Merge branch 'post-07' into post-08

Set `test=true` to enable `main.rs` testing again

.github/workflows/code.yml

@@ -67,6 +67,31 @@ jobs:
         with:
           command: bootimage
 
+      # install QEMU
+      - name: Install QEMU (Linux)
+        run: sudo apt update && sudo apt install qemu-system-x86
+        if: runner.os == 'Linux'
+      - name: Install QEMU (macOS)
+        run: brew install qemu
+        if: runner.os == 'macOS'
+        env:
+          HOMEBREW_NO_AUTO_UPDATE: 1
+          HOMEBREW_NO_BOTTLE_SOURCE_FALLBACK: 1
+          HOMEBREW_NO_INSTALL_CLEANUP: 1
+      - name: Install QEMU (Windows)
+        run: |
+          choco install qemu --version 2021.5.5
+          echo "$Env:Programfiles\qemu" | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append
+        if: runner.os == 'Windows'
+        shell: pwsh
+      - name: "Print QEMU Version"
+        run: qemu-system-x86_64 --version
+
+      - name: Run `cargo test`
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+
   check_formatting:
     name: Check Formatting
     runs-on: ubuntu-latest

Cargo.lock

@@ -2,11 +2,36 @@
 # It is not intended for manual editing.
 version = 4
 
+[[package]]
+name = "bit_field"
+version = "0.10.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dc827186963e592360843fb5ba4b973e145841266c1357f7180c43526f2e5b61"
+
+[[package]]
+name = "bitflags"
+version = "1.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bef38d45163c2f1dde094a7dfd33ccf595c92905c8f8f4fdc18d06fb1037718a"
+
+[[package]]
+name = "bitflags"
+version = "2.9.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6a65b545ab31d687cff52899d4890855fec459eb6afe0da6417b8a18da87aa29"
+
 [[package]]
 name = "blog_os"
 version = "0.1.0"
 dependencies = [
  "bootloader",
+ "lazy_static",
+ "pc-keyboard",
+ "pic8259",
+ "spin 0.5.2",
+ "uart_16550",
+ "volatile 0.2.7",
+ "x86_64",
 ]
 
 [[package]]
@@ -14,3 +39,80 @@ name = "bootloader"
 version = "0.9.32"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1ea119c3ed05625c179e09d17d0914570a3753ca09c890a73d98f6b72aea00d2"
+
+[[package]]
+name = "lazy_static"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bbd2bcb4c963f2ddae06a2efc7e9f3591312473c50c6685e1f298068316e66fe"
+dependencies = [
+ "spin 0.9.8",
+]
+
+[[package]]
+name = "pc-keyboard"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ed089a1fbffe3337a1a345501c981f1eb1e47e69de5a40e852433e12953c3174"
+
+[[package]]
+name = "pic8259"
+version = "0.10.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cb844b5b01db1e0b17938685738f113bfc903846f18932b378bc0eabfa40e194"
+dependencies = [
+ "x86_64",
+]
+
+[[package]]
+name = "rustversion"
+version = "1.0.22"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b39cdef0fa800fc44525c84ccb54a029961a8215f9619753635a9c0d2538d46d"
+
+[[package]]
+name = "spin"
+version = "0.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6e63cff320ae2c57904679ba7cb63280a3dc4613885beafb148ee7bf9aa9042d"
+
+[[package]]
+name = "spin"
+version = "0.9.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6980e8d7511241f8acf4aebddbb1ff938df5eebe98691418c4468d0b72a96a67"
+
+[[package]]
+name = "uart_16550"
+version = "0.2.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "614ff2a87880d4bd4374722268598a970bbad05ced8bf630439417347254ab2e"
+dependencies = [
+ "bitflags 1.3.2",
+ "rustversion",
+ "x86_64",
+]
+
+[[package]]
+name = "volatile"
+version = "0.2.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f6b06ad3ed06fef1713569d547cdbdb439eafed76341820fb0e0344f29a41945"
+
+[[package]]
+name = "volatile"
+version = "0.4.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "442887c63f2c839b346c192d047a7c87e73d0689c9157b00b53dcc27dd5ea793"
+
+[[package]]
+name = "x86_64"
+version = "0.14.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c101112411baafbb4bf8d33e4c4a80ab5b02d74d2612331c61e8192fc9710491"
+dependencies = [
+ "bit_field",
+ "bitflags 2.9.2",
+ "rustversion",
+ "volatile 0.4.6",
+]

Cargo.toml

@@ -4,10 +4,40 @@ version = "0.1.0"
 authors = ["Philipp Oppermann <dev@phil-opp.com>"]
 edition = "2024"
 
+[[test]]
+name = "should_panic"
+harness = false
+
+[[test]]
+name = "stack_overflow"
+harness = false
+
 [dependencies]
 bootloader = "0.9"
+volatile = "0.2.6"
+spin = "0.5.2"
+x86_64 = "0.14.2"
+uart_16550 = "0.2.0"
+pic8259 = "0.10.1"
+pc-keyboard = "0.7.0"
+
+[dependencies.lazy_static]
+version = "1.0"
+features = ["spin_no_std"]
 
 [[bin]]
 name = "blog_os"
-test = false
+test = true
 bench = false
+
+
+[package.metadata.bootimage]
+test-args = [
+    "-device",
+    "isa-debug-exit,iobase=0xf4,iosize=0x04",
+    "-serial",
+    "stdio",
+    "-display",
+    "none",
+]
+test-success-exit-code = 33 # (0x10 << 1) | 1

README.md

@@ -1,10 +1,10 @@
-# Blog OS (A Minimal Rust Kernel)
+# Blog OS (Introduction to Paging)
 
-[![Build Status](https://github.com/phil-opp/blog_os/workflows/Code/badge.svg?branch=post-02)](https://github.com/phil-opp/blog_os/actions?query=workflow%3A%22Code%22+branch%3Apost-02)
+[![Build Status](https://github.com/phil-opp/blog_os/workflows/Code/badge.svg?branch=post-08)](https://github.com/phil-opp/blog_os/actions?query=workflow%3A%22Code%22+branch%3Apost-08)
 
-This repository contains the source code for the [A Minimal Rust Kernel][post] post of the [Writing an OS in Rust](https://os.phil-opp.com) series.
+This repository contains the source code for the [Introduction to Paging][post] post of the [Writing an OS in Rust](https://os.phil-opp.com) series.
 
-[post]: https://os.phil-opp.com/minimal-rust-kernel/
+[post]: https://os.phil-opp.com/paging-introduction/
 
 **Check out the [master branch](https://github.com/phil-opp/blog_os) for more information.**
 
@@ -56,6 +56,10 @@ dd if=target/x86_64-blog_os/debug/bootimage-blog_os.bin of=/dev/sdX && sync
 
 Where `sdX` is the device name of your USB stick. **Be careful** to choose the correct device name, because everything on that device is overwritten.
 
+## Testing
+
+To run the unit and integration tests, execute `cargo xtest`.
+
 ## License
 
 Licensed under either of

src/gdt.rs

@@ -0,0 +1,52 @@
+use lazy_static::lazy_static;
+use x86_64::VirtAddr;
+use x86_64::structures::gdt::{Descriptor, GlobalDescriptorTable, SegmentSelector};
+use x86_64::structures::tss::TaskStateSegment;
+
+pub const DOUBLE_FAULT_IST_INDEX: u16 = 0;
+
+lazy_static! {
+    static ref TSS: TaskStateSegment = {
+        let mut tss = TaskStateSegment::new();
+        tss.interrupt_stack_table[DOUBLE_FAULT_IST_INDEX as usize] = {
+            const STACK_SIZE: usize = 4096 * 5;
+            static mut STACK: [u8; STACK_SIZE] = [0; STACK_SIZE];
+
+            let stack_start = VirtAddr::from_ptr(&raw const STACK);
+            let stack_end = stack_start + STACK_SIZE;
+            stack_end
+        };
+        tss
+    };
+}
+
+lazy_static! {
+    static ref GDT: (GlobalDescriptorTable, Selectors) = {
+        let mut gdt = GlobalDescriptorTable::new();
+        let code_selector = gdt.add_entry(Descriptor::kernel_code_segment());
+        let tss_selector = gdt.add_entry(Descriptor::tss_segment(&TSS));
+        (
+            gdt,
+            Selectors {
+                code_selector,
+                tss_selector,
+            },
+        )
+    };
+}
+
+struct Selectors {
+    code_selector: SegmentSelector,
+    tss_selector: SegmentSelector,
+}
+
+pub fn init() {
+    use x86_64::instructions::segmentation::{CS, Segment};
+    use x86_64::instructions::tables::load_tss;
+
+    GDT.0.load();
+    unsafe {
+        CS::set_reg(GDT.1.code_selector);
+        load_tss(GDT.1.tss_selector);
+    }
+}

src/interrupts.rs

@@ -0,0 +1,119 @@
+use crate::{gdt, hlt_loop, print, println};
+use lazy_static::lazy_static;
+use pic8259::ChainedPics;
+use spin;
+use x86_64::structures::idt::{InterruptDescriptorTable, InterruptStackFrame, PageFaultErrorCode};
+
+pub const PIC_1_OFFSET: u8 = 32;
+pub const PIC_2_OFFSET: u8 = PIC_1_OFFSET + 8;
+
+#[derive(Debug, Clone, Copy)]
+#[repr(u8)]
+pub enum InterruptIndex {
+    Timer = PIC_1_OFFSET,
+    Keyboard,
+}
+
+impl InterruptIndex {
+    fn as_u8(self) -> u8 {
+        self as u8
+    }
+
+    fn as_usize(self) -> usize {
+        usize::from(self.as_u8())
+    }
+}
+
+pub static PICS: spin::Mutex<ChainedPics> =
+    spin::Mutex::new(unsafe { ChainedPics::new(PIC_1_OFFSET, PIC_2_OFFSET) });
+
+lazy_static! {
+    static ref IDT: InterruptDescriptorTable = {
+        let mut idt = InterruptDescriptorTable::new();
+        idt.breakpoint.set_handler_fn(breakpoint_handler);
+        idt.page_fault.set_handler_fn(page_fault_handler);
+        unsafe {
+            idt.double_fault
+                .set_handler_fn(double_fault_handler)
+                .set_stack_index(gdt::DOUBLE_FAULT_IST_INDEX);
+        }
+        idt[InterruptIndex::Timer.as_usize()].set_handler_fn(timer_interrupt_handler);
+        idt[InterruptIndex::Keyboard.as_usize()].set_handler_fn(keyboard_interrupt_handler);
+        idt
+    };
+}
+
+pub fn init_idt() {
+    IDT.load();
+}
+
+extern "x86-interrupt" fn breakpoint_handler(stack_frame: InterruptStackFrame) {
+    println!("EXCEPTION: BREAKPOINT\n{:#?}", stack_frame);
+}
+
+extern "x86-interrupt" fn page_fault_handler(
+    stack_frame: InterruptStackFrame,
+    error_code: PageFaultErrorCode,
+) {
+    use x86_64::registers::control::Cr2;
+
+    println!("EXCEPTION: PAGE FAULT");
+    println!("Accessed Address: {:?}", Cr2::read());
+    println!("Error Code: {:?}", error_code);
+    println!("{:#?}", stack_frame);
+    hlt_loop();
+}
+
+extern "x86-interrupt" fn double_fault_handler(
+    stack_frame: InterruptStackFrame,
+    _error_code: u64,
+) -> ! {
+    panic!("EXCEPTION: DOUBLE FAULT\n{:#?}", stack_frame);
+}
+
+extern "x86-interrupt" fn timer_interrupt_handler(_stack_frame: InterruptStackFrame) {
+    print!(".");
+    unsafe {
+        PICS.lock()
+            .notify_end_of_interrupt(InterruptIndex::Timer.as_u8());
+    }
+}
+
+extern "x86-interrupt" fn keyboard_interrupt_handler(_stack_frame: InterruptStackFrame) {
+    use pc_keyboard::{DecodedKey, HandleControl, Keyboard, ScancodeSet1, layouts};
+    use spin::Mutex;
+    use x86_64::instructions::port::Port;
+
+    lazy_static! {
+        static ref KEYBOARD: Mutex<Keyboard<layouts::Us104Key, ScancodeSet1>> =
+            Mutex::new(Keyboard::new(
+                ScancodeSet1::new(),
+                layouts::Us104Key,
+                HandleControl::Ignore
+            ));
+    }
+
+    let mut keyboard = KEYBOARD.lock();
+    let mut port = Port::new(0x60);
+
+    let scancode: u8 = unsafe { port.read() };
+    if let Ok(Some(key_event)) = keyboard.add_byte(scancode) {
+        if let Some(key) = keyboard.process_keyevent(key_event) {
+            match key {
+                DecodedKey::Unicode(character) => print!("{}", character),
+                DecodedKey::RawKey(key) => print!("{:?}", key),
+            }
+        }
+    }
+
+    unsafe {
+        PICS.lock()
+            .notify_end_of_interrupt(InterruptIndex::Keyboard.as_u8());
+    }
+}
+
+#[test_case]
+fn test_breakpoint_exception() {
+    // invoke a breakpoint exception
+    x86_64::instructions::interrupts::int3();
+}

src/lib.rs

@@ -0,0 +1,86 @@
+#![no_std]
+#![cfg_attr(test, no_main)]
+#![feature(custom_test_frameworks)]
+#![feature(abi_x86_interrupt)]
+#![test_runner(crate::test_runner)]
+#![reexport_test_harness_main = "test_main"]
+
+use core::panic::PanicInfo;
+
+pub mod gdt;
+pub mod interrupts;
+pub mod serial;
+pub mod vga_buffer;
+
+pub fn init() {
+    gdt::init();
+    interrupts::init_idt();
+    unsafe { interrupts::PICS.lock().initialize() };
+    x86_64::instructions::interrupts::enable();
+}
+pub trait Testable {
+    fn run(&self) -> ();
+}
+
+impl<T> Testable for T
+where
+    T: Fn(),
+{
+    fn run(&self) {
+        serial_print!("{}...\t", core::any::type_name::<T>());
+        self();
+        serial_println!("[ok]");
+    }
+}
+
+pub fn test_runner(tests: &[&dyn Testable]) {
+    serial_println!("Running {} tests", tests.len());
+    for test in tests {
+        test.run();
+    }
+    exit_qemu(QemuExitCode::Success);
+}
+
+pub fn test_panic_handler(info: &PanicInfo) -> ! {
+    serial_println!("[failed]\n");
+    serial_println!("Error: {}\n", info);
+    exit_qemu(QemuExitCode::Failed);
+    hlt_loop();
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[repr(u32)]
+pub enum QemuExitCode {
+    Success = 0x10,
+    Failed = 0x11,
+}
+
+pub fn exit_qemu(exit_code: QemuExitCode) {
+    use x86_64::instructions::port::Port;
+
+    unsafe {
+        let mut port = Port::new(0xf4);
+        port.write(exit_code as u32);
+    }
+}
+
+pub fn hlt_loop() -> ! {
+    loop {
+        x86_64::instructions::hlt();
+    }
+}
+
+/// Entry point for `cargo xtest`
+#[cfg(test)]
+#[unsafe(no_mangle)]
+pub extern "C" fn _start() -> ! {
+    init();
+    test_main();
+    hlt_loop();
+}
+
+#[cfg(test)]
+#[panic_handler]
+fn panic(info: &PanicInfo) -> ! {
+    test_panic_handler(info)
+}

src/main.rs

@@ -1,26 +1,47 @@
 #![no_std]
 #![no_main]
+#![feature(custom_test_frameworks)]
+#![test_runner(blog_os::test_runner)]
+#![reexport_test_harness_main = "test_main"]
 
+use blog_os::println;
 use core::panic::PanicInfo;
 
-static HELLO: &[u8] = b"Hello World!";
-
 #[unsafe(no_mangle)]
 pub extern "C" fn _start() -> ! {
-    let vga_buffer = 0xb8000 as *mut u8;
+    use x86_64::registers::control::Cr3;
+    println!("Hello World{}", "!");
 
-    for (i, &byte) in HELLO.iter().enumerate() {
-        unsafe {
-            *vga_buffer.offset(i as isize * 2) = byte;
-            *vga_buffer.offset(i as isize * 2 + 1) = 0xb;
-        }
-    }
+    blog_os::init();
 
-    loop {}
+    let (level_4_page_table, _) = Cr3::read();
+    println!(
+        "Level 4 page table at: {:?}",
+        level_4_page_table.start_address()
+    );
+
+    #[cfg(test)]
+    test_main();
+
+    println!("It did not crash!");
+    blog_os::hlt_loop();
 }
 
 /// This function is called on panic.
+#[cfg(not(test))]
 #[panic_handler]
-fn panic(_info: &PanicInfo) -> ! {
-    loop {}
+fn panic(info: &PanicInfo) -> ! {
+    println!("{}", info);
+    blog_os::hlt_loop();
+}
+
+#[cfg(test)]
+#[panic_handler]
+fn panic(info: &PanicInfo) -> ! {
+    blog_os::test_panic_handler(info)
+}
+
+#[test_case]
+fn trivial_assertion() {
+    assert_eq!(1, 1);
 }

src/serial.rs

@@ -0,0 +1,41 @@
+use lazy_static::lazy_static;
+use spin::Mutex;
+use uart_16550::SerialPort;
+
+lazy_static! {
+    pub static ref SERIAL1: Mutex<SerialPort> = {
+        let mut serial_port = unsafe { SerialPort::new(0x3F8) };
+        serial_port.init();
+        Mutex::new(serial_port)
+    };
+}
+
+#[doc(hidden)]
+pub fn _print(args: ::core::fmt::Arguments) {
+    use core::fmt::Write;
+    use x86_64::instructions::interrupts;
+
+    interrupts::without_interrupts(|| {
+        SERIAL1
+            .lock()
+            .write_fmt(args)
+            .expect("Printing to serial failed");
+    });
+}
+
+/// Prints to the host through the serial interface.
+#[macro_export]
+macro_rules! serial_print {
+    ($($arg:tt)*) => {
+        $crate::serial::_print(format_args!($($arg)*));
+    };
+}
+
+/// Prints to the host through the serial interface, appending a newline.
+#[macro_export]
+macro_rules! serial_println {
+    () => ($crate::serial_print!("\n"));
+    ($fmt:expr) => ($crate::serial_print!(concat!($fmt, "\n")));
+    ($fmt:expr, $($arg:tt)*) => ($crate::serial_print!(
+        concat!($fmt, "\n"), $($arg)*));
+}

src/vga_buffer.rs

@@ -0,0 +1,204 @@
+use core::fmt;
+use lazy_static::lazy_static;
+use spin::Mutex;
+use volatile::Volatile;
+
+lazy_static! {
+    /// A global `Writer` instance that can be used for printing to the VGA text buffer.
+    ///
+    /// Used by the `print!` and `println!` macros.
+    pub static ref WRITER: Mutex<Writer> = Mutex::new(Writer {
+        column_position: 0,
+        color_code: ColorCode::new(Color::Yellow, Color::Black),
+        buffer: unsafe { &mut *(0xb8000 as *mut Buffer) },
+    });
+}
+
+/// The standard color palette in VGA text mode.
+#[allow(dead_code)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[repr(u8)]
+pub enum Color {
+    Black = 0,
+    Blue = 1,
+    Green = 2,
+    Cyan = 3,
+    Red = 4,
+    Magenta = 5,
+    Brown = 6,
+    LightGray = 7,
+    DarkGray = 8,
+    LightBlue = 9,
+    LightGreen = 10,
+    LightCyan = 11,
+    LightRed = 12,
+    Pink = 13,
+    Yellow = 14,
+    White = 15,
+}
+
+/// A combination of a foreground and a background color.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[repr(transparent)]
+struct ColorCode(u8);
+
+impl ColorCode {
+    /// Create a new `ColorCode` with the given foreground and background colors.
+    fn new(foreground: Color, background: Color) -> ColorCode {
+        ColorCode((background as u8) << 4 | (foreground as u8))
+    }
+}
+
+/// A screen character in the VGA text buffer, consisting of an ASCII character and a `ColorCode`.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[repr(C)]
+struct ScreenChar {
+    ascii_character: u8,
+    color_code: ColorCode,
+}
+
+/// The height of the text buffer (normally 25 lines).
+const BUFFER_HEIGHT: usize = 25;
+/// The width of the text buffer (normally 80 columns).
+const BUFFER_WIDTH: usize = 80;
+
+/// A structure representing the VGA text buffer.
+#[repr(transparent)]
+struct Buffer {
+    chars: [[Volatile<ScreenChar>; BUFFER_WIDTH]; BUFFER_HEIGHT],
+}
+
+/// A writer type that allows writing ASCII bytes and strings to an underlying `Buffer`.
+///
+/// Wraps lines at `BUFFER_WIDTH`. Supports newline characters and implements the
+/// `core::fmt::Write` trait.
+pub struct Writer {
+    column_position: usize,
+    color_code: ColorCode,
+    buffer: &'static mut Buffer,
+}
+
+impl Writer {
+    /// Writes an ASCII byte to the buffer.
+    ///
+    /// Wraps lines at `BUFFER_WIDTH`. Supports the `\n` newline character.
+    pub fn write_byte(&mut self, byte: u8) {
+        match byte {
+            b'\n' => self.new_line(),
+            byte => {
+                if self.column_position >= BUFFER_WIDTH {
+                    self.new_line();
+                }
+
+                let row = BUFFER_HEIGHT - 1;
+                let col = self.column_position;
+
+                let color_code = self.color_code;
+                self.buffer.chars[row][col].write(ScreenChar {
+                    ascii_character: byte,
+                    color_code,
+                });
+                self.column_position += 1;
+            }
+        }
+    }
+
+    /// Writes the given ASCII string to the buffer.
+    ///
+    /// Wraps lines at `BUFFER_WIDTH`. Supports the `\n` newline character. Does **not**
+    /// support strings with non-ASCII characters, since they can't be printed in the VGA text
+    /// mode.
+    fn write_string(&mut self, s: &str) {
+        for byte in s.bytes() {
+            match byte {
+                // printable ASCII byte or newline
+                0x20..=0x7e | b'\n' => self.write_byte(byte),
+                // not part of printable ASCII range
+                _ => self.write_byte(0xfe),
+            }
+        }
+    }
+
+    /// Shifts all lines one line up and clears the last row.
+    fn new_line(&mut self) {
+        for row in 1..BUFFER_HEIGHT {
+            for col in 0..BUFFER_WIDTH {
+                let character = self.buffer.chars[row][col].read();
+                self.buffer.chars[row - 1][col].write(character);
+            }
+        }
+        self.clear_row(BUFFER_HEIGHT - 1);
+        self.column_position = 0;
+    }
+
+    /// Clears a row by overwriting it with blank characters.
+    fn clear_row(&mut self, row: usize) {
+        let blank = ScreenChar {
+            ascii_character: b' ',
+            color_code: self.color_code,
+        };
+        for col in 0..BUFFER_WIDTH {
+            self.buffer.chars[row][col].write(blank);
+        }
+    }
+}
+
+impl fmt::Write for Writer {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        self.write_string(s);
+        Ok(())
+    }
+}
+
+/// Like the `print!` macro in the standard library, but prints to the VGA text buffer.
+#[macro_export]
+macro_rules! print {
+    ($($arg:tt)*) => ($crate::vga_buffer::_print(format_args!($($arg)*)));
+}
+
+/// Like the `println!` macro in the standard library, but prints to the VGA text buffer.
+#[macro_export]
+macro_rules! println {
+    () => ($crate::print!("\n"));
+    ($($arg:tt)*) => ($crate::print!("{}\n", format_args!($($arg)*)));
+}
+
+/// Prints the given formatted string to the VGA text buffer
+/// through the global `WRITER` instance.
+#[doc(hidden)]
+pub fn _print(args: fmt::Arguments) {
+    use core::fmt::Write;
+    use x86_64::instructions::interrupts;
+
+    interrupts::without_interrupts(|| {
+        WRITER.lock().write_fmt(args).unwrap();
+    });
+}
+
+#[test_case]
+fn test_println_simple() {
+    println!("test_println_simple output");
+}
+
+#[test_case]
+fn test_println_many() {
+    for _ in 0..200 {
+        println!("test_println_many output");
+    }
+}
+
+#[test_case]
+fn test_println_output() {
+    use core::fmt::Write;
+    use x86_64::instructions::interrupts;
+
+    let s = "Some test string that fits on a single line";
+    interrupts::without_interrupts(|| {
+        let mut writer = WRITER.lock();
+        writeln!(writer, "\n{}", s).expect("writeln failed");
+        for (i, c) in s.chars().enumerate() {
+            let screen_char = writer.buffer.chars[BUFFER_HEIGHT - 2][i].read();
+            assert_eq!(char::from(screen_char.ascii_character), c);
+        }
+    });
+}

tests/basic_boot.rs

@@ -0,0 +1,25 @@
+#![no_std]
+#![no_main]
+#![feature(custom_test_frameworks)]
+#![test_runner(blog_os::test_runner)]
+#![reexport_test_harness_main = "test_main"]
+
+use blog_os::println;
+use core::panic::PanicInfo;
+
+#[unsafe(no_mangle)] // don't mangle the name of this function
+pub extern "C" fn _start() -> ! {
+    test_main();
+
+    loop {}
+}
+
+#[panic_handler]
+fn panic(info: &PanicInfo) -> ! {
+    blog_os::test_panic_handler(info)
+}
+
+#[test_case]
+fn test_println() {
+    println!("test_println output");
+}

tests/should_panic.rs

@@ -0,0 +1,25 @@
+#![no_std]
+#![no_main]
+
+use blog_os::{QemuExitCode, exit_qemu, serial_print, serial_println};
+use core::panic::PanicInfo;
+
+#[unsafe(no_mangle)]
+pub extern "C" fn _start() -> ! {
+    should_fail();
+    serial_println!("[test did not panic]");
+    exit_qemu(QemuExitCode::Failed);
+    loop {}
+}
+
+fn should_fail() {
+    serial_print!("should_panic::should_fail...\t");
+    assert_eq!(0, 1);
+}
+
+#[panic_handler]
+fn panic(_info: &PanicInfo) -> ! {
+    serial_println!("[ok]");
+    exit_qemu(QemuExitCode::Success);
+    loop {}
+}

tests/stack_overflow.rs

@@ -0,0 +1,58 @@
+#![no_std]
+#![no_main]
+#![feature(abi_x86_interrupt)]
+
+use blog_os::{QemuExitCode, exit_qemu, serial_print, serial_println};
+use core::panic::PanicInfo;
+use lazy_static::lazy_static;
+use x86_64::structures::idt::{InterruptDescriptorTable, InterruptStackFrame};
+
+#[unsafe(no_mangle)]
+pub extern "C" fn _start() -> ! {
+    serial_print!("stack_overflow::stack_overflow...\t");
+
+    blog_os::gdt::init();
+    init_test_idt();
+
+    // trigger a stack overflow
+    stack_overflow();
+
+    panic!("Execution continued after stack overflow");
+}
+
+#[allow(unconditional_recursion)]
+fn stack_overflow() {
+    stack_overflow(); // for each recursion, the return address is pushed
+    volatile::Volatile::new(0).read(); // prevent tail recursion optimizations
+}
+
+lazy_static! {
+    static ref TEST_IDT: InterruptDescriptorTable = {
+        let mut idt = InterruptDescriptorTable::new();
+        unsafe {
+            idt.double_fault
+                .set_handler_fn(test_double_fault_handler)
+                .set_stack_index(blog_os::gdt::DOUBLE_FAULT_IST_INDEX);
+        }
+
+        idt
+    };
+}
+
+pub fn init_test_idt() {
+    TEST_IDT.load();
+}
+
+extern "x86-interrupt" fn test_double_fault_handler(
+    _stack_frame: InterruptStackFrame,
+    _error_code: u64,
+) -> ! {
+    serial_println!("[ok]");
+    exit_qemu(QemuExitCode::Success);
+    loop {}
+}
+
+#[panic_handler]
+fn panic(info: &PanicInfo) -> ! {
+    blog_os::test_panic_handler(info)
+}