linux-kernel - Re: [PATCH v7 11/18] perf tools: add mem access sampling core support

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Date:	Wed, 27 Mar 2013 15:48:15 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Namhyung Kim <namhyung.kim@....com>
Subject: Re: [PATCH v7 11/18] perf tools: add mem access sampling core support

On Wed, Mar 27, 2013 at 3:34 PM, Jiri Olsa <jolsa@...hat.com> wrote:
>
> On Wed, Mar 27, 2013 at 03:20:14PM +0100, Peter Zijlstra wrote:
> > On Wed, 2013-03-27 at 15:14 +0100, Jiri Olsa wrote:
> > > we have correct cpumode for sample->ip, but I think it's the
> > > PEBS->dla (sample->addr) where we need to guess.. right?
> >
> > kernel mode very much fakes the cpumode/segment stuff for PEBS. PEBS
> > assumes you're running in a linear/flat mode.
> >
>
> say we hit the sample when kernel accesses the user data, we will endup
> with IP in kernel space and DATA ptr in user space.. in theory ;-)
>
Yes, this is possible. So I think we could probably leaverage ip__resolve_ams()
and pass the extra parameter for MAP_VARIABLE vs. MAP_FUNCTION.


>
> and that would need the cpumode guessing for DATA ptr, because
> cpumode value is deduced from cs register
>
> jirka
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