linux-kernel - Re: [PATCH 05/44] perf data: Fix 'strncat may truncate' build failure with recent gcc

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Date:   Mon, 27 May 2019 17:46:26 -0500
From:   Shawn Landden <slandden@...il.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Clark Williams <williams@...hat.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Adrian Hunter <adrian.hunter@...el.com>,
        Jiri Olsa <jolsa@...hat.com>, Wang Nan <wangnan0@...wei.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH 05/44] perf data: Fix 'strncat may truncate' build failure
 with recent gcc

On Mon, May 27, 2019 at 5:38 PM Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
>
> From: Shawn Landden <shawn@....icu>
>
> This strncat() is safe because the buffer was allocated with zalloc(),
> however gcc doesn't know that. Since the string always has 4 non-null
> bytes, just use memcpy() here.
>
>     CC       /home/shawn/linux/tools/perf/util/data-convert-bt.o
>   In file included from /usr/include/string.h:494,
>                    from /home/shawn/linux/tools/lib/traceevent/event-parse.h:27,
>                    from util/data-convert-bt.c:22:
>   In function ‘strncat’,
>       inlined from ‘string_set_value’ at util/data-convert-bt.c:274:4:
>   /usr/include/powerpc64le-linux-gnu/bits/string_fortified.h:136:10: error: ‘__builtin_strncat’ output may be truncated copying 4 bytes from a string of length 4 [-Werror=stringop-truncation]
>     136 |   return __builtin___strncat_chk (__dest, __src, __len, __bos (__dest));
>         |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Signed-off-by: Shawn Landden <shawn@....icu>
> Cc: Adrian Hunter <adrian.hunter@...el.com>
> Cc: Jiri Olsa <jolsa@...hat.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Wang Nan <wangnan0@...wei.com>
> LPU-Reference: 20190518183238.10954-1-shawn@....icu
> Link: https://lkml.kernel.org/n/tip-289f1jice17ta7tr3tstm9jm@git.kernel.org
> Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> ---
>  tools/perf/util/data-convert-bt.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/data-convert-bt.c b/tools/perf/util/data-convert-bt.c
> index e0311c9750ad..9097543a818b 100644
> --- a/tools/perf/util/data-convert-bt.c
> +++ b/tools/perf/util/data-convert-bt.c
> @@ -271,7 +271,7 @@ static int string_set_value(struct bt_ctf_field *field, const char *string)
>                                 if (i > 0)
>                                         strncpy(buffer, string, i);
>                         }
> -                       strncat(buffer + p, numstr, 4);
> +                       memcpy(buffer + p, numstr, 4);
I took care to have enough context in my patch that you could see what
was going on. I wonder if there is a way to make that care
propate when people add Signed-off-by: lines.
>                         p += 3;
>                 }
>         }
> --
> 2.20.1
>