1. Stack Memory 1 (also called Call Stack)
Yung-Hsiang Lu
Purdue University

2. Return Location
Computer programs are stored in memory. Every statement has a location in memory.
When a function is called, the location of the statement after this function call is stored in the stack memory.
location 1
void f1(int x)
location 2 {
location 3
int a;
location 4
a = x + 3;
location 5
f2(a);
location 6
...
location 7 }

3. Return Location
Computer programs are stored in memory. Every statement has a location in memory.
When a function is called, the location of the statement after this function call is stored in the stack memory.
location 1
void f1(int x)
location 2 {
location 3
int a;
location 4
a = f2(x);
location 5
x = a + 5;
location 6
...
location 7 }
This is a simplified model but it is sufficient here.
This is the return
location of the
function call

4. Return Location in Stack Memory
void f1(int x)
location 2 {
location 3
int a;
location 4
a = f2(x);
location 5
x = a + 5;
location 6
...
location 7 }
This is the return
location of the
function call
location 5

5. Return Location in Stack Memory
void f1(int x)
location 2 {
location 3
int a;
location 4
a = f2(x);
location 5
x = a + 5;
location 6
...
location 7 }
location 8
int f2(int y)
location 9
location 10
location 11
f3( ... );
location 12
This is the return
location of the
function call f2
This is the return
location of the
function call f3
location 12
location 5

6. Return Location in Stack Memory
void f1(int x)
location 2 {
location 3
int a;
location 4
a = f2(x);
location 5
x = a + 5;
location 6
...
location 7 }
location 8
int f2(int y)
location 9
location 10
location 11
f3( ... );
location 12
This is the return
location of the
function call f2
location 5

7. This is always true. There is no exception in any case.
When a function is called, the statement after the call is stored in the stack memory.
This is always true.
There is no exception in any case.

8. Let's Be More Precise
Imagine that every statement has a corresponding line number.
When a function is called, the line number after the call is stored in the stack memory.
(Actually, it is called the "program counter", not the line number. We use the line number for simplicity.) 1
void f1(int x) 2 { 3
int a; 4
a = f2(x); 5
x = a + 5; 6
... 7 } 8
int f2(int y) 9 10 11
f3( ... ); 12
line 5

9. Push and Pop Push Pop Push: adding an item to the top of the stack
Pop: removing the top item from the stack

10. This is a run-time action
Nothing is pushed if there is no function call during execution
In this example, function f2 is not called and the return location (line 7) is not pushed to the stack memory 1
void f1(int x) 2 { 3
int a; 4
if (not true) 5 6
a = f2(x); 7
.... 8

11. Different Call Sites
In this example, function f2 is called in two different locations (lines 4 and 6). Each call has corresponding return location (line 5 and 7 respectively) 1
void f1(int x) 2 { 3
int a; 4
a = f2 (x); 5
.... 6
a = f2(x); 7 8

12. The stack memory can store four types of information
The stack memory can store four types of information. The return location is the first type.