linux-kernel - Re: [PATCH] kbuild: Add '-fms-extensions' to areas with dedicated CFLAGS

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Message-ID: <20251105201522.GB3787308@ax162>
Date: Wed, 5 Nov 2025 13:15:22 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Segher Boessenkool <segher@...nel.crashing.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Huacai Chen <chenhuacai@...nel.org>,
	WANG Xuerui <kernel@...0n.name>,
	"James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
	Helge Deller <deller@....de>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	Ard Biesheuvel <ardb@...nel.org>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	loongarch@...ts.linux.dev, linux-parisc@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
	linux-efi@...r.kernel.org, llvm@...ts.linux.dev,
	Christian Brauner <brauner@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] kbuild: Add '-fms-extensions' to areas with dedicated
 CFLAGS

On Wed, Nov 05, 2025 at 07:44:26AM -0600, Segher Boessenkool wrote:
> On Sat, Nov 01, 2025 at 12:35:47PM -0400, Nathan Chancellor wrote:
> > There are many places within the kernel that use their own CFLAGS
> > instead of the main KBUILD_CFLAGS, meaning code written with the main
> > kernel's use of '-fms-extensions' in mind that may be tangentially
> > included in these areas will result in "error: declaration does not
> > declare anything" messages from the compiler.
> 
> Please fix such non-standard code then, instead?  The only (documented)
> thing -fms-extensions does for C code is give meaning to something that
> otherwise is a syntax error (and it is for a good reason!)

Right, the kernel would like to start taking advantage of one of those
extensions. See these other threads for more information.

https://lore.kernel.org/20251020142228.1819871-1-linux@rasmusvillemoes.dk/
https://lore.kernel.org/20251023082142.2104456-1-linux@rasmusvillemoes.dk/

Cheers,
Nathan