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 "MarkStack.h"
  33 #include "WriteBarrier.h"
  34
  35 namespace JSC {
  36
  37 class JSCell;
  38 class JSGlobalData;
  39
  40 // Needs to be even to appease some of the backends.
  41 #define JITWriteBarrierFlag ((void*)2)
  42 class JITWriteBarrierBase {
  43 public:
  44     typedef void* (JITWriteBarrierBase::*UnspecifiedBoolType);
  45     operator UnspecifiedBoolType*() const { return get() ? reinterpret_cast<UnspecifiedBoolType*>(1) : 0; }
  46     bool operator!() const { return !get(); }
  47
  48     void setFlagOnBarrier()
  49     {
  50         ASSERT(!m_location);
  51         m_location = CodeLocationDataLabelPtr(JITWriteBarrierFlag);
  52     }
  53
  54     bool isFlagged() const
  55     {
  56         return !!m_location;
  57     }
  58
  59     void setLocation(CodeLocationDataLabelPtr location)
  60     {
  61         ASSERT(!m_location);
  62         m_location = location;
  63     }
  64
  65     CodeLocationDataLabelPtr location() const
  66     {
  67         ASSERT((!!m_location) && m_location.executableAddress() != JITWriteBarrierFlag);
  68         return m_location;
  69     }
  70
  71     void clear() { clear(0); }
  72     void clearToMaxUnsigned() { clear(reinterpret_cast<void*>(-1)); }
  73
  74 protected:
  75     JITWriteBarrierBase()
  76     {
  77     }
  78
  79     void set(JSGlobalData&, CodeLocationDataLabelPtr location, JSCell* owner, JSCell* value)
  80     {
  81         Heap::writeBarrier(owner, value);
  82         m_location = location;
  83         ASSERT(((!!m_location) && m_location.executableAddress() != JITWriteBarrierFlag) || (location.executableAddress() == m_location.executableAddress()));
  84         MacroAssembler::repatchPointer(m_location, value);
  85         ASSERT(get() == value);
  86     }
  87
  88     JSCell* get() const
  89     {
  90         if (!m_location || m_location.executableAddress() == JITWriteBarrierFlag)
  91             return 0;
  92         void* result = static_cast<JSCell*>(MacroAssembler::readPointer(m_location));
  93         // We use -1 to indicate a "safe" empty value in the instruction stream
  94         if (result == (void*)-1)
  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(JSGlobalData& globalData, CodeLocationDataLabelPtr location, JSCell* owner, T* value)
 120     {
 121         validateCell(owner);
 122         validateCell(value);
 123         JITWriteBarrierBase::set(globalData, location, owner, value);
 124     }
 125     void set(JSGlobalData& globalData, JSCell* owner, T* value)
 126     {
 127         set(globalData, 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 MarkStack::append(JITWriteBarrier<T>* slot)
 139 {
 140     internalAppend(slot->get());
 141 }
 142
 143 }
 144
 145 #endif // ENABLE(JIT)
 146
 147 #endif