perf tools: Add size to 'struct perf_record_header_build_id'

We do not store size with build ids in perf data, but there's enough
space to do it. Adding misc bit PERF_RECORD_MISC_BUILD_ID_SIZE to mark
build id event with size.

With this fix the dso with md5 build id will have correct build id data
and will be usable for debuginfod processing if needed (coming in
following patches).

Committer notes:

Use %zu with size_t to fix this error on 32-bit arches:

  util/header.c: In function '__event_process_build_id':
  util/header.c:2105:3: error: format '%lu' expects argument of type 'long unsigned int', but argument 6 has type 'size_t' [-Werror=format=]
     pr_debug("build id event received for %s: %s [%lu]\n",
     ^

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20201013192441.1299447-8-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/perf/include/perf/event.h

@@ -201,10 +201,20 @@ struct perf_record_header_tracing_data {
 	__u32			 size;
 };
 
+#define PERF_RECORD_MISC_BUILD_ID_SIZE (1 << 15)
+
 struct perf_record_header_build_id {
 	struct perf_event_header header;
 	pid_t			 pid;
-	__u8			 build_id[24];
+	union {
+		__u8		 build_id[24];
+		struct {
+			__u8	 data[20];
+			__u8	 size;
+			__u8	 reserved1__;
+			__u16	 reserved2__;
+		};
+	};
 	char			 filename[];
 };
 

tools/perf/util/build-id.c

@@ -296,7 +296,7 @@ char *dso__build_id_filename(const struct dso *dso, char *bf, size_t size,
 			continue;		\
 		else
 
-static int write_buildid(const char *name, size_t name_len, u8 *build_id,
+static int write_buildid(const char *name, size_t name_len, struct build_id *bid,
 			 pid_t pid, u16 misc, struct feat_fd *fd)
 {
 	int err;
@@ -307,7 +307,9 @@ static int write_buildid(const char *name, size_t name_len, u8 *build_id,
 	len = PERF_ALIGN(len, NAME_ALIGN);
 
 	memset(&b, 0, sizeof(b));
-	memcpy(&b.build_id, build_id, BUILD_ID_SIZE);
+	memcpy(&b.data, bid->data, bid->size);
+	b.size = (u8) bid->size;
+	misc |= PERF_RECORD_MISC_BUILD_ID_SIZE;
 	b.pid = pid;
 	b.header.misc = misc;
 	b.header.size = sizeof(b) + len;
@@ -354,7 +356,7 @@ static int machine__write_buildid_table(struct machine *machine,
 		in_kernel = pos->kernel ||
 				is_kernel_module(name,
 					PERF_RECORD_MISC_CPUMODE_UNKNOWN);
-		err = write_buildid(name, name_len, pos->bid.data, machine->pid,
+		err = write_buildid(name, name_len, &pos->bid, machine->pid,
 				    in_kernel ? kmisc : umisc, fd);
 		if (err)
 			break;

tools/perf/util/header.c

@@ -2083,8 +2083,12 @@ static int __event_process_build_id(struct perf_record_header_build_id *bev,
 	if (dso != NULL) {
 		char sbuild_id[SBUILD_ID_SIZE];
 		struct build_id bid;
+		size_t size = BUILD_ID_SIZE;
 
-		build_id__init(&bid, bev->build_id, BUILD_ID_SIZE);
+		if (bev->header.misc & PERF_RECORD_MISC_BUILD_ID_SIZE)
+			size = bev->size;
+
+		build_id__init(&bid, bev->data, size);
 		dso__set_build_id(dso, &bid);
 
 		if (dso_space != DSO_SPACE__USER) {
@@ -2098,8 +2102,8 @@ static int __event_process_build_id(struct perf_record_header_build_id *bev,
 		}
 
 		build_id__sprintf(&dso->bid, sbuild_id);
-		pr_debug("build id event received for %s: %s\n",
-			 dso->long_name, sbuild_id);
+		pr_debug("build id event received for %s: %s [%zu]\n",
+			 dso->long_name, sbuild_id, size);
 		dso__put(dso);
 	}