Yes, you can use a core file with GDB. The app to feed to GDB in this case is Perl itself, ex: /usr/bin/perl. This will produce much more useful results in many cases if you compiled your Perl and your XS modules with debugging symbols.

I've found that although GDB can rarely tell me what cased a seg-fault it can sometimes point the way to the right area of code to look at. Sometimes that's the only hint you need.

-sam