Update page_load to create and use the shared read-only pages of executables, w/ G

src/threads/thread.c

@@ -134,9 +134,12 @@ thread_start (void)
                   t))
     PANIC ("Failed to initialise child results table for main thread.");
 
+  /* Initialise the shared files table and lock. */
   if (!hash_init (&shared_files, shared_file_hash, shared_file_less, NULL))
     PANIC ("Failed to initialise shared pages table.");
 
+  lock_init (&shared_files_lock);
+
   /* Create the idle thread. */
   struct semaphore idle_started;
   sema_init (&idle_started, 0);