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

Arnaldo Carvalho de Melo
2018-10-29T17:40:20Z

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