SlopOS

A minimal operating system built with GRUB bootloader

SlopOS is a simple operating system that demonstrates multiboot kernel development using the GRUB bootloader. It resolves the previous boot loop issues by using a proven, reliable bootloader instead of a custom implementation.

Architecture

SlopOS uses the multiboot specification and boots via GRUB, providing a stable and reliable boot process.

Boot Process

1. GRUB Bootloader: Handles hardware initialization and multiboot protocol
2. Multiboot Kernel: 32-bit protected mode kernel with multiboot headers
3. VGA Text Output: Simple text-based output for demonstration

Building and Running

Prerequisites

• NASM assembler
• GCC compiler
• GRUB tools (grub-mkrescue, grub-pc-bin)
• QEMU x86-64 emulator
• Make
• xorriso (for ISO creation)
• mtools

Quick Start

# Build and run the OS (builds ISO and boots with GRUB)
./run.sh

# Or manually:
make all        # Build ISO image
make run        # Run in QEMU (nographic)
make run-gui    # Run in QEMU with graphics
make clean      # Clean build files

Project Structure

• src/ - Kernel source code
  • multiboot_kernel.cpp - Main kernel with process and memory management
  • multiboot_entry.asm - Assembly entry point for multiboot kernel
  • multiboot.ld - Linker script for multiboot ELF kernel
  • terminal.cpp - VGA text mode terminal driver
  • string.cpp - String manipulation functions
  • timer.cpp - Timer functionality
  • memory.cpp - Physical memory allocator and heap management
  • process.cpp - Process control and scheduling
  • context_switch.asm - Assembly context switching code
  • syscall.cpp - System call interface implementation
  • shell.cpp - Shell as separate integrated process
• build/ - Generated build artifacts and ISO image
• Makefile - Build configuration for GRUB-based system with new components
• run.sh - Build and run script

Features

• GRUB-based bootloader (reliable, no boot loops)
• Multiboot-compliant 32-bit protected mode kernel
• VGA text mode output with proper newline and cursor positioning
• Clean build system with ISO generation
• QEMU testing support
• Resolves previous boot loop issues
• Interactive shell with command input/output
• Shell commands (version, hello, uptime, about, help)
• Keyboard input support with character echo
• Hardware cursor positioning management
• Memory management system (physical memory allocator)
• Process management framework (PCB, scheduling)
• System call interface
• Separated shell architecture

Process and Memory Management

SlopOS v2.0 introduces fundamental operating system features:

Memory Management

• Physical memory allocator with bitmap-based free page tracking
• Kernel heap allocator (kmalloc/kfree) for dynamic memory allocation
• Memory initialization and management for 32MB RAM
• Foundation for virtual memory management (paging support prepared)

Process Management

• Process Control Block (PCB) structure for process metadata
• Process creation, termination, and state management
• Basic cooperative multitasking scheduler (round-robin)
• Context switching support with assembly implementation
• Support for up to 32 concurrent processes

System Architecture

• Clear separation between kernel and user space
• System call interface for user-kernel communication
• Shell runs as integrated process with memory management
• Modular design allowing future enhancements

System Calls

• sys_exit - Process termination
• sys_write - Terminal output
• sys_read - Terminal input
• sys_yield - Cooperative multitasking

Boot Loop Fix

This version of SlopOS resolves the previous boot loop issue by:

• Replacing the problematic custom bootloader with GRUB
• Using the multiboot specification for reliable kernel loading
• Implementing proper multiboot headers and entry points
• Providing a stable, tested boot process

The GRUB bootloader successfully loads the kernel and displays a working system with basic shell functionality.

Shell Commands

SlopOS now includes an enhanced shell with process and memory management features:

• version - displays "slopOS 2.0 - Now with process management!"
• hello - displays "world"
• ps - shows running processes (kernel and shell)
• memory - displays memory management status
• yield - demonstrates cooperative multitasking
• exit - exits the shell
• help - displays list of available commands

The shell features:

• Interactive command input with keyboard support
• Proper cursor positioning that follows text input/output
• Command parsing and execution
• Error handling for unknown commands
• Real-time user interaction
• Professional shell prompt "slopOS> "
• Memory management integration
• Process management awareness