The key map is all done for you in stub_entry.S. These things are so easy these days ....
Indeed, I remember some years ago when I followed the Porting Thread of DataGhost et al. for the S5IS camera. That was the time when the development for DryOS just started, if I remember correctly. Everything seemed to be much more complicated, at least to get all the addresses collected.
I already moved the key mapping values from stub_entry.S during the beginning of my porting activities. But I didn't remember again.
I'm not really sure if mykbd_task is really running. I can use keys for normal Canon usage but I'm not able to activate the ALT menu.