Reland "[wasm][eh] Add WebAssembly.Tag.type"

This is a reland of 4cc547c7

Change: prevent a memcpy to nullptr by skipping the call to copy_out()
when the length is zero.

Original change's description:
> [wasm][eh] Add WebAssembly.Tag.type
>
> R=ahaas@chromium.org
>
> Bug: v8:8091
> Change-Id: Id069ffbf76bf836b613287788b1b1fccbb577475
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3021173
> Reviewed-by: Andreas Haas <ahaas@chromium.org>
> Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
> Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#75815}

Bug: v8:8091
Change-Id: I22f400b6e36d1322a4eabd20a68b4bdd70d61377
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3041436Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75847}

src/wasm/wasm-js.cc

@@ -1466,7 +1466,7 @@ void WebAssemblyTag(const v8::FunctionCallbackInfo<v8::Value>& args) {
   // Set the tag index to 0. It is only used for debugging purposes, and has no
   // meaningful value when declared outside of a wasm module.
   auto tag = i::WasmExceptionTag::New(i_isolate, 0);
-  i::Handle<i::Object> exception =
+  i::Handle<i::JSObject> exception =
       i::WasmExceptionObject::New(i_isolate, &sig, tag);
   args.GetReturnValue().Set(Utils::ToLocal(exception));
 }
@@ -1621,6 +1621,7 @@ constexpr const char* kName_WasmGlobalObject = "WebAssembly.Global";
 constexpr const char* kName_WasmMemoryObject = "WebAssembly.Memory";
 constexpr const char* kName_WasmInstanceObject = "WebAssembly.Instance";
 constexpr const char* kName_WasmTableObject = "WebAssembly.Table";
+constexpr const char* kName_WasmExceptionObject = "WebAssembly.Tag";
 
 #define EXTRACT_THIS(var, WasmType)                                  \
   i::Handle<i::WasmType> var;                                        \
@@ -1852,6 +1853,27 @@ void WebAssemblyMemoryType(const v8::FunctionCallbackInfo<v8::Value>& args) {
   args.GetReturnValue().Set(Utils::ToLocal(type));
 }
 
+// WebAssembly.Tag.type() -> FunctionType
+void WebAssemblyTagType(const v8::FunctionCallbackInfo<v8::Value>& args) {
+  v8::Isolate* isolate = args.GetIsolate();
+  HandleScope scope(isolate);
+  i::Isolate* i_isolate = reinterpret_cast<i::Isolate*>(isolate);
+  ScheduledErrorThrower thrower(i_isolate, "WebAssembly.Tag.type()");
+
+  EXTRACT_THIS(tag, WasmExceptionObject);
+  if (thrower.error()) return;
+
+  int n = tag->serialized_signature().length();
+  std::vector<i::wasm::ValueType> data(n);
+  if (n > 0) {
+    tag->serialized_signature().copy_out(0, data.data(), n);
+  }
+  const i::wasm::FunctionSig sig{0, data.size(), data.data()};
+  constexpr bool kForException = true;
+  auto type = i::wasm::GetTypeForFunction(i_isolate, &sig, kForException);
+  args.GetReturnValue().Set(Utils::ToLocal(type));
+}
+
 void WebAssemblyGlobalGetValueCommon(
     const v8::FunctionCallbackInfo<v8::Value>& args, const char* name) {
   v8::Isolate* isolate = args.GetIsolate();
@@ -2290,10 +2312,14 @@ void WasmJs::Install(Isolate* isolate, bool exposed_on_global_object) {
     Handle<JSFunction> exception_constructor =
         InstallConstructorFunc(isolate, webassembly, "Tag", WebAssemblyTag);
     context->set_wasm_exception_constructor(*exception_constructor);
+
     SetDummyInstanceTemplate(isolate, exception_constructor);
     JSFunction::EnsureHasInitialMap(exception_constructor);
     Handle<JSObject> exception_proto(
         JSObject::cast(exception_constructor->instance_prototype()), isolate);
+    if (enabled_features.has_type_reflection()) {
+      InstallFunc(isolate, exception_proto, "type", WebAssemblyTagType, 0);
+    }
     Handle<Map> exception_map = isolate->factory()->NewMap(
         i::WASM_EXCEPTION_OBJECT_TYPE, WasmExceptionObject::kHeaderSize);
     JSFunction::SetInitialMap(isolate, exception_constructor, exception_map,
@@ -2393,6 +2419,9 @@ void WasmJs::InstallConditionalFeatures(Isolate* isolate,
     JSFunction::EnsureHasInitialMap(exception_constructor);
     Handle<JSObject> exception_proto(
         JSObject::cast(exception_constructor->instance_prototype()), isolate);
+    if (enabled_features.has_type_reflection()) {
+      InstallFunc(isolate, exception_proto, "type", WebAssemblyTagType, 0);
+    }
     Handle<Map> exception_map = isolate->factory()->NewMap(
         i::WASM_EXCEPTION_OBJECT_TYPE, WasmExceptionObject::kHeaderSize);
     JSFunction::SetInitialMap(isolate, exception_constructor, exception_map,

src/wasm/wasm-module.cc

@@ -237,7 +237,8 @@ Handle<String> ToValueTypeString(Isolate* isolate, ValueType type) {
 }
 }  // namespace
 
-Handle<JSObject> GetTypeForFunction(Isolate* isolate, const FunctionSig* sig) {
+Handle<JSObject> GetTypeForFunction(Isolate* isolate, const FunctionSig* sig,
+                                    bool for_exception) {
   Factory* factory = isolate->factory();
 
   // Extract values for the {ValueType[]} arrays.
@@ -248,23 +249,29 @@ Handle<JSObject> GetTypeForFunction(Isolate* isolate, const FunctionSig* sig) {
     Handle<String> type_value = ToValueTypeString(isolate, type);
     param_values->set(param_index++, *type_value);
   }
-  int result_index = 0;
-  int result_count = static_cast<int>(sig->return_count());
-  Handle<FixedArray> result_values = factory->NewFixedArray(result_count);
-  for (ValueType type : sig->returns()) {
-    Handle<String> type_value = ToValueTypeString(isolate, type);
-    result_values->set(result_index++, *type_value);
-  }
 
   // Create the resulting {FunctionType} object.
   Handle<JSFunction> object_function = isolate->object_function();
   Handle<JSObject> object = factory->NewJSObject(object_function);
   Handle<JSArray> params = factory->NewJSArrayWithElements(param_values);
-  Handle<JSArray> results = factory->NewJSArrayWithElements(result_values);
   Handle<String> params_string = factory->InternalizeUtf8String("parameters");
   Handle<String> results_string = factory->InternalizeUtf8String("results");
   JSObject::AddProperty(isolate, object, params_string, params, NONE);
-  JSObject::AddProperty(isolate, object, results_string, results, NONE);
+
+  // Now add the result types if needed.
+  if (for_exception) {
+    DCHECK_EQ(sig->returns().size(), 0);
+  } else {
+    int result_index = 0;
+    int result_count = static_cast<int>(sig->return_count());
+    Handle<FixedArray> result_values = factory->NewFixedArray(result_count);
+    for (ValueType type : sig->returns()) {
+      Handle<String> type_value = ToValueTypeString(isolate, type);
+      result_values->set(result_index++, *type_value);
+    }
+    Handle<JSArray> results = factory->NewJSArrayWithElements(result_values);
+    JSObject::AddProperty(isolate, object, results_string, results, NONE);
+  }
 
   return object;
 }

src/wasm/wasm-module.h

@@ -472,7 +472,8 @@ std::ostream& operator<<(std::ostream& os, const WasmFunctionName& name);
 V8_EXPORT_PRIVATE bool IsWasmCodegenAllowed(Isolate* isolate,
                                             Handle<Context> context);
 
-Handle<JSObject> GetTypeForFunction(Isolate* isolate, const FunctionSig* sig);
+Handle<JSObject> GetTypeForFunction(Isolate* isolate, const FunctionSig* sig,
+                                    bool for_exception = false);
 Handle<JSObject> GetTypeForGlobal(Isolate* isolate, bool is_mutable,
                                   ValueType type);
 Handle<JSObject> GetTypeForMemory(Isolate* isolate, uint32_t min_size,

test/mjsunit/wasm/exceptions-type-reflection.js

+// Copyright 2021 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --experimental-wasm-eh --experimental-wasm-type-reflection
+
+load("test/mjsunit/wasm/wasm-module-builder.js");
+
+let testcases = [
+{types: {parameters:[]}, sig: kSig_v_v},
+{types: {parameters:["i32"]}, sig: kSig_v_i},
+{types: {parameters:["i64"]}, sig: kSig_v_l},
+{types: {parameters:["f64", "f64", "i32"]}, sig: kSig_v_ddi},
+{types: {parameters:["f32"]}, sig: kSig_v_f},
+];
+
+(function TestExport() {
+  print(arguments.callee.name);
+  let builder = new WasmModuleBuilder();
+
+  testcases.forEach(function(expected, i) {
+    let except = builder.addException(expected.sig);
+    builder.addExportOfKind("ex" + i, kExternalException, except);
+  });
+
+  let instance = builder.instantiate();
+  testcases.forEach(function(expected, i) {
+    assertEquals(instance.exports["ex" + i].type(), expected.types);
+  });
+})();
+
+(function TestImportExport() {
+  print(arguments.callee.name);
+
+  let builder = new WasmModuleBuilder();
+  let imports = {m: {}};
+
+  testcases.forEach(function(expected, i) {
+    let t = new WebAssembly.Tag(expected.types);
+    let index = builder.addImportedException("m", "ex" + i, expected.sig);
+    builder.addExportOfKind("ex" + i, kExternalException, index);
+    imports.m["ex" + i] = t;
+  });
+
+  let instance = builder.instantiate(imports);
+  testcases.forEach(function(expected, i) {
+    assertEquals(instance.exports["ex" + i].type(), expected.types);
+  })
+})();