JakuJ / bootable-stuff

A two-stage bootloader, an x86-64 kernel, and an OS stub

Bootable stuff

This repository contains a two-stage bootloader, an x86_64 kernel, and a ring 3 OS stub, all written from scratch.

The system is under development. Does not run DOOM yet 👿

Latest feature: mmaping the framebuffer from userspace to draw graphics! The imitation of the DVD logo is rendered by the OS, not the kernel.

Running

Make sure you have the required dependencies:

• make
• nasm
• QEMU (qemu-system-x86_64)
• x86_64-elf-gcc
• x86_64-elf-ld

Then run

make -j qemu64   # anywhere

to build the image and boot it in QEMU.

Features

• Bootloader
  • Protected mode
  • Long mode
  • Enabling SSE, AVX*
  • Loading arbitrarily large images
• VGA controller
  • Printing text to the screen
  • Setting VESA modes automatically
  • Ability to mmap framebuffer from userspace
• Interrupts
  • IDT setup with PIC remapping
  • Event-based system for handing keyboard interrupts
  • Handling special keys and combinations (shift, backspace...)
  • Clock config (IRQ 0)
• Memory management
  • Handling page faults
  • Physical memory manager
  • Virtual memory manager
  • Kernel heap management (kmalloc, kfree) through liballoc
• Operating system
  • Getting to ring 3
  • Handling syscall
  • Handling malloc
    • with brk
    • also free
  • Porting a libc (musl)
  • Porting DOOM
  • Choosing a better name for the project

Caveats

AVX support

Provided that XSAVE is supported by the CPU, we can enable AVX within the kernel. To do this, we enable the avx CPU feature in QEMU.

However, QEMU's TCG cannot translate AVX instructions, and so they cannot be emulated. This means that we cannot actually use AVX to vectorize kernel code. Attempting to compile the kernel with -mavx will result in a General Protection Fault.

HVF acceleration

On MacOS, it is possible to run the kernel with Hypervisor acceleration. However, qemu-system-x86_64 on Mac does not allow unsigned binaries to use it.

To sign the QEMU binary, run the following command from repository root:

codesign -s - --entitlements qemu/app.entitlements --force "$(command -v qemu-system-x86_64)"

Note that the HVF in QEMU does not support SSE. Do not compile with -O3 if you want to use the hvf target. This target will be removed in the future, as x86_64 does need SSE2 to be present.