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

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Message-ID: <CAK8P3a0prDzKW=yoosY0oPQagDkfpmKy7jny6CUaA9Xi_U0e4A@mail.gmail.com>
Date:   Tue, 25 Jul 2017 09:17:32 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Alexander Potapenko <glider@...gle.com>
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 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.

       Arnd