linux-kernel - Re: [RFC/PATCHSET 0/8] perf tools: Minimal build without libelf dependency (v2)

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Message-ID: <20120622153234.GJ17747@infradead.org>
Date:	Fri, 22 Jun 2012 12:32:34 -0300
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	David Ahern <dsahern@...il.com>
Cc:	Namhyung Kim <namhyung@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, Jiri Olsa <jolsa@...hat.com>
Subject: Re: [RFC/PATCHSET 0/8] perf tools: Minimal build without libelf
 dependency (v2)

Em Fri, Jun 22, 2012 at 09:18:34AM -0600, David Ahern escreveu:
> On 6/22/12 9:05 AM, Namhyung Kim wrote:
> >2012-06-22 (금), 11:47 +0200, Peter Zijlstra:
> >>On Fri, 2012-06-22 at 14:37 +0900, Namhyung Kim wrote:
> >>>And then I realized that the perf record needs to know about the
> >>>build-id's anyway. :( So I implemented a poor man's version of elf
> >>>parser only for parsing the build-id info.

> >>Why? the very first versions didn't know about any of that nonsense :-)
> >>It works just fine as long as you don't go change binaries around.
> >>
> >>That said, you did the work already, so no objection, just saying
> >>builtids aren't that important.

> >I'm not sure I understood you correctly. But 'perf record' needs to know
> >about the build-id's to save them to perf.data for 'perf report' later.
> >And 'perf archive' also needs to know about them to select necessary
> >binaries for the session.

> And build-id's are not required for report (-B option for record).

> Also, the intent is for a small footprint binary for embedded
> systems. On such a system I would expect binaries and libraries to
> be stripped, so no point in running perf-archive.

Right, build ids are not a strict requirement, its just a safeguard,
when available, to prevent WTF moments at post processing time (report,
annotate, etc) if different binaries are used to resolve symbols.

- Arnaldo
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