Segmentation fault while trying to write for loop in NASM on Linux

I'm trying to write a simple NASM program for fun, but I can't seem to figure out how to write a for loop in it. With the following code, I get a segmentation fault. The following code is supposed to print out "Hello world!" followed by all of the numbers from one to 100.

section .data
 开发者_开发知识库   message: db 'Hello world!', 10
    messageLength: equ $-message

section .text
    global _start

_start:
    mov eax, 4
    mov ebx, 1
    mov ecx, message
    mov edx, messageLength
    int 80h

    mov ecx, 0
    jmp loop

    mov eax, 1
    mov ebx, 0
    int 80h

loop:
    mov eax, 4
    mov ebx, 1
    mov edx, 1
    int 80h

    add ecx, 1
    cmp ecx, 100
    jl loop

Before you jump to the loop, you are assigning 0 to ECX...

It means your program will try to print a string located at memory address 0, which you don't own, hence the segmentation fault...

Remember you are working with memory addresses. Assigning 10 to a register value wont actually print 10, in ASCII... It just means you are getting memory address 10...

You had two problems: first, your syscall to exit() came before the loop, instead of after; second you are passing an integer instead of a memory pointer to the write() syscall.

Try this instead:

section .data
    message: db 'Hello world!', 10
    messageLength: equ $-message

    digits: db '0123456789'

section .text
    global _start

_start:
    mov eax, 4
    mov ebx, 1
    mov ecx, message
    mov edx, messageLength
    int 80h

    mov ecx, 0
    jmp loop

loop:
    push ecx
    mov eax, digits
    add ecx, eax
    mov eax, 4
    mov ebx, 1
    mov edx, 1
    int 80h
    pop ecx

    add ecx, 1
    cmp ecx, 10
    jl loop

And here is a version that formats numbers and prints the loop counter:

section .data
    message: db 'Hello world!', 10
    messageLength: equ $-message

    number: db '000'
            db 10

section .text
    global _start

_start:
    mov eax, 4
    mov ebx, 1
    mov ecx, message
    mov edx, messageLength
    int 80h

    mov ecx, 0
    jmp loop

loop:
    call _format_number
    push ecx
    mov ecx, number
    mov eax, 4
    mov ebx, 1
    mov edx, 4
    int 80h
    pop ecx

    add ecx, 1
    cmp ecx, 10
    jl loop

    mov eax, 1
    mov ebx, 0
    int 80h

_format_number:
    push ecx
    xor edx, edx
    mov eax, ecx
    mov ecx, 10
    idiv ecx
    add edx, '0'
    mov ebx, number
    mov [ebx+2], dl
    xor edx, edx
    idiv ecx
    add edx, '0'
    mov [ebx+1], dl
    xor edx, edx
    idiv ecx
    add edx, '0'
    mov [ebx+0], dl
    pop ecx
    ret

The problem with your code is that you try to print a integer as a dword. I would rather use printf like this:

extern printf ;make sure we can use printf

section .data
    message: db 'Hello world!', 10
    messageLength: equ $-message
    decFormat   db '%d',10 ;format string to use in printf

section .text
    global main

main:
    ;print hello world the usual way
    mov eax, 4
    mov ebx, 1
    mov ecx, message
    mov edx, messageLength
    int 80h

    mov ecx, 0

loop:
    push ecx ;add counter
    push decFormat ;add format string
    call printf ;execute printf, which will use the stack values as arguments

    pop ecx ;clean the stack
    pop ecx

    inc ecx ;if you just want to add 1 to the value, you should use inc not add
    cmp ecx, 100
    jl loop

mov eax,1
mov ebx,0
int 80h