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The conditions in the agreement between arm and Apple aren't public so you can't say for sure. Historically arm hasn't allowed architecture licensees to do thei

The conditions in the agreement between arm and Apple aren't public so you can't say for sure. Historically arm hasn't allowed architecture licensees to do their own thing. You're implementing arm standard architecture (and passing the conformance test suite) or nothing. Looks like they've given Apple some special dispensation to do things differently (e.g. the custom AMX instructions that have been uncovered https://gist.github.com/dougallj/7a75a3be1ec69ca550e7c36dc75e0d6f https://gist.github.com/dougallj/7a75a3be1ec69ca550e7c36dc75...). For ARMv9 this potentially means they can pick and choose what they want to implement. I'm sure Apple has had plenty of input into the specification (along with other partners).

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 ago
  Except 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 ago
    VHE 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.
ampdepolymerase 6y ago
ARM was founded as an Apple joint venture. Their relationship is probably special.

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 ago
Except 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 ago
  VHE 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.

ampdepolymerase 6y ago

ARM was founded as an Apple joint venture. Their relationship is probably special.