RVOS: A Lightweight RISC-V Operating System

rvos is a bare-metal operating system kernel written in C and Assembly for the RISC-V architecture.
It serves as an educational project for exploring low-level system programming, memory management, and kernel architecture.

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Features

Architecture

• Target: RISC-V
• Tested on QEMU virt machine

Boot Process

• Assembly startup file (start.S)
• Initializes stack pointer
• Handles multi-core (Hart) parking

Memory Management

• Custom kalloc heap allocator
• Stack Safety
  • Kernel stack placed in .bss
  • Ensures writable memory and known bounds for GC
• Direct Memory Mapping
  • Running in Machine Mode
  • Identity mapping: PA = VA

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Project Structure

Directory	Description
kernel/	Core kernel code (allocator, scheduler, main entry).
startup/	Assembly boot code (start.S), hardware init.
include/	Header files & hardware definitions.
lib/	Utility functions (string ops, misc libs).
test/	Kernel-level test code.
kernel.ld	Linker script defining memory layout.

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Building and Running

Prerequisites

• Toolchain: riscv64-unknown-elf-gcc (or riscv32 equivalent)
• Emulator: QEMU (qemu-system-riscv64 / qemu-system-riscv32)
• Build Tool: GNU Make

Build and Run in QEMU

make run

Debugging

make debug

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Memory Layout

The memory layout begins at 0x80000000, defined in kernel.ld:

• .text – Kernel code (read-only, executable)
• .data – Initialized global variables
• .bss – Uninitialized globals & kernel stack
• Heap – Starts after .bss, grows upward to MEMORY_END

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License

This project is open source.