linux-kernel - Re: [PATCH v1] perf build: Pretend scandirat is missing with msan

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Message-ID: <CAP-5=fUVtGgaLgVhoSa3SZdSceifFWs_v1rMnEANj3N=VdpC_A@mail.gmail.com>
Date: Wed, 20 Mar 2024 09:36:19 -0700
From: Ian Rogers <irogers@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] perf build: Pretend scandirat is missing with msan

On Wed, Mar 20, 2024 at 9:32 AM Ian Rogers <irogers@...gle.com> wrote:
>
> Memory sanitizer lacks an interceptor for scandirat, reporting all
> memory it allocates as uninitialized. Memory sanitizer has a scandir
> interceptor so use the fallback function in this case. This allows
> perf test to run under memory sanitizer.
>
> Signed-off-by: Ian Rogers <irogers@...gle.com>

Note, as msan needs to instrument memory allocations libraries need to
be compiled with it. I lacked the msan built libraries and so built
with:
```
$ make -C tools/perf O=/tmp/perf DEBUG=1 EXTRA_CFLAGS="-O0 -g
-fno-omit-frame-pointer -fsanitize=memory
-fsanitize-memory-track-origins" CC=clang CXX=clang++ HOSTCC=clang
NO_LIBTRACEEVENT=1 NO_LIBELF=1 BUILD_BPF_SKEL=0 NO_LIBPFM=1
```
oh, I disabled libbpf here as the bpf system call also lacks msan interceptors.

Thanks,
Ian

> ---
>  tools/perf/Makefile.config | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
> index 1fe8df97fe88..74e0b17050b5 100644
> --- a/tools/perf/Makefile.config
> +++ b/tools/perf/Makefile.config
> @@ -486,7 +486,10 @@ ifdef NO_DWARF
>  endif
>
>  ifeq ($(feature-scandirat), 1)
> -  CFLAGS += -DHAVE_SCANDIRAT_SUPPORT
> +  # Ignore having scandirat with memory sanitizer that lacks an interceptor.
> +  ifeq ($(filter s% -fsanitize=memory%,$(EXTRA_CFLAGS),),)
> +    CFLAGS += -DHAVE_SCANDIRAT_SUPPORT
> +  endif
>  endif
>
>  ifeq ($(feature-sched_getcpu), 1)
> --
> 2.44.0.291.gc1ea87d7ee-goog
>