RISC-V: V vs Z?inx

[Jan Beulich]

On 03.04.2026 01:01, Andrew Waterman wrote:
> There's a normative statement in the spec that V implies D, as you
> pointed out.

Well, really I didn't. It was only later that I actually found that
statement (which I meant to clarify in a reply, when I saw you already
responded).

>  The comment that the vector extension is compatible with
> Zfinx is non-normative, so although there's a contradiction, the
> former statement wins.

Interesting.

> We have a plan to rectify this situation in the future: eventually
> Zfinx will become its own base ISA, and in that new context, V will be
> redefined to imply Zdinx instead of D.  That will happen sometime this
> year.

Is this going to be a good move? Wouldn't V better depend on F/D _or_
Z{f,d}inx? (Which effectively it is as per what's written today, just
not explicitly, and - as you put it - not normatively.)

>  For the time being, it makes the most sense to continue
> rejecting the V + Zfinx combination.

Why would that be? Furthermore, some change is going to be needed anyway
in binutils, as otherwise with the planned change above, V would become
incompatible with F/D.

Jan

> On Thu, Apr 2, 2026 at 8:39 AM Jan Beulich <jbeulich@suse.com> wrote:
>>
>> While Zfinx is specifically documented as compatible with V, there doesn't
>> look to be a way to enable both at the same time. Question is why V implies
>> D in the first place (and similarly why Zvfh implies Zfhmin; oddly it's not
>> Zvfhmin which does so).
>>
>> Below are all sorts of option combinations I tried, but none worked.
>>
>> Jan
>>
>>         .option arch, rv32ivzfinx
>>
>>         .option arch, rv32iv
>>         .option arch, +zfinx
>>
>>         .option arch, rv32izfinx
>>         .option arch, +v
>>
>>         .option arch, rv32iv
>>         .option arch, +zfinx,+v
>>
>>         .option arch, rv32iv
>>         .option arch, +v,+zfinx
>>
>>         .option arch, rv32i
>>         .option arch, +zfinx
>>         .option arch, +v
>>
>>         .option arch, rv32i
>>         .option arch, +v
>>         .option arch, +zfinx