CHAPTER 26 — Simple Subroutine Linkage

All high level languages have the concept of a subroutine (sometimes called procedure, function, or method). A subroutine is a logical division of the code that may be regarded as a self-contained operation. A subroutine might be executed several times with different data as the program executes.

This chapter looks at a simple implementation in assembly language of this idea. The simple implementation is not adequate for the full power of subroutines (as implemented in high level languages), but is a good starting point. It corresponds to the type of subroutines implemented in the very early days of programming.

Chapter Topics:

• Subroutine call.
• Caller and Callee routines.
• jal and jr instructions
• The
$ra register.
• The simple linkage calling convention.
• Register use in subroutines

The following chapters discuss subroutine call methods that are similar to those of modern languages.