Cross compile macOS -> Linux server... really need docker?

help
1

I was able to cross compile from my laptop (macOS) to iOS and Android devices without much problem. I just used the usual cargo build but with a different --target argument. But for some reason that doesn’t work with Linux. I want to deploy the binary to my Linux server (x86_64). I tried the following, and it failed:

% cargo build --target x86_64-unknown-linux-gnu -p hello-cross
   Compiling hello-cross v0.1.0 (/Users/rob/Workspace/MonoRepo3/learning/hello-cross)
error: linking with `cc` failed: exit status: 1
  |
  = note:  "cc" "-m64" "/var/folders/zm/mzv_wcgn0gn4xcj3z6vl4_cm0000gn/T/rustclPzqtP/symbols.o" "<7 object files omitted>" "-Wl,--as-needed" "-Wl,-Bstatic" "<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/lib/{libstd-*,libpanic_unwind-*,libobject-*,libmemchr-*,libaddr2line-*,libgimli-*,librustc_demangle-*,libstd_detect-*,libhashbrown-*,librustc_std_workspace_alloc-*,libminiz_oxide-*,libadler2-*,libunwind-*,libcfg_if-*,liblibc-*,librustc_std_workspace_core-*,liballoc-*,libcore-*,libcompiler_builtins-*}.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-L" "/var/folders/zm/mzv_wcgn0gn4xcj3z6vl4_cm0000gn/T/rustclPzqtP/raw-dylibs" "-Wl,--eh-frame-hdr" "-Wl,-z,noexecstack" "-L" "<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "/Users/rob/Workspace/MonoRepo3/target/x86_64-unknown-linux-gnu/debug/deps/hello_cross-5c3b0cdd7be55a39" "-Wl,--gc-sections" "-pie" "-Wl,-z,relro,-z,now" "-nodefaultlibs"
  = note: some arguments are omitted. use `--verbose` to show all linker arguments
  = note: clang: warning: argument unused during compilation: '-pie' [-Wunused-command-line-argument]
          ld: unknown options: --as-needed -Bstatic -Bdynamic --eh-frame-hdr -z --gc-sections -z -z 
          clang: error: linker command failed with exit code 1 (use -v to see invocation)
          

error: could not compile `hello-cross` (bin "hello-cross") due to 1 previous error

I thought Rust was based on LLVM and that LLVM would have enough to cross compile binaries without other tools.

Someone recommend cross. I installed it with cargo. It appears to want docker. I don’t want to have to learn about docker if I can avoid it, so I wanted to check. Is all this really needed to cross compile to Linux? Why doesn’t a simple cargo build --target ... work like it did for Android and iOS?

 % cross build --target x86_64-unknown-linux-gnu -p hello-cross
ERROR: Cannot connect to the Docker daemon at unix:///Users/rob/.docker/run/docker.sock. Is the docker daemon running?
Error: 
   0: could not run container
   1: when building custom image
   2: when pre-building
   3: `docker build --label 'org.cross-rs.for-cross-target=x86_64-unknown-linux-gnu' --label 'org.cross-rs.workspace_root=/Users/rob/Workspace/MonoRepo3' --tag cross-custom-monorepo:x86_64-unknown-linux-gnu-8a8d0-pre-build --build-arg 'CROSS_CMD=dpkg --add-architecture $CROSS_DEB_ARCH
      apt-get update && apt-get install --assume-yes libssl-dev:$CROSS_DEB_ARCH' --build-arg 'CROSS_DEB_ARCH=amd64' --file /Users/rob/Workspace/MonoRepo3/target/x86_64-unknown-linux-gnu/Dockerfile.x86_64-unknown-linux-gnu-custom /Users/rob/Workspace/MonoRepo3` failed with exit status: 1

Note: CROSS_CMD=dpkg --add-architecture $CROSS_DEB_ARCH
apt-get update && apt-get install --assume-yes libssl-dev:$CROSS_DEB_ARCH
2

Shoot… I just realized that for iOS and Android I was building static libraries and using Xcode and Android Studio to make the binary. So maybe I can try that tactic here. Maybe I could run the last linker step on the Linux server, and just use plain cargo build on my laptop to make a static library for Linux.

3

Yup. That works. Sorry for the noise, but it won’t let me delete the post now. For those that might be searching for same thing, you can cross compile a static library, and then do the final linking step on the linux server. So on my laptop:

// lib.rs
#[unsafe(no_mangle)]
pub extern "C" fn hello_world() {
    println!("Hello, world! (cross compiled, hopefully)");
}

# Cargo.toml
[package]
name = "hello-cross"
version = "0.1.0"
edition = "2024"

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

[dependencies]

Build:

% cargo build --target x86_64-unknown-linux-gnu -p hello-cross --lib --release
% scp target/x86_64-unknown-linux-gnu/release/libhello_cross.a my-cloud-server:

Then on the Linux server:

// main.c
void hello_world();
int main() {
  hello_world();
}

And:

% gcc main.c libhello_cross.a -lpthread -ldl
% ./a.out 
Hello, world! (cross compiled, hopefully)

This works for me. My main goal was to run things on Linux without uploading intellectual property like source code to the server.

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