1  /*
 2   * Copyright (C) 2008 Apple Inc. All rights reserved.
 3   *
 4   * Redistribution and use in source and binary forms, with or without
 5   * modification, are permitted provided that the following conditions
 6   * are met:
 7   * 1. Redistributions of source code must retain the above copyright
 8   *    notice, this list of conditions and the following disclaimer.
 9   * 2. Redistributions in binary form must reproduce the above copyright
10   *    notice, this list of conditions and the following disclaimer in the
11   *    documentation and/or other materials provided with the distribution.
12   *
13   * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
14   * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
16   * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
17   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
18   * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
19   * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
20   * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
21   * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
23   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
24   */
25  
26  #include "config.h"
27  #include "StructureChain.h"
28  
29  #include "JSCInlines.h"
30  
31  namespace JSC {
32      
33  const ClassInfo StructureChain::s_info = { "StructureChain", nullptr, nullptr, nullptr, CREATE_METHOD_TABLE(StructureChain) };
34  
35  StructureChain::StructureChain(VM& vm, Structure* structure, StructureID* vector)
36      : Base(vm, structure)
37      , m_vector(vm, this, vector)
38  {
39  }
40  
41  StructureChain* StructureChain::create(VM& vm, JSObject* head)
42  {
43      // FIXME: Make StructureChain::create fail for large chain. Caching large chain is not so profitable.
44      // By making the size <= UINT16_MAX, we can store length in a high bits of auxiliary pointer.
45      // https://bugs.webkit.org/show_bug.cgi?id=200290
46      size_t size = 0;
47      for (JSObject* current = head; current; current = current->structure(vm)->storedPrototypeObject(current))
48          ++size;
49      ++size; // Sentinel nullptr.
50      size_t bytes = (Checked<size_t>(size) * sizeof(StructureID)).unsafeGet();
51      StructureID* vector = static_cast<StructureID*>(vm.jsValueGigacageAuxiliarySpace.allocateNonVirtual(vm, bytes, nullptr, AllocationFailureMode::Assert));
52      memset(vector, 0, bytes);
53      StructureChain* chain = new (NotNull, allocateCell<StructureChain>(vm.heap)) StructureChain(vm, vm.structureChainStructure.get(), vector);
54      chain->finishCreation(vm, head);
55      return chain;
56  }
57  
58  void StructureChain::finishCreation(VM& vm, JSObject* head)
59  {
60      Base::finishCreation(vm);
61      size_t i = 0;
62      for (JSObject* current = head; current; current = current->structure(vm)->storedPrototypeObject(current)) {
63          Structure* structure = current->structure(vm);
64          m_vector.get()[i++] = structure->id();
65          vm.heap.writeBarrier(this);
66      }
67  }
68  
69  void StructureChain::visitChildren(JSCell* cell, SlotVisitor& visitor)
70  {
71      StructureChain* thisObject = jsCast<StructureChain*>(cell);
72      ASSERT_GC_OBJECT_INHERITS(thisObject, info());
73      Base::visitChildren(thisObject, visitor);
74      visitor.markAuxiliary(thisObject->m_vector.get());
75      VM& vm = visitor.vm();
76      for (auto* current = thisObject->m_vector.get(); *current; ++current) {
77          StructureID structureID = *current;
78          Structure* structure = vm.getStructure(structureID);
79          visitor.appendUnbarriered(structure);
80      }
81  }
82  
83  } // namespace JSC