RustyBoot-RISC-V

A minimal, modular bare-metal bootloader for RISC-V written in Rust. Designed to run directly on RISC-V hardware (and QEMU) without any firmware, loading kernels from memory or disk.

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Features

Implemented

• ✅ Bare-metal assembly entry point with stack setup and BSS clearing
• ✅ Machine-mode trap handling
• ✅ UART driver for debug output (16550-compatible)
• ✅ Frame allocator for memory management
• ✅ ELF64 kernel loader with segment loading
• ✅ VirtIO block device driver
• ✅ Multi-hart support (secondary harts parked)

Planned

• 🔲 MBR/GPT partition table parsing
• 🔲 EXT2/3/4 filesystem support
• 🔲 Device Tree (DTB) parsing and forwarding
• 🔲 Kernel command line support

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Requirements

• Rust nightly toolchain
• QEMU for RISC-V emulation (for testing)

Setup

# Install the RISC-V target
rustup target add riscv64gc-unknown-none-elf

# Install optional tools for binary inspection
rustup component add llvm-tools-preview
cargo install cargo-binutils

Build

# Debug build
cargo build

# Release build (optimized)
cargo build --release

# Or use Make
make release

Run in QEMU

# Using Make
make run

# Or manually
qemu-system-riscv64 \
    -machine virt \
    -bios none \
    -kernel target/riscv64gc-unknown-none-elf/release/rustyboot-riscv \
    -m 128M \
    -nographic \
    -serial mon:stdio

Expected output:

========================================
       RustyBoot-RISCV Bootloader       
========================================

[BOOT] Starting bootloader...
[BOOT] UART initialized
[MEM]  Initializing memory allocator
[MEM]  Frame allocator ready
[DISK] Probing for VirtIO block device...
[DISK] No VirtIO block device found
[BOOT] Loading kernel...
[BOOT] Checking for kernel at 0x80200000
[BOOT] No ELF header found, treating as raw binary
[BOOT] Jumping to kernel at 0x80200000
========================================

Run with VirtIO Disk

qemu-system-riscv64 \
    -machine virt \
    -bios none \
    -kernel target/riscv64gc-unknown-none-elf/release/rustyboot-riscv \
    -m 128M \
    -nographic \
    -serial mon:stdio \
    -drive file=disk.img,if=none,format=raw,id=hd0 \
    -device virtio-blk-device,drive=hd0

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Memory Map

Address Range	Description
0x80000000 - 0x80100000	Bootloader code and stack
0x80100000 - 0x80200000	Bootloader heap
0x80200000 - 0x81000000	Kernel load area
0x81000000 - 0x82000000	Frame allocator pool

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Project Structure

RustyBoot-RISCV/
├── src/
│   ├── main.rs           # Rust entry point
│   ├── entry.S           # Assembly startup code
│   ├── panic.rs          # Panic handler
│   ├── config.rs         # Configuration constants
│   ├── bootloader.rs     # Kernel loading logic
│   ├── uart/             # UART driver
│   ├── memory/           # Frame allocator
│   ├── block/            # VirtIO block driver
│   ├── fs/               # Filesystem support (WIP)
│   └── elf/              # ELF loader
├── linker.ld             # Linker script
├── Cargo.toml
├── Makefile
└── .cargo/config.toml    # Build configuration

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How It Works?

1. Entry Point (entry.S): Sets up stack, clears BSS, installs trap handler
2. UART Init: Enables debug output through serial console
3. Memory Init: Initializes frame allocator for dynamic memory
4. VirtIO Probe: Checks for block devices
5. Kernel Load: Loads kernel from 0x80200000 (ELF or raw binary)
6. Jump to Kernel: Transfers control with hart ID and DTB pointer

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Contributing

Contributions are welcome! Areas of interest:

• Device driver improvements (SPI, I2C, etc.)
• Filesystem support (FAT32, EXT4)
• Real hardware testing
• SBI implementation

Guidelines

• Maintain #![no_std] compatibility
• Follow the modular structure
• Test with QEMU before submitting

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License

GPLv3 - See LICENSE for details.

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Built with ❤️ in Rust