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

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Message-ID: <20130327143437.GE1092@krava.brq.redhat.com>
Date:	Wed, 27 Mar 2013 15:34:37 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Stephane Eranian <eranian@...gle.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, ak@...ux.intel.com,
	acme@...hat.com, namhyung.kim@....com
Subject: Re: [PATCH v7 11/18] perf tools: add mem access sampling core support

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 ;-)

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

jirka
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