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SubjectRe: [PATCH] perf: Adjust perf-inject output data offset for backward compatibility
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On 20/06/22 19:49, Raul Silvera wrote:
> When perf inject creates a new file, it reuses the data offset from the
> input file. If there has been a change on the size of the header, as
> happened in v5.12 -> v5.13, the new offsets will be wrong, resulting in
> a corrupted output file.
>
> This change adds the function perf_session__data_offset to compute the
> data offset based on the current header size, and uses that instead of
> the offset from the original input file.
>
> Signed-off-by: Raul Silvera <rsilvera@google.com>
> ---
> tools/perf/builtin-inject.c | 2 +-
> tools/perf/util/header.c | 16 +++++++++++++++-
> tools/perf/util/header.h | 2 ++
> 3 files changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c
> index a75bf11585b5..1dfdcef36607 100644
> --- a/tools/perf/builtin-inject.c
> +++ b/tools/perf/builtin-inject.c
> @@ -916,7 +916,7 @@ static int __cmd_inject(struct perf_inject *inject)
> inject->tool.tracing_data = perf_event__repipe_tracing_data;
> }
>
> - output_data_offset = session->header.data_offset;
> + output_data_offset = perf_session__data_offset(session->evlist);
>
> if (inject->build_id_all) {
> inject->tool.mmap = perf_event__repipe_buildid_mmap;
> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> index 53332da100e8..93706ae827f1 100644
> --- a/tools/perf/util/header.c
> +++ b/tools/perf/util/header.c
> @@ -3660,7 +3660,7 @@ static int perf_session__do_write_header(struct perf_session *session,
> .size = evlist->core.nr_entries * sizeof(f_attr),
> },
> .data = {
> - .offset = header->data_offset,
> + .offset = attr_offset + evlist->core.nr_entries * sizeof(f_attr),

This looks too late since, although the header comes before the data,
it also gets written afterwards (at_exit == true). It would be
better if we could rely on header->data_offset at this point.

> .size = header->data_size,
> },
> /* event_types is ignored, store zeros */
> @@ -3686,6 +3686,20 @@ int perf_session__write_header(struct perf_session *session,
> return perf_session__do_write_header(session, evlist, fd, at_exit, NULL);
> }
>
> +size_t perf_session__data_offset(const struct evlist *evlist)
> +{
> + struct evsel *evsel;
> + size_t data_offset;
> +
> + data_offset = sizeof(struct perf_file_header);
> + evlist__for_each_entry(evlist, evsel) {
> + data_offset += evsel->core.ids * sizeof(u64);
> + }
> + data_offset += evlist->core.nr_entries * sizeof(struct perf_file_attr);
> +
> + return data_offset;
> +}
> +
> int perf_session__inject_header(struct perf_session *session,
> struct evlist *evlist,
> int fd,
> diff --git a/tools/perf/util/header.h b/tools/perf/util/header.h
> index 08563c1f1bff..56916dabce7b 100644
> --- a/tools/perf/util/header.h
> +++ b/tools/perf/util/header.h
> @@ -136,6 +136,8 @@ int perf_session__inject_header(struct perf_session *session,
> int fd,
> struct feat_copier *fc);
>
> +size_t perf_session__data_offset(const struct evlist *evlist);
> +
> void perf_header__set_feat(struct perf_header *header, int feat);
> void perf_header__clear_feat(struct perf_header *header, int feat);
> bool perf_header__has_feat(const struct perf_header *header, int feat);

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