this and later wish to attach to Nindy,
10817 use @code{target} (@pxref{Target Commands, ,Commands for managing targets}).
10819 @node Nindy Options
10820 @subsubsection Options for Nindy
10822 These are the startup options for beginning your @value{GDBN} session with a
10823 Nindy-960 board attached:
10826 @item -r @var{port}
10827 Specify the serial port name of a serial interface to be used to connect
10828 to the target system. This option is only available when @value{GDBN} is
10829 configured for the Intel 960 target architecture. You may specify
10830 @var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a
10831 device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique
10832 suffix for a specific @code{tty} (e.g. @samp{-r a}).
10835 (An uppercase letter ``O'', not a zero.) Specify that @value{GDBN} should use
10836 the ``old'' Nindy monitor protocol to connect to the target system.
10837 This option is only available when @value{GDBN} is configured for the Intel 960
10838 target architecture.
10841 @emph{Warning:} if you specify @samp{-O}, but are actually trying to
10842 connect to a target system that expects the newer protocol, the connection
10843 fails, appearing to be a speed mismatch. @value{GDBN} repeatedly
10844 attempts to reconnect at several different line speeds. You can abort
10845 this process with an interrupt.
10849 Specify that @value{GDBN} should first send a @code{BREAK} signal to the target
10850 system, in an attempt to reset it, before connecting to a Nindy target.
10853 @emph{Warning:} Many target systems do not have the hardware that this
10854 requires; it only works with a few boards.
10858 The standard @samp{-b} option controls the line speed used on the serial
10863 @subsubsection Nindy reset command
10868 For a Nindy target, this command sends a ``break'' to the remote target
10869 system; this is only useful if the target has been equipped with a
10870 circuit to perform a hard reset (or some other interesting action) when
10871 a break is detected.
10876 @subsection Mitsubishi M32R/D
10880 @kindex target m32r
10881 @item target m32r @var{dev}
10882 Mitsubishi M32R/D ROM monitor.
10889 The Motorola m68k configuration includes ColdFire support, and
10890 target command for the following ROM monitors.
10894 @kindex target abug
10895 @item target abug @var{dev}
10896 ABug ROM monitor for M68K.
10898 @kindex target cpu32bug
10899 @item target cpu32bug @var{dev}
10900 CPU32BUG monitor, running on a CPU32 (M68K) board.
10902 @kindex target dbug
10903 @item target dbug @var{dev}
10904 dBUG ROM monitor for Motorola ColdFire.
10907 @item target est @var{dev}
10908 EST-300 ICE monitor, running on a CPU32 (M68K) board.
10910 @kindex target rom68k
10911 @item target rom68k @var{dev}
10912 ROM 68K monitor, running on an M68K IDP board.
10916 If @value{GDBN} is configured with @code{m68*-ericsson-*}, it will
10917 instead have only a single special target command:
10921 @kindex target es1800
10922 @item target es1800 @var{dev}
10923 ES-1800 emulator for M68K.
10931 @kindex target rombug
10932 @item target rombug @var{dev}
10933 ROMBUG ROM monitor for OS/9000.
10943 @item target bug @var{dev}
10944 BUG monitor, running on a MVME187 (m88k) board.
10948 @node MIPS Embedded
10949 @subsection MIPS Embedded
10951 @cindex MIPS boards
10952 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
10953 MIPS board attached to a serial line. This is available when
10954 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
10957 Use these @value{GDBN} commands to specify the connection to your target board:
10960 @item target mips @var{port}
10961 @kindex target mips @var{port}
10962 To run a program on the board, start up @code{@value{GDBP}} with the
10963 name of your program as the argument. To connect to the board, use the
10964 command @samp{target mips @var{port}}, where @var{port} is the name of
10965 the serial port connected to the board. If the program has not already
10966 been downloaded to the board, you may use the @code{load} command to
10967 download it. You can then use all the usual @value{GDBN} commands.
10969 For example, this sequence connects to the target board through a serial
10970 port, and loads and runs a program called @var{prog} through the
10974 host$ @value{GDBP} @var{prog}
10975 @value{GDBN} is free software and @dots{}
10976 (@value{GDBP}) target mips /dev/ttyb
10977 (@value{GDBP}) load @var{prog}
10981 @item target mips @var{hostname}:@var{portnumber}
10982 On some @value{GDBN} host configurations, you can specify a TCP
10983 connection (for instance, to a serial line managed by a terminal
10984 concentrator) instead of a serial port, using the syntax
10985 @samp{@var{hostname}:@var{portnumber}}.
10987 @item target pmon @var{port}
10988 @kindex target pmon @var{port}
10991 @item target ddb @var{port}
10992 @kindex target ddb @var{port}
10993 NEC's DDB variant of PMON for Vr4300.
10995 @item target lsi @var{port}
10996 @kindex target lsi @var{port}
10997 LSI variant of PMON.
10999 @kindex target r3900
11000 @item target r3900 @var{dev}
11001 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
11003 @kindex target array
11004 @item target array @var{dev}
11005 Array Tech LSI33K RAID controller board.
11011 @value{GDBN} also supports these special commands for MIPS targets:
11014 @item set processor @var{args}
11015 @itemx show processor
11016 @kindex set processor @var{args}
11017 @kindex show processor
11018 Use the @code{set processor} command to set the type of MIPS
11019 processor when you want to access processor-type-specific registers.
11020 For example, @code{set processor @var{r3041}} tells @value{GDBN}
11021 to use the CPU registers appropriate for the 3041 chip.
11022 Use the @code{show processor} command to see what MIPS processor @value{GDBN}
11023 is using. Use the @code{info reg} command to see what registers
11024 @value{GDBN} is using.
11026 @item set mipsfpu double
11027 @itemx set mipsfpu single
11028 @itemx set mipsfpu none
11029 @itemx show mipsfpu
11030 @kindex set mipsfpu
11031 @kindex show mipsfpu
11032 @cindex MIPS remote floating point
11033 @cindex floating point, MIPS remote
11034 If your target board does not support the MIPS floating point
11035 coprocessor, you should use the command @samp{set mipsfpu none} (if you
11036 need this, you may wish to put the command in your @value{GDBN} init
11037 file). This tells @value{GDBN} how to find the return value of
11038 functions which return floating point values. It also allows
11039 @value{GDBN} to avoid saving the floating point registers when calling
11040 functions on the board. If you are using a floating point coprocessor
11041 with only single precision floating point support, as on the @sc{r4650}
11042 processor, use the command @samp{set mipsfpu single}. The default
11043 double precision floating point coprocessor may be selected using
11044 @samp{set mipsfpu double}.
11046 In previous versions the only choices were double precision or no
11047 floating point, so @samp{set mipsfpu on} will select double precision
11048 and @samp{set mipsfpu off} will select no floating point.
11050 As usual, you can inquire about the @code{mipsfpu} variable with
11051 @samp{show mipsfpu}.
11053 @item set remotedebug @var{n}
11054 @itemx show remotedebug
11055 @kindex set remotedebug@r{, MIPS protocol}
11056 @kindex show remotedebug@r{, MIPS protocol}
11057 @cindex @code{remotedebug}, MIPS protocol
11058 @cindex MIPS @code{remotedebug} protocol
11059 @c FIXME! For this to be useful, you must know something about the MIPS
11060 @c FIXME...protocol. Where is it described?
11061 You can see some debugging information about communications with the board
11062 by setting the @code{remotedebug} variable. If you set it to @code{1} using
11063 @samp{set remotedebug 1}, every packet is displayed. If you set it
11064 to @code{2}, every character is displayed. You can check the current value
11065 at any time with the command @samp{show remotedebug}.
11067 @item set timeout @var{seconds}
11068 @itemx set retransmit-timeout @var{seconds}
11069 @itemx show timeout
11070 @itemx show retransmit-timeout
11071 @cindex @code{timeout}, MIPS protocol
11072 @cindex @code{retransmit-timeout}, MIPS protocol
11073 @kindex set timeout
11074 @kindex show timeout
11075 @kindex set retransmit-timeout
11076 @kindex show retransmit-timeout
11077 You can control the timeout used while waiting for a packet, in the MIPS
11078 remote protocol, with the @code{set timeout @var{seconds}} command. The
11079 default is 5 seconds. Similarly, you can control the timeout used while
11080 waiting for an acknowledgement of a packet with the @code{set
11081 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
11082 You can inspect both values with @code{show timeout} and @code{show
11083 retransmit-timeout}. (These commands are @emph{only} available when
11084 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
11086 The timeout set by @code{set timeout} does not apply when @value{GDBN}
11087 is waiting for your program to stop. In that case, @value{GDBN} waits
11088 forever because it has no way of knowing how long the program is going
11089 to run before stopping.
11093 @subsection PowerPC
11097 @kindex target dink32
11098 @item target dink32 @var{dev}
11099 DINK32 ROM monitor.
11101 @kindex target ppcbug
11102 @item target ppcbug @var{dev}
11103 @kindex target ppcbug1
11104 @item target ppcbug1 @var{dev}
11105 PPCBUG ROM monitor for PowerPC.
11108 @item target sds @var{dev}
11109 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
11114 @subsection HP PA Embedded
11118 @kindex target op50n
11119 @item target op50n @var{dev}
11120 OP50N monitor, running on an OKI HPPA board.
11122 @kindex target w89k
11123 @item target w89k @var{dev}
11124 W89K monitor, running on a Winbond HPPA board.
11129 @subsection Hitachi SH
11133 @kindex target hms@r{, with Hitachi SH}
11134 @item target hms @var{dev}
11135 A Hitachi SH board attached via serial line to your host. Use special
11136 commands @code{device} and @code{speed} to control the serial line and
11137 the communications speed used.
11139 @kindex target e7000@r{, with Hitachi SH}
11140 @item target e7000 @var{dev}
11141 E7000 emulator for Hitachi SH.
11143 @kindex target sh3@r{, with SH}
11144 @kindex target sh3e@r{, with SH}
11145 @item target sh3 @var{dev}
11146 @item target sh3e @var{dev}
11147 Hitachi SH-3 and SH-3E target systems.
11152 @subsection Tsqware Sparclet
11156 @value{GDBN} enables developers to debug tasks running on
11157 Sparclet targets from a Unix host.
11158 @value{GDBN} uses code that runs on
11159 both the Unix host and on the Sparclet target. The program
11160 @code{@value{GDBP}} is installed and executed on the Unix host.
11163 @item remotetimeout @var{args}
11164 @kindex remotetimeout
11165 @value{GDBN} supports the option @code{remotetimeout}.
11166 This option is set by the user, and @var{args} represents the number of
11167 seconds @value{GDBN} waits for responses.
11170 @cindex compiling, on Sparclet
11171 When compiling for debugging, include the options @samp{-g} to get debug
11172 information and @samp{-Ttext} to relocate the program to where you wish to
11173 load it on the target. You may also want to add the options @samp{-n} or
11174 @samp{-N} in order to reduce the size of the sections. Example:
11177 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
11180 You can use @code{objdump} to verify that the addresses are what you intended:
11183 sparclet-aout-objdump --headers --syms prog
11186 @cindex running, on Sparclet
11188 your Unix execution search path to find @value{GDBN}, you are ready to
11189 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
11190 (or @code{sparclet-aout-gdb}, depending on your installation).
11192 @value{GDBN} comes up showing the prompt:
11199 * Sparclet File:: Setting the file to debug
11200 * Sparclet Connection:: Connecting to Sparclet
11201 * Sparclet Download:: Sparclet download
11202 * Sparclet Execution:: Running and debugging
11205 @node Sparclet File
11206 @subsubsection Setting file to debug
11208 The @value{GDBN} command @code{file} lets you choose with program to debug.
11211 (gdbslet) file prog
11215 @value{GDBN} then attempts to read the symbol table of @file{prog}.
11216 @value{GDBN} locates
11217 the file by searching the directories listed in the command search
11219 If the file was compiled with debug information (option "-g"), source
11220 files will be searched as well.
11221 @value{GDBN} locates
11222 the source files by searching the directories listed in the directory search
11223 path (@pxref{Environment, ,Your program's environment}).
11225 to find a file, it displays a message such as:
11228 prog: No such file or directory.
11231 When this happens, add the appropriate directories to the search paths with
11232 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
11233 @code{target} command again.
11235 @node Sparclet Connection
11236 @subsubsection Connecting to Sparclet
11238 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
11239 To connect to a target on serial port ``@code{ttya}'', type:
11242 (gdbslet) target sparclet /dev/ttya
11243 Remote target sparclet connected to /dev/ttya
11244 main () at ../prog.c:3
11248 @value{GDBN} displays messages like these:
11254 @node Sparclet Download
11255 @subsubsection Sparclet download
11257 @cindex download to Sparclet
11258 Once connected to the Sparclet target,
11259 you can use the @value{GDBN}
11260 @code{load} command to download the file from the host to the target.
11261 The file name and load offset should be given as arguments to the @code{load}
11263 Since the file format is aout, the program must be loaded to the starting
11264 address. You can use @code{objdump} to find out what this value is. The load
11265 offset is an offset which is added to the VMA (virtual memory address)
11266 of each of the file's sections.
11267 For instance, if the program
11268 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
11269 and bss at 0x12010170, in @value{GDBN}, type:
11272 (gdbslet) load prog 0x12010000
11273 Loading section .text, size 0xdb0 vma 0x12010000
11276 If the code is loaded at a different address then what the program was linked
11277 to, you may need to use the @code{section} and @code{add-symbol-file} commands
11278 to tell @value{GDBN} where to map the symbol table.
11280 @node Sparclet Execution
11281 @subsubsection Running and debugging
11283 @cindex running and debugging Sparclet programs
11284 You can now begin debugging the task using @value{GDBN}'s execution control
11285 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
11286 manual for the list of commands.
11290 Breakpoint 1 at 0x12010000: file prog.c, line 3.
11292 Starting program: prog
11293 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
11294 3 char *symarg = 0;
11296 4 char *execarg = "hello!";
11301 @subsection Fujitsu Sparclite
11305 @kindex target sparclite
11306 @item target sparclite @var{dev}
11307 Fujitsu sparclite boards, used only for the purpose of loading.
11308 You must use an additional command to debug the program.
11309 For example: target remote @var{dev} using @value{GDBN} standard
11315 @subsection Tandem ST2000
11317 @value{GDBN} may be used with a Tandem ST2000 phone switch, running Tandem's
11320 To connect your ST2000 to the host system, see the manufacturer's
11321 manual. Once the ST2000 is physically attached, you can run:
11324 target st2000 @var{dev} @var{speed}
11328 to establish it as your debugging environment. @var{dev} is normally
11329 the name of a serial device, such as @file{/dev/ttya}, connected to the
11330 ST2000 via a serial line. You can instead specify @var{dev} as a TCP
11331 connection (for example, to a serial line attached via a terminal
11332 concentrator) using the syntax @code{@var{hostname}:@var{portnumber}}.
11334 The @code{load} and @code{attach} commands are @emph{not} defined for
11335 this target; you must load your program into the ST2000 as you normally
11336 would for standalone operation. @value{GDBN} reads debugging information
11337 (such as symbols) from a separate, debugging version of the program
11338 available on your host computer.
11339 @c FIXME!! This is terribly vague; what little content is here is
11340 @c basically hearsay.
11342 @cindex ST2000 auxiliary commands
11343 These auxiliary @value{GDBN} commands are available to help you with the ST2000
11347 @item st2000 @var{command}
11348 @kindex st2000 @var{cmd}
11349 @cindex STDBUG commands (ST2000)
11350 @cindex commands to STDBUG (ST2000)
11351 Send a @var{command} to the STDBUG monitor. See the manufacturer's
11352 manual for available commands.
11355 @cindex connect (to STDBUG)
11356 Connect the controlling terminal to the STDBUG command monitor. When
11357 you are done interacting with STDBUG, typing either of two character
11358 sequences gets you back to the @value{GDBN} command prompt:
11359 @kbd{@key{RET}~.} (Return, followed by tilde and period) or
11360 @kbd{@key{RET}~@key{C-d}} (Return, followed by tilde and control-D).
11364 @subsection Zilog Z8000
11367 @cindex simulator, Z8000
11368 @cindex Zilog Z8000 simulator
11370 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
11373 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
11374 unsegmented variant of the Z8000 architecture) or the Z8001 (the
11375 segmented variant). The simulator recognizes which architecture is
11376 appropriate by inspecting the object code.
11379 @item target sim @var{args}
11381 @kindex target sim@r{, with Z8000}
11382 Debug programs on a simulated CPU. If the simulator supports setup
11383 options, specify them via @var{args}.
11387 After specifying this target, you can debug programs for the simulated
11388 CPU in the same style as programs for your host computer; use the
11389 @code{file} command to load a new program image, the @code{run} command
11390 to run your program, and so on.
11392 As well as making available all the usual machine registers
11393 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
11394 additional items of information as specially named registers:
11399 Counts clock-ticks in the simulator.
11402 Counts instructions run in the simulator.
11405 Execution time in 60ths of a second.
11409 You can refer to these values in @value{GDBN} expressions with the usual
11410 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
11411 conditional breakpoint that suspends only after at least 5000
11412 simulated clock ticks.
11414 @node Architectures
11415 @section Architectures
11417 This section describes characteristics of architectures that affect
11418 all uses of @value{GDBN} with the architecture, both native and cross.
11431 @kindex set rstack_high_address
11432 @cindex AMD 29K register stack
11433 @cindex register stack, AMD29K
11434 @item set rstack_high_address @var{address}
11435 On AMD 29000 family processors, registers are saved in a separate
11436 @dfn{register stack}. There is no way for @value{GDBN} to determine the
11437 extent of this stack. Normally, @value{GDBN} just assumes that the
11438 stack is ``large enough''. This may result in @value{GDBN} referencing
11439 memory locations that do not exist. If necessary, you can get around
11440 this problem by specifying the ending address of the register stack with
11441 the @code{set rstack_high_address} command. The argument should be an
11442 address, which you probably want to precede with @samp{0x} to specify in
11445 @kindex show rstack_high_address
11446 @item show rstack_high_address
11447 Display the current limit of the register stack, on AMD 29000 family
11455 See the following section.
11460 @cindex stack on Alpha
11461 @cindex stack on MIPS
11462 @cindex Alpha stack
11464 Alpha- and MIPS-based computers use an unusual stack frame, which
11465 sometimes requires @value{GDBN} to search backward in the object code to
11466 find the beginning of a function.
11468 @cindex response time, MIPS debugging
11469 To improve response time (especially for embedded applications, where
11470 @value{GDBN} may be restricted to a slow serial line for this search)
11471 you may want to limit the size of this search, using one of these
11475 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
11476 @item set heuristic-fence-post @var{limit}
11477 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
11478 search for the beginning of a function. A value of @var{0} (the
11479 default) means there is no limit. However, except for @var{0}, the
11480 larger the limit the more bytes @code{heuristic-fence-post} must search
11481 and therefore the longer it takes to run.
11483 @item show heuristic-fence-post
11484 Display the current limit.
11488 These commands are available @emph{only} when @value{GDBN} is configured
11489 for debugging programs on Alpha or MIPS processors.
11492 @node Controlling GDB
11493 @chapter Controlling @value{GDBN}
11495 You can alter the way @value{GDBN} interacts with you by using the
11496 @code{set} command. For commands controlling how @value{GDBN} displays
11497 data, see @ref{Print Settings, ,Print settings}. Other settings are
11502 * Editing:: Command editing
11503 * History:: Command history
11504 * Screen Size:: Screen size
11505 * Numbers:: Numbers
11506 * Messages/Warnings:: Optional warnings and messages
11507 * Debugging Output:: Optional messages about internal happenings
11515 @value{GDBN} indicates its readiness to read a command by printing a string
11516 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
11517 can change the prompt string with the @code{set prompt} command. For
11518 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
11519 the prompt in one of the @value{GDBN} sessions so that you can always tell
11520 which one you are talking to.
11522 @emph{Note:} @code{set prompt} does not add a space for you after the
11523 prompt you set. This allows you to set a prompt which ends in a space
11524 or a prompt that does not.
11528 @item set prompt @var{newprompt}
11529 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
11531 @kindex show prompt
11533 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
11537 @section Command editing
11539 @cindex command line editing
11541 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
11542 @sc{gnu} library provides consistent behavior for programs which provide a
11543 command line interface to the user. Advantages are @sc{gnu} Emacs-style
11544 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
11545 substitution, and a storage and recall of command history across
11546 debugging sessions.
11548 You may control the behavior of command line editing in @value{GDBN} with the
11549 command @code{set}.
11552 @kindex set editing
11555 @itemx set editing on
11556 Enable command line editing (enabled by default).
11558 @item set editing off
11559 Disable command line editing.
11561 @kindex show editing
11563 Show whether command line editing is enabled.
11567 @section Command history
11569 @value{GDBN} can keep track of the commands you type during your
11570 debugging sessions, so that you can be certain of precisely what
11571 happened. Use these commands to manage the @value{GDBN} command
11575 @cindex history substitution
11576 @cindex history file
11577 @kindex set history filename
11578 @kindex GDBHISTFILE
11579 @item set history filename @var{fname}
11580 Set the name of the @value{GDBN} command history file to @var{fname}.
11581 This is the file where @value{GDBN} reads an initial command history
11582 list, and where it writes the command history from this session when it
11583 exits. You can access this list through history expansion or through
11584 the history command editing characters listed below. This file defaults
11585 to the value of the environment variable @code{GDBHISTFILE}, or to
11586 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
11589 @cindex history save
11590 @kindex set history save
11591 @item set history save
11592 @itemx set history save on
11593 Record command history in a file, whose name may be specified with the
11594 @code{set history filename} command. By default, this option is disabled.
11596 @item set history save off
11597 Stop recording command history in a file.
11599 @cindex history size
11600 @kindex set history size
11601 @item set history size @var{size}
11602 Set the number of commands which @value{GDBN} keeps in its history list.
11603 This defaults to the value of the environment variable
11604 @code{HISTSIZE}, or to 256 if this variable is not set.
11607 @cindex history expansion
11608 History expansion assigns special meaning to the character @kbd{!}.
11609 @ifset have-readline-appendices
11610 @xref{Event Designators}.
11613 Since @kbd{!} is also the logical not operator in C, history expansion
11614 is off by default. If you decide to enable history expansion with the
11615 @code{set history expansion on} command, you may sometimes need to
11616 follow @kbd{!} (when it is used as logical not, in an expression) with
11617 a space or a tab to prevent it from being expanded. The readline
11618 history facilities do not attempt substitution on the strings
11619 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
11621 The commands to control history expansion are:
11624 @kindex set history expansion
11625 @item set history expansion on
11626 @itemx set history expansion
11627 Enable history expansion. History expansion is off by default.
11629 @item set history expansion off
11630 Disable history expansion.
11632 The readline code comes with more complete documentation of
11633 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
11634 or @code{vi} may wish to read it.
11635 @ifset have-readline-appendices
11636 @xref{Command Line Editing}.
11640 @kindex show history
11642 @itemx show history filename
11643 @itemx show history save
11644 @itemx show history size
11645 @itemx show history expansion
11646 These commands display the state of the @value{GDBN} history parameters.
11647 @code{show history} by itself displays all four states.
11653 @item show commands
11654 Display the last ten commands in the command history.
11656 @item show commands @var{n}
11657 Print ten commands centered on command number @var{n}.
11659 @item show commands +
11660 Print ten commands just after the commands last printed.
11664 @section Screen size
11665 @cindex size of screen
11666 @cindex pauses in output
11668 Certain commands to @value{GDBN} may produce large amounts of
11669 information output to the screen. To help you read all of it,
11670 @value{GDBN} pauses and asks you for input at the end of each page of
11671 output. Type @key{RET} when you want to continue the output, or @kbd{q}
11672 to discard the remaining output. Also, the screen width setting
11673 determines when to wrap lines of output. Depending on what is being
11674 printed, @value{GDBN} tries to break the line at a readable place,
11675 rather than simply letting it overflow onto the following line.
11677 Normally @value{GDBN} knows the size of the screen from the terminal
11678 driver software. For example, on Unix @value{GDBN} uses the termcap data base
11679 together with the value of the @code{TERM} environment variable and the
11680 @code{stty rows} and @code{stty cols} settings. If this is not correct,
11681 you can override it with the @code{set height} and @code{set
11688 @kindex show height
11689 @item set height @var{lpp}
11691 @itemx set width @var{cpl}
11693 These @code{set} commands specify a screen height of @var{lpp} lines and
11694 a screen width of @var{cpl} characters. The associated @code{show}
11695 commands display the current settings.
11697 If you specify a height of zero lines, @value{GDBN} does not pause during
11698 output no matter how long the output is. This is useful if output is to a
11699 file or to an editor buffer.
11701 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
11702 from wrapping its output.
11707 @cindex number representation
11708 @cindex entering numbers
11710 You can always enter numbers in octal, decimal, or hexadecimal in
11711 @value{GDBN} by the usual conventions: octal numbers begin with
11712 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
11713 begin with @samp{0x}. Numbers that begin with none of these are, by
11714 default, entered in base 10; likewise, the default display for
11715 numbers---when no particular format is specified---is base 10. You can
11716 change the default base for both input and output with the @code{set
11720 @kindex set input-radix
11721 @item set input-radix @var{base}
11722 Set the default base for numeric input. Supported choices
11723 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
11724 specified either unambiguously or using the current default radix; for
11734 sets the base to decimal. On the other hand, @samp{set radix 10}
11735 leaves the radix unchanged no matter what it was.
11737 @kindex set output-radix
11738 @item set output-radix @var{base}
11739 Set the default base for numeric display. Supported choices
11740 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
11741 specified either unambiguously or using the current default radix.
11743 @kindex show input-radix
11744 @item show input-radix
11745 Display the current default base for numeric input.
11747 @kindex show output-radix
11748 @item show output-radix
11749 Display the current default base for numeric display.
11752 @node Messages/Warnings
11753 @section Optional warnings and messages
11755 By default, @value{GDBN} is silent about its inner workings. If you are
11756 running on a slow machine, you may want to use the @code{set verbose}
11757 command. This makes @value{GDBN} tell you when it does a lengthy
11758 internal operation, so you will not think it has crashed.
11760 Currently, the messages controlled by @code{set verbose} are those
11761 which announce that the symbol table for a source file is being read;
11762 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
11765 @kindex set verbose
11766 @item set verbose on
11767 Enables @value{GDBN} output of certain informational messages.
11769 @item set verbose off
11770 Disables @value{GDBN} output of certain informational messages.
11772 @kindex show verbose
11774 Displays whether @code{set verbose} is on or off.
11777 By default, if @value{GDBN} encounters bugs in the symbol table of an
11778 object file, it is silent; but if you are debugging a compiler, you may
11779 find this information useful (@pxref{Symbol Errors, ,Errors reading
11784 @kindex set complaints
11785 @item set complaints @var{limit}
11786 Permits @value{GDBN} to output @var{limit} complaints about each type of
11787 unusual symbols before becoming silent about the problem. Set
11788 @var{limit} to zero to suppress all complaints; set it to a large number
11789 to prevent complaints from being suppressed.
11791 @kindex show complaints
11792 @item show complaints
11793 Displays how many symbol complaints @value{GDBN} is permitted to produce.
11797 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
11798 lot of stupid questions to confirm certain commands. For example, if
11799 you try to run a program which is already running:
11803 The program being debugged has been started already.
11804 Start it from the beginning? (y or n)
11807 If you are willing to unflinchingly face the consequences of your own
11808 commands, you can disable this ``feature'':
11812 @kindex set confirm
11814 @cindex confirmation
11815 @cindex stupid questions
11816 @item set confirm off
11817 Disables confirmation requests.
11819 @item set confirm on
11820 Enables confirmation requests (the default).
11822 @kindex show confirm
11824 Displays state of confirmation requests.
11828 @node Debugging Output
11829 @section Optional messages about internal happenings
11831 @kindex set debug arch
11832 @item set debug arch
11833 Turns on or off display of gdbarch debugging info. The default is off
11834 @kindex show debug arch
11835 @item show debug arch
11836 Displays the current state of displaying gdbarch debugging info.
11837 @kindex set debug event
11838 @item set debug event
11839 Turns on or off display of @value{GDBN} event debugging info. The
11841 @kindex show debug event
11842 @item show debug event
11843 Displays the current state of displaying @value{GDBN} event debugging
11845 @kindex set debug expression
11846 @item set debug expression
11847 Turns on or off display of @value{GDBN} expression debugging info. The
11849 @kindex show debug expression
11850 @item show debug expression
11851 Displays the current state of displaying @value{GDBN} expression
11853 @kindex set debug overload
11854 @item set debug overload
11855 Turns on or off display of @value{GDBN} C++ overload debugging
11856 info. This includes info such as ranking of functions, etc. The default
11858 @kindex show debug overload
11859 @item show debug overload
11860 Displays the current state of displaying @value{GDBN} C++ overload
11862 @kindex set debug remote
11863 @cindex packets, reporting on stdout
11864 @cindex serial connections, debugging
11865 @item set debug remote
11866 Turns on or off display of reports on all packets sent back and forth across
11867 the serial line to the remote machine. The info is printed on the
11868 @value{GDBN} standard output stream. The default is off.
11869 @kindex show debug remote
11870 @item show debug remote
11871 Displays the state of display of remote packets.
11872 @kindex set debug serial
11873 @item set debug serial
11874 Turns on or off display of @value{GDBN} serial debugging info. The
11876 @kindex show debug serial
11877 @item show debug serial
11878 Displays the current state of displaying @value{GDBN} serial debugging
11880 @kindex set debug target
11881 @item set debug target
11882 Turns on or off display of @value{GDBN} target debugging info. This info
11883 includes what is going on at the target level of GDB, as it happens. The
11885 @kindex show debug target
11886 @item show debug target
11887 Displays the current state of displaying @value{GDBN} target debugging
11889 @kindex set debug varobj
11890 @item set debug varobj
11891 Turns on or off display of @value{GDBN} variable object debugging
11892 info. The default is off.
11893 @kindex show debug varobj
11894 @item show debug varobj
11895 Displays the current state of displaying @value{GDBN} variable object
11900 @chapter Canned Sequences of Commands
11902 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
11903 command lists}), @value{GDBN} provides two ways to store sequences of
11904 commands for execution as a unit: user-defined commands and command
11908 * Define:: User-defined commands
11909 * Hooks:: User-defined command hooks
11910 * Command Files:: Command files
11911 * Output:: Commands for controlled output
11915 @section User-defined commands
11917 @cindex user-defined command
11918 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
11919 which you assign a new name as a command. This is done with the
11920 @code{define} command. User commands may accept up to 10 arguments
11921 separated by whitespace. Arguments are accessed within the user command
11922 via @var{$arg0@dots{}$arg9}. A trivial example:
11926 print $arg0 + $arg1 + $arg2
11930 To execute the command use:
11937 This defines the command @code{adder}, which prints the sum of
11938 its three arguments. Note the arguments are text substitutions, so they may
11939 reference variables, use complex expressions, or even perform inferior
11945 @item define @var{commandname}
11946 Define a command named @var{commandname}. If there is already a command
11947 by that name, you are asked to confirm that you want to redefine it.
11949 The definition of the command is made up of other @value{GDBN} command lines,
11950 which are given following the @code{define} command. The end of these
11951 commands is marked by a line containing @code{end}.
11956 Takes a single argument, which is an expression to evaluate.
11957 It is followed by a series of commands that are executed
11958 only if the expression is true (nonzero).
11959 There can then optionally be a line @code{else}, followed
11960 by a series of commands that are only executed if the expression
11961 was false. The end of the list is marked by a line containing @code{end}.
11965 The syntax is similar to @code{if}: the command takes a single argument,
11966 which is an expression to evaluate, and must be followed by the commands to
11967 execute, one per line, terminated by an @code{end}.
11968 The commands are executed repeatedly as long as the expression
11972 @item document @var{commandname}
11973 Document the user-defined command @var{commandname}, so that it can be
11974 accessed by @code{help}. The command @var{commandname} must already be
11975 defined. This command reads lines of documentation just as @code{define}
11976 reads the lines of the command definition, ending with @code{end}.
11977 After the @code{document} command is finished, @code{help} on command
11978 @var{commandname} displays the documentation you have written.
11980 You may use the @code{document} command again to change the
11981 documentation of a command. Redefining the command with @code{define}
11982 does not change the documentation.
11984 @kindex help user-defined
11985 @item help user-defined
11986 List all user-defined commands, with the first line of the documentation
11991 @itemx show user @var{commandname}
11992 Display the @value{GDBN} commands used to define @var{commandname} (but
11993 not its documentation). If no @var{commandname} is given, display the
11994 definitions for all user-defined commands.
11998 When user-defined commands are executed, the
11999 commands of the definition are not printed. An error in any command
12000 stops execution of the user-defined command.
12002 If used interactively, commands that would ask for confirmation proceed
12003 without asking when used inside a user-defined command. Many @value{GDBN}
12004 commands that normally print messages to say what they are doing omit the
12005 messages when used in a user-defined command.
12008 @section User-defined command hooks
12009 @cindex command hooks
12010 @cindex hooks, for commands
12011 @cindex hooks, pre-command
12015 You may define @dfn{hooks}, which are a special kind of user-defined
12016 command. Whenever you run the command @samp{foo}, if the user-defined
12017 command @samp{hook-foo} exists, it is executed (with no arguments)
12018 before that command.
12020 @cindex hooks, post-command
12023 A hook may also be defined which is run after the command you executed.
12024 Whenever you run the command @samp{foo}, if the user-defined command
12025 @samp{hookpost-foo} exists, it is executed (with no arguments) after
12026 that command. Post-execution hooks may exist simultaneously with
12027 pre-execution hooks, for the same command.
12029 It is valid for a hook to call the command which it hooks. If this
12030 occurs, the hook is not re-executed, thereby avoiding infinte recursion.
12032 @c It would be nice if hookpost could be passed a parameter indicating
12033 @c if the command it hooks executed properly or not. FIXME!
12035 @kindex stop@r{, a pseudo-command}
12036 In addition, a pseudo-command, @samp{stop} exists. Defining
12037 (@samp{hook-stop}) makes the associated commands execute every time
12038 execution stops in your program: before breakpoint commands are run,
12039 displays are printed, or the stack frame is printed.
12041 For example, to ignore @code{SIGALRM} signals while
12042 single-stepping, but treat them normally during normal execution,
12047 handle SIGALRM nopass
12051 handle SIGALRM pass
12054 define hook-continue
12055 handle SIGLARM pass
12059 As a further example, to hook at the begining and end of the @code{echo}
12060 command, and to add extra text to the beginning and end of the message,
12068 define hookpost-echo
12072 (@value{GDBP}) echo Hello World
12073 <<<---Hello World--->>>
12078 You can define a hook for any single-word command in @value{GDBN}, but
12079 not for command aliases; you should define a hook for the basic command
12080 name, e.g. @code{backtrace} rather than @code{bt}.
12081 @c FIXME! So how does Joe User discover whether a command is an alias
12083 If an error occurs during the execution of your hook, execution of
12084 @value{GDBN} commands stops and @value{GDBN} issues a prompt
12085 (before the command that you actually typed had a chance to run).
12087 If you try to define a hook which does not match any known command, you
12088 get a warning from the @code{define} command.
12090 @node Command Files
12091 @section Command files
12093 @cindex command files
12094 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
12095 commands. Comments (lines starting with @kbd{#}) may also be included.
12096 An empty line in a command file does nothing; it does not mean to repeat
12097 the last command, as it would from the terminal.
12100 @cindex @file{.gdbinit}
12101 @cindex @file{gdb.ini}
12102 When you start @value{GDBN}, it automatically executes commands from its
12103 @dfn{init files}. These are files named @file{.gdbinit} on Unix and
12104 @file{gdb.ini} on DOS/Windows. During startup, @value{GDBN} does the
12109 Reads the init file (if any) in your home directory@footnote{On
12110 DOS/Windows systems, the home directory is the one pointed to by the
12111 @code{HOME} environment variable.}.
12114 Processes command line options and operands.
12117 Reads the init file (if any) in the current working directory.
12120 Reads command files specified by the @samp{-x} option.
12123 The init file in your home directory can set options (such as @samp{set
12124 complaints}) that affect subsequent processing of command line options
12125 and operands. Init files are not executed if you use the @samp{-nx}
12126 option (@pxref{Mode Options, ,Choosing modes}).
12128 @cindex init file name
12129 On some configurations of @value{GDBN}, the init file is known by a
12130 different name (these are typically environments where a specialized
12131 form of @value{GDBN} may need to coexist with other forms, hence a
12132 different name for the specialized version's init file). These are the
12133 environments with special init file names:
12135 @cindex @file{.vxgdbinit}
12138 VxWorks (Wind River Systems real-time OS): @file{.vxgdbinit}
12140 @cindex @file{.os68gdbinit}
12142 OS68K (Enea Data Systems real-time OS): @file{.os68gdbinit}
12144 @cindex @file{.esgdbinit}
12146 ES-1800 (Ericsson Telecom AB M68000 emulator): @file{.esgdbinit}
12149 You can also request the execution of a command file with the
12150 @code{source} command:
12154 @item source @var{filename}
12155 Execute the command file @var{filename}.
12158 The lines in a command file are executed sequentially. They are not
12159 printed as they are executed. An error in any command terminates execution
12160 of the command file.
12162 Commands that would ask for confirmation if used interactively proceed
12163 without asking when used in a command file. Many @value{GDBN} commands that
12164 normally print messages to say what they are doing omit the messages
12165 when called from command files.
12168 @section Commands for controlled output
12170 During the execution of a command file or a user-defined command, normal
12171 @value{GDBN} output is suppressed; the only output that appears is what is
12172 explicitly printed by the commands in the definition. This section
12173 describes three commands useful for generating exactly the output you
12178 @item echo @var{text}
12179 @c I do not consider backslash-space a standard C escape sequence
12180 @c because it is not in ANSI.
12181 Print @var{text}. Nonprinting characters can be included in
12182 @var{text} using C escape sequences, such as @samp{\n} to print a
12183 newline. @strong{No newline is printed unless you specify one.}
12184 In addition to the standard C escape sequences, a backslash followed
12185 by a space stands for a space. This is useful for displaying a
12186 string with spaces at the beginning or the end, since leading and
12187 trailing spaces are otherwise trimmed from all arguments.
12188 To print @samp{@w{ }and foo =@w{ }}, use the command
12189 @samp{echo \@w{ }and foo = \@w{ }}.
12191 A backslash at the end of @var{text} can be used, as in C, to continue
12192 the command onto subsequent lines. For example,
12195 echo This is some text\n\
12196 which is continued\n\
12197 onto several lines.\n
12200 produces the same output as
12203 echo This is some text\n
12204 echo which is continued\n
12205 echo onto several lines.\n
12209 @item output @var{expression}
12210 Print the value of @var{expression} and nothing but that value: no
12211 newlines, no @samp{$@var{nn} = }. The value is not entered in the
12212 value history either. @xref{Expressions, ,Expressions}, for more information
12215 @item output/@var{fmt} @var{expression}
12216 Print the value of @var{expression} in format @var{fmt}. You can use
12217 the same formats as for @code{print}. @xref{Output Formats,,Output
12218 formats}, for more information.
12221 @item printf @var{string}, @var{expressions}@dots{}
12222 Print the values of the @var{expressions} under the control of
12223 @var{string}. The @var{expressions} are separated by commas and may be
12224 either numbers or pointers. Their values are printed as specified by
12225 @var{string}, exactly as if your program were to execute the C
12227 @c FIXME: the above implies that at least all ANSI C formats are
12228 @c supported, but it isn't true: %E and %G don't work (or so it seems).
12229 @c Either this is a bug, or the manual should document what formats are
12233 printf (@var{string}, @var{expressions}@dots{});
12236 For example, you can print two values in hex like this:
12239 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
12242 The only backslash-escape sequences that you can use in the format
12243 string are the simple ones that consist of backslash followed by a
12248 @chapter Using @value{GDBN} under @sc{gnu} Emacs
12251 @cindex @sc{gnu} Emacs
12252 A special interface allows you to use @sc{gnu} Emacs to view (and
12253 edit) the source files for the program you are debugging with
12256 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
12257 executable file you want to debug as an argument. This command starts
12258 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
12259 created Emacs buffer.
12260 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
12262 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
12267 All ``terminal'' input and output goes through the Emacs buffer.
12270 This applies both to @value{GDBN} commands and their output, and to the input
12271 and output done by the program you are debugging.
12273 This is useful because it means that you can copy the text of previous
12274 commands and input them again; you can even use parts of the output
12277 All the facilities of Emacs' Shell mode are available for interacting
12278 with your program. In particular, you can send signals the usual
12279 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
12284 @value{GDBN} displays source code through Emacs.
12287 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
12288 source file for that frame and puts an arrow (@samp{=>}) at the
12289 left margin of the current line. Emacs uses a separate buffer for
12290 source display, and splits the screen to show both your @value{GDBN} session
12293 Explicit @value{GDBN} @code{list} or search commands still produce output as
12294 usual, but you probably have no reason to use them from Emacs.
12297 @emph{Warning:} If the directory where your program resides is not your
12298 current directory, it can be easy to confuse Emacs about the location of
12299 the source files, in which case the auxiliary display buffer does not
12300 appear to show your source. @value{GDBN} can find programs by searching your
12301 environment's @code{PATH} variable, so the @value{GDBN} input and output
12302 session proceeds normally; but Emacs does not get enough information
12303 back from @value{GDBN} to locate the source files in this situation. To
12304 avoid this problem, either start @value{GDBN} mode from the directory where
12305 your program resides, or specify an absolute file name when prompted for the
12306 @kbd{M-x gdb} argument.
12308 A similar confusion can result if you use the @value{GDBN} @code{file} command to
12309 switch to debugging a program in some other location, from an existing
12310 @value{GDBN} buffer in Emacs.
12313 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
12314 you need to call @value{GDBN} by a different name (for example, if you keep
12315 several configurations around, with different names) you can set the
12316 Emacs variable @code{gdb-command-name}; for example,
12319 (setq gdb-command-name "mygdb")
12323 (preceded by @kbd{M-:} or @kbd{ESC :}, or typed in the @code{*scratch*} buffer, or
12324 in your @file{.emacs} file) makes Emacs call the program named
12325 ``@code{mygdb}'' instead.
12327 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
12328 addition to the standard Shell mode commands:
12332 Describe the features of Emacs' @value{GDBN} Mode.
12335 Execute to another source line, like the @value{GDBN} @code{step} command; also
12336 update the display window to show the current file and location.
12339 Execute to next source line in this function, skipping all function
12340 calls, like the @value{GDBN} @code{next} command. Then update the display window
12341 to show the current file and location.
12344 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
12345 display window accordingly.
12347 @item M-x gdb-nexti
12348 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
12349 display window accordingly.
12352 Execute until exit from the selected stack frame, like the @value{GDBN}
12353 @code{finish} command.
12356 Continue execution of your program, like the @value{GDBN} @code{continue}
12359 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
12362 Go up the number of frames indicated by the numeric argument
12363 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
12364 like the @value{GDBN} @code{up} command.
12366 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
12369 Go down the number of frames indicated by the numeric argument, like the
12370 @value{GDBN} @code{down} command.
12372 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
12375 Read the number where the cursor is positioned, and insert it at the end
12376 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
12377 around an address that was displayed earlier, type @kbd{disassemble};
12378 then move the cursor to the address display, and pick up the
12379 argument for @code{disassemble} by typing @kbd{C-x &}.
12381 You can customize this further by defining elements of the list
12382 @code{gdb-print-command}; once it is defined, you can format or
12383 otherwise process numbers picked up by @kbd{C-x &} before they are
12384 inserted. A numeric argument to @kbd{C-x &} indicates that you
12385 wish special formatting, and also acts as an index to pick an element of the
12386 list. If the list element is a string, the number to be inserted is
12387 formatted using the Emacs function @code{format}; otherwise the number
12388 is passed as an argument to the corresponding list element.
12391 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
12392 tells @value{GDBN} to set a breakpoint on the source line point is on.
12394 If you accidentally delete the source-display buffer, an easy way to get
12395 it back is to type the command @code{f} in the @value{GDBN} buffer, to
12396 request a frame display; when you run under Emacs, this recreates
12397 the source buffer if necessary to show you the context of the current
12400 The source files displayed in Emacs are in ordinary Emacs buffers
12401 which are visiting the source files in the usual way. You can edit
12402 the files with these buffers if you wish; but keep in mind that @value{GDBN}
12403 communicates with Emacs in terms of line numbers. If you add or
12404 delete lines from the text, the line numbers that @value{GDBN} knows cease
12405 to correspond properly with the code.
12407 @c The following dropped because Epoch is nonstandard. Reactivate
12408 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
12410 @kindex Emacs Epoch environment
12414 Version 18 of @sc{gnu} Emacs has a built-in window system
12415 called the @code{epoch}
12416 environment. Users of this environment can use a new command,
12417 @code{inspect} which performs identically to @code{print} except that
12418 each value is printed in its own window.
12421 @include annotate.texi
12422 @include gdbmi.texinfo
12425 @chapter Reporting Bugs in @value{GDBN}
12426 @cindex bugs in @value{GDBN}
12427 @cindex reporting bugs in @value{GDBN}
12429 Your bug reports play an essential role in making @value{GDBN} reliable.
12431 Reporting a bug may help you by bringing a solution to your problem, or it
12432 may not. But in any case the principal function of a bug report is to help
12433 the entire community by making the next version of @value{GDBN} work better. Bug
12434 reports are your contribution to the maintenance of @value{GDBN}.
12436 In order for a bug report to serve its purpose, you must include the
12437 information that enables us to fix the bug.
12440 * Bug Criteria:: Have you found a bug?
12441 * Bug Reporting:: How to report bugs
12445 @section Have you found a bug?
12446 @cindex bug criteria
12448 If you are not sure whether you have found a bug, here are some guidelines:
12451 @cindex fatal signal
12452 @cindex debugger crash
12453 @cindex crash of debugger
12455 If the debugger gets a fatal signal, for any input whatever, that is a
12456 @value{GDBN} bug. Reliable debuggers never crash.
12458 @cindex error on valid input
12460 If @value{GDBN} produces an error message for valid input, that is a
12461 bug. (Note that if you're cross debugging, the problem may also be
12462 somewhere in the connection to the target.)
12464 @cindex invalid input
12466 If @value{GDBN} does not produce an error message for invalid input,
12467 that is a bug. However, you should note that your idea of
12468 ``invalid input'' might be our idea of ``an extension'' or ``support
12469 for traditional practice''.
12472 If you are an experienced user of debugging tools, your suggestions
12473 for improvement of @value{GDBN} are welcome in any case.
12476 @node Bug Reporting
12477 @section How to report bugs
12478 @cindex bug reports
12479 @cindex @value{GDBN} bugs, reporting
12481 A number of companies and individuals offer support for @sc{gnu} products.
12482 If you obtained @value{GDBN} from a support organization, we recommend you
12483 contact that organization first.
12485 You can find contact information for many support companies and
12486 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
12488 @c should add a web page ref...
12490 In any event, we also recommend that you send bug reports for
12491 @value{GDBN} to this addresses:
12497 @strong{Do not send bug reports to @samp{info-gdb}, or to
12498 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
12499 not want to receive bug reports. Those that do have arranged to receive
12502 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
12503 serves as a repeater. The mailing list and the newsgroup carry exactly
12504 the same messages. Often people think of posting bug reports to the
12505 newsgroup instead of mailing them. This appears to work, but it has one
12506 problem which can be crucial: a newsgroup posting often lacks a mail
12507 path back to the sender. Thus, if we need to ask for more information,
12508 we may be unable to reach you. For this reason, it is better to send
12509 bug reports to the mailing list.
12511 As a last resort, send bug reports on paper to:
12514 @sc{gnu} Debugger Bugs
12515 Free Software Foundation Inc.
12516 59 Temple Place - Suite 330
12517 Boston, MA 02111-1307
12521 The fundamental principle of reporting bugs usefully is this:
12522 @strong{report all the facts}. If you are not sure whether to state a
12523 fact or leave it out, state it!
12525 Often people omit facts because they think they know what causes the
12526 problem and assume that some details do not matter. Thus, you might
12527 assume that the name of the variable you use in an example does not matter.
12528 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
12529 stray memory reference which happens to fetch from the location where that
12530 name is stored in memory; perhaps, if the name were different, the contents
12531 of that location would fool the debugger into doing the right thing despite
12532 the bug. Play it safe and give a specific, complete example. That is the
12533 easiest thing for you to do, and the most helpful.
12535 Keep in mind that the purpose of a bug report is to enable us to fix the
12536 bug. It may be that the bug has been reported previously, but neither
12537 you nor we can know that unless your bug report is complete and
12540 Sometimes people give a few sketchy facts and ask, ``Does this ring a
12541 bell?'' Those bug reports are useless, and we urge everyone to
12542 @emph{refuse to respond to them} except to chide the sender to report
12545 To enable us to fix the bug, you should include all these things:
12549 The version of @value{GDBN}. @value{GDBN} announces it if you start
12550 with no arguments; you can also print it at any time using @code{show
12553 Without this, we will not know whether there is any point in looking for
12554 the bug in the current version of @value{GDBN}.
12557 The type of machine you are using, and the operating system name and
12561 What compiler (and its version) was used to compile @value{GDBN}---e.g.
12562 ``@value{GCC}--2.8.1''.
12565 What compiler (and its version) was used to compile the program you are
12566 debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
12567 C Compiler''. For GCC, you can say @code{gcc --version} to get this
12568 information; for other compilers, see the documentation for those
12572 The command arguments you gave the compiler to compile your example and
12573 observe the bug. For example, did you use @samp{-O}? To guarantee
12574 you will not omit something important, list them all. A copy of the
12575 Makefile (or the output from make) is sufficient.
12577 If we were to try to guess the arguments, we would probably guess wrong
12578 and then we might not encounter the bug.
12581 A complete input script, and all necessary source files, that will
12585 A description of what behavior you observe that you believe is
12586 incorrect. For example, ``It gets a fatal signal.''
12588 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
12589 will certainly notice it. But if the bug is incorrect output, we might
12590 not notice unless it is glaringly wrong. You might as well not give us
12591 a chance to make a mistake.
12593 Even if the problem you experience is a fatal signal, you should still
12594 say so explicitly. Suppose something strange is going on, such as, your
12595 copy of @value{GDBN} is out of synch, or you have encountered a bug in
12596 the C library on your system. (This has happened!) Your copy might
12597 crash and ours would not. If you told us to expect a crash, then when
12598 ours fails to crash, we would know that the bug was not happening for
12599 us. If you had not told us to expect a crash, then we would not be able
12600 to draw any conclusion from our observations.
12603 If you wish to suggest changes to the @value{GDBN} source, send us context
12604 diffs. If you even discuss something in the @value{GDBN} source, refer to
12605 it by context, not by line number.
12607 The line numbers in our development sources will not match those in your
12608 sources. Your line numbers would convey no useful information to us.
12612 Here are some things that are not necessary:
12616 A description of the envelope of the bug.
12618 Often people who encounter a bug spend a lot of time investigating
12619 which changes to the input file will make the bug go away and which
12620 changes will not affect it.
12622 This is often time consuming and not very useful, because the way we
12623 will find the bug is by running a single example under the debugger
12624 with breakpoints, not by pure deduction from a series of examples.
12625 We recommend that you save your time for something else.
12627 Of course, if you can find a simpler example to report @emph{instead}
12628 of the original one, that is a convenience for us. Errors in the
12629 output will be easier to spot, running under the debugger will take
12630 less time, and so on.
12632 However, simplification is not vital; if you do not want to do this,
12633 report the bug anyway and send us the entire test case you used.
12636 A patch for the bug.
12638 A patch for the bug does help us if it is a good one. But do not omit
12639 the necessary information, such as the test case, on the assumption that
12640 a patch is all we need. We might see problems with your patch and decide
12641 to fix the problem another way, or we might not understand it at all.
12643 Sometimes with a program as complicated as @value{GDBN} it is very hard to
12644 construct an example that will make the program follow a certain path
12645 through the code. If you do not send us the example, we will not be able
12646 to construct one, so we will not be able to verify that the bug is fixed.
12648 And if we cannot understand what bug you are trying to fix, or why your
12649 patch should be an improvement, we will not install it. A test case will
12650 help us to understand.
12653 A guess about what the bug is or what it depends on.
12655 Such guesses are usually wrong. Even we cannot guess right about such
12656 things without first using the debugger to find the facts.
12659 @c The readline documentation is distributed with the readline code
12660 @c and consists of the two following files:
12662 @c inc-hist.texinfo
12663 @c Use -I with makeinfo to point to the appropriate directory,
12664 @c environment var TEXINPUTS with TeX.
12665 @include rluser.texinfo
12666 @include inc-hist.texinfo
12669 @node Formatting Documentation
12670 @appendix Formatting Documentation
12672 @cindex @value{GDBN} reference card
12673 @cindex reference card
12674 The @value{GDBN} 4 release includes an already-formatted reference card, ready
12675 for printing with PostScript or Ghostscript, in the @file{gdb}
12676 subdirectory of the main source directory@footnote{In
12677 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
12678 release.}. If you can use PostScript or Ghostscript with your printer,
12679 you can print the reference card immediately with @file{refcard.ps}.
12681 The release also includes the source for the reference card. You
12682 can format it, using @TeX{}, by typing:
12688 The @value{GDBN} reference card is designed to print in @dfn{landscape}
12689 mode on US ``letter'' size paper;
12690 that is, on a sheet 11 inches wide by 8.5 inches
12691 high. You will need to specify this form of printing as an option to
12692 your @sc{dvi} output program.
12694 @cindex documentation
12696 All the documentation for @value{GDBN} comes as part of the machine-readable
12697 distribution. The documentation is written in Texinfo format, which is
12698 a documentation system that uses a single source file to produce both
12699 on-line information and a printed manual. You can use one of the Info
12700 formatting commands to create the on-line version of the documentation
12701 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
12703 @value{GDBN} includes an already formatted copy of the on-line Info
12704 version of this manual in the @file{gdb} subdirectory. The main Info
12705 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
12706 subordinate files matching @samp{gdb.info*} in the same directory. If
12707 necessary, you can print out these files, or read them with any editor;
12708 but they are easier to read using the @code{info} subsystem in @sc{gnu}
12709 Emacs or the standalone @code{info} program, available as part of the
12710 @sc{gnu} Texinfo distribution.
12712 If you want to format these Info files yourself, you need one of the
12713 Info formatting programs, such as @code{texinfo-format-buffer} or
12716 If you have @code{makeinfo} installed, and are in the top level
12717 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
12718 version @value{GDBVN}), you can make the Info file by typing:
12725 If you want to typeset and print copies of this manual, you need @TeX{},
12726 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
12727 Texinfo definitions file.
12729 @TeX{} is a typesetting program; it does not print files directly, but
12730 produces output files called @sc{dvi} files. To print a typeset
12731 document, you need a program to print @sc{dvi} files. If your system
12732 has @TeX{} installed, chances are it has such a program. The precise
12733 command to use depends on your system; @kbd{lpr -d} is common; another
12734 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
12735 require a file name without any extension or a @samp{.dvi} extension.
12737 @TeX{} also requires a macro definitions file called
12738 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
12739 written in Texinfo format. On its own, @TeX{} cannot either read or
12740 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
12741 and is located in the @file{gdb-@var{version-number}/texinfo}
12744 If you have @TeX{} and a @sc{dvi} printer program installed, you can
12745 typeset and print this manual. First switch to the the @file{gdb}
12746 subdirectory of the main source directory (for example, to
12747 @file{gdb-@value{GDBVN}/gdb}) and type:
12753 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
12755 @node Installing GDB
12756 @appendix Installing @value{GDBN}
12757 @cindex configuring @value{GDBN}
12758 @cindex installation
12760 @value{GDBN} comes with a @code{configure} script that automates the process
12761 of preparing @value{GDBN} for installation; you can then use @code{make} to
12762 build the @code{gdb} program.
12764 @c irrelevant in info file; it's as current as the code it lives with.
12765 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
12766 look at the @file{README} file in the sources; we may have improved the
12767 installation procedures since publishing this manual.}
12770 The @value{GDBN} distribution includes all the source code you need for
12771 @value{GDBN} in a single directory, whose name is usually composed by
12772 appending the version number to @samp{gdb}.
12774 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
12775 @file{gdb-@value{GDBVN}} directory. That directory contains:
12778 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
12779 script for configuring @value{GDBN} and all its supporting libraries
12781 @item gdb-@value{GDBVN}/gdb
12782 the source specific to @value{GDBN} itself
12784 @item gdb-@value{GDBVN}/bfd
12785 source for the Binary File Descriptor library
12787 @item gdb-@value{GDBVN}/include
12788 @sc{gnu} include files
12790 @item gdb-@value{GDBVN}/libiberty
12791 source for the @samp{-liberty} free software library
12793 @item gdb-@value{GDBVN}/opcodes
12794 source for the library of opcode tables and disassemblers
12796 @item gdb-@value{GDBVN}/readline
12797 source for the @sc{gnu} command-line interface
12799 @item gdb-@value{GDBVN}/glob
12800 source for the @sc{gnu} filename pattern-matching subroutine
12802 @item gdb-@value{GDBVN}/mmalloc
12803 source for the @sc{gnu} memory-mapped malloc package
12806 The simplest way to configure and build @value{GDBN} is to run @code{configure}
12807 from the @file{gdb-@var{version-number}} source directory, which in
12808 this example is the @file{gdb-@value{GDBVN}} directory.
12810 First switch to the @file{gdb-@var{version-number}} source directory
12811 if you are not already in it; then run @code{configure}. Pass the
12812 identifier for the platform on which @value{GDBN} will run as an
12818 cd gdb-@value{GDBVN}
12819 ./configure @var{host}
12824 where @var{host} is an identifier such as @samp{sun4} or
12825 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
12826 (You can often leave off @var{host}; @code{configure} tries to guess the
12827 correct value by examining your system.)
12829 Running @samp{configure @var{host}} and then running @code{make} builds the
12830 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
12831 libraries, then @code{gdb} itself. The configured source files, and the
12832 binaries, are left in the corresponding source directories.
12835 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
12836 system does not recognize this automatically when you run a different
12837 shell, you may need to run @code{sh} on it explicitly:
12840 sh configure @var{host}
12843 If you run @code{configure} from a directory that contains source
12844 directories for multiple libraries or programs, such as the
12845 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
12846 creates configuration files for every directory level underneath (unless
12847 you tell it not to, with the @samp{--norecursion} option).
12849 You can run the @code{configure} script from any of the
12850 subordinate directories in the @value{GDBN} distribution if you only want to
12851 configure that subdirectory, but be sure to specify a path to it.
12853 For example, with version @value{GDBVN}, type the following to configure only
12854 the @code{bfd} subdirectory:
12858 cd gdb-@value{GDBVN}/bfd
12859 ../configure @var{host}
12863 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
12864 However, you should make sure that the shell on your path (named by
12865 the @samp{SHELL} environment variable) is publicly readable. Remember
12866 that @value{GDBN} uses the shell to start your program---some systems refuse to
12867 let @value{GDBN} debug child processes whose programs are not readable.
12870 * Separate Objdir:: Compiling @value{GDBN} in another directory
12871 * Config Names:: Specifying names for hosts and targets
12872 * Configure Options:: Summary of options for configure
12875 @node Separate Objdir
12876 @section Compiling @value{GDBN} in another directory
12878 If you want to run @value{GDBN} versions for several host or target machines,
12879 you need a different @code{gdb} compiled for each combination of
12880 host and target. @code{configure} is designed to make this easy by
12881 allowing you to generate each configuration in a separate subdirectory,
12882 rather than in the source directory. If your @code{make} program
12883 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
12884 @code{make} in each of these directories builds the @code{gdb}
12885 program specified there.
12887 To build @code{gdb} in a separate directory, run @code{configure}
12888 with the @samp{--srcdir} option to specify where to find the source.
12889 (You also need to specify a path to find @code{configure}
12890 itself from your working directory. If the path to @code{configure}
12891 would be the same as the argument to @samp{--srcdir}, you can leave out
12892 the @samp{--srcdir} option; it is assumed.)
12894 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
12895 separate directory for a Sun 4 like this:
12899 cd gdb-@value{GDBVN}
12902 ../gdb-@value{GDBVN}/configure sun4
12907 When @code{configure} builds a configuration using a remote source
12908 directory, it creates a tree for the binaries with the same structure
12909 (and using the same names) as the tree under the source directory. In
12910 the example, you'd find the Sun 4 library @file{libiberty.a} in the
12911 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
12912 @file{gdb-sun4/gdb}.
12914 One popular reason to build several @value{GDBN} configurations in separate
12915 directories is to configure @value{GDBN} for cross-compiling (where
12916 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
12917 programs that run on another machine---the @dfn{target}).
12918 You specify a cross-debugging target by
12919 giving the @samp{--target=@var{target}} option to @code{configure}.
12921 When you run @code{make} to build a program or library, you must run
12922 it in a configured directory---whatever directory you were in when you
12923 called @code{configure} (or one of its subdirectories).
12925 The @code{Makefile} that @code{configure} generates in each source
12926 directory also runs recursively. If you type @code{make} in a source
12927 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
12928 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
12929 will build all the required libraries, and then build GDB.
12931 When you have multiple hosts or targets configured in separate
12932 directories, you can run @code{make} on them in parallel (for example,
12933 if they are NFS-mounted on each of the hosts); they will not interfere
12937 @section Specifying names for hosts and targets
12939 The specifications used for hosts and targets in the @code{configure}
12940 script are based on a three-part naming scheme, but some short predefined
12941 aliases are also supported. The full naming scheme encodes three pieces
12942 of information in the following pattern:
12945 @var{architecture}-@var{vendor}-@var{os}
12948 For example, you can use the alias @code{sun4} as a @var{host} argument,
12949 or as the value for @var{target} in a @code{--target=@var{target}}
12950 option. The equivalent full name is @samp{sparc-sun-sunos4}.
12952 The @code{configure} script accompanying @value{GDBN} does not provide
12953 any query facility to list all supported host and target names or
12954 aliases. @code{configure} calls the Bourne shell script
12955 @code{config.sub} to map abbreviations to full names; you can read the
12956 script, if you wish, or you can use it to test your guesses on
12957 abbreviations---for example:
12960 % sh config.sub i386-linux
12962 % sh config.sub alpha-linux
12963 alpha-unknown-linux-gnu
12964 % sh config.sub hp9k700
12966 % sh config.sub sun4
12967 sparc-sun-sunos4.1.1
12968 % sh config.sub sun3
12969 m68k-sun-sunos4.1.1
12970 % sh config.sub i986v
12971 Invalid configuration `i986v': machine `i986v' not recognized
12975 @code{config.sub} is also distributed in the @value{GDBN} source
12976 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
12978 @node Configure Options
12979 @section @code{configure} options
12981 Here is a summary of the @code{configure} options and arguments that
12982 are most often useful for building @value{GDBN}. @code{configure} also has
12983 several other options not listed here. @inforef{What Configure
12984 Does,,configure.info}, for a full explanation of @code{configure}.
12987 configure @r{[}--help@r{]}
12988 @r{[}--prefix=@var{dir}@r{]}
12989 @r{[}--exec-prefix=@var{dir}@r{]}
12990 @r{[}--srcdir=@var{dirname}@r{]}
12991 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
12992 @r{[}--target=@var{target}@r{]}
12997 You may introduce options with a single @samp{-} rather than
12998 @samp{--} if you prefer; but you may abbreviate option names if you use
13003 Display a quick summary of how to invoke @code{configure}.
13005 @item --prefix=@var{dir}
13006 Configure the source to install programs and files under directory
13009 @item --exec-prefix=@var{dir}
13010 Configure the source to install programs under directory
13013 @c avoid splitting the warning from the explanation:
13015 @item --srcdir=@var{dirname}
13016 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
13017 @code{make} that implements the @code{VPATH} feature.}@*
13018 Use this option to make configurations in directories separate from the
13019 @value{GDBN} source directories. Among other things, you can use this to
13020 build (or maintain) several configurations simultaneously, in separate
13021 directories. @code{configure} writes configuration specific files in
13022 the current directory, but arranges for them to use the source in the
13023 directory @var{dirname}. @code{configure} creates directories under
13024 the working directory in parallel to the source directories below
13027 @item --norecursion
13028 Configure only the directory level where @code{configure} is executed; do not
13029 propagate configuration to subdirectories.
13031 @item --target=@var{target}
13032 Configure @value{GDBN} for cross-debugging programs running on the specified
13033 @var{target}. Without this option, @value{GDBN} is configured to debug
13034 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
13036 There is no convenient way to generate a list of all available targets.
13038 @item @var{host} @dots{}
13039 Configure @value{GDBN} to run on the specified @var{host}.
13041 There is no convenient way to generate a list of all available hosts.
13044 There are many other options available as well, but they are generally
13045 needed for special purposes only.
13053 % I think something like @colophon should be in texinfo. In the
13055 \long\def\colophon{\hbox to0pt{}\vfill
13056 \centerline{The body of this manual is set in}
13057 \centerline{\fontname\tenrm,}
13058 \centerline{with headings in {\bf\fontname\tenbf}}
13059 \centerline{and examples in {\tt\fontname\tentt}.}
13060 \centerline{{\it\fontname\tenit\/},}
13061 \centerline{{\bf\fontname\tenbf}, and}
13062 \centerline{{\sl\fontname\tensl\/}}
13063 \centerline{are used for emphasis.}\vfill}
13065 % Blame: doc@cygnus.com, 1991.
13068 @c TeX can handle the contents at the start but makeinfo 3.12 can not