From: Masahiro Yamada <yamada.masahiro@socionext.com>
To: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Cc: Joe Perches <joe@perches.com>,
Andrew Morton <akpm@linux-foundation.org>,
Johannes Berg <johannes@sipsolutions.net>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] linux/bits.h: Add compile time sanity check of GENMASK inputs
Date: Sat, 3 Aug 2019 12:03:13 +0900 [thread overview]
Message-ID: <CAK7LNAT+cNxna4SER04MdkBsq_LDg4TwYR_U1ioNNxYOZWXigA@mail.gmail.com> (raw)
In-Reply-To: <20190802181853.GA809@rikard>
On Sat, Aug 3, 2019 at 3:19 AM Rikard Falkeborn
<rikard.falkeborn@gmail.com> wrote:
>
> On Fri, Aug 02, 2019 at 12:25:06PM +0900, Masahiro Yamada wrote:
> > On Fri, Aug 2, 2019 at 12:14 PM Joe Perches <joe@perches.com> wrote:
> > >
> > > On Fri, 2019-08-02 at 10:40 +0900, Masahiro Yamada wrote:
> > > > On Thu, Aug 1, 2019 at 4:27 AM Joe Perches <joe@perches.com> wrote:
> > > > > On Wed, 2019-07-31 at 21:03 +0200, Rikard Falkeborn wrote:
> > > > > > GENMASK() and GENMASK_ULL() are supposed to be called with the high bit
> > > > > > as the first argument and the low bit as the second argument. Mixing
> > > > > > them will return a mask with zero bits set.
> > > > > >
> > > > > > Recent commits show getting this wrong is not uncommon, see e.g.
> > > > > > commit aa4c0c9091b0 ("net: stmmac: Fix misuses of GENMASK macro") and
> > > > > > commit 9bdd7bb3a844 ("clocksource/drivers/npcm: Fix misuse of GENMASK
> > > > > > macro").
> > > > > >
> > > > > > To prevent such mistakes from appearing again, add compile time sanity
> > > > > > checking to the arguments of GENMASK() and GENMASK_ULL(). If both the
> > > > > > arguments are known at compile time, and the low bit is higher than the
> > > > > > high bit, break the build to detect the mistake immediately.
> > > > > >
> > > > > > Since GENMASK() is used in declarations, BUILD_BUG_OR_ZERO() must be
> > > > > > used instead of BUILD_BUG_ON(), and __is_constexpr() must be used instead
> > > > > > of __builtin_constant_p().
> > > > > >
> > > > > > Commit 95b980d62d52 ("linux/bits.h: make BIT(), GENMASK(), and friends
> > > > > > available in assembly") made the macros in linux/bits.h available in
> > > > > > assembly. Since neither BUILD_BUG_OR_ZERO() or __is_constexpr() are asm
> > > > > > compatible, disable the checks if the file is included in an asm file.
> > > > > >
> > > > > > Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
> > > > > > ---
> > > > > > Joe Perches sent a series to fix the existing misuses of GENMASK() that
> > > > > > needs to be merged before this to avoid build failures. Currently, 7 of
> > > > > > the patches were not in Linus tree, and 2 were not in linux-next.
> > > > > >
> > > > > > Also, there's currently no asm users of bits.h, but since it was made
> > > > > > asm-compatible just two weeks ago it would be a shame to break it right
> > > > > > away...
> > > > > []
> > > > > > diff --git a/include/linux/bits.h b/include/linux/bits.h
> > > > > []
> > > > > > @@ -18,12 +18,22 @@
> > > > > > * position @h. For example
> > > > > > * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000.
> > > > > > */
> > > > > > +#ifndef __ASSEMBLY__
> > > > > > +#include <linux/build_bug.h>
> > > > > > +#define GENMASK_INPUT_CHECK(h, l) BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
> > > > > > + __is_constexpr(h) && __is_constexpr(l), (l) > (h), 0))
> > > > > > +#else
> > > > > > +#define GENMASK_INPUT_CHECK(h, l) 0
> > > > >
> > > > > A few things:
> > > > >
> > > > > o Reading the final code is a bit confusing.
> > > > > Perhaps add a comment description saying it's not checked
> > > > > in asm .h uses.
> > > > >
> > > > > o Maybe use:
> > > > > #define GENMASK_INPUT_CHECK(h, l) UL(0)
> > > >
> > > > Why?
> > >
> > > Consistency with the uses in what's now called __GENMASK
> >
> > Inconsistent with __GENMASK_ULL.
>
> Would you prefer to add GENMASK_ULL_INPUT_CHECK?
No.
> Or replace UL(0) with
> 0 and then probably move the cast of BUILD_BUG_OR_ZERO (to avoid
> GENMASK be of type size_t) to GENMASK and GENMASK_ULL?
No.
Your original code is absolutely fine.
C aligns the types to the wider one.
(unsigned long) + (int) -> (unsigned long)
(unsigned long long) + (int) -> (unsigned long long)
Having GENMASK_INPUT_CHECK to return 'int' is OK.
The resulted GENMASK(), GENMASK_ULL() still
have unsigned long, unsigned long long, respectively.
BTW, v2 is already inconsistent.
If you wanted GENMASK_INPUT_CHECK() to return 'unsigned long',,
you would have to cast (low) > (high) as well:
(unsigned long)((low) > (high)), UL(0))))
This is totally redundant, and weird.
--
Best Regards
Masahiro Yamada
next prev parent reply other threads:[~2019-08-03 3:12 UTC|newest]
Thread overview: 109+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20190710050444epcas1p250f7aa0f8798a7757df51d66f5970c2a@epcas1p2.samsung.com>
2019-07-10 5:04 ` [PATCH 00/12] treewide: Fix GENMASK misuses Joe Perches
2019-07-10 5:04 ` [PATCH 01/12] checkpatch: Add GENMASK tests Joe Perches
2019-07-24 18:03 ` Joe Perches
2019-07-10 5:04 ` [PATCH 02/12] clocksource/drivers/npcm: Fix misuse of GENMASK macro Joe Perches
2019-07-10 9:10 ` [tip:timers/urgent] " tip-bot for Joe Perches
2019-07-15 10:00 ` [PATCH 02/12] " Avi Fishman
2019-07-10 5:04 ` [PATCH 03/12] drm: aspeed_gfx: " Joe Perches
2019-07-24 17:16 ` Joe Perches
2019-07-25 1:10 ` Andrew Jeffery
2019-07-25 1:18 ` Joe Perches
2019-07-25 2:52 ` Joel Stanley
2019-07-25 14:37 ` Joe Perches
2019-07-10 5:04 ` [PATCH 04/12] iio: adc: max9611: " Joe Perches
2019-07-14 11:54 ` Jonathan Cameron
2019-07-14 12:19 ` Joe Perches
2019-07-14 14:37 ` Jacopo Mondi
2019-07-29 21:52 ` Jacopo Mondi
2019-07-31 8:37 ` Jonathan Cameron
2019-07-10 5:04 ` [PATCH 05/12] irqchip/gic-v3-its: " Joe Perches
2019-07-10 8:28 ` Marc Zyngier
2019-07-10 9:07 ` [tip:irq/urgent] " tip-bot for Joe Perches
2019-07-10 5:04 ` [PATCH 06/12] mmc: meson-mx-sdio: " Joe Perches
2019-07-22 7:23 ` Neil Armstrong
2019-07-22 13:43 ` Ulf Hansson
2019-07-10 5:04 ` [PATCH 07/12] net: ethernet: mediatek: Fix misuses " Joe Perches
2019-07-10 5:04 ` [PATCH 08/12] net: stmmac: " Joe Perches
2019-07-10 10:33 ` Jose Abreu
2019-07-10 5:04 ` [PATCH 09/12] rtw88: Fix misuse " Joe Perches
2019-07-10 5:07 ` Tony Chuang
2019-07-24 11:48 ` Kalle Valo
2019-07-10 5:04 ` [PATCH 10/12] phy: amlogic: G12A: " Joe Perches
2019-07-22 7:23 ` Neil Armstrong
2019-08-23 2:41 ` Kishon Vijay Abraham I
2019-08-23 4:59 ` Joe Perches
2019-07-10 5:04 ` [PATCH 11/12] staging: media: cedrus: " Joe Perches
2019-07-10 7:23 ` Paul Kocialkowski
2019-07-24 17:09 ` Joe Perches
2019-07-24 18:35 ` Greg Kroah-Hartman
2019-07-24 18:39 ` Joe Perches
2019-07-24 18:55 ` Greg Kroah-Hartman
2019-07-25 6:46 ` Hans Verkuil
2019-07-10 5:04 ` [PATCH 12/12] ASoC: wcd9335: " Joe Perches
2019-07-22 12:22 ` Applied "ASoC: wcd9335: Fix misuse of GENMASK macro" to the asoc tree Mark Brown
2019-07-10 9:17 ` [PATCH 00/12] treewide: Fix GENMASK misuses Johannes Berg
2019-07-10 9:43 ` Russell King - ARM Linux admin
2019-07-10 15:45 ` Joe Perches
2019-07-10 16:01 ` Joe Perches
2019-07-27 19:54 ` Rikard Falkeborn
2019-07-28 23:45 ` Joe Perches
2019-07-31 19:03 ` [PATCH] linux/bits.h: Add compile time sanity check of GENMASK inputs Rikard Falkeborn
2019-07-31 19:27 ` Joe Perches
2019-08-01 23:03 ` Rikard Falkeborn
2019-08-02 1:40 ` Masahiro Yamada
2019-08-02 3:13 ` Joe Perches
2019-08-02 3:25 ` Masahiro Yamada
2019-08-02 18:18 ` Rikard Falkeborn
2019-08-03 3:03 ` Masahiro Yamada [this message]
2019-08-03 3:12 ` Masahiro Yamada
2019-08-03 18:36 ` Rikard Falkeborn
2019-08-04 6:45 ` Masahiro Yamada
2019-08-05 19:55 ` Rikard Falkeborn
2019-08-06 15:19 ` Masahiro Yamada
2019-08-06 19:27 ` Rikard Falkeborn
2019-08-06 21:15 ` Joe Perches
2019-08-07 20:53 ` Rikard Falkeborn
2019-08-01 2:50 ` Masahiro Yamada
2019-08-01 2:57 ` Joe Perches
2019-08-01 23:03 ` Rikard Falkeborn
2019-08-01 23:03 ` [PATCH v2 1/2] linux/bits.h: Clarify macro argument names Rikard Falkeborn
2019-08-01 23:03 ` [PATCH v2 2/2] linux/bits.h: Add compile time sanity check of GENMASK inputs Rikard Falkeborn
2019-08-01 23:14 ` Joe Perches
2019-08-07 14:27 ` Guenter Roeck
2019-08-07 14:55 ` Masahiro Yamada
2019-08-07 16:52 ` Guenter Roeck
2019-08-07 20:07 ` Rikard Falkeborn
2019-08-08 0:07 ` Joe Perches
2019-08-08 0:58 ` Guenter Roeck
2019-08-08 1:08 ` Joe Perches
2019-08-08 1:53 ` Guenter Roeck
2019-08-08 2:44 ` kbuild test robot
2019-08-08 2:44 ` kbuild test robot
2019-08-08 3:46 ` [PATCH v2 1/2] linux/bits.h: Clarify macro argument names Masahiro Yamada
2019-08-10 18:43 ` Rikard Falkeborn
2019-08-10 19:20 ` Joe Perches
2019-08-11 18:49 ` [PATCH v3 0/3] Add compile time sanity check of GENMASK inputs Rikard Falkeborn
2019-08-11 18:49 ` [PATCH v3 1/3] x86/boot: Use common BUILD_BUG_ON Rikard Falkeborn
2019-08-12 18:19 ` [tip:x86/boot] " tip-bot for Rikard Falkeborn
2019-08-16 12:19 ` tip-bot for Rikard Falkeborn
2019-08-11 18:49 ` [PATCH v3 2/3] linux/build_bug.h: Change type to int Rikard Falkeborn
2019-10-06 2:26 ` Masahiro Yamada
2019-08-11 18:49 ` [PATCH v3 3/3] linux/bits.h: Add compile time sanity check of GENMASK inputs Rikard Falkeborn
2019-10-06 2:30 ` Masahiro Yamada
2019-10-08 7:23 ` Geert Uytterhoeven
2019-10-08 7:44 ` Masahiro Yamada
2019-10-08 7:52 ` Masahiro Yamada
2019-10-08 19:06 ` Rikard Falkeborn
2019-08-12 17:58 ` [PATCH v3 0/3] " Kees Cook
2019-10-05 19:46 ` Rikard Falkeborn
2019-10-09 21:45 ` [Patch v4 0/2] " Rikard Falkeborn
2019-10-09 21:45 ` [Patch v4 1/2] linux/build_bug.h: Change type to int Rikard Falkeborn
2019-10-09 21:45 ` [Patch v4 2/2] linux/bits.h: Add compile time sanity check of GENMASK inputs Rikard Falkeborn
2019-10-10 2:24 ` Masahiro Yamada
2019-10-12 2:27 ` Andrew Morton
2019-10-22 19:53 ` Rikard Falkeborn
2019-11-01 21:28 ` Rikard Falkeborn
2020-03-08 19:39 ` [PATCH v5] " Rikard Falkeborn
2020-03-09 16:40 ` Kees Cook
2019-07-11 21:30 ` [PATCH 00/12] treewide: Fix GENMASK misuses David Miller
2019-07-12 12:54 ` Andrzej Hajda
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