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Date: Wed, 27 Jun 2012 17:24:02 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Stephane Eranian <eranian@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>, acme@redhat.com, a.p.zijlstra@chello.nl,
        mingo@elte.hu, paulus@samba.org, cjashfor@linux.vnet.ibm.com,
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        benjamin.redelings@nescent.org
Subject: Re: [PATCH 03/23] perf: Add ability to attach user level registers
 dump to sample
Message-ID: <20120627152359.GI20638@somewhere.redhat.com>
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On Wed, Jun 27, 2012 at 05:13:44PM +0200, Stephane Eranian wrote:
> On Wed, Jun 27, 2012 at 5:11 PM, Frederic Weisbecker <fweisbec@gmail.com> wrote:
> > On Tue, Jun 19, 2012 at 05:47:54PM +0200, Jiri Olsa wrote:
> >> @@ -4061,6 +4105,19 @@ void perf_prepare_sample(struct perf_event_header *header,
> >>               }
> >>               header->size += size;
> >>       }
> >> +
> >> +     if (sample_type & PERF_SAMPLE_REGS_USER) {
> >> +             /* regs dump available bool */
> >> +             int size = sizeof(u64);
> >> +
> >> +             data->regs_user = perf_sample_regs_user(regs);
> >> +             if (data->regs_user) {
> >> +                     u64 mask = event->attr.sample_regs_user;
> >> +                     size += hweight64(mask) * sizeof(u64);
> >> +             }
> >> +
> >> +             header->size += size;
> >
> > We'll need to remove the 64 bits registers for compat tasks but other than
> > that, it looks ok.
> You cannot do this. You cannot remove register values from under the hood.
> The only way the user has to parse the sample is the sample_regs_users bitmask.
> You have to return 0 for those unexisting regs for compat tasks.

You mean fill unexisting reg values with 0? Yeah that works.