linux-kernel - [PATCH v2 1/1] perf: Set build-id using build-id header on new mmap records

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Date:   Fri,  4 Mar 2022 09:09:56 +0000
From:   James Clark <james.clark@....com>
To:     acme@...nel.org, linux-perf-users@...r.kernel.org,
        coresight@...ts.linaro.org, olsajiri@...il.com
Cc:     James Clark <james.clark@....com>,
        Denis Nikitin <denik@...omium.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/1] perf: Set build-id using build-id header on new mmap records

MMAP records that occur after the build-id header is parsed do not have
their build-id set even if the filename matches an entry from the
header. Set the build-id on these dsos as long as the MMAP record
doesn't have its own build-id set.

This fixes an issue with off target analysis where the local version of
a dso is loaded rather than one from ~/.debug via a build-id.

Reported-by: Denis Nikitin <denik@...omium.org>
Signed-off-by: James Clark <james.clark@....com>
---
 tools/perf/util/dso.h    |  1 +
 tools/perf/util/header.c |  1 +
 tools/perf/util/map.c    | 20 +++++++++++++++++---
 3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
index 011da3924fc1..3a9fd4d389b5 100644
--- a/tools/perf/util/dso.h
+++ b/tools/perf/util/dso.h
@@ -167,6 +167,7 @@ struct dso {
 	enum dso_load_errno	load_errno;
 	u8		 adjust_symbols:1;
 	u8		 has_build_id:1;
+	u8		 header_build_id:1;
 	u8		 has_srcline:1;
 	u8		 hit:1;
 	u8		 annotate_warned:1;
diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 6da12e522edc..571d73d4f976 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -2200,6 +2200,7 @@ static int __event_process_build_id(struct perf_record_header_build_id *bev,
 
 		build_id__init(&bid, bev->data, size);
 		dso__set_build_id(dso, &bid);
+		dso->header_build_id = 1;
 
 		if (dso_space != DSO_SPACE__USER) {
 			struct kmod_path m = { .name = NULL, };
diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
index 1803d3887afe..e0aa4a254583 100644
--- a/tools/perf/util/map.c
+++ b/tools/perf/util/map.c
@@ -127,7 +127,7 @@ struct map *map__new(struct machine *machine, u64 start, u64 len,
 
 	if (map != NULL) {
 		char newfilename[PATH_MAX];
-		struct dso *dso;
+		struct dso *dso, *header_bid_dso;
 		int anon, no_dso, vdso, android;
 
 		android = is_android_lib(filename);
@@ -183,9 +183,23 @@ struct map *map__new(struct machine *machine, u64 start, u64 len,
 		}
 		dso->nsinfo = nsi;
 
-		if (build_id__is_defined(bid))
+		if (build_id__is_defined(bid)) {
 			dso__set_build_id(dso, bid);
-
+		} else {
+			/*
+			 * If the mmap event had no build ID, search for an existing dso from the
+			 * build ID header by name. Otherwise only the dso loaded at the time of
+			 * reading the header will have the build ID set and all future mmaps will
+			 * have it missing.
+			 */
+			down_read(&machine->dsos.lock);
+			header_bid_dso = __dsos__find(&machine->dsos, filename, false);
+			up_read(&machine->dsos.lock);
+			if (header_bid_dso && header_bid_dso->header_build_id) {
+				dso__set_build_id(dso, &header_bid_dso->bid);
+				dso->header_build_id = 1;
+			}
+		}
 		dso__put(dso);
 	}
 	return map;
-- 
2.28.0