+;; At compile-time we load the module given by the environment variable
+;; OS_INCLUDE. This module should define the following macros:
+;;
+;; Each of these functions should preserve the value of RSI and RSP. They may
+;; use other registers as they like.
+;;
+;; os_initialize
+;; Called at initialization.
+;;
+;; os_print_string
+;; Takes a string buffer in RCX and the length in RDX, and prints the string
+;; to the console.
+;;
+;; os_read_char
+;; Wait for the user to type a key, and then put the corresponding ASCII byte
+;; into the buffer pointed to by RCX.
+;;
+;; os_terminate
+;; Shut down the system.