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    Subject[PATCH 24/29] perf diff: Do not overwrite valid build id
    Date
    From: Kan Liang <kan.liang@intel.com>

    Fixes a perf diff regression issue which was introduced by commit
    5baecbcd9c9a ("perf symbols: we can now read separate debug-info files
    based on a build ID")

    The binary name could be same when perf diff different binaries. Build
    id is used to distinguish between them.
    However, the previous patch assumes the same binary name has same build
    id. So it overwrites the build id according to the binary name,
    regardless of whether the build id is set or not.

    Check the has_build_id in dso__load. If the build id is already set, use
    it.

    Before the fix:

    $ perf diff 1.perf.data 2.perf.data
    # Event 'cycles'
    #
    # Baseline Delta Shared Object Symbol
    # ........ ....... ................ .............................
    #
    99.83% -99.80% tchain_edit [.] f2
    0.12% +99.81% tchain_edit [.] f3
    0.02% -0.01% [ixgbe] [k] ixgbe_read_reg

    After the fix:
    $ perf diff 1.perf.data 2.perf.data
    # Event 'cycles'
    #
    # Baseline Delta Shared Object Symbol
    # ........ ....... ................ .............................
    #
    99.83% +0.10% tchain_edit [.] f3
    0.12% -0.08% tchain_edit [.] f2

    Signed-off-by: Kan Liang <kan.liang@intel.com>
    Cc: Andi Kleen <andi@firstfloor.org>
    CC: Dima Kogan <dima@secretsauce.net>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Cc: Namhyung Kim <namhyung@kernel.org>
    Fixes: 5baecbcd9c9a ("perf symbols: we can now read separate debug-info files based on a build ID")
    Link: http://lkml.kernel.org/r/1481642984-13593-1-git-send-email-kan.liang@intel.com
    Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
    ---
    tools/perf/util/symbol.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
    index df2482b2ba45..dc93940de351 100644
    --- a/tools/perf/util/symbol.c
    +++ b/tools/perf/util/symbol.c
    @@ -1459,7 +1459,8 @@ int dso__load(struct dso *dso, struct map *map)
    * Read the build id if possible. This is required for
    * DSO_BINARY_TYPE__BUILDID_DEBUGINFO to work
    */
    - if (is_regular_file(dso->long_name) &&
    + if (!dso->has_build_id &&
    + is_regular_file(dso->long_name) &&
    filename__read_build_id(dso->long_name, build_id, BUILD_ID_SIZE) > 0)
    dso__set_build_id(dso, build_id);

    --
    2.9.3
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