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

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Message-ID: <CAP-5=fUQNimNSKjwZaCASyikjXJXBZdw7Z=APYEB4RyX-dXMfQ@mail.gmail.com>
Date:   Mon, 6 Mar 2023 21:56:38 -0800
From:   Ian Rogers <irogers@...gle.com>
To:     Namhyung Kim <namhyung@...nel.org>, bpf@...r.kernel.org
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
Subject: Re: [PATCH] perf lock contention: Fix builtin detection

On Mon, Mar 6, 2023 at 8:43 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> Hi Ian,
>
> On Mon, Mar 6, 2023 at 7:21 PM Ian Rogers <irogers@...gle.com> wrote:
> >
> > __has_builtin was passed the macro rather than the actual builtin
> > feature.
>
> Oh, I missed it's a macro define in tools/lib/bpf/bpf_core_read.h file.
>
> Looking at some BPF test codes, it seems you also need to check the
> clang compiler version.  Please take a look at the file below:
>
>   tools/testing/selftests/bpf/progs/test_core_reloc_type_base.c
>
> Thanks,
> Namhyung

Hmm..

tools/testing/selftests/bpf/progs/test_core_reloc_kernel.c:
...
       /* 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 we require for this test.
        */
#if __has_builtin(__builtin_preserve_type_info) && __clang_major__ >= 15
...

I'm not sure we need to worry about development clang builds and just
the __has_builtin is cleaner. Perhaps the BPF folks can chime in.

Thanks,
Ian

> >
> > Fixes: 1bece1351c65 ("perf lock contention: Support old rw_semaphore type")
> > Signed-off-by: Ian Rogers <irogers@...gle.com>
> > ---
> >  tools/perf/util/bpf_skel/lock_contention.bpf.c | 2 +-
> >  1 file changed, 1 insertion(+), 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..e422eee0f942 100644
> > --- a/tools/perf/util/bpf_skel/lock_contention.bpf.c
> > +++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c
> > @@ -182,7 +182,7 @@ 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)
> > +#if __has_builtin(__builtin_preserve_type_info)
> >                 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
> >