I Wrote An Operating System

no like for real too, it isn't just booting and printing "hello world"

I'm pretty proud of this, it has been quite hard. It runs DOOM, not just in a VM either!

Feature Overview

- x86 64 bit
- Multiboot2 spec. compatible
- VGA/VBE Graphics Drivers, full HD 1080p, 32 bit color support
- Filesystem
- Multi-tasking Kernel
- The only thing that isn't from scratch is the use of GRUB/Multiboot bootloader and the base Doom src which took quite a few tweaks to port
    - Built completely freestanding, custom libc, from scratch standard library, etc.
    - Custom memory allocator/heap, custom scheduler
- C and C++ Support, Custom Toolchain/Cross Compiler via GCC/Binutils
    - Automated Installation and setup! 
- Kernel is written in primarily C and Assembly 
    - I keep saying I will use C++ after being a huge proponent of it for a long time, but then write more C.. wouldn't want to write a 3D engine in C, wouldn't want to write an OS in C++...
    - I don't think 

In Progress

- At this point all it could use is some input tweaks for playing DOOM and a USB Keyboard driver for real hardware (works with ps2! luckily my very new z690 mobo has a port suprisingly)
- I want to rewrite it from scratch, learned so much along the way I could do it better the second time around 

Planned

- double buffering (sorta)
- Port DOOM (as a user mode process) [COMPLETE]
- Cross compiler + C Runtime for easier use of our standard library [COMPLETE]
- UEFI Support to boot on real hardware [COMPLETE]
- now that we have reached user mode a lot of kernel code can be tidied up and moved to userspace, or refactored into a API for usage from user space
    - you can tell what was added in the last stage of this project 
    - I would like to rewrite this someday, learned too many lessons not to

Detailed Features

• VBE Framebuffer, up to 32 bit color, Graphics Driver provides API

• Serial/COM port support, kernel debugging via serial

• Kernel / CPU Exception interupt handlers with memory dumps and many features to make development easy

• Multi-tasking, round robin scheduler

• Fully implemented from scratch heap and malloc/free

  • this has been one of the most fun things I have ever programmed and I have many ideas to improve its efficiency

• a stdout-type buffer and text renderer

• custom standard library, with strings, printf, malloc, memory functions, etc. all implemented from scratch

  • one for kernel and one for user space, user space has it's own C Runtime
  • libc-ish enough that stuff is portable

• it runs Doom, really well too. and in multi-tasked user space... no cheating!

• custom initrd filesystem and VFS implementation, with subdirs, etc.

• A lot more, TODO

Notes/Misc

THIS MIGHT BE OUT OF DATE IN SOME PLACES - MOST STUFF IS DONE AND WORKING AS OF 5.1.24 IT BOOTS ON REAL MODERN UEFI PCS AND RUNS DOOM, IN USER MODE, LOADED FROM A CUSTOM FILESYSTEM AS AN ELF64 EXECUTABLE BUILT WITH OUR CROSS COMPILER, WITH SUPPORT FOR MULTI TASKING ALL ALONG THE WAY BADA BING BADA BOOM

• builds on linux/macos, toolchain scripts still work as of 7.28.24

• writing asm is sorta zen

• this was my first big C project and first I was missing C++ a lot.. then things started coming along and TLDR: C and I are on good terms now

  • when I finally added C++ support thinking I'd want to rewrite/continue with it, I was underwhelmed and went back to C LOL
  • I really see the appeal of a "C+" type language now, like C with QoL stuff (auto, function/operator overloads, basic constexpr, etc.), and "classes" that are just structs with functions, etc. without getting into C++ abstractions like streams and templates too much
    • it should keep C calling conventions too
    • next project ?
  • honestly the only thing I consistently miss from C++ is function over-loading, and some of how C++ handles structs (aka lemme stick functions in there so im not prefixing every function like "structname_dothing(example_t* examplestruct)")
    • im pretty sure if I switched to like the newest C20 / C23 I would get some of these features (unknown if I would without libc / stdlib though)
    • ooh i also miss being able to declare variables inside logical expressions, ie. 'if (int err = get_error(); err > 0 ) { print(err); }' is nice to have

If you want to test your understanding of how a modern computer works, write an OS from scratch. I have been humbled and learned so much about concepts I thought I had down pat. Also you'll never forget the x64 ABI and calling conventions after this too.