linux-kernel - Re: [PATCH] perf tools: Convert legacy map definition to BTF-defined

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Date:   Wed, 29 Jun 2022 13:53:14 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Jiri Olsa <jolsa@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        linux-perf-users@...r.kernel.org, bpf@...r.kernel.org,
        Andrii Nakryiko <andrii@...nel.org>
Subject: Re: [PATCH] perf tools: Convert legacy map definition to BTF-defined

Em Wed, Jun 29, 2022 at 09:43:17AM -0700, Ian Rogers escreveu:
> On Wed, Jun 29, 2022 at 4:27 AM Jiri Olsa <jolsa@...nel.org> wrote:
> > The libbpf is switching off support for legacy map definitions [1],
> > which will break the perf llvm tests.
> >
> > Moving the base source map definition to BTF-defined, so we need
> > to use -g compile option for to add debug/BTF info.
> >
> > [1] https://lore.kernel.org/bpf/20220627211527.2245459-1-andrii@kernel.org/
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >  tools/perf/tests/bpf-script-example.c | 15 +++++++++------
> >  tools/perf/util/llvm-utils.c          |  2 +-
> >  2 files changed, 10 insertions(+), 7 deletions(-)
> >
> > diff --git a/tools/perf/tests/bpf-script-example.c b/tools/perf/tests/bpf-script-example.c
> > index ab4b98b3165d..065a4ac5d8e5 100644
> > --- a/tools/perf/tests/bpf-script-example.c
> > +++ b/tools/perf/tests/bpf-script-example.c
> > @@ -24,13 +24,16 @@ struct bpf_map_def {
> >         unsigned int max_entries;
> >  };
> >
> > +#define __uint(name, val) int (*name)[val]
> > +#define __type(name, val) typeof(val) *name
> 
> This is probably worth a comment, reading it hurts :-) I expect that
> libbpf provides a definition that the rest of the world uses.
> 
> Fwiw, the pre bpf counters BPF in perf needs a good overhaul. Arnaldo
> mentioned switching perf trace's BPF to use BPF skeletons in another
> post. The tests we have on event filters are flaky. One fewer bpf.h in
> the world seems like a service to humanity (I'm looking at you
> tools/perf/include/bpf/bpf.h).

Yeah, bring perf trace to the modern world :-)

- Arnaldo
 
> Thanks,
> Ian
> 
> > +
> >  #define SEC(NAME) __attribute__((section(NAME), used))
> > -struct bpf_map_def SEC("maps") flip_table = {
> > -       .type = BPF_MAP_TYPE_ARRAY,
> > -       .key_size = sizeof(int),
> > -       .value_size = sizeof(int),
> > -       .max_entries = 1,
> > -};
> > +struct {
> > +       __uint(type, BPF_MAP_TYPE_ARRAY);
> > +       __uint(max_entries, 1);
> > +       __type(key, int);
> > +       __type(value, int);
> > +} flip_table SEC(".maps");
> >
> >  SEC("func=do_epoll_wait")
> >  int bpf_func__SyS_epoll_pwait(void *ctx)
> > diff --git a/tools/perf/util/llvm-utils.c b/tools/perf/util/llvm-utils.c
> > index 96c8ef60f4f8..2dc797007419 100644
> > --- a/tools/perf/util/llvm-utils.c
> > +++ b/tools/perf/util/llvm-utils.c
> > @@ -25,7 +25,7 @@
> >                 "$CLANG_OPTIONS $PERF_BPF_INC_OPTIONS $KERNEL_INC_OPTIONS " \
> >                 "-Wno-unused-value -Wno-pointer-sign "          \
> >                 "-working-directory $WORKING_DIR "              \
> > -               "-c \"$CLANG_SOURCE\" -target bpf $CLANG_EMIT_LLVM -O2 -o - $LLVM_OPTIONS_PIPE"
> > +               "-c \"$CLANG_SOURCE\" -target bpf $CLANG_EMIT_LLVM -g -O2 -o - $LLVM_OPTIONS_PIPE"
> >
> >  struct llvm_param llvm_param = {
> >         .clang_path = "clang",
> > --
> > 2.35.3
> >

-- 

- Arnaldo