hehOS

Introduction

This is a 32-bit kernel designed for i386 architecture following the course Developing a Multithreaded Kernel From Scratch! presented by the brilliant instructor Daniel McCarthy.

Repository Content

I made specific folders for my progress in the course---they can be distinguished by their naming scheme that begins with V# and so on. Additionally, for every main section in the course, a README file can be found in its directory with my notes: some of it is just rephrasing the presentation slides and some are my personal explanation for certain points that need clarification.

Compilation & Building

1. Make sure qemu is installed before proceeding.
2. Go to hehOS directory.
3. Enter make clean command to delete all previously-built .o files.
4. Enter make all command to build hehOS from source.
5. Enter make launch command to launch hehOS.

For Debugging Using qemu & GDB

1. Launch GDB

   gdb
   

2. Add symbol file to debugging session (symbol file contains info that helps with debugging like function names) and start address

   add-symbol-file ./build/kernelfull.o 0x1000000
   

3. Tell GDB to connect to a remote target qemu for debugging the passed binary file os.bin along with debugging flags: -hda makes qemu use os.bin as a virtual hard disk to read from; -S tells qemu to start in a suspended state and not start executing unless stated by GDB; -gdb stdio enables GDB's remote debugging support in qemu and directs qemu to use standard input/output (stdio) for communicating with GDB.

   target remote | qemu-system-i386 -hda ./bin/os.bin -S -gdb stdio
   

4. To place a breakpoint (since symbol file is added, gdb will recognize function names):

   break LABEL_NAME
   

5. To continue executing until breakpoint is reached:

   c
   

6. To print a variable's value (if it is a pointer for example):

   print *PTR_NAME
   

7. To single step in C code:

   n
   

8. To switch code layout from C to Assembly:

   layout asm
   

9. To single step in Assembly code:

   stepi
   

   si
   

10. To switch code layout back to C:

layout previous

Features

1. Task and process management.
2. A FAT16 filesystem.
3. Programmable system interrupts.
4. PS/2 keyboard driver.
5. Kernel/user process memory management and paging.
6. Support for .bin and .elf file execution.
7. Solid base to implement multi-tasking.
8. Interactive shell able to parse program names and arguments and launch them.

Future Work

1. Add more programs like the already-implemented echo.
2. Implement multi-tasking.
3. Add more eastereggs like the one showcased down below wink wink.

hehOS_in_Action.mp4