ascjones / cargo-xbuild

Automatically cross-compiles the sysroot crates core, compiler_builtins, and alloc.

cargo-xbuild

Cargo-xbuild is a wrapper for cargo build, which cross compiles the sysroot crates core, compiler_builtins, and alloc for custom targets. It is a simplified fork of xargo, which is in maintainance mode.

Dependencies

• The rust-src component, which you can install with rustup component add rust-src.

• Rust and Cargo.

Installation

$ cargo install cargo-xbuild

Note: The latest version of cargo-xbuild supports all nightlies after 2019-02-04. If you are on an older nightly, you need to install version 0.5.4: cargo install cargo-xbuild --version 0.5.4.

Usage

Just use cargo xbuild instead of cargo build when cross-compiling for a custom target.

cargo xbuild --target your-target-name.json

Instead of the "can't find crate for core" error you would get with a plain cargo build, this crate cross-compiles the core, compiler_builtins, and alloc crates and then invokes cargo build with a modified sysroot. The sysroot is compiled in the target directory of your crate.

All additional arguments (e.g. --release or --verbose) are forwarded to cargo build.

Configuration

To configure cargo-xbuild create a package.metadata.cargo-xbuild table in your Cargo.toml. The following options are available:

[package.metadata.cargo-xbuild]
memcpy = true
sysroot_path = "target/sysroot"

• The memcpy flag defines whether the mem feature of the compiler_builtins crate should be activated. Turning this flag off allows to specify own versions of the memcpy, memset etc. functions.
• The sysroot_path flag specifies the directory where the sysroot should be placed.

Environment Variables

In addition to the above configuration keys, cargo-xbuild can be also configured through the following environment variables:

• The XBUILD_SYSROOT_PATH variable can be used to specify where cargo-xbuild should place the generated sysroot. This variables takes precendence over the package.metadata.cargo-xbuild.sysroot_path configuration key.

Dev channel

If you want to use a local Rust source instead of rust-src rustup component, you can set the XARGO_RUST_SRC environment variable.

# The source of the `core` crate must be in `$XARGO_RUST_SRC/libcore`
$ export XARGO_RUST_SRC=/path/to/rust/src

$ cargo xbuild --target msp430-none-elf.json

Using on Android

It's possible to run cargo-xbuild on your Android phone:

Install Termux and Nightly Rustc

• Install termux
• Install fish shell and set as default (optional): pkg install fish; chsh -s fish; fish
• Install some basic tools: pkg install wget tar
• Add the community repository by its-pointless: wget https://its-pointless.github.io/setup-pointless-repo.sh; bash setup-pointless-repo.sh
• Install rust nightly: pkg install rustc cargo rustc-nightly
• Prepend the nightly rustc path to your $PATH in order to use nightly (fish syntax): set -U fish_user_paths $PREFIX/opt/rust-nightly/bin/ $fish_user_paths
• rustc --version should now return a nightly version

(Optional) Install Git and Clone your Repository

• Install git: pkg install git
• Clone a repository of your choice: git clone https://github.com/phil-opp/blog_os.git

Install Xbuild

• Install cargo-xbuild: cargo install cargo-xbuild
• Add the cargo bin directory to your $PATH (fish syntax): set -U fish_user_paths ~/.cargo/bin/ $fish_user_paths
• Now cargo xbuild should be available.

It does not work yet because it needs access to the rust source code. By default it tries to use rustup for this, but we have no rustup support so we need a different way.

Providing the Rust Source Code

The Rust source code corresponding to our installed nightly is available in the its-pointless repository:

• Download it: wget https://github.com/its-pointless/its-pointless.github.io/raw/master/rust-src-nightly.tar.xz
• Extract it: tar xf rust-src-nightly.tar.xz
• Set the XARGO_RUST_SRC environment variable to tell cargo-xbuild the source path (fish syntax): set -Ux XARGO_RUST_SRC ~/rust-src-nightly/rust-src/lib/rustlib/src/rust/src

Now cargo-xbuild should no longer complain about a missing rust-src component. However it will throw an I/O error after building the sysroot. The problem is that the downloaded Rust source code has a different structure than the source provided by rustup. We can fix this by adding a symbolic link:

ln -s ~/../usr/opt/rust-nightly/bin ~/../usr/opt/rust-nightly/lib/rustlib/aarch64-linux-android/bin

Now cargo xbuild --target your-target.json should work!

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.