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Date: Sun, 28 Sep 2003 22:35:00 -0000
From: Michael Elizabeth Chastain <mec@shout.net>
Message-Id: <200309282225.h8SMP9Rf026649@duracef.shout.net>
To: aurelien.chanudet@enst.fr, gdb@sources.redhat.com
Subject: Re: process attaching gdb to itself
X-SW-Source: 2003-09/txt/msg00353.txt.bz2

Hello,

  char cmd [256];
  sprintf (cmd, "gdb attach %d", getpid ());
  system (cmd);

'system' waits for the program that it calls to finish.
Thus, your program is waiting for gdb to finish before it
does anything.

Try the appended program which uses raw fork/exec.
It works for me on red hat linux 8, native i686-pc-linux-gnu.

If you try to do this in production code then you are likely
to run into a blizzard of race conditions, error cases,
and signal handling problems.  If you are doing this as a learning
experience, that's great -- read up on 'man fork' and
'man execlp', and check out a book on Linux systems programming.

Michael C
GDB QA Guy

===

  #include <stdio.h>

  int main ()
  {
    int pid = fork ();
    if (pid == -1)
    {
      /* error */
      fprintf (stderr, "fork error\n");
      exit (2);
    }

    if (pid != 0)
    {
      /* parent process */
      char spid [256];
      sprintf (spid, "%d", pid);
      execlp ("gdb", "gdb", "a.out", spid, NULL);
      /* execlp returns only if error */
      fprintf (stderr, "execlp error\n");
      _exit (2);
    }

    /* child process */
    sleep (5);
    printf ("hello hacker\n");
    return 0;
  }