1. CS-401 Computer Architecture & Assembly Language Programming
Lecture-44
Interfacing with High Level Languages

2. Lets Revise the Last Lecture

3. Calling Conventions

4. Calling Conventions Naming conventions Parameter passing
Registers that must be preserved
Registers used as scratch
Registers which hold the return value
Responsibility of clearing the parameters

5. C Vs PASCAL Naming Conventions
C PASCAL
An underscore is Case sensitive
Prep ended all uppercase name
Case sensitive

6. C Vs PASCAL Naming Conventions
Parameter Passing
C PASCAL
Pushed in reverse Pushed in proper
Order order

7. C Vs PASCAL Naming Conventions
Registers that must be preserved
C PASCAL
EBX, EDI, EBP, ESP, DS, ES and SS

8. C Vs PASCAL Naming Conventions
Registers used as scratch
C PASCAL
EAX, ECX, EDX, FS, GS, EFLAGS and all others

9. C Vs PASCAL Naming Conventions
Registers which hold the return value
C PASCAL
EAX (32 – bit value)
EDX:EAX (64 – bit value)

10. C Vs PASCAL Naming Conventions
Responsibility of clearing parameters
C PASCAL
Caller Callee

11. Calling C from Assembly
Responsibility of clearing parameters
int divide(int dividend, int divisor);
push dword [mydivisor]
Push dword [mydividend]
Call_divide
Add esp,8
;EAX holds the answer

12. Swap in C void swap (int *p1, int *p2) { int temp = *p1; *p1 = *p2;
*p2 = temp; }

13. Calling Swap from Assembly
[section .text]
extern_swap
x:dd 4
y:dd 7
push dword y
push dword x
call_swap ; will only retain the ; specified registers
add esp,8

14. Swap in Assembly [segment .text] global _swap _swap:
mov ecx,[esp+4] ;copy parameter p1
mov edx,[esp+8] ;copy parameter p2
mov eax,[ecx] ;copy *p1 into eax
xchg eax,[edx] ;copy eax into *p2
mov [ecx],eax ;copy ecx into *p1
ret

15. OBJ file in win32

16. Swap In Assembly Language