diff --git a/defs.h b/defs.h
index a08690f7d09a7d5ed47637f8ef0534c6586d01eb..11f94fbbc910ebaeb0f84a5b25eb7adbc3b99515 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);