card_table.cc revision 5c42c29b89286e5efa4a4613132b09051ce5945b 
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 "runtime.h"
25#include "utils.h"
26
27namespace art {
28namespace gc {
29namespace accounting {
30
31constexpr size_t CardTable::kCardShift;
32constexpr size_t CardTable::kCardSize;
33constexpr uint8_t CardTable::kCardClean;
34constexpr uint8_t CardTable::kCardDirty;
35
36/*
37 * Maintain a card table from the write barrier. All writes of
38 * non-NULL values to heap addresses should go through an entry in
39 * WriteBarrier, and from there to here.
40 *
41 * The heap is divided into "cards" of GC_CARD_SIZE bytes, as
42 * determined by GC_CARD_SHIFT. The card table contains one byte of
43 * data per card, to be used by the GC. The value of the byte will be
44 * one of GC_CARD_CLEAN or GC_CARD_DIRTY.
45 *
46 * After any store of a non-NULL object pointer into a heap object,
47 * code is obliged to mark the card dirty. The setters in
48 * object.h [such as SetFieldObject] do this for you. The
49 * compiler also contains code to mark cards as dirty.
50 *
51 * The card table's base [the "biased card table"] gets set to a
52 * rather strange value.  In order to keep the JIT from having to
53 * fabricate or load GC_DIRTY_CARD to store into the card table,
54 * biased base is within the mmap allocation at a point where its low
55 * byte is equal to GC_DIRTY_CARD. See CardTable::Create for details.
56 */
57
58CardTable* CardTable::Create(const uint8_t* heap_begin, size_t heap_capacity) {
59  /* Set up the card table */
60  size_t capacity = heap_capacity / kCardSize;
61  /* Allocate an extra 256 bytes to allow fixed low-byte of base */
62  std::string error_msg;
63  std::unique_ptr<MemMap> mem_map(
64      MemMap::MapAnonymous("card table", nullptr, capacity + 256, PROT_READ | PROT_WRITE,
65                           false, false, &error_msg));
66  CHECK(mem_map.get() != NULL) << "couldn't allocate card table: " << error_msg;
67  // All zeros is the correct initial value; all clean. Anonymous mmaps are initialized to zero, we
68  // don't clear the card table to avoid unnecessary pages being allocated
69  static_assert(kCardClean == 0, "kCardClean must be 0");
70
71  uint8_t* cardtable_begin = mem_map->Begin();
72  CHECK(cardtable_begin != NULL);
73
74  // We allocated up to a bytes worth of extra space to allow biased_begin's byte value to equal
75  // kCardDirty, compute a offset value to make this the case
76  size_t offset = 0;
77  uint8_t* biased_begin = reinterpret_cast<uint8_t*>(reinterpret_cast<uintptr_t>(cardtable_begin) -
78      (reinterpret_cast<uintptr_t>(heap_begin) >> kCardShift));
79  uintptr_t biased_byte = reinterpret_cast<uintptr_t>(biased_begin) & 0xff;
80  if (biased_byte != kCardDirty) {
81    int delta = kCardDirty - biased_byte;
82    offset = delta + (delta < 0 ? 0x100 : 0);
83    biased_begin += offset;
84  }
85  CHECK_EQ(reinterpret_cast<uintptr_t>(biased_begin) & 0xff, kCardDirty);
86  return new CardTable(mem_map.release(), biased_begin, offset);
87}
88
89CardTable::CardTable(MemMap* mem_map, uint8_t* biased_begin, size_t offset)
90    : mem_map_(mem_map), biased_begin_(biased_begin), offset_(offset) {
91}
92
93void CardTable::ClearSpaceCards(space::ContinuousSpace* space) {
94  // TODO: clear just the range of the table that has been modified
95  uint8_t* card_start = CardFromAddr(space->Begin());
96  uint8_t* card_end = CardFromAddr(space->End());  // Make sure to round up.
97  memset(reinterpret_cast<void*>(card_start), kCardClean, card_end - card_start);
98}
99
100void CardTable::ClearCardTable() {
101  static_assert(kCardClean == 0, "kCardClean must be 0");
102  mem_map_->MadviseDontNeedAndZero();
103}
104
105void CardTable::ClearCardRange(uint8_t* start, uint8_t* end) {
106  if (!kMadviseZeroes) {
107    memset(start, 0, end - start);
108    return;
109  }
110  CHECK_ALIGNED(reinterpret_cast<uintptr_t>(start), kCardSize);
111  CHECK_ALIGNED(reinterpret_cast<uintptr_t>(end), kCardSize);
112  static_assert(kCardClean == 0, "kCardClean must be 0");
113  uint8_t* start_card = CardFromAddr(start);
114  uint8_t* end_card = CardFromAddr(end);
115  uint8_t* round_start = AlignUp(start_card, kPageSize);
116  uint8_t* round_end = AlignDown(end_card, kPageSize);
117  if (round_start < round_end) {
118    madvise(round_start, round_end - round_start, MADV_DONTNEED);
119  }
120  // Handle unaligned regions at start / end.
121  memset(start_card, 0, std::min(round_start, end_card) - start_card);
122  memset(std::max(round_end, start_card), 0, end_card - std::max(round_end, start_card));
123}
124
125bool CardTable::AddrIsInCardTable(const void* addr) const {
126  return IsValidCard(biased_begin_ + ((uintptr_t)addr >> kCardShift));
127}
128
129void CardTable::CheckAddrIsInCardTable(const uint8_t* addr) const {
130  uint8_t* card_addr = biased_begin_ + ((uintptr_t)addr >> kCardShift);
131  uint8_t* begin = mem_map_->Begin() + offset_;
132  uint8_t* end = mem_map_->End();
133  CHECK(AddrIsInCardTable(addr))
134      << "Card table " << this
135      << " begin: " << reinterpret_cast<void*>(begin)
136      << " end: " << reinterpret_cast<void*>(end)
137      << " card_addr: " << reinterpret_cast<void*>(card_addr)
138      << " heap begin: " << AddrFromCard(begin)
139      << " heap end: " << AddrFromCard(end)
140      << " addr: " << reinterpret_cast<const void*>(addr);
141}
142
143void CardTable::VerifyCardTable() {
144  UNIMPLEMENTED(WARNING) << "Card table verification";
145}
146
147}  // namespace accounting
148}  // namespace gc
149}  // namespace art
150