- `armv6l-linux`
- `armv7l-linux`
- `riscv64-linux`

In order to build Nix for a different platform than the one you're currently
on, you need a way for your current Nix installation to build code for that
platform. Common solutions include [remote build machines] and [binary format emulation]
(only supported on NixOS).


Given such a setup, executing the build only requires selecting the respective attribute.
For example, to compile for `aarch64-linux`:

```console
$ nix-build --attr packages.aarch64-linux.default
```

or for Nix with the [`flakes`] and [`nix-command`] experimental features enabled:

```console
$ nix build .#packages.aarch64-linux.default
```

Cross-compiled builds are available for:
- `armv6l-linux`
- `armv7l-linux`
- `riscv64-linux`
Add more [system types](#system-type) to `crossSystems` in `flake.nix` to bootstrap Nix on unsupported platforms.

### Building for multiple platforms at once

It is useful to perform multiple cross and native builds on the same source tree,
for example to ensure that better support for one platform doesn't break the build for another.
Meson thankfully makes this very easy by confining all build products to the build directory --- one simple shares the source directory between multiple build directories, each of which contains the build for Nix to a different platform.

Here's how to do that:

1. Instruct Nixpkgs's infra where we want Meson to put its build directory

   ```bash
   mesonBuildDir=build-my-variant-name
   ```

1. Configure as usual

   ```bash
   configurePhase
   ```

3. Build as usual

   ```bash
   buildPhase
   ```

## System type

Nix uses a string with the following format to identify the *system type* or *platform* it runs on:

```
<cpu>-<os>[-<abi>]
```

It is set when Nix is compiled for the given system, and based on the output of Meson's [`host_machine` information](https://mesonbuild.com/Reference-manual_builtin_host_machine.html)>

```
<cpu>-<vendor>-<os>[<version>][-<abi>]
```

When cross-compiling Nix with Meson for local development, you need to specify a [cross-file](https://mesonbuild.com/Cross-compilation.html) using the `--cross-file` option. Cross-files define the target architecture and toolchain. When cross-compiling Nix with Nix, Nixpkgs takes care of this for you.

In the nix flake we also have some cross-compilation targets available:

```
nix build .#nix-everything-riscv64-unknown-linux-gnu
nix build .#nix-everything-armv7l-unknown-linux-gnueabihf
nix build .#nix-everything-armv7l-unknown-linux-gnueabihf
nix build .#nix-everything-x86_64-unknown-freebsd
nix build .#nix-everything-x86_64-w64-mingw32
```

For historic reasons and backward-compatibility, some CPU and OS identifiers are translated as follows:

| `config.guess`             | Nix                 |
|----------------------------|---------------------|
| `amd64`                    | `x86_64`            |
| `i*86`                     | `i686`              |
| `arm6`                     | `arm6l`             |
| `arm7`                     | `arm7l`             |
| `linux-gnu*`               | `linux`             |
| `linux-musl*`              | `linux`             |