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

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Message-ID: <b56efb52-2458-4d2d-f9d9-4bb2907e52dc@virtuozzo.com>
Date:   Tue, 25 Jul 2017 15:06:18 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Arnd Bergmann <arnd@...db.de>,
        Alexander Potapenko <glider@...gle.com>
Cc:     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 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.