linux-kernel - Re: [RFC][PATCH 07/11] perf: Provide PERF_SAMPLE

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Message-ID: <20100304110429.GC21977@elte.hu>
Date:	Thu, 4 Mar 2010 12:04:29 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, paulus@...ba.org, eranian@...gle.com,
	robert.richter@....com
Subject: Re: [RFC][PATCH 07/11] perf: Provide PERF_SAMPLE_REGS


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Wed, 2010-03-03 at 23:02 +0100, Frederic Weisbecker wrote:
> > On Wed, Mar 03, 2010 at 05:39:43PM +0100, Peter Zijlstra wrote:
> > > Simply copy out the provided pt_regs in a u64 aligned fashion.
> > > 
> > > XXX: do task_pt_regs() and get_irq_regs() always clear everything or
> > >      are we now leaking data?
> > 
> > 
> > It looks like there is a leak in case of non trace syscalls.
> > where we don't appear to save r12-15.
> > 
> > Then task_pt_regs() may leak the top of a process stack...?
> 
> Right, I was afraid of that. I've put this PERF_SAMPLE_REGS thing in the 
> freezer for now as people seem unsure how to deal with it.

Also, we dont want to expose PEBS nor LBR on an ABI level without there being 
a user-space component making good use of it.

For example tools/perf/ support would qualify. Raw libraries alone dont really 
count as they generally lag plus there's no guarantee for a full feedback loop 
either.

Adding ABI details is always a tricky business and we only want to do it if 
there's direct, immediate, close involvement with the user-space side, and 
real, immediate benefits to users.

Thanks,

	Ingo
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