In the section on parameter passing, we saw how to pass parameters from a caller to a callee and how to access those parameters during the execution of the callee.

To make the callreturn protocol complete, we also need to show how to allocte variables local to a particular subprogram. These variables are allocated on the stack. Fortunately, we already have all the architectural support we need for local variables.

We will use the following stack frame layout

Allocation of local variables must now be integrated into the callreturn protocol as follows

Caller Callee
—— ——

compute argument n in R1
push R1
…
compute argument 1 in R1
push R1
jsr callee
addsp -m (to allocate m vars)
compute return value in R0
addsp m (to deallocate vars)
ret
addsp n (to pop arguments)