1. int add3 (int a, int b, int c) { return a + b + c; } int sum = 0; main () sum += add3 (1, 2, 3); sum += 10; sum += add3 (10, 20, 30);

2. int add3 (int a, int b, int c) { return a + b + c; } int sum = 0; main () sum += add3 (1, 2, 3); sum += 10; sum += add3 (10, 20, 30);
main ()
add3 (1, 2, 3)
sum +=
sum += 10
add3 (10, 20, 30)
sum +=

3. 1. Call from anywhere int add3 (int a, int b, int c) {
return a  +  b + c; }
int sum = 0;
main ()
   sum += add3 (1, 2, 3);
   sum += 10;
   sum += add3 (10, 20, 30);
1. Call from anywhere

4. 2. Pass Values to Parameters – can be different
int add3 (int a, int b, int c) {
return a  +  b + c; }
int sum = 0;
main ()
   sum += add3 (1, 2, 3);
   sum += 10;
   sum += add3 (10, 20, 30);
2. Pass Values to Parameters – can be different
1. Call from anywhere

5. 3. Subroutine returns a value
int add3 (int a, int b, int c) {
return a  +  b + c; }
int sum = 0;
main ()
   sum += add3 (1, 2, 3);
   sum += 10;
   sum += add3 (10, 20, 30);
3. Subroutine returns a value
Call from anywhere
Pass Values to Params Can be different

6. 4. Execution Resumes After the Call
int add3 (int a, int b, int c) {
return a  +  b + c; }
int sum = 0;
main ()
   sum += add3 (1, 2, 3);
   sum += 10;
   sum += add3 (10, 20, 30);
4. Execution Resumes After the Call
Call from anywhere
Pass Values to Params Can be different
Sub returns a value

7. 5. Can have local variables
int add3 (int a, int b, int c)
{ int tmp = a  +  b + c ;
return tmp; }
int sum = 0;
main () {
   sum += add3 (1, 2, 3);
   sum += 10;
   sum += add3 (10, 20, 30);
5. Can have local variables
Call from anywhere
Pass Values to Params Can be different
Sub returns a value
Subroutine “returns” to where it was called from

8. Callee Caller Call site
int add3 (int a, int b, int c) { return a + b + c; } int sum = 0; main () sum += add3 (1, 2, 3); sum += 10; sum += add3 (10, 20, 30);
Call from anywhere
Pass Values to Params Can be different
Sub returns a value
Subroutine “returns” to where it was called from
Local variables
Call site

9. Calling Conventions Call from anywhere
Return to where it was called from

10. boo () { coo (); } coo () return;
br coo
boo_1: … 
coo:
br boo_1

11. boo () { coo (); } coo () return;
br coo
boo_1:
boo_2: … 
coo:
br ?????

12. boo () { coo (); } coo () return;
call coo
boo_1:
boo_2: … 
coo:
ret

13. call coo ret r31 = ra boo: call coo boo_1: boo_2: … coo: ret
r31 = PC + 4
PC = coo
ret
PC = r31
r31 = ra
boo:
call coo
boo_1:
boo_2: … 
coo:
ret

14. boo: call coo boo_1: ret coo: call doo coo_1: ret doo:
boo () { coo (); } coo () doo (); return; doo ()
boo:
call coo
boo_1:
ret  
coo:
call doo
coo_1:
ret
doo:

15. .text 0x1000000 Stack PUSH POP .data TOP .bss heap R27 0x17fff80
.data
.bss
heap
0x17fff80
Stack:

16. PUSH (value) ADDI SP, SP, -4 STW R8, 0(SP) 00xFFEC 0xFFF0 0xFFF4
0xFFFC

17. Value = POP () LDW R8, 0(SP) ADDI SP, SP, +4 00xFFEC 0x12345678 0xFFF0
0xaabbccdd
0xFFFC
0xff001122

18. TOP(n) LDW R8, 8(SP) LDW R8, -8(SP) 00xFFEC 0x12345678 0xFFF0
0xaabbccdd
0xFFFC
0xff001122

19. boo () { coo (); return; } coo () doo (); doo ()
addi sp, sp, -4
stw ra, 0(sp)
call coo
boo_1:
ldw ra, 0(sp)
addi sp, sp, +4
ret
coo:
call doo
coo_1:
doo: