Rust cannot use universal LLVM on macOS

[MarcusCalhoun-Lopez]

I install Rust using MacPorts on macOS.
Rust was recently updated from 1.24.1 to 1.25.0.
For version 1.24.1, the Rust compiler did not seem to care if LLVM was built as a universal binary.
Starting with version 1.25.0, I get the error

error: failed to add native library /opt/local/libexec/llvm-6.0/lib/libLLVMX86Disassembler.a: File too small to be an archive

Rust was compiled with --llvm-root=/opt/local/libexec/llvm-6.0.
If I reinstall LLVM so it is not universal, Rust compiles correctly.
There is a MacPorts bug report.

[raphaelcohn]

@MarcusCalhoun-Lopez @awakecoding I get this too, but with libraries built by cmake using the rust cmake crate in a Cargo build.rs script. I can probably introduce a workaround step, but this is a compiler bug that is really unfortunate - and misreports the cause of the error.

[awakecoding]

@raphaelcohn you might be in luck then, have you tried setting the CMAKE_OSX_ARCHITECTURES to a single architecture in your build.rs? If it doesn't fix it, check that the project CMakeLists.txt does not overwrite the CMAKE_OSX_ARCHITECTURES value. It doesn't change the fact that the problem with the Rust linker should definitely be fixed, but in your case you may be able to work around it for now.

[raphaelcohn]

@awakecoding Thanks for the hint - I'll try that out. For now, I'm parsing the cargo TARGET environment variable and putting in some hacks to run lipo -thin (lots of hacks, actually, as lipo uses arm64 and rust uses aarch64, that sort of thing). And it's rather brittle. It'll certainly break in a cross-compilation...

[awakecoding]

@raphaelcohn you can use CARGO_CFG_TARGET_OS and CARGO_CFG_TARGET_ARCH to make a pretty accurate mapping between names used by cargo and names used by CMake. It's glue layer code, but I'm pretty sure if you do the mapping correctly just for macOS and iOS to specify a single parameter to CMAKE_OSX_ARCHITECTURES it should work, saving you the pain of calling lipo. In my case, since the dependency is prebuilt, I guess my only choice at this point would be to add checks for macOS + iOS, call lipo -thin to extract just the right library and copy it to a temporary location, using this library instead of the original. Such a pain :/

[raphaelcohn]

@awakecoding Thanks for the extra tip - that's awesome! I must have missed those. For now, my problem's actually compounded a little that the third party library I'm wrapping (IntelSEAPI) is basically a mess, with a very broken build / install system that makes way to many assumptions, most of them wrong...

[raphaelcohn]

@awakecoding Definitely a pain - and it just makes a reproducible process that much harder. Not least the mental distraction from whatever problem you were actually trying to solve with rust...