diff --git a/defs.h b/defs.h
index a08690f..11f94fb 100644
--- a/defs.h
+++ b/defs.h
@@ -84,6 +84,7 @@ void initlock(struct spinlock*, char*);
 void acquire(struct spinlock*);
 void release(struct spinlock*);
 int holding(struct spinlock*);
+void getcallerpcs(void*, uint*);
 
 // main.c
 void load_icode(struct proc*, uchar*, uint);