There are a few libraries that can help with this.

There are two portable, non-Perl specific libraries: One is libffi. The other is ffcall (ftp server not responding as I write this).

There is a Perl interface to ffcall: FFI.

If you are using Windows, you can use Win32::API.

If you use the FFI or Win32::API Perl modules, you may not need to write any XS code of your own.

Also, I can email a copy of ffcall-1.10.tar.gz if you have trouble downloading it. Just email me at kahirsch at cpan dot org.