linux-kernel - Re: [PATCH v2 2/8] riscv: Add PLATFORM_MAY_SUPPORT_RISCV_ISA

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Date: Fri, 10 May 2024 21:43:33 +0100
From: Conor Dooley <conor@...nel.org>
To: Charlie Jenkins <charlie@...osinc.com>
Cc: Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Conor Dooley <conor.dooley@...rochip.com>,
	Song Liu <song@...nel.org>, Xi Wang <xi.wang@...il.com>,
	Björn Töpel <bjorn@...osinc.com>,
	Clément Léger <cleger@...osinc.com>,
	Jessica Clarke <jrtc27@...c27.com>,
	Andy Chiu <andy.chiu@...ive.com>, linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/8] riscv: Add PLATFORM_MAY_SUPPORT_RISCV_ISA_V
 Kconfig option

Hey Charlie,

On Tue, May 07, 2024 at 06:36:28PM -0700, Charlie Jenkins wrote:
> Current versions of the kernel add "v" to the march and then immeidately
> filter it out such that "v" is not passed to CFLAGS.  Instead of doing
> this filtering, code blocks in the kernel that want to use vector
> assembly have been changed to locally enable vector (using ".option
> arch, +v").

Other content in the series aside, since this is a change that could be
made independently of the main series objectives, I figured it was worth
pointing out that this is not a change without downsides: I think that
it would drop support for vector with most versions of LLVM as
option arch support there is much more recent thing than it is for gcc.
Off the top of my head I don't know exactly the versions involved, but
it is something like LLVM-14 supports vector but only LLVM-17 and later
supports .option arch.

Thanks,
Conor.

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