addressing array elements in nasm

Question

I'm very new to assembly and NASM and there is a code:

    SECTION .data       
array db 89, 10, 67, 1, 4, 27, 12, 34, 86, 3
wordvar dw      123     

    SECTION .text       
        global main     
main:               

    mov eax, [wordvar]
    mov ebx, [array+1]
    mov ebx,0       
    mov eax,1       
    int 0x80

Then I run the executable through GDB eax register is set to value 123 as intended, but in ebx there is some mess instead of the array elements value.

NPE NPE · Accepted Answer · 2011-10-06T14:35:16

Since you're loading 32-bit values from memory, you should declare array and wordvar using dd rather than db/dw so that each entry gets four bytes:

array   dd 89, 10, 67, 1, 4, 27, 12, 34, 86, 3
wordvar dd 123

Also, the indexing in the following is wrong:

mov ebx, [array+1]

You probably meant:

mov ebx, [array+1*4]

addressing array elements in nasm

1 Answers