From: Rikard Falkeborn <rikard.falkeborn@gmail.com>
To: Guenter Roeck <linux@roeck-us.net>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>,
Rikard Falkeborn <rikard.falkeborn@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Joe Perches <joe@perches.com>,
Johannes Berg <johannes@sipsolutions.net>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 2/2] linux/bits.h: Add compile time sanity check of GENMASK inputs
Date: Wed, 7 Aug 2019 22:07:53 +0200 [thread overview]
Message-ID: <20190807200753.GA14779@rikard> (raw)
In-Reply-To: <d1bd1c05-3e92-1a7f-ebd3-3b26981a6f8e@roeck-us.net>
On Wed, Aug 07, 2019 at 09:52:33AM -0700, Guenter Roeck wrote:
> On 8/7/19 7:55 AM, Masahiro Yamada wrote:
> > On Wed, Aug 7, 2019 at 11:27 PM Guenter Roeck <linux@roeck-us.net> wrote:
> > >
> > > On Fri, Aug 02, 2019 at 01:03:58AM +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_ON_ZERO() must be
> > > > used instead of BUILD_BUG_ON(), and __is_constexpr() must be used instead
> > > > of __builtin_constant_p().
> > > >
> > > > If successful, BUILD_BUG_OR_ZERO() returns 0 of type size_t. To avoid
> > > > problems with implicit conversions, cast the result of BUILD_BUG_OR_ZERO
> > > > to unsigned long.
> > > >
> > > > Since both BUILD_BUG_ON_ZERO() and __is_constexpr() only uses sizeof()
> > > > on the arguments passed to them, neither of them evaluate the expression
> > > > unless it is a VLA. Therefore, GENMASK(1, x++) still behaves as
> > > > expected.
> > > >
> > > > 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.
> > > >
> > >
> > > Who is going to fix the fallout ? For example, arm64:defconfig no longer
> > > compiles with this patch applied.
> > >
> > > It seems to me that the benefit of catching misuses of GENMASK is much
> > > less than the fallout from no longer compiling kernels, since those
> > > kernels won't get any test coverage at all anymore.
> >
> >
> > We cannot apply this until we fix all errors.
> >
> > I do not understand why Andrew picked up this so soon.
> >
>
> The same was done with the fallthrough warning in mainline, which still results
> in all "sh" builds failing there (and in -next, obviously). I don't understand
> the logic either, but maybe it is the new normal.
>
> Guenter
Sorry about that. As Masahiro said, the patch was picked up too soon,
I've asked Andrew and Stephen Rothwell to remove the patch in a separate
email thread.
FWIW, there seems to be a patch for the build failure already (all arm
builds seems to have the same build error):
https://lore.kernel.org/lkml/20190807192305.6604-1-natechancellor@gmail.com/T/#u
Rikard
next prev parent reply other threads:[~2019-08-07 20:08 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
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 [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190807200753.GA14779@rikard \
--to=rikard.falkeborn@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=joe@perches.com \
--cc=johannes@sipsolutions.net \
--cc=linux-kernel@vger.kernel.org \
--cc=linux@roeck-us.net \
--cc=yamada.masahiro@socionext.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).