Implement objc_msgSend function for the LoongArch CPU architecture

[basilisk-dev]

Ported objc_msgSend to the LoongArch64 architecture by adding a native assembly implementation. I basically ported the RISC-V implementation to LoongArch64 assembly. You can read more about the LoongArch architecture here if interested.

I ran the relevant tests and they all passed, and I also tested the implementation manually on LoongArch64 to verify it behaves correctly.

Please let me know if you need any additional info.

[davidchisnall]

Thanks, this looks correct but I’d like to see it running in CI. I believe there is QEMU user mode support for Loongarch, can you add it to the workflow runner?

For this to be useful, we will also need a clang patch that enables the assembly message-dispatch function for message sends.

[basilisk-dev]

@davidchisnall I had to make a slight change to allow the implementation to compile on Clang 18 (I used Clang 22 during initial development).

I've added logic to the GitHub Actions workflow to allow the tests to run against LoongArch64 as well. Here is a test run I did: https://github.com/basilisk-dev/libobjc2/actions/runs/23605441514/job/68746795969

I had to exclude LLVM 16 and LLVM 17 on LoongArch64. ld.lld in the Ubuntu LLVM 16 and LLVM 17 packages do not support linking on LoongArch64.

A few of the tests fail because there is no LoongArch64 implementation in block_trampolines.S but I intend to fix that in a separate PR.

For this to be useful, we will also need a clang patch that enables the assembly message-dispatch function for message sends

Makes sense, I'm not familiar with Clang/LLVM internals so I didn't realize this wasn't already the case.

[davidchisnall]

Thanks. Looks like it would be quite easy to tweak to support 32-bit of desirable.

[davidchisnall]

CI is failing because of the missing block-to-IMP logic. This is pretty small, but we need to either skip that test on LoongArch or implement it.

[davidchisnall]

Assuming the immediate operand on ld.d is large enough on LoongArch, I think you should be able to simply copy the MIPS code paths here and replace ld with ld.d and jr with jirl (with a 0 immediate), and define ARG0 to ARG2 in exactly the same way.