Program traces are generated by running VICE's C64 emuluator (x64) with the collect_data program, to generate the list of KERNAL calls that a program makes. This is used to generate the set of entry points that are required in order to provide interoperability with the original C64 KERNAL.
To collect a program trace:
x64 -remotemonitor & build/tools/collect_data localhost 6510 | tee logfile