Re: perf call stacks on 32bit ARM v7

[Milian Wolff <milian.wolff@kdab.com>]

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On Donnerstag, 29. September 2016 09:39:51 CEST Jean Pihet wrote:
> Hi Milian, Wangnan,
> 
> I am pretty busy this week. Let me check and come back to you next week.

Sure, take your time - much appreciated!

> PS: did you check the detailed instructions from the Linaro wiki pages?
> These are linked from the Fosdem presentation slides.

You mean this page, right:

https://wiki.linaro.org/KenWerner/Sandbox/libunwind

That does not mention perf at all, and only talks about libunwind. Note how 
your talk, and the wiki, say .exidx unwinding using libunwind works. But your 
slides also explicitly say that this mechanism is not supported by perf, yet. 
I would like to know the reason for that, or whether this is outdated 
information.

Thanks!

> Le 28 sept. 2016 3:47 AM, "Wangnan (F)" <wangnan0@huawei.com> a écrit :
> > On 2016/9/28 5:25, Milian Wolff wrote:
> >> Hello Jean, others.
> >> 
> >> Can someone please clarify the requirements for getting perf to properly
> >> unwind the call stack on 32bit ARM v7?
> >> 
> >> Looking at [1], it seems that I need either (a) frame pointers, or (b)
> 
> DWARF
> 
> >> debug information. Because (a) is often not available, and (b) is too
> 
> large
> 
> >> for small flash drives on embedded - how do I use perf with split debug
> >> information files? I.e. I have tries to record on the arm board using
> 
> DWARF:
> >> arm-v7$ perf record --call-graph dwarf ...
> >> 
> >> Then transferred the perf.data file over to my host machine. Perf
> 
> archive said
> 
> >> that no build-id's could be found, so I'm not using that. Instead, I try
> 
> to
> 
> >> ask perf to find the split debug packes using symfs:
> >> 
> >> x86-64$ perf report --symfs ... -g graph
> >> 
> >> But that does not work and I'm not seeing any backtraces. Stracing the
> 
> report,
> 
> >> I don't see it even trying to access files - how can I debug this and
> 
> figure
> 
> >> out what I'm supposed to be using?
> > 
> > Unfortunaetly, currently perf only supports corss decoding dwarf
> > for x86_64, x86_32 and arm64. ARM32 is not on the list.
> > 
> > Please see:
> > 
> > http://www.spinics.net/lists/kernel/msg2266293.html
> > 
> > and
> > 
> > tools/perf/util/unwind-libunwind.c
> > 
> > I think adding ARM32 support should not be very hard on perf side.
> > Add He Kuang to the CC list, he is the author of this patch set.
> > 
> > Thank you.


-- 
Milian Wolff | milian.wolff@kdab.com | Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt Experts

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