how to attach to gdb forked child?

[Jeremy C. Reed]

I am trying to figure out where an abort core dump in imake is coming 
from, so I do:

gdb /build/reed/tmp/pkgsrc/devel/imake/work.reed/imake-1.0.2/imake
. ..

(gdb) break main
Breakpoint 1 at 0x8048eb7: file imake.c, line 405.
(gdb) run
Starting program: 
/build/reed/tmp/pkgsrc/devel/imake/work.reed/imake-1.0.2/imake 

Breakpoint 1, main (argc=1, argv=0x0) at imake.c:405
405     {
(gdb) n

. . n several times ...

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


So now I have a new process id.

I run gdb in a new terminal and get:

(gdb) attach 7858
Attaching to program: 
/build/reed/tmp/pkgsrc/devel/imake/work.reed/imake-1.0.2/imake, process 
7858
ptrace: Device busy.
(gdb) n
The program is not being run.


Any pointers?

Now gdb bt of the core dump is:

(gdb) bt
#0  0x280c2978 in kill () from /usr/lib/libc.so.6
#1  0x28117adc in abort () from /usr/lib/libc.so.6
#2  0x0804a0bd in get_stackprotector (inFile=0x281389f4) at imake.c:1061
#3  0x0804a5fc in define_os_defaults (inFile=0x281389f4) at imake.c:1711
#4  0x0804a68b in cppit (imakefile=0x804b40a "Imakefile", 
    template=0x804b250 "Imake.tmpl", masterc=0x804b25b "Imakefile.c", 
    outfd=0x28138880, outfname=0x804b247 "Makefile") at imake.c:1726
#5  0x08049122 in main (argc=1, argv=0xbfbff97c) at imake.c:458
(gdb) quit


But I thought I'd fine more details by stepping through 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.

So I see where the problem is probably at -- but can someone teach me how 
to find it with gdb itself?

Thanks,

  Jeremy C. Reed