linux-kernel - Intel PT decoder switch case fallthrough cases reported by gcc 7

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Date:   Thu, 9 Feb 2017 13:50:39 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <andi@...stfloor.org>, Jiri Olsa <jolsa@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Intel PT decoder switch case fallthrough cases reported by gcc 7

Hi,

	I've updated the container with Fedora Rawhide I use to build
tools/perf/ and samples/bcc/ and it now comes with gcc 7, where I get
things like:

  CC       /tmp/build/perf/tests/code-reading.o
util/intel-pt-decoder/intel-pt-decoder.c: In function 'intel_pt_walk_psb':
util/intel-pt-decoder/intel-pt-decoder.c:1748:31: error: this statement may fall through [-Werror=implicit-fallthrough=]
    decoder->continuous_period = false;
                               ^
util/intel-pt-decoder/intel-pt-decoder.c:1749:3: note: here
   case INTEL_PT_TIP_PGE:
   ^~~~
util/intel-pt-decoder/intel-pt-decoder.c:1801:4: error: this statement may fall through [-Werror=implicit-fallthrough=]
    intel_pt_clear_tx_flags(decoder);
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
util/intel-pt-decoder/intel-pt-decoder.c:1802:3: note: here
   case INTEL_PT_TNT:
   ^~~~
util/intel-pt-decoder/intel-pt-decoder.c: In function 'intel_pt_walk_to_ip':
util/intel-pt-decoder/intel-pt-decoder.c:1841:31: error: this statement may fall through [-Werror=implicit-fallthrough=]
    decoder->continuous_period = false;
                               ^
util/intel-pt-decoder/intel-pt-decoder.c:1842:3: note: here
   case INTEL_PT_TIP_PGE:
   ^~~~
  MKDIR    /tmp/build/perf/util/scripting-engines/


This gets solved with a new attribute, that you have to add where in the past
we added:

	/* Fall through */

To indicate that the fall through to the next case statement block is
intentional, so now I have a __fallthrough and I am addressing all the cases,
please check if the ones below are the ones intended for the Intel PT parts,
please Ack or advise, only one seemed like a bug, i.e. a break should be used,
but I'm not sure.

- Arnaldo


diff --git a/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c b/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
index e4e7dc781d21..d4ed327a4908 100644
--- a/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
+++ b/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
@@ -1746,6 +1746,7 @@ static int intel_pt_walk_psb(struct intel_pt_decoder *decoder)
 		switch (decoder->packet.type) {
 		case INTEL_PT_TIP_PGD:
 			decoder->continuous_period = false;
+			__fallthrough;
 		case INTEL_PT_TIP_PGE:
 		case INTEL_PT_TIP:
 			intel_pt_log("ERROR: Unexpected packet\n");
@@ -1799,6 +1800,8 @@ static int intel_pt_walk_psb(struct intel_pt_decoder *decoder)
 			decoder->pge = false;
 			decoder->continuous_period = false;
 			intel_pt_clear_tx_flags(decoder);
+			break;
+
 		case INTEL_PT_TNT:
 			decoder->have_tma = false;
 			intel_pt_log("ERROR: Unexpected packet\n");
@@ -1839,6 +1842,7 @@ static int intel_pt_walk_to_ip(struct intel_pt_decoder *decoder)
 		switch (decoder->packet.type) {
 		case INTEL_PT_TIP_PGD:
 			decoder->continuous_period = false;
+			__fallthrough;
 		case INTEL_PT_TIP_PGE:
 		case INTEL_PT_TIP:
 			decoder->pge = decoder->packet.type != INTEL_PT_TIP_PGD;
diff --git a/tools/perf/util/intel-pt-decoder/intel-pt-pkt-decoder.c b/tools/perf/util/intel-pt-decoder/intel-pt-pkt-decoder.c
index 4f7b32020487..7528ae4f7e28 100644
--- a/tools/perf/util/intel-pt-decoder/intel-pt-pkt-decoder.c
+++ b/tools/perf/util/intel-pt-decoder/intel-pt-pkt-decoder.c
@@ -17,6 +17,7 @@
 #include <string.h>
 #include <endian.h>
 #include <byteswap.h>
+#include <linux/compiler.h>
 
 #include "intel-pt-pkt-decoder.h"
 
@@ -498,6 +499,7 @@ int intel_pt_pkt_desc(const struct intel_pt_pkt *packet, char *buf,
 	case INTEL_PT_FUP:
 		if (!(packet->count))
 			return snprintf(buf, buf_len, "%s no ip", name);
+		__fallthrough;
 	case INTEL_PT_CYC:
 	case INTEL_PT_VMCS:
 	case INTEL_PT_MTC: