1 /*
2 * Copyright (C) 2010 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "card_table.h"
18
19 #include "base/logging.h"
20 #include "card_table-inl.h"
21 #include "gc/heap.h"
22 #include "gc/space/space.h"
23 #include "heap_bitmap.h"
24 #include "mem_map.h"
25 #include "runtime.h"
26 #include "utils.h"
27
28 namespace art {
29 namespace gc {
30 namespace accounting {
31
32 constexpr size_t CardTable::kCardShift;
33 constexpr size_t CardTable::kCardSize;
34 constexpr uint8_t CardTable::kCardClean;
35 constexpr uint8_t CardTable::kCardDirty;
36
37 /*
38 * Maintain a card table from the write barrier. All writes of
39 * non-null values to heap addresses should go through an entry in
40 * WriteBarrier, and from there to here.
41 *
42 * The heap is divided into "cards" of GC_CARD_SIZE bytes, as
43 * determined by GC_CARD_SHIFT. The card table contains one byte of
44 * data per card, to be used by the GC. The value of the byte will be
45 * one of GC_CARD_CLEAN or GC_CARD_DIRTY.
46 *
47 * After any store of a non-null object pointer into a heap object,
48 * code is obliged to mark the card dirty. The setters in
49 * object.h [such as SetFieldObject] do this for you. The
50 * compiler also contains code to mark cards as dirty.
51 *
52 * The card table's base [the "biased card table"] gets set to a
53 * rather strange value. In order to keep the JIT from having to
54 * fabricate or load GC_DIRTY_CARD to store into the card table,
55 * biased base is within the mmap allocation at a point where its low
56 * byte is equal to GC_DIRTY_CARD. See CardTable::Create for details.
57 */
58
Create(const uint8_t * heap_begin,size_t heap_capacity)59 CardTable* CardTable::Create(const uint8_t* heap_begin, size_t heap_capacity) {
60 /* Set up the card table */
61 size_t capacity = heap_capacity / kCardSize;
62 /* Allocate an extra 256 bytes to allow fixed low-byte of base */
63 std::string error_msg;
64 std::unique_ptr<MemMap> mem_map(
65 MemMap::MapAnonymous("card table", nullptr, capacity + 256, PROT_READ | PROT_WRITE,
66 false, false, &error_msg));
67 CHECK(mem_map.get() != nullptr) << "couldn't allocate card table: " << error_msg;
68 // All zeros is the correct initial value; all clean. Anonymous mmaps are initialized to zero, we
69 // don't clear the card table to avoid unnecessary pages being allocated
70 static_assert(kCardClean == 0, "kCardClean must be 0");
71
72 uint8_t* cardtable_begin = mem_map->Begin();
73 CHECK(cardtable_begin != nullptr);
74
75 // We allocated up to a bytes worth of extra space to allow biased_begin's byte value to equal
76 // kCardDirty, compute a offset value to make this the case
77 size_t offset = 0;
78 uint8_t* biased_begin = reinterpret_cast<uint8_t*>(reinterpret_cast<uintptr_t>(cardtable_begin) -
79 (reinterpret_cast<uintptr_t>(heap_begin) >> kCardShift));
80 uintptr_t biased_byte = reinterpret_cast<uintptr_t>(biased_begin) & 0xff;
81 if (biased_byte != kCardDirty) {
82 int delta = kCardDirty - biased_byte;
83 offset = delta + (delta < 0 ? 0x100 : 0);
84 biased_begin += offset;
85 }
86 CHECK_EQ(reinterpret_cast<uintptr_t>(biased_begin) & 0xff, kCardDirty);
87 return new CardTable(mem_map.release(), biased_begin, offset);
88 }
89
CardTable(MemMap * mem_map,uint8_t * biased_begin,size_t offset)90 CardTable::CardTable(MemMap* mem_map, uint8_t* biased_begin, size_t offset)
91 : mem_map_(mem_map), biased_begin_(biased_begin), offset_(offset) {
92 }
93
~CardTable()94 CardTable::~CardTable() {
95 // Destroys MemMap via std::unique_ptr<>.
96 }
97
ClearSpaceCards(space::ContinuousSpace * space)98 void CardTable::ClearSpaceCards(space::ContinuousSpace* space) {
99 // TODO: clear just the range of the table that has been modified
100 uint8_t* card_start = CardFromAddr(space->Begin());
101 uint8_t* card_end = CardFromAddr(space->End()); // Make sure to round up.
102 memset(reinterpret_cast<void*>(card_start), kCardClean, card_end - card_start);
103 }
104
ClearCardTable()105 void CardTable::ClearCardTable() {
106 static_assert(kCardClean == 0, "kCardClean must be 0");
107 mem_map_->MadviseDontNeedAndZero();
108 }
109
ClearCardRange(uint8_t * start,uint8_t * end)110 void CardTable::ClearCardRange(uint8_t* start, uint8_t* end) {
111 if (!kMadviseZeroes) {
112 memset(start, 0, end - start);
113 return;
114 }
115 CHECK_ALIGNED(reinterpret_cast<uintptr_t>(start), kCardSize);
116 CHECK_ALIGNED(reinterpret_cast<uintptr_t>(end), kCardSize);
117 static_assert(kCardClean == 0, "kCardClean must be 0");
118 uint8_t* start_card = CardFromAddr(start);
119 uint8_t* end_card = CardFromAddr(end);
120 uint8_t* round_start = AlignUp(start_card, kPageSize);
121 uint8_t* round_end = AlignDown(end_card, kPageSize);
122 if (round_start < round_end) {
123 madvise(round_start, round_end - round_start, MADV_DONTNEED);
124 }
125 // Handle unaligned regions at start / end.
126 memset(start_card, 0, std::min(round_start, end_card) - start_card);
127 memset(std::max(round_end, start_card), 0, end_card - std::max(round_end, start_card));
128 }
129
AddrIsInCardTable(const void * addr) const130 bool CardTable::AddrIsInCardTable(const void* addr) const {
131 return IsValidCard(biased_begin_ + ((uintptr_t)addr >> kCardShift));
132 }
133
CheckAddrIsInCardTable(const uint8_t * addr) const134 void CardTable::CheckAddrIsInCardTable(const uint8_t* addr) const {
135 uint8_t* card_addr = biased_begin_ + ((uintptr_t)addr >> kCardShift);
136 uint8_t* begin = mem_map_->Begin() + offset_;
137 uint8_t* end = mem_map_->End();
138 CHECK(AddrIsInCardTable(addr))
139 << "Card table " << this
140 << " begin: " << reinterpret_cast<void*>(begin)
141 << " end: " << reinterpret_cast<void*>(end)
142 << " card_addr: " << reinterpret_cast<void*>(card_addr)
143 << " heap begin: " << AddrFromCard(begin)
144 << " heap end: " << AddrFromCard(end)
145 << " addr: " << reinterpret_cast<const void*>(addr);
146 }
147
VerifyCardTable()148 void CardTable::VerifyCardTable() {
149 UNIMPLEMENTED(WARNING) << "Card table verification";
150 }
151
152 } // namespace accounting
153 } // namespace gc
154 } // namespace art
155