wasm-objects.h

// Copyright 2016 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.

#ifndef V8_WASM_OBJECTS_H_
#define V8_WASM_OBJECTS_H_

#include "src/debug/debug.h"
#include "src/debug/interface-types.h"
#include "src/objects.h"
#include "src/objects/script.h"
#include "src/trap-handler/trap-handler.h"
#include "src/wasm/wasm-limits.h"

namespace v8 {
namespace internal {
namespace wasm {
class InterpretedFrame;
struct WasmModule;
struct WasmInstance;
class WasmInterpreter;
}

class WasmCompiledModule;
class WasmDebugInfo;
class WasmInstanceObject;
class WasmInstanceWrapper;

#define DECLARE_CASTS(name)             \
  static bool Is##name(Object* object); \
  static name* cast(Object* object)

#define DECLARE_GETTER(name, type) type* name()

#define DECLARE_ACCESSORS(name, type) \
  void set_##name(type* value);       \
  DECLARE_GETTER(name, type)

#define DECLARE_OPTIONAL_ACCESSORS(name, type) \
  bool has_##name();                           \
  DECLARE_ACCESSORS(name, type)

#define DECLARE_OPTIONAL_GETTER(name, type) \
  bool has_##name();                        \
  DECLARE_GETTER(name, type)

// Representation of a WebAssembly.Module JavaScript-level object.
class WasmModuleObject : public JSObject {
 public:
  // If a second field is added, we need a kWrapperTracerHeader field as well.
  // TODO(titzer): add the brand as an embedder field instead of a property.
  enum Fields { kCompiledModule, kFieldCount };

  DECLARE_CASTS(WasmModuleObject);

  WasmCompiledModule* compiled_module();

  static Handle<WasmModuleObject> New(
      Isolate* isolate, Handle<WasmCompiledModule> compiled_module);
};

// Representation of a WebAssembly.Table JavaScript-level object.
class WasmTableObject : public JSObject {
 public:
  // The 0-th field is used by the Blink Wrapper Tracer.
  // TODO(titzer): add the brand as an embedder field instead of a property.
  enum Fields {
    kWrapperTracerHeader,
    kFunctions,
    kMaximum,
    kDispatchTables,
    kFieldCount
  };

  DECLARE_CASTS(WasmTableObject);
  DECLARE_ACCESSORS(functions, FixedArray);
  DECLARE_GETTER(dispatch_tables, FixedArray);

  uint32_t current_length();
  bool has_maximum_length();
  int64_t maximum_length();  // Returns < 0 if no maximum.
  void grow(Isolate* isolate, uint32_t count);

  static Handle<WasmTableObject> New(Isolate* isolate, uint32_t initial,
                                     int64_t maximum,
                                     Handle<FixedArray>* js_functions);
  static Handle<FixedArray> AddDispatchTable(
      Isolate* isolate, Handle<WasmTableObject> table,
      Handle<WasmInstanceObject> instance, int table_index,
      Handle<FixedArray> function_table, Handle<FixedArray> signature_table);
};

// Representation of a WebAssembly.Memory JavaScript-level object.
class WasmMemoryObject : public JSObject {
 public:
  // The 0-th field is used by the Blink Wrapper Tracer.
  // TODO(titzer): add the brand as an embedder field instead of a property.
  enum Fields : uint8_t {
    kWrapperTracerHeader,
    kArrayBuffer,
    kMaximum,
    kInstancesLink,
    kFieldCount
  };

  DECLARE_CASTS(WasmMemoryObject);
  DECLARE_ACCESSORS(buffer, JSArrayBuffer);
  DECLARE_OPTIONAL_ACCESSORS(instances_link, WasmInstanceWrapper);

  void AddInstance(Isolate* isolate, Handle<WasmInstanceObject> object);
  void ResetInstancesLink(Isolate* isolate);
  uint32_t current_pages();
  bool has_maximum_pages();
  int32_t maximum_pages();  // Returns < 0 if there is no maximum.

  static Handle<WasmMemoryObject> New(Isolate* isolate,
                                      Handle<JSArrayBuffer> buffer,
                                      int32_t maximum);

  static int32_t Grow(Isolate*, Handle<WasmMemoryObject>, uint32_t pages);
};

// Representation of a WebAssembly.Instance JavaScript-level object.
class WasmInstanceObject : public JSObject {
 public:
  // The 0-th field is used by the Blink Wrapper Tracer.
  // TODO(titzer): add the brand as an embedder field instead of a property.
  enum Fields {
    kWrapperTracerHeader,
    kCompiledModule,
    kMemoryObject,
    kMemoryArrayBuffer,
    kGlobalsArrayBuffer,
    kDebugInfo,
    kWasmMemInstanceWrapper,
    kFieldCount
  };

  DECLARE_CASTS(WasmInstanceObject);

  DECLARE_ACCESSORS(compiled_module, WasmCompiledModule);
  DECLARE_OPTIONAL_ACCESSORS(globals_buffer, JSArrayBuffer);
  DECLARE_OPTIONAL_ACCESSORS(memory_buffer, JSArrayBuffer);
  DECLARE_OPTIONAL_ACCESSORS(memory_object, WasmMemoryObject);
  DECLARE_OPTIONAL_ACCESSORS(debug_info, WasmDebugInfo);
  DECLARE_OPTIONAL_ACCESSORS(instance_wrapper, WasmInstanceWrapper);

  WasmModuleObject* module_object();
  wasm::WasmModule* module();

  // Get the debug info associated with the given wasm object.
  // If no debug info exists yet, it is created automatically.
  static Handle<WasmDebugInfo> GetOrCreateDebugInfo(Handle<WasmInstanceObject>);

  static Handle<WasmInstanceObject> New(Isolate*, Handle<WasmCompiledModule>);

  int32_t GetMemorySize();

  static int32_t GrowMemory(Isolate*, Handle<WasmInstanceObject>,
                            uint32_t pages);

  uint32_t GetMaxMemoryPages();
};

// Representation of an exported WASM function.
class WasmExportedFunction : public JSFunction {
 public:
  // The 0-th field is used by the Blink Wrapper Tracer.
  enum Fields { kWrapperTracerHeader, kInstance, kIndex, kFieldCount };

  DECLARE_CASTS(WasmExportedFunction);

  WasmInstanceObject* instance();
  int function_index();

  static Handle<WasmExportedFunction> New(Isolate* isolate,
                                          Handle<WasmInstanceObject> instance,
                                          MaybeHandle<String> maybe_name,
                                          int func_index, int arity,
                                          Handle<Code> export_wrapper);
};

// Information shared by all WasmCompiledModule objects for the same module.
class WasmSharedModuleData : public FixedArray {
  // The 0-th field is used by the Blink Wrapper Tracer.
  enum Fields {
    kWrapperTracerHeader,
    kModuleWrapper,
    kModuleBytes,
    kScript,
    kAsmJsOffsetTable,
    kBreakPointInfos,
    kLazyCompilationOrchestrator,
    kFieldCount
  };

 public:
  DECLARE_CASTS(WasmSharedModuleData);

  DECLARE_GETTER(module, wasm::WasmModule);
  DECLARE_OPTIONAL_ACCESSORS(module_bytes, SeqOneByteString);
  DECLARE_GETTER(script, Script);
  DECLARE_OPTIONAL_ACCESSORS(asm_js_offset_table, ByteArray);
  DECLARE_OPTIONAL_GETTER(breakpoint_infos, FixedArray);

  static Handle<WasmSharedModuleData> New(
      Isolate* isolate, Handle<Foreign> module_wrapper,
      Handle<SeqOneByteString> module_bytes, Handle<Script> script,
      Handle<ByteArray> asm_js_offset_table);

  // Check whether this module was generated from asm.js source.
  bool is_asm_js();

  static void ReinitializeAfterDeserialization(Isolate*,
                                               Handle<WasmSharedModuleData>);

  static void AddBreakpoint(Handle<WasmSharedModuleData>, int position,
                            Handle<Object> break_point_object);

  static void SetBreakpointsOnNewInstance(Handle<WasmSharedModuleData>,
                                          Handle<WasmInstanceObject>);

  static void PrepareForLazyCompilation(Handle<WasmSharedModuleData>);

 private:
  DECLARE_OPTIONAL_GETTER(lazy_compilation_orchestrator, Foreign);
  friend class WasmCompiledModule;
};

// This represents the set of wasm compiled functions, together
// with all the information necessary for re-specializing them.
//
// We specialize wasm functions to their instance by embedding:
//   - raw interior pointers into the backing store of the array buffer
//     used as memory of a particular WebAssembly.Instance object.
//   - bounds check limits, computed at compile time, relative to the
//     size of the memory.
//   - the objects representing the function tables and signature tables
//   - raw pointer to the globals buffer.
//
// Even without instantiating, we need values for all of these parameters.
// We need to track these values to be able to create new instances and
// to be able to serialize/deserialize.
// The design decisions for how we track these values is not too immediate,
// and it deserves a summary. The "tricky" ones are: memory, globals, and
// the tables (signature and functions).
// The first 2 (memory & globals) are embedded as raw pointers to native
// buffers. All we need to track them is the start addresses and, in the
// case of memory, the size. We model all of them as HeapNumbers, because
// we need to store size_t values (for addresses), and potentially full
// 32 bit unsigned values for the size. Smis are 31 bits.
// For tables, we need to hold a reference to the JS Heap object, because
// we embed them as objects, and they may move.
class WasmCompiledModule : public FixedArray {
 public:
  enum Fields { kFieldCount };

  static WasmCompiledModule* cast(Object* fixed_array) {
    SLOW_DCHECK(IsWasmCompiledModule(fixed_array));
    return reinterpret_cast<WasmCompiledModule*>(fixed_array);
  }

#define WCM_OBJECT_OR_WEAK(TYPE, NAME, ID, TYPE_CHECK, SETTER_MODIFIER) \
 public:                                                                \
  Handle<TYPE> NAME() const { return handle(ptr_to_##NAME()); }         \
                                                                        \
  MaybeHandle<TYPE> maybe_##NAME() const {                              \
    if (has_##NAME()) return NAME();                                    \
    return MaybeHandle<TYPE>();                                         \
  }                                                                     \
                                                                        \
  TYPE* maybe_ptr_to_##NAME() const {                                   \
    Object* obj = get(ID);                                              \
    if (!(TYPE_CHECK)) return nullptr;                                  \
    return TYPE::cast(obj);                                             \
  }                                                                     \
                                                                        \
  TYPE* ptr_to_##NAME() const {                                         \
    Object* obj = get(ID);                                              \
    DCHECK(TYPE_CHECK);                                                 \
    return TYPE::cast(obj);                                             \
  }                                                                     \
                                                                        \
  bool has_##NAME() const {                                             \
    Object* obj = get(ID);                                              \
    return TYPE_CHECK;                                                  \
  }                                                                     \
                                                                        \
  void reset_##NAME() { set_undefined(ID); }                            \
                                                                        \
  SETTER_MODIFIER:                                                      \
  void set_##NAME(Handle<TYPE> value) { set_ptr_to_##NAME(*value); }    \
  void set_ptr_to_##NAME(TYPE* value) { set(ID, value); }

#define WCM_OBJECT(TYPE, NAME) \
  WCM_OBJECT_OR_WEAK(TYPE, NAME, kID_##NAME, obj->Is##TYPE(), public)

#define WCM_CONST_OBJECT(TYPE, NAME) \
  WCM_OBJECT_OR_WEAK(TYPE, NAME, kID_##NAME, obj->Is##TYPE(), private)

#define WCM_WASM_OBJECT(TYPE, NAME) \
  WCM_OBJECT_OR_WEAK(TYPE, NAME, kID_##NAME, TYPE::Is##TYPE(obj), private)

#define WCM_SMALL_CONST_NUMBER(TYPE, NAME)                         \
 public:                                                           \
  TYPE NAME() const {                                              \
    return static_cast<TYPE>(Smi::cast(get(kID_##NAME))->value()); \
  }                                                                \
                                                                   \
 private:                                                          \
  void set_##NAME(TYPE value) { set(kID_##NAME, Smi::FromInt(value)); }

#define WCM_WEAK_LINK(TYPE, NAME)                                          \
  WCM_OBJECT_OR_WEAK(WeakCell, weak_##NAME, kID_##NAME, obj->IsWeakCell(), \
                     public)                                               \
                                                                           \
 public:                                                                   \
  Handle<TYPE> NAME() const {                                              \
    return handle(TYPE::cast(weak_##NAME()->value()));                     \
  }

#define WCM_LARGE_NUMBER(TYPE, NAME)                                   \
 public:                                                               \
  TYPE NAME() const {                                                  \
    Object* value = get(kID_##NAME);                                   \
    DCHECK(value->IsMutableHeapNumber());                              \
    return static_cast<TYPE>(HeapNumber::cast(value)->value());        \
  }                                                                    \
                                                                       \
  void set_##NAME(TYPE value) {                                        \
    Object* number = get(kID_##NAME);                                  \
    DCHECK(number->IsMutableHeapNumber());                             \
    HeapNumber::cast(number)->set_value(static_cast<double>(value));   \
  }                                                                    \
                                                                       \
  static void recreate_##NAME(Handle<WasmCompiledModule> obj,          \
                              Factory* factory, TYPE init_val) {       \
    Handle<HeapNumber> number = factory->NewHeapNumber(                \
        static_cast<double>(init_val), MutableMode::MUTABLE, TENURED); \
    obj->set(kID_##NAME, *number);                                     \
  }                                                                    \
  bool has_##NAME() const { return get(kID_##NAME)->IsMutableHeapNumber(); }

// Add values here if they are required for creating new instances or
// for deserialization, and if they are serializable.
// By default, instance values go to WasmInstanceObject, however, if
// we embed the generated code with a value, then we track that value here.
#define CORE_WCM_PROPERTY_TABLE(MACRO)                        \
  MACRO(WASM_OBJECT, WasmSharedModuleData, shared)            \
  MACRO(OBJECT, Context, native_context)                      \
  MACRO(SMALL_CONST_NUMBER, uint32_t, num_imported_functions) \
  MACRO(CONST_OBJECT, FixedArray, code_table)                 \
  MACRO(OBJECT, FixedArray, weak_exported_functions)          \
  MACRO(OBJECT, FixedArray, function_tables)                  \
  MACRO(OBJECT, FixedArray, signature_tables)                 \
  MACRO(CONST_OBJECT, FixedArray, empty_function_tables)      \
  MACRO(LARGE_NUMBER, size_t, embedded_mem_start)             \
  MACRO(LARGE_NUMBER, size_t, globals_start)                  \
  MACRO(LARGE_NUMBER, uint32_t, embedded_mem_size)            \
  MACRO(SMALL_CONST_NUMBER, uint32_t, min_mem_pages)          \
  MACRO(WEAK_LINK, WasmCompiledModule, next_instance)         \
  MACRO(WEAK_LINK, WasmCompiledModule, prev_instance)         \
  MACRO(WEAK_LINK, JSObject, owning_instance)                 \
  MACRO(WEAK_LINK, WasmModuleObject, wasm_module)

#if DEBUG
#define DEBUG_ONLY_TABLE(MACRO) MACRO(SMALL_CONST_NUMBER, uint32_t, instance_id)
#else
#define DEBUG_ONLY_TABLE(IGNORE)

 public:
  uint32_t instance_id() const { return static_cast<uint32_t>(-1); }
#endif

#define WCM_PROPERTY_TABLE(MACRO) \
  CORE_WCM_PROPERTY_TABLE(MACRO)  \
  DEBUG_ONLY_TABLE(MACRO)

 private:
  enum PropertyIndices {
#define INDICES(IGNORE1, IGNORE2, NAME) kID_##NAME,
    WCM_PROPERTY_TABLE(INDICES) Count
#undef INDICES
  };

 public:
  static Handle<WasmCompiledModule> New(
      Isolate* isolate, Handle<WasmSharedModuleData> shared,
      Handle<FixedArray> code_table,
      MaybeHandle<FixedArray> maybe_empty_function_tables,
      MaybeHandle<FixedArray> maybe_signature_tables);

  static Handle<WasmCompiledModule> Clone(Isolate* isolate,
                                          Handle<WasmCompiledModule> module);
  static void Reset(Isolate* isolate, WasmCompiledModule* module);

  Address GetEmbeddedMemStartOrNull() const {
    DisallowHeapAllocation no_gc;
    if (has_embedded_mem_start()) {
      return reinterpret_cast<Address>(embedded_mem_start());
    }
    return nullptr;
  }

  Address GetGlobalsStartOrNull() const {
    DisallowHeapAllocation no_gc;
    if (has_globals_start()) {
      return reinterpret_cast<Address>(globals_start());
    }
    return nullptr;
  }

  uint32_t mem_size() const;
  uint32_t default_mem_size() const;

  void ResetSpecializationMemInfoIfNeeded();
  static void SetSpecializationMemInfoFrom(
      Factory* factory, Handle<WasmCompiledModule> compiled_module,
      Handle<JSArrayBuffer> buffer);
  static void SetGlobalsStartAddressFrom(
      Factory* factory, Handle<WasmCompiledModule> compiled_module,
      Handle<JSArrayBuffer> buffer);

#define DECLARATION(KIND, TYPE, NAME) WCM_##KIND(TYPE, NAME)
  WCM_PROPERTY_TABLE(DECLARATION)
#undef DECLARATION

 public:
// Allow to call method on WasmSharedModuleData also on this object.
#define FORWARD_SHARED(type, name) \
  type name() { return shared()->name(); }
  FORWARD_SHARED(SeqOneByteString*, module_bytes)
  FORWARD_SHARED(wasm::WasmModule*, module)
  FORWARD_SHARED(Script*, script)
  FORWARD_SHARED(bool, is_asm_js)
#undef FORWARD_SHARED

  static bool IsWasmCompiledModule(Object* obj);

  void PrintInstancesChain();

  static void ReinitializeAfterDeserialization(Isolate*,
                                               Handle<WasmCompiledModule>);

  // Get the function name of the function identified by the given index.
  // Returns a null handle if the function is unnamed or the name is not a valid
  // UTF-8 string.
  static MaybeHandle<String> GetFunctionNameOrNull(
      Isolate* isolate, Handle<WasmCompiledModule> compiled_module,
      uint32_t func_index);

  // Get the function name of the function identified by the given index.
  // Returns "<WASM UNNAMED>" if the function is unnamed or the name is not a
  // valid UTF-8 string.
  static Handle<String> GetFunctionName(
      Isolate* isolate, Handle<WasmCompiledModule> compiled_module,
      uint32_t func_index);

  // Get the raw bytes of the function name of the function identified by the
  // given index.
  // Meant to be used for debugging or frame printing.
  // Does not allocate, hence gc-safe.
  Vector<const uint8_t> GetRawFunctionName(uint32_t func_index);

  // Return the byte offset of the function identified by the given index.
  // The offset will be relative to the start of the module bytes.
  // Returns -1 if the function index is invalid.
  int GetFunctionOffset(uint32_t func_index);

  // Returns the function containing the given byte offset.
  // Returns -1 if the byte offset is not contained in any function of this
  // module.
  int GetContainingFunction(uint32_t byte_offset);

  // Translate from byte offset in the module to function number and byte offset
  // within that function, encoded as line and column in the position info.
  // Returns true if the position is valid inside this module, false otherwise.
  bool GetPositionInfo(uint32_t position, Script::PositionInfo* info);

  // Get the asm.js source position from a byte offset.
  // Must only be called if the associated wasm object was created from asm.js.
  static int GetAsmJsSourcePosition(Handle<WasmCompiledModule> compiled_module,
                                    uint32_t func_index, uint32_t byte_offset,
                                    bool is_at_number_conversion);

  // Compute the disassembly of a wasm function.
  // Returns the disassembly string and a list of <byte_offset, line, column>
  // entries, mapping wasm byte offsets to line and column in the disassembly.
  // The list is guaranteed to be ordered by the byte_offset.
  // Returns an empty string and empty vector if the function index is invalid.
  debug::WasmDisassembly DisassembleFunction(int func_index);

  // Extract a portion of the wire bytes as UTF-8 string.
  // Returns a null handle if the respective bytes do not form a valid UTF-8
  // string.
  static MaybeHandle<String> ExtractUtf8StringFromModuleBytes(
      Isolate* isolate, Handle<WasmCompiledModule> compiled_module,
      uint32_t offset, uint32_t size);

  // Get a list of all possible breakpoints within a given range of this module.
  bool GetPossibleBreakpoints(const debug::Location& start,
                              const debug::Location& end,
                              std::vector<debug::BreakLocation>* locations);

  // Set a breakpoint on the given byte position inside the given module.
  // This will affect all live and future instances of the module.
  // The passed position might be modified to point to the next breakable
  // location inside the same function.
  // If it points outside a function, or behind the last breakable location,
  // this function returns false and does not set any breakpoint.
  static bool SetBreakPoint(Handle<WasmCompiledModule>, int* position,
                            Handle<Object> break_point_object);

  // Return an empty handle if no breakpoint is hit at that location, or a
  // FixedArray with all hit breakpoint objects.
  MaybeHandle<FixedArray> CheckBreakPoints(int position);

  // Compile lazily the function called in the given caller code object at the
  // given offset.
  // If the called function cannot be determined from the caller (indirect
  // call / exported function), func_index must be set. Otherwise it can be -1.
  // If patch_caller is set, then all direct calls to functions which were
  // already lazily compiled are patched (at least the given call site).
  // Returns the Code to be called at the given call site.
  static Handle<Code> CompileLazy(Isolate*, Handle<WasmInstanceObject>,
                                  Handle<Code> caller, int offset,
                                  int func_index, bool patch_caller);

  void ReplaceCodeTableForTesting(Handle<FixedArray> testing_table) {
    set_code_table(testing_table);
  }

 private:
  void InitId();

  DISALLOW_IMPLICIT_CONSTRUCTORS(WasmCompiledModule);
};

class WasmDebugInfo : public FixedArray {
 public:
  // The 0-th field is used by the Blink Wrapper Tracer.
  enum Fields {
    kWrapperTracerHeader,
    kInstance,
    kInterpreterHandle,
    kInterpretedFunctions,
    kFieldCount
  };

  static Handle<WasmDebugInfo> New(Handle<WasmInstanceObject>);

  // Setup a WasmDebugInfo with an existing WasmInstance struct.
  // Returns a pointer to the interpreter instantiated inside this
  // WasmDebugInfo.
  // Use for testing only.
  static wasm::WasmInterpreter* SetupForTesting(Handle<WasmInstanceObject>,
                                                wasm::WasmInstance*);

  static bool IsDebugInfo(Object*);
  static WasmDebugInfo* cast(Object*);

  // Set a breakpoint in the given function at the given byte offset within that
  // function. This will redirect all future calls to this function to the
  // interpreter and will always pause at the given offset.
  static void SetBreakpoint(Handle<WasmDebugInfo>, int func_index, int offset);

  // Make a set of functions always execute in the interpreter without setting
  // breakpoints.
  static void RedirectToInterpreter(Handle<WasmDebugInfo>,
                                    Vector<int> func_indexes);

  void PrepareStep(StepAction);

  // Execute the specified funtion in the interpreter. Read arguments from
  // arg_buffer.
  // The frame_pointer will be used to identify the new activation of the
  // interpreter for unwinding and frame inspection.
  // Returns true if exited regularly, false if a trap occured. In the latter
  // case, a pending exception will have been set on the isolate.
  bool RunInterpreter(Address frame_pointer, int func_index,
                      uint8_t* arg_buffer);

  // Get the stack of the wasm interpreter as pairs of <function index, byte
  // offset>. The list is ordered bottom-to-top, i.e. caller before callee.
  std::vector<std::pair<uint32_t, int>> GetInterpretedStack(
      Address frame_pointer);

  std::unique_ptr<wasm::InterpretedFrame> GetInterpretedFrame(
      Address frame_pointer, int frame_index);

  // Unwind the interpreted stack belonging to the passed interpreter entry
  // frame.
  void Unwind(Address frame_pointer);

  // Returns the number of calls / function frames executed in the interpreter.
  uint64_t NumInterpretedCalls();

  DECLARE_GETTER(wasm_instance, WasmInstanceObject);

  // Update the memory view of the interpreter after executing GrowMemory in
  // compiled code.
  void UpdateMemory(JSArrayBuffer* new_memory);

  // Get scope details for a specific interpreted frame.
  // This returns a JSArray of length two: One entry for the global scope, one
  // for the local scope. Both elements are JSArrays of size
  // ScopeIterator::kScopeDetailsSize and layout as described in debug-scopes.h.
  // The global scope contains information about globals and the memory.
  // The local scope contains information about parameters, locals, and stack
  // values.
  static Handle<JSArray> GetScopeDetails(Handle<WasmDebugInfo>,
                                         Address frame_pointer,
                                         int frame_index);
};

class WasmInstanceWrapper : public FixedArray {
 public:
  static Handle<WasmInstanceWrapper> New(Isolate* isolate,
                                         Handle<WasmInstanceObject> instance);
  static WasmInstanceWrapper* cast(Object* fixed_array) {
    SLOW_DCHECK(IsWasmInstanceWrapper(fixed_array));
    return reinterpret_cast<WasmInstanceWrapper*>(fixed_array);
  }
  static bool IsWasmInstanceWrapper(Object* obj);
  bool has_instance() { return get(kWrapperInstanceObject)->IsWeakCell(); }
  Handle<WasmInstanceObject> instance_object() {
    Object* obj = get(kWrapperInstanceObject);
    DCHECK(obj->IsWeakCell());
    WeakCell* cell = WeakCell::cast(obj);
    DCHECK(cell->value()->IsJSObject());
    return handle(WasmInstanceObject::cast(cell->value()));
  }
  bool has_next() { return IsWasmInstanceWrapper(get(kNextInstanceWrapper)); }
  bool has_previous() {
    return IsWasmInstanceWrapper(get(kPreviousInstanceWrapper));
  }
  void set_next_wrapper(Object* obj) {
    DCHECK(IsWasmInstanceWrapper(obj));
    set(kNextInstanceWrapper, obj);
  }
  void set_previous_wrapper(Object* obj) {
    DCHECK(IsWasmInstanceWrapper(obj));
    set(kPreviousInstanceWrapper, obj);
  }
  Handle<WasmInstanceWrapper> next_wrapper() {
    Object* obj = get(kNextInstanceWrapper);
    DCHECK(IsWasmInstanceWrapper(obj));
    return handle(WasmInstanceWrapper::cast(obj));
  }
  Handle<WasmInstanceWrapper> previous_wrapper() {
    Object* obj = get(kPreviousInstanceWrapper);
    DCHECK(IsWasmInstanceWrapper(obj));
    return handle(WasmInstanceWrapper::cast(obj));
  }
  void reset_next_wrapper() { set_undefined(kNextInstanceWrapper); }
  void reset_previous_wrapper() { set_undefined(kPreviousInstanceWrapper); }
  void reset() {
    for (int kID = 0; kID < kWrapperPropertyCount; kID++) set_undefined(kID);
  }

 private:
  enum {
    kWrapperInstanceObject,
    kNextInstanceWrapper,
    kPreviousInstanceWrapper,
    kWrapperPropertyCount
  };
};

#undef DECLARE_CASTS
#undef DECLARE_GETTER
#undef DECLARE_ACCESSORS
#undef DECLARE_OPTIONAL_ACCESSORS
#undef DECLARE_OPTIONAL_GETTER

}  // namespace internal
}  // namespace v8

#endif  // V8_WASM_OBJECTS_H_