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, Linux Security Modules (LSM), asynchronous io_uring ringbuffers, hypervisor detection, full-screen visual nano editor, and the LazyBox multi-call userland environment.

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🏛️ System Architecture

+-------------------------------------------------------------------------+
|                       USERLAND & SYSTEM SUITE                           |
|  Interactive Shell | GNU Nano 2.0.0 | LazyBox Suite (ls, cat, ping, ...) |
+-------------------------------------------------------------------------+
|                       VIRTUAL FILE SYSTEM (VFS)                         |
|   vfs_namei | Root RAMFS | /dev (devfs) | /proc (procfs) | initramfs   |
+-------------------------------------------------------------------------+
|             ASYNC I/O ENGINE & SECURITY FRAMEWORK                       |
|   io_uring (SQE/CQE Rings) | Linux Security Modules (LSM) | Keyring     |
+-------------------------------------------------------------------------+
|                  CORE SERVICES & CRYPTO ENGINE                          |
|  Preemptive Scheduler | Task Control | SHA-256 | MD5 | CRC32 | PRNG     |
+-------------------------------------------------------------------------+
|                       MEMORY MANAGEMENT (MM)                            |
|     Physical Page Frame Allocator (PMM)  |  Kernel Heap (kmalloc/kfree) |
+-------------------------------------------------------------------------+
|                       DEVICE DRIVER TREE & VIRT                         |
|   VGA / TTY1-4   | 16550 UART Serial | PS/2 Keyboard | ATA / IDE Disk   |
|   PCI Enumerator | Intel E1000 NIC   | VirtIO Core   | PC Speaker       |
+-------------------------------------------------------------------------+
|                  HARDWARE ABSTRACTION LAYER (HAL)                       |
|   x86_64 Long Mode | GDT / TSS | IDT / ISRs | Dual 8259A PIC | 8254 PIT |
+-------------------------------------------------------------------------+

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⚡ 14-Step Master Boot Pipeline

During boot, the kernel executes a deterministic 14-step master initialization sequence:

Step	Subsystem	Description
[1/14]	64-Bit GDT & TSS	Configures flat kernel/user code & data segments and Task State Segment with dedicated 64KB kernel stack.
[2/14]	IDT & ISR Table	Populates 256-entry interrupt descriptor table with CPU exception handlers and hardware IRQ routing.
[3/14]	Dual 8259A PIC	Remaps master (IRQ 0-7 -> 0x20-0x27) and slave (IRQ 8-15 -> 0x28-0x2F) interrupt controllers.
[4/14]	8254 PIT Timer	Configures channel 0 for 100 Hz (10ms resolution) driving quantum preemption.
[5/14]	PS/2 Keyboard	Full scancode translation table with circular ringbuffer, Shift, CapsLock, Ctrl keys, and multi-TTY switching.
[6/14]	Physical Memory Manager	64-bit bitmap frame allocator tracking usable RAM via BIOS E820 map (31,712 free 4KB pages).
[7/14]	Kernel Dynamic Heap	Boundary-tag dynamic heap allocator with 4 MB initial pool, coalescing, and reallocation.
[8/14]	ATA / IDE Storage	28-bit LBA PIO hard disk controller supporting sector read/write operations on primary master.
[9/14]	PCI, VirtIO & Net	PCI bus enumerator, VirtIO core, and Intel 82540EM Gigabit NIC with circular DMA RX/TX descriptors.
[10/14]	Security & Keyring	Loads X.509 trusted certificate authority keyring and enforces POSIX Capabilities Linux Security Module (LSM).
[11/14]	io_uring Subsystem	Lockless Submission Queue Entry (SQE) & Completion Queue Entry (CQE) asynchronous I/O engine.
[12/14]	Virtual File System	Mounts root in-memory RAMFS, synthetic /dev devfs, /proc procfs, and unpacks embedded initramfs tree.
[13/14]	Scheduler & LazyBox	Starts round-robin preemptive scheduler and launches LazyBox interactive userland environment.
[14/14]	Hardware Interrupts	Enables processor interrupts (sti) and transitions to userland shell.

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🌟 Subsystems & Linux Directory Structure

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

• Two-Stage Custom MBR Bootloader:
  • boot/boot.asm: 512-byte MBR sector loaded at 0x7C00 that loads Stage 2 using BIOS INT 13h extensions.
  • boot/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. Early Initialization & Versioning (init/)

• init/cmdline.c: Kernel command line parsing (root=, console=, init=, quiet, etc.) and system runlevel management (RUNLEVEL_SINGLE, RUNLEVEL_MULTIUSER, RUNLEVEL_GRAPHICAL).
• init/version.c: Version metadata and banner formatting.

3. X.509 Cryptographic Keyring (certs/)

• certs/x509.c: ASN.1 DER parser for X.509 v3 public key certificates (Subject, Issuer, Validity, SHA-256 Fingerprint, RSA/ECDSA trust validation).
• System trusted keyring supporting kernel module and executable signature verification.

4. Asynchronous I/O Engine (io_uring/)

• io_uring/io_uring.c: High-performance non-blocking asynchronous I/O ringbuffers with SQE (Submission Queue Entries) and CQE (Completion Queue Entries) for concurrent disk and network I/O.

5. Linux Security Modules & Capabilities (security/)

• security/lsm.c: Hookable security infrastructure with DAC and MAC permission callbacks.
• security/capability.c: POSIX Capabilities model (CAP_CHOWN, CAP_DAC_OVERRIDE, CAP_NET_RAW, CAP_SYS_ADMIN, etc.).

6. Userspace Initramfs & Payload (usr/)

• usr/initramfs.c: Populates filesystem tree (/usr/bin, /var/log, /etc/passwd, /etc/issue, /etc/fstab).

7. Virtualization & VirtIO Subsystem (virt/)

• virt/hypervisor.c: Hypervisor detection via CPUID leaves (QEMU, KVM, VMware, VirtualBox, Hyper-V).
• virt/virtio.c: VirtIO core device driver registration and split virtqueue framework.

8. 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.

9. 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.
• Process Metrics Filesystem (procfs.c): Mounted at /proc, generating dynamic metrics (/proc/version, /proc/meminfo, /proc/cpuinfo, /proc/uptime, /proc/net/dev).

10. Hardware Drivers (drivers/)

• VGA & TTY (vga.c, tty.c): 80x25 text mode driver with 4 Virtual Consoles (TTY1-4 switched via Alt+F1–Alt+F4) and full ANSI escape sequence parsing.
• Serial Port (serial.c): 16550 UART COM1 driver at 115200 baud.
• PS/2 Keyboard (keyboard.c): Interrupt-driven scancode decoder with modifier state machine and full Ctrl+key combination mapping.
• ATA / IDE Disk (ata.c): 28-bit LBA PIO disk controller.
• PCI Bus (pci.c): Enumeration and Base Address Register (BAR) configuration.
• Intel E1000 Gigabit NIC (e1000.c): Intel 82540EM Gigabit NIC driver with hardware DMA ringbuffers.
• PC Speaker (speaker.c): Programmable timer channel 2 tone generator.

11. Cryptography Engine (crypto/)

• SHA-256 (sha256.c): FIPS 180-4 compliant 256-bit cryptographic digest.
• MD5 (md5.c): RFC 1321 compliant 128-bit hash function.
• CRC32 (crc32.c): IEEE 802.3 standard cyclic redundancy check.
• PRNG (prng.c): Xorshift128+ cryptographic pseudo-random number generator.

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📝 Full-Screen Visual Nano Editor

SUB-OS includes a full-screen interactive ANSI text editor (nano):

  GNU nano 2.0.0             File: /home/user/notes.txt               [Modified]
Hello from nano editor in SUB-OS!
This is a production-level modular operating system.
You can write, edit, search, and save files directly to the VFS.
~
~
~
~
~
~
~
~
~
~
~
[ Wrote 148 bytes to /home/user/notes.txt ]
^G Get Help  ^O WriteOut  ^W Where Is  ^K Cut Line  ^U Paste  ^X Exit

Keybindings:

• ^O (Ctrl+O): WriteOut / Save file to Virtual File System.
• ^X (Ctrl+X): Exit Nano and return to shell.
• ^K (Ctrl+K): Cut current line to cut-buffer.
• ^U (Ctrl+U): Uncut / Paste line at cursor position.
• ^G (Ctrl+G): Display help cheat sheet.
• Arrow Keys / Home / End / PgUp / PgDn: Smooth cursor navigation.

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🧰 LazyBox Multi-Call Userland Suite

SUB-OS ships with an extensive multi-call userland binary suite (lazybox):

Category	Commands
Core	lazybox, echo, whoami, id, date, cal
Filesystem & Editor	nano, ls, cat, touch, mkdir, pwd, cd, wc, head, tail, stat, cp, grep, hexdump
Crypto & Security	sha256sum, md5sum, crc32, rand, certcheck, capsh
Network	ifconfig, ping, arp
Storage & Devices	hdparm, lspci, speaker
Virtualization	virtinfo, io_uring_test
System Monitoring	uname, free, uptime, dmesg, ps, top, sleep, reboot, poweroff
Terminal	clear, neofetch, help

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🚀 Building & Running

Prerequisites

• gcc (with -ffreestanding, -fno-pie, -mcmodel=kernel) or x86_64-elf-gcc
• nasm (Netwide Assembler)
• qemu-system-x86_64 (for hardware virtualization)

Compilation

make clean
make

Emulation in QEMU

# Run with Intel Gigabit NIC, ATA drive, PC Speaker, and Serial Console
qemu-system-x86_64 -drive format=raw,file=SUB-OS.img -nic model=e1000 -serial stdio -audiodev id=snd0,driver=pa -machine pcspk-audiodev=snd0