x86 Bootloader Framework (Demo from Production System)

📌 Background

This project is a public, simplified demonstration of a custom bootloader framework I originally developed for enterprise embedded systems.

The production system was deployed in security-critical environments (finance, automotive, industrial control) with features such as:

• TPM-based secure boot and attestation
• Encrypted signature verification and hardware-backed chain of trust
• Deterministic real-time scheduling with sub-millisecond interrupt handling
• Regulatory compliance and hardened fault-tolerance mechanisms

This demo version keeps the architectural spirit and technical patterns, while simplifying security and runtime features for educational and portfolio purposes.

🔧 Live Demo (QEMU Output) — No audio

This 40-second video highlights:

• Real → Protected Mode transition
• GDT / IDT initialization
• Exception vector handling (0–19)
• PIC remapping + IRQ0 timer interrupt
• Preemptive round-robin scheduler (tasks A/B/Idle)

📺 Watch on YouTube — No audio

🎯 Goals of This Demo

• Showcase system programming expertise on x86 boot and kernel primitives
• Provide an architecture-level view of real production bootloaders
• Share educational code with the community (low-level OS concepts)
• Document the translation of enterprise requirements into technical design

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🏗️ Architecture Overview

• Two-stage boot sequence: Stage1 MBR (512B) → Stage2 protected mode framework
• Protected mode setup: GDT/IDT initialization, interrupt remapping, exception handlers
• Feature-toggled build system: Selective compilation of subsystems (EXC, PIC, INTEGRITY, SCHED)
• Preemptive multitasking demo: Hardware timer (IRQ0) driving a round-robin scheduler

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🔑 Feature Matrix (Production vs Demo)

Feature	Production (Enterprise)	Demo (Open Source)
Secure Boot	TPM attestation, encrypted signatures, trust chain	Checksum validation (SGDT/SIDT)
Interrupts	Priority-based routing, deterministic latency	PIC remap + timer IRQ, basic ISR
Scheduling	Priority, RT guarantees, IPC	Round-robin, 3 tasks (A/B/Idle)
Exception Handling	Fault isolation, encrypted crash reports	Simple vector table + hex dump
Portability	Multi-platform x86 embedded	Flat model / runtime-patched GDT

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📂 Project Structure

├── bootloader_stage1.asm   # Stage1: MBR (16-bit real mode)
├── bootloader_stage2.asm   # Stage2: Protected mode + features
├── build_bootloader.sh     # Build script with feature flags
├── build_symbols.sh        # Debug symbol generation
├── load_symbols.gdb        # GDB loader for QEMU debugging
└── README.md               # This document

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⚙️ Build & Run

# Method A: Runtime GDT patch (legacy platforms)
./build_bootloader.sh A

# Method B: Flat addressing (modern platforms)
./build_bootloader.sh B

# With features
./build_bootloader.sh A "EXC PIC INTEGRITY SCHED"

Run in QEMU:

qemu-system-i386 -drive file=bootloader.img,format=raw

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🖥️ Expected Output Highlights

• Base: "METHOD A/B + IDT" → "IDT SETUP" → "INT 0x30 TRIGGERED"
• PIC enabled: TICKS:XX increments in real-time
• Integrity check: Displays GDT/IDT checksums
• Scheduler enabled: Task indicators cycle (A → B → I) with counters updating

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🧩 Technical Concepts Demonstrated

• Real → Protected mode transition
• GDT/IDT setup and exception handling
• PIC reprogramming and hardware interrupt handling
• Preemptive scheduling via context switching
• Boot-time integrity validation mechanisms

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🚀 Skills Demonstrated

• System programming (x86 assembly): low-level bootloader + kernel mechanisms
• Interrupt and scheduling design: hardware timer-driven context switching
• Security mindset: integrity checking, trust chain concepts
• Production experience: Translating enterprise security & real-time requirements into implementable architectures

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📌 Value

This repository demonstrates how production-grade embedded bootloader concepts can be distilled into an open-source educational framework, while still highlighting:

• Engineering depth (secure boot, interrupts, scheduling)
• Architecture clarity (modular feature toggles, dual addressing models)
• Practical coding ability (working bootloader in <5KB)

It bridges the gap between commercial system design and teaching-oriented open source, showcasing both engineering rigor and technical communication.

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📖 Related

💡 When to choose bare-metal vs RTOS?
It depends on requirements — not hype.

👉 Discussion on LinkedIn

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⚠️ Disclaimer

This repository contains no proprietary or confidential code.
It is a clean-room educational implementation, inspired by architectural patterns originally designed for production environments.