[PATCH 1/1] RISC-V: Fix canonical extension order (K and J)

[Nelson Chu]

Seems like gcc and llvm have already committed this patch, so LGTM, committed.

Thanks
Nelson

On Mon, Apr 25, 2022 at 11:53 AM Palmer Dabbelt <palmer@dabbelt.com> wrote:
>
> On Mon, 28 Mar 2022 17:12:55 PDT (-0700), Palmer Dabbelt wrote:
> > On Mon, 28 Mar 2022 06:12:01 PDT (-0700), binutils@sourceware.org wrote:
> >> This commit fixes canonical extension order to follow the RISC-V ISA
> >> Manual draft-20210402-1271737 or later.
> >>
> >> bfd/ChangeLog:
> >>
> >>      * elfxx-riscv.c (riscv_recognized_prefixed_ext): Fix "K" extension
> >>      prefix to be placed before "J".
> >> ---
> >>  bfd/elfxx-riscv.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/bfd/elfxx-riscv.c b/bfd/elfxx-riscv.c
> >> index cb2cc146c04..1219a7b44d4 100644
> >> --- a/bfd/elfxx-riscv.c
> >> +++ b/bfd/elfxx-riscv.c
> >> @@ -1338,7 +1338,7 @@ riscv_recognized_prefixed_ext (const char *ext)
> >>  }
> >>
> >>  /* Canonical order for single letter extensions.  */
> >> -static const char riscv_ext_canonical_order[] = "eigmafdqlcbjktpvn";
> >> +static const char riscv_ext_canonical_order[] = "eigmafdqlcbkjtpvn";
> >>
> >>  /* Array is used to compare the orders of standard extensions quickly.  */
> >>  static int riscv_ext_order[26] = {0};
> >
> > Looks like this was just a bug in binutils: K went from being
> > unspecified to specified in 271737 ("Define canonical location of K
> > extension in ISA string"), thus it was never allowed at that other bit
> > position.
> >
> > It looks like GCC also has this wrong, which sort of doubles the
> > headache: now we've got this odd coupling between the GCC version and
> > binutils version.  I'm not sure what the right thing is to do here:
> > certainly rejecting the valid ISA string should be fixed, but I think we
> > might need to accept the invalid one for compatibility reasons.  That'll
> > be a headache to implement, though, so I'm not sure it's worth it.
> >
> > Maybe someone has a clever solution to this one?
>
> After seeing the GCC patch go by, I think the clever solution here is to
> just say that we never accepted any J stuff in the first place so it's
> not a compatibility break.