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(OBJECT_FUNCTION_INDEX, JSFunction, object_function)                        \
  86   V(JS_OBJECT_STRONG_MAP_INDEX, Map, js_object_strong_map)                     \
  87   V(INTERNAL_ARRAY_FUNCTION_INDEX, JSFunction, internal_array_function)        \
  88   V(ARRAY_FUNCTION_INDEX, JSFunction, array_function)                          \
  89   V(JS_ARRAY_MAPS_INDEX, Object, js_array_maps)                                \
  90   V(JS_ARRAY_STRONG_MAPS_INDEX, Object, js_array_strong_maps)                  \
  91   V(DATE_FUNCTION_INDEX, JSFunction, date_function)                            \
  92   V(JSON_OBJECT_INDEX, JSObject, json_object)                                  \
  93   V(REGEXP_FUNCTION_INDEX, JSFunction, regexp_function)                        \
  94   V(INITIAL_OBJECT_PROTOTYPE_INDEX, JSObject, initial_object_prototype)        \
  95   V(INITIAL_ARRAY_PROTOTYPE_INDEX, JSObject, initial_array_prototype)          \
  96   V(CREATE_DATE_FUN_INDEX, JSFunction, create_date_fun)                        \
  97   V(TO_NUMBER_FUN_INDEX, JSFunction, to_number_fun)                            \
  98   V(TO_STRING_FUN_INDEX, JSFunction, to_string_fun)                            \
  99   V(TO_DETAIL_STRING_FUN_INDEX, JSFunction, to_detail_string_fun)              \
 100   V(TO_OBJECT_FUN_INDEX, JSFunction, to_object_fun)                            \
 101   V(TO_INTEGER_FUN_INDEX, JSFunction, to_integer_fun)                          \
 102   V(TO_UINT32_FUN_INDEX, JSFunction, to_uint32_fun)                            \
 103   V(TO_INT32_FUN_INDEX, JSFunction, to_int32_fun)                              \
 104   V(TO_LENGTH_FUN_INDEX, JSFunction, to_length_fun)                            \
 105   V(GLOBAL_EVAL_FUN_INDEX, JSFunction, global_eval_fun)                        \
 106   V(ARRAY_BUFFER_FUN_INDEX, JSFunction, array_buffer_fun)                      \
 107   V(SHARED_ARRAY_BUFFER_FUN_INDEX, JSFunction, shared_array_buffer_fun)        \
 108   V(ARRAY_BUFFER_MAP_INDEX, Map, array_buffer_map)                             \
 109   V(UINT8_ARRAY_FUN_INDEX, JSFunction, uint8_array_fun)                        \
 110   V(INT8_ARRAY_FUN_INDEX, JSFunction, int8_array_fun)                          \
 111   V(UINT16_ARRAY_FUN_INDEX, JSFunction, uint16_array_fun)                      \
 112   V(INT16_ARRAY_FUN_INDEX, JSFunction, int16_array_fun)                        \
 113   V(UINT32_ARRAY_FUN_INDEX, JSFunction, uint32_array_fun)                      \
 114   V(INT32_ARRAY_FUN_INDEX, JSFunction, int32_array_fun)                        \
 115   V(FLOAT32_ARRAY_FUN_INDEX, JSFunction, float32_array_fun)                    \
 116   V(FLOAT64_ARRAY_FUN_INDEX, JSFunction, float64_array_fun)                    \
 117   V(UINT8_CLAMPED_ARRAY_FUN_INDEX, JSFunction, uint8_clamped_array_fun)        \
 118   V(DATA_VIEW_FUN_INDEX, JSFunction, data_view_fun)                            \
 119   V(SLOPPY_FUNCTION_MAP_INDEX, Map, sloppy_function_map)                       \
 120   V(SLOPPY_FUNCTION_WITH_READONLY_PROTOTYPE_MAP_INDEX, Map,                    \
 121     sloppy_function_with_readonly_prototype_map)                               \
 122   V(STRICT_FUNCTION_MAP_INDEX, Map, strict_function_map)                       \
 123   V(STRONG_FUNCTION_MAP_INDEX, Map, strong_function_map)                       \
 124   V(SLOPPY_FUNCTION_WITHOUT_PROTOTYPE_MAP_INDEX, Map,                          \
 125     sloppy_function_without_prototype_map)                                     \
 126   V(STRICT_FUNCTION_WITHOUT_PROTOTYPE_MAP_INDEX, Map,                          \
 127     strict_function_without_prototype_map)                                     \
 128   V(STRONG_CONSTRUCTOR_MAP_INDEX, Map, strong_constructor_map)                 \
 129   V(BOUND_FUNCTION_MAP_INDEX, Map, bound_function_map)                         \
 130   V(REGEXP_RESULT_MAP_INDEX, Map, regexp_result_map)                           \
 131   V(SLOPPY_ARGUMENTS_MAP_INDEX, Map, sloppy_arguments_map)                     \
 132   V(FAST_ALIASED_ARGUMENTS_MAP_INDEX, Map, fast_aliased_arguments_map)         \
 133   V(SLOW_ALIASED_ARGUMENTS_MAP_INDEX, Map, slow_aliased_arguments_map)         \
 134   V(STRICT_ARGUMENTS_MAP_INDEX, Map, strict_arguments_map)                     \
 135   V(MESSAGE_LISTENERS_INDEX, JSObject, message_listeners)                      \
 136   V(MAKE_MESSAGE_FUN_INDEX, JSFunction, make_message_fun)                      \
 137   V(GET_STACK_TRACE_LINE_INDEX, JSFunction, get_stack_trace_line_fun)          \
 138   V(CONFIGURE_GLOBAL_INDEX, JSFunction, configure_global_fun)                  \
 139   V(FUNCTION_CACHE_INDEX, ObjectHashTable, function_cache)                     \
 140   V(JSFUNCTION_RESULT_CACHES_INDEX, FixedArray, jsfunction_result_caches)      \
 141   V(NORMALIZED_MAP_CACHE_INDEX, Object, normalized_map_cache)                  \
 142   V(RUNTIME_CONTEXT_INDEX, Context, runtime_context)                           \
 143   V(CALL_AS_FUNCTION_DELEGATE_INDEX, JSFunction, call_as_function_delegate)    \
 144   V(CALL_AS_CONSTRUCTOR_DELEGATE_INDEX, JSFunction,                            \
 145     call_as_constructor_delegate)                                              \
 146   V(SCRIPT_FUNCTION_INDEX, JSFunction, script_function)                        \
 147   V(OPAQUE_REFERENCE_FUNCTION_INDEX, JSFunction, opaque_reference_function)    \
 148   V(CONTEXT_EXTENSION_FUNCTION_INDEX, JSFunction, context_extension_function)  \
 149   V(MAP_CACHE_INDEX, Object, map_cache)                                        \
 150   V(STRONG_MAP_CACHE_INDEX, Object, strong_map_cache)                          \
 151   V(EMBEDDER_DATA_INDEX, FixedArray, embedder_data)                            \
 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(PROMISE_STATUS_INDEX, Symbol, promise_status)                              \
 156   V(PROMISE_VALUE_INDEX, Symbol, promise_value)                                \
 157   V(PROMISE_CREATE_INDEX, JSFunction, promise_create)                          \
 158   V(PROMISE_RESOLVE_INDEX, JSFunction, promise_resolve)                        \
 159   V(PROMISE_REJECT_INDEX, JSFunction, promise_reject)                          \
 160   V(PROMISE_CHAIN_INDEX, JSFunction, promise_chain)                            \
 161   V(PROMISE_CATCH_INDEX, JSFunction, promise_catch)                            \
 162   V(PROMISE_THEN_INDEX, JSFunction, promise_then)                              \
 163   V(TO_COMPLETE_PROPERTY_DESCRIPTOR_INDEX, JSFunction,                         \
 164     to_complete_property_descriptor)                                           \
 165   V(DERIVED_HAS_TRAP_INDEX, JSFunction, derived_has_trap)                      \
 166   V(DERIVED_GET_TRAP_INDEX, JSFunction, derived_get_trap)                      \
 167   V(DERIVED_SET_TRAP_INDEX, JSFunction, derived_set_trap)                      \
 168   V(PROXY_ENUMERATE_INDEX, JSFunction, proxy_enumerate)                        \
 169   V(OBSERVERS_NOTIFY_CHANGE_INDEX, JSFunction, observers_notify_change)        \
 170   V(OBSERVERS_ENQUEUE_SPLICE_INDEX, JSFunction, observers_enqueue_splice)      \
 171   V(OBSERVERS_BEGIN_SPLICE_INDEX, JSFunction, observers_begin_perform_splice)  \
 172   V(OBSERVERS_END_SPLICE_INDEX, JSFunction, observers_end_perform_splice)      \
 173   V(NATIVE_OBJECT_OBSERVE_INDEX, JSFunction, native_object_observe)            \
 174   V(NATIVE_OBJECT_GET_NOTIFIER_INDEX, JSFunction, native_object_get_notifier)  \
 175   V(NATIVE_OBJECT_NOTIFIER_PERFORM_CHANGE, JSFunction,                         \
 176     native_object_notifier_perform_change)                                     \
 177   V(SLOPPY_GENERATOR_FUNCTION_MAP_INDEX, Map, sloppy_generator_function_map)   \
 178   V(STRICT_GENERATOR_FUNCTION_MAP_INDEX, Map, strict_generator_function_map)   \
 179   V(STRONG_GENERATOR_FUNCTION_MAP_INDEX, Map, strong_generator_function_map)   \
 180   V(GENERATOR_OBJECT_PROTOTYPE_MAP_INDEX, Map, generator_object_prototype_map) \
 181   V(ITERATOR_RESULT_MAP_INDEX, Map, iterator_result_map)                       \
 182   V(JS_MAP_FUN_INDEX, JSFunction, js_map_fun)                                  \
 183   V(JS_MAP_MAP_INDEX, Map, js_map_map)                                         \
 184   V(JS_SET_FUN_INDEX, JSFunction, js_set_fun)                                  \
 185   V(JS_SET_MAP_INDEX, Map, js_set_map)                                         \
 186   V(MAP_GET_METHOD_INDEX, JSFunction, map_get)                                 \
 187   V(MAP_SET_METHOD_INDEX, JSFunction, map_set)                                 \
 188   V(MAP_HAS_METHOD_INDEX, JSFunction, map_has)                                 \
 189   V(MAP_DELETE_METHOD_INDEX, JSFunction, map_delete)                           \
 190   V(SET_ADD_METHOD_INDEX, JSFunction, set_add)                                 \
 191   V(SET_HAS_METHOD_INDEX, JSFunction, set_has)                                 \
 192   V(SET_DELETE_METHOD_INDEX, JSFunction, set_delete)                           \
 193   V(MAP_FROM_ARRAY_INDEX, JSFunction, map_from_array)                          \
 194   V(SET_FROM_ARRAY_INDEX, JSFunction, set_from_array)                          \
 195   V(MAP_ITERATOR_MAP_INDEX, Map, map_iterator_map)                             \
 196   V(SET_ITERATOR_MAP_INDEX, Map, set_iterator_map)                             \
 197   V(ARRAY_VALUES_ITERATOR_INDEX, JSFunction, array_values_iterator)            \
 198   V(SCRIPT_CONTEXT_TABLE_INDEX, ScriptContextTable, script_context_table)      \
 199   V(NATIVES_UTILS_OBJECT_INDEX, Object, natives_utils_object)                  \
 200   V(EXTRAS_EXPORTS_OBJECT_INDEX, JSObject, extras_exports_object)
 201
 202
 203 // A table of all script contexts. Every loaded top-level script with top-level
 204 // lexical declarations contributes its ScriptContext into this table.
 205 //
 206 // The table is a fixed array, its first slot is the current used count and
 207 // the subsequent slots 1..used contain ScriptContexts.
 208 class ScriptContextTable : public FixedArray {
 209  public:
 210   // Conversions.
 211   static ScriptContextTable* cast(Object* context) {
 212     DCHECK(context->IsScriptContextTable());
 213     return reinterpret_cast<ScriptContextTable*>(context);
 214   }
 215
 216   struct LookupResult {
 217     int context_index;
 218     int slot_index;
 219     VariableMode mode;
 220     VariableLocation location;
 221     InitializationFlag init_flag;
 222     MaybeAssignedFlag maybe_assigned_flag;
 223   };
 224
 225   int used() const { return Smi::cast(get(kUsedSlot))->value(); }
 226
 227   void set_used(int used) { set(kUsedSlot, Smi::FromInt(used)); }
 228
 229   static Handle<Context> GetContext(Handle<ScriptContextTable> table, int i) {
 230     DCHECK(i < table->used());
 231     return Handle<Context>::cast(FixedArray::get(table, i + 1));
 232   }
 233
 234   // Lookup a variable `name` in a ScriptContextTable.
 235   // If it returns true, the variable is found and `result` contains
 236   // valid information about its location.
 237   // If it returns false, `result` is untouched.
 238   MUST_USE_RESULT
 239   static bool Lookup(Handle<ScriptContextTable> table, Handle<String> name,
 240                      LookupResult* result);
 241
 242   MUST_USE_RESULT
 243   static Handle<ScriptContextTable> Extend(Handle<ScriptContextTable> table,
 244                                            Handle<Context> script_context);
 245
 246   static int GetContextOffset(int context_index) {
 247     return kFirstContextOffset + context_index * kPointerSize;
 248   }
 249
 250  private:
 251   static const int kUsedSlot = 0;
 252   static const int kFirstContextOffset =
 253       FixedArray::kHeaderSize + (kUsedSlot + 1) * kPointerSize;
 254
 255   DISALLOW_IMPLICIT_CONSTRUCTORS(ScriptContextTable);
 256 };
 257
 258 // JSFunctions are pairs (context, function code), sometimes also called
 259 // closures. A Context object is used to represent function contexts and
 260 // dynamically pushed 'with' contexts (or 'scopes' in ECMA-262 speak).
 261 //
 262 // At runtime, the contexts build a stack in parallel to the execution
 263 // stack, with the top-most context being the current context. All contexts
 264 // have the following slots:
 265 //
 266 // [ closure   ]  This is the current function. It is the same for all
 267 //                contexts inside a function. It provides access to the
 268 //                incoming context (i.e., the outer context, which may
 269 //                or may not become the current function's context), and
 270 //                it provides access to the functions code and thus it's
 271 //                scope information, which in turn contains the names of
 272 //                statically allocated context slots. The names are needed
 273 //                for dynamic lookups in the presence of 'with' or 'eval'.
 274 //
 275 // [ previous  ]  A pointer to the previous context. It is NULL for
 276 //                function contexts, and non-NULL for 'with' contexts.
 277 //                Used to implement the 'with' statement.
 278 //
 279 // [ extension ]  A pointer to an extension JSObject, or NULL. Used to
 280 //                implement 'with' statements and dynamic declarations
 281 //                (through 'eval'). The object in a 'with' statement is
 282 //                stored in the extension slot of a 'with' context.
 283 //                Dynamically declared variables/functions are also added
 284 //                to lazily allocated extension object. Context::Lookup
 285 //                searches the extension object for properties.
 286 //                For global and block contexts, contains the respective
 287 //                ScopeInfo.
 288 //                For module contexts, points back to the respective JSModule.
 289 //
 290 // [ global_object ]  A pointer to the global object. Provided for quick
 291 //                access to the global object from inside the code (since
 292 //                we always have a context pointer).
 293 //
 294 // In addition, function contexts may have statically allocated context slots
 295 // to store local variables/functions that are accessed from inner functions
 296 // (via static context addresses) or through 'eval' (dynamic context lookups).
 297 // The native context contains additional slots for fast access to native
 298 // properties.
 299 //
 300 // Finally, with Harmony scoping, the JSFunction representing a top level
 301 // script will have the ScriptContext rather than a FunctionContext.
 302 // Script contexts from all top-level scripts are gathered in
 303 // ScriptContextTable.
 304
 305 class Context: public FixedArray {
 306  public:
 307   // Conversions.
 308   static Context* cast(Object* context) {
 309     DCHECK(context->IsContext());
 310     return reinterpret_cast<Context*>(context);
 311   }
 312
 313   // The default context slot layout; indices are FixedArray slot indices.
 314   enum {
 315     // These slots are in all contexts.
 316     CLOSURE_INDEX,
 317     PREVIOUS_INDEX,
 318     // The extension slot is used for either the global object (in global
 319     // contexts), eval extension object (function contexts), subject of with
 320     // (with contexts), or the variable name (catch contexts), the serialized
 321     // scope info (block contexts), or the module instance (module contexts).
 322     EXTENSION_INDEX,
 323     GLOBAL_OBJECT_INDEX,
 324     MIN_CONTEXT_SLOTS,
 325
 326     // This slot holds the thrown value in catch contexts.
 327     THROWN_OBJECT_INDEX = MIN_CONTEXT_SLOTS,
 328
 329     // These slots are only in native contexts.
 330     GLOBAL_PROXY_INDEX = MIN_CONTEXT_SLOTS,
 331     SECURITY_TOKEN_INDEX,
 332     SLOPPY_ARGUMENTS_MAP_INDEX,
 333     FAST_ALIASED_ARGUMENTS_MAP_INDEX,
 334     SLOW_ALIASED_ARGUMENTS_MAP_INDEX,
 335     STRICT_ARGUMENTS_MAP_INDEX,
 336     REGEXP_RESULT_MAP_INDEX,
 337     SLOPPY_FUNCTION_MAP_INDEX,
 338     SLOPPY_FUNCTION_WITH_READONLY_PROTOTYPE_MAP_INDEX,
 339     STRICT_FUNCTION_MAP_INDEX,
 340     STRONG_FUNCTION_MAP_INDEX,
 341     SLOPPY_FUNCTION_WITHOUT_PROTOTYPE_MAP_INDEX,
 342     STRICT_FUNCTION_WITHOUT_PROTOTYPE_MAP_INDEX,
 343     STRONG_CONSTRUCTOR_MAP_INDEX,
 344     BOUND_FUNCTION_MAP_INDEX,
 345     INITIAL_OBJECT_PROTOTYPE_INDEX,
 346     INITIAL_ARRAY_PROTOTYPE_INDEX,
 347     BOOLEAN_FUNCTION_INDEX,
 348     NUMBER_FUNCTION_INDEX,
 349     STRING_FUNCTION_INDEX,
 350     STRING_FUNCTION_PROTOTYPE_MAP_INDEX,
 351     SYMBOL_FUNCTION_INDEX,
 352     FLOAT32X4_FUNCTION_INDEX,
 353     OBJECT_FUNCTION_INDEX,
 354     JS_OBJECT_STRONG_MAP_INDEX,
 355     INTERNAL_ARRAY_FUNCTION_INDEX,
 356     ARRAY_FUNCTION_INDEX,
 357     JS_ARRAY_MAPS_INDEX,
 358     JS_ARRAY_STRONG_MAPS_INDEX,
 359     DATE_FUNCTION_INDEX,
 360     JSON_OBJECT_INDEX,
 361     REGEXP_FUNCTION_INDEX,
 362     CREATE_DATE_FUN_INDEX,
 363     TO_NUMBER_FUN_INDEX,
 364     TO_STRING_FUN_INDEX,
 365     TO_DETAIL_STRING_FUN_INDEX,
 366     TO_OBJECT_FUN_INDEX,
 367     TO_INTEGER_FUN_INDEX,
 368     TO_UINT32_FUN_INDEX,
 369     TO_INT32_FUN_INDEX,
 370     TO_BOOLEAN_FUN_INDEX,
 371     GLOBAL_EVAL_FUN_INDEX,
 372     ARRAY_BUFFER_FUN_INDEX,
 373     ARRAY_BUFFER_MAP_INDEX,
 374     UINT8_ARRAY_FUN_INDEX,
 375     INT8_ARRAY_FUN_INDEX,
 376     UINT16_ARRAY_FUN_INDEX,
 377     INT16_ARRAY_FUN_INDEX,
 378     UINT32_ARRAY_FUN_INDEX,
 379     INT32_ARRAY_FUN_INDEX,
 380     FLOAT32_ARRAY_FUN_INDEX,
 381     FLOAT64_ARRAY_FUN_INDEX,
 382     UINT8_CLAMPED_ARRAY_FUN_INDEX,
 383     INT8_ARRAY_EXTERNAL_MAP_INDEX,
 384     UINT8_ARRAY_EXTERNAL_MAP_INDEX,
 385     INT16_ARRAY_EXTERNAL_MAP_INDEX,
 386     UINT16_ARRAY_EXTERNAL_MAP_INDEX,
 387     INT32_ARRAY_EXTERNAL_MAP_INDEX,
 388     UINT32_ARRAY_EXTERNAL_MAP_INDEX,
 389     FLOAT32_ARRAY_EXTERNAL_MAP_INDEX,
 390     FLOAT64_ARRAY_EXTERNAL_MAP_INDEX,
 391     UINT8_CLAMPED_ARRAY_EXTERNAL_MAP_INDEX,
 392     DATA_VIEW_FUN_INDEX,
 393     SHARED_ARRAY_BUFFER_FUN_INDEX,
 394     MESSAGE_LISTENERS_INDEX,
 395     MAKE_MESSAGE_FUN_INDEX,
 396     GET_STACK_TRACE_LINE_INDEX,
 397     CONFIGURE_GLOBAL_INDEX,
 398     FUNCTION_CACHE_INDEX,
 399     JSFUNCTION_RESULT_CACHES_INDEX,
 400     NORMALIZED_MAP_CACHE_INDEX,
 401     RUNTIME_CONTEXT_INDEX,
 402     CALL_AS_FUNCTION_DELEGATE_INDEX,
 403     CALL_AS_CONSTRUCTOR_DELEGATE_INDEX,
 404     SCRIPT_FUNCTION_INDEX,
 405     OPAQUE_REFERENCE_FUNCTION_INDEX,
 406     CONTEXT_EXTENSION_FUNCTION_INDEX,
 407     OUT_OF_MEMORY_INDEX,
 408     EMBEDDER_DATA_INDEX,
 409     ALLOW_CODE_GEN_FROM_STRINGS_INDEX,
 410     ERROR_MESSAGE_FOR_CODE_GEN_FROM_STRINGS_INDEX,
 411     RUN_MICROTASKS_INDEX,
 412     ENQUEUE_MICROTASK_INDEX,
 413     PROMISE_STATUS_INDEX,
 414     PROMISE_VALUE_INDEX,
 415     PROMISE_CREATE_INDEX,
 416     PROMISE_RESOLVE_INDEX,
 417     PROMISE_REJECT_INDEX,
 418     PROMISE_CHAIN_INDEX,
 419     PROMISE_CATCH_INDEX,
 420     PROMISE_THEN_INDEX,
 421     TO_COMPLETE_PROPERTY_DESCRIPTOR_INDEX,
 422     DERIVED_HAS_TRAP_INDEX,
 423     DERIVED_GET_TRAP_INDEX,
 424     DERIVED_SET_TRAP_INDEX,
 425     PROXY_ENUMERATE_INDEX,
 426     OBSERVERS_NOTIFY_CHANGE_INDEX,
 427     OBSERVERS_ENQUEUE_SPLICE_INDEX,
 428     OBSERVERS_BEGIN_SPLICE_INDEX,
 429     OBSERVERS_END_SPLICE_INDEX,
 430     NATIVE_OBJECT_OBSERVE_INDEX,
 431     NATIVE_OBJECT_GET_NOTIFIER_INDEX,
 432     NATIVE_OBJECT_NOTIFIER_PERFORM_CHANGE,
 433     SLOPPY_GENERATOR_FUNCTION_MAP_INDEX,
 434     STRICT_GENERATOR_FUNCTION_MAP_INDEX,
 435     STRONG_GENERATOR_FUNCTION_MAP_INDEX,
 436     GENERATOR_OBJECT_PROTOTYPE_MAP_INDEX,
 437     ITERATOR_RESULT_MAP_INDEX,
 438     JS_MAP_FUN_INDEX,
 439     JS_MAP_MAP_INDEX,
 440     JS_SET_FUN_INDEX,
 441     JS_SET_MAP_INDEX,
 442     MAP_GET_METHOD_INDEX,
 443     MAP_SET_METHOD_INDEX,
 444     MAP_HAS_METHOD_INDEX,
 445     MAP_DELETE_METHOD_INDEX,
 446     SET_ADD_METHOD_INDEX,
 447     SET_HAS_METHOD_INDEX,
 448     SET_DELETE_METHOD_INDEX,
 449     MAP_FROM_ARRAY_INDEX,
 450     SET_FROM_ARRAY_INDEX,
 451     MAP_ITERATOR_MAP_INDEX,
 452     SET_ITERATOR_MAP_INDEX,
 453     ARRAY_VALUES_ITERATOR_INDEX,
 454     SCRIPT_CONTEXT_TABLE_INDEX,
 455     MAP_CACHE_INDEX,
 456     STRONG_MAP_CACHE_INDEX,
 457     TO_LENGTH_FUN_INDEX,
 458     NATIVES_UTILS_OBJECT_INDEX,
 459     EXTRAS_EXPORTS_OBJECT_INDEX,
 460     CODE_STUB_EXPORTS_OBJECT_INDEX,
 461
 462     // Properties from here are treated as weak references by the full GC.
 463     // Scavenge treats them as strong references.
 464     OPTIMIZED_FUNCTIONS_LIST,  // Weak.
 465     OPTIMIZED_CODE_LIST,       // Weak.
 466     DEOPTIMIZED_CODE_LIST,     // Weak.
 467     NEXT_CONTEXT_LINK,         // Weak.
 468
 469     // Total number of slots.
 470     NATIVE_CONTEXT_SLOTS,
 471     FIRST_WEAK_SLOT = OPTIMIZED_FUNCTIONS_LIST
 472   };
 473
 474   // Direct slot access.
 475   JSFunction* closure() { return JSFunction::cast(get(CLOSURE_INDEX)); }
 476   void set_closure(JSFunction* closure) { set(CLOSURE_INDEX, closure); }
 477
 478   Context* previous() {
 479     Object* result = unchecked_previous();
 480     DCHECK(IsBootstrappingOrValidParentContext(result, this));
 481     return reinterpret_cast<Context*>(result);
 482   }
 483   void set_previous(Context* context) { set(PREVIOUS_INDEX, context); }
 484
 485   bool has_extension() { return extension() != NULL; }
 486   Object* extension() { return get(EXTENSION_INDEX); }
 487   void set_extension(Object* object) { set(EXTENSION_INDEX, object); }
 488
 489   JSModule* module() { return JSModule::cast(get(EXTENSION_INDEX)); }
 490   void set_module(JSModule* module) { set(EXTENSION_INDEX, module); }
 491
 492   // Get the context where var declarations will be hoisted to, which
 493   // may be the context itself.
 494   Context* declaration_context();
 495
 496   GlobalObject* global_object() {
 497     Object* result = get(GLOBAL_OBJECT_INDEX);
 498     DCHECK(IsBootstrappingOrGlobalObject(this->GetIsolate(), result));
 499     return reinterpret_cast<GlobalObject*>(result);
 500   }
 501   void set_global_object(GlobalObject* object) {
 502     set(GLOBAL_OBJECT_INDEX, object);
 503   }
 504
 505   // Returns a JSGlobalProxy object or null.
 506   JSObject* global_proxy();
 507   void set_global_proxy(JSObject* global);
 508
 509   // The builtins object.
 510   JSBuiltinsObject* builtins();
 511
 512   // Get the script context by traversing the context chain.
 513   Context* script_context();
 514
 515   // Compute the native context by traversing the context chain.
 516   Context* native_context();
 517
 518   // Predicates for context types.  IsNativeContext is also defined on Object
 519   // because we frequently have to know if arbitrary objects are natives
 520   // contexts.
 521   bool IsNativeContext() {
 522     Map* map = this->map();
 523     return map == map->GetHeap()->native_context_map();
 524   }
 525   bool IsFunctionContext() {
 526     Map* map = this->map();
 527     return map == map->GetHeap()->function_context_map();
 528   }
 529   bool IsCatchContext() {
 530     Map* map = this->map();
 531     return map == map->GetHeap()->catch_context_map();
 532   }
 533   bool IsWithContext() {
 534     Map* map = this->map();
 535     return map == map->GetHeap()->with_context_map();
 536   }
 537   bool IsBlockContext() {
 538     Map* map = this->map();
 539     return map == map->GetHeap()->block_context_map();
 540   }
 541   bool IsModuleContext() {
 542     Map* map = this->map();
 543     return map == map->GetHeap()->module_context_map();
 544   }
 545   bool IsScriptContext() {
 546     Map* map = this->map();
 547     return map == map->GetHeap()->script_context_map();
 548   }
 549
 550   bool HasSameSecurityTokenAs(Context* that) {
 551     return this->global_object()->native_context()->security_token() ==
 552         that->global_object()->native_context()->security_token();
 553   }
 554
 555   // Initializes global variable bindings in given script context.
 556   void InitializeGlobalSlots();
 557
 558   // A native context holds a list of all functions with optimized code.
 559   void AddOptimizedFunction(JSFunction* function);
 560   void RemoveOptimizedFunction(JSFunction* function);
 561   void SetOptimizedFunctionsListHead(Object* head);
 562   Object* OptimizedFunctionsListHead();
 563
 564   // The native context also stores a list of all optimized code and a
 565   // list of all deoptimized code, which are needed by the deoptimizer.
 566   void AddOptimizedCode(Code* code);
 567   void SetOptimizedCodeListHead(Object* head);
 568   Object* OptimizedCodeListHead();
 569   void SetDeoptimizedCodeListHead(Object* head);
 570   Object* DeoptimizedCodeListHead();
 571
 572   Handle<Object> ErrorMessageForCodeGenerationFromStrings();
 573
 574 #define NATIVE_CONTEXT_FIELD_ACCESSORS(index, type, name) \
 575   void  set_##name(type* value) {                         \
 576     DCHECK(IsNativeContext());                            \
 577     set(index, value);                                    \
 578   }                                                       \
 579   bool is_##name(type* value) {                           \
 580     DCHECK(IsNativeContext());                            \
 581     return type::cast(get(index)) == value;               \
 582   }                                                       \
 583   type* name() {                                          \
 584     DCHECK(IsNativeContext());                            \
 585     return type::cast(get(index));                        \
 586   }
 587   NATIVE_CONTEXT_FIELDS(NATIVE_CONTEXT_FIELD_ACCESSORS)
 588 #undef NATIVE_CONTEXT_FIELD_ACCESSORS
 589
 590   // Lookup the slot called name, starting with the current context.
 591   // There are three possibilities:
 592   //
 593   // 1) result->IsContext():
 594   //    The binding was found in a context.  *index is always the
 595   //    non-negative slot index.  *attributes is NONE for var and let
 596   //    declarations, READ_ONLY for const declarations (never ABSENT).
 597   //
 598   // 2) result->IsJSObject():
 599   //    The binding was found as a named property in a context extension
 600   //    object (i.e., was introduced via eval), as a property on the subject
 601   //    of with, or as a property of the global object.  *index is -1 and
 602   //    *attributes is not ABSENT.
 603   //
 604   // 3) result.is_null():
 605   //    There was no binding found, *index is always -1 and *attributes is
 606   //    always ABSENT.
 607   Handle<Object> Lookup(Handle<String> name,
 608                         ContextLookupFlags flags,
 609                         int* index,
 610                         PropertyAttributes* attributes,
 611                         BindingFlags* binding_flags);
 612
 613   // Code generation support.
 614   static int SlotOffset(int index) {
 615     return kHeaderSize + index * kPointerSize - kHeapObjectTag;
 616   }
 617
 618   static int FunctionMapIndex(LanguageMode language_mode, FunctionKind kind) {
 619     if (IsGeneratorFunction(kind)) {
 620       return is_strong(language_mode) ? STRONG_GENERATOR_FUNCTION_MAP_INDEX :
 621              is_strict(language_mode) ? STRICT_GENERATOR_FUNCTION_MAP_INDEX
 622                                       : SLOPPY_GENERATOR_FUNCTION_MAP_INDEX;
 623     }
 624
 625     if (IsConstructor(kind)) {
 626       // Use strict function map (no own "caller" / "arguments")
 627       return is_strong(language_mode) ? STRONG_CONSTRUCTOR_MAP_INDEX
 628                                       : STRICT_FUNCTION_MAP_INDEX;
 629     }
 630
 631     if (IsArrowFunction(kind) || IsConciseMethod(kind) ||
 632         IsAccessorFunction(kind)) {
 633       return is_strong(language_mode)
 634                  ? STRONG_FUNCTION_MAP_INDEX
 635                  : STRICT_FUNCTION_WITHOUT_PROTOTYPE_MAP_INDEX;
 636     }
 637
 638     return is_strong(language_mode) ? STRONG_FUNCTION_MAP_INDEX :
 639            is_strict(language_mode) ? STRICT_FUNCTION_MAP_INDEX
 640                                     : SLOPPY_FUNCTION_MAP_INDEX;
 641   }
 642
 643   static const int kSize = kHeaderSize + NATIVE_CONTEXT_SLOTS * kPointerSize;
 644
 645   // GC support.
 646   typedef FixedBodyDescriptor<
 647       kHeaderSize, kSize, kSize> ScavengeBodyDescriptor;
 648
 649   typedef FixedBodyDescriptor<
 650       kHeaderSize,
 651       kHeaderSize + FIRST_WEAK_SLOT * kPointerSize,
 652       kSize> MarkCompactBodyDescriptor;
 653
 654  private:
 655   // Unchecked access to the slots.
 656   Object* unchecked_previous() { return get(PREVIOUS_INDEX); }
 657
 658 #ifdef DEBUG
 659   // Bootstrapping-aware type checks.
 660   static bool IsBootstrappingOrValidParentContext(Object* object, Context* kid);
 661   static bool IsBootstrappingOrGlobalObject(Isolate* isolate, Object* object);
 662 #endif
 663
 664   STATIC_ASSERT(kHeaderSize == Internals::kContextHeaderSize);
 665   STATIC_ASSERT(EMBEDDER_DATA_INDEX == Internals::kContextEmbedderDataIndex);
 666 };
 667
 668 } }  // namespace v8::internal
 669
 670 #endif  // V8_CONTEXTS_H_