linux-kernel - [PATCH v1 1/2] perf build-id: Align records to 8 rather than 64 bytes

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Message-Id: <20240813043439.933329-1-irogers@google.com>
Date: Mon, 12 Aug 2024 21:34:38 -0700
From: Ian Rogers <irogers@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	Kan Liang <kan.liang@...ux.intel.com>, Sun Haiyong <sunhaiyong@...ngson.cn>, 
	Yanteng Si <siyanteng@...ngson.cn>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: [PATCH v1 1/2] perf build-id: Align records to 8 rather than 64 bytes

Events are 8-byte aligned in perf.data files, NAME_ALIGN is 64-bytes
which is excessive given the alignment needs. Move the addition the
sizeof so that the alignment considers that the rest of the event is
4-byte aligned.

```
struct perf_record_header_build_id {
        struct perf_event_header   header;               /*     0     8 */
        pid_t                      pid;                  /*     8     4 */
        union {
                __u8               build_id[24];         /*    12    24 */
                struct {
                        __u8       data[20];             /*    12    20 */
                        __u8       size;                 /*    32     1 */
                        __u8       reserved1__;          /*    33     1 */
                        __u16      reserved2__;          /*    34     2 */
                };                                       /*    12    24 */
        };                                               /*    12    24 */
        char                       filename[];           /*    36     0 */

        /* size: 36, cachelines: 1, members: 4 */
        /* last cacheline: 36 bytes */
};
```

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/build-id.c         | 6 +++---
 tools/perf/util/synthetic-events.c | 6 +++---
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/tools/perf/util/build-id.c b/tools/perf/util/build-id.c
index 83a1581e8cf1..8fea17d04468 100644
--- a/tools/perf/util/build-id.c
+++ b/tools/perf/util/build-id.c
@@ -309,8 +309,8 @@ static int write_buildid(const char *name, size_t name_len, struct build_id *bid
 	struct perf_record_header_build_id b;
 	size_t len;
 
-	len = name_len + 1;
-	len = PERF_ALIGN(len, NAME_ALIGN);
+	len = sizeof(b) + name_len + 1;
+	len = PERF_ALIGN(len, sizeof(u64));
 
 	memset(&b, 0, sizeof(b));
 	memcpy(&b.data, bid->data, bid->size);
@@ -318,7 +318,7 @@ static int write_buildid(const char *name, size_t name_len, struct build_id *bid
 	misc |= PERF_RECORD_MISC_BUILD_ID_SIZE;
 	b.pid = pid;
 	b.header.misc = misc;
-	b.header.size = sizeof(b) + len;
+	b.header.size = len;
 
 	err = do_write(fd, &b, sizeof(b));
 	if (err < 0)
diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index 5498048f56ea..a52b85bcb6b6 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -2236,14 +2236,14 @@ int perf_event__synthesize_build_id(struct perf_tool *tool, struct dso *pos, u16
 
 	memset(&ev, 0, sizeof(ev));
 
-	len = dso__long_name_len(pos) + 1;
-	len = PERF_ALIGN(len, NAME_ALIGN);
+	len = sizeof(ev.build_id) + dso__long_name_len(pos) + 1;
+	len = PERF_ALIGN(len, sizeof(u64));
 	ev.build_id.size = min(dso__bid(pos)->size, sizeof(dso__bid(pos)->data));
 	memcpy(&ev.build_id.build_id, dso__bid(pos)->data, ev.build_id.size);
 	ev.build_id.header.type = PERF_RECORD_HEADER_BUILD_ID;
 	ev.build_id.header.misc = misc | PERF_RECORD_MISC_BUILD_ID_SIZE;
 	ev.build_id.pid = machine->pid;
-	ev.build_id.header.size = sizeof(ev.build_id) + len;
+	ev.build_id.header.size = len;
 	memcpy(&ev.build_id.filename, dso__long_name(pos), dso__long_name_len(pos));
 
 	return process(tool, &ev, NULL, machine);
-- 
2.46.0.76.ge559c4bf1a-goog