linux-kernel - Re: [PATCH] perf util: take pgoff into account when reporting elf to libdwfl

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Date:   Mon, 29 Oct 2018 16:26:27 +0100
From:   Milian Wolff <milian.wolff@...b.com>
To:     Milian Wolff <milian.wolff@...b.com>
Cc:     acme@...nel.org, jolsa@...nel.org, Linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH] perf util: take pgoff into account when reporting elf to
 libdwfl

On Monday, October 29, 2018 3:16:44 PM CET Milian Wolff wrote:
> Libdwfl parses an ELF file itself and creates mappings for the
> individual sections. Perf on the other hand sees raw mmap events which
> represent individual sections. When we encounter an address pointing
> into a mapping with pgoff != 0, we must take that into account and
> report the file at the non-offset base address.
> 
> This fixes unwinding with libdwfl in some cases. E.g. for a file like:

<snip>

> Note that the backtrace is still stopping too early, when
> compared to the nice results obtained via libunwind. It's
> unclear so far what the reason for that is.

The remaining issue is due to a bug in elfutils:

https://sourceware.org/ml/elfutils-devel/2018-q4/msg00089.html

With both patches applied, libunwind and elfutils produce the same output for 
the above scenario.

Cheers
-- 
Milian Wolff | milian.wolff@...b.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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