KFS (Kernel From Scratch)

Implementing a very simplistic kernel from scratch to discover the world of OS development for the 32 bits architecture i386.

Overview

This project aims to build a minimalistic kernel from scratch using C and x86 assembly. It requires the installation of an i386 cross compiler to work correctly. The installation can be done using the cross-compiler.sh script, provided in this repo.

Compile and Run

After checking the cross compiler is available (run the installation script if you don't have it), you simply have to run:

make

It will create the kernel binary. If you prefer to have the iso file you have to run this:

make iso

You can now run the kernel using Qemu.

# Needs Qemu installed
make run_kernel

If Qemu is not available on your system, you can run the kernel with any virtual machine manager by using iso or directly the binary

Features Implemented

Despite its minimalist nature, the kernel has a number of features that are as useful for debugging as they are for comfort.

VGA Screen Handling

• Foreground and Background color handling
• Vertical scrolling and cursor support
• Multiple screens like tty available (use LCTRL + <NUMBER> to switch)

Input Handling

• Full control of cursor using arrows, home and end keys
• Insertion and deleting characters at any place on line
• Support QWERTY and AZERTY keyboard layout (LCTRL + F1 to switch)
• French accentuation management with azerty layout

Minimalistic Shell

Commands implemented for debugging purposes:

• reboot (reboot the system)
• halt (halt the system until next interruption)
• stack (dump the kernel stack content)
• dump adr (dump the content located at adr)
• int num (trigger the interruption number num)

Memory Management

• Using pagination to correctly handle write and allocation on heap
• Higher Half Kernel
• Using Slab Allocator design
• Panic if kernel runs out of memory
• Physical Memory Helpers Functions:
  • kmalloc (return phyiscal contigous block of memory)
  • ksize (return physical size of a variable)
• Virtual Memory Helpers Functions:
  • vmalloc (return virtual contigous block of memory)
  • vsize (return virtual size of a variable)

Interruptions Handling

• Handling all of 19 i386 CPU exceptions (Div by 0, Double Fault, ...)
• Interrupt driven keyboard
• PIT (Programmable Interval Timer)
• Handle Kernel Panic when necessary

Minimalistic syscall handler

• Interrupt number 69
• Register EAX contains syscall number and return value
• Registers EBX, ECX, EDX, ESI, EDI contains arguments
• Write syscall implemented as POC