nasm + MinGW gcc test

notes

gynvael:haven-windows>nasm test.asm -f win64 -o test.obj && gcc test.obj

gynvael:haven-windows>a.exe
// this actually shows the message box

gynvael:haven-windows>gcc --version    <----------------------------- make sure you have a 64-bit mingw gcc
                                                                      if you don't, go to [1] and get mingw-w64-install.exe file
                                                                      
gcc (x86_64-posix-seh-rev0, Built by MinGW-W64 project) 8.1.0
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

gynvael:haven-windows>nasm -v
NASM version 2.12rc2 compiled on Jan 27 2016

[1] https://sourceforge.net/projects/mingw-w64/files/?source=navbar (when installing, be sure to install a 64-bit version!)

test.asm

[bits 64]

global WinMain
extern MessageBoxA
extern ExitProcess

section .data
msg:  db "Hi there!", 0

section .text
WinMain:
  push rbp
  mov rbp, rsp
  sub rsp, 0x20

  xor rcx, rcx
  lea rdx, [msg]
  mov r8, rdx
  mov r9, rcx
  call MessageBoxA

  xor rax, rax
  call ExitProcess

  ; pop rbp
  ; ret