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ARM-software / abi-aa

Application Binary Interface for the Arm® Architecture
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Define soft-float PCS for AArch64 #232

Closed ostannard closed 5 months ago

ostannard commented 7 months ago

With the release of the Cortex-R82, we now have an AArch64 CPU which can be built without any floating-point instructions or registers, so I think we should re-consider our decision to not have a soft-float variant of the AArch64 PCS.

I've worded this as a variant over the base PCS, to keep it simple.

No compiler implements this yet, but clang does already allow passing floating-point types without an FPU, and seems to implement the first bullet point correctly. I'm working on LLVM patches which will implement bullet points 2 and 3.

GCC doesn't currently allow any use of floating-point types without an FPU for AArch64, so we don't need to worry about compatibility with existing code there.

For the fourth bullet point, I don't think we need to define the PCS for vector types, because these are only defined by the ACLE when the relevant hardware exists.

smithp35 commented 7 months ago

One further suggestion, that github won't let me comment on as it isn't part of the patch. Please can you add an entry to the Change history table?