Add an example kernel that uses the built-in x86_64-unknown-none target

.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

example-kernel-built-in-target/.cargo/config.toml

@@ -0,0 +1,2 @@
+[unstable]
+build-std = ["core", "compiler_builtins"]

example-kernel-built-in-target/.gitignore

@@ -0,0 +1 @@
+/target/

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"

example-kernel-built-in-target/rust-toolchain

@@ -0,0 +1 @@
+nightly

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
+}