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
  73 protected:
  74     JITWriteBarrierBase()
  75     {
  76     }
  77
  78     void set(JSGlobalData&, CodeLocationDataLabelPtr location, JSCell* owner, JSCell* value)
  79     {
  80         Heap::writeBarrier(owner, value);
  81         m_location = location;
  82         ASSERT(((!!m_location) && m_location.executableAddress() != JITWriteBarrierFlag) || (location.executableAddress() == m_location.executableAddress()));
  83         MacroAssembler::repatchPointer(m_location, value);
  84         ASSERT(get() == value);
  85     }
  86
  87     JSCell* get() const
  88     {
  89         if (!m_location || m_location.executableAddress() == JITWriteBarrierFlag)
  90             return 0;
  91         void* result = static_cast<JSCell*>(MacroAssembler::readPointer(m_location));
  92         // We use -1 to indicate a "safe" empty value in the instruction stream
  93         if (result == (void*)-1)
  94             return 0;
  95         return static_cast<JSCell*>(result);
  96     }
  97
  98 private:
  99     void clear(void* clearedValue)
 100     {
 101         if (!m_location)
 102             return;
 103         if (m_location.executableAddress() != JITWriteBarrierFlag)
 104             MacroAssembler::repatchPointer(m_location, clearedValue);
 105     }
 106
 107     CodeLocationDataLabelPtr m_location;
 108 };
 109
 110 #undef JITWriteBarrierFlag
 111
 112 template <typename T> class JITWriteBarrier : public JITWriteBarrierBase {
 113 public:
 114     JITWriteBarrier()
 115     {
 116     }
 117
 118     void set(JSGlobalData& globalData, CodeLocationDataLabelPtr location, JSCell* owner, T* value)
 119     {
 120         validateCell(owner);
 121         validateCell(value);
 122         JITWriteBarrierBase::set(globalData, location, owner, value);
 123     }
 124     T* get() const
 125     {
 126         T* result = static_cast<T*>(JITWriteBarrierBase::get());
 127         if (result)
 128             validateCell(result);
 129         return result;
 130     }
 131 };
 132
 133 template<typename T> inline void MarkStack::append(JITWriteBarrier<T>* slot)
 134 {
 135     internalAppend(slot->get());
 136 }
 137
 138 }
 139
 140 #endif // ENABLE(JIT)
 141
 142 #endif