1. Lecture 7 Macro Review Stack Frames
CS 2130
Lecture 7
Macro Review
Stack Frames

2. Questions?

3. Macros Revisited
Write a macro to automatically check for return values from printf

4. Recall printf("some stuff %d %f", i, x);
Problem: We're ignoring the return value which could indicate a problem

5. We should write... if(printf("some stuff %d %f", i, x)<0) {
(void)fprintf(stderr,"Yikes!!!");
exit(EXIT_FAILURE); }
Which, of course, is a pain in the neck!

6. First Approach OK? #define PRINTF( stuff ) if(printf stuff <0) \
{ \
(void)fprintf(stderr,"Yikes!!!"); \
exit(EXIT_FAILURE); \ }
and we would use it like this:
PRINTF( "some stuff %d %f", i, x )
OK?

7. Not exactly... #define PRINTF( stuff ) if(printf stuff <0) \ { \
(void)fprintf(stderr,"Yikes!!!"); \
exit(EXIT_FAILURE); \ }
This is the fix:
PRINTF( ( "some stuff %d %f", i, x ) )

8. Questions?

9. Stack Frames

10. Stack Frames
A language supporting subroutines must provide a place to store the data values representing the variables of the subroutine as well as an address to return to once execution of the subroutine is complete.
Languages that don't support recursion can simply have a static "activation record" for each subroutine.
Languages that support recursion must have allocate storage for each call to the subroutine
This is normally implemented using a stack which may be known as the activation stack

11. Buzzwords
Stack pointer: a variable usually maintained in a dedicated register which points to the top of the stack. Note: In reality stacks typically grow down from high memory.
Activation record or stack frame: The area of the stack which is storing the activation information (parameters, local variables and return address, etc.) for a given module or function.
Frame pointer: a variable also maintained in a dedicated register which indicates a known point in the stack frame from whence the location of parameters and variables may be located.

12. Key concept
Converting a C program into assembly language requires that a certain known sequence of operations or at least a certain ordering of data will occur in order to call a function.
Thus when the function code is compiled it will know for certain exactly where to find it's parameters, etc.

13. Basic Idea Caller Pushing arguments on stack Push fp onto stack
MOV fp, sp
JALR Rd, Rs
(RdPC+4; PC  Rs)
Callee
Put return address on stack if necessary
Code may move sp if necessary
fp is fixed.

14. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm fp
main sp
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
Starting out assuming that
values of 15 and 10 have
been read into x and y.
The stack frame for main
is on the stack. The frame
pointer (fp) is pointing at
a known place in the frame
while the stack pointer (sp)
indicates the top of the stack

15. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm fp
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y)); sp
u: 15
Calling sequence for first call
to gcd starts by evaluating
and pushing argument values
onto stack

16. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm fp
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15 sp
v: 10

17. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm fp
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10 sp
control link (fp)
Frame pointer value is pushed
onto stack providing a control
link from new frame back to old

18. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10 fp sp
control link (fp)

19. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10 fp
control link (fp) sp
return address
Pushing return address onto
stack completes stack frame
and function execution may
start by jumping to code

20. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10 fp
control link (fp) sp
return address

21. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10 fp
control link (fp) sp
return address

22. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10 fp
control link (fp)
return address sp
u: 10
Starting second call
to gcd

23. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10 fp
control link (fp)
return address
u: 10 sp
v: 5

24. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10
control link (fp)
return address
u: 10
v: 5 fp sp
control link (fp)

25. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10
control link (fp)
return address
u: 10
v: 5 fp
control link (fp) sp
return address

26. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10
control link (fp)
return address
u: 10
v: 5 fp
control link (fp) sp
return address

27. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10
control link (fp)
return address
u: 10
v: 5 fp
control link (fp) sp
return address

28. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10
control link (fp)
return address
u: 10
v: 5 fp
control link (fp)
return address sp
u: 5
Starting third call
to gcd

29. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10
control link (fp)
return address
u: 10
v: 5 fp
control link (fp)
return address
u: 5 sp
v: 0

30. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10
control link (fp)
return address
u: 10
v: 5
control link (fp)
return address
u: 5
v: 0 fp sp
control link (fp)

31. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10
control link (fp)
return address
u: 10
v: 5
control link (fp)
return address
u: 5
v: 0 fp
control link (fp) sp
return address

32. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10
control link (fp)
return address
u: 10
v: 5
control link (fp)
return address
u: 5
v: 0 fp
control link (fp) sp
return address

33. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10
control link (fp)
return address
u: 10
v: 5
control link (fp)
return address
u: 5
v: 0 fp
control link (fp) sp
return address

34. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10
control link (fp)
return address
u: 10
v: 5
control link (fp)
return address
u: 5
v: 0 fp
control link (fp) sp
return address

35. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10
control link (fp)
return address
u: 10
v: 5
Put the return address into a register
control link (fp)
return address
u: 5
v: 0 fp
control link (fp) sp
return address

36. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10
control link (fp)
return address
u: 10
v: 5
control link (fp)
return address
u: 5
v: 0 sp fp
control link (fp)

37. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10
control link (fp)
return address
u: 10
v: 5 fp
control link (fp)
return address
u: 5
v: 0 sp
control link (fp)
We can move the SP and
jump to the return address

38. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10
control link (fp)
return address
u: 10
v: 5 fp
control link (fp) sp
return address
Put the return address into a register

39. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10
control link (fp)
return address
u: 10
v: 5 sp fp
control link (fp)

40. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10 fp
control link (fp)
return address
u: 10
v: 5 sp
control link (fp)

41. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10 fp
control link (fp) sp
return address

42. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10 fp
control link (fp) sp
return address
Put the return address into a register

43. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10 sp fp
control link (fp)

44. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm fp
main
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));
u: 15
v: 10 sp
control link (fp)

45. Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm fp
main sp
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y));

46. 5 Euclid's Algorithm int x,y; int gcd(int u, int v) { if(v == 0)
Global/static area
x: 15
y: 10
Euclid's Algorithm fp
main sp
return address
int x,y;
int gcd(int u, int v) {
if(v == 0)
return u;
else
return gcd(v,u % v); }
int main() {
scanf("%d%d", &x, &y);
printf
("%d\n",gcd(x,y)); 5

47. Questions?