linux-kernel - Re: [PATCH v3 1/7 UPDATE2] perf tools: Find vdso with the consider of cross-platform

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Date:	Thu, 16 Jun 2016 16:00:12 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	He Kuang <hekuang@...wei.com>, Jiri Olsa <jolsa@...nel.org>
Cc:	peterz@...radead.org, mingo@...hat.com,
	alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
	wangnan0@...wei.com, jpoimboe@...hat.com, ak@...ux.intel.com,
	eranian@...gle.com, namhyung@...nel.org,
	sukadev@...ux.vnet.ibm.com, masami.hiramatsu.pt@...achi.com,
	tumanova@...ux.vnet.ibm.com, kan.liang@...el.com,
	penberg@...nel.org, dsahern@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/7 UPDATE2] perf tools: Find vdso with the consider of
 cross-platform

On 15/06/16 16:34, Arnaldo Carvalho de Melo wrote:
> Em Tue, May 17, 2016 at 09:04:54AM +0000, He Kuang escreveu:
>> There's a problem in machine__findnew_vdso(), vdso buildid generated
>> by a 32-bit machine stores it with the name 'vdso', but when
>> processing buildid on a 64-bit machine with the same 'perf.data', perf
>> will search for vdso named as 'vdso32' and get failed.
> 
> Without looking at the code, just trying to understand your patch by
> reading your description: Why would we look for names if we have
> build-ids? All this type and name comparasions seems wrong if we have a
> build-id, no?
> 
> Adrian?

We match maps to builds ids using the file name - consider
machine__findnew_[v]dso() called in map__new().  So in the context of a perf
data file, we consider the file name to be unique.

A vdso map does not have a file name - all we know is that it is vdso.  We
look at the thread to tell if it is 32-bit, 64-bit or x32.  Then we need to
get the build id which has been recorded using short name "[vdso]" or
"[vdso32]" or "[vdsox32]".

The problem is that on a 32-bit machine, we use the name "[vdso]".  If you
take a 32-bit perf data file to a 64-bit machine, it gets hard to figure out
if "[vdso]" is 32-bit or 64-bit.

This patch solves that problem.

I acked it in another email.