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) that will be passed to your program.
1688 The value of @code{PATH} used by @value{GDBN} does not change.
1689 You may specify several directory names, separated by whitespace or by a
1690 system-dependent separator character (@samp{:} on Unix, @samp{;} on
1691 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
1692 is moved to the front, so it is searched sooner.
1694 You can use the string @samp{$cwd} to refer to whatever is the current
1695 working directory at the time @value{GDBN} searches the path. If you
1696 use @samp{.} instead, it refers to the directory where you executed the
1697 @code{path} command. @value{GDBN} replaces @samp{.} in the
1698 @var{directory} argument (with the current path) before adding
1699 @var{directory} to the search path.
1700 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1701 @c document that, since repeating it would be a no-op.
1705 Display the list of search paths for executables (the @code{PATH}
1706 environment variable).
1708 @kindex show environment
1709 @item show environment @r{[}@var{varname}@r{]}
1710 Print the value of environment variable @var{varname} to be given to
1711 your program when it starts. If you do not supply @var{varname},
1712 print the names and values of all environment variables to be given to
1713 your program. You can abbreviate @code{environment} as @code{env}.
1715 @kindex set environment
1716 @item set environment @var{varname} @r{[}=@var{value}@r{]}
1717 Set environment variable @var{varname} to @var{value}. The value
1718 changes for your program only, not for @value{GDBN} itself. @var{value} may
1719 be any string; the values of environment variables are just strings, and
1720 any interpretation is supplied by your program itself. The @var{value}
1721 parameter is optional; if it is eliminated, the variable is set to a
1723 @c "any string" here does not include leading, trailing
1724 @c blanks. Gnu asks: does anyone care?
1726 For example, this command:
1733 tells the debugged program, when subsequently run, that its user is named
1734 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1735 are not actually required.)
1737 @kindex unset environment
1738 @item unset environment @var{varname}
1739 Remove variable @var{varname} from the environment to be passed to your
1740 program. This is different from @samp{set env @var{varname} =};
1741 @code{unset environment} removes the variable from the environment,
1742 rather than assigning it an empty value.
1745 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
1747 by your @code{SHELL} environment variable if it exists (or
1748 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1749 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1750 @file{.bashrc} for BASH---any variables you set in that file affect
1751 your program. You may wish to move setting of environment variables to
1752 files that are only run when you sign on, such as @file{.login} or
1755 @node Working Directory
1756 @section Your program's working directory
1758 @cindex working directory (of your program)
1759 Each time you start your program with @code{run}, it inherits its
1760 working directory from the current working directory of @value{GDBN}.
1761 The @value{GDBN} working directory is initially whatever it inherited
1762 from its parent process (typically the shell), but you can specify a new
1763 working directory in @value{GDBN} with the @code{cd} command.
1765 The @value{GDBN} working directory also serves as a default for the commands
1766 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1771 @item cd @var{directory}
1772 Set the @value{GDBN} working directory to @var{directory}.
1776 Print the @value{GDBN} working directory.
1780 @section Your program's input and output
1785 By default, the program you run under @value{GDBN} does input and output to
1786 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1787 to its own terminal modes to interact with you, but it records the terminal
1788 modes your program was using and switches back to them when you continue
1789 running your program.
1792 @kindex info terminal
1794 Displays information recorded by @value{GDBN} about the terminal modes your
1798 You can redirect your program's input and/or output using shell
1799 redirection with the @code{run} command. For example,
1806 starts your program, diverting its output to the file @file{outfile}.
1809 @cindex controlling terminal
1810 Another way to specify where your program should do input and output is
1811 with the @code{tty} command. This command accepts a file name as
1812 argument, and causes this file to be the default for future @code{run}
1813 commands. It also resets the controlling terminal for the child
1814 process, for future @code{run} commands. For example,
1821 directs that processes started with subsequent @code{run} commands
1822 default to do input and output on the terminal @file{/dev/ttyb} and have
1823 that as their controlling terminal.
1825 An explicit redirection in @code{run} overrides the @code{tty} command's
1826 effect on the input/output device, but not its effect on the controlling
1829 When you use the @code{tty} command or redirect input in the @code{run}
1830 command, only the input @emph{for your program} is affected. The input
1831 for @value{GDBN} still comes from your terminal.
1834 @section Debugging an already-running process
1839 @item attach @var{process-id}
1840 This command attaches to a running process---one that was started
1841 outside @value{GDBN}. (@code{info files} shows your active
1842 targets.) The command takes as argument a process ID. The usual way to
1843 find out the process-id of a Unix process is with the @code{ps} utility,
1844 or with the @samp{jobs -l} shell command.
1846 @code{attach} does not repeat if you press @key{RET} a second time after
1847 executing the command.
1850 To use @code{attach}, your program must be running in an environment
1851 which supports processes; for example, @code{attach} does not work for
1852 programs on bare-board targets that lack an operating system. You must
1853 also have permission to send the process a signal.
1855 When you use @code{attach}, the debugger finds the program running in
1856 the process first by looking in the current working directory, then (if
1857 the program is not found) by using the source file search path
1858 (@pxref{Source Path, ,Specifying source directories}). You can also use
1859 the @code{file} command to load the program. @xref{Files, ,Commands to
1862 The first thing @value{GDBN} does after arranging to debug the specified
1863 process is to stop it. You can examine and modify an attached process
1864 with all the @value{GDBN} commands that are ordinarily available when
1865 you start processes with @code{run}. You can insert breakpoints; you
1866 can step and continue; you can modify storage. If you would rather the
1867 process continue running, you may use the @code{continue} command after
1868 attaching @value{GDBN} to the process.
1873 When you have finished debugging the attached process, you can use the
1874 @code{detach} command to release it from @value{GDBN} control. Detaching
1875 the process continues its execution. After the @code{detach} command,
1876 that process and @value{GDBN} become completely independent once more, and you
1877 are ready to @code{attach} another process or start one with @code{run}.
1878 @code{detach} does not repeat if you press @key{RET} again after
1879 executing the command.
1882 If you exit @value{GDBN} or use the @code{run} command while you have an
1883 attached process, you kill that process. By default, @value{GDBN} asks
1884 for confirmation if you try to do either of these things; you can
1885 control whether or not you need to confirm by using the @code{set
1886 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1890 @section Killing the child process
1895 Kill the child process in which your program is running under @value{GDBN}.
1898 This command is useful if you wish to debug a core dump instead of a
1899 running process. @value{GDBN} ignores any core dump file while your program
1902 On some operating systems, a program cannot be executed outside @value{GDBN}
1903 while you have breakpoints set on it inside @value{GDBN}. You can use the
1904 @code{kill} command in this situation to permit running your program
1905 outside the debugger.
1907 The @code{kill} command is also useful if you wish to recompile and
1908 relink your program, since on many systems it is impossible to modify an
1909 executable file while it is running in a process. In this case, when you
1910 next type @code{run}, @value{GDBN} notices that the file has changed, and
1911 reads the symbol table again (while trying to preserve your current
1912 breakpoint settings).
1915 @section Debugging programs with multiple threads
1917 @cindex threads of execution
1918 @cindex multiple threads
1919 @cindex switching threads
1920 In some operating systems, such as HP-UX and Solaris, a single program
1921 may have more than one @dfn{thread} of execution. The precise semantics
1922 of threads differ from one operating system to another, but in general
1923 the threads of a single program are akin to multiple processes---except
1924 that they share one address space (that is, they can all examine and
1925 modify the same variables). On the other hand, each thread has its own
1926 registers and execution stack, and perhaps private memory.
1928 @value{GDBN} provides these facilities for debugging multi-thread
1932 @item automatic notification of new threads
1933 @item @samp{thread @var{threadno}}, a command to switch among threads
1934 @item @samp{info threads}, a command to inquire about existing threads
1935 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
1936 a command to apply a command to a list of threads
1937 @item thread-specific breakpoints
1941 @emph{Warning:} These facilities are not yet available on every
1942 @value{GDBN} configuration where the operating system supports threads.
1943 If your @value{GDBN} does not support threads, these commands have no
1944 effect. For example, a system without thread support shows no output
1945 from @samp{info threads}, and always rejects the @code{thread} command,
1949 (@value{GDBP}) info threads
1950 (@value{GDBP}) thread 1
1951 Thread ID 1 not known. Use the "info threads" command to
1952 see the IDs of currently known threads.
1954 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
1955 @c doesn't support threads"?
1958 @cindex focus of debugging
1959 @cindex current thread
1960 The @value{GDBN} thread debugging facility allows you to observe all
1961 threads while your program runs---but whenever @value{GDBN} takes
1962 control, one thread in particular is always the focus of debugging.
1963 This thread is called the @dfn{current thread}. Debugging commands show
1964 program information from the perspective of the current thread.
1966 @cindex @code{New} @var{systag} message
1967 @cindex thread identifier (system)
1968 @c FIXME-implementors!! It would be more helpful if the [New...] message
1969 @c included GDB's numeric thread handle, so you could just go to that
1970 @c thread without first checking `info threads'.
1971 Whenever @value{GDBN} detects a new thread in your program, it displays
1972 the target system's identification for the thread with a message in the
1973 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
1974 whose form varies depending on the particular system. For example, on
1975 LynxOS, you might see
1978 [New process 35 thread 27]
1982 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
1983 the @var{systag} is simply something like @samp{process 368}, with no
1986 @c FIXME!! (1) Does the [New...] message appear even for the very first
1987 @c thread of a program, or does it only appear for the
1988 @c second---i.e., when it becomes obvious we have a multithread
1990 @c (2) *Is* there necessarily a first thread always? Or do some
1991 @c multithread systems permit starting a program with multiple
1992 @c threads ab initio?
1994 @cindex thread number
1995 @cindex thread identifier (GDB)
1996 For debugging purposes, @value{GDBN} associates its own thread
1997 number---always a single integer---with each thread in your program.
2000 @kindex info threads
2002 Display a summary of all threads currently in your
2003 program. @value{GDBN} displays for each thread (in this order):
2006 @item the thread number assigned by @value{GDBN}
2008 @item the target system's thread identifier (@var{systag})
2010 @item the current stack frame summary for that thread
2014 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2015 indicates the current thread.
2019 @c end table here to get a little more width for example
2022 (@value{GDBP}) info threads
2023 3 process 35 thread 27 0x34e5 in sigpause ()
2024 2 process 35 thread 23 0x34e5 in sigpause ()
2025 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2031 @cindex thread number
2032 @cindex thread identifier (GDB)
2033 For debugging purposes, @value{GDBN} associates its own thread
2034 number---a small integer assigned in thread-creation order---with each
2035 thread in your program.
2037 @cindex @code{New} @var{systag} message, on HP-UX
2038 @cindex thread identifier (system), on HP-UX
2039 @c FIXME-implementors!! It would be more helpful if the [New...] message
2040 @c included GDB's numeric thread handle, so you could just go to that
2041 @c thread without first checking `info threads'.
2042 Whenever @value{GDBN} detects a new thread in your program, it displays
2043 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2044 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2045 whose form varies depending on the particular system. For example, on
2049 [New thread 2 (system thread 26594)]
2053 when @value{GDBN} notices a new thread.
2056 @kindex info threads
2058 Display a summary of all threads currently in your
2059 program. @value{GDBN} displays for each thread (in this order):
2062 @item the thread number assigned by @value{GDBN}
2064 @item the target system's thread identifier (@var{systag})
2066 @item the current stack frame summary for that thread
2070 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2071 indicates the current thread.
2075 @c end table here to get a little more width for example
2078 (@value{GDBP}) info threads
2079 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2081 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2082 from /usr/lib/libc.2
2083 1 system thread 27905 0x7b003498 in _brk () \@*
2084 from /usr/lib/libc.2
2088 @kindex thread @var{threadno}
2089 @item thread @var{threadno}
2090 Make thread number @var{threadno} the current thread. The command
2091 argument @var{threadno} is the internal @value{GDBN} thread number, as
2092 shown in the first field of the @samp{info threads} display.
2093 @value{GDBN} responds by displaying the system identifier of the thread
2094 you selected, and its current stack frame summary:
2097 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2098 (@value{GDBP}) thread 2
2099 [Switching to process 35 thread 23]
2100 0x34e5 in sigpause ()
2104 As with the @samp{[New @dots{}]} message, the form of the text after
2105 @samp{Switching to} depends on your system's conventions for identifying
2108 @kindex thread apply
2109 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2110 The @code{thread apply} command allows you to apply a command to one or
2111 more threads. Specify the numbers of the threads that you want affected
2112 with the command argument @var{threadno}. @var{threadno} is the internal
2113 @value{GDBN} thread number, as shown in the first field of the @samp{info
2114 threads} display. To apply a command to all threads, use
2115 @code{thread apply all} @var{args}.
2118 @cindex automatic thread selection
2119 @cindex switching threads automatically
2120 @cindex threads, automatic switching
2121 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2122 signal, it automatically selects the thread where that breakpoint or
2123 signal happened. @value{GDBN} alerts you to the context switch with a
2124 message of the form @samp{[Switching to @var{systag}]} to identify the
2127 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2128 more information about how @value{GDBN} behaves when you stop and start
2129 programs with multiple threads.
2131 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2132 watchpoints in programs with multiple threads.
2135 @section Debugging programs with multiple processes
2137 @cindex fork, debugging programs which call
2138 @cindex multiple processes
2139 @cindex processes, multiple
2140 On most systems, @value{GDBN} has no special support for debugging
2141 programs which create additional processes using the @code{fork}
2142 function. When a program forks, @value{GDBN} will continue to debug the
2143 parent process and the child process will run unimpeded. If you have
2144 set a breakpoint in any code which the child then executes, the child
2145 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2146 will cause it to terminate.
2148 However, if you want to debug the child process there is a workaround
2149 which isn't too painful. Put a call to @code{sleep} in the code which
2150 the child process executes after the fork. It may be useful to sleep
2151 only if a certain environment variable is set, or a certain file exists,
2152 so that the delay need not occur when you don't want to run @value{GDBN}
2153 on the child. While the child is sleeping, use the @code{ps} program to
2154 get its process ID. Then tell @value{GDBN} (a new invocation of
2155 @value{GDBN} if you are also debugging the parent process) to attach to
2156 the child process (@pxref{Attach}). From that point on you can debug
2157 the child process just like any other process which you attached to.
2159 On HP-UX (11.x and later only?), @value{GDBN} provides support for
2160 debugging programs that create additional processes using the
2161 @code{fork} or @code{vfork} function.
2163 By default, when a program forks, @value{GDBN} will continue to debug
2164 the parent process and the child process will run unimpeded.
2166 If you want to follow the child process instead of the parent process,
2167 use the command @w{@code{set follow-fork-mode}}.
2170 @kindex set follow-fork-mode
2171 @item set follow-fork-mode @var{mode}
2172 Set the debugger response to a program call of @code{fork} or
2173 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2174 process. The @var{mode} can be:
2178 The original process is debugged after a fork. The child process runs
2179 unimpeded. This is the default.
2182 The new process is debugged after a fork. The parent process runs
2186 The debugger will ask for one of the above choices.
2189 @item show follow-fork-mode
2190 Display the current debugger response to a @code{fork} or @code{vfork} call.
2193 If you ask to debug a child process and a @code{vfork} is followed by an
2194 @code{exec}, @value{GDBN} executes the new target up to the first
2195 breakpoint in the new target. If you have a breakpoint set on
2196 @code{main} in your original program, the breakpoint will also be set on
2197 the child process's @code{main}.
2199 When a child process is spawned by @code{vfork}, you cannot debug the
2200 child or parent until an @code{exec} call completes.
2202 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2203 call executes, the new target restarts. To restart the parent process,
2204 use the @code{file} command with the parent executable name as its
2207 You can use the @code{catch} command to make @value{GDBN} stop whenever
2208 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2209 Catchpoints, ,Setting catchpoints}.
2212 @chapter Stopping and Continuing
2214 The principal purposes of using a debugger are so that you can stop your
2215 program before it terminates; or so that, if your program runs into
2216 trouble, you can investigate and find out why.
2218 Inside @value{GDBN}, your program may stop for any of several reasons,
2219 such as a signal, a breakpoint, or reaching a new line after a
2220 @value{GDBN} command such as @code{step}. You may then examine and
2221 change variables, set new breakpoints or remove old ones, and then
2222 continue execution. Usually, the messages shown by @value{GDBN} provide
2223 ample explanation of the status of your program---but you can also
2224 explicitly request this information at any time.
2227 @kindex info program
2229 Display information about the status of your program: whether it is
2230 running or not, what process it is, and why it stopped.
2234 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2235 * Continuing and Stepping:: Resuming execution
2237 * Thread Stops:: Stopping and starting multi-thread programs
2241 @section Breakpoints, watchpoints, and catchpoints
2244 A @dfn{breakpoint} makes your program stop whenever a certain point in
2245 the program is reached. For each breakpoint, you can add conditions to
2246 control in finer detail whether your program stops. You can set
2247 breakpoints with the @code{break} command and its variants (@pxref{Set
2248 Breaks, ,Setting breakpoints}), to specify the place where your program
2249 should stop by line number, function name or exact address in the
2252 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2253 breakpoints in shared libraries before the executable is run. There is
2254 a minor limitation on HP-UX systems: you must wait until the executable
2255 is run in order to set breakpoints in shared library routines that are
2256 not called directly by the program (for example, routines that are
2257 arguments in a @code{pthread_create} call).
2260 @cindex memory tracing
2261 @cindex breakpoint on memory address
2262 @cindex breakpoint on variable modification
2263 A @dfn{watchpoint} is a special breakpoint that stops your program
2264 when the value of an expression changes. You must use a different
2265 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2266 watchpoints}), but aside from that, you can manage a watchpoint like
2267 any other breakpoint: you enable, disable, and delete both breakpoints
2268 and watchpoints using the same commands.
2270 You can arrange to have values from your program displayed automatically
2271 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2275 @cindex breakpoint on events
2276 A @dfn{catchpoint} is another special breakpoint that stops your program
2277 when a certain kind of event occurs, such as the throwing of a C++
2278 exception or the loading of a library. As with watchpoints, you use a
2279 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2280 catchpoints}), but aside from that, you can manage a catchpoint like any
2281 other breakpoint. (To stop when your program receives a signal, use the
2282 @code{handle} command; see @ref{Signals, ,Signals}.)
2284 @cindex breakpoint numbers
2285 @cindex numbers for breakpoints
2286 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2287 catchpoint when you create it; these numbers are successive integers
2288 starting with one. In many of the commands for controlling various
2289 features of breakpoints you use the breakpoint number to say which
2290 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2291 @dfn{disabled}; if disabled, it has no effect on your program until you
2294 @cindex breakpoint ranges
2295 @cindex ranges of breakpoints
2296 Some @value{GDBN} commands accept a range of breakpoints on which to
2297 operate. A breakpoint range is either a single breakpoint number, like
2298 @samp{5}, or two such numbers, in increasing order, separated by a
2299 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
2300 all breakpoint in that range are operated on.
2303 * Set Breaks:: Setting breakpoints
2304 * Set Watchpoints:: Setting watchpoints
2305 * Set Catchpoints:: Setting catchpoints
2306 * Delete Breaks:: Deleting breakpoints
2307 * Disabling:: Disabling breakpoints
2308 * Conditions:: Break conditions
2309 * Break Commands:: Breakpoint command lists
2310 * Breakpoint Menus:: Breakpoint menus
2311 * Error in Breakpoints:: ``Cannot insert breakpoints''
2315 @subsection Setting breakpoints
2317 @c FIXME LMB what does GDB do if no code on line of breakpt?
2318 @c consider in particular declaration with/without initialization.
2320 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2323 @kindex b @r{(@code{break})}
2324 @vindex $bpnum@r{, convenience variable}
2325 @cindex latest breakpoint
2326 Breakpoints are set with the @code{break} command (abbreviated
2327 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2328 number of the breakpoint you've set most recently; see @ref{Convenience
2329 Vars,, Convenience variables}, for a discussion of what you can do with
2330 convenience variables.
2332 You have several ways to say where the breakpoint should go.
2335 @item break @var{function}
2336 Set a breakpoint at entry to function @var{function}.
2337 When using source languages that permit overloading of symbols, such as
2338 C++, @var{function} may refer to more than one possible place to break.
2339 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2341 @item break +@var{offset}
2342 @itemx break -@var{offset}
2343 Set a breakpoint some number of lines forward or back from the position
2344 at which execution stopped in the currently selected @dfn{stack frame}.
2345 (@xref{Frames, ,Frames}, for a description of stack frames.)
2347 @item break @var{linenum}
2348 Set a breakpoint at line @var{linenum} in the current source file.
2349 The current source file is the last file whose source text was printed.
2350 The breakpoint will stop your program just before it executes any of the
2353 @item break @var{filename}:@var{linenum}
2354 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2356 @item break @var{filename}:@var{function}
2357 Set a breakpoint at entry to function @var{function} found in file
2358 @var{filename}. Specifying a file name as well as a function name is
2359 superfluous except when multiple files contain similarly named
2362 @item break *@var{address}
2363 Set a breakpoint at address @var{address}. You can use this to set
2364 breakpoints in parts of your program which do not have debugging
2365 information or source files.
2368 When called without any arguments, @code{break} sets a breakpoint at
2369 the next instruction to be executed in the selected stack frame
2370 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2371 innermost, this makes your program stop as soon as control
2372 returns to that frame. This is similar to the effect of a
2373 @code{finish} command in the frame inside the selected frame---except
2374 that @code{finish} does not leave an active breakpoint. If you use
2375 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2376 the next time it reaches the current location; this may be useful
2379 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2380 least one instruction has been executed. If it did not do this, you
2381 would be unable to proceed past a breakpoint without first disabling the
2382 breakpoint. This rule applies whether or not the breakpoint already
2383 existed when your program stopped.
2385 @item break @dots{} if @var{cond}
2386 Set a breakpoint with condition @var{cond}; evaluate the expression
2387 @var{cond} each time the breakpoint is reached, and stop only if the
2388 value is nonzero---that is, if @var{cond} evaluates as true.
2389 @samp{@dots{}} stands for one of the possible arguments described
2390 above (or no argument) specifying where to break. @xref{Conditions,
2391 ,Break conditions}, for more information on breakpoint conditions.
2394 @item tbreak @var{args}
2395 Set a breakpoint enabled only for one stop. @var{args} are the
2396 same as for the @code{break} command, and the breakpoint is set in the same
2397 way, but the breakpoint is automatically deleted after the first time your
2398 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2401 @item hbreak @var{args}
2402 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2403 @code{break} command and the breakpoint is set in the same way, but the
2404 breakpoint requires hardware support and some target hardware may not
2405 have this support. The main purpose of this is EPROM/ROM code
2406 debugging, so you can set a breakpoint at an instruction without
2407 changing the instruction. This can be used with the new trap-generation
2408 provided by SPARClite DSU and some x86-based targets. These targets
2409 will generate traps when a program accesses some data or instruction
2410 address that is assigned to the debug registers. However the hardware
2411 breakpoint registers can take a limited number of breakpoints. For
2412 example, on the DSU, only two data breakpoints can be set at a time, and
2413 @value{GDBN} will reject this command if more than two are used. Delete
2414 or disable unused hardware breakpoints before setting new ones
2415 (@pxref{Disabling, ,Disabling}). @xref{Conditions, ,Break conditions}.
2418 @item thbreak @var{args}
2419 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2420 are the same as for the @code{hbreak} command and the breakpoint is set in
2421 the same way. However, like the @code{tbreak} command,
2422 the breakpoint is automatically deleted after the
2423 first time your program stops there. Also, like the @code{hbreak}
2424 command, the breakpoint requires hardware support and some target hardware
2425 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2426 See also @ref{Conditions, ,Break conditions}.
2429 @cindex regular expression
2430 @item rbreak @var{regex}
2431 Set breakpoints on all functions matching the regular expression
2432 @var{regex}. This command sets an unconditional breakpoint on all
2433 matches, printing a list of all breakpoints it set. Once these
2434 breakpoints are set, they are treated just like the breakpoints set with
2435 the @code{break} command. You can delete them, disable them, or make
2436 them conditional the same way as any other breakpoint.
2438 The syntax of the regular expression is the standard one used with tools
2439 like @file{grep}. Note that this is different from the syntax used by
2440 shells, so for instance @code{foo*} matches all functions that include
2441 an @code{fo} followed by zero or more @code{o}s. There is an implicit
2442 @code{.*} leading and trailing the regular expression you supply, so to
2443 match only functions that begin with @code{foo}, use @code{^foo}.
2445 When debugging C++ programs, @code{rbreak} is useful for setting
2446 breakpoints on overloaded functions that are not members of any special
2449 @kindex info breakpoints
2450 @cindex @code{$_} and @code{info breakpoints}
2451 @item info breakpoints @r{[}@var{n}@r{]}
2452 @itemx info break @r{[}@var{n}@r{]}
2453 @itemx info watchpoints @r{[}@var{n}@r{]}
2454 Print a table of all breakpoints, watchpoints, and catchpoints set and
2455 not deleted, with the following columns for each breakpoint:
2458 @item Breakpoint Numbers
2460 Breakpoint, watchpoint, or catchpoint.
2462 Whether the breakpoint is marked to be disabled or deleted when hit.
2463 @item Enabled or Disabled
2464 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2465 that are not enabled.
2467 Where the breakpoint is in your program, as a memory address.
2469 Where the breakpoint is in the source for your program, as a file and
2474 If a breakpoint is conditional, @code{info break} shows the condition on
2475 the line following the affected breakpoint; breakpoint commands, if any,
2476 are listed after that.
2479 @code{info break} with a breakpoint
2480 number @var{n} as argument lists only that breakpoint. The
2481 convenience variable @code{$_} and the default examining-address for
2482 the @code{x} command are set to the address of the last breakpoint
2483 listed (@pxref{Memory, ,Examining memory}).
2486 @code{info break} displays a count of the number of times the breakpoint
2487 has been hit. This is especially useful in conjunction with the
2488 @code{ignore} command. You can ignore a large number of breakpoint
2489 hits, look at the breakpoint info to see how many times the breakpoint
2490 was hit, and then run again, ignoring one less than that number. This
2491 will get you quickly to the last hit of that breakpoint.
2494 @value{GDBN} allows you to set any number of breakpoints at the same place in
2495 your program. There is nothing silly or meaningless about this. When
2496 the breakpoints are conditional, this is even useful
2497 (@pxref{Conditions, ,Break conditions}).
2499 @cindex negative breakpoint numbers
2500 @cindex internal @value{GDBN} breakpoints
2501 @value{GDBN} itself sometimes sets breakpoints in your program for special
2502 purposes, such as proper handling of @code{longjmp} (in C programs).
2503 These internal breakpoints are assigned negative numbers, starting with
2504 @code{-1}; @samp{info breakpoints} does not display them.
2506 You can see these breakpoints with the @value{GDBN} maintenance command
2507 @samp{maint info breakpoints}.
2510 @kindex maint info breakpoints
2511 @item maint info breakpoints
2512 Using the same format as @samp{info breakpoints}, display both the
2513 breakpoints you've set explicitly, and those @value{GDBN} is using for
2514 internal purposes. Internal breakpoints are shown with negative
2515 breakpoint numbers. The type column identifies what kind of breakpoint
2520 Normal, explicitly set breakpoint.
2523 Normal, explicitly set watchpoint.
2526 Internal breakpoint, used to handle correctly stepping through
2527 @code{longjmp} calls.
2529 @item longjmp resume
2530 Internal breakpoint at the target of a @code{longjmp}.
2533 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2536 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2539 Shared library events.
2546 @node Set Watchpoints
2547 @subsection Setting watchpoints
2549 @cindex setting watchpoints
2550 @cindex software watchpoints
2551 @cindex hardware watchpoints
2552 You can use a watchpoint to stop execution whenever the value of an
2553 expression changes, without having to predict a particular place where
2556 Depending on your system, watchpoints may be implemented in software or
2557 hardware. @value{GDBN} does software watchpointing by single-stepping your
2558 program and testing the variable's value each time, which is hundreds of
2559 times slower than normal execution. (But this may still be worth it, to
2560 catch errors where you have no clue what part of your program is the
2563 On some systems, such as HP-UX, Linux and some other x86-based targets,
2564 @value{GDBN} includes support for
2565 hardware watchpoints, which do not slow down the running of your
2570 @item watch @var{expr}
2571 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2572 is written into by the program and its value changes.
2575 @item rwatch @var{expr}
2576 Set a watchpoint that will break when watch @var{expr} is read by the program.
2579 @item awatch @var{expr}
2580 Set a watchpoint that will break when @var{expr} is either read or written into
2583 @kindex info watchpoints
2584 @item info watchpoints
2585 This command prints a list of watchpoints, breakpoints, and catchpoints;
2586 it is the same as @code{info break}.
2589 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2590 watchpoints execute very quickly, and the debugger reports a change in
2591 value at the exact instruction where the change occurs. If @value{GDBN}
2592 cannot set a hardware watchpoint, it sets a software watchpoint, which
2593 executes more slowly and reports the change in value at the next
2594 statement, not the instruction, after the change occurs.
2596 When you issue the @code{watch} command, @value{GDBN} reports
2599 Hardware watchpoint @var{num}: @var{expr}
2603 if it was able to set a hardware watchpoint.
2605 Currently, the @code{awatch} and @code{rwatch} commands can only set
2606 hardware watchpoints, because accesses to data that don't change the
2607 value of the watched expression cannot be detected without examining
2608 every instruction as it is being executed, and @value{GDBN} does not do
2609 that currently. If @value{GDBN} finds that it is unable to set a
2610 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
2611 will print a message like this:
2614 Expression cannot be implemented with read/access watchpoint.
2617 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
2618 data type of the watched expression is wider than what a hardware
2619 watchpoint on the target machine can handle. For example, some systems
2620 can only watch regions that are up to 4 bytes wide; on such systems you
2621 cannot set hardware watchpoints for an expression that yields a
2622 double-precision floating-point number (which is typically 8 bytes
2623 wide). As a work-around, it might be possible to break the large region
2624 into a series of smaller ones and watch them with separate watchpoints.
2626 If you set too many hardware watchpoints, @value{GDBN} might be unable
2627 to insert all of them when you resume the execution of your program.
2628 Since the precise number of active watchpoints is unknown until such
2629 time as the program is about to be resumed, @value{GDBN} might not be
2630 able to warn you about this when you set the watchpoints, and the
2631 warning will be printed only when the program is resumed:
2634 Hardware watchpoint @var{num}: Could not insert watchpoint
2638 If this happens, delete or disable some of the watchpoints.
2640 The SPARClite DSU will generate traps when a program accesses some data
2641 or instruction address that is assigned to the debug registers. For the
2642 data addresses, DSU facilitates the @code{watch} command. However the
2643 hardware breakpoint registers can only take two data watchpoints, and
2644 both watchpoints must be the same kind. For example, you can set two
2645 watchpoints with @code{watch} commands, two with @code{rwatch} commands,
2646 @strong{or} two with @code{awatch} commands, but you cannot set one
2647 watchpoint with one command and the other with a different command.
2648 @value{GDBN} will reject the command if you try to mix watchpoints.
2649 Delete or disable unused watchpoint commands before setting new ones.
2651 If you call a function interactively using @code{print} or @code{call},
2652 any watchpoints you have set will be inactive until @value{GDBN} reaches another
2653 kind of breakpoint or the call completes.
2655 @value{GDBN} automatically deletes watchpoints that watch local
2656 (automatic) variables, or expressions that involve such variables, when
2657 they go out of scope, that is, when the execution leaves the block in
2658 which these variables were defined. In particular, when the program
2659 being debugged terminates, @emph{all} local variables go out of scope,
2660 and so only watchpoints that watch global variables remain set. If you
2661 rerun the program, you will need to set all such watchpoints again. One
2662 way of doing that would be to set a code breakpoint at the entry to the
2663 @code{main} function and when it breaks, set all the watchpoints.
2666 @cindex watchpoints and threads
2667 @cindex threads and watchpoints
2668 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2669 usefulness. With the current watchpoint implementation, @value{GDBN}
2670 can only watch the value of an expression @emph{in a single thread}. If
2671 you are confident that the expression can only change due to the current
2672 thread's activity (and if you are also confident that no other thread
2673 can become current), then you can use watchpoints as usual. However,
2674 @value{GDBN} may not notice when a non-current thread's activity changes
2677 @c FIXME: this is almost identical to the previous paragraph.
2678 @emph{HP-UX Warning:} In multi-thread programs, software watchpoints
2679 have only limited usefulness. If @value{GDBN} creates a software
2680 watchpoint, it can only watch the value of an expression @emph{in a
2681 single thread}. If you are confident that the expression can only
2682 change due to the current thread's activity (and if you are also
2683 confident that no other thread can become current), then you can use
2684 software watchpoints as usual. However, @value{GDBN} may not notice
2685 when a non-current thread's activity changes the expression. (Hardware
2686 watchpoints, in contrast, watch an expression in all threads.)
2689 @node Set Catchpoints
2690 @subsection Setting catchpoints
2691 @cindex catchpoints, setting
2692 @cindex exception handlers
2693 @cindex event handling
2695 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2696 kinds of program events, such as C++ exceptions or the loading of a
2697 shared library. Use the @code{catch} command to set a catchpoint.
2701 @item catch @var{event}
2702 Stop when @var{event} occurs. @var{event} can be any of the following:
2706 The throwing of a C++ exception.
2710 The catching of a C++ exception.
2714 A call to @code{exec}. This is currently only available for HP-UX.
2718 A call to @code{fork}. This is currently only available for HP-UX.
2722 A call to @code{vfork}. This is currently only available for HP-UX.
2725 @itemx load @var{libname}
2727 The dynamic loading of any shared library, or the loading of the library
2728 @var{libname}. This is currently only available for HP-UX.
2731 @itemx unload @var{libname}
2732 @kindex catch unload
2733 The unloading of any dynamically loaded shared library, or the unloading
2734 of the library @var{libname}. This is currently only available for HP-UX.
2737 @item tcatch @var{event}
2738 Set a catchpoint that is enabled only for one stop. The catchpoint is
2739 automatically deleted after the first time the event is caught.
2743 Use the @code{info break} command to list the current catchpoints.
2745 There are currently some limitations to C++ exception handling
2746 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
2750 If you call a function interactively, @value{GDBN} normally returns
2751 control to you when the function has finished executing. If the call
2752 raises an exception, however, the call may bypass the mechanism that
2753 returns control to you and cause your program either to abort or to
2754 simply continue running until it hits a breakpoint, catches a signal
2755 that @value{GDBN} is listening for, or exits. This is the case even if
2756 you set a catchpoint for the exception; catchpoints on exceptions are
2757 disabled within interactive calls.
2760 You cannot raise an exception interactively.
2763 You cannot install an exception handler interactively.
2766 @cindex raise exceptions
2767 Sometimes @code{catch} is not the best way to debug exception handling:
2768 if you need to know exactly where an exception is raised, it is better to
2769 stop @emph{before} the exception handler is called, since that way you
2770 can see the stack before any unwinding takes place. If you set a
2771 breakpoint in an exception handler instead, it may not be easy to find
2772 out where the exception was raised.
2774 To stop just before an exception handler is called, you need some
2775 knowledge of the implementation. In the case of @sc{gnu} C++, exceptions are
2776 raised by calling a library function named @code{__raise_exception}
2777 which has the following ANSI C interface:
2780 /* @var{addr} is where the exception identifier is stored.
2781 @var{id} is the exception identifier. */
2782 void __raise_exception (void **addr, void *id);
2786 To make the debugger catch all exceptions before any stack
2787 unwinding takes place, set a breakpoint on @code{__raise_exception}
2788 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2790 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2791 that depends on the value of @var{id}, you can stop your program when
2792 a specific exception is raised. You can use multiple conditional
2793 breakpoints to stop your program when any of a number of exceptions are
2798 @subsection Deleting breakpoints
2800 @cindex clearing breakpoints, watchpoints, catchpoints
2801 @cindex deleting breakpoints, watchpoints, catchpoints
2802 It is often necessary to eliminate a breakpoint, watchpoint, or
2803 catchpoint once it has done its job and you no longer want your program
2804 to stop there. This is called @dfn{deleting} the breakpoint. A
2805 breakpoint that has been deleted no longer exists; it is forgotten.
2807 With the @code{clear} command you can delete breakpoints according to
2808 where they are in your program. With the @code{delete} command you can
2809 delete individual breakpoints, watchpoints, or catchpoints by specifying
2810 their breakpoint numbers.
2812 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2813 automatically ignores breakpoints on the first instruction to be executed
2814 when you continue execution without changing the execution address.
2819 Delete any breakpoints at the next instruction to be executed in the
2820 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2821 the innermost frame is selected, this is a good way to delete a
2822 breakpoint where your program just stopped.
2824 @item clear @var{function}
2825 @itemx clear @var{filename}:@var{function}
2826 Delete any breakpoints set at entry to the function @var{function}.
2828 @item clear @var{linenum}
2829 @itemx clear @var{filename}:@var{linenum}
2830 Delete any breakpoints set at or within the code of the specified line.
2832 @cindex delete breakpoints
2834 @kindex d @r{(@code{delete})}
2835 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2836 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
2837 ranges specified as arguments. If no argument is specified, delete all
2838 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
2839 confirm off}). You can abbreviate this command as @code{d}.
2843 @subsection Disabling breakpoints
2845 @kindex disable breakpoints
2846 @kindex enable breakpoints
2847 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
2848 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
2849 it had been deleted, but remembers the information on the breakpoint so
2850 that you can @dfn{enable} it again later.
2852 You disable and enable breakpoints, watchpoints, and catchpoints with
2853 the @code{enable} and @code{disable} commands, optionally specifying one
2854 or more breakpoint numbers as arguments. Use @code{info break} or
2855 @code{info watch} to print a list of breakpoints, watchpoints, and
2856 catchpoints if you do not know which numbers to use.
2858 A breakpoint, watchpoint, or catchpoint can have any of four different
2859 states of enablement:
2863 Enabled. The breakpoint stops your program. A breakpoint set
2864 with the @code{break} command starts out in this state.
2866 Disabled. The breakpoint has no effect on your program.
2868 Enabled once. The breakpoint stops your program, but then becomes
2871 Enabled for deletion. The breakpoint stops your program, but
2872 immediately after it does so it is deleted permanently. A breakpoint
2873 set with the @code{tbreak} command starts out in this state.
2876 You can use the following commands to enable or disable breakpoints,
2877 watchpoints, and catchpoints:
2880 @kindex disable breakpoints
2882 @kindex dis @r{(@code{disable})}
2883 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2884 Disable the specified breakpoints---or all breakpoints, if none are
2885 listed. A disabled breakpoint has no effect but is not forgotten. All
2886 options such as ignore-counts, conditions and commands are remembered in
2887 case the breakpoint is enabled again later. You may abbreviate
2888 @code{disable} as @code{dis}.
2890 @kindex enable breakpoints
2892 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2893 Enable the specified breakpoints (or all defined breakpoints). They
2894 become effective once again in stopping your program.
2896 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
2897 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2898 of these breakpoints immediately after stopping your program.
2900 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
2901 Enable the specified breakpoints to work once, then die. @value{GDBN}
2902 deletes any of these breakpoints as soon as your program stops there.
2905 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
2906 @c confusing: tbreak is also initially enabled.
2907 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2908 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2909 subsequently, they become disabled or enabled only when you use one of
2910 the commands above. (The command @code{until} can set and delete a
2911 breakpoint of its own, but it does not change the state of your other
2912 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2916 @subsection Break conditions
2917 @cindex conditional breakpoints
2918 @cindex breakpoint conditions
2920 @c FIXME what is scope of break condition expr? Context where wanted?
2921 @c in particular for a watchpoint?
2922 The simplest sort of breakpoint breaks every time your program reaches a
2923 specified place. You can also specify a @dfn{condition} for a
2924 breakpoint. A condition is just a Boolean expression in your
2925 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2926 a condition evaluates the expression each time your program reaches it,
2927 and your program stops only if the condition is @emph{true}.
2929 This is the converse of using assertions for program validation; in that
2930 situation, you want to stop when the assertion is violated---that is,
2931 when the condition is false. In C, if you want to test an assertion expressed
2932 by the condition @var{assert}, you should set the condition
2933 @samp{! @var{assert}} on the appropriate breakpoint.
2935 Conditions are also accepted for watchpoints; you may not need them,
2936 since a watchpoint is inspecting the value of an expression anyhow---but
2937 it might be simpler, say, to just set a watchpoint on a variable name,
2938 and specify a condition that tests whether the new value is an interesting
2941 Break conditions can have side effects, and may even call functions in
2942 your program. This can be useful, for example, to activate functions
2943 that log program progress, or to use your own print functions to
2944 format special data structures. The effects are completely predictable
2945 unless there is another enabled breakpoint at the same address. (In
2946 that case, @value{GDBN} might see the other breakpoint first and stop your
2947 program without checking the condition of this one.) Note that
2948 breakpoint commands are usually more convenient and flexible than break
2950 purpose of performing side effects when a breakpoint is reached
2951 (@pxref{Break Commands, ,Breakpoint command lists}).
2953 Break conditions can be specified when a breakpoint is set, by using
2954 @samp{if} in the arguments to the @code{break} command. @xref{Set
2955 Breaks, ,Setting breakpoints}. They can also be changed at any time
2956 with the @code{condition} command.
2958 You can also use the @code{if} keyword with the @code{watch} command.
2959 The @code{catch} command does not recognize the @code{if} keyword;
2960 @code{condition} is the only way to impose a further condition on a
2965 @item condition @var{bnum} @var{expression}
2966 Specify @var{expression} as the break condition for breakpoint,
2967 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
2968 breakpoint @var{bnum} stops your program only if the value of
2969 @var{expression} is true (nonzero, in C). When you use
2970 @code{condition}, @value{GDBN} checks @var{expression} immediately for
2971 syntactic correctness, and to determine whether symbols in it have
2972 referents in the context of your breakpoint. If @var{expression} uses
2973 symbols not referenced in the context of the breakpoint, @value{GDBN}
2974 prints an error message:
2977 No symbol "foo" in current context.
2982 not actually evaluate @var{expression} at the time the @code{condition}
2983 command (or a command that sets a breakpoint with a condition, like
2984 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
2986 @item condition @var{bnum}
2987 Remove the condition from breakpoint number @var{bnum}. It becomes
2988 an ordinary unconditional breakpoint.
2991 @cindex ignore count (of breakpoint)
2992 A special case of a breakpoint condition is to stop only when the
2993 breakpoint has been reached a certain number of times. This is so
2994 useful that there is a special way to do it, using the @dfn{ignore
2995 count} of the breakpoint. Every breakpoint has an ignore count, which
2996 is an integer. Most of the time, the ignore count is zero, and
2997 therefore has no effect. But if your program reaches a breakpoint whose
2998 ignore count is positive, then instead of stopping, it just decrements
2999 the ignore count by one and continues. As a result, if the ignore count
3000 value is @var{n}, the breakpoint does not stop the next @var{n} times
3001 your program reaches it.
3005 @item ignore @var{bnum} @var{count}
3006 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3007 The next @var{count} times the breakpoint is reached, your program's
3008 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3011 To make the breakpoint stop the next time it is reached, specify
3014 When you use @code{continue} to resume execution of your program from a
3015 breakpoint, you can specify an ignore count directly as an argument to
3016 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3017 Stepping,,Continuing and stepping}.
3019 If a breakpoint has a positive ignore count and a condition, the
3020 condition is not checked. Once the ignore count reaches zero,
3021 @value{GDBN} resumes checking the condition.
3023 You could achieve the effect of the ignore count with a condition such
3024 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3025 is decremented each time. @xref{Convenience Vars, ,Convenience
3029 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3032 @node Break Commands
3033 @subsection Breakpoint command lists
3035 @cindex breakpoint commands
3036 You can give any breakpoint (or watchpoint or catchpoint) a series of
3037 commands to execute when your program stops due to that breakpoint. For
3038 example, you might want to print the values of certain expressions, or
3039 enable other breakpoints.
3044 @item commands @r{[}@var{bnum}@r{]}
3045 @itemx @dots{} @var{command-list} @dots{}
3047 Specify a list of commands for breakpoint number @var{bnum}. The commands
3048 themselves appear on the following lines. Type a line containing just
3049 @code{end} to terminate the commands.
3051 To remove all commands from a breakpoint, type @code{commands} and
3052 follow it immediately with @code{end}; that is, give no commands.
3054 With no @var{bnum} argument, @code{commands} refers to the last
3055 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
3056 recently encountered).
3059 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
3060 disabled within a @var{command-list}.
3062 You can use breakpoint commands to start your program up again. Simply
3063 use the @code{continue} command, or @code{step}, or any other command
3064 that resumes execution.
3066 Any other commands in the command list, after a command that resumes
3067 execution, are ignored. This is because any time you resume execution
3068 (even with a simple @code{next} or @code{step}), you may encounter
3069 another breakpoint---which could have its own command list, leading to
3070 ambiguities about which list to execute.
3073 If the first command you specify in a command list is @code{silent}, the
3074 usual message about stopping at a breakpoint is not printed. This may
3075 be desirable for breakpoints that are to print a specific message and
3076 then continue. If none of the remaining commands print anything, you
3077 see no sign that the breakpoint was reached. @code{silent} is
3078 meaningful only at the beginning of a breakpoint command list.
3080 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3081 print precisely controlled output, and are often useful in silent
3082 breakpoints. @xref{Output, ,Commands for controlled output}.
3084 For example, here is how you could use breakpoint commands to print the
3085 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3091 printf "x is %d\n",x
3096 One application for breakpoint commands is to compensate for one bug so
3097 you can test for another. Put a breakpoint just after the erroneous line
3098 of code, give it a condition to detect the case in which something
3099 erroneous has been done, and give it commands to assign correct values
3100 to any variables that need them. End with the @code{continue} command
3101 so that your program does not stop, and start with the @code{silent}
3102 command so that no output is produced. Here is an example:
3113 @node Breakpoint Menus
3114 @subsection Breakpoint menus
3116 @cindex symbol overloading
3118 Some programming languages (notably C++) permit a single function name
3119 to be defined several times, for application in different contexts.
3120 This is called @dfn{overloading}. When a function name is overloaded,
3121 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3122 a breakpoint. If you realize this is a problem, you can use
3123 something like @samp{break @var{function}(@var{types})} to specify which
3124 particular version of the function you want. Otherwise, @value{GDBN} offers
3125 you a menu of numbered choices for different possible breakpoints, and
3126 waits for your selection with the prompt @samp{>}. The first two
3127 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3128 sets a breakpoint at each definition of @var{function}, and typing
3129 @kbd{0} aborts the @code{break} command without setting any new
3132 For example, the following session excerpt shows an attempt to set a
3133 breakpoint at the overloaded symbol @code{String::after}.
3134 We choose three particular definitions of that function name:
3136 @c FIXME! This is likely to change to show arg type lists, at least
3139 (@value{GDBP}) b String::after
3142 [2] file:String.cc; line number:867
3143 [3] file:String.cc; line number:860
3144 [4] file:String.cc; line number:875
3145 [5] file:String.cc; line number:853
3146 [6] file:String.cc; line number:846
3147 [7] file:String.cc; line number:735
3149 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3150 Breakpoint 2 at 0xb344: file String.cc, line 875.
3151 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3152 Multiple breakpoints were set.
3153 Use the "delete" command to delete unwanted
3159 @c @ifclear BARETARGET
3160 @node Error in Breakpoints
3161 @subsection ``Cannot insert breakpoints''
3163 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3165 Under some operating systems, breakpoints cannot be used in a program if
3166 any other process is running that program. In this situation,
3167 attempting to run or continue a program with a breakpoint causes
3168 @value{GDBN} to print an error message:
3171 Cannot insert breakpoints.
3172 The same program may be running in another process.
3175 When this happens, you have three ways to proceed:
3179 Remove or disable the breakpoints, then continue.
3182 Suspend @value{GDBN}, and copy the file containing your program to a new
3183 name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3184 that @value{GDBN} should run your program under that name.
3185 Then start your program again.
3188 Relink your program so that the text segment is nonsharable, using the
3189 linker option @samp{-N}. The operating system limitation may not apply
3190 to nonsharable executables.
3194 A similar message can be printed if you request too many active
3195 hardware-assisted breakpoints and watchpoints:
3197 @c FIXME: the precise wording of this message may change; the relevant
3198 @c source change is not committed yet (Sep 3, 1999).
3200 Stopped; cannot insert breakpoints.
3201 You may have requested too many hardware breakpoints and watchpoints.
3205 This message is printed when you attempt to resume the program, since
3206 only then @value{GDBN} knows exactly how many hardware breakpoints and
3207 watchpoints it needs to insert.
3209 When this message is printed, you need to disable or remove some of the
3210 hardware-assisted breakpoints and watchpoints, and then continue.
3213 @node Continuing and Stepping
3214 @section Continuing and stepping
3218 @cindex resuming execution
3219 @dfn{Continuing} means resuming program execution until your program
3220 completes normally. In contrast, @dfn{stepping} means executing just
3221 one more ``step'' of your program, where ``step'' may mean either one
3222 line of source code, or one machine instruction (depending on what
3223 particular command you use). Either when continuing or when stepping,
3224 your program may stop even sooner, due to a breakpoint or a signal. (If
3225 it stops due to a signal, you may want to use @code{handle}, or use
3226 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
3230 @kindex c @r{(@code{continue})}
3231 @kindex fg @r{(resume foreground execution)}
3232 @item continue @r{[}@var{ignore-count}@r{]}
3233 @itemx c @r{[}@var{ignore-count}@r{]}
3234 @itemx fg @r{[}@var{ignore-count}@r{]}
3235 Resume program execution, at the address where your program last stopped;
3236 any breakpoints set at that address are bypassed. The optional argument
3237 @var{ignore-count} allows you to specify a further number of times to
3238 ignore a breakpoint at this location; its effect is like that of
3239 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3241 The argument @var{ignore-count} is meaningful only when your program
3242 stopped due to a breakpoint. At other times, the argument to
3243 @code{continue} is ignored.
3245 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
3246 debugged program is deemed to be the foreground program) are provided
3247 purely for convenience, and have exactly the same behavior as
3251 To resume execution at a different place, you can use @code{return}
3252 (@pxref{Returning, ,Returning from a function}) to go back to the
3253 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3254 different address}) to go to an arbitrary location in your program.
3256 A typical technique for using stepping is to set a breakpoint
3257 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3258 beginning of the function or the section of your program where a problem
3259 is believed to lie, run your program until it stops at that breakpoint,
3260 and then step through the suspect area, examining the variables that are
3261 interesting, until you see the problem happen.
3265 @kindex s @r{(@code{step})}
3267 Continue running your program until control reaches a different source
3268 line, then stop it and return control to @value{GDBN}. This command is
3269 abbreviated @code{s}.
3272 @c "without debugging information" is imprecise; actually "without line
3273 @c numbers in the debugging information". (gcc -g1 has debugging info but
3274 @c not line numbers). But it seems complex to try to make that
3275 @c distinction here.
3276 @emph{Warning:} If you use the @code{step} command while control is
3277 within a function that was compiled without debugging information,
3278 execution proceeds until control reaches a function that does have
3279 debugging information. Likewise, it will not step into a function which
3280 is compiled without debugging information. To step through functions
3281 without debugging information, use the @code{stepi} command, described
3285 The @code{step} command only stops at the first instruction of a source
3286 line. This prevents the multiple stops that could otherwise occur in
3287 @code{switch} statements, @code{for} loops, etc. @code{step} continues
3288 to stop if a function that has debugging information is called within
3289 the line. In other words, @code{step} @emph{steps inside} any functions
3290 called within the line.
3292 Also, the @code{step} command only enters a function if there is line
3293 number information for the function. Otherwise it acts like the
3294 @code{next} command. This avoids problems when using @code{cc -gl}
3295 on MIPS machines. Previously, @code{step} entered subroutines if there
3296 was any debugging information about the routine.
3298 @item step @var{count}
3299 Continue running as in @code{step}, but do so @var{count} times. If a
3300 breakpoint is reached, or a signal not related to stepping occurs before
3301 @var{count} steps, stepping stops right away.
3304 @kindex n @r{(@code{next})}
3305 @item next @r{[}@var{count}@r{]}
3306 Continue to the next source line in the current (innermost) stack frame.
3307 This is similar to @code{step}, but function calls that appear within
3308 the line of code are executed without stopping. Execution stops when
3309 control reaches a different line of code at the original stack level
3310 that was executing when you gave the @code{next} command. This command
3311 is abbreviated @code{n}.
3313 An argument @var{count} is a repeat count, as for @code{step}.
3316 @c FIX ME!! Do we delete this, or is there a way it fits in with
3317 @c the following paragraph? --- Vctoria
3319 @c @code{next} within a function that lacks debugging information acts like
3320 @c @code{step}, but any function calls appearing within the code of the
3321 @c function are executed without stopping.
3323 The @code{next} command only stops at the first instruction of a
3324 source line. This prevents multiple stops that could otherwise occur in
3325 @code{switch} statements, @code{for} loops, etc.
3327 @kindex set step-mode
3329 @cindex functions without line info, and stepping
3330 @cindex stepping into functions with no line info
3331 @itemx set step-mode on
3332 The @code{set step-mode on} command causes the @code{step} command to
3333 stop at the first instruction of a function which contains no debug line
3334 information rather than stepping over it.
3336 This is useful in cases where you may be interested in inspecting the
3337 machine instructions of a function which has no symbolic info and do not
3338 want @value{GDBN} to automatically skip over this function.
3340 @item set step-mode off
3341 Causes the @code{step} command to step over any functions which contains no
3342 debug information. This is the default.
3346 Continue running until just after function in the selected stack frame
3347 returns. Print the returned value (if any).
3349 Contrast this with the @code{return} command (@pxref{Returning,
3350 ,Returning from a function}).
3353 @kindex u @r{(@code{until})}
3356 Continue running until a source line past the current line, in the
3357 current stack frame, is reached. This command is used to avoid single
3358 stepping through a loop more than once. It is like the @code{next}
3359 command, except that when @code{until} encounters a jump, it
3360 automatically continues execution until the program counter is greater
3361 than the address of the jump.
3363 This means that when you reach the end of a loop after single stepping
3364 though it, @code{until} makes your program continue execution until it
3365 exits the loop. In contrast, a @code{next} command at the end of a loop
3366 simply steps back to the beginning of the loop, which forces you to step
3367 through the next iteration.
3369 @code{until} always stops your program if it attempts to exit the current
3372 @code{until} may produce somewhat counterintuitive results if the order
3373 of machine code does not match the order of the source lines. For
3374 example, in the following excerpt from a debugging session, the @code{f}
3375 (@code{frame}) command shows that execution is stopped at line
3376 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3380 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3382 (@value{GDBP}) until
3383 195 for ( ; argc > 0; NEXTARG) @{
3386 This happened because, for execution efficiency, the compiler had
3387 generated code for the loop closure test at the end, rather than the
3388 start, of the loop---even though the test in a C @code{for}-loop is
3389 written before the body of the loop. The @code{until} command appeared
3390 to step back to the beginning of the loop when it advanced to this
3391 expression; however, it has not really gone to an earlier
3392 statement---not in terms of the actual machine code.
3394 @code{until} with no argument works by means of single
3395 instruction stepping, and hence is slower than @code{until} with an
3398 @item until @var{location}
3399 @itemx u @var{location}
3400 Continue running your program until either the specified location is
3401 reached, or the current stack frame returns. @var{location} is any of
3402 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3403 ,Setting breakpoints}). This form of the command uses breakpoints,
3404 and hence is quicker than @code{until} without an argument.
3407 @kindex si @r{(@code{stepi})}
3409 @itemx stepi @var{arg}
3411 Execute one machine instruction, then stop and return to the debugger.
3413 It is often useful to do @samp{display/i $pc} when stepping by machine
3414 instructions. This makes @value{GDBN} automatically display the next
3415 instruction to be executed, each time your program stops. @xref{Auto
3416 Display,, Automatic display}.
3418 An argument is a repeat count, as in @code{step}.
3422 @kindex ni @r{(@code{nexti})}
3424 @itemx nexti @var{arg}
3426 Execute one machine instruction, but if it is a function call,
3427 proceed until the function returns.
3429 An argument is a repeat count, as in @code{next}.
3436 A signal is an asynchronous event that can happen in a program. The
3437 operating system defines the possible kinds of signals, and gives each
3438 kind a name and a number. For example, in Unix @code{SIGINT} is the
3439 signal a program gets when you type an interrupt character (often @kbd{C-c});
3440 @code{SIGSEGV} is the signal a program gets from referencing a place in
3441 memory far away from all the areas in use; @code{SIGALRM} occurs when
3442 the alarm clock timer goes off (which happens only if your program has
3443 requested an alarm).
3445 @cindex fatal signals
3446 Some signals, including @code{SIGALRM}, are a normal part of the
3447 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3448 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
3449 program has not specified in advance some other way to handle the signal.
3450 @code{SIGINT} does not indicate an error in your program, but it is normally
3451 fatal so it can carry out the purpose of the interrupt: to kill the program.
3453 @value{GDBN} has the ability to detect any occurrence of a signal in your
3454 program. You can tell @value{GDBN} in advance what to do for each kind of
3457 @cindex handling signals
3458 Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM}
3459 (so as not to interfere with their role in the functioning of your program)
3460 but to stop your program immediately whenever an error signal happens.
3461 You can change these settings with the @code{handle} command.
3464 @kindex info signals
3467 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3468 handle each one. You can use this to see the signal numbers of all
3469 the defined types of signals.
3471 @code{info handle} is an alias for @code{info signals}.
3474 @item handle @var{signal} @var{keywords}@dots{}
3475 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
3476 can be the number of a signal or its name (with or without the
3477 @samp{SIG} at the beginning); a list of signal numberss of the form
3478 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
3479 known signals. The @var{keywords} say what change to make.
3483 The keywords allowed by the @code{handle} command can be abbreviated.
3484 Their full names are:
3488 @value{GDBN} should not stop your program when this signal happens. It may
3489 still print a message telling you that the signal has come in.
3492 @value{GDBN} should stop your program when this signal happens. This implies
3493 the @code{print} keyword as well.
3496 @value{GDBN} should print a message when this signal happens.
3499 @value{GDBN} should not mention the occurrence of the signal at all. This
3500 implies the @code{nostop} keyword as well.
3504 @value{GDBN} should allow your program to see this signal; your program
3505 can handle the signal, or else it may terminate if the signal is fatal
3506 and not handled. @code{pass} and @code{noignore} are synonyms.
3510 @value{GDBN} should not allow your program to see this signal.
3511 @code{nopass} and @code{ignore} are synonyms.
3515 When a signal stops your program, the signal is not visible to the
3517 continue. Your program sees the signal then, if @code{pass} is in
3518 effect for the signal in question @emph{at that time}. In other words,
3519 after @value{GDBN} reports a signal, you can use the @code{handle}
3520 command with @code{pass} or @code{nopass} to control whether your
3521 program sees that signal when you continue.
3523 You can also use the @code{signal} command to prevent your program from
3524 seeing a signal, or cause it to see a signal it normally would not see,
3525 or to give it any signal at any time. For example, if your program stopped
3526 due to some sort of memory reference error, you might store correct
3527 values into the erroneous variables and continue, hoping to see more
3528 execution; but your program would probably terminate immediately as
3529 a result of the fatal signal once it saw the signal. To prevent this,
3530 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3534 @section Stopping and starting multi-thread programs
3536 When your program has multiple threads (@pxref{Threads,, Debugging
3537 programs with multiple threads}), you can choose whether to set
3538 breakpoints on all threads, or on a particular thread.
3541 @cindex breakpoints and threads
3542 @cindex thread breakpoints
3543 @kindex break @dots{} thread @var{threadno}
3544 @item break @var{linespec} thread @var{threadno}
3545 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3546 @var{linespec} specifies source lines; there are several ways of
3547 writing them, but the effect is always to specify some source line.
3549 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3550 to specify that you only want @value{GDBN} to stop the program when a
3551 particular thread reaches this breakpoint. @var{threadno} is one of the
3552 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3553 column of the @samp{info threads} display.
3555 If you do not specify @samp{thread @var{threadno}} when you set a
3556 breakpoint, the breakpoint applies to @emph{all} threads of your
3559 You can use the @code{thread} qualifier on conditional breakpoints as
3560 well; in this case, place @samp{thread @var{threadno}} before the
3561 breakpoint condition, like this:
3564 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
3569 @cindex stopped threads
3570 @cindex threads, stopped
3571 Whenever your program stops under @value{GDBN} for any reason,
3572 @emph{all} threads of execution stop, not just the current thread. This
3573 allows you to examine the overall state of the program, including
3574 switching between threads, without worrying that things may change
3577 @cindex continuing threads
3578 @cindex threads, continuing
3579 Conversely, whenever you restart the program, @emph{all} threads start
3580 executing. @emph{This is true even when single-stepping} with commands
3581 like @code{step} or @code{next}.
3583 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3584 Since thread scheduling is up to your debugging target's operating
3585 system (not controlled by @value{GDBN}), other threads may
3586 execute more than one statement while the current thread completes a
3587 single step. Moreover, in general other threads stop in the middle of a
3588 statement, rather than at a clean statement boundary, when the program
3591 You might even find your program stopped in another thread after
3592 continuing or even single-stepping. This happens whenever some other
3593 thread runs into a breakpoint, a signal, or an exception before the
3594 first thread completes whatever you requested.
3596 On some OSes, you can lock the OS scheduler and thus allow only a single
3600 @item set scheduler-locking @var{mode}
3601 Set the scheduler locking mode. If it is @code{off}, then there is no
3602 locking and any thread may run at any time. If @code{on}, then only the
3603 current thread may run when the inferior is resumed. The @code{step}
3604 mode optimizes for single-stepping. It stops other threads from
3605 ``seizing the prompt'' by preempting the current thread while you are
3606 stepping. Other threads will only rarely (or never) get a chance to run
3607 when you step. They are more likely to run when you @samp{next} over a
3608 function call, and they are completely free to run when you use commands
3609 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
3610 thread hits a breakpoint during its timeslice, they will never steal the
3611 @value{GDBN} prompt away from the thread that you are debugging.
3613 @item show scheduler-locking
3614 Display the current scheduler locking mode.
3619 @chapter Examining the Stack
3621 When your program has stopped, the first thing you need to know is where it
3622 stopped and how it got there.
3625 Each time your program performs a function call, information about the call
3627 That information includes the location of the call in your program,
3628 the arguments of the call,
3629 and the local variables of the function being called.
3630 The information is saved in a block of data called a @dfn{stack frame}.
3631 The stack frames are allocated in a region of memory called the @dfn{call
3634 When your program stops, the @value{GDBN} commands for examining the
3635 stack allow you to see all of this information.
3637 @cindex selected frame
3638 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3639 @value{GDBN} commands refer implicitly to the selected frame. In
3640 particular, whenever you ask @value{GDBN} for the value of a variable in
3641 your program, the value is found in the selected frame. There are
3642 special @value{GDBN} commands to select whichever frame you are
3643 interested in. @xref{Selection, ,Selecting a frame}.
3645 When your program stops, @value{GDBN} automatically selects the
3646 currently executing frame and describes it briefly, similar to the
3647 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3650 * Frames:: Stack frames
3651 * Backtrace:: Backtraces
3652 * Selection:: Selecting a frame
3653 * Frame Info:: Information on a frame
3658 @section Stack frames
3660 @cindex frame, definition
3662 The call stack is divided up into contiguous pieces called @dfn{stack
3663 frames}, or @dfn{frames} for short; each frame is the data associated
3664 with one call to one function. The frame contains the arguments given
3665 to the function, the function's local variables, and the address at
3666 which the function is executing.
3668 @cindex initial frame
3669 @cindex outermost frame
3670 @cindex innermost frame
3671 When your program is started, the stack has only one frame, that of the
3672 function @code{main}. This is called the @dfn{initial} frame or the
3673 @dfn{outermost} frame. Each time a function is called, a new frame is
3674 made. Each time a function returns, the frame for that function invocation
3675 is eliminated. If a function is recursive, there can be many frames for
3676 the same function. The frame for the function in which execution is
3677 actually occurring is called the @dfn{innermost} frame. This is the most
3678 recently created of all the stack frames that still exist.
3680 @cindex frame pointer
3681 Inside your program, stack frames are identified by their addresses. A
3682 stack frame consists of many bytes, each of which has its own address; each
3683 kind of computer has a convention for choosing one byte whose
3684 address serves as the address of the frame. Usually this address is kept
3685 in a register called the @dfn{frame pointer register} while execution is
3686 going on in that frame.
3688 @cindex frame number
3689 @value{GDBN} assigns numbers to all existing stack frames, starting with
3690 zero for the innermost frame, one for the frame that called it,
3691 and so on upward. These numbers do not really exist in your program;
3692 they are assigned by @value{GDBN} to give you a way of designating stack
3693 frames in @value{GDBN} commands.
3695 @c The -fomit-frame-pointer below perennially causes hbox overflow
3696 @c underflow problems.
3697 @cindex frameless execution
3698 Some compilers provide a way to compile functions so that they operate
3699 without stack frames. (For example, the @value{GCC} option
3701 @samp{-fomit-frame-pointer}
3703 generates functions without a frame.)
3704 This is occasionally done with heavily used library functions to save
3705 the frame setup time. @value{GDBN} has limited facilities for dealing
3706 with these function invocations. If the innermost function invocation
3707 has no stack frame, @value{GDBN} nevertheless regards it as though
3708 it had a separate frame, which is numbered zero as usual, allowing
3709 correct tracing of the function call chain. However, @value{GDBN} has
3710 no provision for frameless functions elsewhere in the stack.
3713 @kindex frame@r{, command}
3714 @cindex current stack frame
3715 @item frame @var{args}
3716 The @code{frame} command allows you to move from one stack frame to another,
3717 and to print the stack frame you select. @var{args} may be either the
3718 address of the frame or the stack frame number. Without an argument,
3719 @code{frame} prints the current stack frame.
3721 @kindex select-frame
3722 @cindex selecting frame silently
3724 The @code{select-frame} command allows you to move from one stack frame
3725 to another without printing the frame. This is the silent version of
3734 @cindex stack traces
3735 A backtrace is a summary of how your program got where it is. It shows one
3736 line per frame, for many frames, starting with the currently executing
3737 frame (frame zero), followed by its caller (frame one), and on up the
3742 @kindex bt @r{(@code{backtrace})}
3745 Print a backtrace of the entire stack: one line per frame for all
3746 frames in the stack.
3748 You can stop the backtrace at any time by typing the system interrupt
3749 character, normally @kbd{C-c}.
3751 @item backtrace @var{n}
3753 Similar, but print only the innermost @var{n} frames.
3755 @item backtrace -@var{n}
3757 Similar, but print only the outermost @var{n} frames.
3762 @kindex info s @r{(@code{info stack})}
3763 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3764 are additional aliases for @code{backtrace}.
3766 Each line in the backtrace shows the frame number and the function name.
3767 The program counter value is also shown---unless you use @code{set
3768 print address off}. The backtrace also shows the source file name and
3769 line number, as well as the arguments to the function. The program
3770 counter value is omitted if it is at the beginning of the code for that
3773 Here is an example of a backtrace. It was made with the command
3774 @samp{bt 3}, so it shows the innermost three frames.
3778 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3780 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3781 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3783 (More stack frames follow...)
3788 The display for frame zero does not begin with a program counter
3789 value, indicating that your program has stopped at the beginning of the
3790 code for line @code{993} of @code{builtin.c}.
3793 @section Selecting a frame
3795 Most commands for examining the stack and other data in your program work on
3796 whichever stack frame is selected at the moment. Here are the commands for
3797 selecting a stack frame; all of them finish by printing a brief description
3798 of the stack frame just selected.
3801 @kindex frame@r{, selecting}
3802 @kindex f @r{(@code{frame})}
3805 Select frame number @var{n}. Recall that frame zero is the innermost
3806 (currently executing) frame, frame one is the frame that called the
3807 innermost one, and so on. The highest-numbered frame is the one for
3810 @item frame @var{addr}
3812 Select the frame at address @var{addr}. This is useful mainly if the
3813 chaining of stack frames has been damaged by a bug, making it
3814 impossible for @value{GDBN} to assign numbers properly to all frames. In
3815 addition, this can be useful when your program has multiple stacks and
3816 switches between them.
3818 On the SPARC architecture, @code{frame} needs two addresses to
3819 select an arbitrary frame: a frame pointer and a stack pointer.
3821 On the MIPS and Alpha architecture, it needs two addresses: a stack
3822 pointer and a program counter.
3824 On the 29k architecture, it needs three addresses: a register stack
3825 pointer, a program counter, and a memory stack pointer.
3826 @c note to future updaters: this is conditioned on a flag
3827 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3828 @c as of 27 Jan 1994.
3832 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3833 advances toward the outermost frame, to higher frame numbers, to frames
3834 that have existed longer. @var{n} defaults to one.
3837 @kindex do @r{(@code{down})}
3839 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3840 advances toward the innermost frame, to lower frame numbers, to frames
3841 that were created more recently. @var{n} defaults to one. You may
3842 abbreviate @code{down} as @code{do}.
3845 All of these commands end by printing two lines of output describing the
3846 frame. The first line shows the frame number, the function name, the
3847 arguments, and the source file and line number of execution in that
3848 frame. The second line shows the text of that source line.
3856 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3858 10 read_input_file (argv[i]);
3862 After such a printout, the @code{list} command with no arguments
3863 prints ten lines centered on the point of execution in the frame.
3864 @xref{List, ,Printing source lines}.
3867 @kindex down-silently
3869 @item up-silently @var{n}
3870 @itemx down-silently @var{n}
3871 These two commands are variants of @code{up} and @code{down},
3872 respectively; they differ in that they do their work silently, without
3873 causing display of the new frame. They are intended primarily for use
3874 in @value{GDBN} command scripts, where the output might be unnecessary and
3879 @section Information about a frame
3881 There are several other commands to print information about the selected
3887 When used without any argument, this command does not change which
3888 frame is selected, but prints a brief description of the currently
3889 selected stack frame. It can be abbreviated @code{f}. With an
3890 argument, this command is used to select a stack frame.
3891 @xref{Selection, ,Selecting a frame}.
3894 @kindex info f @r{(@code{info frame})}
3897 This command prints a verbose description of the selected stack frame,
3902 the address of the frame
3904 the address of the next frame down (called by this frame)
3906 the address of the next frame up (caller of this frame)
3908 the language in which the source code corresponding to this frame is written
3910 the address of the frame's arguments
3912 the address of the frame's local variables
3914 the program counter saved in it (the address of execution in the caller frame)
3916 which registers were saved in the frame
3919 @noindent The verbose description is useful when
3920 something has gone wrong that has made the stack format fail to fit
3921 the usual conventions.
3923 @item info frame @var{addr}
3924 @itemx info f @var{addr}
3925 Print a verbose description of the frame at address @var{addr}, without
3926 selecting that frame. The selected frame remains unchanged by this
3927 command. This requires the same kind of address (more than one for some
3928 architectures) that you specify in the @code{frame} command.
3929 @xref{Selection, ,Selecting a frame}.
3933 Print the arguments of the selected frame, each on a separate line.
3937 Print the local variables of the selected frame, each on a separate
3938 line. These are all variables (declared either static or automatic)
3939 accessible at the point of execution of the selected frame.
3942 @cindex catch exceptions, list active handlers
3943 @cindex exception handlers, how to list
3945 Print a list of all the exception handlers that are active in the
3946 current stack frame at the current point of execution. To see other
3947 exception handlers, visit the associated frame (using the @code{up},
3948 @code{down}, or @code{frame} commands); then type @code{info catch}.
3949 @xref{Set Catchpoints, , Setting catchpoints}.
3955 @chapter Examining Source Files
3957 @value{GDBN} can print parts of your program's source, since the debugging
3958 information recorded in the program tells @value{GDBN} what source files were
3959 used to build it. When your program stops, @value{GDBN} spontaneously prints
3960 the line where it stopped. Likewise, when you select a stack frame
3961 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
3962 execution in that frame has stopped. You can print other portions of
3963 source files by explicit command.
3965 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
3966 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
3967 @value{GDBN} under @sc{gnu} Emacs}.
3970 * List:: Printing source lines
3971 * Search:: Searching source files
3972 * Source Path:: Specifying source directories
3973 * Machine Code:: Source and machine code
3977 @section Printing source lines
3980 @kindex l @r{(@code{list})}
3981 To print lines from a source file, use the @code{list} command
3982 (abbreviated @code{l}). By default, ten lines are printed.
3983 There are several ways to specify what part of the file you want to print.
3985 Here are the forms of the @code{list} command most commonly used:
3988 @item list @var{linenum}
3989 Print lines centered around line number @var{linenum} in the
3990 current source file.
3992 @item list @var{function}
3993 Print lines centered around the beginning of function
3997 Print more lines. If the last lines printed were printed with a
3998 @code{list} command, this prints lines following the last lines
3999 printed; however, if the last line printed was a solitary line printed
4000 as part of displaying a stack frame (@pxref{Stack, ,Examining the
4001 Stack}), this prints lines centered around that line.
4004 Print lines just before the lines last printed.
4007 By default, @value{GDBN} prints ten source lines with any of these forms of
4008 the @code{list} command. You can change this using @code{set listsize}:
4011 @kindex set listsize
4012 @item set listsize @var{count}
4013 Make the @code{list} command display @var{count} source lines (unless
4014 the @code{list} argument explicitly specifies some other number).
4016 @kindex show listsize
4018 Display the number of lines that @code{list} prints.
4021 Repeating a @code{list} command with @key{RET} discards the argument,
4022 so it is equivalent to typing just @code{list}. This is more useful
4023 than listing the same lines again. An exception is made for an
4024 argument of @samp{-}; that argument is preserved in repetition so that
4025 each repetition moves up in the source file.
4028 In general, the @code{list} command expects you to supply zero, one or two
4029 @dfn{linespecs}. Linespecs specify source lines; there are several ways
4030 of writing them, but the effect is always to specify some source line.
4031 Here is a complete description of the possible arguments for @code{list}:
4034 @item list @var{linespec}
4035 Print lines centered around the line specified by @var{linespec}.
4037 @item list @var{first},@var{last}
4038 Print lines from @var{first} to @var{last}. Both arguments are
4041 @item list ,@var{last}
4042 Print lines ending with @var{last}.
4044 @item list @var{first},
4045 Print lines starting with @var{first}.
4048 Print lines just after the lines last printed.
4051 Print lines just before the lines last printed.
4054 As described in the preceding table.
4057 Here are the ways of specifying a single source line---all the
4062 Specifies line @var{number} of the current source file.
4063 When a @code{list} command has two linespecs, this refers to
4064 the same source file as the first linespec.
4067 Specifies the line @var{offset} lines after the last line printed.
4068 When used as the second linespec in a @code{list} command that has
4069 two, this specifies the line @var{offset} lines down from the
4073 Specifies the line @var{offset} lines before the last line printed.
4075 @item @var{filename}:@var{number}
4076 Specifies line @var{number} in the source file @var{filename}.
4078 @item @var{function}
4079 Specifies the line that begins the body of the function @var{function}.
4080 For example: in C, this is the line with the open brace.
4082 @item @var{filename}:@var{function}
4083 Specifies the line of the open-brace that begins the body of the
4084 function @var{function} in the file @var{filename}. You only need the
4085 file name with a function name to avoid ambiguity when there are
4086 identically named functions in different source files.
4088 @item *@var{address}
4089 Specifies the line containing the program address @var{address}.
4090 @var{address} may be any expression.
4094 @section Searching source files
4096 @kindex reverse-search
4098 There are two commands for searching through the current source file for a
4103 @kindex forward-search
4104 @item forward-search @var{regexp}
4105 @itemx search @var{regexp}
4106 The command @samp{forward-search @var{regexp}} checks each line,
4107 starting with the one following the last line listed, for a match for
4108 @var{regexp}. It lists the line that is found. You can use the
4109 synonym @samp{search @var{regexp}} or abbreviate the command name as
4112 @item reverse-search @var{regexp}
4113 The command @samp{reverse-search @var{regexp}} checks each line, starting
4114 with the one before the last line listed and going backward, for a match
4115 for @var{regexp}. It lists the line that is found. You can abbreviate
4116 this command as @code{rev}.
4120 @section Specifying source directories
4123 @cindex directories for source files
4124 Executable programs sometimes do not record the directories of the source
4125 files from which they were compiled, just the names. Even when they do,
4126 the directories could be moved between the compilation and your debugging
4127 session. @value{GDBN} has a list of directories to search for source files;
4128 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4129 it tries all the directories in the list, in the order they are present
4130 in the list, until it finds a file with the desired name. Note that
4131 the executable search path is @emph{not} used for this purpose. Neither is
4132 the current working directory, unless it happens to be in the source
4135 If @value{GDBN} cannot find a source file in the source path, and the
4136 object program records a directory, @value{GDBN} tries that directory
4137 too. If the source path is empty, and there is no record of the
4138 compilation directory, @value{GDBN} looks in the current directory as a
4141 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4142 any information it has cached about where source files are found and where
4143 each line is in the file.
4147 When you start @value{GDBN}, its source path includes only @samp{cdir}
4148 and @samp{cwd}, in that order.
4149 To add other directories, use the @code{directory} command.
4152 @item directory @var{dirname} @dots{}
4153 @item dir @var{dirname} @dots{}
4154 Add directory @var{dirname} to the front of the source path. Several
4155 directory names may be given to this command, separated by @samp{:}
4156 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
4157 part of absolute file names) or
4158 whitespace. You may specify a directory that is already in the source
4159 path; this moves it forward, so @value{GDBN} searches it sooner.
4163 @vindex $cdir@r{, convenience variable}
4164 @vindex $cwdr@r{, convenience variable}
4165 @cindex compilation directory
4166 @cindex current directory
4167 @cindex working directory
4168 @cindex directory, current
4169 @cindex directory, compilation
4170 You can use the string @samp{$cdir} to refer to the compilation
4171 directory (if one is recorded), and @samp{$cwd} to refer to the current
4172 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4173 tracks the current working directory as it changes during your @value{GDBN}
4174 session, while the latter is immediately expanded to the current
4175 directory at the time you add an entry to the source path.
4178 Reset the source path to empty again. This requires confirmation.
4180 @c RET-repeat for @code{directory} is explicitly disabled, but since
4181 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4183 @item show directories
4184 @kindex show directories
4185 Print the source path: show which directories it contains.
4188 If your source path is cluttered with directories that are no longer of
4189 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4190 versions of source. You can correct the situation as follows:
4194 Use @code{directory} with no argument to reset the source path to empty.
4197 Use @code{directory} with suitable arguments to reinstall the
4198 directories you want in the source path. You can add all the
4199 directories in one command.
4203 @section Source and machine code
4205 You can use the command @code{info line} to map source lines to program
4206 addresses (and vice versa), and the command @code{disassemble} to display
4207 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4208 mode, the @code{info line} command causes the arrow to point to the
4209 line specified. Also, @code{info line} prints addresses in symbolic form as
4214 @item info line @var{linespec}
4215 Print the starting and ending addresses of the compiled code for
4216 source line @var{linespec}. You can specify source lines in any of
4217 the ways understood by the @code{list} command (@pxref{List, ,Printing
4221 For example, we can use @code{info line} to discover the location of
4222 the object code for the first line of function
4223 @code{m4_changequote}:
4225 @c FIXME: I think this example should also show the addresses in
4226 @c symbolic form, as they usually would be displayed.
4228 (@value{GDBP}) info line m4_changequote
4229 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4233 We can also inquire (using @code{*@var{addr}} as the form for
4234 @var{linespec}) what source line covers a particular address:
4236 (@value{GDBP}) info line *0x63ff
4237 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4240 @cindex @code{$_} and @code{info line}
4241 @kindex x@r{(examine), and} info line
4242 After @code{info line}, the default address for the @code{x} command
4243 is changed to the starting address of the line, so that @samp{x/i} is
4244 sufficient to begin examining the machine code (@pxref{Memory,
4245 ,Examining memory}). Also, this address is saved as the value of the
4246 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4251 @cindex assembly instructions
4252 @cindex instructions, assembly
4253 @cindex machine instructions
4254 @cindex listing machine instructions
4256 This specialized command dumps a range of memory as machine
4257 instructions. The default memory range is the function surrounding the
4258 program counter of the selected frame. A single argument to this
4259 command is a program counter value; @value{GDBN} dumps the function
4260 surrounding this value. Two arguments specify a range of addresses
4261 (first inclusive, second exclusive) to dump.
4264 The following example shows the disassembly of a range of addresses of
4265 HP PA-RISC 2.0 code:
4268 (@value{GDBP}) disas 0x32c4 0x32e4
4269 Dump of assembler code from 0x32c4 to 0x32e4:
4270 0x32c4 <main+204>: addil 0,dp
4271 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4272 0x32cc <main+212>: ldil 0x3000,r31
4273 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4274 0x32d4 <main+220>: ldo 0(r31),rp
4275 0x32d8 <main+224>: addil -0x800,dp
4276 0x32dc <main+228>: ldo 0x588(r1),r26
4277 0x32e0 <main+232>: ldil 0x3000,r31
4278 End of assembler dump.
4281 Some architectures have more than one commonly-used set of instruction
4282 mnemonics or other syntax.
4285 @kindex set disassembly-flavor
4286 @cindex assembly instructions
4287 @cindex instructions, assembly
4288 @cindex machine instructions
4289 @cindex listing machine instructions
4290 @cindex Intel disassembly flavor
4291 @cindex AT&T disassembly flavor
4292 @item set disassembly-flavor @var{instruction-set}
4293 Select the instruction set to use when disassembling the
4294 program via the @code{disassemble} or @code{x/i} commands.
4296 Currently this command is only defined for the Intel x86 family. You
4297 can set @var{instruction-set} to either @code{intel} or @code{att}.
4298 The default is @code{att}, the AT&T flavor used by default by Unix
4299 assemblers for x86-based targets.
4304 @chapter Examining Data
4306 @cindex printing data
4307 @cindex examining data
4310 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4311 @c document because it is nonstandard... Under Epoch it displays in a
4312 @c different window or something like that.
4313 The usual way to examine data in your program is with the @code{print}
4314 command (abbreviated @code{p}), or its synonym @code{inspect}. It
4315 evaluates and prints the value of an expression of the language your
4316 program is written in (@pxref{Languages, ,Using @value{GDBN} with
4317 Different Languages}).
4320 @item print @var{expr}
4321 @itemx print /@var{f} @var{expr}
4322 @var{expr} is an expression (in the source language). By default the
4323 value of @var{expr} is printed in a format appropriate to its data type;
4324 you can choose a different format by specifying @samp{/@var{f}}, where
4325 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
4329 @itemx print /@var{f}
4330 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
4331 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4332 conveniently inspect the same value in an alternative format.
4335 A more low-level way of examining data is with the @code{x} command.
4336 It examines data in memory at a specified address and prints it in a
4337 specified format. @xref{Memory, ,Examining memory}.
4339 If you are interested in information about types, or about how the
4340 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
4341 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
4345 * Expressions:: Expressions
4346 * Variables:: Program variables
4347 * Arrays:: Artificial arrays
4348 * Output Formats:: Output formats
4349 * Memory:: Examining memory
4350 * Auto Display:: Automatic display
4351 * Print Settings:: Print settings
4352 * Value History:: Value history
4353 * Convenience Vars:: Convenience variables
4354 * Registers:: Registers
4355 * Floating Point Hardware:: Floating point hardware
4356 * Memory Region Attributes:: Memory region attributes
4360 @section Expressions
4363 @code{print} and many other @value{GDBN} commands accept an expression and
4364 compute its value. Any kind of constant, variable or operator defined
4365 by the programming language you are using is valid in an expression in
4366 @value{GDBN}. This includes conditional expressions, function calls, casts
4367 and string constants. It unfortunately does not include symbols defined
4368 by preprocessor @code{#define} commands.
4370 @value{GDBN} supports array constants in expressions input by
4371 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
4372 you can use the command @code{print @{1, 2, 3@}} to build up an array in
4373 memory that is @code{malloc}ed in the target program.
4375 Because C is so widespread, most of the expressions shown in examples in
4376 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4377 Languages}, for information on how to use expressions in other
4380 In this section, we discuss operators that you can use in @value{GDBN}
4381 expressions regardless of your programming language.
4383 Casts are supported in all languages, not just in C, because it is so
4384 useful to cast a number into a pointer in order to examine a structure
4385 at that address in memory.
4386 @c FIXME: casts supported---Mod2 true?
4388 @value{GDBN} supports these operators, in addition to those common
4389 to programming languages:
4393 @samp{@@} is a binary operator for treating parts of memory as arrays.
4394 @xref{Arrays, ,Artificial arrays}, for more information.
4397 @samp{::} allows you to specify a variable in terms of the file or
4398 function where it is defined. @xref{Variables, ,Program variables}.
4400 @cindex @{@var{type}@}
4401 @cindex type casting memory
4402 @cindex memory, viewing as typed object
4403 @cindex casts, to view memory
4404 @item @{@var{type}@} @var{addr}
4405 Refers to an object of type @var{type} stored at address @var{addr} in
4406 memory. @var{addr} may be any expression whose value is an integer or
4407 pointer (but parentheses are required around binary operators, just as in
4408 a cast). This construct is allowed regardless of what kind of data is
4409 normally supposed to reside at @var{addr}.
4413 @section Program variables
4415 The most common kind of expression to use is the name of a variable
4418 Variables in expressions are understood in the selected stack frame
4419 (@pxref{Selection, ,Selecting a frame}); they must be either:
4423 global (or file-static)
4430 visible according to the scope rules of the
4431 programming language from the point of execution in that frame
4434 @noindent This means that in the function
4449 you can examine and use the variable @code{a} whenever your program is
4450 executing within the function @code{foo}, but you can only use or
4451 examine the variable @code{b} while your program is executing inside
4452 the block where @code{b} is declared.
4454 @cindex variable name conflict
4455 There is an exception: you can refer to a variable or function whose
4456 scope is a single source file even if the current execution point is not
4457 in this file. But it is possible to have more than one such variable or
4458 function with the same name (in different source files). If that
4459 happens, referring to that name has unpredictable effects. If you wish,
4460 you can specify a static variable in a particular function or file,
4461 using the colon-colon notation:
4463 @cindex colon-colon, context for variables/functions
4465 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4466 @cindex @code{::}, context for variables/functions
4469 @var{file}::@var{variable}
4470 @var{function}::@var{variable}
4474 Here @var{file} or @var{function} is the name of the context for the
4475 static @var{variable}. In the case of file names, you can use quotes to
4476 make sure @value{GDBN} parses the file name as a single word---for example,
4477 to print a global value of @code{x} defined in @file{f2.c}:
4480 (@value{GDBP}) p 'f2.c'::x
4483 @cindex C++ scope resolution
4484 This use of @samp{::} is very rarely in conflict with the very similar
4485 use of the same notation in C++. @value{GDBN} also supports use of the C++
4486 scope resolution operator in @value{GDBN} expressions.
4487 @c FIXME: Um, so what happens in one of those rare cases where it's in
4490 @cindex wrong values
4491 @cindex variable values, wrong
4493 @emph{Warning:} Occasionally, a local variable may appear to have the
4494 wrong value at certain points in a function---just after entry to a new
4495 scope, and just before exit.
4497 You may see this problem when you are stepping by machine instructions.
4498 This is because, on most machines, it takes more than one instruction to
4499 set up a stack frame (including local variable definitions); if you are
4500 stepping by machine instructions, variables may appear to have the wrong
4501 values until the stack frame is completely built. On exit, it usually
4502 also takes more than one machine instruction to destroy a stack frame;
4503 after you begin stepping through that group of instructions, local
4504 variable definitions may be gone.
4506 This may also happen when the compiler does significant optimizations.
4507 To be sure of always seeing accurate values, turn off all optimization
4510 @cindex ``No symbol "foo" in current context''
4511 Another possible effect of compiler optimizations is to optimize
4512 unused variables out of existence, or assign variables to registers (as
4513 opposed to memory addresses). Depending on the support for such cases
4514 offered by the debug info format used by the compiler, @value{GDBN}
4515 might not be able to display values for such local variables. If that
4516 happens, @value{GDBN} will print a message like this:
4519 No symbol "foo" in current context.
4522 To solve such problems, either recompile without optimizations, or use a
4523 different debug info format, if the compiler supports several such
4524 formats. For example, @value{NGCC}, the @sc{gnu} C/C++ compiler usually
4525 supports the @samp{-gstabs} option. @samp{-gstabs} produces debug info
4526 in a format that is superior to formats such as COFF. You may be able
4527 to use DWARF2 (@samp{-gdwarf-2}), which is also an effective form for
4528 debug info. See @ref{Debugging Options,,Options for Debugging Your
4529 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
4534 @section Artificial arrays
4536 @cindex artificial array
4537 @kindex @@@r{, referencing memory as an array}
4538 It is often useful to print out several successive objects of the
4539 same type in memory; a section of an array, or an array of
4540 dynamically determined size for which only a pointer exists in the
4543 You can do this by referring to a contiguous span of memory as an
4544 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4545 operand of @samp{@@} should be the first element of the desired array
4546 and be an individual object. The right operand should be the desired length
4547 of the array. The result is an array value whose elements are all of
4548 the type of the left argument. The first element is actually the left
4549 argument; the second element comes from bytes of memory immediately
4550 following those that hold the first element, and so on. Here is an
4551 example. If a program says
4554 int *array = (int *) malloc (len * sizeof (int));
4558 you can print the contents of @code{array} with
4564 The left operand of @samp{@@} must reside in memory. Array values made
4565 with @samp{@@} in this way behave just like other arrays in terms of
4566 subscripting, and are coerced to pointers when used in expressions.
4567 Artificial arrays most often appear in expressions via the value history
4568 (@pxref{Value History, ,Value history}), after printing one out.
4570 Another way to create an artificial array is to use a cast.
4571 This re-interprets a value as if it were an array.
4572 The value need not be in memory:
4574 (@value{GDBP}) p/x (short[2])0x12345678
4575 $1 = @{0x1234, 0x5678@}
4578 As a convenience, if you leave the array length out (as in
4579 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
4580 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4582 (@value{GDBP}) p/x (short[])0x12345678
4583 $2 = @{0x1234, 0x5678@}
4586 Sometimes the artificial array mechanism is not quite enough; in
4587 moderately complex data structures, the elements of interest may not
4588 actually be adjacent---for example, if you are interested in the values
4589 of pointers in an array. One useful work-around in this situation is
4590 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4591 variables}) as a counter in an expression that prints the first
4592 interesting value, and then repeat that expression via @key{RET}. For
4593 instance, suppose you have an array @code{dtab} of pointers to
4594 structures, and you are interested in the values of a field @code{fv}
4595 in each structure. Here is an example of what you might type:
4605 @node Output Formats
4606 @section Output formats
4608 @cindex formatted output
4609 @cindex output formats
4610 By default, @value{GDBN} prints a value according to its data type. Sometimes
4611 this is not what you want. For example, you might want to print a number
4612 in hex, or a pointer in decimal. Or you might want to view data in memory
4613 at a certain address as a character string or as an instruction. To do
4614 these things, specify an @dfn{output format} when you print a value.
4616 The simplest use of output formats is to say how to print a value
4617 already computed. This is done by starting the arguments of the
4618 @code{print} command with a slash and a format letter. The format
4619 letters supported are:
4623 Regard the bits of the value as an integer, and print the integer in
4627 Print as integer in signed decimal.
4630 Print as integer in unsigned decimal.
4633 Print as integer in octal.
4636 Print as integer in binary. The letter @samp{t} stands for ``two''.
4637 @footnote{@samp{b} cannot be used because these format letters are also
4638 used with the @code{x} command, where @samp{b} stands for ``byte'';
4639 see @ref{Memory,,Examining memory}.}
4642 @cindex unknown address, locating
4643 Print as an address, both absolute in hexadecimal and as an offset from
4644 the nearest preceding symbol. You can use this format used to discover
4645 where (in what function) an unknown address is located:
4648 (@value{GDBP}) p/a 0x54320
4649 $3 = 0x54320 <_initialize_vx+396>
4653 Regard as an integer and print it as a character constant.
4656 Regard the bits of the value as a floating point number and print
4657 using typical floating point syntax.
4660 For example, to print the program counter in hex (@pxref{Registers}), type
4667 Note that no space is required before the slash; this is because command
4668 names in @value{GDBN} cannot contain a slash.
4670 To reprint the last value in the value history with a different format,
4671 you can use the @code{print} command with just a format and no
4672 expression. For example, @samp{p/x} reprints the last value in hex.
4675 @section Examining memory
4677 You can use the command @code{x} (for ``examine'') to examine memory in
4678 any of several formats, independently of your program's data types.
4680 @cindex examining memory
4682 @kindex x @r{(examine memory)}
4683 @item x/@var{nfu} @var{addr}
4686 Use the @code{x} command to examine memory.
4689 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4690 much memory to display and how to format it; @var{addr} is an
4691 expression giving the address where you want to start displaying memory.
4692 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4693 Several commands set convenient defaults for @var{addr}.
4696 @item @var{n}, the repeat count
4697 The repeat count is a decimal integer; the default is 1. It specifies
4698 how much memory (counting by units @var{u}) to display.
4699 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4702 @item @var{f}, the display format
4703 The display format is one of the formats used by @code{print},
4704 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4705 The default is @samp{x} (hexadecimal) initially.
4706 The default changes each time you use either @code{x} or @code{print}.
4708 @item @var{u}, the unit size
4709 The unit size is any of
4715 Halfwords (two bytes).
4717 Words (four bytes). This is the initial default.
4719 Giant words (eight bytes).
4722 Each time you specify a unit size with @code{x}, that size becomes the
4723 default unit the next time you use @code{x}. (For the @samp{s} and
4724 @samp{i} formats, the unit size is ignored and is normally not written.)
4726 @item @var{addr}, starting display address
4727 @var{addr} is the address where you want @value{GDBN} to begin displaying
4728 memory. The expression need not have a pointer value (though it may);
4729 it is always interpreted as an integer address of a byte of memory.
4730 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4731 @var{addr} is usually just after the last address examined---but several
4732 other commands also set the default address: @code{info breakpoints} (to
4733 the address of the last breakpoint listed), @code{info line} (to the
4734 starting address of a line), and @code{print} (if you use it to display
4735 a value from memory).
4738 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4739 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4740 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4741 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4742 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
4744 Since the letters indicating unit sizes are all distinct from the
4745 letters specifying output formats, you do not have to remember whether
4746 unit size or format comes first; either order works. The output
4747 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4748 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4750 Even though the unit size @var{u} is ignored for the formats @samp{s}
4751 and @samp{i}, you might still want to use a count @var{n}; for example,
4752 @samp{3i} specifies that you want to see three machine instructions,
4753 including any operands. The command @code{disassemble} gives an
4754 alternative way of inspecting machine instructions; see @ref{Machine
4755 Code,,Source and machine code}.
4757 All the defaults for the arguments to @code{x} are designed to make it
4758 easy to continue scanning memory with minimal specifications each time
4759 you use @code{x}. For example, after you have inspected three machine
4760 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4761 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4762 the repeat count @var{n} is used again; the other arguments default as
4763 for successive uses of @code{x}.
4765 @cindex @code{$_}, @code{$__}, and value history
4766 The addresses and contents printed by the @code{x} command are not saved
4767 in the value history because there is often too much of them and they
4768 would get in the way. Instead, @value{GDBN} makes these values available for
4769 subsequent use in expressions as values of the convenience variables
4770 @code{$_} and @code{$__}. After an @code{x} command, the last address
4771 examined is available for use in expressions in the convenience variable
4772 @code{$_}. The contents of that address, as examined, are available in
4773 the convenience variable @code{$__}.
4775 If the @code{x} command has a repeat count, the address and contents saved
4776 are from the last memory unit printed; this is not the same as the last
4777 address printed if several units were printed on the last line of output.
4780 @section Automatic display
4781 @cindex automatic display
4782 @cindex display of expressions
4784 If you find that you want to print the value of an expression frequently
4785 (to see how it changes), you might want to add it to the @dfn{automatic
4786 display list} so that @value{GDBN} prints its value each time your program stops.
4787 Each expression added to the list is given a number to identify it;
4788 to remove an expression from the list, you specify that number.
4789 The automatic display looks like this:
4793 3: bar[5] = (struct hack *) 0x3804
4797 This display shows item numbers, expressions and their current values. As with
4798 displays you request manually using @code{x} or @code{print}, you can
4799 specify the output format you prefer; in fact, @code{display} decides
4800 whether to use @code{print} or @code{x} depending on how elaborate your
4801 format specification is---it uses @code{x} if you specify a unit size,
4802 or one of the two formats (@samp{i} and @samp{s}) that are only
4803 supported by @code{x}; otherwise it uses @code{print}.
4807 @item display @var{expr}
4808 Add the expression @var{expr} to the list of expressions to display
4809 each time your program stops. @xref{Expressions, ,Expressions}.
4811 @code{display} does not repeat if you press @key{RET} again after using it.
4813 @item display/@var{fmt} @var{expr}
4814 For @var{fmt} specifying only a display format and not a size or
4815 count, add the expression @var{expr} to the auto-display list but
4816 arrange to display it each time in the specified format @var{fmt}.
4817 @xref{Output Formats,,Output formats}.
4819 @item display/@var{fmt} @var{addr}
4820 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4821 number of units, add the expression @var{addr} as a memory address to
4822 be examined each time your program stops. Examining means in effect
4823 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4826 For example, @samp{display/i $pc} can be helpful, to see the machine
4827 instruction about to be executed each time execution stops (@samp{$pc}
4828 is a common name for the program counter; @pxref{Registers, ,Registers}).
4831 @kindex delete display
4833 @item undisplay @var{dnums}@dots{}
4834 @itemx delete display @var{dnums}@dots{}
4835 Remove item numbers @var{dnums} from the list of expressions to display.
4837 @code{undisplay} does not repeat if you press @key{RET} after using it.
4838 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4840 @kindex disable display
4841 @item disable display @var{dnums}@dots{}
4842 Disable the display of item numbers @var{dnums}. A disabled display
4843 item is not printed automatically, but is not forgotten. It may be
4844 enabled again later.
4846 @kindex enable display
4847 @item enable display @var{dnums}@dots{}
4848 Enable display of item numbers @var{dnums}. It becomes effective once
4849 again in auto display of its expression, until you specify otherwise.
4852 Display the current values of the expressions on the list, just as is
4853 done when your program stops.
4855 @kindex info display
4857 Print the list of expressions previously set up to display
4858 automatically, each one with its item number, but without showing the
4859 values. This includes disabled expressions, which are marked as such.
4860 It also includes expressions which would not be displayed right now
4861 because they refer to automatic variables not currently available.
4864 If a display expression refers to local variables, then it does not make
4865 sense outside the lexical context for which it was set up. Such an
4866 expression is disabled when execution enters a context where one of its
4867 variables is not defined. For example, if you give the command
4868 @code{display last_char} while inside a function with an argument
4869 @code{last_char}, @value{GDBN} displays this argument while your program
4870 continues to stop inside that function. When it stops elsewhere---where
4871 there is no variable @code{last_char}---the display is disabled
4872 automatically. The next time your program stops where @code{last_char}
4873 is meaningful, you can enable the display expression once again.
4875 @node Print Settings
4876 @section Print settings
4878 @cindex format options
4879 @cindex print settings
4880 @value{GDBN} provides the following ways to control how arrays, structures,
4881 and symbols are printed.
4884 These settings are useful for debugging programs in any language:
4887 @kindex set print address
4888 @item set print address
4889 @itemx set print address on
4890 @value{GDBN} prints memory addresses showing the location of stack
4891 traces, structure values, pointer values, breakpoints, and so forth,
4892 even when it also displays the contents of those addresses. The default
4893 is @code{on}. For example, this is what a stack frame display looks like with
4894 @code{set print address on}:
4899 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4901 530 if (lquote != def_lquote)
4905 @item set print address off
4906 Do not print addresses when displaying their contents. For example,
4907 this is the same stack frame displayed with @code{set print address off}:
4911 (@value{GDBP}) set print addr off
4913 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4914 530 if (lquote != def_lquote)
4918 You can use @samp{set print address off} to eliminate all machine
4919 dependent displays from the @value{GDBN} interface. For example, with
4920 @code{print address off}, you should get the same text for backtraces on
4921 all machines---whether or not they involve pointer arguments.
4923 @kindex show print address
4924 @item show print address
4925 Show whether or not addresses are to be printed.
4928 When @value{GDBN} prints a symbolic address, it normally prints the
4929 closest earlier symbol plus an offset. If that symbol does not uniquely
4930 identify the address (for example, it is a name whose scope is a single
4931 source file), you may need to clarify. One way to do this is with
4932 @code{info line}, for example @samp{info line *0x4537}. Alternately,
4933 you can set @value{GDBN} to print the source file and line number when
4934 it prints a symbolic address:
4937 @kindex set print symbol-filename
4938 @item set print symbol-filename on
4939 Tell @value{GDBN} to print the source file name and line number of a
4940 symbol in the symbolic form of an address.
4942 @item set print symbol-filename off
4943 Do not print source file name and line number of a symbol. This is the
4946 @kindex show print symbol-filename
4947 @item show print symbol-filename
4948 Show whether or not @value{GDBN} will print the source file name and
4949 line number of a symbol in the symbolic form of an address.
4952 Another situation where it is helpful to show symbol filenames and line
4953 numbers is when disassembling code; @value{GDBN} shows you the line
4954 number and source file that corresponds to each instruction.
4956 Also, you may wish to see the symbolic form only if the address being
4957 printed is reasonably close to the closest earlier symbol:
4960 @kindex set print max-symbolic-offset
4961 @item set print max-symbolic-offset @var{max-offset}
4962 Tell @value{GDBN} to only display the symbolic form of an address if the
4963 offset between the closest earlier symbol and the address is less than
4964 @var{max-offset}. The default is 0, which tells @value{GDBN}
4965 to always print the symbolic form of an address if any symbol precedes it.
4967 @kindex show print max-symbolic-offset
4968 @item show print max-symbolic-offset
4969 Ask how large the maximum offset is that @value{GDBN} prints in a
4973 @cindex wild pointer, interpreting
4974 @cindex pointer, finding referent
4975 If you have a pointer and you are not sure where it points, try
4976 @samp{set print symbol-filename on}. Then you can determine the name
4977 and source file location of the variable where it points, using
4978 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
4979 For example, here @value{GDBN} shows that a variable @code{ptt} points
4980 at another variable @code{t}, defined in @file{hi2.c}:
4983 (@value{GDBP}) set print symbol-filename on
4984 (@value{GDBP}) p/a ptt
4985 $4 = 0xe008 <t in hi2.c>
4989 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
4990 does not show the symbol name and filename of the referent, even with
4991 the appropriate @code{set print} options turned on.
4994 Other settings control how different kinds of objects are printed:
4997 @kindex set print array
4998 @item set print array
4999 @itemx set print array on
5000 Pretty print arrays. This format is more convenient to read,
5001 but uses more space. The default is off.
5003 @item set print array off
5004 Return to compressed format for arrays.
5006 @kindex show print array
5007 @item show print array
5008 Show whether compressed or pretty format is selected for displaying
5011 @kindex set print elements
5012 @item set print elements @var{number-of-elements}
5013 Set a limit on how many elements of an array @value{GDBN} will print.
5014 If @value{GDBN} is printing a large array, it stops printing after it has
5015 printed the number of elements set by the @code{set print elements} command.
5016 This limit also applies to the display of strings.
5017 When @value{GDBN} starts, this limit is set to 200.
5018 Setting @var{number-of-elements} to zero means that the printing is unlimited.
5020 @kindex show print elements
5021 @item show print elements
5022 Display the number of elements of a large array that @value{GDBN} will print.
5023 If the number is 0, then the printing is unlimited.
5025 @kindex set print null-stop
5026 @item set print null-stop
5027 Cause @value{GDBN} to stop printing the characters of an array when the first
5028 @sc{null} is encountered. This is useful when large arrays actually
5029 contain only short strings.
5032 @kindex set print pretty
5033 @item set print pretty on
5034 Cause @value{GDBN} to print structures in an indented format with one member
5035 per line, like this:
5050 @item set print pretty off
5051 Cause @value{GDBN} to print structures in a compact format, like this:
5055 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
5056 meat = 0x54 "Pork"@}
5061 This is the default format.
5063 @kindex show print pretty
5064 @item show print pretty
5065 Show which format @value{GDBN} is using to print structures.
5067 @kindex set print sevenbit-strings
5068 @item set print sevenbit-strings on
5069 Print using only seven-bit characters; if this option is set,
5070 @value{GDBN} displays any eight-bit characters (in strings or
5071 character values) using the notation @code{\}@var{nnn}. This setting is
5072 best if you are working in English (@sc{ascii}) and you use the
5073 high-order bit of characters as a marker or ``meta'' bit.
5075 @item set print sevenbit-strings off
5076 Print full eight-bit characters. This allows the use of more
5077 international character sets, and is the default.
5079 @kindex show print sevenbit-strings
5080 @item show print sevenbit-strings
5081 Show whether or not @value{GDBN} is printing only seven-bit characters.
5083 @kindex set print union
5084 @item set print union on
5085 Tell @value{GDBN} to print unions which are contained in structures. This
5086 is the default setting.
5088 @item set print union off
5089 Tell @value{GDBN} not to print unions which are contained in structures.
5091 @kindex show print union
5092 @item show print union
5093 Ask @value{GDBN} whether or not it will print unions which are contained in
5096 For example, given the declarations
5099 typedef enum @{Tree, Bug@} Species;
5100 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5101 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5112 struct thing foo = @{Tree, @{Acorn@}@};
5116 with @code{set print union on} in effect @samp{p foo} would print
5119 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5123 and with @code{set print union off} in effect it would print
5126 $1 = @{it = Tree, form = @{...@}@}
5132 These settings are of interest when debugging C++ programs:
5136 @kindex set print demangle
5137 @item set print demangle
5138 @itemx set print demangle on
5139 Print C++ names in their source form rather than in the encoded
5140 (``mangled'') form passed to the assembler and linker for type-safe
5141 linkage. The default is on.
5143 @kindex show print demangle
5144 @item show print demangle
5145 Show whether C++ names are printed in mangled or demangled form.
5147 @kindex set print asm-demangle
5148 @item set print asm-demangle
5149 @itemx set print asm-demangle on
5150 Print C++ names in their source form rather than their mangled form, even
5151 in assembler code printouts such as instruction disassemblies.
5154 @kindex show print asm-demangle
5155 @item show print asm-demangle
5156 Show whether C++ names in assembly listings are printed in mangled
5159 @kindex set demangle-style
5160 @cindex C++ symbol decoding style
5161 @cindex symbol decoding style, C++
5162 @item set demangle-style @var{style}
5163 Choose among several encoding schemes used by different compilers to
5164 represent C++ names. The choices for @var{style} are currently:
5168 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5171 Decode based on the @sc{gnu} C++ compiler (@code{g++}) encoding algorithm.
5172 This is the default.
5175 Decode based on the HP ANSI C++ (@code{aCC}) encoding algorithm.
5178 Decode based on the Lucid C++ compiler (@code{lcc}) encoding algorithm.
5181 Decode using the algorithm in the @cite{C++ Annotated Reference Manual}.
5182 @strong{Warning:} this setting alone is not sufficient to allow
5183 debugging @code{cfront}-generated executables. @value{GDBN} would
5184 require further enhancement to permit that.
5187 If you omit @var{style}, you will see a list of possible formats.
5189 @kindex show demangle-style
5190 @item show demangle-style
5191 Display the encoding style currently in use for decoding C++ symbols.
5193 @kindex set print object
5194 @item set print object
5195 @itemx set print object on
5196 When displaying a pointer to an object, identify the @emph{actual}
5197 (derived) type of the object rather than the @emph{declared} type, using
5198 the virtual function table.
5200 @item set print object off
5201 Display only the declared type of objects, without reference to the
5202 virtual function table. This is the default setting.
5204 @kindex show print object
5205 @item show print object
5206 Show whether actual, or declared, object types are displayed.
5208 @kindex set print static-members
5209 @item set print static-members
5210 @itemx set print static-members on
5211 Print static members when displaying a C++ object. The default is on.
5213 @item set print static-members off
5214 Do not print static members when displaying a C++ object.
5216 @kindex show print static-members
5217 @item show print static-members
5218 Show whether C++ static members are printed, or not.
5220 @c These don't work with HP ANSI C++ yet.
5221 @kindex set print vtbl
5222 @item set print vtbl
5223 @itemx set print vtbl on
5224 Pretty print C++ virtual function tables. The default is off.
5225 (The @code{vtbl} commands do not work on programs compiled with the HP
5226 ANSI C++ compiler (@code{aCC}).)
5228 @item set print vtbl off
5229 Do not pretty print C++ virtual function tables.
5231 @kindex show print vtbl
5232 @item show print vtbl
5233 Show whether C++ virtual function tables are pretty printed, or not.
5237 @section Value history
5239 @cindex value history
5240 Values printed by the @code{print} command are saved in the @value{GDBN}
5241 @dfn{value history}. This allows you to refer to them in other expressions.
5242 Values are kept until the symbol table is re-read or discarded
5243 (for example with the @code{file} or @code{symbol-file} commands).
5244 When the symbol table changes, the value history is discarded,
5245 since the values may contain pointers back to the types defined in the
5250 @cindex history number
5251 The values printed are given @dfn{history numbers} by which you can
5252 refer to them. These are successive integers starting with one.
5253 @code{print} shows you the history number assigned to a value by
5254 printing @samp{$@var{num} = } before the value; here @var{num} is the
5257 To refer to any previous value, use @samp{$} followed by the value's
5258 history number. The way @code{print} labels its output is designed to
5259 remind you of this. Just @code{$} refers to the most recent value in
5260 the history, and @code{$$} refers to the value before that.
5261 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5262 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5263 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5265 For example, suppose you have just printed a pointer to a structure and
5266 want to see the contents of the structure. It suffices to type
5272 If you have a chain of structures where the component @code{next} points
5273 to the next one, you can print the contents of the next one with this:
5280 You can print successive links in the chain by repeating this
5281 command---which you can do by just typing @key{RET}.
5283 Note that the history records values, not expressions. If the value of
5284 @code{x} is 4 and you type these commands:
5292 then the value recorded in the value history by the @code{print} command
5293 remains 4 even though the value of @code{x} has changed.
5298 Print the last ten values in the value history, with their item numbers.
5299 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5300 values} does not change the history.
5302 @item show values @var{n}
5303 Print ten history values centered on history item number @var{n}.
5306 Print ten history values just after the values last printed. If no more
5307 values are available, @code{show values +} produces no display.
5310 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5311 same effect as @samp{show values +}.
5313 @node Convenience Vars
5314 @section Convenience variables
5316 @cindex convenience variables
5317 @value{GDBN} provides @dfn{convenience variables} that you can use within
5318 @value{GDBN} to hold on to a value and refer to it later. These variables
5319 exist entirely within @value{GDBN}; they are not part of your program, and
5320 setting a convenience variable has no direct effect on further execution
5321 of your program. That is why you can use them freely.
5323 Convenience variables are prefixed with @samp{$}. Any name preceded by
5324 @samp{$} can be used for a convenience variable, unless it is one of
5325 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
5326 (Value history references, in contrast, are @emph{numbers} preceded
5327 by @samp{$}. @xref{Value History, ,Value history}.)
5329 You can save a value in a convenience variable with an assignment
5330 expression, just as you would set a variable in your program.
5334 set $foo = *object_ptr
5338 would save in @code{$foo} the value contained in the object pointed to by
5341 Using a convenience variable for the first time creates it, but its
5342 value is @code{void} until you assign a new value. You can alter the
5343 value with another assignment at any time.
5345 Convenience variables have no fixed types. You can assign a convenience
5346 variable any type of value, including structures and arrays, even if
5347 that variable already has a value of a different type. The convenience
5348 variable, when used as an expression, has the type of its current value.
5351 @kindex show convenience
5352 @item show convenience
5353 Print a list of convenience variables used so far, and their values.
5354 Abbreviated @code{show conv}.
5357 One of the ways to use a convenience variable is as a counter to be
5358 incremented or a pointer to be advanced. For example, to print
5359 a field from successive elements of an array of structures:
5363 print bar[$i++]->contents
5367 Repeat that command by typing @key{RET}.
5369 Some convenience variables are created automatically by @value{GDBN} and given
5370 values likely to be useful.
5373 @vindex $_@r{, convenience variable}
5375 The variable @code{$_} is automatically set by the @code{x} command to
5376 the last address examined (@pxref{Memory, ,Examining memory}). Other
5377 commands which provide a default address for @code{x} to examine also
5378 set @code{$_} to that address; these commands include @code{info line}
5379 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5380 except when set by the @code{x} command, in which case it is a pointer
5381 to the type of @code{$__}.
5383 @vindex $__@r{, convenience variable}
5385 The variable @code{$__} is automatically set by the @code{x} command
5386 to the value found in the last address examined. Its type is chosen
5387 to match the format in which the data was printed.
5390 @vindex $_exitcode@r{, convenience variable}
5391 The variable @code{$_exitcode} is automatically set to the exit code when
5392 the program being debugged terminates.
5395 On HP-UX systems, if you refer to a function or variable name that
5396 begins with a dollar sign, @value{GDBN} searches for a user or system
5397 name first, before it searches for a convenience variable.
5403 You can refer to machine register contents, in expressions, as variables
5404 with names starting with @samp{$}. The names of registers are different
5405 for each machine; use @code{info registers} to see the names used on
5409 @kindex info registers
5410 @item info registers
5411 Print the names and values of all registers except floating-point
5412 registers (in the selected stack frame).
5414 @kindex info all-registers
5415 @cindex floating point registers
5416 @item info all-registers
5417 Print the names and values of all registers, including floating-point
5420 @item info registers @var{regname} @dots{}
5421 Print the @dfn{relativized} value of each specified register @var{regname}.
5422 As discussed in detail below, register values are normally relative to
5423 the selected stack frame. @var{regname} may be any register name valid on
5424 the machine you are using, with or without the initial @samp{$}.
5427 @value{GDBN} has four ``standard'' register names that are available (in
5428 expressions) on most machines---whenever they do not conflict with an
5429 architecture's canonical mnemonics for registers. The register names
5430 @code{$pc} and @code{$sp} are used for the program counter register and
5431 the stack pointer. @code{$fp} is used for a register that contains a
5432 pointer to the current stack frame, and @code{$ps} is used for a
5433 register that contains the processor status. For example,
5434 you could print the program counter in hex with
5441 or print the instruction to be executed next with
5448 or add four to the stack pointer@footnote{This is a way of removing
5449 one word from the stack, on machines where stacks grow downward in
5450 memory (most machines, nowadays). This assumes that the innermost
5451 stack frame is selected; setting @code{$sp} is not allowed when other
5452 stack frames are selected. To pop entire frames off the stack,
5453 regardless of machine architecture, use @code{return};
5454 see @ref{Returning, ,Returning from a function}.} with
5460 Whenever possible, these four standard register names are available on
5461 your machine even though the machine has different canonical mnemonics,
5462 so long as there is no conflict. The @code{info registers} command
5463 shows the canonical names. For example, on the SPARC, @code{info
5464 registers} displays the processor status register as @code{$psr} but you
5465 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
5466 is an alias for the @sc{eflags} register.
5468 @value{GDBN} always considers the contents of an ordinary register as an
5469 integer when the register is examined in this way. Some machines have
5470 special registers which can hold nothing but floating point; these
5471 registers are considered to have floating point values. There is no way
5472 to refer to the contents of an ordinary register as floating point value
5473 (although you can @emph{print} it as a floating point value with
5474 @samp{print/f $@var{regname}}).
5476 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5477 means that the data format in which the register contents are saved by
5478 the operating system is not the same one that your program normally
5479 sees. For example, the registers of the 68881 floating point
5480 coprocessor are always saved in ``extended'' (raw) format, but all C
5481 programs expect to work with ``double'' (virtual) format. In such
5482 cases, @value{GDBN} normally works with the virtual format only (the format
5483 that makes sense for your program), but the @code{info registers} command
5484 prints the data in both formats.
5486 Normally, register values are relative to the selected stack frame
5487 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5488 value that the register would contain if all stack frames farther in
5489 were exited and their saved registers restored. In order to see the
5490 true contents of hardware registers, you must select the innermost
5491 frame (with @samp{frame 0}).
5493 However, @value{GDBN} must deduce where registers are saved, from the machine
5494 code generated by your compiler. If some registers are not saved, or if
5495 @value{GDBN} is unable to locate the saved registers, the selected stack
5496 frame makes no difference.
5498 @node Floating Point Hardware
5499 @section Floating point hardware
5500 @cindex floating point
5502 Depending on the configuration, @value{GDBN} may be able to give
5503 you more information about the status of the floating point hardware.
5508 Display hardware-dependent information about the floating
5509 point unit. The exact contents and layout vary depending on the
5510 floating point chip. Currently, @samp{info float} is supported on
5511 the ARM and x86 machines.
5514 @node Memory Region Attributes
5515 @section Memory Region Attributes
5516 @cindex memory region attributes
5518 @dfn{Memory region attributes} allow you to describe special handling
5519 required by regions of your target's memory. @value{GDBN} uses attributes
5520 to determine whether to allow certain types of memory accesses; whether to
5521 use specific width accesses; and whether to cache target memory.
5523 Defined memory regions can be individually enabled and disabled. When a
5524 memory region is disabled, @value{GDBN} uses the default attributes when
5525 accessing memory in that region. Similarly, if no memory regions have
5526 been defined, @value{GDBN} uses the default attributes when accessing
5529 When a memory region is defined, it is given a number to identify it;
5530 to enable, disable, or remove a memory region, you specify that number.
5534 @item mem @var{address1} @var{address1} @var{attributes}@dots{}
5535 Define memory region bounded by @var{address1} and @var{address2}
5536 with attributes @var{attributes}@dots{}.
5539 @item delete mem @var{nums}@dots{}
5540 Remove memory region numbers @var{nums}.
5543 @item disable mem @var{nums}@dots{}
5544 Disable memory region numbers @var{nums}.
5545 A disabled memory region is not forgotten.
5546 It may be enabled again later.
5549 @item enable mem @var{nums}@dots{}
5550 Enable memory region numbers @var{nums}.
5554 Print a table of all defined memory regions, with the following columns
5558 @item Memory Region Number
5559 @item Enabled or Disabled.
5560 Enabled memory regions are marked with @samp{y}.
5561 Disabled memory regions are marked with @samp{n}.
5564 The address defining the inclusive lower bound of the memory region.
5567 The address defining the exclusive upper bound of the memory region.
5570 The list of attributes set for this memory region.
5575 @subsection Attributes
5577 @subsubsection Memory Access Mode
5578 The access mode attributes set whether @value{GDBN} may make read or
5579 write accesses to a memory region.
5581 While these attributes prevent @value{GDBN} from performing invalid
5582 memory accesses, they do nothing to prevent the target system, I/O DMA,
5583 etc. from accessing memory.
5587 Memory is read only.
5589 Memory is write only.
5591 Memory is read/write (default).
5594 @subsubsection Memory Access Size
5595 The acccess size attributes tells @value{GDBN} to use specific sized
5596 accesses in the memory region. Often memory mapped device registers
5597 require specific sized accesses. If no access size attribute is
5598 specified, @value{GDBN} may use accesses of any size.
5602 Use 8 bit memory accesses.
5604 Use 16 bit memory accesses.
5606 Use 32 bit memory accesses.
5608 Use 64 bit memory accesses.
5611 @c @subsubsection Hardware/Software Breakpoints
5612 @c The hardware/software breakpoint attributes set whether @value{GDBN}
5613 @c will use hardware or software breakpoints for the internal breakpoints
5614 @c used by the step, next, finish, until, etc. commands.
5618 @c Always use hardware breakpoints
5619 @c @item swbreak (default)
5622 @subsubsection Data Cache
5623 The data cache attributes set whether @value{GDBN} will cache target
5624 memory. While this generally improves performance by reducing debug
5625 protocol overhead, it can lead to incorrect results because @value{GDBN}
5626 does not know about volatile variables or memory mapped device
5631 Enable @value{GDBN} to cache target memory.
5632 @item nocache (default)
5633 Disable @value{GDBN} from caching target memory.
5636 @c @subsubsection Memory Write Verification
5637 @c The memory write verification attributes set whether @value{GDBN}
5638 @c will re-reads data after each write to verify the write was successful.
5642 @c @item noverify (default)
5646 @chapter Using @value{GDBN} with Different Languages
5649 Although programming languages generally have common aspects, they are
5650 rarely expressed in the same manner. For instance, in ANSI C,
5651 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
5652 Modula-2, it is accomplished by @code{p^}. Values can also be
5653 represented (and displayed) differently. Hex numbers in C appear as
5654 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
5656 @cindex working language
5657 Language-specific information is built into @value{GDBN} for some languages,
5658 allowing you to express operations like the above in your program's
5659 native language, and allowing @value{GDBN} to output values in a manner
5660 consistent with the syntax of your program's native language. The
5661 language you use to build expressions is called the @dfn{working
5665 * Setting:: Switching between source languages
5666 * Show:: Displaying the language
5667 * Checks:: Type and range checks
5668 * Support:: Supported languages
5672 @section Switching between source languages
5674 There are two ways to control the working language---either have @value{GDBN}
5675 set it automatically, or select it manually yourself. You can use the
5676 @code{set language} command for either purpose. On startup, @value{GDBN}
5677 defaults to setting the language automatically. The working language is
5678 used to determine how expressions you type are interpreted, how values
5681 In addition to the working language, every source file that
5682 @value{GDBN} knows about has its own working language. For some object
5683 file formats, the compiler might indicate which language a particular
5684 source file is in. However, most of the time @value{GDBN} infers the
5685 language from the name of the file. The language of a source file
5686 controls whether C++ names are demangled---this way @code{backtrace} can
5687 show each frame appropriately for its own language. There is no way to
5688 set the language of a source file from within @value{GDBN}, but you can
5689 set the language associated with a filename extension. @xref{Show, ,
5690 Displaying the language}.
5692 This is most commonly a problem when you use a program, such
5693 as @code{cfront} or @code{f2c}, that generates C but is written in
5694 another language. In that case, make the
5695 program use @code{#line} directives in its C output; that way
5696 @value{GDBN} will know the correct language of the source code of the original
5697 program, and will display that source code, not the generated C code.
5700 * Filenames:: Filename extensions and languages.
5701 * Manually:: Setting the working language manually
5702 * Automatically:: Having @value{GDBN} infer the source language
5706 @subsection List of filename extensions and languages
5708 If a source file name ends in one of the following extensions, then
5709 @value{GDBN} infers that its language is the one indicated.
5734 Modula-2 source file
5738 Assembler source file. This actually behaves almost like C, but
5739 @value{GDBN} does not skip over function prologues when stepping.
5742 In addition, you may set the language associated with a filename
5743 extension. @xref{Show, , Displaying the language}.
5746 @subsection Setting the working language
5748 If you allow @value{GDBN} to set the language automatically,
5749 expressions are interpreted the same way in your debugging session and
5752 @kindex set language
5753 If you wish, you may set the language manually. To do this, issue the
5754 command @samp{set language @var{lang}}, where @var{lang} is the name of
5756 @code{c} or @code{modula-2}.
5757 For a list of the supported languages, type @samp{set language}.
5759 Setting the language manually prevents @value{GDBN} from updating the working
5760 language automatically. This can lead to confusion if you try
5761 to debug a program when the working language is not the same as the
5762 source language, when an expression is acceptable to both
5763 languages---but means different things. For instance, if the current
5764 source file were written in C, and @value{GDBN} was parsing Modula-2, a
5772 might not have the effect you intended. In C, this means to add
5773 @code{b} and @code{c} and place the result in @code{a}. The result
5774 printed would be the value of @code{a}. In Modula-2, this means to compare
5775 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
5778 @subsection Having @value{GDBN} infer the source language
5780 To have @value{GDBN} set the working language automatically, use
5781 @samp{set language local} or @samp{set language auto}. @value{GDBN}
5782 then infers the working language. That is, when your program stops in a
5783 frame (usually by encountering a breakpoint), @value{GDBN} sets the
5784 working language to the language recorded for the function in that
5785 frame. If the language for a frame is unknown (that is, if the function
5786 or block corresponding to the frame was defined in a source file that
5787 does not have a recognized extension), the current working language is
5788 not changed, and @value{GDBN} issues a warning.
5790 This may not seem necessary for most programs, which are written
5791 entirely in one source language. However, program modules and libraries
5792 written in one source language can be used by a main program written in
5793 a different source language. Using @samp{set language auto} in this
5794 case frees you from having to set the working language manually.
5797 @section Displaying the language
5799 The following commands help you find out which language is the
5800 working language, and also what language source files were written in.
5802 @kindex show language
5803 @kindex info frame@r{, show the source language}
5804 @kindex info source@r{, show the source language}
5807 Display the current working language. This is the
5808 language you can use with commands such as @code{print} to
5809 build and compute expressions that may involve variables in your program.
5812 Display the source language for this frame. This language becomes the
5813 working language if you use an identifier from this frame.
5814 @xref{Frame Info, ,Information about a frame}, to identify the other
5815 information listed here.
5818 Display the source language of this source file.
5819 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
5820 information listed here.
5823 In unusual circumstances, you may have source files with extensions
5824 not in the standard list. You can then set the extension associated
5825 with a language explicitly:
5827 @kindex set extension-language
5828 @kindex info extensions
5830 @item set extension-language @var{.ext} @var{language}
5831 Set source files with extension @var{.ext} to be assumed to be in
5832 the source language @var{language}.
5834 @item info extensions
5835 List all the filename extensions and the associated languages.
5839 @section Type and range checking
5842 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
5843 checking are included, but they do not yet have any effect. This
5844 section documents the intended facilities.
5846 @c FIXME remove warning when type/range code added
5848 Some languages are designed to guard you against making seemingly common
5849 errors through a series of compile- and run-time checks. These include
5850 checking the type of arguments to functions and operators, and making
5851 sure mathematical overflows are caught at run time. Checks such as
5852 these help to ensure a program's correctness once it has been compiled
5853 by eliminating type mismatches, and providing active checks for range
5854 errors when your program is running.
5856 @value{GDBN} can check for conditions like the above if you wish.
5857 Although @value{GDBN} does not check the statements in your program, it
5858 can check expressions entered directly into @value{GDBN} for evaluation via
5859 the @code{print} command, for example. As with the working language,
5860 @value{GDBN} can also decide whether or not to check automatically based on
5861 your program's source language. @xref{Support, ,Supported languages},
5862 for the default settings of supported languages.
5865 * Type Checking:: An overview of type checking
5866 * Range Checking:: An overview of range checking
5869 @cindex type checking
5870 @cindex checks, type
5872 @subsection An overview of type checking
5874 Some languages, such as Modula-2, are strongly typed, meaning that the
5875 arguments to operators and functions have to be of the correct type,
5876 otherwise an error occurs. These checks prevent type mismatch
5877 errors from ever causing any run-time problems. For example,
5885 The second example fails because the @code{CARDINAL} 1 is not
5886 type-compatible with the @code{REAL} 2.3.
5888 For the expressions you use in @value{GDBN} commands, you can tell the
5889 @value{GDBN} type checker to skip checking;
5890 to treat any mismatches as errors and abandon the expression;
5891 or to only issue warnings when type mismatches occur,
5892 but evaluate the expression anyway. When you choose the last of
5893 these, @value{GDBN} evaluates expressions like the second example above, but
5894 also issues a warning.
5896 Even if you turn type checking off, there may be other reasons
5897 related to type that prevent @value{GDBN} from evaluating an expression.
5898 For instance, @value{GDBN} does not know how to add an @code{int} and
5899 a @code{struct foo}. These particular type errors have nothing to do
5900 with the language in use, and usually arise from expressions, such as
5901 the one described above, which make little sense to evaluate anyway.
5903 Each language defines to what degree it is strict about type. For
5904 instance, both Modula-2 and C require the arguments to arithmetical
5905 operators to be numbers. In C, enumerated types and pointers can be
5906 represented as numbers, so that they are valid arguments to mathematical
5907 operators. @xref{Support, ,Supported languages}, for further
5908 details on specific languages.
5910 @value{GDBN} provides some additional commands for controlling the type checker:
5912 @kindex set check@r{, type}
5913 @kindex set check type
5914 @kindex show check type
5916 @item set check type auto
5917 Set type checking on or off based on the current working language.
5918 @xref{Support, ,Supported languages}, for the default settings for
5921 @item set check type on
5922 @itemx set check type off
5923 Set type checking on or off, overriding the default setting for the
5924 current working language. Issue a warning if the setting does not
5925 match the language default. If any type mismatches occur in
5926 evaluating an expression while type checking is on, @value{GDBN} prints a
5927 message and aborts evaluation of the expression.
5929 @item set check type warn
5930 Cause the type checker to issue warnings, but to always attempt to
5931 evaluate the expression. Evaluating the expression may still
5932 be impossible for other reasons. For example, @value{GDBN} cannot add
5933 numbers and structures.
5936 Show the current setting of the type checker, and whether or not @value{GDBN}
5937 is setting it automatically.
5940 @cindex range checking
5941 @cindex checks, range
5942 @node Range Checking
5943 @subsection An overview of range checking
5945 In some languages (such as Modula-2), it is an error to exceed the
5946 bounds of a type; this is enforced with run-time checks. Such range
5947 checking is meant to ensure program correctness by making sure
5948 computations do not overflow, or indices on an array element access do
5949 not exceed the bounds of the array.
5951 For expressions you use in @value{GDBN} commands, you can tell
5952 @value{GDBN} to treat range errors in one of three ways: ignore them,
5953 always treat them as errors and abandon the expression, or issue
5954 warnings but evaluate the expression anyway.
5956 A range error can result from numerical overflow, from exceeding an
5957 array index bound, or when you type a constant that is not a member
5958 of any type. Some languages, however, do not treat overflows as an
5959 error. In many implementations of C, mathematical overflow causes the
5960 result to ``wrap around'' to lower values---for example, if @var{m} is
5961 the largest integer value, and @var{s} is the smallest, then
5964 @var{m} + 1 @result{} @var{s}
5967 This, too, is specific to individual languages, and in some cases
5968 specific to individual compilers or machines. @xref{Support, ,
5969 Supported languages}, for further details on specific languages.
5971 @value{GDBN} provides some additional commands for controlling the range checker:
5973 @kindex set check@r{, range}
5974 @kindex set check range
5975 @kindex show check range
5977 @item set check range auto
5978 Set range checking on or off based on the current working language.
5979 @xref{Support, ,Supported languages}, for the default settings for
5982 @item set check range on
5983 @itemx set check range off
5984 Set range checking on or off, overriding the default setting for the
5985 current working language. A warning is issued if the setting does not
5986 match the language default. If a range error occurs and range checking is on,
5987 then a message is printed and evaluation of the expression is aborted.
5989 @item set check range warn
5990 Output messages when the @value{GDBN} range checker detects a range error,
5991 but attempt to evaluate the expression anyway. Evaluating the
5992 expression may still be impossible for other reasons, such as accessing
5993 memory that the process does not own (a typical example from many Unix
5997 Show the current setting of the range checker, and whether or not it is
5998 being set automatically by @value{GDBN}.
6002 @section Supported languages
6004 @value{GDBN} supports C, C++, Fortran, Java, Chill, assembly, and Modula-2.
6005 @c This is false ...
6006 Some @value{GDBN} features may be used in expressions regardless of the
6007 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
6008 and the @samp{@{type@}addr} construct (@pxref{Expressions,
6009 ,Expressions}) can be used with the constructs of any supported
6012 The following sections detail to what degree each source language is
6013 supported by @value{GDBN}. These sections are not meant to be language
6014 tutorials or references, but serve only as a reference guide to what the
6015 @value{GDBN} expression parser accepts, and what input and output
6016 formats should look like for different languages. There are many good
6017 books written on each of these languages; please look to these for a
6018 language reference or tutorial.
6022 * Modula-2:: Modula-2
6027 @subsection C and C++
6030 @cindex expressions in C or C++
6032 Since C and C++ are so closely related, many features of @value{GDBN} apply
6033 to both languages. Whenever this is the case, we discuss those languages
6037 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
6038 @cindex @sc{gnu} C++
6039 The C++ debugging facilities are jointly implemented by the C++
6040 compiler and @value{GDBN}. Therefore, to debug your C++ code
6041 effectively, you must compile your C++ programs with a supported
6042 C++ compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C++
6043 compiler (@code{aCC}).
6045 For best results when using @sc{gnu} C++, use the stabs debugging
6046 format. You can select that format explicitly with the @code{g++}
6047 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
6048 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
6049 CC, gcc.info, Using @sc{gnu} CC}, for more information.
6052 * C Operators:: C and C++ operators
6053 * C Constants:: C and C++ constants
6054 * C plus plus expressions:: C++ expressions
6055 * C Defaults:: Default settings for C and C++
6056 * C Checks:: C and C++ type and range checks
6057 * Debugging C:: @value{GDBN} and C
6058 * Debugging C plus plus:: @value{GDBN} features for C++
6062 @subsubsection C and C++ operators
6064 @cindex C and C++ operators
6066 Operators must be defined on values of specific types. For instance,
6067 @code{+} is defined on numbers, but not on structures. Operators are
6068 often defined on groups of types.
6070 For the purposes of C and C++, the following definitions hold:
6075 @emph{Integral types} include @code{int} with any of its storage-class
6076 specifiers; @code{char}; @code{enum}; and, for C++, @code{bool}.
6079 @emph{Floating-point types} include @code{float}, @code{double}, and
6080 @code{long double} (if supported by the target platform).
6083 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
6086 @emph{Scalar types} include all of the above.
6091 The following operators are supported. They are listed here
6092 in order of increasing precedence:
6096 The comma or sequencing operator. Expressions in a comma-separated list
6097 are evaluated from left to right, with the result of the entire
6098 expression being the last expression evaluated.
6101 Assignment. The value of an assignment expression is the value
6102 assigned. Defined on scalar types.
6105 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
6106 and translated to @w{@code{@var{a} = @var{a op b}}}.
6107 @w{@code{@var{op}=}} and @code{=} have the same precedence.
6108 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
6109 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
6112 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
6113 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
6117 Logical @sc{or}. Defined on integral types.
6120 Logical @sc{and}. Defined on integral types.
6123 Bitwise @sc{or}. Defined on integral types.
6126 Bitwise exclusive-@sc{or}. Defined on integral types.
6129 Bitwise @sc{and}. Defined on integral types.
6132 Equality and inequality. Defined on scalar types. The value of these
6133 expressions is 0 for false and non-zero for true.
6135 @item <@r{, }>@r{, }<=@r{, }>=
6136 Less than, greater than, less than or equal, greater than or equal.
6137 Defined on scalar types. The value of these expressions is 0 for false
6138 and non-zero for true.
6141 left shift, and right shift. Defined on integral types.
6144 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
6147 Addition and subtraction. Defined on integral types, floating-point types and
6150 @item *@r{, }/@r{, }%
6151 Multiplication, division, and modulus. Multiplication and division are
6152 defined on integral and floating-point types. Modulus is defined on
6156 Increment and decrement. When appearing before a variable, the
6157 operation is performed before the variable is used in an expression;
6158 when appearing after it, the variable's value is used before the
6159 operation takes place.
6162 Pointer dereferencing. Defined on pointer types. Same precedence as
6166 Address operator. Defined on variables. Same precedence as @code{++}.
6168 For debugging C++, @value{GDBN} implements a use of @samp{&} beyond what is
6169 allowed in the C++ language itself: you can use @samp{&(&@var{ref})}
6170 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
6171 where a C++ reference variable (declared with @samp{&@var{ref}}) is
6175 Negative. Defined on integral and floating-point types. Same
6176 precedence as @code{++}.
6179 Logical negation. Defined on integral types. Same precedence as
6183 Bitwise complement operator. Defined on integral types. Same precedence as
6188 Structure member, and pointer-to-structure member. For convenience,
6189 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
6190 pointer based on the stored type information.
6191 Defined on @code{struct} and @code{union} data.
6194 Dereferences of pointers to members.
6197 Array indexing. @code{@var{a}[@var{i}]} is defined as
6198 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
6201 Function parameter list. Same precedence as @code{->}.
6204 C++ scope resolution operator. Defined on @code{struct}, @code{union},
6205 and @code{class} types.
6208 Doubled colons also represent the @value{GDBN} scope operator
6209 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
6213 If an operator is redefined in the user code, @value{GDBN} usually
6214 attempts to invoke the redefined version instead of using the operator's
6222 @subsubsection C and C++ constants
6224 @cindex C and C++ constants
6226 @value{GDBN} allows you to express the constants of C and C++ in the
6231 Integer constants are a sequence of digits. Octal constants are
6232 specified by a leading @samp{0} (i.e. zero), and hexadecimal constants by
6233 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
6234 @samp{l}, specifying that the constant should be treated as a
6238 Floating point constants are a sequence of digits, followed by a decimal
6239 point, followed by a sequence of digits, and optionally followed by an
6240 exponent. An exponent is of the form:
6241 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
6242 sequence of digits. The @samp{+} is optional for positive exponents.
6243 A floating-point constant may also end with a letter @samp{f} or
6244 @samp{F}, specifying that the constant should be treated as being of
6245 the @code{float} (as opposed to the default @code{double}) type; or with
6246 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
6250 Enumerated constants consist of enumerated identifiers, or their
6251 integral equivalents.
6254 Character constants are a single character surrounded by single quotes
6255 (@code{'}), or a number---the ordinal value of the corresponding character
6256 (usually its @sc{ascii} value). Within quotes, the single character may
6257 be represented by a letter or by @dfn{escape sequences}, which are of
6258 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
6259 of the character's ordinal value; or of the form @samp{\@var{x}}, where
6260 @samp{@var{x}} is a predefined special character---for example,
6261 @samp{\n} for newline.
6264 String constants are a sequence of character constants surrounded by
6265 double quotes (@code{"}). Any valid character constant (as described
6266 above) may appear. Double quotes within the string must be preceded by
6267 a backslash, so for instance @samp{"a\"b'c"} is a string of five
6271 Pointer constants are an integral value. You can also write pointers
6272 to constants using the C operator @samp{&}.
6275 Array constants are comma-separated lists surrounded by braces @samp{@{}
6276 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
6277 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
6278 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
6282 * C plus plus expressions::
6289 @node C plus plus expressions
6290 @subsubsection C++ expressions
6292 @cindex expressions in C++
6293 @value{GDBN} expression handling can interpret most C++ expressions.
6295 @cindex C++ support, not in @sc{coff}
6296 @cindex @sc{coff} versus C++
6297 @cindex C++ and object formats
6298 @cindex object formats and C++
6299 @cindex a.out and C++
6300 @cindex @sc{ecoff} and C++
6301 @cindex @sc{xcoff} and C++
6302 @cindex @sc{elf}/stabs and C++
6303 @cindex @sc{elf}/@sc{dwarf} and C++
6304 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
6305 @c periodically whether this has happened...
6307 @emph{Warning:} @value{GDBN} can only debug C++ code if you use the
6308 proper compiler. Typically, C++ debugging depends on the use of
6309 additional debugging information in the symbol table, and thus requires
6310 special support. In particular, if your compiler generates a.out, MIPS
6311 @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the
6312 symbol table, these facilities are all available. (With @sc{gnu} CC,
6313 you can use the @samp{-gstabs} option to request stabs debugging
6314 extensions explicitly.) Where the object code format is standard
6315 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C++
6316 support in @value{GDBN} does @emph{not} work.
6321 @cindex member functions
6323 Member function calls are allowed; you can use expressions like
6326 count = aml->GetOriginal(x, y)
6329 @vindex this@r{, inside C@t{++} member functions}
6330 @cindex namespace in C++
6332 While a member function is active (in the selected stack frame), your
6333 expressions have the same namespace available as the member function;
6334 that is, @value{GDBN} allows implicit references to the class instance
6335 pointer @code{this} following the same rules as C++.
6337 @cindex call overloaded functions
6338 @cindex overloaded functions, calling
6339 @cindex type conversions in C++
6341 You can call overloaded functions; @value{GDBN} resolves the function
6342 call to the right definition, with some restrictions. @value{GDBN} does not
6343 perform overload resolution involving user-defined type conversions,
6344 calls to constructors, or instantiations of templates that do not exist
6345 in the program. It also cannot handle ellipsis argument lists or
6348 It does perform integral conversions and promotions, floating-point
6349 promotions, arithmetic conversions, pointer conversions, conversions of
6350 class objects to base classes, and standard conversions such as those of
6351 functions or arrays to pointers; it requires an exact match on the
6352 number of function arguments.
6354 Overload resolution is always performed, unless you have specified
6355 @code{set overload-resolution off}. @xref{Debugging C plus plus,
6356 ,@value{GDBN} features for C++}.
6358 You must specify @code{set overload-resolution off} in order to use an
6359 explicit function signature to call an overloaded function, as in
6361 p 'foo(char,int)'('x', 13)
6364 The @value{GDBN} command-completion facility can simplify this;
6365 see @ref{Completion, ,Command completion}.
6367 @cindex reference declarations
6369 @value{GDBN} understands variables declared as C++ references; you can use
6370 them in expressions just as you do in C++ source---they are automatically
6373 In the parameter list shown when @value{GDBN} displays a frame, the values of
6374 reference variables are not displayed (unlike other variables); this
6375 avoids clutter, since references are often used for large structures.
6376 The @emph{address} of a reference variable is always shown, unless
6377 you have specified @samp{set print address off}.
6380 @value{GDBN} supports the C++ name resolution operator @code{::}---your
6381 expressions can use it just as expressions in your program do. Since
6382 one scope may be defined in another, you can use @code{::} repeatedly if
6383 necessary, for example in an expression like
6384 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
6385 resolving name scope by reference to source files, in both C and C++
6386 debugging (@pxref{Variables, ,Program variables}).
6389 In addition, when used with HP's C++ compiler, @value{GDBN} supports
6390 calling virtual functions correctly, printing out virtual bases of
6391 objects, calling functions in a base subobject, casting objects, and
6392 invoking user-defined operators.
6395 @subsubsection C and C++ defaults
6397 @cindex C and C++ defaults
6399 If you allow @value{GDBN} to set type and range checking automatically, they
6400 both default to @code{off} whenever the working language changes to
6401 C or C++. This happens regardless of whether you or @value{GDBN}
6402 selects the working language.
6404 If you allow @value{GDBN} to set the language automatically, it
6405 recognizes source files whose names end with @file{.c}, @file{.C}, or
6406 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
6407 these files, it sets the working language to C or C++.
6408 @xref{Automatically, ,Having @value{GDBN} infer the source language},
6409 for further details.
6411 @c Type checking is (a) primarily motivated by Modula-2, and (b)
6412 @c unimplemented. If (b) changes, it might make sense to let this node
6413 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
6416 @subsubsection C and C++ type and range checks
6418 @cindex C and C++ checks
6420 By default, when @value{GDBN} parses C or C++ expressions, type checking
6421 is not used. However, if you turn type checking on, @value{GDBN}
6422 considers two variables type equivalent if:
6426 The two variables are structured and have the same structure, union, or
6430 The two variables have the same type name, or types that have been
6431 declared equivalent through @code{typedef}.
6434 @c leaving this out because neither J Gilmore nor R Pesch understand it.
6437 The two @code{struct}, @code{union}, or @code{enum} variables are
6438 declared in the same declaration. (Note: this may not be true for all C
6443 Range checking, if turned on, is done on mathematical operations. Array
6444 indices are not checked, since they are often used to index a pointer
6445 that is not itself an array.
6448 @subsubsection @value{GDBN} and C
6450 The @code{set print union} and @code{show print union} commands apply to
6451 the @code{union} type. When set to @samp{on}, any @code{union} that is
6452 inside a @code{struct} or @code{class} is also printed. Otherwise, it
6453 appears as @samp{@{...@}}.
6455 The @code{@@} operator aids in the debugging of dynamic arrays, formed
6456 with pointers and a memory allocation function. @xref{Expressions,
6460 * Debugging C plus plus::
6463 @node Debugging C plus plus
6464 @subsubsection @value{GDBN} features for C++
6466 @cindex commands for C++
6468 Some @value{GDBN} commands are particularly useful with C++, and some are
6469 designed specifically for use with C++. Here is a summary:
6472 @cindex break in overloaded functions
6473 @item @r{breakpoint menus}
6474 When you want a breakpoint in a function whose name is overloaded,
6475 @value{GDBN} breakpoint menus help you specify which function definition
6476 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
6478 @cindex overloading in C++
6479 @item rbreak @var{regex}
6480 Setting breakpoints using regular expressions is helpful for setting
6481 breakpoints on overloaded functions that are not members of any special
6483 @xref{Set Breaks, ,Setting breakpoints}.
6485 @cindex C++ exception handling
6488 Debug C++ exception handling using these commands. @xref{Set
6489 Catchpoints, , Setting catchpoints}.
6492 @item ptype @var{typename}
6493 Print inheritance relationships as well as other information for type
6495 @xref{Symbols, ,Examining the Symbol Table}.
6497 @cindex C++ symbol display
6498 @item set print demangle
6499 @itemx show print demangle
6500 @itemx set print asm-demangle
6501 @itemx show print asm-demangle
6502 Control whether C++ symbols display in their source form, both when
6503 displaying code as C++ source and when displaying disassemblies.
6504 @xref{Print Settings, ,Print settings}.
6506 @item set print object
6507 @itemx show print object
6508 Choose whether to print derived (actual) or declared types of objects.
6509 @xref{Print Settings, ,Print settings}.
6511 @item set print vtbl
6512 @itemx show print vtbl
6513 Control the format for printing virtual function tables.
6514 @xref{Print Settings, ,Print settings}.
6515 (The @code{vtbl} commands do not work on programs compiled with the HP
6516 ANSI C++ compiler (@code{aCC}).)
6518 @kindex set overload-resolution
6519 @cindex overloaded functions, overload resolution
6520 @item set overload-resolution on
6521 Enable overload resolution for C++ expression evaluation. The default
6522 is on. For overloaded functions, @value{GDBN} evaluates the arguments
6523 and searches for a function whose signature matches the argument types,
6524 using the standard C++ conversion rules (see @ref{C plus plus expressions, ,C++
6525 expressions}, for details). If it cannot find a match, it emits a
6528 @item set overload-resolution off
6529 Disable overload resolution for C++ expression evaluation. For
6530 overloaded functions that are not class member functions, @value{GDBN}
6531 chooses the first function of the specified name that it finds in the
6532 symbol table, whether or not its arguments are of the correct type. For
6533 overloaded functions that are class member functions, @value{GDBN}
6534 searches for a function whose signature @emph{exactly} matches the
6537 @item @r{Overloaded symbol names}
6538 You can specify a particular definition of an overloaded symbol, using
6539 the same notation that is used to declare such symbols in C++: type
6540 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
6541 also use the @value{GDBN} command-line word completion facilities to list the
6542 available choices, or to finish the type list for you.
6543 @xref{Completion,, Command completion}, for details on how to do this.
6547 @subsection Modula-2
6549 @cindex Modula-2, @value{GDBN} support
6551 The extensions made to @value{GDBN} to support Modula-2 only support
6552 output from the @sc{gnu} Modula-2 compiler (which is currently being
6553 developed). Other Modula-2 compilers are not currently supported, and
6554 attempting to debug executables produced by them is most likely
6555 to give an error as @value{GDBN} reads in the executable's symbol
6558 @cindex expressions in Modula-2
6560 * M2 Operators:: Built-in operators
6561 * Built-In Func/Proc:: Built-in functions and procedures
6562 * M2 Constants:: Modula-2 constants
6563 * M2 Defaults:: Default settings for Modula-2
6564 * Deviations:: Deviations from standard Modula-2
6565 * M2 Checks:: Modula-2 type and range checks
6566 * M2 Scope:: The scope operators @code{::} and @code{.}
6567 * GDB/M2:: @value{GDBN} and Modula-2
6571 @subsubsection Operators
6572 @cindex Modula-2 operators
6574 Operators must be defined on values of specific types. For instance,
6575 @code{+} is defined on numbers, but not on structures. Operators are
6576 often defined on groups of types. For the purposes of Modula-2, the
6577 following definitions hold:
6582 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
6586 @emph{Character types} consist of @code{CHAR} and its subranges.
6589 @emph{Floating-point types} consist of @code{REAL}.
6592 @emph{Pointer types} consist of anything declared as @code{POINTER TO
6596 @emph{Scalar types} consist of all of the above.
6599 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
6602 @emph{Boolean types} consist of @code{BOOLEAN}.
6606 The following operators are supported, and appear in order of
6607 increasing precedence:
6611 Function argument or array index separator.
6614 Assignment. The value of @var{var} @code{:=} @var{value} is
6618 Less than, greater than on integral, floating-point, or enumerated
6622 Less than or equal to, greater than or equal to
6623 on integral, floating-point and enumerated types, or set inclusion on
6624 set types. Same precedence as @code{<}.
6626 @item =@r{, }<>@r{, }#
6627 Equality and two ways of expressing inequality, valid on scalar types.
6628 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
6629 available for inequality, since @code{#} conflicts with the script
6633 Set membership. Defined on set types and the types of their members.
6634 Same precedence as @code{<}.
6637 Boolean disjunction. Defined on boolean types.
6640 Boolean conjunction. Defined on boolean types.
6643 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
6646 Addition and subtraction on integral and floating-point types, or union
6647 and difference on set types.
6650 Multiplication on integral and floating-point types, or set intersection
6654 Division on floating-point types, or symmetric set difference on set
6655 types. Same precedence as @code{*}.
6658 Integer division and remainder. Defined on integral types. Same
6659 precedence as @code{*}.
6662 Negative. Defined on @code{INTEGER} and @code{REAL} data.
6665 Pointer dereferencing. Defined on pointer types.
6668 Boolean negation. Defined on boolean types. Same precedence as
6672 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
6673 precedence as @code{^}.
6676 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
6679 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
6683 @value{GDBN} and Modula-2 scope operators.
6687 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
6688 treats the use of the operator @code{IN}, or the use of operators
6689 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
6690 @code{<=}, and @code{>=} on sets as an error.
6693 @cindex Modula-2 built-ins
6694 @node Built-In Func/Proc
6695 @subsubsection Built-in functions and procedures
6697 Modula-2 also makes available several built-in procedures and functions.
6698 In describing these, the following metavariables are used:
6703 represents an @code{ARRAY} variable.
6706 represents a @code{CHAR} constant or variable.
6709 represents a variable or constant of integral type.
6712 represents an identifier that belongs to a set. Generally used in the
6713 same function with the metavariable @var{s}. The type of @var{s} should
6714 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
6717 represents a variable or constant of integral or floating-point type.
6720 represents a variable or constant of floating-point type.
6726 represents a variable.
6729 represents a variable or constant of one of many types. See the
6730 explanation of the function for details.
6733 All Modula-2 built-in procedures also return a result, described below.
6737 Returns the absolute value of @var{n}.
6740 If @var{c} is a lower case letter, it returns its upper case
6741 equivalent, otherwise it returns its argument.
6744 Returns the character whose ordinal value is @var{i}.
6747 Decrements the value in the variable @var{v} by one. Returns the new value.
6749 @item DEC(@var{v},@var{i})
6750 Decrements the value in the variable @var{v} by @var{i}. Returns the
6753 @item EXCL(@var{m},@var{s})
6754 Removes the element @var{m} from the set @var{s}. Returns the new
6757 @item FLOAT(@var{i})
6758 Returns the floating point equivalent of the integer @var{i}.
6761 Returns the index of the last member of @var{a}.
6764 Increments the value in the variable @var{v} by one. Returns the new value.
6766 @item INC(@var{v},@var{i})
6767 Increments the value in the variable @var{v} by @var{i}. Returns the
6770 @item INCL(@var{m},@var{s})
6771 Adds the element @var{m} to the set @var{s} if it is not already
6772 there. Returns the new set.
6775 Returns the maximum value of the type @var{t}.
6778 Returns the minimum value of the type @var{t}.
6781 Returns boolean TRUE if @var{i} is an odd number.
6784 Returns the ordinal value of its argument. For example, the ordinal
6785 value of a character is its @sc{ascii} value (on machines supporting the
6786 @sc{ascii} character set). @var{x} must be of an ordered type, which include
6787 integral, character and enumerated types.
6790 Returns the size of its argument. @var{x} can be a variable or a type.
6792 @item TRUNC(@var{r})
6793 Returns the integral part of @var{r}.
6795 @item VAL(@var{t},@var{i})
6796 Returns the member of the type @var{t} whose ordinal value is @var{i}.
6800 @emph{Warning:} Sets and their operations are not yet supported, so
6801 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
6805 @cindex Modula-2 constants
6807 @subsubsection Constants
6809 @value{GDBN} allows you to express the constants of Modula-2 in the following
6815 Integer constants are simply a sequence of digits. When used in an
6816 expression, a constant is interpreted to be type-compatible with the
6817 rest of the expression. Hexadecimal integers are specified by a
6818 trailing @samp{H}, and octal integers by a trailing @samp{B}.
6821 Floating point constants appear as a sequence of digits, followed by a
6822 decimal point and another sequence of digits. An optional exponent can
6823 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
6824 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
6825 digits of the floating point constant must be valid decimal (base 10)
6829 Character constants consist of a single character enclosed by a pair of
6830 like quotes, either single (@code{'}) or double (@code{"}). They may
6831 also be expressed by their ordinal value (their @sc{ascii} value, usually)
6832 followed by a @samp{C}.
6835 String constants consist of a sequence of characters enclosed by a
6836 pair of like quotes, either single (@code{'}) or double (@code{"}).
6837 Escape sequences in the style of C are also allowed. @xref{C
6838 Constants, ,C and C++ constants}, for a brief explanation of escape
6842 Enumerated constants consist of an enumerated identifier.
6845 Boolean constants consist of the identifiers @code{TRUE} and
6849 Pointer constants consist of integral values only.
6852 Set constants are not yet supported.
6856 @subsubsection Modula-2 defaults
6857 @cindex Modula-2 defaults
6859 If type and range checking are set automatically by @value{GDBN}, they
6860 both default to @code{on} whenever the working language changes to
6861 Modula-2. This happens regardless of whether you or @value{GDBN}
6862 selected the working language.
6864 If you allow @value{GDBN} to set the language automatically, then entering
6865 code compiled from a file whose name ends with @file{.mod} sets the
6866 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
6867 the language automatically}, for further details.
6870 @subsubsection Deviations from standard Modula-2
6871 @cindex Modula-2, deviations from
6873 A few changes have been made to make Modula-2 programs easier to debug.
6874 This is done primarily via loosening its type strictness:
6878 Unlike in standard Modula-2, pointer constants can be formed by
6879 integers. This allows you to modify pointer variables during
6880 debugging. (In standard Modula-2, the actual address contained in a
6881 pointer variable is hidden from you; it can only be modified
6882 through direct assignment to another pointer variable or expression that
6883 returned a pointer.)
6886 C escape sequences can be used in strings and characters to represent
6887 non-printable characters. @value{GDBN} prints out strings with these
6888 escape sequences embedded. Single non-printable characters are
6889 printed using the @samp{CHR(@var{nnn})} format.
6892 The assignment operator (@code{:=}) returns the value of its right-hand
6896 All built-in procedures both modify @emph{and} return their argument.
6900 @subsubsection Modula-2 type and range checks
6901 @cindex Modula-2 checks
6904 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
6907 @c FIXME remove warning when type/range checks added
6909 @value{GDBN} considers two Modula-2 variables type equivalent if:
6913 They are of types that have been declared equivalent via a @code{TYPE
6914 @var{t1} = @var{t2}} statement
6917 They have been declared on the same line. (Note: This is true of the
6918 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
6921 As long as type checking is enabled, any attempt to combine variables
6922 whose types are not equivalent is an error.
6924 Range checking is done on all mathematical operations, assignment, array
6925 index bounds, and all built-in functions and procedures.
6928 @subsubsection The scope operators @code{::} and @code{.}
6930 @cindex @code{.}, Modula-2 scope operator
6931 @cindex colon, doubled as scope operator
6933 @vindex colon-colon@r{, in Modula-2}
6934 @c Info cannot handle :: but TeX can.
6937 @vindex ::@r{, in Modula-2}
6940 There are a few subtle differences between the Modula-2 scope operator
6941 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
6946 @var{module} . @var{id}
6947 @var{scope} :: @var{id}
6951 where @var{scope} is the name of a module or a procedure,
6952 @var{module} the name of a module, and @var{id} is any declared
6953 identifier within your program, except another module.
6955 Using the @code{::} operator makes @value{GDBN} search the scope
6956 specified by @var{scope} for the identifier @var{id}. If it is not
6957 found in the specified scope, then @value{GDBN} searches all scopes
6958 enclosing the one specified by @var{scope}.
6960 Using the @code{.} operator makes @value{GDBN} search the current scope for
6961 the identifier specified by @var{id} that was imported from the
6962 definition module specified by @var{module}. With this operator, it is
6963 an error if the identifier @var{id} was not imported from definition
6964 module @var{module}, or if @var{id} is not an identifier in
6968 @subsubsection @value{GDBN} and Modula-2
6970 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
6971 Five subcommands of @code{set print} and @code{show print} apply
6972 specifically to C and C++: @samp{vtbl}, @samp{demangle},
6973 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
6974 apply to C++, and the last to the C @code{union} type, which has no direct
6975 analogue in Modula-2.
6977 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
6978 with any language, is not useful with Modula-2. Its
6979 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
6980 created in Modula-2 as they can in C or C++. However, because an
6981 address can be specified by an integral constant, the construct
6982 @samp{@{@var{type}@}@var{adrexp}} is still useful.
6984 @cindex @code{#} in Modula-2
6985 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
6986 interpreted as the beginning of a comment. Use @code{<>} instead.
6991 The extensions made to @value{GDBN} to support Chill only support output
6992 from the @sc{gnu} Chill compiler. Other Chill compilers are not currently
6993 supported, and attempting to debug executables produced by them is most
6994 likely to give an error as @value{GDBN} reads in the executable's symbol
6997 @c This used to say "... following Chill related topics ...", but since
6998 @c menus are not shown in the printed manual, it would look awkward.
6999 This section covers the Chill related topics and the features
7000 of @value{GDBN} which support these topics.
7003 * How modes are displayed:: How modes are displayed
7004 * Locations:: Locations and their accesses
7005 * Values and their Operations:: Values and their Operations
7006 * Chill type and range checks::
7010 @node How modes are displayed
7011 @subsubsection How modes are displayed
7013 The Chill Datatype- (Mode) support of @value{GDBN} is directly related
7014 with the functionality of the @sc{gnu} Chill compiler, and therefore deviates
7015 slightly from the standard specification of the Chill language. The
7018 @c FIXME: this @table's contents effectively disable @code by using @r
7019 @c on every @item. So why does it need @code?
7021 @item @r{@emph{Discrete modes:}}
7024 @emph{Integer Modes} which are predefined by @code{BYTE, UBYTE, INT,
7027 @emph{Boolean Mode} which is predefined by @code{BOOL},
7029 @emph{Character Mode} which is predefined by @code{CHAR},
7031 @emph{Set Mode} which is displayed by the keyword @code{SET}.
7033 (@value{GDBP}) ptype x
7034 type = SET (karli = 10, susi = 20, fritzi = 100)
7036 If the type is an unnumbered set the set element values are omitted.
7038 @emph{Range Mode} which is displayed by
7040 @code{type = <basemode>(<lower bound> : <upper bound>)}
7042 where @code{<lower bound>, <upper bound>} can be of any discrete literal
7043 expression (e.g. set element names).
7046 @item @r{@emph{Powerset Mode:}}
7047 A Powerset Mode is displayed by the keyword @code{POWERSET} followed by
7048 the member mode of the powerset. The member mode can be any discrete mode.
7050 (@value{GDBP}) ptype x
7051 type = POWERSET SET (egon, hugo, otto)
7054 @item @r{@emph{Reference Modes:}}
7057 @emph{Bound Reference Mode} which is displayed by the keyword @code{REF}
7058 followed by the mode name to which the reference is bound.
7060 @emph{Free Reference Mode} which is displayed by the keyword @code{PTR}.
7063 @item @r{@emph{Procedure mode}}
7064 The procedure mode is displayed by @code{type = PROC(<parameter list>)
7065 <return mode> EXCEPTIONS (<exception list>)}. The @code{<parameter
7066 list>} is a list of the parameter modes. @code{<return mode>} indicates
7067 the mode of the result of the procedure if any. The exceptionlist lists
7068 all possible exceptions which can be raised by the procedure.
7071 @item @r{@emph{Instance mode}}
7072 The instance mode is represented by a structure, which has a static
7073 type, and is therefore not really of interest.
7076 @item @r{@emph{Synchronization Modes:}}
7079 @emph{Event Mode} which is displayed by
7081 @code{EVENT (<event length>)}
7083 where @code{(<event length>)} is optional.
7085 @emph{Buffer Mode} which is displayed by
7087 @code{BUFFER (<buffer length>)<buffer element mode>}
7089 where @code{(<buffer length>)} is optional.
7092 @item @r{@emph{Timing Modes:}}
7095 @emph{Duration Mode} which is predefined by @code{DURATION}
7097 @emph{Absolute Time Mode} which is predefined by @code{TIME}
7100 @item @r{@emph{Real Modes:}}
7101 Real Modes are predefined with @code{REAL} and @code{LONG_REAL}.
7103 @item @r{@emph{String Modes:}}
7106 @emph{Character String Mode} which is displayed by
7108 @code{CHARS(<string length>)}
7110 followed by the keyword @code{VARYING} if the String Mode is a varying
7113 @emph{Bit String Mode} which is displayed by
7120 @item @r{@emph{Array Mode:}}
7121 The Array Mode is displayed by the keyword @code{ARRAY(<range>)}
7122 followed by the element mode (which may in turn be an array mode).
7124 (@value{GDBP}) ptype x
7127 SET (karli = 10, susi = 20, fritzi = 100)
7130 @item @r{@emph{Structure Mode}}
7131 The Structure mode is displayed by the keyword @code{STRUCT(<field
7132 list>)}. The @code{<field list>} consists of names and modes of fields
7133 of the structure. Variant structures have the keyword @code{CASE <field>
7134 OF <variant fields> ESAC} in their field list. Since the current version
7135 of the GNU Chill compiler doesn't implement tag processing (no runtime
7136 checks of variant fields, and therefore no debugging info), the output
7137 always displays all variant fields.
7139 (@value{GDBP}) ptype str
7154 @subsubsection Locations and their accesses
7156 A location in Chill is an object which can contain values.
7158 A value of a location is generally accessed by the (declared) name of
7159 the location. The output conforms to the specification of values in
7160 Chill programs. How values are specified
7161 is the topic of the next section, @ref{Values and their Operations}.
7163 The pseudo-location @code{RESULT} (or @code{result}) can be used to
7164 display or change the result of a currently-active procedure:
7171 This does the same as the Chill action @code{RESULT EXPR} (which
7172 is not available in @value{GDBN}).
7174 Values of reference mode locations are printed by @code{PTR(<hex
7175 value>)} in case of a free reference mode, and by @code{(REF <reference
7176 mode>) (<hex-value>)} in case of a bound reference. @code{<hex value>}
7177 represents the address where the reference points to. To access the
7178 value of the location referenced by the pointer, use the dereference
7181 Values of procedure mode locations are displayed by
7184 (<argument modes> ) <return mode> @} <address> <name of procedure
7187 @code{<argument modes>} is a list of modes according to the parameter
7188 specification of the procedure and @code{<address>} shows the address of
7192 Locations of instance modes are displayed just like a structure with two
7193 fields specifying the @emph{process type} and the @emph{copy number} of
7194 the investigated instance location@footnote{This comes from the current
7195 implementation of instances. They are implemented as a structure (no
7196 na). The output should be something like @code{[<name of the process>;
7197 <instance number>]}.}. The field names are @code{__proc_type} and
7200 Locations of synchronization modes are displayed like a structure with
7201 the field name @code{__event_data} in case of a event mode location, and
7202 like a structure with the field @code{__buffer_data} in case of a buffer
7203 mode location (refer to previous paragraph).
7205 Structure Mode locations are printed by @code{[.<field name>: <value>,
7206 ...]}. The @code{<field name>} corresponds to the structure mode
7207 definition and the layout of @code{<value>} varies depending of the mode
7208 of the field. If the investigated structure mode location is of variant
7209 structure mode, the variant parts of the structure are enclosed in curled
7210 braces (@samp{@{@}}). Fields enclosed by @samp{@{,@}} are residing
7211 on the same memory location and represent the current values of the
7212 memory location in their specific modes. Since no tag processing is done
7213 all variants are displayed. A variant field is printed by
7214 @code{(<variant name>) = .<field name>: <value>}. (who implements the
7217 (@value{GDBP}) print str1 $4 = [.as: 0, .bs: karli, .<TAG>: { (karli) =
7218 [.cs: []], (susi) = [.ds: susi]}]
7222 Substructures of string mode-, array mode- or structure mode-values
7223 (e.g. array slices, fields of structure locations) are accessed using
7224 certain operations which are described in the next section, @ref{Values
7225 and their Operations}.
7227 A location value may be interpreted as having a different mode using the
7228 location conversion. This mode conversion is written as @code{<mode
7229 name>(<location>)}. The user has to consider that the sizes of the modes
7230 have to be equal otherwise an error occurs. Furthermore, no range
7231 checking of the location against the destination mode is performed, and
7232 therefore the result can be quite confusing.
7235 (@value{GDBP}) print int (s(3 up 4)) XXX TO be filled in !! XXX
7238 @node Values and their Operations
7239 @subsubsection Values and their Operations
7241 Values are used to alter locations, to investigate complex structures in
7242 more detail or to filter relevant information out of a large amount of
7243 data. There are several (mode dependent) operations defined which enable
7244 such investigations. These operations are not only applicable to
7245 constant values but also to locations, which can become quite useful
7246 when debugging complex structures. During parsing the command line
7247 (e.g. evaluating an expression) @value{GDBN} treats location names as
7248 the values behind these locations.
7250 This section describes how values have to be specified and which
7251 operations are legal to be used with such values.
7254 @item Literal Values
7255 Literal values are specified in the same manner as in @sc{gnu} Chill programs.
7256 For detailed specification refer to the @sc{gnu} Chill implementation Manual
7258 @c FIXME: if the Chill Manual is a Texinfo documents, the above should
7259 @c be converted to a @ref.
7264 @emph{Integer Literals} are specified in the same manner as in Chill
7265 programs (refer to the Chill Standard z200/88 chpt 5.2.4.2)
7267 @emph{Boolean Literals} are defined by @code{TRUE} and @code{FALSE}.
7269 @emph{Character Literals} are defined by @code{'<character>'}. (e.g.
7272 @emph{Set Literals} are defined by a name which was specified in a set
7273 mode. The value delivered by a Set Literal is the set value. This is
7274 comparable to an enumeration in C/C++ language.
7276 @emph{Emptiness Literal} is predefined by @code{NULL}. The value of the
7277 emptiness literal delivers either the empty reference value, the empty
7278 procedure value or the empty instance value.
7281 @emph{Character String Literals} are defined by a sequence of characters
7282 enclosed in single- or double quotes. If a single- or double quote has
7283 to be part of the string literal it has to be stuffed (specified twice).
7285 @emph{Bitstring Literals} are specified in the same manner as in Chill
7286 programs (refer z200/88 chpt 5.2.4.8).
7288 @emph{Floating point literals} are specified in the same manner as in
7289 (gnu-)Chill programs (refer @sc{gnu} Chill implementation Manual chapter 1.5).
7294 A tuple is specified by @code{<mode name>[<tuple>]}, where @code{<mode
7295 name>} can be omitted if the mode of the tuple is unambiguous. This
7296 unambiguity is derived from the context of a evaluated expression.
7297 @code{<tuple>} can be one of the following:
7300 @item @emph{Powerset Tuple}
7301 @item @emph{Array Tuple}
7302 @item @emph{Structure Tuple}
7303 Powerset tuples, array tuples and structure tuples are specified in the
7304 same manner as in Chill programs refer to z200/88 chpt 5.2.5.
7307 @item String Element Value
7308 A string element value is specified by
7310 @code{<string value>(<index>)}
7312 where @code{<index>} is a integer expression. It delivers a character
7313 value which is equivalent to the character indexed by @code{<index>} in
7316 @item String Slice Value
7317 A string slice value is specified by @code{<string value>(<slice
7318 spec>)}, where @code{<slice spec>} can be either a range of integer
7319 expressions or specified by @code{<start expr> up <size>}.
7320 @code{<size>} denotes the number of elements which the slice contains.
7321 The delivered value is a string value, which is part of the specified
7324 @item Array Element Values
7325 An array element value is specified by @code{<array value>(<expr>)} and
7326 delivers a array element value of the mode of the specified array.
7328 @item Array Slice Values
7329 An array slice is specified by @code{<array value>(<slice spec>)}, where
7330 @code{<slice spec>} can be either a range specified by expressions or by
7331 @code{<start expr> up <size>}. @code{<size>} denotes the number of
7332 arrayelements the slice contains. The delivered value is an array value
7333 which is part of the specified array.
7335 @item Structure Field Values
7336 A structure field value is derived by @code{<structure value>.<field
7337 name>}, where @code{<field name>} indicates the name of a field specified
7338 in the mode definition of the structure. The mode of the delivered value
7339 corresponds to this mode definition in the structure definition.
7341 @item Procedure Call Value
7342 The procedure call value is derived from the return value of the
7343 procedure@footnote{If a procedure call is used for instance in an
7344 expression, then this procedure is called with all its side
7345 effects. This can lead to confusing results if used carelessly.}.
7347 Values of duration mode locations are represented by @code{ULONG} literals.
7349 Values of time mode locations appear as
7351 @code{TIME(<secs>:<nsecs>)}
7356 This is not implemented yet:
7357 @item Built-in Value
7359 The following built in functions are provided:
7371 @item @code{UPPER()}
7372 @item @code{LOWER()}
7373 @item @code{LENGTH()}
7377 @item @code{ARCSIN()}
7378 @item @code{ARCCOS()}
7379 @item @code{ARCTAN()}
7386 For a detailed description refer to the GNU Chill implementation manual
7390 @item Zero-adic Operator Value
7391 The zero-adic operator value is derived from the instance value for the
7392 current active process.
7394 @item Expression Values
7395 The value delivered by an expression is the result of the evaluation of
7396 the specified expression. If there are error conditions (mode
7397 incompatibility, etc.) the evaluation of expressions is aborted with a
7398 corresponding error message. Expressions may be parenthesised which
7399 causes the evaluation of this expression before any other expression
7400 which uses the result of the parenthesised expression. The following
7401 operators are supported by @value{GDBN}:
7404 @item @code{OR, ORIF, XOR}
7405 @itemx @code{AND, ANDIF}
7407 Logical operators defined over operands of boolean mode.
7410 Equality and inequality operators defined over all modes.
7414 Relational operators defined over predefined modes.
7417 @itemx @code{*, /, MOD, REM}
7418 Arithmetic operators defined over predefined modes.
7421 Change sign operator.
7424 String concatenation operator.
7427 String repetition operator.
7430 Referenced location operator which can be used either to take the
7431 address of a location (@code{->loc}), or to dereference a reference
7432 location (@code{loc->}).
7434 @item @code{OR, XOR}
7437 Powerset and bitstring operators.
7441 Powerset inclusion operators.
7444 Membership operator.
7448 @node Chill type and range checks
7449 @subsubsection Chill type and range checks
7451 @value{GDBN} considers two Chill variables mode equivalent if the sizes
7452 of the two modes are equal. This rule applies recursively to more
7453 complex datatypes which means that complex modes are treated
7454 equivalent if all element modes (which also can be complex modes like
7455 structures, arrays, etc.) have the same size.
7457 Range checking is done on all mathematical operations, assignment, array
7458 index bounds and all built in procedures.
7460 Strong type checks are forced using the @value{GDBN} command @code{set
7461 check strong}. This enforces strong type and range checks on all
7462 operations where Chill constructs are used (expressions, built in
7463 functions, etc.) in respect to the semantics as defined in the z.200
7464 language specification.
7466 All checks can be disabled by the @value{GDBN} command @code{set check
7470 @c Deviations from the Chill Standard Z200/88
7471 see last paragraph ?
7474 @node Chill defaults
7475 @subsubsection Chill defaults
7477 If type and range checking are set automatically by @value{GDBN}, they
7478 both default to @code{on} whenever the working language changes to
7479 Chill. This happens regardless of whether you or @value{GDBN}
7480 selected the working language.
7482 If you allow @value{GDBN} to set the language automatically, then entering
7483 code compiled from a file whose name ends with @file{.ch} sets the
7484 working language to Chill. @xref{Automatically, ,Having @value{GDBN} set
7485 the language automatically}, for further details.
7488 @chapter Examining the Symbol Table
7490 The commands described in this chapter allow you to inquire about the
7491 symbols (names of variables, functions and types) defined in your
7492 program. This information is inherent in the text of your program and
7493 does not change as your program executes. @value{GDBN} finds it in your
7494 program's symbol table, in the file indicated when you started @value{GDBN}
7495 (@pxref{File Options, ,Choosing files}), or by one of the
7496 file-management commands (@pxref{Files, ,Commands to specify files}).
7498 @cindex symbol names
7499 @cindex names of symbols
7500 @cindex quoting names
7501 Occasionally, you may need to refer to symbols that contain unusual
7502 characters, which @value{GDBN} ordinarily treats as word delimiters. The
7503 most frequent case is in referring to static variables in other
7504 source files (@pxref{Variables,,Program variables}). File names
7505 are recorded in object files as debugging symbols, but @value{GDBN} would
7506 ordinarily parse a typical file name, like @file{foo.c}, as the three words
7507 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
7508 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
7515 looks up the value of @code{x} in the scope of the file @file{foo.c}.
7518 @kindex info address
7519 @item info address @var{symbol}
7520 Describe where the data for @var{symbol} is stored. For a register
7521 variable, this says which register it is kept in. For a non-register
7522 local variable, this prints the stack-frame offset at which the variable
7525 Note the contrast with @samp{print &@var{symbol}}, which does not work
7526 at all for a register variable, and for a stack local variable prints
7527 the exact address of the current instantiation of the variable.
7530 @item whatis @var{expr}
7531 Print the data type of expression @var{expr}. @var{expr} is not
7532 actually evaluated, and any side-effecting operations (such as
7533 assignments or function calls) inside it do not take place.
7534 @xref{Expressions, ,Expressions}.
7537 Print the data type of @code{$}, the last value in the value history.
7540 @item ptype @var{typename}
7541 Print a description of data type @var{typename}. @var{typename} may be
7542 the name of a type, or for C code it may have the form @samp{class
7543 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
7544 @var{union-tag}} or @samp{enum @var{enum-tag}}.
7546 @item ptype @var{expr}
7548 Print a description of the type of expression @var{expr}. @code{ptype}
7549 differs from @code{whatis} by printing a detailed description, instead
7550 of just the name of the type.
7552 For example, for this variable declaration:
7555 struct complex @{double real; double imag;@} v;
7559 the two commands give this output:
7563 (@value{GDBP}) whatis v
7564 type = struct complex
7565 (@value{GDBP}) ptype v
7566 type = struct complex @{
7574 As with @code{whatis}, using @code{ptype} without an argument refers to
7575 the type of @code{$}, the last value in the value history.
7578 @item info types @var{regexp}
7580 Print a brief description of all types whose names match @var{regexp}
7581 (or all types in your program, if you supply no argument). Each
7582 complete typename is matched as though it were a complete line; thus,
7583 @samp{i type value} gives information on all types in your program whose
7584 names include the string @code{value}, but @samp{i type ^value$} gives
7585 information only on types whose complete name is @code{value}.
7587 This command differs from @code{ptype} in two ways: first, like
7588 @code{whatis}, it does not print a detailed description; second, it
7589 lists all source files where a type is defined.
7593 Show the name of the current source file---that is, the source file for
7594 the function containing the current point of execution---and the language
7597 @kindex info sources
7599 Print the names of all source files in your program for which there is
7600 debugging information, organized into two lists: files whose symbols
7601 have already been read, and files whose symbols will be read when needed.
7603 @kindex info functions
7604 @item info functions
7605 Print the names and data types of all defined functions.
7607 @item info functions @var{regexp}
7608 Print the names and data types of all defined functions
7609 whose names contain a match for regular expression @var{regexp}.
7610 Thus, @samp{info fun step} finds all functions whose names
7611 include @code{step}; @samp{info fun ^step} finds those whose names
7612 start with @code{step}.
7614 @kindex info variables
7615 @item info variables
7616 Print the names and data types of all variables that are declared
7617 outside of functions (i.e., excluding local variables).
7619 @item info variables @var{regexp}
7620 Print the names and data types of all variables (except for local
7621 variables) whose names contain a match for regular expression
7625 This was never implemented.
7626 @kindex info methods
7628 @itemx info methods @var{regexp}
7629 The @code{info methods} command permits the user to examine all defined
7630 methods within C++ program, or (with the @var{regexp} argument) a
7631 specific set of methods found in the various C++ classes. Many
7632 C++ classes provide a large number of methods. Thus, the output
7633 from the @code{ptype} command can be overwhelming and hard to use. The
7634 @code{info-methods} command filters the methods, printing only those
7635 which match the regular-expression @var{regexp}.
7638 @cindex reloading symbols
7639 Some systems allow individual object files that make up your program to
7640 be replaced without stopping and restarting your program. For example,
7641 in VxWorks you can simply recompile a defective object file and keep on
7642 running. If you are running on one of these systems, you can allow
7643 @value{GDBN} to reload the symbols for automatically relinked modules:
7646 @kindex set symbol-reloading
7647 @item set symbol-reloading on
7648 Replace symbol definitions for the corresponding source file when an
7649 object file with a particular name is seen again.
7651 @item set symbol-reloading off
7652 Do not replace symbol definitions when encountering object files of the
7653 same name more than once. This is the default state; if you are not
7654 running on a system that permits automatic relinking of modules, you
7655 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
7656 may discard symbols when linking large programs, that may contain
7657 several modules (from different directories or libraries) with the same
7660 @kindex show symbol-reloading
7661 @item show symbol-reloading
7662 Show the current @code{on} or @code{off} setting.
7665 @kindex set opaque-type-resolution
7666 @item set opaque-type-resolution on
7667 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
7668 declared as a pointer to a @code{struct}, @code{class}, or
7669 @code{union}---for example, @code{struct MyType *}---that is used in one
7670 source file although the full declaration of @code{struct MyType} is in
7671 another source file. The default is on.
7673 A change in the setting of this subcommand will not take effect until
7674 the next time symbols for a file are loaded.
7676 @item set opaque-type-resolution off
7677 Tell @value{GDBN} not to resolve opaque types. In this case, the type
7678 is printed as follows:
7680 @{<no data fields>@}
7683 @kindex show opaque-type-resolution
7684 @item show opaque-type-resolution
7685 Show whether opaque types are resolved or not.
7687 @kindex maint print symbols
7689 @kindex maint print psymbols
7690 @cindex partial symbol dump
7691 @item maint print symbols @var{filename}
7692 @itemx maint print psymbols @var{filename}
7693 @itemx maint print msymbols @var{filename}
7694 Write a dump of debugging symbol data into the file @var{filename}.
7695 These commands are used to debug the @value{GDBN} symbol-reading code. Only
7696 symbols with debugging data are included. If you use @samp{maint print
7697 symbols}, @value{GDBN} includes all the symbols for which it has already
7698 collected full details: that is, @var{filename} reflects symbols for
7699 only those files whose symbols @value{GDBN} has read. You can use the
7700 command @code{info sources} to find out which files these are. If you
7701 use @samp{maint print psymbols} instead, the dump shows information about
7702 symbols that @value{GDBN} only knows partially---that is, symbols defined in
7703 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
7704 @samp{maint print msymbols} dumps just the minimal symbol information
7705 required for each object file from which @value{GDBN} has read some symbols.
7706 @xref{Files, ,Commands to specify files}, for a discussion of how
7707 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
7711 @chapter Altering Execution
7713 Once you think you have found an error in your program, you might want to
7714 find out for certain whether correcting the apparent error would lead to
7715 correct results in the rest of the run. You can find the answer by
7716 experiment, using the @value{GDBN} features for altering execution of the
7719 For example, you can store new values into variables or memory
7720 locations, give your program a signal, restart it at a different
7721 address, or even return prematurely from a function.
7724 * Assignment:: Assignment to variables
7725 * Jumping:: Continuing at a different address
7726 * Signaling:: Giving your program a signal
7727 * Returning:: Returning from a function
7728 * Calling:: Calling your program's functions
7729 * Patching:: Patching your program
7733 @section Assignment to variables
7736 @cindex setting variables
7737 To alter the value of a variable, evaluate an assignment expression.
7738 @xref{Expressions, ,Expressions}. For example,
7745 stores the value 4 into the variable @code{x}, and then prints the
7746 value of the assignment expression (which is 4).
7747 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
7748 information on operators in supported languages.
7750 @kindex set variable
7751 @cindex variables, setting
7752 If you are not interested in seeing the value of the assignment, use the
7753 @code{set} command instead of the @code{print} command. @code{set} is
7754 really the same as @code{print} except that the expression's value is
7755 not printed and is not put in the value history (@pxref{Value History,
7756 ,Value history}). The expression is evaluated only for its effects.
7758 If the beginning of the argument string of the @code{set} command
7759 appears identical to a @code{set} subcommand, use the @code{set
7760 variable} command instead of just @code{set}. This command is identical
7761 to @code{set} except for its lack of subcommands. For example, if your
7762 program has a variable @code{width}, you get an error if you try to set
7763 a new value with just @samp{set width=13}, because @value{GDBN} has the
7764 command @code{set width}:
7767 (@value{GDBP}) whatis width
7769 (@value{GDBP}) p width
7771 (@value{GDBP}) set width=47
7772 Invalid syntax in expression.
7776 The invalid expression, of course, is @samp{=47}. In
7777 order to actually set the program's variable @code{width}, use
7780 (@value{GDBP}) set var width=47
7783 Because the @code{set} command has many subcommands that can conflict
7784 with the names of program variables, it is a good idea to use the
7785 @code{set variable} command instead of just @code{set}. For example, if
7786 your program has a variable @code{g}, you run into problems if you try
7787 to set a new value with just @samp{set g=4}, because @value{GDBN} has
7788 the command @code{set gnutarget}, abbreviated @code{set g}:
7792 (@value{GDBP}) whatis g
7796 (@value{GDBP}) set g=4
7800 The program being debugged has been started already.
7801 Start it from the beginning? (y or n) y
7802 Starting program: /home/smith/cc_progs/a.out
7803 "/home/smith/cc_progs/a.out": can't open to read symbols:
7805 (@value{GDBP}) show g
7806 The current BFD target is "=4".
7811 The program variable @code{g} did not change, and you silently set the
7812 @code{gnutarget} to an invalid value. In order to set the variable
7816 (@value{GDBP}) set var g=4
7819 @value{GDBN} allows more implicit conversions in assignments than C; you can
7820 freely store an integer value into a pointer variable or vice versa,
7821 and you can convert any structure to any other structure that is the
7822 same length or shorter.
7823 @comment FIXME: how do structs align/pad in these conversions?
7824 @comment /doc@cygnus.com 18dec1990
7826 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
7827 construct to generate a value of specified type at a specified address
7828 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
7829 to memory location @code{0x83040} as an integer (which implies a certain size
7830 and representation in memory), and
7833 set @{int@}0x83040 = 4
7837 stores the value 4 into that memory location.
7840 @section Continuing at a different address
7842 Ordinarily, when you continue your program, you do so at the place where
7843 it stopped, with the @code{continue} command. You can instead continue at
7844 an address of your own choosing, with the following commands:
7848 @item jump @var{linespec}
7849 Resume execution at line @var{linespec}. Execution stops again
7850 immediately if there is a breakpoint there. @xref{List, ,Printing
7851 source lines}, for a description of the different forms of
7852 @var{linespec}. It is common practice to use the @code{tbreak} command
7853 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
7856 The @code{jump} command does not change the current stack frame, or
7857 the stack pointer, or the contents of any memory location or any
7858 register other than the program counter. If line @var{linespec} is in
7859 a different function from the one currently executing, the results may
7860 be bizarre if the two functions expect different patterns of arguments or
7861 of local variables. For this reason, the @code{jump} command requests
7862 confirmation if the specified line is not in the function currently
7863 executing. However, even bizarre results are predictable if you are
7864 well acquainted with the machine-language code of your program.
7866 @item jump *@var{address}
7867 Resume execution at the instruction at address @var{address}.
7870 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
7871 On many systems, you can get much the same effect as the @code{jump}
7872 command by storing a new value into the register @code{$pc}. The
7873 difference is that this does not start your program running; it only
7874 changes the address of where it @emph{will} run when you continue. For
7882 makes the next @code{continue} command or stepping command execute at
7883 address @code{0x485}, rather than at the address where your program stopped.
7884 @xref{Continuing and Stepping, ,Continuing and stepping}.
7886 The most common occasion to use the @code{jump} command is to back
7887 up---perhaps with more breakpoints set---over a portion of a program
7888 that has already executed, in order to examine its execution in more
7893 @section Giving your program a signal
7897 @item signal @var{signal}
7898 Resume execution where your program stopped, but immediately give it the
7899 signal @var{signal}. @var{signal} can be the name or the number of a
7900 signal. For example, on many systems @code{signal 2} and @code{signal
7901 SIGINT} are both ways of sending an interrupt signal.
7903 Alternatively, if @var{signal} is zero, continue execution without
7904 giving a signal. This is useful when your program stopped on account of
7905 a signal and would ordinary see the signal when resumed with the
7906 @code{continue} command; @samp{signal 0} causes it to resume without a
7909 @code{signal} does not repeat when you press @key{RET} a second time
7910 after executing the command.
7914 Invoking the @code{signal} command is not the same as invoking the
7915 @code{kill} utility from the shell. Sending a signal with @code{kill}
7916 causes @value{GDBN} to decide what to do with the signal depending on
7917 the signal handling tables (@pxref{Signals}). The @code{signal} command
7918 passes the signal directly to your program.
7922 @section Returning from a function
7925 @cindex returning from a function
7928 @itemx return @var{expression}
7929 You can cancel execution of a function call with the @code{return}
7930 command. If you give an
7931 @var{expression} argument, its value is used as the function's return
7935 When you use @code{return}, @value{GDBN} discards the selected stack frame
7936 (and all frames within it). You can think of this as making the
7937 discarded frame return prematurely. If you wish to specify a value to
7938 be returned, give that value as the argument to @code{return}.
7940 This pops the selected stack frame (@pxref{Selection, ,Selecting a
7941 frame}), and any other frames inside of it, leaving its caller as the
7942 innermost remaining frame. That frame becomes selected. The
7943 specified value is stored in the registers used for returning values
7946 The @code{return} command does not resume execution; it leaves the
7947 program stopped in the state that would exist if the function had just
7948 returned. In contrast, the @code{finish} command (@pxref{Continuing
7949 and Stepping, ,Continuing and stepping}) resumes execution until the
7950 selected stack frame returns naturally.
7953 @section Calling program functions
7955 @cindex calling functions
7958 @item call @var{expr}
7959 Evaluate the expression @var{expr} without displaying @code{void}
7963 You can use this variant of the @code{print} command if you want to
7964 execute a function from your program, but without cluttering the output
7965 with @code{void} returned values. If the result is not void, it
7966 is printed and saved in the value history.
7968 For the A29K, a user-controlled variable @code{call_scratch_address},
7969 specifies the location of a scratch area to be used when @value{GDBN}
7970 calls a function in the target. This is necessary because the usual
7971 method of putting the scratch area on the stack does not work in systems
7972 that have separate instruction and data spaces.
7975 @section Patching programs
7977 @cindex patching binaries
7978 @cindex writing into executables
7979 @cindex writing into corefiles
7981 By default, @value{GDBN} opens the file containing your program's
7982 executable code (or the corefile) read-only. This prevents accidental
7983 alterations to machine code; but it also prevents you from intentionally
7984 patching your program's binary.
7986 If you'd like to be able to patch the binary, you can specify that
7987 explicitly with the @code{set write} command. For example, you might
7988 want to turn on internal debugging flags, or even to make emergency
7994 @itemx set write off
7995 If you specify @samp{set write on}, @value{GDBN} opens executable and
7996 core files for both reading and writing; if you specify @samp{set write
7997 off} (the default), @value{GDBN} opens them read-only.
7999 If you have already loaded a file, you must load it again (using the
8000 @code{exec-file} or @code{core-file} command) after changing @code{set
8001 write}, for your new setting to take effect.
8005 Display whether executable files and core files are opened for writing
8010 @chapter @value{GDBN} Files
8012 @value{GDBN} needs to know the file name of the program to be debugged,
8013 both in order to read its symbol table and in order to start your
8014 program. To debug a core dump of a previous run, you must also tell
8015 @value{GDBN} the name of the core dump file.
8018 * Files:: Commands to specify files
8019 * Symbol Errors:: Errors reading symbol files
8023 @section Commands to specify files
8025 @cindex symbol table
8026 @cindex core dump file
8028 You may want to specify executable and core dump file names. The usual
8029 way to do this is at start-up time, using the arguments to
8030 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
8031 Out of @value{GDBN}}).
8033 Occasionally it is necessary to change to a different file during a
8034 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
8035 a file you want to use. In these situations the @value{GDBN} commands
8036 to specify new files are useful.
8039 @cindex executable file
8041 @item file @var{filename}
8042 Use @var{filename} as the program to be debugged. It is read for its
8043 symbols and for the contents of pure memory. It is also the program
8044 executed when you use the @code{run} command. If you do not specify a
8045 directory and the file is not found in the @value{GDBN} working directory,
8046 @value{GDBN} uses the environment variable @code{PATH} as a list of
8047 directories to search, just as the shell does when looking for a program
8048 to run. You can change the value of this variable, for both @value{GDBN}
8049 and your program, using the @code{path} command.
8051 On systems with memory-mapped files, an auxiliary file named
8052 @file{@var{filename}.syms} may hold symbol table information for
8053 @var{filename}. If so, @value{GDBN} maps in the symbol table from
8054 @file{@var{filename}.syms}, starting up more quickly. See the
8055 descriptions of the file options @samp{-mapped} and @samp{-readnow}
8056 (available on the command line, and with the commands @code{file},
8057 @code{symbol-file}, or @code{add-symbol-file}, described below),
8058 for more information.
8061 @code{file} with no argument makes @value{GDBN} discard any information it
8062 has on both executable file and the symbol table.
8065 @item exec-file @r{[} @var{filename} @r{]}
8066 Specify that the program to be run (but not the symbol table) is found
8067 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
8068 if necessary to locate your program. Omitting @var{filename} means to
8069 discard information on the executable file.
8072 @item symbol-file @r{[} @var{filename} @r{]}
8073 Read symbol table information from file @var{filename}. @code{PATH} is
8074 searched when necessary. Use the @code{file} command to get both symbol
8075 table and program to run from the same file.
8077 @code{symbol-file} with no argument clears out @value{GDBN} information on your
8078 program's symbol table.
8080 The @code{symbol-file} command causes @value{GDBN} to forget the contents
8081 of its convenience variables, the value history, and all breakpoints and
8082 auto-display expressions. This is because they may contain pointers to
8083 the internal data recording symbols and data types, which are part of
8084 the old symbol table data being discarded inside @value{GDBN}.
8086 @code{symbol-file} does not repeat if you press @key{RET} again after
8089 When @value{GDBN} is configured for a particular environment, it
8090 understands debugging information in whatever format is the standard
8091 generated for that environment; you may use either a @sc{gnu} compiler, or
8092 other compilers that adhere to the local conventions.
8093 Best results are usually obtained from @sc{gnu} compilers; for example,
8094 using @code{@value{GCC}} you can generate debugging information for
8097 For most kinds of object files, with the exception of old SVR3 systems
8098 using COFF, the @code{symbol-file} command does not normally read the
8099 symbol table in full right away. Instead, it scans the symbol table
8100 quickly to find which source files and which symbols are present. The
8101 details are read later, one source file at a time, as they are needed.
8103 The purpose of this two-stage reading strategy is to make @value{GDBN}
8104 start up faster. For the most part, it is invisible except for
8105 occasional pauses while the symbol table details for a particular source
8106 file are being read. (The @code{set verbose} command can turn these
8107 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
8108 warnings and messages}.)
8110 We have not implemented the two-stage strategy for COFF yet. When the
8111 symbol table is stored in COFF format, @code{symbol-file} reads the
8112 symbol table data in full right away. Note that ``stabs-in-COFF''
8113 still does the two-stage strategy, since the debug info is actually
8117 @cindex reading symbols immediately
8118 @cindex symbols, reading immediately
8120 @cindex memory-mapped symbol file
8121 @cindex saving symbol table
8122 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8123 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8124 You can override the @value{GDBN} two-stage strategy for reading symbol
8125 tables by using the @samp{-readnow} option with any of the commands that
8126 load symbol table information, if you want to be sure @value{GDBN} has the
8127 entire symbol table available.
8129 If memory-mapped files are available on your system through the
8130 @code{mmap} system call, you can use another option, @samp{-mapped}, to
8131 cause @value{GDBN} to write the symbols for your program into a reusable
8132 file. Future @value{GDBN} debugging sessions map in symbol information
8133 from this auxiliary symbol file (if the program has not changed), rather
8134 than spending time reading the symbol table from the executable
8135 program. Using the @samp{-mapped} option has the same effect as
8136 starting @value{GDBN} with the @samp{-mapped} command-line option.
8138 You can use both options together, to make sure the auxiliary symbol
8139 file has all the symbol information for your program.
8141 The auxiliary symbol file for a program called @var{myprog} is called
8142 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
8143 than the corresponding executable), @value{GDBN} always attempts to use
8144 it when you debug @var{myprog}; no special options or commands are
8147 The @file{.syms} file is specific to the host machine where you run
8148 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
8149 symbol table. It cannot be shared across multiple host platforms.
8151 @c FIXME: for now no mention of directories, since this seems to be in
8152 @c flux. 13mar1992 status is that in theory GDB would look either in
8153 @c current dir or in same dir as myprog; but issues like competing
8154 @c GDB's, or clutter in system dirs, mean that in practice right now
8155 @c only current dir is used. FFish says maybe a special GDB hierarchy
8156 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
8161 @item core-file @r{[} @var{filename} @r{]}
8162 Specify the whereabouts of a core dump file to be used as the ``contents
8163 of memory''. Traditionally, core files contain only some parts of the
8164 address space of the process that generated them; @value{GDBN} can access the
8165 executable file itself for other parts.
8167 @code{core-file} with no argument specifies that no core file is
8170 Note that the core file is ignored when your program is actually running
8171 under @value{GDBN}. So, if you have been running your program and you
8172 wish to debug a core file instead, you must kill the subprocess in which
8173 the program is running. To do this, use the @code{kill} command
8174 (@pxref{Kill Process, ,Killing the child process}).
8176 @kindex add-symbol-file
8177 @cindex dynamic linking
8178 @item add-symbol-file @var{filename} @var{address}
8179 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8180 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address}
8181 The @code{add-symbol-file} command reads additional symbol table
8182 information from the file @var{filename}. You would use this command
8183 when @var{filename} has been dynamically loaded (by some other means)
8184 into the program that is running. @var{address} should be the memory
8185 address at which the file has been loaded; @value{GDBN} cannot figure
8186 this out for itself. You can additionally specify an arbitrary number
8187 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
8188 section name and base address for that section. You can specify any
8189 @var{address} as an expression.
8191 The symbol table of the file @var{filename} is added to the symbol table
8192 originally read with the @code{symbol-file} command. You can use the
8193 @code{add-symbol-file} command any number of times; the new symbol data
8194 thus read keeps adding to the old. To discard all old symbol data
8195 instead, use the @code{symbol-file} command without any arguments.
8197 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
8199 You can use the @samp{-mapped} and @samp{-readnow} options just as with
8200 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
8201 table information for @var{filename}.
8203 @kindex add-shared-symbol-file
8204 @item add-shared-symbol-file
8205 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
8206 operating system for the Motorola 88k. @value{GDBN} automatically looks for
8207 shared libraries, however if @value{GDBN} does not find yours, you can run
8208 @code{add-shared-symbol-file}. It takes no arguments.
8212 The @code{section} command changes the base address of section SECTION of
8213 the exec file to ADDR. This can be used if the exec file does not contain
8214 section addresses, (such as in the a.out format), or when the addresses
8215 specified in the file itself are wrong. Each section must be changed
8216 separately. The @code{info files} command, described below, lists all
8217 the sections and their addresses.
8223 @code{info files} and @code{info target} are synonymous; both print the
8224 current target (@pxref{Targets, ,Specifying a Debugging Target}),
8225 including the names of the executable and core dump files currently in
8226 use by @value{GDBN}, and the files from which symbols were loaded. The
8227 command @code{help target} lists all possible targets rather than
8232 All file-specifying commands allow both absolute and relative file names
8233 as arguments. @value{GDBN} always converts the file name to an absolute file
8234 name and remembers it that way.
8236 @cindex shared libraries
8237 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
8240 @value{GDBN} automatically loads symbol definitions from shared libraries
8241 when you use the @code{run} command, or when you examine a core file.
8242 (Before you issue the @code{run} command, @value{GDBN} does not understand
8243 references to a function in a shared library, however---unless you are
8244 debugging a core file).
8246 On HP-UX, if the program loads a library explicitly, @value{GDBN}
8247 automatically loads the symbols at the time of the @code{shl_load} call.
8249 @c FIXME: some @value{GDBN} release may permit some refs to undef
8250 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
8251 @c FIXME...lib; check this from time to time when updating manual
8254 @kindex info sharedlibrary
8257 @itemx info sharedlibrary
8258 Print the names of the shared libraries which are currently loaded.
8260 @kindex sharedlibrary
8262 @item sharedlibrary @var{regex}
8263 @itemx share @var{regex}
8264 Load shared object library symbols for files matching a
8265 Unix regular expression.
8266 As with files loaded automatically, it only loads shared libraries
8267 required by your program for a core file or after typing @code{run}. If
8268 @var{regex} is omitted all shared libraries required by your program are
8272 On HP-UX systems, @value{GDBN} detects the loading of a shared library
8273 and automatically reads in symbols from the newly loaded library, up to
8274 a threshold that is initially set but that you can modify if you wish.
8276 Beyond that threshold, symbols from shared libraries must be explicitly
8277 loaded. To load these symbols, use the command @code{sharedlibrary
8278 @var{filename}}. The base address of the shared library is determined
8279 automatically by @value{GDBN} and need not be specified.
8281 To display or set the threshold, use the commands:
8284 @kindex set auto-solib-add
8285 @item set auto-solib-add @var{threshold}
8286 Set the autoloading size threshold, in megabytes. If @var{threshold} is
8287 nonzero, symbols from all shared object libraries will be loaded
8288 automatically when the inferior begins execution or when the dynamic
8289 linker informs @value{GDBN} that a new library has been loaded, until
8290 the symbol table of the program and libraries exceeds this threshold.
8291 Otherwise, symbols must be loaded manually, using the
8292 @code{sharedlibrary} command. The default threshold is 100 megabytes.
8294 @kindex show auto-solib-add
8295 @item show auto-solib-add
8296 Display the current autoloading size threshold, in megabytes.
8300 @section Errors reading symbol files
8302 While reading a symbol file, @value{GDBN} occasionally encounters problems,
8303 such as symbol types it does not recognize, or known bugs in compiler
8304 output. By default, @value{GDBN} does not notify you of such problems, since
8305 they are relatively common and primarily of interest to people
8306 debugging compilers. If you are interested in seeing information
8307 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
8308 only one message about each such type of problem, no matter how many
8309 times the problem occurs; or you can ask @value{GDBN} to print more messages,
8310 to see how many times the problems occur, with the @code{set
8311 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
8314 The messages currently printed, and their meanings, include:
8317 @item inner block not inside outer block in @var{symbol}
8319 The symbol information shows where symbol scopes begin and end
8320 (such as at the start of a function or a block of statements). This
8321 error indicates that an inner scope block is not fully contained
8322 in its outer scope blocks.
8324 @value{GDBN} circumvents the problem by treating the inner block as if it had
8325 the same scope as the outer block. In the error message, @var{symbol}
8326 may be shown as ``@code{(don't know)}'' if the outer block is not a
8329 @item block at @var{address} out of order
8331 The symbol information for symbol scope blocks should occur in
8332 order of increasing addresses. This error indicates that it does not
8335 @value{GDBN} does not circumvent this problem, and has trouble
8336 locating symbols in the source file whose symbols it is reading. (You
8337 can often determine what source file is affected by specifying
8338 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
8341 @item bad block start address patched
8343 The symbol information for a symbol scope block has a start address
8344 smaller than the address of the preceding source line. This is known
8345 to occur in the SunOS 4.1.1 (and earlier) C compiler.
8347 @value{GDBN} circumvents the problem by treating the symbol scope block as
8348 starting on the previous source line.
8350 @item bad string table offset in symbol @var{n}
8353 Symbol number @var{n} contains a pointer into the string table which is
8354 larger than the size of the string table.
8356 @value{GDBN} circumvents the problem by considering the symbol to have the
8357 name @code{foo}, which may cause other problems if many symbols end up
8360 @item unknown symbol type @code{0x@var{nn}}
8362 The symbol information contains new data types that @value{GDBN} does
8363 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
8364 uncomprehended information, in hexadecimal.
8366 @value{GDBN} circumvents the error by ignoring this symbol information.
8367 This usually allows you to debug your program, though certain symbols
8368 are not accessible. If you encounter such a problem and feel like
8369 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
8370 on @code{complain}, then go up to the function @code{read_dbx_symtab}
8371 and examine @code{*bufp} to see the symbol.
8373 @item stub type has NULL name
8375 @value{GDBN} could not find the full definition for a struct or class.
8377 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
8378 The symbol information for a C++ member function is missing some
8379 information that recent versions of the compiler should have output for
8382 @item info mismatch between compiler and debugger
8384 @value{GDBN} could not parse a type specification output by the compiler.
8389 @chapter Specifying a Debugging Target
8391 @cindex debugging target
8394 A @dfn{target} is the execution environment occupied by your program.
8396 Often, @value{GDBN} runs in the same host environment as your program;
8397 in that case, the debugging target is specified as a side effect when
8398 you use the @code{file} or @code{core} commands. When you need more
8399 flexibility---for example, running @value{GDBN} on a physically separate
8400 host, or controlling a standalone system over a serial port or a
8401 realtime system over a TCP/IP connection---you can use the @code{target}
8402 command to specify one of the target types configured for @value{GDBN}
8403 (@pxref{Target Commands, ,Commands for managing targets}).
8406 * Active Targets:: Active targets
8407 * Target Commands:: Commands for managing targets
8408 * Byte Order:: Choosing target byte order
8409 * Remote:: Remote debugging
8410 * KOD:: Kernel Object Display
8414 @node Active Targets
8415 @section Active targets
8417 @cindex stacking targets
8418 @cindex active targets
8419 @cindex multiple targets
8421 There are three classes of targets: processes, core files, and
8422 executable files. @value{GDBN} can work concurrently on up to three
8423 active targets, one in each class. This allows you to (for example)
8424 start a process and inspect its activity without abandoning your work on
8427 For example, if you execute @samp{gdb a.out}, then the executable file
8428 @code{a.out} is the only active target. If you designate a core file as
8429 well---presumably from a prior run that crashed and coredumped---then
8430 @value{GDBN} has two active targets and uses them in tandem, looking
8431 first in the corefile target, then in the executable file, to satisfy
8432 requests for memory addresses. (Typically, these two classes of target
8433 are complementary, since core files contain only a program's
8434 read-write memory---variables and so on---plus machine status, while
8435 executable files contain only the program text and initialized data.)
8437 When you type @code{run}, your executable file becomes an active process
8438 target as well. When a process target is active, all @value{GDBN}
8439 commands requesting memory addresses refer to that target; addresses in
8440 an active core file or executable file target are obscured while the
8441 process target is active.
8443 Use the @code{core-file} and @code{exec-file} commands to select a new
8444 core file or executable target (@pxref{Files, ,Commands to specify
8445 files}). To specify as a target a process that is already running, use
8446 the @code{attach} command (@pxref{Attach, ,Debugging an already-running
8449 @node Target Commands
8450 @section Commands for managing targets
8453 @item target @var{type} @var{parameters}
8454 Connects the @value{GDBN} host environment to a target machine or
8455 process. A target is typically a protocol for talking to debugging
8456 facilities. You use the argument @var{type} to specify the type or
8457 protocol of the target machine.
8459 Further @var{parameters} are interpreted by the target protocol, but
8460 typically include things like device names or host names to connect
8461 with, process numbers, and baud rates.
8463 The @code{target} command does not repeat if you press @key{RET} again
8464 after executing the command.
8468 Displays the names of all targets available. To display targets
8469 currently selected, use either @code{info target} or @code{info files}
8470 (@pxref{Files, ,Commands to specify files}).
8472 @item help target @var{name}
8473 Describe a particular target, including any parameters necessary to
8476 @kindex set gnutarget
8477 @item set gnutarget @var{args}
8478 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
8479 knows whether it is reading an @dfn{executable},
8480 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
8481 with the @code{set gnutarget} command. Unlike most @code{target} commands,
8482 with @code{gnutarget} the @code{target} refers to a program, not a machine.
8485 @emph{Warning:} To specify a file format with @code{set gnutarget},
8486 you must know the actual BFD name.
8490 @xref{Files, , Commands to specify files}.
8492 @kindex show gnutarget
8493 @item show gnutarget
8494 Use the @code{show gnutarget} command to display what file format
8495 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
8496 @value{GDBN} will determine the file format for each file automatically,
8497 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
8500 Here are some common targets (available, or not, depending on the GDB
8505 @item target exec @var{program}
8506 An executable file. @samp{target exec @var{program}} is the same as
8507 @samp{exec-file @var{program}}.
8510 @item target core @var{filename}
8511 A core dump file. @samp{target core @var{filename}} is the same as
8512 @samp{core-file @var{filename}}.
8514 @kindex target remote
8515 @item target remote @var{dev}
8516 Remote serial target in GDB-specific protocol. The argument @var{dev}
8517 specifies what serial device to use for the connection (e.g.
8518 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
8519 supports the @code{load} command. This is only useful if you have
8520 some other way of getting the stub to the target system, and you can put
8521 it somewhere in memory where it won't get clobbered by the download.
8525 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
8533 works; however, you cannot assume that a specific memory map, device
8534 drivers, or even basic I/O is available, although some simulators do
8535 provide these. For info about any processor-specific simulator details,
8536 see the appropriate section in @ref{Embedded Processors, ,Embedded
8541 Some configurations may include these targets as well:
8546 @item target nrom @var{dev}
8547 NetROM ROM emulator. This target only supports downloading.
8551 Different targets are available on different configurations of @value{GDBN};
8552 your configuration may have more or fewer targets.
8554 Many remote targets require you to download the executable's code
8555 once you've successfully established a connection.
8559 @kindex load @var{filename}
8560 @item load @var{filename}
8561 Depending on what remote debugging facilities are configured into
8562 @value{GDBN}, the @code{load} command may be available. Where it exists, it
8563 is meant to make @var{filename} (an executable) available for debugging
8564 on the remote system---by downloading, or dynamic linking, for example.
8565 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
8566 the @code{add-symbol-file} command.
8568 If your @value{GDBN} does not have a @code{load} command, attempting to
8569 execute it gets the error message ``@code{You can't do that when your
8570 target is @dots{}}''
8572 The file is loaded at whatever address is specified in the executable.
8573 For some object file formats, you can specify the load address when you
8574 link the program; for other formats, like a.out, the object file format
8575 specifies a fixed address.
8576 @c FIXME! This would be a good place for an xref to the GNU linker doc.
8578 @code{load} does not repeat if you press @key{RET} again after using it.
8582 @section Choosing target byte order
8584 @cindex choosing target byte order
8585 @cindex target byte order
8587 Some types of processors, such as the MIPS, PowerPC, and Hitachi SH,
8588 offer the ability to run either big-endian or little-endian byte
8589 orders. Usually the executable or symbol will include a bit to
8590 designate the endian-ness, and you will not need to worry about
8591 which to use. However, you may still find it useful to adjust
8592 @value{GDBN}'s idea of processor endian-ness manually.
8595 @kindex set endian big
8596 @item set endian big
8597 Instruct @value{GDBN} to assume the target is big-endian.
8599 @kindex set endian little
8600 @item set endian little
8601 Instruct @value{GDBN} to assume the target is little-endian.
8603 @kindex set endian auto
8604 @item set endian auto
8605 Instruct @value{GDBN} to use the byte order associated with the
8609 Display @value{GDBN}'s current idea of the target byte order.
8613 Note that these commands merely adjust interpretation of symbolic
8614 data on the host, and that they have absolutely no effect on the
8618 @section Remote debugging
8619 @cindex remote debugging
8621 If you are trying to debug a program running on a machine that cannot run
8622 @value{GDBN} in the usual way, it is often useful to use remote debugging.
8623 For example, you might use remote debugging on an operating system kernel,
8624 or on a small system which does not have a general purpose operating system
8625 powerful enough to run a full-featured debugger.
8627 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
8628 to make this work with particular debugging targets. In addition,
8629 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
8630 but not specific to any particular target system) which you can use if you
8631 write the remote stubs---the code that runs on the remote system to
8632 communicate with @value{GDBN}.
8634 Other remote targets may be available in your
8635 configuration of @value{GDBN}; use @code{help target} to list them.
8638 * Remote Serial:: @value{GDBN} remote serial protocol
8642 @subsection The @value{GDBN} remote serial protocol
8644 @cindex remote serial debugging, overview
8645 To debug a program running on another machine (the debugging
8646 @dfn{target} machine), you must first arrange for all the usual
8647 prerequisites for the program to run by itself. For example, for a C
8652 A startup routine to set up the C runtime environment; these usually
8653 have a name like @file{crt0}. The startup routine may be supplied by
8654 your hardware supplier, or you may have to write your own.
8657 A C subroutine library to support your program's
8658 subroutine calls, notably managing input and output.
8661 A way of getting your program to the other machine---for example, a
8662 download program. These are often supplied by the hardware
8663 manufacturer, but you may have to write your own from hardware
8667 The next step is to arrange for your program to use a serial port to
8668 communicate with the machine where @value{GDBN} is running (the @dfn{host}
8669 machine). In general terms, the scheme looks like this:
8673 @value{GDBN} already understands how to use this protocol; when everything
8674 else is set up, you can simply use the @samp{target remote} command
8675 (@pxref{Targets,,Specifying a Debugging Target}).
8677 @item On the target,
8678 you must link with your program a few special-purpose subroutines that
8679 implement the @value{GDBN} remote serial protocol. The file containing these
8680 subroutines is called a @dfn{debugging stub}.
8682 On certain remote targets, you can use an auxiliary program
8683 @code{gdbserver} instead of linking a stub into your program.
8684 @xref{Server,,Using the @code{gdbserver} program}, for details.
8687 The debugging stub is specific to the architecture of the remote
8688 machine; for example, use @file{sparc-stub.c} to debug programs on
8691 @cindex remote serial stub list
8692 These working remote stubs are distributed with @value{GDBN}:
8697 @cindex @file{i386-stub.c}
8700 For Intel 386 and compatible architectures.
8703 @cindex @file{m68k-stub.c}
8704 @cindex Motorola 680x0
8706 For Motorola 680x0 architectures.
8709 @cindex @file{sh-stub.c}
8712 For Hitachi SH architectures.
8715 @cindex @file{sparc-stub.c}
8717 For @sc{sparc} architectures.
8720 @cindex @file{sparcl-stub.c}
8723 For Fujitsu @sc{sparclite} architectures.
8727 The @file{README} file in the @value{GDBN} distribution may list other
8728 recently added stubs.
8731 * Stub Contents:: What the stub can do for you
8732 * Bootstrapping:: What you must do for the stub
8733 * Debug Session:: Putting it all together
8734 * Protocol:: Definition of the communication protocol
8735 * Server:: Using the `gdbserver' program
8736 * NetWare:: Using the `gdbserve.nlm' program
8740 @subsubsection What the stub can do for you
8742 @cindex remote serial stub
8743 The debugging stub for your architecture supplies these three
8747 @item set_debug_traps
8748 @kindex set_debug_traps
8749 @cindex remote serial stub, initialization
8750 This routine arranges for @code{handle_exception} to run when your
8751 program stops. You must call this subroutine explicitly near the
8752 beginning of your program.
8754 @item handle_exception
8755 @kindex handle_exception
8756 @cindex remote serial stub, main routine
8757 This is the central workhorse, but your program never calls it
8758 explicitly---the setup code arranges for @code{handle_exception} to
8759 run when a trap is triggered.
8761 @code{handle_exception} takes control when your program stops during
8762 execution (for example, on a breakpoint), and mediates communications
8763 with @value{GDBN} on the host machine. This is where the communications
8764 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
8765 representative on the target machine. It begins by sending summary
8766 information on the state of your program, then continues to execute,
8767 retrieving and transmitting any information @value{GDBN} needs, until you
8768 execute a @value{GDBN} command that makes your program resume; at that point,
8769 @code{handle_exception} returns control to your own code on the target
8773 @cindex @code{breakpoint} subroutine, remote
8774 Use this auxiliary subroutine to make your program contain a
8775 breakpoint. Depending on the particular situation, this may be the only
8776 way for @value{GDBN} to get control. For instance, if your target
8777 machine has some sort of interrupt button, you won't need to call this;
8778 pressing the interrupt button transfers control to
8779 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
8780 simply receiving characters on the serial port may also trigger a trap;
8781 again, in that situation, you don't need to call @code{breakpoint} from
8782 your own program---simply running @samp{target remote} from the host
8783 @value{GDBN} session gets control.
8785 Call @code{breakpoint} if none of these is true, or if you simply want
8786 to make certain your program stops at a predetermined point for the
8787 start of your debugging session.
8791 @subsubsection What you must do for the stub
8793 @cindex remote stub, support routines
8794 The debugging stubs that come with @value{GDBN} are set up for a particular
8795 chip architecture, but they have no information about the rest of your
8796 debugging target machine.
8798 First of all you need to tell the stub how to communicate with the
8802 @item int getDebugChar()
8803 @kindex getDebugChar
8804 Write this subroutine to read a single character from the serial port.
8805 It may be identical to @code{getchar} for your target system; a
8806 different name is used to allow you to distinguish the two if you wish.
8808 @item void putDebugChar(int)
8809 @kindex putDebugChar
8810 Write this subroutine to write a single character to the serial port.
8811 It may be identical to @code{putchar} for your target system; a
8812 different name is used to allow you to distinguish the two if you wish.
8815 @cindex control C, and remote debugging
8816 @cindex interrupting remote targets
8817 If you want @value{GDBN} to be able to stop your program while it is
8818 running, you need to use an interrupt-driven serial driver, and arrange
8819 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
8820 character). That is the character which @value{GDBN} uses to tell the
8821 remote system to stop.
8823 Getting the debugging target to return the proper status to @value{GDBN}
8824 probably requires changes to the standard stub; one quick and dirty way
8825 is to just execute a breakpoint instruction (the ``dirty'' part is that
8826 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
8828 Other routines you need to supply are:
8831 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
8832 @kindex exceptionHandler
8833 Write this function to install @var{exception_address} in the exception
8834 handling tables. You need to do this because the stub does not have any
8835 way of knowing what the exception handling tables on your target system
8836 are like (for example, the processor's table might be in @sc{rom},
8837 containing entries which point to a table in @sc{ram}).
8838 @var{exception_number} is the exception number which should be changed;
8839 its meaning is architecture-dependent (for example, different numbers
8840 might represent divide by zero, misaligned access, etc). When this
8841 exception occurs, control should be transferred directly to
8842 @var{exception_address}, and the processor state (stack, registers,
8843 and so on) should be just as it is when a processor exception occurs. So if
8844 you want to use a jump instruction to reach @var{exception_address}, it
8845 should be a simple jump, not a jump to subroutine.
8847 For the 386, @var{exception_address} should be installed as an interrupt
8848 gate so that interrupts are masked while the handler runs. The gate
8849 should be at privilege level 0 (the most privileged level). The
8850 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
8851 help from @code{exceptionHandler}.
8853 @item void flush_i_cache()
8854 @kindex flush_i_cache
8855 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
8856 instruction cache, if any, on your target machine. If there is no
8857 instruction cache, this subroutine may be a no-op.
8859 On target machines that have instruction caches, @value{GDBN} requires this
8860 function to make certain that the state of your program is stable.
8864 You must also make sure this library routine is available:
8867 @item void *memset(void *, int, int)
8869 This is the standard library function @code{memset} that sets an area of
8870 memory to a known value. If you have one of the free versions of
8871 @code{libc.a}, @code{memset} can be found there; otherwise, you must
8872 either obtain it from your hardware manufacturer, or write your own.
8875 If you do not use the GNU C compiler, you may need other standard
8876 library subroutines as well; this varies from one stub to another,
8877 but in general the stubs are likely to use any of the common library
8878 subroutines which @code{@value{GCC}} generates as inline code.
8882 @subsubsection Putting it all together
8884 @cindex remote serial debugging summary
8885 In summary, when your program is ready to debug, you must follow these
8890 Make sure you have defined the supporting low-level routines
8891 (@pxref{Bootstrapping,,What you must do for the stub}):
8893 @code{getDebugChar}, @code{putDebugChar},
8894 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
8898 Insert these lines near the top of your program:
8906 For the 680x0 stub only, you need to provide a variable called
8907 @code{exceptionHook}. Normally you just use:
8910 void (*exceptionHook)() = 0;
8914 but if before calling @code{set_debug_traps}, you set it to point to a
8915 function in your program, that function is called when
8916 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
8917 error). The function indicated by @code{exceptionHook} is called with
8918 one parameter: an @code{int} which is the exception number.
8921 Compile and link together: your program, the @value{GDBN} debugging stub for
8922 your target architecture, and the supporting subroutines.
8925 Make sure you have a serial connection between your target machine and
8926 the @value{GDBN} host, and identify the serial port on the host.
8929 @c The "remote" target now provides a `load' command, so we should
8930 @c document that. FIXME.
8931 Download your program to your target machine (or get it there by
8932 whatever means the manufacturer provides), and start it.
8935 To start remote debugging, run @value{GDBN} on the host machine, and specify
8936 as an executable file the program that is running in the remote machine.
8937 This tells @value{GDBN} how to find your program's symbols and the contents
8941 @cindex serial line, @code{target remote}
8942 Establish communication using the @code{target remote} command.
8943 Its argument specifies how to communicate with the target
8944 machine---either via a devicename attached to a direct serial line, or a
8945 TCP port (usually to a terminal server which in turn has a serial line
8946 to the target). For example, to use a serial line connected to the
8947 device named @file{/dev/ttyb}:
8950 target remote /dev/ttyb
8953 @cindex TCP port, @code{target remote}
8954 To use a TCP connection, use an argument of the form
8955 @code{@var{host}:port}. For example, to connect to port 2828 on a
8956 terminal server named @code{manyfarms}:
8959 target remote manyfarms:2828
8963 Now you can use all the usual commands to examine and change data and to
8964 step and continue the remote program.
8966 To resume the remote program and stop debugging it, use the @code{detach}
8969 @cindex interrupting remote programs
8970 @cindex remote programs, interrupting
8971 Whenever @value{GDBN} is waiting for the remote program, if you type the
8972 interrupt character (often @key{C-C}), @value{GDBN} attempts to stop the
8973 program. This may or may not succeed, depending in part on the hardware
8974 and the serial drivers the remote system uses. If you type the
8975 interrupt character once again, @value{GDBN} displays this prompt:
8978 Interrupted while waiting for the program.
8979 Give up (and stop debugging it)? (y or n)
8982 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
8983 (If you decide you want to try again later, you can use @samp{target
8984 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
8985 goes back to waiting.
8988 @subsubsection Communication protocol
8990 @cindex debugging stub, example
8991 @cindex remote stub, example
8992 @cindex stub example, remote debugging
8993 The stub files provided with @value{GDBN} implement the target side of the
8994 communication protocol, and the @value{GDBN} side is implemented in the
8995 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
8996 these subroutines to communicate, and ignore the details. (If you're
8997 implementing your own stub file, you can still ignore the details: start
8998 with one of the existing stub files. @file{sparc-stub.c} is the best
8999 organized, and therefore the easiest to read.)
9001 However, there may be occasions when you need to know something about
9002 the protocol---for example, if there is only one serial port to your
9003 target machine, you might want your program to do something special if
9004 it recognizes a packet meant for @value{GDBN}.
9006 In the examples below, @samp{<-} and @samp{->} are used to indicate
9007 transmitted and received data respectfully.
9009 @cindex protocol, @value{GDBN} remote serial
9010 @cindex serial protocol, @value{GDBN} remote
9011 @cindex remote serial protocol
9012 All @value{GDBN} commands and responses (other than acknowledgments) are
9013 sent as a @var{packet}. A @var{packet} is introduced with the character
9014 @samp{$}, the actual @var{packet-data}, and the terminating character
9015 @samp{#} followed by a two-digit @var{checksum}:
9018 @code{$}@var{packet-data}@code{#}@var{checksum}
9022 @cindex checksum, for @value{GDBN} remote
9024 The two-digit @var{checksum} is computed as the modulo 256 sum of all
9025 characters between the leading @samp{$} and the trailing @samp{#} (an
9026 eight bit unsigned checksum).
9028 Implementors should note that prior to @value{GDBN} 5.0 the protocol
9029 specification also included an optional two-digit @var{sequence-id}:
9032 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
9035 @cindex sequence-id, for @value{GDBN} remote
9037 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
9038 has never output @var{sequence-id}s. Stubs that handle packets added
9039 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
9041 @cindex acknowledgment, for @value{GDBN} remote
9042 When either the host or the target machine receives a packet, the first
9043 response expected is an acknowledgment: either @samp{+} (to indicate
9044 the package was received correctly) or @samp{-} (to request
9048 <- @code{$}@var{packet-data}@code{#}@var{checksum}
9053 The host (@value{GDBN}) sends @var{command}s, and the target (the
9054 debugging stub incorporated in your program) sends a @var{response}. In
9055 the case of step and continue @var{command}s, the response is only sent
9056 when the operation has completed (the target has again stopped).
9058 @var{packet-data} consists of a sequence of characters with the
9059 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
9062 Fields within the packet should be separated using @samp{,} @samp{;} or
9063 @samp{:}. Except where otherwise noted all numbers are represented in
9064 HEX with leading zeros suppressed.
9066 Implementors should note that prior to @value{GDBN} 5.0, the character
9067 @samp{:} could not appear as the third character in a packet (as it
9068 would potentially conflict with the @var{sequence-id}).
9070 Response @var{data} can be run-length encoded to save space. A @samp{*}
9071 means that the next character is an @sc{ascii} encoding giving a repeat count
9072 which stands for that many repetitions of the character preceding the
9073 @samp{*}. The encoding is @code{n+29}, yielding a printable character
9074 where @code{n >=3} (which is where rle starts to win). The printable
9075 characters @samp{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
9076 value greater than 126 should not be used.
9078 Some remote systems have used a different run-length encoding mechanism
9079 loosely refered to as the cisco encoding. Following the @samp{*}
9080 character are two hex digits that indicate the size of the packet.
9087 means the same as "0000".
9089 The error response returned for some packets includes a two character
9090 error number. That number is not well defined.
9092 For any @var{command} not supported by the stub, an empty response
9093 (@samp{$#00}) should be returned. That way it is possible to extend the
9094 protocol. A newer @value{GDBN} can tell if a packet is supported based
9097 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
9098 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
9101 Below is a complete list of all currently defined @var{command}s and
9102 their corresponding response @var{data}:
9104 @multitable @columnfractions .30 .30 .40
9112 Use the extended remote protocol. Sticky---only needs to be set once.
9113 The extended remote protocol supports the @samp{R} packet.
9117 Stubs that support the extended remote protocol return @samp{} which,
9118 unfortunately, is identical to the response returned by stubs that do not
9119 support protocol extensions.
9124 Indicate the reason the target halted. The reply is the same as for step
9133 @tab Reserved for future use
9135 @item set program arguments @strong{(reserved)}
9136 @tab @code{A}@var{arglen}@code{,}@var{argnum}@code{,}@var{arg}@code{,...}
9141 Initialized @samp{argv[]} array passed into program. @var{arglen}
9142 specifies the number of bytes in the hex encoded byte stream @var{arg}.
9143 See @file{gdbserver} for more details.
9145 @tab reply @code{OK}
9147 @tab reply @code{E}@var{NN}
9149 @item set baud @strong{(deprecated)}
9150 @tab @code{b}@var{baud}
9152 Change the serial line speed to @var{baud}. JTC: @emph{When does the
9153 transport layer state change? When it's received, or after the ACK is
9154 transmitted. In either case, there are problems if the command or the
9155 acknowledgment packet is dropped.} Stan: @emph{If people really wanted
9156 to add something like this, and get it working for the first time, they
9157 ought to modify ser-unix.c to send some kind of out-of-band message to a
9158 specially-setup stub and have the switch happen "in between" packets, so
9159 that from remote protocol's point of view, nothing actually
9162 @item set breakpoint @strong{(deprecated)}
9163 @tab @code{B}@var{addr},@var{mode}
9165 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
9166 breakpoint at @var{addr}. @emph{This has been replaced by the @samp{Z} and
9170 @tab @code{c}@var{addr}
9172 @var{addr} is address to resume. If @var{addr} is omitted, resume at
9178 @item continue with signal
9179 @tab @code{C}@var{sig}@code{;}@var{addr}
9181 Continue with signal @var{sig} (hex signal number). If
9182 @code{;}@var{addr} is omitted, resume at same address.
9187 @item toggle debug @strong{(deprecated)}
9195 Detach @value{GDBN} from the remote system. Sent to the remote target before
9196 @value{GDBN} disconnects.
9198 @tab reply @emph{no response}
9200 @value{GDBN} does not check for any response after sending this packet.
9204 @tab Reserved for future use
9208 @tab Reserved for future use
9212 @tab Reserved for future use
9216 @tab Reserved for future use
9218 @item read registers
9220 @tab Read general registers.
9222 @tab reply @var{XX...}
9224 Each byte of register data is described by two hex digits. The bytes
9225 with the register are transmitted in target byte order. The size of
9226 each register and their position within the @samp{g} @var{packet} are
9227 determined by the @value{GDBN} internal macros @var{REGISTER_RAW_SIZE} and
9228 @var{REGISTER_NAME} macros. The specification of several standard
9229 @code{g} packets is specified below.
9231 @tab @code{E}@var{NN}
9235 @tab @code{G}@var{XX...}
9237 See @samp{g} for a description of the @var{XX...} data.
9239 @tab reply @code{OK}
9242 @tab reply @code{E}@var{NN}
9247 @tab Reserved for future use
9250 @tab @code{H}@var{c}@var{t...}
9252 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
9253 @samp{G}, et.al.). @var{c} = @samp{c} for thread used in step and
9254 continue; @var{t...} can be -1 for all threads. @var{c} = @samp{g} for
9255 thread used in other operations. If zero, pick a thread, any thread.
9257 @tab reply @code{OK}
9260 @tab reply @code{E}@var{NN}
9264 @c 'H': How restrictive (or permissive) is the thread model. If a
9265 @c thread is selected and stopped, are other threads allowed
9266 @c to continue to execute? As I mentioned above, I think the
9267 @c semantics of each command when a thread is selected must be
9268 @c described. For example:
9270 @c 'g': If the stub supports threads and a specific thread is
9271 @c selected, returns the register block from that thread;
9272 @c otherwise returns current registers.
9274 @c 'G' If the stub supports threads and a specific thread is
9275 @c selected, sets the registers of the register block of
9276 @c that thread; otherwise sets current registers.
9278 @item cycle step @strong{(draft)}
9279 @tab @code{i}@var{addr}@code{,}@var{nnn}
9281 Step the remote target by a single clock cycle. If @code{,}@var{nnn} is
9282 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
9283 step starting at that address.
9285 @item signal then cycle step @strong{(reserved)}
9288 See @samp{i} and @samp{S} for likely syntax and semantics.
9292 @tab Reserved for future use
9296 @tab Reserved for future use
9301 FIXME: @emph{There is no description of how operate when a specific
9302 thread context has been selected (ie. does 'k' kill only that thread?)}.
9306 @tab Reserved for future use
9310 @tab Reserved for future use
9313 @tab @code{m}@var{addr}@code{,}@var{length}
9315 Read @var{length} bytes of memory starting at address @var{addr}.
9316 Neither @value{GDBN} nor the stub assume that sized memory transfers are assumed
9317 using word alligned accesses. FIXME: @emph{A word aligned memory
9318 transfer mechanism is needed.}
9320 @tab reply @var{XX...}
9322 @var{XX...} is mem contents. Can be fewer bytes than requested if able
9323 to read only part of the data. Neither @value{GDBN} nor the stub assume that
9324 sized memory transfers are assumed using word alligned accesses. FIXME:
9325 @emph{A word aligned memory transfer mechanism is needed.}
9327 @tab reply @code{E}@var{NN}
9328 @tab @var{NN} is errno
9331 @tab @code{M}@var{addr},@var{length}@code{:}@var{XX...}
9333 Write @var{length} bytes of memory starting at address @var{addr}.
9334 @var{XX...} is the data.
9336 @tab reply @code{OK}
9339 @tab reply @code{E}@var{NN}
9341 for an error (this includes the case where only part of the data was
9346 @tab Reserved for future use
9350 @tab Reserved for future use
9354 @tab Reserved for future use
9358 @tab Reserved for future use
9360 @item read reg @strong{(reserved)}
9361 @tab @code{p}@var{n...}
9365 @tab return @var{r....}
9366 @tab The hex encoded value of the register in target byte order.
9369 @tab @code{P}@var{n...}@code{=}@var{r...}
9371 Write register @var{n...} with value @var{r...}, which contains two hex
9372 digits for each byte in the register (target byte order).
9374 @tab reply @code{OK}
9377 @tab reply @code{E}@var{NN}
9381 @tab @code{q}@var{query}
9383 Request info about @var{query}. In general @value{GDBN} queries
9384 have a leading upper case letter. Custom vendor queries should use a
9385 company prefix (in lower case) ex: @samp{qfsf.var}. @var{query} may
9386 optionally be followed by a @samp{,} or @samp{;} separated list. Stubs
9387 must ensure that they match the full @var{query} name.
9389 @tab reply @code{XX...}
9390 @tab Hex encoded data from query. The reply can not be empty.
9392 @tab reply @code{E}@var{NN}
9396 @tab Indicating an unrecognized @var{query}.
9399 @tab @code{Q}@var{var}@code{=}@var{val}
9401 Set value of @var{var} to @var{val}. See @samp{q} for a discussing of
9404 @item reset @strong{(deprecated)}
9407 Reset the entire system.
9409 @item remote restart
9410 @tab @code{R}@var{XX}
9412 Restart the remote server. @var{XX} while needed has no clear
9413 definition. FIXME: @emph{An example interaction explaining how this
9414 packet is used in extended-remote mode is needed}.
9417 @tab @code{s}@var{addr}
9419 @var{addr} is address to resume. If @var{addr} is omitted, resume at
9425 @item step with signal
9426 @tab @code{S}@var{sig}@code{;}@var{addr}
9428 Like @samp{C} but step not continue.
9434 @tab @code{t}@var{addr}@code{:}@var{PP}@code{,}@var{MM}
9436 Search backwards starting at address @var{addr} for a match with pattern
9437 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4
9438 bytes. @var{addr} must be at least 3 digits.
9441 @tab @code{T}@var{XX}
9442 @tab Find out if the thread XX is alive.
9444 @tab reply @code{OK}
9445 @tab thread is still alive
9447 @tab reply @code{E}@var{NN}
9452 @tab Reserved for future use
9456 @tab Reserved for future use
9460 @tab Reserved for future use
9464 @tab Reserved for future use
9468 @tab Reserved for future use
9472 @tab Reserved for future use
9476 @tab Reserved for future use
9478 @item write mem (binary)
9479 @tab @code{X}@var{addr}@code{,}@var{length}@var{:}@var{XX...}
9481 @var{addr} is address, @var{length} is number of bytes, @var{XX...} is
9482 binary data. The characters @code{$}, @code{#}, and @code{0x7d} are
9483 escaped using @code{0x7d}.
9485 @tab reply @code{OK}
9488 @tab reply @code{E}@var{NN}
9493 @tab Reserved for future use
9497 @tab Reserved for future use
9499 @item remove break or watchpoint @strong{(draft)}
9500 @tab @code{z}@var{t}@code{,}@var{addr}@code{,}@var{length}
9504 @item insert break or watchpoint @strong{(draft)}
9505 @tab @code{Z}@var{t}@code{,}@var{addr}@code{,}@var{length}
9507 @var{t} is type: @samp{0} - software breakpoint, @samp{1} - hardware
9508 breakpoint, @samp{2} - write watchpoint, @samp{3} - read watchpoint,
9509 @samp{4} - access watchpoint; @var{addr} is address; @var{length} is in
9510 bytes. For a software breakpoint, @var{length} specifies the size of
9511 the instruction to be patched. For hardware breakpoints and watchpoints
9512 @var{length} specifies the memory region to be monitored. To avoid
9513 potential problems with duplicate packets, the operations should be
9514 implemented in an idempotent way.
9516 @tab reply @code{E}@var{NN}
9519 @tab reply @code{OK}
9523 @tab If not supported.
9527 @tab Reserved for future use
9531 The @samp{C}, @samp{c}, @samp{S}, @samp{s} and @samp{?} packets can
9532 receive any of the below as a reply. In the case of the @samp{C},
9533 @samp{c}, @samp{S} and @samp{s} packets, that reply is only returned
9534 when the target halts. In the below the exact meaning of @samp{signal
9535 number} is poorly defined. In general one of the UNIX signal numbering
9536 conventions is used.
9538 @multitable @columnfractions .4 .6
9540 @item @code{S}@var{AA}
9541 @tab @var{AA} is the signal number
9543 @item @code{T}@var{AA}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}
9545 @var{AA} = two hex digit signal number; @var{n...} = register number
9546 (hex), @var{r...} = target byte ordered register contents, size defined
9547 by @code{REGISTER_RAW_SIZE}; @var{n...} = @samp{thread}, @var{r...} =
9548 thread process ID, this is a hex integer; @var{n...} = other string not
9549 starting with valid hex digit. @value{GDBN} should ignore this
9550 @var{n...}, @var{r...} pair and go on to the next. This way we can
9551 extend the protocol.
9553 @item @code{W}@var{AA}
9555 The process exited, and @var{AA} is the exit status. This is only
9556 applicable for certains sorts of targets.
9558 @item @code{X}@var{AA}
9560 The process terminated with signal @var{AA}.
9562 @item @code{N}@var{AA}@code{;}@var{t...}@code{;}@var{d...}@code{;}@var{b...} @strong{(obsolete)}
9564 @var{AA} = signal number; @var{t...} = address of symbol "_start";
9565 @var{d...} = base of data section; @var{b...} = base of bss section.
9566 @emph{Note: only used by Cisco Systems targets. The difference between
9567 this reply and the "qOffsets" query is that the 'N' packet may arrive
9568 spontaneously whereas the 'qOffsets' is a query initiated by the host
9571 @item @code{O}@var{XX...}
9573 @var{XX...} is hex encoding of @sc{ascii} data. This can happen at any time
9574 while the program is running and the debugger should continue to wait
9579 The following set and query packets have already been defined.
9581 @multitable @columnfractions .2 .2 .6
9583 @item current thread
9584 @tab @code{q}@code{C}
9585 @tab Return the current thread id.
9587 @tab reply @code{QC}@var{pid}
9589 Where @var{pid} is a HEX encoded 16 bit process id.
9592 @tab Any other reply implies the old pid.
9594 @item all thread ids
9595 @tab @code{q}@code{fThreadInfo}
9597 @tab @code{q}@code{sThreadInfo}
9599 Obtain a list of active thread ids from the target (OS). Since there
9600 may be too many active threads to fit into one reply packet, this query
9601 works iteratively: it may require more than one query/reply sequence to
9602 obtain the entire list of threads. The first query of the sequence will
9603 be the @code{qf}@code{ThreadInfo} query; subsequent queries in the
9604 sequence will be the @code{qs}@code{ThreadInfo} query.
9607 @tab NOTE: replaces the @code{qL} query (see below).
9609 @tab reply @code{m}@var{<id>}
9610 @tab A single thread id
9612 @tab reply @code{m}@var{<id>},@var{<id>...}
9613 @tab a comma-separated list of thread ids
9616 @tab (lower case 'el') denotes end of list.
9620 In response to each query, the target will reply with a list of one
9621 or more thread ids, in big-endian hex, separated by commas. GDB will
9622 respond to each reply with a request for more thread ids (using the
9623 @code{qs} form of the query), until the target responds with @code{l}
9624 (lower-case el, for @code{'last'}).
9626 @item extra thread info
9627 @tab @code{q}@code{ThreadExtraInfo}@code{,}@var{id}
9632 Where @var{<id>} is a thread-id in big-endian hex.
9633 Obtain a printable string description of a thread's attributes from
9634 the target OS. This string may contain anything that the target OS
9635 thinks is interesting for @value{GDBN} to tell the user about the thread.
9636 The string is displayed in @value{GDBN}'s @samp{info threads} display.
9637 Some examples of possible thread extra info strings are "Runnable", or
9640 @tab reply @var{XX...}
9642 Where @var{XX...} is a hex encoding of @sc{ascii} data, comprising the
9643 printable string containing the extra information about the thread's
9646 @item query @var{LIST} or @var{threadLIST} @strong{(deprecated)}
9647 @tab @code{q}@code{L}@var{startflag}@var{threadcount}@var{nextthread}
9652 Obtain thread information from RTOS. Where: @var{startflag} (one hex
9653 digit) is one to indicate the first query and zero to indicate a
9654 subsequent query; @var{threadcount} (two hex digits) is the maximum
9655 number of threads the response packet can contain; and @var{nextthread}
9656 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
9657 returned in the response as @var{argthread}.
9660 @tab NOTE: this query is replaced by the @code{q}@code{fThreadInfo}
9663 @tab reply @code{q}@code{M}@var{count}@var{done}@var{argthread}@var{thread...}
9668 Where: @var{count} (two hex digits) is the number of threads being
9669 returned; @var{done} (one hex digit) is zero to indicate more threads
9670 and one indicates no further threads; @var{argthreadid} (eight hex
9671 digits) is @var{nextthread} from the request packet; @var{thread...} is
9672 a sequence of thread IDs from the target. @var{threadid} (eight hex
9673 digits). See @code{remote.c:parse_threadlist_response()}.
9675 @item compute CRC of memory block
9676 @tab @code{q}@code{CRC:}@var{addr}@code{,}@var{length}
9679 @tab reply @code{E}@var{NN}
9680 @tab An error (such as memory fault)
9682 @tab reply @code{C}@var{CRC32}
9683 @tab A 32 bit cyclic redundancy check of the specified memory region.
9685 @item query sect offs
9686 @tab @code{q}@code{Offsets}
9688 Get section offsets that the target used when re-locating the downloaded
9689 image. @emph{Note: while a @code{Bss} offset is included in the
9690 response, @value{GDBN} ignores this and instead applies the @code{Data}
9691 offset to the @code{Bss} section.}
9693 @tab reply @code{Text=}@var{xxx}@code{;Data=}@var{yyy}@code{;Bss=}@var{zzz}
9695 @item thread info request
9696 @tab @code{q}@code{P}@var{mode}@var{threadid}
9701 Returns information on @var{threadid}. Where: @var{mode} is a hex
9702 encoded 32 bit mode; @var{threadid} is a hex encoded 64 bit thread ID.
9706 See @code{remote.c:remote_unpack_thread_info_response()}.
9708 @item remote command
9709 @tab @code{q}@code{Rcmd,}@var{COMMAND}
9714 @var{COMMAND} (hex encoded) is passed to the local interpreter for
9715 execution. Invalid commands should be reported using the output string.
9716 Before the final result packet, the target may also respond with a
9717 number of intermediate @code{O}@var{OUTPUT} console output
9718 packets. @emph{Implementors should note that providing access to a
9719 stubs's interpreter may have security implications}.
9721 @tab reply @code{OK}
9723 A command response with no output.
9725 @tab reply @var{OUTPUT}
9727 A command response with the hex encoded output string @var{OUTPUT}.
9729 @tab reply @code{E}@var{NN}
9731 Indicate a badly formed request.
9736 When @samp{q}@samp{Rcmd} is not recognized.
9740 The following @samp{g}/@samp{G} packets have previously been defined.
9741 In the below, some thirty-two bit registers are transferred as sixty-four
9742 bits. Those registers should be zero/sign extended (which?) to fill the
9743 space allocated. Register bytes are transfered in target byte order.
9744 The two nibbles within a register byte are transfered most-significant -
9747 @multitable @columnfractions .5 .5
9751 All registers are transfered as thirty-two bit quantities in the order:
9752 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
9753 registers; fsr; fir; fp.
9757 All registers are transfered as sixty-four bit quantities (including
9758 thirty-two bit registers such as @code{sr}). The ordering is the same
9763 Example sequence of a target being re-started. Notice how the restart
9764 does not get any direct output:
9769 @emph{target restarts}
9772 -> @code{T001:1234123412341234}
9776 Example sequence of a target being stepped by a single instruction:
9784 -> @code{T001:1234123412341234}
9793 @subsubsection Using the @code{gdbserver} program
9796 @cindex remote connection without stubs
9797 @code{gdbserver} is a control program for Unix-like systems, which
9798 allows you to connect your program with a remote @value{GDBN} via
9799 @code{target remote}---but without linking in the usual debugging stub.
9801 @code{gdbserver} is not a complete replacement for the debugging stubs,
9802 because it requires essentially the same operating-system facilities
9803 that @value{GDBN} itself does. In fact, a system that can run
9804 @code{gdbserver} to connect to a remote @value{GDBN} could also run
9805 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
9806 because it is a much smaller program than @value{GDBN} itself. It is
9807 also easier to port than all of @value{GDBN}, so you may be able to get
9808 started more quickly on a new system by using @code{gdbserver}.
9809 Finally, if you develop code for real-time systems, you may find that
9810 the tradeoffs involved in real-time operation make it more convenient to
9811 do as much development work as possible on another system, for example
9812 by cross-compiling. You can use @code{gdbserver} to make a similar
9813 choice for debugging.
9815 @value{GDBN} and @code{gdbserver} communicate via either a serial line
9816 or a TCP connection, using the standard @value{GDBN} remote serial
9820 @item On the target machine,
9821 you need to have a copy of the program you want to debug.
9822 @code{gdbserver} does not need your program's symbol table, so you can
9823 strip the program if necessary to save space. @value{GDBN} on the host
9824 system does all the symbol handling.
9826 To use the server, you must tell it how to communicate with @value{GDBN};
9827 the name of your program; and the arguments for your program. The
9831 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
9834 @var{comm} is either a device name (to use a serial line) or a TCP
9835 hostname and portnumber. For example, to debug Emacs with the argument
9836 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
9840 target> gdbserver /dev/com1 emacs foo.txt
9843 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
9846 To use a TCP connection instead of a serial line:
9849 target> gdbserver host:2345 emacs foo.txt
9852 The only difference from the previous example is the first argument,
9853 specifying that you are communicating with the host @value{GDBN} via
9854 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
9855 expect a TCP connection from machine @samp{host} to local TCP port 2345.
9856 (Currently, the @samp{host} part is ignored.) You can choose any number
9857 you want for the port number as long as it does not conflict with any
9858 TCP ports already in use on the target system (for example, @code{23} is
9859 reserved for @code{telnet}).@footnote{If you choose a port number that
9860 conflicts with another service, @code{gdbserver} prints an error message
9861 and exits.} You must use the same port number with the host @value{GDBN}
9862 @code{target remote} command.
9864 @item On the @value{GDBN} host machine,
9865 you need an unstripped copy of your program, since @value{GDBN} needs
9866 symbols and debugging information. Start up @value{GDBN} as usual,
9867 using the name of the local copy of your program as the first argument.
9868 (You may also need the @w{@samp{--baud}} option if the serial line is
9869 running at anything other than 9600@dmn{bps}.) After that, use @code{target
9870 remote} to establish communications with @code{gdbserver}. Its argument
9871 is either a device name (usually a serial device, like
9872 @file{/dev/ttyb}), or a TCP port descriptor in the form
9873 @code{@var{host}:@var{PORT}}. For example:
9876 (@value{GDBP}) target remote /dev/ttyb
9880 communicates with the server via serial line @file{/dev/ttyb}, and
9883 (@value{GDBP}) target remote the-target:2345
9887 communicates via a TCP connection to port 2345 on host @w{@file{the-target}}.
9888 For TCP connections, you must start up @code{gdbserver} prior to using
9889 the @code{target remote} command. Otherwise you may get an error whose
9890 text depends on the host system, but which usually looks something like
9891 @samp{Connection refused}.
9895 @subsubsection Using the @code{gdbserve.nlm} program
9897 @kindex gdbserve.nlm
9898 @code{gdbserve.nlm} is a control program for NetWare systems, which
9899 allows you to connect your program with a remote @value{GDBN} via
9900 @code{target remote}.
9902 @value{GDBN} and @code{gdbserve.nlm} communicate via a serial line,
9903 using the standard @value{GDBN} remote serial protocol.
9906 @item On the target machine,
9907 you need to have a copy of the program you want to debug.
9908 @code{gdbserve.nlm} does not need your program's symbol table, so you
9909 can strip the program if necessary to save space. @value{GDBN} on the
9910 host system does all the symbol handling.
9912 To use the server, you must tell it how to communicate with
9913 @value{GDBN}; the name of your program; and the arguments for your
9914 program. The syntax is:
9917 load gdbserve [ BOARD=@var{board} ] [ PORT=@var{port} ]
9918 [ BAUD=@var{baud} ] @var{program} [ @var{args} @dots{} ]
9921 @var{board} and @var{port} specify the serial line; @var{baud} specifies
9922 the baud rate used by the connection. @var{port} and @var{node} default
9923 to 0, @var{baud} defaults to 9600@dmn{bps}.
9925 For example, to debug Emacs with the argument @samp{foo.txt}and
9926 communicate with @value{GDBN} over serial port number 2 or board 1
9927 using a 19200@dmn{bps} connection:
9930 load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
9933 @item On the @value{GDBN} host machine,
9934 you need an unstripped copy of your program, since @value{GDBN} needs
9935 symbols and debugging information. Start up @value{GDBN} as usual,
9936 using the name of the local copy of your program as the first argument.
9937 (You may also need the @w{@samp{--baud}} option if the serial line is
9938 running at anything other than 9600@dmn{bps}. After that, use @code{target
9939 remote} to establish communications with @code{gdbserve.nlm}. Its
9940 argument is a device name (usually a serial device, like
9941 @file{/dev/ttyb}). For example:
9944 (@value{GDBP}) target remote /dev/ttyb
9948 communications with the server via serial line @file{/dev/ttyb}.
9952 @section Kernel Object Display
9954 @cindex kernel object display
9955 @cindex kernel object
9958 Some targets support kernel object display. Using this facility,
9959 @value{GDBN} communicates specially with the underlying operating system
9960 and can display information about operating system-level objects such as
9961 mutexes and other synchronization objects. Exactly which objects can be
9962 displayed is determined on a per-OS basis.
9964 Use the @code{set os} command to set the operating system. This tells
9965 @value{GDBN} which kernel object display module to initialize:
9968 (@value{GDBP}) set os cisco
9971 If @code{set os} succeeds, @value{GDBN} will display some information
9972 about the operating system, and will create a new @code{info} command
9973 which can be used to query the target. The @code{info} command is named
9974 after the operating system:
9977 (@value{GDBP}) info cisco
9978 List of Cisco Kernel Objects
9980 any Any and all objects
9983 Further subcommands can be used to query about particular objects known
9986 There is currently no way to determine whether a given operating system
9987 is supported other than to try it.
9990 @node Configurations
9991 @chapter Configuration-Specific Information
9993 While nearly all @value{GDBN} commands are available for all native and
9994 cross versions of the debugger, there are some exceptions. This chapter
9995 describes things that are only available in certain configurations.
9997 There are three major categories of configurations: native
9998 configurations, where the host and target are the same, embedded
9999 operating system configurations, which are usually the same for several
10000 different processor architectures, and bare embedded processors, which
10001 are quite different from each other.
10006 * Embedded Processors::
10013 This section describes details specific to particular native
10018 * SVR4 Process Information:: SVR4 process information
10024 On HP-UX systems, if you refer to a function or variable name that
10025 begins with a dollar sign, @value{GDBN} searches for a user or system
10026 name first, before it searches for a convenience variable.
10028 @node SVR4 Process Information
10029 @subsection SVR4 process information
10032 @cindex process image
10034 Many versions of SVR4 provide a facility called @samp{/proc} that can be
10035 used to examine the image of a running process using file-system
10036 subroutines. If @value{GDBN} is configured for an operating system with
10037 this facility, the command @code{info proc} is available to report on
10038 several kinds of information about the process running your program.
10039 @code{info proc} works only on SVR4 systems that include the
10040 @code{procfs} code. This includes OSF/1 (Digital Unix), Solaris, Irix,
10041 and Unixware, but not HP-UX or Linux, for example.
10046 Summarize available information about the process.
10048 @kindex info proc mappings
10049 @item info proc mappings
10050 Report on the address ranges accessible in the program, with information
10051 on whether your program may read, write, or execute each range.
10053 @kindex info proc times
10054 @item info proc times
10055 Starting time, user CPU time, and system CPU time for your program and
10058 @kindex info proc id
10060 Report on the process IDs related to your program: its own process ID,
10061 the ID of its parent, the process group ID, and the session ID.
10063 @kindex info proc status
10064 @item info proc status
10065 General information on the state of the process. If the process is
10066 stopped, this report includes the reason for stopping, and any signal
10069 @item info proc all
10070 Show all the above information about the process.
10074 @section Embedded Operating Systems
10076 This section describes configurations involving the debugging of
10077 embedded operating systems that are available for several different
10081 * VxWorks:: Using @value{GDBN} with VxWorks
10084 @value{GDBN} includes the ability to debug programs running on
10085 various real-time operating systems.
10088 @subsection Using @value{GDBN} with VxWorks
10094 @kindex target vxworks
10095 @item target vxworks @var{machinename}
10096 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
10097 is the target system's machine name or IP address.
10101 On VxWorks, @code{load} links @var{filename} dynamically on the
10102 current target system as well as adding its symbols in @value{GDBN}.
10104 @value{GDBN} enables developers to spawn and debug tasks running on networked
10105 VxWorks targets from a Unix host. Already-running tasks spawned from
10106 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
10107 both the Unix host and on the VxWorks target. The program
10108 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
10109 installed with the name @code{vxgdb}, to distinguish it from a
10110 @value{GDBN} for debugging programs on the host itself.)
10113 @item VxWorks-timeout @var{args}
10114 @kindex vxworks-timeout
10115 All VxWorks-based targets now support the option @code{vxworks-timeout}.
10116 This option is set by the user, and @var{args} represents the number of
10117 seconds @value{GDBN} waits for responses to rpc's. You might use this if
10118 your VxWorks target is a slow software simulator or is on the far side
10119 of a thin network line.
10122 The following information on connecting to VxWorks was current when
10123 this manual was produced; newer releases of VxWorks may use revised
10126 @kindex INCLUDE_RDB
10127 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
10128 to include the remote debugging interface routines in the VxWorks
10129 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
10130 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
10131 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
10132 source debugging task @code{tRdbTask} when VxWorks is booted. For more
10133 information on configuring and remaking VxWorks, see the manufacturer's
10135 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
10137 Once you have included @file{rdb.a} in your VxWorks system image and set
10138 your Unix execution search path to find @value{GDBN}, you are ready to
10139 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
10140 @code{vxgdb}, depending on your installation).
10142 @value{GDBN} comes up showing the prompt:
10149 * VxWorks Connection:: Connecting to VxWorks
10150 * VxWorks Download:: VxWorks download
10151 * VxWorks Attach:: Running tasks
10154 @node VxWorks Connection
10155 @subsubsection Connecting to VxWorks
10157 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
10158 network. To connect to a target whose host name is ``@code{tt}'', type:
10161 (vxgdb) target vxworks tt
10165 @value{GDBN} displays messages like these:
10168 Attaching remote machine across net...
10173 @value{GDBN} then attempts to read the symbol tables of any object modules
10174 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
10175 these files by searching the directories listed in the command search
10176 path (@pxref{Environment, ,Your program's environment}); if it fails
10177 to find an object file, it displays a message such as:
10180 prog.o: No such file or directory.
10183 When this happens, add the appropriate directory to the search path with
10184 the @value{GDBN} command @code{path}, and execute the @code{target}
10187 @node VxWorks Download
10188 @subsubsection VxWorks download
10190 @cindex download to VxWorks
10191 If you have connected to the VxWorks target and you want to debug an
10192 object that has not yet been loaded, you can use the @value{GDBN}
10193 @code{load} command to download a file from Unix to VxWorks
10194 incrementally. The object file given as an argument to the @code{load}
10195 command is actually opened twice: first by the VxWorks target in order
10196 to download the code, then by @value{GDBN} in order to read the symbol
10197 table. This can lead to problems if the current working directories on
10198 the two systems differ. If both systems have NFS mounted the same
10199 filesystems, you can avoid these problems by using absolute paths.
10200 Otherwise, it is simplest to set the working directory on both systems
10201 to the directory in which the object file resides, and then to reference
10202 the file by its name, without any path. For instance, a program
10203 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
10204 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
10205 program, type this on VxWorks:
10208 -> cd "@var{vxpath}/vw/demo/rdb"
10212 Then, in @value{GDBN}, type:
10215 (vxgdb) cd @var{hostpath}/vw/demo/rdb
10216 (vxgdb) load prog.o
10219 @value{GDBN} displays a response similar to this:
10222 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
10225 You can also use the @code{load} command to reload an object module
10226 after editing and recompiling the corresponding source file. Note that
10227 this makes @value{GDBN} delete all currently-defined breakpoints,
10228 auto-displays, and convenience variables, and to clear the value
10229 history. (This is necessary in order to preserve the integrity of
10230 debugger's data structures that reference the target system's symbol
10233 @node VxWorks Attach
10234 @subsubsection Running tasks
10236 @cindex running VxWorks tasks
10237 You can also attach to an existing task using the @code{attach} command as
10241 (vxgdb) attach @var{task}
10245 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
10246 or suspended when you attach to it. Running tasks are suspended at
10247 the time of attachment.
10249 @node Embedded Processors
10250 @section Embedded Processors
10252 This section goes into details specific to particular embedded
10256 * A29K Embedded:: AMD A29K Embedded
10258 * H8/300:: Hitachi H8/300
10259 * H8/500:: Hitachi H8/500
10260 * i960:: Intel i960
10261 * M32R/D:: Mitsubishi M32R/D
10262 * M68K:: Motorola M68K
10263 * M88K:: Motorola M88K
10264 * MIPS Embedded:: MIPS Embedded
10265 * PA:: HP PA Embedded
10268 * Sparclet:: Tsqware Sparclet
10269 * Sparclite:: Fujitsu Sparclite
10270 * ST2000:: Tandem ST2000
10271 * Z8000:: Zilog Z8000
10274 @node A29K Embedded
10275 @subsection AMD A29K Embedded
10280 * Comms (EB29K):: Communications setup
10281 * gdb-EB29K:: EB29K cross-debugging
10282 * Remote Log:: Remote log
10287 @kindex target adapt
10288 @item target adapt @var{dev}
10289 Adapt monitor for A29K.
10291 @kindex target amd-eb
10292 @item target amd-eb @var{dev} @var{speed} @var{PROG}
10294 Remote PC-resident AMD EB29K board, attached over serial lines.
10295 @var{dev} is the serial device, as for @code{target remote};
10296 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
10297 name of the program to be debugged, as it appears to DOS on the PC.
10298 @xref{A29K EB29K, ,EBMON protocol for AMD29K}.
10303 @subsubsection A29K UDI
10306 @cindex AMD29K via UDI
10308 @value{GDBN} supports AMD's UDI (``Universal Debugger Interface'')
10309 protocol for debugging the a29k processor family. To use this
10310 configuration with AMD targets running the MiniMON monitor, you need the
10311 program @code{MONTIP}, available from AMD at no charge. You can also
10312 use @value{GDBN} with the UDI-conformant a29k simulator program
10313 @code{ISSTIP}, also available from AMD.
10316 @item target udi @var{keyword}
10318 Select the UDI interface to a remote a29k board or simulator, where
10319 @var{keyword} is an entry in the AMD configuration file @file{udi_soc}.
10320 This file contains keyword entries which specify parameters used to
10321 connect to a29k targets. If the @file{udi_soc} file is not in your
10322 working directory, you must set the environment variable @samp{UDICONF}
10327 @subsubsection EBMON protocol for AMD29K
10329 @cindex EB29K board
10330 @cindex running 29K programs
10332 AMD distributes a 29K development board meant to fit in a PC, together
10333 with a DOS-hosted monitor program called @code{EBMON}. As a shorthand
10334 term, this development system is called the ``EB29K''. To use
10335 @value{GDBN} from a Unix system to run programs on the EB29K board, you
10336 must first connect a serial cable between the PC (which hosts the EB29K
10337 board) and a serial port on the Unix system. In the following, we
10338 assume you've hooked the cable between the PC's @file{COM1} port and
10339 @file{/dev/ttya} on the Unix system.
10341 @node Comms (EB29K)
10342 @subsubsection Communications setup
10344 The next step is to set up the PC's port, by doing something like this
10348 C:\> MODE com1:9600,n,8,1,none
10352 This example---run on an MS DOS 4.0 system---sets the PC port to 9600
10353 bps, no parity, eight data bits, one stop bit, and no ``retry'' action;
10354 you must match the communications parameters when establishing the Unix
10355 end of the connection as well.
10356 @c FIXME: Who knows what this "no retry action" crud from the DOS manual may
10357 @c mean? It's optional; leave it out? ---doc@cygnus.com, 25feb91
10359 @c It's optional, but it's unwise to omit it: who knows what is the
10360 @c default value set when the DOS machines boots? "No retry" means that
10361 @c the DOS serial device driver won't retry the operation if it fails;
10362 @c I understand that this is needed because the GDB serial protocol
10363 @c handles any errors and retransmissions itself. ---Eli Zaretskii, 3sep99
10365 To give control of the PC to the Unix side of the serial line, type
10366 the following at the DOS console:
10373 (Later, if you wish to return control to the DOS console, you can use
10374 the command @code{CTTY con}---but you must send it over the device that
10375 had control, in our example over the @file{COM1} serial line.)
10377 From the Unix host, use a communications program such as @code{tip} or
10378 @code{cu} to communicate with the PC; for example,
10381 cu -s 9600 -l /dev/ttya
10385 The @code{cu} options shown specify, respectively, the linespeed and the
10386 serial port to use. If you use @code{tip} instead, your command line
10387 may look something like the following:
10390 tip -9600 /dev/ttya
10394 Your system may require a different name where we show
10395 @file{/dev/ttya} as the argument to @code{tip}. The communications
10396 parameters, including which port to use, are associated with the
10397 @code{tip} argument in the ``remote'' descriptions file---normally the
10398 system table @file{/etc/remote}.
10399 @c FIXME: What if anything needs doing to match the "n,8,1,none" part of
10400 @c the DOS side's comms setup? cu can support -o (odd
10401 @c parity), -e (even parity)---apparently no settings for no parity or
10402 @c for character size. Taken from stty maybe...? John points out tip
10403 @c can set these as internal variables, eg ~s parity=none; man stty
10404 @c suggests that it *might* work to stty these options with stdin or
10405 @c stdout redirected... ---doc@cygnus.com, 25feb91
10407 @c There's nothing to be done for the "none" part of the DOS MODE
10408 @c command. The rest of the parameters should be matched by the
10409 @c baudrate, bits, and parity used by the Unix side. ---Eli Zaretskii, 3Sep99
10412 Using the @code{tip} or @code{cu} connection, change the DOS working
10413 directory to the directory containing a copy of your 29K program, then
10414 start the PC program @code{EBMON} (an EB29K control program supplied
10415 with your board by AMD). You should see an initial display from
10416 @code{EBMON} similar to the one that follows, ending with the
10417 @code{EBMON} prompt @samp{#}---
10422 G:\> CD \usr\joe\work29k
10424 G:\USR\JOE\WORK29K> EBMON
10425 Am29000 PC Coprocessor Board Monitor, version 3.0-18
10426 Copyright 1990 Advanced Micro Devices, Inc.
10427 Written by Gibbons and Associates, Inc.
10429 Enter '?' or 'H' for help
10431 PC Coprocessor Type = EB29K
10433 Memory Base = 0xd0000
10435 Data Memory Size = 2048KB
10436 Available I-RAM Range = 0x8000 to 0x1fffff
10437 Available D-RAM Range = 0x80002000 to 0x801fffff
10440 Register Stack Size = 0x800
10441 Memory Stack Size = 0x1800
10444 Am29027 Available = No
10445 Byte Write Available = Yes
10450 Then exit the @code{cu} or @code{tip} program (done in the example by
10451 typing @code{~.} at the @code{EBMON} prompt). @code{EBMON} keeps
10452 running, ready for @value{GDBN} to take over.
10454 For this example, we've assumed what is probably the most convenient
10455 way to make sure the same 29K program is on both the PC and the Unix
10456 system: a PC/NFS connection that establishes ``drive @file{G:}'' on the
10457 PC as a file system on the Unix host. If you do not have PC/NFS or
10458 something similar connecting the two systems, you must arrange some
10459 other way---perhaps floppy-disk transfer---of getting the 29K program
10460 from the Unix system to the PC; @value{GDBN} does @emph{not} download it over the
10464 @subsubsection EB29K cross-debugging
10466 Finally, @code{cd} to the directory containing an image of your 29K
10467 program on the Unix system, and start @value{GDBN}---specifying as argument the
10468 name of your 29K program:
10471 cd /usr/joe/work29k
10476 Now you can use the @code{target} command:
10479 target amd-eb /dev/ttya 9600 MYFOO
10480 @c FIXME: test above 'target amd-eb' as spelled, with caps! caps are meant to
10481 @c emphasize that this is the name as seen by DOS (since I think DOS is
10482 @c single-minded about case of letters). ---doc@cygnus.com, 25feb91
10486 In this example, we've assumed your program is in a file called
10487 @file{myfoo}. Note that the filename given as the last argument to
10488 @code{target amd-eb} should be the name of the program as it appears to DOS.
10489 In our example this is simply @code{MYFOO}, but in general it can include
10490 a DOS path, and depending on your transfer mechanism may not resemble
10491 the name on the Unix side.
10493 At this point, you can set any breakpoints you wish; when you are ready
10494 to see your program run on the 29K board, use the @value{GDBN} command
10497 To stop debugging the remote program, use the @value{GDBN} @code{detach}
10500 To return control of the PC to its console, use @code{tip} or @code{cu}
10501 once again, after your @value{GDBN} session has concluded, to attach to
10502 @code{EBMON}. You can then type the command @code{q} to shut down
10503 @code{EBMON}, returning control to the DOS command-line interpreter.
10504 Type @kbd{CTTY con} to return command input to the main DOS console,
10505 and type @kbd{~.} to leave @code{tip} or @code{cu}.
10508 @subsubsection Remote log
10509 @cindex @file{eb.log}, a log file for EB29K
10510 @cindex log file for EB29K
10512 The @code{target amd-eb} command creates a file @file{eb.log} in the
10513 current working directory, to help debug problems with the connection.
10514 @file{eb.log} records all the output from @code{EBMON}, including echoes
10515 of the commands sent to it. Running @samp{tail -f} on this file in
10516 another window often helps to understand trouble with @code{EBMON}, or
10517 unexpected events on the PC side of the connection.
10525 @item target rdi @var{dev}
10526 ARM Angel monitor, via RDI library interface to ADP protocol. You may
10527 use this target to communicate with both boards running the Angel
10528 monitor, or with the EmbeddedICE JTAG debug device.
10531 @item target rdp @var{dev}
10537 @subsection Hitachi H8/300
10541 @kindex target hms@r{, with H8/300}
10542 @item target hms @var{dev}
10543 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
10544 Use special commands @code{device} and @code{speed} to control the serial
10545 line and the communications speed used.
10547 @kindex target e7000@r{, with H8/300}
10548 @item target e7000 @var{dev}
10549 E7000 emulator for Hitachi H8 and SH.
10551 @kindex target sh3@r{, with H8/300}
10552 @kindex target sh3e@r{, with H8/300}
10553 @item target sh3 @var{dev}
10554 @itemx target sh3e @var{dev}
10555 Hitachi SH-3 and SH-3E target systems.
10559 @cindex download to H8/300 or H8/500
10560 @cindex H8/300 or H8/500 download
10561 @cindex download to Hitachi SH
10562 @cindex Hitachi SH download
10563 When you select remote debugging to a Hitachi SH, H8/300, or H8/500
10564 board, the @code{load} command downloads your program to the Hitachi
10565 board and also opens it as the current executable target for
10566 @value{GDBN} on your host (like the @code{file} command).
10568 @value{GDBN} needs to know these things to talk to your
10569 Hitachi SH, H8/300, or H8/500:
10573 that you want to use @samp{target hms}, the remote debugging interface
10574 for Hitachi microprocessors, or @samp{target e7000}, the in-circuit
10575 emulator for the Hitachi SH and the Hitachi 300H. (@samp{target hms} is
10576 the default when @value{GDBN} is configured specifically for the Hitachi SH,
10577 H8/300, or H8/500.)
10580 what serial device connects your host to your Hitachi board (the first
10581 serial device available on your host is the default).
10584 what speed to use over the serial device.
10588 * Hitachi Boards:: Connecting to Hitachi boards.
10589 * Hitachi ICE:: Using the E7000 In-Circuit Emulator.
10590 * Hitachi Special:: Special @value{GDBN} commands for Hitachi micros.
10593 @node Hitachi Boards
10594 @subsubsection Connecting to Hitachi boards
10596 @c only for Unix hosts
10598 @cindex serial device, Hitachi micros
10599 Use the special @code{@value{GDBN}} command @samp{device @var{port}} if you
10600 need to explicitly set the serial device. The default @var{port} is the
10601 first available port on your host. This is only necessary on Unix
10602 hosts, where it is typically something like @file{/dev/ttya}.
10605 @cindex serial line speed, Hitachi micros
10606 @code{@value{GDBN}} has another special command to set the communications
10607 speed: @samp{speed @var{bps}}. This command also is only used from Unix
10608 hosts; on DOS hosts, set the line speed as usual from outside @value{GDBN} with
10609 the DOS @code{mode} command (for instance,
10610 @w{@kbd{mode com2:9600,n,8,1,p}} for a 9600@dmn{bps} connection).
10612 The @samp{device} and @samp{speed} commands are available only when you
10613 use a Unix host to debug your Hitachi microprocessor programs. If you
10615 @value{GDBN} depends on an auxiliary terminate-and-stay-resident program
10616 called @code{asynctsr} to communicate with the development board
10617 through a PC serial port. You must also use the DOS @code{mode} command
10618 to set up the serial port on the DOS side.
10620 The following sample session illustrates the steps needed to start a
10621 program under @value{GDBN} control on an H8/300. The example uses a
10622 sample H8/300 program called @file{t.x}. The procedure is the same for
10623 the Hitachi SH and the H8/500.
10625 First hook up your development board. In this example, we use a
10626 board attached to serial port @code{COM2}; if you use a different serial
10627 port, substitute its name in the argument of the @code{mode} command.
10628 When you call @code{asynctsr}, the auxiliary comms program used by the
10629 debugger, you give it just the numeric part of the serial port's name;
10630 for example, @samp{asyncstr 2} below runs @code{asyncstr} on
10634 C:\H8300\TEST> asynctsr 2
10635 C:\H8300\TEST> mode com2:9600,n,8,1,p
10637 Resident portion of MODE loaded
10639 COM2: 9600, n, 8, 1, p
10644 @emph{Warning:} We have noticed a bug in PC-NFS that conflicts with
10645 @code{asynctsr}. If you also run PC-NFS on your DOS host, you may need to
10646 disable it, or even boot without it, to use @code{asynctsr} to control
10647 your development board.
10650 @kindex target hms@r{, and serial protocol}
10651 Now that serial communications are set up, and the development board is
10652 connected, you can start up @value{GDBN}. Call @code{@value{GDBP}} with
10653 the name of your program as the argument. @code{@value{GDBN}} prompts
10654 you, as usual, with the prompt @samp{(@value{GDBP})}. Use two special
10655 commands to begin your debugging session: @samp{target hms} to specify
10656 cross-debugging to the Hitachi board, and the @code{load} command to
10657 download your program to the board. @code{load} displays the names of
10658 the program's sections, and a @samp{*} for each 2K of data downloaded.
10659 (If you want to refresh @value{GDBN} data on symbols or on the
10660 executable file without downloading, use the @value{GDBN} commands
10661 @code{file} or @code{symbol-file}. These commands, and @code{load}
10662 itself, are described in @ref{Files,,Commands to specify files}.)
10665 (eg-C:\H8300\TEST) @value{GDBP} t.x
10666 @value{GDBN} is free software and you are welcome to distribute copies
10667 of it under certain conditions; type "show copying" to see
10669 There is absolutely no warranty for @value{GDBN}; type "show warranty"
10671 @value{GDBN} @value{GDBVN}, Copyright 1992 Free Software Foundation, Inc...
10672 (@value{GDBP}) target hms
10673 Connected to remote H8/300 HMS system.
10674 (@value{GDBP}) load t.x
10675 .text : 0x8000 .. 0xabde ***********
10676 .data : 0xabde .. 0xad30 *
10677 .stack : 0xf000 .. 0xf014 *
10680 At this point, you're ready to run or debug your program. From here on,
10681 you can use all the usual @value{GDBN} commands. The @code{break} command
10682 sets breakpoints; the @code{run} command starts your program;
10683 @code{print} or @code{x} display data; the @code{continue} command
10684 resumes execution after stopping at a breakpoint. You can use the
10685 @code{help} command at any time to find out more about @value{GDBN} commands.
10687 Remember, however, that @emph{operating system} facilities aren't
10688 available on your development board; for example, if your program hangs,
10689 you can't send an interrupt---but you can press the @sc{reset} switch!
10691 Use the @sc{reset} button on the development board
10694 to interrupt your program (don't use @kbd{ctl-C} on the DOS host---it has
10695 no way to pass an interrupt signal to the development board); and
10698 to return to the @value{GDBN} command prompt after your program finishes
10699 normally. The communications protocol provides no other way for @value{GDBN}
10700 to detect program completion.
10703 In either case, @value{GDBN} sees the effect of a @sc{reset} on the
10704 development board as a ``normal exit'' of your program.
10707 @subsubsection Using the E7000 in-circuit emulator
10709 @kindex target e7000@r{, with Hitachi ICE}
10710 You can use the E7000 in-circuit emulator to develop code for either the
10711 Hitachi SH or the H8/300H. Use one of these forms of the @samp{target
10712 e7000} command to connect @value{GDBN} to your E7000:
10715 @item target e7000 @var{port} @var{speed}
10716 Use this form if your E7000 is connected to a serial port. The
10717 @var{port} argument identifies what serial port to use (for example,
10718 @samp{com2}). The third argument is the line speed in bits per second
10719 (for example, @samp{9600}).
10721 @item target e7000 @var{hostname}
10722 If your E7000 is installed as a host on a TCP/IP network, you can just
10723 specify its hostname; @value{GDBN} uses @code{telnet} to connect.
10726 @node Hitachi Special
10727 @subsubsection Special @value{GDBN} commands for Hitachi micros
10729 Some @value{GDBN} commands are available only for the H8/300:
10733 @kindex set machine
10734 @kindex show machine
10735 @item set machine h8300
10736 @itemx set machine h8300h
10737 Condition @value{GDBN} for one of the two variants of the H8/300
10738 architecture with @samp{set machine}. You can use @samp{show machine}
10739 to check which variant is currently in effect.
10748 @kindex set memory @var{mod}
10749 @cindex memory models, H8/500
10750 @item set memory @var{mod}
10752 Specify which H8/500 memory model (@var{mod}) you are using with
10753 @samp{set memory}; check which memory model is in effect with @samp{show
10754 memory}. The accepted values for @var{mod} are @code{small},
10755 @code{big}, @code{medium}, and @code{compact}.
10760 @subsection Intel i960
10764 @kindex target mon960
10765 @item target mon960 @var{dev}
10766 MON960 monitor for Intel i960.
10768 @kindex target nindy
10769 @item target nindy @var{devicename}
10770 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
10771 the name of the serial device to use for the connection, e.g.
10778 @dfn{Nindy} is a ROM Monitor program for Intel 960 target systems. When
10779 @value{GDBN} is configured to control a remote Intel 960 using Nindy, you can
10780 tell @value{GDBN} how to connect to the 960 in several ways:
10784 Through command line options specifying serial port, version of the
10785 Nindy protocol, and communications speed;
10788 By responding to a prompt on startup;
10791 By using the @code{target} command at any point during your @value{GDBN}
10792 session. @xref{Target Commands, ,Commands for managing targets}.
10796 @cindex download to Nindy-960
10797 With the Nindy interface to an Intel 960 board, @code{load}
10798 downloads @var{filename} to the 960 as well as adding its symbols in
10802 * Nindy Startup:: Startup with Nindy
10803 * Nindy Options:: Options for Nindy
10804 * Nindy Reset:: Nindy reset command
10807 @node Nindy Startup
10808 @subsubsection Startup with Nindy
10810 If you simply start @code{@value{GDBP}} without using any command-line
10811 options, you are prompted for what serial port to use, @emph{before} you
10812 reach the ordinary @value{GDBN} prompt:
10815 Attach /dev/ttyNN -- specify NN, or "quit" to quit:
10819 Respond to the prompt with whatever suffix (after @samp{/dev/tty})
10820 identifies the serial port you want to use. You can, if you choose,
10821 simply start up with no Nindy connection by responding to the prompt
10822 with an empty line. If you do this and later wish to attach to Nindy,
10823 use @code{target} (@pxref{Target Commands, ,Commands for managing targets}).
10825 @node Nindy Options
10826 @subsubsection Options for Nindy
10828 These are the startup options for beginning your @value{GDBN} session with a
10829 Nindy-960 board attached:
10832 @item -r @var{port}
10833 Specify the serial port name of a serial interface to be used to connect
10834 to the target system. This option is only available when @value{GDBN} is
10835 configured for the Intel 960 target architecture. You may specify
10836 @var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a
10837 device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique
10838 suffix for a specific @code{tty} (e.g. @samp{-r a}).
10841 (An uppercase letter ``O'', not a zero.) Specify that @value{GDBN} should use
10842 the ``old'' Nindy monitor protocol to connect to the target system.
10843 This option is only available when @value{GDBN} is configured for the Intel 960
10844 target architecture.
10847 @emph{Warning:} if you specify @samp{-O}, but are actually trying to
10848 connect to a target system that expects the newer protocol, the connection
10849 fails, appearing to be a speed mismatch. @value{GDBN} repeatedly
10850 attempts to reconnect at several different line speeds. You can abort
10851 this process with an interrupt.
10855 Specify that @value{GDBN} should first send a @code{BREAK} signal to the target
10856 system, in an attempt to reset it, before connecting to a Nindy target.
10859 @emph{Warning:} Many target systems do not have the hardware that this
10860 requires; it only works with a few boards.
10864 The standard @samp{-b} option controls the line speed used on the serial
10869 @subsubsection Nindy reset command
10874 For a Nindy target, this command sends a ``break'' to the remote target
10875 system; this is only useful if the target has been equipped with a
10876 circuit to perform a hard reset (or some other interesting action) when
10877 a break is detected.
10882 @subsection Mitsubishi M32R/D
10886 @kindex target m32r
10887 @item target m32r @var{dev}
10888 Mitsubishi M32R/D ROM monitor.
10895 The Motorola m68k configuration includes ColdFire support, and
10896 target command for the following ROM monitors.
10900 @kindex target abug
10901 @item target abug @var{dev}
10902 ABug ROM monitor for M68K.
10904 @kindex target cpu32bug
10905 @item target cpu32bug @var{dev}
10906 CPU32BUG monitor, running on a CPU32 (M68K) board.
10908 @kindex target dbug
10909 @item target dbug @var{dev}
10910 dBUG ROM monitor for Motorola ColdFire.
10913 @item target est @var{dev}
10914 EST-300 ICE monitor, running on a CPU32 (M68K) board.
10916 @kindex target rom68k
10917 @item target rom68k @var{dev}
10918 ROM 68K monitor, running on an M68K IDP board.
10922 If @value{GDBN} is configured with @code{m68*-ericsson-*}, it will
10923 instead have only a single special target command:
10927 @kindex target es1800
10928 @item target es1800 @var{dev}
10929 ES-1800 emulator for M68K.
10937 @kindex target rombug
10938 @item target rombug @var{dev}
10939 ROMBUG ROM monitor for OS/9000.
10949 @item target bug @var{dev}
10950 BUG monitor, running on a MVME187 (m88k) board.
10954 @node MIPS Embedded
10955 @subsection MIPS Embedded
10957 @cindex MIPS boards
10958 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
10959 MIPS board attached to a serial line. This is available when
10960 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
10963 Use these @value{GDBN} commands to specify the connection to your target board:
10966 @item target mips @var{port}
10967 @kindex target mips @var{port}
10968 To run a program on the board, start up @code{@value{GDBP}} with the
10969 name of your program as the argument. To connect to the board, use the
10970 command @samp{target mips @var{port}}, where @var{port} is the name of
10971 the serial port connected to the board. If the program has not already
10972 been downloaded to the board, you may use the @code{load} command to
10973 download it. You can then use all the usual @value{GDBN} commands.
10975 For example, this sequence connects to the target board through a serial
10976 port, and loads and runs a program called @var{prog} through the
10980 host$ @value{GDBP} @var{prog}
10981 @value{GDBN} is free software and @dots{}
10982 (@value{GDBP}) target mips /dev/ttyb
10983 (@value{GDBP}) load @var{prog}
10987 @item target mips @var{hostname}:@var{portnumber}
10988 On some @value{GDBN} host configurations, you can specify a TCP
10989 connection (for instance, to a serial line managed by a terminal
10990 concentrator) instead of a serial port, using the syntax
10991 @samp{@var{hostname}:@var{portnumber}}.
10993 @item target pmon @var{port}
10994 @kindex target pmon @var{port}
10997 @item target ddb @var{port}
10998 @kindex target ddb @var{port}
10999 NEC's DDB variant of PMON for Vr4300.
11001 @item target lsi @var{port}
11002 @kindex target lsi @var{port}
11003 LSI variant of PMON.
11005 @kindex target r3900
11006 @item target r3900 @var{dev}
11007 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
11009 @kindex target array
11010 @item target array @var{dev}
11011 Array Tech LSI33K RAID controller board.
11017 @value{GDBN} also supports these special commands for MIPS targets:
11020 @item set processor @var{args}
11021 @itemx show processor
11022 @kindex set processor @var{args}
11023 @kindex show processor
11024 Use the @code{set processor} command to set the type of MIPS
11025 processor when you want to access processor-type-specific registers.
11026 For example, @code{set processor @var{r3041}} tells @value{GDBN}
11027 to use the CPU registers appropriate for the 3041 chip.
11028 Use the @code{show processor} command to see what MIPS processor @value{GDBN}
11029 is using. Use the @code{info reg} command to see what registers
11030 @value{GDBN} is using.
11032 @item set mipsfpu double
11033 @itemx set mipsfpu single
11034 @itemx set mipsfpu none
11035 @itemx show mipsfpu
11036 @kindex set mipsfpu
11037 @kindex show mipsfpu
11038 @cindex MIPS remote floating point
11039 @cindex floating point, MIPS remote
11040 If your target board does not support the MIPS floating point
11041 coprocessor, you should use the command @samp{set mipsfpu none} (if you
11042 need this, you may wish to put the command in your @value{GDBN} init
11043 file). This tells @value{GDBN} how to find the return value of
11044 functions which return floating point values. It also allows
11045 @value{GDBN} to avoid saving the floating point registers when calling
11046 functions on the board. If you are using a floating point coprocessor
11047 with only single precision floating point support, as on the @sc{r4650}
11048 processor, use the command @samp{set mipsfpu single}. The default
11049 double precision floating point coprocessor may be selected using
11050 @samp{set mipsfpu double}.
11052 In previous versions the only choices were double precision or no
11053 floating point, so @samp{set mipsfpu on} will select double precision
11054 and @samp{set mipsfpu off} will select no floating point.
11056 As usual, you can inquire about the @code{mipsfpu} variable with
11057 @samp{show mipsfpu}.
11059 @item set remotedebug @var{n}
11060 @itemx show remotedebug
11061 @kindex set remotedebug@r{, MIPS protocol}
11062 @kindex show remotedebug@r{, MIPS protocol}
11063 @cindex @code{remotedebug}, MIPS protocol
11064 @cindex MIPS @code{remotedebug} protocol
11065 @c FIXME! For this to be useful, you must know something about the MIPS
11066 @c FIXME...protocol. Where is it described?
11067 You can see some debugging information about communications with the board
11068 by setting the @code{remotedebug} variable. If you set it to @code{1} using
11069 @samp{set remotedebug 1}, every packet is displayed. If you set it
11070 to @code{2}, every character is displayed. You can check the current value
11071 at any time with the command @samp{show remotedebug}.
11073 @item set timeout @var{seconds}
11074 @itemx set retransmit-timeout @var{seconds}
11075 @itemx show timeout
11076 @itemx show retransmit-timeout
11077 @cindex @code{timeout}, MIPS protocol
11078 @cindex @code{retransmit-timeout}, MIPS protocol
11079 @kindex set timeout
11080 @kindex show timeout
11081 @kindex set retransmit-timeout
11082 @kindex show retransmit-timeout
11083 You can control the timeout used while waiting for a packet, in the MIPS
11084 remote protocol, with the @code{set timeout @var{seconds}} command. The
11085 default is 5 seconds. Similarly, you can control the timeout used while
11086 waiting for an acknowledgement of a packet with the @code{set
11087 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
11088 You can inspect both values with @code{show timeout} and @code{show
11089 retransmit-timeout}. (These commands are @emph{only} available when
11090 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
11092 The timeout set by @code{set timeout} does not apply when @value{GDBN}
11093 is waiting for your program to stop. In that case, @value{GDBN} waits
11094 forever because it has no way of knowing how long the program is going
11095 to run before stopping.
11099 @subsection PowerPC
11103 @kindex target dink32
11104 @item target dink32 @var{dev}
11105 DINK32 ROM monitor.
11107 @kindex target ppcbug
11108 @item target ppcbug @var{dev}
11109 @kindex target ppcbug1
11110 @item target ppcbug1 @var{dev}
11111 PPCBUG ROM monitor for PowerPC.
11114 @item target sds @var{dev}
11115 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
11120 @subsection HP PA Embedded
11124 @kindex target op50n
11125 @item target op50n @var{dev}
11126 OP50N monitor, running on an OKI HPPA board.
11128 @kindex target w89k
11129 @item target w89k @var{dev}
11130 W89K monitor, running on a Winbond HPPA board.
11135 @subsection Hitachi SH
11139 @kindex target hms@r{, with Hitachi SH}
11140 @item target hms @var{dev}
11141 A Hitachi SH board attached via serial line to your host. Use special
11142 commands @code{device} and @code{speed} to control the serial line and
11143 the communications speed used.
11145 @kindex target e7000@r{, with Hitachi SH}
11146 @item target e7000 @var{dev}
11147 E7000 emulator for Hitachi SH.
11149 @kindex target sh3@r{, with SH}
11150 @kindex target sh3e@r{, with SH}
11151 @item target sh3 @var{dev}
11152 @item target sh3e @var{dev}
11153 Hitachi SH-3 and SH-3E target systems.
11158 @subsection Tsqware Sparclet
11162 @value{GDBN} enables developers to debug tasks running on
11163 Sparclet targets from a Unix host.
11164 @value{GDBN} uses code that runs on
11165 both the Unix host and on the Sparclet target. The program
11166 @code{@value{GDBP}} is installed and executed on the Unix host.
11169 @item remotetimeout @var{args}
11170 @kindex remotetimeout
11171 @value{GDBN} supports the option @code{remotetimeout}.
11172 This option is set by the user, and @var{args} represents the number of
11173 seconds @value{GDBN} waits for responses.
11176 @cindex compiling, on Sparclet
11177 When compiling for debugging, include the options @samp{-g} to get debug
11178 information and @samp{-Ttext} to relocate the program to where you wish to
11179 load it on the target. You may also want to add the options @samp{-n} or
11180 @samp{-N} in order to reduce the size of the sections. Example:
11183 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
11186 You can use @code{objdump} to verify that the addresses are what you intended:
11189 sparclet-aout-objdump --headers --syms prog
11192 @cindex running, on Sparclet
11194 your Unix execution search path to find @value{GDBN}, you are ready to
11195 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
11196 (or @code{sparclet-aout-gdb}, depending on your installation).
11198 @value{GDBN} comes up showing the prompt:
11205 * Sparclet File:: Setting the file to debug
11206 * Sparclet Connection:: Connecting to Sparclet
11207 * Sparclet Download:: Sparclet download
11208 * Sparclet Execution:: Running and debugging
11211 @node Sparclet File
11212 @subsubsection Setting file to debug
11214 The @value{GDBN} command @code{file} lets you choose with program to debug.
11217 (gdbslet) file prog
11221 @value{GDBN} then attempts to read the symbol table of @file{prog}.
11222 @value{GDBN} locates
11223 the file by searching the directories listed in the command search
11225 If the file was compiled with debug information (option "-g"), source
11226 files will be searched as well.
11227 @value{GDBN} locates
11228 the source files by searching the directories listed in the directory search
11229 path (@pxref{Environment, ,Your program's environment}).
11231 to find a file, it displays a message such as:
11234 prog: No such file or directory.
11237 When this happens, add the appropriate directories to the search paths with
11238 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
11239 @code{target} command again.
11241 @node Sparclet Connection
11242 @subsubsection Connecting to Sparclet
11244 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
11245 To connect to a target on serial port ``@code{ttya}'', type:
11248 (gdbslet) target sparclet /dev/ttya
11249 Remote target sparclet connected to /dev/ttya
11250 main () at ../prog.c:3
11254 @value{GDBN} displays messages like these:
11260 @node Sparclet Download
11261 @subsubsection Sparclet download
11263 @cindex download to Sparclet
11264 Once connected to the Sparclet target,
11265 you can use the @value{GDBN}
11266 @code{load} command to download the file from the host to the target.
11267 The file name and load offset should be given as arguments to the @code{load}
11269 Since the file format is aout, the program must be loaded to the starting
11270 address. You can use @code{objdump} to find out what this value is. The load
11271 offset is an offset which is added to the VMA (virtual memory address)
11272 of each of the file's sections.
11273 For instance, if the program
11274 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
11275 and bss at 0x12010170, in @value{GDBN}, type:
11278 (gdbslet) load prog 0x12010000
11279 Loading section .text, size 0xdb0 vma 0x12010000
11282 If the code is loaded at a different address then what the program was linked
11283 to, you may need to use the @code{section} and @code{add-symbol-file} commands
11284 to tell @value{GDBN} where to map the symbol table.
11286 @node Sparclet Execution
11287 @subsubsection Running and debugging
11289 @cindex running and debugging Sparclet programs
11290 You can now begin debugging the task using @value{GDBN}'s execution control
11291 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
11292 manual for the list of commands.
11296 Breakpoint 1 at 0x12010000: file prog.c, line 3.
11298 Starting program: prog
11299 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
11300 3 char *symarg = 0;
11302 4 char *execarg = "hello!";
11307 @subsection Fujitsu Sparclite
11311 @kindex target sparclite
11312 @item target sparclite @var{dev}
11313 Fujitsu sparclite boards, used only for the purpose of loading.
11314 You must use an additional command to debug the program.
11315 For example: target remote @var{dev} using @value{GDBN} standard
11321 @subsection Tandem ST2000
11323 @value{GDBN} may be used with a Tandem ST2000 phone switch, running Tandem's
11326 To connect your ST2000 to the host system, see the manufacturer's
11327 manual. Once the ST2000 is physically attached, you can run:
11330 target st2000 @var{dev} @var{speed}
11334 to establish it as your debugging environment. @var{dev} is normally
11335 the name of a serial device, such as @file{/dev/ttya}, connected to the
11336 ST2000 via a serial line. You can instead specify @var{dev} as a TCP
11337 connection (for example, to a serial line attached via a terminal
11338 concentrator) using the syntax @code{@var{hostname}:@var{portnumber}}.
11340 The @code{load} and @code{attach} commands are @emph{not} defined for
11341 this target; you must load your program into the ST2000 as you normally
11342 would for standalone operation. @value{GDBN} reads debugging information
11343 (such as symbols) from a separate, debugging version of the program
11344 available on your host computer.
11345 @c FIXME!! This is terribly vague; what little content is here is
11346 @c basically hearsay.
11348 @cindex ST2000 auxiliary commands
11349 These auxiliary @value{GDBN} commands are available to help you with the ST2000
11353 @item st2000 @var{command}
11354 @kindex st2000 @var{cmd}
11355 @cindex STDBUG commands (ST2000)
11356 @cindex commands to STDBUG (ST2000)
11357 Send a @var{command} to the STDBUG monitor. See the manufacturer's
11358 manual for available commands.
11361 @cindex connect (to STDBUG)
11362 Connect the controlling terminal to the STDBUG command monitor. When
11363 you are done interacting with STDBUG, typing either of two character
11364 sequences gets you back to the @value{GDBN} command prompt:
11365 @kbd{@key{RET}~.} (Return, followed by tilde and period) or
11366 @kbd{@key{RET}~@key{C-d}} (Return, followed by tilde and control-D).
11370 @subsection Zilog Z8000
11373 @cindex simulator, Z8000
11374 @cindex Zilog Z8000 simulator
11376 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
11379 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
11380 unsegmented variant of the Z8000 architecture) or the Z8001 (the
11381 segmented variant). The simulator recognizes which architecture is
11382 appropriate by inspecting the object code.
11385 @item target sim @var{args}
11387 @kindex target sim@r{, with Z8000}
11388 Debug programs on a simulated CPU. If the simulator supports setup
11389 options, specify them via @var{args}.
11393 After specifying this target, you can debug programs for the simulated
11394 CPU in the same style as programs for your host computer; use the
11395 @code{file} command to load a new program image, the @code{run} command
11396 to run your program, and so on.
11398 As well as making available all the usual machine registers
11399 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
11400 additional items of information as specially named registers:
11405 Counts clock-ticks in the simulator.
11408 Counts instructions run in the simulator.
11411 Execution time in 60ths of a second.
11415 You can refer to these values in @value{GDBN} expressions with the usual
11416 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
11417 conditional breakpoint that suspends only after at least 5000
11418 simulated clock ticks.
11420 @node Architectures
11421 @section Architectures
11423 This section describes characteristics of architectures that affect
11424 all uses of @value{GDBN} with the architecture, both native and cross.
11437 @kindex set rstack_high_address
11438 @cindex AMD 29K register stack
11439 @cindex register stack, AMD29K
11440 @item set rstack_high_address @var{address}
11441 On AMD 29000 family processors, registers are saved in a separate
11442 @dfn{register stack}. There is no way for @value{GDBN} to determine the
11443 extent of this stack. Normally, @value{GDBN} just assumes that the
11444 stack is ``large enough''. This may result in @value{GDBN} referencing
11445 memory locations that do not exist. If necessary, you can get around
11446 this problem by specifying the ending address of the register stack with
11447 the @code{set rstack_high_address} command. The argument should be an
11448 address, which you probably want to precede with @samp{0x} to specify in
11451 @kindex show rstack_high_address
11452 @item show rstack_high_address
11453 Display the current limit of the register stack, on AMD 29000 family
11461 See the following section.
11466 @cindex stack on Alpha
11467 @cindex stack on MIPS
11468 @cindex Alpha stack
11470 Alpha- and MIPS-based computers use an unusual stack frame, which
11471 sometimes requires @value{GDBN} to search backward in the object code to
11472 find the beginning of a function.
11474 @cindex response time, MIPS debugging
11475 To improve response time (especially for embedded applications, where
11476 @value{GDBN} may be restricted to a slow serial line for this search)
11477 you may want to limit the size of this search, using one of these
11481 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
11482 @item set heuristic-fence-post @var{limit}
11483 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
11484 search for the beginning of a function. A value of @var{0} (the
11485 default) means there is no limit. However, except for @var{0}, the
11486 larger the limit the more bytes @code{heuristic-fence-post} must search
11487 and therefore the longer it takes to run.
11489 @item show heuristic-fence-post
11490 Display the current limit.
11494 These commands are available @emph{only} when @value{GDBN} is configured
11495 for debugging programs on Alpha or MIPS processors.
11498 @node Controlling GDB
11499 @chapter Controlling @value{GDBN}
11501 You can alter the way @value{GDBN} interacts with you by using the
11502 @code{set} command. For commands controlling how @value{GDBN} displays
11503 data, see @ref{Print Settings, ,Print settings}. Other settings are
11508 * Editing:: Command editing
11509 * History:: Command history
11510 * Screen Size:: Screen size
11511 * Numbers:: Numbers
11512 * Messages/Warnings:: Optional warnings and messages
11513 * Debugging Output:: Optional messages about internal happenings
11521 @value{GDBN} indicates its readiness to read a command by printing a string
11522 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
11523 can change the prompt string with the @code{set prompt} command. For
11524 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
11525 the prompt in one of the @value{GDBN} sessions so that you can always tell
11526 which one you are talking to.
11528 @emph{Note:} @code{set prompt} does not add a space for you after the
11529 prompt you set. This allows you to set a prompt which ends in a space
11530 or a prompt that does not.
11534 @item set prompt @var{newprompt}
11535 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
11537 @kindex show prompt
11539 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
11543 @section Command editing
11545 @cindex command line editing
11547 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
11548 @sc{gnu} library provides consistent behavior for programs which provide a
11549 command line interface to the user. Advantages are @sc{gnu} Emacs-style
11550 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
11551 substitution, and a storage and recall of command history across
11552 debugging sessions.
11554 You may control the behavior of command line editing in @value{GDBN} with the
11555 command @code{set}.
11558 @kindex set editing
11561 @itemx set editing on
11562 Enable command line editing (enabled by default).
11564 @item set editing off
11565 Disable command line editing.
11567 @kindex show editing
11569 Show whether command line editing is enabled.
11573 @section Command history
11575 @value{GDBN} can keep track of the commands you type during your
11576 debugging sessions, so that you can be certain of precisely what
11577 happened. Use these commands to manage the @value{GDBN} command
11581 @cindex history substitution
11582 @cindex history file
11583 @kindex set history filename
11584 @kindex GDBHISTFILE
11585 @item set history filename @var{fname}
11586 Set the name of the @value{GDBN} command history file to @var{fname}.
11587 This is the file where @value{GDBN} reads an initial command history
11588 list, and where it writes the command history from this session when it
11589 exits. You can access this list through history expansion or through
11590 the history command editing characters listed below. This file defaults
11591 to the value of the environment variable @code{GDBHISTFILE}, or to
11592 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
11595 @cindex history save
11596 @kindex set history save
11597 @item set history save
11598 @itemx set history save on
11599 Record command history in a file, whose name may be specified with the
11600 @code{set history filename} command. By default, this option is disabled.
11602 @item set history save off
11603 Stop recording command history in a file.
11605 @cindex history size
11606 @kindex set history size
11607 @item set history size @var{size}
11608 Set the number of commands which @value{GDBN} keeps in its history list.
11609 This defaults to the value of the environment variable
11610 @code{HISTSIZE}, or to 256 if this variable is not set.
11613 @cindex history expansion
11614 History expansion assigns special meaning to the character @kbd{!}.
11615 @ifset have-readline-appendices
11616 @xref{Event Designators}.
11619 Since @kbd{!} is also the logical not operator in C, history expansion
11620 is off by default. If you decide to enable history expansion with the
11621 @code{set history expansion on} command, you may sometimes need to
11622 follow @kbd{!} (when it is used as logical not, in an expression) with
11623 a space or a tab to prevent it from being expanded. The readline
11624 history facilities do not attempt substitution on the strings
11625 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
11627 The commands to control history expansion are:
11630 @kindex set history expansion
11631 @item set history expansion on
11632 @itemx set history expansion
11633 Enable history expansion. History expansion is off by default.
11635 @item set history expansion off
11636 Disable history expansion.
11638 The readline code comes with more complete documentation of
11639 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
11640 or @code{vi} may wish to read it.
11641 @ifset have-readline-appendices
11642 @xref{Command Line Editing}.
11646 @kindex show history
11648 @itemx show history filename
11649 @itemx show history save
11650 @itemx show history size
11651 @itemx show history expansion
11652 These commands display the state of the @value{GDBN} history parameters.
11653 @code{show history} by itself displays all four states.
11659 @item show commands
11660 Display the last ten commands in the command history.
11662 @item show commands @var{n}
11663 Print ten commands centered on command number @var{n}.
11665 @item show commands +
11666 Print ten commands just after the commands last printed.
11670 @section Screen size
11671 @cindex size of screen
11672 @cindex pauses in output
11674 Certain commands to @value{GDBN} may produce large amounts of
11675 information output to the screen. To help you read all of it,
11676 @value{GDBN} pauses and asks you for input at the end of each page of
11677 output. Type @key{RET} when you want to continue the output, or @kbd{q}
11678 to discard the remaining output. Also, the screen width setting
11679 determines when to wrap lines of output. Depending on what is being
11680 printed, @value{GDBN} tries to break the line at a readable place,
11681 rather than simply letting it overflow onto the following line.
11683 Normally @value{GDBN} knows the size of the screen from the terminal
11684 driver software. For example, on Unix @value{GDBN} uses the termcap data base
11685 together with the value of the @code{TERM} environment variable and the
11686 @code{stty rows} and @code{stty cols} settings. If this is not correct,
11687 you can override it with the @code{set height} and @code{set
11694 @kindex show height
11695 @item set height @var{lpp}
11697 @itemx set width @var{cpl}
11699 These @code{set} commands specify a screen height of @var{lpp} lines and
11700 a screen width of @var{cpl} characters. The associated @code{show}
11701 commands display the current settings.
11703 If you specify a height of zero lines, @value{GDBN} does not pause during
11704 output no matter how long the output is. This is useful if output is to a
11705 file or to an editor buffer.
11707 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
11708 from wrapping its output.
11713 @cindex number representation
11714 @cindex entering numbers
11716 You can always enter numbers in octal, decimal, or hexadecimal in
11717 @value{GDBN} by the usual conventions: octal numbers begin with
11718 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
11719 begin with @samp{0x}. Numbers that begin with none of these are, by
11720 default, entered in base 10; likewise, the default display for
11721 numbers---when no particular format is specified---is base 10. You can
11722 change the default base for both input and output with the @code{set
11726 @kindex set input-radix
11727 @item set input-radix @var{base}
11728 Set the default base for numeric input. Supported choices
11729 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
11730 specified either unambiguously or using the current default radix; for
11740 sets the base to decimal. On the other hand, @samp{set radix 10}
11741 leaves the radix unchanged no matter what it was.
11743 @kindex set output-radix
11744 @item set output-radix @var{base}
11745 Set the default base for numeric display. Supported choices
11746 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
11747 specified either unambiguously or using the current default radix.
11749 @kindex show input-radix
11750 @item show input-radix
11751 Display the current default base for numeric input.
11753 @kindex show output-radix
11754 @item show output-radix
11755 Display the current default base for numeric display.
11758 @node Messages/Warnings
11759 @section Optional warnings and messages
11761 By default, @value{GDBN} is silent about its inner workings. If you are
11762 running on a slow machine, you may want to use the @code{set verbose}
11763 command. This makes @value{GDBN} tell you when it does a lengthy
11764 internal operation, so you will not think it has crashed.
11766 Currently, the messages controlled by @code{set verbose} are those
11767 which announce that the symbol table for a source file is being read;
11768 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
11771 @kindex set verbose
11772 @item set verbose on
11773 Enables @value{GDBN} output of certain informational messages.
11775 @item set verbose off
11776 Disables @value{GDBN} output of certain informational messages.
11778 @kindex show verbose
11780 Displays whether @code{set verbose} is on or off.
11783 By default, if @value{GDBN} encounters bugs in the symbol table of an
11784 object file, it is silent; but if you are debugging a compiler, you may
11785 find this information useful (@pxref{Symbol Errors, ,Errors reading
11790 @kindex set complaints
11791 @item set complaints @var{limit}
11792 Permits @value{GDBN} to output @var{limit} complaints about each type of
11793 unusual symbols before becoming silent about the problem. Set
11794 @var{limit} to zero to suppress all complaints; set it to a large number
11795 to prevent complaints from being suppressed.
11797 @kindex show complaints
11798 @item show complaints
11799 Displays how many symbol complaints @value{GDBN} is permitted to produce.
11803 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
11804 lot of stupid questions to confirm certain commands. For example, if
11805 you try to run a program which is already running:
11809 The program being debugged has been started already.
11810 Start it from the beginning? (y or n)
11813 If you are willing to unflinchingly face the consequences of your own
11814 commands, you can disable this ``feature'':
11818 @kindex set confirm
11820 @cindex confirmation
11821 @cindex stupid questions
11822 @item set confirm off
11823 Disables confirmation requests.
11825 @item set confirm on
11826 Enables confirmation requests (the default).
11828 @kindex show confirm
11830 Displays state of confirmation requests.
11834 @node Debugging Output
11835 @section Optional messages about internal happenings
11837 @kindex set debug arch
11838 @item set debug arch
11839 Turns on or off display of gdbarch debugging info. The default is off
11840 @kindex show debug arch
11841 @item show debug arch
11842 Displays the current state of displaying gdbarch debugging info.
11843 @kindex set debug event
11844 @item set debug event
11845 Turns on or off display of @value{GDBN} event debugging info. The
11847 @kindex show debug event
11848 @item show debug event
11849 Displays the current state of displaying @value{GDBN} event debugging
11851 @kindex set debug expression
11852 @item set debug expression
11853 Turns on or off display of @value{GDBN} expression debugging info. The
11855 @kindex show debug expression
11856 @item show debug expression
11857 Displays the current state of displaying @value{GDBN} expression
11859 @kindex set debug overload
11860 @item set debug overload
11861 Turns on or off display of @value{GDBN} C++ overload debugging
11862 info. This includes info such as ranking of functions, etc. The default
11864 @kindex show debug overload
11865 @item show debug overload
11866 Displays the current state of displaying @value{GDBN} C++ overload
11868 @kindex set debug remote
11869 @cindex packets, reporting on stdout
11870 @cindex serial connections, debugging
11871 @item set debug remote
11872 Turns on or off display of reports on all packets sent back and forth across
11873 the serial line to the remote machine. The info is printed on the
11874 @value{GDBN} standard output stream. The default is off.
11875 @kindex show debug remote
11876 @item show debug remote
11877 Displays the state of display of remote packets.
11878 @kindex set debug serial
11879 @item set debug serial
11880 Turns on or off display of @value{GDBN} serial debugging info. The
11882 @kindex show debug serial
11883 @item show debug serial
11884 Displays the current state of displaying @value{GDBN} serial debugging
11886 @kindex set debug target
11887 @item set debug target
11888 Turns on or off display of @value{GDBN} target debugging info. This info
11889 includes what is going on at the target level of GDB, as it happens. The
11891 @kindex show debug target
11892 @item show debug target
11893 Displays the current state of displaying @value{GDBN} target debugging
11895 @kindex set debug varobj
11896 @item set debug varobj
11897 Turns on or off display of @value{GDBN} variable object debugging
11898 info. The default is off.
11899 @kindex show debug varobj
11900 @item show debug varobj
11901 Displays the current state of displaying @value{GDBN} variable object
11906 @chapter Canned Sequences of Commands
11908 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
11909 command lists}), @value{GDBN} provides two ways to store sequences of
11910 commands for execution as a unit: user-defined commands and command
11914 * Define:: User-defined commands
11915 * Hooks:: User-defined command hooks
11916 * Command Files:: Command files
11917 * Output:: Commands for controlled output
11921 @section User-defined commands
11923 @cindex user-defined command
11924 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
11925 which you assign a new name as a command. This is done with the
11926 @code{define} command. User commands may accept up to 10 arguments
11927 separated by whitespace. Arguments are accessed within the user command
11928 via @var{$arg0@dots{}$arg9}. A trivial example:
11932 print $arg0 + $arg1 + $arg2
11936 To execute the command use:
11943 This defines the command @code{adder}, which prints the sum of
11944 its three arguments. Note the arguments are text substitutions, so they may
11945 reference variables, use complex expressions, or even perform inferior
11951 @item define @var{commandname}
11952 Define a command named @var{commandname}. If there is already a command
11953 by that name, you are asked to confirm that you want to redefine it.
11955 The definition of the command is made up of other @value{GDBN} command lines,
11956 which are given following the @code{define} command. The end of these
11957 commands is marked by a line containing @code{end}.
11962 Takes a single argument, which is an expression to evaluate.
11963 It is followed by a series of commands that are executed
11964 only if the expression is true (nonzero).
11965 There can then optionally be a line @code{else}, followed
11966 by a series of commands that are only executed if the expression
11967 was false. The end of the list is marked by a line containing @code{end}.
11971 The syntax is similar to @code{if}: the command takes a single argument,
11972 which is an expression to evaluate, and must be followed by the commands to
11973 execute, one per line, terminated by an @code{end}.
11974 The commands are executed repeatedly as long as the expression
11978 @item document @var{commandname}
11979 Document the user-defined command @var{commandname}, so that it can be
11980 accessed by @code{help}. The command @var{commandname} must already be
11981 defined. This command reads lines of documentation just as @code{define}
11982 reads the lines of the command definition, ending with @code{end}.
11983 After the @code{document} command is finished, @code{help} on command
11984 @var{commandname} displays the documentation you have written.
11986 You may use the @code{document} command again to change the
11987 documentation of a command. Redefining the command with @code{define}
11988 does not change the documentation.
11990 @kindex help user-defined
11991 @item help user-defined
11992 List all user-defined commands, with the first line of the documentation
11997 @itemx show user @var{commandname}
11998 Display the @value{GDBN} commands used to define @var{commandname} (but
11999 not its documentation). If no @var{commandname} is given, display the
12000 definitions for all user-defined commands.
12004 When user-defined commands are executed, the
12005 commands of the definition are not printed. An error in any command
12006 stops execution of the user-defined command.
12008 If used interactively, commands that would ask for confirmation proceed
12009 without asking when used inside a user-defined command. Many @value{GDBN}
12010 commands that normally print messages to say what they are doing omit the
12011 messages when used in a user-defined command.
12014 @section User-defined command hooks
12015 @cindex command hooks
12016 @cindex hooks, for commands
12017 @cindex hooks, pre-command
12021 You may define @dfn{hooks}, which are a special kind of user-defined
12022 command. Whenever you run the command @samp{foo}, if the user-defined
12023 command @samp{hook-foo} exists, it is executed (with no arguments)
12024 before that command.
12026 @cindex hooks, post-command
12029 A hook may also be defined which is run after the command you executed.
12030 Whenever you run the command @samp{foo}, if the user-defined command
12031 @samp{hookpost-foo} exists, it is executed (with no arguments) after
12032 that command. Post-execution hooks may exist simultaneously with
12033 pre-execution hooks, for the same command.
12035 It is valid for a hook to call the command which it hooks. If this
12036 occurs, the hook is not re-executed, thereby avoiding infinte recursion.
12038 @c It would be nice if hookpost could be passed a parameter indicating
12039 @c if the command it hooks executed properly or not. FIXME!
12041 @kindex stop@r{, a pseudo-command}
12042 In addition, a pseudo-command, @samp{stop} exists. Defining
12043 (@samp{hook-stop}) makes the associated commands execute every time
12044 execution stops in your program: before breakpoint commands are run,
12045 displays are printed, or the stack frame is printed.
12047 For example, to ignore @code{SIGALRM} signals while
12048 single-stepping, but treat them normally during normal execution,
12053 handle SIGALRM nopass
12057 handle SIGALRM pass
12060 define hook-continue
12061 handle SIGLARM pass
12065 As a further example, to hook at the begining and end of the @code{echo}
12066 command, and to add extra text to the beginning and end of the message,
12074 define hookpost-echo
12078 (@value{GDBP}) echo Hello World
12079 <<<---Hello World--->>>
12084 You can define a hook for any single-word command in @value{GDBN}, but
12085 not for command aliases; you should define a hook for the basic command
12086 name, e.g. @code{backtrace} rather than @code{bt}.
12087 @c FIXME! So how does Joe User discover whether a command is an alias
12089 If an error occurs during the execution of your hook, execution of
12090 @value{GDBN} commands stops and @value{GDBN} issues a prompt
12091 (before the command that you actually typed had a chance to run).
12093 If you try to define a hook which does not match any known command, you
12094 get a warning from the @code{define} command.
12096 @node Command Files
12097 @section Command files
12099 @cindex command files
12100 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
12101 commands. Comments (lines starting with @kbd{#}) may also be included.
12102 An empty line in a command file does nothing; it does not mean to repeat
12103 the last command, as it would from the terminal.
12106 @cindex @file{.gdbinit}
12107 @cindex @file{gdb.ini}
12108 When you start @value{GDBN}, it automatically executes commands from its
12109 @dfn{init files}. These are files named @file{.gdbinit} on Unix and
12110 @file{gdb.ini} on DOS/Windows. During startup, @value{GDBN} does the
12115 Reads the init file (if any) in your home directory@footnote{On
12116 DOS/Windows systems, the home directory is the one pointed to by the
12117 @code{HOME} environment variable.}.
12120 Processes command line options and operands.
12123 Reads the init file (if any) in the current working directory.
12126 Reads command files specified by the @samp{-x} option.
12129 The init file in your home directory can set options (such as @samp{set
12130 complaints}) that affect subsequent processing of command line options
12131 and operands. Init files are not executed if you use the @samp{-nx}
12132 option (@pxref{Mode Options, ,Choosing modes}).
12134 @cindex init file name
12135 On some configurations of @value{GDBN}, the init file is known by a
12136 different name (these are typically environments where a specialized
12137 form of @value{GDBN} may need to coexist with other forms, hence a
12138 different name for the specialized version's init file). These are the
12139 environments with special init file names:
12141 @cindex @file{.vxgdbinit}
12144 VxWorks (Wind River Systems real-time OS): @file{.vxgdbinit}
12146 @cindex @file{.os68gdbinit}
12148 OS68K (Enea Data Systems real-time OS): @file{.os68gdbinit}
12150 @cindex @file{.esgdbinit}
12152 ES-1800 (Ericsson Telecom AB M68000 emulator): @file{.esgdbinit}
12155 You can also request the execution of a command file with the
12156 @code{source} command:
12160 @item source @var{filename}
12161 Execute the command file @var{filename}.
12164 The lines in a command file are executed sequentially. They are not
12165 printed as they are executed. An error in any command terminates execution
12166 of the command file.
12168 Commands that would ask for confirmation if used interactively proceed
12169 without asking when used in a command file. Many @value{GDBN} commands that
12170 normally print messages to say what they are doing omit the messages
12171 when called from command files.
12174 @section Commands for controlled output
12176 During the execution of a command file or a user-defined command, normal
12177 @value{GDBN} output is suppressed; the only output that appears is what is
12178 explicitly printed by the commands in the definition. This section
12179 describes three commands useful for generating exactly the output you
12184 @item echo @var{text}
12185 @c I do not consider backslash-space a standard C escape sequence
12186 @c because it is not in ANSI.
12187 Print @var{text}. Nonprinting characters can be included in
12188 @var{text} using C escape sequences, such as @samp{\n} to print a
12189 newline. @strong{No newline is printed unless you specify one.}
12190 In addition to the standard C escape sequences, a backslash followed
12191 by a space stands for a space. This is useful for displaying a
12192 string with spaces at the beginning or the end, since leading and
12193 trailing spaces are otherwise trimmed from all arguments.
12194 To print @samp{@w{ }and foo =@w{ }}, use the command
12195 @samp{echo \@w{ }and foo = \@w{ }}.
12197 A backslash at the end of @var{text} can be used, as in C, to continue
12198 the command onto subsequent lines. For example,
12201 echo This is some text\n\
12202 which is continued\n\
12203 onto several lines.\n
12206 produces the same output as
12209 echo This is some text\n
12210 echo which is continued\n
12211 echo onto several lines.\n
12215 @item output @var{expression}
12216 Print the value of @var{expression} and nothing but that value: no
12217 newlines, no @samp{$@var{nn} = }. The value is not entered in the
12218 value history either. @xref{Expressions, ,Expressions}, for more information
12221 @item output/@var{fmt} @var{expression}
12222 Print the value of @var{expression} in format @var{fmt}. You can use
12223 the same formats as for @code{print}. @xref{Output Formats,,Output
12224 formats}, for more information.
12227 @item printf @var{string}, @var{expressions}@dots{}
12228 Print the values of the @var{expressions} under the control of
12229 @var{string}. The @var{expressions} are separated by commas and may be
12230 either numbers or pointers. Their values are printed as specified by
12231 @var{string}, exactly as if your program were to execute the C
12233 @c FIXME: the above implies that at least all ANSI C formats are
12234 @c supported, but it isn't true: %E and %G don't work (or so it seems).
12235 @c Either this is a bug, or the manual should document what formats are
12239 printf (@var{string}, @var{expressions}@dots{});
12242 For example, you can print two values in hex like this:
12245 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
12248 The only backslash-escape sequences that you can use in the format
12249 string are the simple ones that consist of backslash followed by a
12254 @chapter Using @value{GDBN} under @sc{gnu} Emacs
12257 @cindex @sc{gnu} Emacs
12258 A special interface allows you to use @sc{gnu} Emacs to view (and
12259 edit) the source files for the program you are debugging with
12262 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
12263 executable file you want to debug as an argument. This command starts
12264 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
12265 created Emacs buffer.
12266 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
12268 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
12273 All ``terminal'' input and output goes through the Emacs buffer.
12276 This applies both to @value{GDBN} commands and their output, and to the input
12277 and output done by the program you are debugging.
12279 This is useful because it means that you can copy the text of previous
12280 commands and input them again; you can even use parts of the output
12283 All the facilities of Emacs' Shell mode are available for interacting
12284 with your program. In particular, you can send signals the usual
12285 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
12290 @value{GDBN} displays source code through Emacs.
12293 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
12294 source file for that frame and puts an arrow (@samp{=>}) at the
12295 left margin of the current line. Emacs uses a separate buffer for
12296 source display, and splits the screen to show both your @value{GDBN} session
12299 Explicit @value{GDBN} @code{list} or search commands still produce output as
12300 usual, but you probably have no reason to use them from Emacs.
12303 @emph{Warning:} If the directory where your program resides is not your
12304 current directory, it can be easy to confuse Emacs about the location of
12305 the source files, in which case the auxiliary display buffer does not
12306 appear to show your source. @value{GDBN} can find programs by searching your
12307 environment's @code{PATH} variable, so the @value{GDBN} input and output
12308 session proceeds normally; but Emacs does not get enough information
12309 back from @value{GDBN} to locate the source files in this situation. To
12310 avoid this problem, either start @value{GDBN} mode from the directory where
12311 your program resides, or specify an absolute file name when prompted for the
12312 @kbd{M-x gdb} argument.
12314 A similar confusion can result if you use the @value{GDBN} @code{file} command to
12315 switch to debugging a program in some other location, from an existing
12316 @value{GDBN} buffer in Emacs.
12319 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
12320 you need to call @value{GDBN} by a different name (for example, if you keep
12321 several configurations around, with different names) you can set the
12322 Emacs variable @code{gdb-command-name}; for example,
12325 (setq gdb-command-name "mygdb")
12329 (preceded by @kbd{M-:} or @kbd{ESC :}, or typed in the @code{*scratch*} buffer, or
12330 in your @file{.emacs} file) makes Emacs call the program named
12331 ``@code{mygdb}'' instead.
12333 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
12334 addition to the standard Shell mode commands:
12338 Describe the features of Emacs' @value{GDBN} Mode.
12341 Execute to another source line, like the @value{GDBN} @code{step} command; also
12342 update the display window to show the current file and location.
12345 Execute to next source line in this function, skipping all function
12346 calls, like the @value{GDBN} @code{next} command. Then update the display window
12347 to show the current file and location.
12350 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
12351 display window accordingly.
12353 @item M-x gdb-nexti
12354 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
12355 display window accordingly.
12358 Execute until exit from the selected stack frame, like the @value{GDBN}
12359 @code{finish} command.
12362 Continue execution of your program, like the @value{GDBN} @code{continue}
12365 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
12368 Go up the number of frames indicated by the numeric argument
12369 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
12370 like the @value{GDBN} @code{up} command.
12372 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
12375 Go down the number of frames indicated by the numeric argument, like the
12376 @value{GDBN} @code{down} command.
12378 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
12381 Read the number where the cursor is positioned, and insert it at the end
12382 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
12383 around an address that was displayed earlier, type @kbd{disassemble};
12384 then move the cursor to the address display, and pick up the
12385 argument for @code{disassemble} by typing @kbd{C-x &}.
12387 You can customize this further by defining elements of the list
12388 @code{gdb-print-command}; once it is defined, you can format or
12389 otherwise process numbers picked up by @kbd{C-x &} before they are
12390 inserted. A numeric argument to @kbd{C-x &} indicates that you
12391 wish special formatting, and also acts as an index to pick an element of the
12392 list. If the list element is a string, the number to be inserted is
12393 formatted using the Emacs function @code{format}; otherwise the number
12394 is passed as an argument to the corresponding list element.
12397 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
12398 tells @value{GDBN} to set a breakpoint on the source line point is on.
12400 If you accidentally delete the source-display buffer, an easy way to get
12401 it back is to type the command @code{f} in the @value{GDBN} buffer, to
12402 request a frame display; when you run under Emacs, this recreates
12403 the source buffer if necessary to show you the context of the current
12406 The source files displayed in Emacs are in ordinary Emacs buffers
12407 which are visiting the source files in the usual way. You can edit
12408 the files with these buffers if you wish; but keep in mind that @value{GDBN}
12409 communicates with Emacs in terms of line numbers. If you add or
12410 delete lines from the text, the line numbers that @value{GDBN} knows cease
12411 to correspond properly with the code.
12413 @c The following dropped because Epoch is nonstandard. Reactivate
12414 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
12416 @kindex Emacs Epoch environment
12420 Version 18 of @sc{gnu} Emacs has a built-in window system
12421 called the @code{epoch}
12422 environment. Users of this environment can use a new command,
12423 @code{inspect} which performs identically to @code{print} except that
12424 each value is printed in its own window.
12427 @include annotate.texi
12428 @include gdbmi.texinfo
12431 @chapter Reporting Bugs in @value{GDBN}
12432 @cindex bugs in @value{GDBN}
12433 @cindex reporting bugs in @value{GDBN}
12435 Your bug reports play an essential role in making @value{GDBN} reliable.
12437 Reporting a bug may help you by bringing a solution to your problem, or it
12438 may not. But in any case the principal function of a bug report is to help
12439 the entire community by making the next version of @value{GDBN} work better. Bug
12440 reports are your contribution to the maintenance of @value{GDBN}.
12442 In order for a bug report to serve its purpose, you must include the
12443 information that enables us to fix the bug.
12446 * Bug Criteria:: Have you found a bug?
12447 * Bug Reporting:: How to report bugs
12451 @section Have you found a bug?
12452 @cindex bug criteria
12454 If you are not sure whether you have found a bug, here are some guidelines:
12457 @cindex fatal signal
12458 @cindex debugger crash
12459 @cindex crash of debugger
12461 If the debugger gets a fatal signal, for any input whatever, that is a
12462 @value{GDBN} bug. Reliable debuggers never crash.
12464 @cindex error on valid input
12466 If @value{GDBN} produces an error message for valid input, that is a
12467 bug. (Note that if you're cross debugging, the problem may also be
12468 somewhere in the connection to the target.)
12470 @cindex invalid input
12472 If @value{GDBN} does not produce an error message for invalid input,
12473 that is a bug. However, you should note that your idea of
12474 ``invalid input'' might be our idea of ``an extension'' or ``support
12475 for traditional practice''.
12478 If you are an experienced user of debugging tools, your suggestions
12479 for improvement of @value{GDBN} are welcome in any case.
12482 @node Bug Reporting
12483 @section How to report bugs
12484 @cindex bug reports
12485 @cindex @value{GDBN} bugs, reporting
12487 A number of companies and individuals offer support for @sc{gnu} products.
12488 If you obtained @value{GDBN} from a support organization, we recommend you
12489 contact that organization first.
12491 You can find contact information for many support companies and
12492 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
12494 @c should add a web page ref...
12496 In any event, we also recommend that you send bug reports for
12497 @value{GDBN} to this addresses:
12503 @strong{Do not send bug reports to @samp{info-gdb}, or to
12504 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
12505 not want to receive bug reports. Those that do have arranged to receive
12508 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
12509 serves as a repeater. The mailing list and the newsgroup carry exactly
12510 the same messages. Often people think of posting bug reports to the
12511 newsgroup instead of mailing them. This appears to work, but it has one
12512 problem which can be crucial: a newsgroup posting often lacks a mail
12513 path back to the sender. Thus, if we need to ask for more information,
12514 we may be unable to reach you. For this reason, it is better to send
12515 bug reports to the mailing list.
12517 As a last resort, send bug reports on paper to:
12520 @sc{gnu} Debugger Bugs
12521 Free Software Foundation Inc.
12522 59 Temple Place - Suite 330
12523 Boston, MA 02111-1307
12527 The fundamental principle of reporting bugs usefully is this:
12528 @strong{report all the facts}. If you are not sure whether to state a
12529 fact or leave it out, state it!
12531 Often people omit facts because they think they know what causes the
12532 problem and assume that some details do not matter. Thus, you might
12533 assume that the name of the variable you use in an example does not matter.
12534 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
12535 stray memory reference which happens to fetch from the location where that
12536 name is stored in memory; perhaps, if the name were different, the contents
12537 of that location would fool the debugger into doing the right thing despite
12538 the bug. Play it safe and give a specific, complete example. That is the
12539 easiest thing for you to do, and the most helpful.
12541 Keep in mind that the purpose of a bug report is to enable us to fix the
12542 bug. It may be that the bug has been reported previously, but neither
12543 you nor we can know that unless your bug report is complete and
12546 Sometimes people give a few sketchy facts and ask, ``Does this ring a
12547 bell?'' Those bug reports are useless, and we urge everyone to
12548 @emph{refuse to respond to them} except to chide the sender to report
12551 To enable us to fix the bug, you should include all these things:
12555 The version of @value{GDBN}. @value{GDBN} announces it if you start
12556 with no arguments; you can also print it at any time using @code{show
12559 Without this, we will not know whether there is any point in looking for
12560 the bug in the current version of @value{GDBN}.
12563 The type of machine you are using, and the operating system name and
12567 What compiler (and its version) was used to compile @value{GDBN}---e.g.
12568 ``@value{GCC}--2.8.1''.
12571 What compiler (and its version) was used to compile the program you are
12572 debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
12573 C Compiler''. For GCC, you can say @code{gcc --version} to get this
12574 information; for other compilers, see the documentation for those
12578 The command arguments you gave the compiler to compile your example and
12579 observe the bug. For example, did you use @samp{-O}? To guarantee
12580 you will not omit something important, list them all. A copy of the
12581 Makefile (or the output from make) is sufficient.
12583 If we were to try to guess the arguments, we would probably guess wrong
12584 and then we might not encounter the bug.
12587 A complete input script, and all necessary source files, that will
12591 A description of what behavior you observe that you believe is
12592 incorrect. For example, ``It gets a fatal signal.''
12594 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
12595 will certainly notice it. But if the bug is incorrect output, we might
12596 not notice unless it is glaringly wrong. You might as well not give us
12597 a chance to make a mistake.
12599 Even if the problem you experience is a fatal signal, you should still
12600 say so explicitly. Suppose something strange is going on, such as, your
12601 copy of @value{GDBN} is out of synch, or you have encountered a bug in
12602 the C library on your system. (This has happened!) Your copy might
12603 crash and ours would not. If you told us to expect a crash, then when
12604 ours fails to crash, we would know that the bug was not happening for
12605 us. If you had not told us to expect a crash, then we would not be able
12606 to draw any conclusion from our observations.
12609 If you wish to suggest changes to the @value{GDBN} source, send us context
12610 diffs. If you even discuss something in the @value{GDBN} source, refer to
12611 it by context, not by line number.
12613 The line numbers in our development sources will not match those in your
12614 sources. Your line numbers would convey no useful information to us.
12618 Here are some things that are not necessary:
12622 A description of the envelope of the bug.
12624 Often people who encounter a bug spend a lot of time investigating
12625 which changes to the input file will make the bug go away and which
12626 changes will not affect it.
12628 This is often time consuming and not very useful, because the way we
12629 will find the bug is by running a single example under the debugger
12630 with breakpoints, not by pure deduction from a series of examples.
12631 We recommend that you save your time for something else.
12633 Of course, if you can find a simpler example to report @emph{instead}
12634 of the original one, that is a convenience for us. Errors in the
12635 output will be easier to spot, running under the debugger will take
12636 less time, and so on.
12638 However, simplification is not vital; if you do not want to do this,
12639 report the bug anyway and send us the entire test case you used.
12642 A patch for the bug.
12644 A patch for the bug does help us if it is a good one. But do not omit
12645 the necessary information, such as the test case, on the assumption that
12646 a patch is all we need. We might see problems with your patch and decide
12647 to fix the problem another way, or we might not understand it at all.
12649 Sometimes with a program as complicated as @value{GDBN} it is very hard to
12650 construct an example that will make the program follow a certain path
12651 through the code. If you do not send us the example, we will not be able
12652 to construct one, so we will not be able to verify that the bug is fixed.
12654 And if we cannot understand what bug you are trying to fix, or why your
12655 patch should be an improvement, we will not install it. A test case will
12656 help us to understand.
12659 A guess about what the bug is or what it depends on.
12661 Such guesses are usually wrong. Even we cannot guess right about such
12662 things without first using the debugger to find the facts.
12665 @c The readline documentation is distributed with the readline code
12666 @c and consists of the two following files:
12668 @c inc-hist.texinfo
12669 @c Use -I with makeinfo to point to the appropriate directory,
12670 @c environment var TEXINPUTS with TeX.
12671 @include rluser.texinfo
12672 @include inc-hist.texinfo
12675 @node Formatting Documentation
12676 @appendix Formatting Documentation
12678 @cindex @value{GDBN} reference card
12679 @cindex reference card
12680 The @value{GDBN} 4 release includes an already-formatted reference card, ready
12681 for printing with PostScript or Ghostscript, in the @file{gdb}
12682 subdirectory of the main source directory@footnote{In
12683 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
12684 release.}. If you can use PostScript or Ghostscript with your printer,
12685 you can print the reference card immediately with @file{refcard.ps}.
12687 The release also includes the source for the reference card. You
12688 can format it, using @TeX{}, by typing:
12694 The @value{GDBN} reference card is designed to print in @dfn{landscape}
12695 mode on US ``letter'' size paper;
12696 that is, on a sheet 11 inches wide by 8.5 inches
12697 high. You will need to specify this form of printing as an option to
12698 your @sc{dvi} output program.
12700 @cindex documentation
12702 All the documentation for @value{GDBN} comes as part of the machine-readable
12703 distribution. The documentation is written in Texinfo format, which is
12704 a documentation system that uses a single source file to produce both
12705 on-line information and a printed manual. You can use one of the Info
12706 formatting commands to create the on-line version of the documentation
12707 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
12709 @value{GDBN} includes an already formatted copy of the on-line Info
12710 version of this manual in the @file{gdb} subdirectory. The main Info
12711 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
12712 subordinate files matching @samp{gdb.info*} in the same directory. If
12713 necessary, you can print out these files, or read them with any editor;
12714 but they are easier to read using the @code{info} subsystem in @sc{gnu}
12715 Emacs or the standalone @code{info} program, available as part of the
12716 @sc{gnu} Texinfo distribution.
12718 If you want to format these Info files yourself, you need one of the
12719 Info formatting programs, such as @code{texinfo-format-buffer} or
12722 If you have @code{makeinfo} installed, and are in the top level
12723 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
12724 version @value{GDBVN}), you can make the Info file by typing:
12731 If you want to typeset and print copies of this manual, you need @TeX{},
12732 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
12733 Texinfo definitions file.
12735 @TeX{} is a typesetting program; it does not print files directly, but
12736 produces output files called @sc{dvi} files. To print a typeset
12737 document, you need a program to print @sc{dvi} files. If your system
12738 has @TeX{} installed, chances are it has such a program. The precise
12739 command to use depends on your system; @kbd{lpr -d} is common; another
12740 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
12741 require a file name without any extension or a @samp{.dvi} extension.
12743 @TeX{} also requires a macro definitions file called
12744 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
12745 written in Texinfo format. On its own, @TeX{} cannot either read or
12746 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
12747 and is located in the @file{gdb-@var{version-number}/texinfo}
12750 If you have @TeX{} and a @sc{dvi} printer program installed, you can
12751 typeset and print this manual. First switch to the the @file{gdb}
12752 subdirectory of the main source directory (for example, to
12753 @file{gdb-@value{GDBVN}/gdb}) and type:
12759 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
12761 @node Installing GDB
12762 @appendix Installing @value{GDBN}
12763 @cindex configuring @value{GDBN}
12764 @cindex installation
12766 @value{GDBN} comes with a @code{configure} script that automates the process
12767 of preparing @value{GDBN} for installation; you can then use @code{make} to
12768 build the @code{gdb} program.
12770 @c irrelevant in info file; it's as current as the code it lives with.
12771 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
12772 look at the @file{README} file in the sources; we may have improved the
12773 installation procedures since publishing this manual.}
12776 The @value{GDBN} distribution includes all the source code you need for
12777 @value{GDBN} in a single directory, whose name is usually composed by
12778 appending the version number to @samp{gdb}.
12780 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
12781 @file{gdb-@value{GDBVN}} directory. That directory contains:
12784 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
12785 script for configuring @value{GDBN} and all its supporting libraries
12787 @item gdb-@value{GDBVN}/gdb
12788 the source specific to @value{GDBN} itself
12790 @item gdb-@value{GDBVN}/bfd
12791 source for the Binary File Descriptor library
12793 @item gdb-@value{GDBVN}/include
12794 @sc{gnu} include files
12796 @item gdb-@value{GDBVN}/libiberty
12797 source for the @samp{-liberty} free software library
12799 @item gdb-@value{GDBVN}/opcodes
12800 source for the library of opcode tables and disassemblers
12802 @item gdb-@value{GDBVN}/readline
12803 source for the @sc{gnu} command-line interface
12805 @item gdb-@value{GDBVN}/glob
12806 source for the @sc{gnu} filename pattern-matching subroutine
12808 @item gdb-@value{GDBVN}/mmalloc
12809 source for the @sc{gnu} memory-mapped malloc package
12812 The simplest way to configure and build @value{GDBN} is to run @code{configure}
12813 from the @file{gdb-@var{version-number}} source directory, which in
12814 this example is the @file{gdb-@value{GDBVN}} directory.
12816 First switch to the @file{gdb-@var{version-number}} source directory
12817 if you are not already in it; then run @code{configure}. Pass the
12818 identifier for the platform on which @value{GDBN} will run as an
12824 cd gdb-@value{GDBVN}
12825 ./configure @var{host}
12830 where @var{host} is an identifier such as @samp{sun4} or
12831 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
12832 (You can often leave off @var{host}; @code{configure} tries to guess the
12833 correct value by examining your system.)
12835 Running @samp{configure @var{host}} and then running @code{make} builds the
12836 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
12837 libraries, then @code{gdb} itself. The configured source files, and the
12838 binaries, are left in the corresponding source directories.
12841 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
12842 system does not recognize this automatically when you run a different
12843 shell, you may need to run @code{sh} on it explicitly:
12846 sh configure @var{host}
12849 If you run @code{configure} from a directory that contains source
12850 directories for multiple libraries or programs, such as the
12851 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
12852 creates configuration files for every directory level underneath (unless
12853 you tell it not to, with the @samp{--norecursion} option).
12855 You can run the @code{configure} script from any of the
12856 subordinate directories in the @value{GDBN} distribution if you only want to
12857 configure that subdirectory, but be sure to specify a path to it.
12859 For example, with version @value{GDBVN}, type the following to configure only
12860 the @code{bfd} subdirectory:
12864 cd gdb-@value{GDBVN}/bfd
12865 ../configure @var{host}
12869 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
12870 However, you should make sure that the shell on your path (named by
12871 the @samp{SHELL} environment variable) is publicly readable. Remember
12872 that @value{GDBN} uses the shell to start your program---some systems refuse to
12873 let @value{GDBN} debug child processes whose programs are not readable.
12876 * Separate Objdir:: Compiling @value{GDBN} in another directory
12877 * Config Names:: Specifying names for hosts and targets
12878 * Configure Options:: Summary of options for configure
12881 @node Separate Objdir
12882 @section Compiling @value{GDBN} in another directory
12884 If you want to run @value{GDBN} versions for several host or target machines,
12885 you need a different @code{gdb} compiled for each combination of
12886 host and target. @code{configure} is designed to make this easy by
12887 allowing you to generate each configuration in a separate subdirectory,
12888 rather than in the source directory. If your @code{make} program
12889 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
12890 @code{make} in each of these directories builds the @code{gdb}
12891 program specified there.
12893 To build @code{gdb} in a separate directory, run @code{configure}
12894 with the @samp{--srcdir} option to specify where to find the source.
12895 (You also need to specify a path to find @code{configure}
12896 itself from your working directory. If the path to @code{configure}
12897 would be the same as the argument to @samp{--srcdir}, you can leave out
12898 the @samp{--srcdir} option; it is assumed.)
12900 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
12901 separate directory for a Sun 4 like this:
12905 cd gdb-@value{GDBVN}
12908 ../gdb-@value{GDBVN}/configure sun4
12913 When @code{configure} builds a configuration using a remote source
12914 directory, it creates a tree for the binaries with the same structure
12915 (and using the same names) as the tree under the source directory. In
12916 the example, you'd find the Sun 4 library @file{libiberty.a} in the
12917 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
12918 @file{gdb-sun4/gdb}.
12920 One popular reason to build several @value{GDBN} configurations in separate
12921 directories is to configure @value{GDBN} for cross-compiling (where
12922 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
12923 programs that run on another machine---the @dfn{target}).
12924 You specify a cross-debugging target by
12925 giving the @samp{--target=@var{target}} option to @code{configure}.
12927 When you run @code{make} to build a program or library, you must run
12928 it in a configured directory---whatever directory you were in when you
12929 called @code{configure} (or one of its subdirectories).
12931 The @code{Makefile} that @code{configure} generates in each source
12932 directory also runs recursively. If you type @code{make} in a source
12933 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
12934 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
12935 will build all the required libraries, and then build GDB.
12937 When you have multiple hosts or targets configured in separate
12938 directories, you can run @code{make} on them in parallel (for example,
12939 if they are NFS-mounted on each of the hosts); they will not interfere
12943 @section Specifying names for hosts and targets
12945 The specifications used for hosts and targets in the @code{configure}
12946 script are based on a three-part naming scheme, but some short predefined
12947 aliases are also supported. The full naming scheme encodes three pieces
12948 of information in the following pattern:
12951 @var{architecture}-@var{vendor}-@var{os}
12954 For example, you can use the alias @code{sun4} as a @var{host} argument,
12955 or as the value for @var{target} in a @code{--target=@var{target}}
12956 option. The equivalent full name is @samp{sparc-sun-sunos4}.
12958 The @code{configure} script accompanying @value{GDBN} does not provide
12959 any query facility to list all supported host and target names or
12960 aliases. @code{configure} calls the Bourne shell script
12961 @code{config.sub} to map abbreviations to full names; you can read the
12962 script, if you wish, or you can use it to test your guesses on
12963 abbreviations---for example:
12966 % sh config.sub i386-linux
12968 % sh config.sub alpha-linux
12969 alpha-unknown-linux-gnu
12970 % sh config.sub hp9k700
12972 % sh config.sub sun4
12973 sparc-sun-sunos4.1.1
12974 % sh config.sub sun3
12975 m68k-sun-sunos4.1.1
12976 % sh config.sub i986v
12977 Invalid configuration `i986v': machine `i986v' not recognized
12981 @code{config.sub} is also distributed in the @value{GDBN} source
12982 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
12984 @node Configure Options
12985 @section @code{configure} options
12987 Here is a summary of the @code{configure} options and arguments that
12988 are most often useful for building @value{GDBN}. @code{configure} also has
12989 several other options not listed here. @inforef{What Configure
12990 Does,,configure.info}, for a full explanation of @code{configure}.
12993 configure @r{[}--help@r{]}
12994 @r{[}--prefix=@var{dir}@r{]}
12995 @r{[}--exec-prefix=@var{dir}@r{]}
12996 @r{[}--srcdir=@var{dirname}@r{]}
12997 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
12998 @r{[}--target=@var{target}@r{]}
13003 You may introduce options with a single @samp{-} rather than
13004 @samp{--} if you prefer; but you may abbreviate option names if you use
13009 Display a quick summary of how to invoke @code{configure}.
13011 @item --prefix=@var{dir}
13012 Configure the source to install programs and files under directory
13015 @item --exec-prefix=@var{dir}
13016 Configure the source to install programs under directory
13019 @c avoid splitting the warning from the explanation:
13021 @item --srcdir=@var{dirname}
13022 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
13023 @code{make} that implements the @code{VPATH} feature.}@*
13024 Use this option to make configurations in directories separate from the
13025 @value{GDBN} source directories. Among other things, you can use this to
13026 build (or maintain) several configurations simultaneously, in separate
13027 directories. @code{configure} writes configuration specific files in
13028 the current directory, but arranges for them to use the source in the
13029 directory @var{dirname}. @code{configure} creates directories under
13030 the working directory in parallel to the source directories below
13033 @item --norecursion
13034 Configure only the directory level where @code{configure} is executed; do not
13035 propagate configuration to subdirectories.
13037 @item --target=@var{target}
13038 Configure @value{GDBN} for cross-debugging programs running on the specified
13039 @var{target}. Without this option, @value{GDBN} is configured to debug
13040 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
13042 There is no convenient way to generate a list of all available targets.
13044 @item @var{host} @dots{}
13045 Configure @value{GDBN} to run on the specified @var{host}.
13047 There is no convenient way to generate a list of all available hosts.
13050 There are many other options available as well, but they are generally
13051 needed for special purposes only.
13059 % I think something like @colophon should be in texinfo. In the
13061 \long\def\colophon{\hbox to0pt{}\vfill
13062 \centerline{The body of this manual is set in}
13063 \centerline{\fontname\tenrm,}
13064 \centerline{with headings in {\bf\fontname\tenbf}}
13065 \centerline{and examples in {\tt\fontname\tentt}.}
13066 \centerline{{\it\fontname\tenit\/},}
13067 \centerline{{\bf\fontname\tenbf}, and}
13068 \centerline{{\sl\fontname\tensl\/}}
13069 \centerline{are used for emphasis.}\vfill}
13071 % Blame: doc@cygnus.com, 1991.
13074 @c TeX can handle the contents at the start but makeinfo 3.12 can not