linux-kernel - [PATCH 4.12 023/196] perf intel-pt: Ensure never to set last

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Message-Id: <20170725192047.364825554@linuxfoundation.org>
Date:   Tue, 25 Jul 2017 12:20:22 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Adrian Hunter <adrian.hunter@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH 4.12 023/196] perf intel-pt: Ensure never to set last_ip when packet count is zero

4.12-stable review patch.  If anyone has any objections, please let me know.

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

From: Adrian Hunter <adrian.hunter@...el.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@...el.com>
Cc: Andi Kleen <ak@...ux.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@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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
@@ -1470,7 +1470,8 @@ 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:
@@ -1756,8 +1757,9 @@ 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. */