[PATCH v1 1/1] riscv: Add RVV memset via multiarch/IFUNC

[Adhemerval Zanella Netto]

On 30/10/25 08:25, Florian Weimer wrote:
> * Palmer Dabbelt:
> 
>> On Wed, 29 Oct 2025 19:01:22 PDT (-0700), bergner@tenstorrent.com wrote:
>>> On 10/29/25 6:36 PM, Palmer Dabbelt wrote:
>>>> You're talking glibc-hwcaps though, right?  Jeff is saying AT_HWCAP,
>>>> which is busted on RISC-V (we allocated a bunch of bits early and then
>>>> vendors did whatever they wanted, V got specifically tied up with the
>>>> V-0.7.1 stuff).
>>>
>>> Yes, I was talking about glibc-hwcaps, not AT_HWCAP.
>>
>> Ya, so I think last time we talked about glibc-hwcaps the basic takeaway 
>> was that we just didn't know what HW was going to look like, so adding a 
>> glibc-hwcap would be premature.
> 
> I think it depends on how serious the ecosystem is about killing off
> the base ISA (at least in the glibc context).  If we don't expect
> distributions to switch to RVA23 in the next year or two, maybe adding
> an RVA23 subdirectory still makes sense.  Of course, if RVA23 gets
> adopted by distributions faster than glibc 2.43, that's unnecessary.

We already have a RFC to add hwcaps for RISC-V [1]. It adds support for
64 bit only with the following subsets:

  * RVA20U64 [2]
  * RVA22U64 [3]
  * RVA23U64 [4]

The usability of RVA22U64 is not clear, but it seems that we already have
hardware support for this.

[1] https://patchwork.sourceware.org/project/glibc/list/?series=52496
[2] https://github.com/riscv/riscv-profiles/blob/main/src/profiles.adoc#512-rva20u64-mandatory-extensions
[3] https://github.com/riscv/riscv-profiles/blob/main/src/profiles.adoc#6-rva22-profiles
[4] https://github.com/riscv/riscv-profiles/blob/main/src/rva23-profile.adoc#rva23u64-profile