Mac Catalyst (macabi) target objects fail to link

[ara4n]

If you attempt to build a library for Mac Catalyst (target aarch64-apple-ios-macabi) on current nightly on Ventura (13.1), it fails to link with errors like:

ld: in /Users/matthew/workspace/matrix-rust-sdk/target/aarch64-apple-ios-macabi/dbg/deps/libstatic_assertions-fdafb4b8ba800a8a.rlib(lib.rmeta), building for Mac Catalyst, but linking in object file built for , file '/Users/matthew/workspace/matrix-rust-sdk/target/aarch64-apple-ios-macabi/dbg/deps/libstatic_assertions-fdafb4b8ba800a8a.rlib' for architecture arm64

This is because the synthetic Mach-O object files (symbols.o and lib.rmeta) emitted by object lack LC_BUILD_VERSION load commands to identify them as compatible with Catalyst, so ld complains they have a blank platform: "linking in object file built for ,".

rustc uses gimli's object to write these object files, so object needs to be extended to support writing LC_BUILD_VERSION, and then rustc needs to be fixed to write it when building for Catalyst.

I hacked this together as per https://gist.github.com/ara4n/320a53ea768aba51afad4c9ed2168536, but a) this is the first time i've written any rust, b) turns out i don't need Catalyst after all, c) i'm not sure the changes to object have the right abstractions, d) I don't have bandwidth to land it. So am opening this issue as a breadcrumb trail in the hope someone else finds it useful and can finish it off.

[thomcc]

Thanks for the report, I can probably take this over (but not until after the new year).

[MikeChongCan]

Hello @thomcc ! Any hint on this bug?

I'm pretty new to LLVM/Rust compiler. If I could have some hint, I may start a draft PR in https://github.com/gimli-rs/object first.

[kgrech]

I see the same error when build for both aarch64-apple-ios-macabi and x86_64-apple-ios-macabi
if I have

[lib]
crate-type = ["cdylib"]

If I change it to crate-type = ["staticlib"], then it links, however the *.a produced fails to link to any xcode project with the same error message :(

[MikeChongCan]

I got a workaround for this problem using mold instead of ld. Use this at your own risk.

I was not able to update my my Catalyst app due to this issue for over half a year. Going to use it.

brew install mold
which mold

vim ~/.cargo/config.toml and add:

[target.aarch64-apple-ios-macabi]
linker = "/usr/bin/clang"
rustflags = ["-C", "link-arg=--ld-path=/opt/homebrew/bin/mold"]

Background:

1. I spent this weekend to set up macOS 11.0 to use old Xcode to build my rust static lib for a Catalyst project. It worked.
2. After that, I was thinking about using old Xcode in a newer version of macOS. However, this didn't work. Possibly because cargo was still using the default ld
3. So I thought: What if I switch to a different linker without so much Apple magic? https://github.com/rui314/mold is a great option
4. Switched to mold and it works perfectly

cc @ara4n @kgrech @thomcc

[MikeChongCan]

I got a workaround for this problem using mold instead of ld. Use this at your own risk.

I was not able to update my my Catalyst app due to this issue for over half a year. Going to use it.

brew install mold
which mold

vim ~/.cargo/config.toml and add:

[target.aarch64-apple-ios-macabi]
linker = "/usr/bin/clang"
rustflags = ["-C", "link-arg=--ld-path=/opt/homebrew/bin/mold"]

Background:

1. I spent this weekend to set up macOS 11.0 to use old Xcode to build my rust static lib for a Catalyst project. It worked.
2. After that, I was thinking about using old Xcode in a newer version of macOS. However, this didn't work. Possibly because cargo was still using the default ld
3. So I thought: What if I switch to a different linker without so much Apple magic? https://github.com/rui314/mold is a great option
4. Switched to mold and it works perfectly

cc @ara4n @kgrech @thomcc

Please note that mold linker does not work for iOS or macOS. We need a commercial license for that.

When build my app end-to-end, there's still a linker error:

Sorry, but I decided to stop working for the Mac Catalyst platform.

[protonjohn]

For those of us wishing to ship Rust code in Mac Catalyst apps, this thread remains very interesting and relevant :) I would encourage you to keep pulling on the thread, but if you've determined it's not worth the effort, I'd appreciate someone else experienced in the Dark Arts picking this up.

[thomcc]

Sorry for the delay here.