src/contexts.h

   1 // Copyright 2012 the V8 project authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef V8_CONTEXTS_H_
   6 #define V8_CONTEXTS_H_
   7
   8 #include "src/heap/heap.h"
   9 #include "src/objects.h"
  10
  11 namespace v8 {
  12 namespace internal {
  13
  14
  15 enum ContextLookupFlags {
  16   FOLLOW_CONTEXT_CHAIN = 1,
  17   FOLLOW_PROTOTYPE_CHAIN = 2,
  18
  19   DONT_FOLLOW_CHAINS = 0,
  20   FOLLOW_CHAINS = FOLLOW_CONTEXT_CHAIN | FOLLOW_PROTOTYPE_CHAIN
  21 };
  22
  23
  24 // ES5 10.2 defines lexical environments with mutable and immutable bindings.
  25 // Immutable bindings have two states, initialized and uninitialized, and
  26 // their state is changed by the InitializeImmutableBinding method. The
  27 // BindingFlags enum represents information if a binding has definitely been
  28 // initialized. A mutable binding does not need to be checked and thus has
  29 // the BindingFlag MUTABLE_IS_INITIALIZED.
  30 //
  31 // There are two possibilities for immutable bindings
  32 //  * 'const' declared variables. They are initialized when evaluating the
  33 //    corresponding declaration statement. They need to be checked for being
  34 //    initialized and thus get the flag IMMUTABLE_CHECK_INITIALIZED.
  35 //  * The function name of a named function literal. The binding is immediately
  36 //    initialized when entering the function and thus does not need to be
  37 //    checked. it gets the BindingFlag IMMUTABLE_IS_INITIALIZED.
  38 // Accessing an uninitialized binding produces the undefined value.
  39 //
  40 // The harmony proposal for block scoped bindings also introduces the
  41 // uninitialized state for mutable bindings.
  42 //  * A 'let' declared variable. They are initialized when evaluating the
  43 //    corresponding declaration statement. They need to be checked for being
  44 //    initialized and thus get the flag MUTABLE_CHECK_INITIALIZED.
  45 //  * A 'var' declared variable. It is initialized immediately upon creation
  46 //    and thus doesn't need to be checked. It gets the flag
  47 //    MUTABLE_IS_INITIALIZED.
  48 //  * Catch bound variables, function parameters and variables introduced by
  49 //    function declarations are initialized immediately and do not need to be
  50 //    checked. Thus they get the flag MUTABLE_IS_INITIALIZED.
  51 // Immutable bindings in harmony mode get the _HARMONY flag variants. Accessing
  52 // an uninitialized binding produces a reference error.
  53 //
  54 // In V8 uninitialized bindings are set to the hole value upon creation and set
  55 // to a different value upon initialization.
  56 enum BindingFlags {
  57   MUTABLE_IS_INITIALIZED,
  58   MUTABLE_CHECK_INITIALIZED,
  59   IMMUTABLE_IS_INITIALIZED,
  60   IMMUTABLE_CHECK_INITIALIZED,
  61   IMMUTABLE_IS_INITIALIZED_HARMONY,
  62   IMMUTABLE_CHECK_INITIALIZED_HARMONY,
  63   MISSING_BINDING
  64 };
  65
  66
  67 // Heap-allocated activation contexts.
  68 //
  69 // Contexts are implemented as FixedArray objects; the Context
  70 // class is a convenience interface casted on a FixedArray object.
  71 //
  72 // Note: Context must have no virtual functions and Context objects
  73 // must always be allocated via Heap::AllocateContext() or
  74 // Factory::NewContext.
  75
  76 #define NATIVE_CONTEXT_IMPORTED_FIELDS(V)                                     \
  77   V(ARRAY_VALUES_ITERATOR_INDEX, JSFunction, array_values_iterator)           \
  78   V(CREATE_DATE_FUN_INDEX, JSFunction, create_date_fun)                       \
  79   V(ERROR_FUNCTION_INDEX, JSFunction, error_function)                         \
  80   V(EVAL_ERROR_FUNCTION_INDEX, JSFunction, eval_error_function)               \
  81   V(GET_STACK_TRACE_LINE_INDEX, JSFunction, get_stack_trace_line_fun)         \
  82   V(GLOBAL_EVAL_FUN_INDEX, JSFunction, global_eval_fun)                       \
  83   V(JSON_SERIALIZE_ADAPTER_INDEX, JSFunction, json_serialize_adapter)         \
  84   V(MAKE_ERROR_FUNCTION_INDEX, JSFunction, make_error_function)               \
  85   V(MAP_DELETE_METHOD_INDEX, JSFunction, map_delete)                          \
  86   V(MAP_FROM_ARRAY_INDEX, JSFunction, map_from_array)                         \
  87   V(MAP_GET_METHOD_INDEX, JSFunction, map_get)                                \
  88   V(MAP_HAS_METHOD_INDEX, JSFunction, map_has)                                \
  89   V(MAP_SET_METHOD_INDEX, JSFunction, map_set)                                \
  90   V(MESSAGE_GET_COLUMN_NUMBER_INDEX, JSFunction, message_get_column_number)   \
  91   V(MESSAGE_GET_LINE_NUMBER_INDEX, JSFunction, message_get_line_number)       \
  92   V(MESSAGE_GET_SOURCE_LINE_INDEX, JSFunction, message_get_source_line)       \
  93   V(NATIVE_OBJECT_GET_NOTIFIER_INDEX, JSFunction, native_object_get_notifier) \
  94   V(NATIVE_OBJECT_NOTIFIER_PERFORM_CHANGE, JSFunction,                        \
  95     native_object_notifier_perform_change)                                    \
  96   V(NATIVE_OBJECT_OBSERVE_INDEX, JSFunction, native_object_observe)           \
  97   V(NO_SIDE_EFFECT_TO_STRING_FUN_INDEX, JSFunction,                           \
  98     no_side_effect_to_string_fun)                                             \
  99   V(OBJECT_DEFINE_OWN_PROPERTY_INDEX, JSFunction, object_define_own_property) \
 100   V(OBJECT_GET_OWN_PROPERTY_DESCROPTOR_INDEX, JSFunction,                     \
 101     object_get_own_property_descriptor)                                       \
 102   V(OBSERVERS_BEGIN_SPLICE_INDEX, JSFunction, observers_begin_perform_splice) \
 103   V(OBSERVERS_END_SPLICE_INDEX, JSFunction, observers_end_perform_splice)     \
 104   V(OBSERVERS_ENQUEUE_SPLICE_INDEX, JSFunction, observers_enqueue_splice)     \
 105   V(OBSERVERS_NOTIFY_CHANGE_INDEX, JSFunction, observers_notify_change)       \
 106   V(PROMISE_CATCH_INDEX, JSFunction, promise_catch)                           \
 107   V(PROMISE_CHAIN_INDEX, JSFunction, promise_chain)                           \
 108   V(PROMISE_CREATE_INDEX, JSFunction, promise_create)                         \
 109   V(PROMISE_HAS_USER_DEFINED_REJECT_HANDLER_INDEX, JSFunction,                \
 110     promise_has_user_defined_reject_handler)                                  \
 111   V(PROMISE_REJECT_INDEX, JSFunction, promise_reject)                         \
 112   V(PROMISE_RESOLVE_INDEX, JSFunction, promise_resolve)                       \
 113   V(PROMISE_THEN_INDEX, JSFunction, promise_then)                             \
 114   V(RANGE_ERROR_FUNCTION_INDEX, JSFunction, range_error_function)             \
 115   V(REFERENCE_ERROR_FUNCTION_INDEX, JSFunction, reference_error_function)     \
 116   V(SET_ADD_METHOD_INDEX, JSFunction, set_add)                                \
 117   V(SET_DELETE_METHOD_INDEX, JSFunction, set_delete)                          \
 118   V(SET_FROM_ARRAY_INDEX, JSFunction, set_from_array)                         \
 119   V(SET_HAS_METHOD_INDEX, JSFunction, set_has)                                \
 120   V(STACK_OVERFLOW_BOILERPLATE_INDEX, JSObject, stack_overflow_boilerplate)   \
 121   V(SYNTAX_ERROR_FUNCTION_INDEX, JSFunction, syntax_error_function)           \
 122   V(TO_COMPLETE_PROPERTY_DESCRIPTOR_INDEX, JSFunction,                        \
 123     to_complete_property_descriptor)                                          \
 124   V(TO_DETAIL_STRING_FUN_INDEX, JSFunction, to_detail_string_fun)             \
 125   V(TO_INTEGER_FUN_INDEX, JSFunction, to_integer_fun)                         \
 126   V(TO_LENGTH_FUN_INDEX, JSFunction, to_length_fun)                           \
 127   V(TO_NUMBER_FUN_INDEX, JSFunction, to_number_fun)                           \
 128   V(TO_STRING_FUN_INDEX, JSFunction, to_string_fun)                           \
 129   V(TYPE_ERROR_FUNCTION_INDEX, JSFunction, type_error_function)               \
 130   V(URI_ERROR_FUNCTION_INDEX, JSFunction, uri_error_function)
 131
 132 #define NATIVE_CONTEXT_IMPORTED_FIELDS_FOR_PROXY(V)       \
 133   V(DERIVED_GET_TRAP_INDEX, JSFunction, derived_get_trap) \
 134   V(DERIVED_HAS_TRAP_INDEX, JSFunction, derived_has_trap) \
 135   V(DERIVED_SET_TRAP_INDEX, JSFunction, derived_set_trap) \
 136   V(PROXY_ENUMERATE_INDEX, JSFunction, proxy_enumerate)
 137
 138 #define NATIVE_CONTEXT_FIELDS(V)                                               \
 139   V(GLOBAL_PROXY_INDEX, JSObject, global_proxy_object)                         \
 140   V(EMBEDDER_DATA_INDEX, FixedArray, embedder_data)                            \
 141   /* Below is alpha-sorted */                                                  \
 142   V(ALLOW_CODE_GEN_FROM_STRINGS_INDEX, Object, allow_code_gen_from_strings)    \
 143   V(ARRAY_BUFFER_FUN_INDEX, JSFunction, array_buffer_fun)                      \
 144   V(ARRAY_BUFFER_MAP_INDEX, Map, array_buffer_map)                             \
 145   V(ARRAY_FUNCTION_INDEX, JSFunction, array_function)                          \
 146   V(BOOL16X8_FUNCTION_INDEX, JSFunction, bool16x8_function)                    \
 147   V(BOOL32X4_FUNCTION_INDEX, JSFunction, bool32x4_function)                    \
 148   V(BOOL8X16_FUNCTION_INDEX, JSFunction, bool8x16_function)                    \
 149   V(BOOLEAN_FUNCTION_INDEX, JSFunction, boolean_function)                      \
 150   V(BOUND_FUNCTION_MAP_INDEX, Map, bound_function_map)                         \
 151   V(CALL_AS_CONSTRUCTOR_DELEGATE_INDEX, JSFunction,                            \
 152     call_as_constructor_delegate)                                              \
 153   V(CALL_AS_FUNCTION_DELEGATE_INDEX, JSFunction, call_as_function_delegate)    \
 154   V(CONTEXT_EXTENSION_FUNCTION_INDEX, JSFunction, context_extension_function)  \
 155   V(DATA_VIEW_FUN_INDEX, JSFunction, data_view_fun)                            \
 156   V(ERROR_MESSAGE_FOR_CODE_GEN_FROM_STRINGS_INDEX, Object,                     \
 157     error_message_for_code_gen_from_strings)                                   \
 158   V(EXTRAS_EXPORTS_OBJECT_INDEX, JSObject, extras_binding_object)              \
 159   V(FAST_ALIASED_ARGUMENTS_MAP_INDEX, Map, fast_aliased_arguments_map)         \
 160   V(FLOAT32_ARRAY_FUN_INDEX, JSFunction, float32_array_fun)                    \
 161   V(FLOAT32X4_FUNCTION_INDEX, JSFunction, float32x4_function)                  \
 162   V(FLOAT64_ARRAY_FUN_INDEX, JSFunction, float64_array_fun)                    \
 163   V(FUNCTION_CACHE_INDEX, ObjectHashTable, function_cache)                     \
 164   V(GENERATOR_OBJECT_PROTOTYPE_MAP_INDEX, Map, generator_object_prototype_map) \
 165   V(INITIAL_ARRAY_PROTOTYPE_INDEX, JSObject, initial_array_prototype)          \
 166   V(INITIAL_OBJECT_PROTOTYPE_INDEX, JSObject, initial_object_prototype)        \
 167   V(INT16_ARRAY_FUN_INDEX, JSFunction, int16_array_fun)                        \
 168   V(INT16X8_FUNCTION_INDEX, JSFunction, int16x8_function)                      \
 169   V(INT32_ARRAY_FUN_INDEX, JSFunction, int32_array_fun)                        \
 170   V(INT32X4_FUNCTION_INDEX, JSFunction, int32x4_function)                      \
 171   V(INT8_ARRAY_FUN_INDEX, JSFunction, int8_array_fun)                          \
 172   V(INT8X16_FUNCTION_INDEX, JSFunction, int8x16_function)                      \
 173   V(INTERNAL_ARRAY_FUNCTION_INDEX, JSFunction, internal_array_function)        \
 174   V(ITERATOR_RESULT_MAP_INDEX, Map, iterator_result_map)                       \
 175   V(JS_ARRAY_MAPS_INDEX, Object, js_array_maps)                                \
 176   V(JS_ARRAY_STRONG_MAPS_INDEX, Object, js_array_strong_maps)                  \
 177   V(JS_MAP_FUN_INDEX, JSFunction, js_map_fun)                                  \
 178   V(JS_MAP_MAP_INDEX, Map, js_map_map)                                         \
 179   V(JS_OBJECT_STRONG_MAP_INDEX, Map, js_object_strong_map)                     \
 180   V(JS_SET_FUN_INDEX, JSFunction, js_set_fun)                                  \
 181   V(JS_SET_MAP_INDEX, Map, js_set_map)                                         \
 182   V(MAP_CACHE_INDEX, Object, map_cache)                                        \
 183   V(MAP_ITERATOR_MAP_INDEX, Map, map_iterator_map)                             \
 184   V(MESSAGE_LISTENERS_INDEX, JSObject, message_listeners)                      \
 185   V(NATIVES_UTILS_OBJECT_INDEX, Object, natives_utils_object)                  \
 186   V(NORMALIZED_MAP_CACHE_INDEX, Object, normalized_map_cache)                  \
 187   V(NUMBER_FUNCTION_INDEX, JSFunction, number_function)                        \
 188   V(OBJECT_FUNCTION_INDEX, JSFunction, object_function)                        \
 189   V(OPAQUE_REFERENCE_FUNCTION_INDEX, JSFunction, opaque_reference_function)    \
 190   V(REGEXP_FUNCTION_INDEX, JSFunction, regexp_function)                        \
 191   V(REGEXP_RESULT_MAP_INDEX, Map, regexp_result_map)                           \
 192   V(RUNTIME_CONTEXT_INDEX, Context, runtime_context)                           \
 193   V(SCRIPT_CONTEXT_TABLE_INDEX, ScriptContextTable, script_context_table)      \
 194   V(SCRIPT_FUNCTION_INDEX, JSFunction, script_function)                        \
 195   V(SECURITY_TOKEN_INDEX, Object, security_token)                              \
 196   V(SET_ITERATOR_MAP_INDEX, Map, set_iterator_map)                             \
 197   V(SHARED_ARRAY_BUFFER_FUN_INDEX, JSFunction, shared_array_buffer_fun)        \
 198   V(SLOPPY_ARGUMENTS_MAP_INDEX, Map, sloppy_arguments_map)                     \
 199   V(SLOPPY_FUNCTION_MAP_INDEX, Map, sloppy_function_map)                       \
 200   V(SLOPPY_FUNCTION_WITHOUT_PROTOTYPE_MAP_INDEX, Map,                          \
 201     sloppy_function_without_prototype_map)                                     \
 202   V(SLOPPY_FUNCTION_WITH_READONLY_PROTOTYPE_MAP_INDEX, Map,                    \
 203     sloppy_function_with_readonly_prototype_map)                               \
 204   V(SLOPPY_GENERATOR_FUNCTION_MAP_INDEX, Map, sloppy_generator_function_map)   \
 205   V(SLOW_ALIASED_ARGUMENTS_MAP_INDEX, Map, slow_aliased_arguments_map)         \
 206   V(STRICT_ARGUMENTS_MAP_INDEX, Map, strict_arguments_map)                     \
 207   V(STRICT_FUNCTION_MAP_INDEX, Map, strict_function_map)                       \
 208   V(STRICT_FUNCTION_WITHOUT_PROTOTYPE_MAP_INDEX, Map,                          \
 209     strict_function_without_prototype_map)                                     \
 210   V(STRICT_GENERATOR_FUNCTION_MAP_INDEX, Map, strict_generator_function_map)   \
 211   V(STRING_FUNCTION_INDEX, JSFunction, string_function)                        \
 212   V(STRING_FUNCTION_PROTOTYPE_MAP_INDEX, Map, string_function_prototype_map)   \
 213   V(STRONG_CONSTRUCTOR_MAP_INDEX, Map, strong_constructor_map)                 \
 214   V(STRONG_FUNCTION_MAP_INDEX, Map, strong_function_map)                       \
 215   V(STRONG_GENERATOR_FUNCTION_MAP_INDEX, Map, strong_generator_function_map)   \
 216   V(STRONG_MAP_CACHE_INDEX, Object, strong_map_cache)                          \
 217   V(SYMBOL_FUNCTION_INDEX, JSFunction, symbol_function)                        \
 218   V(UINT16_ARRAY_FUN_INDEX, JSFunction, uint16_array_fun)                      \
 219   V(UINT32_ARRAY_FUN_INDEX, JSFunction, uint32_array_fun)                      \
 220   V(UINT8_ARRAY_FUN_INDEX, JSFunction, uint8_array_fun)                        \
 221   V(UINT8_CLAMPED_ARRAY_FUN_INDEX, JSFunction, uint8_clamped_array_fun)        \
 222   NATIVE_CONTEXT_IMPORTED_FIELDS(V)                                            \
 223   NATIVE_CONTEXT_IMPORTED_FIELDS_FOR_PROXY(V)
 224
 225 // A table of all script contexts. Every loaded top-level script with top-level
 226 // lexical declarations contributes its ScriptContext into this table.
 227 //
 228 // The table is a fixed array, its first slot is the current used count and
 229 // the subsequent slots 1..used contain ScriptContexts.
 230 class ScriptContextTable : public FixedArray {
 231  public:
 232   // Conversions.
 233   static ScriptContextTable* cast(Object* context) {
 234     DCHECK(context->IsScriptContextTable());
 235     return reinterpret_cast<ScriptContextTable*>(context);
 236   }
 237
 238   struct LookupResult {
 239     int context_index;
 240     int slot_index;
 241     VariableMode mode;
 242     VariableLocation location;
 243     InitializationFlag init_flag;
 244     MaybeAssignedFlag maybe_assigned_flag;
 245   };
 246
 247   int used() const { return Smi::cast(get(kUsedSlot))->value(); }
 248
 249   void set_used(int used) { set(kUsedSlot, Smi::FromInt(used)); }
 250
 251   static Handle<Context> GetContext(Handle<ScriptContextTable> table, int i) {
 252     DCHECK(i < table->used());
 253     return Handle<Context>::cast(FixedArray::get(table, i + 1));
 254   }
 255
 256   // Lookup a variable `name` in a ScriptContextTable.
 257   // If it returns true, the variable is found and `result` contains
 258   // valid information about its location.
 259   // If it returns false, `result` is untouched.
 260   MUST_USE_RESULT
 261   static bool Lookup(Handle<ScriptContextTable> table, Handle<String> name,
 262                      LookupResult* result);
 263
 264   MUST_USE_RESULT
 265   static Handle<ScriptContextTable> Extend(Handle<ScriptContextTable> table,
 266                                            Handle<Context> script_context);
 267
 268   static int GetContextOffset(int context_index) {
 269     return kFirstContextOffset + context_index * kPointerSize;
 270   }
 271
 272  private:
 273   static const int kUsedSlot = 0;
 274   static const int kFirstContextOffset =
 275       FixedArray::kHeaderSize + (kUsedSlot + 1) * kPointerSize;
 276
 277   DISALLOW_IMPLICIT_CONSTRUCTORS(ScriptContextTable);
 278 };
 279
 280 // JSFunctions are pairs (context, function code), sometimes also called
 281 // closures. A Context object is used to represent function contexts and
 282 // dynamically pushed 'with' contexts (or 'scopes' in ECMA-262 speak).
 283 //
 284 // At runtime, the contexts build a stack in parallel to the execution
 285 // stack, with the top-most context being the current context. All contexts
 286 // have the following slots:
 287 //
 288 // [ closure   ]  This is the current function. It is the same for all
 289 //                contexts inside a function. It provides access to the
 290 //                incoming context (i.e., the outer context, which may
 291 //                or may not become the current function's context), and
 292 //                it provides access to the functions code and thus it's
 293 //                scope information, which in turn contains the names of
 294 //                statically allocated context slots. The names are needed
 295 //                for dynamic lookups in the presence of 'with' or 'eval'.
 296 //
 297 // [ previous  ]  A pointer to the previous context. It is NULL for
 298 //                function contexts, and non-NULL for 'with' contexts.
 299 //                Used to implement the 'with' statement.
 300 //
 301 // [ extension ]  A pointer to an extension JSObject, or NULL. Used to
 302 //                implement 'with' statements and dynamic declarations
 303 //                (through 'eval'). The object in a 'with' statement is
 304 //                stored in the extension slot of a 'with' context.
 305 //                Dynamically declared variables/functions are also added
 306 //                to lazily allocated extension object. Context::Lookup
 307 //                searches the extension object for properties.
 308 //                For script and block contexts, contains the respective
 309 //                ScopeInfo. For block contexts representing sloppy declaration
 310 //                block scopes, it may also be a struct being a
 311 //                SloppyBlockWithEvalContextExtension, pairing the ScopeInfo
 312 //                with an extension object.
 313 //                For module contexts, points back to the respective JSModule.
 314 //
 315 // [ global_object ]  A pointer to the global object. Provided for quick
 316 //                access to the global object from inside the code (since
 317 //                we always have a context pointer).
 318 //
 319 // In addition, function contexts may have statically allocated context slots
 320 // to store local variables/functions that are accessed from inner functions
 321 // (via static context addresses) or through 'eval' (dynamic context lookups).
 322 // The native context contains additional slots for fast access to native
 323 // properties.
 324 //
 325 // Finally, with Harmony scoping, the JSFunction representing a top level
 326 // script will have the ScriptContext rather than a FunctionContext.
 327 // Script contexts from all top-level scripts are gathered in
 328 // ScriptContextTable.
 329
 330 class Context: public FixedArray {
 331  public:
 332   // Conversions.
 333   static Context* cast(Object* context) {
 334     DCHECK(context->IsContext());
 335     return reinterpret_cast<Context*>(context);
 336   }
 337
 338   // The default context slot layout; indices are FixedArray slot indices.
 339   enum {
 340     // These slots are in all contexts.
 341     CLOSURE_INDEX,
 342     PREVIOUS_INDEX,
 343     // The extension slot is used for either the global object (in global
 344     // contexts), eval extension object (function contexts), subject of with
 345     // (with contexts), or the variable name (catch contexts), the serialized
 346     // scope info (block contexts), or the module instance (module contexts).
 347     EXTENSION_INDEX,
 348     GLOBAL_OBJECT_INDEX,
 349
 350     // These slots are only in native contexts.
 351 #define NATIVE_CONTEXT_SLOT(index, type, name) index,
 352     NATIVE_CONTEXT_FIELDS(NATIVE_CONTEXT_SLOT)
 353 #undef NATIVE_CONTEXT_SLOT
 354
 355     // Properties from here are treated as weak references by the full GC.
 356     // Scavenge treats them as strong references.
 357     OPTIMIZED_FUNCTIONS_LIST,  // Weak.
 358     OPTIMIZED_CODE_LIST,       // Weak.
 359     DEOPTIMIZED_CODE_LIST,     // Weak.
 360     NEXT_CONTEXT_LINK,         // Weak.
 361
 362     // Total number of slots.
 363     NATIVE_CONTEXT_SLOTS,
 364     FIRST_WEAK_SLOT = OPTIMIZED_FUNCTIONS_LIST,
 365
 366     MIN_CONTEXT_SLOTS = GLOBAL_PROXY_INDEX,
 367     // This slot holds the thrown value in catch contexts.
 368     THROWN_OBJECT_INDEX = MIN_CONTEXT_SLOTS,
 369   };
 370
 371   // Direct slot access.
 372   JSFunction* closure() { return JSFunction::cast(get(CLOSURE_INDEX)); }
 373   void set_closure(JSFunction* closure) { set(CLOSURE_INDEX, closure); }
 374
 375   Context* previous() {
 376     Object* result = unchecked_previous();
 377     DCHECK(IsBootstrappingOrValidParentContext(result, this));
 378     return reinterpret_cast<Context*>(result);
 379   }
 380   void set_previous(Context* context) { set(PREVIOUS_INDEX, context); }
 381
 382   bool has_extension() { return extension() != nullptr; }
 383   Object* extension() { return get(EXTENSION_INDEX); }
 384   void set_extension(Object* object) { set(EXTENSION_INDEX, object); }
 385   JSObject* extension_object();
 386   JSReceiver* extension_receiver();
 387   ScopeInfo* scope_info();
 388   String* catch_name();
 389
 390   JSModule* module() { return JSModule::cast(get(EXTENSION_INDEX)); }
 391   void set_module(JSModule* module) { set(EXTENSION_INDEX, module); }
 392
 393   // Get the context where var declarations will be hoisted to, which
 394   // may be the context itself.
 395   Context* declaration_context();
 396   bool is_declaration_context();
 397
 398   GlobalObject* global_object() {
 399     Object* result = get(GLOBAL_OBJECT_INDEX);
 400     DCHECK(IsBootstrappingOrGlobalObject(this->GetIsolate(), result));
 401     return reinterpret_cast<GlobalObject*>(result);
 402   }
 403   void set_global_object(GlobalObject* object) {
 404     set(GLOBAL_OBJECT_INDEX, object);
 405   }
 406
 407   // Returns a JSGlobalProxy object or null.
 408   JSObject* global_proxy();
 409   void set_global_proxy(JSObject* global);
 410
 411   // The builtins object.
 412   JSBuiltinsObject* builtins();
 413
 414   // Get the script context by traversing the context chain.
 415   Context* script_context();
 416
 417   // Compute the native context by traversing the context chain.
 418   Context* native_context();
 419
 420   // Predicates for context types.  IsNativeContext is also defined on Object
 421   // because we frequently have to know if arbitrary objects are natives
 422   // contexts.
 423   bool IsNativeContext() {
 424     Map* map = this->map();
 425     return map == map->GetHeap()->native_context_map();
 426   }
 427   bool IsFunctionContext() {
 428     Map* map = this->map();
 429     return map == map->GetHeap()->function_context_map();
 430   }
 431   bool IsCatchContext() {
 432     Map* map = this->map();
 433     return map == map->GetHeap()->catch_context_map();
 434   }
 435   bool IsWithContext() {
 436     Map* map = this->map();
 437     return map == map->GetHeap()->with_context_map();
 438   }
 439   bool IsBlockContext() {
 440     Map* map = this->map();
 441     return map == map->GetHeap()->block_context_map();
 442   }
 443   bool IsModuleContext() {
 444     Map* map = this->map();
 445     return map == map->GetHeap()->module_context_map();
 446   }
 447   bool IsScriptContext() {
 448     Map* map = this->map();
 449     return map == map->GetHeap()->script_context_map();
 450   }
 451
 452   bool HasSameSecurityTokenAs(Context* that) {
 453     return this->global_object()->native_context()->security_token() ==
 454         that->global_object()->native_context()->security_token();
 455   }
 456
 457   // Initializes global variable bindings in given script context.
 458   void InitializeGlobalSlots();
 459
 460   // A native context holds a list of all functions with optimized code.
 461   void AddOptimizedFunction(JSFunction* function);
 462   void RemoveOptimizedFunction(JSFunction* function);
 463   void SetOptimizedFunctionsListHead(Object* head);
 464   Object* OptimizedFunctionsListHead();
 465
 466   // The native context also stores a list of all optimized code and a
 467   // list of all deoptimized code, which are needed by the deoptimizer.
 468   void AddOptimizedCode(Code* code);
 469   void SetOptimizedCodeListHead(Object* head);
 470   Object* OptimizedCodeListHead();
 471   void SetDeoptimizedCodeListHead(Object* head);
 472   Object* DeoptimizedCodeListHead();
 473
 474   Handle<Object> ErrorMessageForCodeGenerationFromStrings();
 475
 476 #define NATIVE_CONTEXT_FIELD_ACCESSORS(index, type, name) \
 477   void  set_##name(type* value) {                         \
 478     DCHECK(IsNativeContext());                            \
 479     set(index, value);                                    \
 480   }                                                       \
 481   bool is_##name(type* value) {                           \
 482     DCHECK(IsNativeContext());                            \
 483     return type::cast(get(index)) == value;               \
 484   }                                                       \
 485   type* name() {                                          \
 486     DCHECK(IsNativeContext());                            \
 487     return type::cast(get(index));                        \
 488   }
 489   NATIVE_CONTEXT_FIELDS(NATIVE_CONTEXT_FIELD_ACCESSORS)
 490 #undef NATIVE_CONTEXT_FIELD_ACCESSORS
 491
 492   // Lookup the slot called name, starting with the current context.
 493   // There are three possibilities:
 494   //
 495   // 1) result->IsContext():
 496   //    The binding was found in a context.  *index is always the
 497   //    non-negative slot index.  *attributes is NONE for var and let
 498   //    declarations, READ_ONLY for const declarations (never ABSENT).
 499   //
 500   // 2) result->IsJSObject():
 501   //    The binding was found as a named property in a context extension
 502   //    object (i.e., was introduced via eval), as a property on the subject
 503   //    of with, or as a property of the global object.  *index is -1 and
 504   //    *attributes is not ABSENT.
 505   //
 506   // 3) result.is_null():
 507   //    There was no binding found, *index is always -1 and *attributes is
 508   //    always ABSENT.
 509   Handle<Object> Lookup(Handle<String> name,
 510                         ContextLookupFlags flags,
 511                         int* index,
 512                         PropertyAttributes* attributes,
 513                         BindingFlags* binding_flags);
 514
 515   // Code generation support.
 516   static int SlotOffset(int index) {
 517     return kHeaderSize + index * kPointerSize - kHeapObjectTag;
 518   }
 519
 520   static int FunctionMapIndex(LanguageMode language_mode, FunctionKind kind) {
 521     if (IsGeneratorFunction(kind)) {
 522       return is_strong(language_mode) ? STRONG_GENERATOR_FUNCTION_MAP_INDEX :
 523              is_strict(language_mode) ? STRICT_GENERATOR_FUNCTION_MAP_INDEX
 524                                       : SLOPPY_GENERATOR_FUNCTION_MAP_INDEX;
 525     }
 526
 527     if (IsConstructor(kind)) {
 528       // Use strict function map (no own "caller" / "arguments")
 529       return is_strong(language_mode) ? STRONG_CONSTRUCTOR_MAP_INDEX
 530                                       : STRICT_FUNCTION_MAP_INDEX;
 531     }
 532
 533     if (IsArrowFunction(kind) || IsConciseMethod(kind) ||
 534         IsAccessorFunction(kind)) {
 535       return is_strong(language_mode)
 536                  ? STRONG_FUNCTION_MAP_INDEX
 537                  : STRICT_FUNCTION_WITHOUT_PROTOTYPE_MAP_INDEX;
 538     }
 539
 540     return is_strong(language_mode) ? STRONG_FUNCTION_MAP_INDEX :
 541            is_strict(language_mode) ? STRICT_FUNCTION_MAP_INDEX
 542                                     : SLOPPY_FUNCTION_MAP_INDEX;
 543   }
 544
 545   static const int kSize = kHeaderSize + NATIVE_CONTEXT_SLOTS * kPointerSize;
 546
 547   // GC support.
 548   typedef FixedBodyDescriptor<
 549       kHeaderSize, kSize, kSize> ScavengeBodyDescriptor;
 550
 551   typedef FixedBodyDescriptor<
 552       kHeaderSize,
 553       kHeaderSize + FIRST_WEAK_SLOT * kPointerSize,
 554       kSize> MarkCompactBodyDescriptor;
 555
 556  private:
 557   // Unchecked access to the slots.
 558   Object* unchecked_previous() { return get(PREVIOUS_INDEX); }
 559
 560 #ifdef DEBUG
 561   // Bootstrapping-aware type checks.
 562   static bool IsBootstrappingOrValidParentContext(Object* object, Context* kid);
 563   static bool IsBootstrappingOrGlobalObject(Isolate* isolate, Object* object);
 564 #endif
 565
 566   STATIC_ASSERT(kHeaderSize == Internals::kContextHeaderSize);
 567   STATIC_ASSERT(EMBEDDER_DATA_INDEX == Internals::kContextEmbedderDataIndex);
 568 };
 569
 570 } }  // namespace v8::internal
 571
 572 #endif  // V8_CONTEXTS_H_