Re: [PATCH v2 1/2] perf record: Add 8-byte aligned event type PERF_RECORD_COMPRESSED2

Namhyung Kim
2025-03-15T01:27:07Z

Hello,

On Mon, Mar 03, 2025 at 10:32:40AM -0800, Chun-Tse Shao wrote:
> The original PERF_RECORD_COMPRESS is not 8-byte aligned, which can cause
> asan runtime error:
>
> # Build with asan
> $ make -C tools/perf O=/tmp/perf DEBUG=1 EXTRA_CFLAGS="-O0 -g -fno-omit-frame-pointer -fsanitize=undefined"
> # Test success with many asan runtime errors:
> $ /tmp/perf/perf test "Zstd perf.data compression/decompression" -vv
> 83: Zstd perf.data compression/decompression:
> ...
> util/session.c:1959:13: runtime error: member access within misaligned address 0x7f69e3f99653 for type 'union perf_event', which requires 13 byte alignment
> 0x7f69e3f99653: note: pointer points here
> d0 3a 50 69 44 00 00 00 00 00 08 00 bb 07 00 00 00 00 00 00 44 00 00 00 00 00 00 00 ff 07 00 00
> ^
> util/session.c:2163:22: runtime error: member access within misaligned address 0x7f69e3f99653 for type 'union perf_event', which requires 8 byte alignment
> 0x7f69e3f99653: note: pointer points here
> d0 3a 50 69 44 00 00 00 00 00 08 00 bb 07 00 00 00 00 00 00 44 00 00 00 00 00 00 00 ff 07 00 00
> ^
> ...
>
> Since there is no way to align compressed data in zstd compression, this
> patch add a new event type `PERF_RECORD_COMPRESSED2`, which adds a field
> `data_size` to specify the actual compressed data size. The
> `header.size` contains the total record size, including the padding at
> the end to make it 8-byte aligned.
>
> Tested with `Zstd perf.data compression/decompression`

Looks good to me.

Arnaldo, are you ok with adding a new record type for this?

Thanks,
Namhyung

>
> Signed-off-by: Chun-Tse Shao <ctshao@google.com>
> ---
> v2:
> Add deprecated comment for `PERF_RECORD_COMPRESSED`.
>
> tools/lib/perf/Documentation/libperf.txt | 1 +
> tools/lib/perf/include/perf/event.h | 12 ++++++++++
> .../Documentation/perf.data-file-format.txt | 24 +++++++++++++++----
> tools/perf/builtin-record.c | 23 ++++++++++++++----
> tools/perf/util/event.c | 1 +
> tools/perf/util/session.c | 5 +++-
> tools/perf/util/tool.c | 11 +++++++--
> 7 files changed, 64 insertions(+), 13 deletions(-)
>
> diff --git a/tools/lib/perf/Documentation/libperf.txt b/tools/lib/perf/Documentation/libperf.txt
> index 59aabdd3cabf..4072bc9b7670 100644
> --- a/tools/lib/perf/Documentation/libperf.txt
> +++ b/tools/lib/perf/Documentation/libperf.txt
> @@ -210,6 +210,7 @@ SYNOPSIS
> struct perf_record_time_conv;
> struct perf_record_header_feature;
> struct perf_record_compressed;
> + struct perf_record_compressed2;
> --
>
> DESCRIPTION
> diff --git a/tools/lib/perf/include/perf/event.h b/tools/lib/perf/include/perf/event.h
> index 37bb7771d914..09b7c643ddac 100644
> --- a/tools/lib/perf/include/perf/event.h
> +++ b/tools/lib/perf/include/perf/event.h
> @@ -457,6 +457,16 @@ struct perf_record_compressed {
> char data[];
> };
>
> +/*
> + * `header.size` includes the padding we are going to add while writing the record.
> + * `data_size` only includes the size of `data[]` itself.
> + */
> +struct perf_record_compressed2 {
> + struct perf_event_header header;
> + __u64 data_size;
> + char data[];
> +};
> +
> enum perf_user_event_type { /* above any possible kernel type */
> PERF_RECORD_USER_TYPE_START = 64,
> PERF_RECORD_HEADER_ATTR = 64,
> @@ -478,6 +488,7 @@ enum perf_user_event_type { /* above any possible kernel type */
> PERF_RECORD_HEADER_FEATURE = 80,
> PERF_RECORD_COMPRESSED = 81,
> PERF_RECORD_FINISHED_INIT = 82,
> + PERF_RECORD_COMPRESSED2 = 83,
> PERF_RECORD_HEADER_MAX
> };
>
> @@ -518,6 +529,7 @@ union perf_event {
> struct perf_record_time_conv time_conv;
> struct perf_record_header_feature feat;
> struct perf_record_compressed pack;
> + struct perf_record_compressed2 pack2;
> };
>
> #endif /* __LIBPERF_EVENT_H */
> diff --git a/tools/perf/Documentation/perf.data-file-format.txt b/tools/perf/Documentation/perf.data-file-format.txt
> index 010a4edcd384..cd95ba09f727 100644
> --- a/tools/perf/Documentation/perf.data-file-format.txt
> +++ b/tools/perf/Documentation/perf.data-file-format.txt
> @@ -370,7 +370,7 @@ struct {
> u32 mmap_len;
> };
>
> -Indicates that trace contains records of PERF_RECORD_COMPRESSED type
> +Indicates that trace contains records of PERF_RECORD_COMPRESSED2 type
> that have perf_events records in compressed form.
>
> HEADER_CPU_PMU_CAPS = 28,
> @@ -602,7 +602,14 @@ struct auxtrace_error_event {
> Describes a header feature. These are records used in pipe-mode that
> contain information that otherwise would be in perf.data file's header.
>
> - PERF_RECORD_COMPRESSED = 81,
> + PERF_RECORD_COMPRESSED = 81, /* deprecated */
> +
> +The header is followed by compressed data frame that can be decompressed
> +into array of perf trace records. The size of the entire compressed event
> +record including the header is limited by the max value of header.size.
> +
> +It is deprecated and new files should use PERF_RECORD_COMPRESSED2 to gurantee
> +8-byte alignment.
>
> struct compressed_event {
> struct perf_event_header header;
> @@ -618,10 +625,17 @@ This is used, for instance, to 'perf inject' events after init and before
> regular events, those emitted by the kernel, to support combining guest and
> host records.
>
> + PERF_RECORD_COMPRESSED2 = 83,
>
> -The header is followed by compressed data frame that can be decompressed
> -into array of perf trace records. The size of the entire compressed event
> -record including the header is limited by the max value of header.size.
> +8-byte aligned version of `PERF_RECORD_COMPRESSED`. `header.size` indicates the
> +total record size, including padding for 8-byte alignment, and `data_size`
> +specifies the actual size of the compressed data.
> +
> +struct perf_record_compressed2 {
> + struct perf_event_header header;
> + __u64 data_size;
> + char data[];
> +};
>
> Event types
>
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 9af3f21fd015..d07ad670daa7 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -648,14 +648,27 @@ static int record__pushfn(struct mmap *map, void *to, void *bf, size_t size)
> struct record *rec = to;
>
> if (record__comp_enabled(rec)) {
> + struct perf_record_compressed2 *event = map->data;
> + size_t padding = 0;
> + u8 pad[8] = {0};
> ssize_t compressed = zstd_compress(rec->session, map, map->data,
> mmap__mmap_len(map), bf, size);
>
> if (compressed < 0)
> return (int)compressed;
>
> - size = compressed;
> - bf = map->data;
> + bf = event;
> + thread->samples++;
> +
> + /*
> + * The record from `zstd_compress` is not 8 bytes aligned, which would cause asan
> + * error. We make it aligned here.
> + */
> + event->data_size = compressed - sizeof(struct perf_record_compressed2);
> + event->header.size = PERF_ALIGN(compressed, sizeof(u64));
> + padding = event->header.size - compressed;
> + return record__write(rec, map, bf, compressed) ||
> + record__write(rec, map, &pad, padding);
> }
>
> thread->samples++;
> @@ -1534,7 +1547,7 @@ static void record__adjust_affinity(struct record *rec, struct mmap *map)
>
> static size_t process_comp_header(void *record, size_t increment)
> {
> - struct perf_record_compressed *event = record;
> + struct perf_record_compressed2 *event = record;
> size_t size = sizeof(*event);
>
> if (increment) {
> @@ -1542,7 +1555,7 @@ static size_t process_comp_header(void *record, size_t increment)
> return increment;
> }
>
> - event->header.type = PERF_RECORD_COMPRESSED;
> + event->header.type = PERF_RECORD_COMPRESSED2;
> event->header.size = size;
>
> return size;
> @@ -1552,7 +1565,7 @@ static ssize_t zstd_compress(struct perf_session *session, struct mmap *map,
> void *dst, size_t dst_size, void *src, size_t src_size)
> {
> ssize_t compressed;
> - size_t max_record_size = PERF_SAMPLE_MAX_SIZE - sizeof(struct perf_record_compressed) - 1;
> + size_t max_record_size = PERF_SAMPLE_MAX_SIZE - sizeof(struct perf_record_compressed2) - 1;
> struct zstd_data *zstd_data = &session->zstd_data;
>
> if (map && map->file)
> diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
> index c23b77f8f854..80c9ea682413 100644
> --- a/tools/perf/util/event.c
> +++ b/tools/perf/util/event.c
> @@ -77,6 +77,7 @@ static const char *perf_event__names[] = {
> [PERF_RECORD_HEADER_FEATURE] = "FEATURE",
> [PERF_RECORD_COMPRESSED] = "COMPRESSED",
> [PERF_RECORD_FINISHED_INIT] = "FINISHED_INIT",
> + [PERF_RECORD_COMPRESSED2] = "COMPRESSED2",
> };
>
> const char *perf_event__name(unsigned int id)
> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> index 60fb9997ea0d..db2653322f9f 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -1400,7 +1400,9 @@ static s64 perf_session__process_user_event(struct perf_session *session,
> int err;
>
> perf_sample__init(&sample, /*all=*/true);
> - if (event->header.type != PERF_RECORD_COMPRESSED || perf_tool__compressed_is_stub(tool))
> + if ((event->header.type != PERF_RECORD_COMPRESSED &&
> + event->header.type != PERF_RECORD_COMPRESSED2) ||
> + perf_tool__compressed_is_stub(tool))
> dump_event(session->evlist, event, file_offset, &sample, file_path);
>
> /* These events are processed right away */
> @@ -1481,6 +1483,7 @@ static s64 perf_session__process_user_event(struct perf_session *session,
> err = tool->feature(session, event);
> break;
> case PERF_RECORD_COMPRESSED:
> + case PERF_RECORD_COMPRESSED2:
> err = tool->compressed(session, event, file_offset, file_path);
> if (err)
> dump_event(session->evlist, event, file_offset, &sample, file_path);
> diff --git a/tools/perf/util/tool.c b/tools/perf/util/tool.c
> index 3b7f390f26eb..37bd8ac63b01 100644
> --- a/tools/perf/util/tool.c
> +++ b/tools/perf/util/tool.c
> @@ -43,8 +43,15 @@ static int perf_session__process_compressed_event(struct perf_session *session,
> decomp->size = decomp_last_rem;
> }
>
> - src = (void *)event + sizeof(struct perf_record_compressed);
> - src_size = event->pack.header.size - sizeof(struct perf_record_compressed);
> + if (event->header.type == PERF_RECORD_COMPRESSED) {
> + src = (void *)event + sizeof(struct perf_record_compressed);
> + src_size = event->pack.header.size - sizeof(struct perf_record_compressed);
> + } else if (event->header.type == PERF_RECORD_COMPRESSED2) {
> + src = (void *)event + sizeof(struct perf_record_compressed2);
> + src_size = event->pack2.data_size;
> + } else {
> + return -1;
> + }
>
> decomp_size = zstd_decompress_stream(session->active_decomp->zstd_decomp, src, src_size,
> &(decomp->data[decomp_last_rem]), decomp_len - decomp_last_rem);
> --
> 2.48.1.711.g2feabab25a-goog
>