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/*
* Copyright (C) 2016-2019 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#pragma once
#include <wtf/Noncopyable.h>
#include <wtf/PrintStream.h>
#include <wtf/StdLibExtras.h>
namespace JSC {
class HeapCell;
struct FreeCell {
static ALWAYS_INLINE uint64_t scramble(int32_t offsetToNext, uint32_t lengthInBytes, uint64_t secret)
{
ASSERT(static_cast<uint64_t>(lengthInBytes) << 32 | offsetToNext);
return (static_cast<uint64_t>(lengthInBytes) << 32 | offsetToNext) ^ secret;
}
static ALWAYS_INLINE std::tuple<int32_t, uint32_t> descramble(uint64_t scrambledBits, uint64_t secret)
{
static_assert(WTF::isPowerOfTwo(sizeof(FreeCell))); // Make sure this division isn't super costly.
uint64_t descrambledBits = scrambledBits ^ secret;
return { static_cast<int32_t>(static_cast<uint32_t>(descrambledBits)), static_cast<uint32_t>(descrambledBits >> 32u) };
}
ALWAYS_INLINE void makeLast(uint32_t lengthInBytes, uint64_t secret)
{
scrambledBits = scramble(1, lengthInBytes, secret); // We use a set LSB to indicate a sentinel pointer.
}
ALWAYS_INLINE void setNext(FreeCell* next, uint32_t lengthInBytes, uint64_t secret)
{
scrambledBits = scramble((next - this) * sizeof(FreeCell), lengthInBytes, secret);
}
ALWAYS_INLINE std::tuple<int32_t, uint32_t> decode(uint64_t secret)
{
return descramble(scrambledBits, secret);
}
static ALWAYS_INLINE void advance(uint64_t secret, FreeCell*& interval, char*& intervalStart, char*& intervalEnd)
{
auto [offsetToNext, lengthInBytes] = interval->decode(secret);
intervalStart = bitwise_cast<char*>(interval);
intervalEnd = intervalStart + lengthInBytes;
interval = bitwise_cast<FreeCell*>(intervalStart + offsetToNext);
}
static ALWAYS_INLINE ptrdiff_t offsetOfScrambledBits() { return OBJECT_OFFSETOF(FreeCell, scrambledBits); }
uint64_t preservedBitsForCrashAnalysis;
uint64_t scrambledBits;
};
class FreeList {
public:
FreeList(unsigned cellSize);
~FreeList();
void clear();
JS_EXPORT_PRIVATE void initialize(FreeCell* head, uint64_t secret, unsigned bytes);
bool allocationWillFail() const { return m_intervalStart >= m_intervalEnd && isSentinel(nextInterval()); }
bool allocationWillSucceed() const { return !allocationWillFail(); }
template<typename Func>
HeapCell* allocateWithCellSize(const Func& slowPath, size_t cellSize);
bool contains(HeapCell*) const;
template<typename Func>
void forEach(const Func&) const;
unsigned originalSize() const { return m_originalSize; }
static bool isSentinel(FreeCell* cell) { return bitwise_cast<uintptr_t>(cell) & 1; }
static ptrdiff_t offsetOfNextInterval() { return OBJECT_OFFSETOF(FreeList, m_nextInterval); }
static ptrdiff_t offsetOfSecret() { return OBJECT_OFFSETOF(FreeList, m_secret); }
static ptrdiff_t offsetOfIntervalStart() { return OBJECT_OFFSETOF(FreeList, m_intervalStart); }
static ptrdiff_t offsetOfIntervalEnd() { return OBJECT_OFFSETOF(FreeList, m_intervalEnd); }
static ptrdiff_t offsetOfOriginalSize() { return OBJECT_OFFSETOF(FreeList, m_originalSize); }
static ptrdiff_t offsetOfCellSize() { return OBJECT_OFFSETOF(FreeList, m_cellSize); }
JS_EXPORT_PRIVATE void dump(PrintStream&) const;
unsigned cellSize() const { return m_cellSize; }
private:
FreeCell* nextInterval() const { return m_nextInterval; }
char* m_intervalStart { nullptr };
char* m_intervalEnd { nullptr };
FreeCell* m_nextInterval { bitwise_cast<FreeCell*>(static_cast<uintptr_t>(1)) };
uint64_t m_secret { 0 };
unsigned m_originalSize { 0 };
unsigned m_cellSize { 0 };
};
} // namespace JSC
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