perf dso: Move build_id to dso_id

The dso_id previously contained the major, minor, inode and inode
generation information from a mmap2 event - the inode generation would
be zero when reading from /proc/pid/maps. The build_id was in the
dso. With build ID mmap2 events these fields wouldn't be initialized
which would largely mean the special empty case where any dso would
match for equality. This isn't desirable as if a dso is replaced we
want the comparison to yield a difference.

To support detecting the difference between DSOs based on build_id,
move the build_id out of the DSO and into the dso_id. The dso_id is
also stored in the DSO so nothing is lost. Capture in the dso_id what
parts have been initialized and rename dso_id__inject to
dso_id__improve_id so that it is clear the dso_id is being improved
upon with additional information. With the build_id in the dso_id, use
memcmp to compare for equality.

Signed-off-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250724163302.596743-7-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

1 files changed, 10 insertions, 8 deletions

diff --git a/tools/perf/util/dsos.c b/tools/perf/util/dsos.c
index 47538273915d..0a7645c7fae7 100644
--- a/tools/perf/util/dsos.c
+++ b/tools/perf/util/dsos.c
@@ -72,6 +72,7 @@ static int dsos__read_build_ids_cb(struct dso *dso, void *data)
 {
 	struct dsos__read_build_ids_cb_args *args = data;
 	struct nscookie nsc;
+	struct build_id bid = { .size = 0, };
 
 	if (args->with_hits && !dso__hit(dso) && !dso__is_vdso(dso))
 		return 0;
@@ -80,15 +81,15 @@ static int dsos__read_build_ids_cb(struct dso *dso, void *data)
 		return 0;
 	}
 	nsinfo__mountns_enter(dso__nsinfo(dso), &nsc);
-	if (filename__read_build_id(dso__long_name(dso), dso__bid(dso)) > 0) {
+	if (filename__read_build_id(dso__long_name(dso), &bid) > 0) {
+		dso__set_build_id(dso, &bid);
 		args->have_build_id = true;
-		dso__set_has_build_id(dso);
 	} else if (errno == ENOENT && dso__nsinfo(dso)) {
 		char *new_name = dso__filename_with_chroot(dso, dso__long_name(dso));
 
-		if (new_name && filename__read_build_id(new_name, dso__bid(dso)) > 0) {
+		if (new_name && filename__read_build_id(new_name, &bid) > 0) {
+			dso__set_build_id(dso, &bid);
 			args->have_build_id = true;
-			dso__set_has_build_id(dso);
 		}
 		free(new_name);
 	}
@@ -286,7 +287,7 @@ struct dso *dsos__find(struct dsos *dsos, const char *name, bool cmp_short)
 	struct dso *res;
 
 	down_read(&dsos->lock);
-	res = __dsos__find_id(dsos, name, NULL, cmp_short, /*write_locked=*/false);
+	res = __dsos__find_id(dsos, name, &dso_id_empty, cmp_short, /*write_locked=*/false);
 	up_read(&dsos->lock);
 	return res;
 }
@@ -344,8 +345,8 @@ static struct dso *__dsos__findnew_id(struct dsos *dsos, const char *name, const
 {
 	struct dso *dso = __dsos__find_id(dsos, name, id, false, /*write_locked=*/true);
 
-	if (dso && dso_id__empty(dso__id(dso)) && !dso_id__empty(id))
-		__dso__inject_id(dso, id);
+	if (dso)
+		__dso__improve_id(dso, id);
 
 	return dso ? dso : __dsos__addnew_id(dsos, name, id);
 }
@@ -436,7 +437,8 @@ struct dso *dsos__findnew_module_dso(struct dsos *dsos,
 
 	down_write(&dsos->lock);
 
-	dso = __dsos__find_id(dsos, m->name, NULL, /*cmp_short=*/true, /*write_locked=*/true);
+	dso = __dsos__find_id(dsos, m->name, &dso_id_empty, /*cmp_short=*/true,
+			      /*write_locked=*/true);
 	if (dso) {
 		up_write(&dsos->lock);
 		return dso;