Index: src/synch/semaphore.c
===================================================================
--- src/synch/semaphore.c	(revision e3f41b62d5b503ff9a3beb8ab121cc305d5f2fd7)
+++ src/synch/semaphore.c	(revision ff9f858e06ba17699b8a6270f956c6f6bb1efe94)
@@ -31,4 +31,5 @@
 #include <synch/waitq.h>
 #include <synch/spinlock.h>
+#include <arch/asm.h>
 
 void semaphore_initialize(semaphore_t *s, int val)