A source line simulator system determines a line of source code that corresponds to a virtual return address in response to executing a debugging command on the source code. The simulator system determines whether the line of source code that corresponds to the virtual return address is correct and can enable a simulator mode based on a determination that the line of source code that corresponds to the virtual return address is not correct. The simulator system can generate a debugging graphical user interface (GUI) that displays an indicator at a line of source code that is correct.