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From:   Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Date:   Wed, 7 Aug 2019 17:38:12 -0300
To:     Numfor Mbiziwo-Tiapo <nums@google.com>
Cc:     peterz@infradead.org, mingo@redhat.com,
        alexander.shishkin@linux.intel.com, jolsa@redhat.com,
        namhyung@kernel.org, songliubraving@fb.com, mbd@fb.com,
        linux-kernel@vger.kernel.org, irogers@google.com,
        eranian@google.com
Subject: Re: [PATCH 0/3] Perf uninitialized value fixes
Message-ID: <20190807203812.GA20129@kernel.org>
References: <20190724234500.253358-1-nums@google.com>
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Em Wed, Jul 24, 2019 at 04:44:57PM -0700, Numfor Mbiziwo-Tiapo escreveu:
> These patches are all warnings that the MSAN (Memory Sanitizer) build
> of perf has caught.
> 
> To build perf with MSAN enabled run:
> make -C tools/perf CLANG=1 CC=clang EXTRA_CFLAGS="-fsanitize=memory\
>  -fsanitize-memory-track-origins"
> 
> (The -fsanitizer-memory-track-origins makes the bugs clearer but
> isn't strictly necessary.)
> 
> (Additionally, llvm might have to be installed and clang might have to
> be specified as the compiler - export CC=/usr/bin/clang).
> 
> The patches "Fix util.c use of uninitialized value warning" and "Fix 
> annotate.c use of uninitialized value error" build on top of each other
> (the changes in Fix util.c use of uninitialized value warning must be
> made first).
> 
> When running the commands provided in the repro instructions, MSAN will
> generate false positive uninitialized memory errors. This is happening
> because libc is not MSAN-instrumented. Finding a way to build libc with
> MSAN will get rid of these false positives and allow the real warnings
> mentioned in the patches to be shown. 

So this is because I'm not running a glibc linked with MSAN? Do you have
any pointer to help building glibc with MSAN? I want to do that inside a
container so that I can use these sanitizers, thanks,

[root@quaco ~]# perf record -o - ls / | perf --no-pager annotate -i -  --stdio
==29732==WARNING: MemorySanitizer: use-of-uninitialized-value
==29733==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0xcc136d in add_path /home/acme/git/perf/tools/lib/subcmd/exec-cmd.c:130:6
    #1 0xcc075e in setup_path /home/acme/git/perf/tools/lib/subcmd/exec-cmd.c:146:2
    #2 0x71298d in main /home/acme/git/perf/tools/perf/perf.c:512:2
    #0 0xcc136d in add_path /home/acme/git/perf/tools/lib/subcmd/exec-cmd.c:130:6
    #1 0xcc075e in setup_path /home/acme/git/perf/tools/lib/subcmd/exec-cmd.c:146:2
    #2 0x71298d in main /home/acme/git/perf/tools/perf/perf.c:512:2
    #3 0x7f45b9e29f32 in __libc_start_main (/lib64/libc.so.6+0x23f32)
    #4 0x447dcd in _start (/home/acme/bin/perf+0x447dcd)

  Uninitialized value was created by a heap allocation
    #3 0x7fd6433cff32 in __libc_start_main (/lib64/libc.so.6+0x23f32)
    #4 0x447dcd in _start (/home/acme/bin/perf+0x447dcd)

  Uninitialized value was created by a heap allocation
    #0 0x4507d2 in malloc /home/acme/git/llvm/projects/compiler-rt/lib/msan/msan_interceptors.cc:916:3
    #1 0x7f45b9e7fc47 in __vasprintf_internal (/lib64/libc.so.6+0x79c47)

SUMMARY: MemorySanitizer: use-of-uninitialized-value /home/acme/git/perf/tools/lib/subcmd/exec-cmd.c:130:6 in add_path
Exiting
    #0 0x4507d2 in malloc /home/acme/git/llvm/projects/compiler-rt/lib/msan/msan_interceptors.cc:916:3
    #1 0x7fd643425c47 in __vasprintf_internal (/lib64/libc.so.6+0x79c47)

SUMMARY: MemorySanitizer: use-of-uninitialized-value /home/acme/git/perf/tools/lib/subcmd/exec-cmd.c:130:6 in add_path
Exiting
[root@quaco ~]#
 
> Numfor Mbiziwo-Tiapo (3):
>   Fix util.c use of uninitialized value warning
>   Fix annotate.c use of uninitialized value error
>   Fix sched-messaging.c use of uninitialized value errors
> 
>  tools/perf/bench/sched-messaging.c |  3 ++-
>  tools/perf/util/annotate.c         | 15 +++++++++++----
>  tools/perf/util/header.c           |  2 +-
>  3 files changed, 14 insertions(+), 6 deletions(-)
> 
> -- 
> 2.22.0.657.g960e92d24f-goog

-- 

- Arnaldo