Concepts of Programming Languages

10.3 Implementing Subprograms with Stack-Dynamic Local Variables 445

memory with the code for MAIN. Then, it had to patch in the target addresses for

all calls to A, B, C, and any library subprograms in A, B, C, and MAIN.

10.3 Implementing Subprograms with Stack-Dynamic Local Variables

We now examine the implementation of the subprogram linkage in languages in

which locals are stack dynamic, again focusing on the call and return operations.

One of the most important advantages of stack-dynamic local variables

is support for recursion. Therefore, languages that use stack-dynamic local

variables also support recursion.

A discussion of the additional complexity required when subprograms can

be nested is postponed until Section 10.4.

10.3.1 More Complex Activation Records

Subprogram linkage in languages that use stack-dynamic local variables are

more complex than the linkage of simple subprograms for the following reasons:

• The compiler must generate code to cause the implicit allocation and deal-
  location of local variables.

Figure 10.2

The code and
activation records of
a program with simple
subprograms

MAIN

Data

Code

A

B

C

MAIN

A

B

C

Local variables

Local variables

Parameters

Return address

Local variables

Parameters

Return address

Local variables

Parameters

Return address