This is the start of a core library for STM8S microcontrollers, mainly being done for some of my personal projects. I put this together as the ST library license terms didn't seem to be quite as open as I'd like, especially since it requires modifications to work with SDCC.
Feel free to use this, fork it, etc.
Right now it's pretty much a peripheral register map for STM8S003/STM8S103 chips - since that's what I'm currently playing with - and isn't even quite complete there, though most generally used peripherals are covered.
Also note that at this point, it hasn't been tested in any projects.
If you give this a try, let me know... and if you find any bugs, I'll be happy to fix 'em.