/develop-os-free

Make C programs that run without OS

Primary LanguageCGNU General Public License v3.0GPL-3.0

Description

This is my 5th term coursework on the "Operating Systems" subject at the Department of Computer Science and Technologies, Bauman Moscow State Technical University.
The main aim is to get acquainted with principle of OS kernel operation at low level. As a sequence, develop minimal C libraries for I/O tasks (e.g., functions like putchat, printf, gets, scanf) and memory management (malloc, free, and so on). Finally, write an app demonstrating their efficiency. The coursework was evaluated in mark 5/5.

How it actually works

Project building with Make tool. Makefile contains all the logic. Here are main steps:

  1. Kernel compilation from C source (32 bit);
  2. Disk image creation and partitioning (using ext2 filesystem);
  3. Installing grub into image via grub-install tool;
  4. Embedding kernel into image.

What is done by far

  • A minimal OS kernel supporting Multiboot specification;
  • Embedding grub2 bootloader;
  • Input functions: getchar, gets;
  • Output functions: putchar, puts; also printf function taken from other source;
  • Cursor functions: disable_cursor, enable_cursor, move_cursor, update_cursor;
  • Time functions: delay, sleeps;
  • Memory functions: malloc, free;
  • Random functions: rand, srand, rtc_seed;
  • Example application: the Tetris game.

How to test it without compiling kernel

Get image file (disk.img) from latest release, then just write it to a USB or run with x86 emulator. For QEMU it is the following command:

spam@eggs:~$ sudo qemu-system-i386 -hda disk.img

How to compile kernel

Guide

Dependencies

  • make
  • gcc
  • as
  • ld
  • grub2
  • qemu

Supported hosts

Linux. Currently developing and testing on Ubuntu 18.04 LTS minimal.

First make sure you have all tools listed in Dependencies block installed. Then do the following:

spam@eggs:~$ git clone https://github.com/nexterot/develop-os-free
spam@eggs:~$ cd develop-os-free
spam@eggs:~$ make

In case of errors, or just to clean the directory:

spam@eggs:~$ make clean

Also, the following command is an alias for make clean && make:

spam@eggs:~$ make rebuild

Test with emulator

To test it with QEMU emulator, run:

spam@eggs:~$ make run

If you ran into some problem

Problem:

losetup: bin/disk.img: failed to set up loop device: Device or resource busy

Solution:

Find busy loop devices:

spam@eggs:~$ losetup -a

Then edit next lines in Makefile, changing '/dev/loop2' or\and '/dev/loop3' to any free loop device:

loop_first  = /dev/loop2
loop_second = /dev/loop3

Finally do:

spam@eggs:~$ make rebuild

Screenshots

1.png 2.png