add x86 64
diff --git a/src/lib9/getcallerpc-x86_64.c b/src/lib9/getcallerpc-x86_64.c
new file mode 100644
index 0000000..1367370
--- /dev/null
+++ b/src/lib9/getcallerpc-x86_64.c
@@ -0,0 +1,7 @@
+#include <lib9.h>
+
+ulong
+getcallerpc(void *x)
+{
+	return (((ulong*)(x))[-1]);
+}