[PATCH 17/25] perf cs-etm: Allow history collection for samples with zero IP

[James Clark]

On 15/09/2026 16:49, Leo Yan wrote:
> Perf clears the IP of a user-only PMU sample when its interrupt skids
> into the kernel. The timestamp and TID remain valid, but the zero-IP
> check prevents --itrace=L from attaching decoded branch history.
> 
> Remove the IP check and keep matching samples to trace by time and
> thread.
> 
> Assisted-by: Codex:gpt-6
> Signed-off-by: Leo Yan <leo.yan at arm.com>
> ---
>   tools/perf/util/cs-etm.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index 00407a80933e1c0b76260aed5894dece50b9aecd..baa962085dba5226d9729a0ee8039374d5fcb1a0 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -3097,6 +3097,8 @@ static int cs_etm__br_stack_init(struct cs_etm_auxtrace *etm,
>   /*
>    * Add decoded branch history to an existing sample. The sample keeps its own
>    * ip, callchain and event identity; only an absent branch stack is filled in.
> + * A user-only PMU sample can have a zero IP when the interrupt skids into
> + * the kernel; its thread and trace window still identify valid history.
>    */
>   static int cs_etm__process_sample(struct cs_etm_auxtrace *etm,
>   				  struct perf_session *session,
> @@ -3107,7 +3109,7 @@ static int cs_etm__process_sample(struct cs_etm_auxtrace *etm,
>   	int err;
>   
>   	if (!etm->synth_opts.add_last_branch || sample->branch_stack ||
> -	    !sample->ip || !sample->time || sample->time == (u64)-1)
> +	    !sample->time || sample->time == (u64)-1)
>   		return 0;
>   
>   	/* Adding branch history to existing samples supports the host only */
> 

Looks like we can fix this up in Amir's patch that introduced it when I 
post it as part of the JIT stuff. Then this commit can be dropped.