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Curated Questions for Building a RISC-V OS

Copyright (c) 2025, Rye Stahle-Smith

📌 File Description

This file is a curated set of questions that a developer can use to guide an LLM (ChatGPT, Claude, Gemini, etc.)through the process of building a similar RISC‑V operating system. Each question corresponds to a conceptual milestone in this OS (bootloading, trap handling, scheduling, filesystem design, and user‑program execution, etc.)

🧩 1. Understanding the Goal (High-Level Concepts)

Phase 1: “What am I even building?”

  • “How might I build a simple RISC-V operating system from scratch?”
  • “What are the minimum components the OS might need?”

Phase 2: Tools & Environment

  • “How do I install the RISC-V GCC toolchain?”
  • “How do I run a bare-metal RISC-V binary in QEMU?”

🧱 2. Bootloader & Startup Assembly

Phase 3: Bootloader Basics

  • “How do I write a minimal RISC-V bootloader in assembly?”
  • “How do I set up the stack pointer in RISC-V assembly?”
  • “How do I pass control from a bootloader to a C function?”
  • “How do I configure the RISC-V trap vector during boot?”

Phase 4: Printing Text

  • “How do I print characters to a UART device in bare-metal RISC-V?”
  • “What memory-mapped IO address does QEMU use for UART?”

🔧 3. Kernel Initialization

Phase 5: Kernel Basics

  • “How do I write the entry point of a RISC-V kernel in C?”
  • “How should I structure initialization code in a small OS?”

Phase 6: Services Setup

  • “How do I initialize a bump allocator for dynamic memory?”
  • “What is a trap handler, and how do I install one in RISC-V?”
  • “What’s the simplest way to implement a scheduler?”
  • “How do I mount a simple in-memory filesystem?”

🚨 4. Traps & Syscalls

Phase 7: Entering the Trap World

  • “How do I write a trap handler in RISC-V assembly?”
  • “How do I save and restore registers correctly in the trap handler?”
  • “What does mcause mean in RISC-V?”
  • “How might I detect an ecall from user mode?”

Phase 8: Defining Syscalls

  • “How would I implement a syscall interface on RISC-V?”
  • “How might I add a syscall for exiting user programs?”

🧵 5. User Programs

Phase 9: Writing User Assembly

  • “How do I write a simple assembly program that runs in user mode?”
  • “How do I embed user programs into an OS image?”
  • “How do I compile assembly programs into flat binaries?”

Phase 10: Interacting with the Kernel

  • “How do user programs call syscalls using ecall?”
  • “How does the kernel load and execute a user program?”

📦 6. Filesystem

Phase 11: Directory & File Model

  • “How do I implement a simple memory-based FAT-like filesystem?”
  • “What’s the minimum structure for a directory and file?”
  • “How do I recursively create directories?”

Phase 12: Shell Commands

  • “How do I implement ls, cd, cat, rm, and other related commands?”
  • “How do I store file contents in an in-memory OS?”
  • “How do I run user programs via a shell command like run <file>?”

⚙️ 7. Scheduler & Multitasking

Phase 13: First Steps

  • “What is cooperative multitasking, and how does it differ from preemptive?”
  • “How do I design a process table in C?”
  • “What does RUNNING, READY, ZOMBIE mean?”

Phase 14: Context Switching

  • “How do I save all registers during an exit in RISC-V?”
  • “How does the scheduler switch between processes?”