Is the LISP executable undumped?   It's possible that the SIGIOT is
actually the result of a bad executable - I had that happen quite a
few times before I got Emacs to undump correctly.   There's no way to
prevent that signal from being delivered through GDB.   I haven't
messed with executables on NetBSD/i386, so I can't give you any
specific pointers, but that's where I'd look.

			       _MelloN_