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From:   Guo Ren <guoren@kernel.org>
Date:   Mon, 27 Dec 2021 09:16:00 +0800
Message-ID: <CAJF2gTQ04utyOc9=q9Tu92togGuyygKgq3tWwfPBCuyTfLh2SQ@mail.gmail.com>
Subject: Re: [PATCH 00/13] riscv: compat: Add COMPAT mode support for rv64
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     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>,
        =?UTF-8?B?V2VpIFd1ICjlkLTkvJ8p?= <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>
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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.

>
>        Arnd


-- 
Best Regards
 Guo Ren

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