[ltt-dev] userspace debug symbols in traces

Mathieu Desnoyers compudj at krystal.dyndns.org
Fri Oct 16 10:41:11 EDT 2009

* Joachim Deguara (joachim.deguara at amd.com) wrote:
> Hello,
>   I just used LTT to debug a threading problem on a userspace app that
> was not scaling well.  It was great to see when the systemcalls and
> scheduling happened but I notice I could possibly go one step more. 
> With the systemcall entry or the IRQ entry I see that we have the IP
> from the userspace process.  What would interest me is if we can somehow
> use LTTV to resolve the debug symbols those IPs point to in the
> userspace process.  Has this been tried or implemented and is there
> anything I can start with to do this?

Hi Joachim,

No, it's not been done yet, but you could have a look at the GNU BFD
library, which is part of binutils. If my memory serves me right, it
allows such IP to symbol translation.

Note that for the system calls, they are usually done through the vDSO
page or from the glibc, so it won't give you much information to see
what IP the system call must return to. But it's not out of question to
do a userspace stack dump, which is a much richer source of information.

I had that in really old LTTng versions, but dumped it temporarily. I
think there is a similar feature in the mainline linux kernel now.


> thanks
> -Joachim
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Mathieu Desnoyers
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