Exception Module
Role in the System
A mechanism is needed by which errors that occur during user programs can be trapped, so as not to allow non-sensical results to permeate through the system. Examples of such events are:
- arithmetic overflow
- division by zero
- etc
If such a scenario occurs, control must be passed from the user to the operating system so that the event can be handled. Interrupts are errors generated within the computer system itself, and these handlers are encapsulated in the Interrupt Module. The purpose of this module is to contain the definitions and implementations of routines which signal an exception. The relevant file is located in exception.cc. One of the assignments for NACHOS involves the students implementing some of these exception cases. Related to the exception module is a suite of routines which are known as system calls. These are types of exceptions which may be raised by user programs as processes are executing. The relevant file is syscall.h. One of the assignments for NACHOS involves the students implementing such calls as:
- create
- open
- close
- fork
- yield
- join