runtime/ScopedArgumentsTable.h

   1 /*
   2  * Copyright (C) 2015 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 #ifndef ScopedArgumentsTable_h
  27 #define ScopedArgumentsTable_h
  28
  29 #include "JSCell.h"
  30 #include "ScopeOffset.h"
  31 #include <wtf/Assertions.h>
  32
  33 namespace JSC {
  34
  35 // This class's only job is to hold onto the list of ScopeOffsets for each argument that a
  36 // function has. Most of the time, the BytecodeGenerator will create one of these and it will
  37 // never be modified subsequently. There is a rare case where a ScopedArguments object is created
  38 // and aliases one of these and then decides to modify it; in that case we do copy-on-write. This
  39 // makes sense because such modifications are so uncommon. You'd have to do something crazy like
  40 // "delete arguments[i]" or some variant of defineOwnProperty.
  41 class ScopedArgumentsTable final : public JSCell {
  42 public:
  43     typedef JSCell Base;
  44     static const unsigned StructureFlags = Base::StructureFlags | StructureIsImmortal;
  45
  46 private:
  47     ScopedArgumentsTable(VM&);
  48     ~ScopedArgumentsTable();
  49
  50 public:
  51     static ScopedArgumentsTable* create(VM&);
  52     static ScopedArgumentsTable* create(VM&, uint32_t length);
  53
  54     static const bool needsDestruction = true;
  55     static void destroy(JSCell*);
  56
  57     ScopedArgumentsTable* clone(VM&);
  58
  59     uint32_t length() const { return m_length; }
  60     ScopedArgumentsTable* setLength(VM&, uint32_t newLength);
  61
  62     ScopeOffset get(uint32_t i) const
  63     {
  64         return const_cast<ScopedArgumentsTable*>(this)->at(i);
  65     }
  66
  67     void lock()
  68     {
  69         m_locked = true;
  70     }
  71
  72     ScopedArgumentsTable* set(VM&, uint32_t index, ScopeOffset);
  73
  74     DECLARE_INFO;
  75
  76     static Structure* createStructure(VM&, JSGlobalObject*, JSValue prototype);
  77
  78     static ptrdiff_t offsetOfLength() { return OBJECT_OFFSETOF(ScopedArgumentsTable, m_length); }
  79     static ptrdiff_t offsetOfArguments() { return OBJECT_OFFSETOF(ScopedArgumentsTable, m_arguments); }
  80
  81 private:
  82     ScopeOffset& at(uint32_t i)
  83     {
  84         ASSERT_WITH_SECURITY_IMPLICATION(i < m_length);
  85         return m_arguments[i];
  86     }
  87
  88     uint32_t m_length;
  89     bool m_locked; // Being locked means that there are multiple references to this object and none of them expect to see the others' modifications. This means that modifications need to make a copy first.
  90     std::unique_ptr<ScopeOffset[]> m_arguments;
  91 };
  92
  93 } // namespace JSC
  94
  95 #endif // ScopedArgumentsTable_h
  96