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NAME    [Toc]    [Back]

       gdb - The GNU Debugger

SYNOPSIS    [Toc]    [Back]

       gdb    [-help] [-nx] [-q] [-batch] [-cd=dir] [-f] [-b bps] [-tty=dev]
	      [-s symfile] [-e prog] [-se prog] [-c core] [-x cmds] [-d dir]

DESCRIPTION    [Toc]    [Back]

       The  purpose  of  a debugger such as GDB is to allow you to see what is
       going on ``inside'' another program while it executes--or what  another
       program was doing at the moment it crashed.

       GDB  can  do four main kinds of things (plus other things in support of
       these) to help you catch bugs in the act:

	  o   Start your program, specifying anything that  might  affect  its

	  o   Make your program stop on specified conditions.

	  o   Examine what has happened, when your program has stopped.

	  o   Change  things  in your program, so you can experiment with correcting
 the effects of one bug and go on to learn about another.

       You  can  use  GDB  to  debug programs written in C, C++, and Modula-2.
       Fortran support will be added when a GNU Fortran compiler is ready.

       GDB is invoked with the shell command gdb.  Once started, it reads commands
  from the terminal until you tell it to exit with the GDB command
       quit.  You can get online help from gdb itself  by  using  the  command

       You can run gdb with no arguments or options; but the most usual way to
       start GDB is with one argument or two, specifying an executable program
       as the argument:

       gdb program

       You  can  also  start  with  both an executable program and a core file

       gdb program core

       You can, instead, specify a process ID as a  second  argument,  if  you
       want to debug a running process:

       gdb program 1234

       would  attach  GDB  to  process 1234 (unless you also have a file named
       `1234'; GDB does check for a core file first).

       Here are some of the most frequently needed GDB commands:

       break [file:]function
	       Set a breakpoint at function (in file).

       run [arglist]
	      Start your program (with arglist, if specified).

       bt     Backtrace: display the program stack.

       print expr
	       Display the value of an expression.

       c      Continue running your program (after stopping, e.g. at a	breakpoint).

       next   Execute  next program line (after stopping); step over any function
 calls in the line.

       step   Execute next program line (after stopping); step into any  function
 calls in the line.

       help [name]
	      Show  information about GDB command name, or general information
	      about using GDB.

       quit   Exit from GDB.

       For full details on GDB, see Using GDB: A Guide to the GNU Source-Level
       Debugger, by Richard M. Stallman and Roland H. Pesch.  The same text is
       available online as the gdb entry in the info program.

OPTIONS    [Toc]    [Back]

       Any arguments other than options specify an executable  file  and  core
       file  (or  process ID); that is, the first argument encountered with no
       associated option flag is equivalent to a `-se' option, and the second,
       if  any,  is  equivalent  to  a `-c' option if it's the name of a file.
       Many options have both long and short forms; both are shown here.   The
       long  forms are also recognized if you truncate them, so long as enough
       of the option is present to be unambiguous.  (If you  prefer,  you  can
       flag  option  arguments	with `+' rather than `-', though we illustrate
       the more usual convention.)

       All the options and command line arguments you give  are  processed  in
       sequential order.  The order makes a difference when the `-x' option is


       -h     List all options, with brief explanations.


       -s file
	       Read symbol table from file file.

       -write Enable writing into executable and core files.


       -e file
	       Use file file as the executable file to execute when  appropriate,
  and  for  examining  pure  data in conjunction with a core

	       Read symbol table from file file and use it as  the  executable


       -c file
	       Use file file as a core dump to examine.


       -x file
	       Execute GDB commands from file file.


       -d directory
	       Add directory to the path to search for source files.


       -n     Do  not  execute	commands  from	any  `.gdbinit' initialization
	      files.  Normally, the commands in these files are executed after
	      all the command options and arguments have been processed.


       -q     ``Quiet''.   Do  not  print  the introductory and copyright messages.
  These messages are also suppressed in batch mode.

       -batch Run in batch mode.  Exit with status 0 after processing all  the
	      command files specified with `-x' (and `.gdbinit', if not inhibited).
  Exit with nonzero status if an error occurs in executing
	      the GDB commands in the command files.

	      Batch  mode may be useful for running GDB as a filter, for example
 to download and run a program on another computer; in  order
	      to make this more useful, the message

	      Program exited normally.

	      (which is ordinarily issued whenever a program running under GDB
	      control terminates) is not issued when running in batch mode.

	       Run GDB using directory as its working  directory,  instead  of
	      the current directory.


       -f     Emacs  sets  this  option  when it runs GDB as a subprocess.  It
	      tells GDB to output the full file name  and  line  number  in  a
	      standard,  recognizable  fashion each time a stack frame is displayed
 (which includes each time the program stops).  This  recognizable
  format  looks	like two ` 32' characters, followed by
	      the file name, line number and character position  separated  by
	      colons,  and a newline.  The Emacs-to-GDB interface program uses
	      the two ` 32' characters as a signal to display the source  code
	      for the frame.

       -b bps  Set the line speed (baud rate or bits per second) of any serial
	      interface used by GDB for remote debugging.

	       Run using device for your program's standard input and  output.

SEE ALSO    [Toc]    [Back]

       `gdb'  entry in info; Using GDB: A Guide to the GNU Source-Level Debug-
       ger, Richard M. Stallman and Roland H. Pesch, July 1991.

COPYING    [Toc]    [Back]

       Copyright (c) 1991 Free Software Foundation, Inc.

       Permission is granted to make and distribute verbatim  copies  of  this
       manual  provided  the  copyright  notice and this permission notice are
       preserved on all copies.

       Permission is granted to copy and distribute modified versions of  this
       manual  under  the  conditions  for verbatim copying, provided that the
       entire resulting derived work is distributed under the terms of a  permission
 notice identical to this one.

       Permission  is granted to copy and distribute translations of this manual
 into another language, under the above conditions for modified versions,
  except  that this permission notice may be included in translations
 approved by the Free Software Foundation instead of in the original

GNU Tools			   4nov1991				gdb(1)
[ Back ]
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