NASM - Hello, World¶

2010

Hello, World [windows]¶

This snippet of assembly language code prints the message “Hello, World!” using a dynamically linked library (for the _printf function). The arguments to the _printf function are pushed onto the stack.

 global	_main
	extern	_printf
	extern _exit

	section .data

	message	db	'Hello, World', 10, 0

	section .text
 _main:
	push	message
	call	_printf

	xor eax, eax
	push eax
	call _exit

In link time, libcrtdll.a is adding, this library contains _printf and _exit function.

nasm -f win32 hellworld.asm
ld hellworld.o libcrtdll.a -o hellworld

Alternatively, you can compile using gcc instead of ld.

nasm -f win32 hellworld.asm
gcc hellworld.o

Static and dynamic library¶

Create liberary¶

Writing function myFunction in assembler

; file : libHello.asm
BITS 64

section .data
  hello db \"Hello World !\", 0xa
  len equ $ - hello

section .text
  global      myFunction:function

  myFunction:
    mov rax, 4
    mov rbx, 1
    mov rcx, QWORD hello
    mov rdx, len
    int 0x80
    ret

Compiling the library statically

nasm -f elf64 libHello.asm
ar rcs libHello.a libHello.o

Compiling the dynamic library

nasm -f elf64 libHello.asm
ld -shared -o libHello.so libHello.o

Example of library uses¶

C code using a library function

// file :  main.c
int main(int argc, char **argv) {
  myFunction();
  return 0;
}

Compiling with the static library

gcc -static main.c -L. libHello.a -o statically_linked

Compiling with the dynamic library

gcc main.c -o dynamically_linked -L -l c_printf.so.1.0.1

Refs¶