[PATCH v2 5/6] perf events: Prefer union over variable length array

[Ian Rogers <irogers@google.com>]

It is possible for casts to introduce alignment issues, prefer a union
for perf_record_event_update.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/lib/perf/include/perf/event.h | 11 ++++++++++-
 tools/perf/tests/event_update.c     | 14 ++++----------
 tools/perf/util/header.c            | 24 ++++++++----------------
 tools/perf/util/synthetic-events.c  | 12 +++++-------
 4 files changed, 27 insertions(+), 34 deletions(-)

diff --git a/tools/lib/perf/include/perf/event.h b/tools/lib/perf/include/perf/event.h
index d2d32589758a..21170f5afb61 100644
--- a/tools/lib/perf/include/perf/event.h
+++ b/tools/lib/perf/include/perf/event.h
@@ -221,7 +221,16 @@ struct perf_record_event_update {
 	struct perf_event_header header;
 	__u64			 type;
 	__u64			 id;
-	char			 data[];
+	union {
+		/* Used when type == PERF_EVENT_UPDATE__SCALE. */
+		struct perf_record_event_update_scale scale;
+		/* Used when type == PERF_EVENT_UPDATE__UNIT. */
+		char unit[0];
+		/* Used when type == PERF_EVENT_UPDATE__NAME. */
+		char name[0];
+		/* Used when type == PERF_EVENT_UPDATE__CPUS. */
+		struct perf_record_event_update_cpus cpus;
+	};
 };
 
 #define MAX_EVENT_NAME 64
diff --git a/tools/perf/tests/event_update.c b/tools/perf/tests/event_update.c
index 78db4d704e76..d093a9b878d1 100644
--- a/tools/perf/tests/event_update.c
+++ b/tools/perf/tests/event_update.c
@@ -21,7 +21,7 @@ static int process_event_unit(struct perf_tool *tool __maybe_unused,
 
 	TEST_ASSERT_VAL("wrong id", ev->id == 123);
 	TEST_ASSERT_VAL("wrong id", ev->type == PERF_EVENT_UPDATE__UNIT);
-	TEST_ASSERT_VAL("wrong unit", !strcmp(ev->data, "KRAVA"));
+	TEST_ASSERT_VAL("wrong unit", !strcmp(ev->unit, "KRAVA"));
 	return 0;
 }
 
@@ -31,13 +31,10 @@ static int process_event_scale(struct perf_tool *tool __maybe_unused,
 			       struct machine *machine __maybe_unused)
 {
 	struct perf_record_event_update *ev = (struct perf_record_event_update *)event;
-	struct perf_record_event_update_scale *ev_data;
-
-	ev_data = (struct perf_record_event_update_scale *)ev->data;
 
 	TEST_ASSERT_VAL("wrong id", ev->id == 123);
 	TEST_ASSERT_VAL("wrong id", ev->type == PERF_EVENT_UPDATE__SCALE);
-	TEST_ASSERT_VAL("wrong scale", ev_data->scale == 0.123);
+	TEST_ASSERT_VAL("wrong scale", ev->scale.scale == 0.123);
 	return 0;
 }
 
@@ -56,7 +53,7 @@ static int process_event_name(struct perf_tool *tool,
 
 	TEST_ASSERT_VAL("wrong id", ev->id == 123);
 	TEST_ASSERT_VAL("wrong id", ev->type == PERF_EVENT_UPDATE__NAME);
-	TEST_ASSERT_VAL("wrong name", !strcmp(ev->data, tmp->name));
+	TEST_ASSERT_VAL("wrong name", !strcmp(ev->name, tmp->name));
 	return 0;
 }
 
@@ -66,12 +63,9 @@ static int process_event_cpus(struct perf_tool *tool __maybe_unused,
 			      struct machine *machine __maybe_unused)
 {
 	struct perf_record_event_update *ev = (struct perf_record_event_update *)event;
-	struct perf_record_event_update_cpus *ev_data;
 	struct perf_cpu_map *map;
 
-	ev_data = (struct perf_record_event_update_cpus *) ev->data;
-
-	map = cpu_map__new_data(&ev_data->cpus);
+	map = cpu_map__new_data(&ev->cpus.cpus);
 
 	TEST_ASSERT_VAL("wrong id", ev->id == 123);
 	TEST_ASSERT_VAL("wrong type", ev->type == PERF_EVENT_UPDATE__CPUS);
diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 53332da100e8..108c8da5d2e3 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -4264,8 +4264,6 @@ int perf_event__process_feature(struct perf_session *session,
 size_t perf_event__fprintf_event_update(union perf_event *event, FILE *fp)
 {
 	struct perf_record_event_update *ev = &event->event_update;
-	struct perf_record_event_update_scale *ev_scale;
-	struct perf_record_event_update_cpus *ev_cpus;
 	struct perf_cpu_map *map;
 	size_t ret;
 
@@ -4273,20 +4271,18 @@ size_t perf_event__fprintf_event_update(union perf_event *event, FILE *fp)
 
 	switch (ev->type) {
 	case PERF_EVENT_UPDATE__SCALE:
-		ev_scale = (struct perf_record_event_update_scale *)ev->data;
-		ret += fprintf(fp, "... scale: %f\n", ev_scale->scale);
+		ret += fprintf(fp, "... scale: %f\n", ev->scale.scale);
 		break;
 	case PERF_EVENT_UPDATE__UNIT:
-		ret += fprintf(fp, "... unit:  %s\n", ev->data);
+		ret += fprintf(fp, "... unit:  %s\n", ev->unit);
 		break;
 	case PERF_EVENT_UPDATE__NAME:
-		ret += fprintf(fp, "... name:  %s\n", ev->data);
+		ret += fprintf(fp, "... name:  %s\n", ev->name);
 		break;
 	case PERF_EVENT_UPDATE__CPUS:
-		ev_cpus = (struct perf_record_event_update_cpus *)ev->data;
 		ret += fprintf(fp, "... ");
 
-		map = cpu_map__new_data(&ev_cpus->cpus);
+		map = cpu_map__new_data(&ev->cpus.cpus);
 		if (map)
 			ret += cpu_map__fprintf(map, fp);
 		else
@@ -4343,8 +4339,6 @@ int perf_event__process_event_update(struct perf_tool *tool __maybe_unused,
 				     struct evlist **pevlist)
 {
 	struct perf_record_event_update *ev = &event->event_update;
-	struct perf_record_event_update_scale *ev_scale;
-	struct perf_record_event_update_cpus *ev_cpus;
 	struct evlist *evlist;
 	struct evsel *evsel;
 	struct perf_cpu_map *map;
@@ -4361,19 +4355,17 @@ int perf_event__process_event_update(struct perf_tool *tool __maybe_unused,
 	switch (ev->type) {
 	case PERF_EVENT_UPDATE__UNIT:
 		free((char *)evsel->unit);
-		evsel->unit = strdup(ev->data);
+		evsel->unit = strdup(ev->unit);
 		break;
 	case PERF_EVENT_UPDATE__NAME:
 		free(evsel->name);
-		evsel->name = strdup(ev->data);
+		evsel->name = strdup(ev->name);
 		break;
 	case PERF_EVENT_UPDATE__SCALE:
-		ev_scale = (struct perf_record_event_update_scale *)ev->data;
-		evsel->scale = ev_scale->scale;
+		evsel->scale = ev->scale.scale;
 		break;
 	case PERF_EVENT_UPDATE__CPUS:
-		ev_cpus = (struct perf_record_event_update_cpus *)ev->data;
-		map = cpu_map__new_data(&ev_cpus->cpus);
+		map = cpu_map__new_data(&ev->cpus.cpus);
 		if (map) {
 			perf_cpu_map__put(evsel->core.own_cpus);
 			evsel->core.own_cpus = map;
diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index 4fa7d0d7dbcf..ec54ac1ed96f 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -1848,7 +1848,7 @@ int perf_event__synthesize_event_update_unit(struct perf_tool *tool, struct evse
 	if (ev == NULL)
 		return -ENOMEM;
 
-	strlcpy(ev->data, evsel->unit, size + 1);
+	strlcpy(ev->unit, evsel->unit, size + 1);
 	err = process(tool, (union perf_event *)ev, NULL, NULL);
 	free(ev);
 	return err;
@@ -1865,8 +1865,7 @@ int perf_event__synthesize_event_update_scale(struct perf_tool *tool, struct evs
 	if (ev == NULL)
 		return -ENOMEM;
 
-	ev_data = (struct perf_record_event_update_scale *)ev->data;
-	ev_data->scale = evsel->scale;
+	ev->scale.scale = evsel->scale;
 	err = process(tool, (union perf_event *)ev, NULL, NULL);
 	free(ev);
 	return err;
@@ -1883,7 +1882,7 @@ int perf_event__synthesize_event_update_name(struct perf_tool *tool, struct evse
 	if (ev == NULL)
 		return -ENOMEM;
 
-	strlcpy(ev->data, evsel->name, len + 1);
+	strlcpy(ev->name, evsel->name, len + 1);
 	err = process(tool, (union perf_event *)ev, NULL, NULL);
 	free(ev);
 	return err;
@@ -1892,7 +1891,7 @@ int perf_event__synthesize_event_update_name(struct perf_tool *tool, struct evse
 int perf_event__synthesize_event_update_cpus(struct perf_tool *tool, struct evsel *evsel,
 					     perf_event__handler_t process)
 {
-	size_t size = sizeof(struct perf_record_event_update);
+	size_t size = sizeof(struct perf_event_header) + sizeof(u64) + sizeof(u64);
 	struct perf_record_event_update *ev;
 	int max, err;
 	u16 type;
@@ -1909,8 +1908,7 @@ int perf_event__synthesize_event_update_cpus(struct perf_tool *tool, struct evse
 	ev->type	= PERF_EVENT_UPDATE__CPUS;
 	ev->id		= evsel->core.id[0];
 
-	cpu_map_data__synthesize((struct perf_record_cpu_map_data *)ev->data,
-				 evsel->core.own_cpus, type, max);
+	cpu_map_data__synthesize(&ev->cpus.cpus, evsel->core.own_cpus, type, max);
 
 	err = process(tool, (union perf_event *)ev, NULL, NULL);
 	free(ev);
-- 
2.36.1.476.g0c4daa206d-goog