Wip

WIP
Merge branch 'post-09' into post-10
2025-12-16 14:27:49 +00:00 · 2019-06-17 13:23:39 +02:00 · 2019-03-18 18:28:04 +01:00 · 2019-03-14 11:18:40 +01:00 · 2019-03-14 11:18:22 +01:00 · 2019-03-14 11:18:22 +01:00
22 changed files with 1423 additions and 19 deletions
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -56,6 +56,18 @@ install:
  - rustc -vV
  - cargo -vV

+  # Install qemu
+  - echo %cd%
+  - mkdir "C:\Program Files\qemu"
+  - cd "C:\Program Files\qemu"
+  - if %target%==i686-pc-windows-msvc appveyor DownloadFile "https://qemu.weilnetz.de/w32/2018/qemu-w32-setup-20180801.exe" -FileName "qemu-setup.exe"
+  - if %target%==i686-pc-windows-gnu appveyor DownloadFile "https://qemu.weilnetz.de/w32/2018/qemu-w32-setup-20180801.exe" -FileName "qemu-setup.exe"
+  - if %target%==x86_64-pc-windows-msvc appveyor DownloadFile "https://qemu.weilnetz.de/w64/2018/qemu-w64-setup-20180801.exe" -FileName "qemu-setup.exe"
+  - if %target%==x86_64-pc-windows-gnu appveyor DownloadFile "https://qemu.weilnetz.de/w64/2018/qemu-w64-setup-20180801.exe" -FileName "qemu-setup.exe"
+  - 7z x qemu-setup.exe
+  - set PATH=%PATH%;C:\Program Files\qemu
+  - cd "C:\projects\blog-os"
+
 ## Build Script ##

 # 'cargo test' takes care of building for us, so disable Appveyor's build stage. This prevents
@@ -74,3 +86,6 @@ before_test:

 test_script:
  - bootimage build
+  - if %target%==x86_64-pc-windows-gnu cargo test
+  - if %target%==x86_64-pc-windows-msvc cargo test
+  - bootimage test
--- a/.travis.yml
+++ b/.travis.yml
@@ -27,6 +27,18 @@ branches:
 cache:
  directories:
    - $HOME/.cargo
+    - $HOME/Library/Caches/Homebrew
+
+addons:
+  apt:
+    packages:
+      - qemu-system-x86
+  homebrew:
+    packages:
+      - qemu
+
+install:
+  - if [ $TRAVIS_OS_NAME = windows ]; then choco install qemu; export PATH="/c/Program Files/qemu:$PATH"; fi

 before_script:
  - rustup component add rust-src
@@ -35,4 +47,6 @@ before_script:

 script:
  - bootimage build
+  - cargo test
+  - bootimage test
  - cargo cache --autoclean
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1,5 +1,13 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
+[[package]]
+name = "array-init"
+version = "0.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "nodrop 0.1.13 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "array-init"
 version = "0.0.4"
@@ -22,7 +30,15 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 name = "blog_os"
 version = "0.1.0"
 dependencies = [
+ "array-init 0.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
 "bootloader 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "lazy_static 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "pc-keyboard 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "pic8259_simple 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "spin 0.4.10 (registry+https://github.com/rust-lang/crates.io-index)",
+ "uart_16550 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "volatile 0.2.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "x86_64 0.5.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]

 [[package]]
@@ -37,6 +53,16 @@ dependencies = [
 "xmas-elf 0.6.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]

+[[package]]
+name = "cc"
+version = "1.0.30"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "cpuio"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "fixedvec"
 version = "0.2.3"
@@ -72,6 +98,14 @@ dependencies = [
 "unicode-width 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
 ]

+[[package]]
+name = "lazy_static"
+version = "1.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "spin 0.4.10 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "libc"
 version = "0.2.48"
@@ -87,6 +121,19 @@ name = "os_bootinfo"
 version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"

+[[package]]
+name = "pc-keyboard"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "pic8259_simple"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "cpuio 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "pulldown-cmark"
 version = "0.0.3"
@@ -120,6 +167,16 @@ name = "rand_core"
 version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"

+[[package]]
+name = "raw-cpuid"
+version = "6.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "bitflags 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.30 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rustc_version 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "rdrand"
 version = "0.4.0"
@@ -136,6 +193,27 @@ dependencies = [
 "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
 ]

+[[package]]
+name = "rustc_version"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "semver 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "semver"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "semver-parser 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "semver-parser"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "skeptic"
 version = "0.5.0"
@@ -145,6 +223,11 @@ dependencies = [
 "tempdir 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)",
 ]

+[[package]]
+name = "spin"
+version = "0.4.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "tempdir"
 version = "0.3.7"
@@ -154,6 +237,15 @@ dependencies = [
 "remove_dir_all 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]

+[[package]]
+name = "uart_16550"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "bitflags 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "x86_64 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "unicode-width"
 version = "0.1.5"
@@ -169,6 +261,11 @@ name = "ux"
 version = "0.1.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"

+[[package]]
+name = "volatile"
+version = "0.2.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "winapi"
 version = "0.3.6"
@@ -188,6 +285,18 @@ name = "winapi-x86_64-pc-windows-gnu"
 version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"

+[[package]]
+name = "x86_64"
+version = "0.2.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "bit_field 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "bitflags 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "os_bootinfo 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "usize_conversions 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "ux 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "x86_64"
 version = "0.3.6"
@@ -201,6 +310,19 @@ dependencies = [
 "ux 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
 ]

+[[package]]
+name = "x86_64"
+version = "0.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "array-init 0.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "bit_field 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "bitflags 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "raw-cpuid 6.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "usize_conversions 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "ux 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "xmas-elf"
 version = "0.6.2"
@@ -215,32 +337,47 @@ version = "0.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"

 [metadata]
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--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,7 +5,20 @@ authors = ["Philipp Oppermann <dev@phil-opp.com>"]
 edition = "2018"

 [dependencies]
-bootloader = "0.4.0"
+bootloader = { version = "0.4.0", features = ["map_physical_memory"]}
+volatile = "0.2.3"
+spin = "0.4.9"
+uart_16550 = "0.1.0"
+x86_64 = "0.5.2"
+pic8259_simple = "0.1.1"
+pc-keyboard = "0.3.1"
+
+[dependencies.lazy_static]
+version = "1.0"
+features = ["spin_no_std"]
+
+[dev-dependencies]
+array-init = "0.0.3"

 [profile.dev]
 panic = "abort"
--- a/README.md
+++ b/README.md
@@ -1,10 +1,10 @@
-# Blog OS (A Minimal Rust Kernel)
+# Blog OS (Paging Implementation)

-[![Build Status](https://travis-ci.org/phil-opp/blog_os.svg?branch=post-02)](https://travis-ci.org/phil-opp/blog_os/branches)
+[![Build Status](https://travis-ci.org/phil-opp/blog_os.svg?branch=post-10)](https://travis-ci.org/phil-opp/blog_os/branches)

-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 [Paging Implementation][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-implementation/

 **Check out the [master branch](https://github.com/phil-opp/blog_os) for more information.**

@@ -46,5 +46,9 @@ 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 tests on the host system, execute `cargo test`. To run the integration tests in [QEMU], run `bootimage test`.
+
 ## License
 The source code is dual-licensed under MIT or the Apache License (Version 2.0).
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -66,6 +66,32 @@ steps:
 - script: bootimage build
  displayName: 'Build'

+- script: cargo test
+  displayName: 'Unit Tests'
+
+- script: sudo apt install qemu-system-x86
+  condition: eq( variables['Agent.OS'], 'Linux' )
+  displayName: 'Install QEMU (Linux)'
+
+- script: |
+    export HOMEBREW_NO_AUTO_UPDATE=1
+    export HOMEBREW_NO_BOTTLE_SOURCE_FALLBACK=1
+    export HOMEBREW_NO_INSTALL_CLEANUP=1
+    brew install qemu
+  condition: eq( variables['Agent.OS'], 'Darwin' )
+  displayName: 'Install QEMU (macOS)'
+
+- script: |
+    choco install qemu --limit-output --no-progress
+    echo ##vso[task.setvariable variable=PATH;]%PATH%;C:\Program Files\qemu
+    set PATH=%PATH%;C:\Program Files\qemu
+    qemu-system-x86_64 --version
+  condition: eq( variables['Agent.OS'], 'Windows_NT' )
+  displayName: 'Install QEMU (Windows)'
+
+- script: bootimage test
+  displayName: 'Integration Tests'
+
 - script: rustup component add rustfmt
  displayName: 'Install Rustfmt'

--- a/src/bin/test-basic-boot.rs
+++ b/src/bin/test-basic-boot.rs
@@ -0,0 +1,44 @@
+#![cfg_attr(not(test), no_std)]
+#![cfg_attr(not(test), no_main)] // disable all Rust-level entry points
+#![cfg_attr(test, allow(unused_imports))]
+#![feature(alloc_error_handler)]
+
+use blog_os::memory::allocator::DummyAllocator;
+use blog_os::{exit_qemu, serial_println};
+use core::alloc::Layout;
+use core::panic::PanicInfo;
+
+/// This function is the entry point, since the linker looks for a function
+/// named `_start` by default.
+#[cfg(not(test))]
+#[no_mangle] // don't mangle the name of this function
+pub extern "C" fn _start() -> ! {
+    serial_println!("ok");
+
+    unsafe {
+        exit_qemu();
+    }
+    loop {}
+}
+
+/// This function is called on panic.
+#[cfg(not(test))]
+#[panic_handler]
+fn panic(info: &PanicInfo) -> ! {
+    serial_println!("failed");
+
+    serial_println!("{}", info);
+
+    unsafe {
+        exit_qemu();
+    }
+    loop {}
+}
+
+#[global_allocator]
+static ALLOCATOR: DummyAllocator = DummyAllocator;
+
+#[alloc_error_handler]
+fn out_of_memory(layout: Layout) -> ! {
+    panic!("out of memory: allocation for {:?} failed", layout);
+}
--- a/src/bin/test-exception-breakpoint.rs
+++ b/src/bin/test-exception-breakpoint.rs
@@ -0,0 +1,45 @@
+#![no_std]
+#![cfg_attr(not(test), no_main)]
+#![cfg_attr(test, allow(dead_code, unused_macros, unused_imports))]
+#![feature(alloc_error_handler)]
+
+use blog_os::memory::allocator::DummyAllocator;
+use blog_os::{exit_qemu, serial_println};
+use core::alloc::Layout;
+use core::panic::PanicInfo;
+
+#[cfg(not(test))]
+#[no_mangle]
+pub extern "C" fn _start() -> ! {
+    blog_os::interrupts::init_idt();
+
+    x86_64::instructions::interrupts::int3();
+
+    serial_println!("ok");
+
+    unsafe {
+        exit_qemu();
+    }
+    loop {}
+}
+
+#[cfg(not(test))]
+#[panic_handler]
+fn panic(info: &PanicInfo) -> ! {
+    serial_println!("failed");
+
+    serial_println!("{}", info);
+
+    unsafe {
+        exit_qemu();
+    }
+    loop {}
+}
+
+#[global_allocator]
+static ALLOCATOR: DummyAllocator = DummyAllocator;
+
+#[alloc_error_handler]
+fn out_of_memory(layout: Layout) -> ! {
+    panic!("out of memory: allocation for {:?} failed", layout);
+}
--- a/src/bin/test-exception-double-fault-stack-overflow.rs
+++ b/src/bin/test-exception-double-fault-stack-overflow.rs
@@ -0,0 +1,88 @@
+#![feature(abi_x86_interrupt)]
+#![no_std]
+#![cfg_attr(not(test), no_main)]
+#![cfg_attr(test, allow(dead_code, unused_macros, unused_imports))]
+#![feature(alloc_error_handler)]
+
+use blog_os::memory::allocator::DummyAllocator;
+use blog_os::{exit_qemu, serial_println};
+use core::alloc::Layout;
+use core::panic::PanicInfo;
+use lazy_static::lazy_static;
+
+#[cfg(not(test))]
+#[no_mangle]
+#[allow(unconditional_recursion)]
+pub extern "C" fn _start() -> ! {
+    blog_os::gdt::init();
+    init_test_idt();
+
+    fn stack_overflow() {
+        stack_overflow(); // for each recursion, the return address is pushed
+    }
+
+    // trigger a stack overflow
+    stack_overflow();
+
+    serial_println!("failed");
+    serial_println!("No exception occured");
+
+    unsafe {
+        exit_qemu();
+    }
+
+    loop {}
+}
+
+/// This function is called on panic.
+#[cfg(not(test))]
+#[panic_handler]
+fn panic(info: &PanicInfo) -> ! {
+    serial_println!("failed");
+    serial_println!("{}", info);
+
+    unsafe {
+        exit_qemu();
+    }
+
+    loop {}
+}
+
+#[global_allocator]
+static ALLOCATOR: DummyAllocator = DummyAllocator;
+
+#[alloc_error_handler]
+fn out_of_memory(layout: Layout) -> ! {
+    panic!("out of memory: allocation for {:?} failed", layout);
+}
+
+use x86_64::structures::idt::{InterruptDescriptorTable, InterruptStackFrame};
+
+lazy_static! {
+    static ref TEST_IDT: InterruptDescriptorTable = {
+        let mut idt = InterruptDescriptorTable::new();
+        unsafe {
+            idt.double_fault
+                .set_handler_fn(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 double_fault_handler(
+    _stack_frame: &mut InterruptStackFrame,
+    _error_code: u64,
+) {
+    serial_println!("ok");
+
+    unsafe {
+        exit_qemu();
+    }
+    loop {}
+}
--- a/src/bin/test-panic.rs
+++ b/src/bin/test-panic.rs
@@ -0,0 +1,34 @@
+#![cfg_attr(not(test), no_std)]
+#![cfg_attr(not(test), no_main)]
+#![cfg_attr(test, allow(unused_imports))]
+#![feature(alloc_error_handler)]
+
+use blog_os::memory::allocator::DummyAllocator;
+use blog_os::{exit_qemu, serial_println};
+use core::alloc::Layout;
+use core::panic::PanicInfo;
+
+#[cfg(not(test))]
+#[no_mangle]
+pub extern "C" fn _start() -> ! {
+    panic!();
+}
+
+#[cfg(not(test))]
+#[panic_handler]
+fn panic(_info: &PanicInfo) -> ! {
+    serial_println!("ok");
+
+    unsafe {
+        exit_qemu();
+    }
+    loop {}
+}
+
+#[global_allocator]
+static ALLOCATOR: DummyAllocator = DummyAllocator;
+
+#[alloc_error_handler]
+fn out_of_memory(layout: Layout) -> ! {
+    panic!("out of memory: allocation for {:?} failed", layout);
+}
--- a/src/gdt.rs
+++ b/src/gdt.rs
@@ -0,0 +1,52 @@
+use lazy_static::lazy_static;
+use x86_64::structures::gdt::{Descriptor, GlobalDescriptorTable, SegmentSelector};
+use x86_64::structures::tss::TaskStateSegment;
+use x86_64::VirtAddr;
+
+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;
+            static mut STACK: [u8; STACK_SIZE] = [0; STACK_SIZE];
+
+            let stack_start = VirtAddr::from_ptr(unsafe { &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::set_cs;
+    use x86_64::instructions::tables::load_tss;
+
+    GDT.0.load();
+    unsafe {
+        set_cs(GDT.1.code_selector);
+        load_tss(GDT.1.tss_selector);
+    }
+}
--- a/src/interrupts.rs
+++ b/src/interrupts.rs
@@ -0,0 +1,116 @@
+// The x86-interrupt calling convention leads to the following LLVM error
+// when compiled for a Windows target: "offset is not a multiple of 16". This
+// happens for example when running `cargo test` on Windows. To avoid this
+// problem we skip compilation of this module on Windows.
+#![cfg(not(windows))]
+
+use crate::{gdt, hlt_loop, print, println};
+use lazy_static::lazy_static;
+use pic8259_simple::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: &mut InterruptStackFrame) {
+    println!("EXCEPTION: BREAKPOINT\n{:#?}", stack_frame);
+}
+
+extern "x86-interrupt" fn page_fault_handler(
+    stack_frame: &mut InterruptStackFrame,
+    _error_code: PageFaultErrorCode,
+) {
+    use crate::hlt_loop;
+    use x86_64::registers::control::Cr2;
+
+    println!("EXCEPTION: PAGE FAULT");
+    println!("Accessed Address: {:?}", Cr2::read());
+    println!("{:#?}", stack_frame);
+    hlt_loop();
+}
+
+extern "x86-interrupt" fn double_fault_handler(
+    stack_frame: &mut InterruptStackFrame,
+    _error_code: u64,
+) {
+    println!("EXCEPTION: DOUBLE FAULT\n{:#?}", stack_frame);
+    hlt_loop();
+}
+
+extern "x86-interrupt" fn timer_interrupt_handler(_stack_frame: &mut InterruptStackFrame) {
+    print!(".");
+    unsafe {
+        PICS.lock()
+            .notify_end_of_interrupt(InterruptIndex::Timer.as_u8());
+    }
+}
+
+extern "x86-interrupt" fn keyboard_interrupt_handler(_stack_frame: &mut InterruptStackFrame) {
+    use pc_keyboard::{layouts, DecodedKey, Keyboard, ScancodeSet1};
+    use spin::Mutex;
+    use x86_64::instructions::port::Port;
+
+    lazy_static! {
+        static ref KEYBOARD: Mutex<Keyboard<layouts::Us104Key, ScancodeSet1>> =
+            Mutex::new(Keyboard::new(layouts::Us104Key, ScancodeSet1));
+    }
+
+    let mut keyboard = KEYBOARD.lock();
+    let 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());
+    }
+}
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -0,0 +1,25 @@
+#![cfg_attr(not(test), no_std)]
+#![feature(abi_x86_interrupt)]
+#![feature(alloc)]
+#![feature(const_fn)]
+
+extern crate alloc;
+
+pub mod gdt;
+pub mod interrupts;
+pub mod memory;
+pub mod serial;
+pub mod vga_buffer;
+
+pub unsafe fn exit_qemu() {
+    use x86_64::instructions::port::Port;
+
+    let mut port = Port::<u32>::new(0xf4);
+    port.write(0);
+}
+
+pub fn hlt_loop() -> ! {
+    loop {
+        x86_64::instructions::hlt();
+    }
+}
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,26 +1,74 @@
-#![no_std]
-#![no_main]
+#![cfg_attr(not(test), no_std)]
+#![cfg_attr(not(test), no_main)]
+#![cfg_attr(test, allow(unused_imports))]
+#![feature(alloc)]
+#![feature(alloc_error_handler)]

+extern crate alloc;
+
+use alloc::vec::Vec;
+use blog_os::{
+    memory::allocator::{BumpAllocator, LinkedListAllocator, LockedAllocator, BucketAllocator},
+    println,
+};
+use bootloader::{entry_point, BootInfo};
+use core::alloc::Layout;
 use core::panic::PanicInfo;

-static HELLO: &[u8] = b"Hello World!";
+entry_point!(kernel_main);

-#[no_mangle]
-pub extern "C" fn _start() -> ! {
-    let vga_buffer = 0xb8000 as *mut u8;
+#[cfg(not(test))]
+fn kernel_main(boot_info: &'static BootInfo) -> ! {
+    use blog_os::interrupts::PICS;
+    use blog_os::memory;
+    use x86_64::{structures::paging::Page, VirtAddr};

-    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;
-        }
+    println!("Hello World{}", "!");
+
+    blog_os::gdt::init();
+    blog_os::interrupts::init_idt();
+    unsafe { PICS.lock().initialize() };
+    x86_64::instructions::interrupts::enable();
+
+    let mut mapper = unsafe { memory::init(boot_info.physical_memory_offset) };
+    let mut frame_allocator = memory::init_frame_allocator(&boot_info.memory_map);
+
+    let heap_start = VirtAddr::new(HEAP_START);
+    let heap_end = VirtAddr::new(HEAP_END);
+    memory::map_heap(heap_start, heap_end, &mut mapper, &mut frame_allocator)
+        .expect("map_heap failed");
+
+    ALLOCATOR.lock().underlying().add_memory(heap_start, HEAP_END - HEAP_START);
+
+    //let mut x = Vec::with_capacity(1000);
+    let mut x = Vec::new();
+    for i in 0..1000 {
+        x.push(i);
    }
+    println!("{:?}", *ALLOCATOR.lock());
+    println!("with vec of size {}: {}", x.len(), x.iter().sum::<i32>());
+    println!("with formular: {}", 999 * 1000 / 2);

-    loop {}
+    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();
+}
+
+const HEAP_START: u64 = 0o_001_000_000_0000;
+const HEAP_END: u64 = HEAP_START + 10 * 0x1000;
+
+#[global_allocator]
+static ALLOCATOR: LockedAllocator<BucketAllocator<LinkedListAllocator>> =
+    LockedAllocator::new(BucketAllocator::new(LinkedListAllocator::empty()));
+
+#[alloc_error_handler]
+fn out_of_memory(layout: Layout) -> ! {
+    panic!("out of memory: allocation for {:?} failed", layout);
 }
--- a/src/memory.rs
+++ b/src/memory.rs
@@ -0,0 +1,120 @@
+use bootloader::bootinfo::{MemoryMap, MemoryRegionType};
+use x86_64::{
+    structures::paging::{
+        mapper, FrameAllocator, MappedPageTable, Mapper, MapperAllSizes, Page, PageTable,
+        PhysFrame, Size4KiB,
+    },
+    PhysAddr, VirtAddr,
+};
+
+pub mod allocator;
+
+/// Initialize a new MappedPageTable.
+///
+/// This function is unsafe because the caller must guarantee that the
+/// complete physical memory is mapped to virtual memory at the passed
+/// `physical_memory_offset`. Also, this function must be only called once
+/// to avoid aliasing `&mut` references (which is undefined behavior).
+pub unsafe fn init(physical_memory_offset: u64) -> impl MapperAllSizes {
+    let level_4_table = active_level_4_table(physical_memory_offset);
+    let phys_to_virt = move |frame: PhysFrame| -> *mut PageTable {
+        let phys = frame.start_address().as_u64();
+        let virt = VirtAddr::new(phys + physical_memory_offset);
+        virt.as_mut_ptr()
+    };
+    MappedPageTable::new(level_4_table, phys_to_virt)
+}
+
+/// Create a FrameAllocator from the passed memory map
+pub fn init_frame_allocator(
+    memory_map: &'static MemoryMap,
+) -> BootInfoFrameAllocator<impl Iterator<Item = PhysFrame>> {
+    // get usable regions from memory map
+    let regions = memory_map
+        .iter()
+        .filter(|r| r.region_type == MemoryRegionType::Usable);
+    // map each region to its address range
+    let addr_ranges = regions.map(|r| r.range.start_addr()..r.range.end_addr());
+    // transform to an iterator of frame start addresses
+    let frame_addresses = addr_ranges.flat_map(|r| r.into_iter().step_by(4096));
+    // create `PhysFrame` types from the start addresses
+    let frames = frame_addresses.map(|addr| PhysFrame::containing_address(PhysAddr::new(addr)));
+
+    BootInfoFrameAllocator { frames }
+}
+
+/// Returns a mutable reference to the active level 4 table.
+///
+/// This function is unsafe because the caller must guarantee that the
+/// complete physical memory is mapped to virtual memory at the passed
+/// `physical_memory_offset`. Also, this function must be only called once
+/// to avoid aliasing `&mut` references (which is undefined behavior).
+unsafe fn active_level_4_table(physical_memory_offset: u64) -> &'static mut PageTable {
+    use x86_64::{registers::control::Cr3, VirtAddr};
+
+    let (level_4_table_frame, _) = Cr3::read();
+
+    let phys = level_4_table_frame.start_address();
+    let virt = VirtAddr::new(phys.as_u64() + physical_memory_offset);
+    let page_table_ptr: *mut PageTable = virt.as_mut_ptr();
+
+    &mut *page_table_ptr // unsafe
+}
+
+pub fn map_heap(
+    heap_start: VirtAddr,
+    heap_end: VirtAddr,
+    mapper: &mut impl Mapper<Size4KiB>,
+    frame_allocator: &mut impl FrameAllocator<Size4KiB>,
+) -> Result<(), MapHeapError> {
+    use x86_64::structures::paging::PageTableFlags as Flags;
+
+    let flags = Flags::PRESENT | Flags::WRITABLE;
+    let start_page = Page::containing_address(heap_start);
+    let end_page = Page::containing_address(heap_end - 1u64);
+
+    for page in Page::range_inclusive(start_page, end_page) {
+        let frame = frame_allocator.allocate_frame();
+        let frame = frame.ok_or(MapHeapError::FrameAllocationFailed)?;
+        unsafe { mapper.map_to(page, frame, flags, frame_allocator)?.flush() };
+    }
+
+    Ok(())
+}
+
+#[derive(Debug)]
+pub enum MapHeapError {
+    FrameAllocationFailed,
+    MapToError(mapper::MapToError),
+}
+
+impl From<mapper::MapToError> for MapHeapError {
+    fn from(err: mapper::MapToError) -> Self {
+        MapHeapError::MapToError(err)
+    }
+}
+
+/// A FrameAllocator that always returns `None`.
+pub struct EmptyFrameAllocator;
+
+impl FrameAllocator<Size4KiB> for EmptyFrameAllocator {
+    fn allocate_frame(&mut self) -> Option<PhysFrame> {
+        None
+    }
+}
+
+pub struct BootInfoFrameAllocator<I>
+where
+    I: Iterator<Item = PhysFrame>,
+{
+    frames: I,
+}
+
+impl<I> FrameAllocator<Size4KiB> for BootInfoFrameAllocator<I>
+where
+    I: Iterator<Item = PhysFrame>,
+{
+    fn allocate_frame(&mut self) -> Option<PhysFrame> {
+        self.frames.next()
+    }
+}
--- a/src/memory/allocator.rs
+++ b/src/memory/allocator.rs
@@ -0,0 +1,49 @@
+pub use bump::BumpAllocator;
+pub use dummy::DummyAllocator;
+pub use linked_list::LinkedListAllocator;
+pub use bucket::BucketAllocator;
+
+use core::alloc::{GlobalAlloc, Layout};
+use spin::{Mutex, MutexGuard};
+
+mod bump;
+mod dummy;
+mod linked_list;
+mod bucket;
+
+pub struct LockedAllocator<T> {
+    allocator: Mutex<T>,
+}
+
+impl<T> LockedAllocator<T> {
+    pub const fn new(allocator: T) -> Self {
+        Self {
+            allocator: Mutex::new(allocator),
+        }
+    }
+}
+
+impl<T> LockedAllocator<T> {
+    pub fn lock(&self) -> MutexGuard<T> {
+        self.allocator.lock()
+    }
+}
+
+unsafe impl<T> GlobalAlloc for LockedAllocator<T>
+where
+    T: MutGlobalAlloc,
+{
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        self.allocator.lock().alloc(layout)
+    }
+
+    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
+        self.allocator.lock().dealloc(ptr, layout)
+    }
+}
+
+pub trait MutGlobalAlloc {
+    fn alloc(&mut self, layout: Layout) -> *mut u8;
+
+    fn dealloc(&mut self, ptr: *mut u8, layout: Layout);
+}
--- a/src/memory/allocator/bucket.rs
+++ b/src/memory/allocator/bucket.rs
@@ -0,0 +1,126 @@
+use super::MutGlobalAlloc;
+use core::alloc::Layout;
+use core::mem::size_of;
+use core::fmt::{self, Debug};
+use core::cmp;
+
+#[derive(Debug)]
+pub struct BucketAllocator<A> where A: MutGlobalAlloc + Debug {
+    underlying: A,
+    buckets: [Bucket; 10],
+}
+
+impl<A> BucketAllocator<A> where A: MutGlobalAlloc + Debug {
+    pub const fn new(underlying: A) -> Self {
+        Self {
+            underlying,
+            buckets: [
+                Bucket::new(size_of::<Region>()),
+                Bucket::new(16),
+                Bucket::new(32),
+                Bucket::new(64),
+                Bucket::new(128),
+                Bucket::new(256),
+                Bucket::new(512),
+                Bucket::new(1024),
+                Bucket::new(2048),
+                Bucket::new(4096),
+            ]
+        }
+    }
+
+    pub fn underlying(&mut self) -> &mut A {
+        &mut self.underlying
+    }
+}
+
+pub struct Bucket {
+    size: usize,
+    head: Option<&'static mut Region>,
+}
+
+impl Bucket {
+    const fn new(size: usize) -> Self {
+        Bucket {
+            size,
+            head: None,
+        }
+    }
+
+    fn layout(&self) -> Layout {
+        Layout::from_size_align(self.size, self.size).unwrap()
+    }
+}
+
+impl fmt::Debug for Bucket {
+    fn fmt(&self, f: &mut fmt::Formatter)-> fmt::Result {
+        let mut regions = 0;
+        let mut current = &self.head;
+        while let Some(region) = current {
+            current = &region.next;
+            regions += 1;
+        }
+        f.debug_struct("Bucket").field("size", &self.size).field("regions", &regions).finish()
+    }
+}
+
+#[derive(Debug)]
+struct Region {
+    next: Option<&'static mut Region>,
+}
+
+impl Region {
+    fn new() -> Self {
+        Self {
+            next: None,
+        }
+    }
+
+    fn as_mut_u8(&'static mut self) -> *mut u8 {
+        self as *mut Region as *mut u8
+    }
+
+    unsafe fn from_mut_u8(ptr: *mut u8) -> &'static mut Self {
+        (ptr as *mut Region).write(Region::new());
+        &mut *(ptr as *mut Region)
+    }
+}
+
+impl<A> BucketAllocator<A> where A: MutGlobalAlloc + Debug {
+    fn get_bucket_index(&self, layout: &Layout) -> Option<usize> {
+        let required_bucket_size = cmp::max(layout.size(), layout.align());
+        match self.buckets.binary_search_by(|bucket| bucket.size.cmp(&required_bucket_size)) {
+            Ok(index) => Some(index),
+            Err(index) if index < self.buckets.len() => Some(index),
+            Err(_) => None,
+        }
+    }
+}
+
+impl<A> MutGlobalAlloc for BucketAllocator<A> where A: MutGlobalAlloc + Debug {
+    fn alloc(&mut self, layout: Layout) -> *mut u8 {
+        if let Some(bucket_index) = self.get_bucket_index(&layout) {
+            let bucket = &mut self.buckets[bucket_index];
+            if let Some(head) = bucket.head.take() {
+                let next = head.next.take();
+                bucket.head = next;
+                return head.as_mut_u8();
+            } else {
+                self.underlying.alloc(bucket.layout())
+            }
+        } else {
+            self.underlying.alloc(layout)
+        }
+    }
+
+    fn dealloc(&mut self, ptr: *mut u8, layout: Layout) {
+        if let Some(bucket_index) = self.get_bucket_index(&layout) {
+            let bucket = &mut self.buckets[bucket_index];
+            let region = unsafe {Region::from_mut_u8(ptr)};
+            region.next = bucket.head.take();
+            bucket.head = Some(region);
+        } else {
+            self.underlying.dealloc(ptr, layout);
+        }
+    }
+}
--- a/src/memory/allocator/bump.rs
+++ b/src/memory/allocator/bump.rs
@@ -0,0 +1,38 @@
+use super::MutGlobalAlloc;
+use core::alloc::Layout;
+use x86_64::align_up;
+
+pub struct BumpAllocator {
+    heap_start: u64,
+    heap_end: u64,
+    next: u64,
+}
+
+impl BumpAllocator {
+    pub const fn new(heap_start: u64, heap_end: u64) -> Self {
+        Self {
+            heap_start,
+            heap_end,
+            next: heap_start,
+        }
+    }
+}
+
+impl MutGlobalAlloc for BumpAllocator {
+    fn alloc(&mut self, layout: Layout) -> *mut u8 {
+        let alloc_start = align_up(self.next, layout.align() as u64);
+        let alloc_end = alloc_start.saturating_add(layout.size() as u64);
+
+        if alloc_end >= self.heap_end {
+            // out of memory
+            return 0 as *mut u8;
+        }
+
+        self.next = alloc_end;
+        alloc_start as *mut u8
+    }
+
+    fn dealloc(&mut self, _ptr: *mut u8, _layout: Layout) {
+        panic!("BumpAllocator::dealloc called");
+    }
+}
--- a/src/memory/allocator/dummy.rs
+++ b/src/memory/allocator/dummy.rs
@@ -0,0 +1,16 @@
+use core::alloc::{GlobalAlloc, Layout};
+
+/// A dummy allocator that panics on every `alloc` or `dealloc` call.
+pub struct DummyAllocator;
+
+unsafe impl GlobalAlloc for DummyAllocator {
+    /// Always panics.
+    unsafe fn alloc(&self, _layout: Layout) -> *mut u8 {
+        panic!("DummyAllocator::alloc called");
+    }
+
+    /// Always panics.
+    unsafe fn dealloc(&self, _ptr: *mut u8, _layout: Layout) {
+        panic!("DummyAllocator::dealloc called");
+    }
+}
--- a/src/memory/allocator/linked_list.rs
+++ b/src/memory/allocator/linked_list.rs
@@ -0,0 +1,95 @@
+use super::MutGlobalAlloc;
+use core::alloc::Layout;
+use core::mem;
+use x86_64::{align_up, VirtAddr};
+
+#[derive(Debug)]
+pub struct LinkedListAllocator {
+    head: Region,
+}
+
+impl LinkedListAllocator {
+    pub const fn empty() -> Self {
+        let head = Region {
+            size: 0,
+            next: None,
+        };
+        Self { head }
+    }
+
+    pub unsafe fn new(heap_start: VirtAddr, heap_size: u64) -> Self {
+        let mut allocator = Self::empty();
+        allocator.add_memory(heap_start, heap_size);
+        allocator
+    }
+
+    pub fn add_memory(&mut self, start: VirtAddr, size: u64) {
+        let aligned = start.align_up(mem::size_of::<Region>() as u64);
+        let mut region = Region {
+            size: size - (aligned - start),
+            next: None
+        };
+        mem::swap(&mut self.head.next, &mut region.next);
+
+        let region_ptr: *mut Region = aligned.as_mut_ptr();
+        unsafe { region_ptr.write(region) };
+        self.head.next = Some(unsafe { &mut *region_ptr });
+    }
+}
+
+impl MutGlobalAlloc for LinkedListAllocator {
+    fn alloc(&mut self, layout: Layout) -> *mut u8 {
+        let size = align_up(layout.size() as u64, mem::size_of::<Region>() as u64);
+
+        let mut current = &mut self.head;
+        loop {
+            let next = match current.next {
+                Some(ref mut next) => next,
+                None => break,
+            };
+            let next_start = VirtAddr::new(*next as *mut Region as u64);
+            let next_end = next_start + next.size;
+
+            let alloc_start = next_start.align_up(layout.align() as u64);
+            let alloc_end = alloc_start + size;
+
+            // check if Region large enough
+            if alloc_end <= next_end {
+                // remove Region from list
+                let next_next = next.next.take();
+                current.next = next_next;
+                // insert remaining Region to list
+                self.add_memory(alloc_end, next_end - alloc_end);
+                // return allocated memory
+                return alloc_start.as_mut_ptr();
+            }
+
+            // continue with next element
+            //
+            // This is basically `current = next`, but we need a new `match` expression because
+            // the compiler can't figure the lifetimes out when we use the `next` binding
+            // from above.
+            current = match current.next {
+                Some(ref mut next) => next,
+                None => unreachable!(),
+            };
+        }
+
+        // no large enough Region found
+        0 as *mut u8
+    }
+
+    fn dealloc(&mut self, ptr: *mut u8, layout: Layout) {
+        let size = align_up(layout.size() as u64, mem::size_of::<Region>() as u64);
+        self.add_memory(VirtAddr::new(ptr as u64), size);
+    }
+}
+
+#[derive(Debug)]
+struct Region {
+    size: u64,
+    next: Option<&'static mut Region>,
+}
+
+
+// TODO recycle alignment
--- a/src/serial.rs
+++ b/src/serial.rs
@@ -0,0 +1,40 @@
+use lazy_static::lazy_static;
+use spin::Mutex;
+use uart_16550::SerialPort;
+
+lazy_static! {
+    pub static ref SERIAL1: Mutex<SerialPort> = {
+        let mut serial_port = 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)*));
+}
--- a/src/vga_buffer.rs
+++ b/src/vga_buffer.rs
@@ -0,0 +1,259 @@
+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();
+    });
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    fn construct_writer() -> Writer {
+        use std::boxed::Box;
+
+        let buffer = construct_buffer();
+        Writer {
+            column_position: 0,
+            color_code: ColorCode::new(Color::Blue, Color::Magenta),
+            buffer: Box::leak(Box::new(buffer)),
+        }
+    }
+
+    fn construct_buffer() -> Buffer {
+        use array_init::array_init;
+
+        Buffer {
+            chars: array_init(|_| array_init(|_| Volatile::new(empty_char()))),
+        }
+    }
+
+    fn empty_char() -> ScreenChar {
+        ScreenChar {
+            ascii_character: b' ',
+            color_code: ColorCode::new(Color::Green, Color::Brown),
+        }
+    }
+
+    #[test]
+    fn write_byte() {
+        let mut writer = construct_writer();
+        writer.write_byte(b'X');
+        writer.write_byte(b'Y');
+
+        for (i, row) in writer.buffer.chars.iter().enumerate() {
+            for (j, screen_char) in row.iter().enumerate() {
+                let screen_char = screen_char.read();
+                if i == BUFFER_HEIGHT - 1 && j == 0 {
+                    assert_eq!(screen_char.ascii_character, b'X');
+                    assert_eq!(screen_char.color_code, writer.color_code);
+                } else if i == BUFFER_HEIGHT - 1 && j == 1 {
+                    assert_eq!(screen_char.ascii_character, b'Y');
+                    assert_eq!(screen_char.color_code, writer.color_code);
+                } else {
+                    assert_eq!(screen_char, empty_char());
+                }
+            }
+        }
+    }
+
+    #[test]
+    fn write_formatted() {
+        use core::fmt::Write;
+
+        let mut writer = construct_writer();
+        writeln!(&mut writer, "a").unwrap();
+        writeln!(&mut writer, "b{}", "c").unwrap();
+
+        for (i, row) in writer.buffer.chars.iter().enumerate() {
+            for (j, screen_char) in row.iter().enumerate() {
+                let screen_char = screen_char.read();
+                if i == BUFFER_HEIGHT - 3 && j == 0 {
+                    assert_eq!(screen_char.ascii_character, b'a');
+                    assert_eq!(screen_char.color_code, writer.color_code);
+                } else if i == BUFFER_HEIGHT - 2 && j == 0 {
+                    assert_eq!(screen_char.ascii_character, b'b');
+                    assert_eq!(screen_char.color_code, writer.color_code);
+                } else if i == BUFFER_HEIGHT - 2 && j == 1 {
+                    assert_eq!(screen_char.ascii_character, b'c');
+                    assert_eq!(screen_char.color_code, writer.color_code);
+                } else if i >= BUFFER_HEIGHT - 2 {
+                    assert_eq!(screen_char.ascii_character, b' ');
+                    assert_eq!(screen_char.color_code, writer.color_code);
+                } else {
+                    assert_eq!(screen_char, empty_char());
+                }
+            }
+        }
+    }
+}