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gdb(1)				   GNU Tools				gdb(1)

       gdb - The GNU Debugger

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

       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 cor-
	      recting 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 com-
       mands 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	break-

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

       step   Execute  next program line (after	stopping); step	into any func-
	      tion 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.

       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.


       -e file
	      Use  file	 file as the executable	file to	execute	when appropri-
	      ate, 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  mes-
	      sages.  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	inhib-
	      ited).  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	 exam-
	      ple  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  dis-
	      played  (which includes each time	the program stops).  This rec-
	      ognizable	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.

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

       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 en-
       tire resulting derived work is distributed under	the terms of a permis-
       sion notice identical to	this one.

       Permission  is granted to copy and distribute translations of this man-
       ual into	another	language, under	the above conditions for modified ver-
       sions,  except  that this permission notice may be included in transla-
       tions approved by the Free Software Foundation instead of in the	origi-
       nal English.

GNU Tools			   4nov1991				gdb(1)


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