linux-kernel - Re: Fwd: perf: callchain feature on ARM

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Date:	Thu, 29 Aug 2013 15:52:16 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	David Ahern <dsahern@...il.com>
Cc:	Jean Pihet <jean.pihet@...aro.org>, linux-kernel@...r.kernel.org
Subject: Re: Fwd: perf: callchain feature on ARM - question about libunwind
 API

On Tue, Aug 27, 2013 at 10:12:08AM -0600, David Ahern wrote:
> [Added Jiri who added the feature to perf]
> 
> On 8/27/13 5:58 AM, Jean Pihet wrote:
> >Hi!
> >
> >I am looking for info and help on the libunwind API.
> >
> >What I am trying to achieve is to allow the callchain feature on perf
> >for ARM (v7 to start with, then ARMv8), from the DWARF info found in
> >the .debug_frame section.
> >
> > From the source code in tools/perf I have added the call to
> >dwarf_find_debug_frame to load and parse the debug info from
> >.debug_frame. This works correctly, all IP ranges are found from the
> >debug code (test program and libraries). Then at some point I get an
> >assertion: 'perf: dwarf/Gparser.c:459: fetch_proc_info: Assertion
> >`c->pi.unwind_info' failed.' At that point c->pi is NULL. Cf. below
> >for more info.

I checked the patch and it looks ok, thought I've never touched
the .debug_frames code paths which are separated to some extend
in the libunwind code..

> >
> >It looks like I am not using the libunwind API as it should, so that
> >the perf code apparently builds a list of IP ranges to resolve but
> >cannot use it later on to gather statistics on the runtime info.
> >
> >Any idea on how to progress? I am also looking at the *_proc_info API
> >of libunwind.

keep digging ;-) also I dont have that assert exactly
at dwarf/Gparser.c:459 so maybe try latest code
git://git.sv.gnu.org/libunwind.git

sorry not to help help you much, you might try to ask
Arun Sharma <asharma@...com> who helped me before.

jirka
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