1  /*
  2   * Copyright (C) 2013-2019 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  #include "config.h"
 27  #include "StructureIDTable.h"
 28  
 29  #include <wtf/Atomics.h>
 30  #include <wtf/DataLog.h>
 31  #include <wtf/RawPointer.h>
 32  
 33  namespace JSC {
 34  
 35  #if USE(JSVALUE64)
 36  
 37  namespace StructureIDTableInternal {
 38  static constexpr bool verbose = false;
 39  }
 40  
 41  StructureIDTable::StructureIDTable()
 42      : m_table(makeUniqueArray<StructureOrOffset>(s_initialSize))
 43      , m_size(1)
 44      , m_capacity(s_initialSize)
 45  {
 46      // We pre-allocate the first offset so that the null Structure
 47      // can still be represented as the StructureID '0'.
 48      table()[0].encodedStructureBits = 0;
 49  
 50      makeFreeListFromRange(1, m_capacity - 1);
 51  }
 52  
 53  void StructureIDTable::makeFreeListFromRange(uint32_t first, uint32_t last)
 54  {
 55      ASSERT(!m_firstFreeOffset);
 56      ASSERT(!m_lastFreeOffset);
 57  
 58      // Put all the new IDs on the free list sequentially.
 59      uint32_t head = first;
 60      uint32_t tail = last;
 61      for (uint32_t i = first; i < last; ++i)
 62          table()[i].offset = i + 1;
 63      table()[last].offset = 0;
 64  
 65      // Randomize the free list.
 66      uint32_t size = last - first + 1;
 67      uint32_t maxIterations = (size * 2) / 3;
 68      for (uint32_t count = 0; count < maxIterations; ++count) {
 69          // Move a random pick either to the head or the tail of the free list.
 70          uint32_t random = m_weakRandom.getUint32();
 71          uint32_t nodeBefore = first + (random % size);
 72          uint32_t pick = table()[nodeBefore].offset;
 73          if (pick) {
 74              uint32_t nodeAfter = table()[pick].offset;
 75              table()[nodeBefore].offset = nodeAfter;
 76              if ((random & 1) || !nodeAfter) {
 77                  // Move to the head.
 78                  table()[pick].offset = head;
 79                  head = pick;
 80                  if (!nodeAfter)
 81                      tail = nodeBefore;
 82              } else {
 83                  // Move to the tail.
 84                  table()[pick].offset = 0;
 85                  table()[tail].offset = pick;
 86                  tail = pick;
 87              }
 88          }
 89      }
 90  
 91      // Cut list in half and swap halves.
 92      uint32_t cut = first + (m_weakRandom.getUint32() % size);
 93      uint32_t afterCut = table()[cut].offset;
 94      if (afterCut) {
 95          table()[tail].offset = head;
 96          tail = cut;
 97          head = afterCut;
 98          table()[cut].offset = 0;
 99      }
100  
101      m_firstFreeOffset = head;
102      m_lastFreeOffset = tail;
103  }
104  
105  void StructureIDTable::resize(size_t newCapacity)
106  {
107      if (newCapacity > s_maximumNumberOfStructures)
108          newCapacity = s_maximumNumberOfStructures;
109  
110      // If m_size is already s_maximumNumberOfStructures, newCapacity becomes s_maximumNumberOfStructures in the above code.
111      // In that case, we should crash because of exhaust of StructureIDs.
112      RELEASE_ASSERT_WITH_MESSAGE(m_size < newCapacity, "Crash intentionally because of exhaust of StructureIDs.");
113  
114      // Create the new table.
115      auto newTable = makeUniqueArray<StructureOrOffset>(newCapacity);
116  
117      // Copy the contents of the old table to the new table.
118      memcpy(newTable.get(), table(), m_capacity * sizeof(StructureOrOffset));
119  
120      // Store fence to make sure we've copied everything before doing the swap.
121      WTF::storeStoreFence();
122  
123      // Swap the old and new tables.
124      swap(m_table, newTable);
125  
126      // Put the old table (now labeled as new) into the list of old tables.
127      m_oldTables.append(WTFMove(newTable));
128  
129      // Update the capacity.
130      m_capacity = newCapacity;
131  
132      makeFreeListFromRange(m_size, m_capacity - 1);
133  }
134  
135  void StructureIDTable::flushOldTables()
136  {
137      m_oldTables.clear();
138  }
139  
140  StructureID StructureIDTable::allocateID(Structure* structure)
141  {
142      if (UNLIKELY(!m_firstFreeOffset)) {
143          RELEASE_ASSERT(m_capacity <= s_maximumNumberOfStructures);
144          ASSERT(m_size == m_capacity);
145          resize(m_capacity * 2);
146          ASSERT(m_size < m_capacity);
147          RELEASE_ASSERT(m_firstFreeOffset);
148      }
149  
150      // entropyBits must not be zero. This ensures that if a corrupted
151      // structureID is encountered (with incorrect entropyBits), the decoded
152      // structure pointer for that ID will be always be a bad pointer with
153      // high bits set.
154      constexpr uint32_t entropyBitsMask = (1 << s_numberOfEntropyBits) - 1;
155      uint32_t entropyBits = m_weakRandom.getUint32() & entropyBitsMask;
156      if (UNLIKELY(!entropyBits)) {
157          constexpr uint32_t numberOfValuesToPickFrom = entropyBitsMask;
158          entropyBits = (m_weakRandom.getUint32() % numberOfValuesToPickFrom) + 1;
159      }
160  
161      uint32_t structureIndex = m_firstFreeOffset;
162      m_firstFreeOffset = table()[m_firstFreeOffset].offset;
163      if (!m_firstFreeOffset)
164          m_lastFreeOffset = 0;
165  
166      StructureID result = (structureIndex << s_numberOfEntropyBits) | entropyBits;
167      table()[structureIndex].encodedStructureBits = encode(structure, result);
168      m_size++;
169      ASSERT(!isNuked(result));
170  
171      dataLogLnIf(StructureIDTableInternal::verbose, "Allocated StructureID ", result, " for Structure ", RawPointer(structure));
172      return result;
173  }
174  
175  void StructureIDTable::deallocateID(Structure* structure, StructureID structureID)
176  {
177      dataLogLnIf(StructureIDTableInternal::verbose, "Deallocated StructureID ", structureID);
178      ASSERT(structureID != s_unusedID);
179      uint32_t structureIndex = structureID >> s_numberOfEntropyBits;
180      ASSERT(structureIndex && structureIndex < s_maximumNumberOfStructures);
181      RELEASE_ASSERT(table()[structureIndex].encodedStructureBits == encode(structure, structureID));
182      m_size--;
183      if (!m_firstFreeOffset) {
184          table()[structureIndex].offset = 0;
185          m_firstFreeOffset = structureIndex;
186          m_lastFreeOffset = structureIndex;
187          return;
188      }
189  
190      bool insertAtHead = m_weakRandom.getUint32() & 1;
191      if (insertAtHead) {
192          table()[structureIndex].offset = m_firstFreeOffset;
193          m_firstFreeOffset = structureIndex;
194      } else {
195          table()[structureIndex].offset = 0;
196          table()[m_lastFreeOffset].offset = structureIndex;
197          m_lastFreeOffset = structureIndex;
198      }
199  }
200  
201  #endif // USE(JSVALUE64)
202  
203  } // namespace JSC