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

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Message-ID: <6b05ec695abc465e9b221fb1180a0fa1@AcuMS.aculab.com>
Date: Sat, 7 Dec 2024 20:54:35 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Linus Torvalds' <torvalds@...ux-foundation.org>, Martin Uecker
	<muecker@...g.de>
CC: Vincent Mailhol <vincent.mailhol@...il.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>,
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Subject: RE: [PATCH 02/10] compiler.h: add is_const() as a replacement of
 __is_constexpr()

From: Linus Torvalds
> Sent: 07 December 2024 20:31
...
> 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.

That's going to annoy me.
The system disk in the system I test build kernel on is actually older
than the machine! (not by much).
And Ubuntu 18.04 (still getting some fixes) has gcc 7.5.0.

It isn't as though the 8.1 update is anything really major.
Disabling stack canaries would let an older compiler be used.
(and I might change the tests...)

Much more useful would be mandating 'asm go with outputs' which
would cut out a whole load horrid alternatives.

But that would make it pretty common that a kernel build would
need a later compiler than the one the distribution installed.

It maybe time to consider directly supporting downloading and
building the required compiler as part of a normal kernel build.
That would allow the minimum version to be set to a very recent
build and also make cross architecture build easier.
(In effect all builds become cross builds.)

NetBSD used to (may still do) import gcc into its CVS repository.
So that everything was built with a 'known' compiler.

It is (probably) less of a problem with clang.
People using clang are likely to have explicitly downloaded it.

	David

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