[wasm] Refactor function name table and lookup

The function name table will now always be set; a CHECK will fail if
the length would exceed the integer range.
Also, the resolution of undefined function names to "<WASM UNNAMED>" is
moved over to the wasm side.

R=titzer@chromium.org

Review-Url: https://codereview.chromium.org/2057523002
Cr-Commit-Position: refs/heads/master@{#36918}

src/isolate.cc

@@ -605,16 +605,9 @@ class CaptureStackTraceHelper {
         factory()->NewJSObject(isolate_->object_function());
 
     if (!function_key_.is_null()) {
-      Object* wasm_object = frame->wasm_obj();
-      Handle<String> name;
-      if (!wasm_object->IsUndefined(isolate_)) {
-        Handle<JSObject> wasm = handle(JSObject::cast(wasm_object));
-        wasm::GetWasmFunctionName(wasm, frame->function_index())
-            .ToHandle(&name);
-      }
-      if (name.is_null()) {
-        name = isolate_->factory()->NewStringFromStaticChars("<WASM UNNAMED>");
-      }
+      Handle<String> name = wasm::GetWasmFunctionName(
+          isolate_, handle(frame->wasm_obj(), isolate_),
+          frame->function_index());
       JSObject::AddProperty(stack_frame, function_key_, name, NONE);
     }
     // Encode the function index as line number.

src/messages.cc

@@ -205,10 +205,8 @@ Handle<Object> CallSite::GetFileName() {
 
 Handle<Object> CallSite::GetFunctionName() {
   if (IsWasm()) {
-    MaybeHandle<String> name =
-        wasm::GetWasmFunctionName(wasm_obj_, wasm_func_index_);
-    if (name.is_null()) return isolate_->factory()->null_value();
-    return name.ToHandleChecked();
+    return wasm::GetWasmFunctionNameOrNull(isolate_, wasm_obj_,
+                                           wasm_func_index_);
   }
   Handle<String> result = JSFunction::GetName(fun_);
   if (result->length() != 0) return result;

src/wasm/wasm-function-name-table.cc

@@ -18,9 +18,7 @@ namespace wasm {
 // integer entry is the negative offset of the next function name.
 // After these N+1 integer entries, the second part begins, which holds a
 // concatenation of all function names.
-//
-// Returns undefined if the array length would not fit in an integer value.
-Handle<Object> BuildFunctionNamesTable(Isolate* isolate,
+Handle<ByteArray> BuildFunctionNamesTable(Isolate* isolate,
                                           const WasmModule* module) {
   uint64_t func_names_length = 0;
   for (auto& func : module->functions) func_names_length += func.name_length;
@@ -28,13 +26,11 @@ Handle<Object> BuildFunctionNamesTable(Isolate* isolate,
   int current_offset = (num_funcs_int + 1) * kIntSize;
   uint64_t total_array_length = current_offset + func_names_length;
   int total_array_length_int = static_cast<int>(total_array_length);
-  // Check for overflow. Just skip function names if it happens.
-  if (total_array_length_int != total_array_length || num_funcs_int < 0 ||
-      num_funcs_int != module->functions.size())
-    return isolate->factory()->undefined_value();
+  // Check for overflow.
+  CHECK(total_array_length_int == total_array_length && num_funcs_int >= 0 &&
+        num_funcs_int == module->functions.size());
   Handle<ByteArray> func_names_array =
       isolate->factory()->NewByteArray(total_array_length_int, TENURED);
-  if (func_names_array.is_null()) return isolate->factory()->undefined_value();
   func_names_array->set_int(0, num_funcs_int);
   int func_index = 0;
   for (const WasmFunction& fun : module->functions) {

src/wasm/wasm-function-name-table.h

@@ -16,8 +16,7 @@ namespace wasm {
 struct WasmModule;
 
 // Encode all function names of the WasmModule into one ByteArray.
-// Returns undefined if the array length would not fit in an integer value.
-Handle<Object> BuildFunctionNamesTable(Isolate* isolate,
+Handle<ByteArray> BuildFunctionNamesTable(Isolate* isolate,
                                           const WasmModule* module);
 
 // Extract the function name for the given func_index from the function name

src/wasm/wasm-module.cc

@@ -837,10 +837,9 @@ MaybeHandle<JSObject> WasmModule::Instantiate(
   // Attach an array with function names and an array with offsets into that
   // first array.
   //-------------------------------------------------------------------------
-  {
-    Handle<Object> arr = BuildFunctionNamesTable(isolate, module_env.module);
-    instance.js_object->SetInternalField(kWasmFunctionNamesArray, *arr);
-  }
+  instance.js_object->SetInternalField(
+      kWasmFunctionNamesArray,
+      *BuildFunctionNamesTable(isolate, module_env.module));
 
   code_stats.Report();
 
@@ -983,14 +982,30 @@ int32_t CompileAndRunWasmModule(Isolate* isolate, const WasmModule* module) {
   return -1;
 }
 
-MaybeHandle<String> GetWasmFunctionName(Handle<JSObject> wasm,
+Handle<Object> GetWasmFunctionNameOrNull(Isolate* isolate, Handle<Object> wasm,
                                          uint32_t func_index) {
-  DCHECK(IsWasmObject(wasm));
-  Object* func_names_arr_obj = wasm->GetInternalField(kWasmFunctionNamesArray);
-  Isolate* isolate = wasm->GetIsolate();
-  if (func_names_arr_obj->IsUndefined(isolate)) return Handle<String>::null();
-  return GetWasmFunctionNameFromTable(
-      handle(ByteArray::cast(func_names_arr_obj), isolate), func_index);
+  if (!wasm->IsUndefined()) {
+    Handle<ByteArray> func_names_arr_obj(
+        ByteArray::cast(Handle<JSObject>::cast(wasm)->GetInternalField(
+            kWasmFunctionNamesArray)),
+        isolate);
+    // TODO(clemens): Extract this from the module bytes; skip whole function
+    // name table.
+    Handle<Object> name;
+    if (GetWasmFunctionNameFromTable(func_names_arr_obj, func_index)
+            .ToHandle(&name)) {
+      return name;
+    }
+  }
+  return isolate->factory()->null_value();
+}
+
+Handle<String> GetWasmFunctionName(Isolate* isolate, Handle<Object> wasm,
+                                   uint32_t func_index) {
+  Handle<Object> name_or_null =
+      GetWasmFunctionNameOrNull(isolate, wasm, func_index);
+  if (!name_or_null->IsNull()) return Handle<String>::cast(name_or_null);
+  return isolate->factory()->NewStringFromStaticChars("<WASM UNNAMED>");
 }
 
 bool IsWasmObject(Handle<JSObject> object) {
@@ -998,9 +1013,7 @@ bool IsWasmObject(Handle<JSObject> object) {
   return object->GetInternalFieldCount() == kWasmModuleInternalFieldCount &&
          object->GetInternalField(kWasmModuleCodeTable)->IsFixedArray() &&
          object->GetInternalField(kWasmMemArrayBuffer)->IsJSArrayBuffer() &&
-         (object->GetInternalField(kWasmFunctionNamesArray)->IsByteArray() ||
-          object->GetInternalField(kWasmFunctionNamesArray)
-              ->IsUndefined(object->GetIsolate()));
+         object->GetInternalField(kWasmFunctionNamesArray)->IsByteArray();
 }
 
 }  // namespace wasm

src/wasm/wasm-module.h

@@ -5,11 +5,10 @@
 #ifndef V8_WASM_MODULE_H_
 #define V8_WASM_MODULE_H_
 
-#include "src/wasm/wasm-opcodes.h"
-#include "src/wasm/wasm-result.h"
-
 #include "src/api.h"
 #include "src/handles.h"
+#include "src/wasm/wasm-opcodes.h"
+#include "src/wasm/wasm-result.h"
 
 namespace v8 {
 namespace internal {
@@ -318,10 +317,16 @@ int32_t CompileAndRunWasmModule(Isolate* isolate, const byte* module_start,
 // given decoded module.
 int32_t CompileAndRunWasmModule(Isolate* isolate, const WasmModule* module);
 
+// Extract a function name from the given wasm object.
+// Returns "<WASM UNNAMED>" if the function is unnamed or the name is not a
+// valid UTF-8 string.
+Handle<String> GetWasmFunctionName(Isolate* isolate, Handle<Object> wasm,
+                                   uint32_t func_index);
+
 // Extract a function name from the given wasm object.
 // Returns a null handle if the function is unnamed or the name is not a valid
 // UTF-8 string.
-MaybeHandle<String> GetWasmFunctionName(Handle<JSObject> wasm,
+Handle<Object> GetWasmFunctionNameOrNull(Isolate* isolate, Handle<Object> wasm,
                                          uint32_t func_index);
 
 // Check whether the given object is a wasm object.