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    Subject[PATCH 4.9 023/125] perf intel-pt: Ensure never to set last_ip when packet count is zero
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Adrian Hunter <adrian.hunter@intel.com>

    commit f952eaceb089b691eba7c4e13686e742a8f26bf5 upstream.

    Intel PT uses IP compression based on the last IP. For decoding purposes,
    'last IP' is not updated when a branch target has been suppressed, which is
    indicated by IPBytes == 0. IPBytes is stored in the packet 'count', so
    ensure never to set 'last_ip' when packet 'count' is zero.

    Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
    Cc: Andi Kleen <ak@linux.intel.com>
    Link: http://lkml.kernel.org/r/1495786658-18063-7-git-send-email-adrian.hunter@intel.com
    Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    tools/perf/util/intel-pt-decoder/intel-pt-decoder.c | 8 +++++---
    1 file changed, 5 insertions(+), 3 deletions(-)

    --- a/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
    +++ b/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
    @@ -1468,7 +1468,8 @@ static int intel_pt_walk_psbend(struct i

    case INTEL_PT_FUP:
    decoder->pge = true;
    - intel_pt_set_last_ip(decoder);
    + if (decoder->packet.count)
    + intel_pt_set_last_ip(decoder);
    break;

    case INTEL_PT_MODE_TSX:
    @@ -1754,8 +1755,9 @@ next:

    static inline bool intel_pt_have_ip(struct intel_pt_decoder *decoder)
    {
    - return decoder->have_last_ip || decoder->packet.count == 0 ||
    - decoder->packet.count == 3 || decoder->packet.count == 6;
    + return decoder->packet.count &&
    + (decoder->have_last_ip || decoder->packet.count == 3 ||
    + decoder->packet.count == 6);
    }

    /* Walk PSB+ packets to get in sync. */

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