Impl VGA buffer, serial output, testing and basic interrupts

Cargo.lock

@@ -2,15 +2,88 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "bit_field"
+version = "0.10.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dcb6dd1c2376d2e096796e234a70e17e94cc2d5d54ff8ce42b28cef1d0d359a4"
+
+[[package]]
+name = "bitflags"
+version = "1.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bef38d45163c2f1dde094a7dfd33ccf595c92905c8f8f4fdc18d06fb1037718a"
+
 [[package]]
 name = "bootloader"
 version = "0.9.22"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "de78decc37247c7cfac5dbf3495c7298c6ac97cb355161caa7e15969c6648e6c"
 
+[[package]]
+name = "lazy_static"
+version = "1.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
+dependencies = [
+ "spin",
+]
+
 [[package]]
 name = "plain_os"
 version = "0.1.0"
 dependencies = [
  "bootloader",
+ "lazy_static",
+ "spin",
+ "uart_16550",
+ "volatile 0.2.7",
+ "x86_64",
+]
+
+[[package]]
+name = "rustversion"
+version = "1.0.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a0a5f7c728f5d284929a1cccb5bc19884422bfe6ef4d6c409da2c41838983fcf"
+
+[[package]]
+name = "spin"
+version = "0.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6e63cff320ae2c57904679ba7cb63280a3dc4613885beafb148ee7bf9aa9042d"
+
+[[package]]
+name = "uart_16550"
+version = "0.2.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b074eb9300ad949edd74c529c0e8d451625af71bb948e6b65fe69f72dc1363d9"
+dependencies = [
+ "bitflags",
+ "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 = "0.4.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e3ca98349dda8a60ae74e04fd90c7fb4d6a4fbe01e6d3be095478aa0b76f6c0c"
+
+[[package]]
+name = "x86_64"
+version = "0.14.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "100555a863c0092238c2e0e814c1096c1e5cf066a309c696a87e907b5f8c5d69"
+dependencies = [
+ "bit_field",
+ "bitflags",
+ "rustversion",
+ "volatile 0.4.5",
 ]

Cargo.toml

@@ -8,10 +8,32 @@ resolver = "2"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [profile.dev]
-panic = "abort" # disable stack unwinding on panic
+#panic = "abort" # disable stack unwinding on panic
 
 [profile.release]
 panic = "abort" # disable stack unwinding on panic
 
 [dependencies]
+# FIXME(feliix42): Update to newer version
 bootloader = "0.9"
+
+# FIXME(feliix42): "newer versions of this library are not compatible with this post"
+volatile = "0.2.6"
+lazy_static = { version = "1.4", features = ["spin_no_std"] }
+spin = "0.5.2"
+
+# Data structures for interrupt handling (Interrupt Descriptor Tables, ...)
+x86_64 = "0.14.2"
+
+# Dependency for talking through the Serial Port
+uart_16550 = "0.2.0"
+
+[package.metadata.bootimage]
+# enables a special `isa-debug-exit` device in QEMU which allows us to terminate the OS from the outside
+test-args = [
+    "-device", "isa-debug-exit,iobase=0xf4,iosize=0x04", "-serial", "stdio",
+    "-display", "none"
+]
+# define the correct `success` exit code
+test-success-exit-code = 33         # (0x10 << 1) | 1
+

src/interrupts.rs

@@ -0,0 +1,33 @@
+use x86_64::structures::idt::{InterruptDescriptorTable, InterruptStackFrame};
+use crate::println;
+use lazy_static::lazy_static;
+
+// TODO(feliix42): For best experience, work through
+// https://os.phil-opp.com/edition-1/extra/naked-exceptions/ for manual exception handling without
+// the interrupt descriptor table :)
+
+// Creating the IDT is actually a bit tricky. The location of the IDT in memory needs to be static,
+// as the CPU will store its address in memory. We could declare it `static mut`, but that would
+// require the use of `unsafe {}` to mutate it, which is kinda meh. Hence, we use lazy_static,
+// which allows us to create a static ref lazily.
+lazy_static!{
+    static ref IDT: InterruptDescriptorTable = {
+        let mut idt = InterruptDescriptorTable::new();
+        idt.breakpoint.set_handler_fn(breakpoint_handler);
+        idt
+    };
+}
+
+/// Load the interrupt descriptor table.
+pub fn init_idt() {
+    IDT.load();
+}
+
+extern "x86-interrupt" fn breakpoint_handler(stack_frame: InterruptStackFrame) {
+    println!("[EXCEPTION] BREAKPOINT\n{:#?}", stack_frame);
+}
+
+#[test_case] 
+fn test_breakpoint_exception() {
+    x86_64::instructions::interrupts::int3();
+}

src/lib.rs

@@ -0,0 +1,58 @@
+#![no_std]
+// in the test enviroment, there is still no main function here
+#![cfg_attr(test, no_main)]
+#![feature(custom_test_frameworks)]
+#![feature(abi_x86_interrupt)]
+#![test_runner(crate::test_harness::test_runner)]
+// the `main` function generated by `cargo test` is never called due to our `no_main` macro
+#![reexport_test_harness_main = "test_main"]
+
+pub mod interrupts;
+pub mod serial;
+pub mod test_harness;
+pub mod vga_buffer;
+
+use core::panic::PanicInfo;
+pub use test_harness::{test_runner, test_panic_handler};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[repr(u32)]
+pub enum QemuExitCode {
+    Success = 0x10,
+    Failed = 0x11,
+}
+
+/// Exits QEMU and provides the supplied exit code.
+pub fn exit_qemu(exit_code: QemuExitCode) {
+    use x86_64::instructions::port::Port;
+
+    unsafe {
+        // 0xf4 is a generally unused I/O port on x86's IO bus, so we may use it to send the
+        // shutdown signal (as defined in `Cargo.toml`).
+        let mut port = Port::new(0xf4);
+
+        // writing to an IO port is generally unsafe.
+        port.write(exit_code as u32);
+    }
+}
+
+/// Entry point for `cargo test`
+#[cfg(test)]
+#[no_mangle]
+pub extern "C" fn _start() -> ! {
+    init();
+    test_main();
+    loop {}
+}
+
+#[cfg(test)]
+#[panic_handler]
+fn panic(info: &PanicInfo) -> ! {
+    test_harness::test_panic_handler(info)
+}
+
+/// Performs all kernel initialization
+pub fn init() {
+    // load interrupt descriptor table
+    interrupts::init_idt();
+}

src/main.rs

@@ -1,28 +1,36 @@
 #![no_std]
 #![no_main]
+#![feature(custom_test_frameworks)]
+#![test_runner(plain_os::test_runner)]
+#![reexport_test_harness_main = "test_main"]
 
 use core::panic::PanicInfo;
-
-static HELLO: &[u8] = b"Hello World!";
-
-/// This function defines the panic handler
-#[panic_handler]
-fn panic(_info: &PanicInfo) -> ! {
-    loop{}
-}
+use plain_os::println;
 
 // this function is the entry point, since the linker looks for a function
 // named `_start` by default
 #[no_mangle]
 pub extern "C" fn _start() -> ! {
-    let vga_buffer = 0xb8000 as *mut u8;
+    println!("Commencing boot process");
 
-    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;
-        }
-    }
+    plain_os::init();
+
+    #[cfg(test)]
+    test_main();
 
     loop {}
 }
+
+/// This function defines the panic handler
+#[cfg(not(test))]
+#[panic_handler]
+fn panic(info: &PanicInfo) -> ! {
+    println!("{}", info);
+    loop {}
+}
+
+#[cfg(test)]
+#[panic_handler] 
+fn panic(info: &PanicInfo) -> ! {
+    plain_os::test_panic_handler(info)
+}

src/serial.rs

@@ -0,0 +1,42 @@
+//! Module for communication using the serial port.
+
+use lazy_static::lazy_static;
+use spin::Mutex;
+use uart_16550::SerialPort;
+
+// like with accessing the VGA Text buffer, guard the (global) serial port by a Mutex to make it
+// globally available.
+lazy_static! {
+    pub static ref SERIAL1: Mutex<SerialPort> = {
+        // 0x3F8 is the standard port number for the first serial interface
+        let mut serial_port = unsafe { SerialPort::new(0x3F8) };
+        serial_port.init();
+        Mutex::new(serial_port)
+    };
+}
+
+/// Convenience function to print to the serial port
+#[doc(hidden)]
+pub fn _print(args: ::core::fmt::Arguments) {
+    use core::fmt::Write;
+    SERIAL1
+        .lock()
+        .write_fmt(args)
+        .expect("Printing to serial console failed");
+}
+
+/// Prints to the host through the serial interface
+#[macro_export]
+macro_rules! serial_print {
+    ($($arg:tt)*) => {
+        $crate::serial::_print(format_args!($($arg)*));
+    };
+}
+
+/// Prints to the host through the serial interface, ending with a newline.
+#[macro_export]
+macro_rules! serial_println {
+    () => ($crate::serial_print!("\n"));
+    ($fmt:expr) => ($crate::serial_print!(concat!($fmt, "\n")));
+    ($fmt:expr, $($arg:tt)*) => ($crate::serial_print!(concat!($fmt, "\n"), $($arg)*));
+}

src/test_harness.rs

@@ -0,0 +1,38 @@
+//! The kernels testing harness.
+//!
+//! Defines a simple test runner and a corresponding panic handler that both communicate using the
+//! serial interface of QEMU, printing test messages to the host system terminal.
+
+use crate::{serial_print, serial_println, QemuExitCode};
+use core::panic::PanicInfo;
+
+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();
+    }
+    crate::exit_qemu(QemuExitCode::Success);
+}
+
+/// Panic handler for testing environments (gives feedback via serial port)
+pub fn test_panic_handler(info: &PanicInfo) -> ! {
+    serial_println!("[failed]\n");
+    serial_println!("Error: {}\n", info);
+    crate::exit_qemu(QemuExitCode::Failed);
+    loop {}
+}

src/vga_buffer.rs

@@ -0,0 +1,175 @@
+use core::fmt;
+use volatile::Volatile;
+use lazy_static::lazy_static;
+use spin::Mutex;
+
+lazy_static! {
+    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) },
+    });
+}
+
+/// A single screen character, laid out as defined in the [VGA Text
+/// Mode](https://en.wikipedia.org/wiki/VGA_text_mode) specification.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[repr(C)]
+struct ScreenChar {
+    ascii_character: u8,
+    color_code: ColorCode,
+}
+
+const BUFFER_HEIGHT: usize = 25;
+const BUFFER_WIDTH: usize = 80;
+
+/// Abstraction for a VGA screen buffer.
+#[repr(transparent)]
+struct Buffer {
+    chars: [[Volatile<ScreenChar>; BUFFER_WIDTH]; BUFFER_HEIGHT],
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[repr(transparent)]
+struct ColorCode(u8);
+
+impl ColorCode {
+    fn new(foreground: Color, background: Color) -> ColorCode {
+        ColorCode((background as u8) << 4 | (foreground as u8))
+    }
+}
+
+#[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,
+}
+
+pub struct Writer {
+    column_position: usize,
+    color_code: ColorCode,
+    buffer: &'static mut Buffer,
+}
+
+impl Writer {
+    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;
+            }
+        }
+    }
+
+    /// Make room for a new line by moving up all output by 1 line and resetting the column
+    /// position to 1
+    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;
+    }
+
+    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);
+        }
+    }
+
+    pub 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),
+            }
+        }
+    }
+}
+
+impl fmt::Write for Writer {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        self.write_string(s);
+        Ok(())
+    }
+}
+
+#[macro_export]
+macro_rules! print {
+    ($($arg:tt)*) => ($crate::vga_buffer::_print(format_args!($($arg)*)));
+}
+
+#[macro_export]
+macro_rules! println {
+    () => ($crate::print!("\n"));
+    ($($arg:tt)*) => ($crate::print!("{}\n", format_args!($($arg)*)));
+}
+
+#[doc(hidden)]
+pub fn _print(args: fmt::Arguments) {
+    use core::fmt::Write;
+    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() {
+    let s = "Some test string that fits on a single line";
+    println!("{}", s);
+    for (i, c) in s.chars().enumerate() {
+        let screen_char = WRITER.lock().buffer.chars[BUFFER_HEIGHT - 2][i].read();
+        assert_eq!(char::from(screen_char.ascii_character), c);
+    }
+}
+
+

tests/basic_boot.rs

@@ -0,0 +1,33 @@
+#![no_std]
+#![no_main]
+#![feature(custom_test_frameworks)]
+#![test_runner(plain_os::test_runner)]
+#![reexport_test_harness_main = "test_main"]
+
+use core::panic::PanicInfo;
+use plain_os::println;
+
+#[no_mangle] // don't mangle the name of this function
+pub extern "C" fn _start() -> ! {
+    test_main();
+
+    loop {}
+}
+
+#[panic_handler]
+fn panic(info: &PanicInfo) -> ! {
+    plain_os::test_panic_handler(info)
+}
+
+#[test_case]
+fn test_println() {
+    println!("test_println output");
+}
+
+// TODO(feliix42): Future Test Ideas
+// - CPU Exceptions: validate that performing invalid operations (e.g., division by zero) leads to
+// the correct exception handlers being called
+// - Page Tables: validate/verify page table operations
+// - Userspace Programs:Test userspace programs trying to perform illegal operations and see
+// whether the kernel prevents them.
+//