linux-kernel - [PATCH 1/3] Fix util.c use of unitialized value warning

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Message-Id: <20190724234500.253358-2-nums@google.com>
Date:   Wed, 24 Jul 2019 16:44:58 -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 1/3] Fix util.c use of unitialized value warning

When building our local version of perf with MSAN (Memory Sanitizer)
and running the perf record command, MSAN throws a use of uninitialized
value warning in "tools/perf/util/util.c:333:6".

This warning stems from the "buf" variable being passed into "write".
It originated as the variable "ev" with the type union perf_event*
defined in the "perf_event__synthesize_attr" function in
"tools/perf/util/header.c".

In the "perf_event__synthesize_attr" function they allocate space with
a malloc call using ev, then go on to only assign some of the member
variables before passing "ev" on as a parameter to the "process" function
therefore "ev" contains uninitialized memory. Changing the malloc call
to calloc initializes all the members of "ev" which gets rid of 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 record -o - ls / | tools/perf/perf --no-pager annotate\
 -i - --stdio

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

Signed-off-by: Numfor Mbiziwo-Tiapo <nums@...gle.com>
---
 tools/perf/util/header.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index dec6d218c31c..b9c71fc45ac1 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -3427,7 +3427,7 @@ int perf_event__synthesize_attr(struct perf_tool *tool,
 	size += sizeof(struct perf_event_header);
 	size += ids * sizeof(u64);

-	ev = malloc(size);
+	ev = calloc(1, size);

 	if (ev == NULL)
 		return -ENOMEM;
-- 
2.22.0.657.g960e92d24f-goog