C++ and Rust interoperability

Make a Rust-Library available in C++.

Goals

• The Rust library integrates seamlessly into a C++ project
• Minimal leakage of Rust types to C++
• The Rust library exposes C++ ergonomics for interaction with the library
• The Rust library is easy to integrate into CMake build

Approach

• person is a pure Rust library
  • No FFI-Code
  • easy to re-use in pure Rust context
• person-cpp takes care of the bindings between C++ and Rust
  • A C++ header file is exposed with the declaration of a wrapper class

Building

• Configure cmake -S . -B build
• Configure for release cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
• Build cmake --build build
  • Run Unit Tests cmake --build build --target person-test-rs

Cross Compilation

Cross compilation can be a tricky endeavour. Follwow this guide to cross compile this project for a Raspberry Pi 3 running Debian "Bullseye"

Toolchain Build

Gather information of the target system. Run this on your target platform.

• cat /etc/os-release to get OS information
• uname -srm to get Kernel and CPU architecture information
• ldd --version to find the version of GLIBC

A sensible way to get a cross build toolchain is using crosstool-NG. It offers a lot of configuration options to match your target system well.

Install crosstool-NG following the instructions

Configuring the Toolchain (based on a sample)

• ct-ng list-samples and pick your sample (here aarch64-unknown-linux-gnu)
• ct-ng aarch64-unknown-linux-gnu to build base configuration
• ct-ng menuconfig to adapt compiler, GLIBC version, etc. This is important, the base config gives the latest compiler, libraries, etc.
• ct-ng build to build the toolchain. It is likely placed in ${HOME}/x-tools/aarch64-rpi3-linux-gnu/
  • add the toolchain to your path PATH=$PATH:~/x-tools/aarch64-rpi4-linux-gnu/bin (to .bashrc to make it persistent)

Install the right rust cross compiler with rustup target add aarch64-unknown-linux-gnu

Cross Compilation

• Pass the toolchain file for manual configuration: cmake -S . -B build_target -DCMAKE_TOOLCHAIN_FILE=aarch64-unknown-linux-gnu.cmake
• Build cmake --build build_target

Running the binary on target

• Copy the binary to a running Raspberry Pi using scp: scp <binary> pi@<IP>:/home/pi

• SSH into target and run the binary

• sudo apt-get install gcc-arm-linux-gnueabihf g++-arm-linux-gnueabihf crossbuild-essential-armhf

• rustup target add armv7-unknown-linux-gnueabihf