From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Colin King <colin.king@canonical.com>,
Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>,
Srinivas Neeli <srinivas.neeli@xilinx.com>,
Michal Simek <michal.simek@xilinx.com>,
Linus Walleij <linus.walleij@linaro.org>,
Bartosz Golaszewski <bgolaszewski@baylibre.com>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
linux-arm Mailing List <linux-arm-kernel@lists.infradead.org>,
kernel-janitors <kernel-janitors@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH][next] gpio: xilinx: Fix potential integer overflow on shift of a u32 int
Date: Mon, 17 May 2021 10:07:20 +0300 [thread overview]
Message-ID: <CAHp75Ve-YWh_sfupwQV0xxL7Vk8GNObJ+6O29RqRMXCgAmemCw@mail.gmail.com> (raw)
In-Reply-To: <20210514053754.GZ1955@kadam>
On Fri, May 14, 2021 at 12:26 PM Dan Carpenter <dan.carpenter@oracle.com> wrote:
> On Thu, May 13, 2021 at 09:52:27AM +0100, Colin King wrote:
...
> > const unsigned long offset = (bit % BITS_PER_LONG) & BIT(5);
> >
> > map[index] &= ~(0xFFFFFFFFul << offset);
> > - map[index] |= v << offset;
> > + map[index] |= (unsigned long)v << offset;
>
> Doing a shift by BIT(5) is super weird.
Not the first place in the kernel with such a trick.
> It looks like a double shift
> bug and should probably trigger a static checker warning. It's like
> when people do BIT(BIT(5)).
>
> It would be more readable to write it as:
>
> int shift = (bit % BITS_PER_LONG) ? 32 : 0;
Usually this code is in a kinda fast path. Have you checked if the
compiler generates the same or better code when you are using ternary?
--
With Best Regards,
Andy Shevchenko
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next prev parent reply other threads:[~2021-05-17 7:13 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-13 8:52 [PATCH][next] gpio: xilinx: Fix potential integer overflow on shift of a u32 int Colin King
2021-05-13 9:10 ` David Laight
2021-05-17 7:04 ` Andy Shevchenko
2021-05-14 5:37 ` Dan Carpenter
2021-05-17 7:07 ` Andy Shevchenko [this message]
2021-05-17 13:36 ` Dan Carpenter
2021-05-17 13:49 ` Andy Shevchenko
2021-05-17 7:03 ` Andy Shevchenko
2021-05-17 7:32 ` Andy Shevchenko
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