linux-kernel - Re: [PATCH] x86/percpu: Enable named address spaces for all capable GCC versions

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Date: Tue, 21 May 2024 10:18:27 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Uros Bizjak <ubizjak@...il.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
	Andy Lutomirski <luto@...nel.org>, Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH] x86/percpu: Enable named address spaces for all capable
 GCC versions


* Uros Bizjak <ubizjak@...il.com> wrote:

> Enable named address spaces also for GCC 6, GCC 7 and GCC 8
> releases. These compilers all produce kernel images that boot
> without problems.
> 
> Use compile-time test to detect compiler support for named
> address spaces. The test passes with GCC 6 as the earliest
> compiler version where the support for named address spaces
> was introduced.
> 
> Signed-off-by: Uros Bizjak <ubizjak@...il.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Brian Gerst <brgerst@...il.com>
> Cc: Denys Vlasenko <dvlasenk@...hat.com>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> ---
>  arch/x86/Kconfig | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 9d16fee6bdb8..c9e0a54f469e 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2430,7 +2430,8 @@ source "kernel/livepatch/Kconfig"
>  endmenu
>  
>  config CC_HAS_NAMED_AS
> -	def_bool CC_IS_GCC && GCC_VERSION >= 90100
> +	def_bool $(success,echo 'int __seg_fs fs; int __seg_gs gs;' | $(CC) -x c - -S -o /dev/null)
> +	depends on CC_IS_GCC

So ... will this test also trigger on Clang, which might have a 
__seg_fs/__seg_gs work-alike definition?

Thanks,

	Ingo