组件8088打印AX，BX，AH，AL，BH，BL

Question

I am working on some stuff for a class of mine and I am stuck on an issue to keep me from progressing.

In the code below on line 10, 14 and 16 I need to print out the respective values to what the comments state. Currently I use the testPrint functions a bit lower to print out the values weather its for AX and BX or AH , AL , BH , BL . My issue is when I try to print out vaules at line 10, and use the same function to print out values on line 14, the values on line 14 are messed up and show something that is not the correct answer. When i let the program do all the proper functions like ADD , MUL etc. and print it out once at the end it works perfectly.

I can also only use one of the test print functions because the numbers get messed up if I try to use both at the same time.

I am using 8088 Assembler.

Am I missing something after calling each print function? Could anyone show show me or tell me what I need to do to head in the right direction?

Thank You so much!

This is the code:

_EXIT = 1       ! 1
_PRINTF = 127       ! 2
.SECT .TEXT         ! 3
    start:          ! 4 
MOV AX, 514         ! 5 AX = 514
MOV BX, 2       ! 6 BX = 2

firstOutput:        ! 7output original values of AX and BX
PUSH BX         ! 8
PUSH AX         ! 9
            ! 10 PRINT AX AND BX HERE (SHOULD BE 514,2)

secondOutput:           ! 11 BH = BH + BL; AH= AH - AL
ADDB BH, BL     ! 12
SUBB AH, AL     ! 13
            ! 14 PRINT AX AND BX HERE (SHOULD BE 2, 514)

thirdOutput:        ! 15 MULTIPLY AX AND BX
MUL BX          ! 16
            ! 17 PRINT AH, AL, BH, BL


!testPrint: !THIS WILL PRINT AX AND BX
!PUSH BX
!PUSH AX
!PUSH print
!PUSH _PRINTF
!SYS

testprintall: ! THIS WILL PRINT AH, AL, BH, BL
MOV CX, 0           ! 
MOVB CL, BL         ! 
PUSH CX             ! 
MOVB CL, BH         ! 
PUSH CX             ! 
MOVB CL, AL         ! 
PUSH CX             ! 
MOVB CL, AH         ! 
PUSH CX             ! 
PUSH printahalbhbl  ! 
PUSH _PRINTF        ! 
SYS !

exit:                   ! Exit 
PUSH 0              ! 
PUSH _EXIT          ! 
SYS                 !

 .SECT .DATA            ! 
 print:                 ! 
 .ASCIZ "AX:%d, BX:%d\n" !  
 .SECT .BSS                 ! 

 printahalbhbl:             ! 
 .ASCIZ "AH:%d, AL:%d, BH:%d, BL:%d\n" !
 .SECT .BSS                 !

Answer 1

Two things are missing here:

First is saving all registers that the _printf is allowed to change. AX is among them. Second is cleaning the stack after the call. Generally the called function doesn't know how many parameters the caller has put on the stack, so this is typically left as the responsibility of the caller.

  push ax  ;; or even pusha
  push bx  ;; 

  push ax
  push bx
  call xxx
  pop  ax   ;; dummy pop to clean the stack
  pop  ax   ;; stack cleaning

  pop  bx   ;; restore BX
  pop  ax   ;; restore ax

Because each function is required to save bp , it's also possible to restore the stack after a call by

  push bp
  mov bp, sp

  push ax ; arguments
  push bx ;
  call xxx       ;; 

  mov sp, bp
  pop bp

or when this local stack frame concept is used throughout the system:

  mov [bp - xyz ], sp;   // save current stack pointer at a fixed place
  push cx ; // push a lot of arguments
  call zyx
  mov sp, [bp - xyz]     // restore stack pointer