Re: [PATCH 04/10] linux/bits.h: simplify GENMASK_INPUT_CHECK() by using is_const_true()

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To: David Laight <David.Laight@xxxxxxxxxx>
Subject: Re: [PATCH 04/10] linux/bits.h: simplify GENMASK_INPUT_CHECK() by using is_const_true()
From: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
Date: Fri, 6 Dec 2024 00:49:43 +0900
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>, Nathan Chancellor <nathan@xxxxxxxxxx>, Nick Desaulniers <ndesaulniers@xxxxxxxxxx>, Bill Wendling <morbo@xxxxxxxxxx>, Justin Stitt <justinstitt@xxxxxxxxxx>, Yury Norov <yury.norov@xxxxxxxxx>, Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>, Kees Cook <kees@xxxxxxxxxx>, "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>, Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>, Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>, Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>, Tvrtko Ursulin <tursulin@xxxxxxxxxxx>, David Airlie <airlied@xxxxxxxxx>, Simona Vetter <simona@xxxxxxxx>, Suzuki K Poulose <suzuki.poulose@xxxxxxx>, Mike Leach <mike.leach@xxxxxxxxxx>, James Clark <james.clark@xxxxxxxxxx>, Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>, Rikard Falkeborn <rikard.falkeborn@xxxxxxxxx>, Martin Uecker <Martin.Uecker@xxxxxxxxxxxxxxxxxxxxx>, "linux-sparse@xxxxxxxxxxxxxxx" <linux-sparse@xxxxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, "llvm@xxxxxxxxxxxxxxx" <llvm@xxxxxxxxxxxxxxx>, "linux-hardening@xxxxxxxxxxxxxxx" <linux-hardening@xxxxxxxxxxxxxxx>, "intel-gfx@xxxxxxxxxxxxxxxxxxxxx" <intel-gfx@xxxxxxxxxxxxxxxxxxxxx>, "dri-devel@xxxxxxxxxxxxxxxxxxxxx" <dri-devel@xxxxxxxxxxxxxxxxxxxxx>, "coresight@xxxxxxxxxxxxxxxx" <coresight@xxxxxxxxxxxxxxxx>, "linux-arm-kernel@xxxxxxxxxxxxxxxxxxx" <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>
In-reply-to: <dff4cdd543104e3792e4856375f310c1@AcuMS.aculab.com>
References: <20241203-is_constexpr-refactor-v1-0-4e4cbaecc216@wanadoo.fr> <20241203-is_constexpr-refactor-v1-4-4e4cbaecc216@wanadoo.fr> <dff4cdd543104e3792e4856375f310c1@AcuMS.aculab.com>

On Thu. 5 Dec 2024 at 03:52, David Laight <David.Laight@xxxxxxxxxx> wrote:
> From: Vincent Mailhol
> > Sent: 02 December 2024 17:33
> >
> >   __builtin_choose_expr(__is_constexpr((l) > (h)), (l) > (h), 0)
> >
> > is equivalent to:
> >
> >   is_const_true((l) > (h))
>
> Change it to BUILD_BUG_ON_MSG(statically_true((l) < (h)), "error message")
>
> and then fix all the fallout :-)

BUILD_BUG_ON_MSG() is not suitable for GENMASK_INPUT_CHECK. We need
one of the variants that returns zero here.

But I agree that it is good to have a more meaningful error message
here. I will use __BUILD_BUG_ON_ZERO_MSG() in v2.

Yours sincerely,
Vincent Mailhol

References:
- [PATCH 00/10] compiler.h: refactor __is_constexpr() into is_const{,_true,_false}()
  - From: Vincent Mailhol via B4 Relay
- [PATCH 04/10] linux/bits.h: simplify GENMASK_INPUT_CHECK() by using is_const_true()
  - From: Vincent Mailhol via B4 Relay
- RE: [PATCH 04/10] linux/bits.h: simplify GENMASK_INPUT_CHECK() by using is_const_true()
  - From: David Laight

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