Merge branch 'post-05' into post-06

Merge branch 'post-04' into post-05
Merge pull request #1434 from phil-opp/post-04-test-true
2025-12-16 14:27:49 +00:00 · 2025-08-26 16:41:45 +02:00 · 2025-08-26 16:41:45 +02:00 · 2025-08-26 16:41:21 +02:00 · 2025-08-26 16:21:28 +02:00 · 2025-08-18 09:44:29 +02:00
26 changed files with 279 additions and 1479 deletions
--- a/.cargo/config.toml
+++ b/.cargo/config.toml
@@ -1,3 +1,7 @@
+[unstable]
+build-std = ["core", "compiler_builtins"]
+build-std-features = ["compiler-builtins-mem"]
+
 [build]
 target = "x86_64-blog_os.json"

--- a/.github/workflows/build-code.yml
+++ b/.github/workflows/build-code.yml
@@ -1,96 +0,0 @@
-name: Build Code
-
-on:
-  push:
-    branches:
-      - '*'
-      - '!staging.tmp'
-    tags:
-      - '*'
-  schedule:
-    - cron: '40 3 * * *'   # every day at 3:40
-  pull_request:
-
-jobs:
-  test:
-    name: "Test"
-
-    strategy:
-      matrix:
-        platform: [
-          ubuntu-latest,
-          macos-latest,
-          windows-latest
-        ]
-
-    runs-on: ${{ matrix.platform }}
-    timeout-minutes: 15
-
-    steps:
-    - name: "Checkout Repository"
-      uses: actions/checkout@v1
-
-    - name: Install Rustup
-      run: |
-        curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --default-toolchain nightly
-        echo ::add-path::$HOME/.cargo/bin
-      if: runner.os == 'macOS'
-
-    - name: "Print Rust Version"
-      run: |
-        rustc -Vv
-        cargo -Vv
-
-    - name: "Install Rustup Components"
-      run: rustup component add rust-src llvm-tools-preview
-    - name: "Install cargo-xbuild"
-      run: cargo install cargo-xbuild --debug
-    - name: "Install bootimage"
-      run: cargo install bootimage --debug
-
-    - name: "Run cargo xbuild"
-      run: cargo xbuild
-    - name: "Create Bootimage"
-      run: cargo 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 Scoop (Windows)
-      run: |
-        Invoke-Expression (New-Object System.Net.WebClient).DownloadString('https://get.scoop.sh')
-        echo ::add-path::$HOME\scoop\shims
-      if: runner.os == 'Windows'
-      shell: pwsh
-    - name: Install QEMU (Windows)
-      run: scoop install qemu
-      if: runner.os == 'Windows'
-      shell: pwsh
-    - name: "Print QEMU Version"
-      run: qemu-system-x86_64 --version
-
-    - name: "Run cargo xtest"
-      run: cargo xtest
-
-  check_formatting:
-    name: "Check Formatting"
-    runs-on: ubuntu-latest
-    timeout-minutes: 2
-    steps:
-    - uses: actions/checkout@v1
-    - name: "Use the latest Rust nightly with rustfmt"
-      uses: actions-rs/toolchain@v1
-      with:
-          toolchain: nightly
-          profile: minimal
-          components: rustfmt
-          override: true
-    - run: cargo fmt -- --check
--- a/.github/workflows/code.yml
+++ b/.github/workflows/code.yml
@@ -0,0 +1,130 @@
+name: Code
+
+on:
+  push:
+    branches:
+      - '*'
+      - '!staging.tmp'
+    tags:
+      - '*'
+  schedule:
+    - cron: '40 3 * * *'   # every day at 3:40
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  check:
+    name: Check
+    strategy:
+      fail-fast: false
+      matrix:
+        platform: [
+          ubuntu-latest,
+          macos-latest,
+          windows-latest
+        ]
+    runs-on: ${{ matrix.platform }}
+    steps:
+      - name: Checkout Repository
+        uses: actions/checkout@v2
+      - name: Install Rust Toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: nightly
+      - name: Install `rust-src` Rustup Component
+        run: rustup component add rust-src
+      - name: Run `cargo check`
+        uses: actions-rs/cargo@v1
+        with:
+          command: check
+
+  test:
+    name: Test
+    strategy:
+      fail-fast: false
+      matrix:
+        platform: [
+          ubuntu-latest,
+          macos-latest,
+          windows-latest
+        ]
+    runs-on: ${{ matrix.platform }}
+    steps:
+      - name: Install Rust Toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: nightly
+      - name: Install bootimage
+        run: cargo install bootimage --debug
+      - name: Checkout Repository
+        uses: actions/checkout@v2
+      - name: Install Rustup Components
+        run: rustup component add rust-src llvm-tools-preview
+      - name: Run `cargo bootimage`
+        uses: actions-rs/cargo@v1
+        with:
+          command: bootimage
+
+      # install QEMU
+      - name: Install QEMU (Linux)
+        run: sudo apt update && sudo apt install qemu-system-x86
+        if: runner.os == 'Linux'
+      - name: Install QEMU (macOS)
+        run: brew install qemu
+        if: runner.os == 'macOS'
+        env:
+          HOMEBREW_NO_AUTO_UPDATE: 1
+          HOMEBREW_NO_BOTTLE_SOURCE_FALLBACK: 1
+          HOMEBREW_NO_INSTALL_CLEANUP: 1
+      - name: Install QEMU (Windows)
+        run: |
+          choco install qemu --version 2021.5.5
+          echo "$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
+    steps:
+      - name: Checkout Repository
+        uses: actions/checkout@v2
+      - name: Install Rust Toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: nightly
+          components: rustfmt
+          override: true
+      - name: Run `cargo fmt`
+        uses: actions-rs/cargo@v1
+        with:
+          command: fmt
+          args: --all -- --check
+
+  clippy:
+    name: Clippy
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Repository
+        uses: actions/checkout@v2
+      - name: Install Rust Toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: nightly
+          components: clippy, rust-src
+          override: true
+      - name: Run `cargo clippy`
+        uses: actions-rs/cargo@v1
+        with:
+          command: clippy
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1,25 +1,24 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
-[[package]]
-name = "array-init"
-version = "0.0.4"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "23589ecb866b460d3a0f1278834750268c607e8e28a1b982c907219f3178cd72"
-dependencies = [
- "nodrop",
-]
+version = 4

 [[package]]
 name = "bit_field"
-version = "0.9.0"
+version = "0.10.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ed8765909f9009617974ab6b7d332625b320b33c326b1e9321382ef1999b5d56"
+checksum = "dc827186963e592360843fb5ba4b973e145841266c1357f7180c43526f2e5b61"

 [[package]]
 name = "bitflags"
-version = "1.2.1"
+version = "1.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "cf1de2fe8c75bc145a2f577add951f8134889b4795d47466a54a5c846d691693"
+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"
@@ -27,98 +26,32 @@ version = "0.1.0"
 dependencies = [
 "bootloader",
 "lazy_static",
- "linked_list_allocator",
- "pc-keyboard",
- "pic8259_simple",
- "spin",
+ "spin 0.5.2",
 "uart_16550",
- "volatile",
- "x86_64 0.8.1",
+ "volatile 0.2.7",
+ "x86_64",
 ]

 [[package]]
 name = "bootloader"
-version = "0.8.3"
+version = "0.9.32"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d596849a47f28abdea62d7a6a25c4f6e69c3d9b09b0a2877db6e9cda004ca993"
-
-[[package]]
-name = "cast"
-version = "0.2.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4b9434b9a5aa1450faa3f9cb14ea0e8c53bb5d2b3c1bfd1ab4fc03e9f33fbfb0"
-dependencies = [
- "rustc_version",
-]
-
-[[package]]
-name = "cpuio"
-version = "0.2.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "22b8e308ccfc5acf3b82f79c0eac444cf6114cb2ac67a230ca6c177210068daa"
+checksum = "1ea119c3ed05625c179e09d17d0914570a3753ca09c890a73d98f6b72aea00d2"

 [[package]]
 name = "lazy_static"
-version = "1.4.0"
+version = "1.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
+checksum = "bbd2bcb4c963f2ddae06a2efc7e9f3591312473c50c6685e1f298068316e66fe"
 dependencies = [
- "spin",
+ "spin 0.9.8",
 ]

 [[package]]
-name = "linked_list_allocator"
-version = "0.6.4"
+name = "rustversion"
+version = "1.0.22"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "47314ec1d29aa869ee7cb5a5be57be9b1055c56567d59c3fb6689926743e0bea"
-dependencies = [
- "spin",
-]
-
-[[package]]
-name = "nodrop"
-version = "0.1.14"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "72ef4a56884ca558e5ddb05a1d1e7e1bfd9a68d9ed024c21704cc98872dae1bb"
-
-[[package]]
-name = "pc-keyboard"
-version = "0.3.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "fff50ab09ba31bcebc0669f4e64c0952fae1acdca9e6e0587e68e4e8443808ac"
-
-[[package]]
-name = "pic8259_simple"
-version = "0.1.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "dc64b2fd10828da8521b6cdabe0679385d7d2a3a6d4c336b819d1fa31ba35c72"
-dependencies = [
- "cpuio",
-]
-
-[[package]]
-name = "rustc_version"
-version = "0.2.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "138e3e0acb6c9fb258b19b67cb8abd63c00679d2851805ea151465464fe9030a"
-dependencies = [
- "semver",
-]
-
-[[package]]
-name = "semver"
-version = "0.9.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1d7eb9ef2c18661902cc47e535f9bc51b78acd254da71d375c2f6720d9a40403"
-dependencies = [
- "semver-parser",
-]
-
-[[package]]
-name = "semver-parser"
-version = "0.7.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "388a1df253eca08550bef6c72392cfe7c30914bf41df5269b68cbd6ff8f570a3"
+checksum = "b39cdef0fa800fc44525c84ccb54a029961a8215f9619753635a9c0d2538d46d"

 [[package]]
 name = "spin"
@@ -127,48 +60,42 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6e63cff320ae2c57904679ba7cb63280a3dc4613885beafb148ee7bf9aa9042d"

 [[package]]
-name = "uart_16550"
-version = "0.2.1"
+name = "spin"
+version = "0.9.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "803ea8cb602dbb32c1a657a866d2dd79fe7dbeab0fb2ac667cb4dcc7de12a58b"
-dependencies = [
- "bitflags",
- "x86_64 0.7.7",
-]
+checksum = "6980e8d7511241f8acf4aebddbb1ff938df5eebe98691418c4468d0b72a96a67"

 [[package]]
-name = "ux"
-version = "0.1.3"
+name = "uart_16550"
+version = "0.2.19"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "88dfeb711b61ce620c0cb6fd9f8e3e678622f0c971da2a63c4b3e25e88ed012f"
+checksum = "614ff2a87880d4bd4374722268598a970bbad05ced8bf630439417347254ab2e"
+dependencies = [
+ "bitflags 1.3.2",
+ "rustversion",
+ "x86_64",
+]

 [[package]]
 name = "volatile"
-version = "0.2.6"
+version = "0.2.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6af0edf5b4faacc31fc51159244d78d65ec580f021afcef7bd53c04aeabc7f29"
+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 = "0.7.7"
+version = "0.14.13"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1f27d9168654aee1b0c1b73746caeb4aa33248f8b8c8f6e100e697fcc2a794b2"
+checksum = "c101112411baafbb4bf8d33e4c4a80ab5b02d74d2612331c61e8192fc9710491"
 dependencies = [
- "array-init",
 "bit_field",
- "bitflags",
- "cast",
- "ux",
-]
-
-[[package]]
-name = "x86_64"
-version = "0.8.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f21672dcbed52bc09eea030d189600c0189c66c97bc5b31779eb780e064a201f"
-dependencies = [
- "array-init",
- "bit_field",
- "bitflags",
- "cast",
+ "bitflags 2.9.2",
+ "rustversion",
+ "volatile 0.4.6",
 ]
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -2,7 +2,7 @@
 name = "blog_os"
 version = "0.1.0"
 authors = ["Philipp Oppermann <dev@phil-opp.com>"]
-edition = "2018"
+edition = "2024"

 [[test]]
 name = "should_panic"
@@ -13,26 +13,29 @@ name = "stack_overflow"
 harness = false

 [dependencies]
-bootloader = { version = "0.8.0", features = ["map_physical_memory"]}
+bootloader = "0.9"
 volatile = "0.2.6"
 spin = "0.5.2"
-x86_64 = "0.8.1"
+x86_64 = "0.14.2"
 uart_16550 = "0.2.0"
-pic8259_simple = "0.1.1"
-pc-keyboard = "0.3.1"
-linked_list_allocator = "0.6.4"

 [dependencies.lazy_static]
 version = "1.0"
 features = ["spin_no_std"]

+[[bin]]
+name = "blog_os"
+test = true
+bench = false
+

 [package.metadata.bootimage]
 test-args = [
-    "-device", "isa-debug-exit,iobase=0xf4,iosize=0x04", "-serial", "stdio",
-    "-display", "none"
+    "-device",
+    "isa-debug-exit,iobase=0xf4,iosize=0x04",
+    "-serial",
+    "stdio",
+    "-display",
+    "none",
 ]
-test-success-exit-code = 33         # (0x10 << 1) | 1
-
-[profile.release]
-lto = true
+test-success-exit-code = 33 # (0x10 << 1) | 1
--- a/README.md
+++ b/README.md
@@ -1,28 +1,32 @@
-# Blog OS (Heap Allocation)
+# Blog OS (Double Faults)

-[![Build Status](https://github.com/phil-opp/blog_os/workflows/Build%20Code/badge.svg?branch=post-10)](https://github.com/phil-opp/blog_os/actions?query=workflow%3A%22Build+Code%22+branch%3Apost-10)
+[![Build Status](https://github.com/phil-opp/blog_os/workflows/Code/badge.svg?branch=post-06)](https://github.com/phil-opp/blog_os/actions?query=workflow%3A%22Code%22+branch%3Apost-06)

-This repository contains the source code for the [Heap Allocation][post] post of the [Writing an OS in Rust](https://os.phil-opp.com) series.
+This repository contains the source code for the [Double Faults][post] post of the [Writing an OS in Rust](https://os.phil-opp.com) series.

-[post]: https://os.phil-opp.com/heap-allocation/
+[post]: https://os.phil-opp.com/double-fault-exceptions/

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

 ## Building

-You need a nightly Rust compiler. First you need to install the `cargo-xbuild` and `bootimage` tools:
+This project requires a nightly version of Rust because it uses some unstable features. At least nightly _2020-07-15_ is required for building. You might need to run `rustup update nightly --force` to update to the latest nightly even if some components such as `rustfmt` are missing it.
+
+You can build the project by running:

 ```
-cargo install cargo-xbuild bootimage
+cargo build
 ```

-Then you can build the project by running:
+To create a bootable disk image from the compiled kernel, you need to install the [`bootimage`] tool:
+
+[`bootimage`]: https://github.com/rust-osdev/bootimage

 ```
-cargo xbuild
+cargo install bootimage
 ```

-To create a bootable disk image, run:
+After installing, you can create the bootable disk image by running:

 ```
 cargo bootimage
@@ -39,10 +43,10 @@ You can run the disk image in [QEMU] through:
 [QEMU]: https://www.qemu.org/

 ```
-cargo xrun
+cargo run
 ```

-Of course [QEMU] needs to be installed for this.
+[QEMU] and the [`bootimage`] tool need to be installed for this.

 You can also write the image to an USB stick for booting it on a real machine. On Linux, the command for this is:

--- a/src/allocator/bump.rs
+++ b/src/allocator/bump.rs
@@ -1,58 +0,0 @@
-use super::{align_up, Locked};
-use alloc::alloc::{GlobalAlloc, Layout};
-use core::ptr;
-
-pub struct BumpAllocator {
-    heap_start: usize,
-    heap_end: usize,
-    next: usize,
-    allocations: usize,
-}
-
-impl BumpAllocator {
-    /// Creates a new empty bump allocator.
-    pub const fn new() -> Self {
-        BumpAllocator {
-            heap_start: 0,
-            heap_end: 0,
-            next: 0,
-            allocations: 0,
-        }
-    }
-
-    /// Initializes the bump allocator with the given heap bounds.
-    ///
-    /// This method is unsafe because the caller must ensure that the given
-    /// memory range is unused. Also, this method must be called only once.
-    pub unsafe fn init(&mut self, heap_start: usize, heap_size: usize) {
-        self.heap_start = heap_start;
-        self.heap_end = heap_start + heap_size;
-        self.next = heap_start;
-    }
-}
-
-unsafe impl GlobalAlloc for Locked<BumpAllocator> {
-    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
-        let mut bump = self.lock(); // get a mutable reference
-
-        let alloc_start = align_up(bump.next, layout.align());
-        let alloc_end = alloc_start + layout.size();
-
-        if alloc_end > bump.heap_end {
-            ptr::null_mut() // out of memory
-        } else {
-            bump.next = alloc_end;
-            bump.allocations += 1;
-            alloc_start as *mut u8
-        }
-    }
-
-    unsafe fn dealloc(&self, _ptr: *mut u8, _layout: Layout) {
-        let mut bump = self.lock(); // get a mutable reference
-
-        bump.allocations -= 1;
-        if bump.allocations == 0 {
-            bump.next = bump.heap_start;
-        }
-    }
-}
--- a/src/allocator/fixed_size_block.rs
+++ b/src/allocator/fixed_size_block.rs
@@ -1,102 +0,0 @@
-use super::Locked;
-use alloc::alloc::{GlobalAlloc, Layout};
-use core::{
-    mem,
-    ptr::{self, NonNull},
-};
-
-/// The block sizes to use.
-///
-/// The sizes must each be power of 2 because they are also used as
-/// the block alignment (alignments must be always powers of 2).
-const BLOCK_SIZES: &[usize] = &[8, 16, 32, 64, 128, 256, 512, 1024, 2048];
-
-/// Choose an appropriate block size for the given layout.
-///
-/// Returns an index into the `BLOCK_SIZES` array.
-fn list_index(layout: &Layout) -> Option<usize> {
-    let required_block_size = layout.size().max(layout.align());
-    BLOCK_SIZES.iter().position(|&s| s >= required_block_size)
-}
-
-struct ListNode {
-    next: Option<&'static mut ListNode>,
-}
-
-pub struct FixedSizeBlockAllocator {
-    list_heads: [Option<&'static mut ListNode>; BLOCK_SIZES.len()],
-    fallback_allocator: linked_list_allocator::Heap,
-}
-
-impl FixedSizeBlockAllocator {
-    /// Creates an empty FixedSizeBlockAllocator.
-    pub const fn new() -> Self {
-        FixedSizeBlockAllocator {
-            list_heads: [None; BLOCK_SIZES.len()],
-            fallback_allocator: linked_list_allocator::Heap::empty(),
-        }
-    }
-
-    /// Initialize the allocator with the given heap bounds.
-    ///
-    /// This function is unsafe because the caller must guarantee that the given
-    /// heap bounds are valid and that the heap is unused. This method must be
-    /// called only once.
-    pub unsafe fn init(&mut self, heap_start: usize, heap_size: usize) {
-        self.fallback_allocator.init(heap_start, heap_size);
-    }
-
-    /// Allocates using the fallback allocator.
-    fn fallback_alloc(&mut self, layout: Layout) -> *mut u8 {
-        match self.fallback_allocator.allocate_first_fit(layout) {
-            Ok(ptr) => ptr.as_ptr(),
-            Err(_) => ptr::null_mut(),
-        }
-    }
-}
-
-unsafe impl GlobalAlloc for Locked<FixedSizeBlockAllocator> {
-    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
-        let mut allocator = self.lock();
-        match list_index(&layout) {
-            Some(index) => {
-                match allocator.list_heads[index].take() {
-                    Some(node) => {
-                        allocator.list_heads[index] = node.next.take();
-                        node as *mut ListNode as *mut u8
-                    }
-                    None => {
-                        // no block exists in list => allocate new block
-                        let block_size = BLOCK_SIZES[index];
-                        // only works if all block sizes are a power of 2
-                        let block_align = block_size;
-                        let layout = Layout::from_size_align(block_size, block_align).unwrap();
-                        allocator.fallback_alloc(layout)
-                    }
-                }
-            }
-            None => allocator.fallback_alloc(layout),
-        }
-    }
-
-    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
-        let mut allocator = self.lock();
-        match list_index(&layout) {
-            Some(index) => {
-                let new_node = ListNode {
-                    next: allocator.list_heads[index].take(),
-                };
-                // verify that block has size and alignment required for storing node
-                assert!(mem::size_of::<ListNode>() <= BLOCK_SIZES[index]);
-                assert!(mem::align_of::<ListNode>() <= BLOCK_SIZES[index]);
-                let new_node_ptr = ptr as *mut ListNode;
-                new_node_ptr.write(new_node);
-                allocator.list_heads[index] = Some(&mut *new_node_ptr);
-            }
-            None => {
-                let ptr = NonNull::new(ptr).unwrap();
-                allocator.fallback_allocator.deallocate(ptr, layout);
-            }
-        }
-    }
-}
--- a/src/allocator/linked_list.rs
+++ b/src/allocator/linked_list.rs
@@ -1,145 +0,0 @@
-use super::{align_up, Locked};
-use alloc::alloc::{GlobalAlloc, Layout};
-use core::{mem, ptr};
-
-struct ListNode {
-    size: usize,
-    next: Option<&'static mut ListNode>,
-}
-
-impl ListNode {
-    const fn new(size: usize) -> Self {
-        ListNode { size, next: None }
-    }
-
-    fn start_addr(&self) -> usize {
-        self as *const Self as usize
-    }
-
-    fn end_addr(&self) -> usize {
-        self.start_addr() + self.size
-    }
-}
-
-pub struct LinkedListAllocator {
-    head: ListNode,
-}
-
-impl LinkedListAllocator {
-    /// Creates an empty LinkedListAllocator.
-    pub const fn new() -> Self {
-        Self {
-            head: ListNode::new(0),
-        }
-    }
-
-    /// Initialize the allocator with the given heap bounds.
-    ///
-    /// This function is unsafe because the caller must guarantee that the given
-    /// heap bounds are valid and that the heap is unused. This method must be
-    /// called only once.
-    pub unsafe fn init(&mut self, heap_start: usize, heap_size: usize) {
-        self.add_free_region(heap_start, heap_size);
-    }
-
-    /// Adds the given memory region to the front of the list.
-    unsafe fn add_free_region(&mut self, addr: usize, size: usize) {
-        // ensure that the freed region is capable of holding ListNode
-        assert!(align_up(addr, mem::align_of::<ListNode>()) == addr);
-        assert!(size >= mem::size_of::<ListNode>());
-
-        // create a new list node and append it at the start of the list
-        let mut node = ListNode::new(size);
-        node.next = self.head.next.take();
-        let node_ptr = addr as *mut ListNode;
-        node_ptr.write(node);
-        self.head.next = Some(&mut *node_ptr)
-    }
-
-    /// Looks for a free region with the given size and alignment and removes
-    /// it from the list.
-    ///
-    /// Returns a tuple of the list node and the start address of the allocation.
-    fn find_region(&mut self, size: usize, align: usize) -> Option<(&'static mut ListNode, usize)> {
-        // reference to current list node, updated for each iteration
-        let mut current = &mut self.head;
-        // look for a large enough memory region in linked list
-        while let Some(ref mut region) = current.next {
-            if let Ok(alloc_start) = Self::alloc_from_region(&region, size, align) {
-                // region suitable for allocation -> remove node from list
-                let next = region.next.take();
-                let ret = Some((current.next.take().unwrap(), alloc_start));
-                current.next = next;
-                return ret;
-            } else {
-                // region not suitable -> continue with next region
-                current = current.next.as_mut().unwrap();
-            }
-        }
-
-        // no suitable region found
-        None
-    }
-
-    /// Try to use the given region for an allocation with given size and alignment.
-    ///
-    /// Returns the allocation start address on success.
-    fn alloc_from_region(region: &ListNode, size: usize, align: usize) -> Result<usize, ()> {
-        let alloc_start = align_up(region.start_addr(), align);
-        let alloc_end = alloc_start + size;
-
-        if alloc_end > region.end_addr() {
-            // region too small
-            return Err(());
-        }
-
-        let excess_size = region.end_addr() - alloc_end;
-        if excess_size > 0 && excess_size < mem::size_of::<ListNode>() {
-            // rest of region too small to hold a ListNode (required because the
-            // allocation splits the region in a used and a free part)
-            return Err(());
-        }
-
-        // region suitable for allocation
-        Ok(alloc_start)
-    }
-
-    /// Adjust the given layout so that the resulting allocated memory
-    /// region is also capable of storing a `ListNode`.
-    ///
-    /// Returns the adjusted size and alignment as a (size, align) tuple.
-    fn size_align(layout: Layout) -> (usize, usize) {
-        let layout = layout
-            .align_to(mem::align_of::<ListNode>())
-            .expect("adjusting alignment failed")
-            .pad_to_align();
-        let size = layout.size().max(mem::size_of::<ListNode>());
-        (size, layout.align())
-    }
-}
-
-unsafe impl GlobalAlloc for Locked<LinkedListAllocator> {
-    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
-        // perform layout adjustments
-        let (size, align) = LinkedListAllocator::size_align(layout);
-        let mut allocator = self.inner.lock();
-
-        if let Some((region, alloc_start)) = allocator.find_region(size, align) {
-            let alloc_end = alloc_start + size;
-            let excess_size = region.end_addr() - alloc_end;
-            if excess_size > 0 {
-                allocator.add_free_region(alloc_end, excess_size);
-            }
-            alloc_start as *mut u8
-        } else {
-            ptr::null_mut()
-        }
-    }
-
-    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
-        // perform layout adjustments
-        let (size, _) = LinkedListAllocator::size_align(layout);
-
-        self.inner.lock().add_free_region(ptr as usize, size)
-    }
-}
--- a/src/allocator/mod.rs
+++ b/src/allocator/mod.rs
@@ -1,84 +0,0 @@
-use alloc::alloc::{GlobalAlloc, Layout};
-use core::ptr::null_mut;
-use fixed_size_block::FixedSizeBlockAllocator;
-use x86_64::{
-    structures::paging::{
-        mapper::MapToError, FrameAllocator, Mapper, Page, PageTableFlags, Size4KiB,
-    },
-    VirtAddr,
-};
-
-pub mod bump;
-pub mod fixed_size_block;
-pub mod linked_list;
-
-pub const HEAP_START: usize = 0x_4444_4444_0000;
-pub const HEAP_SIZE: usize = 100 * 1024; // 100 KiB
-
-#[global_allocator]
-static ALLOCATOR: Locked<FixedSizeBlockAllocator> = Locked::new(FixedSizeBlockAllocator::new());
-
-pub fn init_heap(
-    mapper: &mut impl Mapper<Size4KiB>,
-    frame_allocator: &mut impl FrameAllocator<Size4KiB>,
-) -> Result<(), MapToError> {
-    let page_range = {
-        let heap_start = VirtAddr::new(HEAP_START as u64);
-        let heap_end = heap_start + HEAP_SIZE - 1u64;
-        let heap_start_page = Page::containing_address(heap_start);
-        let heap_end_page = Page::containing_address(heap_end);
-        Page::range_inclusive(heap_start_page, heap_end_page)
-    };
-
-    for page in page_range {
-        let frame = frame_allocator
-            .allocate_frame()
-            .ok_or(MapToError::FrameAllocationFailed)?;
-        let flags = PageTableFlags::PRESENT | PageTableFlags::WRITABLE;
-        mapper.map_to(page, frame, flags, frame_allocator)?.flush();
-    }
-
-    unsafe {
-        ALLOCATOR.lock().init(HEAP_START, HEAP_SIZE);
-    }
-
-    Ok(())
-}
-
-pub struct Dummy;
-
-unsafe impl GlobalAlloc for Dummy {
-    unsafe fn alloc(&self, _layout: Layout) -> *mut u8 {
-        null_mut()
-    }
-
-    unsafe fn dealloc(&self, _ptr: *mut u8, _layout: Layout) {
-        panic!("dealloc should be never called")
-    }
-}
-
-/// A wrapper around spin::Mutex to permit trait implementations.
-pub struct Locked<A> {
-    inner: spin::Mutex<A>,
-}
-
-impl<A> Locked<A> {
-    pub const fn new(inner: A) -> Self {
-        Locked {
-            inner: spin::Mutex::new(inner),
-        }
-    }
-
-    pub fn lock(&self) -> spin::MutexGuard<A> {
-        self.inner.lock()
-    }
-}
-
-fn align_up(addr: usize, align: usize) -> usize {
-    let remainder = addr % align;
-    if remainder == 0 {
-        addr // addr already aligned
-    } else {
-        addr - remainder + align
-    }
-}
--- a/src/gdt.rs
+++ b/src/gdt.rs
@@ -1,7 +1,7 @@
 use lazy_static::lazy_static;
+use x86_64::VirtAddr;
 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;

@@ -9,10 +9,10 @@ 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;
+            const STACK_SIZE: usize = 4096 * 5;
            static mut STACK: [u8; STACK_SIZE] = [0; STACK_SIZE];

-            let stack_start = VirtAddr::from_ptr(unsafe { &STACK });
+            let stack_start = VirtAddr::from_ptr(&raw const STACK);
            let stack_end = stack_start + STACK_SIZE;
            stack_end
        };
@@ -41,12 +41,12 @@ struct Selectors {
 }

 pub fn init() {
-    use x86_64::instructions::segmentation::set_cs;
+    use x86_64::instructions::segmentation::{CS, Segment};
    use x86_64::instructions::tables::load_tss;

    GDT.0.load();
    unsafe {
-        set_cs(GDT.1.code_selector);
+        CS::set_reg(GDT.1.code_selector);
        load_tss(GDT.1.tss_selector);
    }
 }
--- a/src/interrupts.rs
+++ b/src/interrupts.rs
@@ -1,44 +1,16 @@
-use crate::{gdt, hlt_loop, print, println};
+use crate::{gdt, 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) });
+use x86_64::structures::idt::{InterruptDescriptorTable, InterruptStackFrame};

 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
    };
 }
@@ -47,75 +19,19 @@ pub fn init_idt() {
    IDT.load();
 }

-extern "x86-interrupt" fn breakpoint_handler(stack_frame: &mut InterruptStackFrame) {
+extern "x86-interrupt" fn breakpoint_handler(stack_frame: InterruptStackFrame) {
    println!("EXCEPTION: BREAKPOINT\n{:#?}", stack_frame);
 }

-extern "x86-interrupt" fn page_fault_handler(
-    stack_frame: &mut 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: &mut InterruptStackFrame,
+    stack_frame: InterruptStackFrame,
    _error_code: u64,
 ) -> ! {
    panic!("EXCEPTION: DOUBLE FAULT\n{:#?}", stack_frame);
 }

-extern "x86-interrupt" fn timer_interrupt_handler(_stack_frame: &mut InterruptStackFrame) {
-    print!(".");
-    unsafe {
-        PICS.lock()
-            .notify_end_of_interrupt(InterruptIndex::Timer.as_u8());
-    }
-    crate::multitasking::invoke_scheduler();
-}
-
-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 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());
-    }
-}
-
-#[cfg(test)]
-use crate::{serial_print, serial_println};
-
 #[test_case]
 fn test_breakpoint_exception() {
-    serial_print!("test_breakpoint_exception...");
    // invoke a breakpoint exception
    x86_64::instructions::interrupts::int3();
-    serial_println!("[ok]");
 }
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -2,42 +2,39 @@
 #![cfg_attr(test, no_main)]
 #![feature(custom_test_frameworks)]
 #![feature(abi_x86_interrupt)]
-#![feature(alloc_error_handler)]
-#![feature(const_fn)]
-#![feature(alloc_layout_extra)]
-#![feature(const_in_array_repeat_expressions)]
-#![feature(global_asm)]
-#![feature(asm)]
-#![feature(raw)]
-#![feature(never_type)]
-#![feature(naked_functions)]
-#![feature(option_expect_none)]
 #![test_runner(crate::test_runner)]
 #![reexport_test_harness_main = "test_main"]

-extern crate alloc;
-
 use core::panic::PanicInfo;

-pub mod allocator;
 pub mod gdt;
 pub mod interrupts;
-pub mod memory;
-pub mod multitasking;
 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) -> ();
 }

-pub fn test_runner(tests: &[&dyn Fn()]) {
+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();
+        test.run();
    }
    exit_qemu(QemuExitCode::Success);
 }
@@ -46,7 +43,7 @@ pub fn test_panic_handler(info: &PanicInfo) -> ! {
    serial_println!("[failed]\n");
    serial_println!("Error: {}\n", info);
    exit_qemu(QemuExitCode::Failed);
-    hlt_loop();
+    loop {}
 }

 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -65,24 +62,13 @@ pub fn exit_qemu(exit_code: QemuExitCode) {
    }
 }

-pub fn hlt_loop() -> ! {
-    loop {
-        x86_64::instructions::hlt();
-    }
-}
-
-#[cfg(test)]
-use bootloader::{entry_point, BootInfo};
-
-#[cfg(test)]
-entry_point!(test_kernel_main);
-
 /// Entry point for `cargo xtest`
 #[cfg(test)]
-fn test_kernel_main(_boot_info: &'static BootInfo) -> ! {
+#[unsafe(no_mangle)]
+pub extern "C" fn _start() -> ! {
    init();
    test_main();
-    hlt_loop();
+    loop {}
 }

 #[cfg(test)]
@@ -90,8 +76,3 @@ fn test_kernel_main(_boot_info: &'static BootInfo) -> ! {
 fn panic(info: &PanicInfo) -> ! {
    test_panic_handler(info)
 }
-
-#[alloc_error_handler]
-fn alloc_error_handler(layout: alloc::alloc::Layout) -> ! {
-    panic!("allocation error: {:?}", layout)
-}
--- a/src/main.rs
+++ b/src/main.rs
@@ -4,98 +4,35 @@
 #![test_runner(blog_os::test_runner)]
 #![reexport_test_harness_main = "test_main"]

-extern crate alloc;
-
-use alloc::{boxed::Box, rc::Rc, vec, vec::Vec};
-use blog_os::multitasking::{self, thread::Thread, with_scheduler};
-use blog_os::{print, println};
-use bootloader::{entry_point, BootInfo};
+use blog_os::println;
 use core::panic::PanicInfo;

-entry_point!(kernel_main);
-
-fn kernel_main(boot_info: &'static BootInfo) -> ! {
-    use blog_os::allocator;
-    use blog_os::memory::{self, BootInfoFrameAllocator};
-    use x86_64::VirtAddr;
-
+#[unsafe(no_mangle)]
+pub extern "C" fn _start() -> ! {
    println!("Hello World{}", "!");
+
    blog_os::init();

-    let phys_mem_offset = VirtAddr::new(boot_info.physical_memory_offset);
-    let mut mapper = unsafe { memory::init(phys_mem_offset) };
-    let mut frame_allocator = unsafe { BootInfoFrameAllocator::init(&boot_info.memory_map) };
-
-    allocator::init_heap(&mut mapper, &mut frame_allocator).expect("heap initialization failed");
-
-    // allocate a number on the heap
-    let heap_value = Box::new(41);
-    println!("heap_value at {:p}", heap_value);
-
-    // create a dynamically sized vector
-    let mut vec = Vec::new();
-    for i in 0..500 {
-        vec.push(i);
+    fn stack_overflow() {
+        stack_overflow(); // for each recursion, the return address is pushed
    }
-    println!("vec at {:p}", vec.as_slice());

-    // create a reference counted vector -> will be freed when count reaches 0
-    let reference_counted = Rc::new(vec![1, 2, 3]);
-    let cloned_reference = reference_counted.clone();
-    println!(
-        "current reference count is {}",
-        Rc::strong_count(&cloned_reference)
-    );
-    core::mem::drop(reference_counted);
-    println!(
-        "reference count is {} now",
-        Rc::strong_count(&cloned_reference)
-    );
+    // uncomment line below to trigger a stack overflow
+    // stack_overflow();

    #[cfg(test)]
    test_main();

-    let idle_thread = Thread::create(idle_thread, 2, &mut mapper, &mut frame_allocator).unwrap();
-    with_scheduler(|s| s.set_idle_thread(idle_thread));
-
-    for _ in 0..10 {
-        let thread = Thread::create(thread_entry, 2, &mut mapper, &mut frame_allocator).unwrap();
-        with_scheduler(|s| s.add_new_thread(thread));
-    }
-    let thread =
-        Thread::create_from_closure(|| thread_entry(), 2, &mut mapper, &mut frame_allocator)
-            .unwrap();
-    with_scheduler(|s| s.add_new_thread(thread));
-
    println!("It did not crash!");
-    thread_entry();
-}
-
-fn idle_thread() -> ! {
-    loop {
-        x86_64::instructions::hlt();
-        multitasking::yield_now();
-    }
-}
-
-fn thread_entry() -> ! {
-    let thread_id = with_scheduler(|s| s.current_thread_id()).as_u64();
-    for _ in 0..=thread_id {
-        print!("{}", thread_id);
-        x86_64::instructions::hlt();
-    }
-    multitasking::exit_thread();
+    loop {}
 }

 /// This function is called on panic.
 #[cfg(not(test))]
 #[panic_handler]
 fn panic(info: &PanicInfo) -> ! {
-    unsafe {
-        blog_os::vga_buffer::WRITER.force_unlock();
-    }
    println!("{}", info);
-    blog_os::hlt_loop();
+    loop {}
 }

 #[cfg(test)]
@@ -103,3 +40,8 @@ fn panic(info: &PanicInfo) -> ! {
 fn panic(info: &PanicInfo) -> ! {
    blog_os::test_panic_handler(info)
 }
+
+#[test_case]
+fn trivial_assertion() {
+    assert_eq!(1, 1);
+}
--- a/src/memory.rs
+++ b/src/memory.rs
@@ -1,154 +0,0 @@
-use bootloader::bootinfo::{MemoryMap, MemoryRegionType};
-use x86_64::{
-    structures::paging::{
-        mapper, FrameAllocator, Mapper, OffsetPageTable, Page, PageTable, PhysFrame, Size4KiB,
-        UnusedPhysFrame,
-    },
-    PhysAddr, VirtAddr,
-};
-
-/// Initialize a new OffsetPageTable.
-///
-/// 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: VirtAddr) -> OffsetPageTable<'static> {
-    let level_4_table = active_level_4_table(physical_memory_offset);
-    OffsetPageTable::new(level_4_table, physical_memory_offset)
-}
-
-/// 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: VirtAddr) -> &'static mut PageTable {
-    use x86_64::registers::control::Cr3;
-
-    let (level_4_table_frame, _) = Cr3::read();
-
-    let phys = level_4_table_frame.start_address();
-    let virt = physical_memory_offset + phys.as_u64();
-    let page_table_ptr: *mut PageTable = virt.as_mut_ptr();
-
-    &mut *page_table_ptr // unsafe
-}
-
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub struct StackBounds {
-    start: VirtAddr,
-    end: VirtAddr,
-}
-
-impl StackBounds {
-    pub fn start(&self) -> VirtAddr {
-        self.start
-    }
-
-    pub fn end(&self) -> VirtAddr {
-        self.end
-    }
-}
-
-pub fn alloc_stack(
-    size_in_pages: u64,
-    mapper: &mut impl Mapper<Size4KiB>,
-    frame_allocator: &mut impl FrameAllocator<Size4KiB>,
-) -> Result<StackBounds, mapper::MapToError> {
-    use core::sync::atomic::{AtomicU64, Ordering};
-    use x86_64::structures::paging::PageTableFlags as Flags;
-
-    static STACK_ALLOC_NEXT: AtomicU64 = AtomicU64::new(0x_5555_5555_0000);
-
-    let guard_page_start = STACK_ALLOC_NEXT.fetch_add(
-        (size_in_pages + 1) * Page::<Size4KiB>::SIZE,
-        Ordering::SeqCst,
-    );
-    let guard_page = Page::from_start_address(VirtAddr::new(guard_page_start))
-        .expect("`STACK_ALLOC_NEXT` not page aligned");
-
-    let stack_start = guard_page + 1;
-    let stack_end = stack_start + size_in_pages;
-    let flags = Flags::PRESENT | Flags::WRITABLE;
-    for page in Page::range(stack_start, stack_end) {
-        let frame = frame_allocator
-            .allocate_frame()
-            .ok_or(mapper::MapToError::FrameAllocationFailed)?;
-        mapper.map_to(page, frame, flags, frame_allocator)?.flush();
-    }
-    Ok(StackBounds {
-        start: stack_start.start_address(),
-        end: stack_end.start_address(),
-    })
-}
-
-/// Creates an example mapping for the given page to frame `0xb8000`.
-pub fn create_example_mapping(
-    page: Page,
-    mapper: &mut OffsetPageTable,
-    frame_allocator: &mut impl FrameAllocator<Size4KiB>,
-) {
-    use x86_64::structures::paging::PageTableFlags as Flags;
-
-    let frame = PhysFrame::containing_address(PhysAddr::new(0xb8000));
-    // FIXME: ONLY FOR TEMPORARY TESTING
-    let unused_frame = unsafe { UnusedPhysFrame::new(frame) };
-    let flags = Flags::PRESENT | Flags::WRITABLE;
-
-    let map_to_result = mapper.map_to(page, unused_frame, flags, frame_allocator);
-    map_to_result.expect("map_to failed").flush();
-}
-
-/// A FrameAllocator that always returns `None`.
-pub struct EmptyFrameAllocator;
-
-unsafe impl FrameAllocator<Size4KiB> for EmptyFrameAllocator {
-    fn allocate_frame(&mut self) -> Option<UnusedPhysFrame> {
-        None
-    }
-}
-
-/// A FrameAllocator that returns usable frames from the bootloader's memory map.
-pub struct BootInfoFrameAllocator {
-    memory_map: &'static MemoryMap,
-    next: usize,
-}
-
-impl BootInfoFrameAllocator {
-    /// Create a FrameAllocator from the passed memory map.
-    ///
-    /// This function is unsafe because the caller must guarantee that the passed
-    /// memory map is valid. The main requirement is that all frames that are marked
-    /// as `USABLE` in it are really unused.
-    pub unsafe fn init(memory_map: &'static MemoryMap) -> Self {
-        BootInfoFrameAllocator {
-            memory_map,
-            next: 0,
-        }
-    }
-
-    /// Returns an iterator over the usable frames specified in the memory map.
-    fn usable_frames(&self) -> impl Iterator<Item = UnusedPhysFrame> {
-        // get usable regions from memory map
-        let regions = self.memory_map.iter();
-        let usable_regions = regions.filter(|r| r.region_type == MemoryRegionType::Usable);
-        // map each region to its address range
-        let addr_ranges = usable_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.step_by(4096));
-        // create `PhysFrame` types from the start addresses
-        let frames = frame_addresses.map(|addr| PhysFrame::containing_address(PhysAddr::new(addr)));
-        // we know that the frames are really unused
-        frames.map(|f| unsafe { UnusedPhysFrame::new(f) })
-    }
-}
-
-unsafe impl FrameAllocator<Size4KiB> for BootInfoFrameAllocator {
-    fn allocate_frame(&mut self) -> Option<UnusedPhysFrame> {
-        let frame = self.usable_frames().nth(self.next);
-        self.next += 1;
-        frame
-    }
-}
--- a/src/multitasking/context_switch.rs
+++ b/src/multitasking/context_switch.rs
@@ -1,105 +0,0 @@
-use super::{with_scheduler, SwitchReason};
-use crate::multitasking::thread::ThreadId;
-use alloc::boxed::Box;
-use core::mem;
-use core::raw::TraitObject;
-use x86_64::VirtAddr;
-
-pub struct Stack {
-    pointer: VirtAddr,
-}
-
-impl Stack {
-    pub unsafe fn new(stack_pointer: VirtAddr) -> Self {
-        Stack {
-            pointer: stack_pointer,
-        }
-    }
-
-    pub fn get_stack_pointer(self) -> VirtAddr {
-        self.pointer
-    }
-
-    pub fn set_up_for_closure(&mut self, closure: Box<dyn FnOnce() -> !>) {
-        let trait_object: TraitObject = unsafe { mem::transmute(closure) };
-        unsafe { self.push(trait_object.data) };
-        unsafe { self.push(trait_object.vtable) };
-
-        self.set_up_for_entry_point(call_closure_entry);
-    }
-
-    pub fn set_up_for_entry_point(&mut self, entry_point: fn() -> !) {
-        unsafe { self.push(entry_point) };
-        let rflags: u64 = 0x200;
-        unsafe { self.push(rflags) };
-    }
-
-    unsafe fn push<T>(&mut self, value: T) {
-        self.pointer -= core::mem::size_of::<T>();
-        let ptr: *mut T = self.pointer.as_mut_ptr();
-        ptr.write(value);
-    }
-}
-
-pub unsafe fn context_switch_to(
-    new_stack_pointer: VirtAddr,
-    prev_thread_id: ThreadId,
-    switch_reason: SwitchReason,
-) {
-    asm!(
-        "call asm_context_switch"
-        :
-        : "{rdi}"(new_stack_pointer), "{rsi}"(prev_thread_id), "{rdx}"(switch_reason as u64)
-        : "rax", "rbx", "rcx", "rdx", "rsi", "rdi", "rbp", "r8", "r9", "r10",
-        "r11", "r12", "r13", "r14", "r15", "rflags", "memory"
-        : "intel", "volatile"
-    );
-}
-
-global_asm!(
-    "
-    .intel_syntax noprefix
-
-    // asm_context_switch(stack_pointer: u64, thread_id: u64)
-    asm_context_switch:
-        pushfq
-
-        mov rax, rsp
-        mov rsp, rdi
-
-        mov rdi, rax
-        call add_paused_thread
-
-        popfq
-        ret
-"
-);
-
-#[no_mangle]
-pub extern "C" fn add_paused_thread(
-    paused_stack_pointer: VirtAddr,
-    paused_thread_id: ThreadId,
-    switch_reason: SwitchReason,
-) {
-    with_scheduler(|s| s.add_paused_thread(paused_stack_pointer, paused_thread_id, switch_reason));
-}
-
-#[naked]
-fn call_closure_entry() -> ! {
-    unsafe {
-        asm!("
-        pop rsi
-        pop rdi
-        call call_closure
-    " ::: "mem" : "intel", "volatile")
-    };
-    unreachable!();
-}
-
-// no_mangle required because of https://github.com/rust-lang/rust/issues/68136
-#[no_mangle]
-extern "C" fn call_closure(data: *mut (), vtable: *mut ()) -> ! {
-    let trait_object = TraitObject { data, vtable };
-    let f: Box<dyn FnOnce() -> !> = unsafe { mem::transmute(trait_object) };
-    f()
-}
--- a/src/multitasking/mod.rs
+++ b/src/multitasking/mod.rs
@@ -1,57 +0,0 @@
-use scheduler::Scheduler;
-
-pub mod context_switch;
-pub mod scheduler;
-pub mod thread;
-
-static SCHEDULER: spin::Mutex<Option<Scheduler>> = spin::Mutex::new(None);
-
-#[repr(u64)]
-pub enum SwitchReason {
-    Paused,
-    Yield,
-    Blocked,
-    Exit,
-}
-
-pub fn invoke_scheduler() {
-    let next = SCHEDULER
-        .try_lock()
-        .and_then(|mut scheduler| scheduler.as_mut().and_then(|s| s.schedule()));
-    if let Some((next_stack_pointer, prev_thread_id)) = next {
-        unsafe {
-            context_switch::context_switch_to(
-                next_stack_pointer,
-                prev_thread_id,
-                SwitchReason::Paused,
-            )
-        };
-    }
-}
-
-pub fn exit_thread() -> ! {
-    synchronous_context_switch(SwitchReason::Exit).expect("can't exit last thread");
-    unreachable!("finished thread continued");
-}
-
-pub fn yield_now() {
-    let _ = synchronous_context_switch(SwitchReason::Yield);
-}
-
-fn synchronous_context_switch(reason: SwitchReason) -> Result<(), ()> {
-    let next = with_scheduler(|s| s.schedule());
-    match next {
-        Some((next_stack_pointer, prev_thread_id)) => unsafe {
-            context_switch::context_switch_to(next_stack_pointer, prev_thread_id, reason);
-            Ok(())
-        },
-        None => Err(()),
-    }
-}
-
-pub fn with_scheduler<F, T>(f: F) -> T
-where
-    F: FnOnce(&mut Scheduler) -> T,
-{
-    f(SCHEDULER.lock().get_or_insert_with(Scheduler::new))
-}
--- a/src/multitasking/scheduler.rs
+++ b/src/multitasking/scheduler.rs
@@ -1,122 +0,0 @@
-use super::SwitchReason;
-use crate::multitasking::thread::{Thread, ThreadId};
-use alloc::collections::{BTreeMap, BTreeSet, VecDeque};
-use core::mem;
-use x86_64::VirtAddr;
-
-pub struct Scheduler {
-    threads: BTreeMap<ThreadId, Thread>,
-    idle_thread_id: Option<ThreadId>,
-    current_thread_id: ThreadId,
-    paused_threads: VecDeque<ThreadId>,
-    blocked_threads: BTreeSet<ThreadId>,
-    wakeups: BTreeSet<ThreadId>,
-}
-
-impl Scheduler {
-    pub fn new() -> Self {
-        let root_thread = Thread::create_root_thread();
-        let root_id = root_thread.id();
-        let mut threads = BTreeMap::new();
-        threads
-            .insert(root_id, root_thread)
-            .expect_none("map is not empty after creation");
-        Scheduler {
-            threads,
-            current_thread_id: root_id,
-            paused_threads: VecDeque::new(),
-            blocked_threads: BTreeSet::new(),
-            wakeups: BTreeSet::new(),
-            idle_thread_id: None,
-        }
-    }
-
-    fn next_thread(&mut self) -> Option<ThreadId> {
-        self.paused_threads.pop_front()
-    }
-
-    pub fn schedule(&mut self) -> Option<(VirtAddr, ThreadId)> {
-        let mut next_thread_id = self.next_thread();
-        if next_thread_id.is_none() && Some(self.current_thread_id) != self.idle_thread_id {
-            next_thread_id = self.idle_thread_id
-        }
-        if let Some(next_id) = next_thread_id {
-            let next_thread = self
-                .threads
-                .get_mut(&next_id)
-                .expect("next thread does not exist");
-            let next_stack_pointer = next_thread
-                .stack_pointer()
-                .take()
-                .expect("paused thread has no stack pointer");
-            let prev_thread_id = mem::replace(&mut self.current_thread_id, next_thread.id());
-            Some((next_stack_pointer, prev_thread_id))
-        } else {
-            None
-        }
-    }
-
-    pub(super) fn add_paused_thread(
-        &mut self,
-        paused_stack_pointer: VirtAddr,
-        paused_thread_id: ThreadId,
-        switch_reason: SwitchReason,
-    ) {
-        let paused_thread = self
-            .threads
-            .get_mut(&paused_thread_id)
-            .expect("paused thread does not exist");
-        paused_thread
-            .stack_pointer()
-            .replace(paused_stack_pointer)
-            .expect_none("running thread should have stack pointer set to None");
-        if Some(paused_thread_id) == self.idle_thread_id {
-            return; // do nothing
-        }
-        match switch_reason {
-            SwitchReason::Paused | SwitchReason::Yield => {
-                self.paused_threads.push_back(paused_thread_id)
-            }
-            SwitchReason::Blocked => {
-                self.blocked_threads.insert(paused_thread_id);
-                self.check_for_wakeup(paused_thread_id);
-            }
-            SwitchReason::Exit => {
-                let thread = self
-                    .threads
-                    .remove(&paused_thread_id)
-                    .expect("thread not found");
-                // TODO: free stack memory again
-            }
-        }
-    }
-
-    pub fn add_new_thread(&mut self, thread: Thread) {
-        let thread_id = thread.id();
-        self.threads
-            .insert(thread_id, thread)
-            .expect_none("thread already exists");
-        self.paused_threads.push_back(thread_id);
-    }
-
-    pub fn set_idle_thread(&mut self, thread: Thread) {
-        let thread_id = thread.id();
-        self.threads
-            .insert(thread_id, thread)
-            .expect_none("thread already exists");
-        self.idle_thread_id
-            .replace(thread_id)
-            .expect_none("idle thread should be set only once");
-    }
-
-    pub fn current_thread_id(&self) -> ThreadId {
-        self.current_thread_id
-    }
-
-    fn check_for_wakeup(&mut self, thread_id: ThreadId) {
-        if self.wakeups.remove(&thread_id) {
-            assert!(self.blocked_threads.remove(&thread_id));
-            self.paused_threads.push_back(thread_id);
-        }
-    }
-}
--- a/src/multitasking/thread.rs
+++ b/src/multitasking/thread.rs
@@ -1,82 +0,0 @@
-use crate::memory::{alloc_stack, StackBounds};
-use crate::multitasking::context_switch::Stack;
-use alloc::boxed::Box;
-use x86_64::{
-    structures::paging::{mapper, FrameAllocator, Mapper, Size4KiB},
-    VirtAddr,
-};
-
-#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
-pub struct ThreadId(u64);
-
-impl ThreadId {
-    pub fn as_u64(&self) -> u64 {
-        self.0
-    }
-
-    fn new() -> Self {
-        use core::sync::atomic::{AtomicU64, Ordering};
-        static NEXT_THREAD_ID: AtomicU64 = AtomicU64::new(1);
-        ThreadId(NEXT_THREAD_ID.fetch_add(1, Ordering::SeqCst))
-    }
-}
-
-#[derive(Debug)]
-pub struct Thread {
-    id: ThreadId,
-    stack_pointer: Option<VirtAddr>,
-    stack_bounds: Option<StackBounds>,
-}
-
-impl Thread {
-    pub fn create(
-        entry_point: fn() -> !,
-        stack_size: u64,
-        mapper: &mut impl Mapper<Size4KiB>,
-        frame_allocator: &mut impl FrameAllocator<Size4KiB>,
-    ) -> Result<Self, mapper::MapToError> {
-        let stack_bounds = alloc_stack(stack_size, mapper, frame_allocator)?;
-        let mut stack = unsafe { Stack::new(stack_bounds.end()) };
-        stack.set_up_for_entry_point(entry_point);
-        Ok(Self::new(stack.get_stack_pointer(), stack_bounds))
-    }
-
-    pub fn create_from_closure<F>(
-        closure: F,
-        stack_size: u64,
-        mapper: &mut impl Mapper<Size4KiB>,
-        frame_allocator: &mut impl FrameAllocator<Size4KiB>,
-    ) -> Result<Self, mapper::MapToError>
-    where
-        F: FnOnce() -> ! + 'static + Send + Sync,
-    {
-        let stack_bounds = alloc_stack(stack_size, mapper, frame_allocator)?;
-        let mut stack = unsafe { Stack::new(stack_bounds.end()) };
-        stack.set_up_for_closure(Box::new(closure));
-        Ok(Self::new(stack.get_stack_pointer(), stack_bounds))
-    }
-
-    fn new(stack_pointer: VirtAddr, stack_bounds: StackBounds) -> Self {
-        Thread {
-            id: ThreadId::new(),
-            stack_pointer: Some(stack_pointer),
-            stack_bounds: Some(stack_bounds),
-        }
-    }
-
-    pub(super) fn create_root_thread() -> Self {
-        Thread {
-            id: ThreadId(0),
-            stack_pointer: None,
-            stack_bounds: None,
-        }
-    }
-
-    pub fn id(&self) -> ThreadId {
-        self.id
-    }
-
-    pub(super) fn stack_pointer(&mut self) -> &mut Option<VirtAddr> {
-        &mut self.stack_pointer
-    }
-}
--- a/src/serial.rs
+++ b/src/serial.rs
@@ -13,14 +13,10 @@ lazy_static! {
 #[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");
-    });
+    SERIAL1
+        .lock()
+        .write_fmt(args)
+        .expect("Printing to serial failed");
 }

 /// Prints to the host through the serial interface.
--- a/src/vga_buffer.rs
+++ b/src/vga_buffer.rs
@@ -3,9 +3,6 @@ use lazy_static::lazy_static;
 use spin::Mutex;
 use volatile::Volatile;

-#[cfg(test)]
-use crate::{serial_print, serial_println};
-
 lazy_static! {
    /// A global `Writer` instance that can be used for printing to the VGA text buffer.
    ///
@@ -166,50 +163,31 @@ macro_rules! println {
    ($($arg:tt)*) => ($crate::print!("{}\n", format_args!($($arg)*)));
 }

-/// Prints the given formatted string to the VGA text buffer
-/// through the global `WRITER` instance.
+/// 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();
-    });
+    WRITER.lock().write_fmt(args).unwrap();
 }

 #[test_case]
 fn test_println_simple() {
-    serial_print!("test_println... ");
    println!("test_println_simple output");
-    serial_println!("[ok]");
 }

 #[test_case]
 fn test_println_many() {
-    serial_print!("test_println_many... ");
    for _ in 0..200 {
        println!("test_println_many output");
    }
-    serial_println!("[ok]");
 }

 #[test_case]
 fn test_println_output() {
-    use core::fmt::Write;
-    use x86_64::instructions::interrupts;
-
-    serial_print!("test_println_output... ");
-
    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);
-        }
-    });
-
-    serial_println!("[ok]");
+    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);
+    }
 }
--- a/tests/basic_boot.rs
+++ b/tests/basic_boot.rs
@@ -4,10 +4,10 @@
 #![test_runner(blog_os::test_runner)]
 #![reexport_test_harness_main = "test_main"]

-use blog_os::{println, serial_print, serial_println};
+use blog_os::println;
 use core::panic::PanicInfo;

-#[no_mangle] // don't mangle the name of this function
+#[unsafe(no_mangle)] // don't mangle the name of this function
 pub extern "C" fn _start() -> ! {
    test_main();

@@ -21,7 +21,5 @@ fn panic(info: &PanicInfo) -> ! {

 #[test_case]
 fn test_println() {
-    serial_print!("test_println... ");
    println!("test_println output");
-    serial_println!("[ok]");
 }
--- a/tests/heap_allocation.rs
+++ b/tests/heap_allocation.rs
@@ -1,76 +0,0 @@
-#![no_std]
-#![no_main]
-#![feature(custom_test_frameworks)]
-#![test_runner(blog_os::test_runner)]
-#![reexport_test_harness_main = "test_main"]
-
-extern crate alloc;
-
-use alloc::{boxed::Box, vec::Vec};
-use blog_os::{allocator::HEAP_SIZE, serial_print, serial_println};
-use bootloader::{entry_point, BootInfo};
-use core::panic::PanicInfo;
-
-entry_point!(main);
-
-fn main(boot_info: &'static BootInfo) -> ! {
-    use blog_os::allocator;
-    use blog_os::memory::{self, BootInfoFrameAllocator};
-    use x86_64::VirtAddr;
-
-    blog_os::init();
-    let phys_mem_offset = VirtAddr::new(boot_info.physical_memory_offset);
-    let mut mapper = unsafe { memory::init(phys_mem_offset) };
-    let mut frame_allocator = unsafe { BootInfoFrameAllocator::init(&boot_info.memory_map) };
-    allocator::init_heap(&mut mapper, &mut frame_allocator).expect("heap initialization failed");
-
-    test_main();
-    loop {}
-}
-
-#[test_case]
-fn simple_allocation() {
-    serial_print!("simple_allocation... ");
-    let heap_value = Box::new(41);
-    assert_eq!(*heap_value, 41);
-    serial_println!("[ok]");
-}
-
-#[test_case]
-fn large_vec() {
-    serial_print!("large_vec... ");
-    let n = 1000;
-    let mut vec = Vec::new();
-    for i in 0..n {
-        vec.push(i);
-    }
-    assert_eq!(vec.iter().sum::<u64>(), (n - 1) * n / 2);
-    serial_println!("[ok]");
-}
-
-#[test_case]
-fn many_boxes() {
-    serial_print!("many_boxes... ");
-    for i in 0..HEAP_SIZE {
-        let x = Box::new(i);
-        assert_eq!(*x, i);
-    }
-    serial_println!("[ok]");
-}
-
-#[test_case]
-fn many_boxes_long_lived() {
-    serial_print!("many_boxes_long_lived... ");
-    let long_lived = Box::new(1); // new
-    for i in 0..HEAP_SIZE {
-        let x = Box::new(i);
-        assert_eq!(*x, i);
-    }
-    assert_eq!(*long_lived, 1); // new
-    serial_println!("[ok]");
-}
-
-#[panic_handler]
-fn panic(info: &PanicInfo) -> ! {
-    blog_os::test_panic_handler(info)
-}
--- a/tests/should_panic.rs
+++ b/tests/should_panic.rs
@@ -1,10 +1,10 @@
 #![no_std]
 #![no_main]

-use blog_os::{exit_qemu, serial_print, serial_println, QemuExitCode};
+use blog_os::{QemuExitCode, exit_qemu, serial_print, serial_println};
 use core::panic::PanicInfo;

-#[no_mangle]
+#[unsafe(no_mangle)]
 pub extern "C" fn _start() -> ! {
    should_fail();
    serial_println!("[test did not panic]");
@@ -13,7 +13,7 @@ pub extern "C" fn _start() -> ! {
 }

 fn should_fail() {
-    serial_print!("should_fail... ");
+    serial_print!("should_panic::should_fail...\t");
    assert_eq!(0, 1);
 }

--- a/tests/stack_overflow.rs
+++ b/tests/stack_overflow.rs
@@ -2,14 +2,14 @@
 #![no_main]
 #![feature(abi_x86_interrupt)]

-use blog_os::{exit_qemu, serial_print, serial_println, QemuExitCode};
+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};

-#[no_mangle]
+#[unsafe(no_mangle)]
 pub extern "C" fn _start() -> ! {
-    serial_print!("stack_overflow... ");
+    serial_print!("stack_overflow::stack_overflow...\t");

    blog_os::gdt::init();
    init_test_idt();
@@ -23,6 +23,7 @@ pub extern "C" fn _start() -> ! {
 #[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! {
@@ -43,7 +44,7 @@ pub fn init_test_idt() {
 }

 extern "x86-interrupt" fn test_double_fault_handler(
-    _stack_frame: &mut InterruptStackFrame,
+    _stack_frame: InterruptStackFrame,
    _error_code: u64,
 ) -> ! {
    serial_println!("[ok]");
--- a/x86_64-blog_os.json
+++ b/x86_64-blog_os.json
@@ -1,15 +1,16 @@
 {
    "llvm-target": "x86_64-unknown-none",
-    "data-layout": "e-m:e-i64:64-f80:128-n8:16:32:64-S128",
+    "data-layout": "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128",
    "arch": "x86_64",
    "target-endian": "little",
    "target-pointer-width": "64",
-    "target-c-int-width": "32",
+    "target-c-int-width": 32,
    "os": "none",
    "executables": true,
    "linker-flavor": "ld.lld",
    "linker": "rust-lld",
    "panic-strategy": "abort",
    "disable-redzone": true,
-    "features": "-mmx,-sse,+soft-float"
+    "features": "-mmx,-sse,+soft-float",
+    "rustc-abi": "x86-softfloat"
  }