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    Subject[PATCH 5.11 585/601] perf jit: Let convert_timestamp() to be backwards-compatible
    Date
    From: Leo Yan <leo.yan@linaro.org>

    [ Upstream commit aa616f5a8a2d22a179d5502ebd85045af66fa656 ]

    Commit d110162cafc80dad ("perf tsc: Support cap_user_time_short for
    event TIME_CONV") supports the extended parameters for event TIME_CONV,
    but it broke the backwards compatibility, so any perf data file with old
    event format fails to convert timestamp.

    This patch introduces a helper event_contains() to check if an event
    contains a specific member or not. For the backwards-compatibility, if
    the event size confirms the extended parameters are supported in the
    event TIME_CONV, then copies these parameters.

    Committer notes:

    To make this compiler backwards compatible add this patch:

    - struct perf_tsc_conversion tc = { 0 };
    + struct perf_tsc_conversion tc = { .time_shift = 0, };

    Fixes: d110162cafc8 ("perf tsc: Support cap_user_time_short for event TIME_CONV")
    Signed-off-by: Leo Yan <leo.yan@linaro.org>
    Acked-by: Adrian Hunter <adrian.hunter@intel.com>
    Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
    Cc: Gustavo A. R. Silva <gustavoars@kernel.org>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Cc: Kan Liang <kan.liang@linux.intel.com>
    Cc: Mark Rutland <mark.rutland@arm.com>
    Cc: Namhyung Kim <namhyung@kernel.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Steve MacLean <Steve.MacLean@Microsoft.com>
    Cc: Yonatan Goldschmidt <yonatan.goldschmidt@granulate.io>
    Link: https://lore.kernel.org/r/20210428120915.7123-3-leo.yan@linaro.org
    Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    tools/lib/perf/include/perf/event.h | 2 ++
    tools/perf/util/jitdump.c | 30 +++++++++++++++++++----------
    2 files changed, 22 insertions(+), 10 deletions(-)

    diff --git a/tools/lib/perf/include/perf/event.h b/tools/lib/perf/include/perf/event.h
    index baf64ea74e10..4a24b855d3ce 100644
    --- a/tools/lib/perf/include/perf/event.h
    +++ b/tools/lib/perf/include/perf/event.h
    @@ -8,6 +8,8 @@
    #include <linux/bpf.h>
    #include <sys/types.h> /* pid_t */

    +#define event_contains(obj, mem) ((obj).header.size > offsetof(typeof(obj), mem))
    +
    struct perf_record_mmap {
    struct perf_event_header header;
    __u32 pid, tid;
    diff --git a/tools/perf/util/jitdump.c b/tools/perf/util/jitdump.c
    index 055bab7a92b3..64d8f9ba8c03 100644
    --- a/tools/perf/util/jitdump.c
    +++ b/tools/perf/util/jitdump.c
    @@ -369,21 +369,31 @@ jit_inject_event(struct jit_buf_desc *jd, union perf_event *event)

    static uint64_t convert_timestamp(struct jit_buf_desc *jd, uint64_t timestamp)
    {
    - struct perf_tsc_conversion tc;
    + struct perf_tsc_conversion tc = { .time_shift = 0, };
    + struct perf_record_time_conv *time_conv = &jd->session->time_conv;

    if (!jd->use_arch_timestamp)
    return timestamp;

    - tc.time_shift = jd->session->time_conv.time_shift;
    - tc.time_mult = jd->session->time_conv.time_mult;
    - tc.time_zero = jd->session->time_conv.time_zero;
    - tc.time_cycles = jd->session->time_conv.time_cycles;
    - tc.time_mask = jd->session->time_conv.time_mask;
    - tc.cap_user_time_zero = jd->session->time_conv.cap_user_time_zero;
    - tc.cap_user_time_short = jd->session->time_conv.cap_user_time_short;
    + tc.time_shift = time_conv->time_shift;
    + tc.time_mult = time_conv->time_mult;
    + tc.time_zero = time_conv->time_zero;

    - if (!tc.cap_user_time_zero)
    - return 0;
    + /*
    + * The event TIME_CONV was extended for the fields from "time_cycles"
    + * when supported cap_user_time_short, for backward compatibility,
    + * checks the event size and assigns these extended fields if these
    + * fields are contained in the event.
    + */
    + if (event_contains(*time_conv, time_cycles)) {
    + tc.time_cycles = time_conv->time_cycles;
    + tc.time_mask = time_conv->time_mask;
    + tc.cap_user_time_zero = time_conv->cap_user_time_zero;
    + tc.cap_user_time_short = time_conv->cap_user_time_short;
    +
    + if (!tc.cap_user_time_zero)
    + return 0;
    + }

    return tsc_to_perf_time(timestamp, &tc);
    }
    --
    2.30.2


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