From: Ian Rogers <irogers@google.com>
To: Numfor Mbiziwo-Tiapo <nums@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
Song Liu <songliubraving@fb.com>,
mbd@fb.com, LKML <linux-kernel@vger.kernel.org>,
Stephane Eranian <eranian@google.com>
Subject: Re: [RFC][PATCH 1/2] Fix event.c misaligned address error
Date: Wed, 11 Sep 2019 02:08:32 -0700 [thread overview]
Message-ID: <CAP-5=fUf1BN634Ojkp-sPUV5iryzZ-qbv_UVS-GoNOgj-454dQ@mail.gmail.com> (raw)
In-Reply-To: <20190724224954.229540-2-nums@google.com>
An idea here is that, if this breaks backward compatibility, we
introduce an aligned variant and work to deprecate the unaligned
variant. I will look into making a patch set.
Thanks,
Ian
On Wed, Jul 24, 2019 at 3:50 PM Numfor Mbiziwo-Tiapo <nums@google.com> wrote:
>
> The ubsan (undefined behavior sanitizer) build of perf throws an
> error when the synthesize "Synthesize cpu map" function from
> perf test is run.
>
> This can be reproduced by running (from the tip directory):
> make -C tools/perf USE_CLANG=1 EXTRA_CFLAGS="-fsanitize=undefined"
>
> (see cover letter for why perf may not build)
>
> then running: tools/perf/perf test 44 -v
>
> This bug occurs because the cpu_map_data__synthesize function in
> event.c calls synthesize_mask, casting the 'data' variable
> (of type cpu_map_data*) to a cpu_map_mask*. Since struct
> cpu_map_data is 2 byte aligned and struct cpu_map_mask is 8 byte
> aligned this causes memory alignment issues.
>
> This is fixed by adding 6 bytes of padding to the struct cpu_map_data,
> however, this will break compatibility between perf data files - a file
> written by an old perf wouldn't work with a perf with this patch due
> to event data alignment changing.
>
> Comments?
>
> Not-Quite-Signed-off-by: Numfor Mbiziwo-Tiapo <nums@google.com>
> ---
> tools/perf/util/event.h | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/tools/perf/util/event.h b/tools/perf/util/event.h
> index eb95f3384958..82eaf06c2604 100644
> --- a/tools/perf/util/event.h
> +++ b/tools/perf/util/event.h
> @@ -433,6 +433,7 @@ struct cpu_map_mask {
>
> struct cpu_map_data {
> u16 type;
> + u8 pad[6];
> char data[];
> };
>
> --
> 2.22.0.657.g960e92d24f-goog
>
next prev parent reply other threads:[~2019-09-11 9:08 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-24 22:49 [RFC][PATCH 0/2] Perf misaligned address fixes Numfor Mbiziwo-Tiapo
2019-07-24 22:49 ` [RFC][PATCH 1/2] Fix event.c misaligned address error Numfor Mbiziwo-Tiapo
2019-09-11 9:08 ` Ian Rogers [this message]
2019-09-12 8:50 ` David Laight
2019-07-24 22:49 ` [RFC][PATCH 2/2] Fix evsel.c misaligned address errors Numfor Mbiziwo-Tiapo
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