perf tools: Allow build-id with trailing zeros

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.

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 <[email protected]>

Signed-off-by Namhyung Kim <[email protected]>

---
 tools/perf/util/dso.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

tools/perf/util/dso.c +10 -0

index ee15db2be2f4..9ed9a5676d35 100644
@@ -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;
 }

Signature · 1 line

2.33.0.309.g3052b89438-goog