nOS is a from-scratch x86 (32-bit i386) operating system.

nOS is primarily developed as an exercise and for the purposes of education of the author. Nevertheless, it can be used as a high-quality example code-base and for code samples.

Status

nOS running in qemu-system-i386 on Mac OS Mojave, displaying:

• The arguments to kmain
• Lines indicating successful load of the kernel and the partition table
• A dump of the partition table
• A dump of the BIOS memory map
• A set of key-press events

Features:

• Robust build system
• Bootloader
  • Memory map read
  • Protected mode
  • Kernel relocation
  • GDT generation
• Partition table format
• Kernel-executable format
• Kernel
  • GDT generation
  • VGA text mode driver
  • ATA PIO driver
  • PS8042 driver
  • PS/2 keyboard scancode decode

Planned fatures:

1. PIC support
2. Physical memory manager
3. Memory virtualization. So far a flat physical memory model is used
4. Virtual memory manager
5. Kernel console
6. IRQ support
7. Kernel and bootloader debugging functionality
8. ?Load time relocation support
9. System shell
10. Inter-process communication
11. Kernel stripping

Known issues:

• Does not enable the A20 line upon boot, relying on it being on by default.
• Kernel overrides the bootloader's GDTR to point to an equivalent GDT
• Driver API makes it easy for the consumer to write buggy code

Building

nOS uses Shake.

Dependency list

• NASM
• clang++ capable of targeting i386
• lld capable of linking ELF
• compiler-rt targetting the x86-none-elf triplet

After installing the dependencies, simply run ./build.sh from the project folder.

Manual

Use ./run.sh to run the application once built.