1 files changed, 16 insertions, 0 deletions
diff --git a/core/cortex-m0/__builtin.c b/core/cortex-m0/__builtin.c
new file mode 100644
index 0000000000..4bf495a011
--- /dev/null
+++ b/core/cortex-m0/__builtin.c
@@ -0,0 +1,16 @@
+/* Copyright 2019 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "common.h"
+
+/*
+ * __builtin_ffs:
+ * Returns one plus the index of the least significant 1-bit of x,
+ * or if x is zero, returns zero.
+ */
+int __keep __ffssi2(int x)
+{
+	return 32 - __builtin_clz(x & -x);
+}