Initialize array to specific values in assembly (x86)

Question

I want to initialize an array in assembly with specific values. I tried doing it in a loop first but got junk in the arrays. I then tried doing it manually and got the same junk. I want the array to repeat 0 1 2 for an n amount of times. Here is some example code I tried.

This is my attempt at manully loading the array. The first value loads just fine. The second value however, loads in junk when I examine it in GDB.

sub esp, 260
mov [ebp - 12], dword -1
mov [ebp - 16], byte 0
mov [ebp - 17], byte 1
mov [ebp - 18], byte 2
mov [ebp - 19], byte 0
mov [ebp - 20], byte 1
mov [ebp - 21], byte 2
mov [ebp - 22], byte 0
mov [ebp - 23], byte 1
mov [ebp - 24], byte 2
mov [ebp - 25], byte 0

Here was my attempt at doing it automatically.

    sub esp, 260
    mov [ebp - 12], dword -1

again:
    add [ebp - 12], dword 1
    lea eax, [ebp - 16]
    sub eax, [ebp - 12]
    mov [eax], byte 0

    add [ebp - 12], dword 1
    lea eax, [ebp - 16]
    sub eax, [ebp - 12]
    mov [eax], byte 1

    add [ebp - 12], dword 1
    lea eax, [ebp - 16]
    sub eax, [ebp - 12]
    mov [eax], byte 2

    cmp [ebp - 12], dword 255
    jne again
    jmp elsewhere

Using NASM, x86-32, Intel syntax.

EDIT: When I convert this code to store the array values as DWORDs instead of bytes both methods work. Why is that?

Answer 1

With NASM, you can easily initialise repeating data by using the times prefix. For instance, to repeat the sequence "0 1 2" n times as requested in your question, you can do something similar to the following:

section .data

    my_array: times n db 0, 1, 2 

Simply replace n by the constant value you want. More information about the times prefix can be found in the NASM Manual.