occasionally extremely sad that the PS2 homebrew scene has been so burned by GPL compliance issues that all the important tools which were once open-source have gone closed-source and are now sporadically maintained by people who are utterly burned out on it
you can get source for some, rather old, versions of Free MCBoot, but if you want the current version with bug fixes and support for booting from the internal HDD, that’s closed source baby and will never not be