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

[Palmer Dabbelt <palmer@dabbelt.com>]

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?