Assembly (Windows)

Assembly on Windows utilizes masm, Microsoft's proprietary assembler and linker.

Compilation, Linking, and Execution


You will first need masm to compile your assembly into machine code. masm can be installed via the MASM32 SDK.

Your First Program

Create a file called hello_world.asm. Copy this into it's contents:

.386                                  ; Tell assembler to use the 386 instruction set
.model flat, stdcall                  ; Specify the flat memory model and use stdcall to pass parameters RtoL
option casemap :none                  ; Force case sensitivity

include \masm32\include\   ; Include Win32 API constants and defs
include \masm32\include\  ; Include ExitProcess
include \masm32\include\    ; Include StdOut

includelib \masm32\lib\kernel32.lib   ; The libraries necessary for the above includes to function
includelib \masm32\lib\masm32.lib

.data                                 ; The section for all initialized data
  HelloWorld db "Hello World!", 0     ; definebyte HelloWorld to equal Hello World! plus a NUL char

.code                                 ; Starting point for program code
start:                                ; All code must live between this and end start
  invoke StdOut, addr HelloWorld      ; Run function StdOut with address of HelloWorld as the param
  invoke ExitProcess, 0               ; Invoke ExitProcess with 0 (success) as the parameter

end start

Assembling Your Code

Assembling your code will translate it from the human readable assembly language into a file object. The following command will run masm and create output hello_world.obj.

\masm32\bin\ml /c /Zd /coff hello_world.asm

Linking Your File

Linking your newly created output file will pull all the needed libraries into a single executable. The following command will run Link, the masmlinker, and finish the creation of your executable.

\masm32\bin\Link /SUBSYSTEM:CONSOLE hello_world.obj

Executing Your File

Hello, World!

Running hello_world.exe in the command line should result in the message being displayed.

masm-specific Syntax


invoke is a special function in masm to call functions without having to push parameters beforehand.

invoke SendMessage, [hWnd], WM_CLOSE, 0, 0

; equivalent to

push 0
push 0
push [hWnd]
call [SendMessage]


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Last modified: 202212070107