# Cross-compiling

Lighthouse supports cross-compiling, allowing users to run a binary on one
platform (e.g., `aarch64`) that was compiled on another platform (e.g.,
`x86_64`).


## Instructions

Cross-compiling requires [`Docker`](https://docs.docker.com/engine/install/),
[`rustembedded/cross`](https://github.com/rust-embedded/cross) and for the
current user to be in the `docker` group.

The binaries will be created in the `target/` directory of the Lighthouse
project.

### Targets

The `Makefile` in the project contains four targets for cross-compiling:

- `build-x86_64`: builds an optimized version for x86_64 processors (suitable
	for most users).
- `build-x86_64-portable`: builds a version x86_64 processors which avoids
	using some modern CPU instructions that might cause an "illegal
	instruction" error on older CPUs.
- `build-aarch64`: builds an optimized version for 64bit ARM processors
	(suitable for Raspberry Pi 4).
- `build-aarch64-portable`: builds a version 64 bit ARM processors which avoids
	using some modern CPU instructions that might cause an "illegal
	instruction" error on older CPUs.


### Example

```bash
cd lighthouse
make build-aarch64
```

The `lighthouse` binary will be compiled inside a Docker container and placed
in `lighthouse/target/aarch64-unknown-linux-gnu/release`.