Commented out code, self modifying code, overlapping code, copy pasted code, code integrated from other species, even code integrated from malware. Execution of fragments requires solving quantum mechanics for large particles and in practice is done by random changes followed up by measurement of the result. Execution of the entire thing past a few initial bootloader steps has never been achieved in vitro, let alone in a controllable simulation with something that resembles a debugger.
Lack of a debugger should not be a problem, as we all know printf is the best debugger. Unfortunately this system's printf implementation has numerous known and unknown output bugs, so what it tells you requires many years of training to interpret with 70% accuracy.
