Pyo3: Can't compile to a 32-bit target with 64-bit python

[fenjalien]

🐛 Bug Reports

Error: "Your Rust target architecture (32-bit) does not match your python interpreter (64-bit)"
I'm writing a program to run on a Raspberry Pi by cross compiling from WSL Debian. This setup has worked nicely with past projects. The rust-cpython crate does compile and work but pyo3 seems like a much nicer crate to work with.
I have tried installing 32-bit python but to no avail and compiling on the Pi itself isn't doable due to how I have it setup.

🌍 Environment

• Your operating system and version: 4.4.0-18362-Microsoft #836-Microsoft Mon May 05 16:04:00 PST 2020 x86_64 GNU/Linux (WSL Debian)
• Your python version: 3.8 (64-bit)
• How did you install python (e.g. apt or pyenv)? Did you use a virtualenv?: apt
• Your Rust version (rustc --version): 1.44.1
• 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")?: No

💥 Reproducing

Taking the example code from the docs, install a 64-bit python interpreter, set the --target to a 32-bit target and build.
e.g. cargo build --target=armv7-unknown-linux-gnueabihf

[davidhewitt]

Thanks for your question.

If you're able to mount the Pi's filesystem you can just point PyO3 in cross-compile mode at the location of the python install on your Pi's disk. See https://pyo3.rs/v0.11.1/building_and_distribution.html#cross-compiling - you'll need to set PYO3_CROSS_LIB_DIR and PYO3_CROSS_INCLUDE_DIR to point at the right directories on your Pi.

Closing for now, but please report back here if that doesn't work.

[fenjalien]

Ah, I should've read the docs more closely.

However having now tried, I can't find a way to mount the Pi's filesystem. And as a desperate attempt I've also tried copying across the python files from the Pi's /usr/lib and /usr/include and pointing pyo3 at them. Unfortunately I get the very unhelpful error:
Error: Os { code: 2, kind: NotFound, message: "No such file or directory" }

[davidhewitt]

Hmm, definitely sounds like an environment issue, but perhaps we can make the experience nicer. Can you try with the branch in #1095 and see if it gives you a better error message?

[fenjalien]

Everything works!
My only difficulty was that I had to set PYO3_LIB_DIR to exactly the directory _sysconfigdata*.py was in not just lib/.

Thank you and keep up the awesome work :)

[Progdrasil]

@fenjalien For reference could you give me the full path of the _sysconfigdata*.py file as well as the path to the libpython3.Y.so file on you raspberry pi please?

[fenjalien]

Sure:

_sysconfigdata*.py = /usr/lib/python3.7/_sysconfigdata_m_linux_arm-linux-gnueabihf
libpython3.Y.so = /usr/lib/python3.7/config-3.7-arm-linux-gnueabihf/libpython3.7.so

[Progdrasil]

is there a symbolic link of libpython3.7.so located directly at /usr/lib/?

[Progdrasil]

@fenjalien thanks for those paths, If you could try with the latest commit in #1095 and setting PYO3_CROSS_LIB_DIR to your rapsberry pi's /usr/lib directory without specifying the python directory does it work now?

[fenjalien]

yep works nicely now, thank you!

[Progdrasil]

Glad to hear it! Thanks for trying it out