linux-kernel - Re: [BUG] perf tools: does not process data mmaps correctly

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Message-ID: <CABPqkBQZZWHF5cRdYxmcq4QxaTg_sT_8gomK2mPm+ksML+DHBg@mail.gmail.com>
Date:	Wed, 31 Oct 2012 10:23:56 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Namhyung Kim <namhyung.kim@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: Re: [BUG] perf tools: does not process data mmaps correctly

On Tue, Oct 30, 2012 at 9:29 PM, Stephane Eranian <eranian@...gle.com> wrote:
> Arnaldo,
>
> A long time ago, I brought up the issue of perf failing to resolve
> data symbols despite having the MAP__VARIABLE map type.
>
> Now that I have posted the PEBS-LL patch series, there is a test
> case to debug this.
>
> I looked again at it today. Start from ip__resolve_data() in my patchset.
> IT is looking for a data symbol given an address.
>
> Seems to me the core of the problem is how perf processes the MMAP
> records in machine__process_mmap_event():
>
> int machine__process_mmap_event(struct machine *machine, union
> perf_event *event)
> {
>       ...
>
>         thread = machine__findnew_thread(machine, event->mmap.pid);
>         if (thread == NULL)
>                 goto out_problem;
>         map = map__new(&machine->user_dsos, event->mmap.start,
>                         event->mmap.len, event->mmap.pgoff,
>                         event->mmap.pid, event->mmap.filename,
>                         MAP__FUNCTION);
>
> I don't see any effort to distinguish code from data here. All mmaps are
> treated as code.
>
> That could be fine, if then you drop MAP__VARIABLE.
>
> So how is this supposed to work?
>

Looking at the kernel code for attr->mmap_data shows a corollary
problem with the RECORD_MMAP. Somehow we lose the fact
that this corresponds to data mmap (!VM_EXEC). Having that
info in the header would help the tool process the record properly,
I think.
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