Re: [PATCH V3 08/17] riscv: compat: syscall: Add compat_sys_call_table implementation

[Guo Ren <guoren@kernel.org>]

On Fri, Jan 21, 2022 at 4:57 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Fri, Jan 21, 2022 at 7:25 AM Guo Ren <guoren@kernel.org> wrote:
> > On Thu, Jan 20, 2022 at 10:43 PM Arnd Bergmann <arnd@arndb.de> wrote:
> > > On Thu, Jan 20, 2022 at 8:39 AM <guoren@kernel.org> wrote:
>
> > > Are you sure these are the right calling conventions? According to [1],
> > > I think the 64-bit argument should be in an aligned pair of registers,
> > > which means you need an extra pad argument as in the arm64 version
> > > of these functions. Same for ftruncate64, pread64, pwrite64, and
> > > readahead.
> >
> > [1] has abandoned.
> >
> > See:
> > https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-cc.adoc
>
> Ok, thanks for the reference, I picked the first one that came up in
> a google search and didn't expect this to ever have changed.
>
> > > I still feel like these should be the common implementations next to the
> > > native handlers inside of an #ifdef CONFIG_COMPAT.
> > >
> > > The names clash with the custom versions defined for powerpc and sparc,
> > > but the duplicates look compatible if you can account for the padded
> > > argument and the lo/hi order of the pairs, so could just be removed here
> > > (all other architectures use custom function names instead).
> > I would try it later.
>
> This becomes easier then, as powerpc and sparc already have the non-padded
> calling conventions, so you could just generalize those without looking at
> the other architectures or adding the padding. The powerpc version already
> has the dual-endian version, so using that will work on big-endian sparc and
> on little-endian riscv as well, though we may need to come up with a better name
> for the arg_u32/arg_u64/merge_64 macros in order to put that into a global
> header without namespace collisions.
Sounds good, thanks!

>
>          Arnd



-- 
Best Regards
 Guo Ren

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