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.

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

See our Getting Started guide for detailed
installation instructions.

• 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 or use rootless docker.
  Read the container engine install guide for the required installation and post-installation steps. Requires version 20.10 (API 1.40) or later.
• Podman. Requires version 3.4.0 or later.

Installation

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

It’s also possible to directly download the pre-compiled release
binaries or use
cargo-binstall.

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 or the docs/ subfolder.

Configuration

Configuring cross behavior

You have four 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 [workspace.metadata.cross] table, i.e. key prefix. An example
config snippet would look like this:

[workspace.metadata.cross.target.aarch64-unknown-linux-gnu]
# Install libssl-dev:arm64, see <https://github.com/cross-rs/cross/blob/main/docs/custom_images.md#adding-dependencies-to-existing-images>
pre-build = [
    "dpkg --add-architecture $CROSS_DEB_ARCH",
    "apt-get update && apt-get --assume-yes install libssl-dev:$CROSS_DEB_ARCH"
]
[workspace.metadata.cross.target.armv7-unknown-linux-gnueabi]
image = "my/image:latest"
[workspace.metadata.cross.build]
env.volumes = ["A_DIRECTORY=/path/to/volume"]

Option 2: Configuring cross via a Cross.toml file

You can put your configuration 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.

Option 4: Configuring cross through environment variables

Besides the TOML-based configuration files, config can be passed through
environment variables, too.

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.

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.

[1] libc = bionic; Only works with native tests, that is, tests that do not
depends on the Android Runtime. For i686 some tests may fails with the
error assertion failed: signal(libc::SIGPIPE, libc::SIG_IGN) != libc::SIG_ERR, see [issue

#140](https://github.com/cross-rs/cross/issues/140) for more information.

[2] No std component available.

[3] For some *BSD and Solaris targets, the libc column indicates the OS
release version from which libc was extracted.

[4] libc = newlib

[5] Must change
image = "ghcr.io/cross-rs/x86_64-unknown-linux-gnu:main-centos" in
Cross.toml for [target.x86_64-unknown-linux-gnu] to use the
CentOS7-compatible target.

[6] libc = emscripten and GCC = clang

[7] Must change
image = "ghcr.io/cross-rs/aarch64-unknown-linux-gnu:main-centos" in
Cross.toml for [target.aarch64-unknown-linux-gnu] to use the
CentOS7-compatible target.

Additional Dockerfiles for other targets can be found in
cross-toolchains. These include
MSVC and Apple Darwin targets, which we cannot ship pre-built images of.

Debugging

QEMU_STRACE (v0.1.9+)

You can set the QEMU_STRACE variable when you use cross run to get a backtrace
of system calls from “foreign” (non x86_64) binaries.

$ cargo new --bin hello && cd $_
$ QEMU_STRACE=1 cross run --target aarch64-unknown-linux-gnu
9 brk(NULL) = 0x0000004000023000
9 uname(0x4000823128) = 0
(..)
9 write(1,0xa06320,14)Hello, world!
 = 14
9 sigaltstack(0x4000823588,(nil)) = 0
9 munmap(0x0000004000b16000,16384) = 0
9 exit_group(0)

Minimum Supported Rust Version (MSRV)

This crate is guaranteed to compile on stable Rust 1.77.2 and up. It might
compile with older versions but that may change in any new patch release.

Some cross-compilation targets require a later Rust version, and using Xargo
requires a nightly Rust toolchain.

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or
  http://www.apache.org/licenses/LICENSE-2.0)
• MIT License (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
dual licensed as above, without any additional terms or conditions.

Code of Conduct

Contribution to this crate is organized under the terms of the Rust Code of
Conduct, the maintainer of this crate, the cross-rs team, promises
to intervene to uphold that code of conduct.