6.2 用 Rust 做作業系統啟動與裸機 hello-world#

rustup component add rust-src llvm-tools-preview
cargo install bootimage
# 需要的系統工具
sudo apt install qemu-system-x86_64 xorriso   # Debian/Ubuntu
brew install qemu                              # macOS

# Cargo.toml
[package]
name = "mini-os"
version = "0.1.0"
edition = "2021"

[dependencies]
bootloader = "0.9"

[profile.dev]
panic = "abort"   # 裸機無法展開堆疊 unwind

// src/main.rs
#![no_std]       // 不連結標準庫
#![no_main]      // 沒有 C main，入口由我們定義

use core::panic::PanicInfo;

/// 沒有 std 的 println 就沒了——之後自己寫
#[no_mangle]
pub extern "C" fn _start() -> ! {
    // 這裡是整個「作業系統」的起點
    // 此刻：沒有堆積、沒有執行緒、沒有檔案系統
    // 只有：CPU 暫存器、實體記憶體、VGA 文字模式
    loop {}
}

#[panic_handler]
fn panic(info: &PanicInfo) -> ! {
    // panic 不能再 panic——裸機裡錯誤處理就是「停機」
    loop {}
}

cargo bootimage     # 產生可開機映像
qemu-system-x86_64 -drive format=raw,file=target/x86_64-debug/bootimage-mini-os.bin

// src/vga.rs
use core::fmt;

const VGA_BUFFER: *mut u8 = 0xb8000 as *mut u8;
const COLS: usize = 80;

pub struct Writer {
    row: usize,
    col: usize,
}

impl Writer {
    pub fn write_byte(&mut self, byte: u8) {
        unsafe {
            match byte {
                b'\n' => { self.newline(); }
                _ => {
                    let offset = (self.row * COLS + self.col) * 2;
                    // 第一位元組：ASCII；第二位元組：顏色（白底黑字→黑底白字 0x0f）
                    VGA_BUFFER.offset(offset as isize).write_volatile(byte);
                    VGA_BUFFER.offset(offset as isize + 1).write_volatile(0x0f);
                    self.col += 1;
                    if self.col >= COLS { self.newline(); }
                }
            }
        }
    }

    fn newline(&mut self) {
        self.col = 0;
        self.row += 1;
        if self.row >= 25 { self.row = 0; }  // 簡化：不清屏捲動
    }

    pub fn write_str(&mut self, s: &str) {
        for b in s.bytes() { self.write_byte(b); }
    }
}

// 讓 println! 風格可用：實作 fmt::Write
impl fmt::Write for Writer {
    fn write_str(&mut self, s: &str) -> fmt::Result {
        self.write_str(s);
        Ok(())
    }
}

use core::fmt::Write;
use spin::Mutex;

pub static WRITER: Mutex<Writer> = Mutex::new(Writer { row: 0, col: 0 });

#[macro_export]
macro_rules! print {
    ($($arg:tt)*) => ({
        use core::fmt::Write;
        let mut w = $crate::vga::WRITER.lock();
        write!(w, format_args!($($arg)*)).unwrap();
    });
}

#[macro_export]
macro_rules! println {
    () => { $crate::print!("\n") };
    ($($arg:tt)*) => { $crate::print!("{}\n", format_args!($($arg)*)) };
}

// src/main.rs
#![no_std]
#![no_main]

mod vga;
use bootloader::{BootInfo, entry_point};

entry_point!(kernel_main);

fn kernel_main(boot_info: &'static BootInfo) -> ! {
    println!("=== mini-os ===");
    println!("physical memory offset: {:#x}", boot_info.physical_memory_offset);
    println!("it works!");
    loop {
        // TODO: 6.3 節在此加入記憶體管理
        // halt：讓 CPU 進入省電等待，而不是空轉
        x86_64::instructions::hlt();
    }
}

#[panic_handler]
fn panic(info: &PanicInfo) -> ! {
    println!("PANIC: {info}");
    loop { x86_64::instructions::hlt(); }
}