Introduction

This sysroot creator can create a sysroot for use in cross compilation. The basic idea is to download package files for the intended target and extract those packages in a folder.

For example, when targetting a raspberry Pi with ubuntu the process consists of:

• Download the ubuntu package databases for arm64
• Select the packages to download
• Download and extract those deb packages to a folder

Notable issues which are handled during this process:

• Some packages contain symlinks to absolute paths. These are modified to a new absolute path, so that the symlink is valid.
• Some packages contain special files, such as /dev/null. These files are skipped, since they are not required for cross compilation. Only header files, libraries and other regular files are unpacked.

Installation

You can install this tool locally like this:

$ cargo build --release
$ ln -s `pwd`/target/release/sysroot-creator ~/.local/bin/sysroot-creator

Usage

Create a configuration file, for example my-sysroot-conf.toml, describing your intended sysroot:

    distribution_version = "focal"
    architecture = "arm64"
    folder = "sysroot-rpi3"

    packages = [
        "libcrypt-dev",
        "libtinyxml2-dev",
        "ros-foxy-rclcpp",
    ]

    [sources]

    [sources.ports]
    url = "http://ports.ubuntu.com/ubuntu-ports"
    sections = [
        "main",
        "universe",
    ]

    [sources.ros2]
    url = "http://packages.ros.org/ros2/ubuntu"
    sections = [
        "main",
    ]

Run this program to create the sysroot:

$ cargo run --release -- my-sysroot-conf.toml

Your sysroot will be located in the folder sysroot-rpi3/sysroot.

Now you can use this sysroot for cross compilation, using for example a CMake toolchain file.

How does it work?

The sysroot creator is a rust application. It first parses the toml file with the settings.

Given these settings, it downloads package database from the given sources. Those files are cached. The contents of the package databases are parsed.

Next up is package selection. Based on the intended packages, dependencies are resolved, and a list of desired packages is created.

Each package is downloaded and cached. Then it is unpacked, and it’s files are placed in the destination folder. Special files (block / character device files) are skipped, and absolute symlinks are handled.

Alternatives

There are many different ways to setup a sysroot for cross compilation.

• Use an actual target, and scp the root filesystem onto your development PC. This could be a fairly simple strategy. Take care to fix eventual symlinks when doing this.
• Use debootstrap to do a cross debootstrap. I was not yet able to do this. This seems worth a try.
• Use labapart/cross_sysroot. This project gave me the idea to attempt this version of the idea in rust. Features I added was the idea of a configuration file, and support for multiple repositories. Also, this project does not use dpkg to extract packages.