Hello World! example

global _start

section .text
    ; function to print reversed text by dword
    ; text string should end in null
    ; ie 'e','l','p','m','a','x','e',0
    ; would print 'example'
    print:
        ; stores esp pointer for later
        push ebp
        mov ebp, esp

        ; sets eax to first char
        mov eax, esp
        add eax, 8

        ; sets ebx to end-of-string identifier, being 0/null/''
        mov ebx, ''

        ; loop through string, reversing it into the correct order
        mainloop:
        cmp [eax], ebx ; check if end-of-string
        je endloop ; if end of string, quit loop to endloop:

        ; push char and continue to next byte
        push dword [eax]
        add eax, 4
        jmp mainloop

        endloop:

        ; reset start of string
        mov edx, eax
        sub edx, esp
        sar edx, 1

        ; display string
        mov ecx, esp
        mov ebx, 1
        mov eax, 4
        int 0x80

        ; return to program
        mov esp, ebp
        pop ebp
        ret

    _start:

        push dword '' ; set end-of-string, being 0/null/''

        push dword 'H'
        push dword 'e'
        push dword 'l'
        push dword 'l'
        push dword 'o'

        call print ; call to print 'Hello'

        push dword '' ; set end-of-string, being 0/null/''

        push dword 10 ; new line

        push dword 'W'
        push dword 'o'
        push dword 'r'
        push dword 'l'
        push dword 'd'
        push dword '!'

        call print ; call to print newline + 'World!'

        mov eax, 1      ;system call number (sys_exit)
        int 0x80        ;call kernel