cargo_configuration.md

• Configuring cross
• Configuring Cargo through environment variables
• Use Xargo instead of Cargo

Configuring cross

Please refer to the following docs:

• config file
• env variables

Configuring Cargo through environment variables

When cross-compiling, cargo does not use environment variables such as RUSTFLAGS, and must be provided using CARGO_TARGET_${TARGET}_${OPTION}. Please note that some of these may be provided by the image themselves, such as runners, and should be overwritten with caution. A list of important flags includes:

• CARGO_TARGET_${TARGET}_LINKER: specify a custom linker passed to rustc.
• CARGO_TARGET_${TARGET}_RUNNER: specify the wrapper to run executables.
• CARGO_TARGET_${TARGET}_RUSTFLAGS: add additional flags passed to rustc.

Any of the following flags can be provided, and are converted to uppercase. For example, changing foo-bar would be provided as CARGO_TARGET_${TARGET}_FOO_BAR.

For example, to run binaries on i686-unknown-linux-gnu with Qemu, first create a custom image containing Qemu, and run with the following command:

CARGO_TARGET_I686_UNKNOWN_LINUX_GNU_RUNNER=qemu-i386 cross run ...

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.