Using systemtap on fedora rawhide

[Mark Wielaard <mjw at redhat dot com>]

Hi,

For those wanting to try our systemtap on fedora rawhide (the in
development version that will become f18), there are two issues to be
aware of. There was a recent switch from the 3.5.0 kernel to the
3.6.0-rc development kernel, which broke some runtime assumptions (e.g.
task_work was renamed to struct callback_head). So stick with 3.5.0 for
now if possible.

Also all user space was rebuild and now uses the dwz compressor:
https://fedoraproject.org/wiki/Features/DwarfCompressor
This introduces some new DWARF forms that are not yet recognized by
elfutils/libdw[fl]. There is a patch for that:
http://thread.gmane.org/gmane.comp.sysutils.elfutils.devel/2210/focus=2272
(Or use the mjw/dwz elfutils branch from git). With that user space
probing should work just fine. Without that you will just get the
message: 

semantic error: while resolving probe point: identifier 'process' at
<input>:1:7
        source: probe process.function("main") { log("hit"); exit(); }
                      ^

semantic error: no match

The issue is that we don't check the result of dwarf_getfuncs (), and so
we just think there are zero functions. But even if we did,
dwarf_getfuncs () doesn't actually tell us there was a problem reading
the debuginfo, it just reports there are no functions.

Cheers,

Mark