perf cpumap: Fix alignment for masks in event encoding

A mask encoding of a cpu map is laid out as:

  u16 nr
  u16 long_size
  unsigned long mask[];

However, the mask may be 8-byte aligned meaning there is a 4-byte pad
after long_size. This means 32-bit and 64-bit builds see the mask as
being at different offsets. On top of this the structure is in the byte
data[] encoded as:

  u16 type
  char data[]

This means the mask's struct isn't the required 4 or 8 byte aligned, but
is offset by 2. Consequently the long reads and writes are causing
undefined behavior as the alignment is broken.

Fix the mask struct by creating explicit 32 and 64-bit variants, use a
union to avoid data[] and casts; the struct must be packed so the
layout matches the existing perf.data layout. Taking an address of a
member of a packed struct breaks alignment so pass the packed
perf_record_cpu_map_data to functions, so they can access variables with
the right alignment.

As the 64-bit version has 4 bytes of padding, optimizing writing to only
write the 32-bit version.

Committer notes:

Disable warnings about 'packed' that break the build in some arches like
riscv64, but just around that specific struct.

Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexey Bayduraev <alexey.v.bayduraev@linux.intel.com>
Cc: Athira Jajeev <atrajeev@linux.vnet.ibm.com>
Cc: Colin Ian King <colin.king@intel.com>
Cc: Dave Marchevsky <davemarchevsky@fb.com>
Cc: German Gomez <german.gomez@arm.com>
Cc: Gustavo A. R. Silva <gustavoars@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Kees Kook <keescook@chromium.org>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Riccardo Mancini <rickyman7@gmail.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20220614143353.1559597-5-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 20 insertions, 14 deletions

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index 3ae7c0f54157..59747c440bd5 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -1184,27 +1184,33 @@ int perf_event__synthesize_thread_map2(struct perf_tool *tool,
 	return err;
 }
 
-static void synthesize_cpus(struct cpu_map_entries *cpus,
+static void synthesize_cpus(struct perf_record_cpu_map_data *data,
 			    const struct perf_cpu_map *map)
 {
 	int i, map_nr = perf_cpu_map__nr(map);
 
-	cpus->nr = map_nr;
+	data->cpus_data.nr = map_nr;
 
 	for (i = 0; i < map_nr; i++)
-		cpus->cpu[i] = perf_cpu_map__cpu(map, i).cpu;
+		data->cpus_data.cpu[i] = perf_cpu_map__cpu(map, i).cpu;
 }
 
-static void synthesize_mask(struct perf_record_record_cpu_map *mask,
+static void synthesize_mask(struct perf_record_cpu_map_data *data,
 			    const struct perf_cpu_map *map, int max)
 {
-	int i;
+	int idx;
+	struct perf_cpu cpu;
+
+	/* Due to padding, the 4bytes per entry mask variant is always smaller. */
+	data->mask32_data.nr = BITS_TO_U32(max);
+	data->mask32_data.long_size = 4;
 
-	mask->nr = BITS_TO_LONGS(max);
-	mask->long_size = sizeof(long);
+	perf_cpu_map__for_each_cpu(cpu, idx, map) {
+		int bit_word = cpu.cpu / 32;
+		__u32 bit_mask = 1U << (cpu.cpu & 31);
 
-	for (i = 0; i < perf_cpu_map__nr(map); i++)
-		set_bit(perf_cpu_map__cpu(map, i).cpu, mask->mask);
+		data->mask32_data.mask[bit_word] |= bit_mask;
+	}
 }
 
 static size_t cpus_size(const struct perf_cpu_map *map)
@@ -1215,7 +1221,7 @@ static size_t cpus_size(const struct perf_cpu_map *map)
 static size_t mask_size(const struct perf_cpu_map *map, int *max)
 {
 	*max = perf_cpu_map__max(map).cpu;
-	return sizeof(struct perf_record_record_cpu_map) + BITS_TO_LONGS(*max) * sizeof(long);
+	return sizeof(struct perf_record_mask_cpu_map32) + BITS_TO_U32(*max) * sizeof(__u32);
 }
 
 static void *cpu_map_data__alloc(const struct perf_cpu_map *map, size_t *size,
@@ -1248,7 +1254,7 @@ static void *cpu_map_data__alloc(const struct perf_cpu_map *map, size_t *size,
 		*type  = PERF_CPU_MAP__MASK;
 	}
 
-	*size += sizeof(struct perf_record_cpu_map_data);
+	*size += sizeof(__u16); /* For perf_record_cpu_map_data.type. */
 	*size = PERF_ALIGN(*size, sizeof(u64));
 	return zalloc(*size);
 }
@@ -1261,10 +1267,10 @@ static void cpu_map_data__synthesize(struct perf_record_cpu_map_data *data,
 
 	switch (type) {
 	case PERF_CPU_MAP__CPUS:
-		synthesize_cpus((struct cpu_map_entries *) data->data, map);
+		synthesize_cpus(data, map);
 		break;
 	case PERF_CPU_MAP__MASK:
-		synthesize_mask((struct perf_record_record_cpu_map *)data->data, map, max);
+		synthesize_mask(data, map, max);
 	default:
 		break;
 	}
@@ -1272,7 +1278,7 @@ static void cpu_map_data__synthesize(struct perf_record_cpu_map_data *data,
 
 static struct perf_record_cpu_map *cpu_map_event__new(const struct perf_cpu_map *map)
 {
-	size_t size = sizeof(struct perf_record_cpu_map);
+	size_t size = sizeof(struct perf_event_header);
 	struct perf_record_cpu_map *event;
 	int max;
 	u16 type;