From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Syed Nayyar Waris <syednwaris@gmail.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Linus Walleij <linus.walleij@linaro.org>,
Andrew Morton <akpm@linux-foundation.org>,
William Breathitt Gray <vilhelm.gray@gmail.com>,
Arnd Bergmann <arnd@arndb.de>,
Linux-Arch <linux-arch@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v7 1/4] bitops: Introduce the the for_each_set_clump macro
Date: Sat, 30 May 2020 01:07:51 +0300 [thread overview]
Message-ID: <CAHp75VfGCLSOwPtygG7Vq8RLhvA3_3EcB-WRCXZzR=jzOP6DsA@mail.gmail.com> (raw)
In-Reply-To: <CAHp75Vdv4V5PLQxM1+ypHacso6rrR6CiXTX43M=6UuZ6xbYY7g@mail.gmail.com>
On Sat, May 30, 2020 at 12:42 AM Andy Shevchenko
<andy.shevchenko@gmail.com> wrote:
> On Fri, May 29, 2020 at 11:07 PM Syed Nayyar Waris <syednwaris@gmail.com> wrote:
> > On Sat, May 30, 2020 at 12:08 AM Andy Shevchenko
> > <andriy.shevchenko@linux.intel.com> wrote:
...
> > Explanation:
> > Actually when nbits (clump size) is 64 (BITS_PER_LONG is 64 on my computer),
> > (BIT(nbits) - 1)
> > gives a value of zero and when this zero is ANDed with any value, it
> > makes it full zero. This is unexpected and incorrect calculation happening.
> >
> > What actually happens is in the macro expansion of BIT(64), that is 1
> > << 64, the '1' overflows from leftmost bit position (most significant
> > bit) and re-enters at the rightmost bit position (least significant
> > bit), therefore 1 << 64 becomes '0x1', and when another '1' is
> > subtracted from this, the final result becomes 0.
> >
> > Since this macro is being used in both bitmap_get_value and
> > bitmap_set_value functions, it will give unexpected results when nbits or clump
> > size is BITS_PER_LONG (32 or 64 depending on arch).
>
> I see, something like
> https://elixir.bootlin.com/linux/latest/source/include/linux/dma-mapping.h#L139
> should be done.
> But yes, let's try to fix GENMASK().
>
> So, if we modify the following
>
> #define GENMASK_INPUT_CHECK(h, l) \
> (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
> __builtin_constant_p((l) > (h)), (l) > (h), 0)))
>
> to be
>
> #define GENMASK_INPUT_CHECK(h, l) \
> (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
> __builtin_constant_p((l) > (h)), (l) ? (l) > (h) : 0, 0)))
>
> would it work?
Actually it needs an amendment for signed types...
(l) ? (l) > (h) : !((h) > 0)
...but today is Friday night, so, mistakes are warranted :-)
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2020-05-29 22:08 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-24 5:00 [PATCH v7 0/4] Introduce the for_each_set_clump macro Syed Nayyar Waris
2020-05-24 5:01 ` [PATCH v7 1/4] bitops: Introduce the " Syed Nayyar Waris
2020-05-24 14:44 ` kbuild test robot
2020-05-29 18:08 ` Syed Nayyar Waris
2020-05-29 18:38 ` Andy Shevchenko
2020-05-29 20:02 ` Syed Nayyar Waris
2020-05-29 21:31 ` William Breathitt Gray
2020-05-29 21:53 ` Syed Nayyar Waris
2020-05-29 21:42 ` Andy Shevchenko
2020-05-29 22:07 ` Andy Shevchenko [this message]
2020-05-29 22:11 ` Syed Nayyar Waris
2020-05-29 22:19 ` Andy Shevchenko
2020-05-30 8:45 ` Syed Nayyar Waris
2020-05-30 9:20 ` Andy Shevchenko
2020-05-31 1:11 ` Syed Nayyar Waris
2020-05-31 11:00 ` Andy Shevchenko
2020-05-31 22:37 ` Rikard Falkeborn
2020-06-01 0:31 ` Syed Nayyar Waris
2020-06-01 8:33 ` Andy Shevchenko
2020-06-02 19:01 ` Rikard Falkeborn
2020-06-03 8:49 ` Andy Shevchenko
2020-06-03 21:53 ` Rikard Falkeborn
2020-06-03 21:58 ` Andy Shevchenko
2020-06-03 21:59 ` Andy Shevchenko
2020-06-03 22:02 ` [PATCH] linux/bits.h: fix unsigned less than zero warnings Rikard Falkeborn
2020-06-04 6:41 ` Andy Shevchenko
2020-06-04 16:49 ` Joe Perches
2020-06-04 23:30 ` Rikard Falkeborn
2020-06-07 20:34 ` [PATCH v2 1/2] " Rikard Falkeborn
2020-06-07 20:34 ` [PATCH v2 2/2] bits: Add tests of GENMASK Rikard Falkeborn
2020-06-08 7:33 ` Geert Uytterhoeven
2020-06-08 18:42 ` Rikard Falkeborn
2020-06-08 22:18 ` [PATCH v3 1/2] linux/bits.h: fix unsigned less than zero warnings Rikard Falkeborn
2020-06-08 22:18 ` [PATCH v3 2/2] bits: Add tests of GENMASK Rikard Falkeborn
2020-06-09 14:11 ` Andy Shevchenko
2020-06-21 4:36 ` Andrew Morton
2020-06-21 5:42 ` [PATCH v4 1/2] linux/bits.h: fix unsigned less than zero warnings Rikard Falkeborn
2020-06-21 5:42 ` [PATCH v4 2/2] bits: Add tests of GENMASK Rikard Falkeborn
2021-04-22 19:40 ` Nico Pache
2021-04-22 21:30 ` Nico Pache
2020-07-09 12:30 ` [PATCH v4 1/2] linux/bits.h: fix unsigned less than zero warnings Herbert Xu
2020-07-09 18:13 ` Linus Torvalds
2020-07-10 6:38 ` Herbert Xu
2020-06-15 19:52 ` [PATCH v3 " Emil Velikov
2020-06-08 8:08 ` [PATCH v2 2/2] bits: Add tests of GENMASK Andy Shevchenko
2020-06-08 8:08 ` Andy Shevchenko
2020-06-08 18:44 ` Rikard Falkeborn
2020-06-08 11:09 ` [PATCH v2 1/2] linux/bits.h: fix unsigned less than zero warnings Andy Shevchenko
2020-05-24 5:04 ` [PATCH v7 2/4] lib/test_bitmap.c: Add for_each_set_clump test cases Syed Nayyar Waris
2020-05-30 19:20 ` kbuild test robot
2020-06-04 20:42 ` Syed Nayyar Waris
2020-06-05 12:24 ` Andy Shevchenko
2020-06-06 23:15 ` Syed Nayyar Waris
2020-06-08 13:18 ` Andy Shevchenko
2020-06-10 5:38 ` Rong Chen
2020-05-24 5:05 ` [PATCH v7 3/4] gpio: thunderx: Utilize for_each_set_clump macro Syed Nayyar Waris
2020-05-24 5:06 ` [PATCH v7 4/4] gpio: xilinx: " Syed Nayyar Waris
2020-05-25 9:36 ` [PATCH v7 0/4] Introduce the " Bartosz Golaszewski
2020-06-15 12:46 ` Syed Nayyar Waris
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