There's even more from Alex: Part 2 [0] covers getting into 32-bit protected mode, and part 3 [1] deals with compiling, linking and running C++ code. There is also a very nice presentation available [2]:

[0] http://3zanders.co.uk/2017/10/16/writing-a-bootloader2/

[1] http://3zanders.co.uk/2017/10/18/writing-a-bootloader3/

[2] http://3zanders.co.uk/2017/10/13/writing-a-bootloader/writin...