PyO3 doesn't build on musl targets (Alpine linux)

[alex]

error: cannot produce cdylib for cryptography-rust v0.1.0 (/tmp/pip-req-build-oczfn6un/src/rust) as the target x86_64-unknown-linux-musl does not support these crate types

This was previously reported as #599, however that referred to a different failure, that proc-macro wasn't supported on musl targets. The corresponding Rust issue was closed, and indeed there's now a new error message. I'm hoping to understand where the blocker to moving this ball forward is, and how I can help!

🐛 Bug Reports

🌍 Environment

• Your operating system and version: Alpine Linux 3.12.0
• Your Rust version (rustc --version): rustc 1.45.2 (d3fb005a3 2020-07-31)
• Your PyO3 version: 0.11.1
• Have you tried using latest PyO3 master (replace version = "0.x.y" with git = "https://github.com/PyO3/pyo3")?: Not yet

💥 Reproducing

pyca/cryptography#5410 see the failing Alpine build https://travis-ci.org/github/pyca/cryptography/jobs/718454323

[alex]

Discovery: Building with RUSTFLAGS="-C target-feature=-crt-static" resolves this. Does this sound like the correct solution to folks? If yes, I'll work up a PR to setuptools-rust to do this automatically when targeting musl. If no... back to the drawing board I guess? :-)

[alex]

Well, I submitted a PR for that approach: PyO3/setuptools-rust#80

[kngwyu]

Thank you for reporting,

RUSTFLAGS="-C target-feature=-crt-static"

Any link or document where you find this solution?
I don't know why it works for musl...

[konstin]

This is explained somehow in rust-lang/rust#59302 (comment), while the reference has some background information (https://doc.rust-lang.org/reference/linkage.html#static-and-dynamic-c-runtimes). I have the same problem with maturin (PyO3/maturin#154) and it appears that target-feature=-crt-static is all you can (and need) to do.

[davidhewitt]

Thanks for reporting & investigating! As we've pushed issues to both of the packaging tools, let's close this one out? I think anyone building software for the musl target regularly probably will know about this target-feature=-crt-static flag.