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

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Date:	Wed, 03 Mar 2010 20:18:30 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Miller <davem@...emloft.net>
Cc:	eranian@...gle.com, mingo@...e.hu, linux-kernel@...r.kernel.org,
	paulus@...ba.org, robert.richter@....com, fweisbec@...il.com
Subject: Re: [RFC][PATCH 07/11] perf: Provide PERF_SAMPLE_REGS

On Wed, 2010-03-03 at 09:55 -0800, David Miller wrote:
> From: Stephane Eranian <eranian@...gle.com>
> Date: Wed, 3 Mar 2010 09:49:33 -0800
> 
> > On Wed, Mar 3, 2010 at 9:39 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> >> On Wed, 2010-03-03 at 09:30 -0800, Stephane Eranian wrote:
> >>> This assumes struct pt_regs is somehow exported to userland.
> >>> Is that the case?
> >>
> >> I seems to have understood they were, and asm/ptrace.h seems to agree
> >> with that, it has !__KERNEL__ definitions for struct pt_regs.
> >>
> > Seems to be the case, indeed.
> 
> BTW, how are you going to cope with compat systems?
> 
> If I build 'perf' on a sparc64 kernel build, it's going to get the
> 64-bit pt_regs.  So I can't then use that binary on a sparc box
> running a 32-bit kernel.
> 
> And vice versa.
> 
> And more generally aren't we supposed to be able to eventually analyze
> perf dumps on any platform not just the one 'perf' was built under?
> 
> We'll need to do something about the encoding of pt_regs, therefore.

Hrm, yes,.. what I can do for the moment is 'cheat' and make the raw
PEBS record available through PERF_SAMPLE_RAW (that also has CAP_ADMIN,
which I guess is a good idea for full reg sets), and then we can work
out how to expose pt_regs later.

If someone has a better suggestion than this, which is basically blurp
out host native pt_regs and cope, please tell ;-)

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