How to write hello world in assembly under Windows?

C

9

127

I wanted to write something basic in assembly under Windows. I'm using NASM, but I can't get anything working.

How do I write and compile a hello world program without the help of C functions on Windows?

Canvasback answered 21/6, 2009 at 10:14 Comment(5)

Also check out Steve Gibson's Small Is Beautiful windows assembly starter kit. – Goeger 16/4, 2010 at 14:51

Not using c-libraries is a somewhat strange constraint. One has to call some library within the MS-Windows operatings system. probably kernel32.dll.Whether Microsoft has written this in c or Pascal seems irrelevant. Is it meant that only OS-supplied functions can be called, what in a Unix-type system would be called system calls? – Demonolater 16/2, 2017 at 11:16

With C libraries I assume he or she means without using an C runtime libraries like the ones that come with GCC or MSVC. Of course he or she will have to use some standard Windows DLLs, like kernel32.dll. – Blinking 13/5, 2017 at 19:23

The distinction between kernel32.dll and a gcc runtime library is not in the format (both are dll) and not in the language (both are probably c, but that is hidden.) The difference is between OS-supplied or not. – Demonolater 18/10, 2019 at 17:1

Ive been looking for this also lol couldn't find anything with fasm without includes – Lamprey 13/8, 2020 at 5:29

U

43

NASM examples.

Calling libc stdio printf, implementing int main(){ return printf(message); }

; ----------------------------------------------------------------------------
; helloworld.asm
;
; This is a Win32 console program that writes "Hello, World" on one line and
; then exits.  It needs to be linked with a C library.
; ----------------------------------------------------------------------------

    global  _main
    extern  _printf

    section .text
_main:
    push    message
    call    _printf
    add     esp, 4
    ret
message:
    db  'Hello, World', 10, 0

Then run

nasm -fwin32 helloworld.asm
gcc helloworld.obj
a

There's also The Clueless Newbies Guide to Hello World in Nasm without the use of a C library. Then the code would look like this.

16-bit code with MS-DOS system calls: works in DOS emulators or in 32-bit Windows with NTVDM support. Can't be run "directly" (transparently) under any 64-bit Windows, because an x86-64 kernel can't use vm86 mode.

org 100h
mov dx,msg
mov ah,9
int 21h
mov ah,4Ch
int 21h
msg db 'Hello, World!',0Dh,0Ah,'$'

Build this into a .com executable so it will be loaded at cs:100h with all segment registers equal to each other (tiny memory model).

Good luck.

Unprecedented answered 21/6, 2009 at 10:17 Comment(12)

The question explicitly mentions "without using C libraries" – Entablement 21/6, 2009 at 10:24

There's no reliable way to do this without calling a C function at some point. Except if by "C function" you mean "standard C function". – Canoewood 21/6, 2009 at 12:36

Wrong. The C library itself obviously can, so it's possible. It's only slightly harder, in fact. You just need to call WriteConsole() with the right 5 parameters. – Glasgow 22/6, 2009 at 13:2

Although the second example doesn't call any C library function it's not a Windows program either. Virtual DOS Machine will be fired to run it. – Maurili 22/6, 2009 at 16:26

Yeah, the second example is one of the classics. Technically interrupt 0x21 is part of the DOS "API" - the interrupt pointed to a chunk of code installed into memory by DOS at startup, unlike the BIOS mapped interrupts which work even before an OS is loaded. Critical however for the ah=0x09 sub-function is that the string is terminated with $ (otherwise it just starts writing junk from memory). Alternatively you can also use the ah=0x40 function, for which you specify the number of characters (this function is also used to write to files, as the "screen" is just another pipe) – Ard 22/6, 2009 at 20:0

Hey, out of interest, I was wondering why we need to offset the beginning of the program? Does this have to do with how the segments are set up? Like, does NASM place the data segment before the code segment in memory? (i.e. code breaks if org 0x100 set to org 0x00) – Annates 14/11, 2010 at 3:44

@Alex Hart, his second example is for DOS, not for Windows. In DOS, the programs in tiny mode (.COM files, under 64Kb total code+data+stack) start at 0x100h because first 256 bytes in the segment are taken by the PSP (command-line args etc.). See this link: en.wikipedia.org/wiki/Program_Segment_Prefix – Multidisciplinary 15/1, 2012 at 3:59

This is not what was asked for. The first example uses the C library and the second one is MS-DOS, not Windows. – Picturize 25/4, 2013 at 20:57

Does anybody know why to make it work I had to remove the underscores before _main and _printf ? I compiled it with: nasm -f win32 helloworld.asm -o hello.obj and linked it with golink /console /entry main hello.obj MSVCRT.dll. If I did not remove underscores I'd get the following error:

Error! The following symbol was not defined in the object file or files:- _printf You may be trying to link object files or lib code with decorated symbols - If so, you could try using the /mix switch Output file not made

– Behalf 13/12, 2014 at 10:44

@OP "How to write and compile hello world without the help of C functions on Windows?" – Peloquin 4/1, 2015 at 20:36

This uses the standard c library which assumes the context of a c-compiler, not assembler. If the poster of this question acccepts this as the best solution, he absolutely must rephrase the question in particular "without the help of c-functions" . – Demonolater 2/6, 2020 at 10:8

The gcc step fails for me with: undefined reference to `_printf'. gcc --version returns realgcc.exe (Rev1, Built by MSYS2 project) 7.2.0 – Glorify 10/3, 2023 at 17:51

T

161

This example shows how to go directly to the Windows API and not link in the C Standard Library.

    global _main
    extern  _GetStdHandle@4
    extern  _WriteFile@20
    extern  _ExitProcess@4

    section .text
_main:
    ; DWORD  bytes;    
    mov     ebp, esp
    sub     esp, 4

    ; hStdOut = GetstdHandle( STD_OUTPUT_HANDLE)
    push    -11
    call    _GetStdHandle@4
    mov     ebx, eax    

    ; WriteFile( hstdOut, message, length(message), &bytes, 0);
    push    0
    lea     eax, [ebp-4]
    push    eax
    push    (message_end - message)
    push    message
    push    ebx
    call    _WriteFile@20

    ; ExitProcess(0)
    push    0
    call    _ExitProcess@4

    ; never here
    hlt
message:
    db      'Hello, World', 10
message_end:

To compile, you'll need NASM and LINK.EXE (from Visual studio Standard Edition)

   nasm -fwin32 hello.asm
   link /subsystem:console /nodefaultlib /entry:main hello.obj

Tenet answered 22/6, 2009 at 19:51 Comment(5)

you likely need to include the kernel32.lib to link this (I did). link /subsystem:console /nodefaultlib /entry:main hello.obj kernel32.lib – Discourse 7/1, 2012 at 2:49

How to do link the obj with ld.exe from MinGW? – Fumarole 18/8, 2013 at 3:3

@Fumarole gcc hello.obj – Summers 10/10, 2013 at 11:39

Would this also work using free linkers like Alink from sourceforge.net/projects/alink or GoLink from godevtool.com/#linker ? I don't want to install visual studio only for that? – Behalf 13/12, 2014 at 8:41

Using my version of link : Microsoft (R) Incremental Linker Version 14.29.30133.0, I get unresolved external symbol _GetStdHandle@4 and so for all the extern items? – Glorify 10/3, 2023 at 17:58

U

43

NASM examples.

Calling libc stdio printf, implementing int main(){ return printf(message); }

; ----------------------------------------------------------------------------
; helloworld.asm
;
; This is a Win32 console program that writes "Hello, World" on one line and
; then exits.  It needs to be linked with a C library.
; ----------------------------------------------------------------------------

    global  _main
    extern  _printf

    section .text
_main:
    push    message
    call    _printf
    add     esp, 4
    ret
message:
    db  'Hello, World', 10, 0

Then run

nasm -fwin32 helloworld.asm
gcc helloworld.obj
a

There's also The Clueless Newbies Guide to Hello World in Nasm without the use of a C library. Then the code would look like this.

16-bit code with MS-DOS system calls: works in DOS emulators or in 32-bit Windows with NTVDM support. Can't be run "directly" (transparently) under any 64-bit Windows, because an x86-64 kernel can't use vm86 mode.

org 100h
mov dx,msg
mov ah,9
int 21h
mov ah,4Ch
int 21h
msg db 'Hello, World!',0Dh,0Ah,'$'