EDIT: Do you think it's a good idea to creat a topic at DryOs Development?
Yes, excellent idea, I just did.

So, this is my status for the day. I'm looking at a470 for reference, and I could almost finish boot.c.
Good job! We should somehow coordinate our work, I created a git repository at github so I could mirror everyone's changes there (I've also started looking at the firmware to locate some functions, but haven't committed anything yet).
Maybe you could drop by on IRC?
However, when I tried to compile a test, it misses some functions, and also, when putting nullsub to this missing functions, it gives lots of errors of linking, like "undefined reference to `malloc`", which had his name detected by sigfinder.
I am not yet familiarized with CHDK's build system, my guess is that some .a/.o is missing from the makefile / linker command, or you didn't put the stubs in the right file so the .a/.o doesn't get built in the first place (?), but it's really nothing but a guess.
@fe50: Thanks
