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

[Guo Ren]

On Mon, Dec 27, 2021 at 4:31 AM Arnd Bergmann <arnd@xxxxxxxx> wrote:
>
> On Sun, Dec 26, 2021 at 7:38 AM Guo Ren <guoren@xxxxxxxxxx> wrote:
> > On Sun, Dec 26, 2021 at 4:36 PM Jisheng Zhang <jszhang3@xxxxxxxxxxxxxxxx> wrote:
> > > On Wed, 22 Dec 2021 20:59:30 +0800 Guo Ren <guoren@xxxxxxxxxx> wrote:
> > > > On Wed, Dec 22, 2021 at 2:10 AM Arnd Bergmann <arnd@xxxxxxxx> 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/