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-rw-r--r--core/cortex-m0/__builtin.c16
-rw-r--r--core/cortex-m0/build.mk2
2 files changed, 17 insertions, 1 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);
+}
diff --git a/core/cortex-m0/build.mk b/core/cortex-m0/build.mk
index f199b09361..a314976bce 100644
--- a/core/cortex-m0/build.mk
+++ b/core/cortex-m0/build.mk
@@ -21,7 +21,7 @@ LDFLAGS_EXTRA+=-flto
endif
core-y=cpu.o init.o thumb_case.o div.o lmul.o ldivmod.o mula.o uldivmod.o
-core-y+=vecttable.o
+core-y+=vecttable.o __builtin.o
core-$(CONFIG_COMMON_PANIC_OUTPUT)+=panic.o
core-$(CONFIG_COMMON_RUNTIME)+=switch.o task.o