or download this
(gdb) run /tmp/blah.pl
Starting program: /usr/bin/debugperl /tmp/blah.pl
[Thread debugging using libthread_db enabled]
...
#9 0xb7ca26aa in S_ithread_run (arg=0x82c0220) at threads.xs:440
#10 0xb7f9c7b0 in start_thread () from /lib/libpthread.so.0
#11 0xb7f1c8fe in clone () from /lib/libc.so.6