GCC CALLING CONVENTION

gcc.asm

.MODEL SMALL
.STACK 100H
.DATA
.CODE

PROC MAIN
    
    MOV AX, @DATA
    MOV DS, AX                                  
    
    PUSH 1                ; SS:BP+6            (a)
    PUSH 2                ; SS:BP+4            (b)
    
    CALL ADD_NUMBERS               
    
    MOV DX, AX            ; SS:BP+2            (return address)
    ADD DX, 48
    MOV AH, 2
    INT 21H
    
    MOV AH, 4CH
    INT 21H
    
ENDP

PROC ADD_NUMBERS
    ;PROLOGUE
    PUSH BP               ; SS:BP             (local stack frame)
    MOV BP, SP
    
    ;SAVE REGISTERS
    PUSH SI               ; SS:BP-2           
    PUSH DI               ; SS:BP-4
    PUSH BX               ; SS:BP-6
    
    ; LOCAL VARIABLE
    SUB SP, 2             ; SS:BP-8           (c)
    
    ; CALCULATE           ; a = b+c
    MOV BX, SS:BP+6       ;                   (mov a to bx)
    ADD BX, SS:BP+4       ;                   (add b to bx)
    MOV SS:BP-8, BX       ;                   (mov bx to c)
    
    ; RETURN
    MOV AX, SS:BP-8       ;                   (save return value c to ax)
    
    ; CLEAN VARIABLES
    ADD SP, 2             ;                   (delete local variable)
    
    ;RESTORE REGISTERS
    POP BX
    POP DI
    POP SI
    
    ;EPILOGUE
    MOV SP, BP            ;                   (reset base frame)
    POP BP
RET    
       
END MAIN