x86 masm hello world

Question

I am trying to compile a hello world on windows with the ML and LINK that ship with VS 2010.

.MODEL FLAT
.STACK 4096
.data
msg db "Hello World!",0
.code
INCLUDELIB MSVCRT
EXTRN printf:NEAR
EXTRN exit:NEAR
PUBLIC _main
_main PROC
mov eax, offset msg
push eax
call printf
mov eax,0
push eax
call exit
_main ENDP
END _main

I keep getting linker errors saying that printf and exit are unresolved external symbols. I have a couple of questions.

1. What are the command line options to use with ML and LINK to compile and resolve the error messages.
2. Is there another way to display text output to the screen using assembly code rather than calling c runtime functions like printf?

Answer 1

1. You need to use underscored names for C functions, since that's how the compiler emits them on assembly level.
2. You should clean up the stack after calling printf and other CRT functions, since they use cdecl calling convention (caller stack cleanup). Strictly speaking you should do it after _exit too, but that's less important since it never returns.
3. To use CRT functions you have to initialize CRT. You can check how it's done in the file VC\crt\src\crt0.c

Here's a minimal file that worked for me (I used static library because I have VS2008 and didn't want to fiddle with manifests to make it work with DLL).

.386
.MODEL FLAT
.STACK 4096
.data
  msg db "Hello World!",0
.code
INCLUDELIB LIBCMT
EXTRN _printf:NEAR
EXTRN _exit:NEAR
EXTRN __heap_init:NEAR
EXTRN __mtinit:NEAR
EXTRN __ioinit:NEAR
PUBLIC _main
_main PROC
  push 1
  call __heap_init
  add esp, 4
  push 1
  call __mtinit
  add esp, 4
  call __ioinit
  mov eax, offset msg
  push eax
  call _printf
  pop ecx
  mov eax,0
  push eax
  call _exit
_main ENDP
END _main

For MSVCRT the initialization is different, e.g. you need to call set_app_type

To not rely on CRT, you have to use the OS APIs. In case of Win32 that would be Win32 functions such as WriteFile (with GetStdHandle(STD_OUTPUT_HANDLE) for the file handle). See some examples here.