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

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Date:	Thu, 26 Jul 2012 19:58:46 +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 Thu, Jul 26, 2012 at 07:42:55PM +0200, Stephane Eranian wrote:
> On Wed, Jul 25, 2012 at 8:27 PM, Jiri Olsa <jolsa@...hat.com> wrote:
> > 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.
> >
> You don't control whether or not you capture compat tasks. So
> you have to deal with those right now.
> 
> > 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.
> >
> Well, why not do it now. You'd have to rename the available field
> into something more sensible. Also need to prepare it for future
> extension if they ever become necessary.

I'll send new version shortly

thanks,
jirka
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