Boot to C in 64-bit long mode

include/console.h

@@ -0,0 +1,27 @@
+/* Nadir early console: VGA text-mode driver.
+ *
+ * Writes straight to the VGA text buffer at 0xB8000, which the stage-2
+ * page tables identity-map. Runs in 64-bit long mode at Ring 0 (CPL 0);
+ * no faults are possible beyond a programming bug. There is no IDT yet,
+ * so a wild pointer here triple-faults the machine.
+ */
+
+#ifndef NADIR_CONSOLE_H
+#define NADIR_CONSOLE_H
+
+#include <stdint.h>
+
+/* Clear the screen and park the cursor at the top left. */
+void console_clear(void);
+
+/* Print one character. '\n' moves to the start of the next line; the
+ * screen scrolls up when the cursor runs past the last line. */
+void console_putchar(char c);
+
+/* Print a NUL-terminated string. */
+void console_puts(const char *s);
+
+/* Print a 64-bit value as 0x-prefixed, zero-padded hexadecimal. */
+void console_puthex64(uint64_t value);
+
+#endif /* NADIR_CONSOLE_H */