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

[Tsukasa OI <research_trasio@irq.a4lg.com>]

On 2022/05/19 12:40, Nelson Chu wrote:
> Seems like gcc and llvm have already committed this patch, so LGTM, committed.

Sorry, the same change is applied to LLVM but not yet on GCC (because I
forgot to add "Signed-off-by" line).  I sent PATCH v2 to gcc-patches
today so that would be okay.  On PATCH v2, I made the same change to
gcc/config/riscv/arch-canonicalize script (not just
gcc/common/config/riscv/riscv-common.cc).

<https://gcc.gnu.org/pipermail/gcc-patches/2022-May/595373.html>

Thanks,
Tsukasa

> 
> 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.
>