linux-kernel - Re: [PATCH] mfd: arizona: fix undefined behavior

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Date:   Fri, 22 Mar 2019 17:03:33 +0000
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Lee Jones <lee.jones@...aro.org>,
        <clang-built-linux@...glegroups.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Sapthagiri Baratam <sapthagiri.baratam@...rus.com>,
        Colin Ian King <colin.king@...onical.com>,
        <patches@...nsource.cirrus.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mfd: arizona: fix undefined behavior

On Fri, Mar 22, 2019 at 03:33:37PM +0100, Arnd Bergmann wrote:
> When the driver is used with a subdevice that is disabled in the
> kernel configuration, clang gets a little confused about the
> control flow and fails to notice that n_subdevs is only
> uninitialized when subdevs is NULL, and we check for that,
> leading to a false-positive warning:
> 
> drivers/mfd/arizona-core.c:1423:19: error: variable 'n_subdevs' is uninitialized when used here
>       [-Werror,-Wuninitialized]
>                               subdevs, n_subdevs, NULL, 0, NULL);
>                                        ^~~~~~~~~
> drivers/mfd/arizona-core.c:999:15: note: initialize the variable 'n_subdevs' to silence this warning
>         int n_subdevs, ret, i;
>                      ^
>                       = 0
> 
> Ideally, we would rearrange the code to avoid all those early
> initializations and have an explicit exit in each disabled case,
> but it's much easier to chicken out and add one more initialization
> here to shut up the warning.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---

Acked-by: Charles Keepax <ckeepax@...nsource.cirrus.com>

Thanks,
Charles