linux-kernel - [PATCH] building libtraceevent with clang

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Date:   Fri, 10 Feb 2017 14:03:17 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Namhyung Kim <namhyung@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH] building libtraceevent with clang

Hi Steven,

	I tried building perf (and thus libtraceevent) with clang and
got this one:

kbuffer-parse.c:312:7: warning: variable 'length' is used uninitialized whenever switch case is taken [-Wsometimes-uninitialized]
        case OLD_RINGBUF_TYPE_TIME_EXTEND:
             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
kbuffer-parse.c:339:29: note: uninitialized use occurs here
        kbuf->next = kbuf->index + length;
                                   ^~~~~~
kbuffer-parse.c:297:21: note: initialize the variable 'length' to silence this warning
        unsigned int length;
                           ^
                            = 0
1 warning generated.


Please take a look if the following is what should be done:

diff --git a/tools/lib/traceevent/kbuffer-parse.c b/tools/lib/traceevent/kbuffer-parse.c
index 65984f1c2974..3f717294cb82 100644
--- a/tools/lib/traceevent/kbuffer-parse.c
+++ b/tools/lib/traceevent/kbuffer-parse.c
@@ -309,20 +309,20 @@ static unsigned int old_update_pointers(struct kbuffer *kbuf)
 		kbuf->next = kbuf->size;
 		return 0;
 
-	case OLD_RINGBUF_TYPE_TIME_EXTEND:
-		extend = read_4(kbuf, ptr);
-		extend <<= TS_SHIFT;
-		extend += delta;
-		delta = extend;
-		ptr += 4;
-		break;
-
 	case OLD_RINGBUF_TYPE_TIME_STAMP:
 		/* should never happen! */
 		kbuf->curr = kbuf->size;
 		kbuf->next = kbuf->size;
 		kbuf->index = kbuf->size;
 		return -1;
+
+	case OLD_RINGBUF_TYPE_TIME_EXTEND:
+		extend = read_4(kbuf, ptr);
+		extend <<= TS_SHIFT;
+		extend += delta;
+		delta = extend;
+		ptr += 4;
+		/* Fall through */
 	default:
 		if (len)
 			length = len * 4;