Advanced Rust Cross Compiling

In the future there may be the need to cross compile KubOS for targets not currently supported. This document gives instructions for setting up cross compiling support for those targets.

First check the Rust Platform Support for your target. If it is not in this list…then contact us via Slack.

If it is in the list, then step one is to attempt to install the triple via rustup:

$ rustup target add target-triple-here

If this installs correctly then all you need is a working gcc toolchain and you should be good to go! There is one piece of necessary cargo configuration needed. A cargo config file named config in either $HOME/.cargo or $PROJECT/.cargo folder. Inside you’ll need to set the following options:

linker = "$TOOLCHAIN/toolchain-name-gcc"
ar = "$TOOLCHAIN/toolchain-name-ar"

If the desired target is under Tier 2.5 or Tier 3 then it likely cannot be added directly via rustup and will required additional work.

First these dependencies need to be installed:

$ cargo install xargo
$ rustup default nightly-2020-01-29
$ rustup component add rust-src

You will also need a functional gcc cross-compiling toolchain in an accessible location that we’ll call $TOOLCHAIN.

The environment variables CC and CXX need to be set prior to beginning to cross compile:

$ export CC=$TOOLCHAIN/bin/target-triple-gcc
$ export CXX=$TOOLCHAIN/bin/target-triple-g++

Now run this command in your Rust project:

$ xargo build --target target-triple-here

If you get an error about can't find crate for 'std' then:

Now create the following files in your Rust project:


stage = 0


linker = "$TOOLCHAIN/toolchain-name-gcc"
ar = "$TOOLCHAIN/toolchain-name-ar"

And rebuild. You may also want to delete the $HOME/.xargo and target folders before rebuilding.

If you get an error about can't find a crate for 'panic_unwind then you may need to define a release profile and start building in release mode.

Add this to Cargo.toml:

panic = "abort"

Then build with:

xargo build --target target --release