[PATCH 2/9] perf thread-stack: Report branch stack hw_idx as not available

[Adrian Hunter]

On 03/08/2026 12:06, Amir Ayupov wrote:
> thread_stack__br_sample() and thread_stack__br_sample_late() fill a
> caller-supplied branch_stack that is typically allocated with zalloc(),
> leaving hw_idx as 0. Zero is a valid hardware index, so consumers that
> honour PERF_SAMPLE_BRANCH_HW_INDEX see a reconstructed branch stack
> claiming to start at LBR TOS entry 0.
> 
> These branch stacks are reconstructed from instruction trace and have no
> hardware index at all. Set hw_idx to -1ULL, which is the established way
> to say "not available" and matches what intel-pt and cs-etm already put
> in the branch stacks they synthesise directly.
> 
> Signed-off-by: Amir Ayupov <aaupov at fb.com>

Fixes tag?

Otherwise:

Reviewed-by: Adrian Hunter <adrian.hunter at intel.com>

> ---
>  tools/perf/util/thread-stack.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/tools/perf/util/thread-stack.c b/tools/perf/util/thread-stack.c
> index c5ce741b07446..1a3dffa83bde2 100644
> --- a/tools/perf/util/thread-stack.c
> +++ b/tools/perf/util/thread-stack.c
> @@ -624,6 +624,7 @@ void thread_stack__br_sample(struct thread *thread, int cpu,
>  	unsigned int nr;
>  
>  	dst->nr = 0;
> +	dst->hw_idx = -1ULL;
>  
>  	if (!ts)
>  		return;
> @@ -686,6 +687,7 @@ void thread_stack__br_sample_late(struct thread *thread, int cpu,
>  	bool start = false;
>  
>  	dst->nr = 0;
> +	dst->hw_idx = -1ULL;
>  
>  	if (!ts)
>  		return;