rust-embedded
`riscv-rt`: ABI incompatibility
I'm working on a project right now that's using a RISCV-32 core with the I, M, F, and C extensions. I know it wouldn't be too difficult to define a custom target for this, but project CI stuff would make actually doing that very difficult (I don't understand Nix). As such, I'm using riscv32imc with --target-features=+f. However, this causes something of an issue - this target uses the ilp32 ABI, but riscv-rt sees the riscvf cfg flag and thus puts some FP instructions into global assembly, which requires ilp32f (as far as I can tell?). Thus I get 33 errors of things like
error: instruction requires the following: 'F' (Single-Precision Floating-Point)
|
note: instantiated into assembly here
--> <inline asm>:99:1
|
99 | fscsr x0
| ^
error: instruction requires the following: 'F' (Single-Precision Floating-Point)
|
note: instantiated into assembly here
--> <inline asm>:100:5
|
100 | fmv.w.x f0, x0
| ^
So then the question is: should I just bite the bullet and figure out Nix well enough to get it happy enough to accept a custom riscv32imfc-uknown-none-elf.json, or would it be acceptable for me to add a no-float-init = [] feature to the crate that would mask out those global_asm! invocations?
Ah, sorry, looks like this can actually be fixed by adjusting the provisional patch at asm.rs line 22. I'll PR this soon.
Not since last working on this sometime last year, no. At least I haven't had any issues with it since then, so I think I can close it for now. I can always reopen this later if the same issue comes up again later.