https://github.com/travorlzh/travoros
A simple OS running on Intel x86 architecture | No longer updating
https://github.com/travorlzh/travoros
assembly bootloader c i386 kernel operating-system os x86
Last synced: 9 days ago
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A simple OS running on Intel x86 architecture | No longer updating
- Host: GitHub
- URL: https://github.com/travorlzh/travoros
- Owner: TravorLZH
- License: gpl-3.0
- Created: 2017-12-02T23:07:08.000Z (over 7 years ago)
- Default Branch: master
- Last Pushed: 2018-08-07T09:05:42.000Z (over 6 years ago)
- Last Synced: 2025-03-29T01:51:37.450Z (27 days ago)
- Topics: assembly, bootloader, c, i386, kernel, operating-system, os, x86
- Language: C
- Homepage:
- Size: 501 KB
- Stars: 29
- Watchers: 3
- Forks: 3
- Open Issues: 5
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
# TravorOS - Developing with Simplification
[](https://github.com/TravorLZH/TravorOS/releases)
[](LICENSE)
[](https://travis-ci.org/TravorLZH/TravorOS)
[](https://ci.appveyor.com/project/TravorLZH/travoros)
[](https://coveralls.io/github/TravorLZH/TravorOS)
This is the first [Operating System](https://en.wikipedia.org/wiki/Operating_System "Operating System Definition") I created. It's written in two languages: C language and Assembly.
This project has been activated since [December 15, 2017](https://github.com/TravorLZH/TravorOS/releases/tag/v0.2-r0)
## Table of Contents
* [Work Plan](#work-plan)
* [Bootloader](#bootloader)
* [Custom](#bootloader)
* [Boot Sector](#boot-sector)
* [Stage 2](#stage-2)
* [GRUB](#grub)
* [Kernel](#kernel)
* [Memory Management](#memory-management)
* [Page Frame Allocator](#page-frame-allocator)
* [Dynamic Memory Allocation](#dynamic-memory-allocation)
* [Building System](#building-system)
## Work Plan
- [x] Write text to VGA
- [x] CPU Interrupt (IDT, ISRs, IRQs, etc.)
- [x] Read character from PS/2 Keyboard
- [x] Read string from PS/2 Keyboard
- [x] Virtual Memory (Paging, Frames, etc.)
- [x] Page Frame Allocation and De-allocation
- [x] Dynamic Memory Allocation (liballoc)
- [x] CPU Timer
- [x] Get CPU Information
- [x] Real-Time Clock: So we can know when the movie starts
- [ ] Kernel Stack Trace
- [ ] Multitasking
- [ ] User-mode processes
- [ ] Hard Disk Driver
- [ ] Floppy Disk Driver
- [ ] File System
- [ ] Graphical User Interface
## Bootloader
### Custom
This OS uses a 2-staged bootloader. In case the second stage is when we entered **Protected Mode** and calls kernel.
#### Boot Sector
The first 512 bytes of my floppy image contains the Boot Sector which does a lot of stuff that **Protected Mode** cannot do. (e.g. Loading stuff from disk). Then it jumps to the second stage loaded at `0x7E00` (just after the boot sector).
#### Stage 2
This stage loads the GDT and enters **Protected Mode**, then it copies the kernel loaded by boot sector at `0x1000` to `0x100000` (1 MB). At last jump!
### GRUB
The size of the kernel is always growing, but I can't always increase the sectors to load. As a solution. I decide to use GRUB. The kernel is stored as an ELF image (`kernel.img`) in a CD which uses `ISO 9660` as its file system. GRUB also supports multiboot, so my Operating System can work together with others (Windows, Linux, etc.).
## Kernel
We entered protected mode which means we don't have access to BIOS functions. So, this kernel needs to re-implement those functions for controlling the hardware.
Now, I have re-implemented standard devices: screen and keyboard. In the further development. I am going to implement disk driver.
## Memory Management
This Operating System uses both segmentation and paging to provide memory protection. In my **Global Descriptor Table**, I put 5 segment descriptors:
1. **Null Segment**
1. **Code Segment for kernel**: The segment where my kernel code belongs to
1. **Data Segment for kernel**: The segment where my kernel global variables belong to
1. **Code Segment for user**: Currently not using
1. **Data Segment for user**: Same as 4
I also enable paging. Now I intentionally maped the fourth page in the first page table to `not-present` and `read-only`, so you can generate a **Page Fault** by executing entering `bsod` in my OS's command line.
### Page Frame Allocator
This kernel provides a **Page Frame Allocator**, so the memory management will be more convenient and I will be easier to approach multitasking.
As [JamesM's Tutorial](http://www.jamesmolloy.co.uk/tutorial_html/6.-Paging.html) suggests, I will use a bitset to determine whether a frame is free or not.
```
1: Allocated 0: Free
v v
frame_bitset: 11110111110101111101111111
^
get_free_frame()
```
### Dynamic Memory Allocation
I have currently implemented a placement **malloc** without **free** because all variables used by kernel never need to be freed until powers off.
```
Heap Allocation
-----------------------------------------------
Allocated |
Memory | Free.......until the end of memory
|
-----------------------------------------------
```
Because I am lazy, I port a 3rd party memory allocator called [`liballoc`](https://github.com/blanham/liballoc) which only required few functions in my OS.
## Building System
This project uses [GNU Make](https://www.gnu.org/software/make "GNU Make Homepage") to build. So, the way to build is to type `make`, if any problems occur during the build, type `make dep` before `make`. Open an issue if still stuck.
[](https://asciinema.org/a/176920)
If you are not using Linux or WSL (Windows Subsystem for Linux), you will need to [download a cross compiler from here](https://github.com/nativeos/i386-elf-toolchain/releases). Then modify `CC` and `LD` in `config.mk`.