[PATCH] RISC-V: Clarufy the behavior when extensions have superset.

[Kito Cheng]

Yeah, I realized the compressed instruction is slightly ambigure,
sometimes it means C extension (Title in ISA spec: "C" Extension for
Compressed Instructions), I mean it's all compressed instructions (c
and all zc*, including all further zc* ext) in my last reply, and I
think we (at least Nelson, Jan and me) didn't mix that here, but it
should be worth to be clarify here to prevent confusion for other
people who join later for this mailing thread.

And as Jan point out, I didn't really carefully thinking for the
`.option rvc` part, I support that should be just turn on C ext only,
although it's not symmetric with `.option norvc`, but that might
satisfy the exception for most people I believe.

On Fri, Jul 4, 2025 at 2:32 PM Nelson Chu <nelson@rivosinc.com> wrote:
>
> Thanks, that's clear enough ;)
>
> Nelson
>
> On Fri, Jul 4, 2025 at 2:14 PM Jan Beulich <jbeulich@suse.com> wrote:
>>
>> On 04.07.2025 07:50, Nelson Chu wrote:
>> > I sent the patch to fix .option norvc and .option arch, -c,
>> > https://inbox.sourceware.org/binutils/20250704054239.29226-1-nelson@rivosinc.com/T/#mea571cc2bf69ceeb0d0ff52ef0158fb92d1c2e8c,
>> > which looks stupid but works.  My problem is - should norvc mean no zca,
>> > zcf and zcd?  Or do we need to disable all non-compressed (zc*)
>> > instructions, including zcb, zce, zcmp, zcmop, zcmt and zclsd?
>>
>> I think in the "off" direction it's pretty clear that, as Kito also said,
>> it should be "turn off compressed instructions" (i.e. all of them). The
>> "on" direction is less clear: Imo, that really should only turn on the
>> base C extension insns.
>>
>> Jan