4 files changed, 62 insertions, 1 deletions
diff --git a/src/support/CMakeLists.txt b/src/support/CMakeLists.txt
index 54ab8b08f..a97863107 100644
--- a/src/support/CMakeLists.txt
+++ b/src/support/CMakeLists.txt
@@ -8,5 +8,6 @@ set(support_SOURCES
   path.cpp
   safe_integer.cpp
   threads.cpp
+  utilities.cpp
 )
 add_library(support OBJECT ${support_SOURCES})
diff --git a/src/support/bits.cpp b/src/support/bits.cpp
index c237807ee..2489a0249 100644
--- a/src/support/bits.cpp
+++ b/src/support/bits.cpp
@@ -17,6 +17,7 @@
 #define wasm_support_bits_definitions
 #include "support/bits.h"
 #include "../compiler-support.h"
+#include "support/utilities.h"
 
 namespace wasm {
 
@@ -91,7 +92,7 @@ template<> int CountLeadingZeroes<uint64_t>(uint64_t v) {
 uint32_t Log2(uint32_t v) {
   switch (v) {
     default:
-      WASM_UNREACHABLE();
+      WASM_UNREACHABLE("invalid value");
     case 1:
       return 0;
     case 2:
diff --git a/src/support/utilities.cpp b/src/support/utilities.cpp
new file mode 100644
index 000000000..ea426df9c
--- /dev/null
+++ b/src/support/utilities.cpp
@@ -0,0 +1,45 @@
+/*
+ * Copyright 2019 WebAssembly Community Group participants
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "utilities.h"
+
+#include <cassert>
+#include <cstdlib>
+#include <iostream>
+
+#if __has_feature(address_sanitizer) || defined(__SANITIZE_ADDRESS__)
+#include "sanitizer/common_interface_defs.h"
+#endif
+
+void wasm::handle_unreachable(const char* msg,
+                              const char* file,
+                              unsigned line) {
+#ifndef NDEBUG
+  if (msg) {
+    std::cerr << msg << "\n";
+  }
+  std::cerr << "UNREACHABLE executed";
+  if (file) {
+    std::cerr << " at " << file << ":" << line;
+  }
+  std::cerr << "!\n";
+#if __has_feature(address_sanitizer) || defined(__SANITIZE_ADDRESS__)
+  __sanitizer_print_stack_trace();
+  __builtin_trap();
+#endif
+#endif
+  abort();
+}
diff --git a/src/support/utilities.h b/src/support/utilities.h
index 71d8ce2e0..5280fcb3b 100644
--- a/src/support/utilities.h
+++ b/src/support/utilities.h
@@ -74,6 +74,20 @@ public:
   }
 };
 
+WASM_NORETURN void handle_unreachable(const char* msg = nullptr,
+                                      const char* file = nullptr,
+                                      unsigned line = 0);
+
+// If control flow reaches the point of the WASM_UNREACHABLE(), the program is
+// undefined.
+#ifndef NDEBUG
+#define WASM_UNREACHABLE(msg) wasm::handle_unreachable(msg, __FILE__, __LINE__)
+#elif defined(WASM_BUILTIN_UNREACHABLE)
+#define WASM_UNREACHABLE(msg) WASM_BUILTIN_UNREACHABLE
+#else
+#define WASM_UNREACHABLE(msg) wasm::handle_unreachable()
+#endif
+
 } // namespace wasm
 
 #endif // wasm_support_utilities_h