MirBSD manpage: gdb(1)

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] [prog[core|procID]]


     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

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

        + Start your  program,  specifying  anything  that  might
          affect its behavior.

        + Make your program stop on specified conditions.

        + Examine  what  has  happened,  when  your  program  has

        + 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 help.

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

     gdb program

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

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gdb(1)                      GNU Tools                      gdb(1)

     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.

     edit [file:]function
          look at the program line where it is presently stopped.

     list [file:]function
          type the text of the program in the vicinity  of  where
          it is presently stopped.

     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,  or as gdb(GNU) in the MirBSD online

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gdb(1)                      GNU Tools                      gdb(1)


     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 pro-
     cessed  in  sequential  order.  The order makes a difference
     when the `-x' option is used.


     -h   List all options, with brief explanations.


     -s file
           Read symbol table from file file.

          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 dump.

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


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


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gdb(1)                      GNU Tools                      gdb(1)

     -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' initializa-
          tion  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

          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  mes-

          Program exited normally.

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

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


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gdb(1)                      GNU Tools                      gdb(1)

     -f   Emacs sets this option when it runs GDB  as  a  subpro-
          cess.   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 pro-
          gram 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


     `gdb' entry in info, also  gdb(GNU)  in  the  MirBSD  online
     documentation;  Using  GDB:  A Guide to the GNU Source-Level
     Debugger, Richard M. Stallman  and  Roland  H.  Pesch,  July

     gdbint(GNU) in the MirBSD online documentation.


     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 per-
     mission notice are preserved on all copies.

     Permission is granted to copy and distribute  modified  ver-
     sions of this manual under the conditions for verbatim copy-
     ing, provided that the entire resulting derived work is dis-
     tributed 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 condi-
     tions for modified versions,  except  that  this  permission
     notice  may be included in translations approved by the Free
     Software Foundation instead of in the original English.

GNU Tools 22may2002 5

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