From fa148bc9b76934bae06e888a066fe2e0ec7fd7e6 Mon Sep 17 00:00:00 2001
From: Philipp Oppermann <dev@phil-opp.com>
Date: Fri, 27 Feb 2026 09:40:00 +0100
Subject: [PATCH] Add an example kernel that uses the built-in
 `x86_64-unknown-none` target

This ensures that bootimage works even if the user doesn't enable the unstable `json-target-spec` feature.
---
 .github/workflows/build.yml                   |  4 ++
 .../.cargo/config.toml                        |  2 +
 example-kernel-built-in-target/.gitignore     |  1 +
 example-kernel-built-in-target/Cargo.lock     | 53 +++++++++++++++++++
 example-kernel-built-in-target/Cargo.toml     |  8 +++
 example-kernel-built-in-target/rust-toolchain |  1 +
 example-kernel-built-in-target/src/main.rs    | 22 ++++++++
 7 files changed, 91 insertions(+)
 create mode 100644 example-kernel-built-in-target/.cargo/config.toml
 create mode 100644 example-kernel-built-in-target/.gitignore
 create mode 100644 example-kernel-built-in-target/Cargo.lock
 create mode 100644 example-kernel-built-in-target/Cargo.toml
 create mode 100644 example-kernel-built-in-target/rust-toolchain
 create mode 100644 example-kernel-built-in-target/src/main.rs

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index fcf00c2..727ab3e 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -90,6 +90,10 @@ jobs:
     - name: "Print QEMU Version"
       run: qemu-system-x86_64 --version
 
+    - name: 'Build kernel with built-in target (no json-target-spec config)'
+      run: cargo bootimage --target x86_64-unknown-none
+      working-directory: example-kernel-built-in-target
+
     - name: 'Build "basic" Kernel'
       run: cargo bootimage --target ../x86_64-bootimage-example-kernels.json
       working-directory: example-kernels/basic
diff --git a/example-kernel-built-in-target/.cargo/config.toml b/example-kernel-built-in-target/.cargo/config.toml
new file mode 100644
index 0000000..92cee48
--- /dev/null
+++ b/example-kernel-built-in-target/.cargo/config.toml
@@ -0,0 +1,2 @@
+[unstable]
+build-std = ["core", "compiler_builtins"]
diff --git a/example-kernel-built-in-target/.gitignore b/example-kernel-built-in-target/.gitignore
new file mode 100644
index 0000000..b83d222
--- /dev/null
+++ b/example-kernel-built-in-target/.gitignore
@@ -0,0 +1 @@
+/target/
diff --git a/example-kernel-built-in-target/Cargo.lock b/example-kernel-built-in-target/Cargo.lock
new file mode 100644
index 0000000..527c5e2
--- /dev/null
+++ b/example-kernel-built-in-target/Cargo.lock
@@ -0,0 +1,53 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "bit_field"
+version = "0.10.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e4b40c7323adcfc0a41c4b88143ed58346ff65a288fc144329c5c45e05d70c6"
+
+[[package]]
+name = "bitflags"
+version = "2.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "843867be96c8daad0d758b57df9392b6d8d271134fce549de6ce169ff98a92af"
+
+[[package]]
+name = "bootloader"
+version = "0.9.34"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "13f6a8a495d2f93fe3d6eb3a224f9aa749a63cfd746ed03eb5ddcbd00ade7d8f"
+
+[[package]]
+name = "built-in-target"
+version = "0.1.0"
+dependencies = [
+ "bootloader",
+ "x86_64",
+]
+
+[[package]]
+name = "rustversion"
+version = "1.0.22"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b39cdef0fa800fc44525c84ccb54a029961a8215f9619753635a9c0d2538d46d"
+
+[[package]]
+name = "volatile"
+version = "0.4.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "442887c63f2c839b346c192d047a7c87e73d0689c9157b00b53dcc27dd5ea793"
+
+[[package]]
+name = "x86_64"
+version = "0.14.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c101112411baafbb4bf8d33e4c4a80ab5b02d74d2612331c61e8192fc9710491"
+dependencies = [
+ "bit_field",
+ "bitflags",
+ "rustversion",
+ "volatile",
+]
diff --git a/example-kernel-built-in-target/Cargo.toml b/example-kernel-built-in-target/Cargo.toml
new file mode 100644
index 0000000..4664912
--- /dev/null
+++ b/example-kernel-built-in-target/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "example-kernel-built-in-target"
+version = "0.1.0"
+edition = "2018"
+
+[dependencies]
+bootloader = "0.9.7"
+x86_64 = "0.14.1"
diff --git a/example-kernel-built-in-target/rust-toolchain b/example-kernel-built-in-target/rust-toolchain
new file mode 100644
index 0000000..bf867e0
--- /dev/null
+++ b/example-kernel-built-in-target/rust-toolchain
@@ -0,0 +1 @@
+nightly
diff --git a/example-kernel-built-in-target/src/main.rs b/example-kernel-built-in-target/src/main.rs
new file mode 100644
index 0000000..f3a34b9
--- /dev/null
+++ b/example-kernel-built-in-target/src/main.rs
@@ -0,0 +1,22 @@
+#![no_std]
+#![no_main]
+
+use core::panic::PanicInfo;
+
+#[panic_handler]
+fn panic(_info: &PanicInfo) -> ! {
+    loop {}
+}
+
+#[no_mangle]
+pub extern "C" fn _start() -> ! {
+    unsafe { exit_qemu(); }
+    loop {}
+}
+
+unsafe fn exit_qemu() {
+    use x86_64::instructions::port::Port;
+
+    let mut port = Port::<u32>::new(0xf4);
+    port.write(51); // exit code is (51 << 1) | 1 = 103
+}