Rust supports a great number of platforms. For many of these platforms The Rust Project publishes binary releases of the standard library, and for some the full compiler. rustup gives easy access to all of them.

When you first install a toolchain, rustup installs only the standard library for your host platform - that is, the architecture and operating system you are presently running. To compile to other platforms you must install other target platforms. This is done with the rustup target add command. For example, to add the Android target:

$ rustup target add arm-linux-androideabi
info: downloading component 'rust-std' for 'arm-linux-androideabi'
info: installing component 'rust-std' for 'arm-linux-androideabi'

With the arm-linux-androideabi target installed you can then build for Android with Cargo by passing the --target flag, as in cargo build --target=arm-linux-androideabi.

Note that rustup target add only installs the Rust standard library for a given target. There are typically other tools necessary to cross-compile, particularly a linker. For example, to cross compile to Android the Android NDK must be installed. In the future, rustup will provide assistance installing the NDK components as well. See the target section of the cargo configuration for how to setup a linker to use for a certain target.

To install a target for a toolchain that isn't the default toolchain use the --toolchain argument of rustup target add, like so:

$ rustup target add --toolchain <toolchain> <target>...

To see a list of available targets, rustup target list. To remove a previously-added target, rustup target remove.