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WMMX was exposed via the ARM coprocessor mechanism (so it was permitted by the architecture). The coprocessor stuff was removed in ARMv8.
by rrss 6y ago
WMMX was exposed via the ARM coprocessor mechanism (so it was permitted by the architecture). The coprocessor stuff was removed in ARMv8.
- my123 6y agoNow custom instructions are directly on the regular instruction space... (+ there's the can of worms of target-specific MSRs being writable from user-space, Apple does this as part of APRR to flip the JIT region from RW- to R-X and vice-versa without going through a trip to the kernel. That also has the advantage that the state is modifiable per-thread)
- Followerer 6y agoIn ARMv8 you have a much cleaner mechanism through system registers(MSR/MRS).
- saagarjha 6y agoApple has been using system registers for years already. AMX is interesting because it's actual instruction encodings that are unused by the spec.