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HelloAssembly

The smallest possible complete Windows application.

From the episode "Hello, Assembly! Retrocoding the World's Smallest Windows App in x86 ASM" on Dave's Garage:
Hello, Assembly! Retrocoding the World's Smallest Windows App in x86 ASM

And the follow-up episode "C vs ASM: Making the World's SMALLEST Windows App":
C vs ASM: Making the World's SMALLEST Windows App

Introduction

Code in the repository:

  • Optimized version of the original code is in the folder "TinyOriginal"
  • Version applying shell coding tactics is in the folder "Lasse"
  • Version using a manually written PE header is in the folder "Theron"
  • QRCode is dead code, was the exe embedded into a QRCode, kept just for posterity

The goal of this project is to make the smallest possible application, without compression, that has the following features:

  • Runs a Windows message loop
  • Has a title bar, minimize, maximize, and close buttons, which all work as expected
  • Has a system menu with the same
  • Paints the background and some text centered in the middle, equal to or larger than "Dave's Tiny App"

Please keep it readable and explain what you're doing in the comments! And the smaller, the better!

Note on virus scanners

The optimizations embedded in the current code in the Lasse directory, and those applied by Crinkler in general (if used) are rather aggressive, and seem to resemble strategies applied by certain types of malware. Because of this, your virus scanner may flag the executables you build out of the source code as "suspected malware". That can make it impossible to start them, or your virus scanner can even put them in quarantine. Depending on the antivirus solution you use, you may be able to whitelist/exclude the executables to restore them and get them to work (this is known to happen with F-Secure SAFE). It's also possible that you have to temporarily disable your virus scanner altogether (which has been observed with Microsoft Defender).

Please note:

  • It is entirely your responsibility to decide if you want to disable your virus scanner or not.
  • If you do temporarily disable your virus scanner, we strongly recommend you re-enable it immediately after you test the executables you build out of this repository's code.
  • Although we do promise that this repository does not contain any malicious code, we cannot guarantee that this is true for any code or executables (like supposed builds of this repository's applications) that you get from other sources.

If your virus scanner intervenes when you try to run the executables that come out of this repository's source code, and you don't feel comfortable with (partly) disabling your virus scanner, then don't do it. We do understand and we really won't hold it against you. :)

Build instructions

Plain MASM32

The code in the Lasse directory can be built with plain MASM32 11.0, which can be obtained from a number of sources. Build instructions using it are:

ml /coff LittleWindows.asm /link /merge:.rdata=.text /merge:.data=.text /align:4 /subsystem:windows LittleWindows.obj

The executable will be named LittleWindows.exe.

MASM32 with Crinkler

Crinkler is a compressing linker for Windows, specifically targeted towards executables with a size of just a few kilobytes. A copy of the tool is included in this repository in the Crinkler directory. It can also be acquired from its GitHub repository.

Crinkler requires the Windows SDK to be installed. Best (i.e. smallest) results have been achieved with version 10.0.20348.0 of the Windows 10 SDK. It, and other versions can be downloaded from the Windows SDK archive page on the Microsoft website.

After installing it, the build instructions for the applications that can be built using it are:

  • Code in the Lasse directory:

    ml /c /coff LittleWindows.asm
crinkler.exe /NODEFAULTLIB /ENTRY:start /SUBSYSTEM:WINDOWS /TINYHEADER /NOINITIALIZERS /UNSAFEIMPORT /ORDERTRIES:1000 /TINYIMPORT /LIBPATH:"C:\Program Files (x86)\Windows Kits\10\Lib\10.0.20348.0\um\x86" kernel32.lib LittleWindows.obj

    The executable will be named out.exe.

  • Code in the TinyOriginal directory:

    ml /c /coff /IC:\masm32\include Tiny.asm 
crinkler.exe /ENTRY:MainEntry /SUBSYSTEM:WINDOWS /TINYHEADER /NOINITIALIZERS /UNSAFEIMPORT /ORDERTRIES:2000 /TINYIMPORT /LIBPATH:"C:\Program Files (x86)\Windows Kits\10\Lib\10.0.20348.0\um\x86" kernel32.lib user32.lib gdi32.lib Tiny.obj /OUT:tiny.exe

    The executable will be named tiny.exe.

Yasm

The code in the Theron directory has to be built with Yasm, which is a rewrite of the NASM assembler under the "new" BSD license. It can be acquired from the Yasm project download page; choose the version "for general use". The assembler is assumed to be renamed to yasm.exe. Build instructions using it are:

yasm -fbin -o HelloWindows.exe HelloWindows.asm

The executable will be named HelloWindows.exe.

Current sizes

Current smallest known working executable sizes as of 03/11/2023 are as follows:

Program Linker Size in bytes
Lasse\LittleWindows.asm MASM32 1104
Lasse\LittleWindows.asm Crinkler 818
Theron\HelloWindows.asm Yasm 383
TinyOriginal\Tiny.asm Crinkler 540