Patch "perf diff: Do not overwrite valid build id" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

perf diff: Do not overwrite valid build id

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
perf-diff-do-not-overwrite-valid-build-id.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Kan Liang <[email protected]>
Date: Tue, 13 Dec 2016 10:29:44 -0500
Subject: perf diff: Do not overwrite valid build id

From: Kan Liang <[email protected]>

commit ed6c166cc7dc329736cace3affd2df984fb22ec8 upstream.

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

---
 tools/perf/util/symbol.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -1459,7 +1459,8 @@ int dso__load(struct dso *dso, struct ma
 	 * 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);
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/perf-diff-do-not-overwrite-valid-build-id.patch