src/wasm/wasm-module.cc

// Copyright 2015 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.

#include "src/base/atomic-utils.h"
#include "src/macro-assembler.h"
#include "src/objects.h"
#include "src/property-descriptor.h"
#include "src/v8.h"

#include "src/simulator.h"

#include "src/wasm/ast-decoder.h"
#include "src/wasm/module-decoder.h"
#include "src/wasm/wasm-function-name-table.h"
#include "src/wasm/wasm-module.h"
#include "src/wasm/wasm-result.h"

#include "src/compiler/wasm-compiler.h"

namespace v8 {
namespace internal {
namespace wasm {

static const char* wasmSections[] = {
#define F(enumerator, order, string) string,
    FOR_EACH_WASM_SECTION_TYPE(F)
#undef F
        "<unknown>"  // entry for "Max"
};

static uint8_t wasmSectionsLengths[]{
#define F(enumerator, order, string) sizeof(string) - 1,
    FOR_EACH_WASM_SECTION_TYPE(F)
#undef F
        9  // entry for "Max"
};

static uint8_t wasmSectionsOrders[]{
#define F(enumerator, order, string) order,
    FOR_EACH_WASM_SECTION_TYPE(F)
#undef F
        0  // entry for "Max"
};

static_assert(sizeof(wasmSections) / sizeof(wasmSections[0]) ==
                  (size_t)WasmSection::Code::Max + 1,
              "expected enum WasmSection::Code to be monotonic from 0");

WasmSection::Code WasmSection::begin() { return (WasmSection::Code)0; }
WasmSection::Code WasmSection::end() { return WasmSection::Code::Max; }
WasmSection::Code WasmSection::next(WasmSection::Code code) {
  return (WasmSection::Code)(1 + (uint32_t)code);
}

const char* WasmSection::getName(WasmSection::Code code) {
  return wasmSections[(size_t)code];
}

size_t WasmSection::getNameLength(WasmSection::Code code) {
  return wasmSectionsLengths[(size_t)code];
}

int WasmSection::getOrder(WasmSection::Code code) {
  return wasmSectionsOrders[(size_t)code];
}

WasmSection::Code WasmSection::lookup(const byte* string, uint32_t length) {
  // TODO(jfb) Linear search, it may be better to do a common-prefix search.
  for (Code i = begin(); i != end(); i = next(i)) {
    if (getNameLength(i) == length && 0 == memcmp(getName(i), string, length)) {
      return i;
    }
  }
  return Code::Max;
}

std::ostream& operator<<(std::ostream& os, const WasmModule& module) {
  os << "WASM module with ";
  os << (module.min_mem_pages * module.kPageSize) << " min mem";
  os << (module.max_mem_pages * module.kPageSize) << " max mem";
  os << module.functions.size() << " functions";
  os << module.functions.size() << " globals";
  os << module.functions.size() << " data segments";
  return os;
}

std::ostream& operator<<(std::ostream& os, const WasmFunction& function) {
  os << "WASM function with signature " << *function.sig;

  os << " code bytes: "
     << (function.code_end_offset - function.code_start_offset);
  return os;
}

std::ostream& operator<<(std::ostream& os, const WasmFunctionName& pair) {
  os << "#" << pair.function_->func_index << ":";
  if (pair.function_->name_offset > 0) {
    if (pair.module_) {
      WasmName name = pair.module_->GetName(pair.function_->name_offset,
                                            pair.function_->name_length);
      os.write(name.start(), name.length());
    } else {
      os << "+" << pair.function_->func_index;
    }
  } else {
    os << "?";
  }
  return os;
}

// A helper class for compiling multiple wasm functions that offers
// placeholder code objects for calling functions that are not yet compiled.
class WasmLinker {
 public:
  WasmLinker(Isolate* isolate, size_t size)
      : isolate_(isolate), placeholder_code_(size), function_code_(size) {}

  // Get the code object for a function, allocating a placeholder if it has
  // not yet been compiled.
  Handle<Code> GetFunctionCode(uint32_t index) {
    DCHECK(index < function_code_.size());
    if (function_code_[index].is_null()) {
      // Create a placeholder code object and encode the corresponding index in
      // the {constant_pool_offset} field of the code object.
      // TODO(titzer): placeholder code objects are somewhat dangerous.
      byte buffer[] = {0, 0, 0, 0, 0, 0, 0, 0};  // fake instructions.
      CodeDesc desc = {buffer, 8, 8, 0, 0, nullptr};
      Handle<Code> code = isolate_->factory()->NewCode(
          desc, Code::KindField::encode(Code::WASM_FUNCTION),
          Handle<Object>::null());
      code->set_constant_pool_offset(index + kPlaceholderMarker);
      placeholder_code_[index] = code;
      function_code_[index] = code;
    }
    return function_code_[index];
  }

  void Finish(uint32_t index, Handle<Code> code) {
    DCHECK(index < function_code_.size());
    function_code_[index] = code;
  }

  void Link(Handle<FixedArray> function_table,
            std::vector<uint16_t>& functions) {
    for (size_t i = 0; i < function_code_.size(); i++) {
      LinkFunction(function_code_[i]);
    }
    if (!function_table.is_null()) {
      int table_size = static_cast<int>(functions.size());
      DCHECK_EQ(function_table->length(), table_size * 2);
      for (int i = 0; i < table_size; i++) {
        function_table->set(i + table_size, *function_code_[functions[i]]);
      }
    }
  }

 private:
  static const int kPlaceholderMarker = 1000000000;

  Isolate* isolate_;
  std::vector<Handle<Code>> placeholder_code_;
  std::vector<Handle<Code>> function_code_;

  void LinkFunction(Handle<Code> code) {
    bool modified = false;
    int mode_mask = RelocInfo::kCodeTargetMask;
    AllowDeferredHandleDereference embedding_raw_address;
    for (RelocIterator it(*code, mode_mask); !it.done(); it.next()) {
      RelocInfo::Mode mode = it.rinfo()->rmode();
      if (RelocInfo::IsCodeTarget(mode)) {
        Code* target =
            Code::GetCodeFromTargetAddress(it.rinfo()->target_address());
        if (target->kind() == Code::WASM_FUNCTION &&
            target->constant_pool_offset() >= kPlaceholderMarker) {
          // Patch direct calls to placeholder code objects.
          uint32_t index = target->constant_pool_offset() - kPlaceholderMarker;
          CHECK(index < function_code_.size());
          Handle<Code> new_target = function_code_[index];
          if (target != *new_target) {
            CHECK_EQ(*placeholder_code_[index], target);
            it.rinfo()->set_target_address(new_target->instruction_start(),
                                           SKIP_WRITE_BARRIER,
                                           SKIP_ICACHE_FLUSH);
            modified = true;
          }
        }
      }
    }
    if (modified) {
      Assembler::FlushICache(isolate_, code->instruction_start(),
                             code->instruction_size());
    }
  }
};

namespace {
// Internal constants for the layout of the module object.
const int kWasmModuleInternalFieldCount = 5;
const int kWasmModuleFunctionTable = 0;
const int kWasmModuleCodeTable = 1;
const int kWasmMemArrayBuffer = 2;
const int kWasmGlobalsArrayBuffer = 3;
const int kWasmFunctionNamesArray = 4;

size_t AllocateGlobalsOffsets(std::vector<WasmGlobal>& globals) {
  uint32_t offset = 0;
  if (globals.size() == 0) return 0;
  for (WasmGlobal& global : globals) {
    byte size = WasmOpcodes::MemSize(global.type);
    offset = (offset + size - 1) & ~(size - 1);  // align
    global.offset = offset;
    offset += size;
  }
  return offset;
}

void LoadDataSegments(WasmModule* module, byte* mem_addr, size_t mem_size) {
  for (const WasmDataSegment& segment : module->data_segments) {
    if (!segment.init) continue;
    if (!segment.source_size) continue;
    CHECK_LT(segment.dest_addr, mem_size);
    CHECK_LE(segment.source_size, mem_size);
    CHECK_LE(segment.dest_addr + segment.source_size, mem_size);
    byte* addr = mem_addr + segment.dest_addr;
    memcpy(addr, module->module_start + segment.source_offset,
           segment.source_size);
  }
}

Handle<FixedArray> BuildFunctionTable(Isolate* isolate, WasmModule* module) {
  if (module->function_table.size() == 0) {
    return Handle<FixedArray>::null();
  }
  int table_size = static_cast<int>(module->function_table.size());
  Handle<FixedArray> fixed = isolate->factory()->NewFixedArray(2 * table_size);
  for (int i = 0; i < table_size; i++) {
    WasmFunction* function = &module->functions[module->function_table[i]];
    fixed->set(i, Smi::FromInt(function->sig_index));
  }
  return fixed;
}

Handle<JSArrayBuffer> NewArrayBuffer(Isolate* isolate, size_t size,
                                     byte** backing_store) {
  if (size > (WasmModule::kMaxMemPages * WasmModule::kPageSize)) {
    // TODO(titzer): lift restriction on maximum memory allocated here.
    *backing_store = nullptr;
    return Handle<JSArrayBuffer>::null();
  }
  void* memory =
      isolate->array_buffer_allocator()->Allocate(static_cast<int>(size));
  if (!memory) {
    *backing_store = nullptr;
    return Handle<JSArrayBuffer>::null();
  }

  *backing_store = reinterpret_cast<byte*>(memory);

#if DEBUG
  // Double check the API allocator actually zero-initialized the memory.
  byte* bytes = reinterpret_cast<byte*>(*backing_store);
  for (size_t i = 0; i < size; i++) {
    DCHECK_EQ(0, bytes[i]);
  }
#endif

  Handle<JSArrayBuffer> buffer = isolate->factory()->NewJSArrayBuffer();
  JSArrayBuffer::Setup(buffer, isolate, false, memory, static_cast<int>(size));
  buffer->set_is_neuterable(false);
  return buffer;
}

// Set the memory for a module instance to be the {memory} array buffer.
void SetMemory(WasmModuleInstance* instance, Handle<JSArrayBuffer> memory) {
  memory->set_is_neuterable(false);
  instance->mem_start = reinterpret_cast<byte*>(memory->backing_store());
  instance->mem_size = memory->byte_length()->Number();
  instance->mem_buffer = memory;
}

// Allocate memory for a module instance as a new JSArrayBuffer.
bool AllocateMemory(ErrorThrower* thrower, Isolate* isolate,
                    WasmModuleInstance* instance) {
  DCHECK(instance->module);
  DCHECK(instance->mem_buffer.is_null());

  if (instance->module->min_mem_pages > WasmModule::kMaxMemPages) {
    thrower->Error("Out of memory: wasm memory too large");
    return false;
  }
  instance->mem_size = WasmModule::kPageSize * instance->module->min_mem_pages;
  instance->mem_buffer =
      NewArrayBuffer(isolate, instance->mem_size, &instance->mem_start);
  if (!instance->mem_start) {
    thrower->Error("Out of memory: wasm memory");
    instance->mem_size = 0;
    return false;
  }
  return true;
}

bool AllocateGlobals(ErrorThrower* thrower, Isolate* isolate,
                     WasmModuleInstance* instance) {
  instance->globals_size = AllocateGlobalsOffsets(instance->module->globals);

  if (instance->globals_size > 0) {
    instance->globals_buffer = NewArrayBuffer(isolate, instance->globals_size,
                                              &instance->globals_start);
    if (!instance->globals_start) {
      // Not enough space for backing store of globals.
      thrower->Error("Out of memory: wasm globals");
      return false;
    }
  }
  return true;
}
}  // namespace

WasmModule::WasmModule()
    : shared_isolate(nullptr),
      module_start(nullptr),
      module_end(nullptr),
      min_mem_pages(0),
      max_mem_pages(0),
      mem_export(false),
      mem_external(false),
      start_function_index(-1),
      origin(kWasmOrigin) {}

static MaybeHandle<JSFunction> ReportFFIError(ErrorThrower& thrower,
                                              const char* error, uint32_t index,
                                              wasm::WasmName module_name,
                                              wasm::WasmName function_name) {
  if (function_name.start()) {
    thrower.Error("Import #%d module=\"%.*s\" function=\"%.*s\" error: %s",
                  index, module_name.length(), module_name.start(),
                  function_name.length(), function_name.start(), error);
  } else {
    thrower.Error("Import #%d module=\"%.*s\" error: %s", index,
                  module_name.length(), module_name.start(), error);
  }
  thrower.Error("Import ");
  return MaybeHandle<JSFunction>();
}

static MaybeHandle<JSFunction> LookupFunction(
    ErrorThrower& thrower, Factory* factory, Handle<JSReceiver> ffi,
    uint32_t index, wasm::WasmName module_name, wasm::WasmName function_name) {
  if (ffi.is_null()) {
    return ReportFFIError(thrower, "FFI is not an object", index, module_name,
                          function_name);
  }

  // Look up the module first.
  Handle<String> name = factory->InternalizeUtf8String(module_name);
  MaybeHandle<Object> result = Object::GetProperty(ffi, name);
  if (result.is_null()) {
    return ReportFFIError(thrower, "module not found", index, module_name,
                          function_name);
  }

  Handle<Object> module = result.ToHandleChecked();

  if (!module->IsJSReceiver()) {
    return ReportFFIError(thrower, "module is not an object or function", index,
                          module_name, function_name);
  }

  Handle<Object> function;
  if (function_name.start()) {
    // Look up the function in the module.
    Handle<String> name = factory->InternalizeUtf8String(function_name);
    MaybeHandle<Object> result = Object::GetProperty(module, name);
    if (result.is_null()) {
      return ReportFFIError(thrower, "function not found", index, module_name,
                            function_name);
    }
    function = result.ToHandleChecked();
  } else {
    // No function specified. Use the "default export".
    function = module;
  }

  if (!function->IsJSFunction()) {
    return ReportFFIError(thrower, "not a function", index, module_name,
                          function_name);
  }

  return Handle<JSFunction>::cast(function);
}

namespace {
// Fetches the compilation unit of a wasm function and executes its parallel
// phase.
bool FetchAndExecuteCompilationUnit(
    Isolate* isolate,
    std::vector<compiler::WasmCompilationUnit*>* compilation_units,
    std::queue<compiler::WasmCompilationUnit*>* executed_units,
    base::Mutex* result_mutex, base::AtomicNumber<size_t>* next_unit) {
  DisallowHeapAllocation no_allocation;
  DisallowHandleAllocation no_handles;
  DisallowHandleDereference no_deref;
  DisallowCodeDependencyChange no_dependency_change;

  // - 1 because AtomicIntrement returns the value after the atomic increment.
  size_t index = next_unit->Increment(1) - 1;
  if (index >= compilation_units->size()) {
    return false;
  }

  compiler::WasmCompilationUnit* unit = compilation_units->at(index);
  if (unit != nullptr) {
    compiler::ExecuteCompilation(unit);
    {
      base::LockGuard<base::Mutex> guard(result_mutex);
      executed_units->push(unit);
    }
  }
  return true;
}

class WasmCompilationTask : public CancelableTask {
 public:
  WasmCompilationTask(
      Isolate* isolate,
      std::vector<compiler::WasmCompilationUnit*>* compilation_units,
      std::queue<compiler::WasmCompilationUnit*>* executed_units,
      base::Semaphore* on_finished, base::Mutex* result_mutex,
      base::AtomicNumber<size_t>* next_unit)
      : CancelableTask(isolate),
        isolate_(isolate),
        compilation_units_(compilation_units),
        executed_units_(executed_units),
        on_finished_(on_finished),
        result_mutex_(result_mutex),
        next_unit_(next_unit) {}

  void RunInternal() override {
    while (FetchAndExecuteCompilationUnit(isolate_, compilation_units_,
                                          executed_units_, result_mutex_,
                                          next_unit_)) {
    }
    on_finished_->Signal();
  }

  Isolate* isolate_;
  std::vector<compiler::WasmCompilationUnit*>* compilation_units_;
  std::queue<compiler::WasmCompilationUnit*>* executed_units_;
  base::Semaphore* on_finished_;
  base::Mutex* result_mutex_;
  base::AtomicNumber<size_t>* next_unit_;
};

void record_code_size(uint32_t& total_code_size, Code* code) {
  if (FLAG_print_wasm_code_size) {
    total_code_size += code->body_size() + code->relocation_info()->length();
  }
}

bool CompileWrappersToImportedFunctions(Isolate* isolate, WasmModule* module,
                                        const Handle<JSReceiver> ffi,
                                        WasmModuleInstance* instance,
                                        ErrorThrower* thrower, Factory* factory,
                                        ModuleEnv* module_env,
                                        uint32_t& total_code_size) {
  uint32_t index = 0;
  if (module->import_table.size() > 0) {
    instance->import_code.reserve(module->import_table.size());
    for (const WasmImport& import : module->import_table) {
      WasmName module_name = module->GetNameOrNull(import.module_name_offset,
                                                   import.module_name_length);
      WasmName function_name = module->GetNameOrNull(
          import.function_name_offset, import.function_name_length);
      MaybeHandle<JSFunction> function = LookupFunction(
          *thrower, factory, ffi, index, module_name, function_name);
      if (function.is_null()) return false;

      Handle<Code> code = compiler::CompileWasmToJSWrapper(
          isolate, module_env, function.ToHandleChecked(), import.sig,
          module_name, function_name);
      instance->import_code.push_back(code);
      record_code_size(total_code_size, *code);
      index++;
    }
  }
  return true;
}

void InitializeParallelCompilation(
    Isolate* isolate, std::vector<WasmFunction>& functions,
    std::vector<compiler::WasmCompilationUnit*>& compilation_units,
    ModuleEnv& module_env, ErrorThrower& thrower) {
  // Create a placeholder code object for all functions.
  // TODO(ahaas): Maybe we could skip this for external functions.
  for (uint32_t i = 0; i < functions.size(); i++) {
    module_env.linker->GetFunctionCode(i);
  }

  for (uint32_t i = FLAG_skip_compiling_wasm_funcs; i < functions.size(); i++) {
    compilation_units[i] = compiler::CreateWasmCompilationUnit(
        &thrower, isolate, &module_env, &functions[i], i);
  }
}

uint32_t* StartCompilationTasks(
    Isolate* isolate,
    std::vector<compiler::WasmCompilationUnit*>& compilation_units,
    std::queue<compiler::WasmCompilationUnit*>& executed_units,
    const base::SmartPointer<base::Semaphore>& pending_tasks,
    base::Mutex& result_mutex, base::AtomicNumber<size_t>& next_unit) {
  const size_t num_tasks =
      Min(static_cast<size_t>(FLAG_wasm_num_compilation_tasks),
          V8::GetCurrentPlatform()->NumberOfAvailableBackgroundThreads());
  uint32_t* task_ids = new uint32_t[num_tasks];
  for (size_t i = 0; i < num_tasks; i++) {
    WasmCompilationTask* task =
        new WasmCompilationTask(isolate, &compilation_units, &executed_units,
                                pending_tasks.get(), &result_mutex, &next_unit);
    task_ids[i] = task->id();
    V8::GetCurrentPlatform()->CallOnBackgroundThread(
        task, v8::Platform::kShortRunningTask);
  }
  return task_ids;
}

void WaitForCompilationTasks(
    Isolate* isolate, uint32_t* task_ids,
    const base::SmartPointer<base::Semaphore>& pending_tasks) {
  const size_t num_tasks =
      Min(static_cast<size_t>(FLAG_wasm_num_compilation_tasks),
          V8::GetCurrentPlatform()->NumberOfAvailableBackgroundThreads());
  for (size_t i = 0; i < num_tasks; i++) {
    // If the task has not started yet, then we abort it. Otherwise we wait for
    // it to finish.
    if (!isolate->cancelable_task_manager()->TryAbort(task_ids[i])) {
      pending_tasks->Wait();
    }
  }
}

void FinishCompilationUnits(
    WasmModule* module,
    std::queue<compiler::WasmCompilationUnit*>& executed_units,
    std::vector<Handle<Code>>& results, base::Mutex& result_mutex) {
  while (true) {
    compiler::WasmCompilationUnit* unit = nullptr;
    {
      base::LockGuard<base::Mutex> guard(&result_mutex);
      if (executed_units.empty()) {
        break;
      }
      unit = executed_units.front();
      executed_units.pop();
    }
    int j = compiler::GetIndexOfWasmCompilationUnit(unit);
    results[j] = compiler::FinishCompilation(unit);
  }
}

bool FinishCompilation(Isolate* isolate, WasmModule* module,
                       const Handle<JSReceiver> ffi,
                       const std::vector<Handle<Code>>& results,
                       const WasmModuleInstance& instance,
                       const Handle<FixedArray>& code_table,
                       ErrorThrower& thrower, Factory* factory,
                       ModuleEnv& module_env, uint32_t& total_code_size,
                       PropertyDescriptor& desc) {
  for (uint32_t i = FLAG_skip_compiling_wasm_funcs;
       i < module->functions.size(); i++) {
    const WasmFunction& func = module->functions[i];
    if (thrower.error()) break;

    DCHECK_EQ(i, func.func_index);
    WasmName str = module->GetName(func.name_offset, func.name_length);
    Handle<Code> code = Handle<Code>::null();
    Handle<JSFunction> function = Handle<JSFunction>::null();
    Handle<String> function_name = Handle<String>::null();
    if (FLAG_wasm_num_compilation_tasks != 0) {
      code = results[i];
    } else {
      // Compile the function.
      code =
          compiler::CompileWasmFunction(&thrower, isolate, &module_env, &func);
    }
    if (code.is_null()) {
      thrower.Error("Compilation of #%d:%.*s failed.", i, str.length(),
                    str.start());
      return false;
    }
    if (func.exported) {
      function_name = factory->InternalizeUtf8String(str);
      function = compiler::CompileJSToWasmWrapper(
          isolate, &module_env, function_name, code, instance.js_object, i);
      record_code_size(total_code_size, function->code());
    }
    if (!code.is_null()) {
      // Install the code into the linker table.
      module_env.linker->Finish(i, code);
      code_table->set(i, *code);
      record_code_size(total_code_size, *code);
    }
    if (func.exported) {
      // Exported functions are installed as read-only properties on the
      // module.
      desc.set_value(function);
      Maybe<bool> status = JSReceiver::DefineOwnProperty(
          isolate, instance.js_object, function_name, &desc,
          Object::THROW_ON_ERROR);
      if (!status.IsJust())
        thrower.Error("export of %.*s failed.", str.length(), str.start());
    }
  }
  return true;
}
}  // namespace

// Instantiates a wasm module as a JSObject.
//  * allocates a backing store of {mem_size} bytes.
//  * installs a named property "memory" for that buffer if exported
//  * installs named properties on the object for exported functions
//  * compiles wasm code to machine code
MaybeHandle<JSObject> WasmModule::Instantiate(Isolate* isolate,
                                              Handle<JSReceiver> ffi,
                                              Handle<JSArrayBuffer> memory) {
  HistogramTimerScope wasm_instantiate_module_time_scope(
      isolate->counters()->wasm_instantiate_module_time());
  this->shared_isolate = isolate;  // TODO(titzer): have a real shared isolate.
  ErrorThrower thrower(isolate, "WasmModule::Instantiate()");
  Factory* factory = isolate->factory();

  PropertyDescriptor desc;
  desc.set_writable(false);

  // If FLAG_print_wasm_code_size is set, this aggregates the sum of all code
  // objects created for this module.
  // TODO(titzer): switch this to TRACE_EVENT
  uint32_t total_code_size = 0;

  //-------------------------------------------------------------------------
  // Allocate the instance and its JS counterpart.
  //-------------------------------------------------------------------------
  Handle<Map> map = factory->NewMap(
      JS_OBJECT_TYPE,
      JSObject::kHeaderSize + kWasmModuleInternalFieldCount * kPointerSize);
  WasmModuleInstance instance(this);
  instance.context = isolate->native_context();
  instance.js_object = factory->NewJSObjectFromMap(map, TENURED);
  Handle<FixedArray> code_table =
      factory->NewFixedArray(static_cast<int>(functions.size()), TENURED);
  instance.js_object->SetInternalField(kWasmModuleCodeTable, *code_table);

  //-------------------------------------------------------------------------
  // Allocate and initialize the linear memory.
  //-------------------------------------------------------------------------
  isolate->counters()->wasm_min_mem_pages_count()->AddSample(
      instance.module->min_mem_pages);
  isolate->counters()->wasm_max_mem_pages_count()->AddSample(
      instance.module->max_mem_pages);
  if (memory.is_null()) {
    if (!AllocateMemory(&thrower, isolate, &instance)) {
      return MaybeHandle<JSObject>();
    }
  } else {
    SetMemory(&instance, memory);
  }
  instance.js_object->SetInternalField(kWasmMemArrayBuffer,
                                       *instance.mem_buffer);
  LoadDataSegments(this, instance.mem_start, instance.mem_size);

  //-------------------------------------------------------------------------
  // Allocate the globals area if necessary.
  //-------------------------------------------------------------------------
  if (!AllocateGlobals(&thrower, isolate, &instance)) {
    return MaybeHandle<JSObject>();
  }
  if (!instance.globals_buffer.is_null()) {
    instance.js_object->SetInternalField(kWasmGlobalsArrayBuffer,
                                         *instance.globals_buffer);
  }

  HistogramTimerScope wasm_compile_module_time_scope(
      isolate->counters()->wasm_compile_module_time());

  instance.function_table = BuildFunctionTable(isolate, this);
  WasmLinker linker(isolate, functions.size());
  ModuleEnv module_env;
  module_env.module = this;
  module_env.instance = &instance;
  module_env.linker = &linker;
  module_env.origin = origin;

  //-------------------------------------------------------------------------
  // Compile wrappers to imported functions.
  //-------------------------------------------------------------------------
  if (!CompileWrappersToImportedFunctions(isolate, this, ffi, &instance,
                                          &thrower, factory, &module_env,
                                          total_code_size)) {
    return MaybeHandle<JSObject>();
  }
  //-------------------------------------------------------------------------
  // Compile all functions in the module.
  //-------------------------------------------------------------------------
  {
    isolate->counters()->wasm_functions_per_module()->AddSample(
        static_cast<int>(functions.size()));

    // Data structures for the parallel compilation.
    std::vector<compiler::WasmCompilationUnit*> compilation_units(
        functions.size());
    std::queue<compiler::WasmCompilationUnit*> executed_units;
    std::vector<Handle<Code>> results(functions.size());

    if (FLAG_wasm_num_compilation_tasks != 0) {
      //-----------------------------------------------------------------------
      // For parallel compilation:
      // 1) The main thread allocates a compilation unit for each wasm function
      //    and stores them in the vector {compilation_units}.
      // 2) The main thread spawns {WasmCompilationTask} instances which run on
      //    the background threads.
      // 3.a) The background threads and the main thread pick one compilation
      //      unit at a time and execute the parallel phase of the compilation
      //      unit. After finishing the execution of the parallel phase, the
      //      result is enqueued in {executed_units}.
      // 3.b) If {executed_units} contains a compilation unit, the main thread
      //      dequeues it and finishes the compilation.
      // 4) After the parallel phase of all compilation units has started, the
      //    main thread waits for all {WasmCompilationTask} instances to finish.
      // 5) The main thread finishes the compilation.

      // Turn on the {CanonicalHandleScope} so that the background threads can
      // use the node cache.
      CanonicalHandleScope canonical(isolate);

      // 1) The main thread allocates a compilation unit for each wasm function
      //    and stores them in the vector {compilation_units}.
      InitializeParallelCompilation(isolate, functions, compilation_units,
                                    module_env, thrower);

      // Objects for the synchronization with the background threads.
      base::SmartPointer<base::Semaphore> pending_tasks(new base::Semaphore(0));
      base::Mutex result_mutex;
      base::AtomicNumber<size_t> next_unit(
          static_cast<size_t>(FLAG_skip_compiling_wasm_funcs));

      // 2) The main thread spawns {WasmCompilationTask} instances which run on
      //    the background threads.
      base::SmartArrayPointer<uint32_t> task_ids(
          StartCompilationTasks(isolate, compilation_units, executed_units,
                                pending_tasks, result_mutex, next_unit));

      // 3.a) The background threads and the main thread pick one compilation
      //      unit at a time and execute the parallel phase of the compilation
      //      unit. After finishing the execution of the parallel phase, the
      //      result is enqueued in {executed_units}.
      while (FetchAndExecuteCompilationUnit(isolate, &compilation_units,
                                            &executed_units, &result_mutex,
                                            &next_unit)) {
        // 3.b) If {executed_units} contains a compilation unit, the main thread
        //      dequeues it and finishes the compilation unit. Compilation units
        //      are finished concurrently to the background threads to save
        //      memory.
        FinishCompilationUnits(this, executed_units, results, result_mutex);
      }
      // 4) After the parallel phase of all compilation units has started, the
      //    main thread waits for all {WasmCompilationTask} instances to finish.
      WaitForCompilationTasks(isolate, task_ids.get(), pending_tasks);
      // Finish the compilation of the remaining compilation units.
      FinishCompilationUnits(this, executed_units, results, result_mutex);
    }
    // 5) The main thread finishes the compilation.
    if (!FinishCompilation(isolate, this, ffi, results, instance, code_table,
                           thrower, factory, module_env, total_code_size,
                           desc)) {
      return MaybeHandle<JSObject>();
    }

    // Patch all direct call sites.
    linker.Link(instance.function_table, this->function_table);
    instance.js_object->SetInternalField(kWasmModuleFunctionTable,
                                         Smi::FromInt(0));

    //-------------------------------------------------------------------------
    // Create and populate the exports object.
    //-------------------------------------------------------------------------
    if (export_table.size() > 0 || mem_export) {
      // Create the "exports" object.
      Handle<JSFunction> object_function = Handle<JSFunction>(
          isolate->native_context()->object_function(), isolate);
      Handle<JSObject> exports_object =
          factory->NewJSObject(object_function, TENURED);
      Handle<String> exports_name = factory->InternalizeUtf8String("exports");
      JSObject::AddProperty(instance.js_object, exports_name, exports_object,
                            READ_ONLY);

      // Compile wrappers and add them to the exports object.
      for (const WasmExport& exp : export_table) {
        if (thrower.error()) break;
        WasmName str = GetName(exp.name_offset, exp.name_length);
        Handle<String> name = factory->InternalizeUtf8String(str);
        Handle<Code> code = linker.GetFunctionCode(exp.func_index);
        Handle<JSFunction> function = compiler::CompileJSToWasmWrapper(
            isolate, &module_env, name, code, instance.js_object,
            exp.func_index);
        record_code_size(total_code_size, function->code());
        desc.set_value(function);
        Maybe<bool> status = JSReceiver::DefineOwnProperty(
            isolate, exports_object, name, &desc, Object::THROW_ON_ERROR);
        if (!status.IsJust())
          thrower.Error("export of %.*s failed.", str.length(), str.start());
      }

      if (mem_export) {
        // Export the memory as a named property.
        Handle<String> name = factory->InternalizeUtf8String("memory");
        JSObject::AddProperty(exports_object, name, instance.mem_buffer,
                              READ_ONLY);
      }
    }
  }

  //-------------------------------------------------------------------------
  // 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);
  }

  if (FLAG_print_wasm_code_size)
    printf("Total generated wasm code: %u bytes\n", total_code_size);

  // Run the start function if one was specified.
  if (this->start_function_index >= 0) {
    HandleScope scope(isolate);
    uint32_t index = static_cast<uint32_t>(this->start_function_index);
    Handle<String> name = isolate->factory()->NewStringFromStaticChars("start");
    Handle<Code> code = linker.GetFunctionCode(index);
    Handle<JSFunction> jsfunc = compiler::CompileJSToWasmWrapper(
        isolate, &module_env, name, code, instance.js_object, index);

    // Call the JS function.
    Handle<Object> undefined(isolate->heap()->undefined_value(), isolate);
    MaybeHandle<Object> retval =
        Execution::Call(isolate, jsfunc, undefined, 0, nullptr);

    if (retval.is_null()) {
      thrower.Error("WASM.instantiateModule(): start function failed");
    }
  }
  return instance.js_object;
}

Handle<Code> ModuleEnv::GetFunctionCode(uint32_t index) {
  DCHECK(IsValidFunction(index));
  if (linker) return linker->GetFunctionCode(index);
  return instance ? instance->function_code[index] : Handle<Code>::null();
}

Handle<Code> ModuleEnv::GetImportCode(uint32_t index) {
  DCHECK(IsValidImport(index));
  return instance ? instance->import_code[index] : Handle<Code>::null();
}

compiler::CallDescriptor* ModuleEnv::GetCallDescriptor(Zone* zone,
                                                       uint32_t index) {
  DCHECK(IsValidFunction(index));
  // Always make a direct call to whatever is in the table at that location.
  // A wrapper will be generated for FFI calls.
  WasmFunction* function = &module->functions[index];
  return GetWasmCallDescriptor(zone, function->sig);
}

int32_t CompileAndRunWasmModule(Isolate* isolate, const byte* module_start,
                                const byte* module_end, bool asm_js) {
  HandleScope scope(isolate);
  Zone zone(isolate->allocator());
  // Decode the module, but don't verify function bodies, since we'll
  // be compiling them anyway.
  ModuleResult result = DecodeWasmModule(isolate, &zone, module_start,
                                         module_end, false, kWasmOrigin);
  if (result.failed()) {
    if (result.val) {
      delete result.val;
    }
    // Module verification failed. throw.
    std::ostringstream str;
    str << "WASM.compileRun() failed: " << result;
    isolate->Throw(
        *isolate->factory()->NewStringFromAsciiChecked(str.str().c_str()));
    return -1;
  }

  int32_t retval = CompileAndRunWasmModule(isolate, result.val);
  delete result.val;
  return retval;
}

int32_t CompileAndRunWasmModule(Isolate* isolate, WasmModule* module) {
  ErrorThrower thrower(isolate, "CompileAndRunWasmModule");
  WasmModuleInstance instance(module);

  // Allocate and initialize the linear memory.
  if (!AllocateMemory(&thrower, isolate, &instance)) {
    return -1;
  }
  LoadDataSegments(module, instance.mem_start, instance.mem_size);

  // Allocate the globals area if necessary.
  if (!AllocateGlobals(&thrower, isolate, &instance)) {
    return -1;
  }

  // Build the function table.
  instance.function_table = BuildFunctionTable(isolate, module);

  // Create module environment.
  WasmLinker linker(isolate, module->functions.size());
  ModuleEnv module_env;
  module_env.module = module;
  module_env.instance = &instance;
  module_env.linker = &linker;
  module_env.origin = module->origin;

  // Compile all functions.
  Handle<Code> main_code = Handle<Code>::null();  // record last code.
  uint32_t index = 0;
  int main_index = 0;
  for (const WasmFunction& func : module->functions) {
    DCHECK_EQ(index, func.func_index);
    // Compile the function and install it in the code table.
    Handle<Code> code =
        compiler::CompileWasmFunction(&thrower, isolate, &module_env, &func);
    if (!code.is_null()) {
      if (func.exported) {
        main_code = code;
        main_index = index;
      }
      linker.Finish(index, code);
    }
    if (thrower.error()) return -1;
    index++;
  }

  if (main_code.is_null()) {
    thrower.Error("WASM.compileRun() failed: no main code found");
    return -1;
  }

  linker.Link(instance.function_table, instance.module->function_table);

  // Wrap the main code so it can be called as a JS function.
  Handle<String> name = isolate->factory()->NewStringFromStaticChars("main");
  Handle<JSObject> module_object = Handle<JSObject>(0, isolate);
  Handle<JSFunction> jsfunc = compiler::CompileJSToWasmWrapper(
      isolate, &module_env, name, main_code, module_object, main_index);

  // Call the JS function.
  Handle<Object> undefined(isolate->heap()->undefined_value(), isolate);
  MaybeHandle<Object> retval =
      Execution::Call(isolate, jsfunc, undefined, 0, nullptr);

  // The result should be a number.
  if (retval.is_null()) {
    thrower.Error("WASM.compileRun() failed: Invocation was null");
    return -1;
  }
  Handle<Object> result = retval.ToHandleChecked();
  if (result->IsSmi()) {
    return Smi::cast(*result)->value();
  }
  if (result->IsHeapNumber()) {
    return static_cast<int32_t>(HeapNumber::cast(*result)->value());
  }
  thrower.Error("WASM.compileRun() failed: Return value should be number");
  return -1;
}

Handle<Object> GetWasmFunctionName(Handle<JSObject> wasm, uint32_t func_index) {
  Handle<Object> func_names_arr_obj = handle(
      wasm->GetInternalField(kWasmFunctionNamesArray), wasm->GetIsolate());
  if (func_names_arr_obj->IsUndefined())
    return func_names_arr_obj;  // Return undefined.
  return GetWasmFunctionNameFromTable(
      Handle<ByteArray>::cast(func_names_arr_obj), func_index);
}

}  // namespace wasm
}  // namespace internal
}  // namespace v8