I was trying to understand what this project is. It's some sort of open firmware for Canon camera that you put on the flash card (SD). The home page has info: https://www.magiclantern.fm/
It's not firmware, which is a nice bonus, no risk of a bad rom flash damaging your camera (only our software!).
We load as normal software from the SD card. The cam is running a variant of uITRON: https://en.wikipedia.org/wiki/ITRON_project
We're a normal program, running on their OS, DryOS, a variant of uITRON.
This has the benefit that we never flash the OS, removing a source of risk.