linux-kernel - Re: [PATCH] [RESEND] floppy: fix harmless clang build warning

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Date:   Thu, 20 Jun 2019 01:36:43 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Arnd Bergmann <arnd@...db.de>, Jiri Kosina <jikos@...nel.org>
Cc:     Robert Elliott <elliott@....com>, Keith Busch <kbusch@...nel.org>,
        Hannes Reinecke <hare@...e.de>, Omar Sandoval <osandov@...com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Andy Whitcroft <apw@...onical.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [RESEND] floppy: fix harmless clang build warning

On 6/19/19 7:19 AM, Arnd Bergmann wrote:
> clang warns about unusual code in floppy.c that looks like it
> was intended to be a bit mask operation, checking for a specific
> bit in the UDP->cmos variable (FLOPPY1_TYPE expands to '4' on
> ARM):
> 
> drivers/block/floppy.c:3902:17: error: use of logical '&&' with constant operand [-Werror,-Wconstant-logical-operand]
>          if (!UDP->cmos && FLOPPY1_TYPE)
>                         ^  ~~~~~~~~~~~~
> drivers/block/floppy.c:3902:17: note: use '&' for a bitwise operation
>          if (!UDP->cmos && FLOPPY1_TYPE)
> 
> The check here is redundant anyway, if FLOPPY1_TYPE is zero, then
> assigning it to a zero UDP->cmos field does not change anything,
> so removing the extra check here has no effect other than shutting
> up the warning.
> 
> On x86, this will no longer read a hardware register, as the
> FLOPPY1_TYPE macro is not expanded if UDP->cmos is already
> zero, but the result is the same.

Applied, thanks.

-- 
Jens Axboe