From: Rikard Falkeborn <rikard.falkeborn@gmail.com>
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Rikard Falkeborn <rikard.falkeborn@gmail.com>,
Emil Velikov <emil.l.velikov@gmail.com>,
Syed Nayyar Waris <syednwaris@gmail.com>,
Masahiro Yamada <yamada.masahiro@socionext.com>,
Kees Cook <keescook@chromium.org>,
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: Wed, 3 Jun 2020 23:53:14 +0200 [thread overview]
Message-ID: <20200603215314.GA916134@rikard> (raw)
In-Reply-To: <CAHp75VdUf8=y+y4Q3OtWc7owxg0uX8LhZY4Nrgnezuv+aSyzUg@mail.gmail.com>
On Wed, Jun 03, 2020 at 11:49:37AM +0300, Andy Shevchenko wrote:
> On Tue, Jun 2, 2020 at 10:01 PM Rikard Falkeborn
> <rikard.falkeborn@gmail.com> wrote:
> > On Mon, Jun 01, 2020 at 11:33:30AM +0300, Andy Shevchenko wrote:
> > > On Mon, Jun 01, 2020 at 12:37:16AM +0200, Rikard Falkeborn wrote:
> > > > On Sun, May 31, 2020 at 02:00:45PM +0300, Andy Shevchenko wrote:
>
> ...
>
> > > > If we cast to int, we don't need to worry about the signedness. If
> > > > someone enters a value that can't be cast to int, there will still
> > > > be a compiler warning about shift out of range.
> > >
> > > If the argument unsigned long long will it be the warning (it should not)?
> >
> > No, there should be no warning there.
> >
> > The inputs to GENMASK() needs to be between 0 and 31 (or 63 depending on the
> > size of unsigned long). For any other values, there will be undefined behaviour,
> > since the operands to the shifts in __GENMASK will be too large (or negative).
>
> What I'm implying here that argument may be not constant, and compiler
> can't know their values at hand.
> So, in the following snippet
>
> foo(unsigned long long x)
> {
> u32 y;
> y = GENMASK(x, 0);
> }
>
> when you cast x to int wouldn't be a warning of possible value
> reduction (even if we know that it won't be higher than 63/31)?
Got it, no I was unable to trigger any warnings like that (but I still
can't reproduce to original warning, so take that with a grain of salt).
I'd be very surprised if compilers warned for explicit casts but I'll
send a proper patch soon to let the build robot try it.
Rikard
>
> --
> With Best Regards,
> Andy Shevchenko
next prev parent reply other threads:[~2020-06-03 21:53 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
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 [this message]
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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