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Reputation: 243

incorrect expected output from assembly loops

I am not getting the expected output. I have a loop that should continue 10x, then the second loop that should continue 10x times. Loops should print seperately

section .data
    msg1:   db  "first",10,0
    msg2:   db  "second",10,0
    len1:   equ $-msg1
    len2:   equ $-msg2
section .bss
    num resb    1    ;reserve 1 byte
section .text
    global main
main:
    mov [num], BYTE 10d ;num = 10
    loop:
    mov edx,    len1
    mov ecx,    msg1
    mov ebx,    1
    mov eax,    4
    int 80h
    dec BYTE [num]      ; num--
    cmp [num], BYTE 0
    jnz loop        ; jump if not equal to zero

    mov [num], BYTE 20d ; num = 20
    loop2:
    mov edx,    len2
    mov ecx,    msg2
    mov ebx,    1
    mov eax,    4
    int 80h
    sub [num], BYTE 2   ; num = num - 2
    cmp [num], BYTE 0
    ja loop2        ; jump if above 0

    mov eax,    1
    mov ebx,    0
    int 80h

I am getting first second first second first second first second first second first second first second first second first second first second second second second second second second second second second second

but im expecting first first first first first first first first first first second second second second second second second second second second

I am new to assembly (NASM), what am i doing wrong?

Upvotes: 0

Views: 79

Answers (1)

Jim Mischel
Jim Mischel

Reputation: 134125

The problem is in your definition here:

section .data
msg1:   db  "first",10,0
msg2:   db  "second",10,0
len1:   equ $-msg1
len2:   equ $-msg2

Here you're saying that msg1 includes all of the first message and the second message.

That should be

msg1:   db  "first",10,0
len1:   equ $-msg1

msg2:   db  "second",10,0
len2:   equ $-msg2

Upvotes: 3

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