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They can only implement a superset of a specification, no mix-and-match allowed. As an exception, an ARMv8.x-A chip can have some ARMv8.x+1-A extensions, but _
by my123 6y ago
They can only implement a superset of a specification, no mix-and-match allowed.
As an exception, an ARMv8.x-A chip can have some ARMv8.x+1-A extensions, but _never_ 8.x+2-A extensions (forbidden by Arm).
You just have one ISA minor revision of wiggle room.
And yes, Arm architectures are co-designed with plenty of output from partners.
- monocasa 6y agoExcept we have evidence that they've been implementing a subset of the specification on M1. Like VHE stuck on. The not well kept rumor is that Apple has a much looser than architectural license due to their very close relationship with ARM, both generally since the early 90s, and that Apple contributed very heavily to early AArch64 design and it's arguably theirs as much as it is ARM's.
- my123 6y agoVHE is implemented and stuck as on indeed. There's also the fact that only pc and sp are retained on WFI, without the other GPRs. Those quirks only affect bare metal kernel-mode (EL2), and do not affect user-mode or virtualised machines at EL1 in any way.