[PATCH v7 01/59] perf inject: Fix itrace branch stack synthesis

Ian Rogers
2026-04-25T22:50:10Z

When using "perf inject --itrace=L" to synthesize branch stacks from
AUX data, several issues caused failures:

1. The synthesized samples were delivered without the
PERF_SAMPLE_BRANCH_STACK flag if it was not in the original event's
sample_type. Fixed by using sample_type | evsel->synth_sample_type
in intel_pt_deliver_synth_event.

2. The record layout was misaligned because of inconsistent handling
of PERF_SAMPLE_BRANCH_HW_INDEX. Fixed by explicitly writing nr and
hw_idx in perf_event__synthesize_sample.

3. Modifying evsel->core.attr.sample_type early in __cmd_inject caused
parse failures for subsequent records in the input file. Fixed by
moving this modification to just before writing the header.

4. perf_event__repipe_sample was narrowed to only synthesize samples
when branch stack injection was requested, and restored the use of
perf_inject__cut_auxtrace_sample as a fallback to preserve
functionality.

Assisted-by: Gemini:gemini-3.1-pro-preview
Signed-off-by: Ian Rogers <irogers@google.com>
---
Issues fixed in v2:

1. Potential Heap Overflow in perf_event__repipe_sample : Addressed by
adding a check that prints an error and returns -EFAULT if the
calculated event size exceeds PERF_SAMPLE_MAX_SIZE , as you
requested.

2. Header vs Payload Mismatch in __cmd_inject : Addressed by narrowing
the condition so that HEADER_BRANCH_STACK is only set in the file
header if add_last_branch was true.

3. NULL Pointer Dereference in intel-pt.c : Addressed by updating the
condition in intel_pt_do_synth_pebs_sample to fill sample.
branch_stack if it was synthesized, even if not in the original
sample_type .

4. Unsafe Reads for events lacking HW_INDEX in synthetic-events.c :
Addressed by using the perf_sample__branch_entries() macro and
checking sample->no_hw_idx .

5. Size mismatch in perf_event__sample_event_size : Addressed by
passing branch_sample_type to it and conditioning the hw_idx size on
PERF_SAMPLE_BRANCH_HW_INDEX .
---
tools/perf/bench/inject-buildid.c | 9 ++--
tools/perf/builtin-inject.c | 77 ++++++++++++++++++++++++++++--
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 | 13 +++--
tools/perf/util/synthetic-events.c | 25 +++++++---
tools/perf/util/synthetic-events.h | 6 ++-
10 files changed, 129 insertions(+), 30 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..88c0ef4f5ff1 100644
--- a/tools/perf/builtin-inject.c
+++ b/tools/perf/builtin-inject.c
@@ -375,7 +375,59 @@ static int perf_event__repipe_sample(const struct perf_tool *tool,

build_id__mark_dso_hit(tool, event, sample, evsel, machine);

- if (inject->itrace_synth_opts.set && sample->aux_sample.size) {
+ if (inject->itrace_synth_opts.set &&
+ (inject->itrace_synth_opts.last_branch ||
+ inject->itrace_synth_opts.add_last_branch)) {
+ union perf_event *event_copy = (void *)inject->event_copy;
+ struct branch_stack dummy_bs = { .nr = 0 };
+ int err;
+ size_t sz;
+ u64 orig_type = evsel->core.attr.sample_type;
+ u64 orig_branch_type = evsel->core.attr.branch_sample_type;
+
+ if (event_copy == NULL) {
+ inject->event_copy = malloc(PERF_SAMPLE_MAX_SIZE);
+ if (!inject->event_copy)
+ return -ENOMEM;
+
+ event_copy = (void *)inject->event_copy;
+ }
+
+ if (!sample->branch_stack)
+ sample->branch_stack = &dummy_bs;
+
+ if (inject->itrace_synth_opts.add_last_branch) {
+ /* Temporarily add in type bits for synthesis. */
+ evsel->core.attr.sample_type |= PERF_SAMPLE_BRANCH_STACK;
+ evsel->core.attr.branch_sample_type |= PERF_SAMPLE_BRANCH_HW_INDEX;
+ evsel->core.attr.sample_type &= ~PERF_SAMPLE_AUX;
+ }
+
+ sz = perf_event__sample_event_size(sample, evsel->core.attr.sample_type,
+ evsel->core.attr.read_format,
+ evsel->core.attr.branch_sample_type);
+
+ if (sz > PERF_SAMPLE_MAX_SIZE) {
+ pr_err("Sample size %zu exceeds max size %d\n", sz, PERF_SAMPLE_MAX_SIZE);
+ return -EFAULT;
+ }
+
+ event_copy->header.type = PERF_RECORD_SAMPLE;
+ event_copy->header.size = sz;
+
+ err = perf_event__synthesize_sample(event_copy, evsel->core.attr.sample_type,
+ evsel->core.attr.read_format,
+ evsel->core.attr.branch_sample_type, sample);
+
+ evsel->core.attr.sample_type = orig_type;
+ evsel->core.attr.branch_sample_type = orig_branch_type;
+
+ if (err) {
+ pr_err("Failed to synthesize sample\n");
+ return err;
+ }
+ event = event_copy;
+ } else if (inject->itrace_synth_opts.set && sample->aux_sample.size) {
event = perf_inject__cut_auxtrace_sample(inject, event, sample);
if (IS_ERR(event))
return PTR_ERR(event);
@@ -464,7 +516,8 @@ static int perf_event__convert_sample_callchain(const struct perf_tool *tool,
sample_type &= ~(PERF_SAMPLE_STACK_USER | PERF_SAMPLE_REGS_USER);

perf_event__synthesize_sample(event_copy, sample_type,
- evsel->core.attr.read_format, sample);
+ evsel->core.attr.read_format,
+ evsel->core.attr.branch_sample_type, sample);
return perf_event__repipe_synth(tool, event_copy);
}

@@ -1100,7 +1153,8 @@ 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);
@@ -2434,12 +2488,25 @@ static int __cmd_inject(struct perf_inject *inject)
* synthesized hardware events, so clear the feature flag.
*/
if (inject->itrace_synth_opts.set) {
+ struct evsel *evsel;
+
perf_header__clear_feat(&session->header,
HEADER_AUXTRACE);
- if (inject->itrace_synth_opts.last_branch ||
- inject->itrace_synth_opts.add_last_branch)
+
+ evlist__for_each_entry(session->evlist, evsel) {
+ evsel->core.attr.sample_type &= ~PERF_SAMPLE_AUX;
+ }
+
+ if (inject->itrace_synth_opts.add_last_branch) {
perf_header__set_feat(&session->header,
HEADER_BRANCH_STACK);
+
+ evlist__for_each_entry(session->evlist, evsel) {
+ evsel->core.attr.sample_type |= PERF_SAMPLE_BRANCH_STACK;
+ evsel->core.attr.branch_sample_type |=
+ PERF_SAMPLE_BRANCH_HW_INDEX;
+ }
+ }
}

/*
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..2dce6106c038 100644
--- a/tools/perf/util/intel-pt.c
+++ b/tools/perf/util/intel-pt.c
@@ -1731,8 +1731,12 @@ 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.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 intel_pt_opt_inject(struct intel_pt *pt,
@@ -2486,7 +2490,7 @@ static int intel_pt_do_synth_pebs_sample(struct intel_pt_queue *ptq, struct evse
intel_pt_add_xmm(intr_regs, pos, items, regs_mask);
}

- if (sample_type & PERF_SAMPLE_BRANCH_STACK) {
+ if ((sample_type | evsel->synth_sample_type) & PERF_SAMPLE_BRANCH_STACK) {
if (items->mask[INTEL_PT_LBR_0_POS] ||
items->mask[INTEL_PT_LBR_1_POS] ||
items->mask[INTEL_PT_LBR_2_POS]) {
@@ -2557,7 +2561,8 @@ static int intel_pt_do_synth_pebs_sample(struct intel_pt_queue *ptq, struct evse
sample.transaction = txn;
}

- ret = intel_pt_deliver_synth_event(pt, event, &sample, sample_type);
+ ret = intel_pt_deliver_synth_event(pt, event, &sample,
+ sample_type | evsel->synth_sample_type);
perf_sample__exit(&sample);
return ret;
}
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