Re: LTTng user-space callstacks

[Valentin Grigorev via lttng-dev <lttng-dev@lists.lttng.org>]

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Yeah, as far as I know, perf [1] is successfully using libunwind to provide
callstacks. Probably, LTTng team should think about it too, if there are no
serious obstacles.

[1]: https://perf.wiki.kernel.org/index.php/Main_Page


Best regards,
Valentin Grigorev


On Thu, Mar 26, 2020 at 11:53 PM Milian Wolff <milian.wolff@kdab.com> wrote:

> On Donnerstag, 26. März 2020 20:41:17 CET Mathieu Desnoyers via lttng-dev
> wrote:
> > ----- On Mar 26, 2020, at 1:39 PM, lttng-dev <lttng-dev@lists.lttng.org>
>
> wrote:
> > > Hello!
> > >
> > > Currently, callstack collection in LTTng is only available for
> > > kernel-space
> > > events with context fields callstack-kernel and callstack-user .
> > >
> > > Is it expected that callstack collection for LTTng-UST will be added
> too?
> > > And if it is expected, then how soon?
> >
> > Hi Valentin,
> >
> > It is something that would be interesting and useful, but a lot of work
> > would be needed to have stack-walking this is fast enough and reentrant
> wrt
> > signal handlers. Unfortunately, the backtrace(3) functions do not meet
> > those requirements.
> >
> > Also, for gathering user-space callstacks from the kernel tracer, it only
> > works if all user-space is compiled with frame pointers. This is also a
> > limitation that would require a lot of work to overcome neatly.
> >
> > None of those features are currently on any roadmap due to lack of
> customers
> > showing interest in getting this done.
>
> libunwind [1] should meet the requirements you need. It is high
> performance
> thanks to extensive caching, signal safe and does not rely on frame
> pointers.
>
> [1]: https://github.com/libunwind/libunwind
>
> --
> Milian Wolff | milian.wolff@kdab.com | Senior Software Engineer
> KDAB (Deutschland) GmbH, a KDAB Group company
> Tel: +49-30-521325470
> KDAB - The Qt, C++ and OpenGL Experts

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