SUB-OS: 64-Bit Production Modular Monolithic Operating System

   _____ _    _ ____          ____   _____ 
  / ____| |  | |  _ \        / __ \ / ____|
 | (___ | |  | | |_) |______| |  | | (___  
  \___ \| |  | |  _ <|______| |  | |\___ \ 
  ____) | |__| | |_) |      | |__| |____) |
 |_____/ \____/|____/        \____/|_____/ 

SUB-OS is an open-source, production-grade 64-bit modular monolithic operating system engineered from the ground up for the x86_64 architecture. It is built adhering to the internal design principles of modern UNIX/Linux kernels, featuring full bare-metal hardware drivers, physical and dynamic memory management, a virtual file system (VFS), networking protocol stack, cryptographic engine, and the LazyBox multi-call userland environment.

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🏛️ System Architecture

+-------------------------------------------------------------------------+
|                       USERLAND & SYSTEM SUITE                           |
|   Interactive Shell  |  LazyBox Applets (ls, cat, ping, sha256sum, ...) |
+-------------------------------------------------------------------------+
|                       VIRTUAL FILE SYSTEM (VFS)                         |
|      vfs_namei  |  Root RAMFS  |  /dev (devfs)  |  /proc (procfs)       |
+-------------------------------------------------------------------------+
|                  CORE SERVICES & CRYPTO ENGINE                          |
|  Preemptive Scheduler | Task Control (PCB) | SHA-256 | MD5 | CRC32|PRNG |
+-------------------------------------------------------------------------+
|                       MEMORY MANAGEMENT (MM)                            |
|     Physical Page Frame Allocator (PMM)  |  Kernel Heap (kmalloc/kfree) |
+-------------------------------------------------------------------------+
|                       DEVICE DRIVER TREE                                |
|   VGA / TTY1-4   | 16550 UART Serial | PS/2 Keyboard | ATA / IDE Disk   |
|   PCI Enumerator | Intel E1000 NIC   | Net (ARP/IPv4/ICMP) | PC Speaker |
+-------------------------------------------------------------------------+
|                  HARDWARE ABSTRACTION LAYER (HAL)                       |
|   x86_64 Long Mode | GDT / TSS | IDT / ISRs | Dual 8259A PIC | 8254 PIT |
+-------------------------------------------------------------------------+

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⚡ 11-Step Master Boot Pipeline

During boot, the kernel executes a deterministic 11-step master initialization sequence:

Step	Subsystem	Description
[1/11]	64-Bit GDT & TSS	Configures flat kernel/user code & data segments and Task State Segment with dedicated 64KB kernel stack.
[2/11]	IDT & ISR Table	Populates 256-entry interrupt descriptor table with CPU exception handlers and hardware IRQ routing.
[3/11]	Dual 8259A PIC	Remaps master (IRQ 0-7 -> 0x20-0x27) and slave (IRQ 8-15 -> 0x28-0x2F) interrupt controllers.
[4/11]	8254 PIT Timer	Configures channel 0 for 100 Hz (10ms resolution) driving quantum preemption.
[5/11]	PS/2 Keyboard	Full scancode translation table with circular ringbuffer, Shift, CapsLock, and multi-TTY switching.
[6/11]	Physical Memory Manager	64-bit bitmap frame allocator tracking usable RAM via BIOS E820 map (31,712 free 4KB pages).
[7/11]	Kernel Dynamic Heap	Boundary-tag dynamic heap allocator with 4 MB initial pool, coalescing, and reallocation.
[8/11]	ATA / IDE Storage	28-bit LBA PIO hard disk controller supporting sector read/write operations on primary master.
[9/11]	PCI & Intel E1000 NIC	PCI bus enumerator, BAR configuration, and Intel 82540EM Gigabit NIC with circular DMA RX/TX descriptors.
[10/11]	Virtual File System	Mounts root in-memory RAMFS, synthetic /dev devfs, and dynamic /proc procfs.
[11/11]	Scheduler & LazyBox	Starts round-robin preemptive scheduler and launches LazyBox interactive userland environment.

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🌟 Subsystems Overview

1. Bootloader & Kernel Core (arch/x86_64/, kernel/)

• Two-Stage Custom MBR Bootloader:
  • stage1.asm: 512-byte MBR sector loaded at 0x7C00 that loads Stage 2 using BIOS INT 13h extensions.
  • stage2.asm: Enables A20 line, queries E820 memory map, builds 4-level PML4 identity paging tables (4GB address space), transitions through 32-bit Protected Mode into 64-bit Long Mode, and loads kernel in 64-sector chunks.
• Preemptive Multi-Tasking: Process Control Blocks (PCB), round-robin task scheduler driven by timer ticks, atomic spinlocks, and semaphores.
• Kernel Logging & Serial Diagnostics: ANSI color printk() supporting loglevels (KERN_INFO, KERN_WARN, KERN_ERR), a 64KB kernel dmesg ring buffer, and simultaneous output to COM1 serial port.

2. Memory Management Subsystem (mm/)

• Physical Memory Manager (pmm.c): Page frame allocator managing physical RAM using a high-efficiency bitmap.
• Kernel Dynamic Heap (kmalloc.c): Provides kmalloc, kzalloc, kcalloc, krealloc, and kfree with boundary tag headers and adjacent block coalescing.

3. Virtual File System (fs/)

• Unified VFS Core (vfs.c): Posix-like file operations (open, read, write, close, lseek, mkdir, create) with hierarchical path resolution (vfs_namei) and support for up to 64 file descriptors.
• Root RAMFS (ramfs.c): Dynamic in-memory directory and file tree with auto-expanding data buffers.
• Synthetic Device Filesystem (devfs.c): Mounted at /dev, providing /dev/null, /dev/zero, /dev/random, /dev/urandom, and /dev/tty.
• Dynamic Information Filesystem (procfs.c): Mounted at /proc, providing live virtual metrics via /proc/version, /proc/meminfo, and /proc/cpuinfo.

4. Device Drivers (drivers/)

• Virtual Terminals (tty.c): Four independent virtual terminals (tty1-tty4) with ANSI escape code processing, cursor positioning, and Alt+F1-Alt+F4 switching.
• Storage Controller (ata.c): ATA PIO mode driver for 28-bit LBA hard disk operations.
• PCI Bus Enumerator (pci.c): Discovers hardware devices across buses, slots, and functions, reading vendor/device IDs and mapping BARs.
• Intel E1000 Gigabit NIC (e1000.c): Configures receive/transmit circular DMA rings, link state auto-negotiation, and hardware packet dispatch.
• Audio (speaker.c): Square-wave audio generation using PIT Channel 2.

5. Network Stack (net/core/)

• Layer 2 Ethernet frame encapsulation and MAC parsing.
• ARP request/reply generation and dynamic ARP caching.
• IPv4 packet validation, header checksumming, and gateway routing.
• ICMP Echo Request/Reply client and server (ping).

6. Cryptography Engine (crypto/)

• SHA-256: FIPS 180-4 compliant 256-bit message digest.
• MD5: RFC 1321 compliant 128-bit hashing algorithm.
• CRC32: IEEE 802.3 standard cyclic redundancy check.
• PRNG: Xorshift128+ cryptographic pseudorandom generator.

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💻 LazyBox Multi-Call Userland Suite

LazyBox (userland/lazybox/) provides a single-binary multi-call command suite inspired by BusyBox:

Category	Applets
Filesystem	ls, cat, touch, mkdir, wc
Crypto	sha256sum, md5sum, crc32
Network	ifconfig, ping, arp
Storage	hdparm
System	uname, free, uptime, dmesg, sleep
Terminal	clear, neofetch
Core	lazybox, echo, calc

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📺 Live Output Demonstrations

1. neofetch

sub-os> neofetch
   _____ _    _ ____     OS:      SUB-OS v0.2.0-lts (Modular Monolithic)
  / ____| |  | |  _ \    Arch:    x86_64 (64-Bit Long Mode)
 | (___ | |  | | |_) |   Kernel:  Modular Drivers + VFS + Crypto + Net
  \___ \| |  | |  _ <    CPU:     QEMU Virtual CPU (AuthenticAMD)
  ____) | |__| | |_) |   Memory:  8 MB / 127 MB (Free: 119 MB)
 |_____/ \____/|____/    Heap:    110 KB used / 4095 KB total
                         Uptime:  00:00:02
                         TTY:     tty1 (Alt+F1-F4 to switch)

2. Network ICMP Ping (ping 10.0.2.2)

sub-os> ping 10.0.2.2
PING 10.0.2.2 (56 data bytes):
64 bytes from 10.0.2.2: icmp_seq=1 ttl=64 time=0 ms
64 bytes from 10.0.2.2: icmp_seq=2 ttl=64 time=0 ms

3. FIPS SHA-256 Cryptographic Hash (sha256sum /readme.txt)

sub-os> sha256sum /readme.txt
4e0391a7fc1a293893645d3d40f103f2eb28d442d0b8815bf86473d0bfd8e7fd  /readme.txt

4. Dynamic Process Information (cat /proc/meminfo)

sub-os> cat /proc/meminfo
MemTotal:         130944 kB
MemFree:          122752 kB
MemAvailable:     122752 kB
Buffers:               0 kB
Cached:              110 kB
HeapTotal:          4096 kB
HeapUsed:            110 kB
HeapFree:           3985 kB

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🛠️ Build and Emulation

Prerequisites

• Assembler: nasm (>= 2.15)
• Cross-Compiler: x86_64-elf-gcc (>= 13.0) & x86_64-elf-ld
• Emulator: qemu-system-x86_64
• Build System: GNU make

Building the OS

# Set cross-compiler path
export PATH="/usr/local/cross/bin:$PATH"

# Build kernel image (SUB-OS.img)
make

# Run in QEMU with Intel E1000 NIC and ATA drive
make run

# Clean build artifacts
make clean

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⌨️ Terminal Keybindings

Keybinding	Action
Alt + F1	Switch to TTY1 (Main Interactive Shell)
Alt + F2	Switch to TTY2 (Secondary Virtual Terminal)
Alt + F3	Switch to TTY3 (System Diagnostics Terminal)
Alt + F4	Switch to TTY4 (Background Task Terminal)
Up / Down	Command History Navigation
Left / Right	Interactive In-Line Cursor Navigation
Backspace	Character Erasure with Terminal Synchronisation
Tab	Command & Path Auto-Completion

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📁 Repository Structure

SUB-OS/
├── arch/x86_64/            # CPU, Paging, GDT/TSS, IDT/ISR, PIC, PIT, CPUID
├── boot/                   # Stage 1 MBR & Stage 2 64-bit Switch Bootloader
├── crypto/                 # SHA-256, MD5, CRC32, CSPRNG
├── drivers/                # Character, Block, PCI, Network (E1000), Sound
├── fs/                     # VFS Core, RAMFS, devfs, procfs
├── include/                # Complete Modular Kernel C Header Files
├── kernel/                 # Main, Scheduler, Tasks, Synchronization, printk, Panic
├── lib/                    # vsprintf, Strings, Bitmap
├── mm/                     # Physical Page Allocator (PMM) & Heap (kmalloc)
├── net/core/               # Ethernet, ARP, IPv4, ICMP Protocol Stack
├── tools/                  # Automated Setup and Cross-Compiler Scripts
├── userland/lazybox/       # LazyBox Multi-Call Binary & Interactive Shell
├── Makefile                # Complete Build Orchestrator
├── linker.ld               # Kernel 64-bit Linker Script
└── README.md               # Documentation & Specifications

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📄 License

This project is licensed under the terms of the MIT License.