linux-kernel - [PATCH 15/37] perf jit: Avoid returning garbage for a ret variable

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Date:   Mon, 24 Oct 2016 13:20:35 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Anton Blanchard <anton@...abs.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Maciej Debski <maciejd@...gle.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Stephane Eranian <eranian@...gle.com>
Subject: [PATCH 15/37] perf jit: Avoid returning garbage for a ret variable

From: Arnaldo Carvalho de Melo <acme@...hat.com>

When the loop body isn't executed at all, then the 'ret' local variable,
that is uninitialized will be used as the return value.

This triggers this error on Alpine Linux:

    CC	   /tmp/build/perf/util/demangle-java.o
    CC	   /tmp/build/perf/util/demangle-rust.o
    CC       /tmp/build/perf/util/jitdump.o
    CC       /tmp/build/perf/util/genelf.o
  util/jitdump.c: In function 'jit_process':
  util/jitdump.c:622:3: error: 'ret' may be used uninitialized in this function [-Werror=maybe-uninitialized]
     fprintf(stderr, "injected: %s (%d)\n", path, ret);
     ^
  util/jitdump.c:584:6: note: 'ret' was declared here
    int ret;
        ^
    FLEX     /tmp/build/perf/util/parse-events-flex.c

  / $ gcc -v
  Using built-in specs.
  COLLECT_GCC=gcc
  COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-alpine-linux-musl/5.3.0/lto-wrapper
  Target: x86_64-alpine-linux-musl
  Configured with: /home/buildozer/aports/main/gcc/src/gcc-5.3.0/configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info
  +--build=x86_64-alpine-linux-musl --host=x86_64-alpine-linux-musl --target=x86_64-alpine-linux-musl --with-pkgversion='Alpine 5.3.0' --enable-checking=release
  +--disable-fixed-point --disable-libstdcxx-pch --disable-multilib --disable-nls --disable-werror --disable-symvers --enable-__cxa_atexit --enable-esp
  +--enable-cloog-backend --enable-languages=c,c++,objc,java,fortran,ada --disable-libssp --disable-libmudflap --disable-libsanitizer --enable-shared
  +--enable-threads --enable-tls --with-system-zlib
  Thread model: posix
  gcc version 5.3.0 (Alpine 5.3.0)

But this so far got under the radar, not causing any build problem, till the
"perf jit: enable jitdump support without dwarf" gets applied, when the above
problem takes place, some combination of inlining or whatever, the problem
is real, so fix it by initializing the variable to zero.

Cc: Anton Blanchard <anton@...abs.org>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Maciej Debski <maciejd@...gle.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Stephane Eranian <eranian@...gle.com>
Link: https://lkml.kernel.org/r/20161013200437.GA12815@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/util/jitdump.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/jitdump.c b/tools/perf/util/jitdump.c
index 95f0884aae02..f3ed3c963c71 100644
--- a/tools/perf/util/jitdump.c
+++ b/tools/perf/util/jitdump.c
@@ -581,7 +581,7 @@ static int
 jit_process_dump(struct jit_buf_desc *jd)
 {
 	union jr_entry *jr;
-	int ret;
+	int ret = 0;
 
 	while ((jr = jit_get_next_entry(jd))) {
 		switch(jr->prefix.id) {
-- 
2.7.4