Re: [RFC][PATCH 07/11] perf: Provide PERF_SAMPLE_REGS

[Peter Zijlstra <peterz@infradead.org>]

On Wed, 2010-03-03 at 09:55 -0800, David Miller wrote:
> From: Stephane Eranian <eranian@google.com>
> Date: Wed, 3 Mar 2010 09:49:33 -0800
> 
> > On Wed, Mar 3, 2010 at 9:39 AM, Peter Zijlstra <peterz@infradead.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 ;-)