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(UINT16X8_FUNCTION_INDEX, JSFunction, uint16x8_function)                    \
 220   V(UINT32_ARRAY_FUN_INDEX, JSFunction, uint32_array_fun)                      \
 221   V(UINT32X4_FUNCTION_INDEX, JSFunction, uint32x4_function)                    \
 222   V(UINT8_ARRAY_FUN_INDEX, JSFunction, uint8_array_fun)                        \
 223   V(UINT8_CLAMPED_ARRAY_FUN_INDEX, JSFunction, uint8_clamped_array_fun)        \
 224   V(UINT8X16_FUNCTION_INDEX, JSFunction, uint8x16_function)                    \
 225   NATIVE_CONTEXT_IMPORTED_FIELDS(V)                                            \
 226   NATIVE_CONTEXT_IMPORTED_FIELDS_FOR_PROXY(V)
 227
 228 // A table of all script contexts. Every loaded top-level script with top-level
 229 // lexical declarations contributes its ScriptContext into this table.
 230 //
 231 // The table is a fixed array, its first slot is the current used count and
 232 // the subsequent slots 1..used contain ScriptContexts.
 233 class ScriptContextTable : public FixedArray {
 234  public:
 235   // Conversions.
 236   static ScriptContextTable* cast(Object* context) {
 237     DCHECK(context->IsScriptContextTable());
 238     return reinterpret_cast<ScriptContextTable*>(context);
 239   }
 240
 241   struct LookupResult {
 242     int context_index;
 243     int slot_index;
 244     VariableMode mode;
 245     VariableLocation location;
 246     InitializationFlag init_flag;
 247     MaybeAssignedFlag maybe_assigned_flag;
 248   };
 249
 250   int used() const { return Smi::cast(get(kUsedSlot))->value(); }
 251
 252   void set_used(int used) { set(kUsedSlot, Smi::FromInt(used)); }
 253
 254   static Handle<Context> GetContext(Handle<ScriptContextTable> table, int i) {
 255     DCHECK(i < table->used());
 256     return Handle<Context>::cast(FixedArray::get(table, i + 1));
 257   }
 258
 259   // Lookup a variable `name` in a ScriptContextTable.
 260   // If it returns true, the variable is found and `result` contains
 261   // valid information about its location.
 262   // If it returns false, `result` is untouched.
 263   MUST_USE_RESULT
 264   static bool Lookup(Handle<ScriptContextTable> table, Handle<String> name,
 265                      LookupResult* result);
 266
 267   MUST_USE_RESULT
 268   static Handle<ScriptContextTable> Extend(Handle<ScriptContextTable> table,
 269                                            Handle<Context> script_context);
 270
 271   static int GetContextOffset(int context_index) {
 272     return kFirstContextOffset + context_index * kPointerSize;
 273   }
 274
 275  private:
 276   static const int kUsedSlot = 0;
 277   static const int kFirstContextOffset =
 278       FixedArray::kHeaderSize + (kUsedSlot + 1) * kPointerSize;
 279
 280   DISALLOW_IMPLICIT_CONSTRUCTORS(ScriptContextTable);
 281 };
 282
 283 // JSFunctions are pairs (context, function code), sometimes also called
 284 // closures. A Context object is used to represent function contexts and
 285 // dynamically pushed 'with' contexts (or 'scopes' in ECMA-262 speak).
 286 //
 287 // At runtime, the contexts build a stack in parallel to the execution
 288 // stack, with the top-most context being the current context. All contexts
 289 // have the following slots:
 290 //
 291 // [ closure   ]  This is the current function. It is the same for all
 292 //                contexts inside a function. It provides access to the
 293 //                incoming context (i.e., the outer context, which may
 294 //                or may not become the current function's context), and
 295 //                it provides access to the functions code and thus it's
 296 //                scope information, which in turn contains the names of
 297 //                statically allocated context slots. The names are needed
 298 //                for dynamic lookups in the presence of 'with' or 'eval'.
 299 //
 300 // [ previous  ]  A pointer to the previous context. It is NULL for
 301 //                function contexts, and non-NULL for 'with' contexts.
 302 //                Used to implement the 'with' statement.
 303 //
 304 // [ extension ]  A pointer to an extension JSObject, or NULL. Used to
 305 //                implement 'with' statements and dynamic declarations
 306 //                (through 'eval'). The object in a 'with' statement is
 307 //                stored in the extension slot of a 'with' context.
 308 //                Dynamically declared variables/functions are also added
 309 //                to lazily allocated extension object. Context::Lookup
 310 //                searches the extension object for properties.
 311 //                For script and block contexts, contains the respective
 312 //                ScopeInfo. For block contexts representing sloppy declaration
 313 //                block scopes, it may also be a struct being a
 314 //                SloppyBlockWithEvalContextExtension, pairing the ScopeInfo
 315 //                with an extension object.
 316 //                For module contexts, points back to the respective JSModule.
 317 //
 318 // [ global_object ]  A pointer to the global object. Provided for quick
 319 //                access to the global object from inside the code (since
 320 //                we always have a context pointer).
 321 //
 322 // In addition, function contexts may have statically allocated context slots
 323 // to store local variables/functions that are accessed from inner functions
 324 // (via static context addresses) or through 'eval' (dynamic context lookups).
 325 // The native context contains additional slots for fast access to native
 326 // properties.
 327 //
 328 // Finally, with Harmony scoping, the JSFunction representing a top level
 329 // script will have the ScriptContext rather than a FunctionContext.
 330 // Script contexts from all top-level scripts are gathered in
 331 // ScriptContextTable.
 332
 333 class Context: public FixedArray {
 334  public:
 335   // Conversions.
 336   static Context* cast(Object* context) {
 337     DCHECK(context->IsContext());
 338     return reinterpret_cast<Context*>(context);
 339   }
 340
 341   // The default context slot layout; indices are FixedArray slot indices.
 342   enum {
 343     // These slots are in all contexts.
 344     CLOSURE_INDEX,
 345     PREVIOUS_INDEX,
 346     // The extension slot is used for either the global object (in global
 347     // contexts), eval extension object (function contexts), subject of with
 348     // (with contexts), or the variable name (catch contexts), the serialized
 349     // scope info (block contexts), or the module instance (module contexts).
 350     EXTENSION_INDEX,
 351     GLOBAL_OBJECT_INDEX,
 352
 353     // These slots are only in native contexts.
 354 #define NATIVE_CONTEXT_SLOT(index, type, name) index,
 355     NATIVE_CONTEXT_FIELDS(NATIVE_CONTEXT_SLOT)
 356 #undef NATIVE_CONTEXT_SLOT
 357
 358     // Properties from here are treated as weak references by the full GC.
 359     // Scavenge treats them as strong references.
 360     OPTIMIZED_FUNCTIONS_LIST,  // Weak.
 361     OPTIMIZED_CODE_LIST,       // Weak.
 362     DEOPTIMIZED_CODE_LIST,     // Weak.
 363     NEXT_CONTEXT_LINK,         // Weak.
 364
 365     // Total number of slots.
 366     NATIVE_CONTEXT_SLOTS,
 367     FIRST_WEAK_SLOT = OPTIMIZED_FUNCTIONS_LIST,
 368
 369     MIN_CONTEXT_SLOTS = GLOBAL_PROXY_INDEX,
 370     // This slot holds the thrown value in catch contexts.
 371     THROWN_OBJECT_INDEX = MIN_CONTEXT_SLOTS,
 372   };
 373
 374   // Direct slot access.
 375   JSFunction* closure() { return JSFunction::cast(get(CLOSURE_INDEX)); }
 376   void set_closure(JSFunction* closure) { set(CLOSURE_INDEX, closure); }
 377
 378   Context* previous() {
 379     Object* result = unchecked_previous();
 380     DCHECK(IsBootstrappingOrValidParentContext(result, this));
 381     return reinterpret_cast<Context*>(result);
 382   }
 383   void set_previous(Context* context) { set(PREVIOUS_INDEX, context); }
 384
 385   bool has_extension() { return extension() != nullptr; }
 386   Object* extension() { return get(EXTENSION_INDEX); }
 387   void set_extension(Object* object) { set(EXTENSION_INDEX, object); }
 388   JSObject* extension_object();
 389   JSReceiver* extension_receiver();
 390   ScopeInfo* scope_info();
 391   String* catch_name();
 392
 393   JSModule* module() { return JSModule::cast(get(EXTENSION_INDEX)); }
 394   void set_module(JSModule* module) { set(EXTENSION_INDEX, module); }
 395
 396   // Get the context where var declarations will be hoisted to, which
 397   // may be the context itself.
 398   Context* declaration_context();
 399   bool is_declaration_context();
 400
 401   GlobalObject* global_object() {
 402     Object* result = get(GLOBAL_OBJECT_INDEX);
 403     DCHECK(IsBootstrappingOrGlobalObject(this->GetIsolate(), result));
 404     return reinterpret_cast<GlobalObject*>(result);
 405   }
 406   void set_global_object(GlobalObject* object) {
 407     set(GLOBAL_OBJECT_INDEX, object);
 408   }
 409
 410   // Returns a JSGlobalProxy object or null.
 411   JSObject* global_proxy();
 412   void set_global_proxy(JSObject* global);
 413
 414   // The builtins object.
 415   JSBuiltinsObject* builtins();
 416
 417   // Get the script context by traversing the context chain.
 418   Context* script_context();
 419
 420   // Compute the native context by traversing the context chain.
 421   Context* native_context();
 422
 423   // Predicates for context types.  IsNativeContext is also defined on Object
 424   // because we frequently have to know if arbitrary objects are natives
 425   // contexts.
 426   bool IsNativeContext() {
 427     Map* map = this->map();
 428     return map == map->GetHeap()->native_context_map();
 429   }
 430   bool IsFunctionContext() {
 431     Map* map = this->map();
 432     return map == map->GetHeap()->function_context_map();
 433   }
 434   bool IsCatchContext() {
 435     Map* map = this->map();
 436     return map == map->GetHeap()->catch_context_map();
 437   }
 438   bool IsWithContext() {
 439     Map* map = this->map();
 440     return map == map->GetHeap()->with_context_map();
 441   }
 442   bool IsBlockContext() {
 443     Map* map = this->map();
 444     return map == map->GetHeap()->block_context_map();
 445   }
 446   bool IsModuleContext() {
 447     Map* map = this->map();
 448     return map == map->GetHeap()->module_context_map();
 449   }
 450   bool IsScriptContext() {
 451     Map* map = this->map();
 452     return map == map->GetHeap()->script_context_map();
 453   }
 454
 455   bool HasSameSecurityTokenAs(Context* that) {
 456     return this->global_object()->native_context()->security_token() ==
 457         that->global_object()->native_context()->security_token();
 458   }
 459
 460   // Initializes global variable bindings in given script context.
 461   void InitializeGlobalSlots();
 462
 463   // A native context holds a list of all functions with optimized code.
 464   void AddOptimizedFunction(JSFunction* function);
 465   void RemoveOptimizedFunction(JSFunction* function);
 466   void SetOptimizedFunctionsListHead(Object* head);
 467   Object* OptimizedFunctionsListHead();
 468
 469   // The native context also stores a list of all optimized code and a
 470   // list of all deoptimized code, which are needed by the deoptimizer.
 471   void AddOptimizedCode(Code* code);
 472   void SetOptimizedCodeListHead(Object* head);
 473   Object* OptimizedCodeListHead();
 474   void SetDeoptimizedCodeListHead(Object* head);
 475   Object* DeoptimizedCodeListHead();
 476
 477   Handle<Object> ErrorMessageForCodeGenerationFromStrings();
 478
 479 #define NATIVE_CONTEXT_FIELD_ACCESSORS(index, type, name) \
 480   void  set_##name(type* value) {                         \
 481     DCHECK(IsNativeContext());                            \
 482     set(index, value);                                    \
 483   }                                                       \
 484   bool is_##name(type* value) {                           \
 485     DCHECK(IsNativeContext());                            \
 486     return type::cast(get(index)) == value;               \
 487   }                                                       \
 488   type* name() {                                          \
 489     DCHECK(IsNativeContext());                            \
 490     return type::cast(get(index));                        \
 491   }
 492   NATIVE_CONTEXT_FIELDS(NATIVE_CONTEXT_FIELD_ACCESSORS)
 493 #undef NATIVE_CONTEXT_FIELD_ACCESSORS
 494
 495   // Lookup the slot called name, starting with the current context.
 496   // There are three possibilities:
 497   //
 498   // 1) result->IsContext():
 499   //    The binding was found in a context.  *index is always the
 500   //    non-negative slot index.  *attributes is NONE for var and let
 501   //    declarations, READ_ONLY for const declarations (never ABSENT).
 502   //
 503   // 2) result->IsJSObject():
 504   //    The binding was found as a named property in a context extension
 505   //    object (i.e., was introduced via eval), as a property on the subject
 506   //    of with, or as a property of the global object.  *index is -1 and
 507   //    *attributes is not ABSENT.
 508   //
 509   // 3) result.is_null():
 510   //    There was no binding found, *index is always -1 and *attributes is
 511   //    always ABSENT.
 512   Handle<Object> Lookup(Handle<String> name,
 513                         ContextLookupFlags flags,
 514                         int* index,
 515                         PropertyAttributes* attributes,
 516                         BindingFlags* binding_flags);
 517
 518   // Code generation support.
 519   static int SlotOffset(int index) {
 520     return kHeaderSize + index * kPointerSize - kHeapObjectTag;
 521   }
 522
 523   static int FunctionMapIndex(LanguageMode language_mode, FunctionKind kind) {
 524     if (IsGeneratorFunction(kind)) {
 525       return is_strong(language_mode) ? STRONG_GENERATOR_FUNCTION_MAP_INDEX :
 526              is_strict(language_mode) ? STRICT_GENERATOR_FUNCTION_MAP_INDEX
 527                                       : SLOPPY_GENERATOR_FUNCTION_MAP_INDEX;
 528     }
 529
 530     if (IsConstructor(kind)) {
 531       // Use strict function map (no own "caller" / "arguments")
 532       return is_strong(language_mode) ? STRONG_CONSTRUCTOR_MAP_INDEX
 533                                       : STRICT_FUNCTION_MAP_INDEX;
 534     }
 535
 536     if (IsArrowFunction(kind) || IsConciseMethod(kind) ||
 537         IsAccessorFunction(kind)) {
 538       return is_strong(language_mode)
 539                  ? STRONG_FUNCTION_MAP_INDEX
 540                  : STRICT_FUNCTION_WITHOUT_PROTOTYPE_MAP_INDEX;
 541     }
 542
 543     return is_strong(language_mode) ? STRONG_FUNCTION_MAP_INDEX :
 544            is_strict(language_mode) ? STRICT_FUNCTION_MAP_INDEX
 545                                     : SLOPPY_FUNCTION_MAP_INDEX;
 546   }
 547
 548   static const int kSize = kHeaderSize + NATIVE_CONTEXT_SLOTS * kPointerSize;
 549
 550   // GC support.
 551   typedef FixedBodyDescriptor<
 552       kHeaderSize, kSize, kSize> ScavengeBodyDescriptor;
 553
 554   typedef FixedBodyDescriptor<
 555       kHeaderSize,
 556       kHeaderSize + FIRST_WEAK_SLOT * kPointerSize,
 557       kSize> MarkCompactBodyDescriptor;
 558
 559  private:
 560   // Unchecked access to the slots.
 561   Object* unchecked_previous() { return get(PREVIOUS_INDEX); }
 562
 563 #ifdef DEBUG
 564   // Bootstrapping-aware type checks.
 565   static bool IsBootstrappingOrValidParentContext(Object* object, Context* kid);
 566   static bool IsBootstrappingOrGlobalObject(Isolate* isolate, Object* object);
 567 #endif
 568
 569   STATIC_ASSERT(kHeaderSize == Internals::kContextHeaderSize);
 570   STATIC_ASSERT(EMBEDDER_DATA_INDEX == Internals::kContextEmbedderDataIndex);
 571 };
 572
 573 } }  // namespace v8::internal
 574
 575 #endif  // V8_CONTEXTS_H_