perf record: Make --buildid-mmap the default

Support for build IDs in mmap2 perf events has been present since
Linux v5.12:
https://lore.kernel.org/lkml/[email protected]/
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.

Unlike the --buildid-mmap option, this chnage 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.

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 <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Namhyung Kim <[email protected]>

Author: captain5050

tools/perf/Documentation/perf-record.txt

@@ -563,7 +563,9 @@ Specify vmlinux path which has debuginfo.
 Record build-id of all DSOs regardless whether it's actually hit or not.
 
 --buildid-mmap::
-Record build ids in mmap2 events, disables build id cache (implies --no-buildid).
+Legacy record build-id in map events option which is now the
+default. Behaves indentically to --no-buildid. Disable with
+--no-buildid-mmap.
 
 --aio[=n]::
 Use <n> control blocks in asynchronous (Posix AIO) trace writing mode (default: 1, max: 4).

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,
+			"Record build-id in mmap events and skip build-id processing."),
 	OPT_BOOLEAN(0, "timestamp-filename", &record.timestamp_filename,
 		    "append timestamp to output filename"),
 	OPT_BOOLEAN(0, "timestamp-boundary", &record.timestamp_boundary,
@@ -4108,19 +4113,24 @@ 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.\n"
+			   "Disable this warning with --no-buildid-mmap\n");
+		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()) {

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,

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));