Re: [PATCH v2] perf lock contention: Fix builtin detection

[Namhyung Kim]

On Tue, Mar 7, 2023 at 4:30 PM Ian Rogers <irogers@xxxxxxxxxx> wrote:
>
> __has_builtin was passed the macro rather than the actual builtin
> feature. The builtin test isn't sufficient and a clang version test
> also needs to be performed.
>
> Fixes: 1bece1351c65 ("perf lock contention: Support old rw_semaphore type")
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>

Reviewed-by: Namhyung Kim <namhyung@xxxxxxxxxx>

Thanks,
Namhyung


> ---
>  tools/perf/util/bpf_skel/lock_contention.bpf.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/bpf_skel/lock_contention.bpf.c b/tools/perf/util/bpf_skel/lock_contention.bpf.c
> index e6007eaeda1a..141b36d13b19 100644
> --- a/tools/perf/util/bpf_skel/lock_contention.bpf.c
> +++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c
> @@ -182,7 +182,13 @@ static inline struct task_struct *get_lock_owner(__u64 lock, __u32 flags)
>                 struct mutex *mutex = (void *)lock;
>                 owner = BPF_CORE_READ(mutex, owner.counter);
>         } else if (flags == LCB_F_READ || flags == LCB_F_WRITE) {
> -#if __has_builtin(bpf_core_type_matches)
> +       /*
> +        * Support for the BPF_TYPE_MATCHES argument to the
> +        * __builtin_preserve_type_info builtin was added at some point during
> +        * development of clang 15 and it's what is needed for
> +        * bpf_core_type_matches.
> +        */
> +#if __has_builtin(__builtin_preserve_type_info) && __clang_major__ >= 15
>                 if (bpf_core_type_matches(struct rw_semaphore___old)) {
>                         struct rw_semaphore___old *rwsem = (void *)lock;
>                         owner = (unsigned long)BPF_CORE_READ(rwsem, owner);
> --
> 2.40.0.rc0.216.gc4246ad0f0-goog
>