how to attach to gdb forked child?

Simon 'corecode' Schubert corecode at
Sun Feb 17 01:02:48 PST 2008

Jeremy C. Reed wrote:
I am trying to figure out where an abort core dump in imake is coming 
from, so I do:
For a core dump, you should be able to get a nice backtrace from the dump.

(gdb) n
458             cppit(cleanedImakefile, Template, ImakefileC, tmpfd, 
(gdb) n

So now I have a new process id.
Are are you sure you have the new process id?  Are you also sure that the 
child process is still running?  It might finish before you can attach to it.

Looking at source I see for its get_stackprotector:

   1059   }
   1060   if (pclose(fp))
   1061     abort();
   1062 }
imake assumes the cc -v output is several lines.
Why would pclose fail in this case?

So I see where the problem is probably at -- but can someone teach me how 
to find it with gdb itself?
That's not so easy.  We'd need to have gdb's follow-fork-mode, which lets 
you choose to debug the child instead.  As we don't have it, you might use 
this "trick":  Add a sleep(10) to the child directly after the fork.  Then 
you have some time to attach to the child.  I don't like this, but it 
seems to be the only possibility so far.

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