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🧰 Development and Toolchain Overview

The R4R operating system is developed from scratch using the GCC compiler with inline assembly, targeting 32-bit i386/i486 processors.
Inline assembly is used because R4R is strictly hardware-oriented and complex due to the multi-ring architecture, so it is essential that the assembly code reside within C files — sharing their scope and context without unnecessary linking.
This approach improves visibility, readability, and direct interaction with system-level constructs.
The core intent is to maintain full control over hardware behavior, particularly across all four x86 protection rings.

🧩 Why I chose C for R4R:
After exploring alternatives like Zig and Rust, I concluded that C remains the most practical, predictable, and hardware-transparent language for low-level system development on 32-bit Intel machines.
My reasoning is explained in detail in this forum post:
👉 “A Warm Acknowledgment and an Objective Conclusion from an Enthusiast” — FreeBSD Forum

Toolchain

  • Compiler: GCC (std=c23) with support for Intel __asm__ syntax
  • Assembler: Inline assembly, no external .S or GAS-based files
  • Bootloaders: GRUB v1 (img build) and GRUB v2 (iso build)
  • Emulators: BOCHS (recommended with GUI debugger), QEMU (partially reliable)
  • Target hardware: Real Intel i486+ CPUs (system tested on physical machines)

Design Principles

  • Core components are written in C and inline assembly, where hardware-level control (like privilege transitions, task state manipulation, or descriptor configuration) is required.
  • The system architecture emphasizes tasks as hardware-managed objects, with extensive use of call gates for controlled transitions across rings.
  • Code is highly non-portable and intentionally focused on leveraging underused features of x86 CPUs, such as hardware task switching and segment-based protection.

Build System

The build system currently supports floppy image (GRUB v1) configuration.

Use the following make targets:

make clean   # recommended before each full build
make         # build folder build/ with objects and floppy-based build/sys_out/grub1.img
make bochs   # run floppy-based grub1.img in Bochs

Emulator Notes

  • BOCHS is recommended for debugging due to its excellent GUI debugger. Older BOCHS versions may be more compatible with Ubuntu 20.04. I am using Ubuntu 24.04 and Bochs x86 Emulator 2.8.
  • QEMU may exhibit inconsistent behavior — some features fail in emulation but succeed on real hardware. Development prioritizes actual hardware over emulator compatibility.

Summary

R4R is a hardware-centric system. While most operating systems abstract away x86-specific features in the name of portability, this project attempts the opposite: to embrace x86 as deeply as possible, using GCC and modern GNU tools while maintaining a low-level, bare-metal mindset.