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

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Message-ID: <CAK8P3a0jd9iBPd-S8R-Wn4Bb=w_C8gcMcDb6ZrD=WS3qPKxOUw@mail.gmail.com>
Date:   Tue, 25 Jul 2017 16:51:33 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     Alexander Potapenko <glider@...gle.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 Tue, Jul 25, 2017 at 2:06 PM, Andrey Ryabinin
<aryabinin@...tuozzo.com> wrote:
> On 07/25/2017 10:17 AM, Arnd Bergmann wrote:
>> On Mon, Jul 24, 2017 at 1:35 PM, Alexander Potapenko <glider@...gle.com> wrote:
>>> On Fri, Jul 21, 2017 at 11:02 PM, Arnd Bergmann <arnd@...db.de> wrote:
>>
>>>> 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?
>>
>> I'm just trying to shut up a particular warning here where gcc can't figure out
>> by itself that it is initialized. Setting an invalid address at
>> allocation time would
>> prevent gcc from warning even for any trivial bug where we use the incorrect
>> value in the normal code path, in case someone later wants to modify the
>> code further and makes a mistake.
>>
>
> 'info->first_bad_addr' could be initialized to the correct value. That would be 'addr' itself
> for 'wild' type of bugs.
> Initialization in get_wild_bug_type() looks a bit odd and off-place.

Yes, that makes sense. I'll send a new version then.

        Arnd