You're reading the documentation for an older, but still supported, version of ROS 2. For information on the latest version, please have a look at Humble.
- Open Robotics provides pre-built ROS 2 packages for multiple platforms, but a number of developers still rely on cross-compilation for different reasons such as:
The development machine does not match the target system.
Tuning the build for specific core architecture (e.g. setting -mcpu=cortex-a53 -mfpu=neon-fp-armv8 when building for Raspberry Pi3).
Targeting a different file systems other than the ones supported by the pre-built images released by Open Robotics.
How does it work ?
Cross-compiling simple software (e.g. no dependencies on external libraries) is relatively simple and only requiring a cross-compiler toolchain to be used instead of the native toolchain.
There are a number of factors which make this process more complex: - The software being built must support the target architecture. Architecture specific code must be properly isolated and enabled during the build according to the target architecture. Examples include assembly code. - All dependencies (e.g. libraries) must be present, either as pre-built packages or also cross-compiled before the target software using them is cross-compiled. - When building software stacks (as opposed to standalone software) using build tools (e.g. colcon), it is expected that the build tool provides a mechanism to allow the developer to enable cross-compilation on the underlying build system used by each piece of software in the stack.
Cross-compiling ROS 2
The ROS 2 cross-compile tool is under shared ownership of Open Robotics and ROS Tooling Working Group. It is a Python script that compiles ROS 2 source files for supported target architectures using an emulator in a docker container. Detailed design of the tool can be found on ROS 2 design. Instructions to use the tool are in the cross_compile package.
If you are using an older version, please follow the cross-compilation guide.