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

[Guo Ren]

On Mon, Dec 27, 2021 at 10:29 AM Jessica Clarke <jrtc27 at jrtc27.com> wrote:
>
> On 27 Dec 2021, at 01:16, Guo Ren <guoren at kernel.org> wrote:
> >
> > On Mon, Dec 27, 2021 at 4:31 AM Arnd Bergmann <arnd at arndb.de> wrote:
> >>
> >> On Sun, Dec 26, 2021 at 7:38 AM Guo Ren <guoren at kernel.org> wrote:
> >>> On Sun, Dec 26, 2021 at 4:36 PM Jisheng Zhang <jszhang3 at mail.ustc.edu.cn> wrote:
> >>>> On Wed, 22 Dec 2021 20:59:30 +0800 Guo Ren <guoren at kernel.org> wrote:
> >>>>> On Wed, Dec 22, 2021 at 2:10 AM Arnd Bergmann <arnd at 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/