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Date:   Mon, 31 Aug 2020 14:38:32 -0600
From:   Mathieu Poirier <mathieu.poirier@linaro.org>
To:     Leo Yan <leo.yan@linaro.org>
Cc:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Mike Leach <mike.leach@linaro.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Andi Kleen <ak@linux.intel.com>,
        Kan Liang <kan.liang@linux.intel.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        AAl Grant <al.grant@arm.com>
Subject: Re: [PATCH 2/2] perf intel-pt: Fix corrupt data after perf inject
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 <20200819084751.17686-2-leo.yan@linaro.org>
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On Wed, Aug 19, 2020 at 04:47:51PM +0800, Leo Yan wrote:
> From: Al Grant <al.grant@arm.com>
> 
> 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 <al.grant@arm.com>
> Signed-off-by: Leo Yan <leo.yan@linaro.org>

Arnaldo, please consider.

Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>

> ---
>  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
>