+ struct semaphore dead; /* 1=child alive, 0=child dead. */
+ };
+
- void thread_init (void);
- void thread_start (void);
- void thread_tick (void);
+ /* If false (default), use round-robin scheduler.
+ If true, use multi-level feedback queue scheduler.
+ Controlled by kernel command-line options "-o mlfqs".
Index: src/userprog/exception.c
diff -u src/userprog/exception.c~ src/userprog/exception.c
--- src/userprog/exception.c~
diff -u src/userprog/syscall.c~ src/userprog/syscall.c
--- src/userprog/syscall.c~
+++ src/userprog/syscall.c
-@@ -1,20 +1,483 @@
+@@ -1,20 +1,486 @@
#include "userprog/syscall.h"
#include <stdio.h>
+#include <string.h>
+ for (length = 0; length < PGSIZE; length++)
+ {
+ if (us >= (char *) PHYS_BASE || !get_user (ks + length, us++))
-+ thread_exit ();
++ {
++ palloc_free_page (ks);
++ thread_exit ();
++ }
+
+ if (ks[length] == '\0')
+ return ks;