Add print* macros; Better panic handler

src/main.rs

@@ -8,6 +8,8 @@ use multiboot2;
 use spin::*;
 use talc::*;
 
+mod print;
+
 static mut START_ARENA: [u8; 10000] = [0; 10000];
 
 #[global_allocator]
@@ -15,7 +17,11 @@ static ALLOCATOR: Talck<spin::Mutex<()>, ClaimOnOom> =
     Talc::new(unsafe { ClaimOnOom::new(Span::from_const_array(core::ptr::addr_of!(START_ARENA))) })
         .lock();
 
-fn main() {}
+#[no_mangle]
+pub extern "C" fn main() -> u32 {
+    println!("{}!", "It works");
+    0
+}
 
 pub fn kernel_entry(mbi_magic: u32, mbi_ptr: u32) {
     if mbi_magic == multiboot2::MAGIC {
@@ -23,7 +29,12 @@ pub fn kernel_entry(mbi_magic: u32, mbi_ptr: u32) {
     };
 }
 
+extern "C" {
+    fn exit(status: i32) -> !;
+}
+
 #[panic_handler]
 fn panic(info: &PanicInfo) -> ! {
-    loop {}
+    println!("{}", info);
+    unsafe { exit(1) }
 }

src/print.rs

@@ -0,0 +1,46 @@
+use core::ffi::c_void;
+use core::fmt;
+
+extern "C" {
+    fn write(fildes: i32, buf: *const c_void, nbyte: usize);
+}
+
+pub fn write_string(s: &str) {
+    unsafe {
+        write(1, s.as_ptr() as *const c_void, s.len());
+    }
+}
+
+pub struct Writer;
+
+impl fmt::Write for Writer {
+    fn write_str(&mut self, s: &str) -> Result<(), fmt::Error> {
+        write_string(s);
+        Ok(())
+    }
+}
+
+#[allow(unused)]
+pub fn print(args: fmt::Arguments) {
+    use fmt::Write;
+    Writer {}.write_fmt(args).unwrap();
+}
+
+#[macro_export]
+macro_rules! print {
+    ($($arg:tt)*) => {{
+        $crate::print::print(format_args!($($arg)*));
+    }}
+}
+
+#[macro_export]
+macro_rules! println {
+    () => {{
+        print!("\n");
+    }};
+
+    ($($arg:tt)*) => {{
+        print!("{}\n", format_args!($($arg)*));
+    }}
+}
+