[PATCH v2 1/2] perf event: Fix size of synthesized sample with branch stacks
From: Ian Rogers
Date: Wed Apr 29 2026 - 14:16:17 EST
Synthesizing branch stacks for Intel-PT highlighed an issue where
PERF_SAMPLE_BRANCH_HW_INDEX was assumed to always be set in the
perf_event_attr branch_sample_type. This caused an incorrect size
calculation.
Fix the writing of the nr and hw_idx values during sample event
synthesis.
Assisted-by: Gemini:gemini-3.1-pro-preview
Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>
---
tools/perf/bench/inject-buildid.c | 9 ++++++---
tools/perf/builtin-inject.c | 12 +++++++++---
tools/perf/tests/dlfilter-test.c | 8 ++++++--
tools/perf/tests/sample-parsing.c | 5 +++--
tools/perf/util/arm-spe.c | 7 +++++--
tools/perf/util/cs-etm.c | 6 ++++--
tools/perf/util/intel-bts.c | 3 ++-
tools/perf/util/intel-pt.c | 7 +++++--
tools/perf/util/synthetic-events.c | 25 ++++++++++++++++++-------
tools/perf/util/synthetic-events.h | 6 ++++--
10 files changed, 62 insertions(+), 26 deletions(-)
diff --git a/tools/perf/bench/inject-buildid.c b/tools/perf/bench/inject-buildid.c
index aad572a78d7f..bfd2c5ec9488 100644
--- a/tools/perf/bench/inject-buildid.c
+++ b/tools/perf/bench/inject-buildid.c
@@ -228,9 +228,12 @@ static ssize_t synthesize_sample(struct bench_data *data, struct bench_dso *dso,
event.header.type = PERF_RECORD_SAMPLE;
event.header.misc = PERF_RECORD_MISC_USER;
- event.header.size = perf_event__sample_event_size(&sample, bench_sample_type, 0);
-
- perf_event__synthesize_sample(&event, bench_sample_type, 0, &sample);
+ event.header.size = perf_event__sample_event_size(&sample, bench_sample_type,
+ /*read_format=*/0,
+ /*branch_sample_type=*/0);
+ perf_event__synthesize_sample(&event, bench_sample_type,
+ /*read_format=*/0,
+ /*branch_sample_type=*/0, &sample);
return writen(data->input_pipe[1], &event, event.header.size);
}
diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c
index f174bc69cec4..0c51cb4250d1 100644
--- a/tools/perf/builtin-inject.c
+++ b/tools/perf/builtin-inject.c
@@ -463,8 +463,13 @@ static int perf_event__convert_sample_callchain(const struct perf_tool *tool,
/* remove sample_type {STACK,REGS}_USER for synthesize */
sample_type &= ~(PERF_SAMPLE_STACK_USER | PERF_SAMPLE_REGS_USER);
- perf_event__synthesize_sample(event_copy, sample_type,
- evsel->core.attr.read_format, sample);
+ ret = perf_event__synthesize_sample(event_copy, evsel->core.attr.sample_type,
+ evsel->core.attr.read_format,
+ evsel->core.attr.branch_sample_type, sample);
+ if (ret) {
+ pr_err("Failed to synthesize sample\n");
+ return ret;
+ }
return perf_event__repipe_synth(tool, event_copy);
}
@@ -1100,7 +1105,8 @@ static int perf_inject__sched_stat(const struct perf_tool *tool,
sample_sw.period = sample->period;
sample_sw.time = sample->time;
perf_event__synthesize_sample(event_sw, evsel->core.attr.sample_type,
- evsel->core.attr.read_format, &sample_sw);
+ evsel->core.attr.read_format,
+ evsel->core.attr.branch_sample_type, &sample_sw);
build_id__mark_dso_hit(tool, event_sw, &sample_sw, evsel, machine);
ret = perf_event__repipe(tool, event_sw, &sample_sw, machine);
perf_sample__exit(&sample_sw);
diff --git a/tools/perf/tests/dlfilter-test.c b/tools/perf/tests/dlfilter-test.c
index e63790c61d53..204663571943 100644
--- a/tools/perf/tests/dlfilter-test.c
+++ b/tools/perf/tests/dlfilter-test.c
@@ -188,8 +188,12 @@ static int write_sample(struct test_data *td, u64 sample_type, u64 id, pid_t pid
event->header.type = PERF_RECORD_SAMPLE;
event->header.misc = PERF_RECORD_MISC_USER;
- event->header.size = perf_event__sample_event_size(&sample, sample_type, 0);
- err = perf_event__synthesize_sample(event, sample_type, 0, &sample);
+ event->header.size = perf_event__sample_event_size(&sample, sample_type,
+ /*read_format=*/0,
+ /*branch_sample_type=*/0);
+ err = perf_event__synthesize_sample(event, sample_type,
+ /*read_format=*/0,
+ /*branch_sample_type=*/0, &sample);
if (err)
return test_result("perf_event__synthesize_sample() failed", TEST_FAIL);
diff --git a/tools/perf/tests/sample-parsing.c b/tools/perf/tests/sample-parsing.c
index a7327c942ca2..55f0b73ca20e 100644
--- a/tools/perf/tests/sample-parsing.c
+++ b/tools/perf/tests/sample-parsing.c
@@ -310,7 +310,8 @@ static int do_test(u64 sample_type, u64 sample_regs, u64 read_format)
sample.read.one.lost = 1;
}
- sz = perf_event__sample_event_size(&sample, sample_type, read_format);
+ sz = perf_event__sample_event_size(&sample, sample_type, read_format,
+ evsel.core.attr.branch_sample_type);
bufsz = sz + 4096; /* Add a bit for overrun checking */
event = malloc(bufsz);
if (!event) {
@@ -324,7 +325,7 @@ static int do_test(u64 sample_type, u64 sample_regs, u64 read_format)
event->header.size = sz;
err = perf_event__synthesize_sample(event, sample_type, read_format,
- &sample);
+ evsel.core.attr.branch_sample_type, &sample);
if (err) {
pr_debug("%s failed for sample_type %#"PRIx64", error %d\n",
"perf_event__synthesize_sample", sample_type, err);
diff --git a/tools/perf/util/arm-spe.c b/tools/perf/util/arm-spe.c
index e5835042acdf..c4ed9f10e731 100644
--- a/tools/perf/util/arm-spe.c
+++ b/tools/perf/util/arm-spe.c
@@ -484,8 +484,11 @@ static void arm_spe__prep_branch_stack(struct arm_spe_queue *speq)
static int arm_spe__inject_event(union perf_event *event, struct perf_sample *sample, u64 type)
{
- event->header.size = perf_event__sample_event_size(sample, type, 0);
- return perf_event__synthesize_sample(event, type, 0, sample);
+ event->header.type = PERF_RECORD_SAMPLE;
+ event->header.size = perf_event__sample_event_size(sample, type, /*read_format=*/0,
+ /*branch_sample_type=*/0);
+ return perf_event__synthesize_sample(event, type, /*read_format=*/0,
+ /*branch_sample_type=*/0, sample);
}
static inline int
diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
index 8a639d2e51a4..1ebc1a6a5e75 100644
--- a/tools/perf/util/cs-etm.c
+++ b/tools/perf/util/cs-etm.c
@@ -1425,8 +1425,10 @@ static void cs_etm__update_last_branch_rb(struct cs_etm_queue *etmq,
static int cs_etm__inject_event(union perf_event *event,
struct perf_sample *sample, u64 type)
{
- event->header.size = perf_event__sample_event_size(sample, type, 0);
- return perf_event__synthesize_sample(event, type, 0, sample);
+ event->header.size = perf_event__sample_event_size(sample, type, /*read_format=*/0,
+ /*branch_sample_type=*/0);
+ return perf_event__synthesize_sample(event, type, /*read_format=*/0,
+ /*branch_sample_type=*/0, sample);
}
diff --git a/tools/perf/util/intel-bts.c b/tools/perf/util/intel-bts.c
index 382255393fb3..0b18ebd13f7c 100644
--- a/tools/perf/util/intel-bts.c
+++ b/tools/perf/util/intel-bts.c
@@ -303,7 +303,8 @@ static int intel_bts_synth_branch_sample(struct intel_bts_queue *btsq,
event.sample.header.size = bts->branches_event_size;
ret = perf_event__synthesize_sample(&event,
bts->branches_sample_type,
- 0, &sample);
+ /*read_format=*/0, /*branch_sample_type=*/0,
+ &sample);
if (ret)
return ret;
}
diff --git a/tools/perf/util/intel-pt.c b/tools/perf/util/intel-pt.c
index fc9eec8b54b8..5142983e3243 100644
--- a/tools/perf/util/intel-pt.c
+++ b/tools/perf/util/intel-pt.c
@@ -1731,8 +1731,11 @@ static void intel_pt_prep_b_sample(struct intel_pt *pt,
static int intel_pt_inject_event(union perf_event *event,
struct perf_sample *sample, u64 type)
{
- event->header.size = perf_event__sample_event_size(sample, type, 0);
- return perf_event__synthesize_sample(event, type, 0, sample);
+ event->header.size = perf_event__sample_event_size(sample, type, /*read_format=*/0,
+ /*branch_sample_type=*/0);
+
+ return perf_event__synthesize_sample(event, type, /*read_format=*/0,
+ /*branch_sample_type=*/0, sample);
}
static inline int intel_pt_opt_inject(struct intel_pt *pt,
diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index 85bee747f4cd..2461f25a4d7d 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -1455,7 +1455,8 @@ int perf_event__synthesize_stat_round(const struct perf_tool *tool,
return process(tool, (union perf_event *) &event, NULL, machine);
}
-size_t perf_event__sample_event_size(const struct perf_sample *sample, u64 type, u64 read_format)
+size_t perf_event__sample_event_size(const struct perf_sample *sample, u64 type, u64 read_format,
+ u64 branch_sample_type)
{
size_t sz, result = sizeof(struct perf_record_sample);
@@ -1515,8 +1516,10 @@ size_t perf_event__sample_event_size(const struct perf_sample *sample, u64 type,
if (type & PERF_SAMPLE_BRANCH_STACK) {
sz = sample->branch_stack->nr * sizeof(struct branch_entry);
- /* nr, hw_idx */
- sz += 2 * sizeof(u64);
+ /* nr */
+ sz += sizeof(u64);
+ if (branch_sample_type & PERF_SAMPLE_BRANCH_HW_INDEX)
+ sz += sizeof(u64);
result += sz;
}
@@ -1605,7 +1608,7 @@ static __u64 *copy_read_group_values(__u64 *array, __u64 read_format,
}
int perf_event__synthesize_sample(union perf_event *event, u64 type, u64 read_format,
- const struct perf_sample *sample)
+ u64 branch_sample_type, const struct perf_sample *sample)
{
__u64 *array;
size_t sz;
@@ -1719,9 +1722,17 @@ int perf_event__synthesize_sample(union perf_event *event, u64 type, u64 read_fo
if (type & PERF_SAMPLE_BRANCH_STACK) {
sz = sample->branch_stack->nr * sizeof(struct branch_entry);
- /* nr, hw_idx */
- sz += 2 * sizeof(u64);
- memcpy(array, sample->branch_stack, sz);
+
+ *array++ = sample->branch_stack->nr;
+
+ if (branch_sample_type & PERF_SAMPLE_BRANCH_HW_INDEX) {
+ if (sample->no_hw_idx)
+ *array++ = 0;
+ else
+ *array++ = sample->branch_stack->hw_idx;
+ }
+
+ memcpy(array, perf_sample__branch_entries((struct perf_sample *)sample), sz);
array = (void *)array + sz;
}
diff --git a/tools/perf/util/synthetic-events.h b/tools/perf/util/synthetic-events.h
index b0edad0c3100..8c7f49f9ccf5 100644
--- a/tools/perf/util/synthetic-events.h
+++ b/tools/perf/util/synthetic-events.h
@@ -81,7 +81,8 @@ int perf_event__synthesize_mmap_events(const struct perf_tool *tool, union perf_
int perf_event__synthesize_modules(const struct perf_tool *tool, perf_event__handler_t process, struct machine *machine);
int perf_event__synthesize_namespaces(const struct perf_tool *tool, union perf_event *event, pid_t pid, pid_t tgid, perf_event__handler_t process, struct machine *machine);
int perf_event__synthesize_cgroups(const struct perf_tool *tool, perf_event__handler_t process, struct machine *machine);
-int perf_event__synthesize_sample(union perf_event *event, u64 type, u64 read_format, const struct perf_sample *sample);
+int perf_event__synthesize_sample(union perf_event *event, u64 type, u64 read_format,
+ u64 branch_sample_type, const struct perf_sample *sample);
int perf_event__synthesize_stat_config(const struct perf_tool *tool, struct perf_stat_config *config, perf_event__handler_t process, struct machine *machine);
int perf_event__synthesize_stat_events(struct perf_stat_config *config, const struct perf_tool *tool, struct evlist *evlist, perf_event__handler_t process, bool attrs);
int perf_event__synthesize_stat_round(const struct perf_tool *tool, u64 time, u64 type, perf_event__handler_t process, struct machine *machine);
@@ -97,7 +98,8 @@ void perf_event__synthesize_final_bpf_metadata(struct perf_session *session,
int perf_tool__process_synth_event(const struct perf_tool *tool, union perf_event *event, struct machine *machine, perf_event__handler_t process);
-size_t perf_event__sample_event_size(const struct perf_sample *sample, u64 type, u64 read_format);
+size_t perf_event__sample_event_size(const struct perf_sample *sample, u64 type,
+ u64 read_format, u64 branch_sample_type);
int __machine__synthesize_threads(struct machine *machine, const struct perf_tool *tool,
struct target *target, struct perf_thread_map *threads,
--
2.54.0.545.g6539524ca2-goog