RustyBoot

A single stage, freestanding x86 bootloader written in Rust. RustyBoot probes the disk MBR, initializes a minimalist EXT2/3/4 reader, loads an ELF32 kernel from common paths, and transfers control to the kernel entry point. It uses a tiny VGA text console and a minimal ATA PIO disk driver.

Part of the Rusty-Suite. Built for learning, experimentation, and low-level OS development.

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WIP

Working on: Porting RustyBoot to UEFI with EFI entry point and SimpleFileSystem kernel loading

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Features

• x86 32-bit freestanding environment, no_std, panic=abort
• Disk bring-up via ATA PIO LBA28 on primary master
• MBR read and parse with active partition selection
• EXT2/3/4 superblock detection with early boot constraints
• Minimal file read with direct, single indirect, and double indirect blocks
• ELF32 little endian loader for PT_LOAD segments
• Simple bump-based memory manager (1 MB – 8 MB region with kernel reservation)
• VGA text console output
• Modular Rust codebase with clear separation of:
  • Config (runtime options & parameters)
  • Hammering (low-level memory & disk probing logic)
  • Logger (diagnostics and debugging output)

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Status

• ✅ Implemented
  • ATA PIO disk identify and sector reads
  • MBR parsing and active partition discovery
  • EXT filesystem init and early boot reads
  • File reads by absolute path
  • Kernel discovery and ELF32 loading
  • Memory initialization and kernel memory reservation
• 🛠️ Planned or partial
  • FAT filesystem implementation (stub only)
  • EXT extents and 64-bit features not supported
  • Triple indirect blocks not implemented (1 MiB file buffer limit)
  • More robust device discovery and error reporting

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Architecture

flowchart TD
  A["Start"] --> B["Config init"]
  B --> C["Logger init"]
  C --> D["Memory init"]
  D --> E["Disk init (ATA PIO)"]
  E --> F["Read LBA0 and parse MBR"]
  F --> G["Init EXT from active partition"]
  G --> H["Find kernel in common paths"]
  H --> I["Load and parse ELF32 PT_LOAD"]
  I --> J["Reserve memory & setup stack"]
  J --> K["Jump to kernel entry"]

Loading

Key Entry Points

• Entrypoint: _start()
• Config: Config::load()
• Logger: init_logger()
• Disk: init(), read_sectors()
• MBR: probe(), find_active_partition()
• EXT: init_with_lba(), read_file()
• Kernel loader: find_and_load_kernel(), parse_and_load_elf(), jump_to_kernel()
• Memory: init(), reserve_for_kernel()

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Filesystem Support

• EXT2/3/4 early boot reader
  • Validates magic 0xEF53
  • Rejects extents and 64-bit features for simplicity
  • Block size: 1–4 KiB (multiple of 512)
  • Supports direct, single indirect, and double indirect blocks
  • Triple indirect not implemented
  • File size limit: 1 MiB (compile-time buffer cap)
  • Absolute path only (example: /boot/vmlinuz)
• FAT
  • Stub only (not yet implemented)

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Kernel Loading

• Search paths: /boot/vmlinuz, /boot/kernel, /kernel, /boot/bzImage
• ELF32 little endian only
• Loads PT_LOAD segments to specified virtual addresses
• Zero-fills memory when mem_size > file_size
• Reserves the loaded region

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Build

Requirements

• Rust toolchain with llvm-tools-preview
• ld.lld or lld
• objcopy (LLVM or GNU)
• qemu-system-i386
• make
• Linux host recommended (example: zypper on openSUSE)

Quick Start

rustup component add llvm-tools-preview

# 1. Build the UEFI bootloader (produces RustyBoot.efi)
make bootloader

# 2. Optional: create a FAT32 disk image and copy the EFI file
make Disk

# 3. Run RustyBoot in QEMU
make run


# 4. Run in QEMU with GDB debugging
make debug

# 5. Clean build artifacts and disk image
make clean

Configuration

• Target: x86_64-uefi.json
• Executables: true
• Endianness: little
• Panic strategy: abort
• Code model: kernel
• Red zone: disabled
• Linker script: generated at build time via build.rs

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Limitations & Caveats

• 32-bit only; no long mode
• Static memory map (no E820 probing)
• No filesystem journaling, extents, or 64-bit EXT features
• ELF64 unsupported
• Serial output minimal (VGA primary console)
• Single disk, primary master ATA PIO assumed

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Contributing

See CONTRIBUTING.md and CODE_OF_CONDUCT.md.

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Trademark Notice

The names Rusty-Suite, RustyTodos, RustyBoot, and Rusty-Checker are part of this project identity. See TRADEMARK.md.

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License

GPLv3. See LICENSE.

Built with ❤️ in Rust.