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From:   Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Date:   Fri, 26 Jul 2019 16:40:44 -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 1/3] Fix backward-ring-buffer.c format-truncation error
Message-ID: <20190726194044.GC24867@kernel.org>
References: <20190724184512.162887-1-nums@google.com>
 <20190724184512.162887-2-nums@google.com>
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Em Wed, Jul 24, 2019 at 11:45:10AM -0700, Numfor Mbiziwo-Tiapo escreveu:
> Perf does not build with the ubsan (undefined behavior sanitizer)
> and there is an error that says:
> 
> tests/backward-ring-buffer.c:23:45: error: ‘%d’ directive output
> may be truncated writing between 1 and 10 bytes into a region of
> size 8 [-Werror=format-truncation=]
>    snprintf(proc_name, sizeof(proc_name), "p:%d\n", i);
> 
> This can be reproduced by running (from the tip directory):
> make -C tools/perf USE_CLANG=1 EXTRA_CFLAGS="-fsanitize=undefined"
> 
> Th error occurs because they are writing to the 10 byte buffer - the
> index 'i' of the for loop and the 2 byte hardcoded string. If somehow 'i'
> was greater than 8 bytes (10 - 2), then the snprintf function would
> truncate the string. Increasing the size of the buffer fixes the error.
> 
> Signed-off-by: Numfor Mbiziwo-Tiapo <nums@google.com>
> ---
>  tools/perf/tests/backward-ring-buffer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/perf/tests/backward-ring-buffer.c b/tools/perf/tests/backward-ring-buffer.c
> index 6d598cc071ae..1a9c3becf5ff 100644
> --- a/tools/perf/tests/backward-ring-buffer.c
> +++ b/tools/perf/tests/backward-ring-buffer.c
> @@ -18,7 +18,7 @@ static void testcase(void)
>  	int i;
>  
>  	for (i = 0; i < NR_ITERS; i++) {
> -		char proc_name[10];
> +		char proc_name[15];
>  
>  		snprintf(proc_name, sizeof(proc_name), "p:%d\n", i);
>  		prctl(PR_SET_NAME, proc_name);

This was fixed already by:

commit 11c1ea6f1a9bc97bf857fd12f72eacb6c69794e2
Author: Changbin Du <changbin.du@gmail.com>
Date:   Sat Mar 16 16:05:43 2019 +0800

    perf tools: Fix errors under optimization level '-Og'

    Optimization level '-Og' offers a reasonable level of optimization while
    maintaining fast compilation and a good debugging experience. This patch
    tries to make it work.

      $ make DEBUG=1 EXTRA_CFLAGS='-Og'
      bench/epoll-ctl.c: In function ‘do_threads’:
      bench/epoll-ctl.c:274:9: error: ‘ret’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
        return ret;
               ^~~
      ...

    Signed-off-by: Changbin Du <changbin.du@gmail.com>
    Reviewed-by: Jiri Olsa <jolsa@kernel.org>