Comment # 18 on bug 1166406 from Jiri Slaby

(In reply to Jiri Slaby from comment #17)
> So it can and does open .xz. Tony, do you have some old version of systemtap?

Stap seems to use libelf to handle that and this was added there by
commit 6ecdead8c0fbba51e8b2561e4d54dd7be3f69204
Author: Roland McGrath <roland@redhat.com>
Date:   Fri Feb 11 12:29:45 2011 -0800

    libdwfl: Search for Linux kernel binaries with compression file name
suffixes.

So xz should not be a problem. That said, I don't understand what your issue
is. Something seems to be broken on your system.