It is clear that booting a system based on an application processor requires multiple binaries and possibly multiple hardware components - at the very least, one to initialize the DRAM and one to run in it. This implies that the various components of the chain, however many, need to be aware of the respective next and previous one somehow: Any component has to know the source, the protocol, and the destination for loading the next one, and the build system needs to create an overall image for the target platform, typically also requiring extra data structures that adhere to the mask ROM or other prior loader, possibly containing signatures or similar for a secure boot flow.

With this presentation, we summarize the development of the oreboot and LinuxBoot build systems over time, what has been considered and attempted, and how things worked out, and compare with other firmware projects, such as U-Boot and coreboot. We explain why it is important to know and understand the full chain and its build process for both security and reliability, and finally provide a list of necessary features to be worked on for the future.