cross

“Zero setup” cross compilation and “cross testing” of Rust crates

This project is developed and maintained by the [cross-rs] team. It was previously maintained by the Rust Embedded Working Group Tools team. New contributors are welcome! Please join our [Matrix room] and say hi.

<img alt="cross testing a crate for the aarch64-unknown-linux-gnu target" src="https://github.com/cross-rs/cross/raw/v0.2.5/assets/cross-test.png" title="cross testing a crate for the aarch64-unknown-linux-gnu target"

cross testing a crate for the aarch64-unknown-linux-gnu target

Features

• cross will provide all the ingredients needed for cross compilation without touching your system installation.

• cross provides an environment, cross toolchain and cross compiled libraries, that produces the most portable binaries.

• “cross testing”, cross can test crates for architectures other than i686 and x86_64.

• The stable, beta and nightly channels are supported.

Dependencies

• rustup

• A Linux kernel with binfmt_misc support is required for cross testing.

One of these container engines is required. If both are installed, cross will default to docker.

• [Docker]. Note that on Linux non-sudo users need to be in the docker group. Read the official post-installation steps. Requires version 1.24 or later.

• [Podman]. Requires version 1.6.3 or later.

Installation

$ cargo install cross --git https://github.com/cross-rs/cross

Usage

cross has the exact same CLI as Cargo but relies on Docker or Podman. For Docker, you'll have to start the daemon before you can use it.

# (ONCE PER BOOT, on Linux)
# Start the Docker daemon, if it's not already running using systemd
# on WSL2 and other systems using SysVinit, use `sudo service docker start`.
$ sudo systemctl start docker

# MAGIC! This Just Works
$ cross build --target aarch64-unknown-linux-gnu

# EVEN MORE MAGICAL! This also Just Works
$ cross test --target mips64-unknown-linux-gnuabi64

# Obviously, this also Just Works
$ cross rustc --target powerpc-unknown-linux-gnu --release -- -C lto

Additional documentation can be found on the wiki.

Configuration

You have three options to configure cross. All of these options use the TOML format for configuration and the possible configuration values are documented here.

Option 1: Configuring cross directly in your Cargo.toml

You can directly set configuration values in your Cargo.toml file, under the [package.metadata.cross] table, i.e. key prefix. An example config snippet would look like this:

```toml,cargo [package.metadata.cross.target.aarch64-unknown-linux-gnu] xargo = false image = "test-image" runner = "custom-runner"

### Option 2: Configuring `cross` via a `Cross.toml` file

You can put your [configuration](docs/cross_toml.md) inside a `Cross.toml` file in your project root directory.

### Option 3: Using `CROSS_CONFIG` to specify the location of your configuration

By setting the `CROSS_CONFIG` environment variable, you can tell `cross` where it should search for the config file. This way you are not limited to a `Cross.toml` file in the project root.

### Custom Docker images

`cross` provides default Docker images for the targets listed below. However, it
can't cover every single use case out there. For other targets, or when the
default image is not enough, you can use the `target.{{TARGET}}.image` field in
`Cross.toml` to use custom Docker image for a specific target:

```toml
[target.aarch64-unknown-linux-gnu]
image = "my/image:tag"

In the example above, cross will use a image named my/image:tag instead of the default one. Normal Docker behavior applies, so:

• Docker will first look for a local image named my/image:tag

• If it doesn't find a local image, then it will look in Docker Hub.

• If only image:tag is specified, then Docker won't look in Docker Hub.

• If only tag is omitted, then Docker will use the latest tag.

Dockerfiles

If you're using a custom Dockerfile, you can use target.{{TARGET}}.dockerfile to automatically build it

[target.aarch64-unknown-linux-gnu]
dockerfile = "./path/to/where/the/Dockerfile/resides"

cross will build and use the image that was built instead of the default image.

It's recommended to base your custom image on the default Docker image that cross uses: ghcr.io/cross-rs/{{TARGET}}:{{VERSION}} (where {{VERSION}} is cross's version). This way you won't have to figure out how to install a cross C toolchain in your custom image.

FROM ghcr.io/cross-rs/aarch64-unknown-linux-gnu:latest

RUN dpkg --add-architecture arm64 && \
    apt-get update && \
    apt-get install --assume-yes libfoo:arm64

If you want cross to provide the FROM instruction, you can do the following

ARG CROSS_BASE_IMAGE
FROM $CROSS_BASE_IMAGE

RUN ...

Pre-build hook

cross enables you to add dependencies and run other necessary commands in the image before using it. This action will be added to the used image, so it won't be ran/built every time you use cross.

[target.x86_64-unknown-linux-gnu]
pre-build = ["dpkg --add-architecture arm64 && apt-get update && apt-get install --assume-yes libfoo:arm64"]

Docker in Docker

When running cross from inside a container, cross needs access to the hosts docker daemon itself. This is normally achieved by mounting the docker daemons socket /var/run/docker.sock. For example:

$ docker run -v /var/run/docker.sock:/var/run/docker.sock -v .:/project \
  -w /project my/development-image:tag cross build --target mips64-unknown-linux-gnuabi64

The image running cross requires the rust development tools to be installed.

With this setup cross must find and mount the correct host paths into the container used for cross compilation. This includes the original project directory as well as the root path of the parent container to give access to the rust build tools.

To inform cross that it is running inside a container set CROSS_CONTAINER_IN_CONTAINER=true.

A development or CI container can be created like this:

FROM rust:1

# set CROSS_CONTAINER_IN_CONTAINER to inform `cross` that it is executed from within a container
ENV CROSS_CONTAINER_IN_CONTAINER=true

# install `cross`
RUN cargo install cross

...

Limitations: Finding the mount point for the containers root directory is currently only available for the overlayfs2 storage driver. In order to access the parent containers rust setup, the child container mounts the parents overlayfs. The parent must not be stopped before the child container, as the overlayfs can not be unmounted correctly by Docker if the child container still accesses it.

Explicitly choose the container engine

By default, cross tries to use [Docker] or [Podman], in that order. If you want to choose a container engine explicitly, you can set the binary name (or path) using the CROSS_CONTAINER_ENGINE environment variable.

For example in case you want use [Podman], you can set CROSS_CONTAINER_ENGINE=podman.

Passing environment variables into the build environment

By default, cross does not pass any environment variables into the build environment from the calling shell. This is chosen as a safe default as most use cases will not want the calling environment leaking into the inner execution environment.

In the instances that you do want to pass through environment variables, this can be done via build.env.passthrough in your Cross.toml:

[build.env]
passthrough = [
    "RUST_BACKTRACE",
    "RUST_LOG",
    "TRAVIS",
]

To pass variables through for one target but not others, you can use this syntax instead:

[target.aarch64-unknown-linux-gnu.env]
passthrough = [
    "RUST_DEBUG",
]

Unstable Features

Certain unstable features can enable additional functionality useful to cross-compiling. Note that these are unstable, and may be removed at any time (particularly if the feature is stabilized or removed), and will only be used on a nightly channel.

• CROSS_UNSTABLE_ENABLE_DOCTESTS=true: also run doctests.

Mounting volumes into the build environment

In addition to passing environment variables, you can also specify environment variables pointing to paths which should be mounted into the container:

[target.aarch64-unknown-linux-gnu.env]
volumes = [
    "BUILD_DIR",
]

Use Xargo instead of Cargo

By default, cross uses xargo to build your Cargo project only for all non-standard targets (i.e. something not reported by rustc/rustup). However, you can use the build.xargo or target.{{TARGET}}.xargo field in Cross.toml to force the use of xargo:

# all the targets will use `xargo`
[build]
xargo = true

Or,

# only this target will use `xargo`
[target.aarch64-unknown-linux-gnu]
xargo = true

xargo = false will work the opposite way (pick cargo always) and is useful when building for custom targets that you know to work with cargo.

Supported targets

A target is considered as “supported” if cross can cross compile a “non-trivial” (binary) crate, usually Cargo, for that target.

Testing support (cross test) is more complicated. It relies on QEMU emulation, so testing may fail due to QEMU bugs rather than bugs in your crate. That said, a target has a ✓ in test column of the table below if it can run the [compiler-builtins] test suite.

Also, testing is very slow. cross test runs units tests sequentially because QEMU gets upset when you spawn multiple threads. This means that, if one of your unit tests spawns threads, then it's more likely to fail or, worst, never terminate.

Target	libc	GCC	C++	QEMU	test
aarch64-linux-android [1]	9.0.8	9.0.8	✓	6.1.0	✓
aarch64-unknown-linux-gnu	2.23	5.4.0	✓	5.1.0	✓
aarch64-unknown-linux-musl	1.1.24	9.2.0	✓	6.1.0	✓
arm-linux-androideabi [1]	9.0.8	9.0.8	✓	6.1.0	✓
arm-unknown-linux-gnueabi	2.23	5.4.0	✓	5.1.0	✓
arm-unknown-linux-gnueabihf	2.17	8.3.0	✓	6.1.0	✓
arm-unknown-linux-musleabi	1.1.24	9.2.0	✓	6.1.0	✓
arm-unknown-linux-musleabihf	1.1.24	9.2.0	✓	6.1.0	✓
armv5te-unknown-linux-gnueabi	2.27	7.5.0	✓	6.1.0	✓
armv5te-unknown-linux-musleabi	1.1.24	9.2.0	✓	6.1.0	✓
armv7-linux-androideabi [1]	9.0.8	9.0.8	✓	6.1.0	✓
armv7-unknown-linux-gnueabi	2.27	7.5.0	✓	6.1.0	✓
armv7-unknown-linux-gnueabihf	2.23	5.4.0	✓	5.1.0	✓
armv7-unknown-linux-musleabi	1.1.24	9.2.0	✓	6.1.0	✓
armv7-unknown-linux-musleabihf	1.1.24	9.2.0	✓	6.1.0	✓
i586-unknown-linux-gnu	2.23	5.4.0	✓	N/A	✓
i586-unknown-linux-musl	1.1.24	9.2.0	✓	N/A	✓
i686-unknown-freebsd	1.5	6.4.0	✓	N/A
i686-linux-android [1]	9.0.8	9.0.8	✓	6.1.0	✓
i686-pc-windows-gnu	N/A	7.5	✓	N/A	✓
i686-unknown-linux-gnu	2.23	5.4.0	✓	5.1.0	✓
i686-unknown-linux-musl	1.1.24	9.2.0	✓	N/A	✓
mips-unknown-linux-gnu	2.23	5.4.0	✓	5.1.0	✓
mips-unknown-linux-musl	1.1.24	9.2.0	✓	6.1.0	✓
mips64-unknown-linux-gnuabi64	2.23	5.4.0	✓	5.1.0	✓
mips64-unknown-linux-muslabi64	1.1.24	9.2.0	✓	6.1.0	✓
mips64el-unknown-linux-gnuabi64	2.23	5.4.0	✓	5.1.0	✓
mips64el-unknown-linux-muslabi64	1.1.24	9.2.0	✓	6.1.0	✓
mipsel-unknown-linux-gnu	2.23	5.4.0	✓	5.1.0	✓
mipsel-unknown-linux-musl	1.1.24	9.2.0	✓	6.1.0	✓
powerpc-unknown-linux-gnu	2.23	5.4.0	✓	5.1.0	✓
powerpc64-unknown-linux-gnu	2.23	5.4.0	✓	5.1.0	✓
powerpc64le-unknown-linux-gnu	2.23	5.4.0	✓	5.1.0	✓
riscv64gc-unknown-linux-gnu	2.27	7.5.0	✓	6.1.0	✓
s390x-unknown-linux-gnu	2.23	5.4.0	✓	5.1.0	✓
sparc64-unknown-linux-gnu	2.23	5.4.0	✓	5.1.0	✓
sparcv9-sun-solaris	1.22.7	8.4.0	✓	N/A
thumbv6m-none-eabi [4]	2.2.0	4.9.3		N/A
thumbv7em-none-eabi [4]	2.2.0