Write a function in NASM Pentium assembly language(save as reverse. ASM file) to

Question

Write a function in NASM Pentium assembly language(save as reverse.ASM file) to output reverse string from user input.

The main procedure reads the string from the user and pass it to the reverse procedure. The reverse procedure returns the reversed string back to main to be displayed.

my latest attempt:

BUF_LEN   EQU 41
%include "io.mac"
.STACK 200H
.DATA
   prompt_msg db "Input a string: ",0
   output_msg db "The reverse is: ",0
.UPDATA
   string   resb BUF_LEN
.CODE
   .STARTUP
   PutStr prompt_msg
   GetStr string,BUF_LEN
   mov ebx,string
   call ReverseString
   PutStr output_msg
   PutStr eax
   nwln
.done:
   .EXIT
ReverseString:
   push ebp
   mov ebp,esp
   push ecx
   push esi
   push edi
   mov edi,[ebp+8]
   mov esi, edi
   push eax
CountLoop:
   cmp byte [esi], 0
   je CountLoopEnd
   inc esi
   jmp CountLoop

CountLoopEnd:
   mov ecx, esi
   sub ecx, edi
   cmp ecx, 0
   je ReverseStringEnd
   dec esi

SwapLoop:
   mov al, [esi]
   mov ah, [edi]
   mov [esi], ah
   mov [edi], al
   cmp edi, esi
   jl SwapLoop

ReverseStringEnd:
   pop edi
   pop esi
   pop ebp
   pop ecx
   pop eax
   ret

I don't know what is my problem. please helpme to fix it :(

Explanation / Answer

DATA SEGMENT
    STRING1 DB “PAULINE$”
    STRING2 DB 7 DUP (‘$’)
    MESSAGE1 DB 10,13,’THE STORED STRING IN THE MEMORY IS : $’
    MESSAGE2 DB 10,13,’THE REVERSE STRING IS THE FOLLOWING : $’
DATA ENDS

DISPLAY MACRO MESSAGE
    MOV AH,9
    LEA DX,MESSAGE
    INT 21H
ENDM   
CODE SEGMENT
    ASSUME CS:CODE,DS:DATA
START:
        MOV AX,DATA
        MOV DS,AX                
               
        DISPLAY MESSAGE1
                    
        DISPLAY STRING1
                       
        LEA SI,STRING2
        LEA DI,STRING1
        ADD DI,5
               
        MOV CX,6
REVERSESTRING:
        MOV AL,[DI]
        MOV [SI],AL
        INC SI
        DEC DI
        LOOP REVERSESTRING
       
        DISPLAY MESSAGE2
                   
        DISPLAY STRING2
                     
        MOV AH,4CH
        INT 21H

CODE ENDS

END START

OUTPUT:

    THE STORED STRING IN THE MEMORY IS:PAULINE

THE REVERSE STRING IS THE FOLLOWING:ENILUAP

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