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

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Date:   Mon, 29 Oct 2018 14:40:14 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Milian Wolff <milian.wolff@...b.com>
Cc:     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

Em Mon, Oct 29, 2018 at 04:26:27PM +0100, Milian Wolff escreveu:
> 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.

I'm updating the patch to remove:

"It's unclear so far what the reason for that is."

Adding:

"See https://sourceware.org/ml/elfutils-devel/2018-q4/msg00089.html for
a patch fixing that."

Ok? Or are you saying that that "unclear" part applies to both libunwind
and elfutils?

- Arnaldo