linux-kernel - Re: [PATCH] [v2] kasan: avoid -Wmaybe-uninitialized warning

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Date:   Mon, 24 Jul 2017 13:35:11 +0200
From:   Alexander Potapenko <glider@...gle.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [v2] kasan: avoid -Wmaybe-uninitialized warning

On Fri, Jul 21, 2017 at 11:02 PM, Arnd Bergmann <arnd@...db.de> wrote:
> gcc-7 produces this warning:
>
> mm/kasan/report.c: In function 'kasan_report':
> mm/kasan/report.c:351:3: error: 'info.first_bad_addr' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>    print_shadow_for_address(info->first_bad_addr);
>    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> mm/kasan/report.c:360:27: note: 'info.first_bad_addr' was declared here
>
> The code seems fine as we only print info.first_bad_addr when there is a shadow,
> and we always initialize it in that case, but this is relatively hard
> for gcc to figure out after the latest rework. Adding an intialization
> in the other code path gets rid of the warning.
>
> Fixes: b235b9808664 ("kasan: unify report headers")
> Link: https://patchwork.kernel.org/patch/9641417/
> Acked-by: Dmitry Vyukov <dvyukov@...gle.com>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> Originally submitted on March 23, but unfortunately is still needed,
> as verified on 4.13-rc1, with aarch64-linux-gcc-7.1.1
>
> v2: add a comment as Andrew suggested
> ---
>  mm/kasan/report.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index 04bb1d3eb9ec..28fb222ab149 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -111,6 +111,9 @@ static const char *get_wild_bug_type(struct kasan_access_info *info)
>  {
>         const char *bug_type = "unknown-crash";
>
> +       /* shut up spurious -Wmaybe-uninitialized warning */
> +       info->first_bad_addr = (void *)(-1ul);
> +
Why don't we initialize info.first_bad_addr in kasan_report(), where
info is allocated?
>         if ((unsigned long)info->access_addr < PAGE_SIZE)
>                 bug_type = "null-ptr-deref";
>         else if ((unsigned long)info->access_addr < TASK_SIZE)
> --
> 2.9.0
>



-- 
Alexander Potapenko
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