Compiling 32 bit Assembler on 64 bit ubuntu

First change _printf to printf and the _start symbol to main, then use gcc to link the object file, which will automatically link it to libc, you need to do that because AFAIK you can't link to libc without a main. Also you should use elf32 not elf64 when assembling because the code has 32 bits instructions :

bits 32
extern printf
global main

section .data
    message db "Hello world!!", 10, 0

section .text

main:
    pushad 
    push dword message
    call printf 
    add esp, 4 
    popad 
    ret

And build with:

nasm -f elf32 vaja4.asm
gcc -m32 vaja4.o -o vaja4
$./test 
$Hello world!!

Edit:

Since you're now compiling 32-bit code on a 64-bit system, you will need to install the 32-bit version of the libraries

apt-get install ia32-libs 

On Ubuntu 12.10, you need to install development packages first

sudo apt-get update
sudo apt-get install libc6-dev-i386

for

gcc -m32 vaja4.o -o vaja4

to work.

I doubt that the error you see is because of 32/64 bit issue. The error that you see i.e

vaja4.asm:(.text+0x7): undefined reference to `_printf'

is clearly telling you the symbol _printf is undefined which means that the library for printf function is not being linked.

your linking step i.e

ld vaja4.o -o vaja4

does not include any libraries. You need to link your program with a library that can provide definition of the printf function. I believe ld should pick the library it self without bothering you with these messages but because it is not able to find a suitable C library for this function, I guess you dont have the required libraries i.e either 32 bit or 64 library is missing.

Anyway, plz try the following sequence of commands to assemble and link your program:

nasm -f elf vaja4.asm
ld -m elf_i386 vaja4.o vaja4
./vaja4