This was originally posted to -current in
<20030207124244.74bf9df7.peter.edwards@openet-telecom.com>

I figured i'd record it here so it's not forgotten.

gdb doesn't find threads in corefiles: The support was just missing.
Attached is a patch, sample program, and gdb output when running it.

How-To-Repeat: 
Compile this:
=09
#include <sys/types.h>
#include <signal.h>
#include <pthread.h>
#include <unistd.h>
#include <stdio.h>
#include <err.h>

void *thr(void *a)
{
    printf("started thread %d\n", (int)a);
    pause();
    return 0;
}

int main(int argc, char **argv)
{
    const int THREADCOUNT =3D 4;
    int i;
    pthread_t threads[THREADCOUNT];

    for (i =3D 0; i < THREADCOUNT; i++)
	if (pthread_create(&threads[i], 0, thr, (void *)i) !=3D 0)
	    errx(-1, "cannot create thread");
    sleep(1);
    kill(0, SIGBUS);
    return 0;
}

like this:

 petere@rocklobster$ cc -o threadcore -Wall -g -pthread threadcore.c

then do this:
 petere@rocklobster$ ./threadcore
 started thread 0
 started thread 1
 started thread 2
 started thread 3
 zsh: bus error (core dumped)  ./threadcore
 petere@rocklobster$ gdb threadcore threadcore.core
 GNU gdb 5.2.1 (FreeBSD)
 Copyright 2002 Free Software Foundation, Inc.
 GDB is free software, covered by the GNU General Public License, and you
 are welcome to change it and/or distribute copies of it under certain
 conditions. Type "show copying" to see the conditions.
 There is absolutely no warranty for GDB.  Type "show warranty" for
 details. This GDB was configured as "i386-undermydesk-freebsd"...
 Core was generated by `threadcore'.
 Program terminated with signal 10, Bus error.
 Reading symbols from /usr/lib/libc_r.so.5...done.
 Loaded symbols for /usr/lib/libc_r.so.5
 Reading symbols from /usr/lib/libc.so.5...done.
 Loaded symbols for /usr/lib/libc.so.5
 Reading symbols from /usr/libexec/ld-elf.so.1...done.
 Loaded symbols for /usr/libexec/ld-elf.so.1
 #0  0x280d5463 in kill () from /usr/lib/libc.so.5
 (gdb) i thr
 * 1 process 41359  0x280d5463 in kill () from /usr/lib/libc.so.5
 (gdb) quit

After applying the patch, try this:
 petere@rocklobster$ /usr/src/gnu/usr.bin/binutils/gdb/gdb threadcore
 threadcore.core GNU gdb 5.2.1 (FreeBSD)
 Copyright 2002 Free Software Foundation, Inc.
 GDB is free software, covered by the GNU General Public License, and you
 are welcome to change it and/or distribute copies of it under certain
 conditions. Type "show copying" to see the conditions.
 There is absolutely no warranty for GDB.  Type "show warranty" for
 details. This GDB was configured as "i386-undermydesk-freebsd"...
 Core was generated by `threadcore'.
 Program terminated with signal 10, Bus error.
 Reading symbols from /usr/lib/libc_r.so.5...done.
 Loaded symbols for /usr/lib/libc_r.so.5
 Reading symbols from /usr/lib/libc.so.5...done.
 Loaded symbols for /usr/lib/libc.so.5
 Reading symbols from /usr/libexec/ld-elf.so.1...done.
 Loaded symbols for /usr/libexec/ld-elf.so.1
 #0  0x280d5463 in kill () from /usr/lib/libc.so.5
 (gdb) i thr
   7 Process 41359  0x280d5463 in kill () from /usr/lib/libc.so.5
   6 Process 41359  0x2807b7ec in _thread_kern_sched () from
/usr/lib/libc_r.so.5
   5 Process 41359  0x2807b7ec in _thread_kern_sched () from
/usr/lib/libc_r.so.5
   4 Process 41359  0x2807b7ec in _thread_kern_sched () from
/usr/lib/libc_r.so.5
   3 Process 41359  0x2807b7ec in _thread_kern_sched () from
/usr/lib/libc_r.so.5
   2 Process 41359  0x2807b7ec in _thread_kern_sched () from
/usr/lib/libc_r.so.5
 * 1 Process 41359  0x280d5463 in kill () from /usr/lib/libc.so.5
 (gdb)=20

Enjoy,
Peter.