This is on NetBSD 3 from the 8th or so. I've got both new cores (from 
NetBSD 3) and old cores (from 1.6.2), and I get the same thing:

lilith: {3} gdb /usr/pkgsrc/lang/clisp/work/clisp-2.33.2/src/avcall/minitests.core
\GNU gdb 5.3nb1
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 "m68k--netbsdelf"..."/usr/pkgsrc/lang/clisp/work/clisp-2.33.2/src/avcall/minitests.core": not in executable format: File format not recognized

and

lilith: {4} file /usr/pkgsrc/lang/clisp/work/clisp-2.33.2/src/avcall/minitests.core
/usr/pkgsrc/lang/clisp/work/clisp-2.33.2/src/avcall/minitests.core: ELF 
32-bit MSB core file, Motorola 68020, version 1 (SYSV), NetBSD-style, from 
'minitests' (signal 11)


Why is that?

John