linux-kernel - Re: [PATCH 02/17] perf: Add ability to attach user level registers dump to sample

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Date:	Wed, 25 Jul 2012 20:27:47 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	acme@...hat.com, a.p.zijlstra@...llo.nl, mingo@...e.hu,
	paulus@...ba.org, cjashfor@...ux.vnet.ibm.com, fweisbec@...il.com,
	gorcunov@...nvz.org, tzanussi@...il.com, mhiramat@...hat.com,
	robert.richter@....com, fche@...hat.com,
	linux-kernel@...r.kernel.org, masami.hiramatsu.pt@...achi.com,
	drepper@...il.com, asharma@...com, benjamin.redelings@...cent.org
Subject: Re: [PATCH 02/17] perf: Add ability to attach user level registers
 dump to sample

On Wed, Jul 25, 2012 at 07:39:18PM +0200, Stephane Eranian wrote:
> On Sun, Jul 22, 2012 at 2:14 PM, Jiri Olsa <jolsa@...hat.com> wrote:

SNIP

> > +       if (sample_type & PERF_SAMPLE_REGS_USER) {
> > +               u64 avail = (data->regs_user != NULL);
> > +
> > +               /*
> > +                * If there are no regs to dump, notice it through
> > +                * first u64 being zero.
> > +                */
> > +               perf_output_put(handle, avail);
> > +
> The only role of avail is to report whether or not you've captured actual
> registers. Could it be used to report the sampled process ABI (32 vs. 64)
> instead? Something like:
>       PERF_SAMPLE_REGS_ABI_NONE -> no regs captured (emulate your
> current behavior)
>       PERF_SAMPLE_REGS_ABI_32 -> 32 bit ABI regs captured
>       PERF_SAMPLE_REGS_ABI_64 -> 64 bit ABI regs captured
> 
> That could help the tools interpret the register values.

Yes, I think that could help once we start dealing with compat tasks.

The current userspace code stays untouched, because it checks for
'avail != 0', which stays even with your change.

I think this could be sent later with all other fixes I'm already
working on. But I can work/send it preferentially before whole patchset
is taken if you like.

thanks,
jirka
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