2020-08-31 22:54:02

by Mathieu Poirier

Subject: Re: [PATCH 2/2] perf intel-pt: Fix corrupt data after perf inject from

On Wed, Aug 19, 2020 at 04:47:51PM +0800, Leo Yan wrote:
> From: Al Grant <[email protected]>
>
> Commit 42bbabed09ce ("perf tools: Add hw_idx in struct branch_stack")
> changed the format of branch stacks in perf samples. When samples use
> this new format, a flag must be set in the corresponding event.
> Synthesized branch stacks generated from Intel PT were using the new
> format, but not setting the event attribute, leading to consumers
> seeing corrupt data. This patch fixes the issue by setting the event
> attribute to indicate use of the new format.
>
> Fixes: 42bbabed09ce ("perf tools: Add hw_idx in struct branch_stack")
> Signed-off-by: Al Grant <[email protected]>
> Signed-off-by: Leo Yan <[email protected]>

Arnaldo, please consider.

Reviewed-by: Mathieu Poirier <[email protected]>

> ---
> tools/perf/util/intel-pt.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/intel-pt.c b/tools/perf/util/intel-pt.c
> index 2a8d245351e7..0af4e81c46e2 100644
> --- a/tools/perf/util/intel-pt.c
> +++ b/tools/perf/util/intel-pt.c
> @@ -3017,8 +3017,15 @@ static int intel_pt_synth_events(struct intel_pt *pt,
>
> if (pt->synth_opts.callchain)
> attr.sample_type |= PERF_SAMPLE_CALLCHAIN;
> - if (pt->synth_opts.last_branch)
> + if (pt->synth_opts.last_branch) {
> attr.sample_type |= PERF_SAMPLE_BRANCH_STACK;
> + /*
> + * We don't use the hardware index, but the sample generation
> + * code uses the new format branch_stack with this field,
> + * so the event attributes must indicate that it's present.
> + */
> + attr.branch_sample_type |= PERF_SAMPLE_BRANCH_HW_INDEX;
> + }
>
> if (pt->synth_opts.instructions) {
> attr.config = PERF_COUNT_HW_INSTRUCTIONS;
> --
> 2.17.1
>

2020-09-01 14:57:46

by Arnaldo Carvalho de Melo

Subject: Re: [PATCH 2/2] perf intel-pt: Fix corrupt data after perf inject from

Em Mon, Aug 31, 2020 at 02:38:32PM -0600, Mathieu Poirier escreveu:
> On Wed, Aug 19, 2020 at 04:47:51PM +0800, Leo Yan wrote:
> > From: Al Grant <[email protected]>
> >
> > Commit 42bbabed09ce ("perf tools: Add hw_idx in struct branch_stack")
> > changed the format of branch stacks in perf samples. When samples use
> > this new format, a flag must be set in the corresponding event.
> > Synthesized branch stacks generated from Intel PT were using the new
> > format, but not setting the event attribute, leading to consumers
> > seeing corrupt data. This patch fixes the issue by setting the event
> > attribute to indicate use of the new format.
> >
> > Fixes: 42bbabed09ce ("perf tools: Add hw_idx in struct branch_stack")
> > Signed-off-by: Al Grant <[email protected]>
> > Signed-off-by: Leo Yan <[email protected]>
>
> Arnaldo, please consider.
>
> Reviewed-by: Mathieu Poirier <[email protected]>

Thanks, applied, and 1/2 too.

- Arnaldo

> > ---
> > tools/perf/util/intel-pt.c | 9 ++++++++-
> > 1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/perf/util/intel-pt.c b/tools/perf/util/intel-pt.c
> > index 2a8d245351e7..0af4e81c46e2 100644
> > --- a/tools/perf/util/intel-pt.c
> > +++ b/tools/perf/util/intel-pt.c
> > @@ -3017,8 +3017,15 @@ static int intel_pt_synth_events(struct intel_pt *pt,
> >
> > if (pt->synth_opts.callchain)
> > attr.sample_type |= PERF_SAMPLE_CALLCHAIN;
> > - if (pt->synth_opts.last_branch)
> > + if (pt->synth_opts.last_branch) {
> > attr.sample_type |= PERF_SAMPLE_BRANCH_STACK;
> > + /*
> > + * We don't use the hardware index, but the sample generation
> > + * code uses the new format branch_stack with this field,
> > + * so the event attributes must indicate that it's present.
> > + */
> > + attr.branch_sample_type |= PERF_SAMPLE_BRANCH_HW_INDEX;
> > + }
> >
> > if (pt->synth_opts.instructions) {
> > attr.config = PERF_COUNT_HW_INSTRUCTIONS;
> > --
> > 2.17.1
> >

--

- Arnaldo