diff --git a/src/userprog/process.c b/src/userprog/process.c
index 49b9bd5..c9f6339 100644
--- a/src/userprog/process.c
+++ b/src/userprog/process.c
@@ -14,6 +14,7 @@
 #include "threads/flags.h"
 #include "threads/init.h"
 #include "threads/interrupt.h"
+#include "threads/synch.h"
 #include "threads/palloc.h"
 #include "threads/thread.h"
 #include "threads/vaddr.h"
@@ -88,7 +89,8 @@ start_process (void *file_name_)
 int
 process_wait (tid_t child_tid UNUSED) 
 {
-  return -1;
+  for (;;)
+    barrier ();
 }
 
 /* Free the current process's resources. */
@@ -451,7 +453,7 @@ setup_stack (void **esp)
     {
       success = install_page (((uint8_t *) PHYS_BASE) - PGSIZE, kpage, true);
       if (success)
-        *esp = PHYS_BASE;
+        *esp = PHYS_BASE - 12;
       else
         palloc_free_page (kpage);
     }