`rust-binary-calls-swift-package` example doesn't work on a Linux environment

[yoching]

Hello.
I'm trying to build a CLI application that is mainly written in Rust and calls some Swift functions, and I'm developing it on a Linux environment.
I tried to run rust-binary-calls-swift-package example, but it didn't run with following errors.
I'm using WSL2 with Ubuntu and swift-5.6.2-RELEASE-ubuntu20.04.

Do you know how I can make it work? Or, are Linux environments not supported?
Thank you in advance!

$ cargo run -p rust-binary-calls-swift-package
   Compiling proc-macro2 v1.0.42
   Compiling unicode-ident v1.0.2
   Compiling quote v1.0.20
   Compiling syn v1.0.98
   Compiling libc v0.2.126
   Compiling fastrand v1.8.0
   Compiling remove_dir_all v0.5.3
   Compiling cfg-if v1.0.0
   Compiling tempfile v3.3.0
   Compiling swift-bridge-ir v0.1.35 (/home/yoshikuni/GitHub/Rust/swift-bridge/crates/swift-bridge-ir)
   Compiling swift-bridge-build v0.1.35 (/home/yoshikuni/GitHub/Rust/swift-bridge/crates/swift-bridge-build)
   Compiling swift-bridge-macro v0.1.35 (/home/yoshikuni/GitHub/Rust/swift-bridge/crates/swift-bridge-macro)
   Compiling rust-binary-calls-swift-package v0.1.0 (/home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package)
   Compiling swift-bridge v0.1.35 (/home/yoshikuni/GitHub/Rust/swift-bridge)
error: linking with `cc` failed: exit status: 1
  |
  = note: "cc" "-m64" "/tmp/rustcBQCunq/symbols.o" "/home/yoshikuni/GitHub/Rust/swift-bridge/target/debug/deps/rust_binary_calls_swift_package-292e71af283f5de2.1w9emz731ogimejr.rcgu.o" "/home/yoshikuni/GitHub/Rust/swift-bridge/target/debug/deps/rust_binary_calls_swift_package-292e71af283f5de2.24kdsva5pt5pnbco.rcgu.o" "/home/yoshikuni/GitHub/Rust/swift-bridge/target/debug/deps/rust_binary_calls_swift_package-292e71af283f5de2.26896tw8fqt0v9fu.rcgu.o" "/home/yoshikuni/GitHub/Rust/swift-bridge/target/debug/deps/rust_binary_calls_swift_package-292e71af283f5de2.2tpci647um6thpo2.rcgu.o" "/home/yoshikuni/GitHub/Rust/swift-bridge/target/debug/deps/rust_binary_calls_swift_package-292e71af283f5de2.4dhdhlqomt6smcj1.rcgu.o" "/home/yoshikuni/GitHub/Rust/swift-bridge/target/debug/deps/rust_binary_calls_swift_package-292e71af283f5de2.4h8n84jaxycwap6v.rcgu.o" "/home/yoshikuni/GitHub/Rust/swift-bridge/target/debug/deps/rust_binary_calls_swift_package-292e71af283f5de2.4hpkoi5vvq6zq02l.rcgu.o" "/home/yoshikuni/GitHub/Rust/swift-bridge/target/debug/deps/rust_binary_calls_swift_package-292e71af283f5de2.abt62j993v3u99r.rcgu.o" "/home/yoshikuni/GitHub/Rust/swift-bridge/target/debug/deps/rust_binary_calls_swift_package-292e71af283f5de2.dj4o1vryudkth0e.rcgu.o" "/home/yoshikuni/GitHub/Rust/swift-bridge/target/debug/deps/rust_binary_calls_swift_package-292e71af283f5de2.zjy3tzpqmre36eq.rcgu.o" "/home/yoshikuni/GitHub/Rust/swift-bridge/target/debug/deps/rust_binary_calls_swift_package-292e71af283f5de2.1zen2gw3lpr0rw58.rcgu.o" "-Wl,--as-needed" "-L" "/home/yoshikuni/GitHub/Rust/swift-bridge/target/debug/deps" "-L" "/home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/.build/debug" "-L" "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/macosx/" "-L" "/usr/lib/swift" "-L" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,-Bstatic" "-lswift-library" "/home/yoshikuni/GitHub/Rust/swift-bridge/target/debug/deps/libswift_bridge-882327837dd14bed.rlib" "-Wl,--start-group" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-69edc9ac8de4d39c.rlib" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libpanic_unwind-254ac8a4d96ed89e.rlib" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libobject-8bed7ede368468ef.rlib" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libmemchr-9da1150e6aeada6b.rlib" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libaddr2line-dec39a40a22b358c.rlib" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libgimli-7a90882341200e38.rlib" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_demangle-6a5da46a37549d0a.rlib" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd_detect-6dc3d1df7e408d5b.rlib" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libhashbrown-9d89ad14c568d44a.rlib" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libminiz_oxide-ecbdf47025adae10.rlib" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libadler-29db3ffec771ef22.rlib" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_alloc-8b55ad9e1a2080d1.rlib" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunwind-f37a55941b8b3bbd.rlib" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcfg_if-c1d45d3d6971ce0d.rlib" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc-18ac7cbb154ecd62.rlib" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc-80c5909c82700e85.rlib" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_core-aa7f747e2f6af7d5.rlib" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-60d544c9f51ce476.rlib" "-Wl,--end-group" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-d1bd89f2a607e488.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-Wl,--eh-frame-hdr" "-Wl,-znoexecstack" "-L" "/home/yoshikuni/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "/home/yoshikuni/GitHub/Rust/swift-bridge/target/debug/deps/rust_binary_calls_swift_package-292e71af283f5de2" "-Wl,--gc-sections" "-pie" "-Wl,-zrelro,-znow" "-nodefaultlibs"
  = note: /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/.build/debug/libswift-library.a(swift_library.swift.o): in function `$s13swift_library0A14_multiply_by_43nums5Int64VAE_tF':
          /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:2: undefined reference to `$ss27_allocateUninitializedArrayySayxG_BptBwlFyp_Tg5'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:2: undefined reference to `$sSS21_builtinStringLiteral17utf8CodeUnitCount7isASCIISSBp_BwBi1_tcfC'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:2: undefined reference to `$sSSN'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:2: undefined reference to `$sypN'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:2: undefined reference to `$ss5print_9separator10terminatoryypd_S2StF'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:2: undefined reference to `swift_bridgeObjectRelease'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:2: undefined reference to `swift_bridgeObjectRelease'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:2: undefined reference to `swift_release'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:4: undefined reference to `$ss27_allocateUninitializedArrayySayxG_BptBwlFyp_Tg5'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:4: undefined reference to `$sSS21_builtinStringLiteral17utf8CodeUnitCount7isASCIISSBp_BwBi1_tcfC'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:4: undefined reference to `$ss5print_9separator10terminatoryypd_S2StF'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:4: undefined reference to `swift_bridgeObjectRelease'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:4: undefined reference to `swift_bridgeObjectRelease'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:4: undefined reference to `swift_release'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:8: undefined reference to `$ss27_allocateUninitializedArrayySayxG_BptBwlFyp_Tg5'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:8: undefined reference to `$sSS21_builtinStringLiteral17utf8CodeUnitCount7isASCIISSBp_BwBi1_tcfC'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:8: undefined reference to `$ss5print_9separator10terminatoryypd_S2StF'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:9: undefined reference to `swift_bridgeObjectRelease'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:9: undefined reference to `swift_bridgeObjectRelease'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/Sources/swift-library/swift_library.swift:9: undefined reference to `swift_release'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/.build/debug/libswift-library.a(swift_library.swift.o): in function `$ss27_finalizeUninitializedArrayySayxGABnlF':
          /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/<compiler-generated>:(.text+0x2a7): undefined reference to `$sSaMa'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/<compiler-generated>:(.text+0x2c0): undefined reference to `swift_retain'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/<compiler-generated>:(.text+0x2c9): undefined reference to `swift_release'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/.build/debug/libswift-library.a(swift_library.swift.o): in function `$ss5print_9separator10terminatoryypd_S2StFfA0_':
          /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/<compiler-generated>:(.text+0x2f6): undefined reference to `$sSS21_builtinStringLiteral17utf8CodeUnitCount7isASCIISSBp_BwBi1_tcfC'
          /usr/bin/ld: /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/.build/debug/libswift-library.a(swift_library.swift.o): in function `$ss5print_9separator10terminatoryypd_S2StFfA1_':
          /home/yoshikuni/GitHub/Rust/swift-bridge/examples/rust-binary-calls-swift-package/swift-library/<compiler-generated>:(.text+0x316): undefined reference to `$sSS21_builtinStringLiteral17utf8CodeUnitCount7isASCIISSBp_BwBi1_tcfC'
          collect2: error: ld returned 1 exit status
          
  = help: some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
  = note: use the `-l` flag to specify native libraries to link
  = note: use the `cargo:rustc-link-lib` directive to specify the native libraries to link with Cargo (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#cargorustc-link-libkindname)

error: could not compile `rust-binary-calls-swift-package` due to previous error

[chinedufn]

I haven't tried swift-bridge on linux so I don't have a lot of experience here. But I'm happy to help get to the bottom of this.

Right now we build this example in CI on macOS, so it works there

swift-bridge/.github/workflows/test.yml

Lines 73 to 74 in e24a115

	- name: Build Rust binary calls Swift Package examaple
	run: cargo build -p rust-binary-calls-swift-package

.

In your error message I see things like undefined reference to$ss5print_9separator10terminatoryypd_S2StF'`.

Seems like a bunch of symbols that have nothing to do with swift-bridge are missing.

Can you try adding import Foundation to the top of the file and seeing if that does anything?

---

Also, are you able to run any of the other examples?

[yoching]

Thank you for your reply. These are my new trials.

• rust-binary-calls-swift-package
  I added import Foundation at the top of swift_library.swift, but the result was the same.
• async-functions
  The build didn't succeed. I pasted the log on gist here, as it's very long.
• codegen-visualizer
  Since Xcode doesn't exist on Linux, this example doesn't run on linux.

[chinedufn]

rust-binary-calls-swift-package

Hmm this one requires more research.. Not sure to what extent this is possible on Linux. Maybe it is with the right flags, I don't know yet.

---

The build didn't succeed. I pasted the log on gist

Hmmm something to do with openssl, which is probably being pulled in by the reqwest dependency.

Really the error is clang-13: error: linker command failed with exit code 1 (use -v to see invocation)..
We'll need to research how to tell the linker to link in openssl.

[terraputix]

I also just ran into this issue on Fedora Linux when I wanted to test whether it is feasible (in a future) to use cross platform binary artifacts via SPM (compare swiftlang/swift-package-manager#7035, the referenced PR and this POC implementation using binary library artifacts). cargo test --all will report missing symbols for rust-binary-calls-swift-package.

I think, at least part of the problem is due to the bridging-header.h and the compiler flag -import-objc-header which is not supported outside of Apple platforms.

I am wondering if this bridging-header.h is even really needed? Instead, I guess there could be a C-Target that provides the required external definitions instead and separate Swift targets that hold generated code. I adapted the rust-binary-calls-swift-package example this way so you can see what I mean: https://github.com/terraputix/swift-bridge-rust-calls-swift/tree/main/Sources.

[chinedufn]

Seems promising.

What are the trade-offs on Apple platforms when using your example approach vs. -import-objc-header?

This will help us understand whether we should guide users towards having platform dependent build process such as using -import-objc-header on Apple platforms and something else on Linux.

If there aren't any meaningful trade-offs then we can consider recommending one cross-platform friendly approach.

[terraputix]

Let me correct myself: -import-objc-header does work outside of Apple platforms (only the name and that it is not listed in swiftc --help was confusing me), but you can only use it for a normal C header on non Darwin platforms (which you are doing), compare this discussion: https://forums.swift.org/t/using-c-in-swift-away-from-xcode/64784/15.

As far as I can tell from this thread, it is mostly about preferences whether to use a dedicated C target or a bridging header when working with SPM packages. I am not sure how that behaves when working directly with swiftc though. So I guess what you are currently doing is fine.

I eventually found additional linker flags to that enabled me to compile the rust-binary-calls-swift-package example and run it locally on Fedora. Will try to prepare a PR with a fix.