Using systemtap on fedora rawhide

Using systemtap on fedora rawhide

[Mark Wielaard]

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

Re: Using systemtap on fedora rawhide

[David Smith]

On 08/01/2012 03:44 AM, Mark Wielaard wrote:
> 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.

I've filed pr14427 (task_work changes need updated runtime support) for
the task_work changes (I've known these changes were coming, just
haven't been able to find the time to fix them).  I should hopefully
have this fixed very soon.

-- 
David Smith
dsmith@redhat.com
Red Hat
http://www.redhat.com
256.217.0141 (direct)
256.837.0057 (fax)

Re: Using systemtap on fedora rawhide

[Mark Wielaard]

On Wed, 2012-08-01 at 12:42 -0500, David Smith wrote:
> I've filed pr14427 (task_work changes need updated runtime support) for
> the task_work changes (I've known these changes were coming, just
> haven't been able to find the time to fix them).  I should hopefully
> have this fixed very soon.

Thanks. I have created fedora rawhide packages of elfutils with
preliminary dwz support, they should go in soon, you can get them here
if you want to test user space probing on rawhide against packages with
dwz compressed debuginfo:
http://koji.fedoraproject.org/koji/buildinfo?buildID=345355

Cheers,

Mark

Re: Using systemtap on fedora rawhide

[David Smith]

On 08/02/2012 05:13 AM, Mark Wielaard wrote:
> On Wed, 2012-08-01 at 12:42 -0500, David Smith wrote:
>> I've filed pr14427 (task_work changes need updated runtime support) for
>> the task_work changes (I've known these changes were coming, just
>> haven't been able to find the time to fix them).  I should hopefully
>> have this fixed very soon.

I just finished up this change, commit 0e0e60b.

> Thanks. I have created fedora rawhide packages of elfutils with
> preliminary dwz support, they should go in soon, you can get them here
> if you want to test user space probing on rawhide against packages with
> dwz compressed debuginfo:
> http://koji.fedoraproject.org/koji/buildinfo?buildID=345355

I had only updated my kernel on my rawhide vm, so I'm not getting dwz
compressed debuginfo there yet.  With the above task_work updates, user
space probing works fine now (with the non-compressed debuginfo).

-- 
David Smith
dsmith@redhat.com
Red Hat
http://www.redhat.com
256.217.0141 (direct)
256.837.0057 (fax)

Re: Using systemtap on fedora rawhide

[Mark Wielaard]

On Thu, 2012-08-02 at 10:06 -0500, David Smith wrote:
> On 08/02/2012 05:13 AM, Mark Wielaard wrote:
> > Thanks. I have created fedora rawhide packages of elfutils with
> > preliminary dwz support, they should go in soon, you can get them here
> > if you want to test user space probing on rawhide against packages with
> > dwz compressed debuginfo:
> > http://koji.fedoraproject.org/koji/buildinfo?buildID=345355
> 
> I had only updated my kernel on my rawhide vm, so I'm not getting dwz
> compressed debuginfo there yet.  With the above task_work updates, user
> space probing works fine now (with the non-compressed debuginfo).

Just tested against systemtap git master (release-1.8-138-g923fc59),
3.6.0-0.rc0.git8.1.fc18.x86_64 and elfutils-0.154-3.fc18.x86_64 on
rawhide and user space probing seems to work like a charm again.

Thanks,

Mark