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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20240515-subpar-implement-6fcf333ce9d3@spud>
Date: Wed, 15 May 2024 15:34:36 +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

On Fri, May 10, 2024 at 11:26:22PM +0100, Conor Dooley wrote:
> On Fri, May 10, 2024 at 02:43:10PM -0700, Charlie Jenkins wrote:
> > On Fri, May 10, 2024 at 09:43:33PM +0100, Conor Dooley wrote:
> > > 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.
> > 
> > Toolchain incompatibilities are always fun. It does look like .option
> > arch was introduced in LLVM-17. That would be a regression. We do use
> > .option arch for every other extension, but vector was treated special
> > when it was introduced unfortunately so maybe we have to live with the
> > weird march parsing hack.
> 
> I wrote out a long message about the history of some of this, but right
> at the end I was scrolling through my chat logs with Andy and realised
> we actually did make it depend on AS_HAS_OPTION_ARCH, so it should be
> safe to do without regressing anything. I didn't notice in the diff that
> the AS_HAS_OPTION_ARCH was a movement, not an addition. Maybe Andy knows
> why, despite the dependency on the assembler having it, we didn't use it
> everywhere.

And while I remember, the bits of this doing the .option arch conversion
should be (IMO) split into a different patch to anything dealing with
Kconfig options etc.

Cheers,
Conor.

Download attachment "signature.asc" of type "application/pgp-signature" (229 bytes)