Do some initialization. (Just in case.)

boot.c

@@ -4,6 +4,11 @@ HEDLEY_ALWAYS_INLINE void putchar(char);
 HEDLEY_ALWAYS_INLINE void write(char*);
 
 void _start(void) {
+	__asm__ volatile (
+		"movl $0x8000, %esp\n"
+		"ljmp $(0),$(start)\n"
+	"start:\n"
+	);
 	write("Hello World!\r\n\0");
 	while(1)
 		;