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