linux-kernel - Re: [PATCH 02/10] compiler.h: add is_const() as a replacement of __is

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Message-ID: <CAHk-=whzFAaksqMdYeYC=T82tny1HnGGcYu_xJTXZF1OZwVziQ@mail.gmail.com>
Date: Sat, 7 Dec 2024 12:31:09 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Martin Uecker <muecker@...g.de>
Cc: Vincent Mailhol <vincent.mailhol@...il.com>, David Laight <David.Laight@...lab.com>, 
	"w@....eu" <w@....eu>, 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>, 
	Kees Cook <kees@...nel.org>, "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>, 
	"linux-sparse@...r.kernel.org" <linux-sparse@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"llvm@...ts.linux.dev" <llvm@...ts.linux.dev>, 
	"linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>, 
	"intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>, 
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>, 
	"coresight@...ts.linaro.org" <coresight@...ts.linaro.org>, 
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 02/10] compiler.h: add is_const() as a replacement of __is_constexpr()

On Sat, 7 Dec 2024 at 11:51, Martin Uecker <muecker@...g.de> wrote:
>
> Am Samstag, dem 07.12.2024 um 10:19 -0800 schrieb Linus Torvalds:
> >
> > If there is one feature of C I would have liked it is "allow inline
> > functions and statement expressions with constant arguments as
> > constant expressions".
>
> There exist proposals along those lines for C2Y.
>
> From a more near-term solution, I wonder if making it possible (or
> easier) to return integer constant expressions from statement
> expressions and allowing a restricted form of statement expressions
> at file scope would help?

Even a more limited form of this would have been useful several times,
but as mentioned, the problem tends to be that we end up supporting
compilers for many years.

So then we end up having to work with older compilers without that
feature, and can't actually clean stuff up until many years after the
fact.

We're currently still accepting gcc-5.1 as a compiler, although it's
time to look at that and probably (judging by what stable distros use)
upgrade to something like gcc-8.1 as the minimum supported compiler
version.

            Linus