18 - Cross-Compilation

# Cross-Compilation

### CIS 198 Lecture 18

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## [Rustup](https://www.rustup.rs/) (beta)

- Successor to Multirust.
    - Currently in beta (try it out! - but not until after your projects.)
    - Written in Rust, not shell - works natively on Windows!

- Still allows you to easily maintain multiple toolchains.
    - e.g. `stable`, `beta`, `nightly-2016-04-15`, `1.8.0`

- Supports cross-compilation nicely!
    - Can download cross-compilation targets & `std` for other targets.
    - `rustup target list` - OS X, iOS, Windows, Android, etc.
    - `rustup target add x86_64-pc-windows-gnu`

- Can still `override` the toolchain for a particular project:
    - `rustup override add nightly` - overrides current directory
    - `rustup override list` - lists overrides

- Run commands with a particular toolchain:
    - `rustup run nightly COMMAND`

---

## Linux to Windows

- [Minimal demo](https://github.com/cis198-2016s/demo-xcompile-win64)
    - Requires MinGW-w64.

- Add the 64-bit Windows target:
    - `rustup target add x86_64-pc-windows-gnu`

- Configure Cargo to target Windows and link using the
    MinGW-w64 linker.
    - `.cargo/config`:
        ```toml
        [target.x86_64-pc-windows-gnu]
        linker = "/usr/bin/x86_64-w64-mingw32-gcc"
        ar = "/usr/x86_64-w64-mingw32-ar"

[build]
        target = "x86_64-pc-windows-gnu"
        ```
    - In the future, this may be handled by:
        - `rustup override add stable-x86_64-pc-windows-gnu`
              - (Currently doesn't quite work for me.)

---

## Linux to Windows

- `cargo build`! Build appears at:
    - `target/x86_64-pc-windows-gnu/debug/xcompile-win.exe`
    - `PE32+ executable (console) x86-64, for MS Windows`

- Executable can be run on Windows (or under Wine).
    - Demo

---

## Linux to Android

- [Minimal demo](https://github.com/cis198-2016s/demo-xcompile-android)

- Rustup has a target for this: `arm-linux-androideabi`
    - But this will only get us a bare binary - not an APK.
    - `ELF 32-bit LSB relocatable, ARM, EABI5 version 1 (SYSV)`

- For APKs, we can use `cargo-apk` ([announcement](https://users.rust-lang.org/t/announcing-cargo-apk/5501)).
    - Compiles Rust code to a shared object (`.so`) file
    - Uses [android-rs-glue](https://github.com/tomaka/android-rs-glue).
        - Simple Java template for loading a shared object (`.so`) file and dynamically links it from Java.
    - Builds using Android build tools.
    - Host must be Linux x86\_64 (currently).

---

## Linux to Android

- `cargo install cargo-apk`

- `Cargo.toml`:
    ```toml
    [package.metadata.android]
    label = "xcompile-198"

[dependencies]
    android_glue = "0.1.3"
    ```

- Build and install:
    ```sh
    export ANDROID_SDK_HOME=/opt/android-sdk
    export NDK_HOME=/opt/android-ndk
    cargo apk install
    ```
    - Demo