33 lines
1.0 KiB
NASM
33 lines
1.0 KiB
NASM
bits 32 ; assembling for the 32 bits architecture
|
|
|
|
; declare the EntryPoint (a label defining the very first instruction of the program)
|
|
global start
|
|
|
|
; declare external functions needed by our program
|
|
extern exit ; tell nasm that exit exists even if we won't be defining it
|
|
import exit msvcrt.dll ; exit is a function that ends the calling process. It is defined in msvcrt.dll
|
|
; msvcrt.dll contains exit, printf and all the other important C-runtime specific functions
|
|
|
|
; our data is declared here (the variables needed by our program)
|
|
segment data use32 class=data
|
|
; ...
|
|
a db 'message'
|
|
l equ $-a
|
|
b resb l
|
|
|
|
; our code starts here
|
|
segment code use32 class=code
|
|
start:
|
|
; ...
|
|
mov ESI,l
|
|
label:
|
|
mov AL,[a+ESI-1]
|
|
|
|
sub AL,'a'-'A'
|
|
mov [b+ESI-1],AL
|
|
dec ESI
|
|
jne label
|
|
; exit(0)
|
|
push dword 0 ; push the parameter for exit onto the stack
|
|
call [exit] ; call exit to terminate the program
|