[wasm] Enable guards on 64-bit systems.

R=eholk@chromium.org

Bug: 
Change-Id: Ia099cf085510da50a87b9f999020d6a66d6eab20
Reviewed-on: https://chromium-review.googlesource.com/838250
Commit-Queue: Brad Nelson <bradnelson@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Eric Holk <eholk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50300}

src/wasm/module-compiler.cc

@@ -3174,7 +3174,14 @@ Handle<JSArrayBuffer> InstanceBuilder::AllocateMemory(uint32_t num_pages) {
     thrower_->RangeError("Out of memory: wasm memory too large");
     return Handle<JSArrayBuffer>::null();
   }
+#if V8_TARGET_ARCH_64_BIT && !defined(THREAD_SANITIZER) && \
+    !defined(LEAK_SANITIZER) && !defined(V8_USE_ADDRESS_SANITIZER)
+  // TODO(eholk): Enable sanitizers once we have back-pressure.
+  // Always turn on guard regions in 64-bit.
+  const bool enable_guard_regions = true;
+#else
   const bool enable_guard_regions = use_trap_handler();
+#endif
   const bool is_shared_memory =
       module_->has_shared_memory && i::FLAG_experimental_wasm_threads;
   Handle<JSArrayBuffer> mem_buffer = NewArrayBuffer(

src/wasm/wasm-js.cc

@@ -600,8 +600,15 @@ void WebAssemblyMemory(const v8::FunctionCallbackInfo<v8::Value>& args) {
 
   size_t size = static_cast<size_t>(i::wasm::WasmModule::kPageSize) *
                 static_cast<size_t>(initial);
+#if V8_TARGET_ARCH_64_BIT && !defined(THREAD_SANITIZER) && \
+    !defined(LEAK_SANITIZER) && !defined(V8_USE_ADDRESS_SANITIZER)
+  // TODO(eholk): Enable sanitizers once we have back-pressure.
+  // Always turn on guard regions in 64-bit.
+  const bool enable_guard_regions = true;
+#else
   const bool enable_guard_regions =
       internal::trap_handler::IsTrapHandlerEnabled();
+#endif
   i::Handle<i::JSArrayBuffer> buffer = i::wasm::NewArrayBuffer(
       i_isolate, size, enable_guard_regions,
       is_shared_memory ? i::SharedFlag::kShared : i::SharedFlag::kNotShared);

src/wasm/wasm-objects.cc

@@ -369,8 +369,17 @@ Handle<JSArrayBuffer> GrowMemoryBuffer(Isolate* isolate,
   if (old_pages > maximum_pages || pages > maximum_pages - old_pages) {
     return Handle<JSArrayBuffer>::null();
   }
+#if V8_TARGET_ARCH_64_BIT && !defined(THREAD_SANITIZER) && \
+    !defined(LEAK_SANITIZER) && !defined(V8_USE_ADDRESS_SANITIZER)
+  // TODO(eholk): Enable sanitizers once we have back-pressure.
+  // Always turn on guard regions in 64-bit.
+  // But allow for previously unguarded memory for some cctests.
+  const bool enable_guard_regions =
+      old_buffer.is_null() ? true : old_buffer->has_guard_region();
+#else
   const bool enable_guard_regions =
       old_buffer.is_null() ? use_trap_handler : old_buffer->has_guard_region();
+#endif
   size_t new_size =
       static_cast<size_t>(old_pages + pages) * WasmModule::kPageSize;
   if (new_size > FLAG_wasm_max_mem_pages * WasmModule::kPageSize ||