1 files changed, 21 insertions, 1 deletions
diff --git a/src/interp/interp-math.h b/src/interp/interp-math.h
index ccbc9cd6..c3876810 100644
--- a/src/interp/interp-math.h
+++ b/src/interp/interp-math.h
@@ -80,7 +80,6 @@ template <typename T> T WABT_VECTORCALL IntNot(T val) { return ~val; }
 template <typename T> T WABT_VECTORCALL IntNeg(T val) { return ~val + 1; }
 template <typename T> T WABT_VECTORCALL Add(T lhs, T rhs) { return CanonNaN(lhs + rhs); }
 template <typename T> T WABT_VECTORCALL Sub(T lhs, T rhs) { return CanonNaN(lhs - rhs); }
-template <typename T> T WABT_VECTORCALL Mul(T lhs, T rhs) { return CanonNaN(lhs * rhs); }
 template <typename T> T WABT_VECTORCALL IntAnd(T lhs, T rhs) { return lhs & rhs; }
 template <typename T> T WABT_VECTORCALL IntOr(T lhs, T rhs) { return lhs | rhs; }
 template <typename T> T WABT_VECTORCALL IntXor(T lhs, T rhs) { return lhs ^ rhs; }
@@ -92,6 +91,27 @@ template <typename T> T WABT_VECTORCALL IntAndNot(T lhs, T rhs) { return lhs & ~
 template <typename T> T WABT_VECTORCALL IntAvgr(T lhs, T rhs) { return (lhs + rhs + 1) / 2; }
 template <typename T> T WABT_VECTORCALL Xchg(T lhs, T rhs) { return rhs; }
 
+// Because of the integer promotion rules [1], any value of a type T which is
+// smaller than `int` will be converted to an `int`, as long as `int` can hold
+// any value of type T.
+//
+// So type `u16` will be promoted to `int`, since all values can be stored in
+// an int. Unfortunately, the product of two `u16` values cannot always be
+// stored in an `int` (e.g. 65535 * 65535). This triggers an error in UBSan.
+//
+// As a result, we make sure to promote the type ahead of time for `u16`. Note
+// that this isn't a problem for any other unsigned types.
+//
+// [1]; https://en.cppreference.com/w/cpp/language/implicit_conversion#Integral_promotion
+template <typename T> struct PromoteMul { using type = T; };
+template <> struct PromoteMul<u16> { using type = u32; };
+
+template <typename T>
+T WABT_VECTORCALL Mul(T lhs, T rhs) {
+  using U = typename PromoteMul<T>::type;
+  return CanonNaN(U(lhs) * U(rhs));
+}
+
 template <typename T> struct Mask { using Type = T; };
 template <> struct Mask<f32> { using Type = u32; };
 template <> struct Mask<f64> { using Type = u64; };