On Fri, Jun 27, 2025 at 09:50:02PM -0700, Ian Rogers wrote:
> Support for build IDs in mmap2 perf events has been present since
> Linux v5.12:
> https://lore.kernel.org/lkml/20210219194619.1780437-1-acme@kernel.org/
> Build ID mmap events don't avoid the need to inject build IDs for DSO
> touched by samples as the build ID cache is populated by perf
> record. They can avoid some cases of symbol mis-resolution caused by
> the file system changing from when a sample occurred and when the DSO
> is sought. To disable build ID scanning
>
> Unlike the --buildid-mmap option, this doesn't disable the build ID
> cache but it does disable the processing of samples looking for DSOs
> to inject build IDs for. To disable the build ID cache the -B
> (--no-buildid) option should be used.
I think we need to add a config option to control this behavior later.
Let me think about this more.
>
> Making this option the default was raised on the list in:
> https://lore.kernel.org/linux-perf-users/CAP-5=fXP7jN_QrGUcd55_QH5J-Y-FCaJ6=NaHVtyx0oyNh8_-Q@mail.gmail.com/
>
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
> tools/perf/builtin-record.c | 33 +++++++++++++++++++-----------
> tools/perf/util/symbol_conf.h | 2 +-
> tools/perf/util/synthetic-events.c | 16 +++++++--------
> 3 files changed, 30 insertions(+), 21 deletions(-)
>
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 53971b9de3ba..29428fb8ac67 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -171,6 +171,7 @@ struct record {
> bool no_buildid_cache_set;
> bool buildid_all;
> bool buildid_mmap;
> + bool buildid_mmap_set;
> bool timestamp_filename;
> bool timestamp_boundary;
> bool off_cpu;
> @@ -1811,6 +1812,7 @@ record__finish_output(struct record *rec)
> data->dir.files[i].size = lseek(data->dir.files[i].fd, 0, SEEK_CUR);
> }
>
> + /* Buildid scanning disabled or build ID in kernel and synthesized map events. */
> if (!rec->no_buildid) {
> process_buildids(rec);
>
> @@ -3005,6 +3007,8 @@ static int perf_record_config(const char *var, const char *value, void *cb)
> rec->no_buildid = true;
> else if (!strcmp(value, "mmap"))
> rec->buildid_mmap = true;
> + else if (!strcmp(value, "no-mmap"))
> + rec->buildid_mmap = false;
> else
> return -1;
> return 0;
> @@ -3411,6 +3415,7 @@ static struct record record = {
> .synth = PERF_SYNTH_ALL,
> .off_cpu_thresh_ns = OFFCPU_THRESH,
> },
> + .buildid_mmap = true,
> };
>
> const char record_callchain_help[] = CALLCHAIN_RECORD_HELP
> @@ -3577,8 +3582,8 @@ static struct option __record_options[] = {
> "file", "vmlinux pathname"),
> OPT_BOOLEAN(0, "buildid-all", &record.buildid_all,
> "Record build-id of all DSOs regardless of hits"),
> - OPT_BOOLEAN(0, "buildid-mmap", &record.buildid_mmap,
> - "Record build-id in map events"),
> + OPT_BOOLEAN_SET(0, "buildid-mmap", &record.buildid_mmap, &record.buildid_mmap_set,
> + "Legacy record build-id in map events option which is now the default. Behaves indentically to --no-buildid. Disable with --no-buildid-mmap"),
Looks too long. Maybe just like below:
"Record build-id in mmap events and skip build-id processing."
The detailed explanation can go to the documentation.
> OPT_BOOLEAN(0, "timestamp-filename", &record.timestamp_filename,
> "append timestamp to output filename"),
> OPT_BOOLEAN(0, "timestamp-boundary", &record.timestamp_boundary,
> @@ -4108,19 +4113,23 @@ int cmd_record(int argc, const char **argv)
> record.opts.record_switch_events = true;
> }
>
> + if (!rec->buildid_mmap) {
> + pr_debug("Disabling build id in synthesized mmap2 events.\n");
> + symbol_conf.no_buildid_mmap2 = true;
> + } else if (rec->buildid_mmap_set) {
> + /*
> + * Explicitly passing --buildid-mmap disables buildid processing
> + * and cache generation.
> + */
> + rec->no_buildid = true;
> + }
> + if (rec->buildid_mmap && !perf_can_record_build_id()) {
> + pr_warning("Missing support for build id in kernel mmap events. Disable this warning with --no-buildid-mmap\n");
This can be in two lines. I can make the changes if you're ok.
Thanks,
Namhyung
> + rec->buildid_mmap = false;
> + }
> if (rec->buildid_mmap) {
> - if (!perf_can_record_build_id()) {
> - pr_err("Failed: no support to record build id in mmap events, update your kernel.\n");
> - err = -EINVAL;
> - goto out_opts;
> - }
> - pr_debug("Enabling build id in mmap2 events.\n");
> - /* Enable mmap build id synthesizing. */
> - symbol_conf.buildid_mmap2 = true;
> /* Enable perf_event_attr::build_id bit. */
> rec->opts.build_id = true;
> - /* Disable build id cache. */
> - rec->no_buildid = true;
> }
>
> if (rec->opts.record_cgroup && !perf_can_record_cgroup()) {
> diff --git a/tools/perf/util/symbol_conf.h b/tools/perf/util/symbol_conf.h
> index cd9aa82c7d5a..7a80d2c14d9b 100644
> --- a/tools/perf/util/symbol_conf.h
> +++ b/tools/perf/util/symbol_conf.h
> @@ -43,7 +43,7 @@ struct symbol_conf {
> report_individual_block,
> inline_name,
> disable_add2line_warn,
> - buildid_mmap2,
> + no_buildid_mmap2,
> guest_code,
> lazy_load_kernel_maps,
> keep_exited_threads,
> diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
> index 69b98023ce74..638d7dd7fa4b 100644
> --- a/tools/perf/util/synthetic-events.c
> +++ b/tools/perf/util/synthetic-events.c
> @@ -532,7 +532,7 @@ int perf_event__synthesize_mmap_events(const struct perf_tool *tool,
> event->mmap2.pid = tgid;
> event->mmap2.tid = pid;
>
> - if (symbol_conf.buildid_mmap2)
> + if (!symbol_conf.no_buildid_mmap2)
> perf_record_mmap2__read_build_id(&event->mmap2, machine, false);
>
> if (perf_tool__process_synth_event(tool, event, machine, process) != 0) {
> @@ -690,7 +690,7 @@ static int perf_event__synthesize_modules_maps_cb(struct map *map, void *data)
> return 0;
>
> dso = map__dso(map);
> - if (symbol_conf.buildid_mmap2) {
> + if (!symbol_conf.no_buildid_mmap2) {
> size = PERF_ALIGN(dso__long_name_len(dso) + 1, sizeof(u64));
> event->mmap2.header.type = PERF_RECORD_MMAP2;
> event->mmap2.header.size = (sizeof(event->mmap2) -
> @@ -734,9 +734,9 @@ int perf_event__synthesize_modules(const struct perf_tool *tool, perf_event__han
> .process = process,
> .machine = machine,
> };
> - size_t size = symbol_conf.buildid_mmap2
> - ? sizeof(args.event->mmap2)
> - : sizeof(args.event->mmap);
> + size_t size = symbol_conf.no_buildid_mmap2
> + ? sizeof(args.event->mmap)
> + : sizeof(args.event->mmap2);
>
> args.event = zalloc(size + machine->id_hdr_size);
> if (args.event == NULL) {
> @@ -1124,8 +1124,8 @@ static int __perf_event__synthesize_kernel_mmap(const struct perf_tool *tool,
> struct machine *machine)
> {
> union perf_event *event;
> - size_t size = symbol_conf.buildid_mmap2 ?
> - sizeof(event->mmap2) : sizeof(event->mmap);
> + size_t size = symbol_conf.no_buildid_mmap2 ?
> + sizeof(event->mmap) : sizeof(event->mmap2);
> struct map *map = machine__kernel_map(machine);
> struct kmap *kmap;
> int err;
> @@ -1159,7 +1159,7 @@ static int __perf_event__synthesize_kernel_mmap(const struct perf_tool *tool,
> event->header.misc = PERF_RECORD_MISC_GUEST_KERNEL;
> }
>
> - if (symbol_conf.buildid_mmap2) {
> + if (!symbol_conf.no_buildid_mmap2) {
> size = snprintf(event->mmap2.filename, sizeof(event->mmap2.filename),
> "%s%s", machine->mmap_name, kmap->ref_reloc_sym->name) + 1;
> size = PERF_ALIGN(size, sizeof(u64));
> --
> 2.50.0.727.gbf7dc18ff4-goog
>