RE: [PATCH] perf diff: bug fix, donot overwrite valid build id

[Liang, Kan]

Hi Arnaldo,

Ping

Are you OK with the fix?

Thanks,
Kan

> 
> From: Kan Liang <kan.liang@xxxxxxxxx>
> 
> 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 applies,
>  sudo ./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 applies,
>  sudo ./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@xxxxxxxxx>
> ---
>  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
> df2482b..dc93940 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);
> 
> --
> 2.4.3