1. A system for tracing and fixing unknowns (Xs) in gate-level simulation, the system comprising: an X-tracing simulation processing component that receives a waveform from a first logic simulation, a design netlist and variables with Xs and time and performs an X-tracing analysis by tracing at least one X backward, and outputting zero or one or more X-pessimism fixes as an auxiliary code; a resimulation processing component that implements the zero or one or more X-pessimism fixes and performs a second logic simulation based upon the implemented X-pessimism fixes, wherein the logic simulation indicated at least one of: the X-tracing analysis is complete, and further X-tracing analysis is needed.