jit/JITWriteBarrier.h

   1 /*
   2  * Copyright (C) 2011 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. AND ITS CONTRIBUTORS ``AS IS''
  14  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  15  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  16  * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
  17  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  18  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  19  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  20  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  21  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  22  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
  23  * THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #ifndef JITWriteBarrier_h
  27 #define JITWriteBarrier_h
  28
  29 #if ENABLE(JIT)
  30
  31 #include "MacroAssembler.h"
  32 #include "SlotVisitor.h"
  33 #include "UnusedPointer.h"
  34 #include "WriteBarrier.h"
  35
  36 namespace JSC {
  37
  38 class JSCell;
  39 class VM;
  40
  41 // Needs to be even to appease some of the backends.
  42 #define JITWriteBarrierFlag ((void*)2)
  43 class JITWriteBarrierBase {
  44 public:
  45     typedef void* (JITWriteBarrierBase::*UnspecifiedBoolType);
  46     operator UnspecifiedBoolType*() const { return get() ? reinterpret_cast<UnspecifiedBoolType*>(1) : 0; }
  47     bool operator!() const { return !get(); }
  48
  49     void setFlagOnBarrier()
  50     {
  51         ASSERT(!m_location);
  52         m_location = CodeLocationDataLabelPtr(JITWriteBarrierFlag);
  53     }
  54
  55     bool isFlagged() const
  56     {
  57         return !!m_location;
  58     }
  59
  60     void setLocation(CodeLocationDataLabelPtr location)
  61     {
  62         ASSERT(!m_location);
  63         m_location = location;
  64     }
  65
  66     CodeLocationDataLabelPtr location() const
  67     {
  68         ASSERT((!!m_location) && m_location.executableAddress() != JITWriteBarrierFlag);
  69         return m_location;
  70     }
  71
  72     void clear() { clear(0); }
  73     void clearToUnusedPointer() { clear(reinterpret_cast<void*>(unusedPointer)); }
  74
  75 protected:
  76     JITWriteBarrierBase()
  77     {
  78     }
  79
  80     void set(VM&, CodeLocationDataLabelPtr location, JSCell* owner, JSCell* value)
  81     {
  82         Heap::writeBarrier(owner, value);
  83         m_location = location;
  84         ASSERT(((!!m_location) && m_location.executableAddress() != JITWriteBarrierFlag) || (location.executableAddress() == m_location.executableAddress()));
  85         MacroAssembler::repatchPointer(m_location, value);
  86         ASSERT(get() == value);
  87     }
  88
  89     JSCell* get() const
  90     {
  91         if (!m_location || m_location.executableAddress() == JITWriteBarrierFlag)
  92             return 0;
  93         void* result = static_cast<JSCell*>(MacroAssembler::readPointer(m_location));
  94         if (result == reinterpret_cast<void*>(unusedPointer))
  95             return 0;
  96         return static_cast<JSCell*>(result);
  97     }
  98
  99 private:
 100     void clear(void* clearedValue)
 101     {
 102         if (!m_location)
 103             return;
 104         if (m_location.executableAddress() != JITWriteBarrierFlag)
 105             MacroAssembler::repatchPointer(m_location, clearedValue);
 106     }
 107
 108     CodeLocationDataLabelPtr m_location;
 109 };
 110
 111 #undef JITWriteBarrierFlag
 112
 113 template <typename T> class JITWriteBarrier : public JITWriteBarrierBase {
 114 public:
 115     JITWriteBarrier()
 116     {
 117     }
 118
 119     void set(VM& vm, CodeLocationDataLabelPtr location, JSCell* owner, T* value)
 120     {
 121         validateCell(owner);
 122         validateCell(value);
 123         JITWriteBarrierBase::set(vm, location, owner, value);
 124     }
 125     void set(VM& vm, JSCell* owner, T* value)
 126     {
 127         set(vm, location(), owner, value);
 128     }
 129     T* get() const
 130     {
 131         T* result = static_cast<T*>(JITWriteBarrierBase::get());
 132         if (result)
 133             validateCell(result);
 134         return result;
 135     }
 136 };
 137
 138 template<typename T> inline void SlotVisitor::append(JITWriteBarrier<T>* slot)
 139 {
 140     internalAppend(slot->get());
 141 }
 142
 143 }
 144
 145 #endif // ENABLE(JIT)
 146
 147 #endif