linux-kernel - Re: [PATCH] char: pcmcia: remove set but not used variable 'tmp'

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Message-ID: <CAK8P3a01oF7QZzjbd703QwiK+6ZPx1w-fSBcLjeMm4KQ0X0amw@mail.gmail.com>
Date:   Fri, 14 May 2021 08:28:17 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Yu Kuai <yukuai3@...wei.com>
Cc:     Harald Welte <laforge@...monks.org>,
        gregkh <gregkh@...uxfoundation.org>, akpm@...l.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "zhangyi (F)" <yi.zhang@...wei.com>
Subject: Re: [PATCH] char: pcmcia: remove set but not used variable 'tmp'

On Fri, May 14, 2021 at 8:21 AM Yu Kuai <yukuai3@...wei.com> wrote:
>
> Fixes gcc '-Wunused-but-set-variable' warning:
>
> drivers/char/pcmcia/cm4000_cs.c:1053:16: warning: variable ‘tmp’
> set but not used [-Wunused-but-set-variable]
>
> It is never used and so can be removed.
>
> Fixes: c1986ee9bea3 ("[PATCH] New Omnikey Cardman 4000 driver")
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>

Looks good to me. This was likely written that way at a time when some
architecture implemented inb() as a macro, and ignoring its value
would cause a different warning.

Since you are already touching this file, can you have a look at this
warning as well:

   drivers/char/pcmcia/cm4000_cs.c: In function 'set_protocol':
>> drivers/char/pcmcia/cm4000_cs.c:569:16: warning: iteration 4 invokes undefined behavior [-Waggressive-loop-optimizations]
     569 |   pts_reply[i] = inb(REG_BUF_DATA(iobase));
         |   ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
   drivers/char/pcmcia/cm4000_cs.c:567:2: note: within this loop
     567 |  for (i = 0; i < num_bytes_read; i++) {

This looks like a preexisting problem that was uncovered by a patch
that is now in linux-next to change the inb() definition once more,
I got a report from the kernel build bot about it after I merged the
patch into the asm-generic tree. It needs a range check on
num_bytes_read, or a Kconfig check to ensure it is not built on
architectures without working inb()/outb() operations.

        Arnd