[PATCH v2 1/2] perf inject: Add --convert-callchain option

Namhyung Kim
2026-01-10T01:17:16Z

There are applications not built with frame pointers, so DWARF is needed
to get the stack traces. So `perf record --call-graph dwarf` saves the
stack and register data for each sample to get the stacktrace offline.
But sometimes those data may have sensitive information and we don't
want to keep them in the file.

This perf inject --convert-callchain option parses the callchains and
discard the stack and register after that. This will save storage space
and processing time for the new data file. Of course, users should
remove the original data file. :)

The down side is that it cannot handle inlined callchain entries as they
all have the same IPs. Maybe we can add an option to perf report to
look up inlined functions using DWARF - IIUC it won't requires stack and
register data.

This is an example.

$ perf record --call-graph dwarf -- perf test -w noploop

$ perf report --stdio --no-children --percent-limit=0 > output-prev

$ perf inject -i perf.data --convert-callchain -o perf.data.out

$ perf report --stdio --no-children --percent-limit=0 -i perf.data.out > output-next

$ diff -u output-prev output-next
...
0.23% perf ld-linux-x86-64.so.2 [.] _dl_relocate_object_no_relro
|
- ---elf_dynamic_do_Rela (inlined)
- _dl_relocate_object_no_relro
+ ---_dl_relocate_object_no_relro
_dl_relocate_object
dl_main
_dl_sysdep_start
- _dl_start_final (inlined)
_dl_start
_start

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
v2 changes)
* Use machine__kernel_ip() instead (James)
* Check sample types for DWARF callchains (James)
* Fix build errors (James)
* Add a new test (Ian)

tools/perf/Documentation/perf-inject.txt | 5 +
tools/perf/builtin-inject.c | 151 +++++++++++++++++++++++
2 files changed, 156 insertions(+)

diff --git a/tools/perf/Documentation/perf-inject.txt b/tools/perf/Documentation/perf-inject.txt
index c972032f4ca0d248..95dfdf39666efe89 100644
--- a/tools/perf/Documentation/perf-inject.txt
+++ b/tools/perf/Documentation/perf-inject.txt
@@ -109,6 +109,11 @@ include::itrace.txt[]
should be used, and also --buildid-all and --switch-events may be
useful.

+--convert-callchain::
+ Parse DWARF callchains and convert them to usual callchains. This also
+ discards stack and register data from the samples. This will lose
+ inlined callchain entries.
+
:GMEXAMPLECMD: inject
:GMEXAMPLESUBCMD:
include::guestmount.txt[]
diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c
index 6080afec537d2178..02bd388d602fdd75 100644
--- a/tools/perf/builtin-inject.c
+++ b/tools/perf/builtin-inject.c
@@ -122,6 +122,7 @@ struct perf_inject {
bool in_place_update;
bool in_place_update_dry_run;
bool copy_kcore_dir;
+ bool convert_callchain;
const char *input_name;
struct perf_data output;
u64 bytes_written;
@@ -133,6 +134,7 @@ struct perf_inject {
struct guest_session guest_session;
struct strlist *known_build_ids;
const struct evsel *mmap_evsel;
+ struct ip_callchain *raw_callchain;
};

struct event_entry {
@@ -383,6 +385,89 @@ static int perf_event__repipe_sample(const struct perf_tool *tool,
return perf_event__repipe_synth(tool, event);
}

+static int perf_event__convert_sample_callchain(const struct perf_tool *tool,
+ union perf_event *event,
+ struct perf_sample *sample,
+ struct evsel *evsel,
+ struct machine *machine)
+{
+ struct perf_inject *inject = container_of(tool, struct perf_inject, tool);
+ struct callchain_cursor *cursor = get_tls_callchain_cursor();
+ union perf_event *event_copy = (void *)inject->event_copy;
+ struct callchain_cursor_node *node;
+ struct thread *thread;
+ u64 sample_type = evsel->core.attr.sample_type;
+ u32 sample_size = event->header.size;
+ u64 i, k;
+ int ret;
+
+ 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 (cursor == NULL)
+ return perf_event__repipe_synth(tool, event);
+
+ callchain_cursor_reset(cursor);
+
+ thread = machine__find_thread(machine, -1, sample->pid);
+ if (thread == NULL)
+ return perf_event__repipe_synth(tool, event);
+
+ /* this will parse DWARF using stack and register data */
+ ret = thread__resolve_callchain(thread, cursor, evsel, sample,
+ /*parent=*/NULL, /*root_al=*/NULL,
+ PERF_MAX_STACK_DEPTH);
+ thread__put(thread);
+ if (ret != 0)
+ return perf_event__repipe_synth(tool, event);
+
+ /* copy kernel callchain and context entries */
+ for (i = 0; i < sample->callchain->nr; i++) {
+ inject->raw_callchain->ips[i] = sample->callchain->ips[i];
+ if (sample->callchain->ips[i] == PERF_CONTEXT_USER) {
+ i++;
+ break;
+ }
+ }
+ if (i == 0 || inject->raw_callchain->ips[i - 1] != PERF_CONTEXT_USER)
+ inject->raw_callchain->ips[i++] = PERF_CONTEXT_USER;
+
+ node = cursor->first;
+ for (k = 0; k < cursor->nr && i < PERF_MAX_STACK_DEPTH; k++) {
+ if (machine__kernel_ip(machine, node->ip))
+ /* kernel IPs were added already */;
+ else if (node->ms.sym && node->ms.sym->inlined)
+ /* we can't handle inlined callchains */;
+ else
+ inject->raw_callchain->ips[i++] = node->ip;
+
+ node = node->next;
+ }
+
+ inject->raw_callchain->nr = i;
+ sample->callchain = inject->raw_callchain;
+
+ memcpy(event_copy, event, sizeof(event->header));
+
+ /* adjust sample size for stack and regs */
+ sample_size -= sample->user_stack.size;
+ sample_size -= (hweight64(evsel->core.attr.sample_regs_user) + 1) * sizeof(u64);
+ sample_size += (sample->callchain->nr + 1) * sizeof(u64);
+ event_copy->header.size = sample_size;
+
+ /* 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);
+ return perf_event__repipe_synth(tool, event_copy);
+}
+
static struct dso *findnew_dso(int pid, int tid, const char *filename,
const struct dso_id *id, struct machine *machine)
{
@@ -2270,6 +2355,15 @@ static int __cmd_inject(struct perf_inject *inject)
/* Allow space in the header for guest attributes */
output_data_offset += gs->session->header.data_offset;
output_data_offset = roundup(output_data_offset, 4096);
+ } else if (inject->convert_callchain) {
+ inject->tool.sample = perf_event__convert_sample_callchain;
+ inject->tool.fork = perf_event__repipe_fork;
+ inject->tool.comm = perf_event__repipe_comm;
+ inject->tool.exit = perf_event__repipe_exit;
+ inject->tool.mmap = perf_event__repipe_mmap;
+ inject->tool.mmap2 = perf_event__repipe_mmap2;
+ inject->tool.ordered_events = true;
+ inject->tool.ordering_requires_timestamps = true;
}

if (!inject->itrace_synth_opts.set)
@@ -2322,6 +2416,23 @@ static int __cmd_inject(struct perf_inject *inject)
perf_header__set_feat(&session->header,
HEADER_BRANCH_STACK);
}
+
+ /*
+ * The converted data file won't have stack and registers.
+ * Update the perf_event_attr to remove them before writing.
+ */
+ if (inject->convert_callchain) {
+ struct evsel *evsel;
+
+ evlist__for_each_entry(session->evlist, evsel) {
+ evsel__reset_sample_bit(evsel, REGS_USER);
+ evsel__reset_sample_bit(evsel, STACK_USER);
+ evsel->core.attr.sample_regs_user = 0;
+ evsel->core.attr.sample_stack_user = 0;
+ evsel->core.attr.exclude_callchain_user = 0;
+ }
+ }
+
session->header.data_offset = output_data_offset;
session->header.data_size = inject->bytes_written;
perf_session__inject_header(session, session->evlist, fd, &inj_fc.fc,
@@ -2346,6 +2457,18 @@ static int __cmd_inject(struct perf_inject *inject)
return ret;
}

+static bool evsel__has_dwarf_callchain(struct evsel *evsel)
+{
+ struct perf_event_attr *attr = &evsel->core.attr;
+ const u64 dwarf_callchain_flags =
+ PERF_SAMPLE_STACK_USER | PERF_SAMPLE_REGS_USER | PERF_SAMPLE_CALLCHAIN;
+
+ if (!attr->exclude_callchain_user)
+ return false;
+
+ return (attr->sample_type & dwarf_callchain_flags) == dwarf_callchain_flags;
+}
+
int cmd_inject(int argc, const char **argv)
{
struct perf_inject inject = {
@@ -2414,6 +2537,8 @@ int cmd_inject(int argc, const char **argv)
OPT_STRING(0, "guestmount", &symbol_conf.guestmount, "directory",
"guest mount directory under which every guest os"
" instance has a subdir"),
+ OPT_BOOLEAN(0, "convert-callchain", &inject.convert_callchain,
+ "Generate callchains using DWARF and drop register/stack data"),
OPT_END()
};
const char * const inject_usage[] = {
@@ -2429,6 +2554,9 @@ int cmd_inject(int argc, const char **argv)

#ifndef HAVE_JITDUMP
set_option_nobuild(options, 'j', "jit", "NO_LIBELF=1", true);
+#endif
+#ifndef HAVE_LIBDW_SUPPORT
+ set_option_nobuild(options, 0, "convert-callchain", "NO_LIBDW=1", true);
#endif
argc = parse_options(argc, argv, options, inject_usage, 0);

@@ -2588,6 +2716,28 @@ int cmd_inject(int argc, const char **argv)
}
}

+ if (inject.convert_callchain) {
+ struct evsel *evsel;
+
+ if (inject.output.is_pipe || inject.session->data->is_pipe) {
+ pr_err("--convert-callchain cannot work with pipe\n");
+ goto out_delete;
+ }
+
+ evlist__for_each_entry(inject.session->evlist, evsel) {
+ if (!evsel__has_dwarf_callchain(evsel)) {
+ pr_err("--convert-callchain requires DWARF call graph.\n");
+ goto out_delete;
+ }
+ }
+
+ inject.raw_callchain = calloc(PERF_MAX_STACK_DEPTH, sizeof(u64));
+ if (inject.raw_callchain == NULL) {
+ pr_err("callchain allocation failed\n");
+ goto out_delete;
+ }
+ }
+
#ifdef HAVE_JITDUMP
if (inject.jit_mode) {
inject.tool.mmap2 = perf_event__repipe_mmap2;
@@ -2618,5 +2768,6 @@ int cmd_inject(int argc, const char **argv)
free(inject.itrace_synth_opts.vm_tm_corr_args);
free(inject.event_copy);
free(inject.guest_session.ev.event_buf);
+ free(inject.raw_callchain);
return ret;
}
--
2.52.0.457.g6b5491de43-goog