Re: [PATCH v6 3/3] RISC-V: Implement TLS Descriptors.

[Palmer Dabbelt <palmer@dabbelt.com>]

On Tue, 02 Apr 2024 08:32:59 PDT (-0700), adhemerval.zanella@linaro.org wrote:
>
>
> On 02/04/24 12:25, Palmer Dabbelt wrote:
>
>>
>>> I am not sure whether RISC-V maintainer would like to move to profilers
>>> or would keep this extensions composability manner.
>>
>> What do you mean by "move to profilers"?  "move to profiles"?
>>
>> We have the profiles in RISC-V, but they don't really fix anything here: there's a ton of them, they still have various optional extensions, and the HW support is all over the place (we don't even have compatibility guarantees with individual extensions, for example).
>>
>> So I think for just sticking to the current base ABIs is the way to go.  Maybe at some point HW vendors will start shipping systems that are compatible with some common extension set and we can promote that to a new base ABI, but we're a way off from that happening.
>
> Indeed I meant 'profiles' here and my understanding was that something like
> RVA22U64 as base would simplify things a bit (at least with the possible
> testing/checking the multiple build permutations that using optional
> extensions would incur).

If we could get all the HW vendors to agree to something it wouldn't 
hurt, but trying to move to one of the newer profiles would mean 
dropping support for existing hardware (and thus breaking users who are 
stuck with it, a lot of this newer hardware seems pretty buggy right 
now).  Vendors seem to be implementing stuff that's close to the 
profiles, but it's still a bit of a mess -- plus we end up with the 
whole vendor self-certification issue, which means it's really hard to 
tell what HW actually does from the marketing material.

I'm hoping that something like Android will help here, as there we'll 
have people who are actually shipping systems defining the compatibility 
requirements.  With any luck that will start getting these issues at 
least understood over at RVI, but it's still going to be a long process 
before we get stuff sane.