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