1 About this module

• Prerequisites:
• Objectives: This module explains various aspects of subroutines and how to implement C subroutines in assembly language using the Toy processor.

2 Calling and returning

First, let us example the following C program:

This program does not do much, but illustrates a single subroutine call. At this point, we are only concerned about the control structure. In other words, we only want to know what happens when f is invoked from main, and what happens at the end of the function f when execution gets back to main to execute the return statement in main.

The invocation on line ?? needs to do the following:

• save the return address, where to continue execution when the invoked subroutine is finished
• continue execution at the beginning of the invoked subroutine