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1 // Copyright 2006-2008 the V8 project authors. All rights reserved.
2 // Redistribution and use in source and binary forms, with or without
3 // modification, are permitted provided that the following conditions are
4 // met:
5 //
6 //     * Redistributions of source code must retain the above copyright
7 //       notice, this list of conditions and the following disclaimer.
8 //     * Redistributions in binary form must reproduce the above
9 //       copyright notice, this list of conditions and the following
10 //       disclaimer in the documentation and/or other materials provided
11 //       with the distribution.
12 //     * Neither the name of Google Inc. nor the names of its
13 //       contributors may be used to endorse or promote products derived
14 //       from this software without specific prior written permission.
15 //
16 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 
28 #ifndef V8_CONTEXTS_H_
29 #define V8_CONTEXTS_H_
30 
31 namespace v8 {
32 namespace internal {
33 
34 
35 enum ContextLookupFlags {
36   FOLLOW_CONTEXT_CHAIN = 1,
37   FOLLOW_PROTOTYPE_CHAIN = 2,
38 
39   DONT_FOLLOW_CHAINS = 0,
40   FOLLOW_CHAINS = FOLLOW_CONTEXT_CHAIN | FOLLOW_PROTOTYPE_CHAIN
41 };
42 
43 
44 // Heap-allocated activation contexts.
45 //
46 // Contexts are implemented as FixedArray objects; the Context
47 // class is a convenience interface casted on a FixedArray object.
48 //
49 // Note: Context must have no virtual functions and Context objects
50 // must always be allocated via Heap::AllocateContext() or
51 // Factory::NewContext.
52 
53 // Comment for special_function_table:
54 // Table for providing optimized/specialized functions.
55 // The array contains triplets [object, general_function, optimized_function].
56 // Primarily added to support built-in optimized variants of
57 // Array.prototype.{push,pop}.
58 
59 #define GLOBAL_CONTEXT_FIELDS(V) \
60   V(GLOBAL_PROXY_INDEX, JSObject, global_proxy_object) \
61   V(SECURITY_TOKEN_INDEX, Object, security_token) \
62   V(BOOLEAN_FUNCTION_INDEX, JSFunction, boolean_function) \
63   V(NUMBER_FUNCTION_INDEX, JSFunction, number_function) \
64   V(STRING_FUNCTION_INDEX, JSFunction, string_function) \
65   V(OBJECT_FUNCTION_INDEX, JSFunction, object_function) \
66   V(ARRAY_FUNCTION_INDEX, JSFunction, array_function) \
67   V(DATE_FUNCTION_INDEX, JSFunction, date_function) \
68   V(JSON_OBJECT_INDEX, JSObject, json_object) \
69   V(REGEXP_FUNCTION_INDEX, JSFunction, regexp_function) \
70   V(INITIAL_OBJECT_PROTOTYPE_INDEX, JSObject, initial_object_prototype) \
71   V(CREATE_DATE_FUN_INDEX, JSFunction,  create_date_fun) \
72   V(TO_NUMBER_FUN_INDEX, JSFunction, to_number_fun) \
73   V(TO_STRING_FUN_INDEX, JSFunction, to_string_fun) \
74   V(TO_DETAIL_STRING_FUN_INDEX, JSFunction, to_detail_string_fun) \
75   V(TO_OBJECT_FUN_INDEX, JSFunction, to_object_fun) \
76   V(TO_INTEGER_FUN_INDEX, JSFunction, to_integer_fun) \
77   V(TO_UINT32_FUN_INDEX, JSFunction, to_uint32_fun) \
78   V(TO_INT32_FUN_INDEX, JSFunction, to_int32_fun) \
79   V(GLOBAL_EVAL_FUN_INDEX, JSFunction, global_eval_fun) \
80   V(INSTANTIATE_FUN_INDEX, JSFunction, instantiate_fun) \
81   V(CONFIGURE_INSTANCE_FUN_INDEX, JSFunction, configure_instance_fun) \
82   V(FUNCTION_MAP_INDEX, Map, function_map) \
83   V(FUNCTION_INSTANCE_MAP_INDEX, Map, function_instance_map) \
84   V(JS_ARRAY_MAP_INDEX, Map, js_array_map)\
85   V(SPECIAL_FUNCTION_TABLE_INDEX, FixedArray, special_function_table) \
86   V(ARGUMENTS_BOILERPLATE_INDEX, JSObject, arguments_boilerplate) \
87   V(MESSAGE_LISTENERS_INDEX, JSObject, message_listeners) \
88   V(MAKE_MESSAGE_FUN_INDEX, JSFunction, make_message_fun) \
89   V(GET_STACK_TRACE_LINE_INDEX, JSFunction, get_stack_trace_line_fun) \
90   V(CONFIGURE_GLOBAL_INDEX, JSFunction, configure_global_fun) \
91   V(FUNCTION_CACHE_INDEX, JSObject, function_cache) \
92   V(RUNTIME_CONTEXT_INDEX, Context, runtime_context) \
93   V(CALL_AS_FUNCTION_DELEGATE_INDEX, JSFunction, call_as_function_delegate) \
94   V(CALL_AS_CONSTRUCTOR_DELEGATE_INDEX, JSFunction, \
95     call_as_constructor_delegate) \
96   V(SCRIPT_FUNCTION_INDEX, JSFunction, script_function) \
97   V(CONTEXT_EXTENSION_FUNCTION_INDEX, JSFunction, context_extension_function) \
98   V(OUT_OF_MEMORY_INDEX, Object, out_of_memory) \
99   V(MAP_CACHE_INDEX, Object, map_cache) \
100   V(CONTEXT_DATA_INDEX, Object, data)
101 
102 // JSFunctions are pairs (context, function code), sometimes also called
103 // closures. A Context object is used to represent function contexts and
104 // dynamically pushed 'with' contexts (or 'scopes' in ECMA-262 speak).
105 //
106 // At runtime, the contexts build a stack in parallel to the execution
107 // stack, with the top-most context being the current context. All contexts
108 // have the following slots:
109 //
110 // [ closure   ]  This is the current function. It is the same for all
111 //                contexts inside a function. It provides access to the
112 //                incoming context (i.e., the outer context, which may
113 //                or may not become the current function's context), and
114 //                it provides access to the functions code and thus it's
115 //                scope information, which in turn contains the names of
116 //                statically allocated context slots. The names are needed
117 //                for dynamic lookups in the presence of 'with' or 'eval'.
118 //
119 // [ fcontext  ]  A pointer to the innermost enclosing function context.
120 //                It is the same for all contexts *allocated* inside a
121 //                function, and the function context's fcontext points
122 //                to itself. It is only needed for fast access of the
123 //                function context (used for declarations, and static
124 //                context slot access).
125 //
126 // [ previous  ]  A pointer to the previous context. It is NULL for
127 //                function contexts, and non-NULL for 'with' contexts.
128 //                Used to implement the 'with' statement.
129 //
130 // [ extension ]  A pointer to an extension JSObject, or NULL. Used to
131 //                implement 'with' statements and dynamic declarations
132 //                (through 'eval'). The object in a 'with' statement is
133 //                stored in the extension slot of a 'with' context.
134 //                Dynamically declared variables/functions are also added
135 //                to lazily allocated extension object. Context::Lookup
136 //                searches the extension object for properties.
137 //
138 // [ global    ]  A pointer to the global object. Provided for quick
139 //                access to the global object from inside the code (since
140 //                we always have a context pointer).
141 //
142 // In addition, function contexts may have statically allocated context slots
143 // to store local variables/functions that are accessed from inner functions
144 // (via static context addresses) or through 'eval' (dynamic context lookups).
145 // Finally, the global context contains additional slots for fast access to
146 // global properties.
147 //
148 // We may be able to simplify the implementation:
149 //
150 // - We may be able to get rid of 'fcontext': We can always use the fact that
151 //   previous == NULL for function contexts and so we can search for them. They
152 //   are only needed when doing dynamic declarations, and the context chains
153 //   tend to be very very short (depth of nesting of 'with' statements). At
154 //   the moment we also use it in generated code for context slot accesses -
155 //   and there we don't want a loop because of code bloat - but we may not
156 //   need it there after all (see comment in codegen_*.cc).
157 //
158 // - If we cannot get rid of fcontext, consider making 'previous' never NULL
159 //   except for the global context. This could simplify Context::Lookup.
160 
161 class Context: public FixedArray {
162  public:
163   // Conversions.
cast(Object * context)164   static Context* cast(Object* context) {
165     ASSERT(context->IsContext());
166     return reinterpret_cast<Context*>(context);
167   }
168 
169   // The default context slot layout; indices are FixedArray slot indices.
170   enum {
171     // These slots are in all contexts.
172     CLOSURE_INDEX,
173     FCONTEXT_INDEX,
174     PREVIOUS_INDEX,
175     EXTENSION_INDEX,
176     GLOBAL_INDEX,
177     MIN_CONTEXT_SLOTS,
178 
179     // These slots are only in global contexts.
180     GLOBAL_PROXY_INDEX = MIN_CONTEXT_SLOTS,
181     SECURITY_TOKEN_INDEX,
182     ARGUMENTS_BOILERPLATE_INDEX,
183     JS_ARRAY_MAP_INDEX,
184     FUNCTION_MAP_INDEX,
185     FUNCTION_INSTANCE_MAP_INDEX,
186     INITIAL_OBJECT_PROTOTYPE_INDEX,
187     BOOLEAN_FUNCTION_INDEX,
188     NUMBER_FUNCTION_INDEX,
189     STRING_FUNCTION_INDEX,
190     OBJECT_FUNCTION_INDEX,
191     ARRAY_FUNCTION_INDEX,
192     DATE_FUNCTION_INDEX,
193     JSON_OBJECT_INDEX,
194     REGEXP_FUNCTION_INDEX,
195     CREATE_DATE_FUN_INDEX,
196     TO_NUMBER_FUN_INDEX,
197     TO_STRING_FUN_INDEX,
198     TO_DETAIL_STRING_FUN_INDEX,
199     TO_OBJECT_FUN_INDEX,
200     TO_INTEGER_FUN_INDEX,
201     TO_UINT32_FUN_INDEX,
202     TO_INT32_FUN_INDEX,
203     TO_BOOLEAN_FUN_INDEX,
204     GLOBAL_EVAL_FUN_INDEX,
205     INSTANTIATE_FUN_INDEX,
206     CONFIGURE_INSTANCE_FUN_INDEX,
207     SPECIAL_FUNCTION_TABLE_INDEX,
208     MESSAGE_LISTENERS_INDEX,
209     MAKE_MESSAGE_FUN_INDEX,
210     GET_STACK_TRACE_LINE_INDEX,
211     CONFIGURE_GLOBAL_INDEX,
212     FUNCTION_CACHE_INDEX,
213     RUNTIME_CONTEXT_INDEX,
214     CALL_AS_FUNCTION_DELEGATE_INDEX,
215     CALL_AS_CONSTRUCTOR_DELEGATE_INDEX,
216     SCRIPT_FUNCTION_INDEX,
217     CONTEXT_EXTENSION_FUNCTION_INDEX,
218     OUT_OF_MEMORY_INDEX,
219     MAP_CACHE_INDEX,
220     CONTEXT_DATA_INDEX,
221     GLOBAL_CONTEXT_SLOTS
222   };
223 
224   // Direct slot access.
closure()225   JSFunction* closure() { return JSFunction::cast(get(CLOSURE_INDEX)); }
set_closure(JSFunction * closure)226   void set_closure(JSFunction* closure) { set(CLOSURE_INDEX, closure); }
227 
fcontext()228   Context* fcontext() { return Context::cast(get(FCONTEXT_INDEX)); }
set_fcontext(Context * context)229   void set_fcontext(Context* context) { set(FCONTEXT_INDEX, context); }
230 
previous()231   Context* previous() {
232     Object* result = unchecked_previous();
233     ASSERT(IsBootstrappingOrContext(result));
234     return reinterpret_cast<Context*>(result);
235   }
set_previous(Context * context)236   void set_previous(Context* context) { set(PREVIOUS_INDEX, context); }
237 
has_extension()238   bool has_extension() { return unchecked_extension() != NULL; }
extension()239   JSObject* extension() { return JSObject::cast(unchecked_extension()); }
set_extension(JSObject * object)240   void set_extension(JSObject* object) { set(EXTENSION_INDEX, object); }
241 
global()242   GlobalObject* global() {
243     Object* result = get(GLOBAL_INDEX);
244     ASSERT(IsBootstrappingOrGlobalObject(result));
245     return reinterpret_cast<GlobalObject*>(result);
246   }
set_global(GlobalObject * global)247   void set_global(GlobalObject* global) { set(GLOBAL_INDEX, global); }
248 
249   // Returns a JSGlobalProxy object or null.
250   JSObject* global_proxy();
251   void set_global_proxy(JSObject* global);
252 
253   // The builtins object.
254   JSBuiltinsObject* builtins();
255 
256   // Compute the global context by traversing the context chain.
257   Context* global_context();
258 
259   // Tells if this is a function context (as opposed to a 'with' context).
is_function_context()260   bool is_function_context() { return unchecked_previous() == NULL; }
261 
262   // Tells whether the global context is marked with out of memory.
has_out_of_memory()263   bool has_out_of_memory() {
264     return global_context()->out_of_memory() == Heap::true_value();
265   }
266 
267   // Mark the global context with out of memory.
mark_out_of_memory()268   void mark_out_of_memory() {
269     global_context()->set_out_of_memory(Heap::true_value());
270   }
271 
272   // The exception holder is the object used as a with object in
273   // the implementation of a catch block.
is_exception_holder(Object * object)274   bool is_exception_holder(Object* object) {
275     return IsCatchContext() && extension() == object;
276   }
277 
278 #define GLOBAL_CONTEXT_FIELD_ACCESSORS(index, type, name) \
279   void  set_##name(type* value) {                         \
280     ASSERT(IsGlobalContext());                            \
281     set(index, value);                                    \
282   }                                                       \
283   type* name() {                                          \
284     ASSERT(IsGlobalContext());                            \
285     return type::cast(get(index));                        \
286   }
287   GLOBAL_CONTEXT_FIELDS(GLOBAL_CONTEXT_FIELD_ACCESSORS)
288 #undef GLOBAL_CONTEXT_FIELD_ACCESSORS
289 
290   // Lookup the the slot called name, starting with the current context.
291   // There are 4 possible outcomes:
292   //
293   // 1) index_ >= 0 && result->IsContext():
294   //    most common case, the result is a Context, and index is the
295   //    context slot index, and the slot exists.
296   //    attributes == READ_ONLY for the function name variable, NONE otherwise.
297   //
298   // 2) index_ >= 0 && result->IsJSObject():
299   //    the result is the JSObject arguments object, the index is the parameter
300   //    index, i.e., key into the arguments object, and the property exists.
301   //    attributes != ABSENT.
302   //
303   // 3) index_ < 0 && result->IsJSObject():
304   //    the result is the JSObject extension context or the global object,
305   //    and the name is the property name, and the property exists.
306   //    attributes != ABSENT.
307   //
308   // 4) index_ < 0 && result.is_null():
309   //    there was no context found with the corresponding property.
310   //    attributes == ABSENT.
311   Handle<Object> Lookup(Handle<String> name, ContextLookupFlags flags,
312                         int* index_, PropertyAttributes* attributes);
313 
314   // Determine if a local variable with the given name exists in a
315   // context.  Do not consider context extension objects.  This is
316   // used for compiling code using eval.  If the context surrounding
317   // the eval call does not have a local variable with this name and
318   // does not contain a with statement the property is global unless
319   // it is shadowed by a property in an extension object introduced by
320   // eval.
321   bool GlobalIfNotShadowedByEval(Handle<String> name);
322 
323   // Code generation support.
SlotOffset(int index)324   static int SlotOffset(int index) {
325     return kHeaderSize + index * kPointerSize - kHeapObjectTag;
326   }
327 
328  private:
329   // Unchecked access to the slots.
unchecked_previous()330   Object* unchecked_previous() { return get(PREVIOUS_INDEX); }
unchecked_extension()331   Object* unchecked_extension() { return get(EXTENSION_INDEX); }
332 
333 #ifdef DEBUG
334   // Bootstrapping-aware type checks.
335   static bool IsBootstrappingOrContext(Object* object);
336   static bool IsBootstrappingOrGlobalObject(Object* object);
337 #endif
338 };
339 
340 } }  // namespace v8::internal
341 
342 #endif  // V8_CONTEXTS_H_
343