Re: [PATCH v2 02/14] perf intel-pt: Preserve return addresses for asynchronous branches

[Adrian Hunter]

On 23/09/2026 18:21, Leo Yan wrote:
> Intel PT uses a zero instruction length for asynchronous branches so
> the thread stack resumes at the source IP. A dlfilter can fetch the
> instruction before call/return processing and replace that zero with
> its opcode length, advancing the saved return address.
> 
> Set sample.ret_addr to sample.ip for asynchronous branch samples so
> instruction fetching cannot change the return address. This also
> covers asynchronous trace-end samples and VM exits.
> 
> Assisted-by: Codex:gpt-6
> Signed-off-by: Leo Yan <leo.yan@xxxxxxx>

Reviewed-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>

> ---
>  tools/perf/util/intel-pt.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/tools/perf/util/intel-pt.c b/tools/perf/util/intel-pt.c
> index 8c21c9f52d572d2dd4e15b3b5c341b253ccea1b5..e8b9c8a67b0a0635e0110eda4b6ccb2511132fc7 100644
> --- a/tools/perf/util/intel-pt.c
> +++ b/tools/perf/util/intel-pt.c
> @@ -1803,6 +1803,13 @@ static int intel_pt_synth_branch_sample(struct intel_pt_queue *ptq)
>  	perf_sample__init(&sample, /*all=*/true);
>  	intel_pt_prep_b_sample(pt, ptq, event, &sample);
>  
> +	/*
> +	 * For asynchronous branches, use the sample IP as the return address
> +	 * instead of advancing it during instruction decoding.
> +	 */
> +	if (sample.flags & PERF_IP_FLAG_ASYNC)
> +		sample.ret_addr = sample.ip;
> +
>  	sample.id = ptq->pt->branches_id;
>  	sample.stream_id = ptq->pt->branches_id;
>  
>