Index: compiler-rt/trunk/lib/cfi/cfi.cc
===================================================================
--- compiler-rt/trunk/lib/cfi/cfi.cc
+++ compiler-rt/trunk/lib/cfi/cfi.cc
@@ -132,7 +132,10 @@
 void ShadowBuilder::AddUnchecked(uptr begin, uptr end) {
   uint16_t *shadow_begin = MemToShadow(begin, shadow_);
   uint16_t *shadow_end = MemToShadow(end - 1, shadow_) + 1;
-  memset(shadow_begin, kUncheckedShadow,
+  // memset takes a byte, so our unchecked shadow value requires both bytes to
+  // be the same. Make sure we're ok during compilation.
+  static_assert(kUncheckedShadow & 0xff == ((kUncheckedShadow >> 8) & 0xff));
+  memset(shadow_begin, kUncheckedShadow & 0xff,
          (shadow_end - shadow_begin) * sizeof(*shadow_begin));
 }