Function Calls and Program Activation records / Stack Frames

1. Nitin Reddy Katkam
nitinkatkam.com
n4express.com
knreddy.com

2.  Also called Stack Frames
 Activation records are entries on a call stack
 They maintain information about functions
being called and their return locations
 They also contain parameters and local
variables

3.  Contains an activation record for each
function that is called
 Grows backwards (higher memory address to
lower memory address)
 Has a stack pointer pointing to the top of the
stack

4. void function2() {
…
Each function call
function2(); adds an activation
…
} record to the call
stack Stack
void function1() { Pointer
…
} function2_1
function2
int main() {
…
function1
function1();
…
} main

5. Register Values
Local Variables
Caller’s Frame/Base Pointer
Return Address
Parameters

6. int main()
{
}
main

7. void func1(int a)
{
int x;
}
int main()
{
func1(3); func1
}
main

8. void func1(int a)
{
int x;
}
Register values
int main()
int x
{
Frame ptr of main()
func1(3); func1
Program counter of
} main() main
int a

9.  An activation record is created on the call
stack when a function is called (winding).
 The activation record is removed from the
call stack when the function returns
(unwinding).
 “Why can’t you return a pointer to a local variable
declared within a function?”

10.  Recursive function calls will add an activation
record to the stack for each call
 “What is a stack overflow?”

11.  You can use pointers to access the activation
record
 Example:
 void func(int a) {
printf(“Return address: %xn”, &a-1);
}

12.  Email: k.nitin.r [at] gmail