trap at Instance error with codegen-backend = "cranelift"

[dimitri-lenkov]

Hi there,

I've created a super-minimal repository that reproduces the problem I'm running into:

https://github.com/dimitri-lenkov/cranelift_aead

Basically I'm seeing the following error while running tests. The text llvm.x86.avx2.permd (at the very end) caught my eye.

trap at Instance { def: Item(DefId(0:45 ~ poly1305[38f7]::backend::avx2::helpers::prepare_keys)), args: [] } (_ZN8poly13057backend4avx27helpers12prepare_keys17hede810be5c1ed765E): llvm.x86.avx2.permd

I did not expect any reference to LLVM when using cranelift. Is this library depending on some instruction that exists within LLVM? Have I mis-configured something?

I found this related issue which is why I'm asking those questions:

RustCrypto/block-ciphers#391

Feel free to close if this is considered spam or if I need to ask the folks in the cranelift repository anything. I just don't know how to proceed so thought I would ask here first. Thank you for your time.

[tarcieri]

You might want to report this to cranelift. It's another missing x86 intrinsic which needs an inline ASM implementation, similar to rust-lang/rustc_codegen_cranelift#1425

llvm.x86.avx2.permd looks correct, although it's probably not the only one which needs to be implemented for the poly1305 AVX2 backend to work.

I believe setting the poly1305_force_soft cfg attribute will disable AVX2 support. Alternatively if there's some way to detect cranelift we can at least temporarily disable the AVX2 backend when compiling there.

[dimitri-lenkov]

Thank you @tarcieri

I saw added the following [build] section in my .cargo/config.toml (link to rustflags docs) and see that it's working as expected now:

[build]
rustflags = [ "--cfg", "poly1305_force_soft" ]

But I ended up using RUSTFLAGS like this (and not the the above solution) because I really only want to use cranelift for a quick builds when testing:

RUSTFLAGS='--cfg=poly1305_force_soft' cargo test

Thanks for helping out this noob ^_^