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

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

For Debugging Using qemu & GDB

Launch GDB
```
gdb
```
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
```
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
```
To place a breakpoint (since symbol file is added, gdb will recognize function names):
```
break LABEL_NAME
```
To continue executing until breakpoint is reached:
```
c
```
To print a variable's value (if it is a pointer for example):
```
print *PTR_NAME
```
To single step in C code:
```
n
```
To switch code layout from C to Assembly:
```
layout asm
```
To single step in Assembly code:
```
stepi
```
```
si
```
To switch code layout back to C:

layout previous

Features

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

Future Work

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

hehOS_in_Action.mp4