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