linux-kernel - Re: [PATCH 00/10] compiler.h: refactor __is_constexpr() into is_const{,_true,

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Message-ID: <FBEB24FF-5885-4938-8D1C-9B7BA9071FB9@kernel.org>
Date: Thu, 05 Dec 2024 09:58:44 +1000
From: Kees Cook <kees@...nel.org>
To: mailhol.vincent@...adoo.fr,
 Vincent Mailhol via B4 Relay <devnull+mailhol.vincent.wanadoo.fr@...nel.org>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 David Laight <David.Laight@...lab.com>,
 Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
 Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling <morbo@...gle.com>,
 Justin Stitt <justinstitt@...gle.com>, Yury Norov <yury.norov@...il.com>,
 Rasmus Villemoes <linux@...musvillemoes.dk>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 Jani Nikula <jani.nikula@...ux.intel.com>,
 Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
 Rodrigo Vivi <rodrigo.vivi@...el.com>, Tvrtko Ursulin <tursulin@...ulin.net>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Suzuki K Poulose <suzuki.poulose@....com>,
 Mike Leach <mike.leach@...aro.org>, James Clark <james.clark@...aro.org>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Rikard Falkeborn <rikard.falkeborn@...il.com>,
 Martin Uecker <Martin.Uecker@....uni-goettingen.de>
CC: linux-sparse@...r.kernel.org, linux-kernel@...r.kernel.org,
 llvm@...ts.linux.dev, linux-hardening@...r.kernel.org,
 intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
 coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
 Vincent Mailhol <mailhol.vincent@...adoo.fr>
Subject: Re: [PATCH 00/10] compiler.h: refactor __is_constexpr() into is_const{,_true,_false}()

On December 3, 2024 3:33:22 AM GMT+10:00, Vincent Mailhol via B4 Relay <devnull+mailhol.vincent.wanadoo.fr@...nel.org> wrote:
>This series is the spiritual successor of [1] which introduced
>const_true(). In [1], following a comment from David Laight, Linus
>came with a suggestion to simplify __is_constexpr() and its derived
>macros using a _Generic() selection. Because of the total change of
>scope, I am starting a new series.
>
>The goal is to introduce a set of three macros:
>
>  - is_const(): a one to one replacement of __is_constexpr() in term
>    of features but written in a less hacky way thanks to _Generic().
>
>  - is_const_true(): tells whether or not the argument is a true
>    integer constant expression.
>
>  - is_const_false(): tells whether or not the argument is a false
>    integer constant expression.

But why make this change? Is something broken? Does it make builds faster?

> 7 files changed, 97 insertions(+), 84 deletions(-)

It makes the code larger too. I don't see what the benefit is, and given how much time has been spent making sure the existing stuff works correctly, I feel like we should have a clear benefit to replacing it all.

-Kees

-- 
Kees Cook