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

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Message-ID: <CAM9d7ciyGagEiM6zSVjh9VpsiShLeRBUFjfGGLrzoqTD+hT9KA@mail.gmail.com>
Date:   Tue, 7 Mar 2023 17:41:19 -0800
From:   Namhyung Kim <namhyung@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Martin KaFai Lau <martin.lau@...nel.org>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH v2] perf lock contention: Fix builtin detection

On Tue, Mar 7, 2023 at 4:30 PM Ian Rogers <irogers@...gle.com> 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@...gle.com>

Reviewed-by: Namhyung Kim <namhyung@...nel.org>

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
>