Overview

MNIST-x86 is a small x86 nasm assembly project that opens a window and runs a two layer neural network for digit recognition. The project uses the Windows API, and has no other dependencies.

Assembly is not portable, so Windows is the only supported operating system.

You can find an assembled binary file in the release section.

The neural network has been trained using the MNIST database. It consists of a 128 neuron layer with ReLU activation, and an unactivated 10 neuron output layer. No further processing of the dataset images has been made, so you will get better results if you write digits in the center of the screen, and similar to these:

Assemble and link the project yourself

First assemble the three source files:

nasm -f win64 .\main.asm    
nasm -f win64 .\graphics.asm
nasm -f win64 .\network.asm

Then link them using:

• for MSVC

link graphics.obj network.obj main.obj /ENTRY:main /OUT:mnist_x86.exe user32.lib gdi32.lib kernel32.lib /LARGEADDRESSAWARE:NO /SUBSYSTEM:WINDOWS

• for gcc

gcc -mwindows -nostartfiles -Wl,-e,main main.obj graphics.obj network.obj -o mnist_x86.exe -luser32 -lgdi32 -lkernel32

Technical details

This project uses the Windows API to open a fixed-size window, and uses GDI to draw pixels to the screen. I don't know about any GDI tutorials in assembly, so I took inspiration from a C tutorial that you can find here. As for assembly resources, I mostly used this document, this series of videos as well as the compiler explorer. For step by step execution, I use x64dbg, which has proven to be very useful.

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Here is a diagram I made for the x64 calling convention to help me get my offsets right. Note that all windows API functions expect a 16 byte aligned stack pointer.

     ┌─────────────┐                    
     │top of stack │◄──── rsp   ▲       
     ├─────────────┤            │       
     │    ....     │            │       
     ├─────────────┤            │stack  
     │  saved rbp  │◄──── rbp   │growth 
     ├─────────────┤            │       
     │return adress│            │       
     ├─────────────┤            │       
     │   rcx home  │                    
     ├─────────────┤                    
     │   rdx home  │                    
     ├─────────────┤                    
     │   r8 home   │                    
     ├─────────────┤            │       
     │   r9 home   │ rbp+40     │       
     ├─────────────┤            │ high  
     │ parameter 1 │ rbp+48     │ address
     ├─────────────┤            │       
     │ parameter 2 │            │       
     ├─────────────┤            │       
     │    ....     │            ▼       
     └─────────────┘