Re: [PATCH 00/13] riscv: compat: Add COMPAT mode support for rv64

From: Guo Ren <guoren@kernel.org>
To: Jessica Clarke <jrtc27@jrtc27.com>
Cc: "Arnd Bergmann" <arnd@arndb.de>,
	"Jisheng Zhang" <jszhang3@mail.ustc.edu.cn>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Anup Patel" <anup.patel@wdc.com>,
	gregkh <gregkh@linuxfoundation.org>,
	liush <liush@allwinnertech.com>, "Wei Fu" <wefu@redhat.com>,
	"Drew Fustini" <drew@beagleboard.org>,
	"Wang Junqiang" <wangjunqiang@iscas.ac.cn>,
	"Wei Wu (吴伟)" <lazyparser@gmail.com>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	linux-riscv <linux-riscv@lists.infradead.org>,
	linux-csky@vger.kernel.org, "Guo Ren" <guoren@linux.alibaba.com>
Subject: Re: [PATCH 00/13] riscv: compat: Add COMPAT mode support for rv64
Date: Tue, 28 Dec 2021 18:45:55 +0800	[thread overview]
Message-ID: <CAJF2gTS20NDDWSacEt0mhBeR-t4pZbeS43CDq9eSqHpjzHHdVA@mail.gmail.com> (raw)
In-Reply-To: <AA7091EA-C3AF-47CE-B0C5-E2ECE4133D09@jrtc27.com>

On Mon, Dec 27, 2021 at 10:29 AM Jessica Clarke <jrtc27@jrtc27.com> wrote:
>
> On 27 Dec 2021, at 01:16, Guo Ren <guoren@kernel.org> wrote:
> >
> > On Mon, Dec 27, 2021 at 4:31 AM Arnd Bergmann <arnd@arndb.de> wrote:
> >>
> >> On Sun, Dec 26, 2021 at 7:38 AM Guo Ren <guoren@kernel.org> wrote:
> >>> On Sun, Dec 26, 2021 at 4:36 PM Jisheng Zhang <jszhang3@mail.ustc.edu.cn> wrote:
> >>>> On Wed, 22 Dec 2021 20:59:30 +0800 Guo Ren <guoren@kernel.org> wrote:
> >>>>> On Wed, Dec 22, 2021 at 2:10 AM Arnd Bergmann <arnd@arndb.de> wrote:
> >>>>
> >>>> What about adding RV64 ILP32 support instead? This don't need HW side
> >>>> modifications so can benefit all RV64.
> >>>
> >>> ILP32 is another topic in C Language Data Type Models and it couldn't
> >>> replace the standard rv32 ecosystem.
> >>> COMPAT is a common framework in Linux (7 arches have been supported),
> >>> so let rv64 support COMPAT mode is considerable.
> >>>
> >>> Customers would choose ILP32 / RV32-compat by themself and that
> >>> depends on which one has a better ecosystem.
> >>
> >> From a kernel perspective, supporting both is not much more work than
> >> supporting either of them. We had the same debate for Arm64, and ended
> >> up never merging the ILP32 patches despite them being well written
> >> and maintainable, to limit the number of supported user space ABIs
> >> as well as the possible attack vectors when there is an exploitable
> >> bug that is specific to an ABI.
> >>
> >> arm64 does support big-endian mode, which is a similar niche, but it
> >> can't easily be removed after it's already supported. Supporting normal
> >> compat mode is the easiest here because it doesn't add another user
> >> space ABI, but I'd strongly recommend not to add any other ones.
> >
> > @Palmer Dabbelt How do you think about supporting ILP32 & COMPAT both
> > in rv64? And let users vote by foot which is better.
>
> As psABI TG co-chair I really do not want an ILP32 RV64 to exist if it
> can at all be avoided. Every single attempt at an ILP32 ABI for a
> 64-bit architecture has failed to take off in the past, so I struggle
> to see why RV64 will be any different. So, in my opinion, there is a
> relatively high barrier to entry for it to be an official frozen ABI,
> and without it being that I doubt upstreams will want to go near it, be
> it Linux, GCC, binutils or GCC, but they can speak for themselves if
> they feel otherwise.
>
> Also, with every year that goes by, ILP32 becomes more and more limited
> in what you can use it for, due to increased memory footprints...
Agree, I think we are on the right road :)

>
> Jess

>


--
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/