Re: [PATCH v2 tip/perf/core 1/6] perf symbols: find symbols in different mount namespace

From: Krister Johansen
Date: Fri Jul 07 2017 - 15:36:48 EST

On Thu, Jul 06, 2017 at 04:41:30PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Wed, Jul 05, 2017 at 06:48:08PM -0700, Krister Johansen escreveu:
> > Teach perf how to resolve symbols from binaries that are in a different
> > mount namespace from the tool. This allows perf to generate meaningful
> > stack traces even if the binary resides in a different mount namespace
> > from the tool.
> I was trying to find a way to test after applying each of the patches in
> this series, when it ocurred to me that if a process that appears on a
> file has exit, how can we access /proc/%ITS_PID/something?

You're correct. We can't access /proc/<PID>/whatever once the process
has exited. That was the impeteus for patches 4 and 6, which allow us
to capture the binary (and debuginfo, if it exists) into the buildid
cache so that if we do have a trace that exists after a process or
container exists, we'll still be able to resolve some of the symbols.