RISCV support

[NathanMcMillan54]

From skimming through this and not looking up anything else, I thought of starting a UEFI application in Rust for RISCV. Could or should this library make support RISCV?

[GabrielMajeri]

Hello. Definitely, uefi-rs aims to support UEFI systems on all possible architectures! The core library and our build/test runner script already has support for multiple architectures (x86_64 + AArch64).

The only possible issues with adding support for RISCV are:

• bugs in the upstream Rust compiler (these might've been fixed already)
• experience with the platform (I haven't personally used this arch before).

If you're familiar with RISCV and want to help add support for it to this project, you're more than welcome to contribute 😄

[NathanMcMillan54]

Lol no I've never done anything with RISCV, I was just wondering if it was possible. But I guess I will fork it and try to do something for RISCV.

[NathanMcMillan54]

I was going through the commits for Aarch64 support 5e7a615 and f02a899, and it looks like the only thing that changed was uefi-test-runner and the documentation. Are those the only things that need to change for a new architecture?

[GabrielMajeri]

@NathanMcMillan54 assuming the upstream Rust compiler supports the UEFI calling convention on that architecture, yes. It was also necessary to define a target .json file for AArch64 since the compiler doesn't yet natively understand how to generate binaries for that architecture.

[NathanMcMillan54]

Rust doesn't have a riscv64-unknown-windows (like x86_64) or a riscv64-pc-windows-msvc (like Aarch64) for a llvm target. So I guess it's just not possible to compile for UEFI right now.

[NathanMcMillan54]

Same, I haven't done anything with RISCV so this is kinda a bug project for me.

[GabrielMajeri]

@orvij the build issue is probably related to #241. The src/proto/shim/mod.rs file has to be commented/removed temporarily, until we get it fixed.

[NathanMcMillan54]

@orvij I don't care if you make RISCV support and I don't. This issue was really just a question.

[NathanMcMillan54]

My summer break from school starts at the end of today so I could do literally nothing but work on RISCV support, but you can decide since you seem like you're already working on it.

[GabrielMajeri]

@orvij I meant #242, but it's fixed now.

[ethindp]

Would you not need to modify LLVM for it to generate PE binaries for UEFI? A target file will work but you'll still output ELF. And converting ELF to PE is hacky.

[sreehax]

I've faced some serious issues with LLVM and generating riscv PE/COFF binaries for LLVM, so it would be interesting if it works with Rust. Basically, no matter what I would do llvm would generate an ELF object file for riscv64 uefi and of course fail to link it as a UEFI binary. I've faced this issue both with clang and zig. If someone gets something working, please let me know what you did.

[sreehax]

given my experience your last point is most definitely true: I've never gotten any lang or compiler that uses LLVM to output a riscv PE object. the only solution I've seen employed in the wild is making a custom crt0 in assembly that fakes a PE/COFF header and calls into your code compiled for freestanding, and the whole thing is objcopy'd to a flat binary to expose the PE header. It's not ideal, but it does work