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SubjectRe: [PATCH v2] perf tools: Allow build-id with trailing zeros
Em Fri, Sep 10, 2021 at 03:46:30PM -0700, Namhyung Kim escreveu:
> Current perf saves a build-id with size but old versions assumes the
> size of 20. In case the build-id is less than 20 (like for MD5), it'd
> fill the rest with 0s.

Thanks, applied.

- Arnaldo


> I saw a problem when old version of perf record saved a binary in the
> build-id cache and new version of perf reads the data. The symbols
> should be read from the build-id cache (as the path no longer has the
> same binary) but it failed due to mismatch in the build-id.
>
> symsrc__init: build id mismatch for /home/namhyung/.debug/.build-id/53/e4c2f42a4c61a2d632d92a72afa08f00000000/elf.
>
> The build-id event in the data has 20 byte build-ids, but it saw a
> different size (16) when it reads the build-id of the elf file in the
> build-id cache.
>
> $ readelf -n ~/.debug/.build-id/53/e4c2f42a4c61a2d632d92a72afa08f00000000/elf
>
> Displaying notes found in: .note.gnu.build-id
> Owner Data size Description
> GNU 0x00000010 NT_GNU_BUILD_ID (unique build ID bitstring)
> Build ID: 53e4c2f42a4c61a2d632d92a72afa08f
>
> Let's fix this by allowing trailing zeros if the size is different.
>
> Fixes: 39be8d0115b3 ("perf tools: Pass build_id object to dso__build_id_equal()")
>
> Acked-by: Jiri Olsa <jolsa@redhat.com>
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> ---
> tools/perf/util/dso.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> index ee15db2be2f4..9ed9a5676d35 100644
> --- a/tools/perf/util/dso.c
> +++ b/tools/perf/util/dso.c
> @@ -1349,6 +1349,16 @@ void dso__set_build_id(struct dso *dso, struct build_id *bid)
>
> bool dso__build_id_equal(const struct dso *dso, struct build_id *bid)
> {
> + if (dso->bid.size > bid->size && dso->bid.size == BUILD_ID_SIZE) {
> + /*
> + * For the backward compatibility, it allows a build-id has
> + * trailing zeros.
> + */
> + return !memcmp(dso->bid.data, bid->data, bid->size) &&
> + !memchr_inv(&dso->bid.data[bid->size], 0,
> + dso->bid.size - bid->size);
> + }
> +
> return dso->bid.size == bid->size &&
> memcmp(dso->bid.data, bid->data, dso->bid.size) == 0;
> }
> --
> 2.33.0.309.g3052b89438-goog

--

- Arnaldo

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