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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.

Alternative: The build-std feature of cargo

Cargo now has its own feature for cross compiling the sysroot: build-std. You can use it by passing -Z build-std=core,alloc to cargo build. Alternatively, you can specify the following in a .cargo/config.toml file:

[unstable]
build-std = ["core", "compiler_builtins", "alloc"]

The above requires at least Rust nightly 2020–07–15. With the above config in place, the normal cargo build command will now automatically cross-compile the specified sysroot crates.

The compiler may emit references to memset, memcpy, etc which are usually provided by the platform's libc but luckily compiler_builtins has a mem feature that will provide implementations of those functions. To enable that feature we can use the unstable cargo flag -Z build-std-features=compiler-builtins-mem or specify the following in a config.toml:

[unstable]
build-std = ["core", "compiler_builtins", "alloc"]
+build-std-features = ["compiler-builtins-mem"]

Note that using the compiler-builtins-mem requires at least Rust nightly 2020-09-30. For older versions you need to add a dependency on the rlibc crate to provide implementations of memset, memcpy, etc, which the compiler expects. Note that you need to add an extern crate rlibc statement in order for this to work (even in the 2018 edition of Rust). This is required to get cargo to link the otherwise unused crate.

Compared to cargo-xbuild, there are many advantages of using cargo's own feature:

So it is strongly recommended to try the build-std feature of cargo instead of using this crate.

Dependencies

Installation of cargo-xbuild

In case you decide to use cargo-xbuild instead of cargo's build-std feature for some reason, you can install this crate through:

$ cargo install cargo-xbuild

Note: The latest version of cargo-xbuild supports all nightlies after 2020-07-30. If you are on an older nightly, you need to install version 0.5.35: cargo install cargo-xbuild --version 0.5.35.

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"
panic_immediate_abort = false

Environment Variables

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

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/core`
$ 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

(Optional) Install Git and Clone your Repository

Install Xbuild

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:

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

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.