Re: your patches enabling Arm64's SVE 2.1 extension

[Jan Beulich <jbeulich@suse.com>]

On 13.02.2024 10:55, Nick Clifton wrote:
> Hi Jan, Hi Srinath,
>> In which case - what is the gas/NEWS entry about? Just in case there would
>> be a 2.42.1, may I ask that it be purged at least there, and perhaps also
>> from the main branch, until support is actually complete?
> 
> I would agree with this.
> 
>> Alternatively,
>> Nick, once support is complete maybe that's then really a(nother) reason
>> to cut a 2.42.1?
> 
> Hmmm... this is a hard decision.  Normally I would only consider a point release
> if we needed to fix an important bug - one which could result in incorrect code
> generation or total failure of a tool like the linker or assembler.  But a release
> just to add some missing instructions which were supposed to be supported but were
> actually not ... well that does not seem to me to be a good enough reason.

Well, the missing insns were merely one out of 7 issues I found (so far,
plus the one or two further issues with GCS, and I didn't get to SME 2.1
yet). Other issues were indeed including wrong encodings being emitted.

> Unless - how significant are these instructions ?  I have not actually looked
> into their semantics.  Are there needed in order for a kernel to be able to
> access specific features of the AArch64 architecture ?  Are they essential for
> atomic operations ?  Are they even likely to be produced by a compiler ?

No atomics, no. But pretty certainly expected to be emitted by a compiler.
For a kernel, GCS is likely of more interest than SVE.

And no, I don't mean to strictly push for an eventual dot release. I
merely wanted to put up the question.

Jan