Unhelpful debug tools on OS X :-(

Dunno if anyone's noticed, but buildfarm member jackal has been crashing
intermittently in the "cluster" regression test. I found out that I can
reproduce that here on a Mac Mini (apparently the same or nearly same
hardware/software as jackal) --- just repeat the parallel tests often
enough, and it'll fail once in awhile. I've got a core file but gdb
is being no help at all:

mini:~/pgsql/src/test/regress tgl$ gdb /Users/tgl/testversion/bin/postmaster /cores/core.23609
GNU gdb 6.3.50-20050815 (Apple version gdb-563) (Wed Jul 19 05:10:58 GMT 2006)
Copyright 2004 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-apple-darwin"...Reading symbols for shared libraries .. done

Core was generated by `/Users/tgl/testversion/bin/postmaster'.
Core file contained no thread-specific data

(gdb) bt
#0 0x00000000 in ?? ()
(gdb)

Any suggestions how to extract some info out of this?

regards, tom lane