linux-kernel - [PATCH 3/3] Fix sched-messaging.c use of uninitialized value errors

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Message-Id: <20190724234500.253358-4-nums@google.com>
Date:   Wed, 24 Jul 2019 16:45:00 -0700
From:   Numfor Mbiziwo-Tiapo <nums@...gle.com>
To:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org, songliubraving@...com, mbd@...com
Cc:     linux-kernel@...r.kernel.org, irogers@...gle.com,
        eranian@...gle.com, Numfor Mbiziwo-Tiapo <nums@...gle.com>
Subject: [PATCH 3/3] Fix sched-messaging.c use of uninitialized value errors

Our local MSAN (Memory Sanitizer) build of perf throws use of
uninitialized value warnings in "tools/perf/bench/sched-messaging.c"
when running perf bench.

The first warning comes from the "ready" function where the "dummy" char
is declared and then passed into "write" without being initialized.
Initializing "dummy" to any character silences the warning.

The second warning comes from the "sender" function where a "write" call
is made to write the contents from the "data" char array when it has not
yet been initialized. Calling memset on "data" silences the warning.

To reproduce this warning, build perf by running:
make -C tools/perf CLANG=1 CC=clang EXTRA_CFLAGS="-fsanitize=memory\
 -fsanitize-memory-track-origins"

(Additionally, llvm might have to be installed and clang might have to
be specified as the compiler - export CC=/usr/bin/clang)

then running: tools/perf/perf bench sched all

Please see the cover letter for why false positive warnings may be
generated.

Signed-off-by: Numfor Mbiziwo-Tiapo <nums@...gle.com>
---
 tools/perf/bench/sched-messaging.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/perf/bench/sched-messaging.c b/tools/perf/bench/sched-messaging.c
index f9d7641ae833..d22d7b7b591d 100644
--- a/tools/perf/bench/sched-messaging.c
+++ b/tools/perf/bench/sched-messaging.c
@@ -69,7 +69,7 @@ static void fdpair(int fds[2])
 /* Block until we're ready to go */
 static void ready(int ready_out, int wakefd)
 {
-	char dummy;
+	char dummy = 'N';
 	struct pollfd pollfd = { .fd = wakefd, .events = POLLIN };
 
 	/* Tell them we're ready. */
@@ -87,6 +87,7 @@ static void *sender(struct sender_context *ctx)
 	char data[DATASIZE];
 	unsigned int i, j;
 
+	memset(data, 'N', DATASIZE);
 	ready(ctx->ready_out, ctx->wakefd);
 
 	/* Now pump to every receiver. */
-- 
2.22.0.657.g960e92d24f-goog